Specific degradation of phosphatidylglycerol is necessary for proper mitochondrial morphology and function

LPGAT1 controls MEGDEL syndrome by coupling phosphatidylglycerol remodeling with mitochondrial transport

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

A patatin-like phospholipase is important for mitochondrial function in malaria parasites

Plasmodium parasites rely on a functional electron transport chain (ETC) within their mitochondrion for proliferation, and compounds targeting mitochondrial functions are validated antimalarials. Here, we localize Plasmodium falciparum patatin-like phospholipase 2 (PfPNPLA2, PF3D7_1358000) to the mitochondrion and reveal that disruption of the PfPNPLA2 gene impairs asexual replication. PfPNPLA2-null parasites are hypersensitive to proguanil and inhibitors of the mitochondrial ETC, including atovaquone. In addition, PfPNPLA2-deficient parasites show reduced mitochondrial respiration and reduced mitochondrial membrane potential, indicating that disruption of PfPNPLA2 leads to a defect in the parasite ETC. Lipidomic analysis of the mitochondrial phospholipid cardiolipin (CL) reveals that loss of PfPNPLA2 is associated with a moderate shift toward shorter-chained and more saturated CL species, implying a contribution of PfPNPLA2 to CL remodeling. PfPNPLA2-deficient parasites display profound defects in gametocytogenesis, underlining the importance of a functional mitochondrial ETC during both the asexual and sexual development of the parasite. IMPORTANCE For their proliferation within red blood cells, malaria parasites depend on a functional electron transport chain (ETC) within their mitochondrion, which is the target of several antimalarial drugs. Here, we have used gene disruption to identify a patatin-like phospholipase, PfPNPLA2, as important for parasite replication and mitochondrial function in Plasmodium falciparum. Parasites lacking PfPNPLA2 show defects in their ETC and become hypersensitive to mitochondrion-targeting drugs. Furthermore, PfPNPLA2-deficient parasites show differences in the composition of their cardiolipins, a unique class of phospholipids with key roles in mitochondrial functions. Finally, we demonstrate that parasites devoid of PfPNPLA2 have a defect in gametocyte maturation, underlining the importance of a functional ETC for parasite transmission to the mosquito vector.

Mitochondrial Complex I Disruption Causes Broad Reorchestration of Plant Lipidome Including Chloroplast Lipids

Mitochondrial complex I (CI) plays a crucial role in oxidising NADH generated by the metabolism (including photorespiration) and thereby participates in the mitochondrial electron transfer chain feeding oxidative phosphorylation that generates ATP. However, CI mutations are not lethal in plants and cause moderate phenotypes, and therefore CI mutants are instrumental to examine consequences of mitochondrial homeostasis disturbance on plant cell metabolisms and signalling. To date, the consequences of CI disruption on the lipidome have not been examined. Yet, in principle, mitochondrial dysfunction should impact on lipid synthesis through chloroplasts (via changes in photorespiration, redox homeostasis, and N metabolism) and the endoplasmic reticulum (ER) (via perturbed mitochondrion-ER crosstalk). Here, we took advantage of lipidomics technology (by LC-MS), phospholipid quantitation by ³¹P-NMR, and total lipid quantitation to assess the impact of CI disruption on leaf, pollen, and seed lipids using three well-characterised CI mutants: CMSII in N. sylvestris and both ndufs4 and ndufs8 in Arabidopsis. Our results show multiple changes in cellular lipids, including galactolipids (chloroplastic), sphingolipids, and ceramides (synthesised by ER), suggesting that mitochondrial homeostasis is essential for the regulation of whole cellular lipidome via specific signalling pathways. In particular, the observed modifications in phospholipid and sphingolipid/ceramide molecular species suggest that CI activity controls phosphatidic acid-mediated signalling.

Two Different Phospholipases C, Isc1 and Pgc1, Cooperate To Regulate Mitochondrial Function

