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Abstract: FR-PO380

A Cross-Talk Between TGFbeta Receptor (TGFbR) and PDGF Receptor-Beta (PDGFRb) Controls mTORC1-Mediated Mesangial Cell (MC) Hypertrophy and Fibrotic Protein Expression

Session Information

Category: Diabetic Kidney Disease

  • 601 Diabetic Kidney Disease: Basic

Authors

  • Maity, Soumya, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States
  • Das, Falguni, UTHSCSA, SAN ANTONIO, Texas, United States
  • Ghosh-choudhury, Nandini, UTHSCSA, SAN ANTONIO, Texas, United States
  • Mariappan, Meenalakshmi M., University of Texas Health Science Center, San Antonio, Texas, United States
  • Kasinath, Balakuntalam S., University of Texas Health Science Center, San Antonio, Texas, United States
  • Ghosh-Choudhury, Goutam, UT Health San Antonio, San Antonio, Texas, United States
Background

TGFb induces MC hypertrophy and matrix protein expression via noncanonical mTORC1 during the progression of diabetic nephropathy. The mechanism of mTORC1 activation is not clear. Since its activation requires tyrosine kinase activity, we considered a cross-talk between TGFb serine-threonine kinase and PDGFRb tyrosine kinase in this process.

Methods

Human glomerular MCs in culture and OVE 26 diabetic mice were used. PDGFRb inhibitor, activation/inactivation-specific phospho-antibodies, siRNA and plasmid-derived expression vector transfection, 35S-Methionine incorporation and immunoblotting were used.

Results

In MCs, TGFb increased the activating phosphorylation of PDGFRb in a time-dependent manner. This phosphorylation was inhibited by the TGFbRI and PDGFRb inhibitors SB431542 and JNJ, respectively. Importantly, JNJ did not have any effect on TGFb-stimulated phosphorylation of receptor-specific Smad 3 while SB inhibited its phosphorylation. JNJ also inhibited the phosphorylation of PDGFRb at Tyr-751, the PI 3 kinase binding site, in response to TGFb, resulting in inhibition of Akt phosphorylation at both Thr-308 and Ser-473. Transfection of siRNA against PDGFRb confirmed these results. Importantly, JNJ and siRNA targeting PDGFRb blocked the phosphorylation of the Akt substrate PRAS40, a negative regulator of mTORC1 activation. To determine the mTORC1 activity, we measured the phosphorylation of S6 kinase and rps6. Inhibition of PDGFRb as well as its siRNA mitigated TGFb-induced mTORC1 activity that resulted in attenuation of MC hypertrophy. Similarly, JNJ and siPDGFRb inhibited TGFb-stimulated fibronectin expression in MCs. Finally, in the renal cortex of OVE 26 diabetic mice, expression of TGFb was significantly increased concomitant with phosphorylation of PDGFRb, which were associated with increased Akt phosphorylation and mTORC1 activation that lead to increased fibronectin expression.

Conclusion

Our results provide the first evidence for a functional role of PDGFRb downstream of TGFbR to activate Akt/mTORC1 axis for MC hypertrophy and matrix protein expression. We propose to test PDGFRb-specific inhibitor in preclinical models of diabetic nephropathy.

Funding

  • Veterans Affairs Support