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Extramitochondrial cardiolipin suggests a novel function of mitochondria in spermatogenesis
Ren, Mindong; Xu, Yang; Erdjument-Bromage, Hediye; Donelian, Alec; Phoon, Colin K L; Terada, Naohiro; Strathdee, Douglas; Neubert, Thomas A; Schlame, Michael
Mitochondria contain cardiolipin (CL), an organelle-specific phospholipid that carries four fatty acids with a strong preference for unsaturated chains. Unsaturation is essential for the stability and for the function of mitochondrial CL. Surprisingly, we found tetrapalmitoyl-CL (TPCL), a fully saturated species, in the testes of humans and mice. TPCL was absent from other mouse tissues but was the most abundant CL species in testicular germ cells. Most intriguingly, TPCL was not localized in mitochondria but was in other cellular membranes even though mitochondrial CL was the substrate from which TPCL was synthesized. During spermiogenesis, TPCL became associated with the acrosome, a sperm-specific organelle, along with a subset of authentic mitochondrial proteins, including Ant4, Suox, and Spata18. Our data suggest that mitochondria-derived membranes are assembled into the acrosome, challenging the concept that this organelle is strictly derived from the Golgi apparatus and revealing a novel function of mitochondria.
PMID: 30914420
ISSN: 1540-8140
CID: 3777022
Loss of tafazzin results in decreased myoblast differentiation in C2C12 cells: A myoblast model of Barth syndrome and cardiolipin deficiency
Lou, Wenjia; Reynolds, Christian A; Li, Yiran; Liu, Jenney; Hüttemann, Maik; Schlame, Michael; Stevenson, David; Strathdee, Douglas; Greenberg, Miriam L
Barth syndrome (BTHS) is an X-linked genetic disorder resulting from mutations in the tafazzin gene (TAZ), which encodes the transacylase that remodels the mitochondrial phospholipid cardiolipin (CL). While most BTHS patients exhibit pronounced skeletal myopathy, the mechanisms linking defective CL remodeling and skeletal myopathy have not been determined. In this study, we constructed a CRISPR-generated stable tafazzin knockout (TAZ-KO) C2C12 myoblast cell line. TAZ-KO cells exhibit mitochondrial deficits consistent with other models of BTHS, including accumulation of monolyso-CL (MLCL), decreased mitochondrial respiratory, and increased mitochondrial ROS production. Additionally, tafazzin-deficiency was associated with impairment of myocyte differentiation. Future studies should determine whether alterations in myogenic determination contribute to the skeletal myopathy observed in BTHS patients. The BTHS myoblast model will enable studies to elucidate mechanisms by which defective CL remodeling interferes with normal myocyte differentiation and skeletal muscle ontogenesis.
PMCID:5976547
PMID: 29694924
ISSN: 0006-3002
CID: 3053122
Substantial Decrease in Plasmalogen in the Heart Associated with Tafazzin Deficiency
Kimura, Tomohiro; Kimura, Atsuko K; Ren, Mindong; Berno, Bob; Xu, Yang; Schlame, Michael; Epand, Richard M
Tafazzin is the mitochondrial enzyme that catalyzes transacylation between a phospholipid and a lysophospholipid in remodeling. Mutations in tafazzin cause Barth syndrome, a potentially life-threatening disease with the major symptom being cardiomyopathy. In the tafazzin-deficient heart, cardiolipin (CL) acyl chains become abnormally heterogeneous unlike those in the normal heart with a single dominant linoleoyl species, tetralinoleoyl CL. In addition, the amount of CL decreases and monolysocardiolipin (MLCL) accumulates. Here we determine using high-resolution 31P nuclear magnetic resonance with cryoprobe technology the fundamental phospholipid composition, including the major but oxidation-labile plasmalogens, in the tafazzin-knockdown (TAZ-KD) mouse heart as a model of Barth syndrome. In addition to confirming a lower level of CL (6.4 ± 0.1 → 2.0 ± 0.4 mol % of the total phospholipid) and accumulation of MLCL (not detected → 3.3 ± 0.5 mol %) in the TAZ-KD, we found a substantial reduction in the level of plasmenylcholine (30.8 ± 2.8 → 18.1 ± 3.1 mol %), the most abundant phospholipid in the control wild type. A quantitative Western blot revealed that while the level of peroxisomes, where early steps of plasmalogen synthesis take place, was normal in the TAZ-KD model, expression of Far1 as a rate-determining enzyme in plasmalogen synthesis was dramatically upregulated by 8.3 (±1.6)-fold to accelerate the synthesis in response to the reduced level of plasmalogen. We confirmed lyso-plasmenylcholine or plasmenylcholine is a substrate of purified tafazzin for transacylation with CL or MLCL, respectively. Our results suggest that plasmenylcholine, abundant in linoleoyl species, is important in remodeling CL in the heart. Tafazzin deficiency thus has a major impact on the cardiac plasmenylcholine level and thereby its functions.
