High-level expression of NRAMP1 in peripheral blood cells and tuberculous granulomas from Mycobacterium bovis-infected bovines

Association between SLC11A1 (NRAMP1) polymorphisms and susceptibility to tuberculosis in Chinese Holstein cattle

We investigated the associations between SLC11A1 polymorphisms and susceptibility to tuberculosis (TB) in Chinese Holstein cattle, using a case-control study of 136 animals that had positive reactions to TB tests and showed symptoms and 96 animals that had negative reactions to tests and showed no symptoms. Polymerase chain reaction (PCR) sequencing and the restriction fragment length polymorphism (RFLP) technique were used to detect and determine SLC11A1 polymorphisms. Association analysis identified significant correlations between SLC11A1 polymorphisms and susceptibility/resistance to TB, and two genetic markers for SLC11A1 were established using PCR-RFLP. Sequence alignment of SLC11A1 revealed seven single-nucleotide polymorphisms (SNPs). This is the first report of MaeII PCR-RFLP markers for the SLC11A1-SNP3 site and PstI PCR-RFLP markers for the SLC11A1-SNP5 and SLC11A1-SNP6 sites in Chinese Holstein cattle. Logistic regression analysis indicated that SLC11A1-SNP1, SLC11A1-SNP3, and SLC11A1-SNP5 were significantly associated with susceptibility/resistance to TB. Two genotypes of SLC11A1-SNP3 were susceptible to TB, whereas one genotype of SLC11A1-SNP1 and two genotypes of SLC11A1-SNP5 were resistant. Haplotype analysis showed that nine haplotypes were potentially resistant to TB. After Bonferroni correction, three of the haplotypes remained significantly associated with TB resistance. SLC11A1 is a useful candidate gene related to TB in Chinese Holstein cattle.

Relationship of bovine TNF-α gene polymorphisms with the risk of bovine tuberculosis in Holstein cattle

Many studies suggest significant genetic variation in the resistance of cattle and humans to infection with Mycobacterium bovis (M. bovis), the causative agent of zoonotic tuberculosis. TNF-α promotes inflammation and induces apoptosis in response to mycobacterial infection. The aim of the present study was to investigate the influence of single nucleotide polymorphisms of the TNF-α gene on bovine tuberculosis (bTB) susceptibility. We genotyped the TNF-α gene in 74 bTB-infected Holstein cows and 90 healthy control animals. The influence in the exon 3 region of TNF-α polymorphisms on bTB susceptibility was subsequently investigated by association analysis. Our finding demonstrated that the g.27534932A>C polymorphism of the TNF-α is associated with bTB in Holstein cattle. The susceptibility of cattle with the g.27534932A>C genotype compared with the CC genotype was 4.11-fold (95% CI, 1.27–13.36; P=0.02) higher. The g.27534932A>C polymorphism located in exon 3 of the TNF-α gene, and the functional consequence was missense. The deduced amino acid sequence for the protein product revealed an arginine to serine conversion at position 159, which may affect initiation of protein synthesis and disrupt normal TNF-α function that protects animals against mycobacterial infection. A significant association was observed with the A allele as a risk factor for bTB susceptibility (OR, 3.84; 95% CI, 1.21–12.17; P=0.02). In conclusion, this is the first report showing that the g.27534932A>C polymorphism may contribute to TNF-α-mediated bTB susceptibility.

A preliminary study of genetic factors that influence susceptibility to bovine tuberculosis in the British cattle herd

Associations between specific host genes and susceptibility to Mycobacterial infections such as tuberculosis have been reported in several species. Bovine tuberculosis (bTB) impacts greatly the UK cattle industry, yet genetic predispositions have yet to be identified. We therefore used a candidate gene approach to study 384 cattle of which 160 had reacted positively to an antigenic skin test ('reactors'). Our approach was unusual in that it used microsatellite markers, embraced high breed diversity and focused particularly on detecting genes showing heterozygote advantage, a mode of action often overlooked in SNP-based studies. A panel of neutral markers was used to control for population substructure and using a general linear model-based approach we were also able to control for age. We found that substructure was surprisingly weak and identified two genomic regions that were strongly associated with reactor status, identified by markers INRA111 and BMS2753. In general the strength of association detected tended to vary depending on whether age was included in the model. At INRA111 a single genotype appears strongly protective with an overall odds ratio of 2.2, the effect being consistent across nine diverse breeds. Our results suggest that breeding strategies could be devised that would appreciably increase genetic resistance of cattle to bTB (strictly, reduce the frequency of incidence of reactors) with implications for the current debate concerning badger-culling.

Primary transcriptomes of Mycobacterium avium subsp. paratuberculosis reveal proprietary pathways in tissue and macrophages

Background

Mycobacterium avium subsp. paratuberculosis (MAP) persistently infects intestines and mesenteric lymph nodes leading to a prolonged subclinical disease. The MAP genome sequence was published in 2005, yet its transcriptional organization in natural infection is unknown. While prior research analyzed regulated gene sets utilizing defined, in vitro stress related or advanced surgical methods with various animal species, we investigated the intracellular lifestyle of MAP in the intestines and lymph nodes to understand the MAP pathways that function to govern this persistence.

