Project description:Cardiolipin is a specific mitochondrial phospholipid that has a high affinity for proteins and that stabilizes the assembly of supercomplexes involved in oxidative phosphorylation. We found that sequestration of cardiolipin in protein complexes is critical to protect it from degradation. The turnover of cardiolipin is slower by almost an order of magnitude than the turnover of other phospholipids. However, in subjects with Barth syndrome, cardiolipin is rapidly degraded via the intermediate monolyso-cardiolipin. Treatments that induce supercomplex assembly decrease the turnover of cardiolipin and the concentration of monolyso-cardiolipin, whereas dissociation of supercomplexes has the opposite effect. Our data suggest that cardiolipin is uniquely protected from normal lipid turnover by its association with proteins, but this association is compromised in subjects with Barth syndrome, leading cardiolipin to become unstable, which in turn causes the accumulation of monolyso-cardiolipin.
Project description:The mitochondrial inner membrane contains a unique phospholipid known as cardiolipin (CL), which stabilises the protein complexes embedded in the membrane and supports its overall structure. Recent evidence indicates that the mitochondrial ribosome may associate with the inner membrane to facilitate co-translational insertion of the hydrophobic oxidative phosphorylation (OXPHOS) proteins into the inner membrane. We generated three mutant knockout cell lines for the cardiolipin biosynthesis gene Crls1 to investigate the effects of cardiolipin loss on mitochondrial protein synthesis. Reduced CL levels caused altered mitochondrial morphology and transcriptome-wide changes that were accompanied by reduced uncoordinated mitochondrial translation rates and impaired respiratory supercomplex formation. Aberrant protein synthesis was caused by impaired formation and distribution of mitochondrial ribosomes. Reduction or loss of cardiolipin resulted in resulted in different mitochondrial and endoplasmic reticulum stress responses. We show that cardiolipin is required to stabilise the interaction of the mitochondrial ribosome with the membrane via its association with OXA1 during active translation. This interaction facilitates insertion of newly synthesised mitochondrial proteins into the inner membrane and stabilises the respiratory supercomplexes.
Project description:Mitochondria fulfill vital metabolic functions and act as crucial cellular signaling hubs integrating their metabolic status into the cellular context. Here, we show that defective cardiolipin-remodeling, upon loss of the cardiolipin acyl transferase Tafazzin, mutes HIF-1a signaling in hypoxia. Tafazzin-deficiency does not affect posttranslational HIF-1a regulation but rather HIF-1a gene-expression, a dysfunction recapitulated in iPSCs-derived cardiomyocytes from Barth Syndrome patients with Tafazzin-deficiency. RNAseq analyses confirmed drastically altered signaling in Tafazzin mutant cells. In hypoxia, Tafazzin-deficient cells display reduced production of reactive oxygen species (ROS) perturbing NF-kB activation and concomitantly HIF-1a gene-expression. In agreement, Tafazzin-deficient mice hearts display reduced HIF-1a levels and undergo maladaptive hypertrophy with heart failure in response to pressure overload challenge. We conclude that defective mitochondrial cardiolipin-remodeling dampens HIF-1a signaling through inactivation of a non-canonical signaling pathway: Lack of NF-kB activation through reduced mitochondrial ROS production diminishes HIF-1a transcription.
Project description:Analysis of the transcriptome of cardiac tissue from mice transgenically expressing human cardiolipin synthesis. The hypothesis tested was that cardiac specific transgenic expression of cardiolipin synthase alters myocardial lipidomic flux resulting in compensatory metabolic gene transcriptional changes that will attenuate pathological environmental and dietary insults on bioenergetics. Total RNA obtained from cardiac tissue from transgenic cardiac specific expressing human cardiolipin synthase 1 (hCLS1) mouse model at 4 months of age compared to wildtype littermates
Project description:Here we show that synthesis of the mitochondrial phospholipid cardiolipin is an indispensable driver of thermogenic fat function. Cardiolipin biosynthesis is robustly induced in brown and beige adipose upon cold exposure. Mimicking this response by overexpressing cardiolipin synthase (Crls1) enhances energy consumption in mouse and human adipocytes. Crls1 deficiency diminishes mitochondrial uncoupling in brown and beige adipocytes and elicits a nuclear transcriptional response through ER stress-mediated retrograde communication. Cardiolipin depletion in brown and beige fat abolishes adipose thermogenesis and glucose uptake and renders animals strikingly insulin resistant. We further identify a rare human CRLS1 variant associated with insulin resistance and show that adipose CRLS1 levels positively correlate with insulin sensitivity. Thus, adipose cardiolipin is a powerful regulator of organismal energy homeostasis through thermogenic fat bioenergetics.
Project description:Mitochondrial trifunctional protein deficiency, due to mutations in hydratase subunit A (HADHA), results in sudden infant death syndrome with no cure. To reveal the disease etiology, we generated stem cell-derived cardiomyocytes from HADHA-deficient hiPSCs and accelerated their maturation via an engineered microRNA maturation cocktail that upregulated the epigenetic regulator, HOPX. Here we report, matured HADHA mutant cardiomyocytes treated with an endogenous mixture of fatty acids manifest the disease phenotype: defective calcium dynamics and repolarization kinetics which results in a pro-arrhythmic state. Single cell RNA-seq reveals a cardiomyocyte developmental intermediate, based on metabolic gene expression. This intermediate gives rise to mature-like cardiomyocytes in control cells but, mutant cells transition to a pathological state with reduced fatty acid beta-oxidation, reduced mitochondrial proton gradient, disrupted cristae structure and defective cardiolipin remodeling. This study reveals that HADHA (tri-functional protein alpha), a monolysocardiolipin acyltransferase-like enzyme, is required for fatty acid beta-oxidation and cardiolipin remodeling, essential for functional mitochondria in human cardiomyocytes.
Project description:Mitochondrial diseases (MD) are a group of inherited diseases with highly varied and complex clinical presentations and their molecular diagnosis has been improved through next generation sequencing. Here, we report four individuals, two of whom are siblings, affected by a progressive mitochondrial encephalopathy who carry biallelic variants in the cardiolipin biosynthesis gene CRLS1. Using patient fibroblasts, we characterised defects in mitochondrial function that were reflective of CRLS1 dysfunctions, providing functional evidence that the CRLS1 I109N variant causes the MD phenotype observed in this patient. Lipid profiling highlighted that the CRLS1 variants reduced cardiolipin levels, altered its acyl-chain composition and caused a significant increase in phosphatidylglycerol, the substrate of cardiolipin synthase. Proteomic profiling of patient cells and Crls1 knockout cell lines identified both endoplasmic reticular and mitochondrial stress responses, and key features that distinguish between varying degrees of cardiolipin insufficiency. Our findings support that deleterious variants in CRLS1 cause a novel autosomal recessive MD, presenting as a severe encephalopathy with multisystemic involvement. Furthermore, we have identified key changes in cardiolipin and proteome profiles across various degrees of cardiolipin dysfunction, facilitating future advances in diagnostic technologies based on curated signatures in high-throughput datasets.
Project description:A causal mediation analysis of DNA methylation as a mediator of nearby genetic association with Sjögren's syndrome using data collected from 131 female members of the Sjögren's International Collaborative Clinical Alliance registry, comprising of 64 Sjögren's syndrome cases and 67 non-cases.