The absence of Isc1, the yeast homologue of mammalian neutral sphingomyelinase type 2, leads to severe mitochondrial dysfunction. We show that the deletion of another type C phospholipase, the phosphatidylglycerol (PG)-specific phospholipase Pgc1, rescues this defect. Phosphatidylethanolamine (PE) levels and cytochrome c oxidase activity, which were reduced in isc1Δ cells, were restored to wild-type levels in the pgc1Δ isc1Δ mutant. The Pgc1 substrate PG inhibited the in vitro activities of Isc1 and the phosphatidylserine decarboxylase Psd1, an enzyme crucial for PE biosynthesis. We also identify a mechanism by which the balance between the current demand for PG and its consumption is controlled. We document that the product of PG hydrolysis, diacylglycerol, competes with the substrate of PG-phosphate synthase, Pgs1, and thereby inhibits the biosynthesis of excess PG. This feedback loop does not work in the absence of Pgc1, which catalyzes PG degradation. Finally, Pgc1 activity is partially inhibited by products of Isc1-mediated hydrolysis. The described functional interconnection of the two phospholipases contributes significantly to lipid homeostasis throughout the cellular architecture. IMPORTANCE In eukaryotic cells, mitochondria are constantly adapting to changes in the biological activity of the cell, i.e., changes in nutrient availability and environmental stresses. We propose a model in which this adaptation is mediated by lipids. Specifically, we show that mitochondrial phospholipids regulate the biosynthesis of cellular sphingolipids and vice versa. To do this, lipids move by free diffusion, which does not require energy and works under any condition. This model represents a simple way for the cell to coordinate mitochondrial structure and performance with the actual needs of overall cellular metabolism. Its simplicity makes it a universally applicable principle of cellular regulation.

Temporal lipid profiling in the progression from acute to chronic heart failure in mice and ischemic human hearts

BACKGROUND AND AIMS

Myocardial infarction (MI) is a leading cause of heart failure (HF). After MI, lipids undergo several phasic changes implicated in cardiac repair if inflammation resolves on time. However, if inflammation continues, that leads to end stage HF progression and development. Numerous studies have analyzed the traditional risk factors; however, temporal lipidomics data for human and animal models are limited. Thus, we aimed to obtain sequential lipid profiling from acute to chronic HF.

METHODS

Here, we report the comprehensive lipidome of the hearts from diseased and healthy subjects. To induce heart failure in mice, we used a non-reperfused model of coronary ligation, and MI was confirmed by echocardiography and histology, then temporal kinetics of lipids in different tissues (heart, spleen, kidney), and plasma was quantitated from heart failure mice and compared with naïve controls. For lipid analysis in mouse and human samples, untargeted liquid chromatography-linear trap quadrupole orbitrap mass spectrometry (LC-LTQ-Orbitrap MS) was performed.

RESULTS

In humans, multivariate analysis revealed distinct cardiac lipid profiles between healthy and ischemic subjects, with 16 lipid species significantly downregulated by 5-fold, mainly phosphatidylethanolamines (PE), in the ischemic heart. In contrast, PE levels were markedly increased in mouse tissues and plasma in chronic MI, indicating possible cardiac remodeling. Further, fold change analysis revealed site-specific lipid biomarkers for acute and chronic HF. A significant decrease in sulfatides (SHexCer (34:1; 2O)) and sphingomyelins (SM (d18:1/16:0)) was observed in mouse tissues and plasma in chronic HF.

CONCLUSIONS

Overall, a significant decreased lipidome in human ischemic LV and differential lipid metabolites in the transition of acute to chronic HF with inter-organ communication could provide novel insights into targeting integrative pathways for the early diagnosis or development of novel therapeutics to delay/prevent HF.

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

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

Mitochondrial Phospholipid Homeostasis Is Regulated by the i-AAA Protease PaIAP and Affects Organismic Aging

Mitochondria are ubiquitous organelles of eukaryotic organisms with a number of essential functions, including synthesis of iron-sulfur clusters, amino acids, lipids, and adenosine triphosphate (ATP). During aging of the fungal aging model Podospora anserina, the inner mitochondrial membrane (IMM) undergoes prominent morphological alterations, ultimately resulting in functional impairments. Since phospholipids (PLs) are key components of biological membranes, maintenance of membrane plasticity and integrity via regulation of PL biosynthesis is indispensable. Here, we report results from a lipidomic analysis of isolated mitochondria from P. anserina that revealed an age-related reorganization of the mitochondrial PL profile and the involvement of the i-AAA protease PaIAP in proteolytic regulation of PL metabolism. The absence of PaIAP enhances biosynthesis of characteristic mitochondrial PLs, leads to significant alterations in the acyl composition of the mitochondrial signature PL cardiolipin (CL), and induces mitophagy. These alterations presumably cause the lifespan increase of the PaIap deletion mutant under standard growth conditions. However, PaIAP is required at elevated temperatures and for degradation of superfluous CL synthase PaCRD1 during glycolytic growth. Overall, our study uncovers a prominent role of PaIAP in the regulation of PL homeostasis in order to adapt membrane plasticity to fluctuating environmental conditions as they occur in nature.

