Lipid metabolism in mitochondrial membranes

Bioprobe-RNA-seq-microRaman system for deep tracking of the live single-cell metabolic pathway chemometrics

The integration between RNA-sequencing and micro-spectroscopic techniques has recently profiled the advanced transcriptomic discoveries on the cellular level. In the current study, by combining the sensation approach (including bio-molecules structural evaluation, high throughput next-generation sequencing (HT-NGS), and confocal Raman microscopy) the functionality on the single live cancer cells' ferroptosis and apoptosis signaling pathways is visualized. Our study reveals a hydrophobic tunnel by phycocyanin-isoprene molecule (PC-SIM) electrostatic charge within hepatoma cells (HepG2) that activates the ferritin light chain (FTL) and caspase-8 associate protein (CASP8AP2) ferroptosis responsible genes. Moreover, this research proves that PC-vanillin (VAN) stimulation induces the actin-binding factor profilin-1 (PFN1), subsequently in situ tracking its expression at 1139.75 cm-1 microRaman wavenumber. While PC-thymol (THY) induces the lysophospholipase-2 (LYPLA2) (p-value = 0.009) and acetylneuraminate-9-O-acetyltransferase (CASD1) (p-value = 0.022) at 1143.19 cm-1. Our findings establish a new concept to promote the cross-disciplinary use of instant cellular-based detection technology for intermediary evaluating the signaling cellular transcriptome.

Lantana camara L. induces a multi-targeted cell death process in Leishmania amazonensis

ETNOPHARMACOLOGICAL RELEVANCE

Lantana camara L. is a species known for its broad spectrum of bioactivities and is commonly used in folk therapy to address inflammatory, dermatological, gastrointestinal, intestinal worms and protozoan diseases. It boasts a diverse array of secondary metabolites such as terpenes, flavonoids, and saponins. However, despite its rich chemical profile, there remains a scarcity of studies investigating its antileishmanial properties.

AIM OF THE STUDY

This research aims to explore the antileishmanial potential of L. camara, focusing also on its mechanism of action against Leishmania amazonensis.

MATERIAL AND METHODS

The ethanolic extract of L. camara leaves (LCE) was obtained through static maceration, and its phytoconstituents were identified using UFLC-QTOF-MS. The colorimetric MTT method was conducted to determine the effect of LCE on promastigotes of L. amazonensis and murine macrophages. The anti-amastigote activity was evaluated by counting intracellular parasites in macrophages after Giemsa staining. Additionally, investigations into the mechanisms underlying its action were conducted using cellular and biochemical approaches.

RESULTS

LCE exhibited significant activity against both promastigotes and intracellular amastigotes of L. amazonensis, with IC50 values of 12.20 μg/mL ± 0.12 and 7.09 μg/mL ± 1.24, respectively. These IC50 values indicate very promising antileishmanial activity, comparable to those found for the positive control miltefosine (5.10 μg/mL ± 1.79 and 8.96 μg/mL ± 0.50, respectively). Notably, LCE exhibited negligible cytotoxicity on macrophages (IC50 = 223.40 μg/mL ± 47.02), demonstrating selectivity towards host cells (SI = 31.50). The antileishmanial activity of LCE involved a multi-targeted cell death process, characterized by morphological and ultrastructural alterations observed through SEM and TEM analyses, as well as oxidative effects evidenced by the inhibition of trypanothione reductase, elevation of ROS and lipid levels, and mitochondrial dysfunction evaluated using DTNB, H2DCFDA, Nile red, and JC-1 assays. Additionally, extraction of ergosterol and double labeling with annexin V and PI revealed modifications to the organization and permeability of the treated parasite's plasma membrane. LCE was found to consist predominantly of terpenes, with lantadenes A, B, and C being among the eleven compounds identified through UFLC-QTOF-MS analysis.

CONCLUSIONS

The extract of L. camara presents a diverse array of chemical constituents, prominently featuring high terpene content, which may underlie its antileishmanial properties through a combination of apoptotic and non-apoptotic mechanisms of cell death induced by LCE. This study underscores the therapeutic potential of L. camara as a candidate for antileishmanial treatment, pending further validation.

Jiawei Dachaihu decoction protects against mitochondrial dysfunction in atherosclerosis (AS) mice with chronic unpredictable mild stress (CUMS) via SIRT1/PGC-1α/TFAM/LON signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

JiaWei DaChaiHu is composed of Bupleurum chinense, Scutellaria baicalensis, Pinellia ternata, Paeonia lactiflora, Zingiber officinaleRoscoe, Poncirus tuifoliata, Rheum palmatum L., Curcumae Radix, Herba Lysimachiae, Ziziphus. JiaWei DaChaiHu is one of the most common traditional Chinese medicines for the treatment of depression.

AIM OF THE STUDY

The chronic unpredictable mild stress (CUMS) has been shown to promote atherosclerosis (AS). Dachaihu has been widely used in traditional Chinese medicine and has been known to exert distinct pharmacological effects. This investigation aims to examine the therapeutic effect of Jiawei Dachaihu extract on AS animal models with CUMS.

METHODS

AS-CUMS mice model was established by Apoe-/- mice. Mice were treated with Jiawei Dachaihu. Serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL-C), high-density lipoprotein (HDL-C) levels were measured using ELISA kits. Aortic tissue pathologic changes detected by oil red O staining. Mice behavioral changes detected by sucrose preference test and sucrose preference test. The relative mRNA expression levels of CRH, ND1, and TFAM were determined by qRT-PCR. 5-HT1A, BDNF, LON, TFAM, PGC-1α, and SIRT1 protein expression determined by western blotting. ATP content detected by ATP kits.

RESULTS

The treatment with Jiawei Dachaihu extract alleviated the veins plaque and reduced stress signs in vitro and in vivo. It increased the ATP and HDL-C levels while decreased the TC, TG, LDL-C levels. Jiawei Dachaihu extract treatment upregulated Lon, SIRT1, TFAM, PGC-1α, BDNF, and 5-HT1A protein expression and regained mitochondrial function.

CONCLUSION

Jiawei Dachaihu extract could alleviate AS and reduce CUMS by upregulating the SIRT1/PGC-1α signaling and promoted its crosstalk with Lon protein to maintain mitochondrial stability.

Mechanisms and Future Research Perspectives on Mitochondrial Diseases Associated with Isoleucyl-tRNA Synthetase Gene Mutations

Aminoacyl-tRNA synthetases are essential enzymes for the accurate translation of genetic information. IARS1 and IARS2 are isoleucyl-tRNA synthetases functioning in the cytoplasm and mitochondria, respectively, with genetic mutations in these enzymes causing diverse clinical phenotypes in specific organs and tissues. Mutations in IARS1 and IARS2 have recently been linked to mitochondrial diseases. This review aims to explore the relationship between IARS1 and IARS2 and these diseases, providing a comprehensive overview of their association with mitochondrial diseases. Mutations in IARS1 cause weak calf syndrome in cattle and mitochondrial diseases in humans, leading to growth retardation and liver dysfunction. Mutations in IARS2 are associated with Leigh syndrome, craniosynostosis and abnormal genitalia syndrome. Future research is expected to involve genetic analysis of a larger number of patients, identifying new mutations in IARS1 and IARS2, and elucidating their impact on mitochondrial function. Additionally, genetically modified mice and the corresponding phenotypic analysis will serve as powerful tools for understanding the functions of these gene products and unraveling disease mechanisms. This will likely promote the development of new therapies and preventive measures.

Cardiolipin clustering promotes mitochondrial membrane dynamics

Cardiolipin (CL) is a mitochondria-specific phospholipid that forms heterotypic interactions with membrane-shaping proteins and regulates the dynamic remodeling and function of mitochondria. However, the precise mechanisms through which CL influences mitochondrial morphology are not well understood. In this study, employing molecular dynamics (MD) simulations, we observed CL localize near the membrane-binding sites of the mitochondrial fusion protein Optic Atrophy 1 (OPA1). To validate these findings experimentally, we developed a bromine-labeled CL probe to enhance cryoEM contrast and characterize the structure of OPA1 assemblies bound to the CL-brominated lipid bilayers. Our images provide direct evidence of interactions between CL and two conserved motifs within the paddle domain (PD) of OPA1, which control membrane-shaping mechanisms. We further observed a decrease in membrane remodeling activity for OPA1 in lipid compositions with increasing concentrations of monolyso-cardiolipin (MLCL). Suggesting that the partial replacement of CL by MLCL accumulation, as observed in Barth syndrome-associated mutations of the tafazzin phospholipid transacylase, compromises the stability of protein-membrane interactions. Our analyses provide insights into how biological membranes regulate the mechanisms governing mitochondrial homeostasis.