Results

Our transcriptional analysis shows that 21%, 8% and 3% of the entire MAP genome was represented either inside tissues, macrophages or both, respectively. Transcripts belonging to latency and cell envelope biogenesis were upregulated in the intestinal tissues whereas those belonging to intracellular trafficking and secretion were upregulated inside the macrophages. Transcriptomes of natural infection and in vitro macrophage infection shared genes involved in transcription and inorganic ion transport and metabolism. MAP specific genes within large sequence polymorphisms of ancestral M. avium complex were downregulated exclusively in natural infection.

Conclusions

We have unveiled common and unique MAP pathways associated with persistence, cell wall biogenesis and virulence in naturally infected cow intestines, lymph nodes and in vitro infected macrophages. This dichotomy also suggests that in vitro macrophage models may be insufficient in providing accurate information on the events that transpire during natural infection. This is the first report to examine the primary transcriptome of MAP at the local infection site (i.e. intestinal tissue). Regulatory pathways that govern the lifecycle of MAP appear to be specified by tissue and cell type. While tissues show a "shut-down" of major MAP metabolic genes, infected macrophages upregulate several MAP specific genes along with a putative pathogenicity island responsible for iron acquisition. Many of these regulatory pathways rely on the advanced interplay of host and pathogen and in order to decipher their message, an interactome must be established using a systems biology approach. Identified MAP pathways place current research into direct alignment in meeting the future challenge of creating a MAP-host interactome.

Investigation of the association of the SLC11A1 gene with resistance/sensitivity of goats (Capra hircus) to paratuberculosis

SLC11A1 (solute carrier family 11 member A1) protein is located on the phagolysosome membrane of macrophages and participates in bacterial killing. Here we have extended our previous work on the investigation of the potential association of polymorphisms of the 3'untranslated region (UTR) of SLC11A1 gene with test-positivity of goats to Mycobacterium avium subsp. paratuberculosis (MAP). Blood, serum and faeces were collected from 223 adult goats, from nine goat farms from Greece with a long-term record of paratuberculosis but no vaccination or tuberculin testing. The samples were subjected to sequence and structure analysis of the SLC11A1 gene and were evaluated by ELISA, culture and real time polymerase chain reaction. The 3'UTR region of the targeted gene revealed 2 microsatellites consisting of a variable number of guanine-thymine repeats named regions A and B. Statistically significant association was recorded between genotypes of region B and ELISA results, whereas the presence of B(7) allele was found to contribute to ELISA negativity. The comparison of the SLC11A1 mRNA level pre- and post-exposure to MAP shows elevated gene expression especially at the 3-h time point, in all macrophages tested regardless of their genotype. Unfortunately the latter could not be linked at a statistically significant level with any of the targeted genetic polymorphisms separately. In conclusion it can be stated that the evidence reported here provide the first indications on the association of B genotypes of the SLC11A1 gene and the detection of MAP-specific antibody by ELISA in goats.

Expression of NRAMP1 and iNOS in Mycobacterium avium subsp. paratuberculosis naturally infected cattle

Paratuberculosis (PTB) is a chronic disease caused by M. avium subsp. paratuberculosis (MAP) that affects several animal species, and some studies have suggested that there may be a relationship between Crohn's disease and PTB. Significant aspects of PTB pathogenesis are not yet completely understood, such as the role of macrophages. Natural resistance-associated macrophage protein 1 (NRAMP1) and the inducible nitric oxide synthase (iNOS) molecules have shown nonspecific effects against several intracellular pathogens residing within macrophages. However, these molecules have been scarcely studied during natural infection with MAP. In this work, changes in NRAMP1 and iNOS expression were surveyed by immunohistochemistry in tissue samples from MAP-infected cattle and healthy controls. Our findings show strong specific immunolabeling against both NRAMP1 and iNOS molecules, throughout granulomatous PTB-compatible lesions in ileum and ileocaecal lymph nodes from paratuberculous cattle compared with uninfected controls, suggesting a relationship between the expression of these molecules and the pathogenesis of PTB disease.

Lesion development and immunohistochemical changes in granulomas from cattle experimentally infected with Mycobacterium bovis

Mycobacterium bovis, the causative agent of bovine tuberculosis, persists within granulomas. Formation of granulomas involves a complex array of immune activation and cellular migration. To examine temporal changes in granuloma development, we inoculated 32 cattle with M. bovis of deer origin. Tissues from 4 calves each were examined at 15, 28, 42, 60, 90, 180, 270, and 370 days after inoculation. Granulomas in the medial retropharyngeal lymph node were staged (I-IV) on the basis of cellular composition and the presence or absence of necrosis and peripheral fibrosis. Immunohistochemistry for inducible nitric oxide synthase (iNOS), CD68, CD4, CD8, and gamma/delta T cells was performed. Fifteen days after inoculation only stage I granulomas were seen, while between 28 and 60 days, there was a steady progression through granuloma stages such that by day 60, granulomas of all 4 stages were seen. Acid-fast bacilli were present in moderate-to-large numbers in stage I granulomas 15-60 days after inoculation. Stage IV granulomas contained large numbers of acid-fast bacteria. Abundant iNOS immunoreactivity was associated with granulomas from day 15 through day 60 but was minimal from day 90 to the termination of the experiment. The relative number of CD4+ and CD68+ cells remained constant throughout the study. In contrast, at time points >60 days, numbers of CD8+ and gamma/delta T cells diminished. Tuberculous granulomas are dynamic lesions that follow an orderly progression through disease stages. Diminished expression of iNOS and reduced numbers of CD8+ and gamma/delta T cells late in the progression of tuberculous granulomas may represent a failure of the host response to control infection.

