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Induktion von NF-κB durch Albumin in immortalisierten humanen proximalen Tubuluszellen (IHKE-1)
(2011)
Hintergurnd: Erhöhte glomeruläre Filtration von Proteinen im Rahmen chronoischer Nierenenerkrankungen geht mit tubulointerstitiellem Schaden einschließlich Entzündung und fortschreitendem Funktionsverlust der Nierenfunktion einher. Proteine wie Albumin scheinen dabei per se eine pathogenetische Rolle zu spielen. Der Transkriptionsfaktor nuclear factor kappa B (NF-kB) scheint an den durch Proteinüberladung verursachten Pathomechanismen der Nierenentzündung beteiligt zu sein. Um die Albumin-induzierte Expression von NF-kB sowie die Expression des NF-kB-regulierten proinflammatorischen Zytokins Tumor Necrosis Faktor alpha (TNF-a) nach Exposition mit Albumin in humanen proximalen Tubuluszellen zu überprüfen, exponierten wir humane, von proximalen Tubuluszellen abstammende Zellen (IHKE-1) mit bovinem Serumalbumin (BSA: 50 und 500 microg/ml). Die NF-KB- und TNF-a-spezifische mRNA-Expression wurde durch RT-PCR bestimmt. NF-kB-spezifische Proteinexpression wurde mit Western-Blot-Verfahren analysiert. Ergebnisse: Albumin-induziert einen Anstieg der NF-kB-spezifischen mRNA-Expression und NF-kB-spezifischen Proteinexpression. Diese Effekte werden durch den Protein Kinase C-Inhibitor Bisindolylmaleimid und den Tyrosin Kinase Inhibitor Herbimycin A gehemmt. Ein Albumin.induzierter Anstieg der TNF-a-spezifischen mRNA-Expression als biologischer inflammatorischer Parameter war als mit der NF-B-Aktivität assoziiert messbar.
Platelets are crucial to inhibit extensive blood loss at sites of vascular injury. However, under pathological conditions such as rupture of an atherosclerotic plaque, activated platelets form aggregates that may occlude the vessel. This can lead to heart attack and stroke. Various and complex signaling pathways in the cell are involved in the steps of platelet adhesion, activation and aggregation. Single aspects of these processes were studied in three different subprojects in this work. The Glycoprotein (GP) Ib-V-IX complex is responsible for the first contact of platelets with the vessel wall. Subsequently, GPVI can bind to collagen of the subendothelium, which initiates a signaling cascade leading to platelet activation, aggregation, characterized by integrin activation and granule secretion and platelet procoagulant activity. The latter is characterized by exposed phosphatidylserine (PS) on the platelet surface, which enhances thrombin generation and thereby the coagulation cascade. A controlled regulation of GP receptors on the platelet surface is vital for an intact response of the cell to platelet agonists. In the first subproject described here the regulation of GPV and GPVI on mouse platelets was investigated and it was found that both receptors are shed from the platelet surface in a metalloproteinase dependent manner. However, GPVI is shed upon mitochondrial injury, while GPV cleavage could be observed upon platelet stimulation. The metalloproteinase responsible for GPVI shedding remains unknown whereas the metallproteinase that sheds GPV was identified in this work as being ADAM17. This shows that the expression of both receptors underlies a controlled mechanism regulated through distinct metalloproteinases. In the second subproject the role of protein kinase C (PKC) in platelet activation and procoagulant response was investigated using PKC specific inhibitors. It was found that PKC blockage reduced platelet activation but enhanced platelet procoagulant activity. This is the first time that a dual role in platelet activation and procoagulant activity is defined for PKC. In the third project the role of the small GTPase Rac1 in platelet signaling was studied using conditional Rac1 knock out mice. It is reported here that Rac1 lies downstream of GPVI and is involved in integrin activation and cytsolic Ca2+ changes in vitro and platelet adhesion and thrombus formation in vivo. This is the first time that Rac1 is demonstrated to have a pivotal role in GPVI signaling and furthermore points to a novel, unknown pathway downstream of GPVI.