NMR identification of a conserved Drp1 cardiolipin-binding motif essential for stress-induced mitochondrial fission

Mitochondria form tubular networks that undergo coordinated cycles of fission and fusion. Emerging evidence suggests that a direct yet unresolved interaction of the mechanoenzymatic GTPase dynamin-related protein 1 (Drp1) with mitochondrial outer membrane-localized cardiolipin (CL), externalized under stress conditions including mitophagy, catalyzes essential mitochondrial hyperfragmentation. Here, using a comprehensive set of structural, biophysical, and cell biological tools, we have uncovered a CL-binding motif (CBM) conserved between the Drp1 variable domain (VD) and the unrelated ADP/ATP carrier (AAC/ANT) that intercalates into the membrane core to effect specific CL interactions. CBM mutations that weaken VD-CL interactions manifestly impair Drp1-dependent fission under stress conditions and induce "donut" mitochondria formation. Importantly, VD membrane insertion and GTP-dependent conformational rearrangements mediate only transient CL nonbilayer topological forays and high local membrane constriction, indicating that Drp1-CL interactions alone are insufficient for fission. Our studies establish the structural and mechanistic bases of Drp1-CL interactions in stress-induced mitochondrial fission.

Untargeted Lipidomics for Determining Cellular and Subcellular Responses in Zebrafish (Danio rerio) Liver Cells Following Exposure to Complex Mixtures in U.S. Streams

Surface waters often contain a variety of chemical contaminants potentially capable of producing adverse outcomes in both humans and wildlife due to impacts from industrial, urban, and agricultural activity. Here, we report the results of a zebrafish liver (ZFL) cell-based lipidomics approach to assess the potential ecotoxicological effects of complex contaminant mixtures using water collected from eight impacted streams across the United States mainland and Puerto Rico. We initially characterized the ZFL lipidome using high resolution mass spectrometry, resulting in the annotation of 508 lipid species covering 27 classes. We then identified lipid changes induced by all streamwater samples (nonspecific stress indicators) as well as those unique to water samples taken from specific streams. Subcellular impacts were classified based on organelle-specific lipid changes, including increased lipid saturation (endoplasmic reticulum stress), elevated bis(monoacylglycero)phosphate (lysosomal overload), decreased ubiquinone (mitochondrial dysfunction), and elevated ether lipids (peroxisomal stress). Finally, we demonstrate how these results can uniquely inform environmental monitoring and risk assessments of surface waters.

Activation of Cytochrome C Peroxidase Function Through Coordinated Foldon Loop Dynamics upon Interaction with Anionic Lipids

Cardiolipin (CL) is a mitochondrial anionic lipid that plays important roles in the regulation and signaling of mitochondrial apoptosis. CL peroxidation catalyzed by the assembly of CL-cytochrome c (cyt c) complexes at the inner mitochondrial membrane is a critical checkpoint. The structural changes in the protein, associated with peroxidase activation by CL and different anionic lipids, are not known at a molecular level. To better understand these peripheral protein-lipid interactions, we compare how phosphatidylglycerol (PG) and CL lipids trigger cyt c peroxidase activation, and correlate functional differences to structural and motional changes in membrane-associated cyt c. Structural and motional studies of the bound protein are enabled by magic angle spinning solid state NMR spectroscopy, while lipid peroxidase activity is assayed by mass spectrometry. PG binding results in a surface-bound state that preserves a nativelike fold, which nonetheless allows for significant peroxidase activity, though at a lower level than binding its native substrate CL. Lipid-specific differences in peroxidase activation are found to correlate to corresponding differences in lipid-induced protein mobility, affecting specific protein segments. The dynamics of omega loops C and D are upregulated by CL binding, in a way that is remarkably controlled by the protein:lipid stoichiometry. In contrast to complete chemical denaturation, membrane-induced protein destabilization reflects a destabilization of select cyt c foldons, while the energetically most stable helices are preserved. Our studies illuminate the interplay of protein and lipid dynamics in the creation of lipid peroxidase-active proteolipid complexes implicated in early stages of mitochondrial apoptosis.

