Circulating Apoptotic Progenitor Cells

DRD4 Mitigates Myocardial Ischemia/Reperfusion Injury in Association With PI3K/AKT Mediated Glucose Metabolism

Ischemia-reperfusion (I/R) could cause heart irreversible damage, which is tightly combined with glucose metabolism disorder. It is demonstrated that GLUT4 (glucose transporter 4) translocation is critical for glucose metabolism in the cardiomyocytes under I/R injury. Moreover, DRD4 (dopamine receptor D4) modulate glucose metabolism, and protect neurocytes from anoxia/reoxygenation (A/R) injury. Thus, DRD4 might regulate myocardial I/R injury in association with GLUT4-mediated glucose metabolism. However, the effects and mechanisms are largely unknown. In the present study, the effect of DRD4 in heart I/R injury were studied ex vivo and in vitro. For I/R injury ex vivo, DRD4 agonist (PD168077) was perfused by Langendorff system in the isolated rat heart. DRD4 activated by PD168077 improved cardiac function in the I/R-injured heart as determined by the left ventricular developed pressure (LVDP), +dp/dt, and left ventricular end diastolic pressure (LVEDP), and reduced heart damage evidenced by infarct size, the release of troponin T (TNT) and lactate dehydrogenase (LDH). DRD4 activation diminished I/R injury induced apoptosis and enhanced cell viability impaired by I/R injury in cardiomyocyte, showed by TUNEL staining, flow cytometer and CCK8 assay. Furthermore, DRD4 activation did not change total GULT4 protein expression level but increased the membrane GULT4 localization determined by western blot. In terms of mechanism, DRD4 activation increased pPI3K/p-AKT but not the total PI3K/AKT during anoxia/reoxygenation (A/R) injury in vitro. Interestingly, PI3K inhibitor, Wortmannin, blocked PI3K/AKT pathway and depleted the membrane GULT4, and further promoted apoptosis showed by TUNEL staining, flow cytometer, western blot of cleaved caspase 3, BAX and BCL2 expression. Thus, DRD4 activation exerted a protective effect against I/R injury by promoting GLUT4 translocation depended on PI3K/AKT pathway, which enhanced the ability of glucose uptake, and ultimately reduced the apoptosis in cardiomyocytes.

CD34+ circulating cells display signs of immune activation in patients with acute coronary syndrome

Bone marrow-derived endothelial progenitor cells (EPC) are released into the peripheral blood in situations of vascular repair/angiogenesis. Regulation of vascular repair and angiogenesis by EPC depends not only on the number of circulating EPC but also on their functionality. As endothelial cells can act as antigen-presenting cells in coronary artery disease (CAD), we postulated that EPC can be immune activated here as well. CD34⁺-EPC were isolated from peripheral blood of patients with ST-elevation myocardial infarction (STEMI, n = 12), non-STEMI/unstable angina (UA, n = 15), and stable CAD (SA, n = 18). Expression of HLA-DR, adhesion and costimulatory molecules by isolated CD34⁺-EPC were compared with levels in healthy controls (n = 18). There were no significant differences in VCAM-1 and CD80 expression by peripheral circulating CD34⁺-EPC between the four groups, yet expression of CD86 was highest in UA (p < 0.05). ICAM-1 expression was lowest in SA (p < 0.01). CD34⁺-EPC constitutively expressed HLA-DR across all groups. Of note, patients pretreated with HMG-CoA reductase inhibitors exhibited lower expression of VCAM-1 by CD34⁺-EPC throughout all patient groups; furthermore, statins significantly limited ex vivo-induced upregulation of ICAM-1 by TNF-alpha. To the best of our knowledge, this is the first study to examine the expression of immune markers in peripheral circulating CD34⁺-EPC ex vivo. We demonstrate that CD34⁺-EPC display different patterns of adhesion and costimulatory molecules in various states of CAD. Expression levels were affected by pretreatment with statins. Hence, immune activity of peripheral circulating CD34⁺ cells might play a pathophysiologic role in evolution of CAD.

