Inhibition of cathepsin X reduces the strength of microglial-mediated neuroinflammation

Neuropharmacology. 2017 Mar 1:114:88-100. doi: 10.1016/j.neuropharm.2016.11.019. Epub 2016 Nov 23.

Abstract

Inflammation plays a central role in the processes associated with neurodegeneration. The inflammatory response is mediated by activated microglia that release inflammatory mediators to the neuronal environment. Microglia-derived lysosomal cathepsins, including cathepsin X, are increasingly recognized as important mediators of the inflammation involved in lipopolysaccharide (LPS)-induced neuroinflammation. The current study was undertaken to investigate the role of cathepsin X and its molecular target, γ-enolase, in neuroinflammation and to elucidate the underlying mechanism. We determined that the exposure of activated BV2 and EOC 13.31 cells to LPS led to increased levels of cathepsin X protein and activity in the culture supernatants in a concentration- and time-dependent manner. In contrast, LPS stimulation of these two cells reduced the release of active γ-enolase in a manner regulated by the cathepsin X activity. Cathepsin X inhibitor AMS36 significantly reduced LPS-induced production of nitric oxide, reactive oxygen species and the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-α from BV2 cells. Inhibition of cathepsin X suppressed microglial activation through the reduced caspase-3 activity, together with diminished microglial cell death and apoptosis, and also through inhibition of the activity of the mitogen-activated protein kinases. Further, SH-SY5Y treatment with culture supernatants of activated microglial cells showed that cathepsin X inhibition reduces microglia-mediated neurotoxicity. These results indicate that up-regulated expression and increased release and activity of microglial cathepsin X leads to microglia activation-mediated neurodegeneration. Cathepsin X inhibitor caused neuroprotection via its inhibition of the activation of microglia. Cathepsin X could thus be a potential therapeutic target for neuroinflammatory disorders.

Keywords: Cathepsin X; Microglia; Neuroinflammation; Neuroprotection; γ-Enolase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminobutyrates / administration & dosage*
  • Animals
  • Cathepsins / antagonists & inhibitors*
  • Cathepsins / metabolism*
  • Cell Line
  • Cell Survival
  • Encephalitis / metabolism*
  • Lipopolysaccharides
  • MAP Kinase Kinase 4 / metabolism
  • Mice
  • Microglia / metabolism*
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Phosphopyruvate Hydratase / metabolism
  • Reactive Oxygen Species
  • Succinates / administration & dosage*
  • p38 Mitogen-Activated Protein Kinases / metabolism

Substances

  • AMS36 compound
  • Aminobutyrates
  • Lipopolysaccharides
  • Reactive Oxygen Species
  • Succinates
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • p38 Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 4
  • Cathepsins
  • cathepsin X, mouse
  • Phosphopyruvate Hydratase