The Molecular Mechanism of Transport by the Mitochondrial ADP/ATP Carrier.

Mitochondrial ADP/ATP carriers transport ADP into the mitochondrial matrix for ATP synthesis, and ATP out to fuel the cell, by cycling between cytoplasmic-open and matrix-open states. The structure of the cytoplasmic-open state is known, but it has proved difficult to understand the transport mechanism in the absence of a structure in the matrix-open state. Here, we describe the structure of the matrix-open state locked by bongkrekic acid bound in the ADP/ATP-binding site at the bottom of the central cavity. The cytoplasmic side of the carrier is closed by conserved hydrophobic residues, and a salt bridge network, braced by tyrosines. Glycine and small amino acid residues allow close-packing of helices on the matrix side. Uniquely, the carrier switches between states by rotation of its three domains about a fulcrum provided by the substrate-binding site. Because these features are highly conserved, this mechanism is likely to apply to the whole mitochondrial carrier family. VIDEO ABSTRACT.

Gasdermin D permeabilization of mitochondrial inner and outer membranes accelerates and enhances pyroptosis.

Gasdermin D (GSDMD)-activated inflammatory cell death (pyroptosis) causes mitochondrial damage, but its underlying mechanism and functional consequences are largely unknown. Here, we show that the N-terminal pore-forming GSDMD fragment (GSDMD-NT) rapidly damaged both inner and outer mitochondrial membranes (OMMs) leading to reduced mitochondrial numbers, mitophagy, ROS, loss of transmembrane potential, attenuated oxidative phosphorylation (OXPHOS), and release of mitochondrial proteins and DNA from the matrix and intermembrane space. Mitochondrial damage occurred as soon as GSDMD was cleaved prior to plasma membrane damage. Mitochondrial damage was independent of the B-cell lymphoma 2 family and depended on GSDMD-NT binding to cardiolipin. Canonical and noncanonical inflammasome activation of mitochondrial damage, pyroptosis, and inflammatory cytokine release were suppressed by genetic ablation of cardiolipin synthase (Crls1) or the scramblase (Plscr3) that transfers cardiolipin to the OMM. Phospholipid scramblase-3 (PLSCR3) deficiency in a tumor compromised pyroptosis-triggered anti-tumor immunity. Thus, mitochondrial damage plays a critical role in pyroptosis.

Functional diversity among cardiolipin binding sites on the mitochondrial ADP/ATP carrier.

Lipid-protein interactions play a multitude of essential roles in membrane homeostasis. Mitochondrial membranes have a unique lipid-protein environment that ensures bioenergetic efficiency. Cardiolipin (CL), the signature mitochondrial lipid, plays multiple roles in promoting oxidative phosphorylation (OXPHOS). In the inner mitochondrial membrane, the ADP/ATP carrier (AAC in yeast; adenine nucleotide translocator, ANT in mammals) exchanges ADP and ATP, enabling OXPHOS. AAC/ANT contains three tightly bound CLs, and these interactions are evolutionarily conserved. Here, we investigated the role of these buried CLs in AAC/ANT using a combination of biochemical approaches, native mass spectrometry, and molecular dynamics simulations. We introduced negatively charged mutations into each CL-binding site of yeast Aac2 and established experimentally that the mutations disrupted the CL interactions. While all mutations destabilized Aac2 tertiary structure, transport activity was impaired in a binding site-specific manner. Additionally, we determined that a disease-associated missense mutation in one CL-binding site in human ANT1 compromised its structure and transport activity, resulting in OXPHOS defects. Our findings highlight the conserved significance of CL in AAC/ANT structure and function, directly tied to specific lipid-protein interactions.

Cristae formation is a mechanical buckling event controlled by the inner mitochondrial membrane lipidome.

