MicroRNA-34a regulates cardiac ageing and function.

Ageing is the predominant risk factor for cardiovascular diseases and contributes to a significantly worse outcome in patients with acute myocardial infarction. MicroRNAs (miRNAs) have emerged as crucial regulators of cardiovascular function and some miRNAs have key roles in ageing. We propose that altered expression of miRNAs in the heart during ageing contributes to the age-dependent decline in cardiac function. Here we show that miR-34a is induced in the ageing heart and that in vivo silencing or genetic deletion of miR-34a reduces age-associated cardiomyocyte cell death. Moreover, miR-34a inhibition reduces cell death and fibrosis following acute myocardial infarction and improves recovery of myocardial function. Mechanistically, we identified PNUTS (also known as PPP1R10) as a novel direct miR-34a target, which reduces telomere shortening, DNA damage responses and cardiomyocyte apoptosis, and improves functional recovery after acute myocardial infarction. Together, these results identify age-induced expression of miR-34a and inhibition of its target PNUTS as a key mechanism that regulates cardiac contractile function during ageing and after acute myocardial infarction, by inducing DNA damage responses and telomere attrition.

IFN-ß affects the angiogenic potential of circulating angiogenic cells by activating calpain 1.

Circulating angiogenic cells (CACs) are monocyte-derived cells with endothelial characteristics, which contribute to both angiogenesis and arteriogenesis in a paracrine way. Interferon-ß (IFN-ß) is known to inhibit these divergent processes in animals and patients. We hypothesized that IFN-ß might act by affecting the differentiation and function of CACs. CACs were cultured from peripheral blood mononuclear cells and phenotypically characterized by surface expression of monocytic and endothelial markers. IFN-ß significantly reduced the number of CACs by 18-64%. Apoptosis was not induced by IFN-ß, neither in mononuclear cells during differentiation, nor after maturation to CACs. Rather, IFN-ß impaired adhesion to, and spreading on, fibronectin, which was dependent on α5ß1 (VLA-5)-integrin. IFN-ß affected the function of VLA-5 in mature CACs, leading to rounding and detachment of cells, by induction of calpain 1 activity. Cell rounding and detachment was completely reversed by inhibition of calpain 1 activity in mature CACs. During in vitro capillary formation, CAC addition and calpain 1 inhibition enhanced sprouting of endothelial cells to a comparable extent, but were not sufficient to rescue tube formation in the presence of IFN-ß. We show that the IFN-ß-induced reduction of the numbers of in vitro differentiated CACs is based on activation of calpain 1, resulting in an attenuated adhesion to extracellular matrix proteins via VLA-5. In vivo, this could lead to inhibition of vessel formation due to reduction of the locally recruited CAC numbers and their paracrine angiogenic factors.

Systemic toll-like receptor and interleukin-18 pathway activation in patients with acute ST elevation myocardial infarction.

Acute myocardial infarction (AMI) is accompanied by increased expression of Toll like receptors (TLR)-2 and TLR4 on circulating monocytes. In animal models, blocking TLR2/4 signaling reduces inflammatory cell influx and infarct size. The clinical consequences of TLR activation during AMI in humans are unknown, including its role in long-term cardiac functional outcome Therefore, we analyzed gene expression in whole blood samples from 28 patients with an acute ST elevation myocardial infarction (STEMI), enrolled in the EXenatide trial for AMI patients (EXAMI), both at admission and after 4-month follow-up, by whole genome expression profiling and real-time PCR. Cardiac function was determined by cardiac magnetic resonance (CMR) imaging at baseline and after 4-month follow-up. TLR pathway activation was shown by increased expression of TLR4 and its downstream genes, including IL-18R1, IL-18R2, IL-8, MMP9, HIF1A, and NFKBIA. In contrast, expression of the classical TLR-induced genes, TNF, was reduced. Bioinformatics analysis and in vitro experiments explained this noncanonical TLR response by identification of a pivotal role for HIF-1α. The extent of TLR activation and IL-18R1/2 expression in circulating cells preceded massive troponin-T release and correlated with the CMR-measured ischemic area (R=0.48, p=0.01). In conclusion, we identified a novel HIF-1-dependent noncanonical TLR activation pathway in circulating leukocytes leading to enhanced IL-18R expression which correlated with the magnitude of the ischemic area. This knowledge may contribute to our mechanistic understanding of the involvement of the innate immune system during STEMI and may yield diagnostic and prognostic value for patients with myocardial infarction.

