Chronic stress induces depression-like behaviors and Parkinsonism via upregulating α-synuclein

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the aggregation of alpha-synuclein (alpha-syn) and the nigrostriatal dopaminergic neuronal degeneration. Depression is one of the most common non-motor symptoms of PD patients. However, the pathogenic connection between PD and depression is not well understood. Herein, we report that chronic stress upregulates the expression of alpha-syn in the mouse brain. Overexpression of alpha-syn in the hippocampus replicates depressive-like phenotypes, whereas the genetic deletion of alpha-syn enhances resistance to chronic stress. Furthermore, chronic stress in early life promoted the deposition of alpha-syn aggregates in a transgenic mouse model that overexpresses human A53T mutant alpha-syn (A53T mice). Chronic stress also exacerbated dopaminergic degeneration and motor impairments in A53T mice. Strikingly, alpha-syn inclusions were also observed in the brains of some aged non-transgenic mice subjected to chronic stress. Together, our findings suggest that chronic stress upregulates alpha-synuclein expression, resulting in depression-like behaviors and parkinsonism.