Sinny Delacroix

Resident Vascular Progenitor Cells—Diverse Origins, Phenotype, and Function

The fundamental contributions that blood vessels make toward organogenesis and tissue homeostasis are reflected by the considerable ramifications that loss of vascular wall integrity has on pre- and postnatal health. During both neovascularization and vessel wall remodeling after insult, the dynamic nature of vascular cell growth and replacement vitiates traditional impressions that blood vessels contain predominantly mature, terminally differentiated cell populations. Recent discoveries have verified the presence of diverse stem/progenitor cells for both vascular and non-vascular progeny within the mural layers of the vasculature. During embryogenesis, this encompasses the emergence of definitive hematopoietic stem cells and multipotent mesoangioblasts from the developing dorsal aorta. Ancestral cells have also been identified and isolated from mature, adult blood vessels, showing variable capacity for endothelial, smooth muscle, and mesenchymal differentiation. At present, the characterization of these different vascular wall progenitors remains somewhat rudimentary, but there is evidence for their constitutive residence within organized compartments in the vessel wall, most compellingly in the tunica adventitia. This review overviews the spectrum of resident stem/progenitor cells that have been documented in macro- and micro-vessels during developmental and adult life and considers the implications for a local, vascular wall stem cell niche(s) in the pathogenesis and treatment of cardiovascular and other diseases.

Identification of a Monocyte-Predisposed Hierarchy of Hematopoietic Progenitor Cells in the Adventitia of Postnatal Murine Aorta

Background— Hematopoiesis originates from the dorsal aorta during embryogenesis. Although adult blood vessels harbor progenitor populations for endothelial and smooth muscle cells, it is not known if they contain hematopoietic progenitor or stem cells. Here, we hypothesized that the arterial wall is a source of hematopoietic progenitor and stem cells in postnatal life. Methods and Results— Single-cell aortic disaggregates were prepared from adult chow-fed C57BL/6 and apolipoprotein E–null (ApoE−/−) mice. In short- and long-term methylcellulose-based culture, aortic cells generated a broad spectrum of multipotent and lineage-specific hematopoietic colony-forming units, with a preponderance of macrophage colony-forming units. This clonogenicity was higher in lesion-free ApoE−/− mice and localized primarily to stem cell antigen-1–positive cells in the adventitia. Expression of stem cell antigen-1 in the aorta colocalized with canonical hematopoietic stem cell markers, as well as CD45 and mature leukocyte antigens. Adoptive transfer of labeled aortic cells from green fluorescent protein transgenic donors to irradiated C57BL/6 recipients confirmed the content of rare hematopoietic stem cells (1 per 4 000 000 cells) capable of self-renewal and durable, low-level reconstitution of leukocytes. Moreover, the predominance of long-term macrophage precursors was evident by late recovery of green fluorescent protein–positive colonies from recipient bone marrow and spleen that were exclusively macrophage colony-forming units. Although trafficking from bone marrow was shown to replenish some of the hematopoietic potential of the aorta after irradiation, the majority of macrophage precursors appeared to arise locally, suggesting long-term residence in the vessel wall. Conclusions— The postnatal murine aorta contains rare multipotent hematopoietic progenitor/stem cells and is selectively enriched with stem cell antigen-1–positive monocyte/macrophage precursors. These populations may represent novel, local vascular sources of inflammatory cells.

Characterization of a Resident Population of Adventitial Macrophage Progenitor Cells in Postnatal Vasculature

