Overexpression of Transforming Growth Factor-β1 Stabilizes Already-Formed Aortic Aneurysms

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Abstract
Background— The cell response to transforming growth factor-β1 (TGF-β1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-β1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis. Methods and Results— Active TGF-β1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-β1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-β1. Transient exogenous TGF-β1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-β1. Overexpression of active TGF-β1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-β1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell–, collagen-, and elastin-rich intima. Conclusions— Local TGF-β1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

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