Cristae are high-curvature structures in the inner mitochondrial membrane (IMM) that are crucial for ATP production. While cristae-shaping proteins have been defined, analogous lipid-based mechanisms have yet to be elucidated. Here, we combine experimental lipidome dissection with multi-scale modeling to investigate how lipid interactions dictate IMM morphology and ATP generation. When modulating phospholipid (PL) saturation in engineered yeast strains, we observed a surprisingly abrupt breakpoint in IMM topology driven by a continuous loss of ATP synthase organization at cristae ridges. We found that cardiolipin (CL) specifically buffers the inner mitochondrial membrane against curvature loss, an effect that is independent of ATP synthase dimerization. To explain this interaction, we developed a continuum model for cristae tubule formation that integrates both lipid and protein-mediated curvatures. This model highlighted a snapthrough instability, which drives IMM collapse upon small changes in membrane properties. We also showed that cardiolipin is essential in low-oxygen conditions that promote PL saturation. These results demonstrate that the mechanical function of cardiolipin is dependent on the surrounding lipid and protein components of the IMM.

Gasdermin D triggers cardiolipin-driven mitochondrial damage and pyroptosis.

In a remarkable recent study, Miao et al. reveal that gasdermin D N-terminal (GSDMD-NT) instigates mitochondrial damage in pyroptosis by forming pores in inner and outer mitochondrial membranes (OMMs). The authors highlight the key role of mitochondrial cardiolipin in the action of GSDMD-NT, and significantly advance our understanding of this inflammatory cell death mechanism.

Small mitochondrial protein NERCLIN regulates cardiolipin homeostasis and mitochondrial ultrastructure.

Cardiolipin (CL) is an essential phospholipid for mitochondrial structure and function. Here, we present a small mitochondrial protein, NERCLIN, as a negative regulator of CL homeostasis and mitochondrial ultrastructure. Primate-specific NERCLIN is expressed ubiquitously from the GRPEL2 locus on a tightly regulated low level. NERCLIN overexpression severely disrupts mitochondrial cristae structure and induces mitochondrial fragmentation. Proximity labeling and immunoprecipitation analysis suggested interactions of NERCLIN with CL synthesis and prohibitin complexes on the matrix side of the inner mitochondrial membrane. Lipid analysis indicated that NERCLIN regulates mitochondrial CL content. Furthermore, NERCLIN is responsive to heat stress ensuring OPA1 processing and cell survival. Thus, we propose that NERCLIN contributes to the stress-induced adaptation of mitochondrial dynamics. Our findings add NERCLIN to the group of recently identified small mitochondrial proteins with important regulatory functions.

Cardiolipin deficiency leads to the destabilization of mitochondrial magnesium channel MRS2 in Barth syndrome.

Barth syndrome (BTHS) is a debilitating X-linked cardio-skeletal myopathy caused by loss-of-function mutations in TAFAZZIN, a cardiolipin (CL)-remodeling enzyme required for the maintenance of normal levels of CL species in mitochondrial membranes. At present, how perturbations in CL abundance and composition lead to many debilitating clinical presentations in BTHS patients have not been fully elucidated. Inspired by our recent findings that CL is essential for optimal mitochondrial calcium uptake, we measured the levels of other biologically important metal ions in BTHS mitochondria and found that in addition to calcium, magnesium levels are significantly reduced. Consistent with this observation, we report a decreased abundance of the mitochondrial magnesium influx channel MRS2 in multiple models of BTHS including yeast, murine myoblast, and BTHS patient cells and cardiac tissue. Mechanistically, we attribute reduced steady-state levels of MRS2 to its increased turnover in CL-deficient BTHS models. By expressing Mrs2 in well-characterized yeast mutants of the phospholipid biosynthetic pathways, we demonstrate a specific requirement of CL for Mrs2 abundance and assembly. Finally, we provide in vitro evidence for the direct binding of CL with human MRS2. Together, our study has identified a critical requirement of CL for MRS2 stability and suggests perturbation of mitochondrial magnesium homeostasis as a novel contributing factor to BTHS pathology.

Mitochondrial phospholipid metabolism in health and disease.

