Mitochondria are cytoplasmic organelles that perform many crucial functions in eukaryotic cells, among them generation of most cellular ATP. Mitochondrial dysfunction is implicated in diverse pathologies such as type 2 diabetes, sarcopenia, neurodegeneration, and cancer. Despite their central importance to human health, mechanisms by which mitochondrial functions are regulated remain incompletely understood. The rationale for this application is that improved insights into such mechanisms may permit development of therapeutics to modulate mitochondrial functions as treatments for a wide variety of human diseases. This application focuses on novel roles for sirtuin proteins in regulating key mitochondrial functions. Sirtuins are a family of deacetylases that promote increased longevity in invertebrate models and modulate diverse processes in mammals. The application is based on two novel observations. First, the mitochondrial sirtuin SIRT5 plays a hitherto undescribed role in deacetylating and suppressing activity of Pyruvate Dehydrogenase Complex (PDC), a mitochondrial holoenzyme with a major role in regulating glucose oxidation in mammalian cells. PDC dysfunction is implicated in type 2 diabetes, cancer, and cardiac ischemia. Novel means of stimulating PDC activity - as by SIRT5 inhibition - would be beneficial in these and other clinical settings. Second, the sirtuin SIRT6 has an unexpected role in stimulating mitochondrial respiration. Adipose tissue- specific SIRT6 knockout (S6AKO) mice show marked adiposity, potentially due in part to mitochondrial respiratory defects in brown adipose tissue (BAT). The overall objective of this application is to elucidate novel mechanisms of mitochondrial regulation by sirtuin proteins, thus addressing a key knowledge gap in mitochondrial biology. The hypotheses of this application are two-fold. The first hypothesis is that SIRT5 inhibits glucose oxidation by attenuating PDC activity. The second hypothesis is that SIRT6 promotes mitochondrial respiration to promote cellular and organismal homeostasis. These hypotheses will be tested in two specific aims. First, the roles of SIRT5 in regulating PDC will be elucidated at a mechanistic level through a combination of mass spectrometry, mutagenesis, in vivo flux analysis, and high fat feeding. Second, the role of SIRT6 in promoting mitochondrial respiration will be defined mechanistically. The function of SIRT6 in suppressing adiposity will be elucidated through detailed characterization of S6AKO mice, and through generation of BAT-specific SIRT6 knockouts. This application is innovative, since it focuses on novel functions for sirtuins in regulating mitochondrial energetics. A variety of cutting-edge techniques will be brought to bear to test these hypotheses. The application is significant, since it will establish novel links between sirtuins and mitochondria, potentially laying the groundwork for future sirtuin-directed therapies to modulate glucose oxidation and/or mitochondrial respiration. Hence this work falls within the overall mission of NIGMS.

Public Health Relevance

This application proposes to elucidate novel roles for the sirtuin deacetylases in mitochondrial regulation. Mitochondria are cytoplasmic organelles that generate the majority of cellular energy. Mitochondrial dysfunction is implicated in a variety of age-associated pathologies such as muscle weaknesss, type 2 diabetes, neurodegeneration, and cardiac disease. Elucidation of novel mechanisms by which mitochondrial functions are regulated may allow development of therapies to enhance mitochondrial functions in these and other diseases.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Integrative Physiology of Obesity and Diabetes Study Section (IPOD)
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Anderson, Vernon
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University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
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Bringman-Rodenbarger, Lauren R; Guo, Angela H; Lyssiotis, Costas A et al. (2018) Emerging Roles for SIRT5 in Metabolism and Cancer. Antioxid Redox Signal 28:677-690
Kumar, Surinder; Lombard, David B (2018) Functions of the sirtuin deacylase SIRT5 in normal physiology and pathobiology. Crit Rev Biochem Mol Biol 53:311-334
Lombard, David B; Zhao, Yingming (2017) ACSF3 and Mal(onate)-Adapted Mitochondria. Cell Chem Biol 24:649-650
Kumar, Surinder; Lombard, David B (2017) Cycling around Lysine Modifications. Trends Biochem Sci 42:501-503
Cho, Chun-Seok; Lombard, David B; Lee, Jun Hee (2017) SIRT3 as a regulator of hepatic autophagy. Hepatology 66:700-702
Giblin, William; Lombard, David B (2017) Sirtuin 6 Builds a Wall Against Inflammation, Trumping Diabetes. Diabetes 66:2535-2537
Kumar, Surinder; Lombard, David B (2017) For Certain, SIRT4 Activities! Trends Biochem Sci 42:499-501
Guetschow, Erik D; Kumar, Surinder; Lombard, David B et al. (2016) Identification of sirtuin 5 inhibitors by ultrafast microchip electrophoresis using nanoliter volume samples. Anal Bioanal Chem 408:721-31
Xie, Zhongyu; Zhang, Di; Chung, Dongjun et al. (2016) Metabolic Regulation of Gene Expression by Histone Lysine ?-Hydroxybutyrylation. Mol Cell 62:194-206
Kumar, Surinder; Lombard, David B (2016) Generation and Purification of Catalytically Active Recombinant Sirtuin5 (SIRT5) Protein. Methods Mol Biol 1436:241-57

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