Biophysical and Lipidomic Biomarkers of Cardiac Remodeling Post-Myocardial Infarction in Humans

Few studies have analyzed the potential of biophysical parameters as markers of cardiac remodeling post-myocardial infarction (MI), particularly in human hearts. Fourier transform infrared spectroscopy (FTIR) illustrates the overall changes in proteins, nucleic acids and lipids in a single signature. The aim of this work was to define the FTIR and lipidomic pattern for human left ventricular remodeling post-MI. A total of nine explanted hearts from ischemic cardiomyopathy patients were collected. Samples from the right ventricle (RV), left ventricle (LV) and infarcted left ventricle (LV INF) were subjected to biophysical (FTIR and differential scanning calorimetry, DSC) and lipidomic (liquid chromatography-high-resolution mass spectrometry, LC-HRMS) studies. FTIR evidenced deep alterations in the myofibers, extracellular matrix proteins, and the hydric response of the LV INF compared to the RV or LV from the same subject. The lipid and esterified lipid FTIR bands were enhanced in LV INF, and both lipid indicators were tightly and positively correlated with remodeling markers such as collagen, lactate, polysaccharides, and glycogen in these samples. Lipidomic analysis revealed an increase in several species of sphingomyelin (SM), hexosylceramide (HexCer), and cholesteryl esters combined with a decrease in glycerophospholipids in the infarcted tissue. Our results validate FTIR indicators and several species of lipids as useful markers of left ventricular remodeling post-MI in humans.

The lipid droplet protein Pgc1 controls the subcellular distribution of phosphatidylglycerol

The biosynthesis of yeast phosphatidylglycerol (PG) takes place in the inner mitochondrial membrane. Outside mitochondria, the abundance of PG is low. Here, we present evidence that the subcellular distribution of PG is maintained by the locally controlled enzymatic activity of the PG-specific phospholipase, Pgc1. A fluorescently labeled Pgc1 protein accumulates on the surface of lipid droplets (LD). We show, however, that LD are not only dispensable for Pgc1-mediated PG degradation, but do not even host any phospholipase activity of Pgc1. Our in vitro assays document the capability of LD-accumulated Pgc1 to degrade PG upon entry to the membranes of the endoplasmic reticulum, mitochondria and even of artificial phospholipid vesicles. Fluorescence recovery after photobleaching analysis confirms the continuous exchange of GFP-Pgc1 within the individual LD in situ, suggesting that a steady-state equilibrium exists between LD and membranes to regulate the immediate phospholipase activity of Pgc1. In this model, LD serve as a storage place and shelter Pgc1, preventing its untimely degradation, while both phospholipase activity and degradation of the enzyme occur in the membranes.

The transfer of specific mitochondrial lipids and proteins to lipid droplets contributes to proteostasis upon stress and aging in the eukaryotic model system Saccharomyces cerevisiae

Originally Lipid droplets (LDs) were considered as being droplets for lipid storage only. Increasing evidence, however, demonstrates that LDs fulfill a pleiotropy of additional functions. Among them is the modulation of protein as well as lipid homeostasis. Under unfavorable pro-oxidative conditions, proteins can form aggregates which may exceed the overall proteolytic capacity of the proteasome. After stress termination LDs can adjust and support the removal of these aggregates. Additionally, LDs interact with mitochondria, specifically take over certain proteins and thus prevent apoptosis. LDs, which are loaded with these harmful proteins, are subsequently eliminated via lipophagy. Recently it was demonstrated that this autophagic process is a modulator of longevity. LDs do not only eliminate potentially dangerous proteins, but they are also able to prevent lipotoxicity by storing specific lipids. In the present study we used the model organism Saccharomyces cerevisiae to compare the proteome as well as lipidome of mitochondria and LDs under different conditions: replicative aging, stress and apoptosis. In this context we found an accumulation of proteins at LDs, supporting the role of LDs in proteostasis. Additionally, the composition of main lipid classes such as phosphatidylcholines, phosphatidylethanolamines, phosphatidylinositols, phosphatidylglycerols, triacylglycerols, ceramides, phosphatidic acids and ergosterol of LDs and mitochondria changed during stress conditions and aging.

