The role of Pdx1-recruited Chd4:NuRD complex in controlling mature #-cell function

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PROJECT SUMMARY Pancreatic β-cells within the islets of Langerhans are required for glucose-stimulated insulin secretion and glucose homeostasis. Dysfunctional β-cell activity and identity results in diabetes, a growing disease affecting millions of Americans, thus creating an enormous fiscal and health burden. Strategies to improve outcomes for the mounting number of diabetic patients requires understanding the complex programs that coordinate a proper insulin release in response to changing blood glucose levels. Developing upon existing knowledge of how islet enriched transcription factors (TFs) coordinate signals that influence gene regulatory programs will allow us to understand how such programs are dramatically altered in islet β-cells of diabetes patients. Pdx1, one of the most important TFs in the developing and postnatal β-cell, has been shown to recruit a diverse set of coregulators which could potentially modulate its activity. This proposal is focused around how Pdx1 interactions with the Nucleosome Remodeling and Deacetylase (NuRD) complex are influential to normal β-cell function and are altered in pathophysiological conditions associated with the development of Type 2 diabetes (T2D). The central ATPase subunit of the NuRD complex, Chd4, was found to interact with and control a subset of Pdx1 target genes and is recruited to genes important for normal β-cell function in vitro. Preliminary studies demonstrate that conditional removal of Chd4 from mature islet β-cells significantly impacts glucose tolerance in vivo. This proposal will test the overall hypothesis that Pdx1-bound Chd4:NuRD complex controls chromatin accessibility and gene expression programs important for physiological β-cell function which are compromised during the development of diabetes. In Aim 1, we will fully characterize how β-cell dysfunction occurs due to the absence of Chd4 in a new conditional Chd4-deleted mouse model and in Aim 2 we will uncover the mechanistic actions of Chd4 in controlling chromatin accessibility and gene expression using unbiased genome-wide RNA-, ATAC- and ChIP-Sequencing approaches. The influence of Chd4:NuRD on human Pdx1 and β-cell action will be investigated. Aim 3 will evaluate how T2D associated stressors influence Pdx1:Chd4 interactions using biochemical and in situ methods from rodent and human islets, in vivo models of T2D and primary human tissues. Upon successful completion of this grant, we will have determined the mechanistic actions of Chd4:NuRD on controlling Pdx1 activity and β-cell function, and defined how stressors associated with diabetes development impact the vital Pdx1:Chd4 regulatory mechanisms. This research will identify critical targets that contribute to the pathogenesis of T2D, which will open new avenues for diabetes research.