Law, D. C. L.; Tang, M. L. F.; Van Steensel, M. A. M.

In this study, we demonstrate that Benzo[a]pyrene (B[a]P) induces keratinocyte senescence and p21Cip1-dependent keratinocyte differentiation. Atmospheric and environmental pollution are known to induce senescence and promote terminal differentiation in human primary keratinocytes, thus driving skin aging. However, much is still unknown about the underlying molecular mechanisms. We observed that B[a]P, a common atmospheric pollutant, induced senescence in primary keratinocytes in both two-dimensional and three-dimensional (reconstructed human epidermis) culture. This was accompanied by signs of DNA damage in B[a]P-treated cells. B[a]P-treated cells also underwent accelerated late-stage terminal differentiation, indicated by increased IVL and FLG expression from 48 to 96 hours post-exposure. While pharmacological and genetic attenuation of p21Cip1 did not rescue cellular senescence, it prevented the expression of IVL and FLG, suggesting that the late-stage terminal differentiation induced by B[a]P exposure was p21-dependent. Our data thus suggest a key role for the p21Cip1 in the keratinocyte response to pollution-induced damage, where p21Cip1 induces terminal differentiation to maintain skin barrier homeostasis.