Critical reevaluation of endothelial progenitor cell phenotypes for therapeutic and diagnostic use

Clinical relevance of circulating angiogenic cells in patients with ischemic stroke

Background

Endothelial progenitor cells (EPCs) are circulating angiogenic cells with endothelial features associated with risk for stroke. We aimed to delve into their functional characteristics. EPCs were isolated and cultured from Ischemic Stroke (IS) patients and predictors of their variance evaluated.

Methods

This is a single-center observational study evaluating 187 consecutively hospitalized patients with IS. EPCs were isolated from blood samples. The number of circulating angiogenic cells (CACs), colony-forming units (CFU-ECs) and the emergence of late outgrowths endothelial cells (LOECs) were counted. We collected clinical variables and measured the stromal cell-derived factor 1 alpha (SDF1α) serum levels. We also examined the relative telomere length and the expression of osteogenic gene markers in CACs.

Results

CACs counts and CFU-ECs colony numbers were positively correlated (rho = 0.41, p < 0.001, n = 187). We found significant differences according to whether thrombolytic treatment was performed in the distribution of CFU-ECs (odds ratio (OR) = 2.5; 95% confidence interval (CI) 1.01–6.35; p = 0.042) and CACs (OR = 4.45; 95% IC 1.2–15.5; p = 0.012). The main determinants of CACs variation were the number of risks factors, thrombolysis treatment, arterial hypertension, LOECs occurrence, and the vascular endothelial growth factor expression, whereas CFU-ECs variations depended on hemoglobin content and the relative reduction in the National Institutes of Health Stroke Scale (NIHSS) criteria. The main predictors of LOECs appearance were thrombolysis and length of hospital stay.

Conclusions

Our study supports the relevance of patient risk factors and treatments in the analysis of the functional properties of EPCs.

The impact of different forms of exercise on endothelial progenitor cells in healthy populations

Circulating endothelial progenitor cells (EPCs) contribute to vascular healing and neovascularisation, while exercise is an effective means to mobilise EPCs into the circulation.

OBJECTIVES

to systematically examine the acute and chronic effects of different forms of exercise on circulating EPCs in healthy populations.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed.

RESULTS

thirty-one articles met the inclusion criteria including 747 participants aged 19 to 76 years. All included trials used flow cytometry for identification of circulating EPCs. Eight and five different EPC phenotypes were identified in the acute and chronic trials, respectively. In the acute trials, moderate intensity continuous (MICON), maximal, prolonged endurance, resistance and high intensity interval training (HIIT) exercise protocols were utilised. Prolonged endurance and resistance exercise had the most profound effect on circulating EPCs followed by maximal exercise. In the chronic trials, MICON exercise, HIIT, HIIT compared to MICON and MICON compared to exergame (exercise modality based on an interactive video game) were identified. MICON exercise had a positive effect on circulating EPCs in older sedentary individuals which was accompanied by improvements in endothelial function and arterial stiffness. Long-stage HIIT (4 min bouts) appears to be an effective means and superior than MICON exercise in mobilising circulating EPCs. In conclusion, both in acute and chronic trials the degree of exercise-induced EPC mobilisation depends upon the exercise regime applied. In future, more research is warranted to examine the dose-response relationship of different exercise forms on circulating EPCs using standardised methodology and EPC phenotype.

Role of endothelial colony forming cells (ECFCs) Tetrahydrobiopterin (BH4) in determining ECFCs functionality in coronary artery disease (CAD) patients

Nitric oxide (NO.) is critical for functionality of endothelial colony forming cells (ECFCs). Dimerization of endothelial nitric oxide synthase (eNOS) is must to produce NO. and tetrahydrobiopterin (BH4) plays a crucial role in stabilizing this state. We investigated BH4 level in ECFCs and its effect on ECFCs functionality in CAD patients. Intracellular biopterin levels and ECFCs functionality in terms of cell viability, adhesion, proliferation, in vitro wound healing and angiogenesis were assessed. Guanosine Triphosphate Cyclohydrolase-1 (GTPCH-1) expression was studied in ECFCs. Serum total reactive oxygen/nitrogen species was measured and effect of nitrosative stress on ECFC's biopterins level and functionality were evaluated by treating with 3-morpholino sydnonimine (SIN-1). BH4 level was significantly lower in ECFCs from CAD patients. Cell proliferation, wound closure reflecting cellular migration as well as in vitro angiogenesis were impaired in ECFCs from CAD patients. Wound healing capacity and angiogenesis were positively correlated with ECFC's BH4. A negative effect of nitrosative stress on biopterins level and cell functionality was observed in SIN-1 treated ECFCs. ECFCs from CAD exhibited impaired functionality and lower BH4 level. Association of BH4 with wound healing capacity and angiogenesis suggest its role in maintaining ECFC's functionality. Oxidative stress may be a determinant of intracellular biopterin levels.

Effect of vinyl chloride exposure on cardiometabolic toxicity

Vinyl chloride (VC) is an organochlorine mainly used to manufacture its polymer polyvinyl chloride, which is extensively used in the manufacturing of consumer products. Recent studies suggest that chronic low dose VC exposure affects glucose homeostasis in high fat diet-fed mice. Our data suggest that even in the absence of high fat diet, exposure to VC (0.8 ppm, 6 h/day, 5 day/week, for 12 weeks) induces glucose intolerance (1.0 g/kg, i.p.) in male C57BL/6 mice. This was accompanied with the depletion of hepatic glutathione and a modest increase in lung interstitial macrophages. VC exposure did not affect the levels of circulating immune cells, endothelial progenitor cells, platelet-immune cell aggregates, and cytokines and chemokines. The acute challenge of VC-exposed mice with LPS did not affect lung immune cell composition or plasma IL-6. To examine the effect of VC exposure on vascular inflammation and atherosclerosis, LDL receptor-KO mice on C57BL/6 background maintained on western diet were exposed to VC for 12 weeks (0.8 ppm, 6 h/day, 5 day/week). Unlike the WT C57BL/6 mice, VC exposure did not affect glucose tolerance in the LDL receptor-KO mice. Plasma cytokines, lesion area in the aortic valve, and markers of lesional inflammation in VC-exposed LDL receptor-KO mice were comparable with the air-exposed controls. Collectively, despite impaired glucose tolerance and modest pulmonary inflammation, chronic low dose VC exposure does not affect surrogate markers of cardiovascular injury, LPS-induced acute inflammation in C57BL/6 mice, and chronic inflammation and atherosclerosis in the LDL receptor-KO mice.

Effects of Shen-Yuan-Dan on Periprocedural Myocardial Injury and the Number of Peripheral Blood Endothelial Progenitor Cells in Patients with Unstable Angina Pectoris Undergoing Elective Percutaneous Coronary Intervention

OBJECTIVES

We aimed to investigate the effects of Shen-Yuan-Dan (SYD), a Chinese medicine preparation, on periprocedural myocardial injury (PMI) and the number of peripheral blood endothelial progenitor cells (EPCs) in patients with unstable angina pectoris (UA) who underwent elective percutaneous coronary intervention (PCI).

METHODS

Patients were randomly divided into the experimental (group A) and control (group B) groups through the random number table method. In group A, patients concurrently received the conventional western treatment and SYD orally (4 capsules/time, 3 times/d, from 3 d before surgery to 7 d after surgery). In group B, patients received conventional Western medicine treatment. Both groups underwent coronary angiography, and patients undergoing PCI were eventually included in the study. The following patient data were collected: incidence of PMI, serum CK-MB content before PCI, 4 h, 24 h, and 7 d after PCI, number of CD45dim/-CD34+CD309+ peripheral venous EPCs, and number of CD184 coexpressed EPCs. The incidence of adverse reactions and 30-day major adverse cardiovascular events (MACEs) were also recorded.

RESULTS

Sixty-two patients were finally included in this study, with 32 and 30 in groups A and B, respectively. In group A, the number of peripheral blood EPCs and the number of CD184 coexpressed EPCs at 1 h before surgery were higher than those at 3 d before surgery (37.24 ± 25.20 vs. 22.78 ± 9.60/ml; P < 0.001 and 23.38 ± 15.30 vs. 13.54 ± 8.08/ml; P < 0.001, resp.). The number of peripheral blood EPCs and number of CD184 coexpressed EPCs at 4 h after surgery were lower than those at 1 h before surgery (25.30 ± 11.90 vs. 37.24 ± 25.20/ml; P=0.019 and 15.38 ± 8.78 vs. 23.38 ± 15.30/ml; P=0.013, resp.), but there was no difference at 24 h and at 7 d after surgery in comparison with that at 1 h before surgery (P > 0.05). In group B, compared with that at 1 h before surgery, there existed a decline in the number of EPCs in peripheral blood and the number of CD184 coexpressed EPCs at 4 h after surgery, but without a statistical difference (P > 0.05). Comparing both groups, it was found that the incidence of PMI in group A was lower (6.25% vs. 26.67%; P=0.04), and the serum CK-MB content at 4 and 24 h after surgery was also lower than that in group B (17.33 ± 5.83 vs. 20.38 ± 4.32 U/l; P=0.048 and 15.79 ± 5.32 vs. 19.10 ± 4.93 U/l; P=0.030, resp.). The number of EPCs in peripheral blood and the number of CD184 coexpressed EPCs in group A were higher than those in group B at 1 h before surgery (37.24 ± 25.20 vs. 22.36 ± 12.26/ml; P=0.034 and 23.38 ± 15.30 vs. 13.12 ± 14.62/ml; P=0.013, resp.). In addition, there were no obvious adverse reactions and no 30-day MACEs in both groups during the trial.

CONCLUSION

SYD can reduce PMI and promote the mobilization of EPCs in the perioperative period of elective PCI in patients with UA.

The impact of different forms of exercise on circulating endothelial progenitor cells in cardiovascular and metabolic disease

Circulating endothelial progenitor cells (EPCs) contribute to vascular repair and their monitoring could have prognostic clinical value. Exercise is often prescribed for the management of cardiometabolic diseases, however, it is not fully understood how it regulates EPCs.

OBJECTIVES

to systematically examine the acute and chronic effects of different exercise modalities on circulating EPCs in patients with cardiovascular and metabolic disease.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed.

RESULTS

six electronic databases and reference lists of eligible studies were searched to April 2021. Thirty-six trials met the inclusion criteria including 1731 participants. Acute trials: in chronic heart failure (CHF), EPC mobilisation was acutely increased after high intensity interval or moderate intensity continuous exercise training, while findings were inconclusive after a cardiopulmonary cycling exercise test. Maximal exercise tests acutely increased EPCs in ischaemic or revascularized coronary artery disease (CAD) patients. In peripheral arterial disease (PAD), EPC levels increased up to 24 h post-exercise. In patients with compromised metabolic health, EPC mobilisation was blunted after a single exercise session. Chronic trials: in CHF and acute coronary syndrome, moderate intensity continuous protocols, with or without resistance exercise or calisthenics, increased EPCs irrespective of EPC identification phenotype. Findings were equivocal in CAD regardless of exercise mode, while in severe PAD disease EPCs increased. High intensity interval training increased EPCs in hypertensive metabolic syndrome and heart failure reduced ejection fraction.

CONCLUSION

the clinical condition and exercise modality influence the degree of EPC mobilisation and magnitude of EPC increases in the long term.

Therapeutic angiogenesis in Buerger's disease: reviewing the treatment landscape

Thromboangiitis obliterans, also known as Buerger's disease, is a rare inflammatory vasculitis that predominantly develops in smokers and characteristically affects the small- and medium-sized peripheral arteries and veins. Patients typically present with extremity claudication, but symptoms may progress to rest pain and tissue loss, especially in those unable to abstain from tobacco use. Unfortunately, traditional medical treatments are largely ineffective and due to the small caliber of affected vessels and lack of suitable distal targets or venous conduits, endovascular and open surgical approaches are often not possible. Eventually, a significant number of patients require major amputation. For these reasons, much research effort has been made in developing techniques of therapeutic angiogenesis to improve limb perfusion, both for atherosclerotic peripheral arterial disease and the smaller subset of patients with critical limb ischemia due to Buerger's disease. Neovascularization in response to ischemia relies on a complex interplay between the local tissue microenvironment and circulating stem and progenitor cells. To date, studies of therapeutic angiogenesis have therefore focused on exploiting known angiogenic factors and stem cells to induce neovascularization in ischemic tissues. This review summarizes the available clinical data regarding the safety and efficacy of various angiogenic therapies, notably injection of naked DNA plasmids, viral gene constructs, and cell-based preparations, and describes techniques for potentiating in vivo efficacy of gene- and cell-based therapies as well as ongoing developments in exosome-based cell-free approaches for therapeutic angiogenesis.

Plain Language Title and Summary

A review of available and emerging treatments for improving blood flow and wound healing in patients with Buerger's disease, a rare disorder of blood vessels Buerger's disease is a rare disorder of the small- and medium-sized blood vessels in the arms and legs that almost exclusively develops in young smokers. Buerger's disease causes inflammation in arteries and veins, which leads to blockage of these vessels and reduces blood flow to and from the extremities. Decreased blood flow to the arms and legs can lead to development of nonhealing wounds and infection for which some patients may eventually require amputation. Unfortunately, traditional medical and surgical treatments are not effective in Buerger's disease, so other methods for improving blood flow are needed for these patients. There are several different ways to stimulate new blood vessel formation, both in humans and animal models. The most common treatments involve injection of DNA or viruses that express genes related to blood vessel formation or, alternatively, stem cell-based treatments that help regenerate blood vessels and repair wound tissue. This review explores how safe and effective these various treatments are and describes recent research developments that may lead to better therapies for patients with Buerger's disease and other vascular disorders.

miRNA-130 Promotes Migration and Angiogenesis of Endothelial Progenitor Cells Through PI3K/AKT/mTOR Pathways

<sec> <title>Aim:</title> In this study, we aimed to investigate the effects and mechanisms of miRNA-130a in human endothelial progenitor cells (EPCs) involved in Deep vein thrombosis (DVT). </sec> <sec> <title>Methods:</title> EPCs were isolated and identified by cell morphology and surface marker detection. The effect of miR-130a on the migration, invasion and angiogenesis of EPCs in vitro were also detected. In addition, whether miR-130a is involved in the MMP-1 expression and Akt/PI3K/mTOR signaling pathway was also demonstrated. </sec> <sec> <title>Results:</title> Results suggested that miRNA-130a promotes migration, invasion, and tube formation of EPCs by positively regulating the expression of MMP-1 through Akt/PI3K/mTOR signaling pathway. </sec> <sec> <title>Conclusion:</title> Thus, as a potential therapeutic target, miRNA-130a may play an important role in the treatment of DVT. </sec>

The challenges and optimization of cell-based therapy for cardiovascular disease

With the hope of achieving real cardiovascular repair, cell-based therapy raised as a promising strategy for the treatment of cardiovascular disease (CVD) in the past two decades. Various types of cells have been studied for their reparative potential for CVD in the ensuing years. Despite the exciting results from animal experiments, the outcome of clinical trials is unsatisfactory and the development of cell-based therapy for CVD has hit a plateau nowadays. Thus, it is important to summarize the obstacles we are facing in this field in order to explore possible solutions for optimizing cell-based therapy and achieving real clinical application.

Endothelial Progenitor Cells: An Appraisal of Relevant Data from Bench to Bedside

The mobilization of endothelial progenitor cells (EPCs) into circulation from bone marrow is well known to be present in several clinical settings, including acute coronary syndrome, heart failure, diabetes and peripheral vascular disease. The aim of this review was to explore the current literature focusing on the great opportunity that EPCs can have in terms of regenerative medicine.

Repetitive spikes of glucose and lipid induce senescence-like phenotypes of bone marrow stem cells through H3K27me3 demethylase-mediated epigenetic regulation

Bone marrow-derived endothelial progenitor cells (EPCs) contribute to endothelial repair and angiogenesis. Reduced number of circulating EPCs is associated with future cardiovascular events. We tested whether dysregulated glucose and/or triglyceride (TG) metabolism has an impact on EPC homeostasis. The analysis of metabolic factors associated with circulating EPC number in humans revealed that postprandial hyperglycemia is negatively correlated with circulating EPC number, and this correlation appears to be further enhanced in the presence of postprandial hypertriglyceridemia (hTG). We therefore examined the effect of glucose/TG spikes on bone marrow lineage-sca-1+ c-kit+ (LSK) cells in mice, because primitive EPCs reside in bone marrow LSK fraction. Repetitive glucose + lipid (GL) spikes, but not glucose (G) or lipid (L) spikes alone, induced senescence-like phenotypes of LSK cells, and this phenomenon was reversible after cessation of GL spikes. G spikes and GL spikes differentially affected transcriptional program of LSK cell metabolism and differentiation. GL spikes upregulated a histone H3K27 demethylase JMJD3, and inhibition of JMJD3 eliminated GL spikes-induced LSK cell senescence-like phenotypes. These observations suggest that postprandial glucose/TG dysmetabolism modulate transcriptional regulation in LSK cells through H3K27 demethylase-mediated epigenetic regulation, leading to senescence-like phenotypes of LSK cells, reduced number of circulating EPCs, and development of atherosclerotic cardiovascular disease.NEW & NOTEWORTHY Combination of hyperglycemia and hypertriglyceridemia is associated with increased risk of atherosclerotic cardiovascular disease. We found that 1) hypertriglyceridemia may enhance the negative impact of hyperglycemia on circulating EPC number in humans and 2) metabolic stress induced by glucose + triglyceride spikes in mice results in senescence-like phenotypes of bone marrow stem/progenitor cells via H3K27me3 demethylase-mediated epigenetic regulation. These findings have important implications for understanding the pathogenesis of atherosclerotic cardiovascular disease in patients with T2DM.

Adiponectin Promotes VEGF Expression in Rheumatoid Arthritis Synovial Fibroblasts and Induces Endothelial Progenitor Cell Angiogenesis by Inhibiting miR-106a-5p

Rheumatoid arthritis (RA) is an erosive polyarthritis that can lead to severe joint destruction and painful disability if left untreated. Angiogenesis, a critical pathogenic mechanism in RA, attracts inflammatory leukocytes into the synovium, which promotes production of proinflammatory cytokines and destructive proteases. Adipokines, inflammatory mediators secreted by adipose tissue, also contribute to the pathophysiology of RA. The most abundant serum adipokine is adiponectin, which demonstrates proinflammatory effects in RA, although the mechanisms linking adiponectin and angiogenic manifestations of RA are not well understood. Our investigations with the human MH7A synovial cell line have revealed that adiponectin dose- and time-dependently increases vascular endothelial growth factor (VEGF) expression, stimulating endothelial progenitor cell (EPC) tube formation and migration. These adiponectin-induced angiogenic activities were facilitated by MEK/ERK signaling. In vivo experiments confirmed adiponectin-induced downregulation of microRNA-106a-5p (miR-106a-5p). Inhibiting adiponectin reduced joint swelling, bone destruction, and angiogenic marker expression in collagen-induced arthritis (CIA) mice. Our evidence suggests that targeting adiponectin has therapeutic potential for patients with RA. Clinical investigations are needed.

