Type 2 Diabetes (T2D) is a disease affecting more than 20 million people in the United States alone. T2D results from the proliferative and functional failure of the insulin-producing ?-cells within the Islets of Langerhans. Successful long-term treatment of T2D may require improvement in both performance and replication of ?-cells. FoxM1 is required for ?-cell replication postnatally and in the adult pancreas. I have previously shown male- specific restoration of aged ?-cell proliferative potential and enhanced insulin secretion in mice that inducibly express a constitutively active FoxM1. Although the mechanisms of these gender-specific effects in ?-cells are unknown, FoxM1 interacts with the estrogen receptor ? (ER?) at transcriptional sites in other cell types. Moreover, the functional targets as FoxM1 as well as its co-regulators and cooperative transcription factor binding partners at both proliferative and functional targets are relatively unknown and completely unexplored in the ?-cells. The experiments proposed here will remedy this dearth of knowledge.
In Aim 1 a, I will determine if FoxM1 and ER? are cooperative binding partners using MOW-ChIP in sorted proliferating and quiescent ?-cells from both male and female islets. I will then investigate the role of ER? during FoxM1-mediated enhanced insulin secretion using genetic and pharmacological inhibition of estrogen signaling.
In Aim 1 b, I will study whether FOXM1 is required for normal insulin secretion in EndoC-?H3 cells. I will identify functional targets of FoxM1 using RNA-Seq on ?-cells FACS-sorted from wild-type and FoxM1- deficient islets. I will then examine the potential roles of these targets downstream of activated FoxM1 in cultured mouse islets using pharmacological or genetic ablation.
In Aim 2, I will explore how FoxM1 distinguishes between proliferative targets, which are expressed in all tissues, and ?-cell-specific functional targets. To accomplish this Aim, I will implement de novo motif analysis by mining the MOW-ChIP data collected in Aim 1. I will also perform immunoprecipitation against FOXM1 in human islets to identify FOXM1 co-factors. Predicted and immunoprecipitated factors will be tested in human islets and pancreatic sections by Re-ChIP, proximity-mediated ligation assays, and assays to identify synergistic effects with FOXM1 on ?-cell function. The experiments proposed in this grant will test the overall hypothesis that FoxM1 upregulates genes that promote glucose-stimulated insulin secretion and that these functional genes are controlled differently than the cell-cycle progression genes controlled by FoxM1.
These Aims collectively will help identify potential druggable targets for future therapies in treating T2D.
In this proposal, ?Regulation of mature ?-cell function by the transcription factor FoxM1,? we will investigate how FoxM1 differentially regulates its targets in males and females. We will also examine the mechanism by which FoxM1 distinguishes between cell cycle genes and genes involved in ?-cell function. Finally, we will use discovery-based and hypothesis-driven approaches to find the functional targets of FoxM1 in the ?-cell.