Brain-muscle communication prevents muscle aging by maintaining daily physiology

A molecular clock network is crucial for daily physiology and maintaining organismal health. We examined the interactions and importance of intratissue clock networks in muscle tissue maintenance. In arrhythmic mice showing premature aging, we created a basic clock module involving a central and a peripheral (muscle) clock. Reconstituting the brain-muscle clock network is sufficient to preserve fundamental daily homeostatic functions and prevent premature muscle aging. However, achieving whole muscle physiology requires contributions from other peripheral clocks. Mechanistically, the muscle peripheral clock acts as a gatekeeper, selectively suppressing detrimental signals from the central clock while integrating important muscle homeostatic functions. Our research reveals the interplay between the central and peripheral clocks in daily muscle function and underscores the impact of eating patterns on these interactions.

The Chemical Reactivity of Membrane Lipids

It is well-known that aqueous dispersions of phospholipids spontaneously assemble into bilayer structures. These structures have numerous applications across chemistry and materials science and form the fundamental structural unit of the biological membrane. The particular environment of the lipid bilayer, with a water-poor low dielectric core surrounded by a more polar and better hydrated interfacial region, gives the membrane particular biophysical and physicochemical properties and presents a unique environment for chemical reactions to occur. Many different types of molecule spanning a range of sizes, from dissolved gases through small organics to proteins, are able to interact with membranes and promote chemical changes to lipids that subsequently affect the physicochemical properties of the bilayer. This Review describes the chemical reactivity exhibited by lipids in their membrane form, with an emphasis on conditions where the lipids are well hydrated in the form of bilayers. Key topics include the following: lytic reactions of glyceryl esters, including hydrolysis, aminolysis, and transesterification; oxidation reactions of alkenes in unsaturated fatty acids and sterols, including autoxidation and oxidation by singlet oxygen; reactivity of headgroups, particularly with reactive carbonyl species; and E/Z isomerization of alkenes. The consequences of reactivity for biological activity and biophysical properties are also discussed.

Multi-omics analysis of innate and adaptive responses to BCG vaccination reveals epigenetic cell states that predict trained immunity

Immune responses are tightly regulated yet highly variable between individuals. To investigate human population variation of trained immunity, we immunized healthy individuals with Bacillus Calmette-Guérin (BCG). This live-attenuated vaccine induces not only an adaptive immune response against tuberculosis but also triggers innate immune activation and memory that are indicative of trained immunity. We established personal immune profiles and chromatin accessibility maps over a 90-day time course of BCG vaccination in 323 individuals. Our analysis uncovered genetic and epigenetic predictors of baseline immunity and immune response. BCG vaccination enhanced the innate immune response specifically in individuals with a dormant immune state at baseline, rather than providing a general boost of innate immunity. This study advances our understanding of BCG's heterologous immune-stimulatory effects and trained immunity in humans. Furthermore, it highlights the value of epigenetic cell states for connecting immune function with genotype and the environment.

BZD9L1 Differentially Regulates Sirtuins in Liver-Derived Cells by Inducing Reactive Oxygen Species

Growing evidence has highlighted that mitochondrial dysfunction contributes to drug-induced toxicities and leads to drug attrition and post-market withdrawals. The acetylation or deacetylation of mitochondrial proteins can affect mitochondrial functions as the cells adapt to various cellular stresses and other metabolic challenges. SIRTs act as critical deacetylases in modulating mitochondrial function in response to drug toxicity, oxidative stress, reactive oxygen species (ROS), and energy metabolism. We previously showed that a recently characterised SIRT inhibitor (BZD9L1) is non-toxic in rodents in a short-term toxicity evaluation. However, the impact of BZD9L1 on mitochondrial function is unknown. This work aims to determine the effects of BZD9L1 on mitochondrial function in human normal liver and kidney-derived cell lines using the Agilent Seahorse Cell Mito Stress Test to complement our short-term toxicity evaluations in vivo. The Mito Stress assay revealed that BZD9L1 could potentially trigger oxidative stress by inducing ROS, which promotes proton leak and reduces coupling efficiency in liver-derived THLE cells. However, the same was not observed in human kidney-derived HEK293 cells. Interestingly, BZD9L1 had no impact on SIRT3 protein expression in both cell lines but affected SOD2 and its acetylated form at 72 h in THLE cells, indicating that BZD9L1 exerted its effect through SIRT3 activity rather than protein expression. In contrast, BZD9L1 reduced SIRT1 protein expression and impacted the p53 protein differently in both cell lines. Although BZD9L1 did not affect the spare respiratory capacity in vitro, these findings call for further validation of mitochondrial function through assessment of other mitochondrial parameters to evaluate the safety of BZD9L1.

What can be lost? Genomic perspective on the lipid metabolism of Mucoromycota

Mucoromycota is a phylum of early diverging fungal (EDF) lineages, of mostly plant-associated terrestrial fungi. Some strains have been selected as promising biotechnological organisms due to their ability to produce polyunsaturated fatty acids and efficient conversion of nutrients into lipids. Others get their lipids from the host plant and are unable to produce even the essential ones on their own. Following the advancement in EDF genome sequencing, we carried out a systematic survey of lipid metabolism protein families across different EDF lineages. This enabled us to explore the genomic basis of the previously documented ability to produce several types of lipids within the fungal tree of life. The core lipid metabolism genes showed no significant diversity in distribution, however specialized lipid metabolic pathways differed in this regard among different fungal lineages. In total 165 out of 202 genes involved in lipid metabolism were present in all tested fungal lineages, while remaining 37 genes were found to be absent in some of fungal lineages. Duplications were observed for 69 genes. For the first time we demonstrate that ergosterol is not being produced by several independent groups of plant-associated fungi due to the losses of different ERG genes. Instead, they possess an ancestral pathway leading to the synthesis of cholesterol, which is absent in other fungal lineages. The lack of diacylglycerol kinase in both Mortierellomycotina and Blastocladiomycota opens the question on sterol equilibrium regulation in these organisms. Early diverging fungi retained most of beta oxidation components common with animals including Nudt7, Nudt12 and Nudt19 pointing at peroxisome divergence in Dikarya. Finally, Glomeromycotina and Mortierellomycotina representatives have a similar set of desaturases and elongases related to the synthesis of complex, polyunsaturated fatty acids pointing at an ancient expansion of fatty acid metabolism currently being explored by biotechnological studies.

The Batten disease gene product CLN5 is the lysosomal bis(monoacylglycero)phosphate synthase

Lysosomes critically rely on bis(monoacylglycero)phosphate (BMP) to stimulate lipid catabolism, cholesterol homeostasis, and lysosomal function. Alterations in BMP levels in monogenic and complex neurodegeneration suggest an essential function in human health. However, the site and mechanism responsible for BMP synthesis have been subject to debate for decades. Here, we report that the Batten disease gene product CLN5 is the elusive BMP synthase (BMPS). BMPS-deficient cells exhibited a massive accumulation of the BMP synthesis precursor lysophosphatidylglycerol (LPG), depletion of BMP species, and dysfunctional lipid metabolism. Mechanistically, we found that BMPS mediated synthesis through an energy-independent base exchange reaction between two LPG molecules with increased activity on BMP-laden vesicles. Our study elucidates BMP biosynthesis and reveals an anabolic function of late endosomes/lysosomes.

Mitochondrial networks through the lens of mathematics

Mitochondria serve a wide range of functions within cells, most notably via their production of ATP. Although their morphology is commonly described as bean-like, mitochondria often form interconnected networks within cells that exhibit dynamic restructuring through a variety of physical changes. Further, though relationships between form and function in biology are well established, the extant toolkit for understanding mitochondrial morphology is limited. Here, we emphasize new and established methods for quantitatively describing mitochondrial networks, ranging from unweighted graph-theoretic representations to multi-scale approaches from applied topology, in particular persistent homology. We also show fundamental relationships between mitochondrial networks, mathematics, and physics, using ideas of graph planarity and statistical mechanics to better understand the full possible morphological space of mitochondrial network structures. Lastly, we provide suggestions for how examination of mitochondrial network form through the language of mathematics can inform biological understanding, and vice versa.

