Barth Syndrome Research Articles

Multifaceted Approach to Enhance Pill-Swallowing Ability in Children and Adults With Barth Syndrome

People with Barth syndrome (BTHS) present with sensory and motor deficits that affect their ability to swallow medications in solid form. Inability to swallow pills can reduce opportunities for people with BTHS to participate in clinical trial research. To evaluate the effectiveness of a brief, multifaceted pill-swallowing program that used evidence-based training methods. Pretest-posttest with 6-mo follow-up. Community setting. A convenience sample of children, adolescents, and adults with a genetically confirmed diagnosis of BTHS. Possible intervention strategies included behavioral approaches (e.g., shaping), adaptive approaches, and positioning approaches. Interventions were tailored to each participant's needs and were carried out by occupational therapy practitioners with advanced training in feeding and eating. Pill-swallowing milestones were ranked on a scale ranging from 0 to 12; participants were scored pretraining, immediately posttraining, and at 6-mo posttraining. Sixteen participants with BTHS, ages 6-34 yr, participated in the training. Fourteen of the 16 participants demonstrated improvement in their pill-swallowing ability. Overall, there was a statistically significant change in pill-swallowing ability from pretraining to posttraining, and these changes were maintained after 6 mo. and Relevance: This study suggests that a brief multifaceted training approach, led by trained professionals, may be effective for helping people with sensory and motor deficits learn to swallow pills independently. Very little has been published in the occupational therapy literature describing how to teach the skill of pill swallowing to clients or how to measure progress toward this goal. This study tested the outcomes of a multifaceted approach to pill swallowing that can be conducted by occupational therapy practitioners; a novel measurement approach is also introduced that can be used with clients in clinical practice.

Barth syndrome: mechanisms and management.

Objectives: Barth syndrome is an ultra-rare, infantile-onset, X-linked recessive mitochondrial disorder, primarily affecting males, due to variants in TAZ encoding for the cardiolipin transacylase tafazzin. This review aimed to summarize and discuss recent and earlier findings concerning the etiology, pathogenesis, clinical presentation, diagnosis, treatment, and outcome of Barth syndrome.Method: A literature review was undertaken through a MEDLINE search.Results: The phenotype of Barth syndrome is highly variable but most frequently patients present with hypertrophic/dilated/non-compaction cardiomyopathy, fibroelastosis, arrhythmias, neutropenia, mitochondrial myopathy, growth retardation, dysmorphism, cognitive impairment, and other, rarer features. Lactic acid and creatine kinase, and blood and urine organic acids, particularly 3-methylglutaconic acid and monolysocardiolipin, are often elevated. Cardiolipin is decreased. Biochemical investigations may show decreased activity of various respiratory chain complexes. The diagnosis is confirmed by documentation of a causative TAZ variant. Treatment is symptomatic and directed toward treating heart failure, arrhythmias, neutropenia, and mitochondrial myopathy.Conclusions: Although Barth syndrome is still an orphan disease, with fewer than 200 cases described so far, there is extensive ongoing research with regard to its pathomechanism and new therapeutic approaches. Although most of these approaches are still experimental, it can be expected that causative strategies will be developed in the near future.

Saturation of acyl chains converts cardiolipin from an antagonist to an activator of Toll-like receptor-4

Cardiolipins (CLs) are tetra-acylated diphosphatidylglycerols found in bacteria, yeast, plants, and animals. In healthy mammals, CLs are unsaturated, whereas saturated CLs are found in blood cells from Barth syndrome patients and in some Gram-positive bacteria. Here, we show that unsaturated but not saturated CLs block LPS-induced NF-κB activation, TNF-α and IP-10 secretion in human and murine macrophages, as well as LPS-induced TNF-α and IL-1β release in human blood mononuclear cells. Using HEK293 cells transfected with Toll-like receptor 4 (TLR4) and its co-receptor Myeloid Differentiation 2 (MD2), we demonstrate that unsaturated CLs compete with LPS for binding TLR4/MD2 preventing its activation, whereas saturated CLs are TLR4/MD2 agonists. As a consequence, saturated CLs induce a pro-inflammatory response in macrophages characterized by TNF-α and IP-10 secretion, and activate the alternative NLRP3 inflammasome pathway in human blood-derived monocytes. Thus, we identify that double bonds discriminate between anti- and pro-inflammatory properties of tetra-acylated molecules, providing a rationale for the development of TLR4 activators and inhibitors for use as vaccine adjuvants or in the treatment of TLR4-related diseases.Graphical abstract

Blunted fat oxidation upon submaximal exercise is partially compensated by enhanced glucose metabolism in children, adolescents, and young adults with Barth syndrome.