Fenofibrate increases circulating haematopoietic stem cells in people with diabetic retinopathy: a randomised, placebo-controlled trial

AIM/HYPOTHESIS

In two large RCTs, fenofibrate reduced the progression of diabetic retinopathy. We investigated whether fenofibrate increases circulating haematopoietic stem/progenitor cells (HSPCs), which have vascular properties and have been shown to protect from retinopathy.

METHODS

We conducted a 12 week parallel-group RCT comparing fenofibrate vs placebo. Patients with diabetic retinopathy and without other conditions that would affect HSPCs were enrolled at a tertiary diabetes outpatient clinic and randomised to receive fenofibrate or placebo based on a computer-generated sequence. Patients and study staff assessing the outcomes were blinded to group assignment. The primary endpoint was the change in the levels of circulating HSPCs, defined by expression of the stem cell markers CD34 and/or CD133. Secondary endpoints were the changes in endothelial progenitor cells, lipids, soluble mediators and gene expression. We used historical data on the association between HSPCs and retinopathy outcomes to estimate the effect of fenofibrate on retinopathy progression.

RESULTS

Forty-two participants with diabetic retinopathy were randomised and 41 completed treatment and were analysed (20 in the placebo group and 21 in the fenofibrate group). Mean age was 57.4 years, diabetes duration was 18.2 years and baseline HbA_1c was 60 mmol/mol (7.6%). When compared with placebo, fenofibrate significantly increased levels of HSPCs expressing CD34 and/or CD133. CD34⁺ HSPCs non-significantly declined in the placebo group (mean ± SD -44.2 ± 31.6 cells/10⁶) and significantly increased in the fenofibrate group (53.8 ± 31.1 cells/10⁶). The placebo-subtracted increase in CD34⁺ HSPCs from baseline was 30% (99.3 ± 43.3 cells/10⁶; p = 0.027) which, projected onto the relationship between HSPC levels and retinopathy outcomes, yielded an OR of retinopathy progression of 0.67 for fenofibrate vs placebo. Endothelial differentiation of CD34⁺ cells, estimated by the %KDR (kinase insert domain receptor) expression, was significantly reduced by fenofibrate. Fenofibrate decreased serum triacylglycerols, but the change in triacylglycerols was unrelated to the change in HSPCs. No effect was observed for endothelial progenitor cells, cytokines/chemokines (stromal-cell derived factor-1, vascular endothelial growth factor, monocyte chemoattractant protein-1) and gene expression in peripheral blood mononuclear cells.

CONCLUSIONS/INTERPRETATION

Fenofibrate increased HSPC levels in participants with diabetic retinopathy and this mechanism may explain why fenofibrate reduced retinopathy progression in previous studies.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01927315.

The Effect of Tafamidis on Circulating Endothelial Progenitor Cells in Patients with Transthyretin Cardiac Amyloidosis

AIMS

Endothelial microvascular dysfunction is a known mechanism of vascular pathology in cardiac amyloidosis (CA). Scientific evidence regarding the possible protective role of the amyloid transthyretin (ATTR) stabilizer, tafamidis, is lacking. Circulating endothelial progenitor cells (cEPCs) have an important role in the process of vascular repair. We aimed to examine the effect of tafamidis on cEPCs.

METHODS AND RESULTS

Study population included patients with ATTR-CA. cEPCs were assessed using flow cytometry by the expression of CD34⁽⁺⁾/CD133⁽⁺⁾ and vascular endothelial growth factor receptor (VEGFR)-2⁽⁺⁾ and by the formation of colony-forming units (CFUs) and production of VEGF. Tests were repeated at pre-specified time-points up to 12 months following the initiation of tafamidis. Included were 18 ATTR-CA patients at a median age of 77 (IQR 71, 85) years and male predominance (n = 15, 83%). Following the initiation of tafamidis and during 12 months of drug treatment, there was a gradual increase in the levels of CD34⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.43 to 2.42% (IQR 1.53, 2.91)%, p = 0.002) and CD133⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.49 to 1.64% (IQR 0.97, 2.90)%, p = 0.004). Functionally, increase in EPCs-CFUs was microscopically evident following treatment with tafamidis (from 0.5 CFUs (IQR 0.0, 1.0) to 3.0 (IQR 1.3, 3.8) p < 0.001) with a concomitant increase in EPC's viability as demonstrated by an MTT assay (from 0.12 (IQR 0.03, 0.16) to 0.30 (IQR 0.18, 0.33), p < 0.001). VEGF levels increased following treatment (from 54 (IQR 52, 72) to 107 (IQR 62, 129) pg/ml, p = 0.039).

CONCLUSIONS

Tafamidis induced the activation of the cEPCs pathway, possibly promoting endothelial repair in ATTR-CA.

Cyclosporine A and Tacrolimus Induce Functional Impairment and Inflammatory Reactions in Endothelial Progenitor Cells

Immunosuppressants are a mandatory therapy for transplant patients to avoid rejection of the transplanted organ by the immune system. However, there are several known side effects, including alterations of the vasculature, which involve a higher occurrence of cardiovascular events. While the effects of the commonly applied immunosuppressive drugs cyclosporine A (CsA) and tacrolimus (Tac) on mature endothelial cells have been addressed in several studies, we focused our research on the unexplored effects of CsA and Tac on endothelial colony-forming cells (ECFCs), a subgroup of endothelial progenitor cells, which play an important role in vascular repair and angiogenesis. We hypothesized that CsA and Tac induce functional defects and activate an inflammatory cascade via NF-κB signaling in ECFCs. ECFCs were incubated with different doses (0.01 µM–10 µM) of CsA or Tac. ECFC function was determined using in vitro models. The expression of inflammatory cytokines and adhesion molecules was explored by quantitative real-time PCR and flow cytometry. NF-κB subunit modification was assessed by immunoblot and immunofluorescence. CsA and Tac significantly impaired ECFC function, including proliferation, migration, and tube formation. TNF-α, IL-6, VCAM, and ICAM mRNA expression, as well as PECAM and VCAM surface expression, were enhanced. Furthermore, CsA and Tac led to NF-κB p65 subunit phosphorylation and nuclear translocation. Pharmacological inhibition of NF-κB by parthenolide diminished CsA- and Tac-mediated proinflammatory effects. The data of functional impairment and activation of inflammatory signals provide new insight into mechanisms associated with CsA and Tac and cardiovascular risk in transplant patients.

Circulating Progenitor Cells and Cognitive Impairment in Men and Women with Coronary Artery Disease

BACKGROUND

Circulating progenitor cells (CPC) have been associated with memory function and cognitive impairment in healthy adults. However, it is unclear whether such associations also exist in patients with coronary artery disease (CAD).

OBJECTIVE

To assess the association between CPCs and memory performance among individuals with CAD.

METHODS

We assessed cognitive function in 509 patients with CAD using the verbal and visual Memory subtests of the Wechsler memory scale-IV and the Trail Making Test parts A and B. CPCs were enumerated with flow cytometry as CD45med/CD34+ blood mononuclear cells, those co-expressing other epitopes representing populations enriched for hematopoietic and endothelial progenitors.

RESULTS

After adjusting for demographic and cardiovascular risk factors, lower number of endothelial progenitor cell counts were independently associated with lower visual and verbal memory scores (p for all < 0.05). There was a significant interaction in the magnitude of this association with race (p < 0.01), such that the association of verbal memory scores with endothelial progenitor subsets was present in Black but not in non-Black participants. No associations were present with the hematopoietic progenitor-enriched cells or with the Trail Making Tests.

CONCLUSION

Lower numbers of circulating endothelial progenitor cells are associated with cognitive impairment in patients with CAD, suggesting a protective effect of repair/regeneration processes in the maintenance of cognitive status. Impairment of verbal memory function was more strongly associated with lower CPC counts in Black compared to non-Black participants with CAD. Whether strategies designed to improve regenerative capacity will improve cognition needs further study.

Exposure to Fine Particulate Matter Air Pollution Alters mRNA and miRNA Expression in Bone Marrow-Derived Endothelial Progenitor Cells from Mice

Exposure to fine particulate matter (PM2.5) air pollution is associated with quantitative deficits of circulating endothelial progenitor cells (EPCs) in humans. Related exposures of mice to concentrated ambient PM2.5 (CAP) likewise reduces levels of circulating EPCs and induces defects in their proliferation and angiogenic potential as well. These changes in EPC number or function are predictive of larger cardiovascular dysfunction. To identify global, PM2.5-dependent mRNA and miRNA expression changes that may contribute to these defects, we performed a transcriptomic analysis of cells isolated from exposed mice. Compared with control samples, we identified 122 upregulated genes and 44 downregulated genes in EPCs derived from CAP-exposed animals. Functions most impacted by these gene expression changes included regulation of cell movement, cell and tissue development, and cellular assembly and organization. With respect to miRNA changes, we found that 55 were upregulated while 53 were downregulated in EPCs from CAP-exposed mice. The top functions impacted by these miRNA changes included cell movement, cell death and survival, cellular development, and cell growth and proliferation. A subset of these mRNA and miRNA changes were confirmed by qRT-PCR, including some reciprocal relationships. These results suggest that PM2.5-induced changes in gene expression may contribute to EPC dysfunction and that such changes may contribute to the adverse cardiovascular outcomes of air pollution exposure.

