In the central nervous system (CNS), connexin and pannexin gap junctions and hemichannels are an integral component of homeostatic neuronal excitability and synaptic plasticity. Neuronal connexin (Cx) gap junctions form electrical synapses across biochemically similar GABAergic networks, allowing rapid and extensive inhibition in response to principle neuron excitation. Glial Cx gap junctions link astrocytes and oligodendrocytes in the pan-glial network that is responsible for removing excitotoxic ions and metabolites. In addition, Cx gap junctions between glia help constrain excessive excitatory activity in neurons and facilitate astrocyte Ca2+ slow wave propagation. Pannexins (Panxs) do not form gap junctions in vivo, but Panx hemichannels participate in autocrine and paracrine gliotransmission alongside connexin hemichannels. ATP and other gliotransmitters released by Cx and Panx hemichannels maintain physiologic glutamatergic tone by strengthening synapses and mitigating aberrant high frequency bursting. Under pathological depolarizing and inflammatory conditions, gap junctions and hemichannels become dysregulated, resulting in aberrant neuronal firing and seizure. In this review, we present known contributions of Cxs and Panxs to physiologic neuronal excitation and explore how disruption of gap junctions and hemichannels lead to aberrant glutamatergic transmission, purinergic signaling, and seizures.

Inflammation plays a critical role in the pathogenesis of ischemic stroke. This process depends, in part, upon proinflammatory factors released by activated resident central nervous system (CNS) microglia (MG). Previous studies demonstrated that transfer of IL-10+ B-cells reduced infarct volumes in male C57BL/6J recipient mice when given 24 h prior to or therapeutically at 4 h or 24 h after experimental stroke induced by 60 min middle cerebral artery occlusion (MCAO). The present study assesses possible sex differences in immunoregulation by IL-10+ B-cells on primary male vs. female MG cultured from naïve and ischemic stroke-induced mice. Thus, MG cultures were treated with recombinant (r)IL-10, rIL-4 or IL-10+ B-cells after lipopolysaccharide (LPS) activation and evaluated by flow cytometry for production of proinflammatory and anti-inflammatory factors. We found that IL-10+ B-cells significantly reduced MG production of TNF-α, IL-1β and CCL3 post-MCAO and increased their expression of the anti-inflammatory M2 marker, CD206, by cell-cell interactions. Moreover, MG from female vs. male mice had higher expression of IL-4 and IL-10 receptors and increased production of IL-4, especially after treatment with IL-10+ B-cells. These findings indicate that IL-10-producing B-cells play a crucial role in regulating MG activation, proinflammatory cytokine release and M2 phenotype induction, post-MCAO, with heightened sensitivity of female MG to IL-4 and IL-10. This study, coupled with our previous demonstration of increased numbers of transferred IL-10+ B-cells in the ischemic hemisphere, provide a mechanistic basis for local regulation by secreted IL-10 and IL-4 as well as direct B-cell/MG interactions that promote M2+-MG.

Multiple sclerosis (MS) patients are three to six times more likely to develop epilepsy compared to the rest of the population. Seizures are more common in patients with early onset or progressive forms of the disease and prognosticate rapid progression to disability and death. Grey matter atrophy, hippocampal lesions, interneuron loss, and elevated juxtacortical lesion burden have been identified in MS patients with seizures; however, translational studies aimed at elucidating the pathophysiological processes underlying MS epileptogenesis are limited. Here, we report that cuprizone-mediated chronically demyelinated (9-12 weeks) mice exhibit marked changes in electroencephalography (EEG) and evidence of overt seizure activity in mice. Subsequently, histopathological correlates were probed by immunohistochemistry, revealing extensive demyelination, loss of parvalbumin inhibitory interneurons in the hippocampus CA1 subregion, widespread gliosis and changes to astrocytic aquaporin-4 expression. Our results suggest that chronically demyelinated mice are a valuable model with which we may begin to understand the mechanisms underlying demyelination-induced seizures.

