Wildfire-Emitted Particulate Matter Induces Ovarian Hyperandrogenism through Aryl Hydrocarbon Receptor Activation

Abstract Wildfires have become more frequent and intense worldwide, and this trend is projected to continue in the coming years. Wildfire-emitted particulate matter (WFPM) can be more toxic than urban background PM due to its greater content of nanosized PM (WFPM0.1) and more polar organic compounds, including polycyclic aromatic hydrocarbons (PAHs). While exposure to WFPMs has been linked to cardiovascular and respiratory diseases, their impact on female reproductive health remains elusive. We examined the female reproductive impacts of lab-synthesized (LS-) and real-world Canadian WFPM0.1 (C-WFPM0,1) collected during the June 2023 Canadian wildfires and investigated the toxic mechanisms involved. An in vivo mouse model through intratracheal exposure and a 3D in vitro ovarian follicle culture system, together with molecular, transcriptomic, and computational approaches, was used to examine the ovarian disrupting effects of LS- and C-WFPM0.1. Intratracheal in vivo exposure to an environmentally relevant dose of LS-WFPM0.1 disrupted mouse ovarian estrus cycles and elevated serum concentrations of testosterone. RT-qPCR and RNA-sequencing (RNA-seq) analyses revealed altered expression of steroidogenic genes, transcriptomic changes, and activation of the aryl hydrocarbon receptor (AhR) in antral follicles from mice treated with LS-WFPM0.1. LS-WFPM0.1 consistently increased testosterone secretion and stimulated genes related to androgen synthesis and AhR in vitro. Single-follicle and single-oocyte RNA-seq analyses identified differentially expressed genes related to inflammation in follicular somatic cells and mitochondrial health in oocytes. Both C-WFPM0.1 and established AhR agonists, including benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), reproduced these ovarian defects. Mechanistically, inhibition of AhR reversed the WFPM0.1-induced transcriptional changes of steroidogenic genes and ovarian hyperandrogenism. Together, our study suggests that exposure to WFPM0.1 disrupts ovarian hormone secretion by inducing hyperandrogenism, which is associated with AhR activation, underscoring an urgent need for further mechanistic and epidemiological studies to define the reproductive risks of wildfire smoke exposure in humans.