Abstract: FR-PO222

Forkhead Box O3 (FoxO3) Regulates Kidney Tubular Autophagy Following Urinary Tract Obstruction

Session Information

Category: Cell Biology

  • 202 Apoptosis, Proliferation, Autophagy, Cell Senescence, Cell Transformation

Authors

  • Li, Ling, Columbia University College of Physicians & Surgeons, New York, New York, United States
  • Zviti, Ronald, Columbia University College of Physicians & Surgeons, New York, New York, United States
  • Ha, Catherine, Columbia University College of Physicians & Surgeons, New York, New York, United States
  • Lin, Fangming, Columbia University College of Physicians & Surgeons, New York, New York, United States
Background

Autophagy has been shown to be important for normal homeostasis and adaptation to stress in the kidney. Yet, molecular mechanisms regulating renal epithelial autophagy are not fully understood.

Methods

We explore the role of the stress-responsive transcription factor forkhead box O3 (FoxO3) in mediating injury-induced proximal tubular autophagy in mice with unilateral ureteral obstruction (UUO), which is a reproducible model of persistent tubular autophagy.

Results

We show that following UUO, FoxO3 is activated over basal level and displays nuclear expression in 34.0 ± 3.4% of proximal tubules at 3 days (n=3, p<0.01) and 45.5 ± 2.8% at 7 days (n=3, p<0.05) when the hypoxic tubules exhibit high levels of autophagy. Activation of FoxO3 by mutating its phosphorylation sites to enhance its nuclear expression induces profound autophagy in primary cultures of renal epithelial cells. Conversely, deleting FoxO3 in mice results in fewer numbers of autophagic cells in the proximal tubules and reduces the conversion of the key autophagy-associated protein LC3-I to LC3-II post-UUO. Interestingly, autophagic cells deficient in FoxO3 contain lower numbers of autophagic vesicles per cell upon stimulation with nutrient deprivation. Analysis of individual cells treated with various autophagic inhibitors to sequentially block the autophagic flux suggests that FoxO3 stimulates the formation of autophagosomes to increase autophagic capacity without significant effects on autophagosome-lysosome fusion or autolysosomal clearance. Furthermore, in kidneys with persistent UUO for 7 days, FoxO3 activation increases the expression of core autophagy-associated (Atg) proteins, including Ulk1, Beclin-1, Atg9A, Atg4B, and Bnip3, suggesting that FoxO3 may also function to replenish components of the autophagic machinery that would otherwise be consumed during sustained autophagy.

Conclusion

In summary, our findings indicate that FoxO3 activation can both induce and maintain autophagic activities in renal epithelial cells in mouse models of prolong tubular stress and injury.

Funding

  • NIDDK Support