Buffering of cytosolic calcium plays a neuroprotective role by preserving the autophagy-lysosome pathway during MPP⁺-induced neuronal death

Parkinson’s disease (PD) is a chronic neurodegenerative disease with no cure. Calbindin, a Ca²⁺-buffering protein, has been suggested to have a neuroprotective effect in the brain tissues of PD patients and in experimental models of PD. However, the underlying mechanisms remain elusive. Here, we report that in 1-methyl-4-phenylpyridinium (MPP⁺)-induced culture models of PD, the buffering of cytosolic Ca²⁺ by calbindin-D28 overexpression or treatment with a chemical Ca²⁺ chelator reversed impaired autophagic flux, protecting cells against MPP⁺-mediated neurotoxicity. When cytosolic Ca²⁺ overload caused by MPP⁺ was ameliorated, the MPP⁺-induced accumulation of autophagosomes decreased and the autophagic flux significantly increased. In addition, the accumulation of damaged mitochondria and p62-positive ubiquitinated protein aggregates, following MPP⁺ intoxication, was alleviated by cytosolic Ca²⁺ buffering. We showed that MPP⁺ treatment suppressed autophagic degradation via raising the lysosomal pH and therefore reducing cytosolic Ca²⁺ elevation restored the lysosomal pH acidity and normal autophagic flux. These results support the notion that functional lysosomes are required for Ca²⁺-mediated cell protection against MPP⁺-mediated neurotoxicity. Thus, our data suggest a novel process in which the modulation of Ca²⁺ confers neuroprotection via the autophagy-lysosome pathway. This may have implications for the pathogenesis and future therapeutic targets of PD.