Deficiency of cardiolipin synthase causes abnormal mitochondrial function and morphology in germ cells of Caenorhabditis elegans

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.

Regulation and functions of membrane lipids: Insights from Caenorhabditis elegans

The Caenorhabditis elegans plasma membrane is composed of glycerophospholipids and sphingolipids with a small cholesterol. The C. elegans obtain the majority of the membrane lipids by modifying fatty acids present in the bacterial diet. The metabolic pathways of membrane lipid biosynthesis are well conserved across the animal kingdom. In C. elegans CDP-DAG and Kennedy pathway produce glycerophospholipids. Meanwhile, the sphingolipids are synthesized through a different pathway. They have evolved remarkably diverse mechanisms to maintain membrane lipid homeostasis. For instance, the lipid bilayer stress operates to accomplish homeostasis during any perturbance in the lipid composition. Meanwhile, the PAQR-2/IGLR-2 complex works with FLD-1 to balance unsaturated to saturated fatty acids to maintain membrane fluidity. The loss of membrane lipid homeostasis is observed in many human genetic and metabolic disorders. Since C. elegans conserved such genes and pathways, it can be used as a model organism.

ATP synthase: Evolution, energetics, and membrane interactions

The synthesis of ATP, life’s “universal energy currency,” is the most prevalent chemical reaction in biological systems and is responsible for fueling nearly all cellular processes, from nerve impulse propagation to DNA synthesis. ATP synthases, the family of enzymes that carry out this endless task, are nearly as ubiquitous as the energy-laden molecule they are responsible for making. The F-type ATP synthase (F-ATPase) is found in every domain of life and has facilitated the survival of organisms in a wide range of habitats, ranging from the deep-sea thermal vents to the human intestine. Accordingly, there has been a large amount of work dedicated toward understanding the structural and functional details of ATP synthases in a wide range of species. Less attention, however, has been paid toward integrating these advances in ATP synthase molecular biology within the context of its evolutionary history. In this review, we present an overview of several structural and functional features of the F-type ATPases that vary across taxa and are purported to be adaptive or otherwise evolutionarily significant: ion channel selectivity, rotor ring size and stoichiometry, ATPase dimeric structure and localization in the mitochondrial inner membrane, and interactions with membrane lipids. We emphasize the importance of studying these features within the context of the enzyme’s particular lipid environment. Just as the interactions between an organism and its physical environment shape its evolutionary trajectory, ATPases are impacted by the membranes within which they reside. We argue that a comprehensive understanding of the structure, function, and evolution of membrane proteins—including ATP synthase—requires such an integrative approach.

HLH-30-dependent rewiring of metabolism during starvation in C. elegans

One of the most fundamental challenges for all living organisms is to sense and respond to alternating nutritional conditions in order to adapt their metabolism and physiology to promote survival and achieve balanced growth. Here, we applied metabolomics and lipidomics to examine temporal regulation of metabolism during starvation in wild‐type Caenorhabditis elegans and in animals lacking the transcription factor HLH‐30. Our findings show for the first time that starvation alters the abundance of hundreds of metabolites and lipid species in a temporal‐ and HLH‐30‐dependent manner. We demonstrate that premature death of hlh‐30 animals under starvation can be prevented by supplementation of exogenous fatty acids, and that HLH‐30 is required for complete oxidation of long‐chain fatty acids. We further show that RNAi‐mediated knockdown of the gene encoding carnitine palmitoyl transferase I (cpt‐1) only impairs survival of wild‐type animals and not of hlh‐30 animals. Strikingly, we also find that compromised generation of peroxisomes by prx‐5 knockdown renders hlh‐30 animals hypersensitive to starvation, which cannot be rescued by supplementation of exogenous fatty acids. Collectively, our observations show that mitochondrial functions are compromised in hlh‐30 animals and that hlh‐30 animals rewire their metabolism to largely depend on functional peroxisomes during starvation, underlining the importance of metabolic plasticity to maintain survival.

