Mechanism of Trypanosoma brucei gambiense resistance to human serum.

The African parasite Trypanosoma brucei gambiense accounts for 97% of human sleeping sickness cases. T. b. gambiense resists the specific human innate immunity acting against several other tsetse-fly-transmitted trypanosome species such as T. b. brucei, the causative agent of nagana disease in cattle. Human immunity to some African trypanosomes is due to two serum complexes designated trypanolytic factors (TLF-1 and -2), which both contain haptoglobin-related protein (HPR) and apolipoprotein LI (APOL1). Whereas HPR association with haemoglobin (Hb) allows TLF-1 binding and uptake via the trypanosome receptor TbHpHbR (ref. 5), TLF-2 enters trypanosomes independently of TbHpHbR (refs 4, 5). APOL1 kills trypanosomes after insertion into endosomal/lysosomal membranes. Here we report that T. b. gambiense resists TLFs via a hydrophobic ß-sheet of the T. b. gambiense-specific glycoprotein (TgsGP), which prevents APOL1 toxicity and induces stiffening of membranes upon interaction with lipids. Two additional features contribute to resistance to TLFs: reduction of sensitivity to APOL1 requiring cysteine protease activity, and TbHpHbR inactivation due to a L210S substitution. According to such a multifactorial defence mechanism, transgenic expression of T. b. brucei TbHpHbR in T. b. gambiense did not cause parasite lysis in normal human serum. However, these transgenic parasites were killed in hypohaptoglobinaemic serum, after high TLF-1 uptake in the absence of haptoglobin (Hp) that competes for Hb and receptor binding. TbHpHbR inactivation preventing high APOL1 loading in hypohaptoglobinaemic serum may have evolved because of the overlapping endemic area of T. b. gambiense infection and malaria, the main cause of haemolysis-induced hypohaptoglobinaemia in western and central Africa.

Myeloperoxidase promotes tube formation, triggers ERK1/2 and Akt pathways and is expressed endogenously in endothelial cells.

Myeloperoxidase is a member of the mammalian peroxidase family, mainly expressed in the myeloblastic cell lineage. It is considered a major bactericidal agent as it is released in the phagosome where it catalyzes the formation of reactive oxygen species. It is also released in the extracellular spaces including blood where it is absorbed on (lipo)proteins and endothelial cell surface, interfering with endothelial function. We performed RNA sequencing on MPO-treated endothelial cells, analyzed their transcriptome and validated the profile of gene expression by individual qRT-PCR. Some of the induced genes could be grouped in several functional networks, including tubulogenesis, angiogenesis, and blood vessel morphogenesis and development as well as signal transduction pathways associated to these mechanisms. MPO treatment mimicked the effects of VEGF on several signal transduction pathways, such as Akt, ERK or FAK involved in angiogenesis. Accordingly MPO, independently of its enzymatic activity, stimulated tube formation by endothelial cells. RNA interference also pointed at a role of endogenous MPO in tubulogenesis and endothelium wound repair in vitro. These data suggest that MPO, whether from endogenous or exogenous sources, could play a role in angiogenesis and vascular repair in vivo.

The presence of modified nucleosides in extracellular fluids leads to the specific incorporation of 5-chlorocytidine into RNA and modulates the transcription and translation.

Myeloperoxidase (MPO) is able to promote several kinds of damage and is involved in mechanisms leading to various diseases such as atherosclerosis or cancers. An example of these damages is the chlorination of nucleic acids, which is considered as a specific marker of the MPO activity. Since 5-chlorocytidine has been recently shown in healthy donor plasmas, this study aimed at discovering if these circulating modified nucleosides could be incorporated into RNA and DNA and if their presence impacts the ability of enzymes involved in the incorporation, transcription, and translation processes. Experimentations, which were carried out in vitro with endothelial and prostatic cells, showed a large penetration of all chloronucleosides but an exclusive incorporation of 5-chlorocytidine into RNA. However, no incorporation into DNA was observed. This specific incorporation is accompanied by an important reduction of translation yield. Although, in vitro, DNA polymerase processed in the presence of chloronucleosides but more slowly than in control conditions, ribonucleotide reductase could not reduce chloronucleotides prior to the replication. This reduction seems to be a limiting step, protecting DNA from chloronucleoside incorporation. This study shows the capacity of transcription enzyme to specifically incorporate 5-chlorocytidine into RNA and the loss of capacity-complete or partial-of different enzymes, involved in replication, transcription or translation, in the presence of chloronucleosides. Questions remain about the long-term impact of such specific incorporation in the RNA and such decrease of protein production on the cell viability and function.