Prognostic biomarkers of cervical squamous cell carcinoma identified via plasma metabolomics

Cervical cancer is the second most common female malignancy worldwide. The metabolic profile of plasma associated with the prognosis of cervical cancer remains poorly understood. In this cross-sectional study, plasma samples were collected from three groups of patients with CSCC, namely primary patients before treatment (BT group), patients with a poor prognosis (PP group, including patients with distant metastasis and local recurrence), and patients with a good prognosis within two years after the first treatment (GP group). The plasma metabolomics was conducted to detect the dynamic changes of metabolites via ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry. Multivariate analyses, including principle component, partial least square-discriminant, and orthogonal projection to latent structure-discriminant analyses, were performed to compare each pair of the three groups. The differential metabolites were identified by comparison of the exact m/z values and mass spectrometry (MS)/MS spectra with the structural information of the metabolites obtained from the Human Metabolome Database (http://www.hmdb.ca/) and LIPID MAPS (http://www.lipidmaps.org/). To screen for potential markers, receiver operating characteristic curve analysis of the differential metabolites. Finally, thirty plasma samples were collected from each group. Multivariate analyses showed that 31 metabolites were significantly different among the 3 groups studied. Of those, the 5 metabolites phosphatidyl choline (15:0/16:0), phosphatidyl glycerol (12:0/13:0), actosylceramide (d18:1/16:0), D-Maltose, and phthalic acid, with an area under the curve above 0.75, were identified as potential biomarkers. The present findings provide evidence for biomarkers to monitor prognosis of patients with CSCC, which may help in better managing the disease.

Lipidomic Alterations in the Mitochondria of Aged Parkin Null Mice Relevant to Autophagy

Mitochondrial quality control is important in neurological diseases, but in genetic Parkinson’s disease caused by mutations in PINK and parkin mitochondrial degradation through autophagy is crucial. Reductions in autophagy and mitophagy are implicated in aging, age related diseases and Parkinson. The parkin null mice (PK-KO) show only a subtle phenotype, apparent with age or with stressors. We have studied the changes in the lipidomic composition of the mitochondrial membranes isolated from the brains of young and old PK-KO mice and compared them to wild type in order to determine possible implications for Parkinson’s disease pathology. We observed an increase in the levels of phosphatidylethanolamine in the young PK-KO mice that is lost in the old and correlate to changes in the phosphatidylserine decarboxylase. PK-KO old mice mitochondria showed lower phosphatidylglicerol and phosphatidylinositol levels and higher levels of some forms of hydroxylated ceramides. Regarding cardiolipins there were changes in the degree of saturation mainly with age. The lipidomic composition discriminates between the study groups using partial least square discriminant analysis. We discuss the relevance of the lipid changes for the autophagic activity, the mitophagy, the mitochondrial activity and the Parkinson’s disease pathology in absence of parkin.

Schizosaccharomyces pombe cardiolipin synthase is part of a mitochondrial fusion protein regulated by intron retention

Cardiolipin (CL) is a unique lipid component of mitochondria in all eukaryotes. It is important for the architecture of mitochondrial membranes and for mitochondrial dynamics. CL also creates a highly specific microenvironment of mitochondrial protein machineries. CL biosynthetic pathway is, however, only partially characterized in the fission yeast Schizosaccharomyces pombe. Here we show that CL synthase is an essential protein in S. pombe. It is encoded by the ORF SPAC22A12.08c as a C terminal part of a tandem fusion protein together with a mitochondrial hydrolase of unknown function. Expression of S. pombe CL synthase is able to complement deletion of the CRD1 gene of Saccharomyces cerevisiae and, vice versa, S. cerevisiae CRD1 gene complements deletion of S. pombe SPAC22A12.08c. The proper expression of CL synthase and its partner in the tandem protein, the mitochondrial hydrolase, is regulated at the level of alternate intron splicing. The first part of the SPAC22A12.08c fusion protein could be translated from both major SPAC22A12.08c derived mRNAs, with and without intron IV. Functional CL synthase, however, is produced only from the minor SPAC22A12.08c derived mRNA that has intron IV retained. Thus, intron retention is a novel mechanism for the differential expression of two proteins that evolved as a fusion protein and are under the control of the same promoter.

The Enzymatic Core of the Parkinson's Disease-Associated Protein LRRK2 Impairs Mitochondrial Biogenesis in Aging Yeast

Mitochondrial dysfunction is a prominent trait of cellular decline during aging and intimately linked to neuronal degeneration during Parkinson's disease (PD). Various proteins associated with PD have been shown to differentially impact mitochondrial dynamics, quality control and function, including the leucine-rich repeat kinase 2 (LRRK2). Here, we demonstrate that high levels of the enzymatic core of human LRRK2, harboring GTPase as well as kinase activity, decreases mitochondrial mass via an impairment of mitochondrial biogenesis in aging yeast. We link mitochondrial depletion to a global downregulation of mitochondria-related gene transcripts and show that this catalytic core of LRRK2 localizes to mitochondria and selectively compromises respiratory chain complex IV formation. With progressing cellular age, this culminates in dissipation of mitochondrial transmembrane potential, decreased respiratory capacity, ATP depletion and generation of reactive oxygen species. Ultimately, the collapse of the mitochondrial network results in cell death. A point mutation in LRRK2 that increases the intrinsic GTPase activity diminishes mitochondrial impairment and consequently provides cytoprotection. In sum, we report that a downregulation of mitochondrial biogenesis rather than excessive degradation of mitochondria underlies the reduction of mitochondrial abundance induced by the enzymatic core of LRRK2 in aging yeast cells. Thus, our data provide a novel perspective for deciphering the causative mechanisms of LRRK2-associated PD pathology.

