The overall goal of this research proposal is to further elucidate the molecular mechanisms that underlie mTORC2 target specificity and their functional implications in the regulation of glucose homeostasis and ion balance, using biochemical, electrophysiological, metabolic, genetic and whole animal physiology techniques. The applicant for the K01 Mentored Career Development Award, Dr. Catherine E. Gleason, is currently a postdoctoral fellow in Dr. David Pearce's laboratory at UCSF. Dr. Gleason's long-term research goal is to study how metabolic signaling pathways intersect and influence pathways controlling various biological functions, notably ion balance by the kidney, for maintenance of physiological homeostasis. Dr. Gleason's long-term career goal is to establish an independent molecular physiology research program as a tenure-track investigator at an academic institution. SGK1 and Akt are highly related protein kinases that function as key mediators of the signaling pathways that control ion and metabolic homeostasis, respectively. Recently, mTORC2 was identified as the kinase responsible for activation of these kinases by phosphorylation of a critical, homologous residue in their hydrophobic motif (HM). Since, stimuli that induce mTORC2 activity, such as insulin and IGF1, trigger phosphorylation of both SGK1 and Akt, how mTORC2 is able to modulate activity of these related kinases in such a way that allows them to mediate distinct effects on electrolyte balance and energy metabolism is not understood. Notably, in addition to its well-established role in ion balance, the kidney also plays an important role in whole animal energy homeostasis due to its significant gluconeogenic capacity. It is unclear how the kidney is able to sort crosstalk from multiple signaling pathways to allow for appropriate, context-dependent regulation of its metabolic and ion balance functions. Thus, understanding the molecular dynamics surrounding mTORC2 selective activation of SGK1 and Akt, in vitro and in vivo, are open and important areas for investigation. Dr. Gleason will build on her background in metabolic physiology and signal transduction with additional training in the cellular and whole animal study of ion transport processes to address the mechanistic basis for mTORC2 specificity towards SGK1 vs. Akt and their functional implications at the cellular and whole animal levels through two specific aims: 1) Investigate the hormonal stimuli and/or cellular conditions that regulate mTORC2 specific activation of SGK1 vs. Akt. 2) Characterize the relative contributions of Akt and SGK1 towards renal glucose metabolism and ion balance in vivo. The training period provided by the K01 Mentored Career Development Award will provide Dr. Gleason with a comprehensive toolbox for her independent career investigating the intersections of metabolism with diverse signaling pathways in health and disease.
The association of hypertension and metabolic disease suggests an intersection of the signaling pathways that control ion balance and energy homeostasis. A potential node for integration of these pathways is the protein mTOR since it has recently been identified as a critical upstream regulator of the related proteins, SGK1 and Akt, primary mediators of the signaling pathways that control ion transport and glucose metabolism, respectively. This research proposal will contribute to a better understanding of the molecular mechanisms that govern mTOR substrate specificity and, therefore, to the development of novel therapies for hypertension and/or metabolic disorders.