The role and characterization of phospholipase A1 in mediating lysophosphatidylcholine synthesis in Trypanosoma brucei

Phospholipases A and Lysophospholipases in protozoan parasites

Phospholipases (PLs) and Lysophospholipases (LysoPLs) are a diverse group of esterases responsible for phospholipid or lysophospholipid hydrolysis. They are involved in several biological processes, including lipid catabolism, modulation of the immune response and membrane maintenance. PLs are classified depending on their site of hydrolysis as PLA1, PLA2, PLC and PLD. In many pathogenic microorganisms, from bacteria to fungi, PLAs and LysoPLs have been described as critical virulence and/or pathogenicity factors. In protozoan parasites, a group containing major human and animal pathogens, growing literature show that PLAs and LysoPLs are also involved in the host infection. Their ubiquitous presence and role in host-pathogen interactions make them particularly interesting to study. In this review, we summarize the literature on PLAs and LysoPLs in several protozoan parasites of medical relevance, and discuss the growing interest for them as potential drug and vaccine targets.

Mass Spectrometry Imaging of In Vitro Cryptosporidium parvum-Infected Cells and Host Tissue

Cryptosporidium parvum is a zoonotic-relevant parasite belonging to the phylum Alveolata (subphylum Apicomplexa). One of the most zoonotic-relevant etiologies of cryptosporidiosis is the species C. parvum, infecting humans, cattle and wildlife. C. parvum-infected intestinal mucosa as well as host cells infected in vitro have not yet been the subject of extensive biochemical investigation. Efficient treatment options or vaccines against cryptosporidiosis are currently not available. Human cryptosporidiosis is currently known as a neglected poverty-related disease (PRD), being potentially fatal in young children or immunocompromised patients. In this study, we used a combination of atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) and liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to determine and locate molecular biomarkers in in vitro C. parvum-infected host cells as well as parasitized neonatal calf intestines. Sections of C. parvum-infected and non-infected host cell pellets and infected intestines were examined to determine potential biomarkers. Human ileocecal adenocarcinoma cells (HCT-8) were used as a suitable in vitro host cell system. More than a thousand different molecular signals were found in both positive- and negative-ion mode, which were significantly increased in C. parvum-infected material. A database search in combination with HPLC-MS/MS experiments was employed for the structural verification of markers. Our results demonstrate some overlap between the identified markers and data obtained from earlier studies on other apicomplexan parasites. Statistically relevant biomarkers were imaged in cell layers of C. parvum-infected and non-infected host cells with 5 µm pixel size and in bovine intestinal tissue with 10 µm pixel size. This allowed us to substantiate their relevance once again. Taken together, the present approach delivers novel metabolic insights on neglected cryptosporidiosis affecting mainly children in developing countries.

A novel lipase with dual localisation in Trypanosoma brucei

Phospholipases are esterases involved in lipid catabolism. In pathogenic micro-organisms (bacteria, fungi, parasites) they often play a critical role in virulence and pathogenicity. A few phospholipases (PL) have been characterised so far at the gene and protein level in unicellular parasites including African trypanosomes (AT). They could play a role in different processes such as host–pathogen interaction, antigenic variation, intermediary metabolism. By mining the genome database of AT we found putative new phospholipase candidate genes and here we provided biochemical evidence that one of these has lipolytic activity. This protein has a unique non-canonical glycosome targeting signal responsible for its dual localisation in the cytosol and the peroxisomes-related organelles named glycosomes. We also show that this new phospholipase is excreted by these pathogens and that antibodies directed against this protein are generated during an experimental infection with T. brucei gambiense, a subspecies responsible for infection in humans. This feature makes this protein a possible tool for diagnosis.

Lysophosphatidic Acid Signaling in Diabetic Nephropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid present in most tissues and body fluids. LPA acts through specific LPA receptors (LPAR1 to LPAR6) coupled with G protein. LPA binds to receptors and activates multiple cellular signaling pathways, subsequently exerting various biological functions, such as cell proliferation, migration, and apoptosis. LPA also induces cell damage through complex overlapping pathways, including the generation of reactive oxygen species, inflammatory cytokines, and fibrosis. Several reports indicate that the LPA–LPAR axis plays an important role in various diseases, including kidney disease, lung fibrosis, and cancer. Diabetic nephropathy (DN) is one of the most common diabetic complications and the main risk factor for chronic kidney diseases, which mostly progress to end-stage renal disease. There is also growing evidence indicating that the LPA–LPAR axis also plays an important role in inducing pathological alterations of cell structure and function in the kidneys. In this review, we will discuss key mediators or signaling pathways activated by LPA and summarize recent research findings associated with DN.

