Deficiency of ARHGAP21 alters megakaryocytic cell lineage responses and enhances platelet hemostatic function.

Abstract Background Microtubules, actin and Rho GTPase proteins are essential players in the megakaryocyte biology for platelet formation and function. Objectives To investigate the role of ARHGAP21, a RhoGAP protein, in megakaryocytic differentiation and platelet function. Methods Cytoskeletal proteins were investigated in HEL cells silenced for ARHGAP21 and submitted to megakaryocyte differentiation. The role of Arhgap21 in platelet function was accessed using haploinsufficient (Arhgap21+/−) mice. Arhgap21+/− platelet aggregation and p-selectin exposure were evaluated in response to thrombin. Vessel occlusion time and thrombus formation were detected after injury of the carotid artery. Platelet morphology was accessed by electronic microscopy. Results ARHGAP21 was upregulated during megakaryocytic differentiation of the cell line and primary mouse cells. In the HEL cell model, ARHGAP21 was detected in the cytoplasmic protrusions, colocalized and associated with α-tubulin and was mostly detected in the protein cell fraction containing the polymerized tubulin. Silencing of ARHGAP21 decreased the expression of Glu-tubulin, suggesting microtubule instability, and enhanced cell spreading. Platelets from Arhgap21+/− mice presented enhanced thrombin-induced aggregation and p-selectin exposure associated with increased size of α-granules. Arhgap21+/− mice also showed increased CDC42 and RHOA activities, shorter tail-bleeding and accelerated thrombus formation. Conclusions Our results indicate that ARHGAP21 may be a critical protein in the regulation of platelet production and function through the control of cytoskeletal rearrangement.