Platelet proteome analysis reveals integrin-dependent aggregation defects in patients with myelodysplastic syndromes

Bleeding complications are a significant clinical problem in patients with myelodysplastic syndromes even at sufficient platelet counts (>50,000/μl). However, the underlying pathology of this hemorrhagic diathesis is still unknown. Here, we analyzed the platelet proteome of patients with myelodysplastic syndromes by quantitative two-dimensional difference gel electrophoresis followed by mass spectrometric protein identification. Proteins identified with lower concentrations, such as Talin-1, Vinculin, Myosin-9, Filmain-A, and Actin play critical roles in integrin α_IIbβ ₃ signaling and thus platelet aggregation. Despite normal agonist receptor expression, calcium flux, and granule release upon activation, the activation capacity of integrin α_IIbβ₃ was diminished in myelodysplastic syndrome platelets. Förster resonance energy transfer analysis showed a reduced co-localization of Talin-1 to the integrin's β₃-subunit, which is required for receptor activation and fibrinogen binding. In addition, platelet spreading on immobilized fibrinogen was incomplete, and platelet aggregation assays confirmed a general defect in integrin-dependent platelet aggregation in patients with myelodysplastic syndromes. Our data provide novel aspects on the molecular pathology of impaired platelet function in myelodysplastic syndromes and suggest a mechanism of defective integrin α_IIbβ₃ signaling that may contribute to the hemorrhagic diathesis observed in these patients.