Protective Effects of Recombinant Lactobacillus paracasei Expressing Porcine β-Defensin 2 Against DSS-Induced Colitis in a Murine Model.

Porcine β-defensin 2 (pBD2) possesses broad-spectrum antimicrobial properties and is crucial for gastrointestinal mucosal repair. Lactic acid bacteria (LAB) serve as optimal vectors for exogenous protein delivery due to their high biosafety, intestinal colonization capacity, and ability to modulate gut microecology. In this study, we engineered a recombinant Lactobacillus paracasei strain (pPG-N1-pBD2/27-2) that efficiently secretes pBD2. In vitro, this recombinant strain significantly enhanced the proliferation and migration of porcine intestinal epithelial cells (IPEC-J2). In vivo, oral administration of pPG-N1-pBD2/27-2 markedly alleviated dextran sulfate sodium (DSS)-induced colitis in mice. This protective effect was evidenced by reduced Disease Activity Index (DAI) scores, prevention of colon shortening, and decreased colonic activities of myeloperoxidase (MPO) and eosinophil peroxidase (EPO), alongside normalized N-acetyl-β-D-glucosaminidase (NAG) levels. Histopathological analysis revealed that the treatment preserved mucosal architecture, including goblet cells and crypts, and fortified the physical barrier by upregulating tight junction proteins. Mechanistically, the recombinant strain suppressed the colonic iNOS/COX-2 inflammatory axis, decreased serum pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α), and elevated the anti-inflammatory cytokine IL-10. Furthermore, it restored systemic immune homeostasis by normalizing the proportions of splenic macrophages, T/B lymphocytes, and natural killer (NK) cells. In conclusion, pPG-N1-pBD2/27-2 mitigates colitis through a dual mechanism: reinforcing the intestinal physical barrier and rebalancing the innate-adaptive immune axis. These findings highlight the potential of pBD2-engineered probiotics as novel biological therapeutics for intestinal inflammatory diseases.