High NOR-1 (Neuron-Derived Orphan Receptor 1) Expression Strengthens the Vascular Wall Response to Angiotensin II Leading to Aneurysm Formation in Mice.

No drug therapy has shown to limit abdominal aortic aneurysm (AAA) growth or rupture, and the understanding of the disease biology is incomplete; whereby, one challenge of vascular medicine is the development of good animal models and therapies for this life-threatening condition. The nuclear receptor NOR-1 (neuron-derived orphan receptor 1) controls biological processes involved in AAA; however, whether it plays a role in this pathology is unknown. Through a gain-of-function approach we assessed the impact of NOR-1 expression on the vascular response to Ang II (angiotensin II). We used 2 mouse models that overexpress human NOR-1 in the vasculature, one of them specifically in vascular smooth muscle cells. NOR-1 transgenesis amplifies the response to Ang II enhancing vascular inflammation (production of proinflammatory cytokines, chemokines, and reactive oxygen species), increasing MMP (matrix metalloproteinase) activity and disturbing elastin integrity, thereby broking the resistance of C57BL/6 mice to Ang II-induced AAA. Genes encoding for proteins critically involved in AAA formation (Il [interleukin]-6, Il-1ß, Cxcl2, [C-X-C motif chemokine ligand 2], Mcp-1 [monocyte chemoattractant protein 1], and Mmp2) were upregulated in aneurysmal tissues. Both animal models show a similar incidence and severity of AAA, suggesting that high expression of NOR-1 in vascular smooth muscle cell is a sufficient condition to strengthen the response to Ang II. These alterations, including AAA formation, were prevented by the MMP inhibitor doxycycline. Microarray analysis identified gene sets that could explain the susceptibility of transgenic animals to Ang II-induced aneurysms, including those related with extracellular matrix remodeling, inflammatory/immune response, sympathetic activity, and vascular smooth muscle cell differentiation. These results involve NOR-1 in AAA and validate mice overexpressing this receptor as useful experimental models.