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Growth Factor Therapy and Autologous Lymph Node Transfer in Lymphedema
REVIEW ARTICLES Growth Factor Therapy and Autologous Lymph Node Transfer in Lymphedema Pauliina Hartiala and Anne M. Saaristo*
Lymphedema after cancer treatment is a common clinical challenge, but curative treatment options are rarely available. Lymph node transfer is a novel technique in lymphedema surgery. Lymphatic tissue can be transferred as a vascularized free flap, but in this technique the lymphatic vascular network is expected to regrow spontaneously. Recently, we have learned how to regulate the growth of lymphatic vessels in experimental models. We envision that lymph node transfer should be combined with lymphatic growth factor therapy in the treatment of lymphedema patients. (Trends Cardiovasc Med 2010;20: 249 –253) © 2010 Elsevier Inc. All rights reserved. • The Lymphatic System and Lymphedema The lymphatic vasculature plays a key role in the maintenance of tissue fluid homeostasis by collecting extravasated fluid and returning macromolecules back to the blood circulation (Alitalo et al. 2005). The lymphatic capillaries in the peripheral tissues merge with larger collecting lymphatic vessels, specialized for the transport of large volumes of lymph, that in turn connect with chains of lymph nodes (Alitalo et al. 2005). From an immunological standpoint, lymph nodes are strategically positioned patrol stations for antigens from peripheral tissues (Banchereau et al. 2000). Naive lymphocytes circulate through lymph nodes to search for their specific antigen. When a foreign microbe enters Pauliina Hartiala and Anne M. Saaristo are at Plastic Surgery, Turku University Central Hospital, 20251 Finland. *Address correspondence to: Anne M. Saaristo, Plastic Surgery, Turku University Central Hospital, PL 52, Kiinamyllynkatu 4-8, 20251 Finland. Tel.: 358-2-3130257; fax: 3582-3132215; e-mail: [email protected] © 2010 Elsevier Inc. All rights reserved. 1050-1738/$-see front matter
TCM Vol. 20, No. 8, 2010
the skin, professional antigen presenting cells, namely dendritic cells (DCs), phagocytose the invading microbes, become mature DCs, and migrate to lymph nodes via lymph vessels. To elicit an adaptive immune response, DCs must interact with antigen-specific T cells and B cells in the lymph node and present the antigens (Banchereau et al. 2000). Thus, lymphatic vessels and lymph nodes are involved in several human diseases, such as lymphedema, inflammation, and tumor metastasis. Chronic lymphedema, commonly caused by infection and surgical or radiation therapy of metastatic cancer, remains a common clinical challenge that often lacks curative treatment options. Rare hereditary forms of lymphedema are caused by structural defects in the lymphatic vessels (Ferrell and Finegold 2008). A globally remarkable cause of lymphedema is filariasis, which affects more than 90 million people (Rockson 2001). It has been estimated that currently several million patients suffer from acquired lymphedema in the United States alone (Tabibiazar et al. 2006). The effective treatment of cancer often requires removal of regional
lymph nodes to eradicate metastases. This leads to a disruption of the lymphatic flow in the operated area, which frequently leads to lymphedema of the affected limb. The incidence of lymphedema varies from 9% to 41% in patients who have undergone axillary lymph node dissection and from 4% to 10% in patients who have undergone sentinel node biopsy (Clark et al. 2005, McLaughlin et al. 2008, Suami and Chang 2010). Lymphedema is a progressive disease characterized by gross swelling of the affected limb, accompanied by adipose tissue hypertrophy and fibrosis, which is most likely induced by slow or absent lymph flow and inflammation (Warren et al. 2007). Lymphedema patients are susceptible to infections as a result of microbial growth due to extravasated fluid and proteins and an impaired local immune response (Rockson 2001). Antigen presenting cells have no direct route to local or close-remaining lymph nodes to present antigens and elicit further adaptive immune responses needed for effective clearance of pathogens. The treatment of lymphedema is currently based on physiotherapy, compression garments, and, occasionally, surgical treatment options including liposuction (Suami and Chang 2010), lymph node transfer (Becker et al. 2006), and lymphaticovenous shunts or lymphaticolymphatic bypasses (Baumeister et al. 1981, Campisi 1991, Chang 2010, Rockson 2001, Weiss et al. 2002). However, identifying and preserving the lymphatic vessels even by modern microsurgical methods is difficult. Another challenge regarding reconstructive surgery is that chronic lymphedema leads to secondary changes in the affected limb, including skin fibrosis, deposition of adipose tissue, and distal lymphatic valve insufficiency (Warren et al. 2007). • Regulation of Lymphangiogenesis Understanding of the molecular mechanisms of lymphangiogenesis has increased considerably in recent years
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(Tammela and Alitalo 2010). Vascular endothelial growth factors (VEGFs) are important regulators of angiogenesis and lymphangiogenesis (Lohela et al. 2009, Oliver 2004). VEGFs stimulate cellular responses by binding to the tyrosine kinase receptors (RTKs) VEGFR-1, VEGFR-2, and VEGFR-3, which are specifically expressed in the luminal surface of the blood and lymphatic endothelial cells. VEGFR activation promotes cell proliferation, migration, and survival (Olsson et al. 2006). VEGF-A binds to VEGFR-1 and VEGFR-2 and induces mainly angiogenesis, whereas VEGF-C and VEGF-D bind VEGFR-3 and induce mainly lymphangiogenesis (Olsson et al. 2006, Tammela and Alitalo 2010). The affinity of VEGF-C and VEGF-D to VEGFR-3 is increased by proteolytic cleavage, and only the fully processed forms can bind VEGFR-2 (Joukov et al. 1997, Olsson et al. 2006, Stacker et al. 1999). VEGF seems to stimulate mainly circumferential hyperplasia of lymphatic capillaries and only indirectly lymphangiogenesis via the recruitment of inflammatory cells (Wirzenius et al. 2007). VEGF-B has been shown to induce cardiac hypertrophy and coronary arteriogenesis (Karpanen et al. 2008, Schaper 2008). VEGFs also bind neuropilin (Nrp)-1 and Nrp-2 co-receptors, which modulate the signaling of VEGF receptors and provide specificity for their signal transduction (Caunt et al. 2008, Lohela et al. 2009). Also, certain integrins, as well as heparan sulfate proteoglycans, can act as co-receptors for the VEGFs expressed in blood and lymphatic endothelial cells that line the luminal surface of vessels (Iozzo and San Antonio, 2001). Results from preclinical lymphedema models employing VEGF-C or VEGF-D gene transfer (Enholm et al. 1997, Karkkainen et al. 2001, Rissanen et al. 2003, Saaristo et al. 2002) or application of recombinant protein (Baker et al. 2010, Szuba et al. 2000) have demonstrated the potential and specificity of these factors for inducing growth of new lymphatic vessels. The short half-life of the VEGF proteins favors the use of transient gene transfer as a mode of treatment (Veikkola et al. 2001). First experimental lymphedema animal models focused on regrowth of new lymphatic 250
capillary vessels in response to lymphatic growth factor therapy (Karkkainen et al. 2001, Saaristo et al. 2002, Yoon et al. 2003). Together with other groups, we have shown that the collecting lymphatic vessels can also be rebuilt with VEGF-C/D therapy (Baker et al. 2010, Lahteenvuo et al. 2011, Tammela et al. 2007). Adenoviral VEGF-C or VEGF-D gene transfer results in transient lymphatic vessel growth factor overexpression in the targeted area (Lahteenvuo et al. 2011, Saaristo et al. 2002, Tammela et al. 2007). During the first 2 weeks, robust growth of lymphatic vessels can be detected, but after 2 weeks, as the adenoviral growth factor expression is downregulated, the lymphatic vessel network will regress (Saaristo et al. 2002). However, the newly formed vessels that have lymphatic flow seem to stabilize and maturate into true collecting lymphatic vessels spontaneously over the course of 6 months (Tammela et al. 2007). Thus, the growth factor-stimulated vessels seem to engage an intrinsic differention program to form collecting vessels. Tumorigenesis and tumor metastasis are multistep processes, and accumulation of several, usually somatic, mutations is required for both. Neovascularization is a rate-limiting step for tumor growth beyond 1 mm in diameter (Kerbel and Folkman, 2002). The VEGF/VEGFR-2 signaling axis appears to be the most important regulator of blood vessel growth in tumors (Ferrara et al. 2007). Elevated levels of VEGF mRNA are found in most human tumors. Furthermore, lymph node metastasis is an important prognostic indicator in many tumor types (Sleeman and Thiele, 2009). In principle, tumor cells can invade either pre-existing lymphatic vessels or new lymphatic vessels formed at the tumor periphery by tumor-induced lymphangiogenesis. Many types of tumors express the lymphangiogenic growth factors VEGF-C and VEGF-D, and several studies have shown that expression of these growth factors actively induces tumor-associated lymphangiogenesis, leading to lymphatic invasion, lymph node and distant metastasis, and subsequently poor patient survival (Holopainen et al. 2011).
