WNT2B impairs endosomal trafficking via WASHC5 to inhibit autophagy: a novel non-secretory WNT pathway

WNT2B is canonically characterized as a secreted WNT-family ligand, which is transported to the extracellular space via the endoplasmic reticulum (ER)-Golgi pathway and binds to cell surface FZDs (frizzled class receptors) to trigger downstream signaling cascades. Here, we identify a previously unrecognized non-secretory intracellular function of WNT2B in impairing endosomal trafficking to inhibit macroautophagy/autophagy, as well as a non-canonical LC3B-II-dependent autophagic secretion mechanism for WNT2B. Specifically, the non-secretory intracellular pool of WNT2B via its conserved middle domain (MD) binds to the spectrin repeat domain (SRD) of WASHC5, competitively displacing WASHC1 and thereby disrupting WASH complex assembly and inhibiting WASHC1-mediated actin polymerization on early endosomes. This disruption impairs endosomal cargo trafficking, including the core autophagy protein ATG9A, leading to defective autophagy initiation and subsequent accumulation of pro-inflammatory and pro-fibrotic factors in fibroblasts. We validated this mechanism in vivo using a TNBS-induced mouse model of chronic colitis. Fibroblast-specific wnt2b deletion restores autophagy, reduces pro-inflammatory cytokine secretion, and ameliorates intestinal fibrosis. Consistently, in Crohn disease (CD) patient tissues, elevated WNT2B in fibrotic regions negatively correlates with autophagy activity, and positively correlates with pro-fibrotic phenotypes, and clinical disease severity. Moreover, we identify a novel LC3B-II-dependent autophagic secretion pathway for WNT2B, which is distinct from the conventional ER-to-Golgi-dependent protein secretion. Collectively, our study delineates a novel non-canonical WNT2B-WASH complex-ATG9A regulatory axis through which WNT2B impairs endosomal trafficking and disrupts autophagy, ultimately amplifying inflammation and fibrosis. This study suggests that WNT2B may serve as a promising therapeutic target for CD and autophagy-associated fibrotic disorders.Abbreviations: 3-MA: 3-methyladenine; AAV: adeno-associated virus; ACTA2: actin alpha 2, smooth muscle; ARPC2: actin related protein 2/3 complex subunit 2; ATG: autophagy related; CCN3: cellular communication network factor 3; CD: Crohn disease; CK666: 2-fluoro-N-[2-(2-methyl-1H-indol-3-yl)ethyl]benzamide; COL1A1: collagen type I alpha 1 chain; Co-IP: co-immunoprecipitation; CTNNB1: catenin beta 1; DBcAMP: dibutyryl cyclic adenosine monophosphate; DPT: dermatopontin; EEA1: early endosome antigen 1; EGFR: epidermal growth factor receptor; ELISA: enzyme-linked immunosorbent assay; ER: endoplasmic reticulum; ESCRT: endosomal sorting complexes required for transport; EV: extracellular vesicle; FRAP: fluorescence recovery after photobleaching; FL: full length; FZD: frizzled class receptor; GST: glutathione S-transferase; HIF: human intestinal fibroblast; HMGB1: high mobility group box 1; IKBKB: inhibitor of nuclear factor kappa B kinase subunit beta; IL6: interleukin 6; LDELS: LC3-dependent EV loading and secretion; LPS: lipopolysaccharide; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MD: middle domain; MEFs: mouse embryonic fibroblasts; MTOR: mechanistic target of rapamycin kinase; MVB: multivesicular body; NFKB: nuclear factor kappa B; NFKBIA: NFKB inhibitor alpha; PDCD6IP: programmed cell death 6 interacting protein; PLA: proximity ligation assay; RELA/p65: RELA proto-oncogene, NF-kB subunit; SAFB: scaffold attachment factor B; SES-CD: Simple Endoscopic Score for Crohn disease; SIM: super-resolution structured illumination microscopy; SMAD3: SMAD family member 3; SQSTM1/p62: sequestosome 1; SRD: spectrin repeat domain; TEM: transmission electron microscopy; TFRC: transferrin receptor; TGFB1: transforming growth factor beta 1; TGOLN2: trans-golgi network protein 2; TNBS: 2,4,6-trinitrobenzenesulfonic acid; TNF: tumor necrosis factor; VCA: Verprolin homology, Central and Acidic; WASHC: WASH complex subunit; WLS: Wnt ligand secretion mediator; WCL: whole cell lysates; WNT: Wnt family member; WT, wild type.