Inorganic arsenic and its methylated metabolites induce pulmonary immunosuppression via the p62-Keap1-Nrf2 positive feedback loop-mediated M2 macrophage polarization.

Abstract

Trivalent inorganic arsenic (iAsIII) is a widespread environmental contaminant associated with adverse health outcomes, including immune dysregulation. However, the mechanisms underlying pulmonary immunotoxicity induced by iAsIII and its methylated metabolites remain unclear. In this study, acute oral exposure to iAsIII in C57BL/6 mice elicited an early immunosuppressive shift in the pulmonary microenvironment, characterized by upregulated expression of M2 macrophage phenotypic markers and reduced inflammatory cytokines. In vitro, iAsIII and its methylated metabolites, monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII), promoted a phenotypic transition of murine alveolar macrophages from an M1- to an M2-like state. This shift was evidenced by decreased expression of the M1 marker iNOS and pro-inflammatory cytokines (IL-6 and IL-1β), along with enhanced expression of the M2 marker ARG1 and the anti-inflammatory cytokine IL-10, with MMAIII exhibiting the strongest immunosuppressive potency. Mechanistically, iAsIII and MMAIII robustly activated the Nrf2-HO-1 pathway, whereas DMAIII elicited relatively weaker activation. Silencing of Nrf2 abolished iAsIII- and MMAIII-driven M2 polarization, indicating an essential role for Nrf2. Furthermore, iAsIII and MMAIII induced aberrant accumulation of the autophagy adaptor p62, accompanied by impaired autophagic flux, lysosomal alkalinization, and increased lysosomal membrane permeability. Knockdown of p62 attenuated Nrf2 activation and reversed the M2-like polarization phenotype. Moreover, the reduction of p62 following Nrf2 silencing further suggests a bidirectional regulatory interaction between p62 and Nrf2. Collectively, these findings demonstrate that iAsIII and MMAIII drive alveolar macrophage polarization toward an immunosuppressive M2 phenotype via a p62-Keap1-Nrf2 positive feedback loop, providing mechanistic insight into iAsIII-induced pulmonary immunosuppression.

Key Findings

• Inorganic arsenic (iAsIII) and its methylated metabolites induce pulmonary immunosuppression by promoting M2 macrophage polarization.
• iAsIII and MMAIII activate the Nrf2-HO-1 pathway, which is essential for M2 polarization, as Nrf2 silencing abolishes this effect.
• A positive feedback loop involving p62, Keap1, and Nrf2 mediates macrophage polarization, with p62 accumulation impairing autophagic flux and enhancing Nrf2 activation.

Clinical Significance

Citation

Wei Xiaoxi, Ma Xinyu, Qu Ruijieet al.. Inorganic arsenic and its methylated metabolites induce pulmonary immunosuppression via the p62-Keap1-Nrf2 positive feedback loop-mediated M2 macrophage polarization. Ecotoxicology and environmental safety. 2026-May-02.