Year 3

Mitochondria are a cell’s power plants that provide almost all the energy a cell needs. When these cellular power plants are damaged by stressful factors present in aging neurons, they release toxins (reactive oxygen species) to the rest of the neuron that can cause neuronal cell death (neurodegeneration). Healthy cells have an elegant mitochondrial quality control system to clear dysfunctional mitochondria and prevent their resultant devastation. It is not surprising that the impairment in this mitochondrial quality control system has been linked to Parkinson’s disease (PD), one of the most common neurodegenerative diseases. Based on our previous work that Parkinson’s associated proteins PINK1 and Parkin halt mitochondrial transport that might be essential for the damaged mitochondrial clearance, we hypothesized that in Parkinson’s mutant neurons mitochondrial quality control is impaired thereby leading to neurodegeneration, in the original application. For the past year, we have made substantial progress in achieving the specific aims. Briefly, using induced pluripotent stem cell (iPSC)-derived neurons and other complementary models, we have uncovered a defect in clearance of damaged mitochondria in PD. We have shown that in mutant cells the mitochondrial outer membrane protein Miro is stabilized and remains on damaged mitochondria for longer than normal, prolonging active transport and inhibiting mitochondrial degradation, in both familial and sporadic PD patients. Thus, impairment in Miro and mitochondrial quality control may constitute a central component of PD pathogenesis. Remarkably, partial reduction of Miro levels in human PD neuron and Drosophila PD models rescues neurodegeneration. We have revealed that prolonged retention of Miro, and the downstream consequences that ensue, may constitute a central component of PD pathogenesis.