L-Arginine Attenuates Heat Stress-Induced Oxidative Damage and Apoptosis in Bovine Neutrophils via NFE2L2-Mediated...

Heat stress severely impairs immune function and threatens dairy cow health and productivity. Although heat stress suppresses bovine neutrophil (PMN) phagocytosis, its effects governing PMN survival remain unclear. L-arginine (L-Arg) exerts immunomodulatory and cytoprotective effects, yet its role in repairing heat-damaged PMN has not been defined. In this study, an in vitro heat stress model (42 °C for 2.5 h) was established. Heat stress significantly reduced cell viability, induced abnormal nuclear morphology, and triggered apoptotic signaling, accompanied by severe oxidative stress (elevated reactive oxygen species (ROS)/Malondialdehyde (MDA), decreased SOD/glutathione peroxidase (GSH-Px)). The ROS scavenger N-Acetylcysteine (NAC) mitigated both oxidative stress and apoptosis, confirming oxidative stress as a core mediator of PMN apoptosis induced by heat stress. Pretreatment with 4 mmol/L L-Arg significantly alleviated heat-induced oxidative damage and apoptosis. Mechanistically, in bovine PMN, we first demonstrated that heat stress blocks nuclear factor erythroid 2-related factor 2 (NFE2L2) nuclear translocation; inhibition of NFE2L2 (ML385) abolished L-Arg's protection, verifying the NFE2L2-dependent ROS scavenging pathway. In conclusion, this study reveals that heat stress induces bovine PMN oxidative injury and apoptosis by suppressing NFE2L2-mediated ROS scavenging, and L-Arg restores PMN viability and immune resilience by reactivating the NFE2L2 antioxidant pathway. These findings provide a targeted L-Arg supplement strategy to improve PMN survival and disease resistance in heat-stressed dairy cows.