Loss of G9a does not phenocopy the requirement for Prdm12 in the development of the nociceptive neuron lineage.

Prdm12 is an epigenetic regulator expressed in developing and mature nociceptive neurons, playing a key role in their specification during neurogenesis and modulating pain sensation at adulthood. In vitro studies suggested that Prdm12 recruits the methyltransferase G9a through its zinc finger domains to regulate target gene expression, but how Prdm12 interacts with G9a and whether G9a plays a role in Prdm12's functional properties in sensory ganglia remain unknown. Here we report that Prdm12-G9a interaction is likely direct and that it involves the SET domain of G9a. We show that both proteins are largely co-expressed in dorsal root ganglia during early murine development, opening the possibility that G9a plays a role in DRG and may act as a mediator of Prdm12's function in the development of nociceptive sensory neurons. To test this hypothesis, we conditionally inactivated G9a in neural crest using a Wnt1-Cre transgenic mouse line. We found that the specific loss of G9a in the neural crest lineage does not lead to dorsal root ganglia hypoplasia due to the loss of somatic nociceptive neurons nor to the ectopic expression of the visceral determinant Phox2b as observed upon Prdm12 ablation. These findings suggest that Prdm12 function in the initiation of the nociceptive lineage does not critically involves its interaction with G9a.

Role of Myeloperoxidase in ROS Generation and Inflammation Response on Prostate Epithelial Cells.

Myeloperoxidase (MPO) has been reported in prostate tissue, and considering its pro-oxidant properties, this location might be linked to prostate pathology. The possibility that the glandular prostatic tissue might be the source of MPO and its potential inflammatory effects must be tested. Human prostate material was obtained from prostate biopsies and radical prostatectomies. Immunohistochemistry was performed using MPO-specific human antibody. In situ hybridization using MPO-specific probes and laser-assisted microdissection for quantitative real-time RT-PCR were performed to observe whether MPO is being produced in prostate tissue. Mass spectrometry on prostate biopsies was used to detect products of MPO activity in nucleic acids (DNA/RNA). MPO contribution to intracellular accumulation of ROS and interleukin-8 in prostatic epithelial cells was monitored in vitro. Immunohistochemistry confirmed cellular localization of MPO in epithelial cells of the prostate. The staining varied from light to high intensity. In situ hybridization did not address the presence of mRNA coding for MPO. No MPO-specific modifications on nucleic acids were detected. Mox-LDL was a major factor inducing ROS and cytokines production in prostatic epithelial cells. We did not demonstrate that MPO was synthetized by prostatic epithelial cells. However, in vitro experiments showed the ability of MPO to potentiate the ROS production and inflammation on prostate epithelial cells. Results do not allow us to demonstrate a role of MPO in prostate to date but further studies are mandatory to focus on the potential impact of MPO in the development of prostatic diseases.

A lipid transfer protein ensures nematode cuticular impermeability.

The cuticle of C. elegans is impermeable to chemicals, toxins, and pathogens. However, increased permeability is a desirable phenotype because it facilitates chemical uptake. Surface lipids contribute to the permeability barrier. Here, we identify the lipid transfer protein GMAP-1 as a critical element setting the permeability of the C. elegans cuticle. A gmap-1 deletion mutant increases cuticular permeability to sodium azide, levamisole, Hoechst, and DiI. Expressing GMAP-1 in the hypodermis or transiently in the adults is sufficient to rescue this gmap-1 permeability phenotype. GMAP-1 protein is secreted from the hypodermis to the aqueous fluid filling the space between collagen fibers of the cuticle. In vitro, GMAP-1 protein binds phosphatidylserine and phosphatidylcholine while in vivo, GMAP-1 sets the surface lipid composition and organization. Altogether, our results suggest GMAP-1 secreted by hypodermis shuttles lipids to the surface to form the permeability barrier of C. elegans.

