Qualitative Changes in Collagen Induced by UV Irradiation Affect Its Interaction with Cells

The extracellular matrix (ECM) is a noncellular component in all tissues and organs. Collagen, a component of the ECM, is the most abundant protein in the body. The amount of collagen decreases with aging, leading to wrinkles and skin sagging. Accelerated aging caused by UV radiation is known as photoaging. Skin fibroblasts exposed to UVB have reduced total collagen content due to accelerated production of collagen-degrading enzymes, matrix metalloproteinases (MMPs), and suppression of collagen production. However, the effects of UVB on the ECM surrounding the cell and its interaction with the cell have not been well reported. This study sought to elucidate the effects of UVB-induced changes in the extracellular environment on cells. UVB-irradiated collagen exhibited irradiation-dependent degradation and accelerated carbonylation, resulting in qualitative changes. UVB-induced changes in collagen led to reduced cell-collagen interactions, such as adhesion, proliferation, and contraction. Moreover, UVB-irradiated collagen was more susceptible to collagen degradation by MMP-1. UVB-induced changes in collagen were analyzed using mass spectrometry (LC-MS/MS). Although alternation of post-translational modification was not detected in the cell-bound regions of collagen, multiple sites of carbonylative modification were detected on proline (Pro), arginine (Arg), and lysine (Lys). The numerous carbonylative modifications to Pro, Arg, and Lys in collagen may cause changes in the overall structure of collagen and affect cellular functions that are regulated by the interaction with collagen. Overall, our findings highlight a photoaging mechanism that focuses on the effects of ECM changes on cells.