Glucose Transporter-2 Regulation of Male versus Female Hypothalamic Astrocyte MAPK Expression and Activation: Impact of Glucose

Abstract

The plasma membrane glucose transporter (GLUT)-2 is unique among GLUT family proteins in that it also functions as a glucose sensor. GLUT2 imposes sex-dimorphic control of hypothalamic astrocyte glucose storage and catabolism by unknown mechanisms. Mitogen-activated protein kinase (MAPK) signaling cascades operate within stress-sensitive signal transduction pathways. The present study employed an established primary astrocyte culture model and gene knockdown tools to investigate whether one or more of the three primary MAP kinase families are regulated by GLUT2. GLUT2 gene knockdown caused opposing adjustments in total ERK1/2 proteins in glucose-supplied male versus female astrocytes, augmenting or reducing the mean phosphorylated/total protein ratio for 44 and 42 kDa variants in these sexes. Glucose deprivation amplified this ratio for both ERK1/2 variants, albeit by a larger magnitude in males; GLUT2 siRNA exacerbated this stimulatory response in males only. Phosphorylated/total p38 MAPK protein ratios were up-regulated by GLUT2 knockdown in male, but not female astrocytes. Glucose-deprived astrocytes exhibited no change (male) or reduction (female) in this ratio after GLUT2 gene silencing. GLUT2 siRNA increased the phosphorylated/total protein ratio for 54 and 46 kDa SAPK/JNK proteins in each sex when glucose was present. However, glucose withdrawal suppressed (male) or amplified (female) these ratios, while GLUT2 knockdown attenuated these inverse responses. The results show that GLUT2 inhibits ERK1/2, p38, and SAPK/JNK MAPK activity in male astrocytes, but differentially stimulates and inhibits activity of these signaling pathways in female hypothalamic astrocytes. Glucoprivation induces divergent adjustments in astrocyte p38 MAPK and SAPK/JNK activities. The findings demonstrate a stimulatory role for GLUT2 in p38 MAPK activation in glucose-starved female astrocytes, but it can act as either an inhibitor or inducer of SAPK/JNK activation in glucose-deprived male versus female glial cells, respectively.

Glucose transporter-2 regulation of VMN GABA neuron metabolic sensor and transmitter gene expression

“…), aided by motorized computer-controlled Neurostar stereotactic drill and injection robot, as described 28 . Our studies show that this knockdown reagent causes significant down-regulation of GLUT2 protein expression in primary hypothalamic astrocytes cultures in vitro 48 , 49 . After surgery, animals were injected with ketoprofen (1 mg/ml/kg bw sc ; Bayer Health Care LLC, Animal Health Division, S. Mission, Kansas) and enrofloxacin (10 mg/0.1 mL IM; Bayer Health), and treated by topical application of 0.25% bupivacaine (Hospira Inc., IL) to closed incisions.…”

“…The plasma membrane glucose transporter/sensor GLUT2 regulates hypothalamic astrocyte glycolytic pathway function, glycogen metabolism, and energy stability in vitro 48 , 49 . Here, an in vivo experimental approach was used to investigate whether GLUT2 function in the VMN, a principal element of the brain glucostatic regulatory network, controls VMN GABAergic neuron neurotransmitter signaling and counterregulatory hormone secretion in the female rat.…”