Chronic obesity has pathologic consequences throughout the body including multi-organ insulin resistance (IR). Nonalcoholic fatty liver disease (NAFLD) is closely associated with hepatic IR. NAFLD can progress to end stage liver disease, but also contributes to development of Type II diabetes and cardiovascular diseases. The liver is the primary site of lipoprotein secretion and glucose output, which maintain macronutrient homeostasis within the body. These processes are localized to hepatocytes of the liver and are primarily under hormonal control by insulin and glucagon. Integrins are the primary signaling relays for the extracellular matrix (ECM), but also mediate cellular responses to endocrine and growth factor signals. Interestingly, ECM expansion and modified response to metabolic hormones are hallmarks of obesity in many tissues. Mechanisms linking integrin signaling to insulin sensitivity remain poorly understood but may represent novel therapeutic avenues for a number of pathologic conditions. High fat (HF)-fed mice have altered expression of several integrin signaling components including integrin-linked kinase (ILK). ILK links the intracellular tail of integrin receptors to various signaling components. The role of ILK in hepatic insulin sensitivity and metabolic functions remain unexplored. My preliminary data demonstrates that mice with hepatocyte-specific knockout of ILK (hILK-KO) have lower fasting blood glucose, lower plasma insulin, depleted liver glycogen, and improved glucose tolerance (GT) compared to their wild type (WT) littermates. I have also shown that hILK-KO mice are protected from hepatic insulin resistance (IR) during diet induced obesity.
Specific Aim 1 will test the hypothesis that ILK stimulates gluconeogenesis in the liver in vivo. ILK dependent gluconeogenesis also contributes to hepatic insulin resistance during obesity, which is reversed in hILK-KO mice. I will utilize novel metabolic flux modeling techniques developed within our lab to elucidate specific pathways contributing to metabolic improvements in hILK-KO mice. Furthermore, hILK-KO mice fed a HF diet for sixteen weeks have improved hepatic insulin sensitivity during hyperinsulinemic- euglycemic clamp compared to WT littermates. I will also determine the regulation of metabolic pathways that contribute to this insulin sensitivity phenotype.
In Specific Aim 2, I will test the hypothesis that ILK controls hepatocyte glucose production through a novel signaling axis of ILK-liver kinase B1 (LKB1)-adenosine monophosphate activated kinase (AMPK). Mice possessing hILK-KO have an increased phosphorylation of AMPK after a 5 hour fast. Activation of this enzyme is confirmed by a parallel increase in the AMPK downstream target acetyl-CoA carboxylase. By implementing pharmacologic, genetic, and bioenergetics tools in primary hepatocytes of hILK-KO and WT mice I will determine the role of AMPK in decreased glucose output of hILK-KO livers. Finally, I will explore the mechanistic link between ILK and AMPK through potential regulation of the AMPK upstream kinase, LKB1.
6 Insulin resistance (IR) contributes to pathologic conditions such as type II diabetes, cardiovascular disease, and nonalcoholic fatty liver disease (NAFLD). The extracellular matrix (ECM) is critical in mediating cellular function, but is compromised in multiple organs during these pathologies. Models of altered ECM signaling by their integrin receptors will elucidate ECM contributions to development of IR in the liver.
