Vitamin C attenuates PM2.5-induced thyroid dysfunction and mitophagy dysregulation by rebalancing ER-mitochondrial Ca²⁺ dynamics.

As a prevalent air pollutant, PM2.5 has been associated with a wide array of adverse health effects; however, the mechanisms by which it damages the thyroid remain only partially understood. In this study, we investigated whether calcium dyshomeostasis driven by endoplasmic reticulum (ER) stress and changes related to mitophagy may contribute to PM2.5-induced thyroid injury in female Sprague-Dawley rats and FRTL5 thyrocytes, as well as whether vitamin C (Vc) could provide protective effects. Our results demonstrated that PM2.5 compromised thyroid function and histoarchitecture, triggered ER stress, altered the expression and spatial distribution of IP3R1, GRP75, and VDAC1 at mitochondria-associated ER membranes (MAMs), and induced mitochondrial Ca²⁺ overload, accumulation of reactive oxygen species (ROS), loss of membrane potential, and changes in PINK1/Parkin-dependent mitophagy markers, accompanied by GPX4 suppression and Fe²⁺ accumulation. Inhibition of ER stress (using 4-PBA), blockade of IP3R-mediated Ca²⁺ release (using 2-APB), or disruption of mitochondrial division (using Mdivi-1) each mitigated cellular damage, providing pharmacological evidence for the proposed ER-mitochondria injury axis. Additionally, Vc similarly attenuated these alterations to varying extents. In conclusion, our findings offer valuable insights into the potential mechanisms through which Vc may alleviate PM2.5-associated thyroid toxicity by restoring the ER-mitochondrial Ca²⁺ balance, which has significant implications for pollutant risk assessment and protective strategies.