Circulating progenitor cells and their interaction with platelets in patients with an acute coronary syndrome

CD34⁺ cells expressing KDR (CD34⁺/KDR⁺) represent a small proportion of circulating progenitor cells that have the capacity to interact with platelets and to differentiate into mature endothelial cells, thus contributing to vascular homeostasis and regeneration as well as to re-endothelialization. We investigated the levels of CD34⁺ and CD34⁺/KDR⁺ progenitor cells as well as their interaction with platelets in acute coronary syndrome (ACS) patients before the initiation (baseline) of their treatment with a P2Y₁₂ receptor antagonist, and at 5-days post-treatment (follow-up). Sixty-seven consecutive ACS patients and thirty healthy subjects (controls) participated in the study. On admission, all patients received 325 mg aspirin, followed by 100 mg/day and then were loaded either with 600 mg clopidogrel or 180 mg ticagrelor, followed by 75 mg/day (n = 36) or 90 mg × 2/day (n = 31), respectively. The levels of circulating CD34⁺ and CD34⁺/KDR⁺ progenitor cells, as well as their interaction with platelets, were determined by flow cytometry, before and after activation with ADP, in vitro. The circulating levels of CD34⁺ and CD34⁺/KDR⁺ cells in both patient groups at baseline were lower compared with controls while they were significantly increased at 5-days of follow-up in both groups, this increase being more pronounced in the ticagrelor group. The platelet/CD34⁺ (CD61⁺/CD34⁺) conjugates were higher at baseline and reduced at follow-up while the platelet/KDR⁺ (CD61⁺/KDR⁺) conjugates were lower at baseline and increased at follow-up, both changes being more pronounced in the ticagrelor group. ADP activation of control samples significantly increased the KDR expression by CD34⁺ cells and the CD61⁺/KDR⁺ conjugates, these parameters being unaffected in patients at baseline but increased at follow-up. Short-term dual antiplatelet therapy in ACS patients restores the low platelet/KDR⁺ conjugates and CD34⁺ cell levels and improves the low membrane expression levels of KDR in these cells, an effect being more pronounced in ticagrelor-treated patients. This may represent a pleiotropic effect of antiplatelet therapy towards vascular endothelial regeneration.

Beneficial Effects of Reconstituted High-Density Lipoprotein (rHDL) on Circulating CD34+ Cells in Patients after an Acute Coronary Syndrome

Background

High-density lipoproteins (HDL) favorably affect endothelial progenitor cells (EPC). Circulating progenitor cell level and function are impaired in patients with acute coronary syndrome (ACS). This study investigates the short-term effects of reconstituted HDL (rHDL) on circulating progenitor cells in patients with ACS.

Methods and Findings

The study population consisted of 33 patients with recent ACS: 20 patients from the ERASE trial (randomized to receive 4 weekly intravenous infusions of CSL-111 40 mg/kg or placebo) and 13 additional patients recruited as controls using the same enrolment criteria. Blood was collected from 16 rHDL (CSL-111)-treated patients and 17 controls at baseline and at 6–7 weeks (i.e. 2–3 weeks after the fourth infusion of CSL-111 in ERASE). CD34⁺ and CD34⁺/kinase insert domain receptor (KDR⁺) progenitor cell counts were analyzed by flow cytometry. We found preserved CD34⁺ cell counts in CSL-111-treated subjects at follow-up (change of 1.6%), while the number of CD34⁺ cells was reduced (-32.9%) in controls (p = 0.017 between groups). The level of circulating SDF-1 (stromal cell-derived factor-1), a chemokine involved in progenitor cell recruitment, increased significantly (change of 21.5%) in controls, while it remained unchanged in CSL-111-treated patients (p = 0.031 between groups). In vitro exposure to CSL-111 of early EPC isolated from healthy volunteers significantly increased CD34⁺ cells, reduced early EPC apoptosis and enhanced their migration capacity towards SDF-1.