Barth syndrome (BTHS) is a rare X-linked condition resulting in abnormal mitochondria, cardioskeletal myopathy, and growth delay; however, the effects of BTHS on substrate metabolism regulation and their relationships with tissue function in humans are unknown. We sought to characterize glucose and fat metabolism during rest, submaximal exercise, and postexercise rest in children, adolescents, and young adults with BTHS and unaffected controls and examine their relationships with cardioskeletal energetics and function. Children/adolescents and young adults with BTHS (n = 29) and children/adolescent and young adult control participants (n = 28, total n = 57) underwent an infusion of 6'6'H2 glucose and U-13 C palmitate and indirect calorimetry during rest, 30-minutes of moderate exercise (50% ), and recovery. Cardiac function, cardioskeletal mitochondrial energetics, and exercise capacity were examined via echocardiography, 31 P magnetic resonance spectroscopy, and peak exercise testing, respectively. The glucose turnover rate was significantly higher in individuals with BTHS during rest (33.2 ± 9.8 vs 27.2 ± 8.1 μmol/kgFFM/min, P < .01) and exercise (34.7 ± 11.2 vs 29.5 ± 8.8 μmol/kgFFM/min, P < .05) and tended to be higher postexercise (33.7 ± 10.2 vs 28.8 ± 8.0 μmol/kgFFM/min, P < .06) compared to controls. Increases in total fat (-3.9 ± 7.5 vs 10.5 ± 8.4 μmol/kgFFM/min, P < .0001) and plasma fatty acid oxidation rates (0.0 ± 1.8 vs 5.1 ± 3.9 μmol/kgFFM/min, P < .0001) from rest to exercise were severely blunted in BTHS compared to controls. Conclusion: An inability to upregulate fat metabolism during moderate intensity exercise appears to be partially compensated by elevations in glucose metabolism. Derangements in fat and glucose metabolism are characteristic of the pathophysiology of BTHS. A severely blunted ability to upregulate fat metabolism during a modest level of physical activity is a defining pathophysiologic characteristic in children, adolescents, and young adults with BTHS.

Plasmalogen Precursors Reverse Lipid Changes in a Barth Syndrome Cell Model

Barth syndrome is rare X chromosome‐linked genetic disorder that is caused by mutations in tafazzin, a phospholipid‐lysophospholipid transacylase responsible for the last step of cardiolipin (CL) biosynthesis in the mitochondria. The lipid alterations in Barth syndrome include loss in total CL content, an increase in the concentration of monolysocardiolipin (MLCL) and a greater heterogeneity of the acyl chains of CL. These changes are so characteristic of Barth syndrome that they have become the basis of diagnostic tests. Recently, one of us has demonstrated that the major change in the lipid composition of organs that have been depleted of tafazzin is the loss of plasmalogens. In several disease states where loss of plasmalogens has been reported, the condition could be reversed by the administration of plasmalogen precursors. Hence, we hypothesized that administration of plasmalogen precursors could reverse the phenotype of Barth syndrome. Here, we present the high‐resolution 31P‐NMR phospholipidomic study of the total lipid extract of a Barth syndrome cell model, i.e., lymphoblasts derived from Barth syndrome patients compared with controls in absence and presence of feeding plasmalogen precursors. Lymphoblasts derived from Barth patients in comparison to controls are ideal for studies of the mechanism as it is a single cell type that can be grown in culture and have all the characteristics of cells from patients with this Syndrome. In agreement with previous results we observed a marked decrease in plasmalogen in Barth lymphoblasts compared to controls together with other lipid alterations reported in those cells. Furthermore, as expected, feeding the cells with plasmalogen precursors restored plasmalogen levels. However, to our surprise the feeding also markedly increased the level of CL. Moreover, we also could show that the CL increase is not a consequence of a decrease in CL hydrolysis by a phospholipase (degradation) as evinced by the lack of MLCL accumulation in cells fed with plasmalogen precursors. In summary, we are able to reverse, at least in part, the lipid changes associated with Barth syndrome by feeding our cell model with plasmalogen precursors. We wish to extend these findings to determine how these changes in lipid composition affect the functioning of their mitochondria. This may present a simple and rapid process to bring these new strategies to the clinic since the precursors we are using are non‐toxic and have been administered to humans for other purposes.Support or Funding InformationAn award from the Barth Syndrome Foundation, Inc. and the Barth Syndrome Foundation of Canada.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mitochondrial dysfunctions in barth syndrome.

