Matrix biology: past, present and future

Pathol Biol 2001 ; 49 : 279-83  2001 Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés S0369-8114(01)00141-9/EDI

Éditorial

Matrix biology: past, present and future L. Robert ∗ Laboratoire de recherche en ophtalmologie, Hôtel-Dieu, 1, place du parvis Notre-Dame, 75181 Paris cedex 04, France Summary Matrix biology (the biology of extracellular matrix) is a relatively recent branch of biomedical sciences and comprises a number of subspecialties. From molecular-cell biology, biochemistry, genetics and clinical science of diseases localised at or affecting the matrix rich tissues (connective tissues) as bone, cartilage, vessel wall, skin, eye and some others. The rapid expansion of all these branches of matrix biology is the combined result of the availability of advanced methods of cell and molecular biology and the increasing awareness of the importance of this field for a number of basic and applied sciences. This introduction is a review for the special issue of Pathologie Biologie devoted to ‘Matrix Biology’ and brushes an impressionistic landscape of the major advances accomplished over the finishing century and tries to predict some of the most important advances to be expected during the coming century.  2001 Éditions scientifiques et médicales Elsevier SAS cell–matrix interactions / connective tissues / matrix biology / matrix macromolecules

Résumé – Biologie de la matrice : passé, présent et futur. La biologie de la matrice extracellulaire est une branche relativement jeune des sciences biomédicales et comporte plusieurs sous-spécialités, allant de la biologie cellulaire et moléculaire à la biochimie, la génétique et la science clinique des affections touchant les tissus riches en matrice extracellulaire, les tissus conjonctifs comme l’os, le cartilage, les parois vasculaires, la peau, les yeux et d’autres tissus encore. La croissance rapide de toutes ces branches de la biologie de la matrice extracellulaire est le résultat de la mise au point récente de méthodes performantes de la biologie cellulaire et moléculaire et de la reconnaissance croissante de son importance pour de nombreux domaines d’application à des sciences fondamentales et cliniques. Cette introduction à ce numéro spécial de Pathologie Biologie, consacré à la biologie de la matrice extracellulaire, tente de brosser un tableau impressionniste des avancées majeures de cette science au cours du siècle qui se termine et essaye de prévoir les avancées les plus importantes que l’on puisse espérer pendant le siècle à venir.  2001 Éditions scientifiques et médicales Elsevier SAS interactions cellule–matrice / macromolécules de la matrice extracellulaire / tissus conjonctifs

PAST AND PRESENT OF MATRIX BIOLOGY Although the study of life in its different manifestations dates back to ancient history, it was only relatively recently acknowledged that the cell is the smallest common denominator of all living beings (see for a detailed description of this chapter of Natural History, the book of Harris [1]). This ‘discovery’ which took more than a century or two involved the contributions of a number of scientists in several countries and was followed

∗ Correspondence and reprints.

after some decades (first part of 20th century) by the ‘invention’ of cell- and tissue culture techniques as the principal tool of biologists and biochemists who wanted to improve their knowledge on the detailed mechanisms of life processes at the cellular level [2 – 4]. In between, histologists and histochemists gave a detailed description of tissue-structures showing clearly the presence of a more or less abundant extracellular matrix surrounding the cellular components of investigated organs. The ‘tissue’ concept was developed by Xavier Bichat in the

