Identification of genetic variation in the swine toll-like receptors and development of a porcine TLR genotyping array

Porcine beta defensin 2 attenuates inflammatory responses in IPEC-J2 cells against Escherichia coli via TLRs-NF-κB/MAPK signaling pathway

BACKGROUND

Porcine beta defensin 2 (pBD2) is one of the porcine beta defensins that has antibacterial activity, and plays an important role in the immunomodulatory activity that protects cells from pathogens. It has been reported that pBD2 plays their immunomodulatory functions related to the TLR4-NF-κB signal pathways. However, it is not completely clear how pBD2 reduces the inflammatory response caused by pathogens.

RESULTS

In this study, the effect of pBD2 on the expression of genes in the TLRs signaling pathway was investigated after IPEC-J2 cells were challenged with E. coli. The results showed that pBD2 decreased the expression of IL-8 induced by E. coli (P < 0.05), and pBD2 significantly decreased the expression of TLR4, TLR5 and TLR7 (P < 0.05), as well as the key downstream genes p38 and JNK which activated by E. coli (P < 0.05). In addition, pBD2 inhibited the p-p65, p-p38 and p-JNK which were up-regulated by E. coli.

CONCLUSIONS

pBD2 could reduce the inflammatory response induced by E. coli perhaps by inhibiting the TLRs-TAK1-NF-κB/MAPK signaling pathway which was activated by E. coli in IPEC-J2 cells. Our study further reveals the immunomodulatory activity of recombinant pBD2 against E. coli, and provides insights into the molecular mechanisms that protect cells from E. coli infection.

Single Nucleotide Polymorphisms of Immunity-Related Genes and Their Effects on Immunophenotypes in Different Pig Breeds

Enhancing resistance and tolerance to pathogens remains an important selection objective in the production of livestock animals. Single nucleotide polymorphisms (SNPs) vary gene expression at the transcriptional level, influencing an individual's immune regulation and susceptibility to diseases. In this study, we investigated the distribution of SNP sites in immune-related genes and their correlations with cell surface markers of immune cells within purebred (Taiwan black, Duroc, Landrace and Yorkshire) and crossbred (Landrace-Yorkshire) pigs. Thirty-nine SNPs of immune-related genes, including 11 cytokines, 5 chemokines and 23 Toll-like receptors (TLRs) (interferon-α and γ (IFN-α, γ), tumor necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), Monocyte chemoattractant protein-1 (MCP-1) and TLR3, TLR4, TLR7, TLR8, and TLR9) were selected, and the percentages of positive cells with five cell surface markers of CD4, CD8, CD80/86, MHCI, and MHCII were analyzed. There were 28 SNPs that were significantly different among breeds, particularly between Landrace and Taiwan black. For instance, the frequency of SNP1 IFN-α -235A/G in Taiwan black and Landrace was 11.11% and 96.15%, respectively. In addition, 18 SNPs significantly correlated with the expression of cell surface markers, including CD4, CD8, CD80/86, and MHCII. The percentage of CD4+ (39.27%) in SNP33 TLR-8 543C/C was significantly higher than those in A/C (24.34%), at p < 0.05. Together, our findings show that Taiwan black pigs had a unique genotype distribution, whereas Landrace and Yorkshire had a more similar genotype distribution. Thus, an understanding of the genetic uniqueness of each breed could help to identify functionally important SNPs in immunoregulation.

A 192 bp ERV fragment insertion in the first intron of porcine TLR6 may act as an enhancer associated with the increased expressions of TLR6 and TLR1

Background

Toll-like receptors (TLRs) play important roles in building innate immune and inducing adaptive immune responses. Associations of the TLR genes polymorphisms with disease susceptibility, which are the basis of molecular breeding for disease resistant animals, have been reported extensively. Retrotransposon insertion polymorphisms (RIPs), as a new type of molecular markers developed recently, have great potential in population genetics and quantitative trait locus mapping. In this study, bioinformatic prediction combined with PCR-based amplification was employed to screen for RIPs in porcine TLR genes. Their population distribution was examined, and for one RIP the impact on gene activity and phenotype was further evaluated.

Results

Five RIPs, located at the 3' flank of TLR3, 5' flank of TLR5, intron 1 of TLR6, intron 1 of TLR7, and 3' flank of TLR8 respectively, were identified. These RIPs were detected in different breeds with an uneven distribution among them. By using the dual luciferase activity assay a 192 bp endogenous retrovirus (ERV) in the intron 1 of TLR6 was shown to act as an enhancer increasing the activities of TLR6 putative promoter and two mini-promoters. Furthermore, real-time quantitative polymerase chain reaction (qPCR) analysis revealed significant association (p < 0.05) of the ERV insertion with increased mRNA expression of TLR6, the neighboring gene TLR1, and genes downstream in the TLR signaling pathway such as MyD88 (Myeloid differentiation factor 88), Rac1 (Rac family small GTPase 1), TIRAP (TIR domain containing adaptor protein), Tollip (Toll interacting protein) as well as the inflammatory factors IL6 (Interleukin 6), IL8 (Interleukin 8), and TNFα (Tumor necrosis factor alpha) in tissues of 30 day-old piglet. In addition, serum IL6 and TNFα concentrations were also significantly upregulated by the ERV insertion (p < 0.05).

