Scientists came up with new discovery. The brain cells that were once considered to be simple place-holders for neurons could actually play an important role in helping to regulate our circadian behavior.
Astrocytes are one kind of glial cell – the support cells, called the glue of the nervous system, because they provide structure and protection for neurons. But a new study show that astrocytes are not just gap-fillers, and they may be crucial for keeping time in our inner body clock.
Scientific consensus has long regarded our internal clock as being controlled by the suprachiasmatic nuclei (SCN). That is a brain region in the hypothalamus made up of around 20,000 neurons. But there’s about 6,000 star-shaped astrocyte cells in the same area, the exact function of which has never been fully explained.
So, scientists from Washington University in St. Louis figured out how to independently control astrocytes in mice – and by altering the astrocytes, they were able to slow down the animals’ sense of time.
One of the researchers, Matt Tso says- “We had no idea they would be that influential.”
Previously, it was thought the suprachiasmatic nuclei was the only part of the brain which regulate circadian rhythms, but scientists now understand that all cells throughout the body have their own circadian clocks.
Neuroscientist Erik Herzog, a member of the team helped figure out that astrocytes also include these clock genes.
His team showed that they glowed rhythmically, which is evidence that they were capable of keeping time like other cells. They did it by isolating the brain cells from rats and coupling them with a bioluminescent protein.
It took more than a decade for the researchers to figure out how to measure the same astrocyte behaviour in a living specimen.
Left to their own devices, mice have circadian clocks that last for approximately 23.7 hours. They came up to this conclusion because mice in constant darkness will start running on a wheel every 23.7 hours, and usually don’t miss their time slot by more than 10 minutes.
A Harvard University study in 1999 found that our internal clocks run a tad overlong, on a daily cycle of 24 hours, 11 minutes.
Although Herzog had demonstrated that astrocytes were involved in keeping time, the team didn’t necessarily expect mice without Bmal1( a clock gene in the astrocytes, which scientists have delete using CRISPR-Cas9 gene-editing) to be affected, because most research surrounding the suprachiasmatic nuclei has demonstrated the controlling effect of neurons, not astrocytes.
“When we deleted the gene in the astrocytes, we had good reason to predict the rhythm would remain unchanged,” “When people deleted this clock gene in neurons, the animals completely lost rhythm, which suggests that the neurons are necessary to sustain a daily rhythm.” -say Tso.
But, the researchers were surprised that with deleting the clock gene in the astrocytes saw the mouse internal clocks run slower, beginning their daily run about 1 hour later than usual.
In another experiment, the team was studing a mice with a mutation that caused their circadian clocks to run fast. By repairing this gene in the animals’ astrocytes – but without fixing the defect in their neurons – they weren’t sure what the affect would be.
“We expected the SCN to follow the neurons’ pace,” explains Tso. “There are 10 times more neurons in the SCN than astrocytes. Why would the behaviour follow the astrocytes?”
With the mutation fixed in the animals’ astrocytes, the mouse began their running routine 2 hours later than mice that hadn’t had the mutation repaired (in either astrocytes or neurons).
While the researchers acknowledge that they don’t fully understand the extent to which astrocytes control circadian behaviour, it’s clear something powerful is going on.
However, we still can’t guarantee whether astrocytes in humans are regulating body clocks in the same way, but even that is something that later studies may be able to confirm.
Although we’ll have to wait the results of future research to know more, one thing’s for sure – these brain cells are definitely there for a lot more than just neuron padding.