Porcine β-defensin-2 alleviates aflatoxin B1 induced intestinal mucosal damage via ROS-Erk1/2 signaling pathway

Aflatoxin B1 (AFB1) is a highly toxic fungal toxin that causes severe damage to animal intestines. Porcine beta-defensin-2 (pBD-2) is a well-studied antimicrobial peptide in pigs that can protect animal intestines and improve productivity. This study aimed to investigate the molecular mechanisms of pBD-2 in alleviating AFB1-induced oxidative stress and intestinal mucosal damage using porcine intestinal epithelial cells (IPEC-J2 cells) and Kunming (KM) mice. The maximum destructive concentration of AFB1 for IPEC-J2 cells and the optimal therapeutic concentration of pBD-2 were determined by CCK-8 and RT-qPCR. We then investigated the oxidative stress and intestinal damage induced by AFB1 and the alleviating effect of pBD-2 by detecting changes of reactive oxygen species (ROS), inflammatory cytokines, tight junction proteins (TJPs) and mucin. Finally, the molecular mechanism of pBD-2 mitigates AFB1-induced oxidative stress and intestinal mucosal damage were explored by adding ROS and Erk1/2 pathway inhibitors to comparative analysis. In vivo, the therapeutic effect of pBD-2 on AFB1-induced intestinal damage was analyzed from aspects such as average daily gain (ADG), pathological damage, inflammation, and mucosal barrier in KM mice. The study found that low doses of pBD-2 promoted cell proliferation and prevented AFB1-induced cell death, and pBD-2 significantly restored the feed conversion rate and ADG of KM mice reduced by long-term exposed AFB1. Increasing the intracellular ROS and the expression and phosphorylation of Erk1/2, AFB1 promoted inflammation by altering inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8, and disrupted the mucosal barrier by interfering with Claudin-3, Occludin, and MUC2, while pBD-2 significantly reduced ROS and decreased the expression and phosphorylation of Erk1/2 to restored their expression to alleviate AFB1-induced oxidative stress and intestinal mucosal damage in IPEC-J2 cells and the small intestine of mice.

Construction of Bacillus subtilis strain engineered for expression of porcine β-defensin-2/cecropin P1 fusion antimicrobial peptides and its growth-promoting effect and antimicrobial activity

Objective

To generate recombinant Bacillus subtilis (B. subtilis) engineered for expression of porcine β-defensin-2 (pBD-2) and cecropin P1 (CP1) fusion antimicrobial peptide and investigate their anti-bacterial activity in vitro and their growth-promoting and disease resisting activity in vivo.

Methods

The pBD-2 and CP1 fused gene was synthesized using the main codons of B. subtilis and inserted into plasmid pMK4 vector to construct their expression vector. The fusion peptide-expressing B. subtilis was constructed by transformation with the vector. The expressed fusion peptide was detected with Western blot. The antimicrobial activity of the expressed fusion peptide and the recovered pBD-2 and CP1 by enterokinase digestion in vitro was analyzed by the bacterial growth-inhibitory activity assay. To analyze the engineered B. subtilis on growth promotion and disease resistance, the weaned piglets were fed with basic diet supplemented with the recombinant B. subtilis. Then the piglets were challenged by enteropathogenic Escherichia coli (E. coli). The weight gain and diarrhea incidence of piglets were measured after challenge.

Results

The recombinant B. subtilis engineered for expression of pBD-2/CP1 fusion peptide was successfully constructed using the main codons of the B. subtilis. Both expressed pBD-2/CP1 fusion peptide and their individual peptides recovered from parental fusion peptide by enterokinase digestion possessed the antimicrobial activities to a variety of the bacteria, including gram-negative bacteria (E. coli, Salmonella typhimurium, and Haemophilus parasuis) and gram-positive bacteria (Staphylococcus aureus). Supplementing the engineered B. subtilis to the pig feed could significantly promote the piglet growth and reduced diarrhea incidence of the piglets.

Conclusion

The generated B. subtilis strain can efficiently express pBD-2/CP1 fusion antimicrobial peptide, the recovered pBD-2 and CP1 peptides possess potent antimicrobial activities to a variety of bacterial species in vitro. Supplementation of the engineered B. subtilis in pig feed obviously promote piglet growth and resistance to the colibacillosis.