Chronic Cadmium Exposure Impairs Macrophage Mitochondrial Homeostasis and Promotes Macrophage Polarization Contributing to Atherosclerosis via Regulating RIPK3 Signaling

Abstract Background: Chronic cadmium (Cd) exposure can contribute to the progression of cardiovascular disease (CVD), especially atherosclerosis (AS), but the underlying mechanism is unclear. Since mitochondrial homeostasis is emerging as a core player in the development of CVD, it might serve as a potential mechanism linking Cd exposure and AS. Here, we aimed to investigate the Cd-induced AS through macrophage polarization and tried to find out the mechanism of mitochondrial dysfunction caused by Cd exposure. Methods and results: In vitro, flow cytometry showed that Cd exposure markedly promoted M1-type polarization of macrophages, manifesting as the increasing expression of NF-kB, NLRP3 and their downstream inflammatory factors, IL-1β and IL-6. Mitochondrial function test revealed that the decreasing mitochondrial membrane potential and increasing superoxide (mROS) and mitochondrial fission were involved in Cd-induced macrophage polarization. Transmission electron microscope observation and immunofluorescence both identified the decrease of mitophage after Cd exposure. And improving mitochondrial function above significantly restored the balance of macrophage polarization. In vivo, Cd exposure was positively correlated with blood Cd concentration, and oil red O staining showed higher blood Cd significantly increased the area of AS plaques. Besides, M1-type polarization of macrophages and mitochondrial dysfunction were observed in mouse aortic roots through immunofluorescence and western blot as the dosage of Cd increasing. And the administered NAC or Mdivi-1, which decreased mROS or mitochondrial fission, markedly attenuated AS plaques and macrophage M1-type polarization in Cd-treated group. Finally, the up-regulated expressions of RIPK3 and p-MLKL were observed both in vitro and in vivo. And knocking out RIPK3 with decreasing expression of p-MLKL followed did improve mitochondrial dysfunction caused by Cd which effectively reversed macrophage polarization. Conclusion: Cd exposure activated RIPK3 pathway and impaired mitochondrial homeostasis, resulting in macrophage polarization to a pro-inflammatory phenotype and subsequent AS. These findings suggest that improving mitochondrial homeostasis may provide a potential therapeutic target for AS induced by chronic Cd exposure.