The complexity of cardiolipin in health and disease

The role of cardiolipin and cytochrome c in mitochondrial metabolism of cancer cells determined by Raman imaging: in vitro study on the brain glioblastoma U-87 MG cell line

In this paper, we present Raman imaging as a non-invasive approach for studying changes in mitochondrial metabolism caused by cardiolipin-cytochrome c interactions. We investigated the effect of mitochondrial dysregulation on cardiolipin (CL) and cytochrome c (Cyt c) interactions for a brain cancer cell line (U-87 MG). Mitochondrial metabolism was monitored by checking the intensities of the Raman bands at 750 cm-1, 1126 cm-1, 1310 cm-1, 1337 cm-1, 1444 cm-1 and 1584 cm-1. The presented results indicate that under pathological conditions, the content and redox status of Cyt c in mitochondria can be used as a Raman marker to characterize changes in cellular metabolism. This work provides evidence that cardiolipin-cytochrome c interactions are crucial for mitochondrial energy homeostasis by controlling the redox status of Cyt c in the electron transport chain, switching from disabling Cyt c reduction and enabling peroxidase activity. This paper provides experimental support for the hypothesis of how cardiolipin-cytochrome c interactions regulate electron transfer in the respiratory chain, apoptosis and mROS production in mitochondria.

The Role of Phospholipid Alterations in Mitochondrial and Brain Dysfunction after Cardiac Arrest

The human brain possesses three predominate phospholipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS), which account for approximately 35-40%, 35-40%, and 20% of the brain's phospholipids, respectively. Mitochondrial membranes are relatively diverse, containing the aforementioned PC, PE, and PS, as well as phosphatidylinositol (PI) and phosphatidic acid (PA); however, cardiolipin (CL) and phosphatidylglycerol (PG) are exclusively present in mitochondrial membranes. These phospholipid interactions play an essential role in mitochondrial fusion and fission dynamics, leading to the maintenance of mitochondrial structural and signaling pathways. The essential nature of these phospholipids is demonstrated through the inability of mitochondria to tolerate alteration in these specific phospholipids, with changes leading to mitochondrial damage resulting in neural degeneration. This review will emphasize how the structure of phospholipids relates to their physiologic function, how their metabolism facilitates signaling, and the role of organ- and mitochondria-specific phospholipid compositions. Finally, we will discuss the effects of global ischemia and reperfusion on organ- and mitochondria-specific phospholipids alongside the novel therapeutics that may protect against injury.

Cardiac lipidomic profiles in mice undergo changes from fetus to adult

AIMS

Lipids are essential cellular components with many important biological functions. Disturbed lipid biosynthesis and metabolism has been shown to cause cardiac developmental abnormality and cardiovascular diseases. In this study, we aimed to investigate the composition and the molecular profiles of lipids in mammalian hearts between embryonic and adult stages and uncover the underlying links between lipid and cardiac development and maturation.

MATERIALS AND METHODS

We collected mouse hearts at the embryonic day 11.5 (E11.5), E15.5, and the age of 2 months, 4 months and 10 months, and performed lipidomic analysis to determine the changes of the composition, molecular species, and relative abundance of cardiac lipids between embryonic and adult stages. Additionally, we also performed the electronic microscopy and RNA sequencing in both embryonic and adult mouse hearts.

KEY FINDINGS

The relative abundances of certain phospholipids and sphingolipids including cardiolipin, phosphatidylglycerol, phosphatidylethanolamine, and ceramide, are different between embryonic and adult hearts. Such lipidomic changes are accompanied with increased densities of mitochondrial membranes and elevated expression of genes related to mitochondrial formation in adult mouse hearts. We also analyzed individual molecular species of phospholipids and sphingolipids, and revealed that the composition and distribution of lipid molecular species in hearts also change with development.

SIGNIFICANCE

Our study provides not only a lipidomic view of mammalian hearts when developing from the embryonic to the adult stage, but also a potential pool of lipid indicators for cardiac cell development and maturation.

Mitochondrial Dysfunction: A Key Player in Brain Aging and Diseases

Mitochondria are thought to have become incorporated within the eukaryotic cell approximately 2 billion years ago and play a role in a variety of cellular processes, such as energy production, calcium buffering and homeostasis, steroid synthesis, cell growth, and apoptosis, as well as inflammation and ROS production. Considering that mitochondria are involved in a multitude of cellular processes, mitochondrial dysfunction has been shown to play a role within several age-related diseases, including cancers, diabetes (type 2), and neurodegenerative diseases, although the underlying mechanisms are not entirely understood. The significant increase in lifespan and increased incidence of age-related diseases over recent decades has confirmed the necessity to understand the mechanisms by which mitochondrial dysfunction impacts the process of aging and age-related diseases. In this review, we will offer a brief overview of mitochondria, along with structure and function of this important organelle. We will then discuss the cause and consequence of mitochondrial dysfunction in the aging process, with a particular focus on its role in inflammation, cognitive decline, and neurodegenerative diseases, such as Huntington's disease, Parkinson's disease, and Alzheimer's disease. We will offer insight into therapies and interventions currently used to preserve or restore mitochondrial functioning during aging and neurodegeneration.

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.

Mitochondrial Mechanisms in Immunity and Inflammatory Conditions: Beyond Energy Management

Significance: The growing importance of mitochondria in the immune response and inflammation is multifaceted. Unraveling the different mechanisms by which mitochondria have a relevant role in the inflammatory response beyond the energy management of the process is necessary for improving our understanding of the host immune defense and the pathogenesis of various inflammatory diseases and syndromes. Critical Issues: Mitochondria are relevant in the immune response at different levels, including releasing activation molecules, changing its structure and function to accompany the immune response, and serving as a structural base for activating intermediates as NLRP3 inflammasome. In this scientific journey of dissecting mitochondrial mechanisms, new questions and interesting aspects arise, such as the involvement of mitochondrial-derived vesicles in the immune response with the putative role of preventing uncontrolled situations. Recent Advances: Researchers are continuously rethinking the role of mitochondria in acute and chronic inflammation and related disorders. As such, mitochondria have important roles as centrally positioned signaling hubs in regulating inflammatory and immune responses. In this review, we present the current understanding of mitochondrial mechanisms involved, beyond the largely known mitochondrial dysfunction, in the onset and development of inflammatory situations. Future Directions: Mitochondria emerge as an interesting and multifaceted platform for studying and developing pharmaceutical and therapeutic approaches. There are many ongoing studies aimed to describe the effects of specific mitochondrial targeted molecules and treatments to ameliorate the consequences of exacerbated inflammatory components of pathologies and syndromes, resulting in an open area of increasing research interest.

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.

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.

