Sirt1 protects against oxidative stress-induced renal tubular cell apoptosis by the bidirectional regulation of catalase expression Kazuhiro Hasegawa, Shu Wakino * , Kyoko Yoshioka, Satoru Tatematsu, Yoshikazu Hara, Hitoshi Minakuchi, Naoki Washida, Hirobumi Tokuyama, Koichi Hayashi, Hiroshi Itoh Department of Internal Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 1608582, Japan article info Article history: Received 19 April 2008 Available online 15 May 2008 Keywords: Sirt1 Renal tubular cell Catalase Apoptosis Oxidative stress Forkhead transcription factor Renal proximal tubular cell FoxO3a ROS Histone deacetylase abstract NAD + -dependent protein deacetylase Sirt1 regulates cellular apoptosis. We examined the role of Sirt1 in renal tubular cell apoptosis by using HK-2 cells, proximal tubular cell lines with or without reactive oxy- gen species (ROS), H 2 O 2 . Without any ROS, Sirt1 inhibitors enhanced apoptosis and the expression of ROS scavenger, catalase, and Sirt1 overexpression downregulated catalase. When apoptosis was induced with H 2 O 2 , Sirt1 was upregulated with the concomitant increase in catalase expression. Sirt1 overexpression rescued H 2 O 2 -induced apoptosis through the upregulation of catalase. H 2 O 2 induced the nuclear accumu- lation of forkhead transcription factor, FoxO3a and the gene silencing of FoxO3a enhanced H 2 O 2 -induced apoptosis. In conclusion, endogenous Sirt1 maintains cell survival by regulating catalase expression and by preventing the depletion of ROS required for cell survival. In contrast, excess ROS upregulates Sirt1, which activates FoxO3a and catalase leading to rescuing apoptosis. Thus, Sirt1 constitutes a determinant of renal tubular cell apoptosis by regulating cellular ROS levels. Ó 2008 Elsevier Inc. All rights reserved. A growing body of evidence has accrued that the balance be- tween growth and death in renal tubular cells plays an important role in determining kidney function [1]. Apoptosis, one of the modes of cell death, participates in kidney physiologic remodeling processes [2] and is thought to contribute to cell loss and structural damage in kidney diseases [3]. For instance, renal proximal tubular cells exhibited apoptosis in streptozotocin-induced diabetic mice [4] as well as in diabetic patients [5], suggesting that tubular apop- tosis might precede tubular injuries. Reactive oxygen species (ROS) is involved in the pathogenesis of tubular cell apoptosis in ische- mia-reperfusion or toxic acute renal failure [6]. ROS includes superoxide anion, hydrogen peroxide (H 2 O 2 ), and hydroxyl radical. Among them, H 2 O 2 is a pathogenic mediator generated during hy- poxia/reoxygenation or ischemia-reperfusion injury [7]. Therefore, understanding the signaling pathways of H 2 O 2 -induced cell apop- tosis would provide important clues to the elucidation of the mechanisms of renal tubular cell injury and acute renal failure. To overcome the ROS generation, cells are equipped with anti- oxidant defense systems that serve to minimize the susceptibility to ROS. Catalase is one of the antioxidant enzymes which metabo- lize H 2 O 2 and contributes critically to the cellular ROS resistance [8]. The overexpression of catalase showed the elongation of life- span in mice, showing its positive regulatory role in mammalian aging [9]. Furthermore, conditional transgenic mice overexpressing catalase in proximal renal tubular cells manifested the attenuation of tubular apoptosis and pro-apoptotic gene expression as well as the decrease in interstitial fibrosis [10]. These results clearly showed that catalase played a critical role in the protection of renal tubular cells against apoptosis. On the other hand, accumulating evidence has demonstrated that H 2 O 2 or ROS mediated intracellu- lar responses to extracellular stimuli and had a beneficial action [11]. It has been reported that the treatment with antioxidants, either pharmacologically or by the overexpression of endogenous anti-oxidative enzymes, increases apoptosis or stops cell prolifera- tion [12]. One genetic pathway that mediates cell survival or response to ROS stress comprises Sir2, an NAD + -dependent protein deacetylase and a founding member of the sirtuin family [13]. Sir2 works in a wide array of cellular processes, including gene silencing, longev- ity, DNA damage repair and cellular apoptosis. Stimulation of Sir2 is sufficient to extend lifespan in yeast, Caenorhabditis elegans, Drosophila melanogaster, and mice [13]. Sirt1, a mammalian ortho- log of Sir2, deacetylates many target proteins, such as p53 and forkhead (FoxO) transcription factors, which provides the protec- tion against apoptosis and plays an essential part in mediating 0006-291X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2008.04.176 * Corresponding author. Fax: +81 3 3359 2745. E-mail address: swakino@sc.itc.keio.ac.jp (S. Wakino). Biochemical and Biophysical Research Communications 372 (2008) 51–56 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc