NLRP3-caspase 1 and caspase 11-gasdermin D pathways jointly promote IL1β-mediated neuroinflammation and behavioral deficits in a rat model of psychosocial stress

Despite serious health and economic burden, borne more prominently by lower and lower middle-income countries, pharmacotherapy for common psychiatric disorders rely on drugs altering neurotransmission, with partial efficacies. The persistence of a chronic yet sub-threshold inflammation across the periphery and the brain is well documented in the patients and animal models of these disorders and can be investigated for augmenting pharmacotherapy. IL1β, a pleiotropic cytokine and a key regulator of neuroinflammation has been of particular interest in this regard. Previous studies on rodent models of anxiogenic stress show activation of a large multiprotein complex - the NLRP3 inflammasome, which increases IL1β production facilitated by caspase 1, through what is considered a canonical inflammasome activation pathway. However, there exists a second non canonical inflammasome activation pathway whose impact on IL1β release, inflammation and behavioral consequences remain unclear. Using rat models of physical and psychosocial stress, we observed stress-induced sex-specific upregulation of activated caspase 11 and gasdermin D N-terminal fragments, the mediators of the non-canonical inflammasome pathway that facilitates IL1β release through pore formations in the plasma membrane. This is the first report of non-canonical inflammasome pathway being activated in the brain and peripheral immune cells in response to psychosocial stress. Inhibition of caspase 11 with wedelolactone, or Gasdermin D cleavage with Disulfiram reduced stress-induced elevation of IL1β levels, anxiety and fear acquisition, facilitated fear extinction and recall, and improved working memory. Combination treatments targeting both canonical (ibrutinib for pBTK/NLRP3 or MCC950 for NLRP3 inhibition) and non-canonical (wedelolactone for caspase 11 or disulfiram for gasdermin D) pathways proved more efficacious in reducing stress-mediated neuroinflammation, dendritic spine elimination in the CA3 region of the hippocampus and behavioral dysfunction. Furthermore, psychosocial stress drove peripheral inflammation, in peripheral blood mononuclear cells, which was mitigated by the combination treatment. Taken together, this study reveals a novel mechanism underlying psychosocial stress involving both canonical and non-canonical inflammasome signaling to facilitate IL1β induction and behavioral changes. Our finding further suggests that combined targeting of the NLRP3 inflammasome and gasdermin D could contribute to the development of future transdiagnostic therapeutic targets for stress, anxiety, and depression.