Elamipretide for Barth syndrome cardiomyopathy: gradual rebuilding of a failed power grid

Cyclic Neutropenia ◽

Inner Membrane ◽

Challenges And Opportunities ◽

Pediatric Cardiomyopathy ◽

Induced Pluripotent ◽

Models Of Disease

AbstractBarth syndrome is a rare and potentially fatal X-linked disease characterized by cardiomyopathy, skeletal muscle weakness, growth delays, and cyclic neutropenia. Patients with Barth syndrome are prone to high risk of mortality in infancy and the development of cardiomyopathy with severe weakening of the immune system. Elamipretide is a water-soluble, aromatic-cationic, mitochondria-targeting tetrapeptide that readily penetrates and transiently localizes to the inner mitochondrial membrane. Therapy with elamipretide facilitates cell health by improving energy production and inhibiting excessive formation of reactive oxygen species, thus alleviating oxidative stress. Elamipretide crosses the outer membrane of the mitochondrion and becomes associated with cardiolipin, a constituent phospholipid of the inner membrane. Elamipretide improves mitochondrial bioenergetics and morphology rapidly in induced pluripotent stem cells from patients with Barth syndrome and other genetically related diseases characterized by pediatric cardiomyopathy. Data with elamipretide across multiple models of disease are especially promising, with results from several studies supporting the use of elamipretide as potential therapy for patients with Barth syndrome, particularly where there is a confirmed diagnosis of cardiomyopathy. This review highlights the challenges and opportunities presented in treating Barth syndrome cardiomyopathy patients with elamipretide and addresses evidence supporting the durability of effect of elamipretide as a therapeutic agent for Barth syndrome, especially its likely durable effects on progression of cardiomyopathy following the cessation of drug treatment and the capability of elamipretide to structurally reverse remodel the failing left ventricle at the global, cellular, and molecular level in a gradual manner through specific targeting of the mitochondrial inner membrane.

The mitochondrial carrier pathway transports non-canonical substrates with an odd number of transmembrane segments

BMC Biology ◽

10.1186/s12915-019-0733-6 ◽

2020 ◽

Vol 18 (1) ◽

Cited By ~ 10

Author(s):

Heike Rampelt ◽

Iva Sucec ◽

Beate Bersch ◽

Patrick Horten ◽

Inge Perschil ◽

...

Keyword(s):

Intermembrane Space ◽

Inner Membrane ◽

Mitochondrial Carrier ◽

Transmembrane Segments ◽

N Terminus ◽

The Matrix ◽

Mitochondrial Carrier Family ◽

Mitochondrial Intermembrane Space

Abstract Background The mitochondrial pyruvate carrier (MPC) plays a central role in energy metabolism by transporting pyruvate across the inner mitochondrial membrane. Its heterodimeric composition and homology to SWEET and semiSWEET transporters set the MPC apart from the canonical mitochondrial carrier family (named MCF or SLC25). The import of the canonical carriers is mediated by the carrier translocase of the inner membrane (TIM22) pathway and is dependent on their structure, which features an even number of transmembrane segments and both termini in the intermembrane space. The import pathway of MPC proteins has not been elucidated. The odd number of transmembrane segments and positioning of the N-terminus in the matrix argues against an import via the TIM22 carrier pathway but favors an import via the flexible presequence pathway. Results Here, we systematically analyzed the import pathways of Mpc2 and Mpc3 and report that, contrary to an expected import via the flexible presequence pathway, yeast MPC proteins with an odd number of transmembrane segments and matrix-exposed N-terminus are imported by the carrier pathway, using the receptor Tom70, small TIM chaperones, and the TIM22 complex. The TIM9·10 complex chaperones MPC proteins through the mitochondrial intermembrane space using conserved hydrophobic motifs that are also required for the interaction with canonical carrier proteins. Conclusions The carrier pathway can import paired and non-paired transmembrane helices and translocate N-termini to either side of the mitochondrial inner membrane, revealing an unexpected versatility of the mitochondrial import pathway for non-cleavable inner membrane proteins.

