Proteinase-activated receptor 2 modulates neuroinflammation in experimental autoimmune encephalomyelitis and multiple sclerosis

The proteinase-activated receptors (PARs) are widely recognized for their modulatory properties of inflammation and neurodegeneration. We investigated the role of PAR(2) in the pathogenesis of multiple sclerosis (MS) in humans and experimental autoimmune encephalomyelitis (EAE) in mice. PAR(2) expression was increased on astrocytes and infiltrating macrophages in human MS and murine EAE central nervous system (CNS) white matter (P < 0.05). Macrophages and astrocytes from PAR(2) wild-type (WT) and knockout (KO) mice exhibited differential immune gene expression with PAR(2) KO macrophages showing significantly higher interleukin 10 production after lipopolysaccharide stimulation (P < 0.001). PAR(2) activation in macrophages resulted in the release of soluble oligodendrocyte cytotoxins (P < 0.01). Myelin oligodendrocyte glycoprotein–induced EAE caused more severe inflammatory gene expression in the CNS of PAR(2) WT animals (P < 0.05), together with enhanced T cell proliferation and interferon γ production (P < 0.05), compared with KO littermates. Indeed, PAR(2) WT animals showed markedly greater microglial activation and T lymphocyte infiltration accompanied by worsened demyelination and axonal injury in the CNS compared with their PAR(2) KO littermates. Enhanced neuropathological changes were associated with a more severe progressive relapsing disease phenotype (P < 0.001) in WT animals. These findings reveal previously unreported pathogenic interactions between CNS PAR(2) expression and neuroinflammation with ensuing demyelination and axonal injury.