Polygonatum cyrtonema Hua fructan ameliorates ulcerative colitis via gut microbiota modulation and follistatin targeting

Ulcerative colitis (UC) is a chronic inflammatory bowel disease with persistent colonic inflammation and inadequate therapeutic options. The medicinal and edible plant Polygonatum cyrtonema Hua from Jiuhua Mountain contains polysaccharides with potent anti-inflammatory activities. In this study, a low-molecular-weight fructan (Mw = 2087 Da), designated PCP2, was isolated and purified from its rhizome. Biologically, PCP2 administration markedly alleviated disease severity in dextran sulfate sodium (DSS)-induced colitis mice, as shown by the improvement in multiple indicators of colon injury and inflammation. Fecal microbiota transplantation and antibiotic depletion experiments revealed that the protective effects of PCP2 are mediated through both modulation of the gut microbiota and additional microbiota-independent pathways. Importantly, through molecular dynamics simulations, microscale thermophoresis, and surface plasmon resonance assays, follistatin (Fst) is identified as a direct binding target of PCP2. Functional validation using siRNA-mediated Fst knockdown in Caco-2 cells, combined with adenovirus-mediated knockdown in the murine colon, confirmed that PCP2 exerts its therapeutic effect by directly interacting with Fst and suppressing the BMP4/Smad1/ID1 signaling axis. In summary, PCP2 ameliorates ulcerative colitis via dual mechanisms involving restoration of gut microbiota homeostasis and direct targeting of Fst. These findings establish a novel therapeutic strategy and support the clinical development of P. cyrtonema Hua from Jiuhua Mountain as a functional food for intestinal health.