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RNA sequencing provides exquisite insight into the manipulation of the alveolar macrophage by tubercle bacilli

ABSTRACT: Mycobacterium bovis, the agent of bovine tuberculosis, causes an estimated $3 billion annual losses to global agriculture due, in part, to the limitations of current diagnostics. Development of next-generation diagnostics requires a greater understanding of the interaction between the pathogen and the bovine host. Therefore, to explore the early response of the alveolar macrophage to infection, we report the first application of RNA-sequencing to define, in exquisite detail, the transcriptomes of M. bovis-infected and non-infected alveolar macrophages from ten calves at 2, 6, 24 and 48 hours post-infection. Differentially expressed sense genes were detected at these time points that revealed enrichment of innate immune signalling functions, and transcriptional suppression of host defence mechanisms (e.g., lysosome maturation). We also detected differentially expressed natural antisense transcripts, which may play a role in subverting innate immune mechanisms following infection. Furthermore, we report differential expression of novel bovine genes, some of which have immune-related functions based on orthology with human proteins. This is the first in-depth transcriptomics investigation of the alveolar macrophage response to the early stages of M. bovis infection and reveals complex patterns of gene expression and regulation that underlie the immunomodulatory mechanisms used by M. bovis to evade host defence mechanisms.

ORGANISM(S): Bos taurus

PROVIDER: GSE62506 | GEO | 2015/10/10

SECONDARY ACCESSION(S): PRJNA264301

REPOSITORIES: GEO

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Project description:Background: Mycobacterium bovis is the causative agent of bovine tuberculosis (BTB), a pathological infection with significant economic impact. Recent studies have highlighted the role of functional genomics to better understand the molecular mechanisms governing the host immune response to M. bovis infection. Furthermore, these studies may enable the identification of novel transcriptional markers of BTB that can augment current diagnostic tests and surveillance programmes. In the present study, we have analysed the transcriptome of peripheral blood leukocytes (PBL) from eight M. bovis-infected and eight control non-infected age-matched and sex-matched Holstein-Friesian cattle using the Affymetrix® GeneChip® Bovine Genome Array with features representing more than 23,000 gene transcripts and over 19,000 gene probe sets. Results: Control and infected animals had similar mean white blood cell counts. However, the mean number of lymphocytes was significantly increased in the infected group relative to the control group (P = 0.001), while the mean number of monocytes was significantly decreased in the BTB group (P = 0.002). Hierarchical clustering analysis using gene expression data from all 5,388 detectable mRNA transcripts unambiguously partitioned the animals according to their disease status. In total, 2,960 gene transcripts were differentially expressed (DE) between the infected and control animal groups (adjusted P-value threshold ≤ 0.05); with the number of genes showing decreased relative expression (1,563) exceeding those displaying increased relative expression (1,397). Systems analysis using the Ingenuity Systems Pathway Analysis (IPA) Knowledge Base revealed an over-representation of DE genes involved in the immune response functional category. More specifically, 64.5% of genes in the affects immune response subcategory displayed decreased relative expression levels in the infected animals compared to the control group. Conclusions: This study demonstrates that genome-wide transcriptional profiling of PBL can distinguish active M. bovis-infected animals from control non-infected animals. Furthermore, the results obtained support previous investigations demonstrating that mycobacterial infection is associated with host transcriptional suppression. These data support the use of transcriptomic technologies to enable the identification of robust, reliable transcriptional markers of active M. bovis infection Affymetrix GeneChip® Bovine Genome Arrays were used to examine gene expression of peripheral blood leukocytes from cattle infected with Mycobacterium bovis

Project description:Purpose: The goal of this RNA-seq study was to profile changes in miRNA expression in bovine alveolar macrophages isolated from Holstein-Friesian and challenged with M. bovis over a 48 hour time course. Background: Mycobacterium bovis, the causative agent of bovine tuberculosis, is a major infectious disease problem for global agriculture, resulting in losses of billions of Euros annually. The bacterium spreads via an airborne route and is taken up by alveolar macrophages in the lung. MicroRNAs (miRNAs) — short non-coding RNAs that post-transcriptionally regulate gene expression — are increasingly being recognised as key regulators of the immune system. There is mounting evidence for the role of miRNAs in regulating the early innate immune response to mycobacterial infections; however, the underlying processes are not fully understood yet. Results: In total, 2.5 billion raw sequencing reads were generated. 93% of post-filtered reads aligned to known miRNAs. The expression of miRNAs varied over a wide range: miR-21 was expressed at approximately 430,000 reads per million (RPM), but the majority were more lowly expressed (1000-10,000 RPM). One, six, and 40 miRNAs were identified as significantly differentially expressed at 2, 24 and 48 h post-infection (hpi), respectively (FDR < 0.05); the differential expression at 48 hpi of three (out of four) of these miRNAs was confirmed by RT-qPCR. No miRNAs were detected to be differentially expressed 6 hpi. Many of the differentially expressed miRNAs have been shown to have a role in the host response to mycobacterial pathogens and other infections in other species. MicroRNA-155, for example, which we observed to be upregulated in response to M. bovis has recently been shown to control autophagy in murine macrophages infected with the human pathogen Mycobacterium tuberculosis. Pathway analysis suggests that upregulated miRNAs target endocytosis and lysosome trafficking, thus potentially enhancing bacterial survival. An independent gene silencing experiment with a bovine macrophage cell line (Bomac) has confirmed downregulation of IRAK1 by miR-146a and miR-146b. Moreover, downregulation of another predicted target, TGFRB2, by miR-146a was also confirmed. These findings support the target prediction and pathway analysis results. Our results suggest that several miRNAs have an important role in the alveolar macrophage response to pathogenic mycobacteria.

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RNA sequencing provides exquisite insight into the manipulation of the alveolar macrophage by tubercle bacilli

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