Valentina Del Dotto
@unibo.it
Dipartimento di Scienze Biomediche e NeuroMotorie (DIBINEM)
University of Bologna
EDUCATION
2015: PhD in Cellular and Molecular Biology, University of Bologna
Thesis title: “OPA1 isoforms and protein domains in the rescue of mitochondrial dysfunctions”.
2011: Master’s Degree in Pharmaceutical Biotechnology, University of Bologna
Thesis title: “Effect of genotoxic and hypotoxic stress on the modulation of mitochondrial biogenesis”.
2009: Bachelor’s Degree in Biotechnology, University of Bologna.
Scopus Publications
Scopus Publications
Serena Jasmine Aleo, Valentina Del Dotto, Martina Romagnoli, Claudio Fiorini, Giada Capirossi, Camille Peron, Alessandra Maresca, Leonardo Caporali, Mariantonietta Capristo, Concetta Valentina Tropeano,et al.
Elsevier BV
Valentina Del Dotto, Francesco Musiani, Alessandra Baracca, and Giancarlo Solaini
MDPI AG
Mitochondrial ATP synthase (Complex V) catalyzes the last step of oxidative phosphorylation and provides most of the energy (ATP) required by human cells. The mitochondrial genes MT-ATP6 and MT-ATP8 encode two subunits of the multi-subunit Complex V. Since the discovery of the first MT-ATP6 variant in the year 1990 as the cause of Neuropathy, Ataxia, and Retinitis Pigmentosa (NARP) syndrome, a large and continuously increasing number of inborn variants in the MT-ATP6 and MT-ATP8 genes have been identified as pathogenic. Variants in these genes correlate with various clinical phenotypes, which include several neurodegenerative and multisystemic disorders. In the present review, we report the pathogenic variants in mitochondrial ATP synthase genes and highlight the molecular mechanisms underlying ATP synthase deficiency that promote biochemical dysfunctions. We discuss the possible structural changes induced by the most common variants found in patients by considering the recent cryo-electron microscopy structure of human ATP synthase. Finally, we provide the state-of-the-art of all therapeutic proposals reported in the literature, including drug interventions targeting mitochondrial dysfunctions, allotopic gene expression- and nuclease-based strategies, and discuss their potential translation into clinical trials.
Gianluca Sgarbi, Riccardo Righetti, Valentina Del Dotto, Silvia Grillini, Valentina Giorgio, Alessandra Baracca, and Giancarlo Solaini
Elsevier BV
Andrea Castellaneta, Vito Porcelli, Ilario Losito, Serena Barile, Alessandra Maresca, Valentina Del Dotto, Ludovica Sofia Guadalupi, Cosima Damiana Calvano, Valerio Carelli, Luigi Palmieri,et al.
Springer Science and Business Media LLC
AbstractThe occurrence of methyl carbamates of phosphatidylethanolamines and phosphatidylserines in the lipid extract of mitochondria obtained from mouse embryonic fibroblasts was ascertained by hydrophilic interaction liquid chromatography with electrospray ionization single and multi-stage mass spectrometry, performed using sinergically a high resolution (quadrupole-Orbitrap) and a low resolution (linear ion trap) spectrometer. Two possible routes to the synthesis of methyl carbamates of phospholipids were postulated and evaluated: (i) a chemical transformation involving phosgene, occurring as a photooxidation by-product in the chloroform used for lipid extraction, and methanol, also used for the latter; (ii) an enzymatic methoxycarbonylation reaction due to an accidental bacterial contamination, that was unveiled subsequently on the murine mitochondrial sample. A specific lipid extraction performed on a couple of standard phosphatidyl-ethanolamines/-serines, based on purposely photo-oxidized chloroform and deuterated methanol, indicated route (i) as negligible in the specific case, thus highlighting the enzymatic route related to bacterial contamination as the most likely source of methyl carbamates. The unambiguous recognition of the latter might represent the starting point toward a better understanding of their generation in biological systems and a minimization of their occurrence when an artefactual formation is ascertained.
