Regulation of tissue injury responses by the exposure of matricryptic sites within extracellular matrix molecules

Extracellular matrix (ECM) is known to provide signals controlling cell sha pe, migration, proliferation, differentiation, morphogenesis, and survival. Recent data shows that some of these signals are derived from biologically active cryptic sites within matrix molecules (matricryptic sites) that are revealed after structural or conformational alteration of these molecules. We propose the name, matricryptins, for enzymatic fragments of ECM contain ing exposed matricryptic sites. Mechanisms regulating the exposure of matri cryptic sites within ECM molecules include the major mechanism of enzymatic breakdown as well as others including ECM protein multimerization, adsorpt ion to other molecules, cell-mediated mechanical forces, and ECM denaturati on. Such matrix alterations occur during or as a result of tissue injury, a nd thus, the appearance of matricryptic sites within an injury site may pro vide important new signals to regulate the repair process. Here, we review the data supporting this concept and provide insight into why the increased exposure of matricryptic sites may be an important regulatory step in tiss ue responses to injury.