Casein Kinase 2α is a crucial regulator of GPVI-mediated in vivo arterial thrombus formation in macro- and microcirculation

Background: Cardiovascular diseases such as myocardial infarction and ischemic stroke depend decisively on platelet functions such as adhesion, secretion and thrombus formation. Since the activation of platelets is regulated by a wide variety of intracellular, phosphorylation-dependent signaling cascades, highly expressed kinases in platelets play a pivotal role in platelet activation. One of these kinases represents the tetrameric serine/threonine kinase casein kinase 2 (CK2), which consists of two regulatory β and two catalytic α or α’ subunits respectively. While deficiency of the regulatory β subunit is characterized by impaired thrombopoiesis and platelet function, nothing is yet known about the role of the α subunit in platelet activation and subsequent in vivo thrombus formation in arterial macro- and microcirculation.

Aims: The present study examined the effects of CK2α-dependent platelet activation as well as macro- and microcirculatory thrombus formation.

Methods and Results: With the use of platelet-specific CK2α-deficient mice (csnk2α^{Pf4∆/Pf4∆}) and wild-type littermates (csnk2α^lox/lox), flow cytometric analysis demonstrated disturbed integrin α_IIbβ₃ activation and P-selectin surface exposure in platelets from csnk2α^{Pf4∆/Pf4∆} mice upon stimulation with GPVI-specific platelet agonist collagen-related peptide (CRP). Csnk2α^{Pf4∆/Pf4∆} mice showed also diminished platelet spreading on a fibrinogen-coated surface and serial spectrofluorimetric measurements detected a significantly decreased intracellular Ca²⁺ release and extracellular Ca²⁺ influx after CRP stimulation in CK2α-deficient platelets. In addition, CRP-dependent platelet aggregation and secretion were abrogated in Csnk2α-deficient platelets. Consistent with these results, we observed a defective in vitro arterial thrombus formation in a flow chamber using a collagen-coated surface and varying shear rates. These results are in line with in vivo models since FeCl₃-induced injury in carotid and mesenteric arteries, which represent macro- or microcirculation respectively, showed decreased thrombus formation in csnk2α^{Pf4∆/Pf4∆} mice when compared to csnk2α^lox/lox mice. However, in a tail tip transection model remarkably no difference between bleeding times in both groups was found, although csnk2α-deficient mice displayed an improved outcome after myocardial ischemia/reperfusion injury.

Conclusions: Our results reveal CK2α as crucial regulator of GPVI-mediated platelet activation and arterial in vivo thrombus formation in macro- and microcirculation. Since the lack of CK2α does not compromise the bleeding time of mice, CK2 could therefore represent a promising new pharmacological target for the treatment of thrombo-occlusive disorders.