Riccardo Righetti, Silvia Grillini, Valentina Del Dotto, Anna Costanzini, Francesca Liuzzi, Claudia Zanna, Gianluca Sgarbi, Giancarlo Solaini, and Alessandra Baracca
MDPI AG
Cancer cells overexpress IF1, the endogenous protein that inhibits the hydrolytic activity of ATP synthase when mitochondrial membrane potential (ΔμH+) falls, as in ischemia. Other roles have been ascribed to IF1, but the associated molecular mechanisms are still under debate. We investigated the ability of IF1 to promote survival and proliferation in osteosarcoma and colon carcinoma cells exposed to conditions mimicking ischemia and reperfusion, as occurs in vivo, particularly in solid tumors. IF1-silenced and parental cells were exposed to the FCCP uncoupler to collapse ΔμH+ and the bioenergetics of cell models were validated. All the uncoupled cells preserved mitochondrial mass, but the implemented mechanisms differed in IF1-expressing and IF1-silenced cells. Indeed, the membrane potential collapse and the energy charge preservation allowed an increase in both mitophagy and mitochondrial biogenesis in IF1-expressing cells only. Interestingly, the presence of IF1 also conferred a proliferative advantage to cells highly dependent on oxidative phosphorylation when the uncoupler was washed out, mimicking cell re-oxygenation. Overall, our results indicate that IF1, by allowing energy preservation and promoting mitochondrial renewal, can favor proliferation of anoxic cells and tumor growth. Therefore, hindering the action of IF1 may be promising for the therapy of tumors that rely on oxidative phosphorylation for energy production.
Mariantonietta Capristo, Valentina Del Dotto, Concetta Valentina Tropeano, Claudio Fiorini, Leonardo Caporali, Chiara La Morgia, Maria Lucia Valentino, Monica Montopoli, Valerio Carelli, and Alessandra Maresca
Springer Science and Business Media LLC
Abstract Background Myoclonus, Epilepsy and Ragged-Red-Fibers (MERRF) is a mitochondrial encephalomyopathy due to heteroplasmic mutations in mitochondrial DNA (mtDNA) most frequently affecting the tRNALys gene at position m.8344A > G. Defective tRNALys severely impairs mitochondrial protein synthesis and respiratory chain when a high percentage of mutant heteroplasmy crosses the threshold for full-blown clinical phenotype. Therapy is currently limited to symptomatic management of myoclonic epilepsy, and supportive measures to counteract muscle weakness with co-factors/supplements. Methods We tested two therapeutic strategies to rescue mitochondrial function in cybrids and fibroblasts carrying different loads of the m.8344A > G mutation. The first strategy was aimed at inducing mitochondrial biogenesis directly, over-expressing the master regulator PGC-1α, or indirectly, through the treatment with nicotinic acid, a NAD+ precursor. The second was aimed at stimulating the removal of damaged mitochondria through prolonged rapamycin treatment. Results The first approach slightly increased mitochondrial protein expression and respiration in the wild type and intermediate-mutation load cells, but was ineffective in high-mutation load cell lines. This suggests that induction of mitochondrial biogenesis may not be sufficient to rescue mitochondrial dysfunction in MERRF cells with high-mutation load. The second approach, when administered chronically (4 weeks), induced a slight increase of mitochondrial respiration in fibroblasts with high-mutation load, and a significant improvement in fibroblasts with intermediate-mutation load, rescuing completely the bioenergetics defect. This effect was mediated by increased mitochondrial biogenesis, possibly related to the rapamycin-induced inhibition of the Mechanistic Target of Rapamycin Complex 1 (mTORC1) and the consequent activation of the Transcription Factor EB (TFEB). Conclusions Overall, our results point to rapamycin-based therapy as a promising therapeutic option for MERRF.
Alberto Danese, Simone Patergnani, Alessandra Maresca, Camille Peron, Andrea Raimondi, Leonardo Caporali, Saverio Marchi, Chiara La Morgia, Valentina Del Dotto, Claudia Zanna,et al.
