Altogether, the results suggest a dominant role of IL-1β-induced NETosis in AAA formation.

Objective B cell depletion therapy is widely used for treatment of cancers and autoimmune diseases. B cells are abundant in abdominal aortic aneurysms (AAA), however, it is unknown whether B cell depletion therapy affects AAA growth. Using experimental models of murine AAA, we aim to examine the effect of B cell depletion on AAA formation. Approach and Results Wild-type or Apolipoprotein E knockout mice were treated with mouse monoclonal anti-CD20 or control antibodies and subjected to an elastase perfusion or angiotensin II-infusion model to induce AAA, respectively. Anti-CD20 antibody treatment significantly depleted B1 and B2 cells, and strikingly suppressed AAA growth in both models. B cell depletion resulted in lower circulating IgM levels, but did not affect the levels of IgG or cytokine/chemokine levels. Although the total number of leukocyte remained unchanged in elastase perfused aortas following anti-CD20 antibody treatment, the number of B cell subtypes was significantly lower. Interestingly, plasmacytoid dendritic cells (pDCs) expressing the immunomodulatory enzyme indole 2,3-dioxygenase (IDO) were detected in the aortas of B cell depleted mice. In accordance with an increase in IDO+ pDCs, the number of regulatory T cells was higher while the expression of pro-inflammatory genes was lower in aortas of B cell depleted mice. In a coculture model, presence of B cells significantly lowered the number of IDO+ pDCs without affecting total pDC number. Conclusions The present results demonstrate that B cell depletion protects mice from experimental AAA formation and promotes emergence of an immunosuppressive environment in aorta.

Objectives: Resolvins have been shown to attenuate inflammation, while NETosis, the process of neutrophils releasing neutrophil extracellular traps (NETs), produces increased inflammation. It is hypothesized that treatment of animals with resolvin D1 (RvD1) would reduce abdominal aortic aneurysm (AAA) formation by inhibiting NETosis. Methods: Wild-type (WT) 8–12-week old C57BL/6 male mice (n=47) and apolipoproteinE deficient (ApoE-/) mice (n=20) were used in two models to demonstrate the effects of RvD1 on AAA growth. In the topical elastase AAA model, WT mice were divided into three groups: (1) Deactivated elastase control group: sham surgery was performed using deactivated elastase and mice were intravenously injected with phosphate buffered saline (PBS) once a day until harvest. (2) Elastase group: active elastase was used to induce AAA and mice were injected with PBS daily until harvest. (3) RvD1 treated group: AAA was induced and mice were injected with RvD1 daily until harvest. In the angiotensin II (Ang II) induced AAA model, ApoE−/− mice were fed high fat diet and implanted with osmotic infusion pumps containing Ang II (1000ng/kg/min). The Ang II model was divided into two groups: (1) Ang II control group: Ang II was delivered and mice were injected with PBS daily until harvest. (2) RvD1 treated group: Ang II was delivered and mice were injected with RvD1 daily until harvest. On postoperative days 3, 14, or 28, aortic and blood samples were collected for western blot, histology, cytokine array, enzyme-linked immunosorbent assay, and gelatin zymography after aortic diameter measurement. Results: Day 14 RvD1 treated group demonstrated 42% reduced AAA diameter compared to elastase group (p<0.001). On postoperative day 3, RvD1 treated group showed decreased levels of NETosis markers citrullinated histone H3 (p=0.04) and neutrophil elastase (p=0.002) compared to the Elastase group. Among important cytokines involved in AAA formation, interleukin (IL) 1β was down-regulated (p=0.02), while IL-10, a protective cytokine, was upregulated (p=0.01) in the RvD1 treated group. Active matrix metalloproteinase 2 (MMP2) also decreased in the RvD1 treated group (p= 0.03). The RvD1 treated group in the Ang II AAA model, a second model, demonstrated reduced AAA diameter compared to Ang II control group on day 28 (p<0.046). RvD1 treated group showed decreased levels of citrullinated histone H3 on day 3 (p=0.002). Cytokines INF-γ, IL-1β, CXCL-10, MCP-1, and RANTES were all decreased on day 28 (p<0.05). Conclusion: Resolvin D1-mediated inhibition of NETosis may represent a future medical treatment for the attenuation of AAA growth.

The formation of an abdominal aortic aneurysm (AAA) is characterized by inflammation, macrophage infiltration, and vascular remodeling. In this study, we tested the hypothesis that mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) immunomodulate aortic inflammation, to mitigate AAA formation via modulation of microRNA-147. An elastase-treatment model of AAA was used in male C57BL/6 wild-type (WT) mice. Administration of EVs in elastase-treated WT mice caused a significant attenuation of aortic diameter and mitigated proinflammatory cytokines, inflammatory cell infiltration, an increase in smooth muscle cell α-actin expression, and a decrease in elastic fiber disruption, compared with untreated mice. A 10-fold up-regulation of microRNA (miR)-147, a key mediator of macrophage inflammatory responses, was observed in murine aortic tissue in elastase-treated mice compared with controls on d 14. EVs derived from MSCs transfected with miR-147 mimic, but not with miR-147 inhibitor, attenuated aortic diameter, inflammation, and leukocyte infiltration in elastase-treated mice. In vitro studies of human aortic tissue explants and murine-derived CD11b macrophages induced proinflammatory cytokines after elastase treatment, and the expression was attenuated by cocultures with EVs transfected with miR-147 mimic, but not with miR-147 inhibitor. Thus, our findings define a critical role of MSC-derived EVs in attenuation of aortic inflammation and macrophage activation via miR-147 during AAA formation.-Spinosa, M., Lu, G., Su, G., Bontha, S. V., Gehrau, R., Salmon, M. D., Smith, J. R., Weiss, M. L., Mas, V. R., Upchurch, G. R., Sharma, A. K. Human mesenchymal stromal cell-derived extracellular vesicles attenuate aortic aneurysm formation and macrophage activation via microRNA-147.