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A highly conserved Toxo1 haplotype directs resistance to toxoplasmosis and its associated caspase-1 dependent killing of parasite and host macrophage.

Cavailles P, Flori P, Papapietro O, Bisanz C, Lagrange D, Pilloux L, Massera C, Cristinelli S, Jublot D, Bastien O, Loeuillet C, Aldebert D, Touquet B, Fournié GJ, Cesbron-Delauw MF - PLoS Pathog. (2014)

Bottom Line: The parasite-induced cell death of infected macrophages bearing the LEW-Toxo1 alleles was found to exhibit pyroptosis-like features with ROS production, the activation of caspase-1 and IL1-β secretion.The pharmacological inactivation of caspase-1 using YVAD and Z-VAD inhibitors prevented the death of both intravacuolar parasites and host non-permissive macrophages but failed to restore parasite proliferation.The NOD-like receptor NLRP1a/Caspase-1 pathway is the best candidate to mediate the parasite-induced cell death.

View Article: PubMed Central - PubMed

Affiliation: UMR 5163, Centre National de la Recherche Scientifique (CNRS), Grenoble, France; Université Grenoble 1, Grenoble, France.

ABSTRACT
Natural immunity or resistance to pathogens most often relies on the genetic make-up of the host. In a LEW rat model of refractoriness to toxoplasmosis, we previously identified on chromosome 10 the Toxo1 locus that directs toxoplasmosis outcome and controls parasite spreading by a macrophage-dependent mechanism. Now, we narrowed down Toxo1 to a 891 kb interval containing 29 genes syntenic to human 17p13 region. Strikingly, Toxo1 is included in a haplotype block strictly conserved among all refractory rat strains. The sequencing of Toxo1 in nine rat strains (5 refractory and 4 susceptible) revealed resistant-restricted conserved polymorphisms displaying a distribution gradient that peaks at the bottom border of Toxo1, and highlighting the NOD-like receptor, Nlrp1a, as a major candidate. The Nlrp1 inflammasome is known to trigger, upon pathogen intracellular sensing, pyroptosis programmed-cell death involving caspase-1 activation and cleavage of IL-1β. Functional studies demonstrated that the Toxo1-dependent refractoriness in vivo correlated with both the ability of macrophages to restrict T. gondii growth and a T. gondii-induced death of intracellular parasites and its host macrophages. The parasite-induced cell death of infected macrophages bearing the LEW-Toxo1 alleles was found to exhibit pyroptosis-like features with ROS production, the activation of caspase-1 and IL1-β secretion. The pharmacological inactivation of caspase-1 using YVAD and Z-VAD inhibitors prevented the death of both intravacuolar parasites and host non-permissive macrophages but failed to restore parasite proliferation. These findings demonstrated that the Toxo1-dependent response of rat macrophages to T. gondii infection may trigger two pathways leading to the control of parasite proliferation and the death of parasites and host macrophages. The NOD-like receptor NLRP1a/Caspase-1 pathway is the best candidate to mediate the parasite-induced cell death. These data represent new insights towards the identification of a major pathway of innate resistance to toxoplasmosis and the prediction of individual resistance.

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Allelic variations in Toxo1 correlating with toxoplasmosis resistance.Sequencing of Toxo1 (between 57.26 and 58.15 Mb) revealed 373 SNPs (red bars) conserved in coding- and non-coding sequences of all resistant strains and missing in susceptible strains. The diagram illustrates the distribution of these SNPs along the sequence of Toxo1 (indicated by the double arrow in the lower part). In the upper part, the 29 genes are represented by black bold lines. The four genes named Inca1, Kif1C, Nlrp1a and Nlrp1b display missense mutations.
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ppat-1004005-g005: Allelic variations in Toxo1 correlating with toxoplasmosis resistance.Sequencing of Toxo1 (between 57.26 and 58.15 Mb) revealed 373 SNPs (red bars) conserved in coding- and non-coding sequences of all resistant strains and missing in susceptible strains. The diagram illustrates the distribution of these SNPs along the sequence of Toxo1 (indicated by the double arrow in the lower part). In the upper part, the 29 genes are represented by black bold lines. The four genes named Inca1, Kif1C, Nlrp1a and Nlrp1b display missense mutations.

Mentions: According to the genome database (www.ensembl.org, RGSC3.4 version), the Toxo1-891 kb interval contains 29 genes. None of these 29 genes could be retained as a candidate on the basis of a significant difference in their level of expression between macrophages from resistant vs. macrophages from susceptible congenic lines (Table S2, TextS1). Therefore, the entire Toxo1 locus of the nine rat strains studied in the haplotype analysis was sequenced to identify resistance-correlated variations in coding- and non-coding sequences. A total of 373 SNPs and 21 insertions/deletions were found strictly conserved among the five resistant strains as compared to susceptible strains. The distribution of these mutations along the locus displays a gradient with a densification at the bottom of Toxo1 (Figure 5). We identified 23 SNPs of which 16 are missense and one is a deletion in the coding sequences leading to the selection of four candidate genes: Inca1 (1 SNP), Kif1C (1 ins/del), Nlrp1a (13 SNPs) and Nlrp1b (2 SNPs). Given that Inca1 and Nlrp1b mRNAs are undetectable in peritoneal macrophages (Table S2) and according to the number of mutations in Nlrp1a vs Kif1C coding sequences, Nlrp1a appeared as the major candidate gene. It encodes the NOD-like receptor (NLR) NLRP1 that acts as an intracellular pattern recognition receptor (PRR) [12]. Both the mouse Nlrp1b and its ortholog rat Nlrp1a have been described as implicated in the control of a cell death process called pyroptosis that is induced by the lethal toxin (LT) from Bacillus anthracis[13].


