Abstract: TH-PO705

Insulin Suppresses Gluconeogenesis in Renal Proximal Tubules via the IRS1/Akt2/mTORC Pathway

Session Information

Category: Diabetes

  • 501 Diabetes Mellitus and Obesity: Basic - Experimental

Authors

  • Nakamura, Motonobu, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Nangaku, Masaomi, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Suzuki, Masashi, Tokyo Gakugei University, Koganei, Tokyo, Japan
  • Satoh, Nobuhiko, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Suzuki, Atsushi, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Tsukada, Hiroyuki, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Seki, George, Yaizu City Hospital , Yaizu, Shizuoka, Japan
  • Sato, Yusuke, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
  • Homma, Yukio, Japanese Red Cross Medical Center, Shibuya, Tokyo, Japan
  • Horita, Shoko, The University of Tokyo, Graduate School of Medicine, Bunkyo, Tokyo, Japan
Background

Previously, we found that the stimulatory effect of insulin on sodium transport in proximal tubules (PTs) is dependent on insulin receptor substrate (IRS)2/Akt2/mammalian target of rapamycin complex (mTORC) 2 and preserved even in insulin resistance and diabetes mellitus (Kidney Int 87:535,2015, ASN Kidney Week 2016). In addition to liver, kidney also significantly contributes to whole body gluconeogenesis particularly after prolonged fasting. Insulin is known to suppress gluconeogenesis in PTs, the only nephron segment where gluconeogenesis takes place. However, little is known about the signaling mechanism underlying this insulin action.

Methods

PTs freshly isolated from rat kidneys were incubated overnight in DMEM with or without 0.2 mM cAMP, and 10-8M insulin was subsequently added for 4-hr. Total RNA was extracted from the PTs, and quantitative PCR was performed to determine the relative mRNA expression levels of glucogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6P). To uncover the signaling mechanism, PTs were incubated in the presence of Akt1/2 inhibitor VIII or an mTORC1 inhibitor rapamycin. PTs were also incubated with siRNAs against IRS1, IRS2, Akt1, Akt2, raptor (a component of mTORC1), or rictor (a component of mTORC2) in the presence of lipofectamine.

Results

cAMP increased the expression levels of PEPCK and G6P 19 and 7-fold, respectively. Insulin decreased both of the cAMP-stimulated expression levels of PEPCK and G6P by more than 80% (n = 12-13). Akt1/2 inhibitor VIII and rapamycin completely abolished this inhibitory effect of insulin on gluconeogenesis. siRNAs against IRS1, Akt2, raptor and rictor also completely abolished the inhibitory effect of insulin. By contrast, siRNAs against IRS2 or Akt1 failed to affect the insulin effect.

Conclusion

Our results, for the first time to our knowledge, revealed that insulin suppresses gluconeogenesis in PTs via IRS1/Akt2/mTORC pathway. In insulin resistance and diabetes mellitus, the reduced expression of IRS1 in PTs that we reported (Kidney Int 87:535,2015, BBRC 461:154,2015) is expected to selectively attenuate the IRS1-dependent insulin action. The resultant enhancement in renal gluconeogenesis may at least partially contribute to hyperglycemia in these conditions.

Funding

  • Government Support - Non-U.S.