ABSTRACT
Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is an autosomal recessively inherited childhood-onset neurodegenerative disorder, characterized by myoclonus, seizures, and ataxia. Mutations in the cystatin B gene (CSTB) underlie EPM1. The CSTB-deficient (Cstb -/- ) mouse model recapitulates key features of EPM1, including myoclonic seizures. The mice show early microglial activation that precedes seizure onset and neuronal loss and leads to neuroinflammation. We here characterized the inflammatory phenotype of Cstb -/- mice in more detail. We found higher concentrations of chemokines and pro-inflammatory cytokines in the serum of Cstb -/- mice and higher CXCL13 expression in activated microglia in Cstb -/- compared to control mouse brains. The elevated chemokine levels were not accompanied by blood-brain barrier disruption, despite increased brain vascularization. Macrophages in the spleen and brain of Cstb -/- mice were predominantly pro-inflammatory. Taken together, these data show that CXCL13 expression is a hallmark of microglial activation in Cstb -/- mice and that the brain inflammation is linked to peripheral inflammatory changes, which might contribute to the disease pathology of EPM1.
Subject(s)
Cystatin B/deficiency , Encephalitis/etiology , Gene Expression Regulation/genetics , Inflammation/etiology , Myoclonic Epilepsies, Progressive/complications , Myoclonic Epilepsies, Progressive/genetics , Animals , Brain/pathology , Cystatin B/genetics , Cytokines/blood , Disease Models, Animal , Encephalitis/blood , Inflammation/blood , Mice , Mice, Knockout , Microglia/metabolismABSTRACT
Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is an autosomal-recessively inherited neurodegenerative disorder characterized by severely incapacitating myoclonus, seizures, and ataxia, and caused by loss-of-function mutations in the cystatin B gene (CSTB). A central neuropathological finding in the Cstb(-/-) mouse, an animal model for EPM1, is early microglial activation, which precedes astroglial activation, neuronal loss, and onset of myoclonus, thus implying a critical role for microglia in EPM1 pathogenesis. Here, we characterized phenotypic and functional properties of microglia from Cstb(-/-) mice utilizing brain tissue, microglia directly isolated from the brain, and primary microglial cultures. Our results show significantly higher Cstb mRNA expression in microglia than in neurons and astrocytes. In Cstb(-/-) mouse brain, expression of the inflammatory marker p-p38 MAPK and the proportion of both pro-inflammatory M1 and anti-inflammatory M2 microglia is higher than in control mice. Moreover, M1/M2 polarization of microglia in presymptomatic Cstb(-/-) mice is, compared to control mice, skewed towards M2 type at postnatal day 14 (P14), but towards M1 type at P30, a time point associated with onset of myoclonus. At this age, the high expression of both pro-inflammatory inducible nitric oxide synthase (iNOS) and anti-inflammatory arginase 1 (ARG1) in Cstb(-/-) mouse cortex is accompanied by the presence of peripheral immune cells. Consistently, activated Cstb(-/-) microglia show elevated chemokine release and chemotaxis. However, their MHCII surface expression is suppressed. Taken together, our results link CSTB deficiency to neuroinflammation with early activation and dysfunction of microglia and will open new avenues for therapeutic interventions for EPM1.