# Zinc‐Mediated Lysosomal Destabilization Links Mitochondrial Damage to Neuronal Death in a Cellular MPP + Model of Parkinson's Disease

## TL;DR

This study shows that mitochondrial damage leads to zinc buildup, which harms lysosomes and causes neuron death in Parkinson's disease.

## Contribution

The paper identifies intracellular zinc as a key mediator linking mitochondrial dysfunction to lysosomal damage and neuronal death in Parkinson's disease.

## Key findings

- Mitochondrial stress increases ROS and zinc, leading to lysosomal membrane permeabilization and cell death.
- MT-3 buffers cytosolic zinc during mitochondrial injury but can release it under oxidative conditions.
- Rho0 cells lacking mitochondrial function are resistant to MPP+ but remain sensitive to zinc and hydrogen peroxide.

## Abstract

Dysregulation of autophagy and lysosomal function is central to Parkinson's disease (PD), yet the upstream mechanisms leading to lysosomal failure remain unclear. Across primary mouse cortical neurons, MT‐3 deficient primary mouse astrocytes, human iPSC‐derived midbrain dopaminergic neurons, and Rho0 CHO cells lacking mitochondrial respiration, we investigated how mitochondrial stress perturbs zinc (Zn2+) homeostasis and lysosomal integrity. We identify intracellular zinc as a critical mediator linking mitochondrial dysfunction to lysosomal membrane permeabilization (LMP) and neuronal death. Inhibition of mitochondrial complex I by 1‐methyl‐4‐phenylpyridinium (MPP+) elevated reactive oxygen species (ROS) and intracellular zinc, jointly driving LMP. Blocking either ROS or zinc markedly attenuated lysosomal damage and cell death, demonstrating that both act upstream of LMP. To define zinc regulation, we examined metallothionein‐3 (MT‐3), a brain‐enriched zinc‐binding protein. MT‐3‐deficient astrocytes were more vulnerable to MPP+ and zinc overload (ZnCl2) but paradoxically resistant to hydrogen peroxide (H2O2), suggesting that MT‐3 buffers cytosolic zinc during mitochondrial injury or extracellular zinc influx yet can release bound zinc under oxidative conditions. Using Rho0 cells, we show that MPP+ toxicity depends on mitochondrial ROS, as loss of mitochondrial function nearly abolished cell death. However, Rho0 cells were highly sensitive to ZnCl2 and H2O2 and exhibited markedly reduced lysosomal abundance, indicating limited capacity to sequester zinc and increased susceptibility to zinc‐mediated injury. These findings support a coordinated system in which lysosomes and zinc‐binding proteins maintain zinc homeostasis. When cytosolic zinc rises, its accumulation within lysosomes induces LMP and accelerates cell death. Collectively, our results identify intracellular zinc as an upstream trigger of lysosomal dysfunction and neurodegeneration. Zinc‐mediated LMP provides a mechanistic link between mitochondrial injury, impaired autophagic flux, and α‐synuclein pathology in PD. Enhancing zinc homeostasis and lysosomal resilience may offer promising therapeutic strategies.

When mitochondria are damaged by MPP+, they produce excess reactive oxygen species (ROS) and release zinc (Zn2+) inside the cell. This surge in zinc overwhelms lysosomes—the cell's major zinc‐buffering organelles—causing their membranes to break down. Leaking lysosomal enzymes then trigger neuronal death. Treatments that reduce ROS, bind zinc, or block lysosomal proteases strongly protect against this damage. Cells lacking mitochondrial respiration do not show ROS or zinc increases and are resistant to MPP+, highlighting mitochondria as the starting point of this process. Because repeated lysosomal injury can diminish lysosomal capacity, these events may also contribute to protein accumulation seen in neurodegeneration.