Distinct peripheral blood RNA responses to Salmonella in pigs differing in Salmonella shedding levels: intersection of IFNG, TLR and miRNA pathways.

Transcriptomic analysis of the response to bacterial pathogens has been reported for several species, yet few studies have investigated the transcriptional differences in whole blood in subjects that differ in their disease response phenotypes. Salmonella species infect many vertebrate species, and pigs colonized with Salmonella enterica serovar Typhimurium (ST) are usually asymptomatic, making detection of these Salmonella-carrier pigs difficult. The variable fecal shedding of Salmonella is an important cause of foodborne illness and zoonotic disease. To investigate gene pathways and biomarkers associated with the variance in Salmonella shedding following experimental inoculation, we initiated the first analysis of the whole blood transcriptional response induced by Salmonella. A population of pigs (n = 40) was inoculated with ST and peripheral blood and fecal Salmonella counts were collected between 2 and 20 days post-inoculation (dpi). Two groups of pigs with either low shedding (LS) or persistent shedding (PS) phenotypes were identified. Global transcriptional changes in response to ST inoculation were identified by Affymetrix Genechip® analysis of peripheral blood RNA at day 0 and 2 dpi. ST inoculation triggered substantial gene expression changes in the pigs and there was differential expression of many genes between LS and PS pigs. Analysis of the differential profiles of gene expression within and between PS and LS phenotypic classes identified distinct regulatory pathways mediated by IFN-γ, TNF, NF-κB, or one of several miRNAs. We confirmed the activation of two regulatory factors, SPI1 and CEBPB, and demonstrated that expression of miR-155 was decreased specifically in the PS animals. These data provide insight into specific pathways associated with extremes in Salmonella fecal shedding that can be targeted for further exploration on why some animals develop a carrier state. This knowledge can also be used to develop rational manipulations of genetics, pharmaceuticals, nutrition or husbandry methods to decrease Salmonella colonization, shedding and spread.

Analysis of porcine transcriptional response to Salmonella enterica serovar Choleraesuis suggests novel targets of NFkappaB are activated in the mesenteric lymph node.

BACKGROUND: Specific knowledge of the molecular pathways controlling host-pathogen interactions can increase our understanding of immune response biology as well as provide targets for drug development and genetic improvement of disease resistance. Toward this end, we have characterized the porcine transcriptional response to Salmonella enterica serovar Choleraesuis (S. Choleraesuis), a Salmonella serovar that predominately colonizes swine, yet can cause serious infections in human patients. Affymetrix technology was used to screen for differentially expressed genes in pig mesenteric lymph nodes (MLN) responding to infection with S. Choleraesuis at acute (8 hours (h), 24 h and 48 h post-inoculation (pi)) and chronic stages (21 days (d) pi). RESULTS: Analysis of variance with false discovery rate control identified 1,853 genes with significant changes in expression level (p-value < 0.01, q-value < 0.26, and fold change (FC) > 2) during infection as compared to un-inoculated control pigs. Down-regulation of translation-related genes at 8 hpi and 24 hpi implied that S. Choleraesuis repressed host protein translation. Genes involved in the Th1, innate immune/inflammation response and apoptosis pathways were induced significantly. However, antigen presentation/dendritic cell (DC) function pathways were not affected significantly during infection. A strong NFkappaB-dependent response was observed, as 58 known NFkappaB target genes were induced at 8, 24 and/or 48 hpi. Quantitative-PCR analyses confirmed the microarray data for 21 of 22 genes tested. Based on expression patterns, these target genes can be classified as an "Early" group (induced at either 8 or 24 hpi) and a "Late" group (induced only at 48 hpi). Cytokine activity or chemokine activity were enriched within the Early group genes GO annotations, while the Late group was predominantly composed of signal transduction and cell metabolism annotated genes. Regulatory motif analysis of the human orthologous promoters for both Early and Late genes revealed that 241 gene promoters were predicted to contain NFkappaB binding sites, and that of these, 51 Early and 145 Late genes were previously not known to be NFkappaB targets. CONCLUSION: Our study provides novel genome-wide transcriptional profiling data on the porcine response to S. Choleraesuis and expands the understanding of NFkappaB signaling in response to Salmonella infection. Comparison of the magnitude and timing of porcine MLN transcriptional response to different Salmonella serovars, S. Choleraesuis and S. Typhimurium, clearly showed a larger but later transcriptional response to S. Choleraesuis. Both microarray and QPCR data provided evidence of a strong NFkappaB-dependent host transcriptional response during S. Choleraesuis infection. Our data indicate that a lack of strong DC-mediated antigen presentation in the MLN may cause S. Choleraesuis infected pigs to develop a systemic infection, and our analysis predicts nearly 200 novel NFkappaB target genes which may be applicable across mammalian species.

