title: Reduced mitochondrial Ca(2+) transients stimulate autophagy in human fibroblasts carrying the 13514A>G mutation of the ND5 subunit of NADH dehydrogenase.
abstract: Mitochondrial disorders are a group of pathologies characterized by impairment of mitochondrial function mainly due to defects of the respiratory chain and consequent organellar energetics. This affects organs and tissues that require an efficient energy supply, such as brain and skeletal muscle. They are caused by mutations in both nuclear- and mitochondrial DNA (mtDNA)-encoded genes and their clinical manifestations show a great heterogeneity in terms of age of onset and severity, suggesting that patient-specific features are key determinants of the pathogenic process. In order to correlate the genetic defect to the clinical phenotype, we used a cell culture model consisting of fibroblasts derived from patients with different mutations in the mtDNA-encoded ND5 complex I subunit and with different severities of the illness. Interestingly, we found that cells from patients with the 13514A>G mutation, who manifested a relatively late onset and slower progression of the disease, display an increased autophagic flux when compared with fibroblasts from other patients or healthy donors. We characterized their mitochondrial phenotype by investigating organelle turnover, morphology, membrane potential and Ca(2+) homeostasis, demonstrating that mitochondrial quality control through mitophagy is upregulated in 13514A>G cells. This is due to a specific downregulation of mitochondrial Ca(2+) uptake that causes the stimulation of the autophagic machinery through the AMPK signaling axis. Genetic and pharmacological manipulation of mitochondrial Ca(2+) homeostasis can revert this phenotype, but concurrently decreases cell viability. This indicates that the higher mitochondrial turnover in complex I deficient cells with this specific mutation is a pro-survival compensatory mechanism that could contribute to the mild clinical phenotype of this patient.
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Granatiero
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Giorgio
authors.affiliation: Department of Biology, University of Padova, Padova, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Calì
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Patron
authors.affiliation: Department of Biology, University of Padova, Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Brini
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Bernardi
authors.affiliation: Department of Experimental Research and Diagnostics, Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, Milan, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Tiranti
authors.affiliation: Mitochondrial Biology Unit, Medical Research Council, Cambridge, UK.
authors.forename: M
authors.initials: M
authors.lastname: Zeviani
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Pallafacchina
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: D
authors.initials: D
authors.lastname: De Stefani
authors.affiliation: Department of Biomedical Sciences, University of Padova and CNR Neuroscience Institute, Padova, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Rizzuto
mesh_terms: D001343:Autophagy; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D042967:Electron Transport Complex I / Q000235:genetics* / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism; D028361:Mitochondrial Diseases / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D063154:Mitochondrial Dynamics; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D024101:Mitochondrial Proteins; D021122:Protein Subunits; C034703:mitochondrial calcium uniporter; C481838:MT-ND5 protein, human; D042967:Electron Transport Complex I; D002118:Calcium