Figure 1. The authors’ vision of how to reconstruct the lymphatic vascular anatomy in the axilla after axillary dissection and oncologic cancer treatment. (A) Lymphatic tissue from the lower abdominal wall can be harvested as a vascularized free flap. (B) Adenoviral gene transfer vector encoding lymphatic growth factor (VEGF-C) is injected into the distal edges of the lymphatic flap to enhance regrowth of lymphatic vessels. (C) Growth factor–treated lymphatic flap is placed into the axilla to replace irradiated scar tissue. Blood vascular anastomosis sites of the free flap are indicated with the black box.
• Lymph Node Transfer Surgical treatment of cancer often requires removal of inguinal or axillary lymph nodes and is associated with lymphedema of the affected limb. The lymph node transfer technique aims to rebuild the lymphatic vascular anatomy after the cancer treatment. The therapeutic effect of this surgical method has been tested in different experimental lymphedema animal models and also in human lymphedema patients. In patients, lymphatic tissue can be harvested as a vascularized free flap from the lower abdominal wall and transferred into the axilla (Becker et al. 2006) (Figure 1A). However, in this technique, the lymphatic vessel anastomoses are expected TCM Vol. 20, No. 8, 2010
to form spontaneously. Chen et al. (1990) demonstrated lymph nodes with normal architecture and size 3 and 6 months after vascularized lymph node transplantation in a canine model. The circumference of the limb was reduced after transplantation compared with preoperative data. Furthermore, postoperative lymphangiography demonstrated regeneration of the lymphatic system 6 months after surgery. Blum et al. (2010) found that autotransplantation of lymph node fragments after lymphadenectomy in minipigs had positive effects on the restoration of lymphatic flow and that larger fragments were more often integrated into the lymphatic system than small lymph node slices. Tobbia et al. (2009) compared the effect of vascularized versus nonvascularized lymph node transplants in the treatment of postsurgical lymphedema in a sheep model and found that the vascularized transplants were associated with a better clinical improvement. Furthermore, platelet-rich plasma, containing various growth factors, has been shown to improve regeneration of lymph node fragments in a rat model (Hadamitzky et al. 2009). Recent clinical articles have shown that autologous microvascular lymph node transfer from the groin area into axillas or wrists of postmastectomy patients may improve lymphatic drainage of the affected limb (Becker et al. 2006, Lin et al. 2009, Saaristo et al. 2011). In a study by Becker et al., 24 women with postsurgical physiotherapy-resistant lymphedema underwent a microsurgical operation in which lymph nodes from the groin area were transferred to the axilla. After treatment, upper limb perimeter returned to normal in 10 patients and was decreased in 12 patients. Fifteen patients were able to discontinue physiotherapeutic treatments of lymphedema (Becker et al. 2006). In our own patient material, one-third of the postmastectomy lymphedema patients no longer needed compression therapy after the lymph node transfer into the axillary area (Saaristo et al. 2011). Lin et al. used a similar vascularized groin flap but transferred the vascularized lymph nodes into the wrist area of the lymphedema patients. All clinical studies also showed an improvement of skin infections (erysipelas, lymphangitis, and cellulitis) after lymph node transfer. TCM Vol. 20, No. 8, 2010
In the lymph node transfer technique, the lymphatic vascular anastomoses are expected to form spontaneously. Our recent report indicates that human lymph nodes express endogenous lymphangiogenic growth factors, namely VEGF-C, providing a biological basis for this surgical method (Saaristo et al. 2011). Clinical and experimental data, however, suggest that although spontaneous lymphangiogenesis after lymph node transfer does occur, the incorporation of the transferred lymph nodes into the existing lymphatic network may fail (Becker et al. 2006, Lahteenvuo et al. 2011, Saaristo et al. 2011, Tammela et al. 2007). This poor incorporation efficiency may compromise the outcome of the operation because connection with lymphatic vessels is required for maintenance and function of the lymph nodes (Mebius et al. 1991, Tammela et al. 2007). Because we are operating on patients who have previously developed lymphedema symptoms in their upper extremities, we need to be extremely careful with the donor site morbidity. Harvesting lymph nodes from the lower abdominal wall seems to induce seroma formation (Saaristo et al. 2011), but to date there are no reports on lymphedema symptoms of the lower limb after the lymph node transfer surgery. • Combining Lymphangiogenic Growth Factor Treatment With Lymph Node Transfer Lymph nodes need lymphatic flow to remain functional (Lahteenvuo et al. 2011, Mebius et al. 1991, Tammela et al. 2007). Without connections with the afferent and efferent lymphatic vessels, lymph nodes regress (Mebius et al. 1991). The idea of combining growth factor treatment with the lymph node transfer as a lymphedema treatment was first presented by Tammela et al. The results of this study showed that the sentinel node function of transferred lymph nodes was regained and intracutaneously injected lung carcinoma cells were trapped in the transferred lymph node (Tammela et al. 2007). Previously, it was shown that transplanted lymph nodes retain the ability to mount a cytotoxic immune response against tumor cells and that they recover a normal architecture (Fu et al. 1998, Rabson et
