Hyperglycemia-induced Bcl-2/Bax-mediated apoptosis of Schwann cells via mTORC1/S6K1 inhibition in diabetic peripheral neuropathy

Exp Cell Res. 2018 Jun 15;367(2):186-195. doi: 10.1016/j.yexcr.2018.03.034. Epub 2018 Apr 3.

Abstract

Schwann cell apoptosis is one of the characteristics of diabetic peripheral neuropathy (DPN). The mammalian target of rapamycin (mTOR) is a multifunctional signaling pathway that regulates cell apoptosis in various types of tissues and cells. To investigate whether the mTOR pathway is involved in cell apoptosis in the Schwann cells of DPN, diabetic mice and rat Schwann cells (RSC96) were chosen to detect phospho-mTOR (Ser 2448), phospho-S6K1 (Thr 389), phospho-4EBP1 (Thr 37/46), Bcl-2, Bax and cleaved caspase-3 by diverse pathological and biological techniques. The results showed that phospho-mTOR (Ser 2448) was decreased in the sciatic nerves of diabetic mice, concomitant with decreased Bcl-2, increased Bax, cleaved caspase-3 and cell apoptosis. In addition, high glucose treatment for 72 h caused a 35.95% decrease in the phospho-mTOR (Ser 2448)/mTOR ratio, a 65.50% decrease in the phospho-S6K1 (Thr 389)/S6K1 ratio, a 3.67-fold increase in the Bax/Bcl-2 ratio and a 1.47-fold increase in the cleaved caspase-3/caspase-3 ratio. Furthermore, mTORC1 inhibition, rather than mTORC2 inhibition, resulted in mitochondrial controlled apoptosis in RSC96 cells by silencing RAPTOR or RICTOR. Again, suppression of the mTORC1 pathway by a chemical inhibitor led to mitochondrial controlled apoptosis in cultured RSC96 cells in vitro. By contrast, activation of the mTORC1 pathway with MHY1485 prevented decreased phospho-S6K1 (Thr 389) levels caused by high glucose and cell apoptosis. Additionally, constitutive activation of S6K1 avoided high glucose-induced cell apoptosis in RSC96 cells. In summary, our findings suggest that activating mTORC1/S6K1 signaling in Schwann cells may be a promising strategy for the prevention and treatment of DPN.

Keywords: Apoptosis; Bax; Bcl-2; Diabetic peripheral neuropathy; S6K1; Schwann cell; mTORC1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Caspase 3 / metabolism
  • Cell Line
  • Diabetic Nephropathies / enzymology
  • Diabetic Nephropathies / metabolism*
  • Diabetic Nephropathies / pathology
  • Glucose / pharmacology
  • Mechanistic Target of Rapamycin Complex 1 / antagonists & inhibitors
  • Mechanistic Target of Rapamycin Complex 1 / metabolism*
  • Mice
  • Mitochondria / drug effects
  • Naphthyridines / pharmacology
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Rapamycin-Insensitive Companion of mTOR Protein / antagonists & inhibitors
  • Rats
  • Regulatory-Associated Protein of mTOR / antagonists & inhibitors
  • Ribosomal Protein S6 Kinases / metabolism*
  • Schwann Cells / drug effects
  • Schwann Cells / enzymology
  • Schwann Cells / metabolism*
  • Sciatic Nerve / enzymology
  • Sciatic Nerve / metabolism
  • Sciatic Nerve / pathology
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • TOR Serine-Threonine Kinases / metabolism
  • bcl-2-Associated X Protein / metabolism

Substances

  • 1-(4-(4-propionylpiperazin-1-yl)-3-(trifluoromethyl)phenyl)-9-(quinolin-3-yl)benzo(h)(1,6)naphthyridin-2(1H)-one
  • Bax protein, mouse
  • Naphthyridines
  • Proto-Oncogene Proteins c-bcl-2
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • bcl-2-Associated X Protein
  • mTOR protein, rat
  • Mechanistic Target of Rapamycin Complex 1
  • Ribosomal Protein S6 Kinases
  • Rps6kb1 protein, rat
  • TOR Serine-Threonine Kinases
  • Caspase 3
  • Glucose
  • Sirolimus