Contribution of Adventitia-Derived Stem and Progenitor Cells to New Vessel Formation in Tumors

Blocking tumor vascularization has not yet come to fruition to the extent it was hoped for, as angiogenesis inhibitors have shown only partial success in the clinic. We hypothesized that under-appreciated vascular wall-resident stem and progenitor cells (VW-SPCs) might be involved in tumor vascularization and influence effectiveness of anti-angiogenic therapy. Indeed, in patient samples, we observed that vascular adventitia-resident CD34⁺ VW-SPCs are recruited to tumors in situ from co-opted vessels. To elucidate this in detail, we established an ex vivo model using concomitant embedding of multi-cellular tumor spheroids (MCTS) and mouse aortic rings (ARs) into collagen gels, similar to the so-called aortic ring assay (ARA). Moreover, ARA was modified by removing the ARs’ adventitia that harbors VW-SPCs. Thus, this model enabled distinguishing the contribution of VW-SPCs from that of mature endothelial cells (ECs) to new vessel formation. Our results show that the formation of capillary-like sprouts is considerably delayed, and their number and network formation were significantly reduced by removing the adventitia. Substituting iPSC-derived neural spheroids for MCTS resulted in distinct sprouting patterns that were also strongly influenced by the presence or absence of VW-SPCs, also underlying the involvement of these cells in non-pathological vascularization. Our data suggest that more comprehensive approaches are needed in order to block all of the mechanisms contributing to tumor vascularization.

Vascular Regenerative Capacity and the Obesity Paradox in Coronary Artery Disease

[Figure: see text].

Characterization and Functional Assessment of Endothelial Progenitor Cells in Ischemic Stroke Patients

Endothelial dysfunction has been implicated in atherosclerosis, ischemic heart disease, and stroke. Endothelial progenitor cells (EPCs), found in the bone marrow and peripheral blood as rare cell population, demonstrated a high proliferation and differentiation capacity. Understanding how such diseases influence the quantity and functionality of EPCs is essential for the development of novel therapies. This study aims to investigate the factors that affect the quantity and functionality of circulating EPCs in stroke patients and healthy controls. Blood samples were collected once from healthy donors (n = 30) and up to 3 times (within 7 days (baseline), 3 and 12 months post-stroke) from stroke patients (n = 207). EPC subpopulations were isolated with flow cytometry for characterization. The Matrigel tubular formation assay was performed as a measure of functionality. An increased amount of circulating EPCs was observed in stroke patients over 45 years when compared to age-matched healthy individuals. EPCs showed a rising trend in stroke patients over the 12-month post-stroke period, reaching statistical significance at 12 months post-stroke. Isolated CD34+KDR+ cells from stroke patients showed impairment in tubular formation capability when compared to cells from healthy donors. The quantity and vasculogenic function of circulating EPCs in peripheral blood have been effectively evaluated in stroke patients and healthy control donors in this study. Age and stroke are found to be 2 influencing factors on the angiogenic capacity. It is suggested that the increase in EPC number is triggered by the recovery response following ischemic stroke. Graphical abstract.

The Role of Inflammation and Immune Activation on Circulating Endothelial Progenitor Cells in Chronic HIV Infection

Endothelial inflammation and damage are the main drivers of cardiovascular risk/disease. Endothelial repair is mediated in part by recruitment of bone marrow endothelial progenitor/endothelial colony forming cells (EPC/ECFC). People with HIV (PWH) have increased cardiovascular risk and the impact of infection in endothelial repair is not well defined. The low frequencies and challenges to in vitro isolation and differentiation of EPC/ECFC from PBMCs had made it difficult to study their role in this context. We hypothesized that HIV driven inflammation induces phenotypic changes that reflects the impact of infection. To test this hypothesis, we evaluated expression of markers of trafficking, endothelial differentiation, and angiogenesis, and study their association with biomarkers of inflammation in a cohort of PWH. In addition, we investigated the relationship of circulating endothelial progenitors and angiogenic T cells, a T cell subset with angiogenic function. Using a flow cytometry approach, we identified two subsets of circulating progenitors LIN4^-CD45^-CD34⁺ and LIN4^-CD45^dimCD34⁺ in PWH. We found that the phenotype but not frequencies were associated with biomarkers of inflammation. In addition, the percentage of LIN4^-CD45^dimCD34⁺ was associated with serum levels of lipids. This data may provide a new tool to better address the impact of HIV infection in endothelial inflammation and repair.

Endogenous PCSK9 may influence circulating CD45neg/CD34bright and CD45neg/CD34bright/CD146neg cells in patients with type 2 diabetes mellitus

Protease proprotein convertase subtilisin/kexin type 9 (PCSK9) is a regulator of LDL cholesterol clearance and has been associated with cardiovascular risk. PCSK9 inhibitors increase in vivo circulating endothelial progenitor cells (EPCs), a subtype of immature cells involved in ongoing endothelial repair. We hypothesized that the effect of PCSK9 on vascular homeostasis may be mediated by EPCs in patients with or without type 2 diabetes mellitus (T2DM). Eighty-two patients (45 with, 37 without T2DM) at high cardiovascular risk were enrolled in this observational study. Statin treatment was associated with higher circulating levels of PCSK9 in patients with and without T2DM (p < 0.001 and p = 0.036) and with reduced CD45neg/CD34bright (total EPC compartment) (p = 0.016) and CD45neg/CD34bright/CD146neg (early EPC) (p = 0.040) only among patients with T2DM. In the whole group of patients, statin treatment was the only independent predictor of low number of CD45neg/CD34bright (β = - 0.230; p = 0.038, adjusted R2 = 0.041). Among T2DM patients, PCSK9 circulating levels were inversely related and predicted both the number of CD45neg/CD34bright (β = - 0.438; p = 0.003, adjusted R2 = 0.173), and CD45neg/CD34bright/CD146neg (β = - 0.458; p = 0.002, adjusted R2 = 0.191) independently of age, gender, BMI and statin treatment. In high-risk T2DM patients, high endogenous levels of PCSK9 may have a detrimental effect on EPCs by reducing the endothelial repair and worsening the progression of atherothrombosis.

CCL8 mediates crosstalk between endothelial colony forming cells and triple-negative breast cancer cells through IL-8, aggravating invasion and tumorigenicity

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer with a poor prognosis for which no effective therapeutic measures are currently available. The present study aimed to investigate whether interactions with endothelial colony-forming cells (ECFCs) promote aggressive progression of TNBC cells. Herein, using an indirect co-culture system, we showed that co-culture increased the invasive and migratory phenotypes of both MDA-MB-231 TNBC cells and ECFCs. Through a cytokine antibody array and RT-PCR analysis, we revealed that co-culture markedly induced secretion of the chemokine C-C motif ligand (CCL)8 from ECFCs and that of interleukin (IL)-8 from MDA-MB-231 cells. CCL8 was crucial for ECFC-induced IL-8 secretion and invasion of MDA-MB-231 cells as well as for MDA-MB-231-enhanced MMP-2 secretion and angiogenesis of ECFCs. We suggest c-Jun as a transcription factor for CCL8-induced IL-8 expression in MDA-MB-231 cells. IL-8 was important for co-culture-induced CCL8 and MMP-2 upregulation and invasion of ECFCs. Notably, our findings reveal a positive feedback loop between CCL8 and IL-8, which contributes to the aggressive phenotypes of both ECFC and TNBC cells. Using an MDA-MB-231 cell-based xenograft model, we show that tumor growth and metastasis are increased by co-injected ECFCs in vivo. Increased expression of IL-8 was observed in tissues with bone metastases in mice injected with conditioned media from co-cultured cells. High IL-8 levels are correlated with poor recurrence-free survival in TNBC patients. Together, these results suggest that CCL8 and IL-8 mediate the crosstalk between ECFCs and TNBC, leading to aggravation of tumorigenicity in TNBC.

In vitro recellularization of decellularized bovine carotid arteries using human endothelial colony forming cells

BACKGROUND

Many patients suffering from peripheral arterial disease (PAD) are dependent on bypass surgery. However, in some patients no suitable replacements (i.e. autologous or prosthetic bypass grafts) are available. Advances have been made to develop autologous tissue engineered vascular grafts (TEVG) using endothelial colony forming cells (ECFC) obtained by peripheral blood draw in large animal trials. Clinical translation of this technique, however, still requires additional data for usability of isolated ECFC from high cardiovascular risk patients. Bovine carotid arteries (BCA) were decellularized using a combined SDS (sodium dodecyl sulfate) -free mechanical-osmotic-enzymatic-detergent approach to show the feasibility of xenogenous vessel decellularization. Decellularized BCA chips were seeded with human ECFC, isolated from a high cardiovascular risk patient group, suffering from diabetes, hypertension and/or chronic renal failure. ECFC were cultured alone or in coculture with rat or human mesenchymal stromal cells (rMSC/hMSC). Decellularized BCA chips were evaluated for biochemical, histological and mechanical properties. Successful isolation of ECFC and recellularization capabilities were analyzed by histology.