Clinical stroke induces inflammatory processes leading to cerebral and splenic injury and profound peripheral immunosuppression. IL-10 expression is elevated during major CNS diseases and limits inflammation in the brain. Recent evidence demonstrated that transfer of IL-10+ B-cells reduced infarct volume in male C57BL/6J (wild-type, WT) recipient mice when given 24 h prior to or 4 h after middle cerebral artery occlusion (MCAO). The purpose of this study was to determine if passively transferred IL-10+ B-cells can exert therapeutic and immunoregulatory effects when injected 24 hours after MCAO induction in B-cell-sufficient male WT mice. The results demonstrated that IL-10+ B-cell treated mice had significantly reduced infarct volumes in the ipsilateral cortex and hemisphere and improved neurological deficits vs. Vehicle-treated control mice after 60 min occlusion and 96 h of reperfusion. The MCAO-protected B-cell recipient mice had less splenic atrophy and reduced numbers of activated, inflammatory T-cells, decreased infiltration of T-cells and a less inflammatory milieu in the ischemic hemispheres compared with Vehicle-treated control mice. These immunoregulatory changes occurred in concert with the predominant appearance of IL-10-secreting CD8+CD122+ Treg cells in both the spleen and the MCAO-affected brain hemisphere. This study for the first time demonstrates a major neuroprotective role for IL-10+ B-cells in treating MCAO in male WT mice at a time point well beyond the ~4 h tPA treatment window, leading to the generation of a dominant IL-10+CD8+CD122+ Treg population associated with spleen preservation and reduced CNS inflammation.

Clinical improvement during pregnancy in multiple sclerosis (MS) patients suggests that sex hormones exert potent regulatory effects on immune function. Our previous studies demonstrated that estrogen-(17β-estradiol; E2) mediated protection against experimental autoimmune encephalomyelitis (EAE), a mouse model for MS, hinges on the B cells, leading to elevated numbers of IL-10 secreting CD1d hi CD5 + B regulatory cells (B regs ) in wild type mice. Our data show that co-administration of E2 and IL-10 + B cells ameliorates EAE disease severity and limits CNS infiltrating leukocytes in B cell deficient mice. Additionally, treatment with E2 and B regs reduces demyelination and dramatically decreases the proportion of CD11b + CD45 hi activated microglia/macrophages found in the CNS of immunized animals compared to vehicle, E2 or B reg cells alone. Furthermore, mice given E2 and B regs exhibit increased numbers of peripheral programmed death-1 positive CD4 + Foxp3 + regulatory T cells (T regs ) and up-regulation of programmed death receptor-ligand-1 and CD80 expression on monocytes. Our study suggests IL-10 producing B regs have powerful therapeutic potential as an agent against EAE when augmented with E2 treatment.

Women with Multiple sclerosis (MS) often experience clinical improvement during pregnancy, indicating that sex hormones might have therapeutic effects in MS. Our previous studies have demonstrated that B cells and PD-L1 are crucial for E2 (17β-estradiol) - mediated protection against experimental autoimmune encephalomyelitis (EAE). We here demonstrate that transfer of IL-10+ B cells into E2-treated PD-L1−/− mice after EAE induction could partially restore E2-mediated protection and decrease the frequency of pro-inflammatory cells in the CNS compared to E2/saline treated PD-L1−/− mice. Hence, co-administration of IL-10+ B cells and E2 might have a powerful therapeutic potential for treatment of EAE.

Background and Purpose Both pathogenic and regulatory immune processes are involved in the middle cerebral artery occlusion (MCAO) model of experimental stroke, including interactions involving the Programmed Death 1 (PD-1) receptor and its two ligands, PD-L1 and PD-L2. Although PD-1 reduced stroke severity, PD-L1 and PD-L2 appeared to play pathogenic roles, suggesting use of anti-PD-L monoclonal Ab (mAb) therapy for MCAO. Methods Male C57BL/6 mice were treated with a single dose of anti-PD-L1 mAb 4 h after MCAO and evaluated for clinical, histological and immunological changes after 96 h reperfusion. Results Blockade of the PD-L1 checkpoint using a single injection of 200μg anti-PD-L1 mAb given i.v. 4 h after occlusion significantly reduced MCAO infarct volumes and improved neurological outcomes after 96 h reperfusion. Treatment partially reversed splenic atrophy and decreased CNS infiltrating immune cells concomitant with enhanced appearance of CD8+ regulatory T cells in the lesioned CNS hemisphere. Conclusions This study demonstrates for the first time the beneficial therapeutic effects of PD-L1 checkpoint blockade on MCAO, thus validating proposed mechanisms obtained in our previous studies using PD-1 and PD-L deficient mice. These results provide strong support for use of available humanized anti-PD-L1 antibodies for treatment of human stroke subjects.

SignificanceCXCL1 is a major neutrophil chemoattractant that binds to the chemokine receptor, CXCR2, on neutrophils and oligodendrocytes. Estrogen receptor β ligand treatment in a mouse model of multiple sclerosis induces an increase in peripheral and brain CXCL1 levels that correlate with an increase in axon remyelination. Oligodendrocyte progenitor recruitment and differentiation by CXCL1, in combination with attenuated IFN-γ production reducing apoptosis, may account for at least one avenue whereby estrogen receptor β ligands exert their clinical benefits.