Related Experiment Video
Updated: Mar 24, 2026
Assessing Microglial Phagocytosis of Myelin Debris in vitro Under Repeated Magnetic Stimulation
Published on: June 17, 2025
MerTK Is a Functional Regulator of Myelin Phagocytosis by Human Myeloid Cells
Luke M Healy1, Gabrielle Perron1, So-Yoon Won1
1Neuroimmunology Unit, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada;
Abstract:
Multifocal inflammatory lesions featuring destruction of lipid-rich myelin are pathologic hallmarks of multiple sclerosis. Lesion activity is assessed by the extent and composition of myelin uptake by myeloid cells present in such lesions. In the inflamed CNS, myeloid cells are comprised of brain-resident microglia, an endogenous cell population, and monocyte-derived macrophages, which infiltrate from the systemic compartment. Using microglia isolated from the adult human brain, we demonstrate that myelin phagocytosis is dependent on the polarization state of the cells. Myelin ingestion is significantly enhanced in cells exposed to TGF-β compared with resting basal conditions and markedly reduced in classically activated polarized cells. Transcriptional analysis indicated that TGF-β-treated microglia closely resembled M0 cells. The tyrosine kinase phagocytic receptor MerTK was one of the most upregulated among a select number of differentially expressed genes in TGF-β-treated microglia. In contrast, MerTK and its known ligands, growth arrest-specific 6 and Protein S, were downregulated in classically activated cells. MerTK expression and myelin phagocytosis were higher in CNS-derived microglia than observed in monocyte-derived macrophages, both basally and under all tested polarization conditions. Specific MerTK inhibitors reduced myelin phagocytosis and the resultant anti-inflammatory biased cytokine responses for both cell types. Defining and modulating the mechanisms that regulate myelin phagocytosis has the potential to impact lesion and disease evolution in multiple sclerosis. Relevant effects would include enhancing myelin clearance, increasing anti-inflammatory molecule production by myeloid cells, and thereby permitting subsequent tissue repair.
Insights
Multiple sclerosis involves myelin destruction. TGF-β enhances microglia’s myelin ingestion via MerTK, while classical activation reduces it, impacting disease progression.
Area of Science:
- Neuroimmunology
- Cellular Biology
- Pathology
Background:
- Multiple sclerosis is characterized by inflammatory lesions and myelin destruction in the central nervous system (CNS).
- Myeloid cells, including microglia and monocyte-derived macrophages, play a critical role in clearing myelin debris within these lesions.
- Understanding the regulation of myelin phagocytosis by these cells is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the influence of cellular polarization states on myelin phagocytosis by human microglia.
- To identify key molecular mechanisms, particularly the MerTK pathway, involved in myelin uptake by microglia and macrophages.
- To assess the potential of modulating these mechanisms for therapeutic benefit in multiple sclerosis.
Main Methods:
- Isolation and polarization of human microglia and monocyte-derived macrophages.
- Assessment of myelin phagocytosis under different polarization conditions (TGF-β, classical activation).
- Transcriptional analysis and gene expression profiling (e.g., MerTK, growth arrest-specific 6, Protein S).
- Pharmacological inhibition of MerTK to evaluate its role in phagocytosis and cytokine response.
Main Results:
- Myelin phagocytosis by microglia is significantly enhanced by TGF-β polarization and reduced by classical activation.
- TGF-β-treated microglia exhibit upregulated MerTK expression, resembling M0 cells.
- MerTK and its ligands are downregulated in classically activated cells.
- CNS-derived microglia show higher MerTK expression and myelin phagocytosis compared to monocyte-derived macrophages.
- MerTK inhibition reduces myelin phagocytosis and promotes anti-inflammatory cytokine production.
Conclusions:
- Cellular polarization state critically regulates myelin phagocytosis in human microglia.
- The MerTK pathway is a key mediator of myelin ingestion and is differentially regulated by polarization states.
- Modulating MerTK activity offers a potential therapeutic avenue for enhancing myelin clearance and promoting tissue repair in multiple sclerosis.
Related Concept Videos
01:15Receptor Downregulation in MVBs
The EGFR can initiate signaling pathways that lead to cell proliferation, migration, and differentiation. Overexpression of EGFR stimulates cells to proliferate. Excessive EGFR...
02:23Master Transcription Regulators
01:25Immune Surveillance by NK Cells and Phagocytes
Natural Killer Cells: The Fast Responders
NK cells are large granular lymphocytes found in the blood and lymphatic system. These...