204-OR: The Chd4 Helicase Modulates ß-Cell Function In Vivo

Abstract

During diabetes progression, a subset of failing β-cells incurs a loss of transcription factors (TFs) such as Pdx1, which drives expression of numerous β-cell functional genes including Ins2, MafA, and Slc2a2. Like other TFs, Pdx1 requires the recruitment of transcriptional coregulators to modulate its transcriptional activity. It has been established that the Pdx1-bound Swi/Snf complex plays a critical role in maintaining β-cell function in part by recruiting Pdx1 to the insulin gene and facilitating its transcription. Furthermore, interactions between Pdx1 and the Swi/Snf ATPase subunit Brg1 are reduced in type 2 diabetes (T2D) β-cells. Recently, through an IP-Mass Spec approach, Pdx1 has been shown to interact with numerous other coregulatory complexes, including the Chd4 ATPase subunit of the Nucleosome Remodeling and Deacetylase complex. Here, we confirmed Pdx1 and Chd4 interact in mouse and human β-cell lines and primary β-cells using co-immunoprecipitation and proximity ligation assays (PLA) . Tissue harvested from mice injected with glucose had more β-cell nuclei containing multiple PLA signals than tissue from fasted mice. Conversely, tissue from high-fat diet mice and T2D human donors had fewer β-cell nuclei containing multiple PLA signals than tissue from control mice and nondiabetes human donors. To investigate the role of Chd4 on mature β-cell function, we generated a tamoxifen inducible, β-cell-specific Chd4 knockout mouse model (Chd4 Δβ ) . Four weeks following Chd4 removal, Chd4 Δβ mutants were glucose intolerant and had elevated ad libitum fed blood glucose levels and impaired insulin secretion from isolated islets. Bulk mRNA-sequencing from flow-sorted lineage labeled Chd4Δβ β-cells identified 1093 upregulated genes (eg Adcy1 and Rapgef3) and 438 downregulated genes (eg MafA, Robo2, and Slc2a2) . Future efforts are focused on defining the mechanisms by which Chd4 controls gene expression in the β-cell, with a current focus on how Chd4 modulates chromatin accessibility and TF recruitment. Disclosure R.K.Davidson: None. N.Casey: None. S.Kanojia: None. J.Spaeth: None. Funding National Institutes of Health (K01DK115633) Showalter Trust Award