Locally Applied Leptin Induces Regional Aortic Wall Degeneration Preceding Aneurysm Formation in Apolipoprotein E–Deficient Mice

Abstract

Leptin promotes atherosclerosis and vessel wall remodeling. As abdominal aortic aneurysm (AAA) formation involves tissue remodeling, we hypothesized that local leptin synthesis initiates and promotes this process. Human surgical AAA walls were analyzed for antigen and mRNA levels of leptin and leptin receptor, as well as mRNA for matrix metalloproteinases (MMP)-9 and MMP-12. Leptin and leptin receptor antigen were evident in all AAAs, and leptin, MMP-9, and MMP-12 mRNA was increased relative to age-matched nondilated controls. To simulate in vivo local leptin synthesis, ApoE(-/-) mice were subjected to a paravisceral periaortic application of low-dose leptin. Leptin-treated aortas exhibited decreased transforming growth factor-β and increased MMP-9 mRNA levels 5 days after surgery, and leptin receptor mRNA was upregulated by day 28. Serial ultrasonography demonstrated accelerated regional aortic diameter growth after 28 days, correlating with local medial degeneration, increased MMP-9, MMP-12, and periadventitial macrophage clustering. Furthermore, the combination of local periaortic leptin and systemic angiotensin II administration augmented medial MMP-9 synthesis and aortic aneurysm size. Leptin is locally synthesized in human AAA wall. Paravisceral aortic leptin in ApoE(-/-) mice induces local medial degeneration and augments angiotensin II-induced AAA, thus suggesting novel mechanistic links between leptin and AAA formation.