Up-regulation of microglial cathepsin C expression and activity in lipopolysaccharide-induced neuroinflammation

Abstract

BackgroundCathepsin 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.MethodsC57BL/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.ResultsCat 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.ConclusionsTaken 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.

Disinhibition of Cathepsin C Caused by Cystatin F Deficiency Aggravates the Demyelination in a Cuprizone Model

“…In our previous study, the up-regulated expression of Cat C was mainly found in microglia/macrophage lineage cells in LPS–induced neuroinflammation (Fan et al, 2012). To further confirm the cellular source of Cat C, we performed c-fms ISH and Iba-1 IHC staining, which are commonly used as a marker of microglia/macrophages, to detect microglia/macrophages in wild and Cys F KO mice after cuprizone treatment.…”

“…Cat C can activate serine proteases in T cells, natural killer cells, neutrophils, and mast cells (Hamilton et al, 2008). Also, we previously found Cat C is predominantly expressed in hippocampal CA2 neurons in normal mice, but up-regulated in activated microglia in neuroinflammation induced by LPS intraperitoneal injection (Fan et al, 2012). Taken together, we believed that knockout of Cys F aggravated cuprizone-induced demyelination might be related to Cat C expression.…”

PI3K signaling: A molecular pathway associated with acute hypophagic response during inflammatory challenges

“…However, the lack of evidence for TLR4 expression in ARC neurons in addition to the scarcity of conclusive studies on the direct effects of the endotoxin over hypothalamic neurons, precludes meaningful assumptions that LPS would directly act on neuronal populations to inhibit feeding. Microglial cells, known for a long time as central sentinels of brain injury, express TLR4 and produce cytokines under LPS stimulation [Milanski et al, 2009; Saijo and Glass, 2011; Borges et al, 2012; Fan et al, 2012]. These findings support the idea of microglia acting to inhibit food intake under endotoxin challenges.…”

Inhibition of Interleukin-1β-Induced Matrix Metalloproteinase Expression in Human Corneal Fibroblasts by Tranilast

“…In addition to MMPs, increased activity of other proteases such as cathepsins has been observed in ulcerating corneas secondary to xerophthalmia 37 or severe burns, 38 indicating that these molecules may also play a role in corneal destruction. IL-1b up-regulates cathepsin expression in microglial cells 39 as well as in gastric epithelial cells and macrophages. 40 Tranilast was found to attenuate inflammation associated with collagen-induced arthritis in mice by inhibiting the expression of inflammatory cytokines as well as that of cathepsins and other proteases.…”