Role of mTOR signaling in the regulation of high glucose‑induced podocyte injury

Abstract

Podocyte injury, which promotes progressive nephropathy, is considered a key factor in the progression of diabetic nephropathy. The mammalian target of rapamycin (mTOR) signaling cascade controls cell growth, survival and metabolism. The present study investigated the role of mTOR signaling in regulating high glucose (HG)-induced podocyte injury. MTT assay and flow cytometry assay results indicated that HG significantly increased podocyte viability and apoptosis. HG effects on podocytes were suppressed by mTOR complex 1 (mTORC1) inhibitor, rapamycin, and further suppressed by dual mTORC1 and mTORC2 inhibitor, KU0063794, when compared with podocytes that received mannitol treatment. In addition, western blot analysis revealed that the expression levels of Thr-389-phosphorylated p70S6 kinase (p-p70S6K) and phosphorylated Akt (p-Akt) were significantly increased by HG when compared with mannitol treatment. Notably, rapamycin significantly inhibited HG-induced p-p70S6K expression, but did not significantly impact p-Akt expression. However, KU0063794 significantly inhibited the HG-induced p-p70S6K and p-Akt expression levels. Furthermore, the expression of ezrin was significantly reduced by HG when compared with mannitol treatment; however, α-smooth muscle actin (α-SMA) expression was significantly increased. Immunofluorescence analysis on ezrin and α-SMA supported the results of western blot analysis. KU0063794, but not rapamycin, suppressed the effect of HG on the expression levels of ezrin and α-SMA. Thus, it was suggested that the increased activation of mTOR signaling mediated HG-induced podocyte injury. In addition, the present findings suggest that the mTORC1 and mTORC2 signaling pathways may be responsible for the cell viability and apoptosis, and that the mTORC2 pathway could be primarily responsible for the regulation of cytoskeleton-associated proteins.

Activation of mTOR mediates hyperglycemia-induced renal glomerular endothelial hyperpermeability via the RhoA/ROCK/pMLC signaling pathway

“…Mechanistic target of rapamycin (mTOR), a protein kinase [ 18 ], is a cytosolic enzyme associated with cellular growth and homeostasis via mTOR complexes 1 and 2. Several lines of evidence suggest that the mTOR pathway may directly regulate GFB function [ 19 , 20 ], which is a key player in diabetic kidney disease.…”

“…The underlying mechanisms of HG-induced aberrant glomerular filtration and the effects of mTOR on changes in the GFB are presently unknown. mTOR controls the expression of a variety of downstream target proteins, including the ribosomal protein S6 kinase (S6K) [ 18 ]. Liu et al demonstrated that mTOR is involved in the expression and activation of RhoA that mediates F-actin reorganization and cell motility [ 22 ].…”

MicroRNAs in Podocyte Injury in Diabetic Nephropathy

“…High glucose causes podocyte apoptosis through the stimulation of oxidative stress and ROS generation with the activation of mTORC1 (Kitada et al, 2017). Indeed, an mTORC1 inhibitor, rapamycin, was shown to suppress podocyte injury caused by high glucose in diabetic nephropathy (Li et al, 2019). In addition, genetic deletion of mTORC1 in mouse podocytes was found to induce proteinuria and progressive glomerulosclerosis (Godel et al, 2011).…”

“…However, curtailing mTORC1 signaling in mice by genetically reducing the copy number of mTORC1 in podocytes was shown to ameliorate the progression of glomerular disease in diabetic nephropathy (Godel et al, 2011). These results suggested the need for tightly balanced mTOR activity in podocyte homeostasis in diabetic nephropathy (Godel et al, 2011;Li et al, 2019).…”

Loss of Mitochondrial Control Impacts Renal Health

“…Activation of the mTOR signaling pathway is the key pathogenic mechanism in diabetic kidney disease ( Lloberas et al, 2006 ). Rapamycin inhibits kidney fibrosis, glomerulosclerosis, proteinuria and mesangial matrix deposition through mitigating the activation of mTOR ( Lloberas et al, 2006 ; Li et al, 2019 ). Rapamycin can inhibit both mTORC1 and mTORC2 ( Kawata et al, 2018 ).…”