Transcriptional Inhibition of AGPAT2 Induces Abnormal Lipid Metabolism and Oxidative Stress in the Liver of Nile Tilapia Oreochromis niloticus

The enzyme 1-acylglycerol-3-phosphate O-acyltransferase 2 (AGPAT2) is an intermediate enzyme in triglyceride synthesis. The aim was to study the regulatory mechanism of AGPAT2 on Nile tilapia, Oreochromis niloticus. In this study, antisense RNA technology was used to knock-down AGPAT2 in Nile tilapia. Compared with the control groups (transfected with ultrapure water or the blank expression vector), the AGPAT2 knock-down group showed a significantly higher weight gain rate, special growth rate, visceral somatic index, and hepatopancreas somatic index; and significantly increased the total cholesterol, triglycerides, glucose, low-density lipoprotein cholesterol, and insulin levels in serum. In addition, the contents of total cholesterol and triglycerides and the abundance of superoxide dismutase, catalase, and glutathione peroxidase in the liver significantly increased, while the malondialdehyde content significantly decreased. The liver cells became severely vacuolated and accumulated lipids in the AGPAT2 knock-down group. Comparative transcriptome analyses (AGPAT2 knock-down vs. control group) revealed 1789 differentially expressed genes (DEGs), including 472 upregulated genes and 1313 downregulated genes in the AGPAT2 knock-down group. Functional analysis showed that the main pathway of differentially expressed genes enrichment was lipid metabolism and oxidative stress, such as steroid biosynthesis, unsaturated fatty acid biosynthesis, the PPAR signaling pathway, and the P53 pathway. We used qRT-PCR to verify the mRNA expression changes of 13 downstream differential genes in related signaling pathways. These findings demonstrate that knock-down of AGPAT2 in tilapia leads to abnormal lipid metabolism and oxidative stress.

The structure of the human LACTB filament reveals the mechanisms of assembly and membrane binding

Mitochondria are complex organelles that play a central role in metabolism. Dynamic membrane-associated processes regulate mitochondrial morphology and bioenergetics in response to cellular demand. In tumor cells, metabolic reprogramming requires active mitochondrial metabolism for providing key metabolites and building blocks for tumor growth and rapid proliferation. To counter this, the mitochondrial serine beta-lactamase-like protein (LACTB) alters mitochondrial lipid metabolism and potently inhibits the proliferation of a variety of tumor cells. Mammalian LACTB is localized in the mitochondrial intermembrane space (IMS), where it assembles into filaments to regulate the efficiency of essential metabolic processes. However, the structural basis of LACTB polymerization and regulation remains incompletely understood. Here, we describe how human LACTB self-assembles into micron-scale filaments that increase their catalytic activity. The electron cryo-microscopy (cryoEM) structure defines the mechanism of assembly and reveals how highly ordered filament bundles stabilize the active state of the enzyme. We identify and characterize residues that are located at the filament-forming interface and further show that mutations that disrupt filamentation reduce enzyme activity. Furthermore, our results provide evidence that LACTB filaments can bind lipid membranes. These data reveal the detailed molecular organization and polymerization-based regulation of human LACTB and provide new insights into the mechanism of mitochondrial membrane organization that modulates lipid metabolism.

Mitochondrial DNA copy number, metabolic syndrome, and insulin sensitivity: Insights from the Sugar, Hypertension, and Physical Exercise studies

Mitochondrial DNA copy number (mtDNA-CN) measured in blood has been associated with many aging-related diseases, with higher mtDNA-CN typically associated with lower disease risk. Exercise training is an excellent preventative tool against aging-related disorders and has been shown to increase mitochondrial function in muscle. Using the Sugar, Hypertension, and Physical Exercise cohorts (N = 105), we evaluated the effect of 6-months of exercise intervention on mtDNA-CN measured in blood. Although there was no significant relationship between exercise intervention and mtDNA-CN change (P = 0.29), there was a nominally significant association between mtDNA-CN and metabolic syndrome (P = 0.04), which has been seen in previous literature. We also identified a nominally significant association between higher mtDNA-CN and higher insulin sensitivity (P = 0.02).

Structural basis for mitoguardin-2 mediated lipid transport at ER-mitochondrial membrane contact sites

The endoplasmic reticulum (ER)-mitochondria contact site (ERMCS) is crucial for exchanging biological molecules such as phospholipids and Ca²⁺ ions between these organelles. Mitoguardin-2 (MIGA2), a mitochondrial outer membrane protein, forms the ERMCS in higher eukaryotic cells. Here, we report the crystal structures of the MIGA2 Lipid Droplet (LD) targeting domain and the ER membrane protein VAPB bound to the phosphorylated FFAT motif of MIGA2. These structures reveal that the MIGA2 LD targeting domain has a large internal hydrophobic pocket that accommodates phospholipids and that two phosphorylations of the FFAT motif are required for tight interaction of MIGA2 with VAPB, which enhances the rate of lipid transport. Further biochemical studies show that MIGA2 transports phospholipids between membranes with a strong preference for binding and trafficking phosphatidylserine (PS). These results provide a structural and molecular basis for understanding how MIGA2 mediates the formation of ERMCS and facilitates lipid trafficking at the ERMCS.

The ER-mitochondria contact sites are crucial for exchanging phospholipids. Here, Kim et al. present crystal structures of mitoguardin-2 (MIGA2) which reveal that MIGA2 directly binds phospholipids and transfers them between the ER and mitochondria.

Mitochondria-actin cytoskeleton crosstalk in cell migration

Mitochondria perform diverse functions in the cell and their roles during processes such as cell survival, differentiation, and migration are increasingly being appreciated. Mitochondrial and actin cytoskeletal networks not only interact with each other, but this multifaceted interaction shapes their functional dynamics. The interrelation between mitochondria and the actin cytoskeleton extends far beyond the requirement of mitochondrial ATP generation to power actin dynamics, and impinges upon several major aspects of cellular physiology. Being situated at the hub of cell signaling pathways, mitochondrial function can alter the activity of actin regulatory proteins and therefore modulate the processes downstream of actin dynamics such as cellular migration. As we will discuss, this regulation is highly nuanced and operates at multiple levels allowing mitochondria to occupy a strategic position in the regulation of migration, as well as pathological events that rely on aberrant cell motility such as cancer metastasis. In this review, we summarize the crosstalk that exists between mitochondria and actin regulatory proteins, and further emphasize on how this interaction holds importance in cell migration in normal as well as dysregulated scenarios as in cancer.

Biallelic variants in TAMM41 are associated with low muscle cardiolipin levels, leading to neonatal mitochondrial disease

Mitochondrial disorders are clinically and genetically heterogeneous, with variants in mitochondrial or nuclear genes leading to varied clinical phenotypes. TAMM41 encodes a mitochondrial protein with cytidine diphosphate-diacylglycerol synthase activity: an essential early step in the biosynthesis of phosphatidylglycerol and cardiolipin. Cardiolipin is a mitochondria-specific phospholipid that is important for many mitochondrial processes. We report three unrelated individuals with mitochondrial disease that share clinical features, including lethargy at birth, hypotonia, developmental delay, myopathy, and ptosis. Whole exome and genome sequencing identified compound heterozygous variants in TAMM41 in each proband. Western blot analysis in fibroblasts showed a mild oxidative phosphorylation (OXPHOS) defect in only one of the three affected individuals. In skeletal muscle samples, however, there was severe loss of subunits of complexes I–IV and a decrease in fully assembled OXPHOS complexes I–V in two subjects as well as decreased TAMM41 protein levels. Similar to the tissue-specific observations on OXPHOS, cardiolipin levels were unchanged in subject fibroblasts but significantly decreased in the skeletal muscle of affected individuals. To assess the functional impact of the TAMM41 missense variants, the equivalent mutations were modeled in yeast. All three mutants failed to rescue the growth defect of the Δtam41 strains on non-fermentable (respiratory) medium compared with wild-type TAM41, confirming the pathogenicity of the variants. We establish that TAMM41 is an additional gene involved in mitochondrial phospholipid biosynthesis and modification and that its deficiency results in a mitochondrial disorder, though unlike families with pathogenic AGK (Sengers syndrome) and TAFAZZIN (Barth syndrome) variants, there was no evidence of cardiomyopathy.