Conclusions

The relative increase in circulating CD34⁺ cells and the low SDF-1 levels observed following rHDL infusions in ACS patients point towards a role of rHDL in cardiovascular repair mechanisms.

miR-1207-3p regulates the androgen receptor in prostate cancer via FNDC1/fibronectin

Prostate cancer (PCa) is frequently diagnosed in men, and dysregulation of microRNAs is characteristic of many cancers. MicroRNA-1207-3p is encoded at the non-protein coding gene locus PVT1 on the 8q24 human chromosomal region, an established PCa susceptibility locus. However, the role of microRNA-1207-3p in PCa is unclear. We discovered that microRNA-1207-3p is significantly underexpressed in PCa cell lines in comparison to normal prostate epithelial cells. Increased expression of microRNA-1207-3p in PCa cells significantly inhibits proliferation, migration, and induces apoptosis via direct molecular targeting of FNDC1, a protein which contains a conserved protein domain of fibronectin (FN1). FNDC1, FN1, and the androgen receptor (AR) are significantly overexpressed in PCa cell lines and human PCa, and positively correlate with aggressive PCa. Prostate tumor FN1 expression in patients that experienced PCa-specific death is significantly higher than in patients that remained alive. Furthermore, FNDC1, FN1 and AR are concomitantly overexpressed in metastatic PCa. Consequently, these studies have revealed a novel microRNA-1207-3p/FNDC1/FN1/AR regulatory pathway in PCa.

Bioluminescence imaging of transplanted human endothelial colony-forming cells in an ischemic mouse model

Ischemic strokes are devastating events responsible for high mortality and morbidity worldwide each year. Endothelial colony-forming cell (ECFC) therapy holds promise for stroke treatment; however, grafted ECFCs need to be monitored better understand their biological behavior in vivo, so as to evaluate their safety and successful delivery. The objectives of this study are to visualize the fate of infused human cord blood derived ECFCs via bioluminescence imaging (BLI) in an ischemic stroke mouse model and to determine the therapeutic effects of ECFC transplantation. ECFCs derived from human umbilical cord blood were infected with lentivirus carrying enhanced green fluorescent protein (eGFP) and firefly luciferase (Luc2) double fusion reporter gene. Labeled ECFCs were grafted into a photothrombotic ischemic stroke mouse model via intra-arterial injection though the left cardiac ventricle. The homing of infused cells and functional recovery of stroke mice were evaluated using BLI, neurological scoring, and immunohistochemistry. Significantly, BLI signals were highest in the brain on day 1 and decreased steadily until day 14. GFP-positive cells were also found surrounding infarct border zones in brain sections using immunohistochemical staining, suggesting that ECFCs properly homed to the ischemic brain tissue. Using a modified neurological severity score assay and histological analysis of brain slices with CD31 immunostaining in brain tissue, double cortin analysis, and the TdT-mediated dUTP nick end labeling (TUNEL) assay, we demonstrated functional restoration, improved angiogenesis, neurogenesis, and decreased apoptosis in ischemic mice after ECFC infusion. Collectively, our data support that ECFCs may be a promising therapeutic agent for stroke.

Circulating autoantibodies to endothelial progenitor cells: binding characteristics and association with risk factors for atherosclerosis

OBJECTIVE

Endothelial progenitor cells (EPC) are committed to transform into EC promoting vasculogenic ischemic repair. Anti-endothelial cells (AECA) have been described in various disorders with an associated vascular damage. Herein, we explored a novel circulating population of IgG reactive with EPC, in patients with differential risk profile for atherosclerotic vascular disease.

APPROACH AND RESULTS

A novel cyto-ELISA system was established where the coated cells were late outgrowth EPC. Levels of anti-EPC antibodies were determined in 100 subjects and differential risk score for atherosclerosis, as well as to circulating EPC levels and the inflammatory markers IL-6 and C-reactive protein. To study endothelial cell (EC) activating properties, sera were tested for their ability to induce VCAM-1 expression in a cell ELISA system. Detectable levels of anti-EPC antibodies, that correlated with age, Framingham risk score and CRP concentrations but did not associate with levels of LDL, HDL, hypertension or diabetes, were detected. Anti-EPC antibodies were distinct from EC binding antibodies as shown by competitive inhibition studies, and have been positively correlated with the extent of EC activation manifested by in vitro VCAM-1 expression.

CONCLUSION

This is the first study showing a newly defined subgroup of self-antibodies binding EPC and associating positively with the Framingham risk score. Further studies are required to characterize and test this interesting subset of EPC binding autoantibodies and their potential significance.