Rationale: Macrophages regulate blood vessel structure and function in health and disease. The origins of tissue macrophages are diverse, with evidence for local production and circulatory renewal. Objective: We identified a vascular adventitial population containing macrophage progenitor cells and investigated their origins and fate. Methods and Results: Single-cell disaggregates from adult C57BL/6 mice were prepared from different tissues and tested for their capacity to form hematopoietic colony-forming units. Aorta showed a unique predilection for generating macrophage colony-forming units. Aortic macrophage colony-forming unit progenitors coexpressed stem cell antigen-1 and CD45 and were adventitially located, where they were the predominant source of proliferating cells in the aortic wall. Aortic Sca-1+CD45+ cells were transcriptionally and phenotypically distinct from neighboring cells lacking stem cell antigen-1 or CD45 and contained a proliferative (Ki67+) Lin−c-Kit+CD135−CD115+CX3CR1+Ly6C+CD11b− subpopulation, consistent with the immunophenotypic profile of macrophage progenitors. Adoptive transfer studies revealed that Sca-1+CD45+ adventitial macrophage progenitor cells were not replenished via the circulation from bone marrow or spleen, nor was their prevalence diminished by depletion of monocytes or macrophages by liposomal clodronate treatment or genetic deficiency of macrophage colony-stimulating factor. Rather adventitial macrophage progenitor cells were upregulated in hyperlipidemic ApoE−/− and LDL-R−/− mice, with adventitial transfer experiments demonstrating their durable contribution to macrophage progeny particularly in the adventitia, and to a lesser extent the atheroma, of atherosclerotic carotid arteries. Conclusions: The discovery and characterization of resident vascular adventitial macrophage progenitor cells provides new insight into adventitial biology and its participation in atherosclerosis and provokes consideration of the broader existence of local macrophage progenitors in other tissues.

Endothelial-derived tissue factor pathway inhibitor regulates arterial thrombosis but is not required for development or hemostasis

The antithrombotic surface of endothelium is regulated in a coordinated manner. Tissue factor pathway inhibitor (TFPI) localized at the endothelial cell surface regulates the production of FXa by inhibiting the TF/VIIa complex. Systemic homozygotic deletion of the first Kunitz (K1) domain of TFPI results in intrauterine lethality in mice. Here we define the cellular sources of TFPI and their role in development, hemostasis, and thrombosis using TFPI conditional knockout mice. We used a Cre-lox strategy and generated mice with a floxed exon 4 (TFPI(Flox)) which encodes for the TFPI-K1 domain. Mice bred into Tie2-Cre and LysM-Cre lines to delete TFPI-K1 in endothelial (TFPI(Tie2)) and myelomonocytic (TFPI(LysM)) cells resulted in viable and fertile offspring. Plasma TFPI activity was reduced in the TFPI(Tie2) (71% ± 0.9%, P < .001) and TFPI(LysM) (19% ± 0.6%, P < .001) compared with TFPI(Flox) littermate controls. Tail and cuticle bleeding were unaffected. However, TFPI(Tie2) mice but not TFPI(LysM) mice had increased ferric chloride-induced arterial thrombosis. Taken together, the data reveal distinct roles for endothelial- and myelomonocytic-derived TFPI.

Tissue Factor Pathway Inhibitor Blocks Angiogenesis via Its Carboxyl Terminus

Objective—Tissue factor pathway inhibitor (TFPI) is the primary regulator of the tissue factor (TF) coagulation pathway. As such, TFPI may regulate the proangiogenic effects of TF. TFPI may also affect angiogenesis independently of TF, through sequences within its polybasic carboxyl terminus (TFPI C terminus [TFPIct]). We aimed to determine the effects of TFPI on angiogenesis and the role of TFPIct. Methods and Results—Transgenic overexpression of TFPI attenuated angiogenesis in the murine hindlimb ischemia model and an aortic sprout assay. In vitro, TFPI inhibited endothelial cell migration. Peptides within the human TFPIct inhibited endothelial cell cord formation and migration in response to vascular endothelial growth factor (VEGF) 165 but not VEGF121. Furthermore, exposure to human TFPIct inhibited the phosphorylation of VEGF receptor 2 at residue Lys951, a residue known to be critical for endothelial cell migration. Finally, systemic delivery of a murine TFPIct peptide inhibited angiogenesis in the hindlimb model. Conclusion—These data demonstrate an inhibitory role for TFPI in angiogenesis that is, in part, mediated through peptides within its carboxyl terminus. In addition to its known role as a TF antagonist, TFPI, via its carboxyl terminus, may regulate angiogenesis by directly blocking VEGF receptor 2 activation and attenuating the migratory capacity of endothelial cells.

