Conditional expression of type 2 angiotensin II receptor in rat vascular smooth muscle cells reveals the interplay of the angiotensin system in matrix metalloproteinase 2 expression and vascular remodeling

Angiotensin II is well implicated in neointimal proliferation and the resulting restenosis, however, the mechanisms involved remain unclear. The type 2 angiotensin II (AT2) receptor, largely unexpressed in the adult vasculature, however, appears at significant levels after vascular injury. To investigate the specific contribution of AT2 receptor and the interplay of the angiotensin system to neointima, we engineered rat vascular smooth muscle cells (VSMCs) to express the AT2 receptor in a tetracycline-regulated system. Several VSMC clones resistant to both hygromycin and G418 were selected, many of which showed high, but regulatable levels of AT2R expression within 48 h of doxycycline (Dox) exposure. In untransfected VSMCs and stable transfectants with no AT2R induction, Ang II significantly increased the expression of matrix metalloproteinase 2 (MMP-2), which is linked to neointimal growth. However, induction of AT2R by Dox addition markedly decreased MMP-2 levels (P<0.01) and this downregulation was further promoted by CV-11974, a specific antagonist of AT1 receptor. In contrast, the PD123319 compound, which selectively curtails the AT2 receptor, reversed the inhibition caused by CV-11974. We conclude that Ang II enhances the MMP-2 expression via AT1R, and that enforces AT2R inhibited the same. These data confirm that AT2R functions to downregulate the effects elicited by Ang II + AT1R signaling and point to the role of MMP and extracellular matrix in vascular injury. The findings provide fresh experimental approaches to prevent or control restenosis through transduction of VSMCs expressing optimal levels of AT2R.