Estrogen Receptor Involvement in Noradrenergic Regulation of Ventromedial Hypothalamic Nucleus Glucoregulatory Neurotransmitter and Stimulus-Specific Glycogen Phosphorylase Enzyme Isoform Expression

Abstract

Norepinephrine (NE) directly regulates ventromedial hypothalamic nucleus (VMN) glucoregulatory neurons and also controls glycogen-derived fuel provision to those cells. VMN nitric oxide (NO) and c-aminobutyric acid (GABA) neurons and astrocytes express estrogen receptor-alpha (ERa) and ER-beta (ERb) proteins. Current research used selective ERa (1,3Bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride) or ERb (4-[2-phenyl-5,7bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol) antagonists to address the premise that these ERs govern basal and/or NE-associated patterns of VMN metabolic neuron signaling and astrocyte glycogen metabolism. Both ERs stimulate expression of the enzyme marker protein neuronal nitric oxide synthase, not glutamate decarboxylase 65/67. NE inhibition or augmentation of neuronal nitric oxide synthase and glutamate decarboxylase 65/67 profiles was ER-independent or-dependent, respectively. In both neuron types, VMN ERb activity inhibited baseline alpha1-(a 1-) and/or alpha2-(a 2-)adrenergic receptor (AR) expression, but ERa and-b signaling was paradoxically crucial for noradrenergic upregulation of a 2-AR. NE inhibited glycogen synthase expression and exerted opposite effects on VMN adenosine monophosphate-sensitive glycogen phosphorylase (GP)-brain type (stimulatory) versus NE-sensitive GP muscle (inhibitory) via ERa orb activity. Results document unique ERa and ERb actions on metabolic transmitter and AR protein expression in VMN nitrergic versus GABAergic neurons. ER effects varied in the presence versus absence of NE, indicating that both neuron types are substrates for estradiol and noradrenergic regulatory interaction. NE-dependent ER control of VMN GP variant expression implies that these signals also act on astrocytes to direct physiological stimulus-specific control of glycogen metabolism, which may in turn influence GABA transmission.

Norepinephrine Regulation of Ventromedial Hypothalamic Nucleus Metabolic-Sensory Neuron 5′-AMP-Activated Protein Kinase Activity: Impact of Estradiol

“…NE has well documented regulatory effects on astrocyte glycogen metabolism in vitro [41,42]. We found that NE inhibits VMN GS protein expression, and promotes divergent adjustments in AMP-sensitive glycogen phosphorylase (GP)-brain type (up-regulated by NE) versus NE-sensitive GP-muscle (down-regulated by NE) variant profiles via ERα or -β activity, respectively [35]. These data uniquely demonstrate ER-dependent NE control of VMN GP variant expression.…”

“…We conducted studies to address the premise that estradiol may modulate NO and/or GAD neuron receptivity to NE. Using pharmacological and high-resolution microdissection tools in a characterized OVX, plus an estradiol replacement model in which plasma estradiol levels are reinstated within the physiological range [32][33][34], we investigated whether VMN ERα and/or ERβ modulate NE control of nitrergic and GABAergic neuron AR and transmitter marker protein expression in the female rat [35]. The research plan involved a pretreatment by intra-VMN administration of MPP, PHTPP, or vehicle, prior to the injection of NE into the same location.…”

“…Estrogen regulation of VMN gluco-regulatory nerve cell AMPK reactivity to NE. Using the same methodological approach for the selective procurement of VMN NO and GABA neurons and techniques for the administration of NE to the VMN [35], our laboratory examined the premise that one or both neuron populations express AMPK and that VMN ERs modulate the noradrenergic regulation of sensor protein expression and/or activation. Whereas both ERα and -β were observed to stimulate total AMPK protein expression in nitrergic neurons under control conditions, this protein profile was diminished in response to NE, an action that required ERβ signaling.…”

Norepinephrine Regulation of Ventromedial Hypothalamic Nucleus Astrocyte Glycogen Metabolism

“…DVC NE governs hypoglycemic patterns of VMN AMPK activation and neurotransmitter marker protein expression [ 48 ]. Noradrenergic regulation of VMN glycogen metabolic enzyme protein expression was initially documented by studies that showed that exogenous NE inhibits GS protein expression but imposes divergent, e.g., stimulatory versus inhibitory, effects on AMP-sensitive GPbb and NE-sensitive GPmm profiles, respectively [ 49 ]. As VMN astrocytes obtained by laser-catapult microdissection express alpha 1 (α 1 ), alpha 2 - (α 2 ) and beta 1 - (β 1 ) adrenergic receptor (AR) proteins [ 50 ], it is reasonable to presume that the noradrenergic regulation of the GP variant expression involves, in part, direct input to these cells.…”

“…VMN glycogen mass and/or turnover is a plausibly important metabolic variable that is subject to careful monitoring. As glycogen-derived substrate fuel stream has documented influence on VMN metabolic regulatory transmitter signaling, as indicated by evidence that NE causes 4CIN-reversible changes in the VMN nNOS and GAD protein expression [ 49 ], the astrocyte glycogen depot can be viewed as a plausible substrate for noradrenergic control of VMN gluco-regulatory function. There is need for consideration, however, whether glycogen-derived lactate affects VMN metabolic neurons as an energy fuel and/or signaling molecule [ 65 ].…”