Phospholipid ebb and flow makes mitochondria go

Mitochondria, so much more than just being energy factories, also have the capacity to synthesize macromolecules including phospholipids, particularly cardiolipin (CL) and phosphatidylethanolamine (PE). Phospholipids are vital constituents of mitochondrial membranes, impacting the plethora of functions performed by this organelle. Hence, the orchestrated movement of phospholipids to and from the mitochondrion is essential for cellular integrity. In this review, we capture recent advances in the field of mitochondrial phospholipid biosynthesis and trafficking, highlighting the significance of interorganellar communication, intramitochondrial contact sites, and lipid transfer proteins in maintaining membrane homeostasis. We then discuss the physiological functions of CL and PE, specifically how they associate with protein complexes in mitochondrial membranes to support bioenergetics and maintain mitochondrial architecture.

Metabolic Alterations Caused by Defective Cardiolipin Remodeling in Inherited Cardiomyopathies

The heart is the most energy-consuming organ in the human body. In heart failure, the homeostasis of energy supply and demand is endangered by an increase in cardiomyocyte workload, or by an insufficiency in energy-providing processes. Energy metabolism is directly associated with mitochondrial redox homeostasis. The production of toxic reactive oxygen species (ROS) may overwhelm mitochondrial and cellular ROS defense mechanisms in case of heart failure. Mitochondria are essential cell organelles and provide 95% of the required energy in the heart. Metabolic remodeling, changes in mitochondrial structure or function, and alterations in mitochondrial calcium signaling diminish mitochondrial energy provision in many forms of cardiomyopathy. The mitochondrial respiratory chain creates a proton gradient across the inner mitochondrial membrane, which couples respiration with oxidative phosphorylation and the preservation of energy in the chemical bonds of ATP. Akin to other mitochondrial enzymes, the respiratory chain is integrated into the inner mitochondrial membrane. The tight association with the mitochondrial phospholipid cardiolipin (CL) ensures its structural integrity and coordinates enzymatic activity. This review focuses on how changes in mitochondrial CL may be associated with heart failure. Dysfunctional CL has been found in diabetic cardiomyopathy, ischemia reperfusion injury and the aging heart. Barth syndrome (BTHS) is caused by an inherited defect in the biosynthesis of cardiolipin. Moreover, a dysfunctional CL pool causes other types of rare inherited cardiomyopathies, such as Sengers syndrome and Dilated Cardiomyopathy with Ataxia (DCMA). Here we review the impact of cardiolipin deficiency on mitochondrial functions in cellular and animal models. We describe the molecular mechanisms concerning mitochondrial dysfunction as an incitement of cardiomyopathy and discuss potential therapeutic strategies.

Cardiolipin is required for membrane docking of mitochondrial ribosomes and protein synthesis

The mitochondrial inner membrane contains a unique phospholipid known as cardiolipin (CL), which stabilises the protein complexes embedded in the membrane and supports its overall structure. Recent evidence indicates that the mitochondrial ribosome may associate with the inner membrane to facilitate co-translational insertion of the hydrophobic oxidative phosphorylation (OXPHOS) proteins into the inner membrane. We generated three mutant knockout cell lines for the CL biosynthesis gene Crls1 to investigate the effects of CL loss on mitochondrial protein synthesis. Reduced CL levels caused altered mitochondrial morphology and transcriptome-wide changes that were accompanied by uncoordinated mitochondrial translation rates and impaired respiratory chain supercomplex formation. Aberrant protein synthesis was caused by impaired formation and distribution of mitochondrial ribosomes. Reduction or loss of CL resulted in divergent mitochondrial and endoplasmic reticulum stress responses. We show that CL is required to stabilise the interaction of the mitochondrial ribosome with the membrane via its association with OXA1 (also known as OXA1L) during active translation. This interaction facilitates insertion of newly synthesised mitochondrial proteins into the inner membrane and stabilises the respiratory supercomplexes.

