Michelle Arlotto

Maternal glucose levels during pregnancy impact the developing fetus, affecting metabolic health both early and later on in life. Both genetic and environmental factors influence maternal metabolism, but little is known about the genetic mechanisms that alter glucose metabolism during pregnancy. Here, we report that haplotypes previously associated with gestational hyperglycaemia in the third trimester disrupt regulatory element activity and reduce expression of the nearby HKDC1 gene. We further find that experimentally reducing or increasing HKDC1 expression reduces or increases hexokinase activity, respectively, in multiple cellular models; in addition, purified HKDC1 protein has hexokinase activity in vitro. Together, these results suggest a novel mechanism of gestational glucose regulation in which the effects of genetic variants in multiple regulatory elements alter glucose homeostasis by coordinately reducing expression of the novel hexokinase HKDC1. Maternal glucose levels during pregnancy can affect the metabolic health of a developing fetus, both early on and later in life. Here, the authors reveal that genetic variants in several regulatory elements alter glucose homeostasis during pregnancy by reducing the expression of a novel hexokinase gene, HKDC1.

Loss of functional β-cell mass is a hallmark of type 1 and type 2 diabetes, and methods for restoring these cells are needed. We have previously reported that overexpression of the homeodomain transcription factor NK6 homeobox 1 (Nkx6.1) in rat pancreatic islets induces β-cell proliferation and enhances glucose-stimulated insulin secretion, but the pathway by which Nkx6.1 activates β-cell expansion has not been defined. Here, we demonstrate that Nkx6.1 induces expression of the nuclear receptor subfamily 4, group A, members 1 and 3 (Nr4a1 and Nr4a3) orphan nuclear receptors, and that these factors are both necessary and sufficient for Nkx6.1-mediated β-cell proliferation. Consistent with this finding, global knockout of Nr4a1 results in a decrease in β-cell area in neonatal and young mice. Overexpression of Nkx6.1 and the Nr4a receptors results in increased expression of key cell cycle inducers E2F transcription factor 1 and cyclin E1. Furthermore, Nkx6.1 and Nr4a receptors induce components of the anaphase-promoting complex, including ubiquitin-conjugating enzyme E2C, resulting in degradation of the cell cycle inhibitor p21. These studies identify a unique bipartite pathway for activation of β-cell proliferation, suggesting several unique targets for expansion of functional β-cell mass.