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first half of the 19th century using only his scalpel to dissect bodies. His work is credited as the foundation of medical pathology [5]. Biochemistry grow out of clinical chemistry during the 1st half of the 20th century [6], with a strong contribution of scientists trained as organic chemists. Their studies used tissue homogenates or, frequently micro-organisms as yeast and bacteria. Most of these studies aimed at the understanding of the metabolic pathways, the intermediary metabolism of carbohydrates, lipids, amino acides. The study of biological macromolecules had to wait the availability of adequate physicochemical methods as ultracentrifugation, electrophoresis, light scattering and others. These methods were completed by ultrastructural investigations as the electron microscope and its techniques which enabled the visualisation of macromolecules. From the late 1950-ies and especially since the 1960-ies the elucidation of the structure of DNA was the starting point for the eclosion of ‘molecular biology’ [7]. The historic description of these events mostly neglected the fact that one of the first scientists (if not the first) to use this expression was Astbury, a specialist of advanced electron microscopy and x-ray crystallography. He studied among others the x-ray diagram of microscopically visible fibers of biological macromolecules, such as collagen and considered fibrillogenesis, a morphogenetic process, as ‘molecular biology’ [8, 9]. The following citations are from Astbury: “Biology is fast becoming a molecular science. . . . Chief among these molecules are the proteins. . .” [8]. A few years later, in his Harvey lecture [9] he wrote: “The name ‘molecular biology’ seems to be passing now into fairly common use, and I am glad of that because, though it is unlikely I invented it first, I am fond of it and have long tried to propagate it. It implies not so much a technique as an approach, an approach from the viewpoint of the so-called basic sciences wit the leading idea of searching below the large-scale manifestations of classical biology for the corresponding molecular plan. It is concerned particularly with the forms of biological molecules, and with the evolution, exploitation and ramification of those forms in the ascent to higher and higher levels of organization. Molecular biology is predominantly three-dimensional and structural-which does not mean, however, that it is merely a refinement of morphology. It must of necessity enquire at the same time into genesis and function” [10]. His studies were partially based on the observations of Nageotte at the Collège de France in Paris who ‘solubilised’ collagen fibers from rat tail tendon and observed ‘fibrillogenesis’ by altering solution conditions by adding salts or changing the pH [11]. These ‘revelations’ concerning the origins of ‘molecular biology’ were published by a committee of the British Biochemical Society as an answer to the Kendrew report on ‘molecular biology’ [10]. As a matter of fact the ‘molecular’ approach of

biology did not wait for the discovery of DNA-structure but was mainly dependent on the availability of adequate methods to detect and fallow biological processes at the molecular level. Only part of ‘molecular biology’ concerns DNA or RNA, the major part of it concerns proteins, glycoproteins, lipoproteins enzymes and their biological roles. The recent emergence of proteomics [12] is one of the consequences of the recent realisation that the knowledge of gene-sequences is only a beginning to the elucidation of biological processes at the molecular level [13]. This is the way also to consider the emergence of the specificity of the biology of extracellular matrix. Among matrix macromolecules collagen was certainly the first to be studied as mentioned above – obtained long ago from bone by heating to obtain gelatin, used as an ingredient for glue and food industry, photography and several other applications. It was the 1st macromolecule to be studies by modern methods, separated in constituent α-chains, sequenced and its biosynthesis intensively studied since the sixties. One important early information was the demonstration of invertebrate collagens from marine sponges [14]. It appeared clearly that extracellular matrix was ‘invented’ latest during the ‘Cambrien explosion’. This conviction which first concerned mainly collagen was later extended to fibronectin, detected in sponges with antibodies to human fibronectin, indication of a strong preservation of structural features of this important structural glycoprotein mediating cell-matrix interactions all though evolution [15]. It appeared thus that the development of multicellular, highly structured organisms was accompanied by and depended certainly on the ‘invention’ of the extracellular matrix. Another family of matrix macromolecules was identified during the early 1900s, the glycosaminoglycans (GAG-s) or ‘acid mucopolysaccharides’ as they were called at that time [16]. Obtained first by relatively harsh hydrolytic extraction procedures, they were considered as regular polysaccharides with alternating hexosamine and uronic acid disaccharides subunits, sulfated or non sulfated as hyaluronane. Amino acids or peptides copurifyed with such polysaccharides were considered as ‘contaminants’. The purification of native, macromolecular proteoglycans by Hascall and Sajdera during the 1960s showed the way to the identification of all the complex molecular forms of this important family of matrix macromolecules, the proteoglycans [16, 17]. This became only possible after the isolation of cDNAs coding the protein components of proteoglycans, revealing a much greater heterogeneity than suspected from the structure of their polysaccharide components. At about the same time, at the end of sixties it became clear that there are several different collagens, as shown first by Ted Miller in Karl Pieze’s lab followed by the identification of several other collagen types, up to 19 in vertebrates only and several others in invertebrates [18, 19].