Anomalous peroxidase activity of cytochrome c is the primary pathogenic target in Barth syndrome

Barth syndrome (BTHS) is a life-threatening genetic disorder with unknown pathogenicity caused by mutations in TAFAZZIN (TAZ) that affect remodeling of mitochondrial cardiolipin (CL). TAZ deficiency leads to accumulation of mono-lyso-CL (MLCL), which forms a peroxidase complex with cytochrome c (cyt c) capable of oxidizing polyunsaturated fatty acid-containing lipids. We hypothesized that accumulation of MLCL facilitates formation of anomalous MLCL-cyt c peroxidase complexes and peroxidation of polyunsaturated fatty acid phospholipids as the primary BTHS pathogenic mechanism. Using genetic, biochemical/biophysical, redox lipidomic and computational approaches, we reveal mechanisms of peroxidase-competent MLCL-cyt c complexation and increased phospholipid peroxidation in different TAZ-deficient cells and animal models and in pre-transplant biopsies from hearts of patients with BTHS. A specific mitochondria-targeted anti-peroxidase agent inhibited MLCL-cyt c peroxidase activity, prevented phospholipid peroxidation, improved mitochondrial respiration of TAZ-deficient C2C12 myoblasts and restored exercise endurance in a BTHS Drosophila model. Targeting MLCL-cyt c peroxidase offers therapeutic approaches to BTHS treatment.

LPGAT1 controls MEGDEL syndrome by coupling phosphatidylglycerol remodeling with mitochondrial transport

Phosphatidylglycerol (PG) is a mitochondrial phospholipid required for mitochondrial cristae structure and cardiolipin synthesis. PG must be remodeled to its mature form at the endoplasmic reticulum (ER) after mitochondrial biosynthesis to achieve its biological functions. Defective PG remodeling causes MEGDEL (non-alcohol fatty liver disease and 3-methylglutaconic aciduria with deafness, encephalopathy, and Leigh-like) syndrome through poorly defined mechanisms. Here, we identify LPGAT1, an acyltransferase that catalyzes PG remodeling, as a candidate gene for MEGDEL syndrome. We show that PG remodeling by LPGAT1 at the ER is closely coordinated with mitochondrial transport through interaction with the prohibitin/TIMM14 mitochondrial import motor. Accordingly, ablation of LPGAT1 or TIMM14 not only causes aberrant fatty acyl compositions but also ER retention of newly remodeled PG, leading to profound loss in mitochondrial crista structure and respiration. Consequently, genetic deletion of the LPGAT1 in mice leads to cardinal features of MEGDEL syndrome, including 3-methylglutaconic aciduria, deafness, dilated cardiomyopathy, and premature death, which are highly reminiscent of those caused by TIMM14 mutations in humans.

Interactions of amyloidogenic proteins with mitochondrial protein import machinery in aging-related neurodegenerative diseases

Most mitochondrial proteins are targeted to the organelle by N-terminal mitochondrial targeting sequences (MTSs, or "presequences") that are recognized by the import machinery and subsequently cleaved to yield the mature protein. MTSs do not have conserved amino acid compositions, but share common physicochemical properties, including the ability to form amphipathic α-helical structures enriched with basic and hydrophobic residues on alternating faces. The lack of strict sequence conservation implies that some polypeptides can be mistargeted to mitochondria, especially under cellular stress. The pathogenic accumulation of proteins within mitochondria is implicated in many aging-related neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases. Mechanistically, these diseases may originate in part from mitochondrial interactions with amyloid-β precursor protein (APP) or its cleavage product amyloid-β (Aβ), α-synuclein (α-syn), and mutant forms of huntingtin (mHtt), respectively, that are mediated in part through their associations with the mitochondrial protein import machinery. Emerging evidence suggests that these amyloidogenic proteins may present cryptic targeting signals that act as MTS mimetics and can be recognized by mitochondrial import receptors and transported into different mitochondrial compartments. Accumulation of these mistargeted proteins could overwhelm the import machinery and its associated quality control mechanisms, thereby contributing to neurological disease progression. Alternatively, the uptake of amyloidogenic proteins into mitochondria may be part of a protein quality control mechanism for clearance of cytotoxic proteins. Here we review the pathomechanisms of these diseases as they relate to mitochondrial protein import and effects on mitochondrial function, what features of APP/Aβ, α-syn and mHtt make them suitable substrates for the import machinery, and how this information can be leveraged for the development of therapeutic interventions.

Revisiting Coley's Toxins: Immunogenic Cardiolipins from Streptococcus pyogenes

Coley's toxins, an early and enigmatic form of cancer (immuno)therapy, were based on preparations of Streptococcus pyogenes. As part of a program to explore bacterial metabolites with immunomodulatory potential, S. pyogenes metabolites were assayed in a cell-based immune assay, and a single membrane lipid, 18:1/18:0/18:1/18:0 cardiolipin, was identified. Its activity was profiled in additional cellular assays, which showed it to be an agonist of a TLR2-TLR1 signaling pathway with a 6 μM EC50 and robust TNF-α induction. A synthetic analog with switched acyl chains had no measurable activity in immune assays. The identification of a single immunogenic cardiolipin with a restricted structure-activity profile has implications for immune regulation, cancer immunotherapy, and poststreptococcal autoimmune diseases.

Cristae formation is a mechanical buckling event controlled by the inner 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 mechanisms for lipids 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 IMM 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. The model highlighted a snapthrough instability, which drives IMM collapse upon small changes in membrane properties. We also showed that CL is essential in low oxygen conditions that promote PL saturation. These results demonstrate that the mechanical function of CL is dependent on the surrounding lipid and protein components of the IMM.

Case report: Variability in clinical features as a potential pitfall for the diagnosis of Barth syndrome

Background

Barth syndrome is a rare genetic disease characterized by cardiomyopathy, skeletal muscle weakness, neutropenia, growth retardation and organic aciduria. This variable phenotype is caused by pathogenic hemizygous variants of the TAFAZZIN gene on the X chromosome, which impair metabolism of the mitochondrial phospholipid cardiolipin. Although most patients are usually diagnosed in the first years of life, the extremely variable clinical picture and the wide range of clinical presentations may both delay diagnosis. This is the case reported here of a man affected with severe neutropenia, who was not diagnosed with Barth syndrome until adulthood.

Case presentation

We describe herein a family case, specifically two Caucasian male cousins sharing the same mutation in the TAFAZZIN gene with a wide phenotypic variability: an infant who was early diagnosed with Barth syndrome due to heart failure, and his maternal cousin with milder and extremely different clinical features who has received the same diagnosis only at 33 years of age.

Conclusions

Our report supports the underestimation of the prevalence of Barth syndrome, which should be always considered in the differential diagnosis of male patients with recurrent neutropenia with or without signs and symptoms of cardiomyopathy.