Metabolic Alterations in Inherited Cardiomyopathies

The normal function of the heart relies on a series of complex metabolic processes orchestrating the proper generation and use of energy. In this context, mitochondria serve a crucial role as a platform for energy transduction by supplying ATP to the varying demand of cardiomyocytes, involving an intricate network of pathways regulating the metabolic flux of substrates. The failure of these processes results in structural and functional deficiencies of the cardiac muscle, including inherited cardiomyopathies. These genetic diseases are characterized by cardiac structural and functional anomalies in the absence of abnormal conditions that can explain the observed myocardial abnormality, and are frequently associated with heart failure. Since their original description, major advances have been achieved in the genetic and phenotype knowledge, highlighting the involvement of metabolic abnormalities in their pathogenesis. This review provides a brief overview of the role of mitochondria in the energy metabolism in the heart and focuses on metabolic abnormalities, mitochondrial dysfunction, and storage diseases associated with inherited cardiomyopathies.

Cardiolipin is essential for early embryonic viability and mitochondrial integrity of neurons in mammals

Cardiolipin (CL) is a hallmark phospholipid of mitochondria and plays a significant role in maintaining the mitochondrial structure and functions. Despite the physiological importance of CL, mutant organisms, yeast, Arabidopsis, C elegans, and Drosophila, which lack CL synthase (Crls1) gene and consequently are deprived of CL, are viable. Here we report conditional Crls1-deficient mice using targeted insertion of loxP sequences flanking the functional domain of CRLS1 enzyme. Homozygous null mutant mice exhibited early embryonic lethality at the peri-implantation stage. We generated neuron-specific Crls1 knockout (cKO) mice by crossing with Camk2α-Cre mice. Neuronal loss and gliosis were gradually manifested in the forebrains, where CL levels were significantly decreased. In the surviving neurons, malformed mitochondria with bubble-like or onion-like inner membrane structures were observed. We showed decreased supercomplex assembly and reduced enzymatic activities of electron transport chain complexes in the forebrain of cKO mice, resulting in affected mitochondrial calcium dynamics, a slower rate of Ca²⁺ uptake and a smaller calcium retention capacity. These observations clearly demonstrate indispensable roles of CL as well as of Crls1 gene in mammals.

Alterations in lipid metabolism of spinal cord linked to amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of upper and lower motor neurons leading to muscle paralysis and death. While a link between dysregulated lipid metabolism and ALS has been proposed, lipidome alterations involved in disease progression are still understudied. Using a rodent model of ALS overexpressing mutant human Cu/Zn-superoxide dismutase gene (SOD1-G93A), we performed a comparative lipidomic analysis in motor cortex and spinal cord tissues of SOD1-G93A and WT rats at asymptomatic (~70 days) and symptomatic stages (~120 days). Interestingly, lipidome alterations in motor cortex were mostly related to age than ALS. In contrast, drastic changes were observed in spinal cord of SOD1-G93A 120d group, including decreased levels of cardiolipin and a 6-fold increase in several cholesteryl esters linked to polyunsaturated fatty acids. Consistent with previous studies, our findings suggest abnormal mitochondria in motor neurons and lipid droplets accumulation in aberrant astrocytes. Although the mechanism leading to cholesteryl esters accumulation remains to be established, we postulate a hypothetical model based on neuroprotection of polyunsaturated fatty acids into lipid droplets in response to increased oxidative stress. Implicated in the pathology of other neurodegenerative diseases, cholesteryl esters appear as attractive targets for further investigations.

Multi-modal regulation of C. elegans hermaphrodite spermatogenesis by the GLD-1-FOG-2 complex