Endothelial progenitor cells in relation to endothelin-1 and endothelin receptor blockade: a randomized, controlled trial

AIMS

Endothelial progenitor cells (EPC) represent an endogenous repair mechanism involving rendothelialization and neoangiogenesis. Patients with both diabetes and vascular disease have low numbers of circulating EPC. The endothelium-derived peptide, endothelin-1 (ET-1), is increased in patients with type 2 diabetes and vascular complications and has been suggested to contribute to endothelial dysfunction. Therefore, we investigated the relation between EPC and plasma ET-1 and the effect of dual ET-1 receptor antagonist treatment.

METHODS

In this double blind study patients with type 2 diabetes mellitus and microalbuminuria were randomized to treatment with the dual ETA/ETB receptor antagonist bosentan treatment (125mg bid; n=17) or placebo (n=19) for four weeks. Different EPC subpopulations were enumerated by flow cytometry using triple staining (CD34, CD133, KDR) at baseline at the end of treatment. Viability was assessed by 7AAD and Annexin-V-staining.

RESULTS

Baseline ET-1 levels correlated significantly with C-reactive protein levels. Patients with ET-1 levels above the median value had higher levels of CD34(+)CD133(+) and CD34(+)KDR(+) EPC. There was no difference in CD34(+) and CD34(+)CD133(+)KDR(+) cells, markers of EPC apoptosis or circulating markers of endothelial damage between patients with ET-1 levels below or above the median. Four week treatment with bosentan did not change EPC levels.

CONCLUSION

Among patients with type 2 diabetes and vascular disease, high plasma levels of ET-1 are associated with higher number of EPC. The recruitment of EPC does not seem to be regulated via ET-1 receptor activation since treatment with a dual ET-1 receptor blocker did not affect circulating EPC numbers.

Circulating mesenchymal stem cells microparticles in patients with cerebrovascular disease

Preclinical and clinical studies have shown that the application of CD105⁺ mesenchymal stem cells (MSCs) is feasible and may lead to recovery after stroke. In addition, circulating microparticles are reportedly functional in various disease conditions. We tested the levels of circulating CD105⁺ microparticles in patients with acute ischemic stroke. The expression of CD105 (a surface marker of MSCs) and CXCR4 (a CXC chemokine receptor for MSC homing) on circulating microparticles was evaluated by flow cytometry of samples from 111 patients and 50 healthy subjects. The percentage of apoptotic CD105 microparticles was determined based on annexin V (AV) expression. The relationship between serum levels of CD105⁺/AV⁻ microparticles, stromal cells derived factor-1α (SDF-1α), and the extensiveness of cerebral infarcts was also evaluated. CD105⁺/AV⁻ microparticles were higher in stroke patients than control subjects. Correlation analysis showed that the levels of CD105⁺/AV⁻ microparticles increased as the baseline stroke severity increased. Multivariate testing showed that the initial severity of stroke was independently associated with circulating CD105⁺/AV⁻ microparticles (OR, 1.103 for 1 point increase in the NIHSS score on admission; 95% CI, 1.032–1.178) after adjusting for other variables. The levels of CD105⁺/CXCR4⁺/AV⁻ microparticles were also increased in patients with severe disability (r = 0.192, p = 0.046 for NIHSS score on admission), but were decreased with time after stroke onset (r = −0.204, p = 0.036). Risk factor profiles were not associated with the levels of circulating microparticles or SDF-1α. In conclusion, our data showed that stroke triggers the mobilization of MSC-derived microparticles, especially in patients with extensive ischemic stroke.

Arterial erectile dysfunction: reliability of new markers of endothelial dysfunction

OBJECTIVE

Blood endothelial progenitor cells (EPC) and microparticles (EMP) have been proposed as markers of endothelial dysfunction. Aim of this study was to evaluate a new immunophenotype of EPC and EMP in patients with arterial erectile dysfunction (AED) compared to psychogenic erectile dysfunction (PED).

MATERIALS AND METHODS

One hundred patients (63.2±2.6 yr) with AED were enrolled in this study. Their EPC and EMP concentrations were compared to those of 40 patients with PED (64.2±2.7 yr). EPC (CD45(neg)/CD34(pos)/ CD144(pos)) and EMP (CD45(neg)/CD144(pos)/AnnexinV(pos)) blood concentrations were evaluated by flow cytometry.

RESULTS

Patients with AED had significantly higher blood pressure, triglycerides, homeostasis model assessment index of insulin resistance, and cavernous artery acceleration time and intima-media thickness than PED; whereas international index of erectile function 5 score, HDL-cholesterol, and cavernous artery peak systolic velocity was lower than PED. Both EPC and EMP were significantly higher in patients with AED compared to patients with PED.

CONCLUSIONS

Patients with AED showed worse metabolic parameters, cavernous artery parameters, and higher EPC and EMP compared to patients with PED. This suggests that AED is an expression of endothelial dysfunction and that EPC and EMP may be considered predictors of endothelial dysfunction in patients with AED.

Blood levels, apoptosis, and homing of the endothelial progenitor cells after skin burns and escharectomy

BACKGROUND

Skin burns are an acute trauma involving an extensive vascular damage and an intense inflammatory response. Bone marrow-derived circulating endothelial progenitor cells (EPC) are known to migrate to sites of neovascularization in response to mediators (vascular endothelial growth factor and stromal cell-derived factor-1) released after trauma and ischemia, to contribute to wound healing, and to increase neovascularization of animal prefabricated flaps. Recent data showed an increase in EPC number in burned patients and a positive correlation between EPC number and total body surface area (TBSA) burnt, but data were limited to the first 5 days after thermal injury.

METHODS

By using flow cytometry, we studied EPC (CD34, CD133, CD45, and KDR cells) blood levels, apoptosis, and homing (stromal cell-derived factor-1 receptor expression and CXC chemokine receptor 4) in a 1-month follow-up postburn in 25 patients with ≥15% TBSA burnt, at least grade II burns and escharectomy performed at days 5 to 6, with respect to 31 controls.

RESULTS

EPC count at admission showed a positive linear correlation with TBSA burnt. The EPC blood levels of the patients were low (50.7 cells/mL±61.8 cells/mL) immediately after thermal injury, then increased with two peaks, at day 1 (188.3 cells/mL±223.2 cells/mL) and day 12 (253.1 cells/mL±430.7 cells/mL) with respect to controls (95.2 cells/mL±28.5 cells/mL, p<0.05), and then returned to normal levels in 1 month. EPC apoptotic rate and inflammatory parameters paralleled EPC blood count. No significant variations were found in CXC chemokine receptor 4 expression.

CONCLUSIONS

Thermal injury and escharectomy seem to induce an intense response in EPC production. In particular, escharectomy could improve physiologic wound repair by increasing EPC levels.

Reduced endothelial progenitor cell number and function in inflammatory bowel disease: a possible link to the pathogenesis

OBJECTIVES

Circulating endothelial progenitor cells (EPCs) are essential for endothelial repair and vascular healing. Patients with inflammatory bowel disease (IBD) may suffer from endothelial dysfunction. Reduced EPC number, impaired mobilization, or increased EPC apoptosis may be crucial in this phenomenon. The aim of our study was to investigate the number and function of EPCs in patients with IBD and to assess their endothelial function.

METHODS

In 100 IBD patients (47 ulcerative colitis (UC) and 53 Crohn's disease (CD)) and 50 healthy controls, EPC number, CXC motif receptor 4 (CXCR4) expression, the percentage of apoptotic circulating EPCs, and the number of colony-forming units were evaluated. Endothelial dysfunction was assessed by luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone levels, and in a subgroup of patients, brachial artery flow-mediated dilation (FMD) was measured. Kruskal-Wallis ANOVA (analysis of variance), Mann-Whitney U two-tailed, and Spearman's rank correlation tests were used to assess differences.

RESULTS

EPC number was significantly lower in UC patients (39.6 (95% confidence interval (95% CI): 30.7-48.6)) and in CD patients (43.1 (95% CI: 35.9-50.4)) than in healthy controls (97.1 (95% CI: 88.3-105.9)), (P<0.001). LH and FSH levels and CXCR4 expression on EPCs did not significantly differ from controls. Testosterone concentrations and FMD were lower in UC patients. Number of apoptotic EPCs was higher in both UC and CD patients with an impaired ability to generate colony in vitro.