Mass Spectrometry Imaging Reveals Abnormalities in Cardiolipin Composition and Distribution in Astrocytoma Tumor Tissues

Cardiolipin (CL) is a mitochondrial lipid with diverse roles in cellular respiration, signaling, and organelle membrane structure. CL content and composition are essential for proper mitochondrial function. Deranged mitochondrial energy production and signaling are key components of glial cell cancers and altered CL molecular species have been observed in mouse brain glial cell xenograft tumors. The objective of this study was to describe CL structural diversity trends in human astrocytoma tumors of varying grades and correlate these trends with histological regions within the heterogeneous astrocytoma microenvironment. To this aim, we applied desorption electrospray ionization coupled with high field asymmetric ion mobility mass spectrometry (DESI-FAIMS-MS) to map CL molecular species in human normal cortex (N = 29), lower-grade astrocytoma (N = 19), and glioblastoma (N = 28) tissues. With this platform, we detected 46 CL species and 12 monolysocardiolipin species from normal cortex samples. CL profiles detected from glioblastoma tissues lacked diversity and abundance of longer chain polyunsaturated fatty acid containing CL species when compared to CL detected from normal and lower-grade tumors. CL profiles correlated with trends in tumor viability and tumor infiltration. Structural characterization of the CL species by tandem MS experiments revealed differences in fatty acid and double bond isomer composition among astrocytoma tissues compared with normal cortex and glioblastoma tissues. The GlioVis platform was used to analyze astrocytoma gene expression data from the CGGA dataset. Decreased expression of several mitochondrial respiratory enzyme encoding-genes was observed for higher-grade versus lower-grade tumors, however no significant difference was observed for cardiolipin synthesis enzyme CRLS1.

Why Don’t More Mitochondrial Diseases Exhibit Cardiomyopathy?

Background: Although the heart requires abundant energy, only 20–40% of children with mitochondrial diseases have cardiomyopathies. Methods: We looked for differences in genes underlying mitochondrial diseases that do versus do not cause cardiomyopathy using the comprehensive Mitochondrial Disease Genes Compendium. Mining additional online resources, we further investigated possible energy deficits caused by non-oxidative phosphorylation (OXPHOS) genes associated with cardiomyopathy, probed the number of amino acids and protein interactors as surrogates for OXPHOS protein cardiac “importance”, and identified mouse models for mitochondrial genes. Results: A total of 107/241 (44%) mitochondrial genes was associated with cardiomyopathy; the highest proportion were OXPHOS genes (46%). OXPHOS (p = 0.001) and fatty acid oxidation (p = 0.009) defects were significantly associated with cardiomyopathy. Notably, 39/58 (67%) non-OXPHOS genes associated with cardiomyopathy were linked to defects in aerobic respiration. Larger OXPHOS proteins were associated with cardiomyopathy (p < 0.05). Mouse models exhibiting cardiomyopathy were found for 52/241 mitochondrial genes, shedding additional insights into biological mechanisms. Conclusions: While energy generation is strongly associated with cardiomyopathy in mitochondrial diseases, many energy generation defects are not linked to cardiomyopathy. The inconsistent link between mitochondrial disease and cardiomyopathy is likely to be multifactorial and includes tissue-specific expression, incomplete clinical data, and genetic background differences.

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.

Gut microbiome lipid metabolism and its impact on host physiology

Metabolites produced by commensal gut microbes impact host health through their recognition by the immune system and their influence on numerous metabolic pathways. Notably, the gut microbiota can both transform and synthesize lipids as well as break down dietary lipids to generate secondary metabolites with host modulatory properties. Although lipids have largely been consigned to structural roles, particularly in cell membranes, recent research has led to an increased appreciation of their signaling activities, with potential impacts on host health and physiology. This review focuses on studies that highlight the functions of bioactive lipids in mammalian physiology, with a special emphasis on immunity and metabolism.

The critical role of cardiolipin in metazoan differentiation, development, and maturation

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

Long-chain polyunsaturated lipids associated with responsiveness to anti-PD-1 therapy are colocalized with immune infiltrates in the tumor microenvironment

The programmed cell death protein-1 (PD-1) is highly expressed on the surface of antigen-specific exhausted T cells and, upon interaction with its ligand PD-L1, can result in inhibition of the immune response. Anti-PD-1 treatment has been shown to extend survival and result in durable responses in several cancers, yet only a subset of patients benefit from this therapy. Despite the implication of metabolic alteration following cancer immunotherapy, mechanistic associations between antitumor responses and metabolic changes remain unclear. Here, we used desorption electrospray ionization mass spectrometry imaging to examine the lipid profiles of tumor tissue from three syngeneic murine models with varying treatment sensitivity at the baseline and at three time points post-anti-PD-1 therapy. These imaging experiments revealed specific alterations in the lipid profiles associated with the degree of response to treatment and allowed us to identify a significant increase of long-chain polyunsaturated lipids within responsive tumors following anti-PD-1 therapy. Immunofluorescence imaging of tumor tissues also demonstrated that the altered lipid profile associated with treatment response is localized to dense regions of tumor immune infiltrates. Overall, these results indicate that effective anti-PD-1 therapy modulates lipid metabolism in tumor immune infiltrates, and we thereby propose that further investigation of the related immune-metabolic pathways may be useful for better understanding success and failure of anti-PD-1 therapy.

Hypolipidemic effect and molecular mechanism of ginsenosides: a review based on oxidative stress

Hyperlipidemia is considered a risk factor for cardiovascular and endocrine diseases. However, effective approaches for treating this common metabolic disorder remain limited. Ginseng has traditionally been used as a natural medicine for invigorating energy or "Qi" and has been demonstrated to possess antioxidative, anti-apoptotic, and anti-inflammatory properties. A large number of studies have shown that ginsenosides, the main active ingredient of ginseng, have lipid-lowering effects. However, there remains a lack of systematic reviews detailing the molecular mechanisms by which ginsenosides reduce blood lipid levels, especially in relation to oxidative stress. For this article, research studies detailing the molecular mechanisms through which ginsenosides regulate oxidative stress and lower blood lipids in the treatment of hyperlipidemia and its related diseases (diabetes, nonalcoholic fatty liver disease, and atherosclerosis) were comprehensively reviewed. The relevant papers were search on seven literature databases. According to the studies reviewed, ginsenosides Rb1, Rb2, Rb3, Re, Rg1, Rg3, Rh2, Rh4, and F2 inhibit oxidative stress by increasing the activity of antioxidant enzymes, promoting fatty acid β-oxidation and autophagy, and regulating the intestinal flora to alleviate high blood pressure and improve the body's lipid status. These effects are related to the regulation of various signaling pathways, such as those of PPARα, Nrf2, mitogen-activated protein kinases, SIRT3/FOXO3/SOD, and AMPK/SIRT1. These findings suggest that ginseng is a natural medicine with lipid-lowering effects.

Linoleate-Enrichment of Mitochondrial Cardiolipin Molecular Species Is Developmentally Regulated and a Determinant of Metabolic Phenotype

Cardiolipin (CL), the major mitochondrial phospholipid, regulates the activity of many mitochondrial membrane proteins. CL composition is shifted in heart failure with decreases in linoleate and increases in oleate side chains, but whether cardiolipin composition directly regulates metabolism is unknown. This study defines cardiolipin composition in rat heart and liver at three distinct ages to determine the influence of CL composition on beta-oxidation (ß-OX). CL species, expression of ß-OX and glycolytic genes, and carnitine palmitoyltransferase (CPT) activity were characterized in heart and liver from neonatal, juvenile, and adult rats. Ventricular myocytes were cultured from neonatal, juvenile, and adult rats and cardiolipin composition and CPT activity were measured. Cardiolipin composition in neonatal rat ventricular cardiomyocytes (NRVMs) was experimentally altered and mitochondrial respiration was assessed. Linoleate-enrichment of CL was observed in rat heart, but not liver, with increasing age. ß-OX genes and CPT activity were generally higher in adult heart and glycolytic genes lower, as a function of age, in contrast to liver. Palmitate oxidation increased in NRVMs when CL was enriched with linoleate. Our results indicate (1) CL is developmentally regulated, (2) linoleate-enrichment is associated with increased ß-OX and a more oxidative mitochondrial phenotype, and (3) experimentally induced linoleate-enriched CL in ventricular myocytes promotes a shift from pyruvate metabolism to fatty acid ß-OX.

