NPC1 defect results in abnormal platelet formation and function: studies in Niemann–Pick disease type C1 patients and zebrafish

Abstract

Niemann-Pick type C is a lysosomal storage disease associated with mutations in NPC1 or NPC2, resulting in an accumulation of cholesterol in the endosomal-lysosomal system. Niemann-Pick type C has a clinical spectrum that ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease combined with remarkably, in some cases, hematological defects such as thrombocytopenia, anemia and petechial rash. A role of NPC1 in hematopoiesis was never shown. Here, we describe platelet function abnormalities in three unrelated patients with a proven genetic and biochemical NPC1 defect. Their platelets have reduced aggregations, P-selectin expression and ATP secretions that are compatible with the observed abnormal alpha and reduced dense granules as studied by electron microscopy and CD63 staining after platelet spreading. Their blood counts were normal. NPC1 expression was shown in platelets and megakaryocytes (MKs). In vitro differentiated MKs from NPC1 patients exhibit hyperproliferation of immature MKs with different CD63(+) granules and abnormal cellular accumulation of cholesterol as shown by filipin stainings. The role of NPC1 in megakaryopoiesis was further studied using zebrafish with GFP-labeled thrombocytes or DsRed-labeled erythrocytes. NPC1 depletion in zebrafish resulted in increased cell death in the brain and abnormal cellular accumulation of filipin. NPC1-depleted embryos presented with thrombocytopenia and mild anemia as studied by flow cytometry and real-time QPCR for specific blood cell markers. In conclusion, this is the first report, showing a role of NPC1 in platelet function and formation but further studies are needed to define how cholesterol storage interferes with these processes.

Biomarkers for disease progression and AAV therapeutic efficacy in feline Sandhoff disease

“…Cholesterol is a secondary storage product in many LSDs, including GM2 gangliosidosis, and is thought to be sequestered in the cell due to its affinity for sphingolipids [49]. Niemann-Pick type C cultured fibroblasts exhibit a marked reduction in exogenous cholesterol, resulting from increased intracellular storage [50]. These reports suggest that cholesterol may be taken up and sequestered intracellularly in the SD cat, resulting in low plasma levels.…”

“…This change in RBC morphology is associated with apoptosis and phagocytosis by macrophages and is a potential etiology for anemia [58, 59]. Anemia is a prominent finding in several lysosomal storage disorders, including Gaucher disease [60] and Niemann-Pick type C [50], and is used as a powerful biomarker to score severity and need for enzyme replacement therapy [61]. Our findings suggest that this may also be an applicable clinical test in SD, though anemia may have numerous causes in storage diseases and its response to gene therapy in the current study is ambiguous.…”

A dominant gain-of-function mutation in universal tyrosine kinase SRC causes thrombocytopenia, myelofibrosis, bleeding, and bone pathologies

“…The analysis of thrombocyte, erythrocyte, and GATA1-positive HSC formation was analyzed as we described before (54, 57). Cartilage structures were stained at 5 dpf with Alcian blue as described (58), and quantification of bones was performed as described (58).…”

A gain-of-function variant in DIAPH1 causes dominant macrothrombocytopenia and hearing loss

“…20,21 MK colony-forming units (CFU-MKs) and MKs were visualized by light or confocal microscopy after staining with May-Grünwald-Giemsa stain, phalloidin, or anti-CD61 antibodies. Proplatelet formation in liquid MK cultures was determined by light microscopy and ploidy by flow cytometry as described previously.…”