Inhibition of mTOR reduces lipotoxic cell death in primary macrophages through an autophagy-independent mechanism

J Leukoc Biol. 2016 Nov;100(5):1113-1124. doi: 10.1189/jlb.3A1015-463R. Epub 2016 Jun 16.

Abstract

Macrophage dysfunction in obesity and diabetes is associated with persistent inflammation and poor wound healing responses. Relevant to these phenotypes, we have previously shown that macrophage activation in a high-fat environment results in cell death via a mechanism that involves lysosome damage. While searching for signaling pathways that were required for this response, we discovered that mTOR inhibitors, torin and rapamycin, were protective against lipotoxic cell death in primary peritoneal macrophages. The protective effect of mTOR inhibition was also confirmed by using genetic loss-of-function approaches. Given the importance of mTOR in regulation of autophagy we hypothesized that this pathway would be important in protection from cell death. We first demonstrated that autophagy was disrupted in response to palmitate and LPS as a consequence of impaired lysosome function. Conversely, the mTOR inhibitor, torin, increased macrophage autophagy and protected against lysosome damage; however, the beneficial effects of torin persisted in autophagy-deficient cells. Inhibition of mTOR also triggered nuclear localization of TFEB, a transcription factor that regulates lysosome biogenesis and function, but the rescue phenotype did not require the presence of TFEB. Instead, we demonstrated that mTOR inhibition reduces mitochondrial oxidative metabolism and attenuates the negative effects of palmitate on LPS-induced mitochondrial respiration. These results suggest that inhibition of mTOR is protective against lipotoxicity via an autophagy-independent mechanism that involves relieving mitochondrial substrate overload. On the basis of these findings, we suggest that therapies to reduce macrophage mTOR activation may protect against dysfunctional inflammation in states of overnutrition, such as diabetes.

Keywords: TFEB; TLRs; diabetes; lysosome; metabolism.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Autophagy / drug effects
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / physiology
  • Blood Proteins / pharmacology*
  • Cell Death / drug effects
  • Cell Death / physiology
  • Cell Nucleus / metabolism
  • Drug Evaluation, Preclinical
  • Lipopolysaccharides / toxicity
  • Lysosomes / drug effects
  • Macrophages, Peritoneal / cytology
  • Macrophages, Peritoneal / drug effects*
  • Macrophages, Peritoneal / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mitochondria / metabolism
  • Palmitates / pharmacology
  • Palmitates / toxicity*
  • RNA Interference
  • RNA, Small Interfering / genetics
  • Sirolimus / pharmacology*
  • Specific Pathogen-Free Organisms
  • Stearates / pharmacology
  • Stearates / toxicity*
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • TOR Serine-Threonine Kinases / genetics

Substances

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Blood Proteins
  • Lipopolysaccharides
  • Palmitates
  • RNA, Small Interfering
  • Stearates
  • Tcfeb protein, mouse
  • torin
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Sirolimus