Abstract: FR-OR027
Autophagy Stimulation of FGF2 in Tubular Cells Activates Renal Fibroblasts and Promotes Interstitial Fibrosis During AKI-CKD Transition
Session Information
- AKI: Mechanisms - Inflammation and AKI-CKD Transition
November 08, 2019 | Location: 202, Walter E. Washington Convention Center
Abstract Time: 05:42 PM - 05:54 PM
Category: Acute Kidney Injury
- 103 AKI: Mechanisms
Authors
- Livingston, Man J., Augusta University Medical College of Georgia, Augusta, Georgia, United States
- Dong, Zheng, Augusta University Medical College of Georgia, Augusta, Georgia, United States
Background
The mechanisms that trigger AKI-CKD transition are poorly understood. We recently reveal an autophagy-mediated tubular maladaptive repair and its contribution to renal fibrosis after ischemic AKI. However, it is unclear how autophagy in renal tubules promotes interstitial fibrosis.
Methods
We generated a doxycycline-inducible, conditional Atg7 knockout mouse model (iAtg7 KO) with Atg7 specifically deleted from renal tubules at a desired time after ischemic AKI without affecting initial injury. We also exposed proximal tubular cells to TGFB1 and collected conditioned medium (CM) to treat renal interstitial fibroblasts. Using these models we examined how tubular cell autophagy regulates fibrosis with a focus on tubular paracrine activation of fibroblasts.
Results
Autophagy was activated in proximal tubules during post-ischemic fibrosis in wild-type (WT) mice. iAtg7 KO blocked tubular autophagy and suppressed fibrosis. Along with autophagy, the expression of several profibrotic cytokines (TGFB1, FGF2, CTGF and PDGFB) was increased in WT fibrotic kidneys. Among them, only the expression of FGF2 (both mRNA and protein) was reduced in iAtg7 KO mice. In WT kidneys FGF2 accumulated predominantly in the basolateral cytoplasm of atrophic tubules, which was suppressed in iAtg7 KO mice. Costaining of FGF2 in autophagy reporter mice further revealed a partial colocalization of FGF2 with LC3 puncta in autophagic tubules. In cultured mouse proximal tubular cells, TGFB1 induced the production of FGF2, CTGF and PDGFB, and also enhanced tubular secretion of FGF2 and CTGF. Defective autophagy by Atg7 KO reduced both the production and tubular secretion of FGF2, but not CTGF or PDGFB. CM from TGFB1-treated WT tubular cells induced proliferation and activation of renal fibroblasts and accumulation of ECM proteins, whereas these effects were attenuated in fibroblasts treated with Atg7 KO tubular cell-CM. FGF2 neutralizing antibody recapitulated the inhibitory effects of Atg7 KO tubular cell-CM on renal fibroblasts, further supporting a role for FGF2 in autophagy-dependent tubular paracrine activation of fibroblasts.
Conclusion
Dysregulated autophagy in renal tubules may specifically stimulate tubular production and secretion of FGF2. This autophagy-mediated paracrine then activates interstitial fibroblasts and promotes kidney fibrosis after AKI.
Funding
- NIDDK Support