Barth syndrome (BTHS) is a rare multisystemic genetic disorder caused by mutations in the TAZ gene. TAZ encodes a mitochondrial enzyme that remodels the acyl chain composition of newly synthesized cardiolipin, a phospholipid unique to mitochondrial membranes. The clinical abnormalities observed in BTHS patients are caused by perturbations in various mitochondrial functions that rely on remodeled cardiolipin. However, the contribution of different cardiolipin-dependent mitochondrial functions to the pathology of BTHS is not fully understood. In this review, we will discuss recent findings from different genetic models of BTHS, including the yeast model of cardiolipin deficiency that has uncovered the specific in vivo roles of cardiolipin in mitochondrial respiratory chain biogenesis, bioenergetics, intermediary metabolism, mitochondrial dynamics, and quality control. We will also describe findings from higher eukaryotic models of BTHS that highlight a link between cardiolipin-dependent mitochondrial function and its impact on tissue and organ function. © 2019 IUBMB Life, 9999(9999):1-11, 2019.

Functional exercise capacity, strength, balance and motion reaction time in Barth syndrome

BackgroundBarth syndrome (BTHS) is an X-linked disorder caused by defects in TAZ with key clinical features including cardiomyopathy, neutropenia and skeletal myopathy. In order to gain a better understanding of the range of clinical features, identify targets for monitoring, and increase knowledge of natural history of the disease, we conducted muscle strength testing, functional exercise capacity testing, physical activity assessment, balance assessment and motion reaction time testing in 33 affected individuals and 14 controls. We analyzed data points to provide a cross-sectional quantitative spectrum of disease characteristics. We also compared these data points to the matched data points collected two years prior to provide insight into effects of BTHS over time.ResultsIn comparison to controls, pediatric subjects with BTHS present with significantly impaired balance and motion reaction time while adult subjects with BTHS present with significantly impaired motion reaction time. In comparison to controls, subjects with BTHS presented with decreased functional exercise capacity (assessed via 6 MWT), knee extensor strength (both assessed via handheld dynamometry and five times sit-to-stand (5 TSTS)), and self-reported physical activity. Comparison of functional exercise capacity, knee extensor strength and self-reported physical activity from identical cohorts in 2014 and 2016 BTHS showed that the deficits in 6 MWT do not change significantly over the 2 year time span.ConclusionIn this comprehensive assessment of musculoskeletal parameters in a cross-section of individuals with BTHS, we uncovered deficits in motion reaction time and balance, which were previously not known to be abnormal in in BTHS. We also confirmed results of our previous study showing that pediatric and adult subjects with BTHS have decreased functional exercise capacity, knee extensor strength, and physical activity in comparison to controls, r, verifying the importance of including these measures as part of the regular clinical assessment in individuals with BTHS, as well as introducing 5 TSTS as an additional testing parameter. Perhaps most importantly, we demonstrated that 6 MWT results do not significantly vary in pediatric and adult cohorts with BTHS over a 2-year period, supporting this as a reliable quantitative measure of therapeutic outcomes in clinical studies and for clinical monitoring.

