Tafazzin deficiency impairs CoA-dependent oxidative metabolism in cardiac mitochondria

Catherine H Le,Lindsay G Benage,Kalyn S Specht,Lance C Li Puma,Christopher M Mulligan,Adam L Heuberger,Jessica E Prenni,Steven M Claypool,Kathryn C Chatfield,Genevieve C Sparagna,Adam J Chicco

doi:10.1074/jbc.ra119.011229

Abstract

Barth syndrome is a mitochondrial myopathy resulting from mutations in the tafazzin (TAZ) gene encoding a phospholipid transacylase required for cardiolipin remodeling. Cardiolipin is a phospholipid of the inner mitochondrial membrane essential for the function of numerous mitochondrial proteins and processes. However, it is unclear how tafazzin deficiency impacts cardiac mitochondrial metabolism. To address this question while avoiding confounding effects of cardiomyopathy on mitochondrial phenotype, we utilized Taz-shRNA knockdown (TazKD ) mice, which exhibit defective cardiolipin remodeling and respiratory supercomplex instability characteristic of human Barth syndrome but normal cardiac function into adulthood. Consistent with previous reports from other models, mitochondrial H2O2 emission and oxidative damage were greater in TazKD than in wild-type (WT) hearts, but there were no differences in oxidative phosphorylation coupling efficiency or membrane potential. Fatty acid and pyruvate oxidation capacities were 40-60% lower in TazKD mitochondria, but an up-regulation of glutamate oxidation supported respiration rates approximating those with pyruvate and palmitoylcarnitine in WT. Deficiencies in mitochondrial CoA and shifts in the cardiac acyl-CoA profile paralleled changes in fatty acid oxidation enzymes and acyl-CoA thioesterases, suggesting limitations of CoA availability or "trapping" in TazKD mitochondrial metabolism. Incubation of TazKD mitochondria with exogenous CoA partially rescued pyruvate and palmitoylcarnitine oxidation capacities, implicating dysregulation of CoA-dependent intermediary metabolism rather than respiratory chain defects in the bioenergetic impacts of tafazzin deficiency. These findings support links among cardiolipin abnormalities, respiratory supercomplex instability, and mitochondrial oxidant production and shed new light on the distinct metabolic consequences of tafazzin deficiency in the mammalian heart.

Highlights

Barth syndrome (3-methylglutaconic aciduria type II; BTHS) is an X-linked mitochondrial disorder that results from loss-offunction mutations in the tafazzin gene (TAZ), leading to debil
We evaluated mitochondrial reactive oxygen species (mtROS) release during OXPHOSlinked respiration by monitoring H2O2 emission from cardiac mitochondria (SS 1 IF populations) using the Amplex Red fluorometric assay coupled to our Oroboros oxygraph chamber (Fig. 3, A and B). mtROS release was higher in Taz-shRNA knockdown (TazKD) versus WT during maximal oxidative phosphorylation (OXPHOS)-linked respiration supported by complex I (CI) 1 complex II (CII) substrates, and elevated further by inhibition of CI with rotenone (S)
The Taz short hairpin RNA (shRNA) mouse proved ideal for this purpose, exhibiting persistent depletion of tetra-linoleoyl cardiolipin (L4CL) and CI–complex III (CIII)–complex IV (CIV) mitochondrial supercomplexes characteristic of BTHS [14, 41] and other cardiac pathologies [42, 43] but preserved cardiac function well into adulthood

Summary

Introduction

Barth syndrome (3-methylglutaconic aciduria type II; BTHS) is an X-linked mitochondrial disorder that results from loss-offunction mutations in the tafazzin gene (TAZ), leading to debil-. The most severe clinical manifestation of BTHS is cardiomyopathy, which can present in infants or develop later in adulthood, despite persistent cardiolipin abnormalities beginning early in life [23] This phenotypic heterogeneity suggests that variations in tafazzin function or compensatory adaptations that preserve cardiac function must occur across affected individuals and highlights an incomplete understanding of how cardiolipin abnormalities impact the heart. Lower doxycycline dosing during gestation produces offspring that live well into adulthood despite ;90% Taz deficiency and characteristic abnormalities in cardiolipin composition and mitochondrial morphology [24, 25] These mice exhibit exercise intolerance and growth delay consistent with human BTHS but maintain relatively normal cardiac function until ;6–7 months of age [24, 25, 28] despite impairments in cardiac mitochondrial function evident by 2–3 months of age [20,21,22, 28]

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