NYMC Student Theses and Dissertations

Date of Award

5-22-2019

Document Type

Doctoral Dissertation - Restricted (NYMC/Touro only) Access

Degree Name

Doctor of Philosophy

Department

Basic Medical Sciences

First Advisor

Dr. Michal L. Schwartzman

Abstract

Studies in humans and animal models have shown that levels of 20-Hydroxyeicosatetraenoic acid (20-HETE), the omega-hydroxylation product of arachidonic acid, positively correlate with body mass index, hyperglycemia and plasma insulin levels. In the present study, we seek to identify a causal relationship between 20-HETE and obesity-driven insulin resistance using two distinct transgenic mouse models with overexpression of Cyp4a12-20-HETE-synthase. These include the Cyp4a14 knockout (Cyp4a14-/-) mice which is an androgen-driven model of 20-HETE overproduction and the Cyp4a12 transgenic mice (Cyp4a12tg) which is an androgen-independent doxycycline (DOX)-inducible model of 20-HETE overproduction. Cyp4a14-/- male mice were fed a regular control (CD) or high-fat diet (HFD) for 15 weeks. 20-SOLA [2,5,8,11,14,17-hexaoxanonadecan-19-yl20-hydroxyeicosa-6(Z),15(Z)-dienoate], a 20-HETE antagonist, was administered from week 0 or week 7 of HFD. HFD-fed Cyp4a14-/- male mice gained significant weight (16.7 ± 3.2 vs. 3.8 ± 0.35 g, P < 0.05) and developed hyperglycemia (157 ± 3 vs. 121 ± 7 mg/dl, P < 0.05) and hyperinsulinemia (2.3 ± 0.4 vs. 0.5 ± 0.1 ng/ml, P < 0.05) compared with corresponding CD-fed mice. 20-SOLA attenuated HFD-induced weight gain (9.4 ± 1 vs. 16.7 ± 3 g, P < 0.05) and normalized the hyperglycemia (157 ± 7 vs. 102 ± 5 mg/dl, P < 0.05) and hyperinsulinemia (1.1 ± 0.1 vs. 2.3 ± 0.4 ng/ml, P < 0.05). The Cyp4a12tg mice in which 20-HETE overproduction occurs in response to DOX were fed either i) control diet (No Dox + CD); ii) high-fat diet (No Dox + HFD); iii) control diet with doxycycline (Dox + CD); or iv) high-fat diet with doxycycline (Dox + HFD) for 15 weeks. 20-SOLA was administered in drinking water from week 0 of HFD (Dox or No Dox). Dox + HFD-fed mice gained significant body weight compared to regular diet-fed mice (20.63 ± 2.9 vs. 3.75 ± 0.6 g, P < 0.05) or mice receiving HFD alone (20.63 ± 2.9 vs. 13.51 ± 0.94 g, P < 0.05). Mice fed HFD with doxycycline developed hyperglycemia (144 ± 3.53 vs. 101.2 ± 6.1 mg/dl, P < 0.05) and hyperinsulinemia (2.52 ± 0.58 vs. 0.55 ± 0.10 ng/ml, P < 0.05) compared to CD-fed mice. However, this effect was not seen in mice fed HFD without doxycycline. 20-SOLA attenuated HFD-induced weight gain (11.37 ± 1.78 vs. 20.63 ± 2.9 g, P < 0.05) and normalized the hyperglycemia (104.2 ± 9.13 vs 144.4 ± 3.53 mg/dl, P < 0.05) and hyperinsulinemia (0.71 ± 0.09 vs 2.52 ± 0.58 ng/ml, P < 0.05) in animals receiving doxycycline. 20-SOLA did not change body-weight gain, plasma glucose levels or plasma insulin levels in animals fed a HFD without doxycycline.

Both transgenic mice overexpressing Cyp4a12-20-HETE synthase, viz. the Cyp4a14-/- and the Cyp4a12tg mice, displayed HFD-induced impairment of glucose homeostasis and insulin resistance evident by reduced insulin and glucose tolerance which was ameliorated by 20-SOLA treatment. HFD feeding to transgenic mice overexpressing Cyp4a12-20-HETE synthase resulted in a significant increase in circulatory and adipose tissue 20-HETE levels correlating with impaired insulin signaling, including reduction in insulin receptor tyrosine (Y972) phosphorylation and increased serine (S307) phosphorylation of the insulin receptor substrate-1 (IRS-1). 20-SOLA treatments prevented changes in insulin signaling. These findings indicate that 20-HETE contributes to HFD-induced obesity, hyperglycemia and insulin resistance, possibly by interfering with insulin signaling and glucose homeostasis.

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