Substrate specificity of the neutral sphingomyelinase from Trypanosoma brucei

The kinetoplastid parasite Trypanosoma brucei causes African trypanosomiasis in both humans and animals. Infections place a significant health and economic burden on developing nations in sub-Saharan Africa, but few effective anti-parasitic treatments are currently available. Hence, there is an urgent need to identify new leads for drug development. The T. brucei neutral sphingomyelinase (TbnSMase) was previously established as essential to parasite survival, consequently being identified as a potential drug target. This enzyme may catalyse the single route to sphingolipid catabolism outside the T. brucei lysosome. To obtain new insight into parasite sphingolipid catabolism, the substrate specificity of TbnSMase was investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Recombinant TbnSMase was shown to degrade sphingomyelin, inositol-phosphoceramide and ethanolamine-phosphoceramide sphingolipid substrates, consistent with the sphingolipid complement of the parasites. TbnSMase also catabolized ceramide-1-phosphate, but was inactive towards sphingosine-1-phosphate. The broad-range specificity of this enzyme towards sphingolipid species is a unique feature of TbnSMase. Additionally, ESI-MS/MS analysis revealed previously uncharacterized activity towards lyso-phosphatidylcholine despite the enzyme's inability to degrade phosphatidylcholine. Collectively, these data underline the enzyme's importance in choline homoeostasis and the turnover of sphingolipids in T. brucei.

Recent advances in trypanosomatid research: genome organization, expression, metabolism, taxonomy and evolution

Unicellular flagellates of the family Trypanosomatidae are obligatory parasites of invertebrates, vertebrates and plants. Dixenous species are aetiological agents of a number of diseases in humans, domestic animals and plants. Their monoxenous relatives are restricted to insects. Because of the high biological diversity, adaptability to dramatically different environmental conditions, and omnipresence, these protists have major impact on all biotic communities that still needs to be fully elucidated. In addition, as these organisms represent a highly divergent evolutionary lineage, they are strikingly different from the common 'model system' eukaryotes, such as some mammals, plants or fungi. A number of excellent reviews, published over the past decade, were dedicated to specialized topics from the areas of trypanosomatid molecular and cell biology, biochemistry, host-parasite relationships or other aspects of these fascinating organisms. However, there is a need for a more comprehensive review that summarizing recent advances in the studies of trypanosomatids in the last 30 years, a task, which we tried to accomplish with the current paper.

Role of lysophosphatidic acid and its receptors in the kidney

Lysophosphatidic acid (LPA) is a bioactive phospholipid that can exert diverse biological effects in various diseased states of the kidney by activating at least six cognate G protein-coupled receptors and its complex network of heterotrimeric G proteins. In many models of acute and chronic kidney injury, pathological elevations in LPA promotes abnormal changes in renal tubular epithelial cell architecture by activating apoptotic signaling, recruits immune cells to the site of injury, and stimulates profibrotic signaling by increasing gene transcription. In renal cancers, LPA can promote vascular cell proliferation and tumor cell invasion. In this review, a summary will be provided to describe the involvement of LPA, its synthetic enzymes, and its associated receptors in normal and diseased kidneys. Further elucidation of the LPA system may open new doors in developing a lipid-receptor therapeutic platform for kidney diseases.

Lipidomics and anti-trypanosomatid chemotherapy

BACKGROUND

Trypanosomatids such as Leishmania, Trypanosoma brucei and Trypanosoma cruzi belong to the order Kinetoplastida and are the source of many significant human and animal diseases. Current treatment is unsatisfactory and is compromised by the rising appearance of drug resistant parasites. Novel and more effective chemotherapeutics are urgently needed to treat and prevent these devastating diseases, which relies on the identification of essential, parasite specific targets that are absent in the host. Lipids constitute essential components of the cell and carry out multiple critical functions from building blocks of biological membranes to regulatory roles in signal transduction, organellar biogenesis, energy storage, and virulence. The recent technological advances of lipidomics has facilitated the broadening of our knowledge in the field of cellular lipid content, structure, functions, and metabolic pathways.