Hypertension: Pathophysiology and Treatment

Hypertension is a significant risk factor for heart disease, stroke and other cardiovascular diseases and an estimated 970 million people worldwide suffer from the disease resulting in significant morbidity, mortality and financial burden globally. Despite significant advances in pharmaceutical treatment only 53% achieve targeted blood pressure goals largely due to poor patient compliance compelling a structured and flexible yet, individually tailored approach for treatment of HTN.1, 2This review addresses the pathophysiology, diagnosis and current management for the disease.

Comparison of Time Trends of Cardiovascular Disease Risk Factors and Framingham Risk Score Between Patients With and Without Acute Coronary Syndrome Undergoing Percutaneous Intervention Over the Last 17 Years: From the Mayo Clinic Percutaneous Coronary Intervention Registry

The objective of this study was to investigate cardiovascular disease risk factor (cvRF) profiles and compare their trends over 17 years in patients with and without acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI).

Regulation of Circulating Progenitor Cells in Left Ventricular Dysfunction

Background—Reductions in numbers of circulating progenitor cells (CD34+ cell subsets) have been demonstrated in patients at risk for, or in the presence of, cardiovascular disease. The mediators of these reductions remain undefined. To determine whether neurohumoral factors might regulate circulating CD34+ cell subsets in vivo, we studied complementary canine models of left ventricular (LV) dysfunction. Methods and Results—A pacing model of severe LV dysfunction and a hypertensive renal wrap model in which dogs were randomized to receive deoxycorticosterone acetate (DOCA) were studied. Circulating CD34+ cell subsets including hematopoietic precursor cells (HPCs: CD34+/CD45dim/VEGFR2−) and endothelial progenitor cells (EPCs: CD34+/CD45−/VEGFR2+) were quantified. Additionally, the effect of mineralocorticoid excess on circulating progenitor cells in normal dogs was studied. The majority of circulating CD34+ cells expressed CD45dimly and did not express VEGFR2, consistent with an HPC phenotype. HPCs were decreased in response to pacing, and this decrease correlated with plasma aldosterone levels (Spearman rank correlation=−0.67, P=0.03). In the hypertensive renal wrap model, administration of DOCA resulted in decreased HPCs. No changes were seen in EPCs in either model. Normal dogs treated with DOCA exhibited a decrease in HPCs in peripheral blood but not bone marrow associated with decreased telomerase activity. Conclusions—This is the first study to demonstrate that mineralocorticoid excess, either endogenous or exogenous, results in reduction in HPCs. These data suggest that mineralocorticoids may induce accelerated senescence of progenitor cells, leading to their reduced survival and decline in numbers.

Tissue Factor-Thrombin–PAR-1 Pathway: A Novel Link Between Bone Marrow and Blood Vessel

Transplant arteriopathy (TA) is an important limitation to graft survival following solid organ transplantation.1 TA is a result of immune-mediated mechanisms and results in intimal hyperplasia (IH) and vascular occlusion. Our understanding of the mechanism for this process is expanding to include an important role for host derived-circulating cells, including cells that adopt a smooth muscle cell phenotype within the intima of vessels.2 In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology , Chen and colleagues3 add to this understanding of TA in a new and unexpected way that suggests that the tissue factor (TF)-thrombin–PAR-1 pathway may provide an important link between the bone marrow and blood vessels. See accompanying article on page 42 To further define the role of circulating cells in TA, Chen and colleagues used a model in which expression of a tethered form of tissue factor pathway inhibitor (TFPI) is driven from the α-smooth muscle actin (α-SMA) promoter. Thus, cells expressing α-SMA express this tethered protein that …

Transcatheter aortic valve implantation: a new standard of care.

Aortic stenosis is the most common valvular lesion requiring intervention and with an ageing population, its burden is likely to increase. Increasing comorbidity and a desire for less invasive treatment strategies has facilitated the expansion of percutaneous aortic valve therapies. Robust clinical trial data are now available to support the role of transcatheter aortic valve implantation (TAVI) in patients of prohibitive, high and now intermediate surgical risk. The introduction of a Medicare Benefits Schedule reimbursement is likely to see TAVI use grow exponentially in Australia over the next 5 years. Clinical trials evaluating low risk patients may be the final frontier to see TAVI become the standard of care for most patients with severe aortic stenosis.