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J. Cosmet. Sci., 66, 57–63 (January/February 2015) 57 Temporal variations in sirtuin expression under normal and ultraviolet B-induced conditions and their correlation to energy levels in normal human epidermal keratinocytes EDWARD PELLE, KELLY DONG, and NADINE PERNODET, Estee Lauder Research Laboratories, Melville, NY 11747 (E.P., K.D., N.P.), and Environmental Medicine, New York University School of Medicine, New York, NY 10987 (E.P.). Accepted for publication January 12, 2015. Synopsis Sirtuins are post-translational modifi ers that affect transcriptional signaling, metabolism, and DNA repair. Although originally identifi ed as gene silencers capable of extending cell lifespan, the involvement of sirtuins in many different areas of cell biology has now become widespread. Our approach has been to study the tem- poral variation and also the effect of environmental stressors, such as ultraviolet B (UVB) and ozone, on sir- tuin expression in human epidermal keratinocytes. In this report, we measured the variation in expression of several sirtuins over time and also show how a low dose of UVB can affect this pattern of expression. More- over, we correlated these changes to variations in hydrogen peroxide (H2O2) and ATP levels. Our data show signifi cant variations in normal sirtuin expression, which may indicate a generalized response by sirtuins to cell cycle kinetics. These results also demonstrate that sirtuins as a family of molecules are sensitive to UVB- induced disruption and may suggest a new paradigm for determining environmental stress on aging and provide direction for the development of new cosmetic products. INTRODUCTION Post-translational modifi cations exert control across a diverse array of cellular functions (1). One area that has generated much recent interest has been the enzymatic activity of sirtuins on various proteins affecting aging (2), metabolism (3), and response to environ- mental trauma (4,5). Although sirtuins have several different modes of action, they are generally classifi ed as Class III nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases that remove an acetyl group from a lysine side chain of its protein substrate (6). In mammalian cells, seven sirtuin (SIRT1-7) homologs have been characterized that are distributed in several sub-cellular compartments (7). Human skin is constantly exposed to environmental hazards, such as ultraviolet B (UVB) radiation, leading to photo aging and skin cancer (8). Although it is well established that Address all correspondence to Edward Pelle at epelle@estee.com.