Studies of rare human genetic disorders of mitochondrial phospholipid metabolism have highlighted the crucial role that membrane phospholipids play in mitochondrial bioenergetics and human health. The phospholipid composition of mitochondrial membranes is highly conserved from yeast to humans, with each class of phospholipid performing a specific function in the assembly and activity of various mitochondrial membrane proteins, including the oxidative phosphorylation complexes. Recent studies have uncovered novel roles of cardiolipin and phosphatidylethanolamine, two crucial mitochondrial phospholipids, in organismal physiology. Studies on inter-organellar and intramitochondrial phospholipid transport have significantly advanced our understanding of the mechanisms that maintain mitochondrial phospholipid homeostasis. Here, we discuss these recent advances in the function and transport of mitochondrial phospholipids while describing their biochemical and biophysical properties and biosynthetic pathways. Additionally, we highlight the roles of mitochondrial phospholipids in human health by describing the various genetic diseases caused by disruptions in their biosynthesis and discuss advances in therapeutic strategies for Barth syndrome, the best-studied disorder of mitochondrial phospholipid metabolism.

Acylglycerol Kinase Mutated in Sengers Syndrome Is a Subunit of the TIM22 Protein Translocase in Mitochondria.

Mutations in mitochondrial acylglycerol kinase (AGK) cause Sengers syndrome, which is characterized by cataracts, hypertrophic cardiomyopathy, and skeletal myopathy. AGK generates phosphatidic acid and lysophosphatidic acid, bioactive phospholipids involved in lipid signaling and the regulation of tumor progression. However, the molecular mechanisms of the mitochondrial pathology remain enigmatic. Determining its mitochondrial interactome, we have identified AGK as a constituent of the TIM22 complex in the mitochondrial inner membrane. AGK assembles with TIMM22 and TIMM29 and supports the import of a subset of multi-spanning membrane proteins. The function of AGK as a subunit of the TIM22 complex does not depend on its kinase activity. However, enzymatically active AGK is required to maintain mitochondrial cristae morphogenesis and the apoptotic resistance of cells. The dual function of AGK as lipid kinase and constituent of the TIM22 complex reveals that disturbances in both phospholipid metabolism and mitochondrial protein biogenesis contribute to the pathogenesis of Sengers syndrome.

In Situ Raman Spectroscopy Reveals Cytochrome c Redox-Controlled Modulation of Mitochondrial Membrane Permeabilization That Triggers Apoptosis.

The selective interaction of cytochrome c (Cyt c) with cardiolipin (CL) is involved in mitochondrial membrane permeabilization, an essential step for the release of apoptosis activators. The structural basis and modulatory mechanism are, however, poorly understood. Here, we report that Cyt c can induce CL peroxidation independent of reactive oxygen species, which is controlled by its redox states. The structural basis of the Cyt c-CL binding was unveiled by comprehensive spectroscopic investigation and mass spectrometry. The Cyt c-induced permeabilization and its effect on membrane collapse, pore formation, and budding are observed by confocal microscopy. Moreover, cytochrome c oxidase dysfunction is found to be associated with the initiation of Cyt c redox-controlled membrane permeabilization. These results verify the significance of a redox-dependent modulation mechanism at the early stage of apoptosis, which can be exploited for the design of cytochrome c oxidase-targeted apoptotic inducers in cancer therapy.

Cardiolipin metabolism regulates expression of muscle transcription factor MyoD1 and muscle development.

The mitochondrial phospholipid cardiolipin (CL) is critical for numerous essential biological processes, including mitochondrial dynamics and energy metabolism. Mutations in the CL remodeling enzyme TAFAZZIN cause Barth syndrome, a life-threatening genetic disorder that results in severe physiological defects, including cardiomyopathy, skeletal myopathy, and neutropenia. To study the molecular mechanisms whereby CL deficiency leads to skeletal myopathy, we carried out transcriptomic analysis of the TAFAZZIN-knockout (TAZ-KO) mouse myoblast C2C12 cell line. Our data indicated that cardiac and muscle development pathways are highly decreased in TAZ-KO cells, consistent with a previous report of defective myogenesis in this cell line. Interestingly, the muscle transcription factor myoblast determination protein 1 (MyoD1) is significantly repressed in TAZ-KO cells and TAZ-KO mouse hearts. Exogenous expression of MyoD1 rescued the myogenesis defects previously observed in TAZ-KO cells. Our data suggest that MyoD1 repression is caused by upregulation of the MyoD1 negative regulator, homeobox protein Mohawk, and decreased Wnt signaling. Our findings reveal, for the first time, that CL metabolism regulates muscle differentiation through MyoD1 and identify the mechanism whereby MyoD1 is repressed in CL-deficient cells.

