The energy-regulatory network of the hypothalamus controls the everyday balance of food intake and energy expenditure. The close proximity of this region to the leaky blood brain barrier (BBB) enables many factors such as hormones to regulate energy homeostasis. This thesis aimed to determine the role of glucocorticoids (Gcs) within the hypothalamus in a model of Gc excess. Recent research has shown that high-fat diet (HFD) induces hypothalamic inflammation, which is detrimental to the energy-regulatory network. Over a series of time-points, the hypothalamic expression of Pomc, Npy, and Agrp were quantified and a decrease in orexigenic neuropeptide expression was observed after 4 and 20 weeks. In contrast to predictions, Pomc was also decreased after 20 weeks. At all time-points, the mRNA expression of inflammatory markers was too low to detect, however after 20 weeks, microglia morphology indicated activation. Mice gained weight throughout the study, but it is unclear whether the very low hypothalamic inflammation contributed to the development of obesity. The pleiotropic actions of Gcs enable them to be used as a treatment for a wide number of conditions, including inflammatory diseases, such as rheumatoid arthritis. Long-term Gc treatment is recognised to cause adverse metabolic side- effects including increased body weight gain and hyperphagia. In order to establish the role of hypothalamic Gcs in the development of Gc-induced metabolic syndrome, mice were treated with either corticosterone (Cort) or vehicle (1% EtOH) in the drinking water alongside a HFD or chow for 4 weeks. Exogenous Cort treatment induced a metabolic phenotype as food intake, body weight, and fed glucose increased during the study. Cort treatment also increased hypothalamic corticosterone levels after 24 hours, which remained elevated after the four week treatment period. HFD+Cort treatment exacerbated this effect, despite HFD alone not altering hypothalamic corticosterone levels. To determine the role of Gcs within the mediobasal hypothalamus (MBH) in the development of Gc-induced obesity and hyperphagia, Cre-lox technology was used to knockdown the glucocorticoid receptor (GR) in the MBH. To ensure that the Cre recombinase enzyme was functional, Cre and YFP expression were co- located within the MBH of AAV-Cre injected ROSA26-EYFP mice. Although the successful injection of AAV-Cre in GR flox mice should reduce GR expression, the low sensitivity of qRT-PCR in micro-punch and laser capture micro-dissections and dual immunofluorescence prevented confirmation of GR knockdown. After 3 weeks Cort treatment, a number of GR flox mice injected with AAV-Cre had a reduced gain in body weight and food intake. Furthermore, AAV-Cre injected GR flox mice were phenotypically monitored over a 6 month period without Cort treatment. These mice did not gain as much weight over time, suggesting that central Gc actions are important in the control of every day energy homeostasis. Collectively, this study has shown that Gcs acting within the hypothalamus have a significant role in the regulation of energy homeostasis. Further investigations will enable the development of co-therapies or âdrug holidaysâ to prevent the negative metabolic sequelae associated with Gc therapies.
|Date of Award
|31 Dec 2017
- The University of Manchester
|Anne White (Supervisor) & Catherine Lawrence (Supervisor)