# Irf5 Knockdown in Bone Marrow-Derived Macrophages Favors M1-to-M2 Transition

## TL;DR

Reducing IRF5 in macrophages shifts them from a pro-inflammatory to an anti-inflammatory state, affecting their function and physical properties.

## Contribution

Demonstrates IRF5's dual role in regulating macrophage polarization and function.

## Key findings

- Irf5 knockdown in M1 macrophages leads to M2-like characteristics, including decreased iNOS and increased CD206.
- Irf5 reduction increases plasma membrane roughness and alters macrophage elasticity, especially in M2 macrophages.
- IRF5 is critical for maintaining metabolic and functional properties in both M1 and M2 macrophage states.

## Abstract

The transcription factor IRF5 maintains macrophages in the pro-inflammatory M1 state. We assessed the effects of siRNA-mediated knockdown of Irf5 on murine bone marrow-derived macrophages (BMDM) in M0, M1 and M2 states. Knockdown of Irf5 in M1 macrophages made them phenotypically similar to M2 macrophages, which was reflected in the decreased expression of the M1 marker iNOS, increased expression of the M2 marker CD206, increased mitochondrial content and respective morphological changes. Interestingly, the M2 phenotype was also affected by the reduction in Irf5. Using atomic force microscopy (AFM), we showed that Irf5 knockdown increases plasma membrane roughness, particularly in M2 macrophages. AFM-based stiffness measurements indicated that Irf5 knockdown altered macrophage elasticity, potentially influencing their functional behavior. Our data suggest a complex role of IRF5 in macrophage polarization, supporting its dual role as a transcriptional activator and repressor both in M1 and M2 states, and highlight the importance of IRF5 in the maintenance of metabolic and functional properties of macrophages.