A highly conserved Toxo1 haplotype directs resistance to toxoplasmosis and its associated caspase-1 dependent killing of parasite and host macrophage.

Cavailles P, Flori P, Papapietro O, Bisanz C, Lagrange D, Pilloux L, Massera C, Cristinelli S, Jublot D, Bastien O, Loeuillet C, Aldebert D, Touquet B, Fournié GJ, Cesbron-Delauw MF - PLoS Pathog. (2014)

Allelic variations in Toxo1 correlating with toxoplasmosis resistance.Sequencing of Toxo1 (between 57.26 and 58.15 Mb) revealed 373 SNPs (red bars) conserved in coding- and non-coding sequences of all resistant strains and missing in susceptible strains. The diagram illustrates the distribution of these SNPs along the sequence of Toxo1 (indicated by the double arrow in the lower part). In the upper part, the 29 genes are represented by black bold lines. The four genes named Inca1, Kif1C, Nlrp1a and Nlrp1b display missense mutations.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974857&req=5

ppat-1004005-g005: Allelic variations in Toxo1 correlating with toxoplasmosis resistance.Sequencing of Toxo1 (between 57.26 and 58.15 Mb) revealed 373 SNPs (red bars) conserved in coding- and non-coding sequences of all resistant strains and missing in susceptible strains. The diagram illustrates the distribution of these SNPs along the sequence of Toxo1 (indicated by the double arrow in the lower part). In the upper part, the 29 genes are represented by black bold lines. The four genes named Inca1, Kif1C, Nlrp1a and Nlrp1b display missense mutations.
Mentions: According to the genome database (www.ensembl.org, RGSC3.4 version), the Toxo1-891 kb interval contains 29 genes. None of these 29 genes could be retained as a candidate on the basis of a significant difference in their level of expression between macrophages from resistant vs. macrophages from susceptible congenic lines (Table S2, TextS1). Therefore, the entire Toxo1 locus of the nine rat strains studied in the haplotype analysis was sequenced to identify resistance-correlated variations in coding- and non-coding sequences. A total of 373 SNPs and 21 insertions/deletions were found strictly conserved among the five resistant strains as compared to susceptible strains. The distribution of these mutations along the locus displays a gradient with a densification at the bottom of Toxo1 (Figure 5). We identified 23 SNPs of which 16 are missense and one is a deletion in the coding sequences leading to the selection of four candidate genes: Inca1 (1 SNP), Kif1C (1 ins/del), Nlrp1a (13 SNPs) and Nlrp1b (2 SNPs). Given that Inca1 and Nlrp1b mRNAs are undetectable in peritoneal macrophages (Table S2) and according to the number of mutations in Nlrp1a vs Kif1C coding sequences, Nlrp1a appeared as the major candidate gene. It encodes the NOD-like receptor (NLR) NLRP1 that acts as an intracellular pattern recognition receptor (PRR) [12]. Both the mouse Nlrp1b and its ortholog rat Nlrp1a have been described as implicated in the control of a cell death process called pyroptosis that is induced by the lethal toxin (LT) from Bacillus anthracis[13].

Bottom Line: The parasite-induced cell death of infected macrophages bearing the LEW-Toxo1 alleles was found to exhibit pyroptosis-like features with ROS production, the activation of caspase-1 and IL1-β secretion.The pharmacological inactivation of caspase-1 using YVAD and Z-VAD inhibitors prevented the death of both intravacuolar parasites and host non-permissive macrophages but failed to restore parasite proliferation.The NOD-like receptor NLRP1a/Caspase-1 pathway is the best candidate to mediate the parasite-induced cell death.

View Article: PubMed Central - PubMed

Affiliation: UMR 5163, Centre National de la Recherche Scientifique (CNRS), Grenoble, France; Université Grenoble 1, Grenoble, France.

ABSTRACT
Natural immunity or resistance to pathogens most often relies on the genetic make-up of the host. In a LEW rat model of refractoriness to toxoplasmosis, we previously identified on chromosome 10 the Toxo1 locus that directs toxoplasmosis outcome and controls parasite spreading by a macrophage-dependent mechanism. Now, we narrowed down Toxo1 to a 891 kb interval containing 29 genes syntenic to human 17p13 region. Strikingly, Toxo1 is included in a haplotype block strictly conserved among all refractory rat strains. The sequencing of Toxo1 in nine rat strains (5 refractory and 4 susceptible) revealed resistant-restricted conserved polymorphisms displaying a distribution gradient that peaks at the bottom border of Toxo1, and highlighting the NOD-like receptor, Nlrp1a, as a major candidate. The Nlrp1 inflammasome is known to trigger, upon pathogen intracellular sensing, pyroptosis programmed-cell death involving caspase-1 activation and cleavage of IL-1β. Functional studies demonstrated that the Toxo1-dependent refractoriness in vivo correlated with both the ability of macrophages to restrict T. gondii growth and a T. gondii-induced death of intracellular parasites and its host macrophages. The parasite-induced cell death of infected macrophages bearing the LEW-Toxo1 alleles was found to exhibit pyroptosis-like features with ROS production, the activation of caspase-1 and IL1-β secretion. The pharmacological inactivation of caspase-1 using YVAD and Z-VAD inhibitors prevented the death of both intravacuolar parasites and host non-permissive macrophages but failed to restore parasite proliferation. These findings demonstrated that the Toxo1-dependent response of rat macrophages to T. gondii infection may trigger two pathways leading to the control of parasite proliferation and the death of parasites and host macrophages. The NOD-like receptor NLRP1a/Caspase-1 pathway is the best candidate to mediate the parasite-induced cell death. These data represent new insights towards the identification of a major pathway of innate resistance to toxoplasmosis and the prediction of individual resistance.

Show MeSH
Related in: MedlinePlus