The Crucial Role of Renal FOXO1 in Gluconeogenesis During Starvation and Its Implications in Kidney Disease
Renal gluconeogenesis accounts for half of systemic gluconeogenesis during starvation, but its regulatory mechanisms and implications in chronic kidney disease (CKD) remain unknown. In this study, using single-cell RNA sequencing of starved kidneys and various animal models, we aimed to identify key pathways involved in renal gluconeogenesis and their role in the development of hypoglycemia during starvation in diseased kidneys. Under the starvation condition, renal gluconeogenesis was highly induced in proximal tubule cells with FOXO1 activation. In renal tubular epithelial cells, starvation-induced FOXO1 activation was required to stimulate gluconeogenesis and promote glucose production. We further analyzed whether renal FOXO1-mediated gluconeogenesis is impaired in CKD. In CKD animal models, the kidneys exhibited reduced FOXO1 and gluconeogenic protein expression; however, serum glucose levels remained unchanged, suggesting that diminished renal gluconeogenesis does not significantly impact circulating glucose levels. When CKD mice were subjected to starvation, serum glucose levels were significantly reduced after 72 hours. In the CKD model, FOXO1 activation failed, accompanied by a lower induction of gluconeogenic protein expression. Similar to diseased condition, aged mice exposed to starvation also showed impaired gluconeogenic response in the kidney, contributing to reduced circulating glucose levels. Under the in vitro condition, we found that profibrotic TGFß1 inhibits starvation-induced gluconeogenesis by directly suppressing the FOXO1 signaling pathway in tubular cells. Finally, we generated tubule-specific FOXO1 knockout (KO) mice by crossing FOXO1 floxed mice with Ksp-cre mice. These tubule-specific FOXO1 KO mice exhibited reduced expression of gluconeogenic genes in the kidney, leading to hypoglycemia during starvation. Collectively, we demonstrated crucial role of renal FOXO1 in gluconeogenesis during starvation, and its implication in kidney disease. Overall design: This study aims to investigate the effects of starvation on the mouse kidney, both with and without kidney damage. Control mice and folic acid-treated mice (250 mg/kg, IP injection) were subjected to starvation, after which their kidneys were collected for analysis.