PPARγ activation but not PPARγ haplodeficiency affects proangiogenic potential of endothelial cells and bone marrow-derived progenitors.

BACKGROUND: Peroxisome proliferator-activated receptor-γ (PPARγ) agonists, which have been used as insulin sensitizers in diabetic patients, may improve functions of endothelial cells (ECs). We investigated the effect of PPARγ on angiogenic activities of murine ECs and bone marrow-derived proangiogenic cells (PACs). METHODS: PACs were isolated from bone marrow of 10-12 weeks old, wild type, db/db and PPARγ heterozygous animals. Cells were cultured on fibronectin and gelatin coated dishes in EGM-2MV medium. For in vitro stimulations, rosiglitazone (10 µmol/L) or GW9662 (10 µmol/L) were added to 80% confluent cell cultures for 24 hours. Angiogenic potential of PACs and ECs was tested in vitro and in vivo in wound healing assay and hind limb ischemia model. RESULTS: ECs and PACs isolated from diabetic db/db mice displayed a reduced angiogenic potential in ex vivo and in vitro assays, the effect partially rescued by incubation of cells with rosiglitazone (PPARγ activator). Correction of diabetes by administration of rosiglitazone in vivo did not improve angiogenic potential of isolated PACs or ECs. In a hind limb ischemia model we demonstrated that local injection of conditioned media harvested from wild type PACs improved the blood flow restoration in db/db mice, confirming the importance of paracrine action of the bone marrow-derived cells. CONCLUSIONS: In summary, activation of PPARγ by rosiglitazone improves angiogenic potential of diabetic ECs and PACs, but decreased expression of PPARγ in diabetes does not impair angiogenesis.

Magnetic resonance imaging-defined areas of microvascular obstruction after acute myocardial infarction represent microvascular destruction and haemorrhage.

AIMS: Lack of gadolinium-contrast wash-in on first-pass perfusion imaging, early gadolinium-enhanced imaging, or late gadolinium-enhanced (LGE) cardiovascular magnetic resonance (CMR) imaging after revascularized ST-elevation myocardial infarction (STEMI) is commonly referred to as microvascular obstruction (MVO). Additionally, T2-weighted imaging allows for the visualization of infarct-related oedema and intramyocardial haemorrhage (IMH) within the infarction. However, the exact histopathological correlate of the contrast-devoid core and its relation to IMH is unknown. METHODS AND RESULTS: In eight Yorkshire swine, the circumflex coronary artery was occluded for 75 min by a balloon catheter. After 7 days, CMR with cine imaging, T2-weighted turbospinecho, and LGE was performed. Cardiovascular magnetic resonance images were compared with histological findings after phosphotungstic acid-haematoxylin and anti-CD31/haematoxylin staining. These findings were compared with CMR findings in 27 consecutive PCI-treated STEMI patients, using the same scanning protocol. In the porcine model, the infarct core contained extensive necrosis and erythrocyte extravasation, without intact vasculature and hence, no MVO. The surrounding-gadolinium-enhanced-area contained granulation tissue, leucocyte infiltration, and necrosis with morphological intact microvessels containing microthrombi, without erythrocyte extravasation. Areas with IMH (median size 1.92 [0.36-5.25] cm(3)) and MVO (median size 2.19 [0.40-4.58] cm(3)) showed close anatomic correlation [intraclass correlation coefficient (ICC) 0.85, r = 0.85, P = 0.03]. Of the 27 STEMI patients, 15 had IMH (median size 6.60 [2.49-9.79] cm(3)) and 16 had MVO (median size 4.31 [1.05-7.57] cm(3)). Again, IMH and MVO showed close anatomic correlation (ICC 0.87, r = 0.93, P < 0.001). CONCLUSION: The contrast-devoid core of revascularized STEMI contains extensive erythrocyte extravasation with microvascular damage. Attenuating the reperfusion-induced haemorrhage may be a novel target in future adjunctive STEMI treatment.

The diverse identity of angiogenic monocytes.

