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Macrophage Differentiation and Polarization into an M2-Like Phenotype using a Human Monocyte-Like THP-1 Leukemia Cell Line
Published on: August 2, 2021
Trypsin, Tryptase, and Thrombin Polarize Macrophages towards a Pro-Fibrotic M2a Phenotype
Michael J V White1, Richard H Gomer1
1Department of Biology, Texas A&M University, College Station, Texas, United States of America.
Abstract:
For both wound healing and the formation of a fibrotic lesion, circulating monocytes enter the tissue and differentiate into fibroblast-like cells called fibrocytes and pro-fibrotic M2a macrophages, which together with fibroblasts form scar tissue. Monocytes can also differentiate into classically activated M1 macrophages and alternatively activated M2 macrophages. The proteases thrombin, which is activated during blood clotting, and tryptase, which is released by activated mast cells, potentiate fibroblast proliferation and fibrocyte differentiation, but their effect on macrophages is unknown. Here we report that thrombin, tryptase, and the protease trypsin bias human macrophage differentiation towards a pro-fibrotic M2a phenotype expressing high levels of galectin-3 from unpolarized monocytes, or from M1 and M2 macrophages, and that these effects appear to operate through protease-activated receptors. These results suggest that proteases can initiate scar tissue formation by affecting fibroblasts, fibrocytes, and macrophages.
Insights
Proteases like thrombin and tryptase promote scar tissue formation by directing monocyte differentiation towards pro-fibrotic M2a macrophages. This research reveals a new mechanism in fibrotic lesion development.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Circulating monocytes differentiate into fibrocytes and M2a macrophages, crucial for scar tissue formation during wound healing and fibrosis.
- Proteases thrombin and tryptase are known to enhance fibroblast proliferation and fibrocyte differentiation.
- The impact of these proteases on macrophage differentiation remains largely uncharacterized.
Purpose of the Study:
- To investigate the effect of proteases (thrombin, tryptase, and trypsin) on human monocyte differentiation.
- To determine if proteases influence macrophage polarization towards a pro-fibrotic phenotype.
- To elucidate the role of protease-activated receptors in this process.
Main Methods:
- Human monocytes were cultured and exposed to thrombin, tryptase, or trypsin.
- Macrophage differentiation and polarization were assessed.
- Expression levels of pro-fibrotic markers, such as galectin-3, were quantified.
- The involvement of protease-activated receptors was examined.
Main Results:
- Thrombin, tryptase, and trypsin biased human monocyte differentiation towards the pro-fibrotic M2a phenotype.
- This M2a polarization occurred from unpolarized monocytes, M1, and M2 macrophages.
- Elevated galectin-3 expression was observed in protease-treated macrophages.
- These effects were mediated through protease-activated receptors.
Conclusions:
- Proteases significantly influence macrophage differentiation, promoting a pro-fibrotic M2a phenotype.
- This protease-driven M2a polarization contributes to scar tissue formation.
- The findings suggest proteases are key initiators in fibrotic processes involving fibroblasts, fibrocytes, and macrophages.
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