Therapeutic potential of endothelial progenitor cells in cardiovascular diseases

Endothelial cell transfusion ameliorates endothelial dysfunction in 5/6 nephrectomized rats

Endothelial dysfunction is prevalent in chronic kidney disease. This study tested the hypothesis that transfusion of rat aortic endothelial cells (ECs) ameliorates endothelial dysfunction in a rat model of chronic kidney disease. Male Sprague-Dawley rats underwent sham surgery or 5/6 nephrectomy (Nx). Five weeks after Nx, EC (1.5 × 10(6) cells/rat) or vehicle were transfused intravenously. One week later, vascular reactivity of mesenteric artery was assessed on a wire myograph. Sensitivity of endothelium-dependent relaxation to acetylcholine and maximum vasodilation were impaired by Nx and improved by EC transfusion. Using selective pharmacological nitric oxide synthase isoform inhibitors, we demonstrated that the negative effect of Nx on endothelial function and rescue by EC transfusion are, at least in part, endothelial nitric oxide synthase mediated. Plasma asymmetric dimethylarginine was increased by Nx and decreased by EC transfusion, whereas mRNA expression of dimethylarginine dimethylaminohydrolases 1 (DDAH1) was decreased by Nx and restored by EC transfusion. Immunohistochemical staining confirmed that local expression of DDAH1 is decreased by Nx and increased by EC transfusion. In conclusion, EC transfusion attenuates Nx-induced endothelium-dependent vascular dysfunction by regulating DDAH1 expression and enhancing endothelial nitric oxide synthase activity. These results suggest that EC-based therapy could provide a novel therapeutic strategy to improve vascular function in chronic kidney disease.

The challenges for cardiac vascular precursor cell therapy: lessons from a very elusive precursor

There is compelling evidence that cardiovascular disorders arise and/or progress due mainly to endothelial dysfunction. Novel therapeutic strategies aim to generate new myocardial tissue using cells with regenerative potential, either alone or in combination with biomaterials, cytokines and advanced monitoring devices. Among the human adult progenitor cells used in such methods, those historically termed 'endothelial progenitor cells' show promise for vascular growth and repair. Asahara et al. [Science 1997;275:964-967] initially described putative endothelial cell precursors in 1997. Subsequently, distinct cell populations termed endothelial colony-forming units-Hill, circulating angiogenic cells and endothelial colony-forming cells were identified that varied in terms of phenotype, vascular homeostasis contribution and purity. Notably, most of these cells are not genuine vascular precursor cells belonging to the endothelial lineage. This review provides a broad overview of the main properties of the endothelium, focusing on the basis governing its growth and repair. We discuss efforts to identify true vascular precursors, a matter of debate for the past 15 years, as well as recent methodological advances in identifying new hierarchies of more homogeneous, clonogenic and proliferative vascular endothelial-lineage precursors. Consideration of these issues provides insights that may help develop more effective therapies against human diseases that involve vascular deficits.

The therapeutic effect of vascular endothelial growth factor gene- or heme oxygenase-1 gene-modified endothelial progenitor cells on neovascularization of rat hindlimb ischemia model

OBJECTIVE

To explore the therapeutic potential of endothelial progenitor cells (EPCs) transfected with vascular endothelial growth factor A (VEGFA) and heme oxygenase-1 (HO-1) on rat hindlimb ischemia model.

METHODS

Eukaryotic expression vectors encoding VEGFA or HO-1 were constructed and introduced into EPCs isolated from rat bone marrow. In total, 150 Sprague Dawley rat hindlimb ischemia models were established and randomized into five groups which were injected via tail vein with phosphate-buffered saline (PBS), nontransfected EPCs, VEGFA-modified EPCs, HO-1-modified EPCs, and both VEGFA- and HO-1-modified EPCs, respectively. The microvessel density, the expressions of VEGFA and HO-1 in the ischemic limbs, the recovery of blood flow as evaluated by laser-Doppler perfusion imaging, and the rate of limb salvage were compared among different groups.

