Aroclor 1254 inhibits anti-inflammatory macrophage polarization through an AhR-dependent mechanism.

Macrophages are critical regulators of tissue homeostasis and inflammation. During the development of chronic inflammatory diseases, tissue-resident macrophages often shift from an anti-inflammatory (M2) to a pro-inflammatory (M1) phenotype. Understanding the factors that drive this polarization shift is essential for elucidating the mechanisms underlying diseases such as cancer, cardiovascular disease, and metabolic syndrome. Environmental toxicants, including polychlorinated biphenyls (PCBs), may be key contributors to this dysregulation. Despite being banned in the United States for nearly 50 years, PCBs persist in the built and natural environment, with mixtures such as Aroclor 1254 still detected at concerning levels in schools and other public spaces. In this study, we investigated how Aroclor 1254 influences human monocyte-derived macrophage polarization. We found that exposure to Aroclor 1254 during differentiation skews naïve macrophages toward a pro-inflammatory phenotype, enhances LPS/IFNγ-driven M1 polarization, and inhibits both IL-4- and dexamethasone-induced M2 polarization. To explore underlying mechanisms, we examined the roles of peroxisome proliferator-activated receptor gamma (PPARγ), pyruvate kinase M2 (PKM2), and the aryl hydrocarbon receptor (AhR). We found AhR inhibition partially rescued PCB-mediated suppression of M2 polarization. Further supporting this mechanism, PCB126, a potent AhR agonist, recapitulated the disruption of polarization. Together, these findings demonstrate that PCB mixtures act through AhR to dysregulate macrophage polarization, driving a pro-inflammatory phenotype. This disruption may represent a key mechanism by which PCBs exacerbate tissue inflammation and contribute to the pathogenesis of chronic inflammatory diseases.