VPS33B regulates protein sorting into and maturation of ?-granule progenitor organelles in mouse megakaryocytes.

ABSTRACT: Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is caused by deficiencies in the trafficking proteins VPS33B or VIPAR, and is associated with a bleeding diathesis and a marked reduction in platelet ?-granules. We generated a tamoxifen-inducible mouse model of VPS33B deficiency, Vps33b(fl/fl)-ER(T2), and studied the platelet phenotype and ?-granule biogenesis. Ultrastructural analysis of Vps33b(fl/fl)-ER(T2) platelets identified a marked reduction in ?-granule count and the presence of small granule-like structures in agreement with the platelet phenotype observed in ARC patients. A reduction of ?65% to 75% was observed in the ?-granule proteins von Willebrand factor and P-selectin. Although platelet aggregation responses were not affected, a defect in ?-granule secretion was observed. Under arteriolar shear conditions, Vps33b(fl/fl)-ER(T2) platelets were unable to form stable aggregates, and tail-bleeding measurement revealed a bleeding diathesis. Analysis of bone marrow-derived megakaryocytes (MKs) by conventional and immuno-electron microscopy from Vps33b(fl/fl)-ER(T2) mice revealed a reduction in mature type-II multivesicular bodies (MVB II) and an accumulation of large vacuoles. Proteins that are normally stored in ?-granules were underrepresented in MVB II and proplatelet extensions. These results demonstrate that abnormal protein trafficking and impairment in MVB maturation in MKs underlie the ?-granule deficiency in Vps33b(fl/fl)-ER(T2) mouse and ARC patients.

SUBMITTER: Bem D 

PROVIDER: S-EPMC4497959 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature