α-Synuclein impairs mitochondrial function and alters cryptochrome regulation in the substantia nigra

Dopaminergic neurons in the substantia nigra pars compacta are key targets of -synuclein pathology and neurodegeneration in Parkinson's disease (PD). It is thought that pathological accumulation of -synuclein significantly contributes to nigral neuronal dysfunction and ensuing neuronal demise. In this study, we further assessed this possibility and interrogated the role of -synuclein burden in compromising neuronal function and altering physiological neuronal pathways. In particular, we focused on nigral mitochondrial impairment and disruption of circadian regulatory pathways triggered by sustained -synuclein expression. Using an in vivo AAV-mediated model, we show that -synuclein accumulation over a period of 12 weeks is associated with mitochondrial complex I and IV deficits and leads to dopaminergic cell loss. Proximity ligation assays revealed association of both total and phosphorylated -synuclein with mitochondrial proteins at a time (between 4 and 12 weeks) that paralleled the development of mitochondrial dysfunction. Spatial transcriptomic analysis of the substantia nigra identified coordinated alterations in genes involved in mitochondrial, metabolic, and circadian pathways, including increased expression of circadian-associated genes such as Nr1d1, Nr1d2, Cry2, Arntl2, and Csnk1e. At the protein level, -synuclein overexpression was associated with a differential shift in cryptochrome protein expression, characterized by reduced CRY1 and increased CRY2. Data provide evidence of a specific window of time during which sustained -synuclein burden results in direct -synuclein-mitochondria interactions and nigral mitochondrial damage. During the same time period, a specific remodeling of molecular clock components occurs, providing a potential new mechanism contributing to metabolic and mitochondrial dysregulations and, ultimately, neuronal injury and degeneration.