β-carotene alleviates PM2.5-induced pulmonary fibrosis via suppression of the Frizzled5-mediated Wnt5a/Ca2+pathway

Exposure to fine particulate matter (PM2.5) is a major environmental risk factor for pulmonary fibrosis, yet the involvement of calcium dyshomeostasis and its upstream Wnt signaling regulators in this process remains incompletely understood. This study investigated whether the dietary antioxidant β-carotene (BC) alleviates PM2.5-induced pulmonary fibrosis by modulating the Wnt5a/Ca2+ pathway and, if so, to identify the receptor mediating this effect. We employed a C57BL/6 murine model of intratracheal PM2.5 instillation, alongside BEAS-2B human bronchial epithelial cells subjected to Fzd5 overexpression. In vivo, PM2.5 exposure induced significant fibrosis, oxidative stress, and calcium homeostasis disruption, characterized by increased mitochondria-associated ER membranes (MAMs), aberrant expression of calcium-handling proteins (IP3R, STIM1, ORAI1, SERCA2), and activation of the Wnt5a/Fzd5/Ca2+ axis. BC treatment effectively reversed these pathological changes. In vitro, Fzd5 overexpression not only exacerbated PM2.5-evoked activation of the Wnt5a/Ca2+ pathway, calcium overload, oxidative stress, and EMT, but also, crucially, abrogated the protective effects of BC against these fibrotic changes. These results identify Fzd5 as a critical mediator through which BC acts. Our findings demonstrate that BC ameliorates PM2.5-induced pulmonary fibrosis by suppressing the Fzd5-mediated Wnt5a/Ca2+ pathway, thereby restoring calcium homeostasis. This study reveals a novel mechanistic axis in PM2.5 pathogenesis and suggests that BC may hold promise as a dietary supplement for mitigating environment-related pulmonary fibrosis.