al. 1982). Recently, the efficacy of the VEGF-C and -D growth factor therapies and lymph node transfer was also tested in a lymphedema large animal model (Lahteenvuo et al. 2011). Postoperative lymphatic drainage was significantly improved in the VEGF-C/D–treated pigs compared with controls. Importantly, the structure of the transferred lymph nodes was best preserved in the VEGFC–treated pigs. Control-treated lymph nodes regressed, and their follicular structure was replaced by adipose and fibrotic tissue. This is in concordance with previous data that indicate that the lymph nodes need lymphatic vasculature and exposure to lymph flow to remain intact (Mebius et al. 1991, Tammela et al. 2007). Other methods for growth factor delivery have also been tested in the postsurgical lymphedema model. Baker et al. (2010) used a gel-based drug delivery system, HAMC, which is a physical blend of hyaluronan and methylcellulose, to deliver VEGF-C and angiopoietin-2 to the operation site after excision of the popliteal lymph node in sheep. Edema was significantly reduced after growth factor treatment, and the lymphatic transport function was improved, although it did not completely normalize within the 6-week follow-up period (Baker et al. 2010). • Conclusions and Future Perspectives Approximately 200,000 new cases of breast cancer are diagnosed annually in the United States alone. In addition to breast cancer, many other cancer types spread via the lymphatic vessels, necessitating regional surgery of the lymph nodes and making a large patient population susceptible to the development of lymphedema. Lymph node transfer is a new technique in lymphedema surgery. Of all postmastectomy patients who ask for breast reconstruction, 9%-41% also have lymphedema symptoms of the upper arm (Clark et al. 2005, McLaughlin et al. 2008, Saaristo et al. 2011, Suami and Chang 2010). Interestingly, building material for both breast reconstruction and lymph node transfer can be harvested from the patient’s own lower abdominal wall (Saaristo et al. 2011) (Figure 1). The fact that lymph node transfer can easily be performed in combination with routine microvascular 251
breast reconstruction has made this method attractive (Saaristo et al. 2011). Preliminary results from the lymph node transfer show best clinical efficacy in patients with early disease (Becker et al. 2006, Saaristo et al. 2011), before deposition fibrosis and deposition of adipose tissue has occurred (Warren et al. 2007). One critical step regarding the operation technique seems to be the complete removal of all old scar tissue, which is then replaced with a healthy patch of adipose tissue containing the lymph nodes. To truly determine the efficacy of this new technique, results from large clinical studies and from different units are needed. More data are also needed on the efficacy of treatment in different stages of lymphedema. Not all patients seem to benefit from the lymph node transfer surgery, which might be partly explained by the temporal and spatial differences in lymph node VEGF-C expression. Findings from experimental animal models clearly favor the use of growth factors in conjunction with lymph node transfer to augment incorporation of the grafted lymph node into the resident lymphatic vascular tree (Lahteenvuo et al. 2011, Tammela et al. 2007). Vectors inducing short-term overexpression of the patient’s own endogenous lymphatic growth factors in the distal edge of the lymphatic tissue flap could be used to enhance the therapeutic effect of the lymph node transfer technique (Figure 1). VEGF-C and -D are also involved in lymphatic metastasis of several human tumors; therefore, patient safety is an important issue. However, human lymph nodes also produce endogenous VEGF-C (Saaristo et al. 2011), and lymph node transfer is already used in cancer patients. In experimental models, newly formed lymphatic vessels seem to stabilize after the short-term (1-week) VEGF-C overexpression (Lahteenvuo et al. 2011, Tammela et al. 2007); thus, long-lasting lymphatic growth factor therapy is not needed. • Acknowledgments This study was supported by the Academy of Finland, the Turku University Foundation, special governmental funding (EVO) allocated to Turku University Central Hospital, the Paavo and Eila Salonen Foundation, the Ida Montini Foundation, the Aarne and Aili Turunen 252
Foundation, the Emil Aaltonen Foundation, and Laurantis Pharma.
Fu K, Izquierdo R, Vandevender D, et al: 1998. Transplantation of lymph node fragments in a rabbit ear lymphedema model: A new method for restoring the lymphatic pathway. Plast Reconstr Surg 101:134 –141.
References
Hadamitzky C, Blum KS, & Pabst R: 2009. Regeneration of autotransplanted avascular lymph nodes in the rat is improved by platelet-rich plasma. J Vasc Res 46:389 – 396.
Alitalo K, Tammela T, & Petrova TV: 2005. Lymphangiogenesis in development and human disease. Nature 438:946 –953. Baker A, Kim H, Semple JL, et al: 2010. Experimental assessment of pro-lymph angiogenic growth factors in the treatment of post-surgical lymphedema following lymphadenectomy. Breast Cancer Res 12:R70. Banchereau J, Briere F, Caux C, et al: 2000. Immunobiology of dendritic cells. Annu Rev Immunol 18:767– 811. Baumeister RG, Seifert J, & Hahn D: 1981. Autotransplantation of lymphatic vessels. Lancet 1:147. Becker C, Assouad J, Riquet M, & Hidden G: 2006. Postmastectomy lymphedema: Longterm results following microsurgical lymph node transplantation. Ann Surg 243:313– 315. Blum KS, Hadamitzky C, Gratz KF, & Pabst R: 2010. Effects of autotransplanted lymph node fragments on the lymphatic system in the pig model. Breast Cancer Res Treat 120:59 – 66. Campisi C: 1991. Use of autologous interposition vein graft in management of lymphedema: Preliminary experimental and clinical observations. Lymphology 24: 71–76. Caunt M, Mak J, Liang WC, et al: 2008. Blocking neuropilin-2 function inhibits tumor cell metastasis. Cancer Cell 13:331– 342. Chang DW: 2010. Lymphaticovenular bypass for lymphedema management in breast cancer patients: A prospective study. Plast Reconstr Surg 126:752–758. Chen HC, O’Brien BM, Rogers IW, et al: 1990. Lymph node transfer for the treatment of obstructive lymphoedema in the canine model. Br J Plast Surg 43:578 –586. Clark B, Sitzia J, & Harlow W: 2005. Incidence and risk of arm oedema following treatment for breast cancer: A three-year follow-up study. QJM 98:343–348. Enholm B, Paavonen K, Ristimaki A, et al: 1997. Comparison of VEGF, VEGF-B, VEGF-C and Ang-1 mRNA regulation by serum, growth factors, oncoproteins and hypoxia. Oncogene 14:2475–2483. Ferrara N, Mass RD, Campa C, & Kim R: 2007. Targeting VEGF-A to treat cancer and age-related macular degeneration. Annu Rev Med 58:491–504. Ferrell RE & Finegold DN: 2008. Research perspectives in inherited lymphatic disease: An update. Ann N Y Acad Sci 1131:134 – 139.
