Reconstitution of the Human Nigro-striatal Pathway on-a-Chip Reveals OPA1-Dependent Mitochondrial Defects and Loss of Dopaminergic Synapses.

Stem cell-derived neurons are generally obtained in mass cultures that lack both spatial organization and any meaningful connectivity. We implement a microfluidic system for long-term culture of human neurons with patterned projections and synaptic terminals. Co-culture of human midbrain dopaminergic and striatal medium spiny neurons on the microchip establishes an orchestrated nigro-striatal circuitry with functional dopaminergic synapses. We use this platform to dissect the mitochondrial dysfunctions associated with a genetic form of Parkinson's disease (PD) with OPA1 mutations. Remarkably, we find that axons of OPA1 mutant dopaminergic neurons exhibit a significant reduction of mitochondrial mass. This defect causes a significant loss of dopaminergic synapses, which worsens in long-term cultures. Therefore, PD-associated depletion of mitochondria at synapses might precede loss of neuronal connectivity and neurodegeneration. In vitro reconstitution of human circuitries by microfluidic technology offers a powerful system to study brain networks by establishing ordered neuronal compartments and correct synapse identity.