BACKGROUND: The role of bone marrow-derived cells in stimulating angiogenesis, vascular repair or remodelling has been well established, but the nature of the circulating angiogenic cells is still controversial. DESIGN: The existing literature on different cell types that contribute to angiogenesis in multiple pathologies, most notably ischaemic and tumour angiogenesis, is reviewed, with a focus on subtypes of angiogenic mononuclear cells and their local recruitment and activation. RESULTS: A large number of different cells of myeloid origin support angiogenesis without incorporating permanently into the newly formed vessel, which distinguishes these circulating angiogenic cells (CAC) from endothelial progenitor cells (EPC). Although CAC frequently express individual endothelial markers, they all share multiple characteristics of monocytes and only express a limited set of discriminative surface markers in the circulation. When cultured ex vivo, or surrounding the angiogenic vessel in vivo, however, many of them acquire similar additional markers, making their discrimination in situ difficult. CONCLUSION: Different subsets of monocytes show angiogenic properties, but the distinct microenvironment, in vitro or in vivo, is needed for the development of their pro-angiogenic function.

MicroRNA-29 in aortic dilation: implications for aneurysm formation.

RATIONALE: Aging represents a major risk factor for coronary artery disease and aortic aneurysm formation. MicroRNAs (miRs) have emerged as key regulators of biological processes, but their role in age-associated vascular pathologies is unknown. OBJECTIVE: We aim to identify miRs in the vasculature that are regulated by age and play a role in age-induced vascular pathologies. METHODS AND RESULTS: Expression profiling of aortic tissue of young versus old mice identified several age-associated miRs. Among the significantly regulated miRs, the increased expression of miR-29 family members was associated with a profound downregulation of numerous extracellular matrix (ECM) components in aortas of aged mice, suggesting that this miR family contributes to ECM loss, thereby sensitizing the aorta for aneurysm formation. Indeed, miR-29 expression was significantly induced in 2 experimental models for aortic dilation: angiotensin II-treated aged mice and genetically induced aneurysms in Fibulin-4(R/R) mice. More importantly, miR-29b levels were profoundly increased in biopsies of human thoracic aneurysms, obtained from patients with either bicuspid (n=79) or tricuspid aortic valves (n=30). Finally, LNA-modified antisense oligonucleotide-mediated silencing of miR-29 induced ECM expression and inhibited angiotensin II-induced dilation of the aorta in mice. CONCLUSION: In conclusion, miR-29-mediated downregulation of ECM proteins may sensitize the aorta to the formation of aneurysms in advanced age. Inhibition of miR-29 in vivo abrogates aortic dilation in mice, suggesting that miR-29 may represent a novel molecular target to augment matrix synthesis and maintain vascular wall structural integrity.

Microvascular proliferations in arteriovenous malformations relate to high-flow characteristics, inflammation, and previous therapeutic embolization of the lesion.

BACKGROUND: Episodes of microvascular proliferation associated with volume expansion have been observed in arteriovenous malformations (AVMs) of skin and soft tissue. OBJECTIVE: We sought to investigate the relationship between a microvascular proliferative response and flow velocity in AVMs. METHODS: Resection specimens of 80 AVMs were clinically categorized as either high- or low-flow lesions, and histopathologically screened for the presence of microvessels, inflammation, thrombosis, or a combination of these. Immunohistochemistry was performed with endoglin (CD105), von Willebrand factor, and fibrinogen antibodies. RESULTS: Clinically, 37 AVMs were classified as high-flow lesions and 43 as low-flow lesions. In 81% of high-flow lesions microvascular proliferations were seen versus in 14% of low-flow lesions (P < .005). In high-flow lesions, which were embolized before surgery (30% of all), 88% showed microvascular proliferation, 88% inflammation, and 33% thrombosis. However, similar vasoproliferative responses were also observed in nonembolized AVM (69% high-flow and 14% low-flow lesions). Endoglin was more frequently expressed in high-flow lesions. Extracellular von Willebrand factor staining was found in most lesions, irrespective of flow type or presence of microvascular proliferations. LIMITATIONS: The study was carried out at a single tertiary referral center. CONCLUSIONS: Microvascular proliferative masses in AVMs appear to be strongly associated with high-flow characteristics. This could be explained to some extent by previous therapeutic embolization and/or inflammation in the lesion. However, occurrence of similar microvascular responses in AVM that were not embolized before surgery suggests that the biomechanical effects of high flow in these lesions may also have an angiogenic effect.

The coronary collateral circulation: genetic and environmental determinants in experimental models and humans.

Obstruction of coronary arteries leads to an arteriogenic response. Pre-existent collateral networks enlarge, forming large conductance arteries with the capability to compensate for the loss of perfusion due to the occlusion. Interestingly, significant differences exist between patients regarding the capacity to develop such a collateral circulation. This heterogeneity in arteriogenic response is also found between and even within animal species and it strongly suggests that next to environmental factors, innate genetic factors play a key role. The present review focuses on this heterogeneity of genetic as well as non-genetic determinants of the coronary collateral circulation. This article is part of a Special Issue entitled "Coronary Blood Flow".

