Date of Award

Summer 2019

Document Type

Open Access Dissertation

Department

Biomedical Science

First Advisor

Mitzi Nagarkatti

Abstract

Obesity is an inflammatory disease involving accumulation of adipose tissue, gut microbiota dysbiosis, and over-activation of the endocannabinoid system (ECS). Mechanisms involved in ECS regulation of obesity-induced inflammation are not well understood. Presented here are three chapters involving microRNA (miR) regulation of inflammatory adipose tissue macrophages (ATM) during high-fat diet (HFD)-induced obesity and cannabinoid receptor-mediated regulation of gut microbiota dysbiosis.

ATMs are innate immune cells that drive chronic low-grade inflammation during obesity. Polarization between pro-(M1) and anti-(M2-like) inflammatory phenotypes influence insulin sensitivity and energy expenditure; however, the mechanisms involved are unclear. In study one, we characterized miRs involved in ATM polarization during diet-induced obesity (DIO). In study two, DIO mice were treated with the cannabinoid receptor 1 (CB1) antagonist AM251 because CB1 antagonists ameliorate DIO and associated inflammation. In both studies, it was found that the miR-30 family regulates ATM Delta-like-4 (DLL4)-Notch signaling, and consequently ATM polarization. Downregulation of miRs 30a-5p, 30c-5p, and 30e-5p in ATMs from DIO mice versus lean mice resulted in Notchsignaling induced M1 polarization. Interestingly, miR-30e-5p was upregulated in ATMs from DIO mice treated with AM251, while DLL4 was downregulated. Subsequently, fat storage and M1 ATM polarization was reduced. Furthermore, AM251-treated macrophages suppressed DLL4-mediated Th1 polarization in CD4+ T cells. The combined effect of miR-30 in ATMs and consequently T cells led to an anti-inflammatory state and attenuation of diet-induced obesity regulated by CB1 blockade.

In the third study, CB1-/- and CB2-/- mice as well as AM251 DIO intervention were used to investigate ECS regulation of DIO-associated gut dysbiosis. CB1-/- mice displayed resistance, whereas, CB2-/- mice displayed accelerated DIO development versus wild-type (WT) mice. Interestingly, CB1 and CB2 reciprocally regulated HFD-induced leukocyte infiltration in the cecal-colonic lamina propria. Microbiota profiling showed that CB1-/-, but not WT or CB2-/- mice were resistant to development of HFD-induced gut dysbiosis. Moreover, AM251 intervention in obese mice shifted their microbiota towards a lean profile. Investigation of host: microbiota interactions revealed ECS-mediated regulation of intestinal barrier defense and gut microbiota-mediated sugar metabolism were involved in the pathogenesis of obesity.

Available for download on Wednesday, August 18, 2021

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