Specific Uptake of Tumor Necrosis Factor-α Is Involved in Growth Control of Trypanosoma brucei

Trypanosoma brucei is lysed by tumor necrosis factor-α (TNF-α) in a dose-dependent way, involving specific binding of the cytokine to a trypanosomal glycoprotein present in the flagellar pocket of the parasite. TNF-α–gold particles are endocytosed via coated pits and vesicles and are directed towards lysosome-like digestive organelles. The specific uptake of the cytokine by the parasite results in a developmentally regulated loss of osmoregulatory capacity. TNF-α specific lysis is prevented when lysis assays are performed at a temperature <26°C, despite uptake of the cytokine. Inhibition of lysis is also observed when a lysosomotropic agent is added during the first 2 h of incubation. Both monomorphic and pleomorphic trypanosomes are lysed but only when isolated during the peak of parasitaemia. Lysis is not observed with early infection stage parasites or procyclic (insect-specific) forms. Anti– TNF-α treatment of T. brucei-infected mice reveals a dramatic increase in parasitaemia in the blood circulation, the spleen, the lymph nodes, and the peritoneal cavity. These data suggest that in the mammalian host, TNF-α is involved in the growth control of T. brucei

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

Thymus‐derived regulatory T cells restrain pro‐inflammatory Th1 responses by downregulating CD

The severity and intensity of autoimmune disease in Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) patients and in scurfy mice emphasizes the critical role played by thymus-derived regulatory T cells (tTregs) in maintaining peripheral immune tolerance. However, although tTregs are critical to prevent lethal autoimmunity and excessive inflammatory responses, their suppressive mechanism remains elusive. Here we demonstrate that tTregs selectively inhibit CD27/CD70-dependent Th1 priming, while leaving the IL-12-dependent pathway unaffected. Immunized mice depleted of tTregs showed an increased response of IFN-γ-secreting CD4+ T cells that was strictly reliant on a functional CD27/CD70 pathway. In vitro studies revealed that tTregs downregulate CD70 from the plasma membrane of dendritic cells (DCs) in a CD27-dependent manner. CD70 downregulation required contact between Tregs and DCs and resulted in endocytosis of CD27 and CD70 into the DC. These findings reveal a novel mechanism by which tTregs can maintain tolerance or prevent excessive, proinflammatory Th1 responsesin pressSCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

APOL1 C-Terminal Variants May Trigger Kidney Disease through Interference with APOL3 Control of Actomyosin

The C-terminal variants G1 and G2 of apolipoprotein L1 (APOL1) confer human resistance to the sleeping sickness parasite Trypanosoma rhodesiense, but they also increase the risk of kidney disease. APOL1 and APOL3 are death-promoting proteins that are partially associated with the endoplasmic reticulum and Golgi membranes. We report that in podocytes, either APOL1 C-terminal helix truncation (APOL1Δ) or APOL3 deletion (APOL3KO) induces similar actomyosin reorganization linked to the inhibition of phosphatidylinositol-4-phosphate [PI(4)P] synthesis by the Golgi PI(4)-kinase IIIB (PI4KB). Both APOL1 and APOL3 can form K+ channels, but only APOL3 exhibits Ca2+-dependent binding of high affinity to neuronal calcium sensor-1 (NCS-1), promoting NCS-1-PI4KB interaction and stimulating PI4KB activity. Alteration of the APOL1 C-terminal helix triggers APOL1 unfolding and increased binding to APOL3, affecting APOL3-NCS-1 interaction. Since the podocytes of G1 and G2 patients exhibit an APOL1Δ or APOL3KO-like phenotype, APOL1 C-terminal variants may induce kidney disease by preventing APOL3 from activating PI4KB, with consecutive actomyosin reorganization of podocytes.info:eu-repo/semantics/publishe

Coupling of lysosomal and mitochondrial membrane permeabilization in trypanolysis by APOL1

Humans resist infection by the African parasite Trypanosoma brucei owing to the trypanolytic activity of the serum apolipoprotein L1 (APOL1). Following uptake by endocytosis in the parasite, APOL1 forms pores in endolysosomal membranes and triggers lysosome swelling. Here we show that APOL1 induces both lysosomal and mitochondrial membrane permeabilization (LMP and MMP). Trypanolysis coincides with MMP and consecutive release of the mitochondrial TbEndoG endonuclease to the nucleus. APOL1 is associated with the kinesin TbKIFC1, of which both the motor and vesicular trafficking VHS domains are required for MMP, but not for LMP. The presence of APOL1 in the mitochondrion is accompanied by mitochondrial membrane fenestration, which can be mimicked by knockdown of a mitochondrial mitofusin-like protein (TbMFNL). The BH3-like peptide of APOL1 is required for LMP, MMP and trypanolysis. Thus, trypanolysis by APOL1 is linked to apoptosis-like MMP occurring together with TbKIFC1-mediated transport of APOL1 from endolysosomal membranes to the mitochondrion

The variant surface glycoprotein as a tool for adaptation in African trypanosomes.

