Cutting Edge: Circadian Rhythm of Astrocytes

Erik has done it again. He is not one to publish 30 papers per year, but whenever he publishes one, it always gives me the chills and thrills! What beautiful science:

Circadian Rhythm Generation and Entrainment in Astrocytes

Laura M. Prolo,1 Joseph S. Takahashi,2 and Erik D. Herzog1

1Department of Biology, Washington University, St. Louis, Missouri 63130-4899, and 2Howard Hughes Medical Institute and Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208

In mammals, the master circadian pacemaker is
considered the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN
consists of a heterogeneous population of neurons and relatively understudied
glia. We investigated whether glia, like neurons, rhythmically express circadian
genes. We generated pure cultures of cortical astrocytes from
Period2::luciferase (Per2::luc) knock-in mice and Period1::luciferase
(Per1::luc) transgenic rats and recorded bioluminescence as a real-time reporter
of gene activity. We found that rat Per1::luc and mouse Per2::luc astroglia
express circadian rhythms with a genetically determined period. These rhythms
damped out after several days but were reinitiated by a variety of treatments,
including a full volume exchange of the medium. If cultures were treated before
damping out, the phase of Per1::luc rhythmicity was shifted, depending on the
time of the pulse relative to the peak of Per1 expression. Glial rhythms
entrained to daily 1.5°C temperature cycles and were significantly sustained
when cocultured with explants of the adult SCN but not with cortical explants.
Thus, multiple signals, including a diffusible factor(s) from the SCN, are
sufficient to either entrain or restart circadian oscillations in cortical glia.

J Neurosci., 25:404-8. http://www.jneurosci.org/cgi/content/abstract/25/2/404