Abstract 213: Notch Activation in Aortic Adventitial Fibroblasts upregulates TGF-ß and may have Implications in Aortic Aneurysms

Abstract

Objectives Aortic adventitial fibroblasts (AoAF) are a rich source of cytokines and extracellular matrix (ECM). They critically participate in arterial wall remodeling and are implicated in the pathophysiology of aortic aneurysms (AA) and atherosclerosis. Little is known about signaling pathway(s) that regulate AoAF in cardiovascular diseases. Here, we examined and compared the status of Notch signaling in AoAF in human samples of normal, AA and atherosclerosis samples. We also explored the role of Notch signaling on AoAF cytokines and ECM production. Methods Immunohistochemistry was conducted to examine the Notch activity in AoAF of normal human aorta, segments with atherosclerotic plaque and segments of AA wall (N=4/type of aorta). Normal human AoAF were tested in vitro to study the effects of enforced Notch activation using lentiviral vector encoding the Notch1 intracellular domain, NIC/Lenti. The effect of Notch activation on cell proliferation was tested by MTT assay, and differentiation into myofibroblasts was tested by smooth muscle actin (α-SMA). The effect of Notch signaling on AoAF release of cytokines and ECM was studied using Pathway-Focused Human Fibrosis PCR Array (QIAGEN). Array findings were validated by Western blot. Results Compared to normal human aorta, significantly increased Notch activity was observed in AoAF from AA samples whereas decreased Notch activity was found in AoAF of atherosclerotic aorta (p<0.01). Notch activation inhibited cell proliferation (~30%, p<0.01) while induced differentiation of AoAF to myofibroblasts in vitro. Notch activation also resulted in a fibrotic response in AoAF as determined by increased expression of genes of collagen I/III, connective tissue growth factor (CTGF) and TGF-β1/2/3. Elevated expression of TGF-β 1/2/3(2.4-5.2-fold, p<0.001) in NIC/Lenti-transduced AoAF was confirmed by Western blot. Conclusions Notch signaling is activated in aortic adventitial fibroblasts at the site of aortic aneurysms and results in increased production of TGF-β by these cells.Our novel findings implicate a potential involvement of Notch-TGF-β signaling in the pathophysiology of aortic aneurysms.