PMCID:5893435
PMID: 29557170
ISSN: 1520-4995
CID: 3044482
Intraoperative Two- and Three-Dimensional Transesophageal Echocardiography in Combined Myectomy-Mitral Operations for Hypertrophic Cardiomyopathy
Nampiaparampil, Robert G; Swistel, Daniel G; Schlame, Michael; Saric, Muhamed; Sherrid, Mark V
Transesophageal echocardiography is essential in guiding the surgical approach for patients with obstructive hypertrophic cardiomyopathy. Septal hypertrophy, elongated mitral valve leaflets, and abnormalities of the subvalvular apparatus are prominent features, all of which may contribute to left ventricular outflow tract obstruction. Surgery aims to alleviate the obstruction via an extended myectomy, often with an intervention on the mitral valve and subvalvular apparatus. The goal of intraoperative echocardiography is to assess the anatomic pathology and pathophysiology in order to achieve a safe intraoperative course and a successful repair. This guide summarizes the systematic evaluation of these patients to determine the best surgical plan.
PMID: 29502589
ISSN: 1097-6795
CID: 2974652
The Basis for Acyl Specificity in the Tafazzin Reaction
Schlame, Michael; Xu, Yang; Ren, Mindong
Tafazzin is a mitochondrial enzyme that transfers fatty acids from phospholipids to lysophospholipids. Mutations in tafazzin cause abnormal molecular species of cardiolipin and the clinical phenotype of Barth syndrome. However, the mechanism by which tafazzin creates acyl specificity has been controversial. We have shown that the lipid phase state can produce acyl specificity in the tafazzin reaction but others have reported that tafazzin itself carries enzymatic specificity. To resolve this issue, we replicated and expanded the controversial experiments, i.e. the transfer of different acyl groups from phosphatidylcholine to monolyso-cardiolipin by yeast tafazzin. Our data show that this reaction requires the presence of detergent and does not take place in liposomes but in mixed micelles. In order to separate thermodynamic (lipid-dependent) from kinetic (enzyme-dependent) parameters, we followed the accumulation of cardiolipin during the reaction from the initial state to the equilibrium state. The transacylation rates of different acyl groups varied over 2 orders of magnitude and correlated tightly with the concentration of cardiolipin in the equilibrium state (lipid-dependent parameter). In contrast, the rates by which different transacylations approached the equilibrium state were very similar (enzyme-dependent parameter). Furthermore, we found that tafazzin catalyzes the remodeling of cardiolipin by combinations of forward and reverse transacylations, essentially creating an equilibrium distribution of acyl groups. These data strongly support the idea that the acyl specificity of the tafazzin reaction results from the physical properties of lipids.
PMCID:5392692
PMID: 28202545
ISSN: 1083-351x
CID: 2449242
Biosynthesis, remodeling and turnover of mitochondrial cardiolipin
Schlame, Michael; Greenberg, Miriam L
Among mitochondrial lipids, cardiolipin occupies a unique place. It is the only phospholipid that is specific to mitochondria and although it is merely a minor component, accounting for 10-20% of the total phospholipid content, cardiolipin plays an important role in the molecular organization, and thus the function of the cristae. This review covers the formation of cardiolipin, a phospholipid dimer containing two phosphatidyl residues, and its assembly into mitochondrial membranes. While a large body of literature exists on this topic, the review focuses on papers that appeared in the past three years. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.
PMCID:5125896
PMID: 27556952
ISSN: 0006-3002
CID: 2221542
Loss of protein association causes cardiolipin degradation in Barth syndrome
Xu, Yang; Phoon, Colin K L; Berno, Bob; D'Souza, Kenneth; Hoedt, Esthelle; Zhang, Guoan; Neubert, Thomas A; Epand, Richard M; Ren, Mindong; Schlame, Michael
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.
PMCID:4955704
PMID: 27348092
ISSN: 1552-4469
CID: 2166952
Cardiolipin as key lipid of mitochondria in health and disease. 2nd Edition, Florence, Italy, September 30-October 1, 2015
Corcelli, Angela; Schlame, Michael
PMID: 27132118
ISSN: 1873-2941
CID: 2101012
Content of Plasmalogen Lipids Markedly Decreases in Barth Syndrome [Meeting Abstract]
Kimura, Tomohiro; Kimura, Atsuko; Berno, Bob; Ren, Mindong; Schlame, Michael; Epand, Richard M
ISI:000375093500427
ISSN: 1542-0086
CID: 2544872
Tafazzins from Drosophila and mammalian cells assemble in large protein complexes with a short half-life
Xu, Yang; Malhotra, Ashim; Claypool, Steven M; Ren, Mindong; Schlame, Michael
Tafazzin is a transacylase that affects cardiolipin fatty acid composition and mitochondrial function. Mutations in human tafazzin cause Barth syndrome yet the enzyme has mostly been characterized in yeast. To study tafazzin in higher organisms, we isolated mitochondria from Drosophila and mammalian cell cultures. Our data indicate that tafazzin binds to multiple protein complexes in these organisms, and that the interactions of tafazzin lack strong specificity. Very large tafazzin complexes could only be detected in the presence of cardiolipin, but smaller complexes remained intact even upon treatment with phospholipase A2. In mammalian cells, tafazzin had a half-life of only 3-6h, which was much shorter than the half-life of other mitochondrial proteins. The data suggest that tafazzin is a transient resident of multiple protein complexes.
PMCID:4693151
PMID: 25598000
ISSN: 1567-7249
CID: 1439892