Chewing the Fat with Microbes: Lipid Crosstalk in the Gut

It is becoming increasingly important for any project aimed at understanding the effects of diet on human health, to also consider the combined effect of the trillions of microbes within the gut which modify and are modified by dietary nutrients. A healthy microbiome is diverse and contributes to host health, partly via the production and subsequent host absorption of secondary metabolites. Many of the beneficial bacteria in the gut rely on specific nutrients, such as dietary fiber, to survive and thrive. In the absence of those nutrients, the relative proportion of good commensal bacteria dwindles while communities of opportunistic, and potentially pathogenic, bacteria expand. Therefore, it is unsurprising that both diet and the gut microbiome have been associated with numerous human diseases. Inflammatory bowel diseases and colorectal cancer are associated with the presence of certain pathogenic bacteria and risk increases with consumption of a Western diet, which is typically high in fat, protein, and refined carbohydrates, but low in plant-based fibers. Indeed, despite increased screening and better care, colorectal cancer is still the 2nd leading cause of cancer death in the US and is the 3rd most diagnosed cancer among US men and women. Rates are rising worldwide as diets are becoming more westernized, alongside rising rates of metabolic diseases like obesity and diabetes. Understanding how a modern diet influences the microbiota and how subsequent microbial alterations effect human health will become essential in guiding personalized nutrition and healthcare in the future. Herein, we will summarize some of the latest advances in understanding of the three-way interaction between the human host, the gut microbiome, and the specific class of dietary nutrients, lipids.

Interplay between cardiolipin and plasmalogens in Barth syndrome

Barth syndrome (BTHS) is a rare inherited metabolic disease resulting from mutations in the gene of the enzyme tafazzin, which catalyzes the acyl chain remodeling of the mitochondrial-specific lipid cardiolipin (CL). Tissue samples of individuals with BTHS present abnormalities in the level and the molecular species of CL. In addition, in tissues of a tafazzin knockdown mouse as well as in cells derived from BTHS patients it has been shown that plasmalogens, a subclass of glycerophospholipids, also have abnormal levels. Likewise, administration of a plasmalogen precursor to cells derived from BTHS patients led to an increase in plasmalogen and to some extent CL levels. These results indicate an interplay between CL and plasmalogens in BTHS. This interdependence is supported by the concomitant loss in these lipids in different pathological conditions. However, currently the molecular mechanism linking CL and plasmalogens is not fully understood. Here, a review of the evidence showing the linkage between the levels of CL and plasmalogens is presented. In addition, putative mechanisms that might play a role in this interplay are proposed. Finally, the opportunity of therapeutic approaches based on the regulation of plasmalogens as new therapies for the treatment of BTHS is discussed.

Lipid Interactions Between Flaviviruses and Mosquito Vectors

Mosquito-borne flaviviruses, such as dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses, threaten a large part of the human populations. In absence of therapeutics and effective vaccines against each flaviviruses, targeting viral metabolic requirements in mosquitoes may hold the key to new intervention strategies. Development of metabolomics in the last decade opened a new field of research: mosquito metabolomics. It is now clear that flaviviruses rely on mosquito lipids, especially phospholipids, for their cellular cycle and propagation. Here, we review the biosyntheses of, biochemical properties of and flaviviral interactions with mosquito phospholipids. Phospholipids are structural lipids with a polar headgroup and apolar acyl chains, enabling the formation of lipid bilayer that form plasma- and endomembranes. Phospholipids are mostly synthesized through the de novo pathway and remodeling cycle. Variations in headgroup and acyl chains influence phospholipid physicochemical properties and consequently the membrane behavior. Flaviviruses interact with cellular membranes at every step of their cellular cycle. Recent evidence demonstrates that flaviviruses reconfigure the phospholipidome in mosquitoes by regulating phospholipid syntheses to increase virus multiplication. Identifying the phospholipids involved and understanding how flaviviruses regulate these in mosquitoes is required to design new interventions.

Mitochondrial nucleoid in cardiac homeostasis: bidirectional signaling of mitochondria and nucleus in cardiac diseases

Metabolic function and energy production in eukaryotic cells are regulated by mitochondria, which have been recognized as the intracellular 'powerhouses' of eukaryotic cells for their regulation of cellular homeostasis. Mitochondrial function is important not only in normal developmental and physiological processes, but also in a variety of human pathologies, including cardiac diseases. An emerging topic in the field of cardiovascular medicine is the implication of mitochondrial nucleoid for metabolic reprogramming. This review describes the linear/3D architecture of the mitochondrial nucleoid (e.g., highly organized protein-DNA structure of nucleoid) and how it is regulated by a variety of factors, such as noncoding RNA and its associated R-loop, for metabolic reprogramming in cardiac diseases. In addition, we highlight many of the presently unsolved questions regarding cardiac metabolism in terms of bidirectional signaling of mitochondrial nucleoid and 3D chromatin structure in the nucleus. In particular, we explore novel techniques to dissect the 3D structure of mitochondrial nucleoid and propose new insights into the mitochondrial retrograde signaling, and how it regulates the nuclear (3D) chromatin structures in mitochondrial diseases.

Oxidized Phosphatidylcholines Induce Multiple Functional Defects in Airway Epithelial Cells

Oxidative stress is a hallmark of numerous airway diseases, contributing to extensive cell and tissue damage. Cell membranes and the airway mucosal lining are rich in phospholipids that are particularly susceptible to oxidative attack, producing bioactive molecules including oxidized phosphatidylcholines (OxPC). With the recent discovery of elevated OxPC in asthmatic patients after allergen challenge, we hypothesized that OxPC directly contribute to disease by inducing airway epithelial cell dysfunction. We found that OxPC induced concentration-dependent cell stress and loss of viability in BEAS-2B and Calu-3 cell lines and primary human epithelial cells. These responses corresponded with significant epithelial barrier dysfunction, which was further compounded when combining OxPC with an epithelial wound. OxPC inhibited DNA synthesis and migration required to re-establish barrier function, but cells recovered if OxPC were washed off soon after treatment. OxPC induced generation of reactive oxygen species, lipid peroxidation and mitochondrial dysfunction, raising the possibility that OxPC cause pathological lipid metabolism in a self-propagating cycle. The oxidative stress induced by OxPC could not be abrogated by putative OxPC receptor blockers, but partial recovery of barrier function, proliferation and lipid peroxidation could be achieved with the antioxidant n-acetyl cysteine. In summary, we have identified OxPC as a group of bioactive molecules that significantly impair multiple facets of epithelial cell function, consistent with pathological features of asthma. Further characterisation of the mechanisms by which OxPC affect epithelial cells could yield new insights into how oxidative stress contributes to the pathogenesis of airway disease.

Acylglycerol Kinase-Targeted Therapies in Oncology

Acylglycerol kinase (AGK) is a recently discovered mitochondrial lipid kinase, and mutation of its gene is the fundamental cause of Sengers syndrome. AGK is not only involved in the stability of lipid metabolism but also closely related to mitochondrial protein transport, glycolysis, and thrombocytopoiesis. Evidence indicates that AGK is an important factor in the occurrence and development of tumors. Specifically, AGK has been identified as an oncogene that partakes in the regulation of tumor cell growth, invasion, metastasis, and drug resistance. The versatility of AGK and its unique role in different types of cancerous and normal cells greatly piqued our interest. We believe that AGK is a promising target for cancer therapy. Therefore, this review summarizes the main research advances concerning AGK, including the discovery of its physiological/pathogenic mechanisms, and provides a reference for the feasible evaluation of AGK as a therapeutic target for human diseases, particularly tumors.

Life in the lumen: The multivesicular endosome

The late endosomes/endo‐lysosomes of vertebrates contain an atypical phospholipid, lysobisphosphatidic acid (LBPA) (also termed bis[monoacylglycero]phosphate [BMP]), which is not detected elsewhere in the cell. LBPA is abundant in the membrane system present in the lumen of this compartment, including intralumenal vesicles (ILVs). In this review, the current knowledge on LBPA and LBPA‐containing membranes will be summarized, and their role in the control of endosomal cholesterol will be outlined. Some speculations will also be made on how this system may be overwhelmed in the cholesterol storage disorder Niemann‐Pick C. Then, the roles of intralumenal membranes in endo‐lysosomal dynamics and functions will be discussed in broader terms. Likewise, the mechanisms that drive the biogenesis of intralumenal membranes, including ESCRTs, will also be discussed, as well as their diverse composition and fate, including degradation in lysosomes and secretion as exosomes. This review will also discuss how intralumenal membranes are hijacked by pathogenic agents during intoxication and infection, and what is the biochemical composition and function of the intra‐endosomal lumenal milieu. Finally, this review will allude to the size limitations imposed on intralumenal vesicle functions and speculate on the possible role of LBPA as calcium chelator in the acidic calcium stores of endo‐lysosomes.

