The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) act through cannabinoid CB1 and CB2 receptors, and are inactivated by a two-step process: Both are transported into cells, and then anandamide is hydrolyzed by fatty acid amide hydrolase (FAAH) and 2-AG by monoacylglycerol lipase (MGL). Selective inhibition of either FAAH or MGL results in the accumulation of either anandamide or 2-AG, respectively, and in non-overlapping therapeutic effects. In a study funded by a NIDA-CEBRA grant, we found that the microglial cell line, BV-2, does not express MGL and yet efficiently hydrolyzes 2-AG, suggesting the existence of a new 2-AG-hydrolyzing enzyme that could be targeted for the treatment of pathologies associated with neuroinflammation. In collaboration with Ben Cravatt, we used a functional proteomics approach and identified ABHD6 as a candidate enzyme for 2-AG hydrolysis in BV-2 cells. More recently, we used shRNA knockdown and a newly developed ABHD6 inhibitor and showed that this enzyme plays a major role in 2-AG hydrolysis in both BV-2 cells and neurons. Because Hungtington's disease (HD) is associated with an early down-regulation of CB1 receptors and a chronic neuroinflammatory response, inhibiting ABHD6 might represent a valid therapeutic approach to treat this degenerative disease. In this grant proposal, we outline experiments designed to: 1) Map ABHD6 expression and activity in healthy and HD mice brains, 2) Determine the pharmacological profile of ABHD6 and develop novel inhibitors 3) Test if ABHD6 controls 2-AG signaling in microglia and neurons, and constitutes a valid target for treating HD mice. The completion of these three aims will provide a comprehensive understanding of the expression, activity and role of ABHD6 in microglia and neurons in healthy and degenerating brain. Our long-term goal is to generate pharmacological and genetic tools that selectively inhibit endocannabinoid inactivation as means to develop therapeutics that lack the abuse liability and adverse effects produced by cannabinoid agonists.
In this grant proposal, we outline experiments designed to 1) Map the expression and activity of the novel endocannabinoid-hydrolyzing enzyme, ABHD6, in the brains of healthy mice, and of two mice models of Huntington's disease, 2) Determine the pharmacological profile and develop inhibitors of this novel enzyme and 3) Test its role in controlling endocannabinoid's ability to regulate microglial and neuronal cell functions, and whether its inhibition affects disease progression in a mouse model of Huntington's disease.
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