Abstract

The intestinal mucosa is crucial for nutrient absorption and barrier function. In this study, a newly identified strain of Ligilactobacillus salivarius ( L. sa. 8-2) exhibited a mucosal protective effect in chick intestinal injury models. However, the underlying mechanisms need to be clarified. In vivo , chicks were pre-fed with L. sa. 8-2 supernatant or its precipitate and then challenged with lipopolysaccharide (LPS) or Salmonella Typhimurium ( STm ). The results showed that L. sa. 8-2 and its supernatant significantly reduced intestinal epithelial apoptosis, increased goblet cell density and Muc2 mRNA abundance, and upregulated Claudin1 protein levels. Specifically, compared with the LPS-challenged group, L. sa. 8-2 supernatant accelerated epithelial renewal, as shown by elevated protein levels of proliferating cell nuclear antigen (PCNA) and increased mRNA abundance of cell cycle regulators Ccnd1 and Cdk2 . Moreover, the L. sa. 8-2 supernatant markedly increased protein levels of both the active intestinal stem cell (aISC) marker LGR5 and the reserve ISC (rISC) marker HOPX in the intestinal crypt. In vitro , the enteroids were pre-treated with L. sa. 8-2 supernatant and then challenged with LPS. It was shown that the L. sa. 8-2 supernatant elevated the protein levels of LGR5 and HOPX compared with the injured group. Moreover, co-staining of LGR5 and HOPX revealed that more HOPX + cells were co-localized with LGR5 + cells in the L. sa. 8-2 supernatant pretreatment group, suggesting the activation of rISCs. Additionally, compared with the injured groups, L. sa. 8-2 supernatant preserved mitochondrial morphology and upregulated the fission-related protein FIS1. At both the mRNA and protein levels, L. sa. 8-2 supernatant upregulated the pyruvate metabolism-related enzyme LDHA and LDHB, while decreasing mRNA levels of Sdha (an oxidative phosphorylation-related enzyme), suggesting a metabolic shift from oxidative phosphorylation towa