RESULTS

Decellularized BCA showed retained extracellular matrix (ECM) composition and mechanical properties upon cell removal. Isolation of ECFC from the intended target group was successfully performed (80% isolation efficiency). Isolated cells showed a typical ECFC-phenotype. Upon recellularization, co-seeding of patient-isolated ECFC with rMSC/hMSC and further incubation was successful for 14 (n = 9) and 23 (n = 5) days. Reendothelialization (rMSC) and partial reendothelialization (hMSC) was achieved. Seeded cells were CD31 and vWF positive, however, human cells were detectable for up to 14 days in xenogenic cell-culture only. Seeding of ECFC without rMSC was not successful.

CONCLUSION

Using our refined decellularization process we generated easily obtainable TEVG with retained ECM- and mechanical quality, serving as a platform to develop small-diameter (< 6 mm) TEVG. ECFC isolation from the cardiovascular risk target group is possible and sufficient. Survival of diabetic ECFC appears to be highly dependent on perivascular support by rMSC/hMSC under static conditions. ECFC survival was limited to 14 days post seeding.

Local application reduces number of needed EPC for beneficial effects on wound healing compared to systemic treatment in mice

Introduction

Stem cell transplantation is one of the most promising strategies to improve healing in chronic wounds as systemic administration of endothelial progenitor cells (EPC) enhances healing by promoting neovascularization and homing though a high amount of cells is needed. In the following study, we analysed whether local application can reduce the number of EPC needed achieving the same beneficial effect on wound healing.

Material and Methods

Wound healing after local or systemic treatment with EPC was monitored in vivo by creating standardized wounds on the dorsum of hairless mice measuring wound closure every second day. Systemic group received 2 × 10⁶ EPC i.v. and locally treated group 2 × 10⁵ EPC, locally injected. As control PBS injection was performed the same way. Expression of CD31, VEGF, CD90 and, SDF-1α was analysed immunohistochemically for evaluation of neovascularisation and amelioration of homing.

Results

Local (7.1 ± 0.45 SD) as well as systemic (6.1 ± 0.23 SD) EPC transplantation led to a significant acceleration of wound closure compared to controls (PBS local: 9.7 ± 0.5 SD, PBS systemic 10.9 ± 0.38 SD). Systemic application enhanced CD31 expression on day 6 after wounding and local EPC on 6 and 9 in comparison to control. VEGF expression was not significantly affected. Systemic and local EPC treatment resulted in a significantly enhanced SDF-1α and CD90 expression on all days investigated.

Conclusion

Local as well as systemic EPC treatment enhances wound healing. Moreover, beneficial effects are obtained with a tenfold decrease number of EPC when applied locally. Thus, local EPC treatment might be more convenient way to enhance wound healing as number of progenitor cells is limited.

Cell Therapy for Critical Limb Ischemia: Advantages, Limitations, and New Perspectives for Treatment of Patients with Critical Diabetic Vasculopathy

PURPOSE OF REVIEW

To provide a highlight of the current state of cell therapy for the treatment of critical limb ischemia in patients with diabetes.

RECENT FINDINGS

The global incidence of diabetes is constantly growing with consequent challenges for healthcare systems worldwide. In the UK only, NHS costs attributed to diabetic complications, such as peripheral vascular disease, amputation, blindness, renal failure, and stroke, average £10 billion each year, with cost pressure being estimated to get worse. Although giant leaps forward have been registered in the scope of early diagnosis and optimal glycaemic control, an effective treatment for critical limb ischemia is still lacking. The present review aims to provide an update of the ongoing work in the field of regenerative medicine. Recent advancements but also limitations imposed by diabetes on the potential of the approach are addressed. In particular, the review focuses on the perturbation of non-coding RNA networks in progenitor cells and the possibility of using emerging knowledge on molecular mechanisms to design refined protocols for personalized therapy. The field of cell therapy showed rapid progress but has limitations. Significant advances are foreseen in the upcoming years thanks to a better understanding of molecular bottlenecks associated with the metabolic disorders.

Autologous Bone-Marrow vs. Peripheral Blood Mononuclear Cells Therapy for Peripheral Artery Disease in Diabetic Patients

Diabetes mellitus (DM) remains one of the most important risk factors for peripheral artery disease (PAD), with approximately 20% of DM patients older than 40 years old are affected with PAD. The current standard management for severe PAD is endovascular intervention with or without surgical bypass. Unfortunately, up to 40% of patients are unable to undergo these revascularization therapies due to excessive surgical risk or adverse vascular side effects. Stem cell therapy has emerged as a novel therapeutic strategy for these ‘no-option’ patients. Several types of stem cells are utilized for PAD therapy, including bone marrow mononuclear cells (BMMNC) and peripheral blood mononuclear cells (PBMNC). Many studies have reported the safety of BMMNC and PBMNC, as well as its efficacy in reducing ischemic pain, ulcer size, pain-free walking distance, ankle-brachial index (ABI), and transcutaneous oxygen pressure (TcPO2). However, the capacity to establish the efficacy of reducing major amputation rates, amputation free survival, and all-cause mortality is limited, as shown by several randomized placebo-controlled trials. The present literature review will focus on comparing safety and efficacy between BMMNC and PBMNC as cell-based management in diabetic patients with PAD who are not suitable for revascularization therapy.

CD34+ cells and endothelial progenitor cell subpopulations are associated with cerebral small vessel disease burden

Background: Endothelial dysfunction is considered to be involved in the pathogenesis of cerebral small vessel disease (CSVD). Endothelial progenitor cells are associated with endothelial dysfunction. The present study was designed to investigate the correlation between the populations of circulating CD34-positive cells and endothelial progenitor cells and CSVD burden. Methodology & results: A total of 364 patients with confirmed diagnosis of CSVD were included in this prospective study. Multiple ordinal logistic regression analyses showed that subjects with higher CSVD burden had significantly decreased circulating CD34+ cell level (odds ratio [OR], 0.42; p = 0.034) and significantly increased levels of circulating CD34+CD133+CD309+ and CD34+CD133+ cells (OR 1.07, p = 0.031; OR 1.03, p = 0.001, respectively), compared with patients with lower CSVD burden. Conclusion: The findings suggest that the levels of circulating CD34+ cells, CD34+CD133+CD309+ cells and CD34+CD133+ cells may be used as potential biomarkers to monitor the disease progression of CSVD.

ACE2 gene transfer ameliorates vasoreparative dysfunction in CD34+ cells derived from diabetic older adults

Diabetes increases the risk for ischemic vascular diseases, which is further elevated in older adults. Bone marrow-derived hematopoietic CD34+ stem/progenitor cells have the potential of revascularization; however, diabetes attenuates vasoreparative functions. Angiotensin-converting enzyme 2 (ACE2) is the vasoprotective enzyme of renin-angiotensin system in contrast with the canonical angiotensin-converting enzyme (ACE). The present study tested the hypothesis that diabetic dysfunction is associated with ACE2/ACE imbalance in hematopoietic stem/progenitor cells (HSPCs) and that increasing ACE2 expression would restore reparative functions. Blood samples from male and female diabetic (n=71) or nondiabetic (n=62) individuals were obtained and CD34+ cells were enumerated by flow cytometry. ACE and ACE2 enzyme activities were determined in cell lysates. Lentiviral (LV) approach was used to increase the expression of soluble ACE2 protein. Cells from diabetic older adults (DB) or nondiabetic individuals (Control) were evaluated for their ability to stimulate revascularization in a mouse model of hindlimb ischemia (HLI). DB cells attenuated the recovery of blood flow to ischemic areas in nondiabetic mice compared with that observed with Control cells. Administration of DB cells modified with LV-ACE2 resulted in complete restoration of blood flow. HLI in diabetic mice resulted in poor recovery with amputations, which was not reversed by either Control or DB cells. LV-ACE2 modification of Control or DB cells resulted in blood flow recovery in diabetic mice. In vitro treatment with Ang-(1-7) modified paracrine profile in diabetic CD34+ cells. The present study suggests that vasoreparative dysfunction in CD34+ cells from diabetic older adults is associated with ACE2/ACE imbalance and that increased ACE2 expression enhances the revascularization potential.

Differential Angiogenic Responses of Human Endothelial Colony-Forming Cells to Different Molecular Subtypes of Breast Cancer Cells

Objective

Triple negative breast cancer (TNBC) is one subtype of breast cancer. It is characterized by lack of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Compared with non-TNBC, TNBC is more aggressive, of higher grade, and frequently metastatic with poor prognosis, which is correlated with upregulated microvascular density. Endothelial colony-forming cells (ECFCs) mediate neovascularization, which is the crucial contributor to cancer growth and metastasis. The present study aimed to determine whether angiogenic responses of ECFCs are regulated differently by TNBC compared with non-TNBC.

