Apelin protects against abdominal aortic aneurysm and the therapeutic role of neutral endopeptidase resistant apelin analogs

Abdominal aortic aneurysm (AAA) remains the second most frequent vascular disease with high mortality but has no approved medical therapy. We investigated the direct role of apelin (APLN) in AAA and identified a unique approach to enhance APLN action as a therapeutic intervention for this disease. Loss of APLN potentiated angiotensin II (Ang II)-induced AAA formation, aortic rupture, and reduced survival. Formation of AAA was driven by increased smooth muscle cell (SMC) apoptosis and oxidative stress in Apln(−/y) aorta and in APLN-deficient cultured murine and human aortic SMCs. Ang II-induced myogenic response and hypertension were greater in Apln(−/y) mice, however, an equivalent hypertension induced by phenylephrine, an α-adrenergic agonist, did not cause AAA or rupture in Apln(−/y) mice. We further identified Ang converting enzyme 2 (ACE2), the major negative regulator of the renin-Ang system (RAS), as an important target of APLN action in the vasculature. Using a combination of genetic, pharmacological, and modeling approaches, we identified neutral endopeptidase (NEP) that is up-regulated in human AAA tissue as a major enzyme that metabolizes and inactivates APLN-17 peptide. We designed and synthesized a potent APLN-17 analog, APLN-NMeLeu9-A2, that is resistant to NEP cleavage. This stable APLN analog ameliorated Ang II-mediated adverse aortic remodeling and AAA formation in an established model of AAA, high-fat diet (HFD) in Ldlr(−/−) mice. Our findings define a critical role of APLN in AAA formation through induction of ACE2 and protection of vascular SMCs, whereas stable APLN analogs provide an effective therapy for vascular diseases.