β-Cell adaptation to metabolic stresses requires prolactin receptor signaling

β-Cell adaptation to maternal insulin resistance of pregnancy involves upregulation of β-cell mass and function, a process we previously showed depends on prolactin receptor (PRLR) signaling. Emerging evidence in humans suggests that prolactin signaling may also influence β-cell function beyond pregnancy. This study aims to investigate how postpregnancy metabolic stress-specifically the combined effects of prior pregnancy followed by high-fat diet (HFD) exposure-impacts β-cell function, with a focus on the role of PRLR. In this study, we found that multiparous transgenic female mice with β-cell-specific PRLR deletion (<i>βPrlr</i>^-/-) have impaired glucose tolerance when challenged with HFD. Unlike in pregnancy, where PRLR signaling upregulates β-cell proliferation and mass, we observed no difference in β-cell mass between the wild-type (<i>βPrlr</i>^+/+) and mutant (<i>βPrlr</i>^-/-) mice when metabolically stressed with HFD. However, <i>βPrlr</i>^-/- mice showed blunted first-phase insulin release in vivo when challenged with glucose orally but not intraperitoneally, suggesting an impaired incretin effect. Moreover, there is a reduction in the expression of incretin hormone receptor, <i>Glp-1r</i>, and several of its upstream regulators, such as <i>E2f1</i>, <i>Nkx6.1</i>, <i>Pax6</i>, <i>Pparγ</i>, and <i>Tcf7l2</i>. Interestingly, isolated islets from <i>βPrlr</i>^-/- mice showed intact in vitro glucose-stimulated insulin secretion (GSIS) but impaired incretin-potentiated GSIS. Islets from <i>βPrlr</i>^-/- mice also had a lower insulin content and expressed lower levels of genes that regulate glucose metabolism. Together, these results suggested that PRLR signaling plays an important role in preserving β-cell function in mice exposed to metabolic stress by maintaining incretin receptor expression and insulin secretory capacity in β-cells.<b>NEW & NOTEWORTHY</b> Prolactin receptor (PRLR) signaling is crucial for β-cell adaptation to metabolic stresses from repeated pregnancies compounded by a high-fat diet (HFD). In PRLR-deficient β-cells, there is a reduction in insulin synthesis, expression of the gene that regulates GSIS, and incretin receptor Glp1r expression and response. This results in lower insulin secretion and impaired glucose tolerance. The link between PRLR and incretin receptor expression and function in islets is novel.