Targeting Insulin Resistance by Estrogen Receptor in Control of Type 2 Diabetes Mellitus

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Project Summary This proposal “Targeting Insulin Resistance by Estrogen Receptor in Control of Type 2 Diabetes Mellitus” addresses a fundamental mechanism based on the gender difference in control of type 2 diabetes. The gender difference exists for the incidence of T2D, with improved insulin sensitivity and survival in females, but the mechanism is unclear. Sex hormone estrogen and its receptor system have shown benefit to metabolic function. This proposal will address the molecular and physiological mechanism by which estrogen and insulin signaling crosstalk at the level of IRS1 and IRS2 proteins and downstream protein kinase Akt and forkhead transcription factor Foxo1 that controls mitochondrial biogenesis and function through the heme oxygenase 1 (HO1) gene. The O-class of the forkhead transcription factor Foxo1 is a key downstream target of the insulin→PI3K→protein kinase B (Akt) signaling pathway, governing multiple physiological functions. Our previous studies have demonstrated Foxo1 is a key substrate of Akt downstream from both insulin and estrogen signaling that controls glucose homeostasis via glucose-6-phosphatase gene expression. Foxo1 also stimulates expression of heme-oxygenase-1 (HO1) that catalyzes degradation of heme, a key component of mitochondrial electron transport chains, then reducing mitochondrial biogenesis and function. In this proposal, we hypothesize that insulin and 17-beta-estradiol (E2) play important roles in activation of PI3K-Akt and suppressing Foxo1-HO1 in control of mitochondrial function, while loss of IRS1/2 and estrogen receptor-alpha (ERα) signaling and resultant HO1 overexpression are fundamental and unifying mechanisms for mitochondrial dysfunction that promotes meta-inflammation. In Aim 1, we use the liver-specific ER-alpha gene knockout mice in insulin resistant mice and examine whether ERα gene is required for IRS1, 2 and associated PI3K-AKT activation and suppression of Foxo1 and HO1 in the liver. In Aim2, we will use protein- protein interaction assays to map out the key domain of ERα for interaction with IRS1 and IRS2, activating PI3K-Akt and inhibiting Foxo1-HO1 in cells. We test the hypothesis that either N-terminal ERα without DNA binding domain (DBD) interacts with IRS1/2, preventing IRS1/2 serine phosphorylation coupled degradation, suppressing Foxo1 and HO1 in cells. In Aim 3, we will use adenovirus-mediated gene expression of N-terminal domain ERα in HFD-fed mice to examine whether there is achievable hepatic protection by activation of IRS- associated PI3K and suppression of Foxo1 and HO1. Moreover, we will target HO1 with nanoparticle-mediated HO1 inhibitor (Zn2+-protoporphyrin) in the liver of mice lacking IRS1/2 and ERα or high fat-diet (HFD)-induced insulin resistance. We will examine whether HO1 inhibition sufficiently protects hepatic mitochondrial dysfunction and inflammation in insulin resistant mice. Therefore, this proposal will provide novel mechanisms of ERα and HO1 in insulin sensitizing and approaches of therapeutic development for insulin sensitizers in the treatment of type 2 diabetes.