We have (a) defined upstream activators of atypical protein kinase C (aPKC) and Akt during insulin action in muscle, adipocytes and liver and (b) showed that aPKC is required for insulin-stimulated increases in glucose transport in muscle and adipocytes and activation of lopogenic enzymes in liver. Also, in multiple rodent models of obesity (O) and type 2 diabetes mellitus (T2DM), we defined the following tissue-specific defects in insulin signaling factors: (a) aPKC activation is impaired in muscle and adipocytes in all O and T2DM models via diminished IRS-1-dependent phosphatidylinositol 3-kinase (PI3K) activation, but, in contrast, fully conserved in liver via IRS-2-dependent PI3K;and (b) Akt activation is impaired via diminished IRS-1/PI3K activation in muscle in most O and T2DM models, and in liver in all T2DM models. Selective conservation of hepatic IRS-2/aPKC activation in O and T2DM is problematic, as hyperinsulinemia therein causes excessive activation of sterol receptor element binding protein-1c (SREBP-1c), which increases expression of multiple enzymes that control hepatic lipid synthesis, and this upregulation provokes many """"""""metabolic syndrome"""""""" (MS) abnormalities. Indeed, using adenoviral-mediated expression methods, selective inhibition of hepatic aPKC in multiple O/MS and T2DM models elicits rapid and dramatic improvements in hepatosteatosis, hyperlipidemia, glucose intolerance, hyperinsulinemia, and insulin signaling in muscle and liver;also, as an added benefit, inhibition of hepatic aPKC surprisingly diminishes expression of glucogenic enzymes, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). In other words, hepatic aPKC inhibition has insulin-like effects on these hepatic enzymes that regulate blood glucose levels. Similarly, in preliminary studies, two newly discovered highly specific aPKC inhibitors preferentially inhibited hepatic aPKC and thereby diminished expression of hepatic enzymes that promote both lipid and glucose synthesis/release in both human hepatocytes and intact rodent liver;furthermore, in an mouse model of O/MS/T2DM, these biochemical agents selectively inhibited hepatic aPKC and this was attended by (a) a rapid and complete or nearly complete reversal of O/MS features, viz., abdominal obesity, hepatosteatosis, and hypertriglyceridemia and (b) restoration of insulin signaling in muscle, fat and liver, and normalization of serum glucose-lowering effects of insulin. Clearly, we need to further develop agents that selectively diminish aPKC activation in liver and thereby effectively control O/MS and T2DM. Accordingly, there is an urgent need to:
Specific Aim 1, define insulin signaling mechanisms and consequences of aPKC inhibition in human hepatocytes;
Specific Aim 2, elucidate molecular mechanisms for aPKC activation;
and Specific Aim 3, further develop our novel biochemical inhibitors of hepatic aPKC and define their metabolic effects in mouse O/MS/T2DM models. We are confident that the proposed studies will provide a new approach for effective treatment of O/MS and T2DM.
These findings will provide new avenues for finding treatments for the metabolic syndrome and type 2 diabetes, which together are estimated to cause at least 50% of the cardiovascular disorders seen in the US population, and which are exceedingly costly health issues.
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