Synunclein dose dependent interaction with mitochondrial membrane regulates its size in a human Parkinson Disease model

ALLOATTI M; POZO-DEVOTO V; FALZONE T; SEVLEVER G; SAEZ T

San Diego

Simposio; Society for Neuroscience; 2016

Society for Neuroscience

In Parkinson?s Disease (PD) many genetic, pathological and pharmacological evidence converge into a common intracellular pathway that involves mitochondrial dysfunctions as an early and relevant event leading to neurodegeneration. Although initially, α-Synuclein (α-Syn) studies associated to PD have focused on its role on aggregation and toxicity and away from the mitochondria, recently, growing interest is dedicated to the possible role that α-Syn exerts over the mitochondrial quality control. Biophysical properties of WT α-Syn or the dominant mutations A30P and A53T α-Syn suggest differential lipid binding affinities, which can give a hint on α-Syn interaction mechanism with mitochondria. To test whether α-Syn drives a mitochondrial phenotype we developed different human PD neuronal models derived from hESC or genetically modified hIPSC to analyze the effect of WT, A30P and A53T α-Syn on mitochondrial axonal transport, membrane potential and morphology. Initially, by live imaging of fluorescent mitochondria in axons we analyzed whether WT α-Syn or PD related mutants impairs the axonal transport of mitochondria. Significant defects in mitochondrial flux were observed for A53T α-Syn overexpression and milder defects for WT and A30P. Interestingly, a reduction in mitochondrial size and increased density was observed upon A53T α-Syn overexpression. These defects correlated with a high to low ratio of α-Syn localization within the mitochondrial fraction for A53T, WT and A30P, respectively, suggesting a relation between α-Syn localization and mitochondrial size reduction. Therefore, we designed a targeting system based on FKBP-FRB dimerization to deliver α-Syn to the OMM and test whether α-Syn association with mitochondria mediates the morphology effect in human neurons. Surprisingly, we found that WT α-Syn delivery to the OMM reduced the size of the mitochondria to similar levels than A53T α-Syn, while A30P induced no effect. Finally, CRISP-r/CAS9 genome edition in hIPSC was generated to test whether the N-terminal domain of α-Syn mediates fragmentation. Human neurons derived from modified IPSC revealed the opposite to fragmentation with abnormal elongated and ramified axonal mitochondria. All together, our findings identify a new and relevant neuronal physiological role for α-Syn in the maintenance of mitochondrial morphology that when impaired by α-Syn overexpression or mutations can lead to abnormal fragmentation phenotypes as a common feature of PD.