Methods

MDA-MB-231 and MCF7 cells were utilized for TNBC and non-TNBC, respectively. Bone-marrow-derived human ECFCs were treated with a conditioned medium (CM) of cancer cells to investigate the paracrine effect on angiogenesis. Also, ECFCs were co-cultured with cancer cells to evaluate the angiogenic effect of direct cell-to-cell interaction. Angiogenic responses of ECFCs were evaluated by proliferation, migration, and tube formation. Gene expression profiles of pro-angiogenic factors were also analyzed.

Results

Migration and tube formation of ECFCs were increased by treatment with CM of MDA-MB-231, which correlated with a higher gene expression profile of pro-angiogenic factors in MDA-MB-231 compared to MCF7. Interestingly, ECFCs co-cultured with MDA-MB-231 showed further increase of tube formation, suggesting synergic mechanisms between the paracrine effect and direct interaction between the cells.

Conclusion

The angiogenic potential of ECFCs was enhanced by TNBC through both direct and indirect mechanisms. Therefore, the investigation of signaling pathways to regulate ECFC-mediated angiogenesis will be important to the discovery of anti-angiogenic therapies to treat TNBC patients.

The Effect of Proprotein Convertase Subtilisin Kexin Type 9 Inhibitors on Circulating Endothelial Progenitor Cells in Patients with Cardiovascular Disease

PURPOSE

Circulating endothelial progenitor cells (cEPCs) are vital to vascular repair by re-endothelialization. We aimed to explore the effect of proprotein convertase subtilisin kexin type 9 inhibitors (PCSK9i) on cEPCs hypothesizing a possible pleiotropic effect.

METHODS

Patients with cardiovascular disease (CVD) were sampled for cEPCs at baseline and following the initiation of PCSK9i. cEPCs were assessed using flow cytometry by the expression of CD34⁽⁺⁾/CD133⁽⁺⁾ and vascular endothelial growth factor receptor (VEGFR)-2⁽⁺⁾, and by the formation of colony-forming units (CFUs) and production of VEGF.

RESULTS

Our cohort included 26 patients (median age 68 (IQR 63, 73) years; 69% male). Following 3 months of treatment with PCSK9i and a decline in low-density lipoprotein cholesterol levels (153 (IQR 116, 176) to 56 (IQR 28, 72) mg/dl), p < 0.001), there was an increase in CD34⁽⁺⁾/CD133⁽⁺⁾ and VEGFR-2⁽⁺⁾ cell levels (0.98% (IQR 0.37, 1.55) to 1.43% (IQR 0.90, 4.51), p = 0.002 and 0.66% (IQR 0.22, 0.99) to 1.53% (IQR 0.73, 2.70), p = 0.05, respectively). Functionally, increase in EPCs-CFUs was microscopically evident following treatment with PCSK9i (1 CFUs (IQR 0.0, 1.0) to 2.5 (IQR 1.5, 3), p < 0.001) with a concomitant increase in EPC's viability as demonstrated by an MTT assay (0.15 (IQR 0.11, 0.19) to 0.21 (IQR 0.18, 0.23), p < 0.001). VEGF levels increased following PCSK9i treatment (57 (IQR 18, 24) to 105 (IQR 43, 245), p = 0.006).

CONCLUSIONS

Patients with CVD treated with PCSK9i demonstrate higher levels of active cEPCs, reflecting the promotion of endothelial repair. These findings may represent a novel mechanism of action of PCSK9i.

Targeting Angiotensin-Converting Enzyme-2/Angiotensin-(1-7)/Mas Receptor Axis in the Vascular Progenitor Cells for Cardiovascular Diseases

Bone marrow-derived hematopoietic stem/progenitor cells are vasculogenic and play an important role in endothelial health and vascular homeostasis by participating in postnatal vasculogenesis. Progenitor cells are mobilized from bone marrow niches in response to remote ischemic injury and migrate to the areas of damage and stimulate revascularization largely by paracrine activation of angiogenic functions in the peri-ischemic vasculature. This innate vasoprotective mechanism is impaired in certain chronic clinical conditions, which leads to the development of cardiovascular complications. Members of the renin-angiotensin system-angiotensin-converting enzymes (ACEs) ACE and ACE2, angiotensin II (Ang II), Ang-(1-7), and receptors AT1 and Mas-are expressed in vasculogenic progenitor cells derived from humans and rodents. Ang-(1-7), generated by ACE2, is known to produce cardiovascular protective effects by acting on Mas receptor and is considered as a counter-regulatory mechanism to the detrimental effects of Ang II. Evidence has now been accumulating in support of the activation of the ACE2/Ang-(1-7)/Mas receptor pathway by pharmacologic or molecular maneuvers, which stimulates mobilization of progenitor cells from bone marrow, migration to areas of vascular damage, and revascularization of ischemic areas in pathologic conditions. This minireview summarizes recent studies that have enhanced our understanding of the physiology and pharmacology of vasoprotective axis in bone marrow-derived progenitor cells in health and disease. SIGNIFICANCE STATEMENT: Hematopoietic stem progenitor cells (HSPCs) stimulate revascularization of ischemic areas. However, the reparative potential is diminished in certain chronic clinical conditions, leading to the development of cardiovascular diseases. ACE2 and Mas receptor are key members of the alternative axis of the renin-angiotensin system and are expressed in HSPCs. Accumulating evidence points to activation of ACE2 or Mas receptor as a promising approach for restoring the reparative potential, thereby preventing the development of ischemic vascular diseases.

Experimental Study on the Effect of Allogeneic Endothelial Progenitor Cells on Wound Healing in Diabetic Mice

Endothelial progenitor cells (EPCs) are involved in the neovascularization in traumatic and ischemic sites, but EPCs are "detained" in bone marrow under diabetic conditions, which results in reduction of the number of EPCs and their biological activity in peripheral blood. Based on our previous study to mobilize autologous bone marrow EPCs by administering AMD3100+G-CSF to realize the optimal effect, our present study is aimed at exploring the effects of transplanting EPCs locally in a wound model of diabetic mice. First, we prepared and identified EPCs, and the biological functions and molecular characteristics were compared between EPCs from DB/+ and DB/DB mice. Then, we performed full-thickness skin resection in DB/DB mice and tested the effect of local transplantation of EPCs on skin wound healing. The wound healing process was recorded using digital photographs. The animals were sacrificed on postoperative days 7, 14, and 17 for histological and molecular analysis. Our results showed that DB/+ EPCs were biologically more active than those of DB/DB EPCs. When compared with the control group, local transplantation of EPCs accelerated wound healing in DB/DB mice by promoting wound granulation tissue formation, angiogenesis, and collagen fiber deposition, but there was no significant difference in wound healing between DB/+ EPCs and DB/DB EPCs transplanted into the wound. Furthermore, local transplantation of EPCs promoted the expression of SDF-1, CXCR4, and VEGF. We speculated that EPC transplantation may promote wound healing through the SDF-1/CXCR4 axis. This point is worth exploring further. Present data are of considerable significance because they raise the possibility of promoting wound healing by isolating autologous EPCs from the patient, which provides a new approach for the clinical treatment of diabetic wounds in the future.

Diabetes pharmacotherapy and circulating stem/progenitor cells. State of the art and evidence gaps

Diabetes is burdened with the development of several end-organ complications leading to excess mortality. Though the causes of such organ damage are far from being clarified, diabetes has been redefined as a disease of impaired damage control, wherein ongoing damage is not adequately compensated by activation of repair processes. Bone marrow-derived hematopoietic stem/progenitor cells (HSPCs) and their descendants endothelial progenitor cells (EPCs) have been extensively studied as major players in tissue homeostasis as well as biomarkers of diabetic complication risk. Thus, strategies to raise the levels of circulating HSPCs/EPCs have attracted interest for their potential to modify the future risk of complications. We herein discuss state-of-the-art of the effects exerted by diabetes pharmacotherapy on such cell populations. Further, we highlight which outstanding questions remain to be addressed for a more comprehensive understanding of this topic.

Endothelial progenitor cells mobilization after maximal exercise according to heart failure severity

BACKGROUND

Vascular endothelial dysfunction is an underlying pathophysiological feature of chronic heart failure (CHF). Patients with CHF are characterized by impaired vasodilation and inflammation of the vascular endothelium. They also have low levels of endothelial progenitor cells (EPCs). EPCs are bone marrow derived cells involved in endothelium regeneration, homeostasis, and neovascularization. Exercise has been shown to improve vasodilation and stimulate the mobilization of EPCs in healthy people and patients with cardiovascular comorbidities. However, the effects of exercise on EPCs in different stages of CHF remain under investigation.

AIM

To evaluate the effect of a symptom-limited maximal cardiopulmonary exercise testing (CPET) on EPCs in CHF patients of different severity.

METHODS

Forty-nine consecutive patients (41 males) with stable CHF [mean age (years): 56 ± 10, ejection fraction (EF, %): 32 ± 8, peak oxygen uptake (VO2, mL/kg/min): 18.1 ± 4.4] underwent a CPET on a cycle ergometer. Venous blood was sampled before and after CPET. Five circulating endothelial populations were quantified by flow cytometry: Three subgroups of EPCs [CD34+/CD45-/CD133+, CD34+/CD45-/CD133+/VEGFR2 and CD34+/CD133+/vascular endothelial growth factor receptor 2 (VEGFR2)] and two subgroups of circulating endothelial cells (CD34+/CD45-/CD133- and CD34+/CD45-/CD133-/VEGFR2). Patients were divided in two groups of severity according to the median value of peak VO2 (18.0 mL/kg/min), predicted peak VO2 (65.5%), ventilation/carbon dioxide output slope (32.5) and EF (reduced and mid-ranged EF). EPCs values are expressed as median (25th-75th percentiles) in cells/106 enucleated cells.