Monolysocardiolipin (MLCL) interactions with mitochondrial membrane proteins

Biochemical Society Transactions ◽

10.1042/bst20190932 ◽

2020 ◽

Vol 48 (3) ◽

pp. 993-1004

Author(s):

Anna L. Duncan

Keyword(s):

Protein Interactions ◽

Mitochondrial Membrane ◽

Barth Syndrome ◽

Mitochondrial Proteins ◽

Mitochondrial Membranes ◽

Inner Membrane ◽

Computational Approaches ◽

Recent Developments ◽

The Stability

Monolysocardiolipin (MLCL) is a three-tailed variant of cardiolipin (CL), the signature lipid of mitochondria. MLCL is not normally found in healthy tissue but accumulates in mitochondria of people with Barth syndrome (BTHS), with an overall increase in the MLCL:CL ratio. The reason for MLCL accumulation remains to be fully understood. The effect of MLCL build-up and decreased CL content in causing the characteristics of BTHS are also unclear. In both cases, an understanding of the nature of MLCL interaction with mitochondrial proteins will be key. Recent work has shown that MLCL associates less tightly than CL with proteins in the mitochondrial inner membrane, suggesting that MLCL accumulation is a result of CL degradation, and that the lack of MLCL–protein interactions compromises the stability of the protein-dense mitochondrial inner membrane, leading to a decrease in optimal respiration. There is some data on MLCL–protein interactions for proteins involved in the respiratory chain and in apoptosis, but there remains much to be understood regarding the nature of MLCL–protein interactions. Recent developments in structural, analytical and computational approaches mean that these investigations are now possible. Such an understanding will be key to further insights into how MLCL accumulation impacts mitochondrial membranes. In turn, these insights will help to support the development of therapies for people with BTHS and give a broader understanding of other diseases involving defective CL content.

Increased ROS-Mediated CaMKII Activation Contributes to Calcium Handling Abnormalities and Impaired Contraction in Barth Syndrome

Circulation ◽

10.1161/circulationaha.120.048698 ◽

2021 ◽

Author(s):

Xujie Liu ◽

Suya Wang ◽

Xiaoling Guo ◽

Yifei Li ◽

Roza Ogurlu ◽

...

Keyword(s):

Genome Editing ◽

Knockout Mice ◽

Contractile Function ◽

Barth Syndrome ◽

Model Systems ◽

Calcium Handling ◽

Cardiomyocyte Contractility ◽

Induced Pluripotent

Background: Mutations in tafazzin ( TAZ ), a gene required for biogenesis of cardiolipin, the signature phospholipid of the inner mitochondrial membrane, causes Barth syndrome (BTHS). Cardiomyopathy and risk of sudden cardiac death are prominent features of BTHS, but the mechanisms by which impaired cardiolipin biogenesis causes cardiac muscle weakness and arrhythmia are poorly understood. Methods: We performed in vivo electrophysiology to define arrhythmia vulnerability in cardiac specific TAZ knockout mice. Using cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs) and cardiac specific TAZ knockout mice as model systems, we investigated the effect of TAZ inactivation on Ca 2+ handling. Through genome editing and pharmacology, we defined a molecular link between TAZ mutation and abnormal Ca 2+ handling and contractility. Results: A subset of mice with cardiac-specific TAZ inactivation developed arrhythmias including bidirectional ventricular tachycardia, atrial tachycardia, and complete atrioventricular block. Compared to WT, BTHS iPSC-CMs had increased diastolic Ca 2+ and decreased Ca 2+ transient amplitude. BTHS iPSC-CMs had higher levels of mitochondrial and cellular ROS than WT, which activated Ca 2+ /calmodulin-dependent protein kinase II (CaMKII). Activated CaMKII phosphorylated the cardiac ryanodine receptor (RYR2) on serine 2814, increasing Ca 2+ leak through RYR2. Inhibition of this ROS-CaMKII-RYR2 pathway through pharmacological inhibitors or genome editing normalized aberrant Ca 2+ handling in BTHS iPSC-CMs and improved their contractile function. Murine Taz knockout cardiomyocytes also exhibited elevated diastolic Ca 2+ and decreased Ca 2+ transient amplitude. These abnormalities were ameliorated by CaMKII or ROS inhibition. Conclusions: This study identified a molecular pathway that links TAZ mutation to abnormal Ca 2+ handling and decreased cardiomyocyte contractility. This pathway may offer therapeutic opportunities to treat BTHS and potentially other diseases with elevated mitochondrial ROS production.

