Heat stress induced gut microbiota changes activate TLR4 / NF-κB signaling pathway contributing to inflammatory bowel disease in pigs

Abstract

Background Various stressors alter the 'brain-gut axis' and contribute to many gastrointestinal disorders such as inflammatory bowel disease. However, the pathological mechanisms of these perturbations are poorly understood. Here, we report on the induction of intestinal inflammation in heat-stressed pigs and apply fecal microbiota transplantation from pigs to mice to elucidate the role of intestinal microbiota in TLR4/NF-κB signaling pathway activation. Results Twelve healthy adult pigs were subjected to heat stress (34 ± 1 °C and 75–85% relative humidity) and compared with 12 control pigs exposed to 25 ± 3 °C and the same humidity level. The pigs were sacrificed on days 1, 7, 14, and 21. Their colonic contents were collected for microbiome analyses and their colonic epithelia underwent transcriptome analyses. Pseudo-germ-free mice were gavaged with fecal bacteria from heat-stressed and control pigs on the collection days to determine whether gut microbiomes and immune responses resembling those in the pigs could be induced in the mice. Heat-stressed pigs presented with fever and diarrhea from day 7 and their colonic villus length, crypt depth/width, and goblet cell number were significantly lower than those of the controls. Their TLR4, TRAF6, and nuclear p65 were upregulated at the RNA and protein levels. Their proinflammatory IL-6, IL-8, and IL-17 were also upregulated. Colonic microflora composition in the heat-stressed pigs markedly differed from that of the controls. By day 14, the former presented with substantial increases in opportunistic pathogens such as Campylobacterales , Veillonellaceae , and Megasphaera . Intestinal lipopolysaccharide concentrations were higher in the heat-stressed than the control pigs. Mice administered fecal transplantation from heat-stressed pigs had a distinctly different colonic microflora composition from those receiving control pig fecal transplantation. Bacteroides were significantly diminished and Akkermansia were significantly augmented in mice administered feces from heat-stressed pigs for 14 d. In the colonic tissues of mice given feces from heat-stressed pigs, the TLR4/NF-κB signaling pathway was activated and there was a mild inflammatory response. Conclusion Heat stress promotes changes in gut microflora composition which, in turn, activates the TLR4/NF-κB signaling pathway and causes inflammatory bowel disease in pigs.

Alterations in intestinal microbiota composition coincide with impaired intestinal morphology and dysfunctional ileal immune response in growing-finishing pigs under constant chronic heat stress

“…Toll-like receptors are a class of classical recognition receptors, such as TLR-2 and TLR-4 , which can recognize the damage-associated molecular patterns to produce several pro-inflammatory cytokines to evoke the host immune response during heat stress [ 15 , 17 ]. In this study, we found that HS up-regulated TLR2/4 mRNA expression meanwhile elevated the expression of pro-inflammatory cytokines TNF-α, IL-6, IL-8 as well as P65 , indicated the activated intestinal immune response under HS, which is consistent with previous report [ 18 ]. Epithelial cells can produce mucins and anti-microbial peptides, which can enhance the intestinal epithelial barrier function by selective microbial permeation and directly influencing microbial populations [ 43 , 44 ].…”

“…We found the mucosal immune activation via TLR4/ nuclear factor kappa-B (TLR4/NF-κB) signaling pathway in the ileum by HS. The results of the fecal transplantation experiment also indicated that changes in gut microbial composition promoted by HS could activate the TLR4/NF-κB signaling pathway and cause inflammation in the colon of pigs [ 18 ]. Moreover, stress induces increased permeability of the gut allowing bacteria translocation and mucosal immune activation, which were reported to alter gut microbial composition in turn [ 48 ].…”

“…Especially, ileum was reported more sensitive to HS than other intestinal sections [ 10 ]. Gut microbiota changes induced by HS were speculated to activate TLR4/NF-κB signaling pathway contributing to inflammatory response in the colon of pigs [ 18 ]. However, the research about the ileal immune response and the associations with gut microbiota alterations is limited.…”

Heat stress on microbiota composition, barrier integrity, and nutrient transport in gut, production performance, and its amelioration in farm animals

“…In the phylum level, Firmicutes, Bacteroidetes, Proteobacteria , and Spirochetes in ruminal fluid were not changed at different temperatures and humidity levels [ 26 ]. In the same study, the quantification of the bacterial composition using oligonucleotide probes, the relative abundances of the Fibrobacter genus decreased, whereas that of Clostridium coccoides-Eubacterium rectale group, and Streptococcus genus increased due to increasing temperature [ 35 ]. In lactating cows, the relative abundance of fecal Firmicutes was lower and that of fecal Bacteroidetes was higher in the HS (temperature humidity index of 80.5 vs. 66.0) conditions [ 36 ].…”