Proper germ cell sex determination in Caenorhabditis nematodes requires a network of RNA-binding proteins (RBPs) and their target mRNAs. In some species, changes in this network enabled limited XX spermatogenesis, and thus self-fertility. In C. elegans, one of these selfing species, the global sex-determining gene tra-2 is regulated in germ cells by a conserved RBP, GLD-1, via the 3' untranslated region (3'UTR) of its transcript. A C. elegans-specific GLD-1 cofactor, FOG-2, is also required for hermaphrodite sperm fate, but how it modifies GLD-1 function is unknown. Germline feminization in gld-1 and fog-2 null mutants has been interpreted as due to cell-autonomous elevation of TRA-2 translation. Consistent with the proposed role of FOG-2 in translational control, the abundance of nearly all GLD-1 target mRNAs (including tra-2) is unchanged in fog-2 mutants. Epitope tagging reveals abundant TRA-2 expression in somatic tissues, but an undetectably low level in wild-type germ cells. Loss of gld-1 function elevates germline TRA-2 expression to detectable levels, but loss of fog-2 function does not. A simple quantitative model of tra-2 activity constrained by these results can successfully sort genotypes into normal or feminized groups. Surprisingly, fog-2 and gld-1 activity enable the sperm fate even when GLD-1 cannot bind to the tra-2 3' UTR. This suggests the GLD-1-FOG-2 complex regulates uncharacterized sites within tra-2, or other mRNA targets. Finally, we quantify the RNA-binding capacities of dominant missense alleles of GLD-1 that act genetically as "hyper-repressors" of tra-2 activity. These variants bind RNA more weakly in vitro than does wild-type GLD-1. These results indicate that gld-1 and fog-2 regulate germline sex via multiple interactions, and that our understanding of the control and evolution of germ cell sex determination in the C. elegans hermaphrodite is far from complete.

Cell Biology of the Mitochondrion

Mitochondria are best known for harboring pathways involved in ATP synthesis through the tricarboxylic acid cycle and oxidative phosphorylation. Major advances in understanding these roles were made with Caenorhabditiselegans mutants affecting key components of the metabolic pathways. These mutants have not only helped elucidate some of the intricacies of metabolism pathways, but they have also served as jumping off points for pharmacology, toxicology, and aging studies. The field of mitochondria research has also undergone a renaissance, with the increased appreciation of the role of mitochondria in cell processes other than energy production. Here, we focus on discoveries that were made using C. elegans, with a few excursions into areas that were studied more thoroughly in other organisms, like mitochondrial protein import in yeast. Advances in mitochondrial biogenesis and membrane dynamics were made through the discoveries of novel functions in mitochondrial fission and fusion proteins. Some of these functions were only apparent through the use of diverse model systems, such as C. elegans Studies of stress responses, exemplified by mitophagy and the mitochondrial unfolded protein response, have also benefitted greatly from the use of model organisms. Recent developments include the discoveries in C. elegans of cell autonomous and nonautonomous pathways controlling the mitochondrial unfolded protein response, as well as mechanisms for degradation of paternal mitochondria after fertilization. The evolutionary conservation of many, if not all, of these pathways ensures that results obtained with C. elegans are equally applicable to studies of human mitochondria in health and disease.

Lipid and Carbohydrate Metabolism in Caenorhabditis elegans

Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology. Caenorhabditis elegans eat bacteria, which consist of lipids, carbohydrates, and proteins that are broken down during digestion into fatty acids, simple sugars, and amino acid precursors. With these nutrients, C. elegans synthesizes a wide range of metabolites that are required for development and behavior. In this review, we outline lipid and carbohydrate structures as well as biosynthesis and breakdown pathways that have been characterized in C. elegans We bring attention to functional studies using mutant strains that reveal physiological roles for specific lipids and carbohydrates during development, aging, and adaptation to changing environmental conditions.

Unraveling the expression of genes involved in the biosynthesis pathway of cardiolipin and phosphatidylethanolamine in Salmonella Hadar grown under static magnetic field 200 mT

We aimed in this work to evaluate the effect of static magnetic field 200 mT (SMF) on the expression of genes involved in the biosynthetic pathway of cardiolipin: g3pd, plsB, cdsA, pgsA, pgpA, cls and phosphatidylethanolamine: pssA and psd in Salmonella enterica subsp enterica serovar Hadar. Bacteria were exposed to a SMF during 3, 6 and 9 h. RNA extraction was followed by Reverse Transcriptase Polymerase Chain Reaction RT-PCR. The relative quantification of mRNA expression levels using 16S rRNA doesn't change during the time exposure. RT-PCR was done for two exposure experiments. The gene expression using RT-PCR present no significant difference in case of plsB, cdsA, pgpA, pgsA and psd genes during the different exposure times. However, a significant increase was observed in the expression of g3pd and pssA genes after 6 h and for cls gene after 3 h of exposure, but any variation was notified after 9 h of exposure. So we can conclude from this study that cls, g3pd and pssA genes are required in the adaptation of Salmonella Hadar to SMF.

