Scientists Discover Constant Myelin Production in Adult Brain

Research conducted by scientists at Johns Hopkins Medicine has revealed significant insights into the behavior of oligodendrocyte precursor cells (OPCs) in the adult brain. In a study published on January 22, 2024, in the journal Science, the team found that OPCs consistently differentiate into myelin-producing oligodendrocytes at a steady rate, rather than only in response to injury or aging, as previously thought. This breakthrough could have important implications for treating myelin-damaging conditions, such as multiple sclerosis.

Oligodendrocytes are essential brain cells that produce myelin, a fatty substance that insulates nerve cell axons and facilitates the rapid transmission of electrical signals throughout the central nervous system. Demyelinating disorders, which can be caused by autoimmune attacks, infections, or genetic factors, lead to various symptoms, including vision problems, weakness, and lack of coordination. Unlike neurons, which do not regenerate, oligodendrocytes can be produced throughout a person’s life, thanks to the ongoing presence of OPCs that can evolve into new oligodendrocytes.

According to Dwight Bergles, Ph.D., the Diana Sylvestre and Charles Homcy Professor of Neuroscience at Johns Hopkins University School of Medicine, the ability of OPCs to self-renew allows them to persist in the adult brain for decades. He emphasizes that this unique characteristic is crucial for the continuous production of myelin.

The study investigated how OPCs differentiate into oligodendrocytes. The researchers discovered that the process is inefficient, with many OPCs failing to successfully transform into new oligodendrocytes. To explore how this differentiation is regulated, the team utilized existing gene databases from various mammals, including mice, marmosets, and humans. They identified a common molecular marker that signals the beginning of this transformation.

During their investigation, the researchers noticed that as OPCs differentiate, they alter their gene expression, affecting the extracellular matrix, which is a protein mesh surrounding the cells. This change leads to the formation of novel structures termed “dandelion clock-like structures” (DACS), named for their resemblance to the seed heads of dandelions. This discovery provided a new method for tracking the differentiation of OPCs in the brain.

The research team, led by Bergles and research associate Yevgeniya Mironova, Ph.D., successfully tracked DACS in the brains of mice. Using genetic labeling and imaging tools, they demonstrated that each differentiating OPC produces a DACS that remains until the precursor cells mature into oligodendrocytes. Remarkably, the scientists found that OPCs were attempting to differentiate throughout the entire mouse brain, even in regions lacking oligodendrocytes and myelination.

“This indicates that OPC differentiation is a constant process across the brain,” stated Bergles. “Despite appearing inefficient, this mechanism may have evolved to ensure that the potential for new oligodendrocytes and myelin formation exists throughout the brain, with neurons determining which differentiating cells survive.”

In further experiments, the researchers simulated myelin-related diseases by stripping away oligodendrocytes and myelin from mouse brains. They found that OPCs continued their steady differentiation process, even without a pressing need for new myelin. While there was no increase in OPC differentiation, a greater number of these cells survived to produce new oligodendrocytes, suggesting that changes in cellular integration rather than direct mobilization of precursor cells led to the increase in myelin after injury.

Bergles noted, “This constant differentiation process seems to be designed for brain development, not for repair.” He suggests that treatments focusing on the developmental aspects of oligodendrocyte production may enhance the chances of rapid myelin repair in individuals suffering from demyelinating diseases.

The study was funded by the National Institutes of Health and supported by various organizations, including the National Multiple Sclerosis Society. Other contributors to the research included Brendan Dang, Dongeun Heo, Yu Kang Xu, Angela Yu-Huey Hsu, Jaime Eugenin von Bernhardi, Gian Carlo Molina-Castro, Anya A. Kim, and Jing-Ping Lin from Johns Hopkins, as well as Daniel Reich from the National Institutes of Health.

This groundbreaking study sets the stage for further exploration into OPC behavior and its potential for advancing treatments for demyelinating conditions, ultimately enhancing the quality of life for those affected.