Adaptation of Glucokinase Gene Expression in the Rat Dorsal Vagal Complex in a Model for Recurrent Intermediate Insulin-Induced Hypoglycemia: Impact of Gender

Abstract

Standard therapeutic management of insulin-dependent diabetes mellitus with intermediate-acting insulin poses a significant risk for iatrogenic hypoglycemia and associated hypoglycemia-associated autonomic failure. Gender differences in preservation of counterregulatory function during recurring hypoglycemia have been documented in the clinical setting. In rats, repeated induction of prolonged hypoglycemia by neutral protamine Hagadorn insulin (NPH) results in diminished neuronal transcriptional activation in several key metabolic loci in male, but not female rat brain, including the hindbrain dorsal vagal complex (DVC). Glucose is committed to glycolytic catabolism by hexokinase-mediated phosphorylation. The low-affinity, high K (m) hexokinase, glucokinase (GCK), monitors intracellular glucose levels in pancreatic beta cells, and is purported to fulfill a similar function in the CNS. GCK is expressed in the rat DVC, where mRNA is localized to neurons that exhibit electrophysiological sensitivity to glucose imbalance. The current study investigated the hypothesis that DVC GCK gene expression acclimates to RIIH in a gender-dependent manner. Quantitative real-time RT-PCR was used to evaluate GCK mRNA levels in microdissected DVC tissue obtained from male and female rats before or after one or serial doses of NPH. Basal DVC GCK transcripts were equal between ovariectomized (OVX) female rats implanted with estradiol benzoate (EB) or oil (O). Tissue mRNA levels were increased following a single NPH injection in both groups, but this response was greater in the presence of estrogen. Basal GCK gene expression was elevated by precedent insulin dosing in both O- and EB-implanted rats; however, transcripts were not modified relative to this adjusted baseline during subsequent NPH treatment in either group of females. While acute NPH treatment did not modify tissue transcript levels in orchidectomized (ORDX) or sham-ORDX rats, precedent NPH dosing increased basal GCK mRNA levels and further enhanced gene expression during ensuring hypoglycemia in sham males. These studies provide novel evidence for gender-dimorphic DVC GCK gene responses to single and serial intermediate-acting insulin administration. Further research is required to determine if and how stimulatory versus inhibitory transcriptional adaptation of this gene profile in male and female rats, respectively, impacts glucose-sensing functions in the DVC, and whether such adjustments may contribute to gender differences in magnitude of precedent hypoglycemic impairment of counterregulation.

Effects of hypoglycaemia on neuronal metabolism in the adult brain: role of alternative substrates to glucose

“…These studies provided further evidence on the existence of mechanisms to enhance lactate and glucose transport mechanisms and promote local lactate utilization during hypoglycaemia in neurons. In addition, they show that gender differences appear to play a role on the magnitude of precedent hypoglycaemic impairment of counterregulation (Genabai et al 2009).…”

Effects of short-term food deprivation on catecholamine and metabolic-sensory biomarker gene expression in hindbrain A2 noradrenergic neurons projecting to the forebrain rostral preoptic area: Impact of negative versus positive estradiol feedback

“…no. 415190–9181–000; Carl Zeiss MicroImaging) for qPCR gene expression analysis by methods established in our laboratory ( Vavaiya and Briski, 2008 ; Briski et al, 2009 ; Genabai et al, 2009 ; Cherian and Briski, 2011 ). A cell collection strategy outlined in earlier work ( Briski et al, 2009 ) was implemented here, wherein two TH-ir-/epifluorescence-positive A2 neurons were acquired from each animal per treatment group; one was nuclear GKRP-ir-positive, while the other was GKRP-ir-negative.…”

Insights into the role of neuronal glucokinase

“…Each of the DVC nuclei expresses low levels of glucokinase ( 5 , 42 ). IIH increased glucokinase mRNA expression in the DVC ( 53 ), whereas prolonged hyperglycemia in streptozotocin-induced diabetic rats decreased it ( 59 ). This suggests a role for glucokinase in glucose sensing.…”