Estrogen regulates energy metabolic pathway and upstream adenosine 5′‐monophosphate‐activated protein kinase and phosphatase enzyme expression in dorsal vagal complex metabolosensory neurons during glucostasis and hypoglycemia

Abstract

The ability of estrogen to shield the brain from the bio-energetic insult, hypoglycemia, is unclear. Estradiol prevents hypoglycemic activation of the energy deficit sensor, adenosine 5′-monophosphate-activated protein kinase (AMPK), in hindbrain metabolo-sensory A2 noradrenergic neurons. Here, we investigated the hypothesis that estrogen regulates A2 AMPK through control of fuel metabolism and/or upstream protein kinase/phosphatase enzyme expression. A2 cells were harvested by laser-microdissection after insulin (INS) or vehicle (V) injection of estradiol (E)- or oil (O)-implanted ovariectomized female rats. Cell lysates were evaluated by immunoblot for glycolytic, tricarboxylic acid cycle (TCA), respiratory chain, and acetyl CoA-malonyl CoA pathway enzymes. A2 phosphofructokinase (PFKL), isocitrate dehydrogenase, and pyruvate dehydrogenase and ATP synthase subunit profiles were elevated in E/V versus O/V; hypoglycemia augmented PFKL and alpha-ketoglutarate dehydrogenase expression in E only. Hypoglycemia increased A2 Ca++/calmodulin-dependent protein kinase-beta in O, while reducing PP2A in both groups. A2 phosphoAMPK levels were equivalent in O/V versus E/V, but elevated during hypoglycemia in O only. These results implicate estradiol in compensatory up-regulation of substrate catabolism and corresponding maintenance of energy stability of A2 metabolo-sensory neurons during hypoglycemia, outcomes that support the potential viability of molecular substrates for hormone action as targets for therapies alleviating hypoglycemic brain injury.

Impact of recurrent hypoglycemic stress on hindbrain A2 nerve cell energy metabolism and catecholamine biosynthesis: modulation by estradiol

“…A fourth of four hypoglycemic bouts did not modify A2 CaMMκβ protein content in E-I 4 or O-I 4 , but diminished PP2A levels only in the former group. As a single hypoglycemic episode was previously observed to increase CaMMκβ and reduce PP2A protein profiles in OVX+oil rats (Tamrakar et al 2015), current data suggest that when estradiol is absent, precedent exposure eliminates these responses. As we did not directly compare incremental changes in AMPK activity in acute vs. chronic hypoglycemic rats, we do not know if precedent hypoglycemia alters the magnitude of A2 energy debilitation in OVX+oil rats.…”

“…A potential ensuing lack of change in malonyl CoA levels may impede fatty acid utilization for energy. Acute hypoglycemia had no effect on ACC, pACC, or FAS protein profiles in estradiol-or oil-implanted OVX rats (Tamrakar et al 2015); current observations of concurrent augmentation of ACC and FAS protein profiles in the E-I 4 group imply a gain in positive reactivity of these proteins in this group.…”

“…A fourth hypoglycemic bout did not elevate A2 ATP synthase-α protein levels relative to now-diminished basal profiles in E-I 4 , but suppressed this protein below baseline in O-I 4 , inferring that mitochondrial energy production may adaptively down-regulate in the latter treatment group. Since acute hypoglycemia did not modify ATP synthase-α expression in E or O (Tamrakar et al 2015), current results infer continuation of this lack of response in E-I 4 and development of negative reactivity in O-I…”

Mechanistic studies on ketamine-induced mitochondrial toxicity in zebrafish embryos

“…Taken together, these reports suggest that the expression of both α and β subunit polypeptides of ATP synthase is altered in various organs upon exposure to drugs that cause mitochondrial dysfunction. On the other hand, estradiol that protects the brain cells from bio-energetic dysfunction caused by conditions such as hypoxia, stroke, and degenerative disease by stimulating the energy-producing pathway (Nilsen and Brinton, 2004), induces the expression of ATP synthase α protein (Tamrakar et al, 2015). In this context, our current study shows altered expression of the transcripts for both subunits ( atp5α1 and atp5β ) of ATP synthase upon exposure to ketamine in the absence and presence of ALCAR.…”

Hindbrain lactate regulates preoptic gonadotropin-releasing hormone (GnRH) neuron GnRH-I protein but not AMPK responses to hypoglycemia in the steroid-primed ovariectomized female rat

“…ERα is implicated in positive-feedback induction of the LH surge as that event is abolished by ER knockdown [Wintermantel et al, 2006; Christian et al, 2008]. A2 neurons are likely substrates for estrogen feedback as these cells express ERα and -β mRNAs and proteins [Ibrahim et al, 2013; Tamrakar et al, 2015]. Hypoglycemia stimulates A2 ERβ and PR proteins; lactate infusion normalized the former, but not latter profile, suggesting that ERβ and PR proteins correspondingly respond to local versus extra-hindbrain sequelae of hypoglycemia.…”