C-terminal mutants of apolipoprotein L-I efficiently kill both Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense.

Apolipoprotein L-I (apoL1) is a human-specific serum protein that kills Trypanosoma brucei through ionic pore formation in endosomal membranes of the parasite. The T. brucei subspecies rhodesiense and gambiense resist this lytic activity and can infect humans, causing sleeping sickness. In the case of T. b. rhodesiense, resistance to lysis involves interaction of the Serum Resistance-Associated (SRA) protein with the C-terminal helix of apoL1. We undertook a mutational and deletional analysis of the C-terminal helix of apoL1 to investigate the linkage between interaction with SRA and lytic potential for different T. brucei subspecies. We confirm that the C-terminal helix is the SRA-interacting domain. Although in E. coli this domain was dispensable for ionic pore-forming activity, its interaction with SRA resulted in inhibition of this activity. Different mutations affecting the C-terminal helix reduced the interaction of apoL1 with SRA. However, mutants in the L370-L392 leucine zipper also lost in vitro trypanolytic activity. Truncating and/or mutating the C-terminal sequence of human apoL1 like that of apoL1-like sequences of Papio anubis resulted in both loss of interaction with SRA and acquired ability to efficiently kill human serum-resistant T. b. rhodesiense parasites, in vitro as well as in transgenic mice. These findings demonstrate that SRA interaction with the C-terminal helix of apoL1 inhibits its pore-forming activity and determines resistance of T. b. rhodesiense to human serum. In addition, they provide a possible explanation for the ability of Papio serum to kill T. b. rhodesiense, and offer a perspective to generate transgenic cattle resistant to both T. b. brucei and T. b. rhodesiense.

Human apolipoprotein L1 interferes with mitochondrial function in Saccharomyces cerevisiae.

To the best of our knowledge, the vertebrate apolipoprotein L (APOL) family has not previously been ascribed to any definite pathophysiological function, although the conserved BH3 protein domain suggests a role in programmed cell death or an interference with mitochondrial processes. In the present study, the human APOL1 was expressed in the yeast Saccharomyces cerevisiae in order to determine the molecular action of APOL1. APOL1 inhibited cell proliferation in a non­fermentable carbon source, such as glycerol, while it had no effect on proliferation in fermentable carbon sources, such as galactose. APOL1, expressed in yeast, is localized in the mitochondrial fraction, as determined via western blotting. APOL1 induced a loss of mitochondrial function, demonstrated by a loss of respiratory index, and mitochondrial membrane potential. Green fluorescent protein tagging of mitochondrial protein revealed that APOL1 was associated with abnormal mitochondrial and lysosomal morphologies, observed by a loss of the normal mitochondrial tubular network. Thus, the results of the present study suggest that APOL1 could be a physiological regulator of mitochondrial function.

Human Trypanosoma evansi infection linked to a lack of apolipoprotein L-I.

Humans have innate immunity against Trypanosoma brucei brucei that is known to involve apolipoprotein L-I (APOL1). Recently, a case of T. evansi infection in a human was identified in India. We investigated whether the APOL1 pathway was involved in this occurrence. The serum of the infected patient was found to have no trypanolytic activity, and the finding was linked to the lack of APOL1, which was due to frameshift mutations in both APOL1 alleles. Trypanolytic activity was restored by the addition of recombinant APOL1. The lack of APOL1 explained the patient's infection with T. evansi.

Identification and characterization of the Onchocerca volvulus Excretory Secretory Product Ov28CRP, a putative GM2 activator protein.

