scholarly journals Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation

2019 ◽  
Vol 56 (8) ◽  
pp. 499-511 ◽  
Author(s):  
Susanna Tulli ◽  
Andrea Del Bondio ◽  
Valentina Baderna ◽  
Davide Mazza ◽  
Franca Codazzi ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Protein Quality ◽  
Mitochondrial Protein ◽  
Pathogenic Variant ◽  
Mitochondrial Fusion ◽  
Spinocerebellar Ataxia Type ◽  
Mitochondrial Morphology ◽  
Pathogenic Variants ◽  
Control Objective ◽  
Mitochondrial Calcium Uptake

BackgroundSpinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date.MethodsWe derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2+/− HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2−/− murine fibroblasts.ResultsWe found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells.ConclusionOur data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2+/− cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.

scholarly journals When the Balance Tips: Dysregulation of Mitochondrial Dynamics as a Culprit in Disease

2021 ◽  
Vol 22 (9) ◽  
pp. 4617
Author(s):  
Styliana Kyriakoudi ◽  
Anthi Drousiotou ◽  
Petros P. Petrou
Keyword(s):  
Insulin Resistance ◽  
Mitochondrial Function ◽  
Human Disease ◽  
Molecular Mechanisms ◽  
Mitochondrial Dynamics ◽  
Mitochondrial Fusion ◽  
Mitochondrial Morphology ◽  
Disease Development ◽  
Pathological Conditions ◽  
Wide Range

Mitochondria are dynamic organelles, the morphology of which is tightly linked to their functions. The interplay between the coordinated events of fusion and fission that are collectively described as mitochondrial dynamics regulates mitochondrial morphology and adjusts mitochondrial function. Over the last few years, accruing evidence established a connection between dysregulated mitochondrial dynamics and disease development and progression. Defects in key components of the machinery mediating mitochondrial fusion and fission have been linked to a wide range of pathological conditions, such as insulin resistance and obesity, neurodegenerative diseases and cancer. Here, we provide an update on the molecular mechanisms promoting mitochondrial fusion and fission in mammals and discuss the emerging association of disturbed mitochondrial dynamics with human disease.

Abstract 613: Exercise Training Improves Cardiac Mitofusin 2 Expression In Diabetes

Hypertension ◽  
2013 ◽  
Vol 62 (suppl_1) ◽  
Author(s):  
Luciana Jorge ◽  
Janaina Paulini ◽  
Cleiton Silva ◽  
Rodolfo Rampaso ◽  
rafael luiz ◽  
...  
Keyword(s):  
Exercise Training ◽  
Molecular Mechanisms ◽  
Mitochondrial Protein ◽  
Cardiac Metabolism ◽  
Mitochondrial Fusion ◽  
Heart Weight ◽  
Mitofusin 2 ◽  
Male Wistar Rats ◽  
Important Pathway ◽  
Independent Effects

Introduction: DM increases the risk of developing cardiovascular disease, although the specific molecular mechanisms underlying DM are not well understood, perhaps the most important pathway regulating metabolism in muscle is mitochondrial biogenesis. The mitofusin 2 is a important protein to mitochondrial fusion. Additionally, muscle mitochondrial metabolism is regulated by a group of morphogenesis machinery proteins which are important for mitochondrial fusion and fission events and also for their independent effects on bioenergetics. The exercise training is a strategy for reversing the effects of mitochondrial dysfunction trough the regulation of mitochondrial protein transcription and biogenegis. The aim of this study was to verify if endurance exercise increases the expression of Mitofusin 2 in cardiac myocytes in experimental diabetes. Male Wistar rats were divided into 4 groups: control (C:8), control trained (CT=8), diabetic (D=8), diabetic trained (DT=8). DM was induced by STZ (50mg/kg). Trained groups were submitted to an exercise training (ET) protocol on a treadmill (8 wk). BPS, HR were analyzed using a data acquisition system (PowerLab). The ratio between heart weight and tibia length was used to determination of cardiac hypertrophy. The expression of protein mitofusin 2 was evaluated by western blotting. The BPS was similar between grups (CS:124, CT:128; DS:122; DT:130 mmHg), however the HR was decreased in the DS group (323bpm) and ET was able to normalize this (DT 342bpm ). DM decreased 23% of the cardiac mass, but ET prevented this reduction (DT 13%). The expression mft2 was reduced in the DS and the exercise normalized this expression. Conclusion: ET was able to avoid the cardiac muscle deterioration leading to the normalization of HR. This hemodynamic adaptation can be related with a bigger expression of mitofusin 2 and it could be associated with an improvement of cardiac metabolism. The importance of ET as a non pharmacological approach to treat the DM complications was demonstrated by the improvement of cardiac function and molecular mechanisms.