Linoleic Acid-Enriched Diet Increases Mitochondrial Tetralinoleoyl Cardiolipin, OXPHOS Protein Levels, and Uncoupling in Interscapular Brown Adipose Tissue during Diet-Induced Weight Gain

Cardiolipin (CL) is a phospholipid unique to the inner mitochondrial membrane that supports respiratory chain structure and function and is demonstrated to be influenced by types of dietary fats. However, the influence of dietary fat on CL species and how this best supports mitochondrial function in brown adipose tissue (BAT), which exhibits an alternative method of energy utilization through the uncoupling of the mitochondrial proton gradient to generate heat, is not well understood. Therefore, the aim of our study was to evaluate metabolic parameters, interscapular BAT CL quantity, species, and mitochondrial function in mice consuming isocaloric moderate-fat diets with either lard (LD; similar fatty acid profile to western dietary patterns) or safflower oil high in linoleic acid (SO), shown to be metabolically favorable in large clinical meta-analyses. Mice fed the SO diet exhibited decreased adiposity, improved insulin sensitivity, and enrichment of LA-containing CL species in BAT CL. Furthermore, mice fed the SO diet exhibit higher levels of OXPHOS complex proteins and increased oxygen consumption in BAT. Our findings demonstrate that dietary consumption of LA-rich oil improves metabolic parameters, increases LA-containing CL species, and improves BAT function when compared to the consumption of lard in mice during diet-induced weight gain.

Mitochondria-associated niches in health and disease

The appreciation of the importance of interorganelle contacts has steadily increased over the past decades. Advances in imaging, molecular biology and bioinformatic techniques allowed the discovery of new mechanisms involved in the interaction and communication between organelles, providing novel insights into the inner works of a cell. In this Review, with the mitochondria under the spotlight, we discuss the most recent findings on the mechanisms mediating the communication between organelles, focusing on Ca2+ signaling, lipid exchange, cell death and stress responses. Notably, we introduce a new integrative perspective to signaling networks that is regulated by interorganelle interactions – the mitochondria-associated niches – focusing on the link between the molecular determinants of contact sites and their functional outputs, rather than simply physical and structural communication. In addition, we highlight the neuropathological and metabolic implications of alterations in mitochondria-associated niches and outline how this concept might improve our understanding of multi-organelle interactions.

Beneficial effects of SS-31 peptide on cardiac mitochondrial dysfunction in tafazzin knockdown mice

Barth Syndrome (BTHS), a genetic disease associated with early-onset cardioskeletal myopathy, is caused by loss-of-function mutations of the TAFAZZIN gene, which is responsible for remodeling the mitochondrial phospholipid cardiolipin (CL). Deregulation of CL biosynthesis and maturation in BTHS mitochondria result in a dramatically increased monolysocardiolipin (MLCL)/CL ratio associated with bioenergetic dysfunction. One of the most promising therapeutic approaches for BTHS includes the mitochondria-targeted tetrapeptide SS-31, which interacts with CL. Here, we used TAFAZZIN knockdown (Taz^KD) mice to investigate for the first time whether in vivo administration of SS-31 could affect phospholipid profiles and mitochondrial dysfunction. The CL fingerprinting of Taz^KD cardiac mitochondria obtained by MALDI-TOF/MS revealed the typical lipid changes associated with BTHS. Taz^KD mitochondria showed lower respiratory rates in state 3 and 4 together with a decreased in maximal respiratory rates. Treatment of Taz^KD mice with SS-31 improved mitochondrial respiratory capacity and promoted supercomplex organization, without affecting the MLCL/CL ratio. We hypothesize that SS-31 exerts its effect by influencing the function of the respiratory chain rather than affecting CL directly. In conclusion, our results indicate that SS-31 have beneficial effects on improving cardiac mitochondrial dysfunction in a BTHS animal model, suggesting the peptide as future pharmacologic agent for therapy.

The multiple facets of mitochondrial regulations controlling cellular thermogenesis

Understanding temperature production and regulation in endotherm organisms becomes a crucial challenge facing the increased frequency and intensity of heat strokes related to global warming. Mitochondria, located at the crossroad of metabolism, respiration, Ca²⁺ homeostasis, and apoptosis, were recently proposed to further act as cellular radiators, with an estimated inner temperature reaching 50 °C in common cell lines. This inner thermogenesis might be further exacerbated in organs devoted to produce consistent efforts as muscles, or heat as brown adipose tissue, in response to acute solicitations. Consequently, pathways promoting respiratory chain uncoupling and mitochondrial activity, such as Ca²⁺ fluxes, uncoupling proteins, futile cycling, and substrate supplies, provide the main processes controlling heat production and cell temperature. The mitochondrial thermogenesis might be further amplified by cytoplasmic mechanisms promoting the over-consumption of ATP pools. Considering these new thermic paradigms, we discuss here all conventional wisdoms linking mitochondrial functions to cellular thermogenesis in different physiological conditions.

Restoration of mitophagy ameliorates cardiomyopathy in Barth syndrome

Barth syndrome (BTHS) is an X-linked genetic disorder caused by mutations in the TAFAZZIN/Taz gene which encodes a transacylase required for cardiolipin remodeling. Cardiolipin is a mitochondrial signature phospholipid that plays a pivotal role in maintaining mitochondrial membrane structure, respiration, mtDNA biogenesis, and mitophagy. Mutations in the TAFAZZIN gene deplete mature cardiolipin, leading to mitochondrial dysfunction, dilated cardiomyopathy, and premature death in BTHS patients. Currently, there is no effective treatment for this debilitating condition. In this study, we showed that TAFAZZIN deficiency caused hyperactivation of MTORC1 signaling and defective mitophagy, leading to accumulation of autophagic vacuoles and dysfunctional mitochondria in the heart of Tafazzin knockdown mice, a rodent model of BTHS. Consequently, treatment of TAFAZZIN knockdown mice with rapamycin, a potent inhibitor of MTORC1, not only restored mitophagy, but also mitigated mitochondrial dysfunction and dilated cardiomyopathy. Taken together, these findings identify MTORC1 as a novel therapeutic target for BTHS, suggesting that pharmacological restoration of mitophagy may provide a novel treatment for BTHS.Abbreviations: BTHS: Barth syndrome; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CL: cardiolipin; EIF4EBP1/4E-BP1: eukaryotic translation initiation factor 4E binding protein 1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; KD: knockdown; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LV: left ventricle; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MEFs: mouse embryonic fibroblasts; MTORC1: mechanistic target of rapamycin kinase complex 1; OCR: oxygen consumption rate; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced putative kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; qRT-PCR: quantitative real-time polymerase chain reaction; RPS6KB/S6K: ribosomal protein S6 kinase beta; SQSTM1/p62: sequestosome 1; TLCL: tetralinoleoyl cardiolipin; WT: wild-type.