Holopainen T, Bry M, Alitalo K, & Saaristo A: 2011. Perspectives on lymphangiogenesis and angiogenesis in cancer. J Surg Oncol 103:484 – 488. Iozzo RV & San Antonio JD: 2001. Heparan sulfate proteoglycans: Heavy hitters in the angiogenesis arena. J Clin Invest 108:349 – 355. Joukov V, Sorsa T, Kumar V, et al: 1997. Proteolytic processing regulates receptor specificity and activity of VEGF-C. EMBO J 16:3898 –3911. Karkkainen MJ, Saaristo A, Jussila L, et al: 2001. A model for gene therapy of human hereditary lymphedema. Proc Natl Acad Sci USA 98:12677–12682. Karpanen T, Bry M, Ollila HM, et al: 2008. Overexpression of vascular endothelial growth factor-B in mouse heart alters cardiac lipid metabolism and induces myocardial hypertrophy. Circ Res 103:1018 –1026. Kerbel R & Folkman J: 2002. Clinical translation of angiogenesis inhibitors. Nat Rev Cancer 2:727–739. Lahteenvuo M, Honkonen K, Tervala T, et al: 2011. Growth factor therapy and autologous lymph node transfer in lymphedema. Circulation 123:613– 620. Lin CH, Ali R, Chen SC, et al: 2009. Vascularized groin lymph node transfer using the wrist as a recipient site for management of postmastectomy upper extremity lymphedema. Plast Reconstr Surg 123: 1265–1275. Lohela M, Bry M, Tammela T, & Alitalo K: 2009. VEGFs and receptors involved in angiogenesis versus lymphangiogenesis. Curr Opin Cell Biol 21:154 –165. McLaughlin SA, Wright MJ, Morris KT, et al: 2008. Prevalence of lymphedema in women with breast cancer 5 years after sentinel lymph node biopsy or axillary dissection: Patient perceptions and precautionary behaviors. J Clin Oncol 26:5220 –5226. Mebius RE, Streeter PR, Breve J, et al: 1991. The influence of afferent lymphatic vessel interruption on vascular addressin expression. J Cell Biol 115:85–95. Oliver G: 2004. Lymphatic vasculature development. Nat Rev Immunol 4:35– 45. Olsson AK, Dimberg A, Kreuger J, et al: 2006. VEGF receptor signalling—In control of vascular function. Nat Rev Mol Cell Biol 7:359 –371. Rabson JA, Geyer SJ, Levine G, et al: 1982. Tumor immunity in rat lymph nodes fol-
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lowing transplantation. Ann Surg 196: 92–99. Rissanen TT, Markkanen JE, Gruchala M, et al: 2003. VEGF-D is the strongest angiogenic and lymphangiogenic effector among VEGFs delivered into skeletal muscle via adenoviruses. Circ Res 92:1098 –1106. Rockson SG: 2001. Lymphedema. Am J Med 110:288 –295. Saaristo A, Veikkola T, Tammela T, et al: 2002. Lymphangiogenic gene therapy with minimal blood vascular side effects. J Exp Med 196:719 –730. Saaristo AM, Niemi T, Viitanen T, et al: 2011. Microvascular breast reconstruction and lymph node transfer for postmastectomy lymphedema patients. Ann Surg (in press): Schaper W: 2008. The renaissance of vascular endothelial growth factor, part B. Circ Res 103:903–904. Sleeman JP & Thiele W: 2009. Tumor metastasis and the lymphatic vasculature. Int J Cancer 125:2747–2756. Stacker SA, Stenvers K, Caesar C, et al: 1999. Biosynthesis of vascular endothelial growth factor-D involves proteolytic processing which generates non-covalent homodimers. J Biol Chem 274:32127–32136. Suami H & Chang DW: 2010. Overview of surgical treatments for breast cancer-related lymphedema. Plast Reconstr Surg 126:1853–1863. Szuba A, Cooke JP, Yousuf S, & Rockson SG: 2000. Decongestive lymphatic therapy for patients with cancer-related or primary lymphedema. Am J Med 109:296 –300. Tabibiazar R, Cheung L, Han J, et al: 2006. Inflammatory manifestations of experimental lymphatic insufficiency. PLoS Med 3:e254.
Tammela T & Alitalo K: 2010. Lymphangiogenesis: Molecular mechanisms and future promise. Cell 140:460 – 476. Tammela T, Saaristo A, Holopainen T, et al: 2007. Therapeutic differentiation and maturation of lymphatic vessels after lymph node dissection and transplantation. Nat Med 13:1458 –1466. Tobbia D, Semple J, Baker A, et al: 2009. Experimental assessment of autologous lymph node transplantation as treatment of postsurgical lymphedema. Plast Reconstr Surg 124:777–786. Veikkola T, Jussila L, Makinen T, et al: 2001. Signalling via vascular endothelial growth factor receptor-3 is sufficient for lymphangiogenesis in transgenic mice. EMBO J 20: 1223–1231. Warren AG, Brorson H, Borud LJ, & Slavin SA: 2007. Lymphedema: A comprehensive review. Ann Plast Surg 59:464 – 472. Weiss M, Baumeister RG, & Hahn K: 2002. Post-therapeutic lymphedema: Scintigraphy before and after autologous lymph vessel transplantation: 8 years of longterm follow-up. Clin Nucl Med 27:788 – 792. Wirzenius M, Tammela T, Uutela M, et al: 2007. Distinct vascular endothelial growth factor signals for lymphatic vessel enlargement and sprouting. J Exp Med 204:1431– 1440. Yoon YS, Murayama T, Gravereaux E, et al: 2003. VEGF-C gene therapy augments postnatal lymphangiogenesis and ameliorates secondary lymphedema. J Clin Invest 111: 717–725.
PII S1050-1738(11)00087-9
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MicroRNA Regulation of Angiogenesis and Arteriogenesis Felix P. Hans, Martin Moser, Christoph Bode, and Sebastian Grundmann*
MicroRNAs are short, nonprotein-coding RNA molecules that play a crucial role in the post-transcriptional regulation of gene expression. By binding to specific target sequences, mostly located in the 3=-untranslated region of their target mRNA, they can induce mRNA decay or translational inhibition. Unlike siRNA, microRNAs show imperfect matching to their target mRNAs and can therefore modulate the expression of several mRNA genes at once. Although TCM Vol. 20, No. 8, 2010
microRNAs have already been extensively studied in invertebrates, their function in mammalian organisms and in human disease is largely unknown. Several studies have shown an important regulatory function of microRNAs in embryonic and postnatal blood vessel development. Here, we provide an overview on these recent findings and summarize these so-called “angiomiRs” and their mode of action. (Trends Cardiovasc Med 2010; 20:253–262) © 2010 Elsevier Inc. All rights reserved. • Introduction The mechanisms of the growth and proliferation of blood vessels can be divided into three different entities. In early development, vasculogenesis describes the de novo formation of a premature cardiovascular system in the growing embryo by the differentiation of mesenchymal cell populations into hemangioblasts. Vascular endothelial growth factor (VEGF) stimulation of these hemangioblasts triggers differentiation into both the progenitor populations for vessel structures and for the blood components. Fusing of the blood island leads to a primitive cardiovascular plexus that is the fundament of a differentiated venous and arterial system. In the adult, vasculogenesis is a rare process because the mode of action for adaptive vessel growth is conciliated by two other important mechanisms: angiogenesis and arteriogenesis. Although hypoxic conditions lead to endothelial activation via hypoxia-inducible factor (HIF) stabilization and VEGF Felix P. Hans, Martin Moser, Christoph Bode, and Sebastian Grundmann are at the Department of Internal Medicine III, University Hospital Freiburg, 79106 Freiburg, Germany. *Address correspondence to: Sebastian Grundmann, M.D., Ph.D., Department of Internal Medicine III (Cardiology and Angiology), University Hospital Freiburg, Breisacher Str. 33, 79106 Freiburg, Germany. Tel.: (⫹49) 761 270 70460; fax: (⫹49) 761 270 70450; e-mail: sebastian.grundmann@ uniklinik-freiburg.de. © 2010 Elsevier Inc. All rights reserved. 1050-1738/$-see front matter