Proteomic screen identifies IGFBP7 as a novel component of endothelial cell-specific Weibel-Palade bodies.

Vascular endothelial cells contain unique storage organelles, designated Weibel-Palade bodies (WPBs), that deliver inflammatory and hemostatic mediators to the vascular lumen in response to agonists like thrombin and vasopressin. The main component of WPBs is von Willebrand factor (VWF), a multimeric glycoprotein crucial for platelet plug formation. In addition to VWF, several other components are known to be stored in WPBs, like osteoprotegerin, monocyte chemoattractant protein-1 and angiopoetin-2 (Ang-2). Here, we used an unbiased proteomics approach to identify additional residents of WPBs. Mass spectrometry analysis of purified WPBs revealed the presence of several known components such as VWF, Ang-2, and P-selectin. Thirty-five novel candidate WPB residents were identified that included insulin-like growth factor binding protein-7 (IGFBP7), which has been proposed to regulate angiogenesis. Immunocytochemistry revealed that IGFBP7 is a bona fide WPB component. Cotransfection studies showed that IGFBP7 trafficked to pseudo-WPB in HEK293 cells. Using a series of deletion variants of VWF, we showed that targeting of IGFBP7 to pseudo-WPBs was dependent on the carboxy-terminal D4-C1-C2-C3-CK domains of VWF. IGFBP7 remained attached to ultralarge VWF strings released upon exocytosis of WPBs under flow. The presence of IGFBP7 in WPBs highlights the role of this subcellular compartment in regulation of angiogenesis.

KLF2-induced actin shear fibers control both alignment to flow and JNK signaling in vascular endothelium.

The shear stress-induced transcription factor Krüppel-like factor 2 (KLF2) confers antiinflammatory properties to endothelial cells through the inhibition of activator protein 1, presumably by interfering with mitogen-activated protein kinase (MAPK) cascades. To gain insight into the regulation of these cascades by KLF2, we used antibody arrays in combination with time-course mRNA microarray analysis. No gross changes in MAPKs were detected; rather, phosphorylation of actin cytoskeleton-associated proteins, including focal adhesion kinase, was markedly repressed by KLF2. Furthermore, we demonstrate that KLF2-mediated inhibition of Jun NH(2)-terminal kinase (JNK) and its downstream targets ATF2/c-Jun is dependent on the cytoskeleton. Specifically, KLF2 directs the formation of typical short basal actin filaments, termed shear fibers by us, which are distinct from thrombin- or tumor necrosis factor-alpha-induced stress fibers. KLF2 is shown to be essential for shear stress-induced cell alignment, concomitant shear fiber assembly, and inhibition of JNK signaling. These findings link the specific effects of shear-induced KLF2 on endothelial morphology to the suppression of JNK MAPK signaling in vascular homeostasis via novel actin shear fibers.

Activin A induces a non-fibrotic phenotype in smooth muscle cells in contrast to TGF-ß.

AIMS: Activin A and transforming growth factor-ß1 (TGF-ß1) belong to the same family of growth and differentiation factors that modulate vascular lesion formation in distinct ways, which we wish to understand mechanistically. METHODS AND RESULTS: We investigated the expression of cell-surface receptors and activation of Smads in human vascular smooth muscle cells (SMCs) and demonstrated that activin receptor-like kinase-1 (ALK-1), ALK-4, ALK-5 and endoglin are expressed in human SMCs. As expected, TGF-ß1 activates Smad1 and Smad2 in these cells. Interestingly, activin A also induces phosphorylation of both Smads, which has not been reported for Smad1 before. Transcriptome analyses of activin A and TGF-ß1 treated SMCs with subsequent Gene-Set Enrichment Analyses revealed that many downstream gene networks are induced by both factors. However, the effect of activin A on expression kinetics of individual genes is less pronounced than for TGF-ß1, which is explained by a more rapid dephosphorylation of Smads and p38-MAPK in response to activin A. Substantial differences in expression of fibronectin, alpha-V integrin and total extracellular collagen synthesis were observed. CONCLUSIONS: Genome-wide mRNA expression analyses clarify the distinct modulation of vascular lesion formation by activin A and TGF-ß1, most significantly because activin A is non-fibrotic.