Natural Antioxidants Improve the Vulnerability of Cardiomyocytes and Vascular Endothelial Cells under Stress Conditions: A Focus on Mitochondrial Quality Control

Cardiovascular disease has become one of the main causes of human death. In addition, many cardiovascular diseases are accompanied by a series of irreversible damages that lead to organ and vascular complications. In recent years, the potential therapeutic strategy of natural antioxidants in the treatment of cardiovascular diseases through mitochondrial quality control has received extensive attention. Mitochondria are the main site of energy metabolism in eukaryotic cells, including myocardial and vascular endothelial cells. Mitochondrial quality control processes ensure normal activities of mitochondria and cells by maintaining stable mitochondrial quantity and quality, thus protecting myocardial and endothelial cells against stress. Various stresses can affect mitochondrial morphology and function. Natural antioxidants extracted from plants and natural medicines are becoming increasingly common in the clinical treatment of diseases, especially in the treatment of cardiovascular diseases. Natural antioxidants can effectively protect myocardial and endothelial cells from stress-induced injury by regulating mitochondrial quality control, and their safety and effectiveness have been preliminarily verified. This review summarises the damage mechanisms of various stresses in cardiomyocytes and vascular endothelial cells and the mechanisms of natural antioxidants in improving the vulnerability of these cell types to stress by regulating mitochondrial quality control. This review is aimed at paving the way for novel treatments for cardiovascular diseases and the development of natural antioxidant drugs.

Effects of 9,10-phenanthrenequione on antioxidant indices and metabolite profiles in Takifugu obscurus plasma

Derived from polycyclic aromatic hydrocarbons (PAHs), oxygenated-PAHs (oxy-PAHs) may pose hazards to aquatic organisms, which remain largely unknown. Takifugu obscurus is an important anadromous fish species of high economic and ecological values. In the present study, T. obscurus was acutely exposed to 44.29 µg l-1 9,10-phenanthrenequione (9,10-PQ) for 96 h. Changes of antioxidant indices and metabolite profiles in plasma were compared between 9,10-PQ treatment and the control. The results showed that 9,10-PQ treatment significantly increased malondialdehyde (MDA) content during 6 to 96 h, increased superoxide dismutase (SOD) and catalase (CAT) activities at 6 h, but decreased them at 96 h. These results indicated that 9,10-PQ induced oxidative stress to fish. Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis revealed that four metabolic pathways were influenced in response to treatment with 9,10-PQ, including glycerophospholipid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, purine metabolism and sulfur metabolism. These pathways are associated with antioxidant mechanisms, biosynthesis of neurotransmitters and innate immune functions. Thus, the as-obtained results confirmed that 9,10-PQ induced oxidative stress and raised concerns of neurotoxicity and immunotoxicity to fish. Overall, the present study posed a high environmental risk of oxy-PAHs to aquatic ecosystems.

Physiological status and functional anatomy of zebra fish (Danio rerio) exposed to various levels of Ga3

Gallium (Ga) is one of the intermetallic elements that has been used in cancer treatment for a long time. However, Ga compounds are increasingly being used to make high-speed semiconductors and photoelectric devices. The current work investigated physiological and pathological changes in zebra fish (Danio rerio) exposed to various Ga³⁺ levels (0.55, 1.5, and 3.85 mg/L) over a 14-day test period. Decreases in oxygen consumption were significant (p < 0.05) for groups exposed to 3.85 Ga³⁺ mg/L; this was associated with the fusion of zebra fish gills lamellae. Serum biochemical changes (including aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase) were consistent with observations of damage to organelles within the hepatocytes at higher Ga³⁺ exposure levels (1.5 and 3.85 mg/L) in zebra fish. We propose <0.55 Ga³⁺ mg/L as a biologically safe concentration that can be used to establish water quality criteria for this teleost model.

Group 1 CD1-restricted T cells contribute to control of systemic Staphylococcus aureus infection

Staphylococcus aureus (SA) is the causative agent of both skin/soft tissue infections as well as invasive bloodstream infections. Though vaccines have been developed to target both humoral and T cell-mediated immune responses against SA, they have largely failed due to lack of protective efficacy. Group 1 CD1-restricted T cells recognize lipid rather than peptide antigens. Previously found to recognize lipids derived from cell wall of Mycobacterium tuberculosis (Mtb), these cells were associated with protection against Mtb infection in humans. Using a transgenic mouse model expressing human group 1 CD1 molecules (hCD1Tg), we demonstrate that group 1 CD1-restricted T cells can recognize SA-derived lipids in both immunization and infection settings. Systemic infection of hCD1Tg mice showed that SA-specific group 1 CD1-restricted T cell response peaked at 10 days post-infection, and hCD1Tg mice displayed significantly decreased kidney pathology at this time point compared with WT control mice. Immunodominant SA lipid antigens recognized by group 1 CD1-restricted T cells were comprised mainly of cardiolipin and phosphatidyl glycerol, with little contribution from lysyl-phosphatidyl glycerol which is a unique bacterial lipid not present in mammals. Group 1 CD1-restricted T cell lines specific for SA lipids also conferred protection against SA infection in the kidney after adoptive transfer. They were further able to effectively control SA replication in vitro through direct antigen presentation by group 1 CD1-expressing BMDCs. Together, our data demonstrate a previously unknown role for group 1 CD1-restricted SA lipid-specific T cells in the control of systemic MRSA infection.

Knockdown of TFAM in Tumor Cells Retarded Autophagic Flux through Regulating p53 Acetylation and PISD Expression

Mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA replication and transcription, which are essential for mitochondrial biogenesis. Previous studies reported that depleting mitochondrial functions by genetic deletion of TFAM impaired autophagic activities. However, the underlying mechanisms remain largely unknown. In the current study, we identified that knockdown of TFAM repressed the synthesis of autophagy bio-marker LC3-II in tumor cells and decreased the expression of phosphatidyl-serine decarboxylase (PISD). Besides, downregulation of PISD with siRNA reduced the level of LC3-II, indicating that depletion of TFAM retarded autophagy via inhibiting PISD expression. Furthermore, it was found that the tumor repressor p53 could stimulate the transcription and expression of PISD by binding the PISD enhancer. Additionally, the protein stability and transcriptional activity of p53 in TFAM knockdown tumor cells was attenuated, and this was associated with decreased acetylation, especially the acetylation of lysine 382 of p53. Finally, we identified that TFAM knockdown increased the NAD⁺/NADH ratio in tumor cells. This led to the upregulation of Sirtuin1 (SIRT1), a NAD-dependent protein deacetylase, to deacetylate p53 and attenuated its transcriptional activation on PISD. In summary, our study discovered a new mechanism regarding disturbed autophagy in tumor cells with mitochondrial dysfunction due to the depletion of TFAM.

Elevated Choline Kinase α-Mediated Choline Metabolism Supports the Prolonged Survival of TRAF3-Deficient B Lymphocytes

Specific deletion of the tumor suppressor TRAF3 from B lymphocytes in mice leads to the prolonged survival of mature B cells and expanded B cell compartments in secondary lymphoid organs. In the current study, we investigated the metabolic basis of TRAF3-mediated regulation of B cell survival by employing metabolomic, lipidomic, and transcriptomic analyses. We compared the polar metabolites, lipids, and metabolic enzymes of resting splenic B cells purified from young adult B cell-specific Traf3 ^-/- and littermate control mice. We found that multiple metabolites, lipids, and enzymes regulated by TRAF3 in B cells are clustered in the choline metabolic pathway. Using stable isotope labeling, we demonstrated that phosphocholine and phosphatidylcholine biosynthesis was markedly elevated in Traf3 ^-/- mouse B cells and decreased in TRAF3-reconstituted human multiple myeloma cells. Furthermore, pharmacological inhibition of choline kinase α, an enzyme that catalyzes phosphocholine synthesis and was strikingly increased in Traf3 ^-/- B cells, substantially reversed the survival phenotype of Traf3 ^-/- B cells both in vitro and in vivo. Taken together, our results indicate that enhanced phosphocholine and phosphatidylcholine synthesis supports the prolonged survival of Traf3 ^-/- B lymphocytes. Our findings suggest that TRAF3-regulated choline metabolism has diagnostic and therapeutic value for B cell malignancies with TRAF3 deletions or relevant mutations.

