Acetylated histone H3 was increased, but HDAC activity and expression levels of HDAC4, HDAC11, and SIRT4 were decreased in UV-irradiated human skin in vivo. The buttock skin of young subjects was obtained by punch biopsy at 24 h after UV irradiation (two minimal erythema doses (MEDs)). Immunofluorescence analysis of AcH3 and DAPI staining of paraffin-embedded sections (n = 6). Original magnification: ×200 (a). Western blot analysis of AcH3. The bands are representative of the results obtained for 10 subjects. The bar graph shows densitometric quantification of AcH3 levels. (n = 10) (b). Total HDAC activity was measured using an HDAC assay kit (n = 10) (c). Expression levels of HDAC and SIRT mRNAs following UV irradiation were compared with those in non-irradiated control skin by qPCR (n = 10) (d,e). Data were normalized to the control. Data are presented as means ± SEM. Statistical significances were determined using a two-tailed paired t-test. * p < 0.05, ** p < 0.01, *** p < 0.001 vs. non-irradiated skin (Cont). Cont: control.