Collagen-receptor signaling in health and disease.

Collagens are not only essential for the mechanical resistance and resilience of multicellular organisms, but are also signaling molecules defining cellular shape and behavior. The communication between collagens and cells is achieved by cell surface receptors. Three types of cell surface receptors for collagen are known: integrins, discoidin domain receptors and glycoprotein VI. All three types independently trigger a variety of signaling pathways upon collagen-binding. Besides regulating numerous cellular responses, both integrin and discoidin domain receptors monitor the integrity of the collagenous extracellular matrix by triggering matrix degradation and renewal. Some recently discovered mechanisms of locally controlled expression of collagen, collagen-binding receptors and collagen-degrading proteases in the cellular microenvironment are described.