Elsevier BV
Valentina Del Dotto and Valerio Carelli
Frontiers Media SA
In the year 2000, the discovery of OPA1 mutations as causative for dominant optic atrophy (DOA) was pivotal to rapidly expand the field of mitochondrial dynamics and describe the complex machinery governing this pathway, with a multitude of other genes and encoded proteins involved in neurodegenerative disorders of the optic nerve. OPA1 turned out to be a much more complex protein than initially envisaged, connecting multiple pathways beyond its strict role in mitochondrial fusion, such as sensing of OXPHOS needs and mitochondrial DNA maintenance. As a consequence, an increasing need to investigate OPA1 functions at multiple levels has imposed the development of multiple tools and models that are here reviewed. Translational mitochondrial medicine, with the ultimate objective of translating basic science necessary to understand pathogenic mechanisms into therapeutic strategies, requires disease modeling at multiple levels: from the simplest, like in yeast, to cell models, including the increasing use of reprogrammed stem cells (iPSCs) from patients, to animal models. In the present review, we thoroughly examine and provide the state of the art of all these approaches.
Chiara La Morgia, Alessandra Maresca, Giulia Amore, Laura Ludovica Gramegna, Michele Carbonelli, Emanuela Scimonelli, Alberto Danese, Simone Patergnani, Leonardo Caporali, Francesca Tagliavini,et al.
Springer Science and Business Media LLC
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Chiara La Morgia, Alessandra Maresca, Giulia Amore, Laura Ludovica Gramegna, Michele Carbonelli, Emanuela Scimonelli, Alberto Danese, Simone Patergnani, Leonardo Caporali, Francesca Tagliavini,et al.
Springer Science and Business Media LLC
Wolfram syndrome (WS) is a recessive multisystem disorder defined by the association of diabetes mellitus and optic atrophy, reminiscent of mitochondrial diseases. The role played by mitochondria remains elusive, with contradictory results on the occurrence of mitochondrial dysfunction. We evaluated 13 recessive WS patients by deep clinical phenotyping, including optical coherence tomography (OCT), serum lactic acid at rest and after standardized exercise, brain Magnetic Resonance Imaging, and brain and muscle Magnetic Resonance Spectroscopy (MRS). Finally, we investigated mitochondrial bioenergetics, network morphology, and calcium handling in patient-derived fibroblasts. Our results do not support a primary mitochondrial dysfunction in WS patients, as suggested by MRS studies, OCT pattern of retinal nerve fiber layer loss, and, in fibroblasts, by mitochondrial bioenergetics and network morphology results. However, we clearly found calcium mishandling between endoplasmic reticulum (ER) and mitochondria, which, under specific metabolic conditions of increased energy requirements and in selected tissue or cell types, may turn into a secondary mitochondrial dysfunction. Critically, we showed that Wolframin (WFS1) protein is enriched at mitochondrial-associated ER membranes and that in patient-derived fibroblasts WFS1 protein is completely absent. These findings support a loss-of-function pathogenic mechanism for missense mutations in WFS1 , ultimately leading to defective calcium influx within mitochondria.
Serena J Aleo, Valentina Del Dotto, Mario Fogazza, Alessandra Maresca, Tiziana Lodi, Paola Goffrini, Anna Ghelli, Michela Rugolo, Valerio Carelli, Enrico Baruffini,et al.
Oxford University Press (OUP)
Abstract OPA1 mutations are the major cause of dominant optic atrophy (DOA) and the syndromic form DOA plus, pathologies for which there is no established cure. We used a ‘drug repurposing’ approach to identify FDA-approved molecules able to rescue the mitochondrial dysfunctions induced by OPA1 mutations. We screened two different chemical libraries by using two yeast strains carrying the mgm1I322M and the chim3P646L mutations, identifying 26 drugs able to rescue their oxidative growth phenotype. Six of them, able to reduce the mitochondrial DNA instability in yeast, have been then tested in Opa1 deleted mouse embryonic fibroblasts expressing the human OPA1 isoform 1 bearing the R445H and D603H mutations. Some of these molecules were able to ameliorate the energetic functions and/or the mitochondrial network morphology, depending on the type of OPA1 mutation. The final validation has been performed in patients’ fibroblasts, allowing to select the most effective molecules. Our current results are instrumental to rapidly translating the findings of this drug repurposing approach into clinical trial for DOA and other neurodegenerations caused by OPA1 mutations.
