Ca2+ transfer via the ER-mitochondria tethering complex in neuronal cells contribute to cadmium-induced autophagy.

Mitochondrial-associated endoplasmic reticulum (ER) membranes (MAMs) play a key role in several physiological functions, including calcium ion (Ca2+) transfer and autophagy; however, the molecular mechanism controlling this interaction in cadmium (Cd)-induced neurotoxicity is unknown. This study shows that Cd induces alterations in MAMs and mitochondrial Ca2+ levels in PC12 cells and primary neurons. Ablation or silencing of mitofusin 2 (Mfn2) in PC12 cells or primary neurons blocks the colocalization of ER and mitochondria while reducing the efficiency of mitochondrial Ca2+ uptake. Moreover, Mfn2 defects reduce interactions or colocalization between GRP75 and VDAC1. Interestingly, the enhancement of autophagic protein levels, colocalization of LC3 and Lamp2, and GFP-LC3 puncta induced by Cd decreased in Mfn2-/- or Grp75-/- PC12 cells and Mfn2- or Grp75-silenced primary neurons. Notably, the specific Ca2+ uniporter inhibitor RuR blocked both mitochondrial Ca2+ uptake and autophagy induced by Cd. Finally, this study proves that the mechanism by which IP3R-Grp75-VDAC1 tethers in MAMs is associated with the regulation of autophagy by Mfn2 and involves their role in mediating mitochondrial Ca2+ uptake from ER stores. These results give new evidence into the organelle metabolic process by demonstrating that Ca2+ transport between ER-mitochondria is important in autophagosome formation in Cd-induced neurodegeneration.

Cadmium induces mitophagy via AMP-activated protein kinases activation in a PINK1/Parkin-dependent manner in PC12 cells.

OBJECTIVES: Cadmium (Cd) induces mitophagy in neuronal cells, but the underlying mechanisms remain unknown. In this study, we aimed to investigate these mechanisms. MATERIALS AND METHODS: The effects of Cd on the mitophagy in rat pheochromocytoma PC12 cells were detected, and the role of PINK1/Parkin pathway in Cd-induced mitophagy was also analysed by using PINK1 siRNA. In order to explore the relationship between AMPK and PINK1/Parkin in Cd-induced mitophagy in PC12 cells, the CRISPR-Cas9 system was used to knock down AMPK expression. RESULTS: The results showed that Cd treatment triggered a significant increase in mitophagosome formation and the colocalization of mitochondria and lysosomes, which was further proved by the colocalization of LC3 puncta and its receptors NDP52 or P62 with mitochondria in PC12 cells. Moreover, an accumulation of PINK1 and Parkin was found in mitochondria. Additionally, upon PINK1 knock-down using PINK1 siRNA, Cd-induced mitophagy was efficiently suppressed. Interestingly, chemical or genetic reversal of AMPK activation: (a) significantly inhibited the activation of mitophagy and (b) promoted NLRP3 activation by inhibiting PINK/Parkin translocation. CONCLUSIONS: These results suggest that Cd induces mitophagy via the PINK/Parkin pathway following AMPK activation in PC12 cells. Targeting the balanced activity of AMPK/PINK1/Parkin-mediated mitophagy signalling may be a potential therapeutic approach to treat Cd-induced neurotoxicity.