[Molecular Mechanism Underlying Inflammatory Cell Death via Necroptosis in M1 Macrophages]

M1 macrophages, also known as inflammatory macrophages, play an important role in the innate and adaptative immune responses against pathogens. However, the overactivation of these macrophages leads to the development and progression of various inflammatory diseases. Thus, the regulation of these macrophages is necessary to prevent such diseases. Necroptosis, a programmed form of necrosis, induces several damage-associated molecular patterns, such as high-mobility group box 1, adenosine triphosphate, and mitochondrial DNA, which activate various immune cells, thus leading to inflammation. Recent studies have shown that necroptosis in M1 macrophages is associated with inflammation in many pathological conditions. However, the molecular mechanisms underlying necroptosis in M1 macrophages are not completely understood. Thus, we examined the effects of a broad-spectrum caspase inhibitor, zVAD-fmk, on cell death in lipopolysaccharide (LPS)-induced M1 macrophages. Necrostatin-1, an inhibitor of necroptosis, partially inhibited zVAD-fmk-induced cell death and phosphorylation of mixed lineage kinase domain-like protein (MLKL) in M1 macrophages. Moreover, the inhibition of generation of reactive oxygen species (ROS) and activation of p38 mitogen-activated protein kinase (MAPK) reduced zVAD-fmk-induced necroptosis in M1 macrophages. Furthermore, the inhibition of ROS generation suppressed the activation of MLKL and p38 MAPK in zVAD-fmk-treated M1 macrophages. These results indicate that zVAD-fmk-induced cell death occurs via necroptosis through ROS-mediated activation of MLKL and p38 MAPK in M1 macrophages. Unraveling the molecular mechanisms of necroptosis in M1 macrophages might help understand their significance in inflammatory diseases.