Mutations in Neurobeachin-like 2 do not impact Weibel-Palade body biogenesis and von Willebrand factor secretion in gray platelet syndrome Endothelial Colony Forming Cells

• Published in: Research and practice in thrombosis and haemostasis 2023-02, Vol.7 (2), p.100086, Article 100086
• Main Authors: Kat, Marije, van Moort, Iris, Bürgisser, Petra E., Kuijpers, Taco W., Hofman, Menno, Favier, Marie, Favier, Rémi, Margadant, Coert, Voorberg, Jan, Bierings, Ruben
• Format: Article
• Language: English
• Subjects: Brief Report; endothelial cells; gray platelet syndrome; NBEAL2 protein; SEC22B; von Willebrand factor; Weibel-Palade bodies
• ISSN: 2475-0379; 2475-0379
• DOI: 10.1016/j.rpth.2023.100086

Patients with gray platelet syndrome (GPS) and Neurobeachin-like 2 (NBEAL2) deficiency produce platelets lacking alpha-granules (AGs) and present with lifelong bleeding symptoms. AGs are lysosome-related organelles and store the hemostatic protein von Willebrand factor (VWF) and the transmembrane protein P-selectin. Weibel-Palade bodies (WPBs) are lysosome-related organelles of endothelial cells and also store VWF and P-selectin. In megakaryocytes, NBEAL2 links P-selectin on AGs to the SNARE protein SEC22B on the endoplasmic reticulum, thereby preventing premature release of cargo from AG precursors. In endothelial cells, SEC22B drives VWF trafficking from the endoplasmic reticulum to Golgi and promotes the formation of elongated WPBs, but it is unclear whether this requires NBEAL2. To investigate a potential role for NBEAL2 in WPB biogenesis and VWF secretion using NBEAL2-deficient endothelial cells. The interaction of SEC22B with NBEAL2 in endothelial cells was investigated by interatomic mass spectrometry and pull-down analysis. Endothelial colony forming cells were isolated from healthy controls and 3 unrelated patients with GPS and mutations in NBEAL2. We showed that SEC22B binds to NBEAL2 in ECs. Endothelial colony forming cells derived from a patient with GPS are deficient in NBEAL2 but reveal normal formation and maturation of WPBs and normal WPB cargo recruitment. Neither basal nor histamine-induced VWF secretion is altered in the absence of NBEAL2. Although NBEAL2 deficiency causes the absence of AGs in patients with GPS, it does not impact WPB functionality in ECs. Our data highlight the differences in the regulatory mechanisms between these 2 hemostatic storage compartments. [Display omitted] •Biallelic mutations in Neurobeachin-like 2 (NBEAL2) lead to gray platelet syndrome (GPS), which affects α-granules.•NBEAL2 interactor SEC22B controls the formation of α-granules and Weibel-Palade bodies (WPBs).•Endothelial cells with NBEAL2 mutations derived from a patient with GPS were characterized ex vivo.•NBEAL2 is not essential for WPB formation, maturation, and VWF secretion from endothelial cells.