Long‐chain fatty acid oxidation and respiratory complex I deficiencies distinguish Barth Syndrome from idiopathic pediatric cardiomyopathy

Abstract

Barth syndrome (BTHS) is an X-linked disorder that results from mutations in the TAFAZZIN gene, which encodes a phospholipid transacylase responsible for generating the mature form of cardiolipin in inner mitochondrial membranes. BTHS patients develop early onset cardiomyopathy and a derangement of intermediary metabolism consistent with mitochondrial disease, but the precise alterations in cardiac metabolism that distinguish BTHS from idiopathic forms of cardiomyopathy are unknown. We performed the first metabolic analysis of myocardial tissue from BTHS cardiomyopathy patients compared to age-and sex-matched patients with idiopathic dilated cardiomyopathy (DCM) and nonfailing controls. Results corroborate previous evidence for deficiencies in cardiolipin content and its linoleoyl enrichment as defining features of BTHS cardiomyopathy, and reveal a dramatic accumulation of hydrolyzed (monolyso-) cardiolipin molecular species. Respiratory chain protein deficiencies were observed in both BTHS and DCM, but a selective depletion of complex I was seen only in BTHS after controlling for an apparent loss of mitochondrial density in cardiomyopathic hearts. Distinct shifts in the expression of long-chain fatty acid oxidation enzymes and the tissue acyl-CoA profile of BTHS hearts suggest a specific block in mitochondrial fatty acid oxidation upstream of the conventional matrix beta-oxidation cycle, which may be compensated for by a greater reliance upon peroxisomal fatty acid oxidation and the catabolism of ketones, amino acids, and pyruvate to meet cardiac energy demands. These results provide a comprehensive foundation for exploring novel therapeutic strategies that target the adaptive and maladaptive metabolic features of BTHS cardiomyopathy.

Myocardial disturbances of intermediary metabolism in Barth syndrome

“…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 ). Protein expression of fatty acid binding protein and acyl-CoA synthetase, which mediate intracellular fatty acid transport and fatty acid esterification to CoA, respectively, were similar in LV tissue from male patients with BTHS and non-failing hearts ( 20 ). Furthermore, similar enzymatic activities of carnitine palmitoyltransferase I and 2 (CPT-1 and CPT-2) were observed in LV tissue homogenates from male patients with BTHS-related cardiomyopathy compared to non-failing controls ( 20 ).…”

“…Protein expression of fatty acid binding protein and acyl-CoA synthetase, which mediate intracellular fatty acid transport and fatty acid esterification to CoA, respectively, were similar in LV tissue from male patients with BTHS and non-failing hearts ( 20 ). Furthermore, similar enzymatic activities of carnitine palmitoyltransferase I and 2 (CPT-1 and CPT-2) were observed in LV tissue homogenates from male patients with BTHS-related cardiomyopathy compared to non-failing controls ( 20 ). This suggests that BTHS-related defects in myocardial fatty acid metabolism may be downstream of mitochondrial fatty acid uptake.…”

“…Alternatively, impaired tafazzin-mediated CL remodeling in BTHS may result in a selective block in long-chain fatty acid β-oxidation. Protein levels of very long-chain acyl CoA dehydrogenase (VLCAD) were decreased in LV tissue from male BTHS subjects compared to age-matched, non-failing male subjects and male subjects diagnosed with idiopathic dilated cardiomyopathy, as assessed by both immunoblotting and LC-MS/MS based proteomic profiling ( 20 ). Likewise, VLCAD protein expression was also decreased in cardiac mitochondria from 4–6-month-old TazKD mice compared to their WT littermates, as determined via LC-MS/MS based proteomic profiling ( 16 ).…”

“…In a Tafazzin deficient mouse model that relies on cre-mediated deletion of the Tafazzin gene containing loxP sites flanking exons 5–10, label-free quantitative proteomics revealed reductions in the relative abundances of all ETC complexes (complexes I-V) ( 19 ). Moreover, liquid chromatography (LC)-mass spectrometry (MS)/MS analysis of the cardiac proteome demonstrated a reduction in complex 1 (following normalization to citrate synthase) in left ventricular (LV) tissue from individuals with BTHS compared to non-failing control heart samples ( 20 ). 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 ).…”

Barth syndrome and the many fascinating aspects of cardiolipin

“…These results point to an intricate interplay between cardiolipin synthesis and ether lipid synthesis and may have consequences for future therapeutic endeavors in Barth syndrome. The last paper in this Special Issue is by Chatfield and coworkers 12 and represents the first comprehensive metabolic analysis of cardiac tissue from patients with Barth syndrome, including proteomic and metabolomic analyses, notably of the acyl‐CoA and cardiolipin molecular species, which provides unprecedented insight into the complex alterations induced by Tafazzin deficiency. The results presented are strongly suggestive of a secondary impairment in mitochondrial fatty acid oxidation affecting acyl‐CoA metabolism, in line with studies in the Barth syndrome mouse model.…”