Publikationsserver der RWTH Aachen University
Einfluss von BMP-7 und Endoglin auf den TGF-beta Signalweg bei fibrosierenden Lebererkrankungen
Abstract
dc:descriptionThe main task of this doctoral thesis was to analyze the influence of BMP-7 on the TGF-b1 pathway and to characterize the role of endoglin within these two pathways. Using the endoglin deficient myoblast cell line L6E9 it was possible to show the antagonistic character of these two cytokines and further to determine their involvement within the myogenic differentiation. Both cytokines induce specific target genes, such as Id-1 (induced by BMP-7) and Collagen I (induced by TGF-b1). It is supposed that BMP-7 activates three different Type I Receptors, ALK-2, ALK-3 and ALK-6, while TGF-b activates ALK1 and ALK5. As a consequence of activation of the ALK5/Smad3 pathway the Collagen I expression is induced and as a consequence of the ALK1/Smad1/5 pathway a transient expression of Id-1 is induced. The BMP-7 signal is exclusively mediated through Smad1/5 and results in long term Id-1 expression. While BMP-7 applied alone does not influence Collagen I expression, in combination with TGF-b1 it does antagonize the Collagen I expression and (CAGA)12-MLP-Luc activity which are stimulated by TGF-b1. These effects are negotiated using the ALK5/Smad3 pathway. Furthermore, it could be shown that over expression of endoglin in these cells leads on the one hand to an inhibition of the ALK5/Smad3 pathway and on the other hand to an amplification of the BMP-7/Smad1/5 pathway. To further characterize the interaction between BMP-7 and TGF-b1 within liver fibrogenesis hepatic stellate cells, as one of the most important cellular modulators of fibrosis were analyzed. In hepatic stellate cells the TGF-b signal is translocated via ALK1 and ALK5 such as already mentioned for L6E9, resulting in phosphorylation of Smad1 and Smad3. On the other hand the BMP-7 signal is translocated using Activin and other BMP-7 receptors, resulting in phosphorylation of Smad1 and Smad5. Likewise specific target genes are induced through BMP-7 (Id-1) and TGF-b1 (PAI-1, Collagen I) in hepatic stellate cells. Here BMP-7 antagonizes the TGF-b induced Collagen I and PAI-1 expression and the (CAGA)12-MLP-Luc activity. This results in an inhibition of the profibrogenic activity of HSC in vitro. BMP-7 oneself does not induce any Collagen I expression. The third cell type analyzed in this thesis is the endoglin deficient hepatocyte (PC). Hepatocytes represent the main component of the liverparenchym. In the same way as L6E9 and HSC do, the PC transmit the TGF-b signal using ALK1/Smad1/5 and ALK5/Smad3 while the BMP-7 signal is transmitted using Smad1 and Smad5. Overexpression of endoglin results, as already mentioned for L6E9, in inhibition of the TGF-b1 induced ALK5/Smad3 pathway and in an increased BMP-7/Smad1/5 pathway. An antagonistic effect of BMP-7 towards the TGF-b1 pathway could not be shown in PC, neither on the level of target gene expression nor on the level of (CAGA)12-MLP-Luc reporter assay. But it was possible to decrease TGF-b1 induced apoptosis by applying BMP-7. In contrast to L6E9 and HSC it was possible to detect BMP-7 in PC using RT-PCR and immuno-histochemical staining. Finally, by using an animal model it could be shown, that the amount of BMP-7 does increase in liver lysates while formation of liver fibrosis, which are caused by bile duct ligation. For this experiment the adenoviral (BRE)2-Luc reporter was used. In the end it is possible to spotlight the functional antagonism of BMP-7 towards TGF-b1, which is further modulated by endoglin. Thus endoglin amplifies the BMP-7 pathway while inhibiting the TGF-b1 pathway.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2008
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Scherner, Olaf Andreas
- Contributors dc:contributor
-
- Kreuzaler, Fritz
Subjects
dc:subject × 10Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger