Stories about: Beth Stevens

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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Targeting synapse loss in Alzheimer’s to preserve cognition — before plaques appear

Alzheimer's microglia complement
Microglia (in red) consume synapses (in green) after mice are injected with the oligomeric form of beta-amyloid, before plaques appear in the brain. (Soyon Hong, Boston Children’s Hospital)

Currently, there are five FDA-approved drugs for Alzheimer’s disease, but these only boost cognition temporarily and don’t address the root causes of Alzheimer’s dementia. Many newer drugs in the pipeline seek to eliminate amyloid plaque deposits or reduce inflammation in the brain, but by the time this pathology is detectable, it’s unlikely medications can do much to slow the disease.

New research published in Science today suggests several ways that Alzheimer’s could be targeted much earlier to preserve cognitive function — before plaques or inflammation are evident.

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Genetic analysis backs a neuroimmune view of schizophrenia: Complement gone amok

schizophrenia C4
C4 (in green) located at the synapses of human neurons. (Courtesy Heather de Rivera, McCarroll lab)

A deep genetic analysis, involving nearly 65,000 people, finds a surprising risk factor for schizophrenia: variation in an immune molecule best known for its role in containing infection, known as complement component 4 or C4.

The findings, published this week in Nature, also support the emerging idea that schizophrenia is a disease of synaptic pruning, and could lead to much-needed new approaches to this elusive, devastating illness.

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Behind the scenes in the brain: The work and life of Beth Stevens, PhD

As far back as she can remember, neuroscientist Beth Stevens, PhD, of the Boston Children’s Hospital Department of Neurology and the F.M. Kirby Neurobiology Center, has loved science. The concept of a career in the field began to take root in high school, nurtured in part by her biology teacher — a scientist on the side — who was both encouraging and inspiring.

Today, Stevens, winner of the 2015 MacArthur “genius” grant for her groundbreaking research on microglia cells, is doing her part to inspire a new generation of scientists and show them, as she says, “Scientists aren’t just nerdy guys in white coats.”

Hover over the objects in Stevens’s office to learn more about her work, life and innovations, and read more about her science.

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Beth Stevens: A transformative thinker in neuroscience

When 2015 MacArthur “genius” grant winner Beth Stevens, PhD, began studying the role of glia in the brain in the 1990s, these cells—“glue” from the Greek—weren’t given much thought. Traditionally, glia were thought to merely protect and support neurons, the brain’s real players.

But Stevens, from the Department of Neurology and the F.M. Kirby Neurobiology Center at Boston Children’s Hospital, has made the case that glia are key actors in the brain, not just caretakers. Her work—at the interface between the nervous and immune systems—is helping transform how neurologic disorders like autism, amyotrophic lateral sclerosis (ALS), Alzheimer’s disease and schizophrenia are viewed.

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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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Immune cells “sculpt” brain circuits — by eating excess connections

The above movie shows an immune cell caught in the act of tending the brain—it’s just eaten away unnecessary connections, or synapses, between neurons.

That’s not something these cells, known as microglia, were previously thought to do. As immune cells, it was thought that their job was to rid the body of unwanted pathogens and debris, by engulfing and digesting them.

The involvement of microglia in the brain’s development has started to be recognized only recently. The latest research finds that microglia tune into the brain’s cues, akin to the way they survey their environment for invading microbes, and get rid of excess synapses the same way they’d dispatch these invaders—by eating them.

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