Alessandra Maresca, , Valentina Del Dotto, Martina Romagnoli, Chiara La Morgia, Lidia Di Vito, Mariantonietta Capristo, Maria Lucia Valentino, and Valerio Carelli
Springer Science and Business Media LLC
Abstract Mitochondrial diseases are highly heterogeneous metabolic disorders caused by genetic alterations in the mitochondrial DNA (mtDNA) or in the nuclear genome. In this study, we investigated a panel of blood biomarkers in a cohort of 123 mitochondrial patients, with prominent neurological and muscular manifestations. These biomarkers included creatine, fibroblast growth factor 21 (FGF21) and growth/differentiation factor 15 (GDF-15), and the novel cell free circulating-mtDNA (ccf-mtDNA). All biomarkers were significantly increased in the patient group. After stratification by the specific phenotypes, ccf-mtDNA was significantly increased in the Mitochondrial Encephalomyopathy Lactic Acidosis Stroke-like episodes syndrome (MELAS) group, and FGF21 and GDF-15 were significantly elevated in patients with MELAS and Myoclonic Epilepsy Ragged Red Fibers syndrome. On the contrary, in our cohort, creatine was not associated to a specific clinical phenotype. Longitudinal assessment in four MELAS patients showed increased levels of ccf-mtDNA in relation to acute events (stroke-like episodes/status epilepticus) or progression of neurodegeneration. Our results confirm the association of FGF21 and GDF-15 with mitochondrial translation defects due to tRNA mutations. Most notably, the novel ccf-mtDNA was strongly associated with MELAS and may be used for monitoring the disease course or to evaluate the efficacy of therapies, especially in the acute phase. Key messages • FGF21/GDF15 efficiently identifies mitochondrial diseases due to mutations in tRNA genes. • The novel ccf-mtDNA is associated with MELAS and increases during acute events. • Creatine only discriminates severe mitochondrial patients. • FGF21, GDF-15, and ccf-mtDNA are possibly useful for monitoring therapy efficacy.
Leonardo Caporali, Stefania Magri, Andrea Legati, Valentina Del Dotto, Francesca Tagliavini, Francesca Balistreri, Alessia Nasca, Chiara La Morgia, Michele Carbonelli, Maria L. Valentino,et al.
Wiley
Dominant optic atrophy (DOA) is the most common inherited optic neuropathy, with a prevalence of 1:12,000 to 1:25,000. OPA1 mutations are found in 70% of DOA patients, with a significant number remaining undiagnosed.
Juan Manuel Chao de la Barca, Mario Fogazza, Michela Rugolo, Stéphanie Chupin, Valentina Del Dotto, Anna Maria Ghelli, Valerio Carelli, Gilles Simard, Vincent Procaccio, Dominique Bonneau,et al.
Oxford University Press (OUP)
Abstract Interpretation of variants of uncertain significance is an actual major challenge. We addressed this question on a set of OPA1 missense variants responsible for variable severity of neurological impairments. We used targeted metabolomics to explore the different signatures of OPA1 variants expressed in Opa1 deleted mouse embryonic fibroblasts (Opa1−/− MEFs), grown under selective conditions. Multivariate analyses of data discriminated Opa1+/+ from Opa1−/− MEFs metabolic signatures and classified OPA1 variants according to their in vitro severity. Indeed, the mild p.I382M hypomorphic variant was segregating close to the wild-type allele, while the most severe p.R445H variant was close to Opa1−/− MEFs, and the p.D603H and p.G439V alleles, responsible for isolated and syndromic presentations, respectively, were intermediary between the p.I382M and the p.R445H variants. The most discriminant metabolic features were hydroxyproline, the spermine/spermidine ratio, amino acid pool and several phospholipids, emphasizing proteostasis, endoplasmic reticulum (ER) stress and phospholipid remodeling as the main mechanisms ranking OPA1 allele impacts on metabolism. These results demonstrate the high resolving power of metabolomics in hierarchizing OPA1 missense mutations by their in vitro severity, fitting clinical expressivity. This suggests that our methodological approach can be used to discriminate the pathological significance of variants in genes responsible for other rare metabolic diseases and may be instrumental to select possible compounds eligible for supplementation treatment.
