Exploring the Molecular Mechanisms of Sex Hormones and NRF2 in Rodent Diabetic Gastroparesis

• Main Author: Sprouse, Jeremy Charles
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2021
• Subjects: Neurosciences; Physiology
• ISBN: 9798383560754

Gastroparesis (Gp) is a multifactorial syndrome of abnormally delayed or rapidgastric emptying (GE). Although Gp is more prevalent (~80% of reported cases) in healthy and diabetic female patients, the role of endogenous ovarian hormones in Gp is elusive. Some evidence suggest that altered sex hormones, notably estrogens, and gastric neuronal nitric oxide synthase (nNOS) /nitric oxide (NO) synthesis in female rodents areresponsible for this observed sexual dimorphism. Moreover, increased oxidative stress is one of the leading causes for the development of diabetes mellitus. Nrf2 (NF-E2-related factor 2) is a redox-sensitive, transcriptional factor that upregulates antioxidant gene expression by binding to the promoter region of the antioxidant response element (ARE) to ultimately suppress elevated oxidative stress. With this fundamental understanding, wefirst hypothesized is that supplementation of sex hormones and/or their receptor agonists regulate nNOS mediated gastric emptying in streptozotocin and obesity-induced diabetic female rodents. Secondly, we hypothesize that activation of Nrf2 improves gastric estrogen receptors and nNOS mediated gastric motility in high fat diet (HFD) induced diabetic female. To prove the above hypotheses, we have employed well-versed methodologies using in vitro and in vivo rodent models.Results from our experiments indicate that in-vitro sex hormones/receptor agonists significantly (*p<0.05) restored Nrf2 and nNOSα expression in the gastric specimens exposed to in-vitro hyperglycemia (HG). Furthermore, our studies show that selective activation of estrogen receptor beta(ERβ) slowed gastric emptying rates, while improving nitrergic function in healthy adult ovariectomized (OVX) mice to suggest that female stomachs depend on elevated levels of endogenous sex hormones to maintain slower gastric emptying. Additionally, we examined the effects of OVX and HFD on metabolic homeostasis, solid gastric emptying, nNOS -mediated gastric relaxation, systemic hormone and total nitrite levels, and neuronal nitric oxide synthase (nNOSα) and its cofactor synthesis proteins levels in various groups of female mice. Our results show that obesity and chronic loss of hormones significantly delayed GE and impaired nitrergic function when compared to healthy sham mice (p<0.05). The combination of OVX and HFD exacerbates glycemia and insulinemia, while accelerating GE (p<0.05) though nitrergic relaxation was impaired. Exogenous estradiol (E2), but not progesterone (P4),attenuated rapid GE and nitrergic relaxation while elevating total nitrite and gastric nNOSαexpression in OVX+HFD mice. Next, we examined whether activation of Nrf2 by cinnamaldehyde (CNM) restores delayed gastric emptying in HFD mice. Our data show that supplementation of CNM attenuated (p<0.05) DGE. CNM (1) normalized serum estradiol-17β levels, (2) induced gastric nNOS/Nrf2 and phase II antioxidant enzymes. These findings emphasize the importance of Nrf2 in maintaining nNOSα mediated GE and may have a translational relevance to treat obese/diabetic gastroparesis in women. Taken together, our findingssuggest that sex hormones may regulate nitrergic function via their gastric receptors by improving NRF2/BH4/nNOS expression in health and diabetes. Within this dissertation, we categorized studies into separate, yet related specific aims to uncover the differences in healthy, and diabetic gastric motility in female rodents.