Cadmium Induces Mitophagy Through ROS-mediated PINK1/Parkin Pathway In Mouse Kidney And Brain

Cadmium (Cd), as a heavy metal and an environmental toxicant, widely exists in the air, soil and water. Cd mainly originates from industry and agriculture, causes toxic and carcinogenic effects on the human body. Cd could accumulate on organism to affect growth, development and reproduction, induce excess reactive oxygen species (ROS) production, and could also lead to autophagy and mitophagy.Mitophagy is a specific process happening under various factors such as hypoxia, nutrient deprivation, photoirradiation and oxidative stress. During mitophagy, dysfunctional or excess mitochondria are selectively enclosed by autophagosome, and then merge with lysosomes. At last, damaged mitochondria are degraded by hydrolytic enzymes. Cd-activated mitophagy has been reported very recently, however, its potential molecular mechanism has not been completely explored.In this study, mice were intraperitoneally injected with cadmium chloride (CdCl2) for3days, and then mouse kidneys and brains were dissected to investigate Cd-induced mitophagy and its potential mechanisms:(1) Mitochondrial membrane potential (MMP), mitophagosomes, LC3-â…¡/LC3-â…  ratio, PINK1levels and mitochondrial mass were chosen as the mitophagy markers to reflect the occurrence and process of mitophagy after different concentrations of Cd (0.05,0.20,0.80mg/kg) exposure;(2) Exogenous ROS scavengers N-acetyl-L-cysteine (NAC) and Acetyl-1-carnitine (ALC) were respectively added to explore the potential roles of ROS in Cd-induced mitophagy and PINK1/Parkin pathway;(3) The mitophagy inhibitor Cyclosporine A (CsA) was used to further address the upstream signal of Cd-induced ROS in mitophagy and PINK1/Parkin pathway.The results were as follows:1. Cd (0.20,0.80mg/kg) significantly induced the MMP collapse (P<0.01) and typical mitophagosomes formation, increased LC3-â…¡/LC3-â…  ratio and PINK1levels (P<0.01), and decreased mitochondrial mass (P<0.01), revealing that Cd induced mitophagy in mouse kidney and brain.2. Cd (0.20,0.80mg/kg) significantly caused excess ROS production in mouse kidney and brain cells (P<0.01), which served for further exploring the roles of ROS in Cd-induced mitophagy and PINKl/Parkin pathway.3. The combination of NAC (100mg/kg) or ALC (30mg/kg) with Cd (0.20mg/kg) markedly decreased Cd-induced ROS levels (P<0.01) and simultaneously decreased Cd-induced LC3-â…¡/LC3-â…  ratio (P<0.01) and rescued MMP and mitochondrial mass (P<0.01), suggesting mat ROS played a crucial role in regulating Cd-induced mitophagy.4. The combination of NAC (100mg/kg) or ALC (30mg/kg) with Cd (0.20mg/kg) also dramatically decreased PINK1levels and mitochondrial accumulation of Parkin (P<0.01), indicating that ROS were involved in Cd-induced PINK1/Parkin pathway.5. The combination of mitophagy inhibitor CsA (10mg/kg) with Cd (0.20mg/kg) significantly lessened mitophagy process, during which Cd-induced LC3-â…¡/LC3-â…  ratio was decreased (P<0.01) and MMP and mitochondrial mass were rescued (P<0.01). Meanwhile, the combination of CsA with Cd also lessened PINK1levels and blocked mitochondrial accumulation of Parkin (P<0.01) while failed to affect ROS levels, showing that Cd-induced ROS functioned on the upstream of PINK1/Parkin pathway and eventually induced mitophagy.In conclusion, the present study demonstrated that Cd induced PINK1/Parkin-mediated mitophagy in mouse kidney and brain, and during which, Cd-induced ROS played ultimate roles on the upstream of PINK1/Parkin pathway to mediate mitophagy. The present study proposes a new evidence and perspective to evaluate the toxicity effects of Cd in vivo on kidney and brain as well as its molecular mechanism.