Soluble Siglec-9 Improves Intestinal Barrier Function in a Mouse Model of Metabolic Dysfunction-Associated Steatohepatitis

Background/Objectives: Metabolic dysfunction-associated steatohepatitis (MASH), characterized by liver inflammation, fibrosis, and fat accumulation, can develop into cirrhosis and liver cancer. Despite its increasing prevalence worldwide, there are few established therapies for advanced MASH. We previously demonstrated that stem cells from human exfoliated deciduous teeth-conditioned media (SHED-CM) exerted therapeutic effects in a MASH mouse model. The gut–liver axis is thought to be associated with liver disease progression, and soluble Siglec-9 (sSiglec-9), an immunoinhibitory receptor, is a key protein in SHED-CM that induces anti-inflammatory macrophages and has intestinal epithelial protective effects. Therefore, we evaluated sSiglec-9’s role in intestinal barrier protection in MASH mice. Methods: We evaluated sSiglec-9 effects on intestinal barrier function using in vitro Caco-2 cell monolayers injured by TNF-α and IFN-γ. For the MASH mouse model, male C57BL/6J mice were given a Western diet and high-sugar solution orally; to induce liver injury, CCl4 was intraperitoneally administered for 12 weeks. Mice were treated weekly with 10 ng/g sSiglec-9 or vehicle. Intestinal permeability was assessed by blood 4 kDa FITC-dextran concentration, and intestinal transcriptomes and liver histology were analyzed. Results: sSiglec-9 decreased intestinal permeability and liver inflammation in MASH mice. sSiglec-9 and SHED-CM reduced 4 kDa FITC-dextran permeability in injured Caco-2 cells, and sSiglec-9 significantly reduced intestinal permeability and modulated expression of 34 intestinal genes. The NAFLD Activity Score indicated significantly reduced inflammation following sSiglec-9 treatment. Conclusions: sSiglec-9 may protect intestinal barrier function by mitigating mucosal inflammation. sSiglec-9 treatment may represent a novel therapeutic approach for MASH via gut–liver axis modulation.