Background: In diabetes, exposure to frequent episodes of hypoglycaemia diminishes a persons awareness of hypoglycaemia, by poorly defined mechanisms. Evidence suggests that, at least in part, changes in cell behaviour within the ventromedial hypothalamus may contribute to this defect and that changes in AMP-activated protein kinase (AMPK), a key glucose-sensing enzyme are involved. Evidence suggests there are (mal)adaptations within neurons, however, little is known about changes within the astrocyte, which make up at least 50% of the cells within the hypothalamus.
Methods: Human U373 cells and primary mouse hypothalamic and cortical astrocytes were exposed to 2.5 or 0.1 mM glucose containing DMEM for up to three hours. Supernatants were collected for further analysis and cellular lysates were analysed by Western blotting.
Results: Application of low glucose (0.1 mM) increased AMPK (thr172) and acetyl CoA carboxylase (ser79) phosphorylation, indicating an increase in AMPK activity when compared to control (2.5 mM). Extracellular lactate (eATP) levels decreased with low glucose by ~60% (2.5 vs 0.1 mM), which was much less than the 25-fold reduction in glucose availability, indicating that under low glucose conditions, astrocytes may be preferentially more glycolytic. Acute low glucose application also increased extracellular ATP levels, a universal danger signal. Astrocytes were exposed to three episodes of low glucose to mimic recurrent hypoglycaemia (RH). The change in eATP mediated by low glucose was similar between control and RH. There was a trend toward reduced AMPK activation following exposure to low glucose following RH, which did not reach significance. However, there was a significant attenuation of decrease in lactate release by low glucose following RH, suggesting a relative enhancement of lactate release.
Conclusion: Astrocytes are functionally altered by exposure to acute and recurrent low glucose suggesting that changes within the astrocyte may contribute to defective glucose counterregulation in diabetes.