Carbonylation analysis of normal or photoaged collagen

The extracellular matrix (ECM) is a non-cellular component present in all tissues and organs. Collagen is the most abundant protein in the body and an important aesthetic molecule that maintains skin tension. With age, the amount of collagen decreases, causing wrinkles and skin sagging. Continuous exposure to sunlight further accelerates collagen loss. Although ultraviolet (UV) radiation accounts for only 7% of the energy in sunlight, it has strong effects on the skin. UVB radiation is the most damaging type of UV radiation that reaches the Earth’s surface. Overexposure to UVB can cause sunburn, staining due to melanin production, and deep wrinkles due to photoaging. Skin fibroblasts exposed to UVB have been reported to produce MMPs, which are collagen-degrading enzymes, and to decrease the production of TIMPs, which are inhibitors of MMPs. Disruption of the balance between MMPs and TIMPs promotes collagen degradation. However, it has been reported that various post-translational modifications, such as cross-link formation, degradation, glycation, oxidation, and racemization, accumulate in the extracellular matrix of UVB-exposed skin. In this study, we focused on the effects of UVΒ-induced changes in the pericellular environment on cells, rather than on the direct effects of UVB on cells. Since carbonylation is a major post-translational modification of proteins induced by UVB exposure, we prepared carbonylated collagen and examined its effects on cells. Carbonylated collagen decreased cell adhesion and significantly reduced cell proliferation. However, detailed post-translational modification analysis using mass spectrometry revealed that carbonylation was undetectable in the cell-binding region of collagen. Carbonylation was detected in large amounts on proline (Pro), arginine (Arg), and lysine (Lys) in collagen. These results suggest that numerous carbonylative modifications of collagen to Pro, Arg, and Lys induce changes in the overall structure of collagen and affect cellular functions regulated by interactions with collagen.