Dual Regulation of Gluconeogenesis by Insulin and Glucose in the Proximal Tubules of the Kidney Motohiro Sasaki, 1,2 Takayoshi Sasako, 1,3,4 Naoto Kubota, 1,3,5,6,7 Yoshitaka Sakurai, 1 Iseki Takamoto, 1 Tetsuya Kubota, 1,6,7,8 Reiko Inagi, 9 George Seki, 10 Moritaka Goto, 2 Kohjiro Ueki, 1,3,4 Masaomi Nangaku, 9 Takahito Jomori, 2 and Takashi Kadowaki 1,3 Diabetes 2017;66:2339–2350 | https://doi.org/10.2337/db16-1602 Growing attention has been focused on the roles of the proximal tubules (PTs) of the kidney in glucose metabolism, including the mechanism of regulation of gluconeogenesis. In this study, we found that PT-specific insulin receptor substrate 1/2 double-knockout mice, established by using the newly generated sodium–glucose cotransporter 2 (SGLT2)-Cre transgenic mice, exhibited impaired insulin signaling and upregulated gluconeogenic gene expression and renal gluconeogenesis, resulting in systemic insulin resistance. In contrast, in streptozotocin-treated mice, al- though insulin action was impaired in the PTs, the gluconeo- genic gene expression was unexpectedly downregulated in the renal cortex, which was restored by administration of an SGLT1/2 inhibitor. In the HK-2 cells, the gluconeogenic gene expression was suppressed by insulin, accompanied by phosphorylation and inactivation of forkhead box transcrip- tion factor 1 (FoxO1). In contrast, glucose deacetylated per- oxisome proliferator–activated receptor g coactivator 1-a (PGC1a), a coactivator of FoxO1, via sirtuin 1, suppressing the gluconeogenic gene expression, which was reversed by inhibition of glucose reabsorption. These data suggest that both insulin signaling and glucose reabsorption sup- press the gluconeogenic gene expression by inactivation of FoxO1 and PGC1a, respectively, providing insight into novel mechanisms underlying the regulation of gluconeo- genesis in the PTs. The kidney plays a pivotal role in systemic glucose metab- olism by regulation of glucose reabsorption, glycolysis, and gluconeogenesis. Gluconeogenesis occurs exclusively in the liver and the kidney (1). In the absorptive state, the kidney accounts for only 10% of the systemic gluconeogenesis, whereas in the prolonged fasting state, the rate rises to as much as 40% (2). Among precursors of gluconeogenesis, glutamine is used as the major glucogenic amino acid in the kidney, whereas alanine is used as the major amino acid in the liver (3,4). Gluconeogenic enzymes, including phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), are expressed mainly in the proximal tubules (PTs) of the kidney and in the liver (5,6). In the process of gluconeogen- esis in the PTs, glucose diffuses outward through glucose transporter 2 (GLUT2) in the basolateral membrane (7,8). On the contrary, GLUT2 plays an important role in glucose uptake in the liver, and sodium–glucose cotransporters (SGLTs) in the luminal membrane are involved instead in inward efflux of glucose in the PTs (9,10). It is well known that gluconeogenic gene expression in the liver is mainly regulated by insulin, especially via sup- pression of forkhead box transcription factor 1 (FoxO1). FoxO1 is a major transcription factor that binds to the promoter regions of PEPCK and G6Pase to induce the gene expression (11–13). Insulin signaling activated after feeding, 1 Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan 2 Mie Research Laboratories, Sanwa Kagaku Kenkyusho Co., Ltd., Mie, Japan 3 Translational Systems Biology and Medicine Initiative, The University of Tokyo, Tokyo, Japan 4 Department of Molecular Diabetic Medicine, Diabetes Research Center, National Center for Global Health and Medicine, Tokyo, Japan 5 Department of Clinical Nutrition Therapy, The University of Tokyo Hospital, The University of Tokyo, Tokyo, Japan 6 Clinical Nutrition Program, National Institute of Health and Nutrition, Tokyo, Japan 7 Laboratory for Metabolic Homeostasis, RIKEN Center for Integrative Medical Sciences, Kanagawa, Japan 8 Division of Cardiovascular Medicine, Toho University Ohashi Medical Center, Tokyo, Japan 9 Department of Nephrology and Endocrinology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan 10 Yaizu City Hospital, Shizuoka, Japan Corresponding authors: Takashi Kadowaki, kadowaki-3im@h.u-tokyo.ac.jp, and Naoto Kubota, nkubota-tky@umin.ac.jp. Received 15 January 2017 and accepted 13 June 2017. This article contains Supplementary Data online at http://diabetes .diabetesjournals.org/lookup/suppl/doi:10.2337/db16-1602/-/DC1. M.S. and T.S. contributed equally to this work. © 2017 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. More information is available at http://www.diabetesjournals .org/content/license. Diabetes Volume 66, September 2017 2339 METABOLISM Downloaded from http://diabetesjournals.org/diabetes/article-pdf/66/9/2339/583868/db161602.pdf by guest on 30 March 2023