Research Regulation of Mature Beta Cell Function by the Transcription Factor FoxM1

University Of Pennsylvania, Philadelphia PA

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Abstract

Abstract 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 1a, 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 1b, 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.