What is the role of peptide fragments of collagen I and IV in health and disease?

Collagen is the most abundant protein in mammalian systems; it can be found in organs such as bones, the liver, kidney, heart, teeth, and skin. Collagen provides the necessary structural framework for tissues in which it is found. However, if there are any alterations in the delicate balance of collagen types in the extracellular matrix (ECM), then problems arise. For example, increasing collagen I:III ratio would provide additional rigidity to tissue structure, whereas decreasing this ratio would provide elasticity and flexibility to the tissue. The proper function of tissues is reliant on this scale not tipping too far in either direction. Major players in the process of ECM remodeling, both normal and adverse, are the fibroblast cells via the secretion of collagen precursors and matrix metalloproteinases, with the latter responsible for ECM degradation. The collagen peptides created by the proteolytic cleavage of these collagen fibrils, while once thought to have an absence of function, have been shown over recent years to potentiate and regulate a variety of cellular processes acting through integrin receptors. Many collagen peptides have been identified from many different collagen types and have been shown to regulate processes such as cell proliferation, migration, apoptosis, and reduce angiogenesis. The collagen peptides of interest are those generated from the primary collagen type of tissue interstitial matrix, collagen type I, and the basement membrane, collagen type IV. Thus, this review looks to highlight some examples of unorthodox functional roles of collagen and its peptides in regulating physiological health and disease.