Valentina Del Dotto, Farid Ullah, Ivano Di Meo, Pamela Magini, Mirjana Gusic, Alessandra Maresca, Leonardo Caporali, Flavia Palombo, Francesca Tagliavini, Evan Harris Baugh,et al.
American Society for Clinical Investigation
Inherited optic neuropathies include complex phenotypes, mostly driven by mitochondrial dysfunction. We report an optic atrophy spectrum disorder, including retinal macular dystrophy and kidney insufficiency leading to transplantation, associated with mitochondrial DNA (mtDNA) depletion without accumulation of multiple deletions. By whole-exome sequencing, we identified mutations affecting the mitochondrial single strand binding protein (SSBP1) in four families with dominant and one with recessive inheritance. We show that SSBP1 mutations in patient-derived fibroblasts variably affect its amount and alter multimer formation, but not the binding to ssDNA. SSBP1 mutations impaired mtDNA, nucleoids and 7S-DNA amounts as well as mtDNA replication, impacting replisome machinery. The variable mtDNA depletion in cells reflected in severity of mitochondrial dysfunction, including respiratory efficiency, OXPHOS subunits and complexes amount and assembly. mtDNA depletion and cytochrome c oxidase-negative cells were found ex-vivo in biopsies of affected tissues, like kidney and skeletal muscle. Reduced efficiency of mtDNA replication was also reproduced in vitro, confirming the pathogenic mechanism. Furthermore, ssbp1 suppression in zebrafish induced signs of nephropathy and reduced optic nerve size, the latter phenotype complemented by wild-type mRNA but not by SSBP1 mutant transcripts. This previously unrecognized disease of mtDNA maintenance implicates SSBP1 mutations as cause of human pathology.
Alessandra Maresca, Valentina Del Dotto, Mariantonietta Capristo, Emanuela Scimonelli, Francesca Tagliavini, Luca Morandi, Concetta Valentina Tropeano, Leonardo Caporali, Susan Mohamed, Marina Roberti,et al.
Oxford University Press (OUP)
Abstract ADCA-DN and HSN-IE are rare neurodegenerative syndromes caused by dominant mutations in the replication foci targeting sequence (RFTS) of the DNA methyltransferase 1 (DNMT1) gene. Both phenotypes resemble mitochondrial disorders, and mitochondrial dysfunction was first observed in ADCA-DN. To explore mitochondrial involvement, we studied the effects of DNMT1 mutations in fibroblasts from four ADCA-DN and two HSN-IE patients. We documented impaired activity of purified DNMT1 mutant proteins, which in fibroblasts results in increased DNMT1 amount. We demonstrated that DNMT1 is not localized within mitochondria, but it is associated with the mitochondrial outer membrane. Concordantly, mitochondrial DNA failed to show meaningful CpG methylation. Strikingly, we found activated mitobiogenesis and OXPHOS with significant increase of H2O2, sharply contrasting with a reduced ATP content. Metabolomics profiling of mutant cells highlighted purine, arginine/urea cycle and glutamate metabolisms as the most consistently altered pathways, similar to primary mitochondrial diseases. The most severe mutations showed activation of energy shortage AMPK-dependent sensing, leading to mTORC1 inhibition. We propose that DNMT1 RFTS mutations deregulate metabolism lowering ATP levels, as a result of increased purine catabolism and urea cycle pathways. This is associated with a paradoxical mitochondrial hyper-function and increased oxidative stress, possibly resulting in neurodegeneration in non-dividing cells.