MAIN BODY

This review highlights the application of lipidomics (i) in the characterization of the lipidome of kinetoplastid parasites or of their subcellular structure(s), (ii) in the identification of unique lipid species or metabolic pathways that can be targeted for novel drug therapies, (iii) as an analytic tool to gain a deeper insight into the roles of specific enzymes in lipid metabolism using genetically modified microorganisms, and (iv) in deciphering the mechanism of action of anti-microbial drugs on lipid metabolism. Lastly, an outlook stating where the field is evolving is presented.

CONCLUSION

Lipidomics has contributed to the expanding knowledge related to lipid metabolism, mechanism of drug action and resistance, and pathogen-host interaction of trypanosomatids, which provides a solid basis for the development of better anti-parasitic pharmaceuticals.

Leishmania parasites possess a platelet-activating factor acetylhydrolase important for virulence

Leishmania parasites are intracellular protozoans capable of salvaging and remodeling lipids from the host. To understand the role of lipid metabolism in Leishmania virulence, it is necessary to characterize the enzymes involved in the uptake and turnover of phospholipids. This study focuses on a putative phospholipase A2 (PLA2)/platelet-activating factor acetylhydrolase (PAF-AH) in Leishmania major. In mammals, PAF-AH is a subgroup of PLA2 catalyzing the hydrolysis/inactivation of platelet-activating factor (PAF), a potent mediator of many leukocyte functions. By immunofluorescence microscopy, L. major PLA2/PAF-AH is predominantly localized in the ER. While wild type L. major parasites are able to hydrolyze PAF, this activity is completely absent in the PLA2/PAF-AH-null mutants. Meanwhile, deletion of PLA2/PAF-AH had no significant effect on the turnover of common glycerophospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol. PLA2/PAF-AH is not required for the growth of L. major parasites in culture, or the production of GPI-anchored virulence factors. Nonetheless, it does play a key role in the mammalian host as the PLA2/PAF-AH null mutants exhibit attenuated virulence in BALB/c mice. In conclusion, these data suggest that Leishmania parasites possess a functional PAF-AH and the degradation of PAF or PAF-like lipids is an important step in infection.

Phospholipases a in trypanosomatids

Phospholipases are a complex and important group of enzymes widespread in nature, that play crucial roles in diverse biochemical processes and are classified as A₁, A₂, C, and D. Phospholipases A₁ and A₂ activities have been linked to pathogenesis in various microorganisms, and particularly in pathogenic protozoa they have been implicated in cell invasion. Kinetoplastids are a group of flagellated protozoa, including extra- and intracellular parasites that cause severe disease in humans and animals. In the present paper, we will mainly focus on the three most important kinetoplastid human pathogens, Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp., giving a perspective of the research done up to now regarding biochemical, biological, and molecular characteristics of Phospholipases A₁ and A₂ and their contribution to pathogenesis.

Phospholipases A₁

Phospholipase A(1) (PLA(1)) is an enzyme that hydrolyzes phospholipids and produces 2-acyl-lysophospholipids and fatty acids. This lipolytic activity is conserved in a wide range of organisms but is carried out by a diverse set of PLA(1) enzymes. Where their function is known, PLA(1)s have been shown to act as digestive enzymes, possess central roles in membrane maintenance and remodeling, or regulate important cellular mechanisms by the production of various lysophospholipid mediators, such as lysophosphatidylserine and lysophosphatidic acid, which in turn have multiple biological functions.

Reporting the Implementation of the Three Rs in European Primate and Mouse Research Papers: Are We Making Progress?

