Irgm1 is required for the inflammatory function of M1 macrophage in early experimental autoimmune encephalomyelitis

Area of Science:

• Immunology
• Neuroscience
• Cell Biology

Background:

• Classically activated (M1) macrophages are vital in experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis (MS).
• Existing research primarily examines M1 macrophage impact on central nervous system (CNS) demyelination in EAE.
• The role of M1 macrophages in early EAE and their underlying molecular mechanisms remain largely unexplored.

Purpose of the Study:

• To investigate the role of immunity-related GTPase family member 1 (Irgm1) in M1 macrophage function during the early stages of EAE.
• To elucidate the molecular mechanisms by which Irgm1 influences M1 macrophage activity and T cell differentiation in EAE.

Main Methods:

• Analysis of Irgm1 expression in M1 macrophages from EAE mice.
• In vitro silencing and knockout of IRGM1 in M1 macrophages.
• Assessment of M1 macrophage markers (NOS2), inflammatory cytokine release, and signaling pathways (Akt, NF-κB p65).
• In vivo macrophage depletion studies.
• Evaluation of T cell differentiation (Th1, Th17, T regulatory cells) in spleen and draining lymph nodes (dLNs).

Main Results:

• Irgm1 was expressed in M1 macrophages in dLNs during early EAE.
• IRGM1 heterozygosity reduced M1 macrophage accumulation in dLNs and spleen.
• In vitro IRGM1 silencing impaired NOS2 expression and inflammatory cytokine release from M1 macrophages.
• IRGM1 knockout in M1 macrophages altered Akt and NF-κB p65 activation.
• Macrophage depletion inhibited Th1/Th17 differentiation and promoted T regulatory cell polarization.
• M1 macrophages promoted Th1/Th17 differentiation in vitro, an effect reversed by IRGM1 siRNA or anti-cytokine antibodies.

Conclusions:

• M1 macrophages promote Th1/Th17 cell differentiation in early EAE.
• The pro-inflammatory function of M1 macrophages in EAE is dependent on Irgm1.
• Irgm1 plays a critical role in regulating M1 macrophage activity and subsequent T cell responses during the initial phase of EAE.