Cardiolipin Remodeling Defects Impair Mitochondrial Architecture and Function in a Murine Model of Barth Syndrome Cardiomyopathy

BACKGROUND

Cardiomyopathy is a major clinical feature in Barth syndrome (BTHS), an X-linked mitochondrial lipid disorder caused by mutations in Tafazzin (TAZ), encoding a mitochondrial acyltransferase required for cardiolipin remodeling. Despite recent description of a mouse model of BTHS cardiomyopathy, an in-depth analysis of specific lipid abnormalities and mitochondrial form and function in an in vivo BTHS cardiomyopathy model is lacking.

METHODS

We performed in-depth assessment of cardiac function, cardiolipin species profiles, and mitochondrial structure and function in our newly generated Taz cardiomyocyte-specific knockout mice and Cre-negative control mice (n≥3 per group).

RESULTS

Taz cardiomyocyte-specific knockout mice recapitulate typical features of BTHS and mitochondrial cardiomyopathy. Fewer than 5% of cardiomyocyte-specific knockout mice exhibited lethality before 2 months of age, with significantly enlarged hearts. More than 80% of cardiomyocyte-specific knockout displayed ventricular dilation at 16 weeks of age and survived until 50 weeks of age. Full parameter analysis of cardiac cardiolipin profiles demonstrated lower total cardiolipin concentration, abnormal cardiolipin fatty acyl composition, and elevated monolysocardiolipin to cardiolipin ratios in Taz cardiomyocyte-specific knockout, relative to controls. Mitochondrial contact site and cristae organizing system and F1F0-ATP synthase complexes, required for cristae morphogenesis, were abnormal, resulting in onion-shaped mitochondria. Organization of high molecular weight respiratory chain supercomplexes was also impaired. In keeping with observed mitochondrial abnormalities, seahorse experiments demonstrated impaired mitochondrial respiration capacity.

CONCLUSIONS

Our mouse model mirrors multiple physiological and biochemical aspects of BTHS cardiomyopathy. Our results give important insights into the underlying cause of BTHS cardiomyopathy and provide a framework for testing therapeutic approaches to BTHS cardiomyopathy, or other mitochondrial-related cardiomyopathies.

The PPAR pan-agonist bezafibrate ameliorates cardiomyopathy in a mouse model of Barth syndrome

BACKGROUND

The PGC-1α/PPAR axis has been proposed as a potential therapeutic target for several metabolic disorders. The aim was to evaluate the efficacy of the pan-PPAR agonist, bezafibrate, in tafazzin knockdown mice (TazKD), a mouse model of Barth syndrome that exhibits age-dependent dilated cardiomyopathy with left ventricular (LV) dysfunction.

RESULTS

The effect of bezafibrate on cardiac function was evaluated by echocardiography in TazKD mice with or without beta-adrenergic stress. Adrenergic stress by chronic isoproterenol infusion exacerbates the cardiac phenotype in TazKD mice, significantly depressing LV systolic function by 4.5 months of age. Bezafibrate intake over 2 months substantially ameliorates the development of LV systolic dysfunction in isoproterenol-stressed TazKD mice. Without beta-adrenergic stress, TazKD mice develop dilated cardiomyopathy by 7 months of age. Prolonged treatment with suprapharmacological dose of bezafibrate (0.5% in rodent diet) over a 4-month period effectively prevented LV dilation in mice isoproterenol treatment. Bezafibrate increased mitochondrial biogenesis, however also promoted oxidative stress in cardiomyocytes. Surprisingly, improvement of systolic function in bezafibrate-treated mice was accompanied with simultaneous reduction of cardiolipin content and increase of monolysocardiolipin levels in cardiac muscle.

CONCLUSIONS

Thus, we demonstrate that bezafibrate has a potent therapeutic effect on preventing cardiac dysfunction in a mouse model of Barth syndrome with obvious implications for treating the human disease. Additional studies are needed to assess the potential benefits of PPAR agonists in humans with Barth syndrome.