Anna Costanzini, Gianluca Sgarbi, Alessandra Maresca, Valentina Del Dotto, Giancarlo Solaini, and Alessandra Baracca
MDPI AG
Changes of quantity and/or morphology of cell mitochondria are often associated with metabolic modulation, pathology, and apoptosis. Exogenous fluorescent probes used to investigate changes in mitochondrial content and dynamics are strongly dependent, for their internalization, on the mitochondrial membrane potential and composition, thus limiting the reliability of measurements. To overcome this limitation, genetically encoded recombinant fluorescent proteins, targeted to different cellular districts, were used as reporters. Here, we explored the potential use of mitochondrially targeted red fluorescent probe (mtRFP) to quantify, by flow cytometry, mitochondrial mass changes in cells exposed to different experimental conditions. We first demonstrated that the mtRFP fluorescence intensity is stable during cell culture and it is related with the citrate synthase activity, an established marker of the mitochondrial mass. Incidentally, the expression of mtRFP inside mitochondria did not alter the oxygen consumption rate under both state 3 and 4 respiration conditions. In addition, using this method, we showed for the first time that different inducers of mitochondrial mass change, such as hypoxia exposure or resveratrol treatment of cells, could be consistently detected. We suggest that transfection and selection of stable clones expressing mtRFP is a reliable method to monitor mitochondrial mass changes, particularly when pathophysiological or experimental conditions change ΔΨm, as it occurs during mitochondrial uncoupling or hypoxia/anoxia conditions.
Valentina Del Dotto, Mario Fogazza, Francesco Musiani, Alessandra Maresca, Serena J. Aleo, Leonardo Caporali, Chiara La Morgia, Cecilia Nolli, Tiziana Lodi, Paola Goffrini,et al.
Elsevier BV
OPA1 is the major gene responsible for Dominant Optic Atrophy (DOA) and the syndromic form DOA "plus". Over 370 OPA1 mutations have been identified so far, although their pathogenicity is not always clear. We have analyzed one novel and a set of known OPA1 mutations to investigate their impact on protein functions in primary skin fibroblasts and in two "ad hoc" generated cell systems: the MGM1/OPA1 chimera yeast model and the Opa1-/- MEFs model expressing the mutated human OPA1 isoform 1. The yeast model allowed us to confirm the deleterious effects of these mutations and to gain information on their dominance/recessivity. The MEFs model enhanced the phenotypic alteration caused by mutations, nicely correlating with the clinical severity observed in patients, and suggested that the DOA "plus" phenotype could be induced by the combinatorial effect of mitochondrial network fragmentation with variable degrees of mtDNA depletion. Overall, the two models proved to be valuable tools to functionally assess and define the deleterious mechanism and the pathogenicity of novel OPA1 mutations, and useful to testing new therapeutic interventions.
Valentina Del Dotto, Mario Fogazza, Guy Lenaers, Michela Rugolo, Valerio Carelli, and Claudia Zanna
Elsevier BV
Graphical abstract Figure. No caption available. ABSTRACT OPA1 is a GTPase that controls several functions, such as mitochondrial dynamics and energetics, mtDNA maintenance and cristae integrity. In the last years, there have been described other cellular pathways and mechanisms involving OPA1 directly or through its interaction. All this new information, by implementing our knowledge on OPA1 is instrumental to elucidating the pathogenic mechanisms of OPA1 mutations. Indeed, these are associated with dominant optic atrophy (DOA), one of the most common inherited optic neuropathies, and with an increasing number of heterogeneous neurodegenerative disorders. In this review, we overview all recent findings on OPA1 protein functions, on its dysfunction and related clinical phenotypes, focusing on the current therapeutic options and future perspectives to treat DOA and the other associated neurological disorders due to OPA1 mutations.
