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Abstract: FR-PO501

mTORC2 Coordinates Renal Gluconeogenesis and Glucose Reabsorption

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1101 Fluid, Electrolyte, and Acid-Base Disorders: Basic

Authors

  • Demko, John Eric, 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
  • Pearce, David, University of California San Francisco, San Francisco, California, United States
Background

The proximal tubule is uniquely responsible for both gluconeogenesis (GNG) and glucose reabsorption from the filtrate. Insulin signaling in the proximal tubule suppresses gluconeogenesis and stimulates glucose transport. However, the coordinated regulation of these processes is poorly understood. The kinase mTORC2 is 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. Inducible tubule-specific Rictor knockout (TRKO) mice were made with Pax8-rtTA TetOCre Rictorflox/flox. Male and female TRKO mice and wild-type (WT) littermates were fasted for 18 hours then refed 4 hours before sacrifice. Whole kidney relative mRNA was measured via RT-PCR. Kidney plasma membrane and cytosolic proteins were separated using the BioVision Plasma Membrane Protein Extraction Kit, and protein abundance was measured with western blotting.

Results

There were no differences in serum glucose between TRKO and WT mice during refeeding (n=6–10 per group for all experiments). However, the mean ± standard error of the mean urine glucose excretion was 1824.9±768.5 μg in TRKO mice compared to 69.2±15.0 μg in WT animals during refeeding (p<0.05). TRKO kidneys compared to WT had significantly higher relative PEPCK protein abundance (0.54±0.05 vs 0.28±0.03 AU; p<0.001) and mRNA levels (0.54±0.17 vs 0.17±0.01 AU; p<0.05). TRKO kidneys compared to WT had statistically similar G6Pase protein abundance and significantly higher relative mRNA levels (0.58±0.17 vs 0.18±0.05 AU; p<0.05). Refed TRKO kidneys showed a decrease in plasma membrane SGLT2 after refeeding (0.64±0.07 vs 1.22±0.24 AU; p<0.05) and no significant difference in SGLT2 mRNA levels compared to WT mice. There were no significant differences in plasma membrane protein abundance or mRNA levels for SGLT1 or GLUT2 between TRKO and WT kidneys.

Conclusion

TRKO mice have glycosuria with normal serum glucose. TRKO mice fail to suppress renal GNG and have decreased plasma membrane SGLT2. Coordinated suppression of GNG and stimulation of glucose reabsorption by mTORC2 is critical to conserve energy by preventing excess glucose production and urinary glucose loss. Future studies will examine changes in the insulin and mTORC2 signaling pathways which mediate these findings.

Funding

  • NIDDK Support