Linoleate-Rich Safflower Oil Diet Increases Linoleate-Derived Bioactive Lipid Mediators in Plasma, and Brown and White Adipose Depots of Healthy Mice

Polyunsaturated fats are energy substrates and precursors to the biosynthesis of lipid mediators of cellular processes. Adipose tissue not only provides energy storage, but influences whole-body energy metabolism through endocrine functions. How diet influences adipose-lipid mediator balance may have broad impacts on energy metabolism. To determine how dietary lipid sources modulate brown and white adipose tissue and plasma lipid mediators, mice were fed low-fat (15% kcal fat) isocaloric diets, containing either palm oil (POLF) or linoleate-rich safflower oil (SOLF). Baseline and post body weight, adiposity, and 2-week and post fasting blood glucose were measured and lipid mediators were profiled in plasma, and inguinal white and interscapular brown adipose tissues. We identified over 30 species of altered lipid mediators between diets and found that these changes were unique to each tissue. We identified changes to lipid mediators with known functional roles in the regulation of adipose tissue expansion and function, and found that there was a relationship between the average fold difference in lipid mediators between brown adipose tissue and plasma in mice consuming the SOLF diet. Our findings emphasize that even with a low-fat diet, dietary fat quality has a profound effect on lipid mediator profiles in adipose tissues and plasma.

Longitudinal Observational Study of Cardiac Outcome Risk Factor Prediction in Children, Adolescents, and Adults with Barth Syndrome

Barth Syndrome (BTHS) is an X-linked mitochondrial cardioskeletal myopathy caused by defects in TAFAZZIN, a gene responsible for cardiolipin remodeling. Altered mitochondrial levels of cardiolipin lead to cardiomyopathy (CM), muscle weakness, exercise intolerance, and mortality. Cardiac risk factors predicting outcome are unknown. Therefore, we conducted a longitudinal observational study to determine risk factors for outcome in BTHS. Subjects with minimum two evaluations (or one followed by death or transplant) were included. Cardiac size, function, and QTc data were measured by echocardiography and electrocardiography at 7 time points from 2002 to 2018. Analysis included baseline, continuous, and categorical variables. Categorical risk factors included prolonged QTc, abnormal right ventricle fractional area change (RV FAC), left ventricle (LV) or RV non-compaction, and restrictive CM phenotype. The association between variables and cardiac death or transplant (CD/TX) was assessed. Median enrollment age was 7 years (range 0.5-22; n = 44). Transplant-free survival (TFS) was 74.4% at 15 years from first evaluation. The cohort demonstrated longitudinal declines in LV size and stroke volume z-scores (end-diastolic volume, p = 0.0002; stroke volume p < 0.0001), worsening RV FAC (p = 0.0405), and global longitudinal strain (GLS) (p = 0.0001) with stable ejection (EF) and shortening (FS) fraction. CD/TX subjects (n = 9) displayed worsening LV dilation (p = 0.0066), EF (p ≤ 0.0001), FS (p = 0.0028), and RV FAC (p = .0032) versus stability in TFS. Having ≥ 2 categorical risk factors predicted CD/TX (p = 0.0073). Over 15 years, 25% of BTHS subjects progressed to CD/TX. Those with progressive LV enlargement, dysfunction, and multiple cardiac risk factors warrant increased surveillance and intense therapy.

Extracellular superoxide dismutase (EC-SOD) R213G variant reduces mitochondrial ROS and preserves mitochondrial function in bleomycin-induced lung injury: EC-SOD R213G variant and intracellular redox regulation

Extracellular superoxide dismutase (EC-SOD) is highly expressed in the lung and vasculature. A common human single nucleotide polymorphism (SNP) in the matrix binding region of EC-SOD leads to a single amino acid substitution, R213G, and alters EC-SOD tissue binding affinity. The change in tissue binding affinity redistributes EC-SOD from tissue to extracellular fluids. Mice (R213G mice) expressing a knock-in of this EC-SOD SNP exhibit elevated plasma and reduced lung EC-SOD content and activity and are protected against bleomycin-induced lung injury and inflammation. It is unknown how the redistribution of EC-SOD alters site-specific redox-regulated molecules relevant for protection. In this study, we tested the hypothesis that the change in the local EC-SOD content would influence not only the extracellular redox microenvironment where EC-SOD is localized but also protect the intracellular redox status of the lung. Mice were treated with bleomycin and harvested 7 days post-treatment. Superoxide levels, measured by electron paramagnetic resonance (EPR), were lower in plasma and Bronchoalveolar lavage fluid (BALF) cells in R213G mice compared to wild-type (WT) mice, while lung cellular superoxide levels in R213G mice were not elevated post-bleomycin compared to WT mice despite low lung EC-SOD levels. Lung glutathione redox potential (EhGSSG), determined by HPLC and fluorescence, was more oxidized in WT compared to R213G mice. In R213G mice, lung mitochondrial oxidative stress was reduced shown by mitochondrial superoxide level measured by EPR in lung and the resistance to bleomycin-induced cardiolipin oxidation. Bleomycin treatment suppressed mitochondrial respiration in WT mice. Mitochondrial function was impaired at baseline in R213G mice but did not exhibit further suppression in respiration post-bleomycin. Collectively, the results indicate that R213G variant preserves intracellular redox state and protects mitochondrial function in the setting of bleomycin-induced inflammation.

Pharmacological Inhibition of ALCAT1 Mitigates Amyotrophic Lateral Sclerosis by Attenuating SOD1 Protein Aggregation

Objective

Mutations in the copper-zinc superoxide dismutase (SOD1) gene cause familial amyotrophic lateral sclerosis (ALS), a progressive fatal neuromuscular disease characterized by motor neurons death and severe skeletal muscle degeneration. However, there is no effective treatment for this debilitating disease, since the underlying cause for the pathogenesis remains poorly understood. Here, we investigated a role of acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase that promotes mitochondrial dysfunction in age-related diseases by catalyzing pathological remodeling of cardiolipin, in promoting the development of ALS in the SOD1^G93A transgenic mice.

Methods

Using SOD1^G93A transgenic mice with targeted deletion of the ALCAT1 gene and treated with Dafaglitapin (Dafa), a very potent and highly selective ALCAT1 inhibitor, we determined whether ablation or pharmaceutical inhibition of ALCAT1 by Dafa would mitigate ALS and the underlying pathogenesis by preventing pathological remodeling of cardiolipin, oxidative stress, and mitochondrial dysfunction by multiple approaches, including lifespan analysis, behavioral tests, morphological and functional analysis of skeletal muscle, electron microscopic and Seahorse analysis of mitochondrial morphology and respiration, western blot analysis of the SOD1^G93A protein aggregation, and lipidomic analysis of cardiolipin content and acyl composition in mice spinal cord.

