Adiponectin Promotes Maternal β-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 (<i>Adipoq^-/-</i>) 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 β-cell proliferation rates, β-cell areas, and blood insulin concentrations was detected in <i>Adipoq^-/-</i> mice at mid-pregnancy. Surprisingly, conditionally knocking down adiponectin receptor 1 (<i>AdipoR1</i>) or <i>AdipoR2</i> genes in β-cells during pregnancy did not reduce β-cell proliferation rates or blood insulin concentrations. <i>In vitro</i> adiponectin treatment also failed to show any effect on β-cell proliferation of isolated pancreatic islets. It was reported that placental lactogen (PL) plays a crucial role in pregnancy-induced maternal β-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 <i>Adipoq^-/-</i> dams. The mRNA levels of mouse PL genes were robustly decreased in the placentas of <i>Adipoq^-/-</i> dams. In contrast, adiponectin treatment increased PL expression in human placenta explants and JEG3 trophoblast cells. Most importantly, bovine PL injection restored β-cell proliferation and blood insulin concentrations in <i>Adipoq^-/-</i> dams. Together, these results demonstrate that adiponectin plays a vital role in pregnancy-induced β-cell proliferation by promoting PL expression in trophoblast cells.