P0726ENDOTHELIAL DYSFUNCTION ASSOCIATED TO ATHEROSCLEROSIS OF KNOCKOUT APOE MICE COULD BE MEDIATED BY VASCULAR FIBROSIS
Authors: Asenjo-Bueno Ana , Alcalde-Estevez Elena , Sosa Patricia , Plaza Patricia , Serrano-Garcia Lucia , El Assar de la Fuente Mariam , Rodriguez-Puyol Manuel , Olmos Gemma , Ruiz Maria Piedad , López-Ongil Susana 
Published: June 2020

Abstract

Background and Aims
Patients with chronic kidney disease (CKD) present a high rate of cardiovascular mortality mainly associated with endothelial dysfunction, which causes more cardiovascular events in presence of atherosclerosis. Atherosclerosis is characterized by a significant increase of low density lipoproteins (LDL), reactive oxygen species (ROS) and inflammation. ROS can oxidize LDL generating oxidized-LDL (oxLDL) that promotes the development of cardiovascular pathologies. The aim of this study was to evaluate whether oxLDL induce endothelial dysfunction analysing the involvement of vascular fibrosis.

Method
The model used for in vivo studies was the Knockout apolipoprotein E (KO-apoE) mice, which resemble human atherosclerosis and shown high levels of cholesterol (LDL) that can be oxidized to oxLDL. In mice, blood pressure was registered before sacrificed them. After that, we measured different parameters as serum cholesterol levels, vascular function by vascular reactivity in mesenteric arteries and vascular fibrosis in aorta by Sirius Red staining and by the protein expression of fibronectin and collagen-I by immunohistochemistry. In order to investigate the mechanism of action of oxLDL, in vitro studios were performed on human smooth muscle cells (SMC) incubated with oxLDL at different times. Fibrosis was evaluated by the expression of TGF- β and extracellular matrix proteins such as fibronectin and collagen-I by Western blot and by immunofluorescence. ROS production was also measured by fluorescence confocal microscopy, using the CellROX Deep Red probe.

Results
KO-apoE mice shown higher levels of serum cholesterol and blood pressure than WT animals. Moreover, KO-apoE mice showed endothelial dysfunction since their arteries were less relaxed and more contracted. In addition, these mice presented thickening of vascular wall (SMC layer), more fibrosis showing intense Sirius Red staining and less expression of elastin, all compatible with their vascular dysfunction compared to WT mice. Furthermore, aortas from KO-apoE mice showed a slight increase in fibronectin and collagen-I expression assessed by immunohistochemistry. In vivo studies were confirmed in vitro after treating SMC with oxLDL. oxLDL induced fibrosis in SMC by increasing TGF-β, fibronectin and collagen-I protein expressions evaluated by Western blot and immunofluorescence assays. Treatment with oxLDL also increased ROS production, which seem to be responsible of oxLDL-induced fibrosis in human SMC, as it was blocked in the presence of the antioxidant N-Acetyl-cysteine.

Conclusion
In summary, these results point to endothelial dysfunction associated to atherosclerosis (oxLDL) could be mediated by an increase in the development of vascular fibrosis where ROS could play an important role. Therefore, the endothelial dysfunction typical of CKD patients could impair with more vascular fibrosis when atherosclerosis is also present.