| Energy homeostasis is a vital physiological function of the brain. Estrogen (E) plays an important role in central regulation of energy balance. As a result, postmenopausal women may be at higher risk of the developing of metabolic diseases such as obesity due to diminished E levels in their circulation. There is a need to understand the mechanisms that delineate E actions to regulate energy which will facilitate in the development of promising therapies to protect against energy imbalance complications. Our study investigated the ability of E to regulate 5' adenosine monophosphate-activated protein kinase (AMPK) in the caudal hindbrain dorsal vagal complex (DVC) during different energy situations. In addition, the impact of DVC AMPK activation on the performance of hypothalamic nuclei to control feeding, glucostasis, and reproduction, was examined. We designed different in-vivo experiments using ovariectomized(OVX) female rats as a model. Diverse techniques including stereotaxi surgeries, immunohistochemistry, laser-capture microdissection, Western Blot, radioimmunoassay, qRT-PCR, and PCR array were used. Results reveal that 17beta-estradiol (EB) protects from acute and post-acute adverse effects of disrupted fuel acquisition on energy balance by regulating DVC AMPK activity. It also strengthens cross-talk between hindbrain AMPK and hypothalamic neuropeptides such as neuropeptide Y (NPY) and orexin A (ORX-A) during distinctive states of suspended versus non-interrupted fuel acquisition. In this regard, EB mediates its actions through NF&kgr;B, STAT3, Hedgehog, PPAR, Notch, and STAT5 signal pathways. AMP augmentation or acute interruption of feeding each inhibit DVC phosphoAMPK (pAMPK) and estrogen receptor-Beta (ER-beta) protein profiles in OVX female rats treated with EB; In combination, however, these treatments increase the levels of both proteins indicating that AMPK activation is ER-beta dependant. E-sensitive (TNF, WNT6) and --insensitive (FABP1, SOCS3) gene transcription delineate changes of AMPK activation. Genetecin (GE) and quercetin (QU), two phytoestrogens isolated from Peuraria lobata, as well as the flavonoids rich-fraction (FR) isolated from its flower buds have the ability to activate DVC AMPK via possible ER-beta dependant mechanisms during insulin-induced hypoglycemia (IIH) in OVX rats. This was correlated with increased blood glucose levels in GE and QU groups. Molecular modeling studies showed that GE, QU, and kaempferol (KA), the predominant compounds of FR, bind to the regulatory binding cleft of AMPK-gamma-subunit, which protects pAMPK from dephosphorylation. Data demonstrate the efficacy of these compounds to promote endogenous defense against energy deficit conditions. A2 noradrenergic neurons, electroreactive cells to substrate fuels, express ER-alpha and -beta, which imply sensitivity to EB actions. EB expedites A2 nerve cell AMPK activation and induction of hyperglycemia during pharmacological augmentation of intracellular AMP/ATP and is required for upregulation of Fos, ER-alpha, and substrate fuel transporter protein expression by A2 cells and for enhancement of corticosterone secretion. Dissimilar effects of CV4 AICAR on ARH, VMH, DMH, and caudal LHA Fos- ir in EB versus vehicle rats imply that estrogenic control of AMPKdriven A2 signaling may determine the transcriptional status in those sites. Results implicate DVC A2 neurons as a source of metabolic inhibitory signals from hindbrain DVC to attenuate LH surge, owing to reduction of nor-epinephrine out-flow from A2 neurons to GnRH neurons and the hypothalamic AVPV. Moreover, AMPK deactivation, indicative of an intracellular state of increased positive metabolic balance, does not override inhibitory effects of glucoprivic signals on GnRH neurons. In conclusion, this research demonstrates the important role of EB in neuronal control of energy homeostasis through effects on DVC AMPK. In addition, this work sheds light on the critical contribution of DVC A2 neurons in glucostasis and reproduction. Moreover, these outcomes point to estrogenic enhancement of A2 nerve cell metabolo-sensory functions. |