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Besides these two major families of matrix macromolecules two other families were also identified: elastin(s) and structural glycoproteins. Elastin was first ‘seen’ as a yellowish residue after hydrolytic removal of crosslinked collagens, especially in bovine ligamentum nuchae and large arteries. This protein appeared only with the vertebrates during phylogenesis. Its study was hampered by its insolubility and resistance even to hot aqueous alcaline hydrolysis [20]. This difficulty was overcome during the fifties thanks to the discovery of pancreatic elastase by Balo and Banga [21] and later by the production of large peptides by mild hydrolytic procedures [22, 23]. The biosynthetic precursor of elastin, tropoelastin was first isolated from the aortas of pigs raised on a copper free diet, decreasing crosslinking by lysyloxydase, by the team of Bill Carns and Larry Sandberg [24]. More recently the genes coding for elastin were sequenced and compared from several species [20]. The story of structural glycoproteins is even more complicated. Glycoproteins were first identified in the blood plasma and their glycan constituants as well as the linkage to proteins elucidated during the sixties [25]. Besides macromolecular glycosaminoglycans no other glycoconjugates were known in extracellular matrix. Jayle with whom I trained in the Biochemical Department of the Medical Faculty of Paris described plasma haptoglobin, showed its strong increase during inflammatory processes and beleived that it was derived from inflammatory connective tissues. As a matter of fact it was possible to demonstrate in carrageenin granulomas as well as in circulating blood of granuloma carrying animals glycoproteins and glycopeptides [26, 27]. The isolation of a glycoprotein from avascular bovine corneas was a convincing argument for the presence of glycoproteins distinst from proteoglycans and collagens in the extracellular matrix [28]. We could show at the same time that corneal collagen contained glucose and galactose, later identified as typical mono- and disaccharide components of collagens [29]. In order to distinguish circulating glycoproteins from matrix derived glycoproteins we proposed to designate this new family of ECM-components as ‘structural glycoproteins’ [28]. The identification of fibronectin during the seventies justified the designation of this 4th family of matrix components, soon enriched by a number of other matrix glycoproteins such as laminins, thrombospondins and many more [30]. Elastin remained the only matrix component devoid of cabohydrate components. It was shown however that it was closely associated with ‘microfibrillar’ components which analysed as glycoproteins [31]. At least 12 different glycoprotein components were described as belonging to this microfibrillar components of elastic fiber, fibrillins beeing the most intensly studied, partly because of the mutation of their genes in some forms of the Marfan syndrom [32].

It became thus clear at the end of this century that there are many matrix components, their nature and relative quantities define the structure and properties of tissues, as much or even more than its cellular components. A final important advance of the last decades of this finishing century was the identification of some of the mechanisms of cell-matrix interactions. The first receptors identified, members of the now wide spread integrin family [33], were involved in fibronectin cell interactions. Integrins were shown to mediate a variety of such interactions between different cell-types and most (but not all) matrix components (see the article of J. Labat-Robert in this issue). Elastin was one of the few matrix components not to interact with Integrins. For this reason we undertook a search for elastin-recognising receptors, on vascular smooth muscle cells (SMC-s) the major source of elastic fibers in large vessels, and also on fibroblasts [34]. During their contraction and relaxation SMC-s must adhere to elastic fibers in order to transduce the variation of tension to the vascular wall. Skin fibroblasts are also the source of a dense elastic network, profoundly remodeled during aging (see the articles of MP Jacob and T. Fülöp in this issue). The elastin receptor we identified appeared to share a subunit with the ‘Elastin Binding Protein’ studied in Bob Mecham’s lab by Alec Hinek [35]. Our work on this receptor, recognising also laminine concerned its functional properties, such as mediation of cell-elastin adhesion, vascular tension transduction, regulation of elastase-type enzyme production and some others [36 – 40]. It remains however possible that elastin associated microfibrillar glycoproteins, fibrillin, MAGP, Emiline and others might mediate cell elastic fiber interactions through some integrins. All these advances led to the intense study in a number of laboratories of exchange of information between cells and their surrounding matrix (see the article by J. Labat-Robert in this issue).

THE FUTURE We leave this finishing century with the beginning of an understanding of the functional properties of extracellular matrix. Although we can not claim yet the end of the descriptive period, probably some more matrix components still wait isolation and characterisation. The major problem still waiting solution is beyond doubt the elucidation of the mechanisms of oriented, selective matrix biosynthesis. How does a cell determine which genes, coding for specific matrix components to express at a given moment of its life cycle? What are the mechanisms of the spatiotemporal regulations of matrix biosynthesis? Let us take cornea as one of the interesting examples (see article L. Robert et al. in this issue). Collagen fibers, composed of type I, V and VI collagens mainly are deposited in a regular ‘ply-wood’ pattern, with a precise regulation of