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Lymphedema after cancer treatment is a common clinical challenge, but curative treatment options are rarely available. Lymph node transfer is a novel technique in lymphedema surgery. Lymphatic tissue can be transferred as a vascularized free flap, but in this technique the lymphatic vascular network is expected to regrow spontaneously. Recently, we have learned how to regulate the growth of lymphatic vessels in experimental models. We envision that lymph node transfer should be combined with lymphatic growth factor therapy in the treatment of lymphedema patients. (Trends Cardiovasc Med 2010;20: 249 –253) © 2010 Elsevier Inc. All rights reserved. • The Lymphatic System and Lymphedema The lymphatic vasculature plays a key role in the maintenance of tissue fluid homeostasis by collecting extravasated fluid and returning macromolecules back to the blood circulation (Alitalo et al. 2005). The lymphatic capillaries in the peripheral tissues merge with larger collecting lymphatic vessels, specialized for the transport of large volumes of lymph, that in turn connect with chains of lymph nodes (Alitalo et al. 2005). From an immunological standpoint, lymph nodes are strategically positioned patrol stations for antigens from peripheral tissues (Banchereau et al. 2000). Naive lymphocytes circulate through lymph nodes to search for their specific antigen. When a foreign microbe enters Pauliina Hartiala and Anne M. Saaristo are at Plastic Surgery, Turku University Central Hospital, 20251 Finland. *Address correspondence to: Anne M. Saaristo, Plastic Surgery, Turku University Central Hospital, PL 52, Kiinamyllynkatu 4-8, 20251 Finland. Tel.: 358-2-3130257; fax: 3582-3132215; e-mail: [email protected] © 2010 Elsevier Inc. All rights reserved. 1050-1738/$-see front matter
TCM Vol. 20, No. 8, 2010
the skin, professional antigen presenting cells, namely dendritic cells (DCs), phagocytose the invading microbes, become mature DCs, and migrate to lymph nodes via lymph vessels. To elicit an adaptive immune response, DCs must interact with antigen-specific T cells and B cells in the lymph node and present the antigens (Banchereau et al. 2000). Thus, lymphatic vessels and lymph nodes are involved in several human diseases, such as lymphedema, inflammation, and tumor metastasis. Chronic lymphedema, commonly caused by infection and surgical or radiation therapy of metastatic cancer, remains a common clinical challenge that often lacks curative treatment options. Rare hereditary forms of lymphedema are caused by structural defects in the lymphatic vessels (Ferrell and Finegold 2008). A globally remarkable cause of lymphedema is filariasis, which affects more than 90 million people (Rockson 2001). It has been estimated that currently several million patients suffer from acquired lymphedema in the United States alone (Tabibiazar et al. 2006). The effective treatment of cancer often requires removal of regional
lymph nodes to eradicate metastases. This leads to a disruption of the lymphatic flow in the operated area, which frequently leads to lymphedema of the affected limb. The incidence of lymphedema varies from 9% to 41% in patients who have undergone axillary lymph node dissection and from 4% to 10% in patients who have undergone sentinel node biopsy (Clark et al. 2005, McLaughlin et al. 2008, Suami and Chang 2010). Lymphedema is a progressive disease characterized by gross swelling of the affected limb, accompanied by adipose tissue hypertrophy and fibrosis, which is most likely induced by slow or absent lymph flow and inflammation (Warren et al. 2007). Lymphedema patients are susceptible to infections as a result of microbial growth due to extravasated fluid and proteins and an impaired local immune response (Rockson 2001). Antigen presenting cells have no direct route to local or close-remaining lymph nodes to present antigens and elicit further adaptive immune responses needed for effective clearance of pathogens. The treatment of lymphedema is currently based on physiotherapy, compression garments, and, occasionally, surgical treatment options including liposuction (Suami and Chang 2010), lymph node transfer (Becker et al. 2006), and lymphaticovenous shunts or lymphaticolymphatic bypasses (Baumeister et al. 1981, Campisi 1991, Chang 2010, Rockson 2001, Weiss et al. 2002). However, identifying and preserving the lymphatic vessels even by modern microsurgical methods is difficult. Another challenge regarding reconstructive surgery is that chronic lymphedema leads to secondary changes in the affected limb, including skin fibrosis, deposition of adipose tissue, and distal lymphatic valve insufficiency (Warren et al. 2007). • Regulation of Lymphangiogenesis Understanding of the molecular mechanisms of lymphangiogenesis has increased considerably in recent years
249
(Tammela and Alitalo 2010). Vascular endothelial growth factors (VEGFs) are important regulators of angiogenesis and lymphangiogenesis (Lohela et al. 2009, Oliver 2004). VEGFs stimulate cellular responses by binding to the tyrosine kinase receptors (RTKs) VEGFR-1, VEGFR-2, and VEGFR-3, which are specifically expressed in the luminal surface of the blood and lymphatic endothelial cells. VEGFR activation promotes cell proliferation, migration, and survival (Olsson et al. 2006). VEGF-A binds to VEGFR-1 and VEGFR-2 and induces mainly angiogenesis, whereas VEGF-C and VEGF-D bind VEGFR-3 and induce mainly lymphangiogenesis (Olsson et al. 2006, Tammela and Alitalo 2010). The affinity of VEGF-C and VEGF-D to VEGFR-3 is increased by proteolytic cleavage, and only the fully processed forms can bind VEGFR-2 (Joukov et al. 1997, Olsson et al. 2006, Stacker et al. 1999). VEGF seems to stimulate mainly circumferential hyperplasia of lymphatic capillaries and only indirectly lymphangiogenesis via the recruitment of inflammatory cells (Wirzenius et al. 2007). VEGF-B has been shown to induce cardiac hypertrophy and coronary arteriogenesis (Karpanen et al. 2008, Schaper 2008). VEGFs also bind neuropilin (Nrp)-1 and Nrp-2 co-receptors, which modulate the signaling of VEGF receptors and provide specificity for their signal transduction (Caunt et al. 2008, Lohela et al. 2009). Also, certain integrins, as well as heparan sulfate proteoglycans, can act as co-receptors for the VEGFs expressed in blood and lymphatic endothelial cells that line the luminal surface of vessels (Iozzo and San Antonio, 2001). Results from preclinical lymphedema models employing VEGF-C or VEGF-D gene transfer (Enholm et al. 1997, Karkkainen et al. 2001, Rissanen et al. 2003, Saaristo et al. 2002) or application of recombinant protein (Baker et al. 2010, Szuba et al. 2000) have demonstrated the potential and specificity of these factors for inducing growth of new lymphatic vessels. The short half-life of the VEGF proteins favors the use of transient gene transfer as a mode of treatment (Veikkola et al. 2001). First experimental lymphedema animal models focused on regrowth of new lymphatic 250
capillary vessels in response to lymphatic growth factor therapy (Karkkainen et al. 2001, Saaristo et al. 2002, Yoon et al. 2003). Together with other groups, we have shown that the collecting lymphatic vessels can also be rebuilt with VEGF-C/D therapy (Baker et al. 2010, Lahteenvuo et al. 2011, Tammela et al. 2007). Adenoviral VEGF-C or VEGF-D gene transfer results in transient lymphatic vessel growth factor overexpression in the targeted area (Lahteenvuo et al. 2011, Saaristo et al. 2002, Tammela et al. 2007). During the first 2 weeks, robust growth of lymphatic vessels can be detected, but after 2 weeks, as the adenoviral growth factor expression is downregulated, the lymphatic vessel network will regress (Saaristo et al. 2002). However, the newly formed vessels that have lymphatic flow seem to stabilize and maturate into true collecting lymphatic vessels spontaneously over the course of 6 months (Tammela et al. 2007). Thus, the growth factor-stimulated vessels seem to engage an intrinsic differention program to form collecting vessels. Tumorigenesis and tumor metastasis are multistep processes, and accumulation of several, usually somatic, mutations is required for both. Neovascularization is a rate-limiting step for tumor growth beyond 1 mm in diameter (Kerbel and Folkman, 2002). The VEGF/VEGFR-2 signaling axis appears to be the most important regulator of blood vessel growth in tumors (Ferrara et al. 2007). Elevated levels of VEGF mRNA are found in most human tumors. Furthermore, lymph node metastasis is an important prognostic indicator in many tumor types (Sleeman and Thiele, 2009). In principle, tumor cells can invade either pre-existing lymphatic vessels or new lymphatic vessels formed at the tumor periphery by tumor-induced lymphangiogenesis. Many types of tumors express the lymphangiogenic growth factors VEGF-C and VEGF-D, and several studies have shown that expression of these growth factors actively induces tumor-associated lymphangiogenesis, leading to lymphatic invasion, lymph node and distant metastasis, and subsequently poor patient survival (Holopainen et al. 2011).
