Dietary bile acids supplementation improves the growth performance and alleviates fatty liver in broilers fed a high-fat diet via improving the gut microbiota.

This experiment aims to evaluate the effect of bile acids (BAs) in alleviating fatty liver disease induced by a high-fat diet (HFD) in broilers, and the modulation of the gut microbiota involved in this process. A total of 192 one-day-old Arbor Acres (AA) commercial male broilers were randomly divided into 4 groups and treated with the following diet: a basal-fat diet (BFD), a basal-fat diet plus bile acids (BFD + BAs), an HFD, and a high-fat diet plus bile acids (HFD + BAs). Bile acids were supplemented at the early growth stage (3-7 d), middle stage (17-21 d), and late stage (31-35 d). Results showed that BAs treatment had a significant effect on body weight on 14 d and 35 d, and increased the breast muscle weight and its index, but decreased the liver weight and abdominal fat weight on 35 d (P < 0.05). The supplementation of BAs significantly improved the serum lipid profile and decreased the level of triglycerides (TG), total cholesterol (TCHO), and nonesterified fatty acids (NEFA) on 35 d (P < 0.05). Dietary BAs supplementation significantly alleviated the hepatic TG deposition induced by HFD (P < 0.05), which was accompanied by upregulation of peroxisome proliferator-activated receptor gamma (PPARγ) and lipoprotein lipase (LPL) gene expression (P < 0.05). Moreover, the expression levels of hepatic gene adipose triglyceride lipase (ATGL), peroxisome proliferator-activated receptor α (PPARα), and apolipoprotein B (APOB) were greatly increased by BAs treatment. The analysis of 16S rRNA sequencing showed that the microbial diversity of the cecal digesta was increased by BAs in broilers with elevated abundances of Firmicutes, Lactobacillus, Anaerostipes, Sellimonas, and CHKCI002 and decreased abundances of Barnesiella and Akkermansia genus (P < 0.05). Hepatic TG content was positively correlated with the abundance of Oscillospiraceae, but it was negatively correlated with the abundance of Lactobacillus in cecal digesta (P < 0.05). These results indicate that dietary BAs can improve growth performance and alleviate fatty liver disease induced by an HFD via modulating gut microbiota in broilers.

Hcp2a of APEC affects mRNA splicing and protein quality control in DF-1 cells.

BACKGROUND: Bacteria deliver effector proteins into the host cell via a secretory system that can directly act on the target to cause disease. As an important pipeline structural protein of the type VI secretion system (T6SS) complex, Hcp acts together with other virulence factors in the target cell. There is growing evidence that T6SS plays a key role in the pathogenic mechanism of APEC. However, the regulatory function played by the effector protein Hcp during its interaction with host cells is not clear. Here, tandem mass tag (TMT) analysis was used to quantify the proteins affected by increased expression of Hcp2a in DF-1 cells. RESULTS: The host response was significantly different between the overexpression and null groups at the protein level. A total of 195 differentially expressed proteins (DEPs) were detected in the overexpression group (upregulated, n = 144, downregulated, n = 51). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the biological functions and pathways of differentially expressed proteins. The results showed that these DEPs were mainly enriched in RNA degradation, spliceosome, and mRNA surveillance pathways. CONCLUSIONS: This study suggests that Hcp2a, the effector protein of APEC, plays an important role in regulating mRNA splicing and protein quality control in DF-1 cells. These findings provide useful clues to elucidate the pathogenic mechanism of effector protein Hcp2a on host target cells.

Hcp2b of T6SS affects colonization of avian pathogenic Escherichia coli and host keratin filament expression.

T6SS (type VI secretion system) is a type of nano-syringe that exists in APEC (avian pathogenic Escherichia coli). Hcp (haemolysin-coregulated protein) of T6SS participates in the regulation of virulence during APEC infection. However, whether hcp plays a role in bacterial colonization by expression in host cells remains unclear. In this study, we analysed the biological characteristics of the mutant hcp2b strain. Our results showed that the hcp2b gene was involved in the regulation of bacterial motility, biofilm formation, anti-serum and anti-oxidative stress. Moreover, our data indicate that the colonization of the hcp2b mutation strain (Δhcp2b) in the lung, liver and kidney of chickens decreased significantly. Hence, overexpression of Hcp2b protein in DF-1 cells was used to analyse the effect of Hcp2b on colonization of APEC. Proteomics analysis showed that overexpression of Hcp2b induced differentially expressed proteins in DF-1 cells (230 were significantly upregulated and 96 were significantly downregulated) and differentially expressed proteins were enriched in keratin filament. In conclusion, our data indicated that hcp2b promoted the colonization of APEC by affecting the expression of keratin filament.

Hcp2a of type VI secretion system contributes to IL8 and IL1ß expression of chicken tracheal epithelium by affecting APEC colonization.

Avian pathogenic Escherichia coli (APEC) is an important pathogen that causes avian colibacillosis in poultry. APEC infection can lead to pathological changes in chicken trachea. The type VI secretion system (T6SS) of APEC contribute to the pathogenicity of APEC. However, whether T6SS plays a role in infection of the trachea remains unclear. We constructed mutant strain Δhcp2a by the Red recombination method system. The role of hcp2a (the structural secretion components and secretory protein of the T6SS) in the infection of trachea was investigated. The mutation strain displayed a significant increase in biofilm formation and a decrease in resistance to chicken serum. Moreover, RNA sequencing analyses showed that infection of chicken tracheal epithelium by the mutant strain Δhcp2a induced differential expression of genes. The result also showed that 14 genes (13 genes were downregulated) were enriched in cytokine-cytokine receptor interaction signalling pathway at 12 and 24 h post infection. The mutation Δhcp2a resulted in significant decreases in the bacterial loads in trachea at 6 and 12 h post infection. Real-time PCR analyses showed that the hcp2a mutation downregulated the expression of IL8 and IL1ß at mRNA level in chicken tracheal epithelium. Our results indicate that mutation of hcp2a influenced genes expression of the cytokine-cytokine receptor interaction pathway by decreasing APEC colonization in the trachea.

Outer membrane proteins YbjX and PagP co-regulate motility in Escherichia coli via the bacterial chemotaxis pathway.

Mutation of the PhoP/Q two-component system decreases the expression of ybjX and pagP encoding outer membrane proteins, and mutation of ybjX or pagP attenuates avian pathogenic Escherichia coli (APEC) pathogenicity. However, whether ybjX/pagP mutation (double-deletion mutant) has a synergistic effect on pathogenicity remains unknown. Herein, electrophoresis mobility shift assay (EMSA) experiments showed that the PhoP/Q system regulated ybjX and pagP transcription indirectly. The APECΔybjX/pagP mutant strain, constructed using the Red recombination method, exhibited reduced invasion of chicken embryo fibroblast (DF-1) cells, but had no effect on virulence in a chicken model. Using RNA sequencing to identify differential mRNAs in APECΔybjXΔpagP and native strains, we revealed up-regulation of genes involved in the bacterial chemotaxis pathway. The ybjX/pagP mutant strain displayed significantly increased motility, suggesting that double deletion of ybjX and pagP enhances motility via the bacterial chemotaxis pathway.