Results

ALCAT1 protein expression is potently upregulated in the skeletal muscle of the SOD1^G93A mice. Consequently, ablation or pharmacological inhibition of ALCAT1 by Dafa attenuates motor neuron dysfunction, neuronal inflammation, and skeletal muscle atrophy in SOD1^G93A mice by preventing SOD1^G93A protein aggregation, mitochondrial dysfunction, and pathological CL remodeling, leading to moderate extension of lifespan in the SOD1^G93A transgenic mice.

Conclusions

ALCAT1 promotes the development of ALS by linking SOD1^G93A protein aggregation to mitochondrial dysfunction, implicating Dafa as a potential treatment for this debilitating disorder.

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ALCAT1 is potently upregulated in the skeletal muscle of SOD1^G93A mice, a mouse model of amyotrophic lateral sclerosis.

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Upregulated ALCAT1 promotes SOD1^G93A protein aggregation through oxidative stress and pathological cardiolipin remodeling.

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Inactivation of ALCAT1 attenuates neuronal mitochondrial dysfunction and extends the lifespan of SOD1^G93A mice.

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Targeting ALCAT1 as a potential strategy for the treatment of amyotrophic lateral sclerosis.

In Search of the Holy Grail: Toward a Unified Hypothesis on Mitochondrial Dysfunction in Age-Related Diseases

Cardiolipin (CL) is a mitochondrial signature phospholipid that plays a pivotal role in mitochondrial dynamics, membrane structure, oxidative phosphorylation, mtDNA bioenergetics, and mitophagy. The depletion or abnormal acyl composition of CL causes mitochondrial dysfunction, which is implicated in the pathogenesis of aging and age-related disorders. However, the molecular mechanisms by which mitochondrial dysfunction causes age-related diseases remain poorly understood. Recent development in the field has identified acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase upregulated by oxidative stress, as a key enzyme that promotes mitochondrial dysfunction in age-related diseases. ALCAT1 catalyzes CL remodeling with very-long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA). Enrichment of DHA renders CL highly sensitive to oxidative damage by reactive oxygen species (ROS). Oxidized CL becomes a new source of ROS in the form of lipid peroxides, leading to a vicious cycle of oxidative stress, CL depletion, and mitochondrial dysfunction. Consequently, ablation or the pharmacological inhibition of ALCAT1 have been shown to mitigate obesity, type 2 diabetes, heart failure, cardiomyopathy, fatty liver diseases, neurodegenerative diseases, and cancer. The findings suggest that age-related disorders are one disease (aging) manifested by different mitochondrion-sensitive tissues, and therefore should be treated as one disease. This review will discuss a unified hypothesis on CL remodeling by ALCAT1 as the common denominator of mitochondrial dysfunction, linking mitochondrial dysfunction to the development of age-related diseases.

Phospholipid Membrane Transport and Associated Diseases

Phospholipids are the basic structure block of eukaryotic membranes, in both the outer and inner membranes, which delimit cell organelles. Phospholipids can also be damaged by oxidative stress produced by mitochondria, for instance, becoming oxidized phospholipids. These damaged phospholipids have been related to prevalent diseases such as atherosclerosis or non-alcoholic steatohepatitis (NASH) because they alter gene expression and induce cellular stress and apoptosis. One of the main sites of phospholipid synthesis is the endoplasmic reticulum (ER). ER association with other organelles through membrane contact sites (MCS) provides a close apposition for lipid transport. Additionally, an important advance in this small cytosolic gap are lipid transfer proteins (LTPs), which accelerate and modulate the distribution of phospholipids in other organelles. In this regard, LTPs can be established as an essential point within phospholipid circulation, as relevant data show impaired phospholipid transport when LTPs are defected. This review will focus on phospholipid function, metabolism, non-vesicular transport, and associated diseases.

Crosstalk between Mitochondrial Protein Import and Lipids

Mitochondria import about 1000 precursor proteins from the cytosol. The translocase of the outer membrane (TOM complex) forms the major entry site for precursor proteins. Subsequently, membrane-bound protein translocases sort the precursor proteins into the outer and inner membrane, the intermembrane space, and the matrix. The phospholipid composition of mitochondrial membranes is critical for protein import. Structural and biochemical data revealed that phospholipids affect the stability and activity of mitochondrial protein translocases. Integration of proteins into the target membrane involves rearrangement of phospholipids and distortion of the lipid bilayer. Phospholipids are present in the interface between subunits of protein translocases and affect the dynamic coupling of partner proteins. Phospholipids are required for full activity of the respiratory chain to generate membrane potential, which in turn drives protein import across and into the inner membrane. Finally, outer membrane protein translocases are closely linked to organellar contact sites that mediate lipid trafficking. Altogether, intensive crosstalk between mitochondrial protein import and lipid biogenesis controls mitochondrial biogenesis.

Targeted Lipidomics Reveal the Effects of Different Phospholipids on the Phospholipid Profiles of Hepatic Mitochondria and Endoplasmic Reticulum in High-Fat/High-Fructose-Diet-Induced Nonalcoholic Fatty Liver Disease Mice

The lipid alternation in mitochondria and endoplasmic reticulum (ER) might be indicative of their abnormal morphology and function, which contribute to development of nonalcoholic fatty liver disease (NAFLD). However, the influence of dietary phospholipids (PLs) on the PL composition of the organellar membrane is largely unknown. High-fat/high-fructose (HFHF)-diet-induced NAFLD mice were administrated with different PLs (2%, w/w) with specific fatty acids and headgroups, including eicosapentaenoic acid (EPA)-phosphatidylcholine (PC)/phosphatidylethanolamine (PE)/phosphatidylserine (PS), docosahexaenoic acid (DHA)-PC/PE/PS, egg-PC/PE/PS, and soy-PC/PE/PS. After 8 weeks of feeding, PLs dramatically decreased hepatic lipid accumulation, in which EPA/DHA-PS had the best efficiency. Furthermore, lipidomic analysis revealed that the HFHF diet narrowed the difference in PL composition between mitochondria and ER, significantly reduced the PC/PE ratio, and changed the unsaturation of cardiolipin in mitochondria. Dietary PLs reversed these alterations. Heatmap analysis indicated that dietary PL groups containing the same fatty acids clustered together. Moreover, dietary PLs significantly increased the ratio of PC/PE in both hepatic mitochondria and ER, especially EPA-PE. This study showed that fatty acid composition of PLs might represent greater impact on the PL composition of the organellar membrane than headgroups.

Defining the mammalian coactivation of hepatic 12-h clock and lipid metabolism

The 12-h clock coordinates lipid homeostasis, energy metabolism, and stress rhythms via the transcriptional regulator XBP1. However, the biochemical and physiological bases for integrated control of the 12-h clock and diverse metabolic pathways remain unclear. Here, we show that steroid receptor coactivator SRC-3 coactivates XBP1 transcription and regulates hepatic 12-h cistrome and gene rhythmicity. Mice lacking SRC-3 show abnormal 12-h rhythms in hepatic transcription, metabolic functions, systemic energetics, and rate-limiting lipid metabolic processes, including triglyceride, phospholipid, and cardiolipin pathways. Notably, 12-h clock coactivation is not only preserved, with its cistromic activation priming ahead of the zeitgeber cue of light, but concomitant with rhythmic remodeling in the absence of food. These findings reveal that SRC-3 integrates the mammalian 12-h clock, energy metabolism, and membrane and lipid homeostasis and demonstrates a role for the 12-h clock machinery as an active transcriptional mechanism in anticipating physiological and metabolic energy needs and stresses.

