López de Maturana, R. , del Río, P. , Sousa, A. , Vázquez, N. , Azkona, G. , Zubiarrain, A. & Sánchez-Pernaute, R.
Laboratory of Stem Cells and Neural Repair, Fundación Inbiomed, Donostia-San Sebastián, 20009
Several genes associated to PD, namely PINK1 (PTEN-induced kinase 1), LRRK2 (leucine-rich repeat kinase 2) and alpha-synuclein, activate pathogenic pathways that converge in mitochondrial dysfunction. In this study, we reprogrammed skin fibroblasts from patients with PD-associated mutations in PINK1 that inactivate kinase function to generate patient-specific iPSCs (induced pluripotent stem cells). PINK1-iPSCs were differentiated into dopamine neurons, which are lost in PD. Confocal analysis of mitochondrial morphology revealed a highly fragmented network that was not observed in patient-derived fibroblasts. Fission proteins were upregulated in the fibroblasts but not in neurons, suggesting that fibroblasts can compensate the PINK1 defect. Next, we characterized the expression of alpha-synuclein, which inhibits mitochondrial fusion. There was no difference between control and patient-derived neurons at the times examined, suggesting that the increased fragmentation is not caused by dysregulation of alpha-synuclein. Accordingly, over-expression of alpha-synuclein did not modify RNA levels of the fission proteins. In contrast, we found a remarkable increase in LRRK2 both at RNA and protein levels in patients' fibroblasts and neurons with PINK1 mutations. Currently, we are testing the effect of LRRK2 knockdown and wild-type PINK1 over-expression in patients' cells to mechanistically define the observed alterations. Since we have detected increased mitochondrial fragmentation also in PD-associated LRRK2 mutations we propose that dysregulation of mitochondrial dynamics is a common pathogenic event in multiple forms of PD.