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Mesenchymal stem cells and bone regeneration: Current status
Injury, Int. J. Care Injured 42 (2011) 562–568
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Injury journal homepage: www.elsevier.com/locate/injury
Mesenchymal stem cells and bone regeneration: Current status Elena Jones a,*, Xuebin Yang b a Rheumatology, Mesenchymal Stem Cell Biology Group, Academic Unit of Musculoskeletal Disease, Leeds Institute of Molecular Medicine, Room 5.24 Clinical Sciences Building, St. James’s University Hospital, University of Leeds, Beckett Street, Leeds LS9 7TF, United Kingdom b Tissue Engineering Research, Biomaterials & Tissue Engineering Group, Department of Oral Biology, Leeds Dental Institute, University of Leeds, United Kingdom
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 17 March 2011
The enhancement of bone regeneration with biological agents including osteogenic growth factors and mesenchymal stem cells (MSCs) is becoming a clinical reality. Many exciting findings have been obtained following MSC implantation in animal models, and the data demonstrating their clinical efficacy in humans are promising. The overwhelming majority of experimental work has been performed with MSCs ‘‘amplified’’ in vitro. The nature of native MSCs in skeletal tissues however, remains poorly understood. This review summarizes recent findings pertaining to the definition and characterisation of MSCs in skeletal tissues and discusses the mechanisms of their actions in regenerating of bone in vivo. In respect to traditional tissue engineering paradigm, we bring together literature showing that the ways MSCs are extracted, expanded and implanted can considerably affect bone formation outcomes. Additionally, we discuss current animal models used in MSC research and highlight recent experiments showing important contribution of the host, and not only donor MSCs, in bone tissue formation. This knowledge provides a platform for novel therapy development for bone regeneration based on pharmacologically manipulated endogenous MSCs. ß 2011 Elsevier Ltd. All rights reserved.
Keywords: Mesenchymal stem cells Osteoprogenitors Bone regeneration Tissue engineering
MSCs and osteoprogenitors – current definitions and assays Regeneration of bone is believed to be mediated via osteoprogenitors and their ancestors, the mesenchymal stem cells (MSCs). Whilst the term MSC is commonly used in scientific and clinical literature, many stem cell biologists recognise that MSCs fall short of being true ‘‘stem cells’’.11,33 To reflect this, the International Society for Cellular Therapy position statement has declared an alternative terminology, referring to these cells as ‘‘multipotent mesenchymal stromal cells’’.33 One of the main reasons for scientific community’s reluctance to use the term ‘‘stem cells’’ in relation to MSCs lies in the fact that their life-long self-renewal in vivo has not yet been demonstrated using reliable animal models.11 To put MSCs in a context of other adult stem cells, it is worth comparing them with hematopoietic stem cells (HSCs). HSCs give rise to all blood cell lineages; they have a well-defined niche in the bone marrow (BM),66 and their development during embryogenesis is very clearly mapped.74 In contrast, MSCs reside in virtually all peri- and post-natal tissues72,73 and their origins and migration patterns during embryonic development remain obscure.31,84 In our view, the main reason for such disparity lies in the
* Corresponding author. Tel.: +44 113 2065647; fax: +44 113 3438502. E-mail address: [email protected] (E. Jones). 0020–1383/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.injury.2011.03.030
retrospective way of defining MSCs. Whereas HSCs are defined prospectively, based on their native phenotype in vivo,20,85 MSCs defined based on the phenotype of their culture-amplified progeny, i.e., retrospectively.86 In late 1990s, several surface molecules have been described to be specific for cultured MSCs,5 but these molecules, including CD73 and CD105, later turned out to be expressed on ordinary fibroblasts54,56 limiting their utility for defining MSCs in vivo. Concurrently, several markers have been identified as specific for native MSCs, but they are absent on their cultured progeny. These markers include Stro-1100 and CD271.13,56,57,88 The current lack of uniformly accepted, reliable markers that are expressed stably on both native and cultured MSCs, precludes their accurate tracing in development as well as during tissue regeneration. A similar lack of clarity currently pertains to defining osteoprogenitors. MSCs and HSCs were discovered around the same time40 and the same concept of their lineage maturation via committed progenitors was adopted.15,86 Compared to stem cells, these committed progenitors, commonly termed colony-forming units, have diminished proliferative capacities and a limited differentiation. In the HSCs field, colony-forming units-myeloid, erythroid, etc., have very distinct morphologies74 and clear cell surface phenotypes.20,85 In the MSC field, colony-forming assays exist only for osteo-28 and adipogenic progenitors,94 but not for chondrogenic progenitors or putative myogenic progenitors. After several decades of searching, no universally accepted surface
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markers for any of these mesenchymal progenitors have been found. To complicate things further, an inter-conversion from an adipogenic to osteogenic lineage and vice versa have been achieved experimentally.60 Such ‘‘plasticity’’ of the MSC lineage84 makes the interpretation of colony-forming unit-osteoblast and adipocyte data very difficult. Therefore specific markers for osteoprogenitors as distinct from more immature MSCs are yet to be developed. Recently, a model of the MSC hierarchy based on cell proliferation rate was proposed.68 Within the MSC pool of progenitors, more rapidly growing cells have been shown to possess multilineage differentiation capacities whereas slowergrowing cells were preferentially osteogenic.68 Observations like these should ultimately lead to the discovery of definitive markers for both MSCs and osteoprogenitors. Identity of MSCs in the BM, bone and periosteum Due to considerations described in the above section, many laboratories around the world have invested huge efforts into prospective purification of native BM MSCs.11,31,56,72 Several reviews, including ours,31,56,72 have provided lists of potential candidate markers of native BM MSCs. Apart from CD271, these novel markers include GD2,69 SSEA441 and, more recently, CD146.92 Despite an ongoing debate on relative merits of individual markers, a general consensus is now emerging in relation to the topography of MSCs in the BM.11,31,56 According to this view, MSCs ‘‘hide’’ under a guise of reticular stromal cells, which traverse marrow cavities and extend to bone surfaces.11,56 Because BM endothelium has no clearly discernible perivascular cells, these reticular cells are considered as bone fide pericytes in the marrow.10 In accordance with their MSC nature, these perivascular/ reticular cells can give rise to adipocytes9 and be involved in organising bone remodelling units.75 Furthermore, they support hematopoiesis by releasing cytokines essential for HSC trafficking and maturation, including stromal-derived factor 1, SDF-1.19,102,105 All of this goes well with experimental phenomenon of MSC ‘‘plasticity’’ mentioned above. Early findings demonstrating relative abundance of reticular cells in situ19 have put into question an original concept of rare BM MSCs.86 Following an initial findings by Sakaguchi et al.93 we have recently demonstrated that high numbers of MSCs could be extracted from trabecular bone cavities by enzymatic breakdown of marrow extracellular matrix.55 This finding suggested that only a proportion of native MSCs have been actually obtained by marrow aspiration.55 Our data also suggest that a concept of systemic circulation of rare BM MSCs to the sites of injury34 may become outdated. Instead, an activation and chemotactic migration of fairly abundant local MSCs adjacent to injury area is likely to represent a much more plausible explanation, as proposed by others.21,39 Periosteum is another tissue that plays an essential role in callus formation following fracture.32,37 The existence of periosteal MSCs78 has been more recently confirmed at the single cell level,30 however their topography remains unknown. Single periosteal MSCs appear to be ‘‘defaulted’’ to an osteogenic differentiation programme.29 A similar propensity to osteogenesis, following in vitro expansion, has been demonstrated for BM MSCs,76 albeit using somewhat older methodology. This makes perfect sense considering the local microenvironment these MSCs are residing and a continuing need for bone remodelling that occurs physiologically during the lifetime of an individual. MSCs have been also found in frank bone experimentally devoid of soft marrow.81,99,107 The cells that grow out of bone explants generating cultures identical to MSCs81,107 are likely to be derived
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from pericytes. Perivascular topography of MSCs in many tissues is now commonly accepted.11,72 However, MSCs are likely to form only a fraction of perycites26,72; otherwise the most vascularised tissues would be automatically the richest for MSCs. Furthermore, tissues like cartilage superficial layer lack the blood supply with vessels and pericytes, yet possess some level of the MSC activity.35 Based on these data one can conclude that, although MSC as a pericyte concept provides an excellent explanation for the abundance of MSCs in almost every tissue in the body, it does not exhaustively explain all the experimental data observed so far. New methods for extraction of pericytes from cortical bone would be needed to establish the identity of bone-resident MSCs. Fabrication of tissue engineered bone – not only MSCs! From a tissue engineer perspective an argument whether MSCs are true stem cells or not may not be relevant. Indeed, cultureexpanded BM MSCs have clearly shown excellent repair in animal models67,87 and their safety profiles in clinical cohort studies for osteogenesis imperfecta48,49 and osteonecrosis of femoral head42,45,58 have been satisfactory. However, the translation of these pilot trials into clinical practice faces many challenges, beyond the safety concerns regarding the use of foetal calf serum, described elsewhere.12 There is still a debate as to which expansion conditions are the best for the manufacture of MSCs intended for bone repair. For example, cell seeding density,27,101 FGF2 supplementation8 and low oxygen tension,17,27 have all been shown to improve the longevity and the osteogenic potency of cultured MSCs, but which conditions are optimal remain to be established. For repairing large bone defects, massive quantities of MSCs are required. However, cultured MSCs gradually loose their potency and, eventually, stop growing following extensive cultivation.3,6,109 Rare MSCs from autologous BM aspirates may become senescent during numerous rounds of amplification required. Consequently, many tissue engineers turn their attention to adipose,110 dental pulp1,51 or umbilical cord111 tissues, which appear to be richer for MSCs. The utility of adipose-derived MSCs for bone repair application is however still debatable,52,80,89 with some studies showing their inferiority compared to BM MSCs.53,79 The osteogenic capacity of umbilical cord matrix-derived MSCs, on the other hand, appears to be similar to BM MSCs, in both 2dimentional (2D)98 and 3D differentiation conditions.96 Some examples of in vitro trilineage differentiation from BM-, adiposeand dental pulp-derived MSCs obtained in our laboratories are shown in Fig. 1. Another interesting recent development relates to scaffolds seeded with pre-differentiated MSCs97 or to composites of MSCs mixed with endothelial lineage cells.59,95,108 Vascularisation approaches for large bone grafts are described in detail elsewhere (reviewed in Santos and Reis and Kanczler and Oreffo59,95). In brief, scaffolds loaded with angiogenic growth factors have been used initially.4,77 Nowadays, the implantation of autologous endothelial progenitors cells (EPCs) is considered as an alternative.31,95,108,115,116 In one study, peripheral blood CD34+ autologous EPCs, were transplanted systemically leading to the enhancement of angiogenesis and osteogenesis in delayed fracture unions.70 Based on these findings, a ‘‘mobilisation’’ of host endothelial lineage cells with growth factors may be envisaged as a novel way to treat non-unions and complex fractures. An existence of circulating osteoblastic progenitors61 or circulating cells with dual propensity to become EPCs and osteoblasts has been recently proposed;71 although very interesting, these results await further validation by other investigators. Altogether these data show that MSCs of different origins as well as other cell types including EPCs can now be used to engineer new bone.
