Increased expression of PDGF receptor-β (PDGFRβ) has been shown in the diabetic renal proximal tubules. The core molecular network used by high glucose to induce proximal tubular epithelial cell collagen I (α2) expression is poorly understood. We hypothesized that activation of PDGFRβ by high glucose increases collagen I (α2) production via Akt/mTORC1 signaling pathway in proximal tubular epithelial cells. Using biochemical and molecular biological techniques, we investigated this hypothesis. We show that high glucose increases activating phosphorylation of the PDGFRβ, resulting in the phosphorylation of the phosphatidylinositol 3 kinase. A specific inhibitor JNJ-10198409 and siRNAs targeting PDGFRβ blocked this phosphorylation without having any effect on MEK/Erk1/2 activation. We also found that PDGFRβ regulates high glucose-induced Akt activation, its targets tuberin and PRAS40 phosphorylation, and finally, mTORC1 activation. Furthermore, inhibition of PDGFRβ suppressed high glucose-induced expression of collagen I (α2) in proximal tubular cells. Importantly, expression of constitutively active Akt or mTORC1 reversed these processes. As a mechanism, we found that JNJ and PDGFRβ knockdown inhibited high glucose-stimulated Hif1α expression. Furthermore, overexpression of Hif1α restored the expression of collagen I (α2) inhibited by PDGFRβ knockdown in high glucose-stimulated cells. Finally, we show increased phosphorylation of PDGFRβ and its association with Akt/mTORC1 activation, Hif1α expression and elevated collagen I (α2) levels in the renal cortex of mice with diabetes. Our results identify PDGFRβ as a driver in activating Akt/mTORC1 nexus for high glucose-mediated expression of collagen I (α2) in proximal tubular epithelial cells, which contributes to tubulo-interstitial fibrosis in diabetic nephropathy.
- Diabetic nephropathy
- Tyrosine kinase recrptor
- mTOR complex (mTORC)
- Copyright © 2016, American Journal of Physiology-Renal Physiology