Stem cell modeling of mitochondrial parkinsonism reveals key functions of OPA1

Abstract

ObjectiveDefective mitochondrial function attributed to optic atrophy 1 (OPA1) mutations causes primarily optic atrophy and, less commonly, neurodegenerative syndromes. The pathomechanism by which OPA1 mutations trigger diffuse loss of neurons in some, but not all, patients is unknown. Here, we used a tractable induced pluripotent stem cell (iPSC)‐based model to capture the biology of OPA1 haploinsufficiency in cases presenting with classic eye disease versus syndromic parkinsonism.MethodsiPSCs were generated from 2 patients with OPA1 haploinsufficiency and 2 controls and differentiated into dopaminergic neurons. Metabolic profile was determined by extracellular flux analysis, respiratory complex levels using immunoblotting, and complex I activity by a colorimetric assay. Mitochondria were examined by transmission electron microscopy. Mitochondrial DNA copy number and deletions were assayed using long‐range PCR. Mitochondrial membrane potential was measured by tetramethylrhodamine methyl ester uptake, and mitochondrial fragmentation was assessed by confocal microscopy. Exome sequencing was used to screen for pathogenic variants.ResultsOPA1 haploinsufficient iPSCs differentiated into dopaminergic neurons and exhibited marked reduction in OPA1 protein levels. Loss of OPA1 caused a late defect in oxidative phosphorylation, reduced complex I levels, and activity without a significant change in the ultrastructure of mitochondria. Loss of neurons in culture recapitulated dopaminergic degeneration in syndromic disease and correlated with mitochondrial fragmentation.InterpretationOPA1 levels maintain oxidative phosphorylation in iPSC‐derived neurons, at least in part, by regulating the stability of complex I. Severity of OPA1 disease associates primarily with the extent of OPA1‐mediated fusion, suggesting that activation of this mechanism or identification of its genetic modifiers may have therapeutic or prognostic value. Ann Neurol 2018;83:915–925

Optic Atrophy 1 Controls Human Neuronal Development by Preventing Aberrant Nuclear DNA Methylation

“…Other studies also show significant mitochondrial fragmentation in mouse cerebellar granule (Jahani-Asl et al, 2011) and HeLa cells (Arnoult et al, 2005). In these studies OPA1 expression was almost completely abolished, whereas in our cells 50% OPA1 proteins remain, which might explain the mild changes in mitochondrial morphology in our In line with this, a recent study using OPA1 haploinsufficient iPSCs derived from patients with syndromic parkinsonism also shows only subtle changes in the mitochondrial ultrastructure in iPSC-derived dopaminergic neurons (Jonikas et al, 2018).…”

Mitochondrial OMA1 and OPA1 as Gatekeepers of Organellar Structure/Function and Cellular Stress Response

“…Consistent with this, a modest but growing literature is emerging to reveal key roles for OPA1 in neuronal and cardiac differentiation. Recently, OPA1 was shown to be required for development of GABAergic neurons from embryonic stem cells ( Caglayan et al, 2020 ), while haploinsufficient OPA1 iPSCs demonstrate degeneration of dopaminergic neurons ( Jonikas et al, 2018 ). Gene trapping of OPA1 in murine ESCs causes impaired cardiac differentiation and development ( Kasahara et al, 2013 ).…”

Characterizing relevant microRNA editing sites in Parkinson’s disease

“…PD patients carrying the G2019S mutation showed decreased levels of mature OPA1 [27]. OPA1 haploinsufficinecy leads to progressive loss of iPSC-derived dopaminergic neurons [28]. Autosomal dominant LRRK2 mutations are associated with both familial and sporadic PD [27,29].…”