Toll-like receptor 4 deficiency alleviates lipopolysaccharide-induced intestinal barrier dysfunction

Background: The intestinal tract is considered the body's "engine" and the most impacted organ during sepsis. In this study, we explored toll-like receptor 4 (TLR4) functions in sepsis-induced intestinal barrier dysfunction.Methods: Wild-type and TLR4-knockout (KO) mice were used to establish a sepsis-induced dysfunctional intes-tinal barrier model via the intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg). Hematoxylin and eosin staining, Transmission electron microscope, enzyme linked immunosorbent assay, western blot, quanti-tative real-time polymerase chain reaction, TdT-mediated dUTP nick end labeling staining, 16 S rRNA gene sequencing were used to explore differences in inflammatory cytokines, apoptosis, tight junction (TJ) protein expression, and intestinal flora diversity between groups. Results: TLR4-deficiency reduced procalcitonin and C-reactive protein to prevent sepsis, and also inhibited in-flammatory response by decreasing interleukin (IL)-1 beta, IL-6 and tumor necrosis factor-alpha levels. Also, BAX/Bcl2 and cleaved-caspase 3 expressions were decreased in TLR4-KO mice to suppress the intestinal mucosal cell apoptosis. TJ proteins, including zonula occludens protein, Occludin and Claudin-5 were significantly increased and intestinal fatty acid binding protein, myosin light chain and myosin light chain kinase were reduced in TLR4-KO mice. Additionally, 16 S rRNA gene sequencing indicated that TLR4-deficiency improved flora diversity and altered normal and abnormal bacterial proportions. Conclusions: TLR4 deficiency alleviated LPS-induced intestinal barrier dysfunction by reducing inflammatory responses and apoptosis, impairing intestinal damage, and regulating intestinal flora disturbance.