Abstract: TH-PO311
Glycosuria in Tubule-Specific mTORC2 Knockout Mice Resolves on a High Potassium Diet
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Basic
November 03, 2022 | Location: Exhibit Hall, Orange County Convention Center‚ West Building
Abstract Time: 10:00 AM - 12:00 PM
Category: Fluid‚ Electrolyte‚ and Acid-Base Disorders
- 1001 Fluid‚ Electrolyte‚ and Acid-Base Disorders: Basic
Authors
- Demko, John E., University of California San Francisco, San Francisco, California, United States
- Saha, Bidisha, University of California San Francisco, San Francisco, California, United States
- Takagi, Enzo, University of California San Francisco, San Francisco, California, United States
- Manis, Anna D., University of California San Francisco, San Francisco, California, United States
- Pearce, David, University of California San Francisco, San Francisco, California, United States
Background
Insulin signaling promotes proximal tubule glucose transport and suppresses gluconeogenesis (GNG). An important feature of proximal tubule GNG is dual regulation by insulin and pH. The kinase mTORC2 is known to be regulated by insulin signaling in multiple cell types, but its mechanistic role in proximal tubule glucose homeostasis is unknown.
Methods
Rictor is a critical component of the mTORC2 complex. Tubule-specific Rictor KO mice (TRKO) were generated using doxycycline inducible Pax8-Cre Rictorfl/fl. Mice were adapted to 1% K+ diet and then switched to either a 0.5% K+ or 3% K+ diet for 2 days. An additional cohort of mice were maintained on a 0.5% K+ diet for 2 weeks for glucose (1g/kg), insulin (0.75U/kg), and pyruvate (2g/kg) tolerance testing after overnight fasts. Renal function, serum glucose, and urine glucose were measured in metabolic cages during the last 24 hours of all experiments. Proteins were measured via Western blot from whole kidneys.
Results
TRKO mice on a 0.5% K+ diet had urinary glucose of 470±96.7mg/dL (n=5) and control mice had 30.0±7.98mg/dL (n=7; p<0.001). After 12 hours (n=3 per group) and 2 days (n=6 per group) on a 3% K+ diet, there was no significant difference in urinary glucose between TRKO and control mice. TRKO mice on a 3% K+ diet also developed hyperkalemia and elevated BUN after 2 days. There were no differences in serum glucose during glucose and insulin tolerance tests between groups at any timepoint. Serum glucose during pyruvate tolerance test was higher in TRKO mice compared to controls (n=6 per group) at 90 (194 vs 149mg/dL; p<0.01) and 120 minutes (182 vs 150mg/dL; p<0.05). There was no difference in PEPCK, plasma membrane SGLT2 or GLUT2 abundance between TRKO and control mice after 2 days on either 0.5% or 3% K+ diets.
Conclusion
This study demonstrates the importance of mTORC2 in glucose handling and metabolism by the renal tubules. Increased serum glucose during pyruvate tolerance testing in TRKO mice suggests increased GNG, likely because mTORC2 KO impairs insulin signaling and fails to suppress renal GNG. The resolution of glycosuria in TRKO mice on a 3% K+ diet may be due to mTORC2-independent suppression of GNG by K+ and merits further investigation. Future studies will focus on identifying the molecular defect causing increased GNG in TRKO mice, and the basis for glycosuria suppression by K+.
Funding
- NIDDK Support