| Diabetes is a growing public health challenge worldwide. Type-2 diabetes is the most common form of diabetes. The molecular basis of type-2 diabetes development is still elusive and a matter of debate. However, fatty acid accessibility and accumulation within skeletal muscle have been demonstrated to play a role. Therefore, the focus of this thesis was to (i) elucidate the cellular mechanisms by which palmitate availability induces insulin resistance and (ii) determine whether AICAR and/or leptin treatment ameliorate insulin resistance, and the mechanisms involved.; In initial experiments, it was determined that the isolated soleus muscle was suitable for long-term metabolic studies. This preparation remained metabolically viable for up to 18 h despite the presence of palmitate (2mM), as in this model ATP and PCr concentrations remained constant and the expression of key insulin signaling proteins was generally not altered.; The purpose of the second study of this thesis was to examine the mechanism(s) by which long-term exposure to a high concentration of palmitate induced insulin resistance in isolated soleus muscle. For this purpose, isolated soleus muscles were exposed to a high concentration (2mM) of palmitate for up to 18h. During this treatment, insulin-stimulated glucose transport was progressively reduced by a maximum of 100% at 18 h, to basal rates of glucose transport.; The purpose of the third study was to determine whether selected approaches, including complete removal of palmitate or activating AMPK (i.e. with AICAR or leptin) for the last 6 h of incubation, were able to rescue the experimentally-induced, insulin resistance in muscle. Complete removal of palmitate for the last 6 h of incubation failed to ameliorate the palmitate-induced insulin resistance. However palmitate-induced insulin resistance was completely, or almost completely, rescued by treatment with AICAR (2mM) and leptin (10mug/ml) during the last 6h of incubation, despite the presence of palmitate. This recovery in insulin-stimulated 3OMG transport, in both AICAR- and leptin-treated muscles, was largely due to an increased ability of insulin to induce the translocation of GLUT4 to the plasma membrane, involving the restoration of PKB/Akt functionality as measured by PRAS40 phosphorylation.; In summary, these studies have shown that isolated soleus muscles are a metabolically stable and responsive model in which to examine substrate metabolism (study 1). In addition, it was also shown that there is a close association between the impairment in the rate of fatty acid oxidation and the induction of insulin resistance (study 2), as well as between the recovery of fatty acid oxidation and the rescue of insulin resistance (study 3). (Abstract shortened by UMI.)... |
