Nucling, a stress-inducible protein associated with apoptosomes, is important for microglial polarization/activation in the brain neuroinflammation.

Microglia, the central nervous system's resident macrophages, are critical for immune defense, protecting neurons during infection. Their role in postnatal brain development, particularly after injury, remains unclear. Nucling, a protein up-regulated during cardiac muscle differentiation, regulates NF-κB, influencing apoptosis and cell proliferation. In this study, we examined the role of Nucling in microglial activation using wild-type (WT) and Nucling-knockout (KO) neonatal mice subjected to poly(I:C), a viral mimic. Poly(I:C) treatment increased Iba1-positive microglia in both genotypes; however, KO mice showed a significantly exaggerated response in both cortical and hippocampal regions. Furthermore, while proinflammatory M1 markers (iNOS, CD86, TNFα, IL-6) were upregulated in both WT and KO mice, the anti-inflammatory M2 marker Arginase 1 (Arg1) was induced in WT but significantly suppressed in KO mice, indicating impaired M2 polarization. These findings suggest that Nucling is essential for maintaining microglial polarization, supporting immunological processes against pathogens and aiding central nervous system development.