Differential G Protein-Coupled Estrogen Receptor-1 Regulation of Counter-Regulatory Transmitter Marker and 5′-AMP-Activated Protein Kinase Expression in Ventrolateral versus Dorsomedial Ventromedial Hypothalamic Nucleus

Abstract

<b><i>Introduction:</i></b> The ventromedial hypothalamic nucleus (VMN) is an estrogen receptor (ER)-rich structure that regulates glucostasis. The role of nuclear but not membrane G protein-coupled ER-1 (GPER) in that function has been studied. <b><i>Methods:</i></b> Gene silencing and laser-catapult microdissection/immunoblot tools were used to examine whether GPER regulates transmitter and energy sensor function in dorsomedial (VMNdm) and/or ventrolateral (VMNvl) VMN counter-regulatory nitrergic and γ-Aminobutyric acid (GABA) neurons. <b><i>Results:</i></b> Intra-VMN GPER siRNA administration to euglycemic animals did not affect VMNdm or -vl nitrergic neuron nitric oxide synthase (nNOS), but upregulated (VMNdm) or lacked influence on (VMNvl) GABA nerve cell glutamate decarboxylase_65/67 (GAD) protein. Insulin-induced hypoglycemia (IIH) caused GPER knockdown-reversible augmentation of nNOS, 5′-AMP-activated protein kinase (AMPK), and phospho-AMPK proteins in nitrergic neurons in both divisions. IIH had dissimilar effects on VMNvl (unchanged) versus VMNdm (increased) GABAergic neuron GAD levels, yet GPER knockdown affected these profiles. GPER siRNA prevented hypoglycemic upregulation of VMNvl and -dm GABA neuron AMPK without altering pAMPK expression. <b><i>Conclusions:</i></b> Outcomes infer that GPER exerts differential control of VMNdm versus -vl GABA transmission during glucostasis and is required for hypoglycemic upregulated nitrergic (VMNdm and -vl) and GABA (VMNdm) signaling. Glycogen metabolism is reported to regulate VMN nNOS and GAD proteins. Data show that GPER limits VMNvl glycogen phosphorylase (GP) protein expression and glycogen buildup during euglycemia but mediates hypoglycemic augmentation of VMNvl GP protein and glycogen content; VMNdm glycogen mass is refractory to GPER control. GPER regulation of VMNvl glycogen metabolism infers that this receptor may govern local counter-regulatory transmission in part by astrocyte metabolic coupling.