Valentina Del Dotto, Mario Fogazza, Valerio Carelli, Michela Rugolo, and Claudia Zanna
Elsevier BV
OPA1 is a dynamin-related GTPase that controls mitochondrial dynamics, cristae integrity, energetics and mtDNA maintenance. The exceptional complexity of this protein is determined by the presence, in humans, of eight different isoforms that, in turn, are proteolytically cleaved into combinations of membrane-anchored long forms and soluble short forms. Recent advances highlight how each OPA1 isoform is able to fulfill "essential" mitochondrial functions, whereas only some variants carry out "specialized" features. Long forms determine fusion, long or short forms alone build cristae, whereas long and short forms together tune mitochondrial morphology. These findings offer novel challenging therapeutic potential to gene therapy.
Leonardo Caporali, Luisa Iommarini, Chiara La Morgia, Anna Olivieri, Alessandro Achilli, Alessandra Maresca, Maria Lucia Valentino, Mariantonietta Capristo, Francesca Tagliavini, Valentina Del Dotto,et al.
Public Library of Science (PLoS)
We here report on the existence of Leber’s hereditary optic neuropathy (LHON) associated with peculiar combinations of individually non-pathogenic missense mitochondrial DNA (mtDNA) variants, affecting the MT-ND4, MT-ND4L and MT-ND6 subunit genes of Complex I. The pathogenic potential of these mtDNA haplotypes is supported by multiple evidences: first, the LHON phenotype is strictly inherited along the maternal line in one very large family; second, the combinations of mtDNA variants are unique to the two maternal lineages that are characterized by recurrence of LHON; third, the Complex I-dependent respiratory and oxidative phosphorylation defect is co-transferred from the proband’s fibroblasts into the cybrid cell model. Finally, all but one of these missense mtDNA variants cluster along the same predicted fourth E-channel deputed to proton translocation within the transmembrane domain of Complex I, involving the ND1, ND4L and ND6 subunits. Hence, the definition of the pathogenic role of a specific mtDNA mutation becomes blurrier than ever and only an accurate evaluation of mitogenome sequence variation data from the general population, combined with functional analyses using the cybrid cell model, may lead to final validation. Our study conclusively shows that even in the absence of a clearly established LHON primary mutation, unprecedented combinations of missense mtDNA variants, individually known as polymorphisms, may lead to reduced OXPHOS efficiency sufficient to trigger LHON. In this context, we introduce a new diagnostic perspective that implies the complete sequence analysis of mitogenomes in LHON as mandatory gold standard diagnostic approach.
Leonardo Caporali, Alessandra Maresca, Mariantonietta Capristo, Valentina Del Dotto, Francesca Tagliavini, Maria Lucia Valentino, Chiara La Morgia, and Valerio Carelli
Elsevier BV
Incomplete penetrance characterizes the two most frequent inherited optic neuropathies, Leber's Hereditary Optic Neuropathy (LHON) and dominant optic atrophy (DOA), due to genetic errors in the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA), respectively. For LHON, compelling evidence has accumulated on the complex interplay of mtDNA haplogroups and environmental interacting factors, whereas the nDNA remains essentially non informative. However, a compensatory mechanism of activated mitochondrial biogenesis and increased mtDNA copy number, possibly driven by a permissive nDNA background, is documented in LHON; when successful it maintains unaffected the mutation carriers, but in some individuals it might be hampered by tobacco smoking or other environmental factors, resulting in disease onset. In females, mitochondrial biogenesis is promoted and maintained within the compensatory range by estrogens, partially explaining the gender bias in LHON. Concerning DOA, none of the above mechanisms has been fully explored, thus mtDNA haplogroups, environmental factors such as tobacco and alcohol, and further nDNA variants may all participate as protective factors or, on the contrary, favor disease expression and severity. Next generation sequencing, complemented by transcriptomics and proteomics, may provide some answers in the next future, even if the multifactorial model that seems to apply to incomplete penetrance in mitochondrial optic neuropathies remains problematic, and careful stratification of patients will play a key role for data interpretation. The deep understanding of which factors impinge on incomplete penetrance may shed light on the pathogenic mechanisms leading to optic nerve atrophy, on their possible compensation and, thus, on development of therapeutic strategies.