RESULTS

Patients with lower peak VO2 increased the mobilization of CD34+/CD45-/CD133+ [pre CPET: 60 (25-76) vs post CPET: 90 (70-103) cells/106 enucleated cells, P < 0.001], CD34+/CD45-/CD133+/VEGFR2 [pre CPET: 1 (1-4) vs post CPET: 5 (3-8) cells/106 enucleated cells, P < 0.001], CD34+/CD45-/CD133- [pre CPET: 186 (141-361) vs post CPET: 488 (247-658) cells/106 enucleated cells, P < 0.001] and CD34+/CD45-/CD133-/VEGFR2 [pre CPET: 2 (1-2) vs post CPET: 3 (2-5) cells/106 enucleated cells, P < 0.001], while patients with higher VO2 increased the mobilization of CD34+/CD45-/CD133+ [pre CPET: 42 (19-73) vs post CPET: 90 (39-118) cells/106 enucleated cells, P < 0.001], CD34+/CD45-/CD133+/VEGFR2 [pre CPET: 2 (1-3) vs post CPET: 6 (3-9) cells/106 enucleated cells, P < 0.001], CD34+/CD133+/VEGFR2 [pre CPET: 10 (7-18) vs post CPET: 14 (10-19) cells/106 enucleated cells, P < 0.01], CD34+/CD45-/CD133- [pre CPET: 218 (158-247) vs post CPET: 311 (254-569) cells/106 enucleated cells, P < 0.001] and CD34+/CD45-/CD133-/VEGFR2 [pre CPET: 1 (1-2) vs post CPET: 4 (2-6) cells/106 enucleated cells, P < 0.001]. A similar increase in the mobilization of at least four out of five cellular populations was observed after maximal exercise within each severity group regarding predicted peak, ventilation/carbon dioxide output slope and EF as well (P < 0.05). However, there were no statistically significant differences in the mobilization of endothelial cellular populations between severity groups in each comparison (P > 0.05).

CONCLUSION

Our study has shown an increased EPCs and circulating endothelial cells mobilization after maximal exercise in CHF patients, but this increase was not associated with syndrome severity. Further investigation, however, is needed.

Circulating stem cells and cardiovascular outcomes: from basic science to the clinic

The cardiovascular and haematopoietic systems have fundamental inter-relationships during development, as well as in health and disease of the adult organism. Although haematopoietic stem cells (HSCs) emerge from a specialized haemogenic endothelium in the embryo, persistence of haemangioblasts in adulthood is debated. Rather, the vast majority of circulating stem cells (CSCs) is composed of bone marrow-derived HSCs and the downstream haematopoietic stem/progenitors (HSPCs). A fraction of these cells, known as endothelial progenitor cells (EPCs), has endothelial specification and vascular tropism. In general, the levels of HSCs, HSPCs, and EPCs are considered indicative of the endogenous regenerative capacity of the organism as a whole and, particularly, of the cardiovascular system. In the last two decades, the research on CSCs has focused on their physiologic role in tissue/organ homoeostasis, their potential application in cell therapies, and their use as clinical biomarkers. In this review, we provide background information on the biology of CSCs and discuss in detail the clinical implications of changing CSC levels in patients with cardiovascular risk factors or established cardiovascular disease. Of particular interest is the mounting evidence available in the literature on the close relationships between reduced levels of CSCs and adverse cardiovascular outcomes in different cohorts of patients. We also discuss potential mechanisms that explain this association. Beyond CSCs' ability to participate in cardiovascular repair, levels of CSCs need to be interpreted in the context of the broader connections between haematopoiesis and cardiovascular function, including the role of clonal haematopoiesis and inflammatory myelopoiesis.

Antifibrotic and Regenerative Effects of Treamid in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease characterized by interstitial fibrosis and progressive respiratory failure. Pirfenidone and nintedanib slow down but do not stop the progression of IPF. Thus, new compounds with high antifibrotic activity and simultaneously regenerative activity are an unmet clinical need. Recently, we showed that Treamid can help restoring the pancreas and testicular tissue in mice with metabolic disorders. We hypothesized that Treamid may be effective in antifibrotic therapy and regeneration of damaged lung tissue in pulmonary fibrosis. In this study, experiments were performed on male C57BL/6 mice with bleomycin-induced pulmonary fibrosis. We applied histological and immunohistochemical methods, ELISA, and assessed the expression of markers of endothelial and epithelial cells in primary cultures of CD31⁺ and CD326⁺ lung cells. Finally, we evaluated esterase activity and apoptosis of lung cells in vitro. Our data indicate that Treamid exhibits antifibrotic activity in mice with pulmonary fibrosis and has a positive effect on capillaries of the lungs. Treamid also increases the number of endothelial progenitor cells in the lungs of animals with pulmonary fibrosis. Lastly, Treamid increases esterase activity and decreases apoptosis of CD31⁺ lung cells in vitro. Based on these findings, we suggest that Treamid may represent a promising compound for the development of new antifibrotic agents, which are capable of stimulating regeneration of lung endothelium in IPF patients.

Effects of Exercise Training on the Paracrine Function of Circulating Angiogenic Cells

Exercise training has various benefits on cardiovascular health, and circulating angiogenic cells have been proposed as executing these changes. Work from the late 1990s supported an important role of these circulating post-natal cells in contributing to the maintenance and repair of the endothelium and vasculature. It was later found that circulating angiogenic cells were a heterogenous population of cells and primarily functioned in a paracrine manner by adhering to damaged endothelium and releasing growth factors. Many studies have discovered novel circulating angiogenic cell secreted proteins, microRNA and extracellular vesicles that mediate their angiogenic potential, and some studies have shown that both acute and chronic aerobic exercise training have distinct benefits. This review highlights work establishing an essential role of secreted factors from circulating angiogenic cells and summarizes studies regarding the effects of exercise training on these factors. Finally, we highlight the various gaps in the literature in hopes of guiding future work.

Rab27a deletion impairs the therapeutic potential of endothelial progenitor cells for myocardial infarction

Endothelial progenitor cell (EPC) transplantation has shown advantages in the treatment of myocardial infarction (MI) in animal models and clinical trials through mechanisms of direct intercellular contacts, autocrine, and paracrine. However, the effects of EPC transplantation for MI treatment remain controversial and the underlying mechanisms have not been fully elucidated. Here, we explored the role of Rab27a in the therapeutic potential of EPC transplantation in MI. We found that Rab27a knockout impaired the viability, and reduced the proliferation and tube formation function of ECPs. The recovery of cardiac function and improvement of ventricular remodeling from EPCs transplantation were significantly damaged by Rab27a deletion in vivo. Rab27a deletion inhibited the protein expression of phosphoinositide 3-kinase (PI3K) and cyclin D1 and the phosphorylation levels of Akt and FoxO3a. Therefore, Rab27a knockout suppressed the PI3K-Akt-FoxO3a/cyclin D1 signaling pathway. Furthermore, Rab27a ablation dramatically reduced exosome release in EPCs. These results demonstrated that Rab27a plays an essential role in EPC functions. The elucidation of this mechanism provides novel insights into EPC transplantation as a promising treatment for post-MI injuries.

Notch pathway activation mediated the senescence of endothelial progenitor cells in hypercholesterolemic mice

Hyperlipidemia is an important factor in the induction of cardiovascular diseases. However, the molecular mechanisms underlying the vascular injury involved in hyperlipidemia remains unclear. This study aimed to investigate the Notch pathway of endothelial progenitor cells (EPCs) in reendothelialization after vascular injury and to explore the involvement of Notch pathway in the senescence of EPCs. Our results demonstrated that high-fat diet (HFD) treatment inhibited reendothelialization after vascular injury in the mice model. In vitro studies showed that 7-ketocholesterol (7-keto) stimulation induced senescence in the isolated EPCs from mice. In addition, 7-keto markedly upregulated the protein expression of Notch1 and Delta-like ligand 4 and induced the transport of notch intracellular domain (NICD) to the nucleus. Mechanistically, treatment with NICD inhibitor reduced the senescence of the EPCs stimulated by cholesterol. In summary, our results showed that HFD treatment caused the disruption of reendothelialization after vascular injury in the mouse model. In vitro studies indicated that 7-keto-induced senescence of EPCs was at least via the activation of the Notch1 pathway. Mechanistic data suggested that 7-keto may activate the Notch1 pathway by regulating the generation and transport of NICD to the nucleus. Future investigations are warranted to confirm the role of Notch1 in the dysfunction of EPCs during obesity.