Barth syndrome cardiomyopathy

Barth syndrome (BTHS) is an inherited form of cardiomyopathy, caused by a mutation within the gene encoding the mitochondrial transacylase tafazzin. Tafazzin is involved in the biosynthesis of the unique phospholipid cardiolipin (CL), which is almost exclusively found in mitochondrial membranes. CL directly interacts with a number of essential protein complexes in the mitochondrial membranes including the respiratory chain, mitochondrial metabolite carriers, and proteins, involved in shaping mitochondrial morphology. Here we describe, how in BTHS CL deficiency causes changes in the morphology of mitochondria, structural changes in the respiratory chain, decreased respiration, and increased generation of reactive oxygen species. A large number of cellular and animal models for BTHS have been established to elucidate how mitochondrial dysfunction induces sarcomere disorganization and reduced contractility, resulting in dilated cardiomyopathy in vivo.

Restoration of Mitochondrial Cardiolipin Attenuates Cardiac Damage in Swine Renovascular Hypertension

Background

Renovascular hypertension (RVH) impairs cardiac structure and left ventricular (LV) function, but whether mitochondrial injury is implicated in RVH‐induced myocardial damage and dysfunction has not been defined. We hypothesized that cardiac remodeling in swine RVH is partly attributable to cardiac mitochondrial injury.

Methods and Results

After 12 weeks of hypercholesterolemic (HC)‐RVH or control (n=14 each), pigs were treated for another 4 weeks with vehicle or with the mitochondrial‐targeted peptide (MTP), Bendavia (0.1 mg/kg subcutaneously, 5 days/week), which stabilizes mitochondrial inner‐membrane cardiolipin (n=7 each). Cardiac function was subsequently assessed by multidetector‐computed tomography and oxygenation by blood‐oxygen‐level–dependent magnetic resonance imaging. Cardiolipin content, mitochondrial biogenesis, as well as sarcoplasmic‐reticulum calcium cycling, myocardial tissue injury, and coronary endothelial function were assessed ex vivo. Additionally, mitochondrial cardiolipin content, oxidative stress, and bioenergetics were assessed in rat cardiomyocytes incubated with tert‐butyl hydroperoxide (tBHP) untreated or treated with MTP. Chronic mitoprotection in vivo restored cardiolipin content and mitochondrial biogenesis. Thapsigargin‐sensitive sarcoplasmic reticulum Ca²⁺‐ATPase activity that declined in HC‐RVH normalized in MTP‐treated pigs. Mitoprotection also improved LV relaxation (E/A ratio) and ameliorated cardiac hypertrophy, without affecting blood pressure or systolic function. Myocardial remodeling and coronary endothelial function improved only in MTP‐treated pigs. In tBHP‐treated cardiomyocytes, mitochondrial targeting attenuated a fall in cardiolipin content and bioenergetics.

Conclusions

Chronic mitoprotection blunted myocardial hypertrophy, improved LV relaxation, and attenuated myocardial cellular and microvascular remodeling, despite sustained HC‐RVH, suggesting that mitochondrial injury partly contributes to hypertensive cardiomyopathy.

Cardiolipin or MTCH2 can serve as tBID receptors during apoptosis

During apoptosis, proapoptotic BAX and BAK trigger mitochondrial outer membrane (MOM) permeabilization by a mechanism that is not yet fully understood. BH3-only proteins such as tBID, together with lipids of the MOM, are thought to play a key role in BAX and BAK activation. In particular, cardiolipin (CL) has been shown to stimulate tBID-induced BAX activation in vitro. However, it is still unclear whether this process also relies on CL in the cell, or whether it is more dependent on MTCH2, a proposed receptor for tBID present in the MOM. To address this issue, we deleted both alleles of cardiolipin synthase in human HCT116 cells by homologous recombination, which resulted in a complete absence of CL. The CL-deficient cells were fully viable in glucose but displayed impaired oxidative phosphorylation and an inability to grow in galactose. Using these cells, we found that CL was not required for either tBID-induced BAX activation, or for apoptosis in response to treatment with TRAIL. Downregulation of MTCH2 in HCT116 cells also failed to prevent recruitment of tBID to mitochondria in apoptotic conditions. However, when both CL and MTCH2 were depleted, a significant reduction in tBID recruitment was observed, suggesting that in HCT116 cells, CL and MTCH2 can have redundant functions in this process.