Altered cardiolipin metabolism is associated with cardiac mitochondrial dysfunction in pulmonary vascular remodeled perinatal rat pups

Pulmonary vascular remodeling (PVR) in utero results in the development of heart failure. The alterations that occur in cardiac lipid and mitochondrial bioenergetics during the development of in utero PVR was unknown. In this study, PVR was induced in pups in utero by exposure of pregnant dams to indomethacin and hypoxia and cardiac lipids, echocardiographic function and cardiomyocyte mitochondrial function were subsequently examined. Perinatal rat pups with PVR exhibited elevated left and right cardiac ventricular internal dimensions and reduced ejection fraction and fractional shortening compared to controls. Cardiac myocytes from these pups exhibited increased glycolytic capacity and glycolytic reserve compared to controls. However, respiration with glucose as substrate was unaltered. Fatty acid oxidation and ATP-insensitive respiration were increased in isolated cardiac myocytes from these pups compared to controls indicating a mitochondrial dysfunction. Although abundance of mitochondrial respiratory chain complexes was unaltered, increased trilinoleoyl-lysocardiolipin levels in these pups was observed. A compensatory increase in both cardiolipin and phosphatidylethanolamine content were observed due to increased synthesis of these phospholipids. These data indicate that alterations in cardiac cardiolipin and phospholipid metabolism in PVR rat pups is associated with the mitochondrial bioenergetic and cardiac functional defects observed in their hearts.

Sequential lipidomic, metabolomic, and proteomic analyses of serum, liver, and heart tissue specimens from peroxisomal biogenesis factor 11α knockout mice

Peroxisomes are versatile single membrane-enclosed cytoplasmic organelles, involved in reactive oxygen species (ROS) and lipid metabolism and diverse other metabolic processes. Peroxisomal disorders result from mutations in Pex genes-encoded proteins named peroxins (PEX proteins) and single peroxisomal enzyme deficiencies. The PEX11 protein family (α, β, and γ isoforms) plays an important role in peroxisomal proliferation and fission. However, their specific functions and the metabolic impact caused by their deficiencies have not been precisely characterized. To understand the systemic molecular alterations caused by peroxisomal defects, here we utilized untreated peroxisomal biogenesis factor 11α knockout (Pex11α KO) mouse model and performed serial relative-quantitative lipidomic, metabolomic, and proteomic analyses of serum, liver, and heart tissue homogenates. We demonstrated significant specific changes in the abundances of multiple lipid species, polar metabolites, and proteins and dysregulated metabolic pathways in distinct biological specimens of the Pex11α KO adult mice in comparison to the wild type (WT) controls. Overall, the present study reports comprehensive semi-quantitative molecular omics information of the Pex11α KO mice, which might serve in the future as a reference for a better understanding of the roles of Pex11α and underlying pathophysiological mechanisms of peroxisomal biogenesis disorders.

Mitochondrial Membrane Remodeling

Mitochondria are key regulators of many important cellular processes and their dysfunction has been implicated in a large number of human disorders. Importantly, mitochondrial function is tightly linked to their ultrastructure, which possesses an intricate membrane architecture defining specific submitochondrial compartments. In particular, the mitochondrial inner membrane is highly folded into membrane invaginations that are essential for oxidative phosphorylation. Furthermore, mitochondrial membranes are highly dynamic and undergo constant membrane remodeling during mitochondrial fusion and fission. It has remained enigmatic how these membrane curvatures are generated and maintained, and specific factors involved in these processes are largely unknown. This review focuses on the current understanding of the molecular mechanism of mitochondrial membrane architectural organization and factors critical for mitochondrial morphogenesis, as well as their functional link to human diseases.

Targeting mitochondrial dysfunction with elamipretide

Although currently employed therapies for heart failure decrease overall mortality and improve patient quality of life temporarily, the disease is known to progress even for patients who receive all guideline-recommended therapies. This indicates that our concise understanding of heart failure and of disease progression is incomplete, and there is a need for new interventions that may augment, or even supplant, currently available options. A literature review reveals that an exciting, novel area of current research is focused on mitochondria, which are uniquely juxtaposed at the sites of both generation of high-energy molecules and initiation of programmed cell death. Elamipretide is being studied both to maintain cellular biogenetics and prevent reactive oxygen species-induced cell damage by targeting and stabilizing the cardiolipin-cytochrome c supercomplex. Thus far, elamipretide has been shown to increase left ventricular ejection fraction in dog models of heart failure with reduced ejection fraction and to prevent left ventricular remodeling in rats. In early-phase clinical trials, elamipretide administration has not resulted in any severe adverse events, and it has shown promising improvements in cardiac hemodynamics at highest doses. Nonetheless, additional studies are necessary to describe the long-term safety and efficacy of elamipretide.

ost in promiscuity? An evolutionary and biochemical evaluation of HSD10 function in cardiolipin metabolism

Multifunctional proteins are challenging as it can be difficult to confirm pathomechanisms associated with disease-causing genetic variants. The human 17β-hydroxysteroid dehydrogenase 10 (HSD10) is a moonlighting enzyme with at least two structurally and catalytically unrelated functions. HSD10 disease was originally described as a disorder of isoleucine metabolism, but the clinical manifestations were subsequently shown to be linked to impaired mtDNA transcript processing due to deficient function of HSD10 in the mtRNase P complex. A surprisingly large number of other, mostly enzymatic and potentially clinically relevant functions have been attributed to HSD10. Recently, HSD10 was reported to exhibit phospholipase C-like activity towards cardiolipins (CL), important mitochondrial phospholipids. To assess the physiological role of the proposed CL-cleaving function, we studied CL architectures in living cells and patient fibroblasts in different genetic backgrounds and lipid environments using our well-established LC-MS/MS cardiolipidomic pipeline. These experiments revealed no measurable effect on CLs, indicating that HSD10 does not have a physiologically relevant function towards CL metabolism. Evolutionary constraints could explain the broad range of reported substrates for HSD10 in vitro. The combination of an essential structural with a non-essential enzymatic function in the same protein could direct the evolutionary trajectory towards improvement of the former, thereby increasing the flexibility of the binding pocket, which is consistent with the results presented here.

