Adiponectin Promotes Maternal beta-Cell Expansion Through Placental Lactogen Expression

Hypoadiponectinemia is a risk factor of gestational diabetes mellitus (GDM). Our previous study reported that adiponectin gene knockout mice (Adipoq(-/-)) develop GDM due to insulin insufficiency. The main objective of this study was to elucidate the underlying mechanism through which adiponectin controls islet expansion during pregnancy. A significant reduction in beta-cell proliferation rates, beta-cell areas, and blood insulin concentrations was detected in Adipoq(-/-) mice at midpregnancy. Surprisingly, conditionally knocking down adiponectin receptor 1 (AdipoR1) or AdipoR2 genes in beta-cells during pregnancy did not reduce beta-cell proliferation rates or blood insulin concentrations. In vitro adiponectin treatment also failed to show any effect on beta-cell proliferation of isolated pancreatic islets. It was reported that placental lactogen (PL) plays a crucial role in pregnancy-induced maternal beta-cell proliferation. A significant decrease in phosphorylation of signal transducer and activator of transcription 5, a downstream molecule of PL signaling, was observed in islets from Adipoq(-/-) dams. The mRNA levels of mouse PL genes were robustly decreased in the placentas of Adipoq(-/-) dams. In contrast, adiponectin treatment increased PL expression in human placenta explants and JEG3 trophoblast cells. Most importantly, bovine PL injection restored beta-cell proliferation and blood insulin concentrations in Adipoq(-/-) dams. Together, these results demonstrate that adiponectin plays a vital role in pregnancy-induced beta-cell proliferation by promoting PL expression in trophoblast cells.