Sex-Dimorphic Effects of Hypoglycemia on Metabolic Sensor mRNA Expression in Ventromedial Hypothalamic Nucleus-Dorsomedial Division (VMNdm) Growth Hormone-Releasing Hormone Neurons

Growth hormone-releasing hormone (Ghrh) neurons in the
dorsomedial
ventromedial hypothalamic nucleus (VMNdm) express the metabolic transcription
factor steroidogenic factor-1 and hypoglycemia-sensitive neurochemicals
of diverse chemical structures, transmission modes, and temporal signaling
profiles. Ghrh imposes neuromodulatory control of coexpressed transmitters.
Multiple metabolic sensory mechanisms are employed in the brain, including
screening of the critical nutrient glucose or the energy currency
ATP. Here, combinatory laser-catapult-microdissection/single-cell
multiplex qPCR tools were used to investigate whether these neurons
possess molecular machinery for monitoring cellular metabolic status
and if these biomarkers exhibit sex-specific sensitivity to insulin-induced
hypoglycemia. Data show that hypoglycemia up- (male) or downregulated
(female) Ghrh neuron glucokinase (Gck) mRNA; Ghrh gene silencing decreased
baseline and hypoglycemic patterns of Gck gene expression in each
sex. Ghrh neuron glucokinase regulatory protein (Gckr) transcript
levels were respectively diminished or augmented in hypoglycemic male
vs female rats; this mRNA profile was decreased by Ghrh siRNA in both
sexes. Gene transcripts encoding catalytic alpha subunits of the energy
monitor 5-AMP-activated protein kinase (AMPK), i.e., Prkaa1 and 2,
were increased by hypoglycemia in males, yet only the former mRNA
was hypoglycemia-sensitive in females. Ghrh siRNA downregulated baseline
and hypoglycemia-associated Prkaa subunit mRNAs in males but elicited
divergent changes in Prkaa2 transcripts in eu- vs hypoglycemic females.
Results provide unique evidence that VMNdm Ghrh neurons express the
characterized metabolic sensor biomarkers glucokinase and AMPK and
that the corresponding gene profiles exhibit distinctive sex-dimorphic
transcriptional responses to hypoglycemia. Data further document Ghrh
neuromodulation of baseline and hypoglycemic transcription patterns
of these metabolic gene profiles.