Cannabinoid inhibition of CNS inflammasome activation via modulation of the gut-brain axis

ABSTRACT The primary objective of this proposal is to investigate Cocaine/HIV/SIV induced changes in inflammasome activation and their epigenetic regulation in the intestine and brain and its modulation by long-term, low-dose cannabinoids and combination antiretroviral therapy. The NLRP3 (NOD-like receptor family, pyrin domain containing) inflammasome is a multiprotein complex that elicits an innate immune response to infection and cell stress through activation of caspase-1 and processing of pro-interleukin-1β (pro-IL-1β) and pro-IL-18 to the bioactive IL-1β and IL18, respectively. Cocaine induces expression of inflammasomes and their associated genes in chronic HIV/SIV infection leading to persistent CNS and gastrointestinal tract (GIT) inflammation, which contributes to microbial translocation, immune activation, and HIV disease progression. Nevertheless, the epigenetic regulation of HIV/SIV and cocaine-induced inflammasome activation and its modulation remains unknown and needs to the investigated to better understand disease pathogenesis. Therefore, here we propose that supplementing 9-THC along with cART may reduce cocaine-induced inflammasome activation, dysbiosis, restore immune function, and slow HIV/SIV disease progression by modulating DNA methylation and gene expression. Our preliminary data showed marked to significant upregulation of caspase-1, gasdermin and NLRP6 inflammasome gene expression in basal ganglia (BG) and colonic epithelium (CE), respectively of chronically SIV-infected rhesus macaques. Interestingly, increased NLRP6 gene expression in CE was accompanied by extensive CpG promoter hypomethylation of up to 12 CpG sites. More importantly, long-term 9-THC administration significantly reduced CASP1 and IFN stimulated gene expression in BG and NLRP6 DNA hypomethylation in CE. Therefore, we will test the central hypothesis that a) aberrant DNA hypomethylation of inflammasomes and their associated genes in cocaine induced during chronic HIV/SIV infection results in their elevated expression leading to persistent CNS and GIT inflammation, which in turn contributes to microbial translocation, immune activation (microglial and T cells), and HIV disease progression; b) combining cART with low-dose of THC as a therapeutic may reduce cocaine-induced inflammasome activation, gut dysbiosis, and restore immune function. In order to test this hypothesis, we have proposed three specific aims. We will first investigate epigenetic mechanisms underlying cannabinoid-mediated reduction of cocaine-induced inflammasome activation in blood monocytes, brain, and CE during chronic SIV infection (aim 1). Next, we will determine the ability of THC administered in conjunction with cART to reverse cocaine-induced dysregulation of the microbiota-gut-brain axis (aim 2) and finally identify potential molecular mechanisms associated with THC counteraction of cocaine-induced DNA hypomethylation and inflammasome activation in in vitro cultured microglia, and CE cells (aim 3). The new findings from these studies will have important therapeutic implications for immune modulation in not only HIV but also other chronic intestinal inflammatory/neurodegenerative disease.