Optogenetic Rescue of Locomotor Dysfunction and Dopaminergic Degeneration Caused by Alpha-Synuclein and EKO Genes.

alpha-Synuclein (alpha-Syn) is a small presynaptic protein and its mutant forms (e. g. A53T) are known to be directly associated with Parkinson's disease (PD). Pathophysiological mechanisms underlying alpha-Syn-mediated neurodegeneration in PD still remain to be explored. However, several studies strongly support that overexpression of mutant alpha-Syn causes reduced release of dopamine (DA) in the brain, and contributes to motor deficits in PD. Using a favorable genetic model Drosophila larva, we examined whether reduced DA release is enough to induce key PD symptoms (i.e. locomotion deficiency and DA neurodegeneration), mimicking a PD gene alpha-Syn. In order to reduce DA release, we expressed electrical knockout (EKO) gene in DA neurons, which is known to make neurons hypo-excitable. EKO led to a decrease in a DA neuronal marker signal (i.e., TH-tyrosine hydroxylase) and locomotion deficits in Drosophila larva. In contrast, acute and prolonged exposure to blue light (BL, 470 nm) was sufficient to activate channelrhodopsin 2 (ChR2) and rescue PD symptoms caused by both alpha-Syn and EKO. We believe this is for the first time to confirm that locomotion defects by a genetic PD factor such as alpha-Syn can be rescued by increasing DA neuronal excitability with an optogenetic approach. Our findings strongly support that PD is a failure of DA synaptic transmission, which can be rescued by optogenetic activation of ChR2.