PI3 kinase dependent regulation of ion channels and carriers in platelets

• Applicant: Professor Dr. Oliver Borst
• Subject Area: Cardiology, Angiology ; Anatomy and Physiology
• Term: from 2011 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 190538538

Platelets are pivotal for primary hemostasis at sites of vascular injury and by the same token decisive for the development of acute thrombosis and thrombotic vascular occlusion. Platelet activation involves several signaling pathways including activation of phosphoinositide-3-kinase (PI3K), which is critically important for the function of activated platelets. Activation eventually leads to increase of cytosolic Ca2+-concentration, which is decisive for triggering of secretion, integrin activation and thrombus formation.In the first funding period the applicants identified several PI3K-dependent signaling pathways, which are required for platelet activation and thrombus formation. They could show that the PI3K-sensitive serum- and glucocorticoid-inducible kinase SGK1 regulates the nuclear factor kappa B (NF-kB), which in turn governs the expression of several megakaryocytic proteins. Specifically, NF-kB was identified as powerful transcriptional regulator of the channel protein Orai1 and its regulator STIM1. Orai1 and STIM1 accomplish store operated Ca2+-entry (SOCE). Moreover, the applicants could show that the similarly PI3K-dependent protein kinase B/Akt plays a decisive role for inflammation-triggered platelet activation.The second funding period shall address the impact and regulation of further kinases, which interact with the PI3K signaling pathway. The applicants plan to generate respective platelet specific knockout- mouse models in order to reveal the impact on thrombo-occlusive disease models such as stroke and myocardial infarction. The signaling molecules particularly studied include casein kinase 2 beta (CK2-beta), phosphoinositide-dependent kinase 1 (PDK1), I kappa kinase beta (IKK-beta) and p38 mitogen activated protein kinase alpha (p38MAPK-alpha). Moreover, further experiments will be done to the define the significance of those signaling molecules identified in the first funding period, such as SGK1, chorein, Akt1, Akt2 and acid sphingomyelinase (aSM), for the development of thrombi. The intended experiments particularly address the role of SGK1 for the granule biogenesis, SGK1-sensitive regulation of Pendrin, Na+/H+ exchanger, Na+/K+ ATPase and Na+/Ca2+ exchanger in megakaryocytes and platelets, as well as platelet function and thrombo-occlusive complications at diseases known to be associated with strong upregulation of SGK1 expression (e.g. hyperaldosteronism in chronic renal failure and hyperinsulinism in diabetes mellitus). The significance of acid sphingomyelinase (aSM) for the composition of the platelet cell membrane and the function of platelets shall be defined by studying platelets from aSM knockout mice (smpd1-/-) and from patients suffering from Niemann-Pickdisease.

• DFG Programme: Clinical Research Units
• Subproject of: KFO 274: Platelets - Molecular Mechanisms and Translational Implications
• Participating Person: Professor Dr. Florian Lang