Iron regulated genes of Salmonella enterica serovar Typhimurium in response to norepinephrine and the requirement of fepDGC for norepinephrine-enhanced growth.

Catecholamines may stimulate enteric bacteria including the foodborne pathogen Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) by two mechanisms in vivo: as a quorum sensing signal and a supplier of iron. To identify genes of Salmonella Typhimurium that respond to norepinephrine, transposon mutagenesis and DNA microarray analysis were performed. Insertional mutations in the following genes decreased norepinephrine-enhanced growth: degS, entE, entF, fes, gpmA, hfq, STM3846. DNA microarray and real-time RT-PCR analyses revealed a decrease in the expression of several genes involved in iron acquisition and utilization during norepinephrine exposure, signifying the iron-limiting conditions of serum-SAPI minimal medium and the siderophore-like activity of norepinephrine. Unlike the wild-type parent strain, growth of neither a fepA iroN cirA mutant nor a fepC mutant, harboring deletional mutations in the outer and inner membrane transporters of enterochelin, respectively, was enhanced by norepinephrine. However, growth of the fepC and the fepA iroN cirA mutants could be rescued by an alternative siderophore, ferrioxamine E, further validating the role of norepinephrine in supplying the organism with iron via the catecholate-specific iron transport system. Contrary to previous reports using small animal models, the fepA iroN cirA mutant of Salmonella Typhimurium colonized the swine gastrointestinal tract, as did the fepC mutant.

Global transcriptional response of porcine mesenteric lymph nodes to Salmonella enterica serovar Typhimurium.

To elucidate the host transcriptional response to Salmonella enterica serovar Typhimurium, Affymetrix porcine GeneChip analysis of pig mesenteric lymph nodes was used to identify 848 genes showing differential expression across different times after inoculation or when compared to non-inoculated controls. Annotation analyses showed that a high proportion of these differentially expressed (DE) genes are involved in immune and inflammatory responses. T helper 1, innate/inflammatory, and antigen-processing pathways were induced at 24 h post-inoculation (hpi) and/or 48 hpi, while apoptosis and antigen presentation/dendritic cell function pathways were downregulated at 8 hpi. Cluster analyses revealed that most DE genes annotated as NFkappaB targets were grouped into a specific induced subcluster, while many translation-related DE genes were found in a repressed subcluster. Quantitative polymerase chain reaction analyses confirmed the Affymetrix results, revealing transcriptional induction of NFkappaB target genes at 24 hpi and suppression of the NFkappaB pathway from 24 to 48 hpi. We propose that such NFkappaB suppression in antigen-presenting cells may be the mechanism by which S. Typhimurium eludes a strong inflammatory response to establish a carrier status in pigs.

Porcine differential gene expression in response to Salmonella enterica serovars Choleraesuis and Typhimurium.