Mitochondrial dysfunction, AMPK activation and peroxisomal metabolism: A coherent scenario for non-canonical 3-methylglutaconic acidurias

The occurrence of 3-methylglutaconic aciduria (3-MGA) is a well understood phenomenon in leucine oxidation and ketogenesis disorders (primary 3-MGAs). In contrast, its genesis in non-canonical (secondary) 3-MGAs, a growing-up group of disorders encompassing more than a dozen of inherited metabolic diseases, is a mystery still remaining unresolved for three decades. To puzzle out this anthologic problem of metabolism, three clues were considered: (i) the variety of disorders suggests a common cellular target at the cross-road of metabolic and signaling pathways, (ii) the response to leucine loading test only discriminative for primary but not secondary 3-MGAs suggests these latter are disorders of extramitochondrial HMG-CoA metabolism as also attested by their failure to increase 3-hydroxyisovalerate, a mitochondrial metabolite accumulating only in primary 3-MGAs, (iii) the peroxisome is an extramitochondrial site possessing its own pool and displaying metabolism of HMG-CoA, suggesting its possible involvement in producing extramitochondrial 3-methylglutaconate (3-MG). Following these clues provides a unifying common basis to non-canonical 3-MGAs: constitutive mitochondrial dysfunction induces AMPK activation which, by inhibiting early steps in cholesterol and fatty acid syntheses, pipelines cytoplasmic acetyl-CoA to peroxisomes where a rise in HMG-CoA followed by local dehydration and hydrolysis may lead to 3-MGA yield. Additional contributors are considered, notably for 3-MGAs associated with hyperammonemia, and to a lesser extent in CLPB deficiency. Metabolic and signaling itineraries followed by the proposed scenario are essentially sketched, being provided with compelling evidence from the literature coming in their support.

Marek's Disease Virus Infection Induced Mitochondria Changes in Chickens

Mitochondria are crucial cellular organelles in eukaryotes and participate in many cell processes including immune response, growth development, and tumorigenesis. Marek’s disease (MD), caused by an avian alpha-herpesvirus Marek’s disease virus (MDV), is characterized with lymphomas and immunosuppression. In this research, we hypothesize that mitochondria may play roles in response to MDV infection. To test it, mitochondrial DNA (mtDNA) abundance and gene expression in immune organs were examined in two well-defined and highly inbred lines of chickens, the MD-susceptible line 7₂ and the MD-resistant line 6₃. We found that mitochondrial DNA contents decreased significantly at the transformation phase in spleen of the MD-susceptible line 7₂ birds in contrast to the MD-resistant line 6₃. The mtDNA-genes and the nucleus-genes relevant to mtDNA maintenance and transcription, however, were significantly up-regulated. Interestingly, we found that POLG2 might play a potential role that led to the imbalance of mtDNA copy number and gene expression alteration. MDV infection induced imbalance of mitochondrial contents and gene expression, demonstrating the indispensability of mitochondria in virus-induced cell transformation and subsequent lymphoma formation, such as MD development in chicken. This is the first report on relationship between virus infection and mitochondria in chicken, which provides important insights into the understanding on pathogenesis and tumorigenesis due to viral infection.

IL-2 augments the sorafenib-induced apoptosis in liver cancer by promoting mitochondrial fission and activating the JNK/TAZ pathway

Background

Sorafenib is the standard targeted drug used to treat hepatocellular carcinoma (HCC), but the therapeutic response between individuals varies markedly. Recently, cytokine-based immunotherapy has been a topic of intense discussion in the fight against cancer. The aim of this study was to explore whether cytokine IL-2 could augment the anti-tumour effects of sorafenib on HCC.

Methods

HepG2 and Huh7 cells were co-treated with sorafenib and IL-2 in vitro, and cellular viability and death were analysed through the MTT assay, TUNEL staining, LDH release assay, and western blotting. Mitochondrial function was measured via ELISA, immunofluorescence, and western blotting. Pathway blockers were used to establish the role of the JNK-TAZ pathways in regulating cancer cell phenotypes.

Results

Our data demonstrated that sorafenib treatment increased the HCC apoptotic rate, repressed cell proliferation, and inhibited migratory responses, and these effects were enhanced by IL-2 supplementation. Mechanistically, the combination of IL-2 and sorafenib interrupted mitochondrial energy metabolism by downregulating mitochondrial respiratory proteins. In addition, IL-2 and sorafenib co-treatment promoted mitochondrial dysfunction, as evidenced by the decreased mitochondrial potential, elevated mitochondrial ROS production, increased leakage of mitochondrial pro-apoptotic factors, and activation of the mitochondrial death pathway. A molecular investigation revealed that mitochondrial fission was required for the IL-2/sorafenib-mediated mitochondrial dysfunction. Mitochondrial fission was triggered by sorafenib and was largely amplified by IL-2 supplementation. Finally, we found that IL-2/sorafenib regulated mitochondrial fission via the JNK-TAZ pathways; blockade of the JNK-TAZ pathways abrogated the inhibitory effects of L-2/sorafenib on cancer survival, growth and mobility.

Conclusions

Altogether, these data strongly suggest that additional supplementation with IL-2 enhances the anti-tumour activity of sorafenib by promoting the JNK-TAZ-mitochondrial fission axis. This finding will pave the way for new treatment modalities to control HCC progression by optimizing sorafenib-based therapy.

Mitochondrial medicine in the omics era

Mitochondria are dynamic bioenergetic organelles whose maintenance requires around 1500 proteins from two genomes. Mutations in either the mitochondrial or nuclear genome can disrupt a plethora of cellular metabolic and homoeostatic functions. Mitochondrial diseases represent one of the most common and severe groups of inherited genetic disorders, characterised by clinical, biochemical, and genetic heterogeneity, diagnostic odysseys, and absence of disease-modifying curative therapies. This Review aims to discuss recent advances in mitochondrial biology and medicine arising from widespread use of high-throughput omics technologies, and also includes a broad discussion of emerging therapies for mitochondrial disease. New insights into both bioenergetic and biosynthetic mitochondrial functionalities have expedited the genetic diagnosis of primary mitochondrial disorders, and identified novel mitochondrial pathomechanisms and new targets for therapeutic intervention. As we enter this new era of mitochondrial medicine, underpinned by global unbiased approaches and multifaceted investigation of mitochondrial function, omics technologies will continue to shed light on unresolved mitochondrial questions, paving the way for improved outcomes for patients with mitochondrial diseases.

Lipidomic signature of serum from the rats exposed to alcohol for one year

Alcohol abuse and its related diseases are the major risk factors for human health. Although the mechanism of alcohol-related disorders has been widely investigated, serum metabolites associated with long-term alcohol intake have not been well explored. In this study, we aimed to investigate the profiles of serum metabolites and lipid species of rats chronically exposed to alcohol, which may be involved in the pathogenesis of alcohol-associated disease. An ¹H NMR-based metabolomics and Q-TOF/MS-based lipidomics approach were applied to investigate the profile of serum metabolites and lipid species of rats administrated daily with alcohol (12% vol/vol, 10 ml/kg per day, i.g.) for one year continuously. The rats administered with sterile water (10 ml/kg per day, i.g.) were used as control. We found that alcohol affected mostly the lipid species rather than small molecule metabolites in the serum of both female and male rats. Among the modified lipids, glycerophospholipid, sphingolipid and glycerolipids metabolism pathways were profoundly altered. The prominent changes in lipid profiles included diacylglycerol (DG), lysophosphatidylcholine (LysoPC), phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and triacylglycerol (TG). Moreover, fatty-acyl profile of lipids and total degree of unsaturation of fatty acid were also significantly altered by alcohol. The modified lipidomic profile may help to understand the pathogenesis of alcohol-associated diseases and also be of value for clinical evaluation of alcohol abuse, alcohol-associated disease diagnosis.

