Abstract 4278: Angiotensin II Receptor Antagonism and Transforming Growth Factor Beta and SMAD Signalling in Thoracic Aortic Aneurysm: Implications for Aneurysm Progression
Increased expression of transforming growth factor-beta (TGFβ) and Smad3 is associated with fibrosis and inflammatory cell infiltration in abdominal aortic aneurysm. In Smad3-null mice there is reduced extracellular matrix (ECM) deposition but enhanced neointimal hyperplasia in response to vascular injury suggesting a TGFβ/Smad3 role in ECM regulation and cell proliferation. In vitro studies show that exogenous TGFβ administration leads to phosphorylation and nuclear translocation of Smad3 while angiotensin II (AngII) induces fibrosis through TGFβ and Smad3 pathways. We investigated TGFβ/Smad3 signaling using immunohistochemical and cell culture studies in thoracic aortic aneurysm tissue derived from subjects with Marfan syndrome (MFS; 3M, 2F, 46±24yr, mean +/−SD) and bicuspid aortic valve malformation (BAV; (3M, 2F, 65±13yr) as well as normal aorta from organ donor subjects (3M, 2F 40±11yr). MFS and BAV tissue showed co-localisation of TGFβ1–3 and Smad3 in myofibroblasts, vascular smooth muscle cells (VSMCs) and chronic inflammatory cells in the subintimal layer and tunica media and in fibroblasts in tunica adventitia. In normal aortic wall there was minimal TGFβ and Smad3 staining. Cultured VSMCs (passage 1–5) from MFS and BAV showed nuclear Smad3 and strong cytoplasmic TGFβ1–3 expression in numerous vesicles and in areas of exocytosis and extracellular localisation. In control cells there was much weaker TGFβ1–3 staining compared to aneurysm derived cells. Smad3 staining in normal cells was located in the cytoplasm alone. Compared to normal tissue and cells AngII receptor type1 and 2 (ATR1 and 2) expression was increased in both aneurysm tissue and in cultured VSMCs derived from aneurysm. Cultured VSMCs were treated for 48h with the ATR1 antagonist losartan (10μM). This caused disappearance of TGFβ1–3 vesicle localisation and nuclear expression of Smad3. The findings of increased TGFβ1–3 and Smad3 expression in aneurysm tissue and cultured cells are consistent with aberrant TGFβ signalling and with activation of the Smad3 signalling pathway. Furthermore reduction in extracellular TGFβ and de-activation of Smad3 expression associated with losartan treatment supports a role for ATR1 antagonism in inhibition of aneurysm progression.