Deletion of the Duffy Antigen Receptor for Chemokines (DARC) Confers Protection Against Abdominal Aortic Aneurysm (AAA) Formation

Abstract

IntroductionAbdominal aortic aneurysms (AAA) are characterized by inflammation and matrix metalloproteinase (MMP)‐mediated degradation of extra cellular matrix proteins leading to aortic dilation and potentially rupture. Inflammatory chemokines that promote AAA are modulated by binding to the Duffy antigen receptor for chemokines (DARC), a non‐signaling receptor expressed primarily on erythrocytes. Interestingly, African Americans exhibit reduced frequency of AAA, and greater than 70% of individuals of African descent do not express DARC on their erythrocytes due to evolutionary pressure from malaria. Here, we tested the hypothesis that DARC gene deletion protects against the development of AAA.MethodsThe induction of AAA was performed using both angiotensin II (AngII) infusion and calcium chloride (CaCl2) application models. In brief, eight week old LDLR knockout (KO, control) and LDLR KO/DARC KO mice were infused with angiotensin II via osmotic minipumps for four weeks at a rate of 1,000 ng/kg/min. For the CaCl2 application model, 12 week old WT and DARC KO mice underwent laparotomy and 0.5 mol/L was applied to the infrarenal aorta. For both models, aortic dilation and AAA formation was assessed using ultrasound, mice were then euthanized and tissues were harvested for histology and biochemical analysis.ResultsLDLR KO/DARC KO mice were protected from the formation of AngII‐induced AAA, as only ~20% developed an aneurysm compared to ~80% in the control group. Concordantly, the aortic diameter of LDLR KO/DARC KO mice was significantly lower relative to control mice after AngII infusion (P=0.02). There was no difference in the pressor response to AngII between groups, but LDLR KO/DARC KO mice exhibited reduced macrophage infiltration, and aortic dilation compared to the control group. Furthermore, IL‐6 levels were significantly reduced in the aortas of LDLR KO/DARC KO mice compared to control mice (P=0.001). Interestingly, however, expression of MCP‐1, which has strong affinity for DARC, tended to be higher in aortas from LDLR KO/DARC KO mice compared to control (P=0.063). In contrast, plasma IL‐6 levels were similar in both LDLR KO/DARC KO and control mice, while MCP‐1 tended to be lower in the plasma of LDLR KO/DARC KO (P=0.07). Interestingly, DARC appears to be upregulated in the aortas of mice in response to AngII. Furthermore, DARC KO mice likewise exhibited reduced aortic dilation in the CaCl2 application model compared to controls.ConclusionsDARC KO mice are protected against AAA formation, perhaps through differential regulation of aortic chemokine trafficking. Understanding the mechanisms by which loss of DARC confers protection from AAA formation may be relevant to ethnic differences in susceptibility to AAA.Support or Funding InformationThis study was supported by the AHA [19PRE34400043 to T.W.B] and the National Institutes of Health [HL124097, HL126949, HL134354 and AR070029 to N.L.W].