NRAMP1 3' untranslated region polymorphisms are not associated with natural resistance to Brucella abortus in cattle

The NRAMP1 gene encodes a divalent cation transporter, located in the phagolysosomal membrane of macrophages, that has been associated with resistance to intracellular pathogens. In cattle, natural resistance against brucellosis has been associated with polymorphisms at the 3' untranslated region (3'UTR) of the NRAMP1 gene, which are detectable by single-strand conformational analysis (SSCA). This study aimed to evaluate the association between NRAMP1 3'UTR polymorphisms and resistance against bovine brucellosis in experimental and natural infections. In experimentally infected pregnant cows, abortion occurred in 42.1% of cows with a resistant genotype (SSCA(r); n = 19) and in 43.1% of those with a susceptible genotype (SSCA(s); n = 23). Furthermore, no association between intensity of pathological changes and genotype was detected. In a farm with a very high prevalence of bovine brucellosis, the percentages of strains of the SSCA(r) genotype were 86 and 84% in serologically positive (n = 64) and negative (n = 36) cows, respectively. Therefore, no association was found between the NRAMP1-resistant allele and the resistant phenotype in either experimental or naturally occurring brucellosis. To further support these results, bacterial intracellular survival was assessed in bovine monocyte-derived macrophages from cattle with either the resistant or susceptible genotype. In agreement with our previous results, no difference was observed in the rates of intracellular survival of B. abortus within macrophages from cattle with susceptible or resistant genotypes. Taken together, these results indicate that these polymorphisms at the NRAMP1 3'UTR do not affect resistance against B. abortus in cattle and that they are therefore not suitable markers of natural resistance against bovine brucellosis.

Coexpression of NRAMP1, iNOS, and nitrotyrosine in bovine tuberculosis

In murine models the inducible nitric oxide synthase (iNOS) and the natural resistance associated macrophage protein (NRAMP1) play major roles in host defense against mycobacteria. iNOS regulates nitric oxide (NO) production, which is noxious for ingested mycobacteria, and NRAMP1 displays pleiotropic antimicrobial effects, including upregulation of iNOS expression. Little is known about the role of these molecules in bovine tuberculosis (TB). In this work we demonstrate by Western blot a high expression of NRAMP1 in peripheral blood mononuclear cells (PBMCs), alveolar macrophages (obtained by bronchioalveolar lavage), and lymph node granulomas from 8 Holstein-Freisian cattle with autopsy-proven bovine TB. Immunohistochemistry revealed the abundant expression of NRAMP1 and iNOS in lymph node and lung granulomas. Immunoreactivity was abundant in the cytoplasm of many epithelioid macrophages and multinucleated giant cells of the Langhans type. A striking accumulation of nitrotyrosine (NT), an indicator of iNOS activity and local NO production, was observed in granuloma cells, particularly in multinucleated Langhans cells. This study shows that the expression of NRAMP1 and iNOS is costimulated in granulomas, which are protective T-cell reactions against mycobacteria.

RNA-binding protein HuR is required for stabilization of SLC11A1 mRNA and SLC11A1 protein expression

The solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1) gene is associated with infectious and autoimmune diseases and plays an important role in macrophage activation. Human SLC11A1 mRNA contains an AU-rich element (ARE) within the 3' untranslated region; however, its role in the regulation of SLC11A1 gene expression has not been elucidated. Here we analyze the expression of SLC11A1 in human monocytes and HL-60 cells and then use HL-60 cells as a model to determine whether RNA-binding protein HuR is associated with the ARE and involved in SLC11A1 mRNA turnover. Our results demonstrate a binding of HuR to the SLC11A1 ARE in phorbol myristate acetate (PMA)-differentiated cells dramatically increased compared to that in undifferentiated cells. Interestingly, PMA-induced accumulation of cytoplasmic HuR occurs in parallel with an increase in the binding of HuR to SLC11A1 ARE and with an increase in the SLC11A1 mRNA level. This suggests that HuR's cytoplasmic localization plays an important role in the regulation of SLC11A1 expression. We also observe that down-regulation of HuR expression by RNA interference (RNAi) results in a decrease in SLC11A1 expression which can be restored by the addition of recombinant HuR protein to the RNAi-treated cells. Finally, we show that HuR overexpression in HL-60 cells significantly increases the SLC11A1 mRNA stability. Taken together, our data demonstrate that HuR is a key mediator of posttranscriptional regulation and expression of the SLC11A1 gene.