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Fig. 1. Dissimilar in vitro differentiation capacities of MSCs expanded from human bone marrow, dental pulp and adipose tissue (infrapatella fat pad). BM and adipose MSCs have robust tri-lineage differentiation, whereas dental pulp MSCs have very low adipogenesis. Adipogenesis – Oil Red staining, chondrogenesis – Toluidine Blue staining, osteogenesis – Alizarin Red staining on day 21 post-induction. Original magnification 100 (adipogenesis) and 50 (chondrogenesis).
Animal models for investigations of the role of MSCs in bone repair As a norm, in vitro differentiation experiments provide only initial points of reference to explore MSC differentiation capabilities. Investigations in animal models are next needed for the study of safety and efficacy of MSC preparations. An ideal animal model for bone regeneration should mimic clinical conditions of bone injury, create a permissive microenvironment for diffusion of nutrients, gases and growth factors, utilise fixation and mechanical load through the defect, as in the clinic, and permit angiogenesis.47 Currently available animal models for bone repair are not yet ideal and vary from simple subcutaneous implantation (Fig. 2) to functional complex tissue regeneration, including in vivo bioreactors.47 The ectopic subcutaneous implant model (Fig. 2) is the most commonly used; it is the least invasive and more suitable for preliminary screening of MSC formulations, scaffolds and growth factors.47 Although a number of different species have been used for this model,23,38,112 to date, the immunocompromised (Nude) mouse is the most popular.113 Its limitations include eventual reabsorption of newly formed bone due to lack of appropriate mechanical stimulation and the uncertainty regarding interactions between the implanted cells and host tissues.47 The most recent work from Cancedda Laboratory has brought some light on donor and host MSC involvement in subcutaneous implant model. It has shown that the origin of new bone depended
on the maturation status of the implanted cells.106 When they implanted osteoblasts, a new bone was of donor origin, formed directly via the intramembranous ossification. However, when they implanted MSCs, a new bone was of the host origin and formed via endochondral ossification.106 In a follow-up paper, the same group showed that MSC-seeded scaffolds have ‘‘induced’’ two consecutive waves of host cell migration.104 Host endothelial cells were attracted to the scaffolds first, followed by a wave of host perivascular cells, potentially responsible for the formation of a new bone. Osteochondral ossification in subcutaneous model has also been achieved following implantation of MSCs pre-differentiated to chondrocytes.97 The chondrocytes could indeed attract host vasculature to the developing graft.22 Another animal model, the diffusion chamber model, provides an enclosed, permissive environment within a host animal to allow free exchange of nutrients but effectively isolates the experimental cells from the host tissues.2,44,83 All new bone is therefore of a donor origin. Although the diffusion chamber model has been successfully used to test bone tissue regeneration,44,50,114 it lacks effective mechanical stimuli needed for bone remodelling. Therefore site-specific bone defect models, particularly for weight bearing testing and tissue engineering of large bone constructs, are being actively developed.25,63,82 For non-weight bearing testing, the bone defect can be made within the calvaria, rib or mandibles, which have relatively low mechanical forces.46 In this model, most scaffold materials can be moulded to fit the bone defect and do not require further fixation.
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Fig. 2. Subcutaneously implant model (A and B), diffusion chamber model (C and D) and bone defect model (E and F) in vivo. (A) Human bone marrow stromal cellsbiomaterial construct implanted subcutaneously in nude mice and vascular supply to the implants (arrow); (B) Sirius red staining showed new bone formation within the pleiotrophin absorbed PLGA porous scaffold (reproduced from J Bone Miner Res 2003;18:45–57, Yang et al., Copyright (2003) with permission from the American Society from Bone and Mineral Research); (C) X-ray images showed high density bone nodule formation and (D) Alcian blue staining showed cartilage matrix formation within the diffusion chamber (Reprinted from BBRC, 292:144–152, Yang et al., Copyright (2002), with permission from Elsevier) (Partridge et al., 2002); (E) segmental bone defect model in which a 2 mm bone defect created in a mouse femur, and (F) the mouse femur defect was repaired by a porous poly(-lactic acid) scaffold and intramedullar pin fixation (scale bars: 2 mm). A, E and F are reprinted from Advances in Tissue Engineering, J Polak et al., Copyright @ Imperial College Press.
The periosteum can then be closed to cover the bone defect.24 For weight bearing testing, the defect can be made in long bones (e.g., the femur or tibia). Although the methods for creating a critical defect are various, the most commonly used two methods use either an osteotomy approach or a traumatic approach. Osteotomy can surgically remove the required length of bone from a predetermined site, producing a consistent defect with a ‘clean’ cut. However, this does not reflect the real conditions following traumatic injury which produce a jagged cut edge bone fracture including the trauma of surrounding soft tissue. To achieve this, a three-point bending device and/or impact device has been designed.63 Then the bone defect is reconstructed with the test material alone and/or in combination with cells and growth factors and fixed using external or internal fixation. Since the animal will start to move after recovery, the biomechanical properties of the selected scaffold are crucial for optimum bone regeneration in a weight bearing bone defect. Scaffolds need to be initially strong enough to allow weight-bearing during the first stage of the regenerative process but also biodegradable at the right time to allow bone remodelling.47 The contribution of host and donor MSCs to bone formation in these complex animal models remains to be elucidated. ‘‘Indirect’’ actions of implanted MSCs As mentioned in previous sections, the main rationale for the use of MSCs in bone repair applications was based on their direct ability to generate osteoprogenitors and osteoblasts. The MSC osteogenesis have been further enhanced by simultaneous introduction of bone morphogenic protein 2 (BMP2) or other osteoinductive growth factors, either in slow-release system or as genes delivered into MSCs by viral or non-viral delivery systems.103 The addition of supporting growth factors has become particularly relevant when bone repair in older, osteoporotic or diabetic individuals was considered, since the osteogenic function
of autologous MSCs in these conditions is known to be compromised.7,58,90,91 However, more recent experimental evidence has suggested that the therapeutic action of implanted MSCs may not be solely limited to their direct conversion into osteoblasts. Based on a wealth of evidence from the cardiovascular field, where MSC therapy has been used extensively, it appears that transplanted MSC possess other poorly defined functionalities, broadly referred as ‘‘trophic’’ or paracrine effects.16,84 These include anti-apoptotic effects, immunoregulatory function, and stimulation of host cell migration. Molecular mechanisms of these effects are yet poorly understood, but recent animal studies by Tortelli et al. and Scotti et al. highlighted above97,106 suggest that these ‘‘indirect’’ actions of implanted MSCs, particularly in attracting host vasculature, may be as important in bone tissue regeneration as their direct ability to form new bone. In this respect, it is reasonable to hypothesis that implanted MSCs can act as ‘‘seeds’’ or ‘‘signalling centres’’, orchestrating and organising the host response to the injury; and this is in addition to their direct role as a source of new osteoblasts. In fracture repair settings, such ‘‘trophic’’ functionalities of MSCs at the initial inflammatory phases may be critically important, considering that MSCs are known to switch off inflammatory responses.64,65 The knowledge of the ‘‘trophic’’ actions of MSCs and their temporal sequence is fracture repair, in particular, may lead to novel therapeutic approaches in the treatment of nonunions. For example, SDF-1 chemotactic gradients have been shown to affect migration patterns of both injected43 and host MSCs.62 Targeted delivery of SDF-1 can therefore be used as a novel approach of creating an artificial ‘‘signalling centre’’ to trigger the migration of host MSCs, without implantation of exogenous MSCs. Alternatively, autologous MSCs can be injected into fracture haematoma to manipulate the transition from the inflammatory phases to the callus formation stages of fracture repair.
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Back to native MSCs As highlighted above, recent in vivo evidence suggests that the understanding of the biology of native MSCs in vivo, as well as their relationship with local endothelial cells, are critical for the development of novel bone repair strategies. MSC cultureexpansion will still be necessary for generating enough MSCs to populate large scaffolds designed for repairing critical-size bone defects.18,36 A careful selection of MSC sources and ‘‘priming’’ of scaffolds with mixed MSC formulations will lead to ‘‘quality’’ replacement tissues for these indications. In fracture repair, on the other hand, where defects are often small and host factors are significant,14 novel in situ approaches for the enhancement of local responses by host MSCs appear to be more practical and costeffective. Therefore, studies aimed at isolation and characterisation of MSCs in different tissues, in health and disease, should continue. When precise dysfunctions of native MSCs in these diseases are uncovered, corrective pharmaceutical agents could be designed and manufactured, leading to novel, cell-free and cost-effective treatments for bone repair. Scientific advances in the understanding of the biology of native MSCs in vivo have therefore significant implications for future strategies to repair bone. Conflict of interest EJ and XBY declare no conflict of interest. Role of the funding source The work of both authors is supported by WELMEC, a Centre of Excellence in Medical Engineering funded by the Wellcome Trust and EPSRC, under grant number WT 088908/Z/09/Z and also by NIHR Leeds Biomedical Research Unit grant. EJ work is supported by European Commission FP7 Purstem project and XBY work is supported by TSB, WUN and RegN8. References 1. Alge DL, Zhou D, Adams LL, et al. Donor-matched comparison of dental pulp stem cells and bone marrow-derived mesenchymal stem cells in a rat model. J Tissue Eng Regen Med 2010;4:73–81. 2. Ashton BA, Allen TD, Howlett CR, et al. Formation of bone and cartilage by marrow stromal cells in diffusion-chambers invivo. Clin Orthop 1980:294–307. 3. Banfi A, Bianchi G, Galotto M, et al. Bone marrow stromal damage after chemo/ radiotherapy: occurrence, consequences and possibilities of treatment. Leuk Lymphoma 2001;42:863–70. 4. Barralet J, Gbureck U, Habibovic P, et al. Angiogenesis in calcium phosphate scaffolds by inorganic copper ion release. Tissue Eng Part A 2009;15:1601–9. 5. Barry FP, Boynton RE, Haynesworth S, et al. The monoclonal antibody SH-2, raised against human mesenchymal stem cells, recognizes an epitope on endoglin (CD105). Biochem Biophys Res Commun 1999;265:134–9. 6. Baxter MA, Wynn RF, Jowitt SN, et al. Study of telomere length reveals rapid aging of human marrow stromal cells following in vitro expansion. Stem Cells 2004;22:675–82. 7. Bellantuono I, Aldahmash A, Kassem M. Aging of marrow stromal (skeletal) stem cells and their contribution to age-related bone loss. Biochim Biophys Acta – Mol Basis Dis 2009;1792:364–70. 8. Bianchi G, Banfi A, Mastrogiacomo M, et al. Ex vivo enrichment of mesenchymal cell progenitors by fibroblast growth factor 2. Exp Cell Res 2003;287: 98–105. 9. Bianco P, Costantini M, Dearden LC, Bonucci E. Alkaline phosphatase positive precursors of adipocytes in the human bone marrow. Br J Haematol 1988;68:401–4. 10. Bianco P, Riminucci M, Gronthos S, Robey PG. Bone marrow stromal stem cells: nature, biology, and potential applications. Stem Cells 2001;19:180–92. 11. Bianco P, Robey PG, Simmons PJ. Mesenchymal stem cells: revisiting history, concepts, and assays. Cell Stem Cell 2008;2:313–9. 12. Bieback K, Hecker A, Kocaomer A, et al. Human alternatives to fetal bovine serum for the expansion of mesenchymal stromal cells from bone marrow. Stem Cells 2009;27:2331–41. 13. Buhring H-J, Battula VL, Treml S, et al. Novel markers for the prospective isolation of human MSC. Ann NY Acad Sci 2007;1392:1000. 14. Calori GM, Albisetti W, Agus A, et al. Risk factors contributing to fracture nonunions. Inj – Int J Care Inj 2007;38:S11–8. 15. Caplan AI. Mesenchymal stem-cells. J Orthop Res 1991;9:641–50.
