Endoplasmic Reticulum Stress Drives Copper-Induced Reticulophagy in Porcine Hepatocytes.

Copper (Cu) supplementation for growth promotion in agriculture poses toxicological risks to animals and humans. Although Cu overload is known to trigger endoplasmic reticulum (ER) stress, the downstream cellular mechanisms driven by this stress are not fully characterized. Here, we identify the ER stress response as the primary initiator of reticulophagy (ER-phagy) in porcine liver models. Using an in vivo weaned piglet model exposed to agriculturally relevant Cu doses and an in vitro hepatocyte system, we demonstrate that Cu exposure activates UPR branches, including PERK/eIF2α phosphorylation, IRE1 and ATF6 proteins, and promotes GRP78-FAM134B association. This activation precipitated ER-phagy, evidenced by autophagosome formation, receptor upregulation, and LC3-II conversion. Pharmacological inhibition of ER stress (4-PBA) attenuated this autophagic response, whereas induction (PR-619) potentiated it. These findings suggest that the ER stress-ER-phagy axis contributes to Cu-induced hepatocellular stress, providing a mechanistic framework for reassessing Cu safety thresholds in livestock feed.