Browsing M.Sc. Applied Health Sciences by Subject "Thermogenesis"
Now showing items 1-2 of 2
Low-Dose Lithium as a Therapy for High-Fat Diet Induced Obesity: A Burning Topic in Metabolic Research and Adipose Tissue BrowningThe prevalence of obesity is rising at an alarming rate around the globe. As a way to combat obesity, the activation of white adipose tissue thermogenesis has been a burning topic in metabolic research. Recent findings from our lab demonstrate that this thermogenic program is inhibited by a protein kinase known as glycogen synthase kinase 3-β (GSK3β); and the inhibition of GSK3β provides a mechanism to activate adipose tissue browning. Lithium (Li) is a well-known inhibitor of GSK3β and also a known sensitizer of insulin signalling. Our previous work has demonstrated that low dose lithium inhibits GSK3β and induces adipose browning in healthy male chow-fed mice. The purpose of this thesis was to examine the efficacy of low-dose lithium supplementation to inhibit adipose tissue GSK3β to activate the browning process to overcome the effects of high-fat diet (HFD) induced obesity and insulin resistance. 72 male C57BL/6J mice were divided into three experimental groups: 1) control (CON; n=24), 2) HFD (60% fat; n=24), and 3) HFD supplemented with a low-dose of lithium in their drinking water (10mg/kg body weight/day; HFD+Li; n=24) for 12 weeks. Inguinal white adipose tissue (iWAT), epididymal white adipose tissue (eWAT), and interscapular brown adipose tissue (BAT) were collected and underwent western blot and histological analysis. Lithium supplementation did not blunt the diet induced gain in body mass with the HFD. However, the HFD+Li mice ingested more calories than the HFD mice indicative of decreased metabolic efficiency. Lithium supplementation blunted the initial spike in a glucose tolerance test but exhibited no effects on insulin sensitivity at the whole body or tissue specific level. Lithium supplementation did not blunt the HFD induced reduction in GSK3β inhibition (Ser9) in iWAT, however, in eWAT the HFD+Li mice demonstrated higher GSK3β inhibition. Additionally, mitochondrial markers such as PGC-1α and cytochrome C were higher in HFD+Li eWAT compared to control, with cytochrome C being higher compared to HFD mice. This data provides evidence that low-dose lithium supplementation alone can increase the thermogenic program in visceral WAT depots but may not be robust enough to increase thermogenesis in subcutaneous WAT depots under HFD conditions.
Low-dose lithium supplementation and SERCA uncoupling in C2C12 cells and murine skeletal muscle.Adaptive thermogenesis is a cellular process that accelerates energy expenditure while increasing heat production in response to prolonged cold exposure or caloric excess. The prevalence of obesity along with its comorbidities is continually rising. Obesity is a result of energy intake superseding energy expenditure, however, a balance between energy intake versus energy expenditure is key in weight maintenance. Therefore, enhancing adaptive thermogenesis may be relevant in combatting diet-induced obesity. Skeletal muscle via sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) uncoupling and brown/beige adipose via mitochondrial uncoupling are the two sites for adaptive thermogenesis in mammals. Recent evidence has shown that glycogen synthase kinase 3 (GSK3) negatively regulates adipose-based thermogenesis by repressing uncoupling protein-1 expression in brown adipocytes. However, to our knowledge, no studies have examined whether GSK3 also negatively regulates muscle-based thermogenesis via SERCA uncoupling. The SERCA pump catalyzes the active transport of 2 Ca2+ ions into the sarcoplasmic reticulum per 1 ATP hydrolyzed under optimal conditions. Sarcolipin (SLN), an uncoupler of SERCA makes Ca2+ transport less efficient by reducing SERCA coupling ratio. The objective of this thesis was to determine whether GSK3 inhibition with low dose lithium (Li) supplementation can increase SLN expression and promote SERCA uncoupling in both C2C12 cells and in murine soleus muscle. Our results show that in C2C12 cells, 0.5mM LiCl promotes GSK3 inhibition and SERCA uncoupling via an increase in ryanodine receptor (RYR) but not SLN. In contrast, soleus muscles from chow-fed and lithium supplemented mice did not result in any notable changes in SERCA coupling ratio or the content of SERCA associated proteins. We next determined whether this would differ under an added stress of a high-fat diet. Our results show that soleus homogenates of HFD+Li supplemented mice have significant reductions in SERCA coupling ratio compared with HFD alone, which was presumably due to an increase in SERCA uncoupling proteins SLN and NNAT. Altogether these data suggest the potential role of GSK3 inhibition via low dose lithium supplementation in activating muscle-based thermogenesis, particularly under the stress of a HFD.