Mitofilin complexes: conserved organizers of mitochondrial membrane architecture

Biological Chemistry ◽

10.1515/hsz-2012-0239 ◽

2012 ◽

Vol 393 (11) ◽

pp. 1247-1261 ◽

Cited By ~ 78

Author(s):

Ralf M. Zerbes ◽

Ida J. van der Klei ◽

Marten Veenhuis ◽

Nikolaus Pfanner ◽

Martin van der Laan ◽

...

Keyword(s):

Outer Membrane ◽

Mitochondrial Membrane ◽

Protein Complexes ◽

Boundary Region ◽

Inner Membrane ◽

Oligomeric Protein ◽

Enzyme Complexes ◽

Boundary Membrane

Abstract Mitofilin proteins are crucial organizers of mitochondrial architecture. They are located in the inner mitochondrial membrane and interact with several protein complexes of the outer membrane, thereby generating contact sites between the two membrane systems of mitochondria. Within the inner membrane, mitofilins are part of hetero-oligomeric protein complexes that have been termed the mitochondrial inner membrane organizing system (MINOS). MINOS integrity is required for the maintenance of the characteristic morphology of the inner mitochondrial membrane, with an inner boundary region closely apposed to the outer membrane and cristae membranes, which form large tubular invaginations that protrude into the mitochondrial matrix and harbor the enzyme complexes of the oxidative phosphorylation machinery. MINOS deficiency comes along with a loss of crista junction structures and the detachment of cristae from the inner boundary membrane. MINOS has been conserved in evolution from unicellular eukaryotes to humans, where alterations of MINOS subunits are associated with multiple pathological conditions.

Proteolipid domains form in biomimetic and cardiac mitochondrial vesicles and are regulated by cardiolipin concentration but not monolyso-cardiolipin

Journal of Biological Chemistry ◽

10.1074/jbc.ra118.004948 ◽

2018 ◽

Vol 293 (41) ◽

pp. 15933-15946 ◽

Cited By ~ 8

Author(s):

Edward Ross Pennington ◽

E. Madison Sullivan ◽

Amy Fix ◽

Sahil Dadoo ◽

Tonya N. Zeczycki ◽

...

Keyword(s):

Morphological Changes ◽

Fluorescent Imaging ◽

Domain Formation ◽

Anionic Phospholipid ◽

Inner Membrane ◽

Mixing Properties ◽

Acyl Chains ◽

Underlying Mechanisms

Cardiolipin (CL) is an anionic phospholipid mainly located in the inner mitochondrial membrane, where it helps regulate bioenergetics, membrane structure, and apoptosis. Localized, phase-segregated domains of CL are hypothesized to control mitochondrial inner membrane organization. However, the existence and underlying mechanisms regulating these mitochondrial domains are unclear. Here, we first isolated detergent-resistant cardiac mitochondrial membranes that have been reported to be CL-enriched domains. Experiments with different detergents yielded only nonspecific solubilization of mitochondrial phospholipids, suggesting that CL domains are not recoverable with detergents. Next, domain formation was investigated in biomimetic giant unilamellar vesicles (GUVs) and newly synthesized giant mitochondrial vesicles (GMVs) from mouse hearts. Confocal fluorescent imaging revealed that introduction of cytochrome c into membranes promotes macroscopic proteolipid domain formation associated with membrane morphological changes in both GUVs and GMVs. Domain organization was also investigated after lowering tetralinoleoyl-CL concentration and substitution with monolyso-CL, two common modifications observed in cardiac pathologies. Loss of tetralinoleoyl-CL decreased proteolipid domain formation in GUVs, because of a favorable Gibbs-free energy of lipid mixing, whereas addition of monolyso-CL had no effect on lipid mixing. Moreover, murine GMVs generated from cardiac acyl-CoA synthetase-1 knockouts, which have remodeled CL acyl chains, did not perturb proteolipid domains. Finally, lowering the tetralinoleoyl-CL content had a stronger influence on the oxidation status of cytochrome c than did incorporation of monolyso-CL. These results indicate that proteolipid domain formation in the cardiac mitochondrial inner membrane depends on tetralinoleoyl-CL concentration, driven by underlying lipid-mixing properties, but not the presence of monolyso-CL.

