Gut-engineered Bacillus subtilis-mediated BAMBI delivery for the treatment of thioacetamide-induced liver fibrosis through mechanotransduction inhibition

Liver fibrosis, driven by chronic injury and excessive extracellular matrix (ECM) deposition, lacks effective clinical therapies. This study pioneers a strategy employing genetically engineered Bacillus subtilis (strain Bs-BAMBI-8) to constitutively secrete bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI), which is subsequently delivered to the liver via the gut-liver axis to therapeutically antagonize liver fibrosis. Methodologically, liver fibrosis was induced in mice via 6-week intraperitoneal injections of thioacetamide (TAA), followed by a 19-week daily oral gavage of live Bs-BAMBI-8 (10 9 CFU). This longitudinal intervention achieved sustained intestinal colonization (>10 5 CFU) and BAMBI translocation via the gut-liver axis. This intervention significantly reduced hepatic fibrosis, evidenced by decreased NAFLD Activity Score from six to four and regression of fibrosis stage from S3 to S2. Mechanistically, BAMBI acted as a decoy receptor for transforming growth factor-beta (TGF-β), inhibiting TGF-β signaling and downregulating fibrotic markers (α-smooth muscle actin, collagen I, phosphorylated focal adhesion kinase). This suppression disrupted ECM-mediated mechanotransduction pathways, attenuating hepatic stellate cell activation. Concomitantly, serum markers (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin) recovered, while albumin synthesis and platelet count recovered. Crucially, this engineered microbiome-based approach integrates synthetic biology with mechanobiology to simultaneously target biochemical signaling and mechanical transduction. It establishes a potentially translatable paradigm for chronic liver disease therapy.