Stories about: microglia

Microglia in the brain: Which are good and which are bad?

Timothy Hammond studying brain microglia in the Stevens Lab at Boston Children's Hospital
If we see microglia in brain disease, are they part of the problem, or part of the solution? asks Timothy Hammond. (PHOTOS: MICHAEL GODERRE / BOSTON CHILDREN’S HOSPITAL)

Microglia are known to be important to brain function. The immune cells have been found to protect the brain from injury and infection and are critical during brain development, helping circuits wire properly. They also seem to play a role in disease — showing up, for example, around brain plaques in people with Alzheimer’s.

It turns out microglia aren’t monolithic. They come in different flavors, and unlike the brain’s neurons, they’re always changing. Tim Hammond, PhD, a neuroscientist in the Stevens lab at Boston Children’s Hospital, showed this in an ambitious study, perhaps the most comprehensive survey of microglia ever conducted. Published last week in Immunity, the findings open a new chapter in brain exploration.

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Synapse ‘protection’ signal found; helps to refine brain circuits

a combination of 'eat me' and 'don't eat me' signals fine-tune synapse pruning
New evidence suggests that a ‘yin/yang’ system fine-tunes brain connections and synapse pruning (IMAGE: NANCY FLIESLER/ADOBE STOCK)

The developing brain is constantly forming new connections, or synapses, between nerve cells. Many connections are eventually lost, while others are strengthened. In 2012, Beth Stevens, PhD and her lab at Boston Children’s Hospital showed that microglia, immune cells that live in the brain, prune back unwanted synapses by engulfing or “eating” them. They also identified a set of “eat me” signals required to promote this process: complement proteins, best known for helping the immune system combat infection.

In new work published today in Neuron, Stevens and colleagues reveal the flip side: a “don’t eat me” signal that prevents microglia from pruning useful connections away.

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Microglia’s role in brain development: A neuroscientist looks back

The journal Neuron, celebrating its 25th anniversary, recently picked one influential neuroscience paper from each year of the publication. In this two-part series, we feature the two Boston Children’s Hospital’s scientists who made the cut. The Q&A below is adapted with kind permission from Cell Press.

Microglial cell with synapses
CAUGHT IN THE ACT: This microglial cell is from the lateral geniculate nucleus, which receives visual input from the eyes. The red and blue are synapses that it has engulfed. (Blue synapses represent inputs from the same-side eye; red, the opposite-side eye.)

In 2012, Beth Stevens, PhD, and colleagues provided a new understanding of how glial cells shape healthy brain development. Glia were once thought to be merely nerve “glue” (the meaning of “glia” from the Greek), serving only to protect and support neurons. “In the field of neuroscience, glia have often been ignored,” Stevens told Vector last year.

No longer. Stevens’s 2012 paper documented that microglia—glial cells best known for their immune function—are no passive bystanders. They get rid of excess connections, or synapses, in the developing brain the same way they’d dispatch an invading pathogen—by eating them.

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