It is now more than 20 years since both Council of Europe Convention ETS123 and EU Directive 86/609?EEC were introduced, to promote the implementation of the Three Rs in animal experimentation and to provide guidance on animal housing and care. It might therefore be expected that reports of the implementation of the Three Rs in animal research papers would have increased during this period. In order to test this hypothesis, a literature survey of animal-based research was conducted. A randomly-selected sample from 16 high-profile medical journals, of original research papers arising from European institutions that featured experiments which involved either mice or primates, were identified for the years 1986 and 2006 (Total sample = 250 papers). Each paper was scored out of 10 for the incidence of reporting on the implementation of Three Rs-related factors corresponding to Replacement (justification of non-use of non-animal methods), Reduction (statistical analysis of the number of animals needed) and Refinement (housing aspects, i.e. increased cage size, social housing, enrichment of cage environment and food; and procedural aspects, i.e. the use of anaesthesia, analgesia, humane endpoints, and training for procedures with positive reinforcement). There was no significant increase in overall reporting score over time, for either mouse or primate research. By 2006, mouse research papers scored an average of 0 out of a possible 10, and primate research papers scored an average of 1.5. This review provides systematic evidence that animal research is still not properly reported, and supports the call within the scientific community for action to be taken by journals to update their policies.

Lipidomic analysis of bloodstream and procyclic form Trypanosoma brucei

The biological membranes of Trypanosoma brucei contain a complex array of phospholipids that are synthesized de novo from precursors obtained either directly from the host, or as catabolised endocytosed lipids. This paper describes the use of nanoflow electrospray tandem mass spectrometry and high resolution mass spectrometry in both positive and negative ion modes, allowing the identification of approximately 500 individual molecular phospholipids species from total lipid extracts of cultured bloodstream and procyclic form T. brucei. Various molecular species of all of the major subclasses of glycerophospholipids were identified including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol as well as phosphatidic acid, phosphatidylglycerol and cardolipin, and the sphingolipids sphingomyelin, inositol phosphoceramide and ethanolamine phosphoceramide. The lipidomic data obtained in this study will aid future biochemical phenotyping of either genetically or chemically manipulated commonly used bloodstream and procyclic strains of Trypanosoma brucei. Hopefully this will allow a greater understanding of the bizarre world of lipids in this important human pathogen.

Lipid metabolism in Trypanosoma brucei

Trypanosoma brucei membranes consist of all major eukaryotic glycerophospholipid and sphingolipid classes. These are de novo synthesized from precursors obtained either from the host or from catabolised endocytosed lipids. In recent years, substantial progress has been made in the molecular and biochemical characterisation of several of these lipid biosynthetic pathways, using gene knockout or RNA interference strategies or by enzymatic characterization of individual reactions. Together with the completed genome, these studies have highlighted several possible differences between mammalian and trypanosome lipid biosynthesis that could be exploited for the development of drugs against the diseases caused by these parasites.

The Trypanosoma brucei sphingolipid synthase, an essential enzyme and drug target

Sphingolipids are important components of eukaryotic membranes, particularly the plasma membrane, and are involved in a diverse array of signal transduction processes. In the Eukaryota the biosynthetic pathway for the formation of these lipid species is largely conserved. However, in contrast to mammals which produce sphingomyelin (SM), several pathogenic fungi and protozoa synthesize inositol phosphorylceramide (IPC) as the primary phosphosphingolipid. This process is catalyzed by the enzyme IPC synthase, a recognized target for anti-fungals encoded by the AUR1 gene in yeast. Recently, functional orthologues of the AUR1p have been identified in a group of insect vector-borne pathogenic protozoa, the Kinetoplastida, which are responsible for a range of so-called neglected diseases. Of these the Trypanosoma brucei species are the causative agents of human African trypanosomiasis in many of the most under-developed regions of Africa. The available treatments for these diseases are limited, of decreasing efficacy, and often demonstrate severe side-effects. Against this background the T. brucei sphingolipid synthase, an orthologue of the yeast AUR1p, may represent a promising target for novel anti-protozoals. Our studies identify an isoform of this protein as a novel bi-functional enzyme capable of catalyzing the synthesis of both IPC and SM, both known to be present in the parasite. Furthermore, the synthase is essential for parasite growth and can be inhibited by a known anti-fungal at low nanomolar levels in vitro. Most notably this drug demonstrates trypanocidal activity against cultured bloodstream form parasites. Thus, the T. brucei sphingolipid synthase represents a valid and promising drug target.