Endocannabinoid System Control of Mucosal Function in Health and Disease
The endocannabinoid (eCB) system is a complex lipid signaling system consistent of the endogenously produced ligands, 2-arachidonoyl-sn-glycerol (2-AG) and anandamide (AEA), which signal along the cannabinoid receptors [cannabinoid receptor subtype-1 (CB1R), -2 (CB2R) and others] and the enzymes which produce and degrade 2-AG and AEA. The eCB system is expressed throughout the human body controlling a wide variety of homeostatic functions. It was previously reported that blockade of host peripheral CB1R signaling exacerbated metrics of infection with the soil-transmitted nematode Nippostrongylus brasiliensis (N. brasiliensis). Therefore, I hypothesized that host CB1R signaling is protective in host-helminth interactions using N. brasiliensis as a model for hookworm infection in rodents. This study identified that peripheral blockade of CB1R, but not CB2R, lead to significant increases in lung tissue damage, lung hemorrhaging, and lung eosinophilia in response to N. brasiliensis infection with no changes in parasite burden. Because N. brasiliensis can produce eCBs at a quantifiable levels, I developed novel enzyme assays to quantitate enzyme activity for the biosynthetic and degradative eCB enzymatic machinery, including a novel assay to determine the rate of AEA metabolism which does not require the use of radioactive materials. These methods identified that the enzyme alpha/beta hydrolase domain containing-6 contributes to ~55% of all monoacylglycerol metabolism in the lungs of rodents. Furthermore, when these methods were applied to a mouse model of diet induced obesity (DIO) in the large intestine, I found that the eCB system of the colon is severely dysregulated in response to DIO and that mice lacking intestinal epithelial CB1R signaling have exacerbated metrics of diet-induced gut-barrier dysfunction in the large intestine. Furthermore, the RNA expression/regulation in the colon mucosa of the DIO mice lacking intestinal epithelial CB1R signaling is dysregulated with a decrease in tight-junction protein RNA expression and an increase in the inflammatory profile. These studies suggest a potential role for the eCB system in several disease models in mucosal tissues providing novel methods for quantitation of eCB metabolism and evidence that CB1R signaling has a strong role in inflammatory processes.