Figure 1. The authors’ vision of how to reconstruct the lymphatic vascular anatomy in the axilla after axillary dissection and oncologic cancer treatment. (A) Lymphatic tissue from the lower abdominal wall can be harvested as a vascularized free flap. (B) Adenoviral gene transfer vector encoding lymphatic growth factor (VEGF-C) is injected into the distal edges of the lymphatic flap to enhance regrowth of lymphatic vessels. (C) Growth factor–treated lymphatic flap is placed into the axilla to replace irradiated scar tissue. Blood vascular anastomosis sites of the free flap are indicated with the black box.
• Lymph Node Transfer Surgical treatment of cancer often requires removal of inguinal or axillary lymph nodes and is associated with lymphedema of the affected limb. The lymph node transfer technique aims to rebuild the lymphatic vascular anatomy after the cancer treatment. The therapeutic effect of this surgical method has been tested in different experimental lymphedema animal models and also in human lymphedema patients. In patients, lymphatic tissue can be harvested as a vascularized free flap from the lower abdominal wall and transferred into the axilla (Becker et al. 2006) (Figure 1A). However, in this technique, the lymphatic vessel anastomoses are expected TCM Vol. 20, No. 8, 2010
to form spontaneously. Chen et al. (1990) demonstrated lymph nodes with normal architecture and size 3 and 6 months after vascularized lymph node transplantation in a canine model. The circumference of the limb was reduced after transplantation compared with preoperative data. Furthermore, postoperative lymphangiography demonstrated regeneration of the lymphatic system 6 months after surgery. Blum et al. (2010) found that autotransplantation of lymph node fragments after lymphadenectomy in minipigs had positive effects on the restoration of lymphatic flow and that larger fragments were more often integrated into the lymphatic system than small lymph node slices. Tobbia et al. (2009) compared the effect of vascularized versus nonvascularized lymph node transplants in the treatment of postsurgical lymphedema in a sheep model and found that the vascularized transplants were associated with a better clinical improvement. Furthermore, platelet-rich plasma, containing various growth factors, has been shown to improve regeneration of lymph node fragments in a rat model (Hadamitzky et al. 2009). Recent clinical articles have shown that autologous microvascular lymph node transfer from the groin area into axillas or wrists of postmastectomy patients may improve lymphatic drainage of the affected limb (Becker et al. 2006, Lin et al. 2009, Saaristo et al. 2011). In a study by Becker et al., 24 women with postsurgical physiotherapy-resistant lymphedema underwent a microsurgical operation in which lymph nodes from the groin area were transferred to the axilla. After treatment, upper limb perimeter returned to normal in 10 patients and was decreased in 12 patients. Fifteen patients were able to discontinue physiotherapeutic treatments of lymphedema (Becker et al. 2006). In our own patient material, one-third of the postmastectomy lymphedema patients no longer needed compression therapy after the lymph node transfer into the axillary area (Saaristo et al. 2011). Lin et al. used a similar vascularized groin flap but transferred the vascularized lymph nodes into the wrist area of the lymphedema patients. All clinical studies also showed an improvement of skin infections (erysipelas, lymphangitis, and cellulitis) after lymph node transfer. TCM Vol. 20, No. 8, 2010
In the lymph node transfer technique, the lymphatic vascular anastomoses are expected to form spontaneously. Our recent report indicates that human lymph nodes express endogenous lymphangiogenic growth factors, namely VEGF-C, providing a biological basis for this surgical method (Saaristo et al. 2011). Clinical and experimental data, however, suggest that although spontaneous lymphangiogenesis after lymph node transfer does occur, the incorporation of the transferred lymph nodes into the existing lymphatic network may fail (Becker et al. 2006, Lahteenvuo et al. 2011, Saaristo et al. 2011, Tammela et al. 2007). This poor incorporation efficiency may compromise the outcome of the operation because connection with lymphatic vessels is required for maintenance and function of the lymph nodes (Mebius et al. 1991, Tammela et al. 2007). Because we are operating on patients who have previously developed lymphedema symptoms in their upper extremities, we need to be extremely careful with the donor site morbidity. Harvesting lymph nodes from the lower abdominal wall seems to induce seroma formation (Saaristo et al. 2011), but to date there are no reports on lymphedema symptoms of the lower limb after the lymph node transfer surgery. • Combining Lymphangiogenic Growth Factor Treatment With Lymph Node Transfer Lymph nodes need lymphatic flow to remain functional (Lahteenvuo et al. 2011, Mebius et al. 1991, Tammela et al. 2007). Without connections with the afferent and efferent lymphatic vessels, lymph nodes regress (Mebius et al. 1991). The idea of combining growth factor treatment with the lymph node transfer as a lymphedema treatment was first presented by Tammela et al. The results of this study showed that the sentinel node function of transferred lymph nodes was regained and intracutaneously injected lung carcinoma cells were trapped in the transferred lymph node (Tammela et al. 2007). Previously, it was shown that transplanted lymph nodes retain the ability to mount a cytotoxic immune response against tumor cells and that they recover a normal architecture (Fu et al. 1998, Rabson et
