Metabolomics Reveals New Mechanisms for Pathogenesis in Barth Syndrome and Introduces Novel Roles for Cardiolipin in Cellular Function

Abstract

Barth Syndrome is the only known Mendelian disorder of cardiolipin remodeling, with characteristic clinical features of cardiomyopathy, skeletal myopathy, and neutropenia. While the primary biochemical defects of reduced mature cardiolipin and increased monolysocardiolipin are well-described, much of the downstream biochemical dysregulation has not been uncovered, and biomarkers are limited. In order to further expand upon the knowledge of the biochemical abnormalities in Barth Syndrome, we analyzed metabolite profiles in plasma from a cohort of individuals with Barth Syndrome compared to age-matched controls via 1H nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry. A clear distinction between metabolite profiles of individuals with Barth Syndrome and controls was observed, and was defined by an array of metabolite classes including amino acids and lipids. Pathway analysis of these discriminating metabolites revealed involvement of mitochondrial and extra-mitochondrial biochemical pathways including: insulin regulation of fatty acid metabolism, lipid metabolism, biogenic amine metabolism, amino acid metabolism, endothelial nitric oxide synthase signaling, and tRNA biosynthesis. Taken together, this data indicates broad metabolic dysregulation in Barth Syndrome with wide cellular effects.

Barth Syndrome: Exploring Cardiac Metabolism with Induced Pluripotent Stem Cell-Derived Cardiomyocytes

“…Decreased plasma arginine and increased plasma proline are consistent findings in clinical studies among BTHS patients [11,[23][24][25]. We measured levels of arginine in control and TAZ 517delG -iPS-CMs under our standard culture conditions (RPMI 1640, 10 mM glucose) and proline under standard culture conditions and after 12 h of glucose deprivation.…”

“…(b) Calculated fold changes (FC) for arginine and proline in TAZ 517delG -iPS-CMs vs. control-iPS-CM and in BTHS affected individuals vs. healthy reveals the same phenotypic pattern. Plasma clinical studies calculated fold change (FC) [24] 0.5 1.5 [11] 0.6 1.8 [23] 0.4 NA…”

“…Furthermore, TAZ 517delG -iPS-CMs also exhibited an accumulation of palmitic acid ( Figure 8) and of long chain acyl-carnitines ( Figure 9). Plasma clinical studies calculated fold change (FC) [24] 0.5 1.5 [11] 0.6 1.8 [23] 0.4 NA…”

Mitochondrial dysfunctions in barth syndrome

“…Consistent with the perturbation in the expression of genes involved in amino acid metabolism in TAZ‐KD mice, Sandlers et al found alterations in the amino acid profile in plasma from BTHS patients . Specifically, they showed an increase in proline and tyrosine and a decrease in arginine levels . Although the mechanism for increased levels of proline in BTHS is not known, a defect in mitochondrial proline uptake could explain the observed decrease in arginine levels because proline contributes to arginine biosynthesis.…”

“…For example, genes involved in amino acid synthesis, protein translation, and GTP hydrolysis were upregulated, whereas genes involved in the catabolism of branched chain amino acids (leucine, isoleucine, and valine) were downregulated . Consistent with the perturbation in the expression of genes involved in amino acid metabolism in TAZ‐KD mice, Sandlers et al found alterations in the amino acid profile in plasma from BTHS patients . Specifically, they showed an increase in proline and tyrosine and a decrease in arginine levels .…”