CONCLUSIONS

We hypothesize that in IBD patients, apoptosis contributes to the reduction of circulating EPC number and to their ability to proliferate in vitro. As this condition represents a risk factor for cardiovascular disease, endothelial function should be evaluated in these patients.

Clopidogrel attenuates atheroma formation and induces a stable plaque phenotype in apolipoprotein E knockout mice

AIM

Clopidogrel is a widely used anti-thrombotic for the prevention of stent thrombosis and cardiovascular events in patients with coronary atherosclerosis. Clopidogrel has been shown to exhibit anti-inflammatory effects that are related to the attenuated activation of platelets. Atherosclerosis is a complex process in which the immune system and the endothelium appear to play a prominent role. Herein, we tested the hypothesis that clopidogrel will influence plaque size and composition in the atherosclerosis prone apolipoprotein E knockout (apoE KO) mouse model.

METHODS AND RESULTS

Eight week old mice were fed daily with either PBS, 1 mg or 2 mg of clopidogrel for 10 weeks. Plaque size was evaluated in the aortic sinus and cellular and humoral responses were studied as well as splenic and bone marrow endothelial progenitors by FACS. Treatment with either 1 mg and 2 mg of clopidogrel significantly reduced plaque size and augmented its stability by increasing atheromatous fibrous area. Whereas antigen specific oxLDL immune response was not influenced by clopidogrel feeding, the number of atheroprotective regulatory CD4+CD25+ T cells was significantly increased. Moreover, clopidogrel treatment resulted in a prominent rise in splenic but not bone marrow derived Sca-1+/flk-1+ endothelial progenitors.

CONCLUSION

Clopidogrel significantly reduces atheroma burden and stabilizes aortic sinus plaques in apoE KO mice. These effects may partially be mediated by upregulation of the regulatory T cell pool and splenic endothelial progenitor cells. These findings may expand the potential applications of clopidogrel in human subjects.

Circulating apoptotic progenitor cells in patients with congestive heart failure

Background

Circulating CD34+ endothelial progenitor cells (EPCs) are capable of differentiating into mature endothelial cells to assist in angiogenesis and vasculogenesis. We sought to quantify the numbers of apoptotic progenitors in patients with congestive heart failure.

Methods and Results

Peripheral blood mononuclear cells were isolated by Ficoll density-gradient from 58 patients with various degrees of heart failure and 23 matched controls. Apoptosis in progenitor CD34+ cells was assessed using the Annexin V-PE/PI detection kit, and FACS analysis was performed with triple staining for CD34, annexin-V and propidium iodide. The percentage of early and late apoptotic progenitor cells was determined in the subject groups and was correlated with clinical characteristics. While there was no significant difference in total CD34 positive cells or early apoptotic progenitors between control subjects and CHF patients (p = 0.42) or between severe and mild/moderate CHF groups (p = 0.544), there was an elevated number of late apoptotic progenitors in the severe CHF group compared with the mild/moderate CHF group (p =  0.03). Late apoptotic progenitors were significantly increased in CHF patients as compared to matched controls. There was also an inverse correlation between late apoptotic progenitors and ejection fraction (r = −0.252, p = 0.028) as well as a positive association with NYHA class (r = 0.223, p = 0.046).

Conclusion

Severe heart failure patients exhibited higher numbers of late apoptotic progenitors, and this was positively associated with NYHA class and negatively correlated with ejection fraction. This finding may shed light on the numerous factors governing the pathophysiology of CHF.