16. Caplan AI, Dennis JE. Mesenchymal stem cells as trophic mediators. J Cell Biochem 2006;98:1076–84. 17. Carrancio S, Lopez-Holgado N, Sanchez-Guijo FM, et al. Optimization of mesenchymal stem cell expansion procedures by cell separation and culture conditions modification. Exp Hematol 2008;36:1014–21. 18. Carson JS, Bostrom MPG. Synthetic bone scaffolds and fracture repair. Inj – Int J Care Inj 2007;38:S33–7. 19. Cattoretti G, Schiro R, Orazi A, et al. Bone-marrow stroma in humans – antinerve growth-factor receptor antibodies selectively stain reticular cells in vivo and in vitro. Blood 1993;81:1726–38. 20. Challen GA, Boles N, Lin KKY, Goodell MA. Mouse hematopoietic stem cell identification and analysis. Cytometry Part A 2009;75A:14–24. 21. Chamberlain G, Fox J, Ashton B, Middleton J. Concise review: mesenchymal stem cells: their phenotype, differentiation capacity, immunological features, and potential for homing. Stem Cells 2007;25:2739–49. 22. Chan CKF, Chen CC, Luppen CA, et al. Endochondral ossification is required for haematopoietic stem-cell niche formation. Nature 2009;457:U490–9. 23. Chehroudi B, Ghrebi S, Murakami H, et al. Bone formation on rough, but not polished, subcutaneously implanted Ti surfaces is preceded by macrophage accumulation. J Biomed Mater Res Part A 2010;93A:724–37. 24. Chen TM, Shih C, Lin TF, Lin FH. Reconstruction of calvarial bone defects using an osteoconductive material and post-implantation hyperbaric oxygen treatment. Mater Sci Eng C 2004;24:855–60. 25. Cook SD, Wolfe MW, Salkeld SL, Rueger DC. Effect of recombinant human osteogenic protein-1 on healing of segmental defects in nonhuman-primates. J Bone Joint Surg – American Volume 1995;77A:734–50. 26. Corselli M, Chen CW, Crisan M, et al. Perivascular ancestors of adult multipotent stem cells. Arterioscler Thromb Vasc Biol 2010;30:1104–9. 27. D’Ippolito G, Diabira S, Howard GA, et al. Marrow-isolated adult multilineage inducible (MIAMI) cells, a unique population of postnatal young and old human cells with extensive expansion and differentiation potential. J Cell Sci 2004;117:2971–81. 28. D’Ippolito G, Schiller PC, Ricordi C, et al. Age-related osteogenic potential of mesenchymal stromal stem cells from human vertebral bone marrow. J Bone Miner Res 1999;14:1115–22. 29. De Bari C, Dell’Accio F, Karystinou A, et al. A biomarker-based mathematical model to predict bone-forming potency of human synovial and periosteal mesenchymal stem cells. Arthritis Rheum 2008;58:240–50. 30. De Bari C, Dell’Accio F, Vanlauwe J, et al. Mesenchymal multipotency of adult human periosteal cells demonstrated by single-cell lineage analysis. Arthritis Rheum 2006;54:1209–21. 31. Deschaseaux F, Pontikoglou C, Sensebe L. Bone regeneration: the stem/progenitor cells point of view. J Cell Mol Med 2010;14:103–15. 32. Dimitriou R, Tsiridis E, Giannoudis PV. Current concepts of molecular aspects of bone healing. Inj – Int J Care Inj 2005;36:1392–404. 33. Dominici M, Le Blanc K, Mueller I, et al. Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy 2006;8:315–7. 34. Dominici M, Pritchard C, Garlits JE, et al. Hematopoietic cells and osteoblasts are derived from a common marrow progenitor after bone marrow transplantation. Proc Natl Acad Sci U S A 2004;101:11761–6. 35. Dowthwaite GP, Bishop JC, Redman SN, et al. The surface of articular cartilage contains a progenitor cell population. J Cell Sci 2004;117:889–97. 36. Drosse I, Volkmer E, Capanna R, et al. Tissue engineering for bone defect heating: an update on a multi-component approach. Inj – Int J Care Inj 2008;39:S9–20. 37. Einhorn TA. The science of fracture healing. J Orthop Trauma 2005;19:S4–6. 38. Eyckmans J, Luyten FP. Species specificity of ectopic bone formation using periosteum-derived mesenchymal progenitor cells. Tissue Eng 2006;12: 2203–13. 39. Fox JM, Chamberlain G, Ashton BA, Middleton J. Recent advances into the understanding of mesenchymal stem cell trafficking. Br J Haematol 2007;137:491–502. 40. Friedenstein AJ, Latzinik NW, Grosheva AG, Gorskaya UF. Marrow microenvironment transfer by heterotopic transplantation of freshly isolated and cultured-cells in porous sponges. Exp Hematol 1982;10:217–27. 41. Gang EJ, Bosnakovski D, Figueiredo CA, et al. SSEA-4 identifies mesenchymal stem cells from bone marrow. Blood 2007;109:1743–51. 42. Gangji V, Hauzeur JP, Matos C, et al. Treatment of osteonecrosis of the femoral head with implantation of autologous bone-marrow cells – a pilot study. J Bone Joint Surg – American Volume 2004;86A:1153–60. 43. Granero-Molto F, Weis JA, Miga MI, et al. Regenerative effects of transplanted mesenchymal stem cells in fracture healing. Stem Cells 2009;27:1887–98. 44. Gundle R, Joyner CJ, Triffitt JT. Human bone tissue formation in-diffusion chamber culture in-vivo by bone-derived cells and marrow stromal fibroblastic cells. Bone 1995;16:597–601. 45. Hernigou P, Beaujean F. Treatment of osteonecrosis with autologous bone marrow grafting. Clin Orthop 2002:14–23. 46. Hillam R, Jackson M, Goodship A, et al. Comparison of physiological strains in the human skull and tibia. Bone 1996;19:686–1686. 47. Horner EA, Kirkham J, Wood D, et al. Long bone defect models for tissue engineering applications: criteria for choice. Tissue Eng Part B – Rev 2010;16:263–71. 48. Horwitz EM, Gordon PL, Koo WKK, et al. Isolated allogeneic bone marrowderived mesenchymal cells engraft and stimulate growth in children with osteogenesis imperfecta: implications for cell therapy of bone. Proc Natl Acad Sci U S A 2002;99:8932–7.