al. 1982). Recently, the efficacy of the VEGF-C and -D growth factor therapies and lymph node transfer was also tested in a lymphedema large animal model (Lahteenvuo et al. 2011). Postoperative lymphatic drainage was significantly improved in the VEGF-C/D–treated pigs compared with controls. Importantly, the structure of the transferred lymph nodes was best preserved in the VEGFC–treated pigs. Control-treated lymph nodes regressed, and their follicular structure was replaced by adipose and fibrotic tissue. This is in concordance with previous data that indicate that the lymph nodes need lymphatic vasculature and exposure to lymph flow to remain intact (Mebius et al. 1991, Tammela et al. 2007). Other methods for growth factor delivery have also been tested in the postsurgical lymphedema model. Baker et al. (2010) used a gel-based drug delivery system, HAMC, which is a physical blend of hyaluronan and methylcellulose, to deliver VEGF-C and angiopoietin-2 to the operation site after excision of the popliteal lymph node in sheep. Edema was significantly reduced after growth factor treatment, and the lymphatic transport function was improved, although it did not completely normalize within the 6-week follow-up period (Baker et al. 2010). • Conclusions and Future Perspectives Approximately 200,000 new cases of breast cancer are diagnosed annually in the United States alone. In addition to breast cancer, many other cancer types spread via the lymphatic vessels, necessitating regional surgery of the lymph nodes and making a large patient population susceptible to the development of lymphedema. Lymph node transfer is a new technique in lymphedema surgery. Of all postmastectomy patients who ask for breast reconstruction, 9%-41% also have lymphedema symptoms of the upper arm (Clark et al. 2005, McLaughlin et al. 2008, Saaristo et al. 2011, Suami and Chang 2010). Interestingly, building material for both breast reconstruction and lymph node transfer can be harvested from the patient’s own lower abdominal wall (Saaristo et al. 2011) (Figure 1). The fact that lymph node transfer can easily be performed in combination with routine microvascular 251
breast reconstruction has made this method attractive (Saaristo et al. 2011). Preliminary results from the lymph node transfer show best clinical efficacy in patients with early disease (Becker et al. 2006, Saaristo et al. 2011), before deposition fibrosis and deposition of adipose tissue has occurred (Warren et al. 2007). One critical step regarding the operation technique seems to be the complete removal of all old scar tissue, which is then replaced with a healthy patch of adipose tissue containing the lymph nodes. To truly determine the efficacy of this new technique, results from large clinical studies and from different units are needed. More data are also needed on the efficacy of treatment in different stages of lymphedema. Not all patients seem to benefit from the lymph node transfer surgery, which might be partly explained by the temporal and spatial differences in lymph node VEGF-C expression. Findings from experimental animal models clearly favor the use of growth factors in conjunction with lymph node transfer to augment incorporation of the grafted lymph node into the resident lymphatic vascular tree (Lahteenvuo et al. 2011, Tammela et al. 2007). Vectors inducing short-term overexpression of the patient’s own endogenous lymphatic growth factors in the distal edge of the lymphatic tissue flap could be used to enhance the therapeutic effect of the lymph node transfer technique (Figure 1). VEGF-C and -D are also involved in lymphatic metastasis of several human tumors; therefore, patient safety is an important issue. However, human lymph nodes also produce endogenous VEGF-C (Saaristo et al. 2011), and lymph node transfer is already used in cancer patients. In experimental models, newly formed lymphatic vessels seem to stabilize after the short-term (1-week) VEGF-C overexpression (Lahteenvuo et al. 2011, Tammela et al. 2007); thus, long-lasting lymphatic growth factor therapy is not needed. • Acknowledgments This study was supported by the Academy of Finland, the Turku University Foundation, special governmental funding (EVO) allocated to Turku University Central Hospital, the Paavo and Eila Salonen Foundation, the Ida Montini Foundation, the Aarne and Aili Turunen 252
Foundation, the Emil Aaltonen Foundation, and Laurantis Pharma.
Fu K, Izquierdo R, Vandevender D, et al: 1998. Transplantation of lymph node fragments in a rabbit ear lymphedema model: A new method for restoring the lymphatic pathway. Plast Reconstr Surg 101:134 –141.
References
Hadamitzky C, Blum KS, & Pabst R: 2009. Regeneration of autotransplanted avascular lymph nodes in the rat is improved by platelet-rich plasma. J Vasc Res 46:389 – 396.
Alitalo K, Tammela T, & Petrova TV: 2005. Lymphangiogenesis in development and human disease. Nature 438:946 –953. Baker A, Kim H, Semple JL, et al: 2010. Experimental assessment of pro-lymph angiogenic growth factors in the treatment of post-surgical lymphedema following lymphadenectomy. Breast Cancer Res 12:R70. Banchereau J, Briere F, Caux C, et al: 2000. Immunobiology of dendritic cells. Annu Rev Immunol 18:767– 811. Baumeister RG, Seifert J, & Hahn D: 1981. Autotransplantation of lymphatic vessels. Lancet 1:147. Becker C, Assouad J, Riquet M, & Hidden G: 2006. Postmastectomy lymphedema: Longterm results following microsurgical lymph node transplantation. Ann Surg 243:313– 315. Blum KS, Hadamitzky C, Gratz KF, & Pabst R: 2010. Effects of autotransplanted lymph node fragments on the lymphatic system in the pig model. Breast Cancer Res Treat 120:59 – 66. Campisi C: 1991. Use of autologous interposition vein graft in management of lymphedema: Preliminary experimental and clinical observations. Lymphology 24: 71–76. Caunt M, Mak J, Liang WC, et al: 2008. Blocking neuropilin-2 function inhibits tumor cell metastasis. Cancer Cell 13:331– 342. Chang DW: 2010. Lymphaticovenular bypass for lymphedema management in breast cancer patients: A prospective study. Plast Reconstr Surg 126:752–758. Chen HC, O’Brien BM, Rogers IW, et al: 1990. Lymph node transfer for the treatment of obstructive lymphoedema in the canine model. Br J Plast Surg 43:578 –586. Clark B, Sitzia J, & Harlow W: 2005. Incidence and risk of arm oedema following treatment for breast cancer: A three-year follow-up study. QJM 98:343–348. Enholm B, Paavonen K, Ristimaki A, et al: 1997. Comparison of VEGF, VEGF-B, VEGF-C and Ang-1 mRNA regulation by serum, growth factors, oncoproteins and hypoxia. Oncogene 14:2475–2483. Ferrara N, Mass RD, Campa C, & Kim R: 2007. Targeting VEGF-A to treat cancer and age-related macular degeneration. Annu Rev Med 58:491–504. Ferrell RE & Finegold DN: 2008. Research perspectives in inherited lymphatic disease: An update. Ann N Y Acad Sci 1131:134 – 139.
