Sex-dimorphic glucose transporter-2 regulation of cAMP-protein kinase A (PKA) C-alpha pathway activity and phosphorylation in rat hypothalamic primary astrocyte cultures.

Abstract

Brain astrocyte glycogenolysis is regulated in part by the second messenger adenosine 3'5'-cyclic monophosphate (cAMP). Hypothalamic astrocyte glycogen metabolism shapes glucose counterregulation, under the control of glucose transporter-2 (GLUT2), a plasma membrane glucose carrier and sensor. Hypothalamic astrocyte cAMP is subject to neurotransmitter control, but effects of nutrient cues on this messenger are unclear. Here, an established hypothalamic primary astrocyte culture model and gene knockdown tools were used to investigate the premise that GLUT2 exerts sex-dimorphic regulation of cAMP-protein kinase A (PKA) signalling in these glia. Data show that basal cAMP was elevated in female versus male; GLUT2 gene silencing up-regulated or down-regulated this profile in male versus female. Glucoprivation increased cAMP content in astrocytes of each sex, yet GLUT2 siRNA pretreatment exacerbated (male) or blunted (female) this stimulatory effect. PKA and phosphoPKA levels in glucose-supplied astrocytes were increased (male) or decreased (female) by GLUT2 knockdown. PKA protein was amplified, yet phosphoPKA was refractory to glucose withdrawal in male, while females showed sustained PKA expression alongside diminished phosphoPKA. GLUT2 siRNA pretreatment exacerbated glucoprivic augmentation of PKA content in male but down-regulated both PKA and phosphoPKA proteins in female. Evidence for parallel GLUT2 siRNA-associated changes in cAMP and PKA, albeit in opposing directions in the two sexes, infers that GLUT2 control of hypothalamic astrocyte cAMP-dependent PKA signalling is sex-specific. Data also disclose that in the female, GLUT2 curbs the baseline phosphoPKA/PKA expression ratio but is not involved in glucoprivic suppression of this ratio.