Circadian modulation of gene expression, but not glutamate uptake, in mouse and rat cortical astrocytes.
BACKGROUND
Circadian clocks control daily rhythms including sleep-wake, hormone secretion, and metabolism. These clocks are based on intracellular transcription-translation feedback loops that sustain daily oscillations of gene expression in many cell types. Mammalian astrocytes display circadian rhythms in the expression of the clock genes Period1 (Per1) and Period2 (Per2). However, a functional role for circadian oscillations in astrocytes is unknown. Because uptake of extrasynaptic glutamate depends on the presence of Per2 in astrocytes, we asked whether glutamate uptake by glia is circadian.


RESULTS
We measured glutamate uptake, transcript and protein levels of the astrocyte-specific glutamate transporter, Glast, and the expression of Per1 and Per2 from cultured cortical astrocytes and from explants of somatosensory cortex. We found that glutamate uptake and Glast mRNA and protein expression were significantly reduced in Clock/Clock, Per2- or NPAS2-deficient glia. Uptake was augmented when the medium was supplemented with dibutyryl-cAMP or B27. Critically, glutamate uptake was not circadian in cortical astrocytes cultured from rats or mice or in cortical slices from mice.


CONCLUSIONS
We conclude that glutamate uptake levels are modulated by CLOCK, PER2, NPAS2, and the composition of the culture medium, and that uptake does not show circadian variations.
Beaulé
Christian
C
Department of Biology, Washington University, Saint Louis, Missouri, USA.
Swanstrom
Adrienne
A
Leone
María Juliana
MJ
Herzog
Erik D
ED
D000818:Animals; D030801:Animals, Genetically Modified; D001253:Astrocytes / Q000166:cytology*; D002540:Cerebral Cortex / Q000378:metabolism; D002940:Circadian Rhythm; D003470:Culture Media / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009457:Neuroglia / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014157:Transcription Factors / Q000378:metabolism
D003470:Culture Media; D014157:Transcription Factors; D018698:Glutamic Acid