An investigation of the porcine response to gastrointestinal infection with Salmonella enterica serovars Choleraesuis (narrow host range) and Typhimurium (broad host range) revealed markedly different transcriptional profiles. Seven genes identified by suppression subtractive hybridization as up-regulated in the mesenteric lymph nodes at 24h (h) post-inoculation (p.i.) in serovar Choleraesuis-infected pigs (ARPC2, CCT7, HSPH1, LCP1, PTMA, SDCBP, VCP) and three genes in serovar Typhimurium-infected pigs (CD47/IAP, CXCL10, SCARB2) were analyzed by real-time PCR at 8h, 24 h, 48 h, 7 days (d) and 21 d p.i. A comparison between the two Salmonella infections revealed significant differences in transcriptional induction early in the infection (8-24h) for the serovar Typhimurium-infected pigs, whereas the serovar Choleraesuis-infected pigs exhibited significantly higher levels of gene expression at the later time points (48h-21 d), except for HSPH1. A similar gene expression trend was observed for immune-related genes involved in innate immunity and the inflammatory T helper 1 (Th1) response. Initial repression of gene expression in the serovar Choleraesuis-infected pigs from 8 to 48h p.i. (IFNG, IL12A, IL4, IL8, CSF2) coincided with extended transcriptional activation throughout the 21 d infection (IFNG, INDO, SOCS1, STAT1, IL1B, IL6, IL8, SLC11A1). The serovar Typhimurium-infected swine presented a more transient induction of immune-related genes (IFNG, INDO, IRF1, SOCS1, STAT1, IL1B, IL8, SLC11A1) early in the infection (24-48 h) followed by a significant repression of IL12A, IL12B, IL4, IL8 and CSF2. Collectively, these data reveal specific porcine genes with differences in gene expression kinetics that may be responsible for the variation in disease progression observed in swine infected with Typhimurium compared to Choleraesuis.

Gene expression profiling in Salmonella Choleraesuis-infected porcine lung using a long oligonucleotide microarray.

Understanding the transcriptional response to pathogenic bacterial infection within food animals is of fundamental and applied interest. To determine the transcriptional response to Salmonella enterica serovar Choleraesuis (SC) infection, a 13,297-oligonucleotide swine array was used to analyze RNA from control, 24-h postinoculation (hpi), and 48-hpi porcine lung tissue from pigs infected with SC. In total, 57 genes showed differential expression (p < 0.001; false discovery rate = 12%). Quantitative real-time PCR (qRT-PCR) of 61 genes was used to confirm the microarray results and to identify pathways responding to infection. Of the 33 genes identified by microarray analysis as differentially expressed, 23 were confirmed by qRT-PCR results. A novel finding was that two transglutaminase family genes (TGM1 and TGM3) showed dramatic increases in expression postinoculation; combined with several other apoptotic genes, they indicated the induction of apoptotic pathways during SC infection. A predominant T helper 1-type immune response occurred during infection, with interferon gamma (IFNG) significantly increased at 48 hpi. Genes induced by IFNs (GBP1, GBP2, C1S, C1R, MHC2TA, PSMB8, TAP1, TAP2) showed increased expression during porcine lung infection. These data represent the first thorough investigation of gene regulation pathways that control an important porcine respiratory and foodborne bacterial infection.

Analysis of porcine differential gene expression following challenge with Salmonella enterica serovar Choleraesuis using suppression subtractive hybridization.

Swine-adapted Salmonella enterica subsp. enterica serovar Choleraesuis (S. Choleraesuis) is the pathogen most frequently isolated from diseased pigs and may affect host gene expression in a species-specific manner. To characterize the porcine transcriptional response to S. Choleraesuis infection, the mRNA profiles from the mesenteric lymph nodes of three non-infected and three experimentally infected pigs at 24 h post-inoculation were analyzed by suppression subtractive hybridization (SSH). Forty-four up-regulated and 44 down-regulated genes were revealed by differential cDNA screening of 384 forward and 288 reverse subtracted cDNA clones. The DNA sequence of the cDNA clones identified genes with a role in a variety of cellular functions as well as gene products of unknown function. Seven up-regulated genes (CXCL10, CXCR4, SDCBP, DNAJA1, HSPH1, HSP90 and ANXA5) and two functionally related genes (HSP70 and DNAJA4:pDJA1) were selected for further analysis based on their predicted roles in infection and immunity. Real-time RT-PCR was performed using RNA collected from a time course of infection spanning from the acute phase (8 h) to the chronic phase (21 days) to confirm and quantitate the up-regulation of the SSH-enriched genes. Correlating with the clinical signs of infection (fever, diarrhea and lethargy), the most dramatic induction of gene expression for all nine genes occurred at 48 h post-inoculation. This investigation further defines the porcine response to a host-adapted strain of Salmonella by revealing the differential expression of genes with a role in a variety of host cellular functions including innate immunity and cytoskeleton regulation.