Collagen Fibril Formation

Abstract

We present a concept for reducing formation of fibrotic deposits by inhibiting self-assembly of collagen molecules into fibrils, a main component of fibrotic lesions. Employing monoclonal antibodies that bind to the telopeptide region of a collagen molecule, we found that blocking telopeptide-mediated collagen/collagen interactions reduces the amount of collagen fibrils accumulated in vitro and in keloid-like organotypic constructs. We conclude that inhibiting extracellular steps of the fibrotic process provides a novel approach to limit fibrosis in a number of tissues and organs.Collagen I is the most abundant structural protein of connective tissues such as skin, bone, and tendon. This protein is first synthesized as a precursor molecule, procollagen, that is characterized by the presence of a rod-like central triple-helical domain flanked by short linear telopeptides and globular N-terminal and C-terminal propeptides (1). Single procollagen molecules are the building blocks for the biologically and mechanically relevant collagen fibrils. Formation of collagen fibrils is initiated by enzymatic cleavage of the N-terminal and the C-terminal propeptides. The N-terminal propeptides are cleaved by a group of enzymes that includes a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS)-2, -3, and -14, whereas the C-terminal propeptides are cleaved by the metalloprotease bone morphogenetic protein 1 (BMP-1) 2 and by the other members of a closely related family of mammalian tolloid-like metalloproteases (2-4). Such a removal of procollagen propeptides exposes telopeptides, which by engaging in site-specific intermolecular interactions drive collagen self-assembly.In native tissues a precise balance between the processes of biosynthesis and degradation maintains the physiological homeostasis of tissue collagens. At the same time, accelerated biosynthesis is required for proper wound healing, whereas excessive accumulation of collagen is the hallmark of a number of localized fibrotic diseases, such as keloids and hypertrophic scars, and systemic fibrosis, such as systemic scleroderma.Localized fibrotic reactions are quite common and frequently develop as a consequence of surgical procedures. For instance, after surgery of the abdomen, the formation of excessive scar tissue around abdominal organs, such as the intestines, can interfere with the functionality of such organs and may cause severe pain and even death. Another situation where excessive scar formation presents a major complication is in the eye after glaucoma surgery performed to create a pressuremaintenance valve. Frequently, however, excessive scar formation closes this pressure-reducing valve, thereby forcing the intraocular pressure to rise (5). Moreover, excessive scarring of the vocal folds may severely alter their ability to vibrate, thereby causing a number of voice disorders (6).At present, several biological processes critical for development of fibrotic lesions are considered potential targets for inhibitors of fibrosis. These inhibit...

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“…2F). Covalent cross-linking of collagen and fibrillogenesis is highly dependent on collagen's C-terminal telopeptide region, which is exposed after cleavage of the C-terminal propeptide in the process of maturation (37)(38)(39). Our experimental findings show that IGF-1 significantly increased expression of mature ␣1(I) (exposed C-telopeptide, Fig.…”

“…Because LARP6 is implicated in ensuring proper assembly of collagen type I (10 -13), we also determined expression of mature collagen type I in the cultured medium using an antibody, which recognizes the ␣1(I) C-telopeptide. The ␣1(I) C-telopeptide is exposed after cleavage of the C'-terminal propeptide, and is crucial for crosslinking and fibril formation (37)(38)(39). In presence of the p74MUT control RNA, IGF-1 increased intracellular pro-␣1(I) expression as well as pro-␣1(I) and mature ␣1(I) expression in the cultured medium (Fig.…”

Lumican, an extracellular matrix proteoglycan, is a novel requisite for hepatic fibrosis

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