scholarly journals Nonredundant Roles of Mitochondria-associated F-Box Proteins Mfb1 and Mdm30 in Maintenance of Mitochondrial Morphology in Yeast

2006 ◽  
Vol 17 (9) ◽  
pp. 3745-3755 ◽  
Author(s):  
Mark Dürr ◽  
Mafalda Escobar-Henriques ◽  
Sandra Merz ◽  
Stefan Geimer ◽  
Thomas Langer ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Mitochondrial Dynamics ◽  
Mitochondrial Fusion ◽  
Mitochondrial Morphology ◽  
Mitochondrial Inheritance ◽  
Physiological Conditions ◽  
Cellular Processes ◽  
Protein Mutants ◽  
Homozygous Diploid ◽  
F Box Protein

Mitochondria constantly fuse and divide to adapt organellar morphology to the cell’s ever-changing physiological conditions. Little is known about the molecular mechanisms regulating mitochondrial dynamics. F-box proteins are subunits of both Skp1-Cullin-F-box (SCF) ubiquitin ligases and non-SCF complexes that regulate a large number of cellular processes. Here, we analyzed the roles of two yeast F-box proteins, Mfb1 and Mdm30, in mitochondrial dynamics. Mfb1 is a novel mitochondria-associated F-box protein. Mitochondria in mutants lacking Mfb1 are fusion competent, but they form aberrant aggregates of interconnected tubules. In contrast, mitochondria in mutants lacking Mdm30 are highly fragmented due to a defect in mitochondrial fusion. Fragmented mitochondria are docked but nonfused in Δmdm30 cells. Mitochondrial fusion is also blocked during sporulation of homozygous diploid mutants lacking Mdm30, leading to a mitochondrial inheritance defect in ascospores. Mfb1 and Mdm30 exert nonredundant functions and likely have different target proteins. Because defects in F-box protein mutants could not be mimicked by depletion of SCF complex and proteasome core subunits, additional yet unknown factors are likely involved in regulating mitochondrial dynamics. We propose that mitochondria-associated F-box proteins Mfb1 and Mdm30 are key components of a complex machinery that regulates mitochondrial dynamics throughout yeast’s entire life cycle.

scholarly journals The pathogenic p.(R391G) ABCC6 displays incomplete penetrance implying the necessity of an interacting partner for the development of pseudoxanthoma elasticum

2020 ◽  
Author(s):  
Flora Szeri ◽  
Agnes Miko ◽  
Nastassia Navasiolava ◽  
Ambrus Kaposi ◽  
Shana Verschuere ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Pseudoxanthoma Elasticum ◽  
Reference Population ◽  
Pathogenic Variant ◽  
Ectopic Calcification ◽  
Incomplete Penetrance ◽  
Sequence Variant ◽  
Primary Role ◽  
Inorganic Pyrophosphate ◽  
Pathogenic Variants

AbstractABCC6 encodes a transmembrane transporter playing a primary role in the efflux of ATP from hepatocytes to the bloodstream. ATP is then cleaved to AMP and inorganic pyrophosphate, a major inhibitor of ectopic calcification. Pathogenic variants of ABCC6 cause pseudoxanthoma elasticum, a multisystemic recessive ectopic calcification disease of variable severity. One of the mechanisms influencing the heterogeneity of a disorder is the penetrance of pathogenic variants. The penetrance of a sequence variant shows the proportion of individuals developing the expected phenotype in the presence of the variant. Incomplete penetrance indicates that the disease does not develop in all the cases when the pathogenic variant is present. Here, we investigated whether incomplete penetrance participates in the heterogeneity of pseudoxanthoma elasticum. By integrating the clinical and genetic data of 590 patients, we created the largest European pseudoxanthoma elasticum cohort. We identified two incomplete penetrant pathogenic variants, p.(V787I) and p.(R391G), based on their allele frequencies in our cohort and in the European reference population of gnomAD. The detailed characterization of the frequent p.(R391G) pathogenic variant suggested only 2% penetrance with an unaltered severity of the clinical phenotype. Based on our biochemical analysis, we hypothesize that the variant becomes deleterious only if an interacting partner is mutated simultaneously. These data point to new molecular mechanisms by revealing the potential existence of the first interacting partner of ABCC6. Our data are important for genetic counseling of pseudoxanthoma elasticum, suggesting a much lower disease heritability of these pathogenic variants.

scholarly journals Reassessment of Gene-Elusive Familial Dilated Cardiomyopathy Leading to the Discovery of a Homozygous AARS2 Variant—The Importance of Regular Reassessment of Genetic Findings

