Abstract: FR-PO639

Distinct Patterns of Dysregulated Autophagy in Type 1 and 2 Diabetic Nephropathy

Session Information

Category: Diabetes

  • 501 Diabetes Mellitus and Obesity: Basic - Experimental

Authors

  • Sakai, Shinsuke, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Matsusaka, Taiji, Tokai University School of Medicine, Isehara, KANAGAWA, Japan
  • Niimura, Fumio, Tokai University School of Medicine, Isehara, KANAGAWA, Japan
  • Isaka, Yoshitaka, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Yamamoto, Takeshi, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Takabatake, Yoshitsugu, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Takahashi, Atsushi, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Namba, Tomoko, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Minami, Satoshi, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Fujimura, Ryuta, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Matsuda, Jun, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
  • Kimura, Tomonori, Osaka University Graduate School of Medicine, Suita, OSAKA-FU, Japan
Background

Autophagy maintains cellular homeostasis and has protective roles against several stresses. Although it has been reported that high blood glucose can impair some nutrient signalings, suppress autophagy induction during type 2 diabetic nephropathy, how autophagy is dysregulated is still largely unknown.

Methods

1) We accessed the autophagic flux in vivo by investigating the difference in the numbers of GFP-LC3-positive dots by chloroquine administration under fed or starved condition in streptozotocin (STZ)-treated GFP-LC3 transgenic mice (type 1 diabetes) or in obese db/db mice crossed with GFP-LC3 transgenic mice (type 2 diabetes).
2) We compared the inhibitory effects of glucose, insulin, and amino acids on autophagic activity in proximal tubules of 24 h-starved GFP-LC3 transgenic mice.
3) We examined the consequences of long-term autophagy deficiency using STZ-treated proximal tubular cell (PTC)-specific Atg5-deficient mice (Atg5F/F;KAP) or Atg5F/F;KAP crossed with db/db mice. Then, we examined the effects of rapamycin (an inhibitor of the mechanistic target of rapamycin; mTOR) on vulnerability to ischemia-reperfusion (I/R) injury in these mice.

Results

1) Autophagy induction was suppressed even under starvation in the PTCs of db/db mice. In contrast, autophagic activity was enhanced in STZ-treated mice even under fed condition.
2) Insulin and amino acids, but not glucose, suppressed starvation-induced autophagy by activating mTOR pathway.
3) Urinary albumin excretion, mitochondrial damage (assessed by COX and SDH staining) and fibrosis (type I collagen immunostaining) were significantly increased in STZ-treated Atg5F/F;KAP mice compared with control STZ-treated mice. In contrast, these were increased in db/db mice regardless of autophagy deficiency. I/R lead to more severe injury in both diabetic mice compared with nondiabetic mice. Rapamycin exaggerated I/R injury in STZ-induced mice, while it attenuated in db/db mice.

Conclusion

Distinct patterns of dysregulated autophagy in type 1 and 2 diabetic nephropathy should be considered in prevention and treatment.