RESULTS

Transplantation of both VEGFA- and HO-1-modified EPCs in recipient rats significantly increased the microvessel density (expressed as capillaries/m(2) at day 21 after operation, group vascular endothelial growth factor (VEGF)+HO-1, 357 ± 14.1; group VEGF, 253.7 ± 9.9; group HO-1, 255.5 ± 12.5; group EPC, 210.7 ± 10.3; group PBS, 144.3 ± 9.3; P < .001), the expressions of VEGFA and HO-1 in ischemic tissue, the recovery of blood flow (at day 21, VEGF+HO-1 group, 85.4 ± 17.8%; VEGF group, 51.2 ± 13.2%; HO-1 group, 50.4 ± 12.9%; EPC group, 39.9 ± 8.5%; PBS group, 28.3 ± 7.8%; P < .001), and the rate of limb salvage (VEGF+HO-1 group, 94.4%; VEGF group or HO-1 group, 63.6%; EPC group, 50.0%; PBS group, 11.1%), compared with transplantation of either VEGFA- or HO-1-modified EPCs alone, or of nontransfected EPCs, or PBS injection. The order of therapeutic effectiveness on ischemic limbs was VEGFA- + HO-1-modifed EPC > either VEGFA- or HO-1-modified EPC alone > nontransfected EPC > PBS.

CONCLUSIONS

VEGFA-modified EPC and HO-1-modified EPC synergized with each other in promoting angiogenesis in ischemic limbs of rat hindlimb ischemia model. In addition to VEGF, the introduction of HO-1 in EPC-based transplantation may serve as a novel and useful therapeutic strategy for ischemic disease of lower extremity.

Bone marrow transplantation improves endothelial function in hypertensive Dahl salt-sensitive rats

Bone marrow-derived endothelial progenitor cells (EPCs) constitute an important endogenous system in the maintenance of endothelial integrity and vascular homeostasis. Cardiovascular risk factors are associated with a reduced number and functional capacity of EPCs. Here we investigated the effect of transplantation of bone marrow-derived cells from Dahl salt-resistant rat into age-matched Dahl salt-sensitive (DS) rat on blood pressure, endothelial function, and circulating EPC number. The recipient DS rats were fed a normal (0.5% NaCl, NS) or high-salt (4% NaCl, HS) diet for 6 weeks after bone marrow transplantation (BMT). DS rats on a NS or a HS diet without BMT were used as controls. Hypertensive DS (HS-DS) rat (systolic blood pressure: 213 ± 4 mm Hg vs. 152 ± 4 mm Hg in NS, P < .05) manifested impaired endothelium-dependent relaxation to acetylcholine (EDR), increased gene expression of vascular oxidative stress and proinflamamtory cytokines, and decreased eNOS expression. BMT on HS-DS rat significantly improved EDR and eNOS expression, reduced oxidative stress without reduction in SBP (206 ± 6 mm Hg). Flow cytometry analysis showed that there was no difference in the number of circulating EPCs, demonstrated by expression of EPC markers CD34, cKit, and vascular endothelial growth factor, between hypertensive and normotensive rats. Surprisingly, BMT resulted in a 5- to 10-fold increase in the previously mentioned EPC markers in hypertensive, but not normotensive rat. These results suggest that DS rat has an impaired ability to increase bone marrow-derived EPCs in response to HS diet challenge, which may contribute to endothelial dysfunction.

First in vitro and in vivo results of an anti-human CD133-antibody coated coronary stent in the porcine model

BACKGROUND

Drug-eluting stents successfully reduce restenosis at the cost of delayed re-endothelialization. A novel concept to enhance re-endothelialization is the use of antibody-coated stents which capture circulating progenitor cells. A CD34-positive-cell-capturing stent was recently developed with conflicting clinical results. CD133 is a glycoprotein expressed on circulating hematopoietic and putative endothelial-regenerating cells and may be superior to CD34.

OBJECTIVE

The aim of our study was to develop a CD133-cell-capturing bare-metal stent and investigate feasibility, safety, and efficacy of CD133-stents in terms of re-endothelialization and neointima inhibition.

METHODS AND RESULTS

Anti-human CD133-antibodies were covalently attached to bare-metal stents. In vitro, binding capacity of CD133-stents was studied, revealing a significantly higher affinity of human CD133-positive cells to CD133-stents compared with mononuclear cells (MNCs). In vivo, 15 landrace pigs received BMS and CD133-stents in either RCX or LAD (n = 30 stents). Re-endothelialization was examined on day 1 (n = 4), 3 (n = 4) and day 7 (n = 4) using scanning electron microscopy. In histology, injury and inflammatory scores, as well as diameter restenosis were evaluated after day 7 (n = 3), 14 (n = 4), and 28 (n = 2). Overall no reduction in re-endothelialization, diameter stenosis or inflammatory score was seen with CD133-stents.

CONCLUSION

Stent coating with anti-human CD133-antibodies was successfully achieved with effective binding of CD133-positive cells. However, in vivo, no difference in re-endothelialization or neointima formation was evident with the use of CD133-stents compared with BMS. The low number of circulating CD133-positive cells and an increase in unspecific binding of MNCs over time may account for the observed lack of efficacy.