E. Jones, X. Yang / Injury, Int. J. Care Injured 42 (2011) 562–568 49. Horwitz EM, Prockop DJ, Fitzpatrick LA, et al. Transplantability and therapeutic effects of bone marrow-derived mesenchymal cells in children with osteogenesis imperfecta. Nat Med 1999;5:309–13. 50. Howard D, Partridge K, Yang XB, et al. Immunoselection and adenoviral genetic modulation of human osteoprogenitors: in vivo bone formation on PLA scaffold. Biochem Biophys Res Commun 2002;299:208–15. 51. Huang GTJ, Gronthos S, Shi S. Mesenchymal stem cells derived from dental tissues vs. those from other sources: their biology and role in regenerative medicine. J Dent Res 2009;88:792–806. 52. Hui JHP, Li L, Teo YH, et al. Comparative study of the ability of mesenchymal stem cells derived from bone marrow, periosteum, and adipose tissue in treatment of partial growth arrest in rabbit. Tissue Eng 2005;11:904–12. 53. Im GI, Shin YW, Lee KB. Do adipose tissue-derived mesenchymal stem cells have the same osteogenic and chondrogenic potential as bone marrowderived cells? Osteoarthritis Cartilage 2005;13:845–53. 54. Ishii M, Koike C, Igarashi A, et al. Molecular markers distinguish bone marrow mesenchymal stem cells from fibroblasts. Biochem Biophys Res Commun 2005;332:297–303. 55. Jones E, English A, Churchman SM, et al. Large-scale extraction and characterization of CD271+ multipotential stromal cells from trabecular bone in health and osteoarthritis: implications for bone regeneration strategies based on uncultured or minimally cultured multipotential stromal cells. Arthritis Rheum 2010;62:1944–54. 56. Jones E, McGonagle D. Human bone marrow mesenchymal stem cells in vivo. Rheumatology 2008;47:126–31. 57. Jones EA, Kinsey SE, English A, et al. Isolation and characterization of bone marrow multipotential mesenchymal progenitor cells. Arthritis Rheum 2002;46:3349–60. 58. Jones KB, Seshadri T, Krantz R, et al. Cell-based therapies for osteonecrosis of the femoral head. Biol Blood Marrow Transplant 2008;14:1081–7. 59. Kanczler JM, Oreffo ROC. Osteogenesis and angiogenesis: the potential for engineering bone. Eur Cell Mater 2008;15:100–14. 60. Kassem M, Abdallah BM, Saleed H. Osteoblastic cells: differentiation and trans-differentiation. Arch Biochem Biophys 2008;473:183–7. 61. Khosla S, Eghbali-Fatourechi GZ. Circulating cells with osteogenic potential. Skeletal development and remodeling in health, disease, and aging. 2006. pp. 489–97. 62. Kitaori T, Ito H, Schwarz EA, et al. Stromal cell-derived factor 1/CXCR4 signaling is critical for the recruitment of mesenchymal stem cells to the fracture site during skeletal repair in a mouse model. Arthritis Rheum 2009;60:813–23. 63. Kokubu T, Hak DJ, Hazelwood SJ, Reddi AH. Development of an atrophic nonunion model and comparison to a closed healing fracture in rat femur. J Orthop Res 2003;21:503–10. 64. Le Blanc K, Pittenger MF. Mesenchymal stem cells: progress toward promise. Cytotherapy 2005;7:36–45. 65. Le Blanc K, Rasmusson I, Sundberg B, et al. Treatment of severe acute graftversus-host disease with third party haploidentical mesenchymal stem cells. Lancet 2004;363:1439–41. 66. Lymperi S, Ferraro F, Scadden DT. The HSC niche concept has turned 31 Has our knowledge matured? In: Zaidi M, editor. Skeletal biology and medicine. 2010:12–8. 67. Marcacci M, Kon E, Moukhachev V, et al. Stem cells associated with macroporous bioceramics for long bone repair: 6-to 7-year outcome of a pilot clinical study. Tissue Eng 2007;13:947–55. 68. Mareddy A, Crawford R, Brooke G, Xiao Y. Clonal isolation and characterisation of bone marrow stromal cells from patients with osteoarthritis. Tissue Eng 2007;13:819–29. 69. Martinez C, Hofmann TJ, Marino R, et al. Human bone marrow mesenchymal stromal cells express the neural ganglioside GD2: a novel surface marker for the identification of MSCs. Blood 2007;109:4245–8. 70. Matsumoto T, Kawamoto A, Kuroda R, et al. Therapeutic potential of vasculogenesis and osteogenesis promoted by peripheral blood CD34-positive cells for functional bone healing. Am J Pathol 2006;169:1440–57. 71. Matsumoto T, Kuroda R, Mifune Y, et al. Circulating endothelial/skeletal progenitor cells for bone regeneration and healing. Bone 2008;43:434–9. 72. Meirelles LD, Caplan AI, Nardi NB. In search of the in vivo identity of mesenchymal stem cells. Stem Cells 2008;26:2287–99. 73. Meirelles LDS, Chagastelles PC, Nardi NB. Mesenchymal stem cells reside in virtually all post-natal organs and tissues. J Cell Sci 2006;119:2204–13. 74. Metcalf D. Concise review: hematopoietic stem cells and tissue stem cells: current concepts and unanswered questions. Stem Cells 2007-0544 2007. 75. Modder UI, Khosla S. Skeletal stem/osteoprogenitor cells: current concepts, alternate hypotheses, and relationship to the bone remodeling compartment. J Cell Biochem 2008;103:393–400. 76. Muraglia A, Cancedda R, Quarto R. Clonal mesenchymal progenitors from human bone marrow differentiate in vitro according to a hierarchical model. J Cell Sci 2000;113:1161–6. 77. Murphy WL, Simmons CA, Kaigler D, Mooney DJ. Bone regeneration via a mineral substrate and induced angiogenesis. J Dent Res 2004;83:204–10. 78. Nakahara H, Bruder SP, Haynesworth SE, et al. Bone and cartilage formation in diffusion-chambers by subcultured cells derived from the periosteum. Bone 1990;11:181–8. 79. Niemeyer P, Fechner K, Milz S, et al. Comparison of mesenchymal stem cells from bone marrow and adipose tissue for bone regeneration in a critical size defect of the sheep tibia and the influence of platelet-rich plasma. Biomaterials 2010;31:3572–9.
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80. Noel D, Caton D, Roche S, et al. Cell specific differences between human adipose-derived and mesenchymal-stromal cells despite similar differentiation potentials. Exp Cell Res 2008;314:1575–84. 81. Noth U, Osyczka AM, Tuli R, et al. Multilineage mesenchymal differentiation potential of human trabecular bone-derived cells. J Orthop Res 2002;20: 1060–9. 82. Nuss KMR, Auer JA, Boos A, Von Rechenberg B. An animal model in sheep for biocompatibility testing of biomaterials in cancellous bones. BMC Musculoskelet Disord 2006;7. 83. Partridge K, Yang XB, Clarke NMP, et al. Adenoviral BMP-2 gene transfer in mesenchymal stem cells: in vitro and in vivo bone formation on biodegradable polymer scaffolds. Biochem Biophys Res Commun 2002;292:144–52. 84. Phinney DG, Prockop DJ. Concise review: mesenchymal stem/multipotent stromal cells: the state of transdifferentiation and modes of tissue repair – current views. Stem Cells 2007;25:2896–902. 85. Pierre-Louis O, Clay D, de la Grange PB, et al. Dual SP/ALDH functionalities refine the human hematopoietic Lin( )CD34(+)CD38( ) stem/progenitor cell compartment. Stem Cells (Miamisburg) 2009;27:2552–62. 86. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999;284:143–7. 87. Quarto R, Mastrogiacomo M, Cancedda R, et al. Repair of large bone defects with the use of autologous bone marrow stromal cells. N Engl J Med 2001;344:385–6. 88. Quirici N, Soligo D, Bossolasco P, et al. Isolation of bone marrow mesenchymal stem cells by anti-nerve growth factor receptor antibodies. Exp Hematol 2002;30:783–91. 89. Rebelatto CK, Aguiar AM, Moretao MP, et al. Dissimilar differentiation of mesenchymal stem cells from bone marrow, umbilical cord blood, and adipose tissue. Exp Biol Med 2008;233:901–13. 90. Rodriguez JP, Garat S, Gajardo H, et al. Abnormal osteogenesis in osteoporotic patients is reflected by altered mesenchymal stem cells dynamics. J Cell Biochem 1999;75:414–23. 91. Rodriguez JP, Montecinos L, Rios S, et al. Mesenchymal stem cells from osteoporotic patients produce a type I collagen-deficient extracellular matrix favoring adipogenic differentiation. J Cell Biochem 2000;79:557–65. 92. Sacchetti B, Funari A, Michienzi S, et al. Self-renewing osteoprogenitors in bone marrow sinusoids can organize a hematopoietic microenvironment. Cell 2007;131:324–36. 93. Sakaguchi Y, Sekiya I, Yagishita K, et al. Suspended cells from trabecular bone by collagenase digestion become virtually identical to mesenchymal stem cells obtained from marrow aspirates. Blood 2004;104:2728–35. 94. Sakaguchi Y, Sekiya I, Yagishita K, Muneta T. Comparison of human stem cells derived from various mesenchymal tissues – superiority of synovium as a cell source. Arthritis Rheum 2005;52:2521–9. 95. Santos MI, Reis RL. Vascularization in bone tissue engineering: physiology, current strategies, major hurdles and future challenges. Macromol Biosci 2010;10:12–27. 96. Schneider RK, Puellen A, Kramann R, et al. The osteogenic differentiation of adult bone marrow and perinatal umbilical mesenchymal stem cells and matrix remodelling in three-dimensional collagen scaffolds. Biomaterials 2010;31:467–80. 97. Scotti C, Tonnarelli B, Papadimitropoulos A, et al. Recapitulation of endochondral bone formation using human adult mesenchymal stem cells as a paradigm for developmental engineering. Proc Natl Acad Sci U S A 2010;107:7251–6. 98. Shetty P, Cooper K, Viswanathan C. Comparison of proliferative and multilineage differentiation potentials of cord matrix, cord blood, and bone marrow mesenchymal stem cells. Asian J Transfus Sci 2010;4:14–24. 99. Short B, Brouard N, Occhiodoro-Scott T, et al. Mesenchymal stem cells. Arch Med Res 2003;34:565–71. 100. Simmons PJ, Torokstorb B. Identification of stromal cell precursors in human bone-marrow by a novel monoclonal-antibody, Stro-1. Blood 1991;78:55–62. 101. Sotiropoulou PA, Perez SA, Salagianni M, et al. Characterization of the optimal culture conditions for clinical scale production of human mesenchymal stem cells. Stem Cells (Miamisburg) 2006;24:462–71. 102. Sugiyama T, Kohara H, Noda M, Nagasawa T. Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches. Immunity 2006;25:977–88. 103. Tao J, Sun Y, Wang QG, Liu CW. Induced endothelial cells enhance osteogenesis and vascularization of mesenchymal stem cells (vol. 190, 185, 2009). Cells Tissues Organs 2010;191:430–1430. 104. Tasso R, Fais F, Reverberi D, et al. The recruitment of two consecutive and different waves of host stem/progenitor cells during the development of tissue-engineered bone in a murine model. Biomaterials 2010;31:2121–9. 105. Tokoyoda K, Egawa T, Sugiyama T, et al. Cellular niches controlling B lymphocyte behavior within bone marrow during development. Immunity 2004;20:707–18. 106. Tortelli F, Tasso R, Loiacono F, Cancedda R. The development of tissueengineered bone of different origin through endochondral and intramembranous ossification following the implantation of mesenchymal stem cells and osteoblasts in a murine model. Biomaterials 2010;31:242–9. 107. Tuli R, Tuli S, Nandi S, et al. Characterization of multipotential mesenchymal progenitor cells derived from human trabecular bone. Stem Cells 2003;21:681– 93. 108. Usami K, Mizuno H, Okada K, et al. Composite implantation of mesenchymal stem cells with endothelial progenitor cells enhances tissue-engineered bone formation. J Biomed Mater Res Part A 2009;90A:730–41.
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109. Wagner W, Horn P, Castoldi M, et al. Replicative senescence of mesenchymal stem cells: a continuous and organized process. PLoS One 2008;3:e2213. 110. Wagner W, Wein F, Seckinger A, et al. Comparative characteristics of mesenchymal stem cells from human bone marrow, adipose tissue, and umbilical cord blood. Exp Hematol 2005;33:1402. 111. Weiss ML, Medicetty S, Bledsoe AR, et al. Human umbilical cord matrix stem cells: preliminary characterization and effect of transplantation in a rodent model of Parkinson’s disease. Stem Cells 2006;24:781–92. 112. Yang XB, Whitaker MJ, Clarke NMP, et al. In vivo human bone and cartilage formation using porous polymer scaffolds encapsulated with bone morphogenetic protein-2. J Bone Miner Res 2003;18:1366–11366.
113. Yang XBB, Webb D, Blaker J, et al. Evaluation of human bone marrow stromal cell growth on biodegradable polymer/bioglass (R) composites. Biochem Biophys Res Commun 2006;342:1098–107. 114. Yang XBB, Whitaker MJ, Sebald W, et al. Human osteoprogenitor bone formation using encapsulated bone morphogenetic protein 2 in porous polymer scaffolds. Tissue Eng 2004;10:1037–45. 115. Yu HY, VandeVord PJ, Gong WM, et al. Promotion of osteogenesis in tissueengineered bone by pre-seeding endothelial progenitor cells-derived endothelial cells. J Orthop Res 2008;26:1147–52. 116. Yu HY, VandeVord PJ, Mao L, et al. Improved tissue-engineered bone regeneration by endothelial cell mediated vascularization. Biomaterials 2009;30:508–17.
