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

Abstract

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.

Stimulating myocardial pyruvate dehydrogenase activity fails to alleviate cardiac abnormalities in a mouse model of human Barth syndrome

“…This raises the important question as to why stimulating myocardial PDH activity would fail to yield benefit in TazKD mice, considering numerous other cardiac pathologies are corrected by such a metabolic strategy? We posit that the persistent destabilization of ETC supercomplexes and reduced ETC complex activity coupled with consequent elevations of mitochondrial reactive oxygen species and oxidative stress (10,11,(30)(31)(32), likely supersede intermediary metabolism defects present in BTHS. This may explain the failure of DCA treatment to attenuate the LV hypertrophic remodeling in TazKD mice despite an improvement of myocardial glucose oxidation.…”

“…Although disruption of tafazzin mediated CL remodeling is associated with electron transport chain (ETC) dysfunction (8)(9)(10), evidence has identified that derangements in oxidative metabolism may be substrate-specific, thus implicating upstream intermediary metabolism pathway defects in the pathogenesis of BTHS-related cardiomyopathy (11)(12)(13). Notably, studies utilizing the Tafazzin knockdown (TazKD) mouse model and Tafazzin knockout cell lines have identified a selective defect in the activity of pyruvate dehydrogenase (PDH), the rate-limiting enzyme of glucose oxidation (10,13). Furthermore, glucose oxidation rates are markedly impaired in perfused isolated working hearts from TazKD mice (13).…”

Myocardial disturbances of intermediary metabolism in Barth syndrome

“…Of interest, CL has been shown to be essential for the assembly of ETC supercomplexes, and supercomplexes were shown to be destabilized in hearts of Tafazzin knockdown (TazKD) mice secondary to doxycycline-mediated induction of a short-hairpin RNA against Tafazzin ( 21 ). Analysis of cardiac mitochondria isolated from cardiac-specific Tafazzin deficient mice prior to the development of cardiomyopathy, also revealed structural remodeling of the respiratory chain with a shift from high molecular weight supercomplexes in the ETC toward lower molecular weight forms such as heterooligomers and individual complexes ( 22 ). Furthermore, complex III activity is decreased in cardiac mitochondria isolated from TazKD mice ( 15 , 23 , 24 ), whereas complex V (F 1 F 0 -ATP synthase) activity is decreased in both TazKD mice and inducible pluripotent stem cell-derived cardiomyocytes from BTHS patients ( 15 , 25 ).…”

“…Myocardial fatty acid extraction and uptake following positron emission tomography (PET) imaging with [1-11 C]palmitate were significantly reduced in young adults with BTHS compared to healthy, age-matched controls, though myocardial fatty acid β-oxidation remained similar (14). Furthermore, cardiac mitochondria isolated from TazKD mice at 2 months or 4-6 months of age, and from 2month-old mice with a cardiac-specific Tafazzin deficiency demonstrated a significant repression of state 3 (ADPstimulated) respiration rates supported by palmitoylcarnitine and malate (15,16,22). A decrease in palmitoylcarnitine supported state 3 respiration was also observed in permeabilized cardiac fibers with intact mitochondrial matrices from 4-6-month-old TazKD mice with preserved cardiac function, as determined by high-resolution respirometry (16).…”

Phosphatidylglycerol Supplementation Alters Mitochondrial Morphology and Cardiolipin Composition

“…After tafazzin lost its function, the CL remodeling process in mitochondria ceased, which resulted in a relatively high percentage of newly synthesized immature CLs [58]. Immature CLs in cardiomyocytes exhibited a short saturated fatty acyl chain with relatively few double bonds.…”