2021 ◽  
Vol 11 (3) ◽  
pp. 122-128
Author(s):  
Priya Bhardwaj ◽  
Christoffer Rasmus Vissing ◽  
Niels Kjær Stampe ◽  
Kasper Rossing ◽  
Alex Hørby Christensen ◽  
...  
Keyword(s):  
Dilated Cardiomyopathy ◽  
Genetic Screening ◽  
Sanger Sequencing ◽  
Mitochondrial Protein ◽  
Trna Synthetase ◽  
Familial Dilated Cardiomyopathy ◽  
Pathogenic Variants ◽  
Case Summary ◽  
Heterozygous Carriers ◽  
Important Enzyme

Background: AARS2 encodes the mitochondrial protein alanyl-tRNA synthetase 2 (MT-AlaRS), an important enzyme in oxidative phosphorylation. Variants in AARS2 have previously been associated with infantile cardiomyopathy. Case summary: A 4-year-old girl died of infantile-onset dilated cardiomyopathy (DCM) in 1996. Fifteen years later, her 21-year-old brother was diagnosed with DCM and ultimately underwent heart transplantation. Initial sequencing of 15 genes discovered no pathogenic variants in the brother at the time of his diagnosis. However, 9 years later re-screening in an updated screening panel of 129 genes identified a homozygous AARS2 (c.1774C > T) variant. Sanger sequencing of the deceased girl confirmed her to be homozygous for the AARS2 variant, while both parents and a third sibling were all found to be unaffected heterozygous carriers of the AARS2 variant. Discussion: This report underlines the importance of repeated and extended genetic screening of elusive families with suspected hereditary cardiomyopathies, as our knowledge of disease-causing mutations continuously grows. Although identification of the genetic etiology in the reported family would not have changed the clinical management, the genetic finding allows genetic counselling and holds substantial value in identifying at-risk relatives.

scholarly journals Unsuspected somatic mosaicism for FBN1 gene contributes to Marfan syndrome

2021 ◽  
Author(s):  
Pauline Arnaud ◽  
Hélène Morel ◽  
Olivier Milleron ◽  
Laurent Gouya ◽  
Christine Francannet ◽  
...  
Keyword(s):  
Marfan Syndrome ◽  
Somatic Mosaicism ◽  
Variant Calling ◽  
Copy Number Variations ◽  
Pathogenic Variant ◽  
Single Nucleotide Variants ◽  
Bioinformatics Analyses ◽  
Single Nucleotide ◽  
Fbn1 Gene ◽  
Pathogenic Variants

Abstract Purpose Individuals with mosaic pathogenic variants in the FBN1 gene are mainly described in the course of familial screening. In the literature, almost all these mosaic individuals are asymptomatic. In this study, we report the experience of our team on more than 5,000 Marfan syndrome (MFS) probands. Methods Next-generation sequencing (NGS) capture technology allowed us to identify five cases of MFS probands who harbored a mosaic pathogenic variant in the FBN1 gene. Results These five sporadic mosaic probands displayed classical features usually seen in Marfan syndrome. Combined with the results of the literature, these rare findings concerned both single-nucleotide variants and copy-number variations. Conclusion This underestimated finding should not be overlooked in the molecular diagnosis of MFS patients and warrants an adaptation of the parameters used in bioinformatics analyses. The five present cases of symptomatic MFS probands harboring a mosaic FBN1 pathogenic variant reinforce the fact that apparently asymptomatic mosaic parents should have a complete clinical examination and a regular cardiovascular follow-up. We advise that individuals with a typical MFS for whom no single-nucleotide pathogenic variant or exon deletion/duplication was identified should be tested by NGS capture panel with an adapted variant calling analysis.

scholarly journals Exploring the Ability of LARS2 Carboxy-Terminal Domain in Rescuing the MELAS Phenotype

Life ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 674
Author(s):  
Francesco Capriglia ◽  
Francesca Rizzo ◽  
Giuseppe Petrosillo ◽  
Veronica Morea ◽  
Giulia d’Amati ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Molecular Mechanisms ◽  
Mitochondrial Protein ◽  
Trna Synthetase ◽  
Mitochondrial Protein Synthesis ◽  
Mitochondrial Translation ◽  
Terminal Domain ◽  
Carboxy Terminal Domain ◽  
Mitochondrial Functions ◽  
Carboxy Terminal

