Connexin 43 Hemichannel Blockade in an Experimental Mouse Model of Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is a chronic, demyelinating, and inflammatory disease of the central nervous system that at present has no cure. Current therapeutics used to treat disease onset, progression, and symptoms, are often associated with an array of limitations impeding their administration and prolonged use. Newer therapeutics are required to help diminish current limitations while providing a safe enduring therapeutic effect. Blockade of connexin 43 (Cx43) hemichannels has been seen to prevent NLRP3 inflammasome activation and the secretion of a number of pro-inflammatory cytokines through obstructing numerous signalling components required for the inflammasome activation. The exact role of Cx43 in MS is not clear but may serve as a potential new therapeutic target for reducing disease severity and progression. In this study we conducted fluorescent immunohistochemistry using the experimental autoimmune encephalomyelitis (EAE) mouse model of MS to examine the effects of the Cx43 hemichannel blocker, tonabersat, on inflammation and NLRP3 inflammasome activation in the mouse corpus callosum, motor cortex and striatum. 3,3’-diaminobenzidine immunohistochemistry using post-mortem human MS inferior parietal lobe tissue was also performed to examine and broaden the understanding of inflammation and Cx43 expression in the human brain. We observed that EAE mice presented a high level of inflammation and had a severe clinical behavioral outcome, whilst EAE mice treated with tonabersat showed both an inflammatory profile and clinical behavioral outcome highly analogous of control mice. No significant differences of Cx43 expression were seen between the experimental arms. Analysis of NLRP3 expression reveled tonabersat treated mice appeared to have a diminished expression of NLRP3 relative to EAE mice, proposing that tonabersat has some effect in NLRP3 inflammasome inactivation and possibly in reducing the secretion of pro-inflammatory cytokines. We further observed that lesions in the human MS inferior parietal lobe showed a substantial level of gliosis and an upregulation of Cx43 relative to perilesional areas, which typically showed less inflammation and a downregulated expression of Cx43. In conclusion, we have demonstrated for the first time that Cx43 hemichannel blockade in a mouse model of MS reduces inflammation and inflammasome activation, overall alleviating the clinical outcome. These findings suggest tonabersat may be a potential pharmacological candidate for the treatment of MS.