Notch signaling and mTOR complex 1 play opposing roles in regulation of kidney collecting duct cell type plasticity

Intercalated cell (IC) types are intermingled among principal cell (PC) types along the kidney collecting duct segments. The ratio of PC to IC types increases along the cortico-medullary axis to ensure water, electrolyte and pH homeostasis. Previous studies have shown that Notch signaling via Hes1 is necessary for maintenance of PC types without which they convert to IC types resulting in diminished urine concentrating capacity. Here we sought to determine the molecular mechanisms by which Hes1 prevents cell type conversion and the physiological conditions that trigger PC to IC conversions. The molecular signature of the transitional cell (TC) state during the PC to IC conversion was determined by single cell RNA-sequencing of adult wild type and Hes1-deficient mouse kidney samples enriched for epithelial cells of the loop of Henle, distal nephron and collecting duct segments. Based on the TC molecular signature we determined that the mechanistic target of rapamycin complex 1 (mTORC1) activity is increased in Hes1-deficient PCs of adult kidneys and tested if mTORC1 activity regulates collecting duct cell type plasticity. Conditional inactivation of Raptor reduced mTORC1 activity, decreased IC specific gene expression in adult mouse kidneys and resulted in production of more acidic urine, while activation of mTORC1 in PCs triggered expression of IC specific genes and conversion to IC state. Interestingly, inhibiting mTORC1 by conditionally inactivating Raptor rescues the deficiency in PCs and urine concentration defect observed in Hes1 conditional knock out adult mouse kidneys. Collectively, our results indicate that Notch signaling and mTORC1 activity play opposing roles in promoting PC versus IC state within the adult kidney collecting ducts to ensure water and pH homeostasis. It is likely that certain physiological stressors, medications and diets that activate mTORC1 and/or suppress Notch signaling promote the conversion of PCs to ICs. While transient and limited PC to IC conversion is perhaps part of the adaptive cell type plasticity necessary for water and electrolyte balance, chronic and excessive PC to IC conversions likely underlie acquired forms of nephrogenic diabetes insipidus. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.