Contents lists available at ScienceDirect
Injury journal homepage: www.elsevier.com/locate/injury
Mesenchymal stem cells and bone regeneration: Current status Elena Jones a,*, Xuebin Yang b a Rheumatology, Mesenchymal Stem Cell Biology Group, Academic Unit of Musculoskeletal Disease, Leeds Institute of Molecular Medicine, Room 5.24 Clinical Sciences Building, St. James’s University Hospital, University of Leeds, Beckett Street, Leeds LS9 7TF, United Kingdom b Tissue Engineering Research, Biomaterials & Tissue Engineering Group, Department of Oral Biology, Leeds Dental Institute, University of Leeds, United Kingdom
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 17 March 2011
The enhancement of bone regeneration with biological agents including osteogenic growth factors and mesenchymal stem cells (MSCs) is becoming a clinical reality. Many exciting findings have been obtained following MSC implantation in animal models, and the data demonstrating their clinical efficacy in humans are promising. The overwhelming majority of experimental work has been performed with MSCs ‘‘amplified’’ in vitro. The nature of native MSCs in skeletal tissues however, remains poorly understood. This review summarizes recent findings pertaining to the definition and characterisation of MSCs in skeletal tissues and discusses the mechanisms of their actions in regenerating of bone in vivo. In respect to traditional tissue engineering paradigm, we bring together literature showing that the ways MSCs are extracted, expanded and implanted can considerably affect bone formation outcomes. Additionally, we discuss current animal models used in MSC research and highlight recent experiments showing important contribution of the host, and not only donor MSCs, in bone tissue formation. This knowledge provides a platform for novel therapy development for bone regeneration based on pharmacologically manipulated endogenous MSCs. ß 2011 Elsevier Ltd. All rights reserved.
Keywords: Mesenchymal stem cells Osteoprogenitors Bone regeneration Tissue engineering
MSCs and osteoprogenitors – current definitions and assays Regeneration of bone is believed to be mediated via osteoprogenitors and their ancestors, the mesenchymal stem cells (MSCs). Whilst the term MSC is commonly used in scientific and clinical literature, many stem cell biologists recognise that MSCs fall short of being true ‘‘stem cells’’.11,33 To reflect this, the International Society for Cellular Therapy position statement has declared an alternative terminology, referring to these cells as ‘‘multipotent mesenchymal stromal cells’’.33 One of the main reasons for scientific community’s reluctance to use the term ‘‘stem cells’’ in relation to MSCs lies in the fact that their life-long self-renewal in vivo has not yet been demonstrated using reliable animal models.11 To put MSCs in a context of other adult stem cells, it is worth comparing them with hematopoietic stem cells (HSCs). HSCs give rise to all blood cell lineages; they have a well-defined niche in the bone marrow (BM),66 and their development during embryogenesis is very clearly mapped.74 In contrast, MSCs reside in virtually all peri- and post-natal tissues72,73 and their origins and migration patterns during embryonic development remain obscure.31,84 In our view, the main reason for such disparity lies in the
* Corresponding author. Tel.: +44 113 2065647; fax: +44 113 3438502. E-mail address: [email protected] (E. Jones). 0020–1383/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.injury.2011.03.030
retrospective way of defining MSCs. Whereas HSCs are defined prospectively, based on their native phenotype in vivo,20,85 MSCs defined based on the phenotype of their culture-amplified progeny, i.e., retrospectively.86 In late 1990s, several surface molecules have been described to be specific for cultured MSCs,5 but these molecules, including CD73 and CD105, later turned out to be expressed on ordinary fibroblasts54,56 limiting their utility for defining MSCs in vivo. Concurrently, several markers have been identified as specific for native MSCs, but they are absent on their cultured progeny. These markers include Stro-1100 and CD271.13,56,57,88 The current lack of uniformly accepted, reliable markers that are expressed stably on both native and cultured MSCs, precludes their accurate tracing in development as well as during tissue regeneration. A similar lack of clarity currently pertains to defining osteoprogenitors. MSCs and HSCs were discovered around the same time40 and the same concept of their lineage maturation via committed progenitors was adopted.15,86 Compared to stem cells, these committed progenitors, commonly termed colony-forming units, have diminished proliferative capacities and a limited differentiation. In the HSCs field, colony-forming units-myeloid, erythroid, etc., have very distinct morphologies74 and clear cell surface phenotypes.20,85 In the MSC field, colony-forming assays exist only for osteo-28 and adipogenic progenitors,94 but not for chondrogenic progenitors or putative myogenic progenitors. After several decades of searching, no universally accepted surface
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markers for any of these mesenchymal progenitors have been found. To complicate things further, an inter-conversion from an adipogenic to osteogenic lineage and vice versa have been achieved experimentally.60 Such ‘‘plasticity’’ of the MSC lineage84 makes the interpretation of colony-forming unit-osteoblast and adipocyte data very difficult. Therefore specific markers for osteoprogenitors as distinct from more immature MSCs are yet to be developed. Recently, a model of the MSC hierarchy based on cell proliferation rate was proposed.68 Within the MSC pool of progenitors, more rapidly growing cells have been shown to possess multilineage differentiation capacities whereas slowergrowing cells were preferentially osteogenic.68 Observations like these should ultimately lead to the discovery of definitive markers for both MSCs and osteoprogenitors. Identity of MSCs in the BM, bone and periosteum Due to considerations described in the above section, many laboratories around the world have invested huge efforts into prospective purification of native BM MSCs.11,31,56,72 Several reviews, including ours,31,56,72 have provided lists of potential candidate markers of native BM MSCs. Apart from CD271, these novel markers include GD2,69 SSEA441 and, more recently, CD146.92 Despite an ongoing debate on relative merits of individual markers, a general consensus is now emerging in relation to the topography of MSCs in the BM.11,31,56 According to this view, MSCs ‘‘hide’’ under a guise of reticular stromal cells, which traverse marrow cavities and extend to bone surfaces.11,56 Because BM endothelium has no clearly discernible perivascular cells, these reticular cells are considered as bone fide pericytes in the marrow.10 In accordance with their MSC nature, these perivascular/ reticular cells can give rise to adipocytes9 and be involved in organising bone remodelling units.75 Furthermore, they support hematopoiesis by releasing cytokines essential for HSC trafficking and maturation, including stromal-derived factor 1, SDF-1.19,102,105 All of this goes well with experimental phenomenon of MSC ‘‘plasticity’’ mentioned above. Early findings demonstrating relative abundance of reticular cells in situ19 have put into question an original concept of rare BM MSCs.86 Following an initial findings by Sakaguchi et al.93 we have recently demonstrated that high numbers of MSCs could be extracted from trabecular bone cavities by enzymatic breakdown of marrow extracellular matrix.55 This finding suggested that only a proportion of native MSCs have been actually obtained by marrow aspiration.55 Our data also suggest that a concept of systemic circulation of rare BM MSCs to the sites of injury34 may become outdated. Instead, an activation and chemotactic migration of fairly abundant local MSCs adjacent to injury area is likely to represent a much more plausible explanation, as proposed by others.21,39 Periosteum is another tissue that plays an essential role in callus formation following fracture.32,37 The existence of periosteal MSCs78 has been more recently confirmed at the single cell level,30 however their topography remains unknown. Single periosteal MSCs appear to be ‘‘defaulted’’ to an osteogenic differentiation programme.29 A similar propensity to osteogenesis, following in vitro expansion, has been demonstrated for BM MSCs,76 albeit using somewhat older methodology. This makes perfect sense considering the local microenvironment these MSCs are residing and a continuing need for bone remodelling that occurs physiologically during the lifetime of an individual. MSCs have been also found in frank bone experimentally devoid of soft marrow.81,99,107 The cells that grow out of bone explants generating cultures identical to MSCs81,107 are likely to be derived
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from pericytes. Perivascular topography of MSCs in many tissues is now commonly accepted.11,72 However, MSCs are likely to form only a fraction of perycites26,72; otherwise the most vascularised tissues would be automatically the richest for MSCs. Furthermore, tissues like cartilage superficial layer lack the blood supply with vessels and pericytes, yet possess some level of the MSC activity.35 Based on these data one can conclude that, although MSC as a pericyte concept provides an excellent explanation for the abundance of MSCs in almost every tissue in the body, it does not exhaustively explain all the experimental data observed so far. New methods for extraction of pericytes from cortical bone would be needed to establish the identity of bone-resident MSCs. Fabrication of tissue engineered bone – not only MSCs! From a tissue engineer perspective an argument whether MSCs are true stem cells or not may not be relevant. Indeed, cultureexpanded BM MSCs have clearly shown excellent repair in animal models67,87 and their safety profiles in clinical cohort studies for osteogenesis imperfecta48,49 and osteonecrosis of femoral head42,45,58 have been satisfactory. However, the translation of these pilot trials into clinical practice faces many challenges, beyond the safety concerns regarding the use of foetal calf serum, described elsewhere.12 There is still a debate as to which expansion conditions are the best for the manufacture of MSCs intended for bone repair. For example, cell seeding density,27,101 FGF2 supplementation8 and low oxygen tension,17,27 have all been shown to improve the longevity and the osteogenic potency of cultured MSCs, but which conditions are optimal remain to be established. For repairing large bone defects, massive quantities of MSCs are required. However, cultured MSCs gradually loose their potency and, eventually, stop growing following extensive cultivation.3,6,109 Rare MSCs from autologous BM aspirates may become senescent during numerous rounds of amplification required. Consequently, many tissue engineers turn their attention to adipose,110 dental pulp1,51 or umbilical cord111 tissues, which appear to be richer for MSCs. The utility of adipose-derived MSCs for bone repair application is however still debatable,52,80,89 with some studies showing their inferiority compared to BM MSCs.53,79 The osteogenic capacity of umbilical cord matrix-derived MSCs, on the other hand, appears to be similar to BM MSCs, in both 2dimentional (2D)98 and 3D differentiation conditions.96 Some examples of in vitro trilineage differentiation from BM-, adiposeand dental pulp-derived MSCs obtained in our laboratories are shown in Fig. 1. Another interesting recent development relates to scaffolds seeded with pre-differentiated MSCs97 or to composites of MSCs mixed with endothelial lineage cells.59,95,108 Vascularisation approaches for large bone grafts are described in detail elsewhere (reviewed in Santos and Reis and Kanczler and Oreffo59,95). In brief, scaffolds loaded with angiogenic growth factors have been used initially.4,77 Nowadays, the implantation of autologous endothelial progenitors cells (EPCs) is considered as an alternative.31,95,108,115,116 In one study, peripheral blood CD34+ autologous EPCs, were transplanted systemically leading to the enhancement of angiogenesis and osteogenesis in delayed fracture unions.70 Based on these findings, a ‘‘mobilisation’’ of host endothelial lineage cells with growth factors may be envisaged as a novel way to treat non-unions and complex fractures. An existence of circulating osteoblastic progenitors61 or circulating cells with dual propensity to become EPCs and osteoblasts has been recently proposed;71 although very interesting, these results await further validation by other investigators. Altogether these data show that MSCs of different origins as well as other cell types including EPCs can now be used to engineer new bone.
