Skin commensal bacteria Staphylococcus epidermidis promote survival of melanocytes bearing UVB‐induced DNA damage, while bacteria Propionibacterium acnes inhibit survival of melanocytes by increasing apoptosis

BACKGROUND/PURPOSE: Skin commensal bacteria have been described to help orchestrate skin homeostasis, signaling through innate immunity pathways. This study for the first time aimed at studying the relationship between skin commensals and melanocytes after UVB exposure. METHODS: An in vitro UVB radiation model with normal human epidermal melanocytes (NHMs) and skin commensal bacteria supernatant from Staphylococcus epidermidis and Propionibacterium acnes was established. Melanocytes DNA damage, cyclobutane pyrimidine dimers (CPD), and cellular proliferation marker Ki-67 were measured by ELISA and immunofluorescence staining. Cell apoptosis was assessed by flow cytometry and PCR array and RT-qPCR. RESULTS: Normal human epidermal melanocytes are able to survive and proliferate while bearing DNA damage after UVB radiation. Skin commensal bacteria S. epidermidis and its by-product LTA promote melanocytes survival by inducing upregulation of TRAF1, CASP14, CASP5, and TP73. On the other hand, P. acnes can inhibit UVB-irradiated melanocytes survival by increasing apoptosis. CONCLUSION: Our studies show different aspects of commensal activity on melanocytes during irradiation. The possible balance achieved by the different skin commensal can influence NHM potential to become cancer cells.