Adventitial recruitment of Lyve-1- macrophages drives aortic aneurysm in an angiotensin-2-based murine model.

Objective: Aortic macrophage accumulation is characteristic of the pathogenesis of abdominal aortic aneurysm (AAA) but the mechanisms of macrophage accumulation and their phenotype are poorly understood. Lyve-1+ resident aortic macrophages independently self-renew and are functionally distinct from monocyte-derived macrophages recruited during inflammation. We hypothesized that Lyve-1+ and Lyve-1- macrophages differentially contribute to aortic aneurysm. Approach and Results: Angiotensin-2 and beta-aminopropionitrile (AT2/BAPN) were administered to induce AAA in C57BL/6J mice. Using immunohistochemistry, we demonstrated primarily adventitial accumulation of aortic macrophages, and in association with areas of elastin fragmentation and aortic dissection. Compared to controls, AAA was associated with a relative percent depletion of Lyve-1+ resident aortic macrophages and accumulation of Lyve-1- macrophages. Using CD45.1/CD45.2 parabiosis, we demonstrated aortic macrophage recruitment in AAA. Depletion of aortic macrophages in CCR2-/- mice was associated with reduced aortic dilatation indicating the functional role of recruitment from the bone marrow. Depletion of aortic macrophages using anti- Macrophage Colony Stimulating Factor 1 Receptor (MCSF1R)-neutralizing antibody reduced the incidence of AAA. Conditional depletion of Lyve-1+ aortic macrophages was achieved by generating Lyve-1 wt/cre Csf1rfl/fl mice. Selective depletion of Lyve-1+ aortic macrophages had no protective effects following AT2/BAPN administration and resulted in increased aortic dilatation in the suprarenal aorta. Conclusions: Aortic macrophage accumulation in AAA derives from adventitial recruitment of Lyve-1- macrophages, with relative percent depletion of Lyve-1+ macrophages. Selective targeting of macrophage subtypes represents a potential novel therapeutic avenue for the medical treatment of AAA.

Kallikrein‐1 Blockade Inhibits Aortic Expansion in a Mouse Model and Reduces Prostaglandin E2 Secretion From Human Aortic Aneurysm Explants

Background Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. The kinin B2 receptor agonist, bradykinin, has been implicated in AAA pathogenesis through promoting inflammation. Bradykinin is generated from high‐ and low‐molecular‐weight kininogen by the serine protease kallikrein‐1. The aims of this study were first to examine the effect of neutralizing kallikrein‐1 on AAA development in a mouse model and second to test how blocking kallikrein‐1 affected cyclooxygenase‐2 and prostaglandin E 2 in human AAA explants. Methods and Results Neutralization of kallikrein‐1 in apolipoprotein E‐deficient ( ApoE −/− ) mice via administration of a blocking antibody inhibited suprarenal aorta expansion in response to angiotensin (Ang) II infusion. Kallikrein‐1 neutralization decreased suprarenal aorta concentrations of bradykinin and prostaglandin E 2 and reduced cyclooxygenase‐2 activity. Kallikrein‐1 neutralization also decreased protein kinase B and extracellular signal‐regulated kinase 1/2 phosphorylation and reduced levels of active matrix metalloproteinase 2 and matrix metalloproteinase 9. Kallikrein‐1 blocking antibody reduced levels of cyclooxygenase‐2 and secretion of prostaglandin E 2 and active matrix metalloproteinase 2 and matrix metalloproteinase 9 from human AAA explants and vascular smooth muscle cells exposed to activated neutrophils. Conclusions These findings suggest that kallikrein‐1 neutralization could be a treatment target for AAA.

Early Morphofunctional Changes in AngII-Infused Mice Contribute to Regional Onset of Aortic Aneurysm and Dissection

Aortic aneurysms and dissections are silent and lethal conditions, whose pathogenesis remains incompletely understood. Although angiotensin II (AngII)-infused ApoE−/− mice have been widely used to study aortic aneurysm and dissection, early morphofunctional alterations preceding the onset of these conditions remain unknown. The goal of this study was to unveil early morphofunctional changes underlying the onset of aneurysm and dissection. At 3 days post-AngII infusion, suprarenal abdominal aorta presented significant volumetric dilatation and microstructural damage. Ex vivo assessment of vascular reactivity of the suprarenal dissection-prone aorta and its side branches, showed an endothelial and contractile dysfunctions that were severe in the suprarenal aorta, moderate distally, and absent in the side branches, mirroring the susceptibility to dissection of these different vascular segments. Early and specific morphofunctional changes of the suprarenal aorta may contribute to the regional onset of aortic aneurysm and dissection by exacerbating the biomechanical burden arising from its side branches.