Progenitor cells and vascular disease

Vascular progenitor cells have been the focus of much attention in recent years; both from the point of view of their pathophysiological roles and their potential as therapeutic agents. However, there is as yet no definitive description of either endothelial or vascular smooth muscle progenitor cells. Cells with the ability to differentiate into mature endothelial and vascular smooth muscle reportedly reside within a number of different tissues, including bone marrow, spleen, cardiac muscle, skeletal muscle and adipose tissue. Within these niches, vascular progenitor cells remain quiescent, until mobilized in response to injury or disease. Once mobilized, these progenitor cells enter the circulation and migrate to sites of damage, where they contribute to the remodelling process. It is generally perceived that endothelial progenitors are reparative, acting to restore vascular homeostasis, while smooth muscle progenitors contribute to pathological changes. Indeed, the number of circulating endothelial progenitor cells inversely correlates with exposure to cardiovascular risk factors and numbers of animal models and human studies have demonstrated therapeutic roles for endothelial progenitor cells, which can be enhanced by manipulating them to overexpress vasculo-protective genes. It remains to be determined whether smooth muscle progenitor cells, which are less well studied than their endothelial counterparts, can likewise be manipulated to achieve therapeutic benefit. This review outlines our current understanding of endothelial and smooth muscle progenitor cell biology, their roles in vascular disease and their potential as therapeutic agents.

Electronegative LDL circulating in smokers impairs endothelial progenitor cell differentiation by inhibiting Akt phosphorylation via LOX-1

Endothelial progenitor cells (EPCs), important for endothelial regeneration and vasculogenesis, are reduced by cigarette smoking. To elucidate the mechanisms, we examined the effects of electronegative LDL, circulating in chronic smokers, on EPC differentiation. Using ion-exchange chromatography, we purified smoker LDL into five subfractions, L1-L5. In matched, nonsmoking healthy subjects, L5, the most electronegative subfraction, was either absent or scanty. Sustained L5 treatment inhibited CD31 and KDR expression and EPC differentiation, whereas L1-L4 had no effect. L5 also inhibited telomerase activity to accelerate EPC senescence in correlation with reduced Akt phosphorylation. Transfection of day 3 EPCs with dominant negative Akt constructs inhibited CD31 and KDR expression, stalled EPC differentiation, and promoted early senescence. In contrast, transfection with constitutively active Akt rendered the EPCs resistant to L5, allowing normal maturation. L5 upregulated the lectin-like oxidized low density lipoprotein receptor 1 (LOX-1), and pretreatment of EPCs with TS20, a LOX-1-neutralizing antibody, blocked internalization of L5 by EPCs and prevented L5-mediated inhibition of EPC differentiation. Mixing L5 with L1 to physiological L5/L1 ratios did not attenuate L5's effects. These findings suggest that cigarette smoking is associated with the formation of L5, which inhibits EPC differentiation by impairing Akt phosphorylation via the LOX-1 receptor.

Microparticles derived from endothelial progenitor cells in patients at different cardiovascular risk

OBJECTIVES

Exposure to cardiovascular risk factors causes the release of pro-atherogenic microparticles from vascular cells and reduces the number of the atheroprotective endothelial progenitor cells (EPCs). We investigated whether microparticles shedding from EPCs are detectable in cultures of EPCs and in the circulation of subjects with various degrees of cardiovascular risk. We also investigated the relationship of EPCs-derived microparticles to cardiovascular risk factors and aortic stiffness, a marker of cardiovascular risk and impaired vascular repair by EPCs.

METHODS AND RESULTS

We estimated the 10-year Framingham risk score in 105 individuals with various degrees of cardiovascular risk and measured the number of circulating EPCs, EPCs-derived microparticles (CD34+/KDR+) and aortic stiffness. Release of CD34+/KDR+ microparticles was tested in cultures of EPCs exposed to hydrogen-peroxide. CD34+/KDR+ microparticles were found in EPCs cultures incubated with hydrogen-peroxide. Framingham risk was associated with EPCs (r=-0.47, p<0.001) and CD34+/KDR+ microparticles (r=0.56, p<0.001). Low EPCs (r=-0.59, p<0.001) and high CD34+/KDR+ microparticle (r=0.57, p<0.001) levels were predictors of aortic stiffness, independent of the Framingham risk.

CONCLUSIONS

EPCs undergo fragmentation into microparticles when exposed to a pro-apoptotic milieu. Increased microparticle shedding from EPCs may reduce circulating EPCs levels and may thus contribute to increase aortic stiffness beside traditional risk factors.