Sirtuin 4 identification in normal human epidermal keratinocytes and its relation to sirtuin 3 and energy metabolism under normal conditions and UVB-induced stress.

Sirtuins (SIRT) are NAD(+) -dependent deacetylases and ADP-ribosyltransferases that play a critical role in metabolism and epigenetics. SIRT3 and SIRT4 are of particular interest because they are localized in the mitochondria where energy is generated and their expression is inversely proportional to each other. Here, we report data, for the first time, demonstrating the presence of SIRT4 in normal human epidermal keratinocytes (NHEK) and confirm that its expression is inversely related to SIRT3 in these cells and that they follow a temporal cycle. Further, UVB radiation modified their expression, as well as ATP and H2 O2 levels. These deviations from the normal sirtuin cycles after UVB exposure can be an epigenetic indicator of lower metabolism levels.