Subcellular Localization Dictates Therapeutic Function: Spatially Targeted Delivery of Amuc_1100 by Engineered Lacticaseibacillus paracasei L9 Enhances Intestinal Barrier in Colitis

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Background/Objectives: Impaired intestinal barrier function is a hallmark of inflammatory bowel disease (IBD). Akkermansia muciniphila and its outer membrane protein Amuc_1100 can enhance this barrier, but the clinical application of Amuc_1100 is limited by the fastidious growth of its native host. This study aimed to overcome this by utilizing the robust probiotic Lacticaseibacillus paracasei L9 for targeted Amuc_1100 delivery. Methods: We engineered Lc. paracasei L9 to express Amuc_1100 via intracellular (pA-L9), secretory (pUA-L9), and surface-display (pUPA-L9) strategies. Their efficacy was assessed in Lipopolysaccharide (LPS)-induced macrophages and a dextran sulfate sodium (DSS)-induced colitis mouse model, evaluating inflammation, barrier integrity, and mucosal repair. Results: The secretory (pUA-L9) and surface-display (pUPA-L9) strains most effectively suppressed pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) in macrophages. In mice, both strains alleviated colitis and outperformed native A. muciniphila in improving disease activity. Crucially, they exhibited distinct, specialized functions: pUA-L9 acted as a systemic immunomodulator, reducing pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α), elevating anti-inflammatory mediators (IL-4 and IL-10), and promoting goblet cell differentiation; notably, the inhibitory effect of pUA-L9 on IL-6 expression was approximately 2-fold greater than that of pUPA-L9. In contrast, pUPA-L9 excelled in local barrier repair, uniquely restoring mucus layer integrity (Muc1, Muc2, and Tff3) and reinforcing tight junctions (ZO-1, Occludin, Claudin1, Claudin3, and Claudin4). In particular, pUPA-L9 increased Muc2 expression by approximately 3.6-fold compared with pUA-L9. Conclusions: We demonstrate that the subcellular localization of Amuc_1100 within an engineered probiotic dictates its therapeutic mode of action. The complementary effects of secretory and surface-displayed Amuc_1100 offer a novel, spatially targeted strategy for precision microbiome therapy in IBD.