Inflammasome induction in Rasmussen’s encephalitis: cortical and associated white matter pathogenesis

Abstract

BackgroundRasmussen’s encephalitis (RE) is an inflammatory encephalopathy of unknown cause defined by seizures with progressive neurological disabilities. Herein, the pathogenesis of RE was investigated focusing on inflammasome activation in the brain.MethodsPatients with RE at the University of Alberta, Edmonton, AB, Canada, were identified and analyzed by neuroimaging, neuropsychological, molecular, and pathological tools. Primary human microglia, astrocytes, and neurons were examined using RT-PCR, enzyme-linked immunosorbent assay (ELISA), and western blotting.ResultsFour patients with RE were identified at the University of Alberta. Magnetic resonance imaging (MRI) disclosed increased signal intensities in cerebral white matter adjacent to cortical lesions of RE patients, accompanied by a decline in neurocognitive processing speed (P <0.05). CD3ϵ, HLA-DRA, and TNFα together with several inflammasome-associated genes (IL-1β, IL-18, NLRP1, NLRP3, and CASP1) showed increased transcript levels in RE brains compared to non-RE controls (n = 6; P <0.05). Cultured human microglia displayed expression of inflammasome-associated genes and responded to inflammasome activators by releasing IL-1β, which was inhibited by the caspase inhibitor, zVAD-fmk. Major histocompatibility complex (MHC) class II, IL-1β, caspase-1, and alanine/serine/cysteine (ASC) immunoreactivity were increased in RE brain tissues, especially in white matter myeloid cells, in conjunction with mononuclear cell infiltration and gliosis. Neuroinflammation in RE brains was present in both white matter and adjacent cortex with associated induction of inflammasome components, which was correlated with neuroimaging and neuropsychological deficits.ConclusionInflammasome activation likely contributes to the disease process underlying RE and offers a mechanistic target for future therapeutic interventions.

Epilepsy and the inflammasome: Targeting inflammation as a novel therapeutic strategy for seizure disorders

“…Elevated IL-1β and IL-1R1 have also been observed in brain tissue from patients with temporal lobe epilepsy and hippocampal sclerosis, and elevated IL-1β has been reported in cerebrospinal fluid (CSF) from children with febrile seizures [28,29]. In addition to increased IL-1 expression in patients with temporal lobe epilepsy, increases in IL-1β and inflammasome components have also been observed in other seizure disorders such as Rasmussen's encephalitis [30] and malformations of cortical development [31].…”

Neuronal NLRP1 inflammasome activation of Caspase-1 coordinately regulates inflammatory interleukin-1-beta production and axonal degeneration-associated Caspase-6 activation

“…Microglia were lost in FDUtreated cultures. Another difference is that Ramaswamy et al, 37 cultured their cells in 10% serum whereas we used 5% decomplemented serum. It has been reported that complement can activate the NLRP3 inflammasome in dendritic cells 46 and a similar mechanism in primary human neurons would explain the difference between our results.…”

“…23,24,44 Furthermore, spatial memory deficits induced in familial AD-associated mutant APP/ PS1 mice were abrogated on a null NLRP3 background. 45 Although this differential expression could be species dependent, others have observed NLRP3 in human neuronal cultures, 37 suggesting that culture conditions may alter the levels of inflammasome receptors in primary human neuronal cell types. Cells respond to their extracellular environment so the conditions of cell culture could strongly influence the expression of certain genes.…”

“…Cells respond to their extracellular environment so the conditions of cell culture could strongly influence the expression of certain genes. In the study by Ramaswamy et al, 37 the methods indicated that cells were passaged once for astrocytes, neurons, and microglia, whereas in our cultures, neurons were maintained as primary cells (no passage) and treated with fluorodeoxyuridine (FDU) to prevent astrocyte proliferation. Microglia were lost in FDUtreated cultures.…”

“…35 Nlrp1 has been reported in human brain pyramidal neurons 36 and inflammasome receptor mRNAs were observed in human neuron cultures and human Rasmussen's encephalitis. 37 Here, we assessed which inflammasome could activate Casp1 and subsequently Casp6 in human primary CNS cultures. We determined which inflammasomes were expressed in naive and stressed neurons and used siRNAs and S-100 cell-free extracts treated with specific inflammasome activators, or antibody blockers, to identify the functional inflammasome.…”