Activation of the endoplasmic reticulum unfolded protein response by lipid disequilibrium without disturbed proteostasis in vivo

The Mediator is a conserved transcriptional coregulator complex required for eukaryotic gene expression. In Caenorhabditis elegans, the Mediator subunit mdt-15 is essential for the expression of genes involved in fatty acid metabolism and ingestion-associated stress responses. mdt-15 loss of function causes defects in reproduction and mobility and shortens lifespan. In the present study, we find that worms with mutated or depleted mdt-15 (mdt-15 worms) exhibit decreased membrane phospholipid desaturation, especially in phosphatidylcholine. Accordingly, mdt-15 worms exhibit disturbed endoplasmic reticulum (ER) homeostasis, as indicated by a constitutively activated ER unfolded protein response (UPR(ER)). Activation of this stress response is only partially the consequence of reduced membrane lipid desaturation, implicating other mdt-15-regulated processes in maintaining ER homeostasis. Interestingly, mdt-15 inactivation or depletion of the lipid metabolism enzymes stearoyl-CoA-desaturases (SCD) and S-adenosyl methionine synthetase (sams-1) activates the UPR(ER) without promoting misfolded protein aggregates. Moreover, these worms exhibit wild-type sensitivity to chemically induced protein misfolding, and they do not display synthetic lethality with mutations in UPR(ER) genes, which cause protein misfolding. Therefore, the constitutively activated UPR(ER) in mdt-15, SCD, and sams-1 worms is not the consequence of proteotoxic stress but likely is the direct result of changes in ER membrane fluidity and composition. Together, our data suggest that the UPR(ER) is induced directly upon membrane disequilibrium and thus monitors altered ER homeostasis.

Metabolism and function of mitochondrial cardiolipin

Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes. Indeed, cardiolipin is a universal component of mitochondria in all eukaryotes. It has a unique dimeric structure comprised of two phosphatidic acid residues linked by a glycerol bridge, which gives rise to unique physicochemical properties. Cardiolipin plays an important role in the structural organization and the function of mitochondrial membranes. In this article, we review the literature on cardiolipin biology, focusing on the most important discoveries of the past decade. Specifically, we describe the formation, the migration, and the degradation of cardiolipin and we discuss how cardiolipin affects mitochondrial function. We also give an overview of the various phenotypes of cardiolipin deficiency in different organisms.

APOOL is a cardiolipin-binding constituent of the Mitofilin/MINOS protein complex determining cristae morphology in mammalian mitochondria

Mitochondrial cristae morphology is highly variable and altered under numerous pathological conditions. The protein complexes involved are largely unknown or only insufficiently characterized. Using complexome profiling we identified apolipoprotein O (APOO) and apolipoprotein O-like protein (APOOL) as putative components of the Mitofilin/MINOS protein complex which was recently implicated in determining cristae morphology. We show that APOOL is a mitochondrial membrane protein facing the intermembrane space. It specifically binds to cardiolipin in vitro but not to the precursor lipid phosphatidylglycerol. Overexpression of APOOL led to fragmentation of mitochondria, a reduced basal oxygen consumption rate, and altered cristae morphology. Downregulation of APOOL impaired mitochondrial respiration and caused major alterations in cristae morphology. We further show that APOOL physically interacts with several subunits of the MINOS complex, namely Mitofilin, MINOS1, and SAMM50. We conclude that APOOL is a cardiolipin-binding component of the Mitofilin/MINOS protein complex determining cristae morphology in mammalian mitochondria. Our findings further assign an intracellular role to a member of the apolipoprotein family in mammals.

