Macrophages are vital components of the immune system and serve as the first line of defense against pathogens. Macrophage colony-stimulating factor (M-CSF) induces macrophage differentiation from bone marrow-derived cells (BMDCs). Δ9-tetrahydrocannabiol (THC), a phytocannabinoid from the Cannabis plant, has profound anti-inflammatory properties with significant effects on myeloid cells. To investigate the effect of THC on macrophage differentiation, we cultured BMDCs with M-CSF in the presence of THC. Interestingly, THC markedly blocked the differentiation of BMDCs into CD45 + CD11b + F4/80+ macrophages. The effect of THC was independent of cannabinoid receptors CB1, and CB2, as well as other potential receptors such as GPR18, GPR55, and Adenosine 2A Receptor. RNA-seq analysis revealed that the THC-treated BMDCs displayed a significant increase in the expression of NRF2-ARE-related genes. KEGG pathway analysis revealed that the expression profiles of THC-treated cells correlated with ferroptosis and glutathione metabolism pathways. Fluorescence-based labile iron assays showed that the THC-treated BMDCs had significantly increased iron levels. Finally, THC-exposed BMDCs showed decreased levels of intracellular ROS. THC has the unique molecular property to block the Fenton Reaction, thus preventing the increase in intracellular ROS that is normally induced by high iron levels. Together, these studies demonstrated that THC blocks M-CSF-induced macrophage differentiation by inhibiting ROS production through both the induction of NRF2-ARE-related gene expression and the prevention of ROS formation via the Fenton Reaction.

Acute respiratory distress syndrome (ARDS) is a severe inflammatory lung disorder triggered by pneumonia, sepsis, trauma, and COVID-19, leading to high mortality. In this study, we investigated the effect of aryl hydrocarbon receptor (AhR) activation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent ligand, on LPS-induced ARDS in mice using single-cell RNA sequencing (scRNA-seq). scRNA-seq revealed 16 transcriptionally distinct cell clusters in the lungs. AhR activation reversed the decreased pulmonary functions caused by LPS, and significantly reduced pulmonary infiltration of monocytes, neutrophils, and macrophages. Interestingly, AhR activation during ARDS led to increased proportions of alveolar macrophages and angiogenic and quiescent endothelial cells. Among the downregulated pathways, prostaglandin signaling was the most broadly suppressed across many cell types in the LPS + TCDD group. AhR activation suppressed the neutrophil chemotaxis pathway involving Cxcl2, Cxcl3, and Cxcl10. The damage to endothelial and epithelial cells induced during ARDS was also blocked by AhR activation. This was associated with decreased expression of S100a8 and S100a9. Notably, multiple pathways related to cellular junction organization were enriched following AhR activation. Additionally, Scgb1a1, also called club cell protein 16 (CC16), primarily secreted by club cells in the respiratory epithelium, was highly upregulated following AhR activation, accounting for lung homeostasis. Together, these findings demonstrate that AhR activation mitigates key inflammatory and barrier-disruptive processes involving multiple cell types in LPS-induced ARDS. These data identify AhR as a central regulator of pulmonary inflammation and epithelial–endothelial integrity and support the future evaluation of AhR-targeted therapeutics as potential treatment for ARDS.