Cardiolipin-deficient cells depend on anaplerotic pathways to ameliorate defective TCA cycle function

Previous studies have shown that the cardiolipin (CL)-deficient yeast mutant, crd1Δ, has decreased levels of acetyl-CoA and decreased activities of the TCA cycle enzymes aconitase and succinate dehydrogenase. These biochemical phenotypes are expected to lead to defective TCA cycle function. In this study, we report that signaling and anaplerotic metabolic pathways that supplement defects in the TCA cycle are essential in crd1Δ mutant cells. The crd1Δ mutant is synthetically lethal with mutants in the TCA cycle, retrograde (RTG) pathway, glyoxylate cycle, and pyruvate carboxylase 1. Glutamate levels were decreased, and the mutant exhibited glutamate auxotrophy. Glyoxylate cycle genes were up-regulated, and the levels of glyoxylate metabolites succinate and citrate were increased in crd1Δ. Import of acetyl-CoA from the cytosol into mitochondria is essential in crd1Δ, as deletion of the carnitine-acetylcarnitine translocase led to lethality in the CL mutant. β-oxidation was functional in the mutant, and oleate supplementation rescued growth defects. These findings suggest that TCA cycle deficiency caused by the absence of CL necessitates activation of anaplerotic pathways to replenish acetyl-CoA and TCA cycle intermediates. Implications for Barth syndrome, a genetic disorder of CL metabolism, are discussed.

Barth syndrome in a case

患儿男，12日龄，因"纳减、呕吐半天"入院。心脏彩色多普勒超声：卵圆孔未闭。80日龄因"纳减、呕吐半天"再次入院。心脏彩色多普勒超声：全心增大，以左室左房增大为著，左室心内膜增厚，左心收缩功能降低。5月龄心脏超声：左心增大，心肌受累疾患（心肌致密化不全）。外周血白细胞计数及中性粒细胞绝对值降低。基因检测结果：TAZ基因c.348delc（p.Gly116fs）半合子变异，Sanger证明变异来源于患儿母亲，Barth综合征诊断明确。文献复习发现7例Barth综合征患儿，基因变异5种，所有患儿均为男性，均有心肌病、生长发育迟缓、肌无力等表现，其中5例合并中性粒细胞减少。.

AAV9-TAZ Gene Replacement Ameliorates Cardiac TMT Proteomic Profiles in a Mouse Model of Barth Syndrome

Barth syndrome (BTHS) is a rare mitochondrial disease that causes severe cardiomyopathy and has no disease-modifying therapy. It is caused by recessive mutations in the gene tafazzin (TAZ), which encodes tafazzin—an acyltransferase that remodels the inner mitochondrial membrane lipid cardiolipin. To identify novel mechanistic pathways involved in BTHS and evaluate the effects of gene therapy on proteomic profiles, we performed a multiplex tandem mass tagging (TMT) quantitative proteomics analysis to compare protein expression profiles from heart lysates isolated from BTHS, healthy wild-type (WT), and BTHS treated with adeno-associated virus serotype 9 (AAV9)-TAZ gene replacement as neonates or adults. 197 proteins with ≥2 unique peptides were identified. Of these, 91 proteins were significantly differentially expressed in BTHS compared to WT controls. Cause-effect relationships between tafazzin deficiency and altered protein profiles were confirmed through demonstrated significant improvements in expression levels following administration of AAV9-TAZ. The importance of TMEM65 in Cx43 localization to cardiac intercalated discs was revealed as a novel consequence of tafazzin deficiency that was improved following gene therapy. This study identifies novel mechanistic pathways involved in the pathophysiology of BTHS, demonstrates the ability of gene delivery to improve protein expression profiles, and provides support for clinical translation of AAV9-TAZ gene therapy.

COmplexome Profiling ALignment (COPAL) reveals remodeling of mitochondrial protein complexes in Barth syndrome.

MotivationComplexome profiling combines native gel electrophoresis with mass spectrometry to obtain the inventory, composition and abundance of multiprotein assemblies in an organelle. Applying complexome profiling to determine the effect of a mutation on protein complexes requires separating technical and biological variations from the variations caused by that mutation.ResultsWe have developed the COmplexome Profiling ALignment (COPAL) tool that aligns multiple complexome profiles with each other. It includes the abundance profiles of all proteins on two gels, using a multi-dimensional implementation of the dynamic time warping algorithm to align the gels. Subsequent progressive alignment allows us to align multiple profiles with each other. We tested COPAL on complexome profiles from control mitochondria and from Barth syndrome (BTHS) mitochondria, which have a mutation in tafazzin gene that is involved in remodeling the inner mitochondrial membrane phospholipid cardiolipin. By comparing the variation between BTHS mitochondria and controls with the variation among either, we assessed the effects of BTHS on the abundance profiles of individual proteins. Combining those profiles with gene set enrichment analysis allows detecting significantly affected protein complexes. Most of the significantly affected protein complexes are located in the inner mitochondrial membrane (mitochondrial contact site and cristae organizing system, prohibitins), or are attached to it (the large ribosomal subunit).Availability and implementationCOPAL is written in python and is available from http://github.com/cmbi/copal.Supplementary information Supplementary data are available at Bioinformatics online.

