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Abstract: TH-PO197

A Signaling Module Linking DJ-1, PTEN, and PDGF Receptor β (PDGFR) Governs Activation of mTORC1 to Induce Proximal Tubular Epithelial Cell (PTEC) Injury in Diabetic Nephropathy (DN)

Session Information

Category: Diabetic Kidney Disease

  • 601 Diabetic Kidney Disease: Basic

Authors

  • Das, Falguni, UTHSCSA, San Antonio, Texas, United States
  • Ghosh-choudhury, Nandini, UTHSCSA, San Antonio, Texas, United States
  • Kasinath, Balakuntalam S., UTHSCSA, San Antonio, Texas, United States
  • Ghosh-Choudhury, Goutam, UTHSCSA, San Antonio, Texas, United States
Background

PTEN inactivation and PDGFR tyrosine kinase-mediated mTORC1 activation have emerged as the centerpiece in pathogenesis of DN and tumorigenesis. The familial Parkinson’s disease protein DJ-1 causes cancer. We investigated the hypothesis that DJ-1 acts as a driver of PDGFR-mediated mTORC1 activation in the progression of DN.

Methods

Human PTECs, OVE26 and db/db mice, and activation-specific antibodies, immunoblotting, plasmid-derived expression vector, siRNAs and promoter-reporter transfections were employed.

Results

In PTECs, 25 mM glucose (HG) increased expression of DJ-1. In determining its role in PTEC pathology, we showed that siRNAs against DJ-1 inhibited HG-induced PTEC hypertrophy and fibronectin and collagen I (α2) protein expression and their transcription, while forced expression of FLAG-DJ-1 increased these phenomena. As Akt/mTORC1 signaling regulates these effects of HG, we tested involvement of DJ-1. siDJ-1 inhibited HG-stimulated phosphorylation of Akt, its substrates GSK3β, tuberin and PRAS40, and phosphorylation of S6 kinase, 4EBP-1 and mTOR. In contrast, FLAG-DJ-1 increased these phosphorylation events similar to HG. We have shown previously that HG-stimulated PTEC injury requires PDGFR stimulation of mTORC1 activity. Crucially, we showed that siDJ-1 decreased HG-stimulated phosphorylation of PDGFR at its docking sites of PI 3 kinase, whose function is known to be inactivated by PTEN, a dual specificity tyrosine and lipid phosphatase. Furthermore, we showed that HG increased association of DJ-1 with PTEN. We hypothesized that DJ-1-bound and inactivated PTEN lead to PDGFR phosphorylation. Interestingly, we showed that plasmid-derived expression of PTEN decreased HG-induced tyrosine phosphorylation of PDGFR and its substrate PI 3 kinase. In addressing the in vivo relevance of our results, in the renal cortex of OVE26 and db/db mice models of type 1 and type 2 diabetes, we found increased expression of DJ-1, PDGFR phosphorylation, mTORC1 activation and fibronectin and collagen I (α2) expression.

Conclusion

Together our results uncover a novel three layered molecular circuitry where PDGFR serves as a substrate of PTEN that is quenched by DJ-1 in PTEC injury in DN.

Funding

  • Veterans Affairs Support