Conclusions

A total of five RIPs were identified in five different TLR loci. The 192 bp ERV insertion in the first intron of TLR6 was associated with higher expression of TLR6, TLR1, and several genes downstream in the signaling cascade. Thus, the ERV insertion may act as an enhancer affecting regulation of the TLR signaling pathways, and can be potentially applied in breeding of disease resistant animals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13100-021-00248-w.

Cytokine and inflammatory mediator effects on TRPV4 function in choroid plexus epithelial cells

The choroid plexus (CP), composed of capillaries surrounded by a barrier epithelium, is the main producer of cerebrospinal fluid (CSF). The CP epithelium regulates the transport of ions and water between the blood and the ventricles, contributing to CSF production and composition. Several studies suggest a connection between the cation channel transient receptor potential vanilloid-4 (TRPV4) and transepithelial ion movement. TRPV4 is a nonselective, calcium-permeable cation channel present in CP epithelia reported to be activated by cytokines and inflammatory mediators. Utilizing the PCP-R (porcine choroid plexus-Riems) cell line, we investigated the effects of various cytokines and inflammatory mediators on TRPV4-mediated activity. Select proinflammatory cytokines (TNF-α, IL-1β, TGF-β1) had inhibitory effects on TRPV4-stimulated transepithelial ion flux and permeability changes, whereas anti-inflammatory cytokines (IL-10, IL-4, and IL-6) had none. Quantitative mRNA analysis showed that these cytokines had no effect on TRPV4 transcription levels. Inhibition of the transcription factor NF-κB, involved in the production and regulation of several inflammatory cytokines, inhibited TRPV4-mediated activity, suggesting a link between TRPV4 and cytokine production. Contrary to published studies, the proinflammatory mediator arachidonic acid (AA) had inhibitory rather than stimulatory effects on TRPV4-mediated responses. However, inhibition of AA metabolism also caused inhibitory effects on TRPV4, suggesting a complex interaction of AA and its metabolites in the regulation of TRPV4 activity. Together these data imply that TRPV4 activity is involved in the inflammatory response; it is negatively affected by proinflammatory mediators. Furthermore, arachidonic acid metabolites, but not arachidonic acid itself, are positive regulators of TRPV4.

Analysis of stage-specific expression of the toll-like receptor family in the porcine endometrium throughout the estrous cycle and pregnancy

Toll-like receptors (TLRs) play critical roles in innate immunity by regulating antimicrobial responses in mucosal tissues. The expression and function of TLRs in female reproductive tissues have been studied in several species, but the expression and function of TLRs and MYD88, an adaptor molecule in the TLR signaling pathway, at the maternal-conceptus interface are not well understood in pigs. Thus, we determined the expression of TLR1 - TLR10 and MYD88 in the endometrium, conceptus, and chorioallantoic tissues of pigs. TLR1 - TLR10 and MYD88 mRNAs were expressed in the endometrium during the estrous cycle and pregnancy in a stage-dependent manner. TLR and MYD88 mRNAs were also detected in early stage conceptuses and chorioallantoic tissues from Day 30 to term pregnancy. The expression of TLR2, TLR4, TLR5, and TLR7 was localized to epithelial and stromal cells in endometrial and chorioallantoic tissues. Increasing doses of P₄, but not E₂, induced the expression of TLR4, TLR5, TLR6, TLR7, and TLR8, while interferon-γ increased the expression of TLR2 and TLR7 in endometrial explant tissues. Expression of TLR3, TLR5, TLR6, TLR7, and MYD88 was higher in the endometrium with somatic cell nucleus transfer-derived conceptuses than conceptuses derived from natural mating on Day 12. These results indicate that the expression of TLR1 - TLR10 and MYD88 is dynamically regulated at the maternal-conceptus interface in pigs, suggesting that TLRs expressed in the endometrium and the placenta may play a critical role in regulating mucosal immune responses to support the establishment and maintenance of pregnancy.

Effects of dietary lysine restriction on inflammatory responses in piglets

The aim of this study was to investigate the effects of lysine restriction on inflammatory responses in piglets. 38 male piglets with similar body weight of 9.62 kg were randomly divided into control group (basal diet) and lysine-restricted group (diet containing 70% lysine of the control diet). The results showed that lysine restriction increased the serum concentration of IgG an IgM. Piglets fed the lysine-restricted diet exhibited overexpression of interleukin-8 (IL-8) in the kidney (P < 0.05) and IL-6 and IL-4 in the spleen (P < 0.05). The mRNA abundances of IL-4 in the kidney (P < 0.05) and IL-10 in the liver (P < 0.05) were significantly lower in the lysine-restricted group compared with the control group. Meanwhile, lysine restriction increased the mRNA level of Tlr8 in the kidney (P < 0.05) but decreased the mRNA level of Tlr8 in the liver (P < 0.05). Finally, lysine restriction markedly enhanced extracellular signal regulated kinases 1/2 (ERK1/2) phosphorylation in the kidney and liver and nuclear transcription factor kappa B (NF-κB) was activated in the liver and spleen in response to dietary lysine restriction. In conclusion, lysine restriction affected inflammatory responses in the kidney, liver, and spleen via mediating serum antibody volume, inflammatory cytokines, Tlrs system, and ERK1/2 and NF-κB signals in piglets.