Maturation of the malarial phosphatidylserine decarboxylase is mediated by high affinity binding to anionic phospholipids.

Decarboxylation of phosphatidylserine (PS) to form phosphatidylethanolamine by PS decarboxylases (PSDs) is an essential process in most eukaryotes. Processing of a malarial PSD proenzyme into its active alpha and beta subunits is by an autoendoproteolytic mechanism regulated by anionic phospholipids, with PS serving as an activator and phosphatidylglycerol (PG), phosphatidylinositol, and phosphatidic acid acting as inhibitors. The biophysical mechanism underlying this regulation remains unknown. We used solid phase lipid binding, liposome-binding assays, and surface plasmon resonance to examine the binding specificity of a processing-deficient Plasmodium PSD (PkPSDS308A) mutant enzyme and demonstrated that the PSD proenzyme binds strongly to PS and PG but not to phosphatidylethanolamine and phosphatidylcholine. The equilibrium dissociation constants (Kd) of PkPSD with PS and PG were 80.4 nM and 66.4 nM, respectively. The interaction of PSD with PS is inhibited by calcium, suggesting that the binding mechanism involves ionic interactions. In vitro processing of WT PkPSD proenzyme was also inhibited by calcium, consistent with the conclusion that PS binding to PkPSD through ionic interactions is required for the proenzyme processing. Peptide mapping identified polybasic amino acid motifs in the proenzyme responsible for binding to PS. Altogether, the data demonstrate that malarial PSD maturation is regulated through a strong physical association between PkPSD proenzyme and anionic lipids. Inhibition of the specific interaction between the proenzyme and the lipids can provide a novel mechanism to disrupt PSD enzyme activity, which has been suggested as a target for antimicrobials, and anticancer therapies.

Cytidine diphosphate diacylglycerol synthase is essential for mitochondrial structure and energy production in Arabidopsis thaliana.

Cytidine diphosphate diacylglycerol (CDP-DAG), an important intermediate for glycerolipid biosynthesis, is synthesized under the catalytic activity of CDP-DAG synthase (CDS) to produce anionic phosphoglycerolipids such as phosphatidylglycerol (PG) and cardiolipin (CL). Previous studies showed that Arabidopsis CDSs are encoded by a small gene family, termed CDS1-CDS5, the members of which are integral membrane proteins in endoplasmic reticulum (ER) and in plastids. However, the details on how CDP-DAG is provided for mitochondrial membrane-specific phosphoglycerolipids are missing. Here we present the identification of a mitochondrion-specific CDS, designated CDS6. Enzymatic activity of CDS6 was demonstrated by the complementation of CL synthesis in the yeast CDS-deficient tam41Δ mutant. The Arabidopsis cds6 mutant lacking CDS6 activity showed decreased mitochondrial PG and CL biosynthesis capacity, a severe growth deficiency finally leading to plant death. These defects were rescued partly by complementation with CDS6 or supplementation with PG and CL. The ultrastructure of mitochondria in cds6 was abnormal, missing the structures of cristae. The degradation of triacylglycerol (TAG) in lipid droplets and starch in chloroplasts in the cds6 mutant was impaired. The expression of most differentially expressed genes involved in the mitochondrial electron transport chain was upregulated, suggesting an energy-demanding stage in cds6. Furthermore, the contents of polar glycerolipids in cds6 were dramatically altered. In addition, cds6 seedlings lost the capacity for cell proliferation and showed a higher oxidase activity. Thus, CDS6 is indispensable for the biosynthesis of PG and CL in mitochondria, which is critical for establishing mitochondrial structure, TAG degradation, energy production and seedling development.

Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER.