Effects of siRNA-dependent knock-down of cardiolipin synthase and tafazzin on mitochondria and proliferation of glioma cells

The mitochondrial phospholipid cardiolipin (CL) has been implicated with mitochondrial morphology, function, and cell proliferation. Changes in CL are often paralleled by changes in the lipid environment of mitochondria that may contribute to mitochondrial function and proliferation. This study aimed to separate the effects of CL content and CL composition from cellular free fatty acid distribution on bioenergetics and proliferation in C6 glioma cells. To this end, cardiolipin synthase and the CL remodelling enzyme, tafazzin, were knocked-down by siRNA in C6 cells. After 72 h of cultivation, we analysed CL composition by means of LC/MS/MS, distribution of cellular fatty acids by means of gas chromatography, and determined oxygen consumption and proliferation. Knock-down of cardiolipin synthase affected the cellular CL content in the presence of linoleic acid (LA) in the culture medium. Knock-down of tafazzin had no consequence with respect to the pattern of cellular fatty acids but caused a decrease in cell proliferation. It significantly changed the distribution of molecular CL species, increased CL content, decreased oxygen consumption, and decreased cell proliferation when cultured in the presence of linoleic acid (LA). The addition of linoleic acid to the culture medium caused significant changes in the pattern of cellular fatty acids and the composition of molecular CL species. These data suggest that tafazzin is required for efficient bioenergetics and for proliferation of glioma cells. Supplementation of fatty acids can be a powerful tool to direct specific changes in these parameters.

Regulation of mitochondrial structure and function by protein import: A current review

By generating the majority of a cell's ATP, mitochondria permit a vast range of reactions necessary for life. Mitochondria also perform other vital functions including biogenesis and assembly of iron-sulfur proteins, maintenance of calcium homeostasis, and activation of apoptosis. Accordingly, mitochondrial dysfunction has been linked with the pathology of many clinical conditions including cancer, type 2 diabetes, cardiomyopathy, and atherosclerosis. The ongoing maintenance of mitochondrial structure and function requires the import of nuclear-encoded proteins and for this reason, mitochondrial protein import is indispensible for cell viability. As mitochondria play central roles in determining if cells live or die, a comprehensive understanding of mitochondrial structure, protein import, and function is necessary for identifying novel drugs that may destroy harmful cells while rescuing or protecting normal ones to preserve tissue integrity. This review summarizes our current knowledge on mitochondrial architecture, mitochondrial protein import, and mitochondrial function. Our current comprehension of how mitochondrial functions maintain cell homeostasis and how cell death occurs as a result of mitochondrial stress are also discussed.

Lipidomics for studying metabolism

Many thousands of lipid species exist and their metabolism is interwoven via numerous pathways and networks. These networks can also change in response to cellular environment alterations, such as exercise or development of a disease. Measuring such alterations and understanding the pathways involved is crucial to fully understand cellular metabolism. Such demands have catalysed the emergence of lipidomics, which enables the large-scale study of lipids using the principles of analytical chemistry. Mass spectrometry, largely due to its analytical power and rapid development of new instruments and techniques, has been widely used in lipidomics and greatly accelerated advances in the field. This Review provides an introduction to lipidomics and describes some common, but important, cellular metabolic networks that can aid our understanding of metabolic pathways. Some representative applications of lipidomics for studying lipid metabolism and metabolic diseases are highlighted, as well as future applications for the use of lipidomics in studying metabolic pathways.

QIL1 mutation causes MICOS disassembly and early onset fatal mitochondrial encephalopathy with liver disease

Previously, we identified QIL1 as a subunit of mitochondrial contact site (MICOS) complex and demonstrated a role for QIL1 in MICOS assembly, mitochondrial respiration, and cristae formation critical for mitochondrial architecture (Guarani et al., 2015). Here, we identify QIL1 null alleles in two siblings displaying multiple clinical symptoms of early-onset fatal mitochondrial encephalopathy with liver disease, including defects in respiratory chain function in patient muscle. QIL1 absence in patients' fibroblasts was associated with MICOS disassembly, abnormal cristae, mild cytochrome c oxidase defect, and sensitivity to glucose withdrawal. QIL1 expression rescued cristae defects, and promoted re-accumulation of MICOS subunits to facilitate MICOS assembly. MICOS assembly and cristae morphology were not efficiently rescued by over-expression of other MICOS subunits in patient fibroblasts. Taken together, these data provide the first evidence of altered MICOS assembly linked with a human mitochondrial disease and confirm a central role for QIL1 in stable MICOS complex formation.

Looking Beyond Structure: Membrane Phospholipids of Skeletal Muscle Mitochondria

Skeletal muscle mitochondria are highly dynamic and are capable of tremendous expansion to meet cellular energetic demands. Such proliferation in mitochondrial mass requires a synchronized supply of enzymes and structural phospholipids. While transcriptional regulation of mitochondrial enzymes has been extensively studied, there is limited information on how mitochondrial membrane lipids are generated in skeletal muscle. Herein we describe how each class of phospholipids that constitute mitochondrial membranes are synthesized and/or imported, and summarize genetic evidence indicating that membrane phospholipid composition represents a significant modulator of skeletal muscle mitochondrial respiratory function. We also discuss how skeletal muscle mitochondrial phospholipids may mediate the effect of diet and exercise on oxidative metabolism.

Transient neonatal renal failure and massive polyuria in MEGDEL syndrome

BACKGROUND

MEGDEL (3-methylglutaconic aciduria with deafness, encephalopathy, and Leigh-like syndrome) syndrome is a mitochondrial disorder associated with recessive mutations in SERAC1.

OBJECTIVES

To report transient neonatal renal findings in MEGDEL syndrome.

RESULTS

This 7 year-old girl was the first child of consanguineous Turkish parents. She exhibited an acute neonatal deterioration with severe lactic acidosis and liver failure. Initial evaluation revealed massive polyuria and renal failure with 3-methylglutaconic aciduria. Symptoms and biological findings progressively improved with symptomatic treatment but lactic acidosis and high lactate to pyruvate ratio along with 3-methylglutaconic aciduria persisted. At 8 months of age, a subacute neurological degradation occurred with severe hypotonia, dystonia with extrapyramidal movements and failure to thrive. Brain MRI revealed basal ganglia lesions suggestive of Leigh syndrome. At 3 years of age, sensorineural deafness was documented. MEGDEL syndrome was further confirmed by the identification of an already reported homozygous mutation in SERAC1.

CONCLUSION

Transient neonatal polyuria and renal failure have not been reported to date in SERAC1 defective patients. Such neonatal kidney findings expand the clinical spectrum of MEGDEL syndrome.

Mitochondrial Dysfunction in Cancer and Neurodegenerative Diseases: Spotlight on Fatty Acid Oxidation and Lipoperoxidation Products

In several human diseases, such as cancer and neurodegenerative diseases, the levels of reactive oxygen species (ROS), produced mainly by mitochondrial oxidative phosphorylation, is increased. In cancer cells, the increase of ROS production has been associated with mtDNA mutations that, in turn, seem to be functional in the alterations of the bioenergetics and the biosynthetic state of cancer cells. Moreover, ROS overproduction can enhance the peroxidation of fatty acids in mitochondrial membranes. In particular, the peroxidation of mitochondrial phospholipid cardiolipin leads to the formation of reactive aldehydes, such as 4-hydroxynonenal (HNE) and malondialdehyde (MDA), which are able to react with proteins and DNA. Covalent modifications of mitochondrial proteins by the products of lipid peroxidation (LPO) in the course of oxidative cell stress are involved in the mitochondrial dysfunctions observed in cancer and neurodegenerative diseases. Such modifications appear to affect negatively mitochondrial integrity and function, in particular energy metabolism, adenosine triphosphate (ATP) production, antioxidant defenses and stress responses. In neurodegenerative diseases, indirect confirmation for the pathogenetic relevance of LPO-dependent modifications of mitochondrial proteins comes from the disease phenotypes associated with their genetic alterations.

PPARα in lysosomal biogenesis: A perspective

Lysosomes are membrane-bound vesicles containing hydrolytic enzymes, ubiquitously present in all eukaryotic cells. Classically considered to be central to the cellular waste management machinery, recent studies revealed the role of lysosomes in a wide array of cellular processes like, degradation, cellular development, programmed cell death, secretion, plasma membrane repair, nutritional responses, and lipid metabolism. We recently studied the regulation of TFEB, considered to be the master regulator of lysosomal biogenesis, by activation of peroxisomal proliferator activated receptor α (PPARα), one of the key regulators of lipid metabolism. In this article, we discuss how the recent finding could be put in to perspective with the previous findings that relate lysosomal biogenesis to lipid metabolism, and comment on the possibility of a bi-directional interplay between these two distinct cellular processes upon activation of PPARα.

