The intestinal microbiota mediates inflammatory responses in heat-stressed pigs via the NOD1/RIP2/NF-κB signaling pathway.

Intestinal inflammation in pigs is widespread, involving complex pathogens, and is exacerbated by heat stress (HS). This study investigated HS alters gut microbiota to activate NOD1/RIP2/NF-κB signaling and induce intestinal inflammation. Twenty pigs exposed to HS (34 ± 1 °C) were compared to 20 controls (25 ± 3 °C). Tissues and feces were collected at intervals. Ninety germ-free mice were randomly divided into nine groups for fecal microbiota transplantation (FMT) experiments. Histopathological changes in colonic tissue were observed, and inflammatory factors in peripheral blood were quantified. The effects of HS on key proteins in the NOD1/RIP2 pathway were evaluated. An IPEC-J2 in vitro model was established, and a NOD1 overexpression vector was constructed to examine the effect of NOD1 overexpression on NF-κB activity. A high-performance liquid chromatography (HPLC) method was developed to measure IE-DAP concentrations in fecal samples from heat-stressed pigs. Results showed HS caused intestinal damage and increased inflammatory factors (MCP-1, TNF-α, IL-8, IL-18) in pigs, especially on days 7 and 14. Protein levels of HSP70, NOD1, RIP2, and nuclear p65 were significantly altered in colon tissues from day 7. FMT from heat-stressed pigs resulted in damaged colonic tissues, accompanied by increased numbers of white blood cells and neutrophils. The NOD1/RIP2/NF-κB signaling pathway was activated in colon tissues receiving feces from heat-stressed pigs, triggering a mild inflammatory response for mice. Fecal IE-DAP concentrations were higher in heat-stressed pigs. HS causes changes in IE-DAP levels of intestinal digesta, subsequently activating the NOD1/RIP2/NF-κB signaling pathway and promoting intestinal inflammation in pigs.