1243-P: The Chd4 Helicase Regulates Pdx1-Controlled Genes Involved in ß-Cell Function

Abstract

Diabetes progression is partly characterized by a loss of key transcription factors (TFs) in a subset of failing β-cells. Among these TFs is Pdx1, which coordinates the expression of numerous genes related to β-cell function (MafA, Ins2, Ucn3), mitochondrial function (Tfam), and calcium signaling (Cacna1d, Camkk2, Atp2a2). Pdx1 requires the recruitment of transcriptional coregulators to modulate its activity and has recently been shown to interact with the Chd4 ATPase subunit of the Nucleosome Remodeling and Deacetylase complex. In other cellular contexts, Chd4 is required to maintain cellular identity and mitochondrial function; however, the contribution of Chd4 in controlling Pdx1-target genes in the β-cell has yet to be explored. Here, we confirmed the Pdx1:Chd4 interaction using co-IP in mouse β-cell lines and proximity ligation assay in mouse and human β-cell lines and tissue. We found, by ChIP-Sequencing, that Chd4 binds to 4796 genes in β-cell lines, 4463 of which are also bound by Pdx1, including MafA, Cacna1d, and Atp2a2. Transient siRNA knockdown of Chd4 in the βTC-3 murine insulinoma cell line led to a reduction of MafA at the transcript (41% ± 3, p < 0.05) and protein level, as well as reduced expression of mitochondrial TF Tfam (39% ± 8, p <0.05) and calcium regulators Camkk2 (53% ± 6, p <0.05) and Serca2b (51% ± 13, p <0.05). Furthermore, glucose-stimulated insulin secretion in the INS1 832/13 rat insulinoma cell line was impaired (p = 0.0504) in Chd4 knockdown cells. We next generated a tamoxifen-inducible, β-cell-specific (MIP-CreERT) mouse knockout line of Chd4 and found significant impairment in glucose tolerance in male mice 2 weeks post-tamoxifen. Together, these data indicate Chd4 is required for the expression of numerous Pdx1-controlled genes important for β-cell function and whole-body glucose homeostasis. Future efforts are focused on defining the contributions of Chd4 in regulating gene expression and chromatin accessibility in β-cells using our β-cell-specific Chd4 knockout model. Disclosure R. K. Davidson: None. N. Casey: None. S. Kanojia: None. J. Spaeth: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (K01DK115633)