A18 - Braun

Summary:

Elevation of the intracellular Ca²⁺ concentration ([Ca²⁺]i) is a central event during platelet activation. We have identified the Ca²⁺ sensor stromal interaction molecule 1 (STIM1) and the Ca²⁺ channel proteins Orai1 and TRPC6 as key regulators of Ca²⁺ homeostasis in platelets, and provided evidence that blocking of Ca²⁺ signalling in platelets might become a promising antithrombotic approach. On the other hand, it has been known for more than 50 years that Mg²⁺ is a natural antagonist of Ca²⁺ signalling and altered Mg2+ homeostasis is described in many cardiovascular diseases, especially in patients with coronary heart disease, arrhythmias, acute myocardial infarction, hypertension and stroke. We hypothesise that the abnormal function of Mg²⁺ channels may contribute to the development of aberrant Ca²⁺ homeostasis in platelets thereby inducing abnormal platelet activation and a pro-thrombotic phenotype in vivo. Although Mg²⁺ entry has been described in megakaryocytes (MKs) and platelets, the molecular composites of Mg²⁺ channels and their signalling functions are unknown.

In preliminary studies, we have identified TRPM7 channel and MagT1 transporter to be expressed in murine platelets and started to analyse their functions in MKs and platelets under normal and pathological conditions using knock-out (MagT1^-/-, Trpm7^{fl/fl Pf4-Cre}) and knock-in (Trpm7^ΔKIN) mouse models. First results show that the Trpm7^ΔKIN mutation, which deletes the kinase activity of TRPM7, causes a marked Ca²⁺ signalling defect downstream of GPVI activation in platelets resulting in defective thrombus formation under flow and protection of Trpm7^ΔKIN mice in models of arterial thrombosis and ischaemic stroke.

In a second part of the project, we want to study the effect of hypomagnesaemia on megakaryopoiesis and platelet function in vivo. For these studies we intend to use Trpm6^-/- mice, which develop severe hypomagnesaemia 6-10 weeks after birth. This in vivo model will provide important information on how the blood Mg²⁺ concentration influences platelet function in vivo.