High Glucose-Induced Podocyte Injury Involves Activation of Mammalian Target of Rapamycin (mTOR)-Induced Endoplasmic Reticulum (ER) Stress

Abstract

Background/Aims: The mechanisms by which high glucose (HG) results in podocyte damage remains unclear. We investigated the potential role of endoplasmic reticulum (ER) stress and mTOR signaling in HG injured podocyte. Methods: In cultured mouse podocytes, cellular apoptosis was assessed using FITC-Annexin V and propidium iodide staining followed by flow cytometry analysis. Apoptosis-related proteins as well as the ER stress and the mTOR signals were evaluated using immunoblot assay. Results: Compared to normal glucose (NG) and osmotic mannitol (MN) control, the percentage of apoptotic cells was increased significantly in HG-treated podocytes. The levels of CHOP, Grp78, phospho-PERKThr982, and caspase-12 were increased significantly following HG treatment. The downstream effects of ER stress were obtained in HG-treated podocytes, showing upregulation of Bax, Bak and cytochrome c, and downregulation of Bcl-2. HG-induced increase of cytochrome c, Bax and active caspase-3 was prevented by both ER inhibitor sodium 4-phenylbultyrate (PBA) and CHOP siRNA (siCHOP). PBA and CHOP knockdown remarkably decreased HG-induced apoptosis. In addition, the levels of phospho-mTORSer2448 and phospho- p70S6kThr389 as well as phospho-AMPKα (a sensor of energy consumption) were increased significantly in HG-treated cells. Moreover, the Erk inhibitor U0126 prevented HG-induced mTOR activation. Increased phospho-AMPKα, CHOP and Grp78 as well as cellular apoptosis were prevented by mTOR inhibitor rapamycin in HG-treated podocytes. Conclusion: Our data demonstrate that the activated mTOR by Erk1/2 results in energy consumption, which in turn leads to ER stress signaling and thus induces apoptosis in HG-treated podocytes.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

“…113,[135][136][137][138][139][140][141] It is well established that ER stress pathways are activated in fibrotic renal disease, including in diabetic nephropathy and in ischemia, and that chemical chaperones such as 4-phenylbutyrate and tauroursodeoxycholic acid have been shown to reduce ER stress and result in fibrosis in animal models of renal disease. [142][143][144][145][146][147][148][149] It is unclear how TSP1 and other TSP family members might be participating in the UPR and other branches of the ER stress response and whether intracellular TSP1 functions are involved in fibrogenic processes. Studies on mutant COMP (TSP5) in models of pseudoachondroplasia showed a more severe phenotype in animals in which the mutant protein was expressed than in knockout mice.…”

Activation of Cyclooxygenase-2 by ATF4 During Endoplasmic Reticulum Stress Regulates Kidney Podocyte Autophagy Induced by Lupus Nephritis

“…Inhibition of the PI3K-AKT-mTOR pathway can activate autophagy [33]. However, inhibition of mTOR by pharmacological agents, such as rapamycin, can prevent cellular apopotosis induced by HG-treatment [34] and promote AKT phosphorylation by blocking the phosphorylation of insulin receptor substrate 1 and p70 ribosomal S6 kinase [32,35], which are part of a negative feedback mechanism of PI3K-AKT signal transduction [36]. Our results demonstrate that LN inhibits mTOR, but increases the phosphorylation of AKT, suggesting that LN inhibited mTOR independent of AKT activation.…”

Erzhi Formula Extracts Reverse Renal Injury in Diabetic Nephropathy Rats by Protecting the Renal Podocytes

“…High blood glucose level causes the damage of glomerular and podocyte [61]. In this paper, the positive drug, Irbesartan, was not a hypoglycemic drug, but it showed the hypoglycemic effect which deserves further study.…”