Relationship between circulating endothelial progenitor cells and endothelial dysfunction in children with type 1 diabetes: a novel paradigm of early atherosclerosis in high-risk young patients

OBJECTIVE

The low number of circulating endothelial progenitor cells (EPCs) has emerged as a biomarker of cardiovascular (CV) risk in adults. Data regarding EPCs in paediatric populations with CV risk factors are limited. The aim of the study was to estimate the EPC number and its relationship with vascular function and structure in children with type 1 diabetes mellitus (T1DM).

DESIGN AND METHODS

We performed a comparative analysis of 52 children with T1DM (mean age 14.5 years; diabetes duration, 6.0 years; HbA1c level, 8.5%) and 36 healthy age- and gender-matched control children. EPCs were identified and analysed by flow cytometry with the use of MABs directed against CD34, CD144 (VE-cadherin) and CD309 (VEGFR-2). sICAM-1, hsCRP, thrombomodulin and adiponectin levels were also assessed. We evaluated vascular function (flow-mediated dilation (FMD)) and structure (carotid intima-media thickness (IMT)) ultrasonographically.

RESULTS

Frequencies of CD34+ cells were similar in both groups (P=0.30). In contrast, frequencies of CD34+VE-cadherin+ cells were significantly higher in diabetic children compared with the healthy group (P=0.003). Similarly, diabetic patients tended to present with higher frequencies of CD34+VEGFR+ cells (P=0.06). FMD was lower (6.9 vs 10.5%, P=0.002) and IMT was higher (0.50 vs 0.44 mm, P=0.0006) in diabetic children. We demonstrated a significant relationship between CD34+VEGFR-2+ cells and BMI (r=0.3, P=0.014), HDL (r=-0.27, P=0.04), sICAM-1 (r=0.47, P=0.023) and FMD (r=-0.45, P<0.001). Similarly, frequencies of CD34+VE-cadherin+ cells were significantly correlated with BMI (r=0.32, P=0.02) and FMD (r=-0.31, P=0.03).

CONCLUSIONS

We demonstrated here that increased frequencies of EPCs observed in diabetic children are negatively correlated with endothelial function. Further studies are warranted to assess whether this phenomenon might result from effective mobilisation of EPCs in order to repair damaged endothelium in children at increased risk for atherosclerosis.

Endothelial cells derived from nuclear reprogramming

The endothelium plays a pivotal role in vascular homeostasis, regulating the tone of the vascular wall, and its interaction with circulating blood elements. Alterations in endothelial functions facilitate the infiltration of inflammatory cells and permit vascular smooth muscle proliferation and platelet aggregation. Therefore, endothelial dysfunction is an early event in disease processes including atherosclerosis, and because of its critical role in vascular health, the endothelium is worthy of the intense focus it has received. However, there are limitations to studying human endothelial function in vivo, or human vascular segments ex vivo. Thus, methods for endothelial cell (EC) culture have been developed and refined. Recently, methods to derive ECs from pluripotent cells have extended the scientific range of human EC studies. Pluripotent stem cells may be generated, expanded, and then differentiated into ECs for in vitro studies. Constructs for molecular imaging can also be employed to facilitate tracking these cells in vivo. Furthermore, one can generate patient-specific ECs to study the effects of genetic or epigenetic alterations on endothelial behavior. Finally, there is the opportunity to apply these cells for vascular therapy. This review focuses on the generation of ECs from stem cells; their characterization by genetic, histological, and functional studies; and their translational applications.

Altered profile of circulating endothelial progenitor cells in obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is independently associated with endothelial dysfunction, which may be perpetuated by alteration in endothelial repair capacity. Our study evaluates changes in endothelial progenitor cell (EPC) profile in relation to OSA and the role of advanced glycation end-products (AGE) in this relationship.

Methods

Consecutive Chinese adults undergoing sleep studies, who had no medical illnesses or regular medications, were enrolled. Subjects with morbid obesity or grossly elevated lipoprotein levels were excluded from analysis. Circulating EPC was measured with flow cytometry analysis.

Results

Seventy-two subjects, 64 % with OSA defined by apnea–hypopnea index (AHI) ≥ 5, were analyzed. CD34+ cell counts were positively correlated with oxygen desaturation index (ODI) (r = 0.250, p = 0.041) and duration of oxygen desaturation <90 % (T90) (r = 0.261, p = 0.033) and negatively with minimal oxygen saturation (r = −0.247, p = 0.044) after adjusting for age, glucose, body weight, and smoking status. AGE was positively correlated with indices of OSA severity (AHI, r = 0.249, p = 0.042; ODI, r = 0.244, p = 0.047; T90, r = 0.243, p = 0.047; minimal oxygen saturation, r = −0.251, p = 0.041) and negatively with CD133+ cells (r = −0.281, p = 0.021). On stepwise multiple linear regression analysis, minimal oxygen saturation (p = 0.013) and CD133+ cell counts (p = 0.029) were found to be significant determinants of AGE level (R² = 0.147).

