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Energy reprogramming to glycolysis is closely associated with the development of chronic kidney disease. As an important negative regulatory factor of the mammalian target of rapamycin complex 1 (mTORC1) signal, tuberous sclerosis complex 1 (Tsc1) is also a key regulatory point of glycolysis. Here, we investigated whether Tsc1 could mediate the progression of kidney interstitial fibrosis by regulating glycolysis in proximal tubular epithelial cells. We induced mTORC1 signal activation in tubular epithelial cells in kidneys with fibrosis via unilateral ureteral occlusion. This resulted in increased tubular epithelial cell proliferation and glycolytic enzyme upregulation. Prior incubation with rapamycin inhibited mTORC1 activation and abolished the enhanced glycolysis and tubular epithelial cell proliferation. Furthermore, knockdown of Tsc1 expression promoted glycolysis in the rat kidney epithelial cell line NRK-52E. Specific deletion of Tsc1 in the proximal tubules of mice resulted in enlarged kidneys characterized by a high proportion of proliferative tubular epithelial cells, dilated tubules with cyst formation, and a large area of interstitial fibrosis in conjunction with elevated glycolysis. Treatment of the mice with the glycolysis inhibitor 2-deoxyglucose notably ameliorated tubular epithelial cell proliferation, cystogenesis, and kidney fibrosis. Thus, our findings suggest that Tsc1-associated mTORC1 signaling mediates the progression of kidney interstitial fibrosis by regulating glycolysis in proximal tubular epithelial cells.

The mammalian target of rapamycin (mTOR) plays a critical role for cell growth and survival in many cell types. While substantial progress has been made in understanding the abnormal activation of mTORC1 in the pathogenesis of kidney disease, little is known about mTORC2 in kidney disease such as acute kidney injury (AKI). To study this, we generated a mouse model with tubule-specific deletion of Rictor (Tubule-Rictor-/-). The knockouts were born normal and no obvious kidney dysfunction or kidney morphologic abnormality was found within 2 months of birth. However, ablation of Rictor in the tubular cells exacerbated cisplatin-induced AKI compared to that in the control littermates. As expected, tubular cell apoptosis, Akt phosphorylation (Ser473), and autophagy were induced in the kidneys from the control littermates by cisplatin treatment. Less cell autophagy or Akt phosphorylation and more cell apoptosis in the kidneys of the knockout mice were identified compared with those in the control littermates. In NRK-52E cells in vitro , Rictor siRNA transfection sensitized cell apoptosis to cisplatin but with reduced cisplatin-induced autophagy. Metformin, an inducer of autophagy, abolished cell death induced by Rictor siRNA and cisplatin. Thus, endogenous Rictor/mTORC2 protects against cisplatin-induced AKI, probably mediated by promoting cell survival through Akt signaling activation and induction of autophagy.

Growing evidence suggests that active vitamin D slows the progression of chronic kidney diseases. Here we compared the individual renal protective efficacy of paricalcitol and trandolapril (an angiotensin-converting enzyme inhibitor) in obstructive nephropathy, and examined any potential additive effects of their combination on attenuating renal fibrosis and inflammation. Mice underwent unilateral ureteral obstruction and were treated individually with paricalcitol or trandolapril or their combination. Compared to vehicle-treated controls, monotherapy with paricalcitol or trandolapril inhibited the expression and accumulation of fibronectin and type I and type III collagen, suppressed alpha-smooth muscle actin, vimentin, and Snail1 expression, and reduced total collagen content in the obstructed kidney. Combination therapy led to a more profound inhibition of all parameters. Monotherapy also suppressed renal RANTES (regulated on activation, normal T cell expressed and secreted) and tumor necrosis factor (TNF)-alpha expression and inhibited renal infiltration of T cells and macrophages, whereas the combination had additive effects. Renin expression was induced in the fibrotic kidney and was augmented by trandolapril. Paricalcitol blocked renin induction in the absence or presence of trandolapril. Our study indicates that paricalcitol has renal protective effects, comparable to that of trandolapril, in reducing interstitial fibrosis and inflammation. Combination therapy had additive efficacy in retarding renal scar formation during obstructive nephropathy.

The mammalian target of rapamycin (mTOR) was recently identified in two structurally distinct multiprotein complexes: mTORC1 and mTORC2. Previously, we found that Rictor/mTORC2 protects against cisplatin-induced acute kidney injury, but the role and mechanisms for Rictor/mTORC2 in TGFβ1-induced fibroblast activation and kidney fibrosis remains unknown. To study this, we initially treated NRK-49F cells with TGFβ1 and found that TGFβ1 could activate Rictor/mTORC2 signaling in cultured cells. Blocking Rictor/mTORC2 signaling with Rictor or Akt1 small interfering RNAs markedly inhibited TGFβ1-induced fibronection and α-smooth muscle actin expression. Ensuing western blotting or immunostaining results showed that Rictor/mTORC2 signaling was activated in kidney interstitial myofibroblasts from mice with unilateral ureteral obstruction. Next, a mouse model with fibroblast-specific deletion of Rictor was generated. These knockout mice were normal at birth and had no obvious kidney dysfunction or kidney morphological abnormality within 2 months of birth. Compared with control littermates, the kidneys of Rictor knockout mice developed less interstitial extracellular matrix deposition and inflammatory cell infiltration at 1 or 2 weeks after ureteral obstruction. Thus our study suggests that Rictor/mTORC2 signaling activation mediates TGFβ1-induced fibroblast activation and contributes to the development of kidney fibrosis. This may provide a therapeutic target for chronic kidney diseases.