Targeted overexpression of catalase to mitochondria does not prevent cardioskeletal myopathy in Barth syndrome

Abstract

Barth Syndrome (BTHS) is an X-linked recessive disorder characterized by cardiomyopathy and muscle weakness. The underlying cause of BTHS is a mutation in the tafazzin (TAZ) gene, a key enzyme of cardiolipin biosynthesis. The lack of CL arising from loss of TAZ function results in destabilization of the electron transport system, promoting oxidative stress that is thought to contribute to development of cardioskeletal myopathy. Indeed, in vitro studies demonstrate that mitochondria-targeted antioxidants improve contractile capacity in TAZ-deficient cardiomyocytes. The purpose of the present study was to determine if resolving mitochondrial oxidative stress would be sufficient to prevent cardiomyopathy and skeletal myopathy in vivo using a mouse model of BTHS. To this end we crossed mice that overexpress catalase in the mitochondria (MCAT mice) with TAZ-deficient mice (TAZKD) to produce TAZKD mice that selectively overexpress catalase in the mitochondria (TAZKD+MCAT mice). TAZKD+MCAT mice exhibited decreased mitochondrial HO emission and lipid peroxidation compared to TAZKD littermates, indicating decreased oxidative stress. Despite the improvements in oxidative stress, TAZKD+MCAT mice developed cardiomyopathy and mild muscle weakness similar to TAZKD littermates. These findings indicate that resolving oxidative stress is not sufficient to suppress cardioskeletal myopathy associated with BTHS.

Respiratory chain signalling is essential for adaptive remodelling following cardiac ischaemia

“…Due to the absence of cardiac progenitor cells, other mechanisms must be considered in the mouse heart, although the underlying mechanism, a failure of regular stress signalling and repair processes, may be similar. Our study also recapitulates a study showing that mitochondria‐targeted overexpression of catalase does not prevent cardioskeletal myopathy in a mouse model of Barth syndrome . It is important to note, however, that whilst catalase facilitates the turnover of hydrogen peroxide to water and oxygen, AOX prevents the production of superoxide at the impaired ETC and thus acts far upstream.…”

“…Our study also recapitulates a study showing that mitochondria-targeted overexpression of catalase does not prevent cardioskeletal myopathy in a mouse model of Barth syndrome. 70 It is important to note, however, that whilst catalase facilitates the turnover of hydrogen peroxide to water and oxygen, AOX prevents the production of superoxide at the impaired ETC and thus acts far upstream.…”

Mitochondrial PE potentiates respiratory enzymes to amplify skeletal muscle aerobic capacity

“…Respiration in permeabilized muscle fiber bundles and isolated mitochondria was performed as previously described. 46,47 Briefly, a small portion of freshly dissected red gastrocnemius muscle tissue was placed in Buffer X (7.23 mM K 2 EGTA, 2.77 mM Ca K 2 EGTA, 20 mM imidazole, 20 mM taurine, 5.7 mM ATP, 14.3 mM phosphocreatine, 6.56 mM MgCl 2 .6H 2 O, and 50 mM K-MES, pH = 7.1), Fiber bundles were separated and permeabilized for 30 min at 4°C with saponin (30 µg/ml) and immediately washed in Buffer Z (105 mM K-MES, 30 mM KCl, 10 mM K 2 HPO 4 , 5 mM MgCl 2 .6H 2 O, 0.5 mg/ml BSA, and 1 mM EGTA, pH = 7.4) for 15 min. After washing, high-resolution respiration rates were measured using an OROBOROS Oxygraph-2k.…”

“…The Amplex Ultra Red (10 µM) / horseradish peroxidase (3 U/ml) detection system was used to measure mitochondrial H 2 O 2 emission and production fluorometrically (Ex:Em 565:600, HORIBA Jobin Yvon Fluorolog) at 37°C. 47 Permeabilized muscle fibers were placed into a glass cuvette with Amplex Ultra Red reagents and buffer Z (with 1 mM EGTA and 23 U superoxide dismutase). Initially, an 8-min background rate was obtained, followed by addition of palmitoyl-L-carnitine / malate (50 µM / 1 mM) into the cuvette for measurement of H 2 O 2 emission rate.…”

“…Echocardiographic measurements were made as previously described. 47 Briefly, mice were anesthetized with a 0.5-2% isoflurane in an oxygen mixture and kept on a heated monitoring plate to maintain body temperature. Heart rate was kept between 400-500 bpm for all measurements to ensure physiological relevance.…”