Progenitor/Stem Cell Delivery by Suprarenal Aorta Route in Acute Kidney Injury

Progenitor/stem cell-based kidney regenerative strategies are a key step towards the development of novel therapeutic regimens for kidney disease treatment. However, the route of cell delivery, e.g., intravenous, intra-arterial, or intra-parenchymal, may affect the efficiency for kidney repair in different models of acute and chronic injury. Here, we describe a protocol of intra-aorta progenitor/stem cell injection in rats following either acute ischemia-reperfusion injury or acute proteinuria induced by puromycin aminonucleoside (PAN) – the experimental prototype of human minimal change disease and early stages of focal and segmental glomerulosclerosis. Vascular clips were applied across both renal pedicles for 35 min, or a single dose of PAN was injected via intra-peritoneal route, respectively. Subsequently, 2 x 106 stem cells [green fluorescent protein (GFP)-labeled c-Kit+ progenitor/stem cells or GFP-mesenchymal stem cells] or saline were injected into the suprarenal aorta, above the renal arteries, after application of a vascular clip to the abdominal aorta below the renal arteries. This approach contributed to engraftment rates of ∼10% at day 8 post ischemia-reperfusion injury, when c-Kit+ progenitor/stem cells were injected, which accelerated kidney recovery. Similar rates of engraftment were found after PAN-induced podocyte damage at day 21. With practice and gentle surgical technique, 100% of the rats could be injected successfully, and, in the week following injection, ∼ 85% of the injected rats will recover completely. Given the similarities in mammals, much of the data obtained from intra-arterial delivery of progenitor/stem cells in rodents can be tested in translational research and clinical trials with endovascular catheters in humans.

Anatomical Considerations and Open Surgery to Treat Juxtarenal Abdominal Aortic Aneurysms

Introduction: Historically, the open approach to the abdominal aorta has been transperitoneal (TP). In comparison, a retroperitoneal (RP) incision exposes the lateral wall of the suprarenal aorta for clamp application and midline structures such as the duodenum and pancreas are not encountered. Proximal clamp position for open repair of juxtarenal abdominal aortic aneurysm (JR-AAA) is suprarenal, supra-superior mesenteric, or supraceliac. While RP and TP approaches have previously been compared for physiological reasons, there are currently no randomized controlled trials comparing these methods from an anatomical perspective. Aims: The primary aim is to examine the evidence for adopting an RP approach for JR-AAA and compare it with TP approach from an anatomical perspective. The secondary aim is to assess optimum proximal clamp position and its effect on renal function and mortality for the 2 approaches. Methods/Design: Literature was reviewed searching databases Medline and Embase for studies on clamp positioning in JR-AAA repair using a TP or RP approach, up to December 2017. Conclusions: There is no clear evidence for the optimum cross-clamp position for open repair of JR-AAAs. More proximal clamps provide adequate operative space with the possible downside of increased afterload leading to visceral and renal ischemia. Clamps placed inferior to the superior mesenteric artery allow continued bowel and hepatic perfusion with the potential to cause trauma to the adjacent aortic branches during application. As far as the optimum approach is concerned, many series show a strong trend for RP as a more proximal clamp is required. Significant numbers develop renal failure after JR-AAA repair, with most recovering fully irrespective of the clamp position.

Resveratrol Inhibits Growth of Experimental Abdominal Aortic Aneurysm Associated With Upregulation of Angiotensin-Converting Enzyme 2

Objective— Recent evidence suggests an important role for angiotensin-converting enzyme 2 (ACE2) in limiting abdominal aortic aneurysm (AAA). This study examined the effect of ACE2 deficiency on AAA development and the efficacy of resveratrol to upregulate ACE2 in experimental AAA. Approach and Results— Ace2 deletion in apolipoprotein-deficient mice ( ApoE −/− Ace2 −/y ) resulted in increased aortic diameter and spontaneous aneurysm of the suprarenal aorta associated with increased expression of inflammation and proteolytic enzyme markers. In humans, serum ACE2 activity was negatively associated with AAA diagnosis. ACE2 expression was lower in infrarenal biopsies of patients with AAA than organ donors. AAA was more severe in ApoE −/− Ace2 −/y mice compared with controls in 2 experimental models. Resveratrol (0.05/100-g chow) inhibited growth of pre-established AAAs in ApoE −/− mice fed high-fat chow and infused with angiotensin II continuously for 56 days. Reduced suprarenal aorta dilatation in mice receiving resveratrol was associated with elevated serum ACE2 and increased suprarenal aorta tissue levels of ACE2 and sirtuin 1 activity. In addition, the relative phosphorylation of Akt and ERK (extracellular signal-regulated kinase) 1/2 within suprarenal aorta tissue and gene expression for nuclear factor of kappa light polypeptide gene enhancer in B cells 1, angiotensin type-1 receptor, and metallopeptidase 2 and 9 were significantly reduced. Upregulation of ACE2 in human aortic smooth muscle cells by resveratrol in vitro was sirtuin 1-dependent. Conclusions— This study provides experimental evidence of an important role for ACE2 in limiting AAA development and growth. Resveratrol upregulated ACE2 and inhibited AAA growth in a mouse model.