Caudal fourth ventricular administration of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside regulates glucose and counterregulatory hormone profiles, dorsal vagal complex metabolosensory neuron function, and hypothalamic fos expression

Abstract

This study investigated the hypothesis that estrogen controls hindbrain AMP-activated protein kinase (AMPK) activity and regulation of blood glucose, counterregulatory hormone secretion, and hypothalamic nerve cell transcriptional status. Dorsal vagal complex A2 noradrenergic neurons were laser microdissected from estradiol benzoate (E)- or oil (O)-implanted ovariectomized female rats after caudal fourth ventricular (CV4) delivery of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR), for Western blot analysis. E advanced AICAR-induced increases in A2 phospho-AMPK (pAMPK) expression and in blood glucose levels and was required for augmentation of Fos, estrogen receptor-α (ERα), monocarboxylate transporter-2, and glucose transporter-3 protein in A2 neurons and enhancement of corticosterone secretion by this treatment paradigm. CV4 AICAR also resulted in site-specific modifications in Fos immunolabeling of hypothalamic metabolic structures, including the paraventricular, ventromedial, and arcuate nuclei. The current studies demonstrate that estrogen regulates AMPK activation in caudal hindbrain A2 noradrenergic neurons during pharmacological replication of energy shortage in this area of the brain, and that this sensor is involved in neural regulation of glucostasis, in part, through control of corticosterone secretion. The data provide unique evidence that A2 neurons express both ERα and -β proteins and that AMPK upregulates cellular sensitivity to ERα-mediated signaling during simulated energy insufficiency. The results also imply that estrogen promotes glucose and lactate uptake by these cells under those conditions. Evidence for correlation between hindbrain AMPK and hypothalamic nerve cell genomic activation provides novel proof for functional connectivity between this hindbrain sensor and higher order metabolic brain loci while demonstrating a modulatory role for estrogen in this interaction.

Hindbrain lactostasis regulates hypothalamic AMPK activity and metabolic neurotransmitter mRNA and protein responses to hypoglycemia

“…Initial research on central AMPK regulation of bodywide metabolic stasis focused on the hypothalamus, but recent studies implicate hindbrain DVC AMPK in neural control of food intake (23) and glucostasis (25). Our work was the first to localize this sensor to a specific neurochemical phenotype in the DVC, e.g., A2 noradrenergic neurons, where it is revealed to be hypoglycemia sensitive (13).…”

Role of dorsal vagal complex A2 noradrenergic neurons in hindbrain glucoprivic inhibition of the luteinizing hormone surge in the steroid-primed ovariectomized female rat: Effects of 5-thioglucose on A2 functional biomarker and AMPK activity

“…DVC A2 neurons are a logical conduit of metabolic input to the GnRH-pituitary LH neuroendocrine axis as norepinephrine (NE) has a well-defined role in its regulation and these cells express molecular biomarkers for metabolo-sensory function, e.g. glucokinase, K ATP , and the ultra-sensitive energy sensor, adenosine 5’-monophosphate-activated protein kinase (AMPK) [Briski et al, 2009; Cherian and Briski, 2011; Ibrahim et al, 2013]. It is also likely that A2 cells are direct substrates for steroid regulatory actions as they express estrogen receptor-alpha (ERα) and -beta (ERβ) mRNAs and proteins [Tamrakar et al, 2012; Ibrahim et al, 2013].…”

Energy metabolism and hindbrain AMPK: regulation by estradiol

“…A role for ERβ in cDVC mechanisms controlling energy balance, albeit a departure from the consensus view that ERα globally subserve this function [31], is supported by our findings that intra-CV4 ERβ, but not ERα, antisense oligonucleotide administration suppresses not only acute hypoglycemic hyperphagia but, interestingly, also food intake occurring several hours later in conjunction with circadian cues associated with light-to-dark switch ( Figure 5). We presume that A2 neurons are direct substrates for ERβ-mediated control of counter-regulation as these cells express this protein [28]. Ongoing research seeks to determine if a causal relationship between pAMPK and ERβ protein expression exists and, if so, to elucidate the basis for functional interaction between these proteins.…”

“…In addition, studies involving intra-CV4 delivery of the AMPK activity inhibitor, compound C, show that estrogen is required for DVC AMPK induction of hypoglycemia hyperphagia in FD animals ( Figure 4). Assessment of AICAR effects on A2 nerve cell functional biomarkers and physiological endpoints in FD-E vs. FD-O rats shows that estradiol advances AICARinduced elevations in A2 pAMPK protein expression and circulating glucose and is required for augmented A2 Fos, estrogen receptor-α (ERα), monocarboxylate transporter-2, and glucose transporter-3 protein expression and adrenal corticosterone secretory responses to AICAR [28]. AICAR also elicits estrogen-dependent patterns of Fos immunolabeling in hypothalamic metabolic loci such as the paraventricular, ventromedial, and arcuate nuclei.…”