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Updated: Apr 11, 2026
An Ex vivo Model of an Oligodendrocyte-directed T-Cell Attack in Acute Brain Slices
Published on: February 5, 2015
Semaphorin4A Is Cytotoxic to Oligodendrocytes and Is Elevated in Microglia and Multiple Sclerosis
Dominique F Leitner1, Bozho Todorich2, Xuesheng Zhang3
1Department of Neurosurgery, Penn State University College of Medicine, Hershey, PA, USA.
Abstract:
We have previously established that T cell immunoglobulin and mucin domain containing 2 (Tim2) is an H-ferritin receptor on oligodendrocytes (OLs). Tim2 also binds Semaphorin4A (Sema4A). Sema4A is expressed by lymphocytes, and its role in immune activation is known; however, its relationship to diseases that are known to have myelin damage has not been studied. In this study, we demonstrate that Sema4A is cytotoxic to OLs in culture: an effect accompanied by process collapse, membrane blebbing, and phosphatidylserine inversion. We further demonstrate that Sema4A preferentially binds to primary OLs but not astrocytes: an observation consistent with the lack of expression of Tim2 on astrocytes. We found that Sema4A protein levels are increased within multiple sclerosis plaques compared with normal-appearing white matter and that Sema4A induces lactate dehydrogenase release in a human OL cell line. The chief cellular source of Sema4A within the multiple sclerosis plaques appears to be infiltrating lymphocytes and microglia. Macrophages are known to express Sema4A, so we interrogated microglia as a potential source of Sema4A in the brain. We found that rat primary microglia express Sema4A which increased after lipopolysaccharide activation. Because activated microglia accumulate iron, we determined whether iron status influenced Sema4A and found that iron chelation decreased Sema4A and iron loading increased Sema4A in activated microglia. Overall, our data implicate Sema4A in the destruction of OLs and reveal that its expression is sensitive to iron levels.
Insights
Semaphorin4A (Sema4A) is cytotoxic to oligodendrocytes (OLs), contributing to myelin damage in diseases like multiple sclerosis. Its expression is increased by iron and it originates from activated microglia and lymphocytes.
Area of Science:
- Neuroimmunology
- Cell Biology
- Demyelinating Diseases
Background:
- T cell immunoglobulin and mucin domain containing 2 (Tim2) acts as an H-ferritin receptor on oligodendrocytes (OLs).
- Tim2 also binds Semaphorin4A (Sema4A), a molecule expressed by lymphocytes with known immune activation roles.
- The relationship between Sema4A and myelin damage in diseases has not been previously studied.
Purpose of the Study:
- To investigate the role of Sema4A in oligodendrocyte (OL) damage and its potential involvement in demyelinating diseases.
- To determine the cellular sources and regulation of Sema4A in the context of brain inflammation and iron metabolism.
Main Methods:
- In vitro studies using primary OLs and astrocytes to assess Sema4A cytotoxicity and binding.
- Analysis of Sema4A protein levels in multiple sclerosis (MS) plaques.
- Investigation of Sema4A expression in primary microglia, including the effect of lipopolysaccharide activation and iron status.
Main Results:
- Sema4A demonstrated direct cytotoxicity to OLs in culture, causing process collapse and membrane blebbing.
- Sema4A preferentially bound to OLs, consistent with Tim2 expression on these cells, but not astrocytes.
- Elevated Sema4A protein levels were observed in MS plaques, primarily from infiltrating lymphocytes and microglia.
- Microglial Sema4A expression increased upon activation and was sensitive to iron levels, decreasing with chelation and increasing with iron loading.
Conclusions:
- Sema4A is implicated in the destruction of oligodendrocytes (OLs), a key event in myelin damage.
- Infiltrating lymphocytes and activated microglia are significant sources of Sema4A in demyelinating lesions.
- Iron metabolism directly influences Sema4A expression in activated microglia, suggesting a novel regulatory mechanism in neuroinflammation.