PURPOSE: Evaluate long-term efficacy and safety of elamipretide during the open-label extension (OLE) of the TAZPOWER trial in individuals with Barth syndrome (BTHS). METHODS: TAZPOWER was a 28-week randomized, double-blind, and placebo-controlled trial followed by a 168-week OLE. Patients entering the OLE continued elamipretide 40 mg subcutaneous daily. OLE primary endpoints were safety and tolerability; secondary endpoints included change from baseline in the 6-minute walk test (6MWT) and BarTH Syndrome Symptom Assessment (BTHS-SA) Total Fatigue score. Muscle strength, physician- and patient-assessed outcomes, echocardiographic parameters, and biomarkers, including cardiolipin (CL) and monolysocardiolipin (MLCL), were assessed. RESULTS: Ten patients entered the OLE; 8 reached the week 168 visit. Elamipretide was well tolerated, with injection-site reactions being the most common adverse events. Significant improvements from OLE baseline on 6MWT occurred at all OLE time points (cumulative 96.1 m of improvement [week 168, P = .003]). Mean BTHS-SA Total Fatigue scores were below baseline (improved) at all OLE time points. Three-dimensional (3D) left ventricular stroke, end-diastolic, and end-systolic volumes improved, showing significant trends for improvement from baseline to week 168. MLCL/CL values showed improvement, correlating to important clinical outcomes. CONCLUSION: Elamipretide was associated with sustained long-term tolerability and efficacy, with improvements in functional assessments and cardiac function in BTHS.

Uncovering the mechanisms of host mitochondrial cardiolipin release in syphilis: Insights from human microvascular endothelial cells.

The release of host mitochondrial cardiolipin is believed to be the main factor that contributes to the production of anti-cardiolipin antibodies in syphilis. However, the precise mechanism by which mitochondria release cardiolipin in this context remains elusive. This study aimed to elucidate the mechanisms underlying mitochondrial cardiolipin release in syphilis. We conducted a cardiolipin quantitative assay and immunofluorescence analysis to detect mitochondrial cardiolipin release in human microvascular endothelial cells (HMEC-1), with and without Treponema pallidum (Tp) infection. Furthermore, we explored apoptosis, a key mechanism for mitochondrial cardiolipin release. The potential mediator molecules were then analyzed through RNA-sequence and subsequently validated using in vitro knockout techniques mediated by CRISPR-Cas9 and pathway-specific inhibitors. Our findings confirm that live-Tp is capable of initiating the release of mitochondrial cardiolipin, whereas inactivated-Tp does not exhibit this capability. Additionally, apoptosis detection further supports the notion that the release of mitochondrial cardiolipin occurs independently of apoptosis. The RNA-sequencing results indicated that microtubule-associated protein2 (MAP2), an axonogenesis and dendrite development gene, was up-regulated in HMEC-1 treated with Tp, which was further confirmed in syphilitic lesions by immunofluorescence. Notably, genetic knockout of MAP2 inhibited Tp-induced mitochondrial cardiolipin release in HMEC-1. Mechanically, Tp-infection regulated MAP2 expression via the MEK-ERK-HES1 pathway, and MEK/ERK phosphorylation inhibitors effectively block Tp-induced mitochondrial cardiolipin release. This study demonstrated that the infection of live-Tp enhanced the expression of MAP2 via the MEK-ERK-HES1 pathway, thereby contributing to our understanding of the role of anti-cardiolipin antibodies in the diagnosis of syphilis.

Polysaccharide intercellular adhesin and proper phospholipid composition are important for aggregation in Tetragenococcus halophilus SL10.