Kruppel-like factor 2 improves neovascularization capacity of aged proangiogenic cells.

AIMS: Coronary artery disease (CAD) patients have less circulating proangiogenic cells (PACs), formerly known as endothelial progenitor cells, which exhibit impaired neovascularization properties. Inverse correlations were also found between PAC function and risk factors like age. Krüppel-like factor 2 (KLF2) is expressed by mature endothelial cells (ECs), is induced by both shear stress and statins, and provokes endothelial functional differentiation. The aim of this study is to identify whether KLF2 can reverse negative effects of ageing on PAC function. METHODS AND RESULTS: We describe that progenitor cells in the bone marrow and PACs also express KLF2 at a comparable level to mature ECs and that senescence decreases KLF2 levels. To study the effects of ageing on KLF2 levels, we compared progenitor cells of 4 weeks and 16- to 18-month-old C57BL/6 mice. In addition to the three-fold reduction of circulating Sca1(+)/c-Kit(+)/Lin(-) progenitor cells and the 15% reduction of Sca1(+)/Flk1(+) endothelial-committed progenitor cells, the spleen-derived PACs and bone marrow-derived progenitor cells isolated from aged mice showed a lower level of KLF2 when compared with young mice. Lentiviral overexpression of KLF2 increased human PAC numbers and endothelial nitric oxide synthase expression by 60% during in vitro culture. Endothelial lineage-specific KLF2 overexpression in aged bone marrow-derived mononuclear cells strongly augments neovascularization in vivo in a murine hind-limb ischaemia model. CONCLUSION: These results imply that KLF2 is an attractive novel target to rejuvenate PACs before autologous administration to CAD patients.

Blocking interferon {beta} stimulates vascular smooth muscle cell proliferation and arteriogenesis.

Increased interferon (IFN)-ß signaling in patients with insufficient coronary collateralization and an inhibitory effect of IFNß on collateral artery growth in mice have been reported. The mechanisms of IFNß-induced inhibition of arteriogenesis are unknown. In stimulated monocytes from patients with chronic total coronary artery occlusion and decreased arteriogenic response, whole genome expression analysis showed increased expression of IFNß-regulated genes. Immunohistochemically, the IFNß receptor was localized in the vascular media of murine collateral arteries. Treatment of vascular smooth muscle cells (VSMC) with IFNß resulted in an attenuated proliferation, cell-cycle arrest, and increased expression of cyclin-dependent kinase inhibitor-1A (p21). The growth inhibitory effect of IFNß was attenuated by inhibition of p21 by RNA interference. IFNß-treated THP1 monocytes showed enhanced apoptosis. Subsequently, we tested if collateral artery growth can be stimulated by inhibition of IFNß-signaling. RNA interference of the IFNß receptor-1 (IFNAR1) increased VSMC proliferation, cell cycle progression, and reduced p21 gene expression. IFNß signaling and FAS and TRAIL expression were attenuated in monocytes from IFNAR1(-/-) mice, indicating reduced monocyte apoptosis. Hindlimb perfusion restoration 1 week after femoral artery ligation was improved in IFNAR1(-/-) mice compared with wild-type mice as assessed by infusion of fluorescent microspheres. These results demonstrate that IFNß inhibits collateral artery growth and VSMC proliferation through p21-dependent cell cycle arrest and induction of monocyte apoptosis. Inhibition of IFNß stimulates VSMC proliferation and collateral artery growth.

Characterization of the differential response of endothelial cells exposed to normal and elevated laminar shear stress.

Most acute coronary events occur in the upstream region of stenotic atherosclerotic plaques that experience laminar shear stress (LSS) elevated above normal physiological levels. Many studies have described the atheroprotective effect on endothelial behavior of normal physiological LSS (approximately 15 dynes/cm(2)) compared to static or oscillatory shear stress (OSS), but it is unknown whether the levels of elevated shear stress imposed by a stenotic plaque would preserve, enhance or reverse this effect. Therefore we used transcriptomics and related functional analyses to compare human endothelial cells exposed to laminar shear stress of 15 (LSS15-normal) or 75 dynes/cm(2) (LSS75-elevated). LSS75 upregulated expression of 145 and downregulated expression of 158 genes more than twofold relative to LSS15. Modulation of the metallothioneins (MT1-G, -M, -X) and NADPH oxidase subunits (NOX2, NOX4, NOX5, and p67phox) accompanied suppression of reactive oxygen species production at LSS75. Shear induced changes in dual specificity phosphatases (DUSPs 1, 5, 8, and 16 increasing and DUSPs 6 and 23 decreasing) were observed as well as reduced ERK1/2 but increased p38 MAP kinase phosphorylation. Amongst vasoactive substances, endothelin-1 expression decreased whereas vasoactive intestinal peptide (VIP) and prostacyclin expression increased, despite which intracellular cAMP levels were reduced. Promoter analysis by rVISTA identified a significant over representation of ATF and Nrf2 transcription factor binding sites in genes upregulated by LSS75 compared to LSS15. In summary, LSS75 induced a specific change in behavior, modifying gene expression, reducing ROS levels, altering MAP kinase signaling and reducing cAMP levels, opening multiple avenues for future study.

