Gray platelet syndrome and defective thrombo-inflammation in Nbeal2-deficient mice
Abstract:
Platelets are anuclear organelle-rich cell fragments derived from bone marrow megakaryocytes (MKs) that safeguard vascular integrity. The major platelet organelles, α-granules, release proteins that participate in thrombus formation and hemostasis. Proteins stored in α-granules are also thought to play a role in inflammation and wound healing, but their functional significance in vivo is unknown. Mutations in NBEAL2 have been linked to gray platelet syndrome (GPS), a rare bleeding disorder characterized by macrothrombocytopenia, with platelets lacking α-granules. Here we show that Nbeal2-knockout mice display the characteristics of human GPS, with defective α-granule biogenesis in MKs and their absence from platelets. Nbeal2 deficiency did not affect MK differentiation and proplatelet formation in vitro or platelet life span in vivo. Nbeal2-deficient platelets displayed impaired adhesion, aggregation, and coagulant activity ex vivo that translated into defective arterial thrombus formation and protection from thrombo-inflammatory brain infarction following focal cerebral ischemia. In a model of excisional skin wound repair, Nbeal2-deficient mice exhibited impaired development of functional granulation tissue due to severely reduced differentiation of myofibroblasts in the absence of α-granule secretion. This study demonstrates that platelet α-granule constituents are critically required not only for hemostasis but also thrombosis, acute thrombo-inflammatory disease states, and tissue reconstitution after injury.
Insights
Platelets lacking alpha-granules due to NBEAL2 deficiency impair hemostasis and thrombosis. This study reveals alpha-granule constituents are vital for vascular integrity, wound healing, and preventing thrombo-inflammatory brain injury.
Area of Science:
- Hematology
- Cell Biology
- Vascular Biology
Background:
- Platelets, derived from megakaryocytes (MKs), are crucial for vascular integrity via alpha-granule release.
- Alpha-granule proteins are implicated in hemostasis, inflammation, and wound healing, but their in vivo roles are unclear.
- Gray Platelet Syndrome (GPS) is a bleeding disorder linked to NBEAL2 mutations, characterized by absent alpha-granules.
Purpose of the Study:
- To investigate the in vivo function of platelet alpha-granules using a Nbeal2-knockout mouse model.
- To elucidate the role of NBEAL2 in alpha-granule biogenesis and platelet function.
- To determine the contribution of alpha-granules to hemostasis, thrombosis, and tissue repair.
Main Methods:
- Generated Nbeal2-knockout mice to model human Gray Platelet Syndrome.
- Assessed megakaryocyte differentiation, proplatelet formation, and platelet counts.
- Evaluated platelet function ex vivo (adhesion, aggregation, coagulation) and in vivo (arterial thrombosis, cerebral ischemia, wound repair).
Main Results:
- Nbeal2-knockout mice exhibited defective alpha-granule biogenesis and absence in platelets, mirroring human GPS.
- Nbeal2 deficiency impaired platelet adhesion, aggregation, and coagulant activity, leading to defective arterial thrombus formation.
- Nbeal2-deficient mice showed impaired wound healing due to reduced myofibroblast differentiation and lack of alpha-granule secretion.
Conclusions:
- Platelet alpha-granule constituents are essential for hemostasis and thrombosis.
- Alpha-granules play a critical role in acute thrombo-inflammatory conditions and tissue repair.
- NBEAL2 is indispensable for alpha-granule biogenesis and overall platelet function in vivo.
