title: Up-regulation of microglial cathepsin C expression and activity in lipopolysaccharide-induced neuroinflammation.
abstract: BACKGROUND
  Cathepsin C (Cat C) functions as a central coordinator for activation of many serine proteases in inflammatory cells. It has been recognized that Cat C is responsible for neutrophil recruitment and production of chemokines and cytokines in many inflammatory diseases. However, Cat C expression and its functional role in the brain under normal conditions or in neuroinflammatory processes remain unclear. Our previous study showed that Cat C promoted the progress of brain demyelination in cuprizone-treated mice. The present study further investigated the Cat C expression and activity in lipopolysaccharide (LPS)-induced neuroinflammation in vivo and in vitro.
  
  
  METHODS
  C57BL/6 J mice were intraperitoneally injected with either 0.9% saline or lipopolysaccharide (LPS, 5 mg/kg). Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to analyze microglial activation, TNF-α, IL-1β, IL-6, iNOS mRNAs expressions and cellular localization of Cat C in the brain. Nitrite assay was used to examine microglial activation in vitro; RT-PCR and ELISA were used to determine the expression and release of Cat C. Cat C activity was analyzed by cellular Cat C assay kit. Data were evaluated for statistical significance with paired t test.
  
  
  RESULTS
  Cat C was predominantly expressed in hippocampal CA2 neurons in C57BL/6 J mice under normal conditions. Six hours after LPS injection, Cat C expression was detected in cerebral cortical neurons; whereas, twenty-four hours later, Cat C expression was captured in activated microglial cells throughout the entire brain. The duration of induced Cat C expression in neurons and in microglial cells was ten days and three days, respectively. In vitro, LPS, IL-1β and IL-6 treatments increased microglial Cat C expression in a dose-dependent manner and upregulated Cat C secretion and its activity.
  
  
  CONCLUSIONS
  Taken together, these data indicate that LPS and proinflammatory cytokines IL-1β, IL-6 induce the expression, release and upregulate enzymatic activity of Cat C in microglial cells. Further investigation is required to determine the functional role of Cat C in the progression of neuroinflammation, which may have implications for therapeutics for the prevention of neuroinflammation-involved neurological disorders in the future.
authors.affiliation: Department of Anatomy, Dalian Medical University, No, 9, West Segment of South Lvshun Road, Dalian, Liaoning, 116044, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Fan
authors.forename: Xuefei
authors.initials: X
authors.lastname: Wu
authors.forename: Bin
authors.initials: B
authors.lastname: Fan
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Yongzhong
authors.initials: Y
authors.lastname: Lin
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Yao
authors.forename: Jianmei
authors.initials: J
authors.lastname: Ma
mesh_terms: D000818:Animals; D001921:Brain / Q000098:blood supply / Q000201:enzymology / Q000473:pathology; D020789:Cathepsin C / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D018450:Disease Progression; D004789:Enzyme Activation / Q000235:genetics / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D007249:Inflammation / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology*; D008070:Lipopolysaccharides / Q000008:administration & dosage / Q000633:toxicity*; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000378:metabolism* / Q000473:pathology; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D015854:Up-Regulation / Q000235:genetics / Q000502:physiology*
chemical_list: D008070:Lipopolysaccharides; D020789:Cathepsin C