Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Kaplan, Barbara L.F.

Committee Member

Ross, Matthew K.

Committee Member

Pruett, Stephen B.

Committee Member

Crow, John Allen

Committee Member

Gaunt, Patricia S.

Date of Degree

4-30-2021

Original embargo terms

Visible to MSU only for 1 year

Document Type

Dissertation - Campus Access Only

Major

Environmental Toxicology

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Department

Department of Comparative Biomedical Sciences

Abstract

The endocannabinoid system is composed of endocannabinoids (eCBs), their cognate receptors, and their biosynthetic and catabolic enzymes. Inhibition of serine hydrolases (catabolic enzymes), such as carboxylesterases (CES), might result in the accumulation of eCBs. eCBs, such as 2-arachidonoylglycerol (2-AG), have been shown to increase or reduce inflammation via engagement with cannabinoid receptors on immune cells. This research focuses on exploring the ability of eCBs and their metabolizing enzymes to regulate inflammation. First, a negative feedback mechanism between inflammation and the eCB system was examined by identifying serine hydrolases inhibited by lipopolysaccharide (LPS) stimulation in mice. Ces2g activity was inhibited and Il6 levels were induced in the murine spleen, suggesting a role for this enzyme in an inflammatory response, possibly to limit inflammation. IL-6 did not influence 2-AG hydrolytic activity in human peripheral blood mononuclear cells (PBMCs), but monocytic MAGL was shown to be the predominant 2-AG hydrolytic enzyme in these cells. To investigate a separate mechanism by which serine hydrolases and eCBs may regulate immune responses, mice were treated with chlorpyrifos (CPF), a pesticide known to inhibit serine hydrolases, at doses that do not inhibit acetylcholinesterase in the nervous system. This research is focused on lung tissue since epidemiologic studies have linked pesticide exposures to respiratory diseases. At low doses, Ces1c (adult and neonatal mice) and Ces1d (neonatal mice) were markedly inhibited by CPF (2.5 mg/kg, 7 d, PO). Stimulation with LPS (1.25 mg/kg, IP) following the final CPF dose produced minimal differences in lung immune responses to LPS. In follow up experiments utilizing wild-type and Ces1d-/- mice, a downregulation of Ces1c mRNA in adult Ces1d-/- mice corresponded to an upregulation of Tnfa mRNA in response to LPS in CPF-treated mice. Additionally, Ces1d was found to be expressed in murine alveolar macrophages, suggesting these cells could be used to study the role of CES1 in immunity. Overall, Ces enzymes appear to play a role in immune homeostasis either through a protective mechanism or a negative feedback mechanism to control inflammation.

Sponsorship

Mississippi State University College of Veterinary Medicine, NIH R15GM128206

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