Metabolomic profiling for the identification of potential biomarkers involved in a laboratory azole resistance in Candida albicans

Candida albicans, one of the most common fungal pathogens, is responsible for several yeast infections in human hosts, being resistant to classically used antifungal drugs, such as azole drugs. Multifactorial and multistep alterations are involved in the azole resistance in Candida albicans. In this study, a FCZ-resistant C. albicans strain was obtained by serial cultures of a FCZ-susceptible C. albicans strain in incrementally increasing concentrations of FCZ. We performed an integrated profile of different classes of molecules related to azole resistance in C. albicans by combining several mass-spectrometry based methodologies. The comparative metabolomic study was performed with the sensitive and resistant strains of C.albicans to identify metabolites altered during the development of resistance to fluconazole, while the intervention strains and non-intervention strains of C.albicans to identify metabolites altered involved in cross-resistant to azole drugs. Our analysis of the different metabolites identified molecules mainly involved in metabolic processes such as amino acid metabolism, tricarboxylic acid cycle and phospholipid metabolism. We also compared the phospholipid composition of each group, revealing that the relative content of phospholipids significantly changed during the development of resistance to azole drugs. According with these results, we hypothesized that the metabolism shift might contribute to azole drugs resistance in C.albicans from multifactorial alterations. Our result paves the way to understand processes underlying the resistance to azole drugs in C. albicans, providing the basis for developing new antifungal drugs.

Mitochondrial dynamics: The dynamin superfamily and execution by collusion

Distinct dynamin superfamily GTPases catalyze the constant fission and fusion of the elaborate mitochondrial networks that navigate the eukaryotic cytoplasm. Long believed to be the singular handiwork of dynamin-related protein 1 (Drp1), a cytosolic family member that transiently localizes to the mitochondrial surface, the execution of mitochondrial fission is now arguably believed to entail membrane remodeling events that are initiated upstream of Drp1 by ER-associated cytoskeletal networks and completed downstream by the prototypical dynamin, dynamin 2 (Dyn2). Recent developments in the field have also placed a sharp focus on the membrane microenvironment around the division apparatus and the potential facilitatory role of specific lipids in mitochondrial fission. Here, I will review current progress, as well as highlight the most visible gaps in knowledge, in elucidating the varied functions of the dynamin superfamily in the coordinated events of mitochondrial fission and fusion. The essential roles of protein and lipid cofactors are also highlighted.

Misregulation of a DDHD Domain-containing Lipase Causes Mitochondrial Dysfunction in Yeast

The DDHD domain-containing proteins, which belong to the intracellular phospholipase A1 (iPLA1) family, have been predicted to be involved in phospholipid metabolism, lipid trafficking, membrane turnover, and signaling. Defective cardiolipin (CL), phosphatidylethanolamine, and phosphatidylglycerol remodeling cause Barth syndrome and mitochondrial dysfunction. Here, we report that Yor022c is a Ddl1 (DDHD domain-containing lipase 1) that hydrolyzes CL, phosphatidylethanolamine, and phosphatidylglycerol. Ddl1 has been implicated in the remodeling of mitochondrial phospholipids and CL degradation. Our data also suggested that the accumulation of monolysocardiolipin is deleterious to the cells. We show that Aft1 and Aft2 transcription factors antagonistically regulate the DDL1 gene. This study reveals that the misregulation of DDL1 by Aft1/2 transcription factors alters CL metabolism and causes mitochondrial dysfunction in the cells. In humans, mutations in the DDHD1 and DDHD2 genes cause specific types of hereditary spastic paraplegia (SPG28 and SPG54, respectively), and the yeast DDL1-defective strain produces similar phenotypes of hereditary spastic paraplegia (mitochondrial dysfunction and defects in lipid metabolism). Therefore, the DDL1-defective strain could be a good model system for understanding hereditary spastic paraplegia.