Atomic structure of the mitochondrial inner membrane AAA+ protease YME1 reveals the mechanism of substrate processing

10.1101/189316 ◽

2017 ◽

Cited By ~ 4

Author(s):

Cristina Puchades ◽

Anthony J. Rampello ◽

Mia Shin ◽

Christopher J. Giuliano ◽

R. Luke Wiseman ◽

...

Keyword(s):

Large Scale ◽

Atp Hydrolysis ◽

Inner Membrane ◽

Conserved Residues ◽

Translocation Mechanism ◽

Substrate Processing ◽

Aaa Atpases ◽

Proteolytic Chamber

AbstractWe present the first atomic model of a substrate-bound inner mitochondrial membrane AAA+ quality control protease, YME1. Our ~3.4 Å cryo-EM structure reveals how the ATPases form a closed spiral staircase encircling an unfolded substrate, directing it toward the flat, symmetric protease ring. Importantly, the structure reveals how three coexisting nucleotide states allosterically induce distinct positioning of tyrosines in the central channel, resulting in substrate engagement and translocation to the negatively charged proteolytic chamber. This tight coordination by a network of conserved residues defines a sequential, around-the-ring ATP hydrolysis cycle that results in step-wise substrate translocation. Furthermore, we identify a hinge-like linker that accommodates the large-scale nucleotide-driven motions of the ATPase spiral independently of the contiguous planar proteolytic base. These results define the first molecular mechanism for a mitochondrial inner membrane AAA+ protease and reveal a translocation mechanism likely conserved for other AAA+ ATPases.

Deacylation on the matrix side of the mitochondrial inner membrane regulates cardiolipin remodeling

Molecular Biology of the Cell ◽

10.1091/mbc.e13-03-0121 ◽

2013 ◽

Vol 24 (12) ◽

pp. 2008-2020 ◽

Cited By ~ 44

Author(s):

Matthew G. Baile ◽

Kevin Whited ◽

Steven M. Claypool

Keyword(s):

Acyl Chain ◽

Growth Conditions ◽

Feedback Mechanism ◽

Barth Syndrome ◽

Intermembrane Space ◽

Inner Membrane ◽

Physiological Importance ◽

The Matrix ◽

Gain Access

The mitochondrial-specific lipid cardiolipin (CL) is required for numerous processes therein. After its synthesis on the matrix-facing leaflet of the inner membrane (IM), CL undergoes acyl chain remodeling to achieve its final form. In yeast, this process is completed by the transacylase tafazzin, which associates with intermembrane space (IMS)-facing membrane leaflets. Mutations in TAZ1 result in the X-linked cardiomyopathy Barth syndrome. Amazingly, despite this clear pathophysiological association, the physiological importance of CL remodeling is unresolved. In this paper, we show that the lipase initiating CL remodeling, Cld1p, is associated with the matrix-facing leaflet of the mitochondrial IM. Thus monolysocardiolipin generated by Cld1p must be transported to IMS-facing membrane leaflets to gain access to tafazzin, identifying a previously unknown step required for CL remodeling. Additionally, we show that Cld1p is the major site of regulation in CL remodeling; and that, like CL biosynthesis, CL remodeling is augmented in growth conditions requiring mitochondrially produced energy. However, unlike CL biosynthesis, dissipation of the mitochondrial membrane potential stimulates CL remodeling, identifying a novel feedback mechanism linking CL remodeling to oxidative phosphorylation capacity.