Recombinant expression, biophysical characterization, and cardiolipin-induced changes of two Caenorhabditis elegans cytochrome c proteins

Cytochrome c (cyt c) is one of the most widely studied biomolecules, but not much is known about this protein from nematodes. Recombinant expression of Caenorhabditis elegans CYC-2.1 and CYC-2.2 allowed for detailed characterization of their structural features, redox properties, stabilities, and interactions with cardiolipin (CL)-containing liposomes. Using a variety of spectroscopic tools, we show that CYC-2.1 and CYC-2.2 adopt a globular α-helical fold with His/Met heme ligation. The longer CYC-2.2 has a lower thermodynamic stability than CYC-2.1 and lacks His residues to misligate to the heme in the protein's denatured state. Both C. elegans proteins bind to CL-containing liposomes, and these interactions promote the proteins' peroxidase activity but to a much greater degree for CYC-2.2. Dye-to-heme distance distributions from time-resolved fluorescence resonance energy transfer in bimane-labeled CYC-2.1 and CYC-2.2 revealed similar populations of extended and compact conformers for CL-bound proteins, suggesting that their distinct peroxidase activities in the presence of CL arise from differences in the local heme environments for the two polypeptide ensembles. Without inhibition from His misligation, a less stable and more prone to unfolding CYC-2.2 allows for better access of substrates to the heme and thus exhibits higher peroxidase activity. Similar features of the conformational ensembles of CYC-2.1 and CYC-2.2 to those of mammalian cyt c suggest that C. elegans proteins, particularly the former, could serve as useful models for examining the mechanism of cyt c-CL interactions in live organisms.

Phosphatidylserine decarboxylase 1 (Psd1) promotes mitochondrial fusion by regulating the biophysical properties of the mitochondrial membrane and alternative topogenesis of mitochondrial genome maintenance protein 1 (Mgm1)

BACKGROUND

Phosphatidylethanolamine is proposed to regulate mitochondrial fusion, but its mechanism of action is unknown.

RESULTS

Decreasing phosphatidylethanolamine reduces the rate of lipid mixing and the biogenesis of Mgm1, a mitochondrial fusion protein.

CONCLUSION

Psd1 regulates the lipid and protein machineries of mitochondrial fusion.

SIGNIFICANCE

Understanding how lipid metabolism regulates mitochondrial dynamics will reveal its role in cellular functions such as apoptosis and autophagy. Non-bilayer-forming lipids such as cardiolipin, phosphatidic acid, and phosphatidylethanolamine (PE) are proposed to generate negative membrane curvature, promoting membrane fusion. However, the mechanism by which lipids regulate mitochondrial fusion remains poorly understood. Here, we show that mitochondrial-localized Psd1, the key yeast enzyme that synthesizes PE, is required for proper mitochondrial morphology and fusion. Yeast cells lacking Psd1 exhibit fragmented and aggregated mitochondria with impaired mitochondrial fusion during mating. More importantly, we demonstrate that a reduction in PE reduces the rate of lipid mixing during fusion of liposomes with lipid compositions reflecting the mitochondrial membrane. This suggests that the mitochondrial fusion defect in the Δpsd1 strain could be due to the altered biophysical properties of the mitochondrial membrane, resulting in reduced fusion kinetics. The Δpsd1 strain also has impaired mitochondrial activity such as oxidative phosphorylation and reduced mitochondrial ATP levels which are due to a reduction in mitochondrial PE. The loss of Psd1 also impairs the biogenesis of s-Mgm1, a protein essential for mitochondrial fusion, further exacerbating the mitochondrial fusion defect of the Δpsd1 strain. Increasing s-Mgm1 levels in Δpsd1 cells markedly reduced mitochondrial aggregation. Our results demonstrate that mitochondrial PE regulates mitochondrial fusion by regulating the biophysical properties of the mitochondrial membrane and by enhancing the biogenesis of s-Mgm1. While several proteins are required to orchestrate the intricate process of membrane fusion, we propose that specific phospholipids of the mitochondrial membrane promote fusion by enhancing lipid mixing kinetics and by regulating the action of profusion proteins.