Aggregating strains of Tetragenococcus halophilus tend to be trapped during soy sauce mash-pressing process and are, therefore, critical for clear soy sauce production. However, the precise molecular mechanism involved in T. halophilus aggregation remains elusive. In previous studies, we isolated a number of aggregating strains, including T. halophilus AB4 and AL1, and showed that a cell surface proteinaceous aggregation factor is responsible for their aggregation phenotype. In the present study, we explored the role of polysaccharide intercellular adhesin (PIA) in aggregate formation in T. halophilus SL10, isolated from soy sauce. SL10 exhibited similar aggregation to AB4 and AL1 but formed a non-uniform precipitate with distinctive wrinkles at the bottom of the test tube, unlike AB4 and AL1. Insertion sequence mutations in each gene of the ica operon diminished aggregation and PIA production, highlighting the critical role of IcaADBC-mediated PIA production in T. halophilus aggregation. Furthermore, two non-aggregating cardiolipin synthase (cls) gene mutants with intact ica operon did not produce detectable PIA. Phospholipid composition analysis in cls mutants revealed a decrease in cardiolipin and an increase in phosphatidylglycerol levels, highlighting the association between phospholipid composition and PIA production. These findings provide evidence for the pivotal role of cls in PIA-mediated aggregation and lay the foundation for future studies to understand the intricate networks of the multiple aggregation factors governing microbial aggregation.IMPORTANCEAggregation, commonly observed in various microbes, triggers biofilm formation in pathogenic variants and plays a beneficial role in efficient food production in those used for food production. Here, we showed that Tetragenococcus halophilus, a microorganism used in soy sauce fermentation, forms aggregates in a polysaccharide intercellular adhesin (PIA)-mediated manner. Additionally, we unveiled the relationship between phospholipid composition and PIA production. This study provides evidence for the presence of aggregation factors in T. halophilus other than the proteinaceous aggregation factor and suggests that further understanding of the coordinated action of these factors may improve clarified soy sauce production.

Consuming a Linoleate-Rich Diet Increases Concentrations of Tetralinoleoyl Cardiolipin in Mouse Liver and Alters Hepatic Mitochondrial Respiration.

BACKGROUND: Hepatic mitochondrial dysfunction is a major cause of fat accumulation in the liver. Individuals with fatty liver conditions have hepatic mitochondrial structural abnormalities and a switch in the side chain composition of the mitochondrial phospholipid, cardiolipin, from poly- to monounsaturated fatty acids. Linoleic acid (LA), an essential dietary fatty acid, is required to remodel nascent cardiolipin (CL) to its tetralinoleoyl cardiolipin (L4CL, CL with 4 LA side chains) form, which is integral for mitochondrial membrane structure and function to promote fatty acid oxidation. It is unknown, however, whether increasing LA in the diet can increase hepatic L4CL concentrations and improve mitochondrial respiration in the liver compared with a diet rich in monounsaturated and saturated fatty acids. OBJECTIVES: The main aim of this study was to test the ability of a diet fortified with LA-rich safflower oil (SO), compared with the one fortified with lard (LD), to increase concentrations of L4CL and improve mitochondrial respiration in the livers of mice. METHODS: Twenty-four (9-wk-old) C57 BL/J6 male mice were fed either the SO or LD diets for ∼100 d, whereas food intake and body weight, fasting glucose, and glucose tolerance tests were performed to determine any changes in glycemic control. RESULTS: Livers from mice fed SO diet had higher relative concentrations of hepatic L4CL species compared with LD diet-fed mice (P value = 0.004). Uncoupled mitochondria of mice fed the SO diet, compared with LD diet, had an increased baseline oxygen consumption rate (OCR) and succinate-driven respiration (P values = 0.03 and 0.01). SO diet-fed mice had increased LA content in all phospholipid classes compared with LD-fed mice (P < 0.05). CONCLUSIONS: Our findings reveal that maintaining or increasing hepatic L4CL may result in increased OCR in uncoupled hepatic mitochondria in healthy mice whereas higher oleate content of CL reduced mitochondrial function shown by lower OCR in uncoupled mitochondria.

ALCAT1-mediated abnormal cardiolipin remodelling promotes mitochondrial injury in podocytes in diabetic kidney disease.

