Proteomic analysis indicates lower abundance of platelet α-granule proteins in Glanzmann thrombasthenia

Background: Glanzmann thrombasthenia (GT) is an inherited platelet function disorder caused by mutations in the fibrinogen receptor α_IIbβ₃. The deficiency can be quantitative (type I/II) or qualitative (type III). It causes lack of platelet aggregation and leads to a moderate to severe bleeding tendency. Besides the absence or functional alteration of the integrins α_IIb and β₃, little is known about the proteomic landscape of platelets from GT patients. Objectives: To evaluate the platelet proteome in GT. Methods: Label-free quantification of platelet proteins was performed in 13 genetically confirmed GT patients (11 type I and 2 type III) and 13 healthy controls with liquid chromatography coupled with tandem mass spectrometry. α_IIbβ₃ expression was quantified with whole blood flow cytometry. Medical ethics committee approval was obtained and all participants provided informed consent. Results: Of 3664 identified proteins, 2677 were considered quantified. Dynamic range spanned 5 orders of magnitude, and the mean coefficient of variation was 1.2%, indicating data were robust. Flow cytometry-based α_IIb expression correlated well with α_IIb abundance according to liquid chromatography-tandem mass spectrometry. Twenty-nine proteins were less abundant, and 32 proteins were more abundant in GT patients than in controls. Downregulated proteins were enriched for α-granule proteins, including secreted protein acidic and cyteine rich, amyloid β precursor-like protein 2, TIMP metallopeptidase inhibitor 1, and TREM-like transcript-1, in addition to the subunits of integrin α_IIbβ₃, fibrinogen, and plasminogen. Upregulated proteins were mostly plasma proteins annotated to blood microparticles. Conclusion: GT platelets show reduced abundance of specific platelet α-granule proteins compared with healthy controls.