One of the major contributors to
sickle cell disease (SCD) pathobiology is the
hemolysis of sickle red blood cells (RBCs), which release free
hemoglobin and platelet agonists including
adenosine 5'-diphosphate (
ADP) into the plasma. While platelet activation/aggregation may promote tissue
ischemia and
pulmonary hypertension in SCD, modulation of sickle platelet dysfunction remains poorly understood. Calpain-1, a ubiquitous
calcium-activated
cysteine protease expressed in hematopoietic cells, mediates aggregation of platelets in healthy mice. We generated calpain-1 knockout Townes sickle (SSCKO) mice to investigate the role of calpain-1 in steady state and
hypoxia/reoxygenation (H/R)-induced sickle platelet activation and aggregation, clot retraction, and
pulmonary arterial hypertension. Using multi-
electrode aggregometry, which measures platelet adhesion and aggregation in whole blood, we determined that steady state SSCKO mice exhibit significantly impaired PAR4-TRAP-stimulated platelet aggregation as compared to Townes sickle (SS) and humanized control (AA) mice. Interestingly, the H/R injury induced platelet hyperactivity in SS and SSCKO, but not AA mice, and partially rescued the aggregation defect in SSCKO mice. The PAR4-TRAP-stimulated GPIIb-IIIa (αIIbβ3)
integrin activation was normal in SSCKO platelets suggesting that an alternate mechanism mediates the impaired platelet aggregation in steady state SSCKO mice. Taken together, we provide the first evidence that calpain-1 regulates platelet hyperactivity in sickle mice, and may offer a viable pharmacological target to reduce platelet hyperactivity in SCD.