Overexpression of branched-chain amino acid aminotransferases rescues the growth defects of cells lacking the Barth syndrome-related gene TAZ1.

The yeast protein Taz1 is the orthologue of human Tafazzin, a phospholipid acyltransferase involved in cardiolipin (CL) remodeling via a monolyso CL (MLCL) intermediate. Mutations in Tafazzin lead to Barth syndrome (BTHS), a metabolic and neuromuscular disorder that primarily affects the heart, muscles, and immune system. Similar to observations in fibroblasts and platelets from patients with BTHS or from animal models, abolishing yeast Taz1 results in decreased total CL amounts, increased levels of MLCL, and mitochondrial dysfunction. However, the biochemical mechanisms underlying the mitochondrial dysfunction in BTHS remain unclear. To better understand the pathomechanism of BTHS, we searched for multi-copy suppressors of the taz1Δ growth defect in yeast cells. We identified the branched-chain amino acid transaminases (BCATs) Bat1 and Bat2 as such suppressors. Similarly, overexpression of the mitochondrial isoform BCAT2 in mammalian cells lacking TAZ improves their growth. Elevated levels of Bat1 or Bat2 did not restore the reduced membrane potential, altered stability of respiratory complexes, or the defective accumulation of MLCL species in yeast taz1Δ cells. Importantly, supplying yeast or mammalian cells lacking TAZ1 with certain amino acids restored their growth behavior. Hence, our findings suggest that the metabolism of amino acids has an important and disease-relevant role in cells lacking Taz1 function. KEY MESSAGES: Bat1 and Bat2 are multi-copy suppressors of retarded growth of taz1Δ yeast cells. Overexpression of Bat1/2 in taz1Δ cells does not rescue known mitochondrial defects. Supplementation of amino acids enhances growth of cells lacking Taz1 or Tafazzin. Altered metabolism of amino acids might be involved in the pathomechanism of BTSH.

HRQoL in Barth Syndrome: Agreement between Child Self-reports and Parent Proxy-reports and Its Relationship to Parental HRQoL.

Purpose:Barth syndrome is an X-linked rare disorder that typically affects only males. This study investigates 1) agreement between child self-reports and parent proxy-reports of HRQoL in boys with Barth syndrome and 2) relationship between parental HRQoL and parent proxy-reports of HRQoL for the child.Materials and methods:Twenty-eight boys with Barth syndrome and their parents participated in this study. The PedsQL™ 4.0 and the PedsQL™ Family Impact Module were used to measure HRQoL of the boys, and the parents’ HRQoL, respectively. The Intraclass Correlation Coefficient was used to test agreement between the child self-reports and parent proxy-reports of HRQoL. The Spearman correlation coefficient was used to test the relationship between parental HRQoL and parent proxy-reports of HRQoL for the child.Results:The agreement between the child self-reports and the parent proxy-reports showed moderate-to-good agreement. Higher parental HRQoL was significantly related to higher ratings of the parents on their children’s HRQoL (p < .05).Conclusions:This study broadens understanding of HRQoL of boys with Barth syndrome using both child self-reports and parent proxy-reports. The findings indicate that the parent proxy-report of HRQoL should be used in conjunction with the child self-report when making client-centered health decisions.