Onchocerca volvulus is the nematode pathogen responsible for human onchocerciasis also known as "River blindness", a neglected tropical disease that affects up to 18 million people worldwide. Helminths Excretory Secretory Products (ESPs) constitute a rich repertoire of molecules that can be exploited for host-parasite relationship, diagnosis and vaccine studies. Here, we report, using a range of molecular techniques including PCR, western blot, recombinant DNA technology, ELISA, high performance thin-layer chromatography and mass spectrometry that the 28 KDa cysteine-rich protein (Ov28CRP) is a reliable component of the O. volvulus ESPs to address the biology of this parasite. We showed that (1) Ov28CRP is a putative ganglioside GM2 Activator Protein (GM2AP) conserved in nematode; (2) OvGM2AP gene is transcriptionally activated in all investigated stages of the parasitic life cycle, including larval and adult stages; (3) The full-length OvGM2AP was detected in in-vitro O. volvulus ESPs of adult and larval stages; (4) the mass expressed and purified recombinant OvGM2AP purified from insect cell culture medium was found to be glycosylated at asparagine 173 and lacked N-terminal signal peptide sequence; (5) the recombinant OvGM2AP discriminated serum samples of infected and uninfected individuals; (6) OvGM2AP competitively inhibits MUG degradation by recombinant ß-hexosaminidase A but not MUGS, and could not hydrolyze the GM2 to GM3; (7) humoral immune responses to the recombinant OvGM2AP revealed a negative correlation with ivermectin treatment. Altogether, our findings suggest for the first time that OvGM2AP is an antigenic molecule whose biochemical and immunological features are important to gain more insight into our understanding of host-parasite relationship, as well as its function in parasite development at large.

Apoliporotein L3 interferes with endothelial tube formation via regulation of ERK1/2, FAK and Akt signaling pathway.

BACKGROUND AND AIMS: Endothelial cells are main actors in vascular homeostasis as they regulate vascular pressure and permeability as well as hemostasis and inflammation. Disturbed stimuli delivered to and by endothelial cells correlate with the so-called endothelial dysfunction and disrupt this homeostasis. As constituents of the inner layer of blood vessels, endothelial cells are also involved in angiogenesis. Apolipoprotein Ls (APOL) comprise a family of newly discovered apolipoproteins with yet poorly understood function, and are suggested to be involved in inflammatory processes and cell death mechanisms. Here we investigate the role of APOLs in endothelial cells stimulated with factors known to be involved in atherogenesis and their possible contribution to endothelial dysfunction with an emphasis on inflammation driven-angiogenesis in vitro. METHODS: Using the CRISPR/Cas9 technique, we analyzed the effect of APOL3 gene knock out in HMEC-1 endothelial cells on cell migration, tubulogenesis, endothelial permeability, intracellular signal transduction as assessed by kinase phosphorylation, and angiogenesis gene expression (measured by qRT-PCR). RESULTS: Our results indicate that among the family, APOL3 was the only member induced by myeloperoxidase, oxidized LDL, VEGF and FGF treatments. APOL3 invalidation increased endothelial permeability, reduced wound repair and tubule formation in vitro, the latter only in MPO and VEGF-induced conditions. Accordingly, some pro-angiogenic signaling pathways (ERK1/2 and FAK but not Akt) and some pro-angiogenic genes were partially inhibited in APOL3 knock out cells. CONCLUSIONS: These findings suggest the involvement of APOL3 in angiogenesis in vitro and as a modulator of MAPK and FAK signaling in endothelial cells.

Prediction and validation of the structural features of Ov58GPCR, an immunogenic determinant of Onchocerca volvulus.

Onchocerciasis is a severely debilitating yet neglected tropical disease (NTD) that creates social stigma, generates and perpetuates poverty, and leads ultimately in some cases to irreversible unilateral or bilateral blindness if untreated. Consequently, the disease is a major impediment to socioeconomic development. Many control programs have been launched for the disease with moderate successes achieved. This mitigated hit is partially due to the lingering need for reliable, non-invasive and easily applicable tools for mapping endemic regions and post-elimination surveillance. In this work, bioinformatics analyses combined with immunological assays were applied in a bid to develop potential tools for diagnosis and assessing the success of drug treatment programs. We report that (i) the O. volvulus antigen, Ov58GPCR is a G-protein coupled receptor (GPCR) conserved in related nematodes, (ii) synthetic peptides predicted to be in the extracellular domain (ECD) of Ov58GPCR are indeed immunogenic epitopes in actively-infected individuals, (iii) synthetic peptide cocktails discriminate between actively-infected individuals, treated individuals and healthy African controls, (iv) polyclonal antibodies against one of the peptides or against the bacterially-expressed ECD reacted specifically with the native antigen of O. volvulus total and surface extracts, (v) Ov58GPCR is transcribed in both larvae and adult parasite stages, (vi) IgG and IgE responses to the recombinant ECD decline with ivermectin treatment. All these findings suggest that the extracellular domain and synthetic peptides of Ov58GPCR, as well as the specific immune response generated could be harnessed in the context of disease diagnosis and surveillance.

