Abstract 248: Adipose Stromal Cells Mitigate Excessive Aortic Inflammation and Aortic Aneurysm Expansion through Paracrine Factors in an Elastase-induced Murine Abdominal Aortic Aneurysm Model

Objective: Abdominal aortic aneurysm (AAA) formation is characterized by activation of innate and adaptive immune responses that initiate aortic wall degradation. We hypothesize that human adipose stromal cells (ASC) favorably modulate these immune responses through paracrine mechanisms and attenuate AAA expansion in a murine elastase model. Methods: AAA was induced in C57BL/6 mice by topical treatment of the abdominal aorta with elastase. Human ASC or saline was injected i.v. within 4 hours of elastase treatment. The aortic diameter was measured by ultrasound and video micrometry. Monocytes/macrophages and lymphocyte sub-populations were quantified by flow cytometry. Regulatory T cells (Treg) and M2 macrophages were quantified by immunohistochemical (IHC) staining. ASC were labeled with Hoechst and their distributions in the lung and aorta were imaged by fluorescent microscopy and confirmed by real-time PCR for human-specific Alu sequence. Results: ASC significantly suppressed AAA expansion at 14 days (percent change from baseline: 64.1±4.2% (saline) vs. 24.6±6.2% (ASC), n=10/group, p<0.01). At Day 1 there was a significant increase in Treg in ASC treated mice (n=5/group, p<0.01) with a concurrent decrease of CD4+CD28-, CD8+CD28- T cells, and neutrophils (n=5/group, p<0.05). At Day 7, activated monocytes (CD115+CXCR1-LY6C+) and total aortic tissue resident macrophages were decreased (n=10/group, p<0.05) with a significant polarization to the tissue reparative M2 phenotype (n=5/group, p<0.05). Hoechst labeled ASC were detected in the lung without engraftment in the aorta at 24 hrs and were cleared at 96 hrs. Transmembrane co-culture of human peripheral blood mononuclear cells with ASC induced Treg, polarized macrophages to the M2 phenotype, inhibited neutrophil transmigration, and suppressed lymphocyte proliferation, as further supporting the mechanism of paracrine immunomodulation in the in vivo model of AAA. Conclusion: Systemic injection of ASC significantly induced anti-inflammatory immune cell phenotypes and suppressed AAA formation. These effects are mediated by release of paracrine factors and suggest that further characterization of the ASC secretome may lead to more potent recombinant protein therapies for AAA.