Mitochondria-targeted antioxidant prevents cardiac dysfunction induced by tafazzin gene knockdown in cardiac myocytes

Tafazzin, a mitochondrial acyltransferase, plays an important role in cardiolipin side chain remodeling. Previous studies have shown that dysfunction of tafazzin reduces cardiolipin content, impairs mitochondrial function, and causes dilated cardiomyopathy in Barth syndrome. Reactive oxygen species (ROS) have been implicated in the development of cardiomyopathy and are also the obligated byproducts of mitochondria. We hypothesized that tafazzin knockdown increases ROS production from mitochondria, and a mitochondria-targeted antioxidant prevents tafazzin knockdown induced mitochondrial and cardiac dysfunction. We employed cardiac myocytes transduced with an adenovirus containing tafazzin shRNA as a model to investigate the effects of the mitochondrial antioxidant, mito-Tempo. Knocking down tafazzin decreased steady state levels of cardiolipin and increased mitochondrial ROS. Treatment of cardiac myocytes with mito-Tempo normalized tafazzin knockdown enhanced mitochondrial ROS production and cellular ATP decline. Mito-Tempo also significantly abrogated tafazzin knockdown induced cardiac hypertrophy, contractile dysfunction, and cell death. We conclude that mitochondria-targeted antioxidant prevents cardiac dysfunction induced by tafazzin gene knockdown in cardiac myocytes and suggest mito-Tempo as a potential therapeutic for Barth syndrome and other dilated cardiomyopathies resulting from mitochondrial oxidative stress.

Pharmacogenomic considerations in the treatment of the pediatric cardiomyopathy called Barth syndrome

Barth syndrome (BTHS) is a genetic, X-linked, rare but often fatal, pediatric skeletal- and cardiomyopathy occurring due to mutations in the tafazzin gene (TAZ). TAZ encodes a transacylase involved in phospholipid biosynthesis, also called tafazzin, which is responsible for remodeling the inner mitochondrial membrane phospholipid, cardiolipin (CL). Tafazzin mutations lead to compositional alterations in CL molecular species, causing extensive mitochondrial aberrations and ultrastructural muscle damage. There are no specific treatments or cure for BTHS. Current therapy is largely palliative and aimed at treatment of organ-specific complications during disease progression. Polypharmacy frequently occurs during treatment and may lead to severe adverse events. Adverse reactions may originate from exogenous factors such as the inadvertent co-administration of contraindicated drugs. Theoretically, endogenous factors such as polymorphic variations in genes encoding drug metabolizing enzymes may also precipitate fatal toxicity. Investigation of the consequences of pharmacogenomic variations on BTHS therapy is lacking. To our knowledge, this review presents the first examination of the possible sources of pharmacogenomic variations that may affect BTHS therapy. We also explore BTHSspecific patents for possible treatment options. The patents discussed suggest innovative strategies for treatment, including feeding linoleic acid to patients to overcome compositional CL deficiency; or the use of 2S,4R ketoconazole formulations to augment CL levels; or the delivery of mitochondrial stabilizing cargo. Future research directions are also discussed.

[A familial form of ventricular non compaction in a mother and two of his sons in St. Louis, Senegal]

We report a familial form of ventricular non compaction in a mother and two of her sons. It was a young man of 25 years who presented with NYHA stage III dyspnea and a cough with bloody sputum. The clinical examination found left ventricular failure. The echocardiogram done showed left ventricular dilatation with large trabeculae separated by deep intertrabecular recesses in both ventricles suggestive of a non-biventricular compaction. It was possible to note from the family screening by echocardiography of the mother and half-brother a left ventricular non compaction while they were asymptomatic. Thus we concluded a familial form of ventricular non-compaction. This is the first familial case described in Senegal.

[Family form of isolated left ventricular noncompaction; case of a mother and her son observed in Gabon]

We describe a case report of a young Gabonese lady who presented an acute pulmonary oedema and we suspected a paripartum cardiomyopathy. Subsequent investigations showed isolated left ventricular noncompaction. A few months later, the same disease was disclosed at her 9 year-old son who presented a cardiac insufficiency. Therefore, we suspect a family form of left ventricular noncompaction. And it is the first description in subsaharan Africa. The hereditary character of this new form of cardiomyopathy linked to a genetic mutation on the X chromosome is well known. This disease is associated with heart failure, high incidence of systemic thromboembolism complications or ventricular arrhythmia. The echocardiography and the cardiac magnetic resonance imaging has been reported to be tools for diagnosis. In Africa, access to these techniques remains a privilege. So the discovery of illness is often late and the family screening are special. In our area, the therapeutic management is the medical treatment of heart failure. Implatable cardioverter defibrillator or heart transplantation are not available. So long-term prognosis of our patients with congestive heart failure stays poor. With best equipment in our hospitals and good training of African cardiologists, we should improve the management of our patients.