Certain aspects of childhood are retained in us through adult life, such as food preference, personality traits, hobbies and interests. Similarly, a unique immune cell in the brain, microglia, also persists throughout the many chapters of our lives, from early embryonic development to old age.
Microglia, which are brain-resident macrophages, keep the complex neural circuitry running like clockwork by eliminating damaged cells, clearing infectious agents, and fine-tuning cell-to-cell connections. Recent studies have revealed that microglia encompasses an incredibly diverse collection of highly specialised subtypes, though the precise function of each group has remained obscure.
The origin of some neurodegenerative conditions such as Alzheimer’s disease can be traced back to faulty microglia, said Aymeric Silvin, an Associate Postdoctoral Researcher at A*STAR’s Singapore Immunology Network (SIgN). The dysregulation of microglia engenders a build-up of protein aggregates and inflammatory markers that block neural pathways, he explained.
“A better understanding of microglia heterogeneity and function in neurodegenerative diseases is crucial for developing therapeutical strategies to remove these aggregates and dampen inflammation,” he said.
In an ambitious effort to map the vast universe of microglia subtypes one cell at a time, Silvin and a team of researchers, led by Florent Ginhoux, a Senior Principal Investigator at SIgN, built their analytical platform by merging six large datasets from single-cell RNA sequencing studies.
They called it the M-Verse—a first-of-its-kind online tool that serves to map microglial subpopulations in the developing mouse brain, from foetus to adult, and in models of Alzheimer’s disease.
Using the M-Verse tool, they found two distinct classes of disease-associated microglia, or DAMs, which had a yin-and-yang effect on the aging brain. One group of DAMs is protective, while the other, termed TREM2-independent disease inflammatory macrophages (DIMs), stoked the fires of inflammation associated with neurodegenerative disease.
Silvin said that the ‘good’ microglia reactivated processes used during early foetal development in a bid to lessen the inflammatory damage in the brain. “Through the M-Verse, we observed that TREM-2 dependent DAMs reacquired a programme used naturally during embryogenesis to ensure proper brain development,” said Silvin, adding that this likely mirrors what happens in the ageing human brain.
The M-Verse provides researchers with a glimpse of valuable future therapeutic targets based on the specific cell surface proteins associated with Alzheimer’s disease. The team has patented this technology as part of their commercialisation efforts.
“We could design antibody therapies that target these proteins,” suggested Silvin, adding that this approach has been used extensively (and successfully) to treat cancer by other research groups. For now, the team is exploring the subtle signals put out by microglia to dial down inflammation and investigating potential strategies to remove aggregates in the ageing brain.