Chronic heat treatment causes skin wrinkle formation and oxidative damage in hairless mice

We have previously demonstrated that heat shock could induce expression of matrix metalloproteinases (MMPs) in skin cells. These results implicated that chronic heat treatment may cause skin wrinkles. Therefore, in the present study, we investigated the effects of chronic heat treatment (43 °C, 30 min, 3 times/week, 6 weeks) on wrinkle formation in skin of hairless mice. We found that repetitive heat treatment induced skin wrinkles after a period of 6 weeks in skin of hairless mice. Histologically, heat treatment resulted in increased thickness of the epidermis and dermis. And repetitive heat treatment resulted in significantly increased expression of MMP-13 protein and mRNA, but not MMP-2 and -9, in skin of hairless mice. We also demonstrated that activities of antioxidant enzymes, catalase, and superoxide dismutase (SOD), were reduced by chronic heat treatment. In addition, oxidative damage was increased in skin of mice after chronic exposure to heat shock. Taken together, our results suggested that chronic exposure of the skin to heat can cause skin wrinkling. And, increase of MMP-13, decrease of antioxidant enzymes activity, and consequent oxidative damage by chronic heat treatment may play an important role in development of skin aging in hairless mice.