IBRV induces mitochondrial apoptosis via the ER-mitochondrial calcium axis mediated by unfolded protein response in MDBK cells.

Infectious bovine rhinotracheitis virus (IBRV), also known as bovine herpesvirus 1 (BoHV-1), is a globally important pathogen causing severe cattle diseases and substantial economic losses. However, the molecular mechanism by which IBRV induces host cell apoptosis through endoplasmic reticulum (ER)-mitochondria crosstalk remains largely unclear. In this study, Madin-Darby bovine kidney (MDBK) cells were used as an in vitro experimental model. Multiple experimental approaches including transmission electron microscopy, laser confocal microscopy, western blotting, flow cytometry, pharmacological inhibition, and siRNA interference, were applied to investigate the apoptotic mechanism triggered by IBRV infection. The results showed that IBRV infection destroyed ER ultrastructure and upregulated the expression of ER stress biomarker GRP78, accompanied by the full activation of three core branches of the unfolded protein response (UPR), including PERK, IRE1, and ATF6. Meanwhile, IBRV significantly promoted the formation of ER-mitochondrial membrane contact sites (MCSs) and triggered excessive Ca2+ release from the ER, leading to mitochondrial Ca2+ overload. Such Ca2+ dyshomeostasis further induced mitochondrial dysfunction, including reduced ATP production, collapsed mitochondrial membrane potential, and excessive reactive oxygen species accumulation, which ultimately activated caspase-dependent mitochondrial apoptosis. Inhibition of UPR signaling or ER-mitochondrial Ca2+ transport markedly alleviated mitochondrial damage, suppressed apoptosis, and reduced viral protein expression. Collectively, these findings demonstrate that the UPR-Ca2+-mitochondria axis serves as a key signaling pathway for IBRV-induced cell apoptosis, and that host UPR signaling is exploited by IBRV to support efficient viral replication, revealing a novel molecular pathogenic mechanism of IBRV and providing potential targets for the development of anti-IBRV therapeutic strategies.