Bicuspid Aortic Valve and Endothelial Dysfunction: Current Evidence and Potential Therapeutic Targets

Bicuspid aortic valve (BAV), the most frequent congenital heart malformation, is characterized by the presence of a two-leaflet aortic valve instead of a three-leaflet one. BAV disease progression is associated with valvular dysfunction (in the form of stenosis or regurgitation) and aortopathy, which can lead to aneurysm and aortic dissection. This morphological abnormality modifies valve dynamics and promotes eccentric blood flow, which gives rise to alterations of the flow pattern and wall shear stress (WSS) of the ascending aorta. Recently, evidence of endothelial dysfunction (ED) in BAV disease has emerged. Different studies have addressed a reduced endothelial functionality by analyzing various molecular biomarkers and cellular parameters in BAV patients. Some authors have found impaired functionality of circulating endothelial progenitors in these patients, associating it with valvular dysfunction and aortic dilation. Others focused on systemic endothelial function by measuring artery flow-mediated dilation (FMD), showing a reduced FMD in BAV individuals. Novel biomarkers like increased endothelial microparticles (EMP), which are related to ED, have also been discovered in BAV patients. Finally, latest studies indicate that in BAV, endothelial-to-mesenchymal transition (EndoMT) may also be de-regulated, which could be caused by genetic, hemodynamic alterations, or both. Different hypothesis about the pathology of ED in BAV are nowadays being debated. Some authors blamed this impaired functionality just on genetic abnormalities, which could lead to a pathological aorta. Nevertheless, thanks to the development of new and high-resolution imaging techniques like 4D flow MRI, hemodynamics has gained great attention. Based on latest studies, alterations in blood flow seem to cause proper modification of the endothelial cells (ECs) function and morphology. It also seems to be associated with aortic dilation and decreased vasodilators expression, like nitric oxide (NO). Although nowadays ED in BAV has been reported by many, it is not clear which its main cause may be. Comprehending the pathways that promote ED and its relevance in BAV could help further understand and maybe prevent the serious consequences of this disease. This review will discuss the ED present in BAV, focusing on the latest evidence, biomarkers for ED and potential therapeutic targets (Figure 1).

Autologous Bone Marrow Mononuclear Cell Transplantation Therapy Improved Symptoms in Patients with Refractory Diabetic Sensorimotor Polyneuropathy via the Mechanisms of Paracrine and Immunomodulation: A Controlled Study

We recently reported that transplantation of autologous bone marrow mononuclear cells (BM-MNCs) may be an effective and promising therapy to treat refractory diabetic sensorimotor polyneuropathy (DSPN) in patients with type 2 diabetes mellitus (T2DM). This study was designed to investigate the potential mechanisms of BM-MNCs therapy, which recruited 60 patients with DSPN, 30 T2DM patients without complications, and 30 healthy control participants. All clinical parameters, the levels of inflammatory markers, and growth factors in the three groups were compared. Patients in DSPN group had higher level of tumor necrosis factor-α (TNF-α) (DSPN vs control, 412.90 ± 64.58 vs 374.81 ± 63.18 pg/mL, P < 0.01) and lower level of vascular endothelial growth factor (VEGF) (DSPN vs control, 140.93 ± 24.78 vs 157.39 ± 25.11 pg/mL, P < 0.01) than those in control group. DSPN group had the highest level of soluble intercellular adhesion molecule-1 (sICAM-1) among three groups (DSPN and DM vs control, 1477.56 ± 228.00 and 1342.17 ± 237.54 vs 1308.00 ± 200.94 ng/mL, P < 0.05). The level of nerve growth factor in the DSPN group was slightly lower than that in the DM group (DSPN vs DM, 3509.11 ± 438.39 vs 3734.87 ± 647.50 pg/mL, P < 0.05). All patients with DSPN received one intramuscular injection of BM-MNCs and clinical follow-ups after the therapy for 2 days, 1, 4, 12, 24, and 48 weeks. Neuropathic symptoms of foot pain, numbness, and weakness were significantly improved within 4 weeks after BM-MNCs injection. Patients with DSPN were divided into the responder (n = 35) and nonresponder groups (n = 19) based on the improvement of nerve conduction velocity at 12 weeks post-transplantation. Compared with nonresponders, responders were younger (57.3 ± 5.2 vs 62.0 ± 4.8, P < 0.01), had a shorter history of diabetes (7.1 ± 2.7 vs 11.2 ± 5.4 years, P < 0.01), and had higher numbers of mobilized CD34⁺ cells (17.61 ± 2.64 vs 14.79 ± 1.62 ×10⁵/L, P < 0.01) and BM-MNCs (12.05 ± 2.16 vs 9.84 ± 1.53 ×10⁸/L, P < 0.01). The levels of TNF-α and sICAM-1 decreased just after BM-MNCs injection in both groups and slowly reverted to baseline levels. The duration of the downtrend of TNF-α and sICAM-1 in the responder group lasted longer than that in the nonresponder group. Serum level of VEGF in the responder group increased immediately after BM-MNC therapy and reached the highest point after the injection for 12 weeks. On the other hand, VEGF levels in the nonresponder group only increased slightly. Binary logistic regression was performed to evaluate the corresponding prognostic factors for BM-MNCs treatment. The number of applied CD34⁺ cells and the duration of diabetes were the independent predictors of responding to BM-MNCs therapy. No adverse event associated with the treatment was observed during follow-up observations. These results indicated that BM-MNCs transplantation is an effective and promising therapeutic strategy to treat refractory DSPN. The immune regulation and paracrine function of BM-MNCs may contribute to the improvement of DSPN.

Circulating Progenitor Cells in Patients With Coronary Artery Disease and Renal Insufficiency

Patients with coronary artery disease and renal insufficiency (RI) (estimated glomerular filtration rate <60 ml/min/1.73 m²) are at an increased risk of cardiovascular events. The contribution of regenerative capacity, measured as circulating progenitor cell (CPC) counts, to this increased risk is unclear. CPCs were enumerated as cluster of differentiation (CD) 45^med+ mononuclear cells expressing CD34+, CD133+, CXCR4+ (chemokine [C-X-C motif] receptor 4), and VEGF2R+ (vascular endothelial growth factor receptor 2) epitopes in 1,281 subjects with coronary artery disease (35% with RI). Patients with RI and low (<median) hematopoietic CPCs (CD34+, CD34+/CD133+, and CD34+/CXCR4+) were at an increased risk of cardiovascular death or myocardial infarction events (hazard ratios: 1.75 to 1.80) during 3.5-year follow-up, while those with RI and high CPCs (>median) were at a similar risk as those without RI.

Vascular Remodeling in Moyamoya Angiopathy: From Peripheral Blood Mononuclear Cells to Endothelial Cells

The pathophysiological mechanisms of Moyamoya angiopathy (MA), which is a rare cerebrovascular condition characterized by recurrent ischemic/hemorrhagic strokes, are still largely unknown. An imbalance of vasculogenic/angiogenic mechanisms has been proposed as one possible disease aspect. Circulating endothelial progenitor cells (cEPCs) have been hypothesized to contribute to vascular remodeling of MA, but it remains unclear whether they might be considered a disease effect or have a role in disease pathogenesis. The aim of the present study was to provide a morphological, phenotypical, and functional characterization of the cEPCs from MA patients to uncover their role in the disease pathophysiology. cEPCs were identified from whole blood as CD45^dimCD34⁺CD133⁺ mononuclear cells. Morphological, biochemical, and functional assays were performed to characterize cEPCs. A significant reduced level of cEPCs was found in blood samples collected from a homogeneous group of adult (mean age 46.86 ± 11.7; 86.36% females), Caucasian, non-operated MA patients with respect to healthy donors (HD; p = 0.032). Since no difference in cEPC characteristics and functionality was observed between MA patients and HD, a defective recruitment mechanism could be involved in the disease pathophysiology. Collectively, our results suggest that cEPC level more than endothelial progenitor cell (EPC) functionality seems to be a potential marker of MA. The validation of our results on a larger population and the correlation with clinical data as well as the use of more complex cellular model could help our understanding of EPC role in MA pathophysiology.

Endothelial Overexpression of Metallothionein Prevents Diabetes-Induced Impairment in Ischemia Angiogenesis Through Preservation of HIF-1α/SDF-1/VEGF Signaling in Endothelial Progenitor Cells

Diabetes-induced oxidative stress is one of the major contributors to dysfunction of endothelial progenitor cells (EPCs) and impaired endothelial regeneration. Thus, we tested whether increasing antioxidant protein metallothionein (MT) in EPCs promotes angiogenesis in a hind limb ischemia (HLI) model in endothelial MT transgenic (JTMT) mice with high-fat diet- and streptozocin-induced diabetes. Compared with littermate wild-type (WT) diabetic mice, JTMT diabetic mice had improved blood flow recovery and angiogenesis after HLI. Similarly, transplantation of JTMT bone marrow-derived mononuclear cells (BM-MNCs) stimulated greater blood flow recovery in db/db mice with HLI than did WT BM-MNCs. The improved recovery was associated with augmented EPC mobilization and angiogenic function. Further, cultured EPCs from patients with diabetes exhibited decreased MT expression, increased cell apoptosis, and impaired tube formation, while cultured JTMT EPCs had enhanced cell survival, migration, and tube formation in hypoxic/hyperglycemic conditions compared with WT EPCs. Mechanistically, MT overexpression enhanced hypoxia-inducible factor 1α (HIF-1α), stromal cell-derived factor (SDF-1), and vascular endothelial growth factor (VEGF) expression and reduced oxidative stress in ischemic tissues. MT's pro-EPC effects were abrogated by siRNA knockdown of HIF-1α without affecting its antioxidant action. These results indicate that endothelial MT overexpression is sufficient to protect against diabetes-induced impairment of angiogenesis by promoting EPC function, most likely through upregulation of HIF-1α/SDF-1/VEGF signaling and reducing oxidative stress.