| || |
|Title:||CIRCADIAN MODULATION OF CLOCK GENES, BUT NOT GLUTAMATE UPTAKE IN CULTURED ASTROCYTES|
| || |
|Authors/Affiliations:||1 Christian Beaule*; 1 Adrienne Swanstrom; 1 Erik D. Herzog; |
1 Washington University Saint Louis, USA
| || |
|Content:||Objectives: Circadian clocks control daily rhythms in behavior, physiology, 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. Astrocytes play a critical role in the regulation of extrasynaptic glutamate levels via high-affinity glutamate transporters. Mutation in the clock gene Per2 was shown to reduce glutamate uptake by astrocytes (Spanagel R. et al, 2005). Because of this link between circadian gene expression and glutamate uptake by astrocytes, we asked whether glutamate uptake by glia is circadian. |
Material and methods: We monitored bioluminescence from pure cortical astrocytes cultured from transgenic rats carrying a bioluminescent reporter of Period1 transcription (Per1::luc) or from knock-in mice with a bioluminescent reporter of Period2 protein levels (Per2::luc). We also measured glutamate uptake as a function of time of day and glutamate concentration from bioluminescent cultures as well as from astrocytes derived form Clock/Clock mutant mice. RESULTS: We found that glutamate uptake and Period-driven bioluminescence levels depended on the Clock gene and on culture conditions, but not on circadian time.
Conclusion: We conclude that, although maximal glutamate uptake by astrocytes is modulated by the mutant CLOCK protein and factors in culture media, the circadian clock does not confer rhythmicity to this physiological measure.
| || |