HbS Binding to GP1bα Activates Platelets in Sickle Cell Disease

Area of Science:

• Hematology
• Molecular Biology
• Pathophysiology

Background:

• Intravascular hemolysis elevates thrombosis risk in hemolytic disorders.
• Previous research linked adult hemoglobin (HbA) binding to GP1bα with platelet activation.
• Elevated plasma or platelet-bound Hb correlates with platelet activation in paroxysmal nocturnal hemoglobinuria (PNH).

Purpose of the Study:

• To investigate the interaction between sickle hemoglobin (HbS) and platelets.
• To determine if HbS binding to GP1bα activates platelets.
• To explore the role of HbS-induced platelet activation in sickle cell disease (SCD) pathophysiology.

Main Methods:

• Investigated HbS binding to GP1bα using purified components.
• Assessed platelet activation markers (P-selectin, PAC1 binding) via flow cytometry.
• Measured platelet microparticle generation and thrombus formation.
• Correlated plasma Hb levels with platelet activation markers in SCD patients.

Main Results:

• HbS binds to GP1bα (KD ~ 10.46 ± 3 μM) and activates platelets concentration-dependently.
• HbS induces phosphorylation of Lyn, PI3K, Akt, and ERK signaling proteins.
• HbS significantly increases P-selectin expression (10.7-fold), PAC1 binding (10.4-fold), microparticle generation (4.7-fold), and thrombus formation (4.3-fold).
• Elevated plasma Hb directly correlates with P-selectin (r=0.7947), PAC1 binding (r=0.5914), and microparticle levels (r=0.7834) in SCD patients.

Conclusions:

• HbS binding to GP1bα is a key mechanism for platelet activation in SCD.
• HbS-induced platelet activation contributes to the hypercoagulable state and thrombosis risk in SCD.
• Targeting HbS-platelet interactions may offer therapeutic strategies for SCD-related vascular complications.