SUN-216 Prolactin Regulates Chromatin Accessibility in Pancreatic Β-Cells

Abstract Disclosure: N. Ruiz Otero: None. J. Chung: None. R.R. Banerjee: None. Maternal pancreatic β-cells undergo functional and structural changes to adapt to increased metabolic demands during pregnancy. Lactogen signaling via the prolactin receptor (PRLR) contributes to these adaptations by increasing β-cell mass, insulin transcription and glucose-stimulated insulin secretion (Banerjee et al. 2016, Sorenson et al. 2009, Huang et al. 2009). Lactogen-responsive tissues, such as the mammary gland and certain hypothalamic nuclei, display gestationally-induced epigenetic changes, some of which persist after birth. We have previously found that prolactin treatment in islets regulates the expression of epigenetic modifiers, including the DNA methylation regulators DNA methyltransferase 3B (Dnmt3b) and growth and DNA damage inducible 45g (Gadd45g) (Pepin et al. 2019, unpublished data). However, whether lactogen signaling in β-cells mediates epigenetic changes to regulate chromatin accessibility had not been examined. Therefore, our objective was to determine whether PRLR signaling alters chromatin accessibility of β-cells to facilitate transcriptional regulation. We performed single cell ATAC-sequencing in murine islets treated with recombinant prolactin from wild type (C57BL/6J) or mice lacking β-cell PRLR (β-PrlrKO). We used RNA-sequencing of whole islets to correlate differentially accessible regions (DARs) to transcriptional changes regulated by PRLR signaling. We identified over 5500 DARs following prolactin treatment in wild type β-cells. In contrast, β-cells from β-PrlrKO islets treated with prolactin had ∼2800 DARs, compared to untreated controls; only 300 of which overlapped with DARs in wild types. We found 718 overrepresented motifs in DARs enriched in wild type but not β-PrlrKO β-cells. These included motifs bound by established PRLR signaling effectors such as the STAT family of transcription factors (TFs). Using RNA-sequencing we found transcriptional changes in 41 TFs whose motifs were overrepresented in DARs. These TFs included several previously linked to PRLR signaling within β-cells, including MYC, MAFB and ESR1 (Banerjee et al. 2016, Pepin et al. 2019). Interestingly, amongst the other TFs were c-Jun, EGR4, and MYC, which have been reported to bind DNMT3B (Loaeza-Loaeza et al. 2022), pointing at DNA methylation as a potential PRLR-dependent mechanism of chromatin remodeling and transcriptional regulation. We also identified several TFs not previously associated with PRLR signaling, including GLI3, ALX4, and OVOL2. In sum, we provide the first direct evidence that PRLR signaling regulates chromatin accessibility in β-cells. We identified 41 TFs whose motifs were enriched in DARs and transcriptionally regulated by prolactin treatment, encompassing both established TFs downstream of PRLR, and new candidate TFs to examine as mediators of epigenetic changes downstream of PRLR. Presentation: Sunday, July 13, 2025