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β-Cell mass increases during pregnancy to accommodate for insulin resistance. This increase is mainly due to β-cell proliferation, a process that requires intact prolactin receptor (Prlr) signaling. Signaling molecules that are known to regulate β-cell proliferation include Jak2, Akt, the tumor suppressor menin, and cell cycle proteins. Whether these pathways are involved in prolactin-mediated β-cell proliferation is unknown. Using the heterozygous prolactin receptor-null (Prlr+/−) mice, we isolated pancreatic islets from both Prlr+/+ and Prlr+/− mice on d 0 and 15 of pregnancy and examined the expression levels of these signaling molecules. In the wild-type mice (Prlr+/+), both phospho-Jak2 and phospho-Akt expression in pancreatic islets increased during pregnancy, which were attenuated in the pregnant Prlr+/− mice. During pregnancy, menin expression was reduced by 50 and 20% in the Prlr+/+ and the Prlr+/− mice, respectively, and the pregnant Prlr+/− mice had higher islet p18 levels than the Prlr+/+ mice. Interestingly, between d 0 and 15 of pregnancy, expression of cyclin inhibitory protein p21cip was increased in the Prlr+/+ mice, but this increase was blunted in the Prlr+/− mice. Lastly, we did not find any difference in the expression levels of cyclins D1, D2, and inhibitory kinases between the pregnant Prlr+/+ and Prlr+/− mice. Therefore, we conclude that during pregnancy, placental hormones act through the prolactin receptor to increase β-cell mass by up regulating β-cell proliferation by engaging Jak2, Akt, menin/p18, and p21. Future studies will determine the relative contribution of these molecules in maintaining normal glucose homeostasis during pregnancy.

Participation of Akt, Menin, and p21 in Pregnancy-Induced β-Cell Proliferation