Valentina Del Dotto, Prashant Mishra, Sara Vidoni, Mario Fogazza, Alessandra Maresca, Leonardo Caporali, J. Michael McCaffery, Martina Cappelletti, Enrico Baruffini, Guy Lenaers,et al.
Elsevier BV
OPA1 is a GTPase that controls mitochondrial fusion, cristae integrity, and mtDNA maintenance. In humans, eight isoforms are expressed as combinations of long and short forms, but it is unclear whether OPA1 functions are associated with specific isoforms and/or domains. To address this, we expressed each of the eight isoforms or different constructs of isoform 1 in Opa1-/- MEFs. We observed that any isoform could restore cristae structure, mtDNA abundance, and energetic efficiency independently of mitochondrial network morphology. Long forms supported mitochondrial fusion; short forms were better able to restore energetic efficiency. The complete rescue of mitochondrial network morphology required a balance of long and short forms of at least two isoforms, as shown by combinatorial isoform silencing and co-expression experiments. Thus, multiple OPA1 isoforms are required for mitochondrial dynamics, while any single isoform can support all other functions. These findings will be useful in designing gene therapies for patients with OPA1 haploinsufficiency.
L Giordano, S Deceglie, P d'Adamo, M L Valentino, C La Morgia, F Fracasso, M Roberti, M Cappellari, G Petrosillo, S Ciaravolo,et al.
Springer Science and Business Media LLC
Leber’s hereditary optic neuropathy (LHON), the most frequent mitochondrial disease, is associated with mitochondrial DNA (mtDNA) point mutations affecting Complex I subunits, usually homoplasmic. This blinding disorder is characterized by incomplete penetrance, possibly related to several genetic modifying factors. We recently reported that increased mitochondrial biogenesis in unaffected mutation carriers is a compensatory mechanism, which reduces penetrance. Also, environmental factors such as cigarette smoking have been implicated as disease triggers. To investigate this issue further, we first assessed the relationship between cigarette smoke and mtDNA copy number in blood cells from large cohorts of LHON families, finding that smoking was significantly associated with the lowest mtDNA content in affected individuals. To unwrap the mechanism of tobacco toxicity in LHON, we exposed fibroblasts from affected individuals, unaffected mutation carriers and controls to cigarette smoke condensate (CSC). CSC decreased mtDNA copy number in all cells; moreover, it caused significant reduction of ATP level only in mutated cells including carriers. This implies that the bioenergetic compensation in carriers is hampered by exposure to smoke derivatives. We also observed that in untreated cells the level of carbonylated proteins was highest in affected individuals, whereas the level of several detoxifying enzymes was highest in carriers. Thus, carriers are particularly successful in reactive oxygen species (ROS) scavenging capacity. After CSC exposure, the amount of detoxifying enzymes increased in all cells, but carbonylated proteins increased only in LHON mutant cells, mostly from affected individuals. All considered, it appears that exposure to smoke derivatives has a more deleterious effect in affected individuals, whereas carriers are the most efficient in mitigating ROS rather than recovering bioenergetics. Therefore, the identification of genetic modifiers that modulate LHON penetrance must take into account also the exposure to environmental triggers such as tobacco smoke.
Valerio Carelli, Olimpia Musumeci, Leonardo Caporali, Claudia Zanna, Chiara La Morgia, Valentina Del Dotto, Anna Maria Porcelli, Michela Rugolo, Maria Lucia Valentino, Luisa Iommarini,et al.
Wiley
Mounting evidence links neurodegenerative disorders such as Parkinson disease and Alzheimer disease with mitochondrial dysfunction, and recent emphasis has focused on mitochondrial dynamics and quality control. Mitochondrial dynamics and mtDNA maintenance is another link recently emerged, implicating mutations in the mitochondrial fusion genes OPA1 and MFN2 in the pathogenesis of multisystem syndromes characterized by neurodegeneration and accumulation of mtDNA multiple deletions in postmitotic tissues. Here, we report 2 Italian families affected by dominant chronic progressive external ophthalmoplegia (CPEO) complicated by parkinsonism and dementia.