The skin microbiome varies across individuals. The causes of these variations are inadequately understood. We tested the hypothesis that inter-individual variation in facial skin microbiome can be significantly explained by variation in sebum and hydration levels in specific facial regions of humans. We measured sebum and hydration from forehead and cheek regions of healthy female volunteers (n = 30). Metagenomic DNA from skin swabs were sequenced for V3-V5 regions of 16S rRNA gene. Altogether, 34 phyla were identified; predominantly Actinobacteria (66.3%), Firmicutes (17.7%), Proteobacteria (13.1%) and Bacteroidetes (1.4%). About 1000 genera were identified; predominantly Propionibacterium (58.6%), Staphylococcus (8.6%), Streptococcus (4.0%), Corynebacterium (3.6%) and Paracoccus (3.3%). A subset (n = 24) of individuals were sampled two months later. Stepwise multiple regression analysis showed that cheek sebum level was the most significant predictor of microbiome composition and diversity followed by forehead hydration level; forehead sebum and cheek hydration levels were not. With increase in cheek sebum, the prevalence of Actinobacteria (p = 0.001)/Propionibacterium (p = 0.002) increased, whereas microbiome diversity decreased (Shannon Index, p = 0.032); this was opposite for other phyla/genera. These trends were reversed for forehead hydration levels. Therefore, the nature and diversity of facial skin microbiome is jointly determined by site-specific lipid and water levels in the stratum corneum.
DDB2 is an essential subunit of the damaged-DNA recognition factor DDB, which is involved in global genomic repair in human cells. Moreover, DDB2 is mutated in the repair-deficiency disease xeroderma pigmentosum (Group E). Expression of DDB2 in human cells is induced by P53, BRCA1 and by ionizing radiation. The DDB2 protein associates with transcriptional activator and coactivator proteins. In addition, DDB2 in conjunction with DDB1 associates with cullin 4A and the Cop9/signalosome. We generated a mouse strain deficient for DDB2 (DDB2À/À). Consistent with the human disease (XP-E), the DDB2À/À mice were susceptible to UV-induced skin carcinogenesis. We observed a significant difference in the initial rate of cyclobutane pyrimidine dimer (CPD)-removal from the skin following UV irradiation. Also, the DDB2-deficient mice exhibited a significantly reduced life span compared to their wild-type littermates. Moreover, unlike other XP-deficient mice, the DDB2-deficient mice developed spontaneous malignant tumors at a high rate between the ages of 20 and 25 months. The observations suggest that, in addition to DNA repair, the other interactions of DDB2 are significant in its tumor suppression function.
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