Holopainen T, Bry M, Alitalo K, & Saaristo A: 2011. Perspectives on lymphangiogenesis and angiogenesis in cancer. J Surg Oncol 103:484 – 488. Iozzo RV & San Antonio JD: 2001. Heparan sulfate proteoglycans: Heavy hitters in the angiogenesis arena. J Clin Invest 108:349 – 355. Joukov V, Sorsa T, Kumar V, et al: 1997. Proteolytic processing regulates receptor specificity and activity of VEGF-C. EMBO J 16:3898 –3911. Karkkainen MJ, Saaristo A, Jussila L, et al: 2001. A model for gene therapy of human hereditary lymphedema. Proc Natl Acad Sci USA 98:12677–12682. Karpanen T, Bry M, Ollila HM, et al: 2008. Overexpression of vascular endothelial growth factor-B in mouse heart alters cardiac lipid metabolism and induces myocardial hypertrophy. Circ Res 103:1018 –1026. Kerbel R & Folkman J: 2002. Clinical translation of angiogenesis inhibitors. Nat Rev Cancer 2:727–739. Lahteenvuo M, Honkonen K, Tervala T, et al: 2011. Growth factor therapy and autologous lymph node transfer in lymphedema. Circulation 123:613– 620. Lin CH, Ali R, Chen SC, et al: 2009. Vascularized groin lymph node transfer using the wrist as a recipient site for management of postmastectomy upper extremity lymphedema. Plast Reconstr Surg 123: 1265–1275. Lohela M, Bry M, Tammela T, & Alitalo K: 2009. VEGFs and receptors involved in angiogenesis versus lymphangiogenesis. Curr Opin Cell Biol 21:154 –165. McLaughlin SA, Wright MJ, Morris KT, et al: 2008. Prevalence of lymphedema in women with breast cancer 5 years after sentinel lymph node biopsy or axillary dissection: Patient perceptions and precautionary behaviors. J Clin Oncol 26:5220 –5226. Mebius RE, Streeter PR, Breve J, et al: 1991. The influence of afferent lymphatic vessel interruption on vascular addressin expression. J Cell Biol 115:85–95. Oliver G: 2004. Lymphatic vasculature development. Nat Rev Immunol 4:35– 45. Olsson AK, Dimberg A, Kreuger J, et al: 2006. VEGF receptor signalling—In control of vascular function. Nat Rev Mol Cell Biol 7:359 –371. Rabson JA, Geyer SJ, Levine G, et al: 1982. Tumor immunity in rat lymph nodes fol-
TCM Vol. 20, No. 8, 2010
lowing transplantation. Ann Surg 196: 92–99. Rissanen TT, Markkanen JE, Gruchala M, et al: 2003. VEGF-D is the strongest angiogenic and lymphangiogenic effector among VEGFs delivered into skeletal muscle via adenoviruses. Circ Res 92:1098 –1106. Rockson SG: 2001. Lymphedema. Am J Med 110:288 –295. Saaristo A, Veikkola T, Tammela T, et al: 2002. Lymphangiogenic gene therapy with minimal blood vascular side effects. J Exp Med 196:719 –730. Saaristo AM, Niemi T, Viitanen T, et al: 2011. Microvascular breast reconstruction and lymph node transfer for postmastectomy lymphedema patients. Ann Surg (in press): Schaper W: 2008. The renaissance of vascular endothelial growth factor, part B. Circ Res 103:903–904. Sleeman JP & Thiele W: 2009. Tumor metastasis and the lymphatic vasculature. Int J Cancer 125:2747–2756. Stacker SA, Stenvers K, Caesar C, et al: 1999. Biosynthesis of vascular endothelial growth factor-D involves proteolytic processing which generates non-covalent homodimers. J Biol Chem 274:32127–32136. Suami H & Chang DW: 2010. Overview of surgical treatments for breast cancer-related lymphedema. Plast Reconstr Surg 126:1853–1863. Szuba A, Cooke JP, Yousuf S, & Rockson SG: 2000. Decongestive lymphatic therapy for patients with cancer-related or primary lymphedema. Am J Med 109:296 –300. Tabibiazar R, Cheung L, Han J, et al: 2006. Inflammatory manifestations of experimental lymphatic insufficiency. PLoS Med 3:e254.
Tammela T & Alitalo K: 2010. Lymphangiogenesis: Molecular mechanisms and future promise. Cell 140:460 – 476. Tammela T, Saaristo A, Holopainen T, et al: 2007. Therapeutic differentiation and maturation of lymphatic vessels after lymph node dissection and transplantation. Nat Med 13:1458 –1466. Tobbia D, Semple J, Baker A, et al: 2009. Experimental assessment of autologous lymph node transplantation as treatment of postsurgical lymphedema. Plast Reconstr Surg 124:777–786. Veikkola T, Jussila L, Makinen T, et al: 2001. Signalling via vascular endothelial growth factor receptor-3 is sufficient for lymphangiogenesis in transgenic mice. EMBO J 20: 1223–1231. Warren AG, Brorson H, Borud LJ, & Slavin SA: 2007. Lymphedema: A comprehensive review. Ann Plast Surg 59:464 – 472. Weiss M, Baumeister RG, & Hahn K: 2002. Post-therapeutic lymphedema: Scintigraphy before and after autologous lymph vessel transplantation: 8 years of longterm follow-up. Clin Nucl Med 27:788 – 792. Wirzenius M, Tammela T, Uutela M, et al: 2007. Distinct vascular endothelial growth factor signals for lymphatic vessel enlargement and sprouting. J Exp Med 204:1431– 1440. Yoon YS, Murayama T, Gravereaux E, et al: 2003. VEGF-C gene therapy augments postnatal lymphangiogenesis and ameliorates secondary lymphedema. J Clin Invest 111: 717–725.
PII S1050-1738(11)00087-9
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MicroRNA Regulation of Angiogenesis and Arteriogenesis Felix P. Hans, Martin Moser, Christoph Bode, and Sebastian Grundmann*
MicroRNAs are short, nonprotein-coding RNA molecules that play a crucial role in the post-transcriptional regulation of gene expression. By binding to specific target sequences, mostly located in the 3=-untranslated region of their target mRNA, they can induce mRNA decay or translational inhibition. Unlike siRNA, microRNAs show imperfect matching to their target mRNAs and can therefore modulate the expression of several mRNA genes at once. Although TCM Vol. 20, No. 8, 2010
microRNAs have already been extensively studied in invertebrates, their function in mammalian organisms and in human disease is largely unknown. Several studies have shown an important regulatory function of microRNAs in embryonic and postnatal blood vessel development. Here, we provide an overview on these recent findings and summarize these so-called “angiomiRs” and their mode of action. (Trends Cardiovasc Med 2010; 20:253–262) © 2010 Elsevier Inc. All rights reserved. • Introduction The mechanisms of the growth and proliferation of blood vessels can be divided into three different entities. In early development, vasculogenesis describes the de novo formation of a premature cardiovascular system in the growing embryo by the differentiation of mesenchymal cell populations into hemangioblasts. Vascular endothelial growth factor (VEGF) stimulation of these hemangioblasts triggers differentiation into both the progenitor populations for vessel structures and for the blood components. Fusing of the blood island leads to a primitive cardiovascular plexus that is the fundament of a differentiated venous and arterial system. In the adult, vasculogenesis is a rare process because the mode of action for adaptive vessel growth is conciliated by two other important mechanisms: angiogenesis and arteriogenesis. Although hypoxic conditions lead to endothelial activation via hypoxia-inducible factor (HIF) stabilization and VEGF Felix P. Hans, Martin Moser, Christoph Bode, and Sebastian Grundmann are at the Department of Internal Medicine III, University Hospital Freiburg, 79106 Freiburg, Germany. *Address correspondence to: Sebastian Grundmann, M.D., Ph.D., Department of Internal Medicine III (Cardiology and Angiology), University Hospital Freiburg, Breisacher Str. 33, 79106 Freiburg, Germany. Tel.: (⫹49) 761 270 70460; fax: (⫹49) 761 270 70450; e-mail: sebastian.grundmann@ uniklinik-freiburg.de. © 2010 Elsevier Inc. All rights reserved. 1050-1738/$-see front matter
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