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fiber diameter and orientation. The direction of rotation of collagen fibers is identical on both right and left eye, and not symmetrical (anti parallel) as could have been expected. How do the keratocytes ‘know’ in which direction to orient the fibers, how is gene-expression for the major collagen types co-regulated with widely different half-lifes for the above mentioned three major collagen types of cornea [41]. Those are only some of the questions which wait answer during the coming century. The same is true for the regulation of the expression of other matrix components also, such as proteoglycans, glycosaminoglycans and glycoproteins. Skin fibroblasts do not make (much) keratane sulfate, corneal keratocytes do continue to synthesise this special type of GAG even in serum containing medium and in the presence of oxygen [42]. The phenotype of fibroblasts and keratocytes is distinctly different and remains different even after several passages in conventional culture conditions [42]. Keratocytes make large proportions of collagen type VI, skin fibroblasts make much less [41]. Another intriguing problem waiting answer is the progressive modification of this ‘program’ of matrix biosynthesis with age and in a number of pathological conditions. Osteoarthritic chondrocytes, as well as in vitro passaged chondrocytes ‘dedifferentiate’. They loose irreversibly their specific program of matrix biosynthesis, guaranty of their specific phenotype. The elucidation of the underlying mechanisms might well represent necessary steps towards the rational cure of such degenerative diseases. Another important topic will remain for years to come the mediation of cell-matrix interactions. Integrines and other receptors were first considered as ‘hengers’ keeping cells attached to the matrix. Our studies on the elastinreceptor, published since the mid 1980-ies were the first to show the importance and variety of the functional aspects of matrix receptors [36 – 40]. This is now a hot topic for integrin biology also, waiting the identification of further receptors mediating cell-matrix communication as well as the detailed mechanisms of message transfer between cells and extracellular matrix [43]. For all these reasons I believed we start only to understand the importance of matrix biology. A lot remains to be done. The increasing number of young teams orienting themselves to these new vistas of matrix biology is a promising sign for those who pioneered the biochemistry of extracellular matrix during this finishing century.

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5 Albury WR. Experiment and explanation in the physiology of Bichat and Magendie. In: Coleman W, Limoges C, editors. Studies in history of biology. Baltimore: The Johns Hopkins University Press; 1977, p. 47-132. 6 Kohler RE. From medical chemistry to biochemistry. Cambridge: Cambridge University Press; 1982. 7 Morange M. Histoire de la biologie moléculaire. Paris: La Découverte; 1994. 8 Astbury WT. X-ray studies of the structure of compounds of biological interest. Ann Rev Biochem 1939; 8: 113-32. 9 Astbury WT. Adventures in molecular biology. Harvey Lecture Series 1951; 4: 3. 10 Biochemistry, ‘molecular biology’ and biological sciences. London: The Biochemical Society; 1969. 11 Nageotte J. Coagulation fibrillaire in vitro du collagène dissous dans un acide dilué. CR Acad Sci 1927; 18: 11. 12 Banks RE, Dunn MJ, Hochstrasser DF, Sanchez JC, Blackstock W, Pappin DJ, Selby PJ. Proteomics: new perspectives, new biomedical opportunities. Lancet 2000; 356: 1749-56. 13 Morange M. La part des gènes. Paris: Éditions Odile Jacob; 1998. 14 Tanzer ML, Kimura S. Phylogenetic aspects of collagen structure and function. In: Nimni ME, editor. Collagen, vol. II. Boca Raton: CRC Press Inc; p. 26-40. 15 Labat-Robert J, Robert L, Auger C, Lethias C, Garrone R. A fibronectin-like protein in porifera; its role in cell aggregation. Proc Nat Acad Sci 1981; 78: 6261-5. 16 Hascall VC, editor. Functions of the proteoglycans. Chichester: John Wiley & Son; 1986. 17 Wight TN, Mecham RP, editors. Biology of proteoglycans. Orlando: Academic Press Inc; 1987. 18 Brown JC, Timpl R. The collagen superfamily. Int Arch Allergy Immunol 1995; 107: 484-90. 19 Ricard-Blum S, Dublet B, Van der Rest M. Unconventional collagens. Oxford: University Press; 2000. 20 Robert L, Hornebeck W. Elastin and elastases, vol. I, II. Boca Raton, Fla: CRC Press; 1989. 21 Balo J, Banga I. Elastase and elastase inhibitor. Nature 1949; 164: 491. 22 Partridge SM, Davis HF. The chemistry of connective tissues. III. Composition of the soluble proteins derived from elastin. Biochem J 1955; 61: 21. 23 Robert L, Poullain N. Études sur la structure de l’élastine et le mode d’action de l’élastase. I. Nouvelle méthode de préparation de dérivés solubles de l’élastine. Bull Soc Chim Biol 1963; 45: 131726. 24 Sandberg LB, Leach CT, Leslie JG, Torres RA, Alvarez VL. Structural studies of porcine aortic tropoelastin. Robert AM, Robert L, editors. Biology and pathology of elastic tissues. Frontiers of Matrix Biology 1980; 8: 69-77. 25 Horowitz MI, Pigman W. The glycoconjugates, vol. I-II. New York: Academic Press; 1977. 26 Robert B, Robert L. Sur les rapports entre les polysaccharides neutres du tissu conjonctif et du sang. In: Peeters H, editor. Protides of the biological fluids. Amsterdam: Elsevier; 1959, p. 116-22. 27 Robert B, Robert L, Jayle MF. Les glycoprotéines sériques dans le granulome expérimental provoqué par la Carragéenine. Experientia 1959; 15: 385-90. 28 Robert L. Structural glycoproteins: Historical remarks. LabatRobert I, Timpl R, Robert L, editors. Frontiers of Matrix Biology 1986; 11: 1-16. 29 Dische Z, Robert L. Protein linked carbohydrate of the corneal stroma. Fed Proc 1962; 21: 172. 30 Labat-Robert J, Timpl R, Robert L. Structural glycoproteins in cellmatrix interactions. Basel: Karger; 1986. 31 Robert B, Szigeti M, Derouette JC, Robert L, Bouissou H, Fabre MT. Studies on the nature of the ‘microfibrillar’ component of elastic fibers. Eur J Biochem 1971; 21: 507-16.

