Mesenchymal stem cells attenuate angiotensin II-induced aortic aneurysm growth in apolipoprotein E-deficient mice.

OBJECTIVE: Aortic aneurysm (AA) is associated with loss of elastin and structural integrity, accompanied by increased matrix metalloproteinase (MMP) expression. These processes are supported by inflammatory macrophages, with mediators such as tumor necrosis factor-α (TNF-α). Mesenchymal stem cells (MSCs) contribute to aortic remodeling. Therefore, to clarify whether MSCs might be useful for AA cell therapy, we examined the effect of MSCs on vascular smooth muscle cells (SMCs) and macrophages in vitro, on aortic tissue ex vivo, and on aorta in vivo.
METHODS: Murine macrophages and SMCs were cultured, with or without bone marrow-derived murine MSCs, for 96 hours in vitro. Gene expression of MMPs and TNF-α from macrophages and that of elastin from SMCs were measured. The murine aortic tissues were cultured with or without MSCs for up to 14 days, followed by measurement of MMP enzyme activity and elastin content. The in vivo aneurysm model used apolipoprotein E-deficient (apoE(-/-)) male mice receiving angiotensin II (Ang II) infusion for 28 days. MSCs were implanted by laparotomy to the abdominal aortic adventitial surface from the superior mesenteric artery origin to the left renal artery. Age-matched apoE(-/-) mice with or without Ang II infusion were used for control groups. At the end point, aortic diameter, elastin content, MMPs' activity, and cytokines expressed, including interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1), TNF-α, insulin-like growth factor-1 (IGF-1), and tissue inhibitor of metalloproteinases-1 (TIMP-1) were quantified.
RESULTS: MSCs suppressed MMP-2 with or without MSCs (2.59 vs 3.94, P < .05), MMP-9 (5.83 vs 9.70, P < .05), and TNF-α (2.79 vs 3.38, P < .05) expression in macrophages, and promoted elastin expression in SMCs (19.35 vs 3.23, P < .05) in vitro. MSCs also decreased active MMP-2 activity (0.310 vs 0.0609 U/μL, P < .05) and preserved elastin content (68.05 vs 40.29 μg/mg, P < .05) ex vivo. AA development was site-specifically inhibited (0.73 vs 1.04 mm aortic diameter, P < .05) and elastin content was preserved (46.9 vs 25.6 μg/mg, P < .05) at 4 weeks. Downregulation of MMPs and IL-6, MCP-1, and TNF-α, and upregulation of IGF-1 and TIMP-1 were demonstrated with MSC implantation in vivo.
CONCLUSIONS: MSC implantation inhibits Ang II-induced AA development in apoE(-/-) mice through elastin preservation in the aortic wall and is associated with attenuated levels of MMPs and inflammatory cytokines.