Clinical, morphological, biochemical, imaging and outcome parameters in 21 individuals with mitochondrial maintenance defect related to FBXL4 mutations

FBXL4 deficiency is a recently described disorder of mitochondrial maintenance associated with a loss of mitochondrial DNA in cells. To date, the genetic diagnosis of FBXL4 deficiency has been established in 28 individuals. This paper retrospectively reviews proxy-reported clinical and biochemical findings and evaluates brain imaging, morphological and genetic data in 21 of those patients. Neonatal/early-onset severe lactic acidosis, muscular hypotonia, feeding problems and failure to thrive is the characteristic pattern at first presentation. Facial dysmorphic features are present in 67% of cases. Seven children died (mean age 37 months); 11 children were alive (mean age at follow-up 46 months), three children were lost to follow-up. All survivors developed severe psychomotor retardation. Brain imaging was non-specific in neonates but a later-onset, rapidly progressive brain atrophy was noted. Elevated blood lactate and metabolic acidosis were observed in all individuals; creatine kinase was elevated in 45% of measurements. Diagnostic workup in patient tissues and cells revealed a severe combined respiratory chain defect with a general decrease of enzymes associated with mitochondrial energy metabolism and a relative depletion of mitochondrial DNA content. Mutations were detected throughout the FBXL4 gene albeit with no clear delineation of a genotype-phenotype correlation. Treatment with "mitochondrial medications" did not prove effective. In conclusion, a clinical pattern of early-onset encephalopathy, persistent lactic acidosis, profound muscular hypotonia and typical facial dysmorphism should prompt initiation of molecular genetic analysis of FBXL4. Establishment of the diagnosis permits genetic counselling, prevents patients undergoing unhelpful diagnostic procedures and allows for accurate prognosis.

Successful management of Barth syndrome: a systematic review highlighting the importance of a flexible and multidisciplinary approach

This review describes and summarizes the available evidence related to the treatment and management of Barth syndrome. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards were used to identify articles published between December 2004 and January 2015. The Cochrane Population, Intervention, Control, Outcome, Study Design (PICOS) approach was used to guide the article selection and evaluation process. Of the 128 articles screened, 28 articles matched the systematic review inclusion criteria. The results of this review indicate the need for a flexible and multidisciplinary approach to manage the symptoms most commonly associated with Barth syndrome. It is recommended that a comprehensive care team should include individuals with Barth syndrome, their family members and caregivers, as well as medical, rehabilitative, nutritional, psychological, and educational professionals. The evidence for specific treatments, therapies, and techniques for individuals with Barth syndrome is currently lacking in both quality and quantity.

Spectrum of combined respiratory chain defects

Inherited disorders of mitochondrial energy metabolism form a large and heterogeneous group of metabolic diseases. More than 250 gene defects have been reported to date and this number continues to grow. Mitochondrial diseases can be grouped into (1) disorders of oxidative phosphorylation (OXPHOS) subunits and their assembly factors, (2) defects of mitochondrial DNA, RNA and protein synthesis, (3) defects in the substrate-generating upstream reactions of OXPHOS, (4) defects in relevant cofactors and (5) defects in mitochondrial homeostasis. Deficiency of more than one respiratory chain enzyme is a common finding. Combined defects are found in 49 % of the known disease-causing genes of mitochondrial energy metabolism and in 57 % of patients with OXPHOS defects identified in our diagnostic centre. Combined defects of complexes I, III, IV and V are typically due to deficiency of mitochondrial DNA replication, RNA metabolism or translation. Defects in cofactors can result in combined defects of various combinations, and defects of mitochondrial homeostasis can result in a generalised decrease of all OXPHOS enzymes. Noteworthy, identification of combined defects can be complicated by different degrees of severity of each affected enzyme. Furthermore, even defects of single respiratory chain enzymes can result in combined defects due to aberrant formation of respiratory chain supercomplexes. Combined OXPHOS defects have a great variety of clinical manifestations in terms of onset, course severity and tissue involvement. They can present as classical encephalomyopathy but also with hepatopathy, nephropathy, haematologic findings and Perrault syndrome in a subset of disorders.

Isotope-reinforced polyunsaturated fatty acids protect mitochondria from oxidative stress

Polyunsaturated fatty acid (PUFA) peroxidation is initiated by hydrogen atom abstraction at bis-allylic sites and sets in motion a chain reaction that generates multiple toxic products associated with numerous disorders. Replacement of bis-allylic hydrogens of PUFAs with deuterium atoms (D-PUFAs), termed site-specific isotope reinforcement, inhibits PUFA peroxidation and confers cell protection against oxidative stress. We demonstrate that structurally diverse deuterated PUFAs similarly protect against oxidative stress-induced injury in both yeast and mammalian (myoblast H9C2) cells. Cell protection occurs specifically at the lipid peroxidation step, as the formation of isoprostanes, immediate products of lipid peroxidation, is drastically suppressed by D-PUFAs. Mitochondrial bioenergetics function is a likely downstream target of oxidative stress and a subject of protection by D-PUFAs. Pretreatment of cells with D-PUFAs is shown to prevent inhibition of maximal uncoupler-stimulated respiration as well as increased mitochondrial uncoupling, in response to oxidative stress induced by agents with diverse mechanisms of action, including t-butylhydroperoxide, ethacrynic acid, or ferrous iron. Analysis of structure-activity relationships of PUFAs harboring deuterium at distinct sites suggests that there may be a mechanism supplementary to the kinetic isotope effect of deuterium abstraction off the bis-allylic sites that accounts for the protection rendered by deuteration of PUFAs. Paradoxically, PUFAs with partially deuterated bis-allylic positions that retain vulnerable hydrogen atoms (e.g., monodeuterated 11-D1-Lin) protect in a manner similar to that of PUFAs with completely deuterated bis-allylic positions (e.g., 11,11-D2-Lin). Moreover, inclusion of just a fraction of deuterated PUFAs (20-50%) in the total pool of PUFAs preserves mitochondrial respiratory function and confers cell protection. The results indicate that the therapeutic potential of D-PUFAs may derive from the preservation of mitochondrial function.

Clinical, biochemical, and genetic spectrum of seven patients with NFU1 deficiency

Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An increasingly recognized subgroup is caused by defective mitochondrial iron–sulfur (Fe–S) cluster biosynthesis, with defects in 13 genes being linked to human disease to date. Mutations in three of them, NFU1, BOLA3, and IBA57, affect the assembly of mitochondrial [4Fe–4S] proteins leading to an impairment of diverse mitochondrial metabolic pathways and ATP production. Patients with defects in these three genes present with lactic acidosis, hyperglycinemia, and reduced activities of respiratory chain complexes I and II, the four lipoic acid-dependent 2-oxoacid dehydrogenases and the glycine cleavage system (GCS). To date, five different NFU1 pathogenic variants have been reported in 15 patients from 12 families. We report on seven new patients from five families carrying compound heterozygous or homozygous pathogenic NFU1 mutations identified by candidate gene screening and exome sequencing. Six out of eight different disease alleles were novel and functional studies were performed to support the pathogenicity of five of them. Characteristic clinical features included fatal infantile encephalopathy and pulmonary hypertension leading to death within the first 6 months of life in six out of seven patients. Laboratory investigations revealed combined defects of pyruvate dehydrogenase complex (five out of five) and respiratory chain complexes I and II+III (four out of five) in skeletal muscle and/or cultured skin fibroblasts as well as increased lactate (five out of six) and glycine concentration (seven out of seven). Our study contributes to a better definition of the phenotypic spectrum associated with NFU1 mutations and to the diagnostic workup of future patients.

CLPB variants associated with autosomal-recessive mitochondrial disorder with cataract, neutropenia, epilepsy, and methylglutaconic aciduria

3-methylglutaconic aciduria (3-MGA-uria) is a nonspecific finding associated with mitochondrial dysfunction, including defects of oxidative phosphorylation. 3-MGA-uria is classified into five groups, of which one, type IV, is genetically heterogeneous. Here we report five children with a form of type IV 3-MGA-uria characterized by cataracts, severe psychomotor regression during febrile episodes, epilepsy, neutropenia with frequent infections, and death in early childhood. Four of the individuals were of Greenlandic descent, and one was North American, of Northern European and Asian descent. Through a combination of homozygosity mapping in the Greenlandic individuals and exome sequencing in the North American, we identified biallelic variants in the caseinolytic peptidase B homolog (CLPB). The causative variants included one missense variant, c.803C>T (p.Thr268Met), and two nonsense variants, c.961A>T (p.Lys321*) and c.1249C>T (p.Arg417*). The level of CLPB protein was markedly decreased in fibroblasts and liver of affected individuals. CLPB is proposed to function as a mitochondrial chaperone involved in disaggregation of misfolded proteins, resulting from stress such as heat denaturation.