Pulmonary arterial hypertension (PAH) is a rare but serious condition. In PAH abnormal proliferation of smooth muscle cells (SMCs) leads to a decreasing diameter of the vessel and an increase in resistance, resulting in an elevated pulmonary arterial pressure and right heart failure.PAH can be found as idiopathic, heritable or in association with multiple other conditions. This thesis focuses on PAH in context to the members of the transforming growth factor beta (TGF-beta) family and especially activin receptor like kinase 1 (ALK1) in human pulmonary artery smooth muscle cells (hPASMCs), since mutations in the genes coding for the TGF-beta family members BMPR-II and ALK1 have been linked to the development of PAH. To imitate PAH, cells were exposed to hypoxia as a stimulus of PAH.On mRNA level significant upregulation was observed for the TGF-beta receptors ALK1 and ALK5 after exposure of hPASMCs to hypoxia for 48 hours compared to the control group. The TGF-beta receptors ALK2, ALK3, ALK4, ALK6, TGF-betaRII, BMPRII and Endoglin also showed the tendency of upregulation after 48 hours exposure to hypoxia. Of the mediators of the TGF-beta pathway Smad2 - Smad5 and Smad8 showed the tendency of increased mRNA expression after 48 hours exposure to hypoxia. Among the target genes of the TGF-beta family members ID2 was significantly upregulated after 48 hours exposure to hypoxia and ID1 as well as PAI-1 showed a general tendency of upregulation upon exposure to hypoxia. On protein level no significant changes in expression could be detected when comparing hypoxia to normoxia exposed cells. The proliferation assay of hPASMCs indicated that proliferation of not transfected hPASMCs takes place under hypoxic stimulation, while for ALK1 siRNA transfected cells no significant data could be shown. Furthermore ALK1 could be localised in the hPASMCs by immunofluorescence both under normoxic and hypoxic conditions.This work explores the characteristics of TGF-beta pathway family members, especially the role of ALK1, in hPASMCs under hypoxia and normoxia. For some of the investigated genes, an altered expression under hypoxic conditions on mRNA level could be demonstrated, yet there were no corresponding changes on protein level. An influence of ALK1 on migration and proliferation of hPASMCS could not be shown. To further evaluate the impact of the TGF-beta pathway family members on the behaviour of hPASMCs under hypoxic and normoxic conditions, additional experiments need to be performed.
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