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Fig. 1. Dissimilar in vitro differentiation capacities of MSCs expanded from human bone marrow, dental pulp and adipose tissue (infrapatella fat pad). BM and adipose MSCs have robust tri-lineage differentiation, whereas dental pulp MSCs have very low adipogenesis. Adipogenesis – Oil Red staining, chondrogenesis – Toluidine Blue staining, osteogenesis – Alizarin Red staining on day 21 post-induction. Original magnification 100 (adipogenesis) and 50 (chondrogenesis).
Animal models for investigations of the role of MSCs in bone repair As a norm, in vitro differentiation experiments provide only initial points of reference to explore MSC differentiation capabilities. Investigations in animal models are next needed for the study of safety and efficacy of MSC preparations. An ideal animal model for bone regeneration should mimic clinical conditions of bone injury, create a permissive microenvironment for diffusion of nutrients, gases and growth factors, utilise fixation and mechanical load through the defect, as in the clinic, and permit angiogenesis.47 Currently available animal models for bone repair are not yet ideal and vary from simple subcutaneous implantation (Fig. 2) to functional complex tissue regeneration, including in vivo bioreactors.47 The ectopic subcutaneous implant model (Fig. 2) is the most commonly used; it is the least invasive and more suitable for preliminary screening of MSC formulations, scaffolds and growth factors.47 Although a number of different species have been used for this model,23,38,112 to date, the immunocompromised (Nude) mouse is the most popular.113 Its limitations include eventual reabsorption of newly formed bone due to lack of appropriate mechanical stimulation and the uncertainty regarding interactions between the implanted cells and host tissues.47 The most recent work from Cancedda Laboratory has brought some light on donor and host MSC involvement in subcutaneous implant model. It has shown that the origin of new bone depended
on the maturation status of the implanted cells.106 When they implanted osteoblasts, a new bone was of donor origin, formed directly via the intramembranous ossification. However, when they implanted MSCs, a new bone was of the host origin and formed via endochondral ossification.106 In a follow-up paper, the same group showed that MSC-seeded scaffolds have ‘‘induced’’ two consecutive waves of host cell migration.104 Host endothelial cells were attracted to the scaffolds first, followed by a wave of host perivascular cells, potentially responsible for the formation of a new bone. Osteochondral ossification in subcutaneous model has also been achieved following implantation of MSCs pre-differentiated to chondrocytes.97 The chondrocytes could indeed attract host vasculature to the developing graft.22 Another animal model, the diffusion chamber model, provides an enclosed, permissive environment within a host animal to allow free exchange of nutrients but effectively isolates the experimental cells from the host tissues.2,44,83 All new bone is therefore of a donor origin. Although the diffusion chamber model has been successfully used to test bone tissue regeneration,44,50,114 it lacks effective mechanical stimuli needed for bone remodelling. Therefore site-specific bone defect models, particularly for weight bearing testing and tissue engineering of large bone constructs, are being actively developed.25,63,82 For non-weight bearing testing, the bone defect can be made within the calvaria, rib or mandibles, which have relatively low mechanical forces.46 In this model, most scaffold materials can be moulded to fit the bone defect and do not require further fixation.
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Fig. 2. Subcutaneously implant model (A and B), diffusion chamber model (C and D) and bone defect model (E and F) in vivo. (A) Human bone marrow stromal cellsbiomaterial construct implanted subcutaneously in nude mice and vascular supply to the implants (arrow); (B) Sirius red staining showed new bone formation within the pleiotrophin absorbed PLGA porous scaffold (reproduced from J Bone Miner Res 2003;18:45–57, Yang et al., Copyright (2003) with permission from the American Society from Bone and Mineral Research); (C) X-ray images showed high density bone nodule formation and (D) Alcian blue staining showed cartilage matrix formation within the diffusion chamber (Reprinted from BBRC, 292:144–152, Yang et al., Copyright (2002), with permission from Elsevier) (Partridge et al., 2002); (E) segmental bone defect model in which a 2 mm bone defect created in a mouse femur, and (F) the mouse femur defect was repaired by a porous poly(-lactic acid) scaffold and intramedullar pin fixation (scale bars: 2 mm). A, E and F are reprinted from Advances in Tissue Engineering, J Polak et al., Copyright @ Imperial College Press.
The periosteum can then be closed to cover the bone defect.24 For weight bearing testing, the defect can be made in long bones (e.g., the femur or tibia). Although the methods for creating a critical defect are various, the most commonly used two methods use either an osteotomy approach or a traumatic approach. Osteotomy can surgically remove the required length of bone from a predetermined site, producing a consistent defect with a ‘clean’ cut. However, this does not reflect the real conditions following traumatic injury which produce a jagged cut edge bone fracture including the trauma of surrounding soft tissue. To achieve this, a three-point bending device and/or impact device has been designed.63 Then the bone defect is reconstructed with the test material alone and/or in combination with cells and growth factors and fixed using external or internal fixation. Since the animal will start to move after recovery, the biomechanical properties of the selected scaffold are crucial for optimum bone regeneration in a weight bearing bone defect. Scaffolds need to be initially strong enough to allow weight-bearing during the first stage of the regenerative process but also biodegradable at the right time to allow bone remodelling.47 The contribution of host and donor MSCs to bone formation in these complex animal models remains to be elucidated. ‘‘Indirect’’ actions of implanted MSCs As mentioned in previous sections, the main rationale for the use of MSCs in bone repair applications was based on their direct ability to generate osteoprogenitors and osteoblasts. The MSC osteogenesis have been further enhanced by simultaneous introduction of bone morphogenic protein 2 (BMP2) or other osteoinductive growth factors, either in slow-release system or as genes delivered into MSCs by viral or non-viral delivery systems.103 The addition of supporting growth factors has become particularly relevant when bone repair in older, osteoporotic or diabetic individuals was considered, since the osteogenic function
of autologous MSCs in these conditions is known to be compromised.7,58,90,91 However, more recent experimental evidence has suggested that the therapeutic action of implanted MSCs may not be solely limited to their direct conversion into osteoblasts. Based on a wealth of evidence from the cardiovascular field, where MSC therapy has been used extensively, it appears that transplanted MSC possess other poorly defined functionalities, broadly referred as ‘‘trophic’’ or paracrine effects.16,84 These include anti-apoptotic effects, immunoregulatory function, and stimulation of host cell migration. Molecular mechanisms of these effects are yet poorly understood, but recent animal studies by Tortelli et al. and Scotti et al. highlighted above97,106 suggest that these ‘‘indirect’’ actions of implanted MSCs, particularly in attracting host vasculature, may be as important in bone tissue regeneration as their direct ability to form new bone. In this respect, it is reasonable to hypothesis that implanted MSCs can act as ‘‘seeds’’ or ‘‘signalling centres’’, orchestrating and organising the host response to the injury; and this is in addition to their direct role as a source of new osteoblasts. In fracture repair settings, such ‘‘trophic’’ functionalities of MSCs at the initial inflammatory phases may be critically important, considering that MSCs are known to switch off inflammatory responses.64,65 The knowledge of the ‘‘trophic’’ actions of MSCs and their temporal sequence is fracture repair, in particular, may lead to novel therapeutic approaches in the treatment of nonunions. For example, SDF-1 chemotactic gradients have been shown to affect migration patterns of both injected43 and host MSCs.62 Targeted delivery of SDF-1 can therefore be used as a novel approach of creating an artificial ‘‘signalling centre’’ to trigger the migration of host MSCs, without implantation of exogenous MSCs. Alternatively, autologous MSCs can be injected into fracture haematoma to manipulate the transition from the inflammatory phases to the callus formation stages of fracture repair.
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Back to native MSCs As highlighted above, recent in vivo evidence suggests that the understanding of the biology of native MSCs in vivo, as well as their relationship with local endothelial cells, are critical for the development of novel bone repair strategies. MSC cultureexpansion will still be necessary for generating enough MSCs to populate large scaffolds designed for repairing critical-size bone defects.18,36 A careful selection of MSC sources and ‘‘priming’’ of scaffolds with mixed MSC formulations will lead to ‘‘quality’’ replacement tissues for these indications. In fracture repair, on the other hand, where defects are often small and host factors are significant,14 novel in situ approaches for the enhancement of local responses by host MSCs appear to be more practical and costeffective. Therefore, studies aimed at isolation and characterisation of MSCs in different tissues, in health and disease, should continue. When precise dysfunctions of native MSCs in these diseases are uncovered, corrective pharmaceutical agents could be designed and manufactured, leading to novel, cell-free and cost-effective treatments for bone repair. Scientific advances in the understanding of the biology of native MSCs in vivo have therefore significant implications for future strategies to repair bone. Conflict of interest EJ and XBY declare no conflict of interest. Role of the funding source The work of both authors is supported by WELMEC, a Centre of Excellence in Medical Engineering funded by the Wellcome Trust and EPSRC, under grant number WT 088908/Z/09/Z and also by NIHR Leeds Biomedical Research Unit grant. EJ work is supported by European Commission FP7 Purstem project and XBY work is supported by TSB, WUN and RegN8. References 1. Alge DL, Zhou D, Adams LL, et al. Donor-matched comparison of dental pulp stem cells and bone marrow-derived mesenchymal stem cells in a rat model. J Tissue Eng Regen Med 2010;4:73–81. 2. Ashton BA, Allen TD, Howlett CR, et al. Formation of bone and cartilage by marrow stromal cells in diffusion-chambers invivo. Clin Orthop 1980:294–307. 3. Banfi A, Bianchi G, Galotto M, et al. Bone marrow stromal damage after chemo/ radiotherapy: occurrence, consequences and possibilities of treatment. Leuk Lymphoma 2001;42:863–70. 4. Barralet J, Gbureck U, Habibovic P, et al. Angiogenesis in calcium phosphate scaffolds by inorganic copper ion release. Tissue Eng Part A 2009;15:1601–9. 5. Barry FP, Boynton RE, Haynesworth S, et al. The monoclonal antibody SH-2, raised against human mesenchymal stem cells, recognizes an epitope on endoglin (CD105). Biochem Biophys Res Commun 1999;265:134–9. 6. Baxter MA, Wynn RF, Jowitt SN, et al. Study of telomere length reveals rapid aging of human marrow stromal cells following in vitro expansion. Stem Cells 2004;22:675–82. 7. Bellantuono I, Aldahmash A, Kassem M. Aging of marrow stromal (skeletal) stem cells and their contribution to age-related bone loss. Biochim Biophys Acta – Mol Basis Dis 2009;1792:364–70. 8. Bianchi G, Banfi A, Mastrogiacomo M, et al. Ex vivo enrichment of mesenchymal cell progenitors by fibroblast growth factor 2. Exp Cell Res 2003;287: 98–105. 9. Bianco P, Costantini M, Dearden LC, Bonucci E. Alkaline phosphatase positive precursors of adipocytes in the human bone marrow. Br J Haematol 1988;68:401–4. 10. Bianco P, Riminucci M, Gronthos S, Robey PG. Bone marrow stromal stem cells: nature, biology, and potential applications. Stem Cells 2001;19:180–92. 11. Bianco P, Robey PG, Simmons PJ. Mesenchymal stem cells: revisiting history, concepts, and assays. Cell Stem Cell 2008;2:313–9. 12. Bieback K, Hecker A, Kocaomer A, et al. Human alternatives to fetal bovine serum for the expansion of mesenchymal stromal cells from bone marrow. Stem Cells 2009;27:2331–41. 13. Buhring H-J, Battula VL, Treml S, et al. Novel markers for the prospective isolation of human MSC. Ann NY Acad Sci 2007;1392:1000. 14. Calori GM, Albisetti W, Agus A, et al. Risk factors contributing to fracture nonunions. Inj – Int J Care Inj 2007;38:S11–8. 15. Caplan AI. Mesenchymal stem-cells. J Orthop Res 1991;9:641–50.
16. Caplan AI, Dennis JE. Mesenchymal stem cells as trophic mediators. J Cell Biochem 2006;98:1076–84. 17. Carrancio S, Lopez-Holgado N, Sanchez-Guijo FM, et al. Optimization of mesenchymal stem cell expansion procedures by cell separation and culture conditions modification. Exp Hematol 2008;36:1014–21. 18. Carson JS, Bostrom MPG. Synthetic bone scaffolds and fracture repair. Inj – Int J Care Inj 2007;38:S33–7. 19. Cattoretti G, Schiro R, Orazi A, et al. Bone-marrow stroma in humans – antinerve growth-factor receptor antibodies selectively stain reticular cells in vivo and in vitro. Blood 1993;81:1726–38. 20. Challen GA, Boles N, Lin KKY, Goodell MA. Mouse hematopoietic stem cell identification and analysis. Cytometry Part A 2009;75A:14–24. 21. Chamberlain G, Fox J, Ashton B, Middleton J. Concise review: mesenchymal stem cells: their phenotype, differentiation capacity, immunological features, and potential for homing. Stem Cells 2007;25:2739–49. 22. Chan CKF, Chen CC, Luppen CA, et al. Endochondral ossification is required for haematopoietic stem-cell niche formation. Nature 2009;457:U490–9. 23. Chehroudi B, Ghrebi S, Murakami H, et al. Bone formation on rough, but not polished, subcutaneously implanted Ti surfaces is preceded by macrophage accumulation. J Biomed Mater Res Part A 2010;93A:724–37. 24. Chen TM, Shih C, Lin TF, Lin FH. Reconstruction of calvarial bone defects using an osteoconductive material and post-implantation hyperbaric oxygen treatment. Mater Sci Eng C 2004;24:855–60. 25. Cook SD, Wolfe MW, Salkeld SL, Rueger DC. Effect of recombinant human osteogenic protein-1 on healing of segmental defects in nonhuman-primates. J Bone Joint Surg – American Volume 1995;77A:734–50. 26. Corselli M, Chen CW, Crisan M, et al. Perivascular ancestors of adult multipotent stem cells. Arterioscler Thromb Vasc Biol 2010;30:1104–9. 27. D’Ippolito G, Diabira S, Howard GA, et al. Marrow-isolated adult multilineage inducible (MIAMI) cells, a unique population of postnatal young and old human cells with extensive expansion and differentiation potential. J Cell Sci 2004;117:2971–81. 28. D’Ippolito G, Schiller PC, Ricordi C, et al. Age-related osteogenic potential of mesenchymal stromal stem cells from human vertebral bone marrow. J Bone Miner Res 1999;14:1115–22. 29. De Bari C, Dell’Accio F, Karystinou A, et al. A biomarker-based mathematical model to predict bone-forming potency of human synovial and periosteal mesenchymal stem cells. Arthritis Rheum 2008;58:240–50. 30. De Bari C, Dell’Accio F, Vanlauwe J, et al. Mesenchymal multipotency of adult human periosteal cells demonstrated by single-cell lineage analysis. Arthritis Rheum 2006;54:1209–21. 31. Deschaseaux F, Pontikoglou C, Sensebe L. Bone regeneration: the stem/progenitor cells point of view. J Cell Mol Med 2010;14:103–15. 32. Dimitriou R, Tsiridis E, Giannoudis PV. Current concepts of molecular aspects of bone healing. Inj – Int J Care Inj 2005;36:1392–404. 33. Dominici M, Le Blanc K, Mueller I, et al. Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy 2006;8:315–7. 34. Dominici M, Pritchard C, Garlits JE, et al. Hematopoietic cells and osteoblasts are derived from a common marrow progenitor after bone marrow transplantation. Proc Natl Acad Sci U S A 2004;101:11761–6. 35. Dowthwaite GP, Bishop JC, Redman SN, et al. The surface of articular cartilage contains a progenitor cell population. J Cell Sci 2004;117:889–97. 36. Drosse I, Volkmer E, Capanna R, et al. Tissue engineering for bone defect heating: an update on a multi-component approach. Inj – Int J Care Inj 2008;39:S9–20. 37. Einhorn TA. The science of fracture healing. J Orthop Trauma 2005;19:S4–6. 38. Eyckmans J, Luyten FP. Species specificity of ectopic bone formation using periosteum-derived mesenchymal progenitor cells. Tissue Eng 2006;12: 2203–13. 39. Fox JM, Chamberlain G, Ashton BA, Middleton J. Recent advances into the understanding of mesenchymal stem cell trafficking. Br J Haematol 2007;137:491–502. 40. Friedenstein AJ, Latzinik NW, Grosheva AG, Gorskaya UF. Marrow microenvironment transfer by heterotopic transplantation of freshly isolated and cultured-cells in porous sponges. Exp Hematol 1982;10:217–27. 41. Gang EJ, Bosnakovski D, Figueiredo CA, et al. SSEA-4 identifies mesenchymal stem cells from bone marrow. Blood 2007;109:1743–51. 42. Gangji V, Hauzeur JP, Matos C, et al. Treatment of osteonecrosis of the femoral head with implantation of autologous bone-marrow cells – a pilot study. J Bone Joint Surg – American Volume 2004;86A:1153–60. 43. Granero-Molto F, Weis JA, Miga MI, et al. Regenerative effects of transplanted mesenchymal stem cells in fracture healing. Stem Cells 2009;27:1887–98. 44. Gundle R, Joyner CJ, Triffitt JT. Human bone tissue formation in-diffusion chamber culture in-vivo by bone-derived cells and marrow stromal fibroblastic cells. Bone 1995;16:597–601. 45. Hernigou P, Beaujean F. Treatment of osteonecrosis with autologous bone marrow grafting. Clin Orthop 2002:14–23. 46. Hillam R, Jackson M, Goodship A, et al. Comparison of physiological strains in the human skull and tibia. Bone 1996;19:686–1686. 47. Horner EA, Kirkham J, Wood D, et al. Long bone defect models for tissue engineering applications: criteria for choice. Tissue Eng Part B – Rev 2010;16:263–71. 48. Horwitz EM, Gordon PL, Koo WKK, et al. Isolated allogeneic bone marrowderived mesenchymal cells engraft and stimulate growth in children with osteogenesis imperfecta: implications for cell therapy of bone. Proc Natl Acad Sci U S A 2002;99:8932–7.
E. Jones, X. Yang / Injury, Int. J. Care Injured 42 (2011) 562–568 49. Horwitz EM, Prockop DJ, Fitzpatrick LA, et al. Transplantability and therapeutic effects of bone marrow-derived mesenchymal cells in children with osteogenesis imperfecta. Nat Med 1999;5:309–13. 50. Howard D, Partridge K, Yang XB, et al. Immunoselection and adenoviral genetic modulation of human osteoprogenitors: in vivo bone formation on PLA scaffold. Biochem Biophys Res Commun 2002;299:208–15. 51. Huang GTJ, Gronthos S, Shi S. Mesenchymal stem cells derived from dental tissues vs. those from other sources: their biology and role in regenerative medicine. J Dent Res 2009;88:792–806. 52. Hui JHP, Li L, Teo YH, et al. Comparative study of the ability of mesenchymal stem cells derived from bone marrow, periosteum, and adipose tissue in treatment of partial growth arrest in rabbit. Tissue Eng 2005;11:904–12. 53. Im GI, Shin YW, Lee KB. Do adipose tissue-derived mesenchymal stem cells have the same osteogenic and chondrogenic potential as bone marrowderived cells? Osteoarthritis Cartilage 2005;13:845–53. 54. Ishii M, Koike C, Igarashi A, et al. Molecular markers distinguish bone marrow mesenchymal stem cells from fibroblasts. Biochem Biophys Res Commun 2005;332:297–303. 55. Jones E, English A, Churchman SM, et al. Large-scale extraction and characterization of CD271+ multipotential stromal cells from trabecular bone in health and osteoarthritis: implications for bone regeneration strategies based on uncultured or minimally cultured multipotential stromal cells. Arthritis Rheum 2010;62:1944–54. 56. Jones E, McGonagle D. Human bone marrow mesenchymal stem cells in vivo. Rheumatology 2008;47:126–31. 57. Jones EA, Kinsey SE, English A, et al. Isolation and characterization of bone marrow multipotential mesenchymal progenitor cells. Arthritis Rheum 2002;46:3349–60. 58. Jones KB, Seshadri T, Krantz R, et al. Cell-based therapies for osteonecrosis of the femoral head. Biol Blood Marrow Transplant 2008;14:1081–7. 59. Kanczler JM, Oreffo ROC. Osteogenesis and angiogenesis: the potential for engineering bone. Eur Cell Mater 2008;15:100–14. 60. Kassem M, Abdallah BM, Saleed H. Osteoblastic cells: differentiation and trans-differentiation. Arch Biochem Biophys 2008;473:183–7. 61. Khosla S, Eghbali-Fatourechi GZ. Circulating cells with osteogenic potential. Skeletal development and remodeling in health, disease, and aging. 2006. pp. 489–97. 62. Kitaori T, Ito H, Schwarz EA, et al. Stromal cell-derived factor 1/CXCR4 signaling is critical for the recruitment of mesenchymal stem cells to the fracture site during skeletal repair in a mouse model. Arthritis Rheum 2009;60:813–23. 63. Kokubu T, Hak DJ, Hazelwood SJ, Reddi AH. Development of an atrophic nonunion model and comparison to a closed healing fracture in rat femur. J Orthop Res 2003;21:503–10. 64. Le Blanc K, Pittenger MF. Mesenchymal stem cells: progress toward promise. Cytotherapy 2005;7:36–45. 65. Le Blanc K, Rasmusson I, Sundberg B, et al. Treatment of severe acute graftversus-host disease with third party haploidentical mesenchymal stem cells. Lancet 2004;363:1439–41. 66. Lymperi S, Ferraro F, Scadden DT. The HSC niche concept has turned 31 Has our knowledge matured? In: Zaidi M, editor. Skeletal biology and medicine. 2010:12–8. 67. Marcacci M, Kon E, Moukhachev V, et al. Stem cells associated with macroporous bioceramics for long bone repair: 6-to 7-year outcome of a pilot clinical study. Tissue Eng 2007;13:947–55. 68. Mareddy A, Crawford R, Brooke G, Xiao Y. Clonal isolation and characterisation of bone marrow stromal cells from patients with osteoarthritis. Tissue Eng 2007;13:819–29. 69. Martinez C, Hofmann TJ, Marino R, et al. Human bone marrow mesenchymal stromal cells express the neural ganglioside GD2: a novel surface marker for the identification of MSCs. Blood 2007;109:4245–8. 70. Matsumoto T, Kawamoto A, Kuroda R, et al. Therapeutic potential of vasculogenesis and osteogenesis promoted by peripheral blood CD34-positive cells for functional bone healing. Am J Pathol 2006;169:1440–57. 71. Matsumoto T, Kuroda R, Mifune Y, et al. Circulating endothelial/skeletal progenitor cells for bone regeneration and healing. Bone 2008;43:434–9. 72. Meirelles LD, Caplan AI, Nardi NB. In search of the in vivo identity of mesenchymal stem cells. Stem Cells 2008;26:2287–99. 73. Meirelles LDS, Chagastelles PC, Nardi NB. Mesenchymal stem cells reside in virtually all post-natal organs and tissues. J Cell Sci 2006;119:2204–13. 74. Metcalf D. Concise review: hematopoietic stem cells and tissue stem cells: current concepts and unanswered questions. Stem Cells 2007-0544 2007. 75. Modder UI, Khosla S. Skeletal stem/osteoprogenitor cells: current concepts, alternate hypotheses, and relationship to the bone remodeling compartment. J Cell Biochem 2008;103:393–400. 76. Muraglia A, Cancedda R, Quarto R. Clonal mesenchymal progenitors from human bone marrow differentiate in vitro according to a hierarchical model. J Cell Sci 2000;113:1161–6. 77. Murphy WL, Simmons CA, Kaigler D, Mooney DJ. Bone regeneration via a mineral substrate and induced angiogenesis. J Dent Res 2004;83:204–10. 78. Nakahara H, Bruder SP, Haynesworth SE, et al. Bone and cartilage formation in diffusion-chambers by subcultured cells derived from the periosteum. Bone 1990;11:181–8. 79. Niemeyer P, Fechner K, Milz S, et al. Comparison of mesenchymal stem cells from bone marrow and adipose tissue for bone regeneration in a critical size defect of the sheep tibia and the influence of platelet-rich plasma. Biomaterials 2010;31:3572–9.