Gemcitabine versus Modified Gemcitabine: a review of several promising chemical modifications

Gemcitabine, an anticancer agent which acts against a wide range of solid tumors, is known to be rapidly deaminated in blood to the inactive metabolite 2',2'-difluorodeoxyuridine and to be rapidly excreted by the urine. Moreover, many cancers develop resistance against this drug, such as loss of transporters and kinases responsible for the first phosphorylation step. To increase its therapeutic levels, gemcitabine is administered at high doses (1000 mg/m(2)) causing side effects (neutropenia, nausea, and so forth). To improve its metabolic stability and cytotoxic activity and to limit the phenomena of resistance many alternatives have emerged, such as the synthesis of prodrugs. Modifying an anticancer agent is not new; paclitaxel or ara-C has been subjected to such changes. This review summarizes the various chemical modifications that can be found in the 4-(N)- and 5'-positions of gemcitabine. They can provide (i) a protection against deamination, (ii) a better storage and (iii) a prolonged release in the cell, (iv) a possible use in the case of deoxycytidine kinase deficiency, and (v) transporter deficiency. These new gemcitabine-based sysems have the potential to improve the clinical outcome of a chemotherapy strategy.

αSynuclein and Mitochondrial Dysfunction: A Pathogenic Partnership in Parkinson's Disease?

Parkinson's Disease (PD) is a complex, chronic, progressive, and debilitating neurodegenerative disorder. Neither a cure nor effective long-term therapy exist and the lack of knowledge of the molecular mechanisms responsible for PD development is a major impediment to therapeutic advances. The protein αSynuclein is a central component in PD pathogenesis yet its cellular targets and mechanism of toxicity remains unknown. Mitochondrial dysfunction is also a common theme in PD patients and this review explores the strong possibility that αSynuclein and mitochondrial dysfunction have an inter-relationship responsible for underlying the disease pathology. Amplifying cycles of mitochondrial dysfunction and αSynuclein toxicity can be envisaged, with either being the disease-initiating factor yet acting together during disease progression. Multiple potential mechanisms exist in which mitochondrial dysfunction and αSynuclein could interact to exacerbate their neurodegenerative properties. Candidates discussed within this review include autophagy, mitophagy, mitochondrial dynamics/fusion/fission, oxidative stress and reactive oxygen species, endoplasmic reticulum stress, calcium, nitrosative stress and αSynuclein Oligomerization.

Function and Regulation of Lipid Biology in Caenorhabditis elegans Aging

Rapidly expanding aging populations and a concomitant increase in the prevalence of age-related diseases are global health problems today. Over the past three decades, a large body of work has led to the identification of genes and regulatory networks that affect longevity and health span, often benefiting from the tremendous power of genetics in vertebrate and invertebrate model organisms. Interestingly, many of these factors appear linked to lipids, important molecules that participate in cellular signaling, energy metabolism, and structural compartmentalization. Despite the putative link between lipids and longevity, the role of lipids in aging remains poorly understood. Emerging data from the model organism Caenorhabditis elegans suggest that lipid composition may change during aging, as several pathways that influence aging also regulate lipid metabolism enzymes; moreover, some of these enzymes apparently play key roles in the pathways that affect the rate of aging. By understanding how lipid biology is regulated during C. elegans aging, and how it impacts molecular, cellular, and organismal function, we may gain insight into novel ways to delay aging using genetic or pharmacological interventions. In the present review we discuss recent insights into the roles of lipids in C. elegans aging, including regulatory roles played by lipids themselves, the regulation of lipid metabolic enzymes, and the roles of lipid metabolism genes in the pathways that affect aging.

Emerging roles for specific fatty acids in developmental processes

Animals synthesize a vast range of fatty acids serving diverse cellular functions. The roles of specific fatty acids in early development are just beginning to be characterized. In the March 15, 2012, issue of Genes & Development, Kniazeva and colleagues (pp. 554-566) describe how the particular combination of a branched chain fatty acid and an acyl-CoA synthetase is required for critical cellular processes during early embryogenesis in Caenorhabditis elegans.