Heart and Muscle in Barth Syndrome

Heart and Muscle in Barth Syndrome

Understanding left ventricular hypertrabeculation/noncompaction: pathomorphologic findings and prognostic impact of neuromuscular comorbidities

ABSTRACTIntroduction: When >3 trabeculations associated with interventricular recesses are found, this is termed ‘left ventricular hypertrabeculation/noncompaction’ (LVHT). Cardiac-imaging methods detect LVHT in all ages, isolated or associated with extracardiac, especially neuromuscular disorders (NMDs). Many issues about LVHT are unclear. The review gives an update about pathomorphologic findings in patients >14 years and the role of NMDs in LVHT.Areas covered: A PubMed-search for the terms “noncompaction“ or “non-compaction“ or “hypertrabeculation“ AND “autopsy“ or ‘biopsy’ or ‘ultrastructure’ or ‘electron microscopy’ AND ‘neuromuscular’ or ‘myopathy’ or ‘neuropathy’ was carried out from 1985 to July 2018.Expert commentary: Macroanatomic (n = 65), histopathologic (n = 59) and ultrastructural (n = 7) reports were found. A comparison with echocardiography was described in 45 cases. Measurements of non-compacted and compacted layer were only given from hearts investigated in short-axis cuts after formaldehyde-fixation. Endocardial, subendocardial and interstitial fibrosis were frequent findings. When LVHT-patients were systematically investigated, a NMD was found in 80%, most frequently mitochondrial disorders, Barth syndrome, zaspopathy, and myotonic dystrophy type 1. LVHT does not seem to be a special type of cardiac involvement of NMDs. NMDs affect prognosis in LVHT as well as LVHT affects prognosis in patients with Duchenne muscular dystrophy.

Abstract 16604: Recombinant Tafazzin Enzyme Replacement Therapy Rescues Metabolic and Functional Defects in a Mouse Model of Barth Syndrome

Barth syndrome (BTHS) is an X-linked autosomal recessive disease caused by mutations in the tafazzin (TAZ) gene. These mutations lead to hypotonia, cyclic neutropenia, 3-methyglutaconic aciduria, and the most common cause of mortality in patients, cardiomyopathy. The TAZ gene encodes an enzyme that generates mature cardiolipin (CL) from monolysocardiolipin (MLCL)in the mitochondrial membrane, which is essential for normal mitochondrial morphology and function. Currently, there is no effective therapy for BTHS. In this study, we test an enzyme replacement therapy for BTHS in myocardial-specific TAZ conditional knockout mice which model the cardiomyopathy of BTHS. Serial echocardiograms showed that the BTHS mice developed increased septal wall thickness at 5 weeks of age. The BTHS mice were treated for 12 weeks with either vehicle or recombinant human TAZ fused to a cell penetrating peptide (hTAZ-CTP) to facilitate tissue uptake. During the treatment period, septal wall thickness in the vehicle-treated mouse continued to increase, whereas it remained stable in those treated with hTAZ-CTP . Pressure-volume (PV) loop analysis indicated that heart function was impaired in the vehicle-treated BTHS mouse while the protein-treated mice were shown to have PV loops similar to normal mice. The ratio of MLCL/CL, a direct measure of TAZ enzymatic activity, was measured in heart mitochondria isolated from BTHS and control floxed allele mice after treatment. The MLCL/CL ratio in the vehicle treated BTHS mouse was 20.4, consistent with a BTHS phenotype, whereas the MLCL/CL ratios in protein-treated and control mice were 0.01, indicating that injection of hTAZ-CTP successfully rescued the function of TAZ in BTHS mice. Histological observation of liver, spleen, kidney, and heart did not show any sign of toxicity for hTAZ-CTP injection. These results indicate that TAZ enzyme replacement therapy has great potential as a future treatment for BTHS.

Cardiac mitochondrial structure and function in tafazzin-knockdown mice

Mutations in the tafazzin gene are the basis of Barth syndrome. The tafazzin protein is responsible for the synthesis of cardiolipin. Doxycycline-induced tafazzin-knockdown mice have been used as a model for Barth syndrome. In the current study, we examined subsarcolemmal and interfibrillar mitochondria from hearts of tafazzin-knockdown mice, focusing on mitochondrial ultrastructure, oxidative phosphorylation, electron transport chain complex activity, and phospholipid and supercomplex content. We then compared the result with mitochondrial pathology in Barth syndrome patients. Although tafazzin-knockdown mouse is a reasonable model for the study of Barth syndrome pathophysiology, it is not a precise simulacrum of the human condition.

AAV-Mediated TAZ Gene Replacement Restores Mitochondrial and Cardioskeletal Function in Barth Syndrome.