Characterization of RNA polymerase II subunits of Trypanosoma brucei.

The Trypanosoma brucei homolog of the RNA polymerase II (RNA Pol II) subunit RPB9 was cloned and characterized. Contrary to what occurs in Saccharomyces cerevisiae, in T. brucei this protein was found to be essential since the knock down of its expression by RNAi led to lethality in both bloodstream and procyclic forms of the parasite. As expected, TbRPB9 knock down specifically inhibited transcription by RNA Pol II, but not by RNA Pol I and III. TbRPB9 was used as bait to isolate the RNA Pol II core complex by tandem affinity purification. Nine subunits homologous to the other eukaryotic RNA Pol II, namely RPB1, RPB2, RPB3, RPB4, RPB5, RPB6, RPB7, RPB8 and RPB11, were identified in the purified complex. Interestingly, the RPB5 homolog associated with RNA Pol II was different from the one previously found in RNA Pol I. Analysis of the genome database revealed the presence of genes for all purified subunits plus RPB10. As in the case of TbRPB5, two genes coding for different isoforms of TbRPB6 were identified, suggesting the existence of polymerase-specific isoforms for both TbRPB5 and TbRPB6.

Validation of a sensitive LC/MSMS method for chloronucleoside analysis in biological matrixes and its applications.

Myeloperoxidase promotes several kinds of damage and is involved in the development of various diseases (as atherosclerosis and cancers). An example of these damage is the chlorination of nucleic acids, which is considered as a specific marker of the MPO activity on those acids. This study aimed to develop and validate a method to analyze oxidized and MPO-specific chlorinated nucleosides in biological matrixes (cells, tissues and plasma). Although a lot of methods to quantify oxidized or chlorinated nucleosides have already been established, none of them took into account all these derivatives together. The new method used a Triple Quadrupole mass spectrometer fitted with a Jet Stream electrospray ionization source. This approach has two advantages compared with existing LC/MSMS analyses: it includes MPO-induced modifications in a unique analysis and obtains a better sensitivity. Our optimized method reached LOQs of 1.50pg and 1.42pg respectively for oxoG and oxo(d)G, being 4 times more sensitive than previous methods, and LOQs of 1.39pg, 1.30pg and 63.4 fg respectively for 5-chlorocytidine, 5-chloro-2'-deoxycytidine and 8-chloroguanosine. Developed method is also 25 times more sensitive for chloroguanosine than the best existing method. Nevertheless, this method is not specific enough for 8-chloro-(2'-deoxy)adenosine analysis. Examples of applications demonstrate the interest of this validated method. Indeed analysis of plasma from healthy donors highlighted exclusively the presence of 5-chlorocytidine (1.0±0.2nM) whereas analysis of treated endothelial cells by HOCl showed chlorination of guanosine and cytidine in cytoplasmic pools and chlorination of (deoxy)cytidine in DNA and RNA. In conclusion, this study shows that 5-chloro-2'-deoxycytidine, 5-chlorocytidine and 8-chloroguanosine are good markers allowing us to detect the MPO activity in biological fluids. The robust, specific and sensitive developed method enables future studies on MPO implications in human diseases.

ApolipoproteinL1 is expressed in papillary thyroid carcinomas.

