Calpastatin is a crucial regulator of macrophage activation that limits in vivo inflammation (66.1)

Abstract Calpain enzymes regulate cellular function through the proteolytic modulation of structural and signaling proteins. Calpain activity is positively regulated by the binding of calcium and negatively regulated by the endogenous inhibitor, calpastatin (CAST). We have revealed a novel role for CAST in attenuating macrophage activation. While calpain is constitutively expressed in macrophages, CAST levels increase upon activation of macrophages and decreases cleavage of specific calpain targets. Interestingly, we found that CAST increased when macrophages were stimulated with LPS, IFNγ, and TNFα, but not with IL-4, -10, or -17A. We utilized siRNA to inhibit the increase in CAST protein levels that arises from stimulation with TNFα, and decreased CAST expression led to increased NF-κB nuclear translocation and over-production of IL-6 upon stimulation with CpG DNA. CAST knockout mice were examined for markers of inflammation, and results showed that CAST-deficiency led to increased inflammation in the colons of these mice. In addition, serum levels of the pro-inflammatory chemokine, MCP-1, was increased in CAST knockout mice compared to wild-type mice. Overall, CAST plays a key role in limiting macrophage activation and defects in CAST expression increase susceptibility to the development of inflammation in vivo.