Barth syndrome (BTHS) is a rare mitochondrial disease that affects heart and skeletal muscle and has no curative treatment. It is caused by recessive mutations in the X-linked gene TAZ, which encodes tafazzin. To develop a clinically relevant gene therapy to restore tafazzin function and treat BTHS, three different adeno-associated virus serotype 9 vectors were tested and compared to identify the optimal promoter-cytomegalovirus (CMV), desmin (Des), or a native tafazzin promoter (Taz)-for TAZ expression following intravenous administration of 1 × 1013 vector genomes/kilogram to a mouse model of BTHS as either neonates (1-2 days of age) or adults (3 months of age). At 5 months of age, evaluations of biodistribution and TAZ expression levels, mouse activity assessments, fatigue in response to exercise, muscle strength, cardiac function, mitochondrial structure, oxygen consumption, and electron transport chain complex activity assays were performed to measure the extent of improvement in treated mice. Each promoter was scored for significant improvement over untreated control mice and significant improvement compared with the other two promoters for every measurement and within each age of administration. All three of the promoters resulted in significant improvements in a majority of the assessments compared with untreated BTHS controls. When scored for overall effectiveness as a gene therapy, the Des promoter was found to provide improvement in the most assessments, followed by the CMV promoter, and finally Taz regardless of injection age. This study provides substantial support for translation of an adeno-associated virus serotype 9-mediated TAZ gene replacement strategy using a Des promoter for human BTHS patients in the clinic.

Defective Mitochondrial Cardiolipin Remodeling Dampens HIF-1α Expression in Hypoxia

SummaryMitochondria fulfill vital metabolic functions and act as crucial cellular signaling hubs, integrating their metabolic status into the cellular context. Here, we show that defective cardiolipin remodeling, upon loss of the cardiolipin acyl transferase tafazzin, decreases HIF-1α signaling in hypoxia. Tafazzin deficiency does not affect posttranslational HIF-1α regulation but rather HIF-1α gene expression, a dysfunction recapitulated in iPSC-derived cardiomyocytes from Barth syndrome patients with tafazzin deficiency. RNA-seq analyses confirmed drastically altered signaling in tafazzin mutant cells. In hypoxia, tafazzin-deficient cells display reduced production of reactive oxygen species (ROS) perturbing NF-κB activation and concomitantly HIF-1α gene expression. Tafazzin-deficient mice hearts display reduced HIF-1α levels and undergo maladaptive hypertrophy with heart failure in response to pressure overload challenge. We conclude that defective mitochondrial cardiolipin remodeling dampens HIF-1α signaling due to a lack of NF-κB activation through reduced mitochondrial ROS production, decreasing HIF-1α transcription.

Barth syndrome cells display widespread remodeling of mitochondrial complexes without affecting metabolic flux distribution

Barth syndrome (BTHS) is a rare X-linked disorder that is characterized by cardiac and skeletal myopathy, neutropenia and growth abnormalities. The disease is caused by mutations in the tafazzin (TAZ) gene encoding an enzyme involved in the acyl chain remodeling of the mitochondrial phospholipid cardiolipin (CL). Biochemically, this leads to decreased levels of mature CL and accumulation of the intermediate monolysocardiolipin (MLCL). At a cellular level, this causes mitochondrial fragmentation and reduced stability of the respiratory chain supercomplexes. However, the exact mechanism through which tafazzin deficiency leads to disease development remains unclear. We therefore aimed to elucidate the pathways affected in BTHS cells by employing proteomic and metabolic profiling assays. Complexome profiling of patient skin fibroblasts revealed significant effects for about 200 different mitochondrial proteins. Prominently, we found a specific destabilization of higher order oxidative phosphorylation (OXPHOS) supercomplexes, as well as changes in complexes involved in cristae organization and CL trafficking. Moreover, the key metabolic complexes 2-oxoglutarate dehydrogenase (OGDH) and branched-chain ketoacid dehydrogenase (BCKD) were profoundly destabilized in BTHS patient samples. Surprisingly, metabolic flux distribution assays using stable isotope tracer-based metabolomics did not show reduced flux through the TCA cycle. Overall, insights from analyzing the impact of TAZ mutations on the mitochondrial complexome provided a better understanding of the resulting functional and structural consequences and thus the pathological mechanisms leading to Barth syndrome.