Enteric fungi protect against intestinal ischemia–reperfusion injury via inhibiting the SAA1-GSDMD pathway

Introduction: Prophylactic antifungal therapy has been widely used for critical patients, but it has failed to improve patient prognosis and has become a hot topic. This may be related to disruption of fungal homeostasis, but the mechanism of fungi action is not clear. As a common pathway in critical patients, intestinal ischemia–reperfusion (IIR) injury is fatal and regulated by gut microbiota. However, the exact role of enteric fungi in IIR injury remains unclear. Objectives: This is a clinical study that aims to provide new perspectives in clarifying the underlying mechanism of IIR injury and propose potential strategies that could be relevant for the prevention and treatment of IIR injury in the near future. Methods: ITS sequencing was performed to detect the changes in fungi before and after IIR injury. The composition of enteric fungi was altered by pretreatment with single-fungal strains, fluconazole and mannan, respectively. Intestinal morphology and function impairment were evaluated in the IIR injury mouse model. Intestinal epithelial MODE-K cells and macrophage RAW264.7 cells were cultured for in vitro tests. Results: Fecal fungi diversity revealed the obvious alteration in IIR patients and mice, accompanied by intestinal epithelial barrier dysfunction. Fungal colonization and mannan supplementation could reverse intestinal morphology and function impairment that were exacerbated by fluconazole via inhibiting the expression of SAA1 from macrophages and decreasing pyroptosis of intestinal epithelial cells. Clodronate liposomes were used to deplete the number of macrophages, and it was demonstrated that the protective effect of mannan was dependent on macrophage involvement. Conclusion: This finding firstly validates that enteric fungi play a crucial role in IIR injury. Preventive antifungal treatment should consider damaging fungal balance. This study provides a novel clue to clarify the role of enteric fungi in maintaining intestinal homeostasis.