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32 Reinhardt DP, Chalberg SC, Sakai LY. The structure and function of fibrillin. In: Robert L, editor. The molecular biology and pathology of elastic tissues. Ciba Foundation Symposium. Chichester: John Wiley & Sons; 1995. 33 Labat-Robert J, Robert L. Interaction between cells and extracellular matrix: signaling by integrins and the elastin-laminin receptor. Mecicira-Coelho A, editors. Progress in molecular and subcellular biology 2000; 25: 57-70. 34 Robert L, Jacob MP, Fülöp TJR, Timar J, Hornebeck W. Elastonectin and the elastin receptor. Pathol Biol 1989; 37: 736-41. 35 Hinek A, Wrenn DS, Mecham RP, Barondes SH. The elastin receptor: a galactoside-binding protein. Science 1988; 239: 1539-41. 36 Hornebeck W, Tixier JM, Robert L. Inducible adhesion of mesenchymal cells to elastic fiber: elastonectin. Proc Natl Acad Sci 1986; 83: 5517-20. 37 Jacob MP, Fülöp T, Foris G, Robert L. Effect of elastin peptides on ion fluxes in mononuclear cells, fibroblasts, and smooth muscle cells. Proc Natl Acad Sci 1987; 84: 995-9.

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38 Perdomo JJ, Gounon P, Schaeverbeke M, Schaeverbeke J, Groult V, Jacob MP, Robert L. Interaction between cells and elastin fibers: an ultrastructural and immunocytochemical study. J Cell Physiol 1994; 158: 451-8. 39 Faury G, Ristori MT, Verdetti J, Jacob MP, Robert L. Effect of elastin peptides on vascular tone. J Vasc Res 1995; 32: 112-9. 40 Fülöp T, Jacob MP, Khalil A, Wallach J, Robert L. Biological effects of elastin peptides. Pathol Biol 1998; 46: 497-506. 41 Kern P, Menasche M, Robert L. Relative rates of biosynthesis of collagen type I, type V and type VI in calf cornea. Biochem J 1991; 27: 615-7. 42 Dupuy F, Peterszegi G, Legeais JM, Robert AM, Robert L, Renard G. Stability of glycosaminoglycan biosynthesis during in vitro aging of human keratocytes. Biogerontology 2000. (Submitted). 43 Labat-Robert J, Robert L. Interaction between cells and extracellular matrix: signaling by integrins and the elastin-laminin receptor. In: Macieira-Coelho A, editor. Progress in molecular and subcellular biology, vol. 25, 2000, p. 57-70.