Blocking phosphatidylglycerol degradation in yeast defective in cardiolipin remodeling results in a new model of the Barth syndrome cellular phenotype

Barth syndrome (BTHS) is an inherited mitochondrial disorder characterized by a decrease in total cardiolipin and the accumulation of its precursor monolysocardiolipin due to the loss of the transacylase enzyme tafazzin. However, the molecular basis of BTHS pathology is still not well understood. Here we characterize the double mutant pgc1Δtaz1Δ of Saccharomyces cerevisiae deficient in phosphatidylglycerol-specific phospholipase C and tafazzin as a new yeast model of BTHS. Unlike the taz1Δ mutant used to date, this model accumulates phosphatidylglycerol, thus better approximating the human BTHS cells. We demonstrate that increased phosphatidylglycerol in this strain leads to more pronounced mitochondrial respiratory defects and an increased incidence of aberrant mitochondria compared to the single taz1Δ mutant. We also show that the mitochondria of the pgc1Δtaz1Δ mutant exhibit a reduced rate of respiration due to decreased cytochrome c oxidase and ATP synthase activities. Finally, we determined that the mood-stabilizing anticonvulsant valproic acid has a positive effect on both lipid composition and mitochondrial function in these yeast BTHS models. Overall, our results show that the pgc1Δtaz1Δ mutant better mimics the cellular phenotype of BTHS patients than taz1Δ cells, both in terms of lipid composition and the degree of disruption of mitochondrial structure and function. This favors the new model for use in future studies.

Molecular and mesoscopic geometries in autophagosome generation. A review

Autophagy is an essential process in cell self-repair and survival. The centre of the autophagic event is the generation of the so-called autophagosome (AP), a vesicle surrounded by a double membrane (two bilayers). The AP delivers its cargo to a lysosome, for degradation and re-use of the hydrolysis products as new building blocks. AP formation is a very complex event, requiring dozens of specific proteins, and involving numerous instances of membrane biogenesis and architecture, including membrane fusion and fission. Many stages of AP generation can be rationalised in terms of curvature, both the molecular geometry of lipids interpreted in terms of 'intrinsic curvature', and the overall mesoscopic curvature of the whole membrane, as observed with microscopy techniques. The present contribution intends to bring together the worlds of biophysics and cell biology of autophagy, in the hope that the resulting cross-pollination will generate abundant fruit.

Mitochondria as a Cellular Hub in Infection and Inflammation

Mitochondria are the energy center of the cell. They are found in the cell cytoplasm as dynamic networks where they adapt energy production based on the cell’s needs. They are also at the center of the proinflammatory response and have essential roles in the response against pathogenic infections. Mitochondria are a major site for production of Reactive Oxygen Species (ROS; or free radicals), which are essential to fight infection. However, excessive and uncontrolled production can become deleterious to the cell, leading to mitochondrial and tissue damage. Pathogens exploit the role of mitochondria during infection by affecting the oxidative phosphorylation mechanism (OXPHOS), mitochondrial network and disrupting the communication between the nucleus and the mitochondria. The role of mitochondria in these biological processes makes these organelle good targets for the development of therapeutic strategies. In this review, we presented a summary of the endosymbiotic origin of mitochondria and their involvement in the pathogen response, as well as the potential promising mitochondrial targets for the fight against infectious diseases and chronic inflammatory diseases.

Lipidomic and Proteomic Alterations Induced by Even and Odd Medium-Chain Fatty Acids on Fibroblasts of Long-Chain Fatty Acid Oxidation Disorders

Medium-chain fatty acids (mc-FAs) are currently applied in the treatment of long-chain fatty acid oxidation disorders (lc-FAOD) characterized by impaired β-oxidation. Here, we performed lipidomic and proteomic analysis in fibroblasts from patients with very long-chain acyl-CoA dehydrogenase (VLCADD) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHADD) deficiencies after incubation with heptanoate (C7) and octanoate (C8). Defects of β-oxidation induced striking proteomic alterations, whereas the effect of treatment with mc-FAs was minor. However, mc-FAs induced a remodeling of complex lipids. Especially C7 appeared to act protectively by restoring sphingolipid biosynthesis flux and improving the observed dysregulation of protein homeostasis in LCHADD under control conditions.

A mouse model of short-term, diet-induced fatty liver with abnormal cardiolipin remodeling via downregulated Tafazzin gene expression

BACKGROUND

Cardiolipin (CL) helps maintain mitochondrial structure and function. Here we investigated whether a high carbohydrate diet (HCD) fed to mice for a short period (5 days) could modulate the CL level, including that of monolysoCL (MLCL) in the liver.

RESULTS

Total CL in the HCD group was 22% lower than that in the normal chow diet (NCD) group (P < 0.05). The CL72:8 level strikingly decreased by 93% (P < 0.0001), whereas total nascent CLs (CLs other than CL72:8) increased (P < 0.01) in the HCD group. The total MLCL in the HCD group increased by 2.4-fold compared with that in the NCD group (P < 0.05). Tafazzin expression in the HCD group was significantly downregulated compared with that in the NCD group (P < 0.05). A strong positive correlation between nascent CL and total MLCL (r = 0.955, P < 0.0001), and a negative correlation between MLCL and Tafazzin expression (r = -0.593, P = 0.0883) were observed.

CONCLUSION

A HCD modulated the fatty acid composition of CL and MLCL via Tafazzin in the liver, which could lead to mitochondrial dysfunction. This model may be useful for elucidating the relationship between fatty liver and mitochondrial dysfunction. © 2021 Society of Chemical Industry.

Fatty acyl availability modulates cardiolipin composition and alters mitochondrial function in HeLa cells

The molecular assembly of cells depends not only on the balance between anabolism and catabolism but to a large degree on the building blocks available in the environment. For cultured mammalian cells, this is largely determined by the composition of the applied growth medium. Here, we study the impact of lipids in the medium on mitochondrial membrane architecture and function by combining LC-MS/MS lipidomics and functional tests with lipid supplementation experiments in an otherwise serum-free and lipid-free cell culture model. We demonstrate that the composition of mitochondrial cardiolipins strongly depends on the lipid environment in cultured cells and favors the incorporation of essential linoleic acid over other fatty acids. Simultaneously, the mitochondrial respiratory complex I activity was altered, whereas the matrix-localized enzyme citrate synthase was unaffected. This raises the question on a link between membrane composition and respiratory control. In summary, we found a strong dependency of central mitochondrial features on the type of lipids contained in the growth medium. This underlines the importance of considering these factors when using and establishing cell culture models in biomedical research. In summary, we found a strong dependency of central mitochondrial features on the type of lipids contained in the growth medium.

Qualitative Characterization of the Rat Liver Mitochondrial Lipidome Using All Ion Fragmentation on an Exactive Benchtop Orbitrap MS

Untargeted lipidomics profiling by liquid chromatography -mass spectrometry (LC-MS) allows researchers to observe the occurrences of lipids in a biological sample without showing intentional bias to any specific class of lipids and allows retrospective reanalysis of data collected. Typically, and in the specific method described, a general extraction method followed by LC separation is used to achieve nonspecific class coverage of the lipidome prior to high resolution accurate mass (HRAM) MS detection . Here we describe a workflow including the isolation of mitochondria from liver tissue, followed by mitochondrial lipid extraction and the LC-MS conditions used for data acquisition. We also highlight how, in this method, all ion fragmentation can be used to identify species of lower abundances, often missed by data dependent fragmentation techniques. Here we describe the isolation of mitochondria from liver tissue, followed by mitochondrial lipid extraction and the LC-MS conditions used for data acquisition.