Resistance of mitochondrial DNA-depleted cells against oxidized low-density lipoprotein-induced macrophage pyroptosis

Oxidized low-density lipoprotein (Ox-LDL)-induced macrophage pyroptosis is critical in atherosclerosis inflammation and plaque instability. It has been reported that mitochondrial (mt)DNA-depleted (rho0) cells demonstrate resistance to apoptosis. However, little is known about the susceptibility of rho0 cells to Ox-LDL-induced macrophage pyroptosis. Pyroptosis, a caspase-1-dependent programmed cell death, which compromises membrane integrity, cleaves pro-interleukin (IL)-1 beta and pro-IL-18 into IL-1 beta and IL-18, respectively and releases damage-associated molecular pattern molecules, is triggered by a variety of stimuli, including Ox-LDL. In the present study, the expression levels of cleaved caspase-1 and IL-1 beta in Ox-LDL-treated J774A.1 rho0 cells were observed to be significantly decreased when compared with Ox-LDL-treated J774A.1 normal cells. Furthermore, J774A.1 rho0 cells exhibited a significant reduction in the ratios of dead cells and lactate dehydrogenase release following Ox-LDL stimulation compared with the J774A.1 normal cells. In addition, the loss of mtDNA did not influence Ox-LDL-induced cholesterol accumulation in J774A.1 rho0 cells, which was observed by Oil Red O staining and CHOD-PAP assay. Finally, J774A.1 rho0 cells exhibited reduced reactive oxygen species (ROS) production and were capable of maintaining the mitochondrial membrane potential following Ox-LDL treatment. Thus, the results indicate that the loss of mtDNA potentially rendered murine macrophage J774A.1 resistant to Ox-LDL-induced pyroptosis by mitigating NACHT, LRR and PYD domains-containing protein 3 inflammasome activation through reducing ROS production. In addition, mtDNA depletion did not interrupt Ox-LDL-induced intracellular lipid accumulation and continued to maintain the mitochondrial membrane potential.