African trypanosomes (prototype: Trypanosoma brucei) are flagellated protozoan parasites that infect a wide variety of mammals, causing nagana in cattle and sleeping sickness in humans. These organisms can cause prolonged chronic infections due to their ability to successively expose different antigenic variants of the variant surface glycoprotein (VSG). The genomic loci where the VSG genes are expressed are telomeric and contain polycistronic transcription units with several genes that are involved in adaptation of the parasite to the host. At least three of these genes, which respectively encode the two subunits of the heterodimeric receptor for transferrin and a protein conferring resistance to the human trypanolytic factor apolipoprotein L-I, share the same origin as the VSG. The high recombination potential of the telomeric VSG expression sites, coupled to their dynamic mono-allelic expression control, provides trypanosomes with a powerful capacity for adaptation to their hosts.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: sh.jinfo:eu-repo/semantics/publishe

Variation antigénique des trypanosomes africains

Although several hundred of different antigen genes exist in the trypanosome genome, only one is usually expressed at a time. This expression occurs in one of several possible telomeric expression sites. Besides being exclusively telomeric, transcription of the antigen gene exhibits other particular characteristics: the RNA polymerase is highly resistant to alpha-amanitin, and the transcription unit comprises several other genes, one of which may encode an adenylate cyclase. Post-transcriptional controls modulate the activity of this transcription unit during the parasite life-cycle. Antigenic variation is achieved through either alternative activation of different expression sites, or gene recombination within a given expression site. These mechanisms ensure a relative programming of antigen expression.English AbstractJournal ArticleResearch Support, Non-U.S. Gov'tReviewinfo:eu-repo/semantics/publishe

Distinct APOL1 functions in trypanosomes and kidney podocytes

The human serum protein apolipoprotein L1 (APOL1) kills Trypanosoma brucei but not the sleeping sickness agent Trypanosoma rhodesiense. APOL1 C-terminal variants can kill T. rhodesiense but they also induce kidney disease. Given topological and functional differences between intracellular and extracellular APOL1 isoforms, I propose that trypanolysis and kidney disease result from distinct APOL1 activities.SCOPUS: sh.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Dialogue moléculaire entre trypanosomes Africains et l'homme.

The evolutionary origin of Man in the African continent has imposed the requirement to resist endemic parasites, in particular African trypanosomes (prototype: Trypanosoma brucei). Therefore, human serum is provided with an efficient system of innate immunity against these parasites, as discovered by A. Laveran in 1902. However, two T. brucei clones, termed T. b. rhodesiense and T. b. gambiense, managed to escape this immunity system, enabling them to grow in humans where they cause sleeping sickness. We have identified the gene allowing T. b. rhodesiense to resist trypanolysis by human serum, which led us to discover that the trypanolytic factor is apolipoprotein L1 (apoL1). ApoL1 is a human-specific serum protein bound to HDL particles that also contain another human-specific protein termed "haptoglobin-related protein " (Hpr). Following the binding of hemoglobin (Hb) to Hpr, the apoL1-bearing HDL particles are avidly taken up by the trypanosome through their binding to a parasite surface receptor for the Hp-Hb complex. After endocytosis apoL1 kills the parasite by generating anionic pores in the lysosomal membrane. In our laboratory, mutant versions of apoL1 have been constructed, which are no longer neutralized by the resistance protein of T. b. rhodesiense and are therefore able to kill this human pathogen. Unexpectedly, we have recently discovered that similar mutants do actually exist in nature :in Africans and Americans of recent African origin, even a single allele of these mutants allows protection against infection by T. b. rhodesiense, but the price to pay is a high frequency of end-stage renal disease when doubly allelic. The evidence of natural selection of these apoL1 mutations despite their deleterious potential for kidneys highlights the importance of the resistance to trypanosomes in the evolution of Man. The mechanism by which mutant apoL1 triggers end-stage renal disease is currently studied.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Could cholesterol hold the key to defeating sleeping sickness?

info:eu-repo/semantics/publishe