The apolipoprotein L (apoL) family has not yet been ascribed any definite patho-physiological function although the conserved BH3 protein domain suggests a role in programmed cell death. As repression of the regular apoptotic program is considered a hallmark of tumor progression, we investigated apoL expression in cancer. We show that the levels of one member of the family, apolipoprotein L1 (apoL1) is higher in papillary thyroid carcinoma compared to normal tissue. A combination of qRTPCR, immunohistochemistry and in situ hybridization allowed us to ascribe this increase to endogenous overexpression in carcinoma cells. Whether apoL1 plays an instrumental role in refraining cell death is the subject of ongoing molecular biology experiments.

The Trypanosoma brucei reference strain TREU927/4 contains T. brucei rhodesiense-specific SRA sequences, but displays a distinct phenotype of relative resistance to human serum.

The Trypanosoma brucei reference strain TREU927/4 exhibits some resistance to lysis by normal human serum (NHS), but this resistance is never complete even after selection. The genome of this strain contains a minimum of eight sequences related to the T. brucei rhodesiense-specific serum resistance-associated gene (SRA), which encodes a truncated variant surface glycoprotein (VSG) conferring full resistance to lysis by NHS. We selected two sequences showing the highest similarity to SRA and also preceded by a region ("cotransposed region") present immediately upstream from SRA in the VSG expression site termed R-ES, where SRA is expressed in T. brucei rhodesiense. Whereas one of these sequences appears to be a pseudogene, the other, which is contained within a cluster of VSG basic copies (BCs), encodes a VSG truncated in the C-terminal domain. In the latter gene, an inserted region encoding surface-exposed loops similar to those of the BoTat 1.20 VSG interrupts the full SRA sequence. Therefore, this gene was termed SRA-BC, for the putative VSG basic copy from which SRA was derived. Neither this gene nor other SRA-like sequences appeared to be responsible for the relative resistance of TREU927/4 to NHS, since (i) transfection of SRA-BC in T. brucei brucei did not confer increased resistance; (ii) SRA transcripts could not be detected in this strain, even when focusing the search on the limited SRA sequence necessary to confer resistance and when using strain-specific SRA probes on RNA from cells selected in the presence of NHS.

Characterization of a TFIIH homologue from Trypanosoma brucei.

Trypanosomes are protozoans showing unique transcription characteristics. We describe in Trypanosoma brucei a complex homologous to TFIIH, a multisubunit transcription factor involved in the control of transcription by RNA Pol I and RNA Pol II, but also in DNA repair and cell cycle control. Bioinformatics analyses allowed the detection of five genes encoding four putative core TFIIH subunits (TbXPD, TbXPB, Tbp44, Tbp52), including a novel XPB variant, TbXPBz. In all cases sequences known to be important for TFIIH functions were conserved. We performed a molecular analysis of this core complex, focusing on the two subunits endowed with a known enzymatic (helicase) activity, XPD and XPB. The involvement of these T. brucei proteins in a bona fide TFIIH core complex was supported by (i) colocalization by immunofluorescence in the nucleus, (ii) direct physical interaction of TbXPD and its interacting regulatory subunit Tbp44 as determined by double-hybrid assay and tandem affinity purification of the core TFIIH, (iii) involvement of the core proteins in a high molecular weight complex and (iv) occurrence of transcription, cell cycle and DNA repair phenotypes upon either RNAi knock-down or overexpression of essential subunits.

Trypanosoma brucei: growth differences in different mammalian sera are not due to the species-specificity of transferrin.

The heterodimeric transferrin receptors of Trypanosoma brucei (Tf-Rs) are encoded by two genes termed ESAG7 and ESAG6. These genes belong to polycistronic transcription units contained in the multiple expression sites for the variant surface glycoprotein (VSG ESs), only one of which is active at a time. Each VSG ES carries a different copy of these genes, leading to alternative expression of Tf-Rs with quite distinct binding affinities for transferrins from various mammals. T. brucei clones exhibit marked growth differences depending on the species-specificity of the serum. Since transferrin is a vital growth factor for the parasite, we investigated whether it could be responsible for these observations. We analyzed the cases of Tf-Rs from two ESs preferentially selected for expression in man and mouse, respectively. We show that serum-dependent growth variations of trypanosomes expressing these receptors are independent of transferrin, and that both high- and low-affinity Tf-Rs allow efficient trypanosome growth in various sera, either in vivo or in vitro.