Can RAP save your brain?

In this issue of Blood, Suzuki and colleagues report that the bleeding complications associated with thrombolytic therapy after ischemic stroke might be counteracted by RAP, the receptor-associated protein that inhibits ischemia-induced LRP, a signaling receptor for t-PA.

Equivalence testing in microarray analysis: similarities in the transcriptome of human atherosclerotic and nonatherosclerotic macrophages.

We focus on similarities in the transcriptome of human Kupffer cells and alveolar, splenic, and atherosclerotic plaque-residing macrophages. We hypothesized that these macrophages share a common expression signature. We performed microarray analysis on mRNA from these subsets (4 patients) and developed a novel statistical method to identify genes with significantly similar expression levels. Phenotypic and functional diversity between macrophage subpopulations reflects their plasticity to respond to microenvironmental signals. Apart from detecting differences in expression profiles, the comparison of the transcriptomes of different macrophage populations may also allow the definition of molecular similarities between these subsets. This new method calculates the maximum difference in gene expression level, based on the estimated confidence interval on that gene's expression variance. We listed the genes by equivalence ranking relative to expression level. FDR estimation was used to determine significance. We identified 500 genes with significantly equivalent expression levels in the macrophage subsets at 5.5% FDR using a confidence level of α = 0.05 for equivalence. Among these are the established macrophage marker CD68, IL1 receptor antagonist, and MHC-related CD1C. These 500 genes were submitted to IPA and GO clustering using DAVID. Additionally, hierarchical clustering of these genes in the Novartis human gene expression atlas revealed a subset of 200 genes specifically expressed in macrophages. Equivalently expressed genes, identified by this new method, may not only help to dissect common molecular mechanisms, but also to identify cell- or condition-specific sets of marker genes that can be used for drug targeting and molecular imaging.

Expression of a retinoic acid signature in circulating CD34 cells from coronary artery disease patients.

BACKGROUND: Circulating CD34+ progenitor cells have the potential to differentiate into a variety of cells, including endothelial cells. Knowledge is still scarce about the transcriptional programs used by CD34+ cells from peripheral blood, and how these are affected in coronary artery disease (CAD) patients. RESULTS: We performed a whole genome transcriptome analysis of CD34+ cells, CD4+ T cells, CD14+ monocytes, and macrophages from 12 patients with CAD and 11 matched controls. CD34+ cells, compared to other mononuclear cells from the same individuals, showed high levels of KRAB box transcription factors, known to be involved in gene silencing. This correlated with high expression levels in CD34+ cells for the progenitor markers HOXA5 and HOXA9, which are known to control expression of KRAB factor genes. The comparison of expression profiles of CD34+ cells from CAD patients and controls revealed a less naïve phenotype in patients' CD34+ cells, with increased expression of genes from the Mitogen Activated Kinase network and a lowered expression of a panel of histone genes, reaching levels comparable to that in more differentiated circulating cells. Furthermore, we observed a reduced expression of several genes involved in CXCR4-signaling and migration to SDF1/CXCL12. CONCLUSIONS: The altered gene expression profile of CD34+ cells in CAD patients was related to activation/differentiation by a retinoic acid-induced differentiation program. These results suggest that circulating CD34+ cells in CAD patients are programmed by retinoic acid, leading to a reduced capacity to migrate to ischemic tissues.

Angiogenic monocytes: another colorful blow to endothelial progenitors.

This Commentary provides perspective on a related article by Sun-Jin Kim and coworkers (Am J Pathol: 172 AJP08-0819), who assess the contribution of bone marrow-derived cells to tumor angiogenesis in a physiologic, non-myeloablative setting and conclude that the actual angiogenic cell type incorporated in the newly formed vessels is actually monocytes/macrophages.