Brain guardians remove dying neurons

By adolescence, your brain already contains
most of the neurons that you’ll have for the rest of your life. But a
few regions continue to grow new nerve cells—and require the services of
cellular sentinels, specialized immune cells that keep the brain safe
by getting rid of dead or dysfunctional cells.

Now, Salk
scientists have uncovered the surprising extent to which both dying and
dead neurons are cleared away, and have identified specific cellular
switches that are key to this process. The work was detailed in Nature on April 6, 2016.

“We discovered that receptors on immune cells in the brain
are vital for both healthy and injured states,” says Greg Lemke, senior
author of the work, a Salk professor of molecular neurobiology and the
holder of the Françoise Gilot-Salk Chair. “These receptors could be
potential therapeutic targets for neurodegenerative conditions or
inflammation-related disorders, such as Parkinson’s disease.”

Salk scientists show that two immune cell receptors, called Mer and Axl,
are responsible for consuming dead or dysfunctional brain cells. An
accumulation of dead cells (green spots) is seen in the subventricular
zone (SVZ) – a neurogenic region – of the brain in a mouse lacking the
receptors Mer and Axl. (Blue staining marks all cells.) No green spots
are seen in the SVZ from a normal mouse. Credit: Salk Institute


Clearing away dead and dying neurons is essential to brain health and cognition. This is a huge step in figuring out how to treat brain disorders where that goes awry.


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