567
80. Noel D, Caton D, Roche S, et al. Cell specific differences between human adipose-derived and mesenchymal-stromal cells despite similar differentiation potentials. Exp Cell Res 2008;314:1575–84. 81. Noth U, Osyczka AM, Tuli R, et al. Multilineage mesenchymal differentiation potential of human trabecular bone-derived cells. J Orthop Res 2002;20: 1060–9. 82. Nuss KMR, Auer JA, Boos A, Von Rechenberg B. An animal model in sheep for biocompatibility testing of biomaterials in cancellous bones. BMC Musculoskelet Disord 2006;7. 83. Partridge K, Yang XB, Clarke NMP, et al. Adenoviral BMP-2 gene transfer in mesenchymal stem cells: in vitro and in vivo bone formation on biodegradable polymer scaffolds. Biochem Biophys Res Commun 2002;292:144–52. 84. Phinney DG, Prockop DJ. Concise review: mesenchymal stem/multipotent stromal cells: the state of transdifferentiation and modes of tissue repair – current views. Stem Cells 2007;25:2896–902. 85. Pierre-Louis O, Clay D, de la Grange PB, et al. Dual SP/ALDH functionalities refine the human hematopoietic Lin( )CD34(+)CD38( ) stem/progenitor cell compartment. Stem Cells (Miamisburg) 2009;27:2552–62. 86. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999;284:143–7. 87. Quarto R, Mastrogiacomo M, Cancedda R, et al. Repair of large bone defects with the use of autologous bone marrow stromal cells. N Engl J Med 2001;344:385–6. 88. Quirici N, Soligo D, Bossolasco P, et al. Isolation of bone marrow mesenchymal stem cells by anti-nerve growth factor receptor antibodies. Exp Hematol 2002;30:783–91. 89. Rebelatto CK, Aguiar AM, Moretao MP, et al. Dissimilar differentiation of mesenchymal stem cells from bone marrow, umbilical cord blood, and adipose tissue. Exp Biol Med 2008;233:901–13. 90. Rodriguez JP, Garat S, Gajardo H, et al. Abnormal osteogenesis in osteoporotic patients is reflected by altered mesenchymal stem cells dynamics. J Cell Biochem 1999;75:414–23. 91. Rodriguez JP, Montecinos L, Rios S, et al. Mesenchymal stem cells from osteoporotic patients produce a type I collagen-deficient extracellular matrix favoring adipogenic differentiation. J Cell Biochem 2000;79:557–65. 92. Sacchetti B, Funari A, Michienzi S, et al. Self-renewing osteoprogenitors in bone marrow sinusoids can organize a hematopoietic microenvironment. Cell 2007;131:324–36. 93. Sakaguchi Y, Sekiya I, Yagishita K, et al. Suspended cells from trabecular bone by collagenase digestion become virtually identical to mesenchymal stem cells obtained from marrow aspirates. Blood 2004;104:2728–35. 94. Sakaguchi Y, Sekiya I, Yagishita K, Muneta T. Comparison of human stem cells derived from various mesenchymal tissues – superiority of synovium as a cell source. Arthritis Rheum 2005;52:2521–9. 95. Santos MI, Reis RL. Vascularization in bone tissue engineering: physiology, current strategies, major hurdles and future challenges. Macromol Biosci 2010;10:12–27. 96. Schneider RK, Puellen A, Kramann R, et al. The osteogenic differentiation of adult bone marrow and perinatal umbilical mesenchymal stem cells and matrix remodelling in three-dimensional collagen scaffolds. Biomaterials 2010;31:467–80. 97. Scotti C, Tonnarelli B, Papadimitropoulos A, et al. Recapitulation of endochondral bone formation using human adult mesenchymal stem cells as a paradigm for developmental engineering. Proc Natl Acad Sci U S A 2010;107:7251–6. 98. Shetty P, Cooper K, Viswanathan C. Comparison of proliferative and multilineage differentiation potentials of cord matrix, cord blood, and bone marrow mesenchymal stem cells. Asian J Transfus Sci 2010;4:14–24. 99. Short B, Brouard N, Occhiodoro-Scott T, et al. Mesenchymal stem cells. Arch Med Res 2003;34:565–71. 100. Simmons PJ, Torokstorb B. Identification of stromal cell precursors in human bone-marrow by a novel monoclonal-antibody, Stro-1. Blood 1991;78:55–62. 101. Sotiropoulou PA, Perez SA, Salagianni M, et al. Characterization of the optimal culture conditions for clinical scale production of human mesenchymal stem cells. Stem Cells (Miamisburg) 2006;24:462–71. 102. Sugiyama T, Kohara H, Noda M, Nagasawa T. Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches. Immunity 2006;25:977–88. 103. Tao J, Sun Y, Wang QG, Liu CW. Induced endothelial cells enhance osteogenesis and vascularization of mesenchymal stem cells (vol. 190, 185, 2009). Cells Tissues Organs 2010;191:430–1430. 104. Tasso R, Fais F, Reverberi D, et al. The recruitment of two consecutive and different waves of host stem/progenitor cells during the development of tissue-engineered bone in a murine model. Biomaterials 2010;31:2121–9. 105. Tokoyoda K, Egawa T, Sugiyama T, et al. Cellular niches controlling B lymphocyte behavior within bone marrow during development. Immunity 2004;20:707–18. 106. Tortelli F, Tasso R, Loiacono F, Cancedda R. The development of tissueengineered bone of different origin through endochondral and intramembranous ossification following the implantation of mesenchymal stem cells and osteoblasts in a murine model. Biomaterials 2010;31:242–9. 107. Tuli R, Tuli S, Nandi S, et al. Characterization of multipotential mesenchymal progenitor cells derived from human trabecular bone. Stem Cells 2003;21:681– 93. 108. Usami K, Mizuno H, Okada K, et al. Composite implantation of mesenchymal stem cells with endothelial progenitor cells enhances tissue-engineered bone formation. J Biomed Mater Res Part A 2009;90A:730–41.
568
E. Jones, X. Yang / Injury, Int. J. Care Injured 42 (2011) 562–568
109. Wagner W, Horn P, Castoldi M, et al. Replicative senescence of mesenchymal stem cells: a continuous and organized process. PLoS One 2008;3:e2213. 110. Wagner W, Wein F, Seckinger A, et al. Comparative characteristics of mesenchymal stem cells from human bone marrow, adipose tissue, and umbilical cord blood. Exp Hematol 2005;33:1402. 111. Weiss ML, Medicetty S, Bledsoe AR, et al. Human umbilical cord matrix stem cells: preliminary characterization and effect of transplantation in a rodent model of Parkinson’s disease. Stem Cells 2006;24:781–92. 112. Yang XB, Whitaker MJ, Clarke NMP, et al. In vivo human bone and cartilage formation using porous polymer scaffolds encapsulated with bone morphogenetic protein-2. J Bone Miner Res 2003;18:1366–11366.
113. Yang XBB, Webb D, Blaker J, et al. Evaluation of human bone marrow stromal cell growth on biodegradable polymer/bioglass (R) composites. Biochem Biophys Res Commun 2006;342:1098–107. 114. Yang XBB, Whitaker MJ, Sebald W, et al. Human osteoprogenitor bone formation using encapsulated bone morphogenetic protein 2 in porous polymer scaffolds. Tissue Eng 2004;10:1037–45. 115. Yu HY, VandeVord PJ, Gong WM, et al. Promotion of osteogenesis in tissueengineered bone by pre-seeding endothelial progenitor cells-derived endothelial cells. J Orthop Res 2008;26:1147–52. 116. Yu HY, VandeVord PJ, Mao L, et al. Improved tissue-engineered bone regeneration by endothelial cell mediated vascularization. Biomaterials 2009;30:508–17.