BACKGROUND: Cardiolipin (CL) plays a critical role in maintaining mitochondrial membrane integrity and overall mitochondrial homeostasis. Recent studies have suggested that mitochondrial damage resulting from abnormal cardiolipin remodelling is associated with the pathogenesis of diabetic kidney disease (DKD). Acyl-coenzyme A:lyso-cardiolipin acyltransferase-1 (ALCAT1) was confirmed to be involved in the progression of Parkinson's disease, diet-induced obesity and other ageing-related diseases by regulating pathological cardiolipin remodelling. Thus, the purpose of this investigation was to determine the role of ALCAT1-mediated CL remodelling in DKD and to explore the potential underlying mechanism. METHODS: In vivo study, the mitochondrial structure was examined by transmission electron microscopy (TEM). The colocalization of ALCAT1 and synaptopodin was evaluated by double immunolabelling. Western blotting (WB) was performed to assess ALCAT1 expression in glomeruli. Lipidomics analysis was conducted to evaluate the composition of reconstructed cardiolipins. In vitro study, the lipidomics, TEM and WB analyses were similar to those in vivo. Mitochondrial function was evaluated by measuring the mitochondrial membrane potential (MMP) and the production of ATP and ROS. RESULTS: Here, we showed that increased oxidized cardiolipin (ox-CL) and significant mitochondrial damage were accompanied by increased ALCAT1 expression in the glomeruli of patients with DKD. Similar results were found in db/db mouse kidneys and in cultured podocytes stimulated with high glucose (HG). ALCAT1 deficiency effectively prevented HG-induced ox-CL production and mitochondrial damage in podocytes. In contrast, ALCAT1 upregulation enhanced ox-CL levels and podocyte mitochondrial dysfunction. Moreover, treatment with the cardiolipin antioxidant SS-31 markedly inhibited mitochondrial dysfunction and cell injury, and SS-31 treatment partly reversed the damage mediated by ALCAT1 overexpression. We further found that ALCAT1 could mediate the key regulators of mitochondrial dynamics and mitophagy through the AMPK pathway. CONCLUSIONS: Collectively, our studies demonstrated that ALCAT1-mediated cardiolipin remodelling played a crucial role in DKD, which might provide new insights for DKD treatment. Video Abstract.

Mitochondrial membrane synthesis, remodelling and cellular trafficking.

Mitochondria are dynamic cellular organelles with complex roles in metabolism and signalling. Primary mitochondrial disorders are a group of approximately 400 monogenic disorders arising from pathogenic genetic variants impacting mitochondrial structure, ultrastructure and/or function. Amongst these disorders, defects of complex lipid biosynthesis, especially of the unique mitochondrial membrane lipid cardiolipin, and membrane biology are an emerging group characterised by clinical heterogeneity, but with recurrent features including cardiomyopathy, encephalopathy, neurodegeneration, neuropathy and 3-methylglutaconic aciduria. This review discusses lipid synthesis in the mitochondrial membrane, the mitochondrial contact site and cristae organising system (MICOS), mitochondrial dynamics and trafficking, and the disorders associated with defects of each of these processes. We highlight overlapping functions of proteins involved in lipid biosynthesis and protein import into the mitochondria, pointing to an overarching coordination and synchronisation of mitochondrial functions. This review also focuses on membrane interactions between mitochondria and other organelles, namely the endoplasmic reticulum, peroxisomes, lysosomes and lipid droplets. We signpost disorders of these membrane interactions that may explain the observation of secondary mitochondrial dysfunction in heterogeneous pathological processes. Disruption of these organellar interactions ultimately impairs cellular homeostasis and organismal health, highlighting the central role of mitochondria in human health and disease.

EPA stronger than DHA increases the mitochondrial membrane potential and cardiolipin levels but does not change the ATP level in astrocytes.

Astrocytes are highly energy-consuming glial cells critical for metabolic support to neurons. A growing body of evidence suggests that mitochondrial dysfunction in astrocytes is involved in age-related neurodegenerative disorders and that fish oil, rich in docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids, may alleviate cognition impairment in Parkinson's and Alzheimer's diseases. The present study examines the effect of DHA and EPA on mitochondrial membrane potential (MMP), apoptosis activation and ATP levels in astrocytes cultured in medium containing glucose or galactose, which limits oxidative phosphorylation (OXPHOS). MMP, expressed as the ratio of red to green JC-10 and MitoTracker fluorescence, increased in EPA-incubated cells in a dose dependent manner and was higher than in DHA-incubated astrocytes, also after uncoupling of OXPHOS by carbonyl cyanide 3-chlorophenylhydrazone (CCCP). In cells cultured in glucose and galactose medium mitochondrial hyperpolarization had no impact on intracellular ATP level. Furthermore, both EPA and DHA elevated mitochondrial cardiolipin content, however only EPA did so in a dose-dependent manner and reduced apoptosis which was analyzed by flow cytometry.