ID2 Regulates Macrophage Polarization and Mediates Methotrexate Responsiveness in Rheumatoid Arthritis

Area of Science:

• Immunology
• Molecular Biology
• Rheumatology

Background:

• Rheumatoid arthritis (RA) is a chronic inflammatory disease.
• Methotrexate (MTX) is the primary therapy for RA, but patient responses are inconsistent.
• Macrophages play a key role in RA pathogenesis, but their specific role in MTX response is not fully understood.

Purpose of the Study:

• To investigate the heterogeneity of monocytes/macrophages in RA patients.
• To identify immune cell transcriptional programs influencing MTX responsiveness.
• To explore the role of inhibitor of differentiation 2 (ID2) in MTX resistance.

Main Methods:

• Single-cell RNA sequencing of peripheral blood mononuclear cells from MTX-responsive and unresponsive RA patients.
• Gene-signature scoring and pseudotime analysis for assessing macrophage polarization.
• Gain- and loss-of-function studies, cytokine assays, and ChIP assays to investigate ID2 function.

Main Results:

• Macrophage-like monocytes from MTX-unresponsive patients showed increased M1 polarization.
• Specific monocyte subsets (PLBD1+, CDKN1A+) were enriched in non-responders, while others (RLIM+) were reduced.
• Elevated ID2 expression in macrophage-like monocytes correlated with M1 polarization and MTX resistance.
• In vitro, ID2 overexpression counteracted MTX's inhibitory effects on inflammation.

Conclusions:

• Monocyte/macrophage heterogeneity, particularly M1 polarization, is associated with MTX resistance in RA.
• ID2 acts as a regulator promoting pro-inflammatory macrophage polarization and potentially contributing to MTX resistance in RA.
• Targeting ID2 may offer a novel therapeutic strategy for improving MTX efficacy in RA patients.