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

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.