Mutations in PARK2, encoding Parkin, cause an autosomal recessive form of juvenile Parkinson Disease (JPD). The aim of the present study was to investigate the impact of PARK2 mutations on mitochondrial function and morphology in human skin fibroblasts. We analyzed cells obtained from four patients clinically characterized by JPD, harboring recessive mutations in PARK2. By quantitative PCR we found a reduction (<50%) of PARK2 transcript in all patients but one; however Western Blot analysis demonstrated the virtual absence of Parkin protein in all mutant fibroblasts. Respiration assays showed an increment of oxygen consumption, which was uncoupled to ATP cellular levels. This finding was probably due to presence of altered mitochondrial membrane potential (ΔΨm), confirmed by JC-1 analysis. The mitochondrial network was comparable between mutant and control cells but, interestingly, a “chain-like” network was found only in mutant fibroblasts. Dissipation of ΔΨm usually leads to mitochondrial fragmentation in healthy cells and eventually to mitophagy; however, this behavior was not observed in patients' fibroblasts. The absence of mitochondrial fragmentation in mutant Parkin fibroblasts could results in accumulation of damaged mitochondria not targeted to mitophagy. This condition should increase the oxidative stress and lead to cellular dysfunction and death. Our results suggest that PARK2 mutations cause mitochondrial impairment, in particular reduction in ATP cellular levels and alteration of ΔΨm, even in non-neuronal cells and confirm the hypothesis that Parkin holds a pivotal role in pro-fission events.
Human induced pluripotent stem cells (iPSCs) are a powerful tool for studying development and disease. However, different iPSC lines show considerable phenotypic variation. The lack of common well-characterized cell lines that are used widely frustrates efforts to integrate data across research groups or replicate key findings. Inspired by model organism communities who addressed this issue by establishing a limited number of widely accepted strains, we characterised candidate iPSC lines in unprecedented detail to select a well-performing line to underpin collaborative studies. Specifically, we characterised the morphology, growth rates, and single-cell transcriptomes of iPSC lines in the pluripotent state and assessed their genomic integrity using karyotyping, DNA microarrays, whole genome sequencing, and functional assays for p53 activity. We further tested their ability to be edited by CRISPR/Cas9 and used single-cell RNA sequencing to compare the efficiency with which they could be differentiated into multiple lineages. We found that there was significant variability in the performance of lines across the tested assays that enabled the rational selection of a lead line, KOLF2.1J, which is a gene-corrected derivative of a publicly available line from the Human Induced Pluripotent Stem Cells Initiative (HipSci) resource. We are now using this line in an initiative from the NIH Center for Alzheimer’s and Related Dementias to derive hundreds of gene-edited and functionalized sub-clones to be distributed widely throughout the research community along with associated datasets, with the aim of promoting the standardisation required for large-scale collaborative science in the stem cell field.SummaryThe authors of this collaborative science study describe a deep characterization of widely available induced pluripotent stem cell (iPSC) lines to rationally select a line that performs well in multiple experimental approaches. Analysis of transcriptional patterns in the pluripotent state, whole genome sequencing, genomic stability after highly efficient CRISPR-mediated gene editing, integrity of the p53 pathway, and differentiation efficiency towards multiple lineages identified KOLF2.1J as a well-performing cell line. The widespread distribution and use of this line makes it an attractive cell line for comparative and collaborative efforts in the stem cell field.HighlightsDeep genotyping and phenotyping reveals KOLF2.1J as well-performing cell line that is readily distributed and could serve as common reference lineDespite rare copy-neutral loss of heterozygosity (CN-LOH) events, iPSC lines retain genomic fidelity after CRISPR/Cas9-based gene editingOur multifactorial pipeline serves as a blueprint for future efforts to identify other lead iPSC linesGraphical abstract
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