Translocation of gut microbes to epididymal white adipose tissue drives lipid metabolism disorder under heat stress

Heat stress induces multi-organ damage and serious physiological dysfunction in mammals,and gut bacteria may translocate to extra-intestinal tissues under heat stress pathology.However,whether gut bacteria translocate to the key metabolic organs and impair function as a result of heat stress remains unknown.Using a heat stress-induced mouse model,heat stress inhibited epididymal white adipose tissue(eWAT)expansion and induced lipid metabolic disorder but did not damage other organs,such as the heart,liver,spleen,or muscle.Microbial profiling analysis revealed that heat stress shifted the bacterial community in the cecum and eWAT but not in the inguinal white adipose tissue,blood,heart,liver,spleen,or muscle.Notably,gut-vascular barrier function was impaired,and the levels of some bacteria,particularly Lactobacillus,were higher in the eWAT,as confirmed by catalyzed reporter deposition fluorescence in situ hybridization(CARD-FISH)staining when mice were under heat stress.Moreover,integrated multi-omics analysis showed that the eWAT microbiota was associated with host lipid metabolism,and the expression of genes involved in the lipid metabolism in eWAT was upregulated under heat stress.A follow-up microbial supplementation study after introducing Lactobacillus plantarum to heat-stressed mice revealed that the probiotic ameliorated heat stress-induced loss of eWAT and dyslipidemia and reduced gut bacterial translocation to the eWAT by improving gut barrier function.Overall,our findings suggest that gut bacteria,particularly Lactobacillus spp.,play a crucial role in heat stress-induced lipid metabolism disorder and that there is therapeutic potential for using probiotics,such as Lactobacillus plantarum.

Duodenum has the greatest potential to absorb soluble non-ammonia nitrogen in the nonmesenteric gastrointestinal tissues of dairy cows

In cattle, dietary protein is gradually degraded into peptide-bound amino acids（PBAAs）, free amino acids（FAAs）, and ultimately into ammonia by the rumen microbes. Both PBAA and FAA are milk protein precursors, and the rumen and small intestines are the main sites where such precursors are produced and absorbed. This work was designed to investigate the expression of the peptide transporter Pep T1 and the AA transporters ASCT2, y＋LAT1, and ATB0,＋, and the concentrations of PBAA, FAA, and soluble protein in the rumen, omasum, and duodenum of dairy cows. Tissues and digesta were collected from six healthy Chinese Holstein dairy cows immediately after the animals were slaughtered. The expression of transporters was analyzed by real-time quantitative polymerase chain reaction（PCR）. The FAA concentration was assessed using an amino acid（AA） analyzer, PBAA concentration by quantification of AA before and after acid-hydrolysis by 6 mol/L HCl, and soluble protein concentration by quantification of the bicinchoninic acid content. The results showed that the relative abundance of m RNA of the transporters and the soluble non-ammonia nitrogen（SNAN） concentration of each fraction were greater in the duodenum than in the rumen or omasum. These results indicate that the duodenum is the predominant location within the nonmesenteric digestive tract for producing milk protein precursors. In addition, PBAA was the largest component of SNAN in the digesta from the rumen, omasum, and duodenum. In conclusion, the duodenum has the greatest concentrations of SNAN and PBAA, and the greatest potential for absorption of SNAN in the form of PBAA in the nonmesenteric gastrointestinal tissues of dairy cows.