Characterisation of TbSmee1 suggests endocytosis allows surface-bound cargo to enter the trypanosome flagellar pocket.

All endocytosis and exocytosis in the African trypanosome Trypanosoma brucei occurs at a single subdomain of the plasma membrane. This subdomain, the flagellar pocket, is a small vase-shaped invagination containing the root of the single flagellum of the cell. Several cytoskeleton-associated multiprotein complexes are coiled around the neck of the flagellar pocket on its cytoplasmic face. One of these, the hook complex, was proposed to affect macromolecule entry into the flagellar pocket lumen. In previous work, knockdown of T. brucei (Tb)MORN1, a hook complex component, resulted in larger cargo being unable to enter the flagellar pocket. In this study, the hook complex component TbSmee1 was characterised in bloodstream form T. brucei and found to be essential for cell viability. TbSmee1 knockdown resulted in flagellar pocket enlargement and impaired access to the flagellar pocket membrane by surface-bound cargo, similar to depletion of TbMORN1. Unexpectedly, inhibition of endocytosis by knockdown of clathrin phenocopied TbSmee1 knockdown, suggesting that endocytic activity itself is a prerequisite for the entry of surface-bound cargo into the flagellar pocket.

Integrin αVß6 - autoantigen and driver of epithelial remodeling in colon and bile ducts in primary sclerosing cholangitis and inflammatory bowel disease.

OBJECTIVE: Recently, autoantibodies directed against the epithelial adhesion protein integrin αVß6 have been identified which strongly associate with ulcerative colitis (UC). We aimed to elucidate whether anti-integrin αVß6 (anti- αVß6) is present in primary sclerosing cholangitis (PSC), its associated inflammatory bowel disease or other cholestatic liver diseases and their persistence after proctocolectomy. DESIGN: We detected anti- αVß6 by an enzyme-linked immunosorbent assay in sera collected at two German tertiary centers, including healthy controls (N=62), UC (N=36), Crohn's disease (CD, N=65), PSC-IBD (78 samples from N=41 patients), PSC without IBD (PSC, 41 samples from N=18 patients), primary biliary cholangitis (PBC, N=24), autoimmune hepatitis (AIH, N=32), secondary sclerosing cholangitis (SSC, N=12) and metabolic dysfunction-associated steatotic liver disease (MASLD, N=24). Additionally, sera after proctocolectomy were studied (44 samples / N= 10 patients). Immunofluorescent analyses were performed in tissue samples from liver, large bile duct from surgical resections and colon of PSC patients. RESULTS: Anti- αVß6 occurred in 91% of UC, 17% of CD, 73% of PSC-IBD, 39% of PSC, 4% of PBC, 14% of AIH, and 0% of healthy controls, SSC or MASLD. Integrin αVß6 is selectively expressed in disease-associated epithelia of both bile duct and colon. Anti- αVß6 levels correlate moderately with intestinal disease activity in PSC-IBD, but only weakly with biliary disease. CONCLUSION: Anti- αVß6 frequently occur in patients suffering from PSC, especially in PSC-IBD. Anti- αVß6 levels positively correlate to IBD activity in PSC-IBD, but may also occur in the absence of clinically manifest IBD in PSC.