The m.3243A>G mutation within the mitochondrial mt-tRNALeu(UUR) gene is the most prevalent variant linked to mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome. This pathogenic mutation causes severe impairment of mitochondrial protein synthesis due to alterations of the mutated tRNA, such as reduced aminoacylation and a lack of post-transcriptional modification. In transmitochondrial cybrids, overexpression of human mitochondrial leucyl-tRNA synthetase (LARS2) has proven effective in rescuing the phenotype associated with m.3243A>G substitution. The rescuing activity resides in the carboxy-terminal domain (Cterm) of the enzyme; however, the precise molecular mechanisms underlying this process have not been fully elucidated. To deepen our knowledge on the rescuing mechanisms, we demonstrated the interactions of the Cterm with mutated mt-tRNALeu(UUR) and its precursor in MELAS cybrids. Further, the effect of Cterm expression on mitochondrial functions was evaluated. We found that Cterm ameliorates de novo mitochondrial protein synthesis, whilst it has no effect on mt-tRNALeu(UUR) steady-state levels and aminoacylation. Despite the complete recovery of cell viability and the increase in mitochondrial translation, Cterm-overexpressing cybrids were not able to recover bioenergetic competence. These data suggest that, in our MELAS cell model, the beneficial effect of Cterm may be mediated by factors that are independent of the mitochondrial bioenergetics.

scholarly journals Quantitative Approach to Fragmented QRS in Arrhythmogenic Cardiomyopathy: From Disease towards Asymptomatic Carriers of Pathogenic Variants

2020 ◽  
Vol 9 (2) ◽  
pp. 545 ◽  
Author(s):  
Rob W. Roudijk ◽  
Laurens P. Bosman ◽  
Jeroen F. van der Heijden ◽  
Jacques M. T. de Bakker ◽  
Richard N. W. Hauer ◽  
...  
Keyword(s):  
Early Stage ◽  
Pathogenic Variant ◽  
Observer Agreement ◽  
Arrhythmogenic Cardiomyopathy ◽  
Fragmented Qrs ◽  
Early Disease Detection ◽  
Pathogenic Variants ◽  
Disease Penetrance ◽  
Ecg Leads ◽  
And Control

Fragmented QRS complexes (fQRS) are common in patients with arrhythmogenic cardiomyopathy (ACM). A new method of fQRS quantification may aid early disease detection in pathogenic variant carriers and assessment of prognosis in patients with early stage ACM. Patients with definite ACM (n = 221, 66%), carriers of a pathogenic ACM-associated variant without a definite ACM diagnosis (n = 57, 17%) and control subjects (n = 58, 17%) were included. Quantitative fQRS (Q-fQRS) was defined as the total amount of deflections in the QRS complex in all 12 electrocardiography (ECG) leads. Q-fQRS was scored by a single observer and reproducibility was determined by three independent observers. Q-fQRS count was feasible with acceptable intra- and inter-observer agreement. Q-fQRS count is significantly higher in patients with definite ACM (54 ± 15) and pathogenic variant carriers (55 ± 10) compared to controls (35 ± 5) (p < 0.001). In patients with ACM, Q-fQRS was not associated with sustained ventricular arrhythmia (p = 0.701) at baseline or during follow-up (p = 0.335). Both definite ACM patients and pathogenic variant carriers not fulfilling ACM diagnosis have a higher Q-fQRS than controls. This may indicate that increased Q-fQRS is an early sign of disease penetrance. In concealed and early stages of ACM the role of Q-fQRS for risk stratification is limited.

scholarly journals FAM92A1 is a BAR domain protein required for mitochondrial ultrastructure and function

2018 ◽  
Vol 218 (1) ◽  
pp. 97-111 ◽  
Author(s):  
Liang Wang ◽  
Ziyi Yan ◽  
Helena Vihinen ◽  
Ove Eriksson ◽  
Weihuan Wang ◽  
...  
Keyword(s):  
Mitochondrial Function ◽  
Molecular Mechanisms ◽  
Membrane Curvature ◽  
Mitochondrial Morphology ◽  
Membrane Remodeling ◽  
Mitochondrial Ultrastructure ◽  
Bar Domain ◽  
Bar Domain Proteins ◽  
Domain Protein

Mitochondrial function is closely linked to its dynamic membrane ultrastructure. The mitochondrial inner membrane (MIM) can form extensive membrane invaginations known as cristae, which contain the respiratory chain and ATP synthase for oxidative phosphorylation. The molecular mechanisms regulating mitochondrial ultrastructure remain poorly understood. The Bin-Amphiphysin-Rvs (BAR) domain proteins are central regulators of diverse cellular processes related to membrane remodeling and dynamics. Whether BAR domain proteins are involved in sculpting membranes in specific submitochondrial compartments is largely unknown. In this study, we report FAM92A1 as a novel BAR domain protein localizes to the matrix side of the MIM. Loss of FAM92A1 caused a severe disruption to mitochondrial morphology and ultrastructure, impairing organelle bioenergetics. Furthermore, FAM92A1 displayed a membrane-remodeling activity in vitro, inducing a high degree of membrane curvature. Collectively, our findings uncover a role for a BAR domain protein as a critical organizer of the mitochondrial ultrastructure that is indispensable for mitochondrial function.

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