Conclusions

Nocturnal hypoxemia in OSA subjects was associated with increase in endothelial cells (CD34+) which may promote vascular repair. Accumulation of AGE in OSA may lead to diminution in early EPC (CD133+) and endothelial repair capacity over time, thus contributing to vascular pathogenesis.

A novel autologous cell-based therapy to promote diabetic wound healing

OBJECTIVES

We have previously shown that stromal cell-derived factor-1α (SDF-1α) is downregulated within diabetic cutaneous wounds, and that direct application of recombinant SDF-1α increases wound closure rates, neovascularization, and endothelial progenitor cell (EPC) recruitment. However, increased wound levels of exogenous SDF-1α results in elevated systemic levels of this proangiogenic chemokine that raises concerns for tumorigenesis and inflammation. We now seek to test the efficacy of a novel, safer cell-based therapy (CBT) employing ex vivo primed bone marrow-derived stem cells (BMDSC) with SDF-1α. We also elucidate the mechanism of action of this new approach for accelerating diabetic wound healing.

METHODS

Unfractionated BMDSC from diabetic Lepr mice were incubated for 20 hours with SDF-1α (100 ng/mL) or bovine serum albumin (control). Pretreated BMDSC (1 × 10) were injected subcutaneously into full-thickness skin wounds in Lepr mice (n = 8 per group). Wound closure rates, capillary density, and the recruitment of EPC were assessed with serial photography, DiI perfusion, confocal microscopy, and immunohistochemistry. The expression of molecular targets, which may mediate prohealing/proangiogenic effects of SDF-1α-primed BMDSC was evaluated by polymerase chain reaction array and immunoblotting assay. The biological function of a potential mediator was tested in a mouse wound-healing model. Serum SDF-1α levels were measured with enzyme-linked immunosorbent assay (ELISA).

RESULTS

SDF-1α-primed BMDSC significantly promote wound healing (P < 0.0001), neovascularization (P = 0.0028), and EPC recruitment (P = 0.0059). Gene/protein expression studies demonstrate upregulation of Ephrin Receptor B4 and plasminogen as downstream targets potentially mediating the prohealing and proangiogenic responses. Ex vivo BMDSC activation and the subsequent inoculation of cells into wounds does not increase systemic SDF-1α levels.

CONCLUSIONS

We report a novel CBT that is highly effective in promoting healing and neovascularization in a murine model of type 2 diabetes. Furthermore, we identify new molecular targets that may be important for advancing the field of wound healing.

Histone deacetylase (HDAC) inhibitors down-regulate endothelial lineage commitment of umbilical cord blood derived endothelial progenitor cells

To test the involvement of histone deacetylases (HDACs) activity in endothelial lineage progression, we investigated the effects of HDAC inhibitors on endothelial progenitors cells (EPCs) derived from umbilical cord blood (UCB). Adherent EPCs, that expressed the endothelial marker proteins (PCAM-1, CD105, CD133, and VEGFR₂) revealed by flow cytometry were treated with three HDAC inhibitors: Butyrate (BuA), Trichostatin A (TSA), and Valproic acid (VPA). RT-PCR assay showed that HDAC inhibitors down-regulated the expression of endothelial genes such as VE-cadherin, CD133, CXCR4 and Tie-2. Furthermore, flow cytometry analysis illustrated that HDAC inhibitors selectively reduce the expression of VEGFR₂, CD117, VE-cadherin, and ICAM-1, whereas the expression of CD34 and CD45 remained unchanged, demonstrating that HDAC is involved in endothelial differentiation of progenitor cells. Real-Time PCR demonstrated that TSA down-regulated telomerase activity probably via suppression of hTERT expression, suggesting that HDAC inhibitor decreased cell proliferation. Cell motility was also decreased after treatment with HDAC inhibitors as shown by wound-healing assay. The balance of acethylation/deacethylation kept in control by the activity of HAT (histone acetyltransferases)/HDAC enzymes play an important role in differentiation of stem cells by regulating proliferation and endothelial lineage commitment.

Endothelial progenitor cells homing to the orthotopic implanted liver tumor of nude mice

This study investigated the "homing" phenomenon in hepatocellular carcinoma (HCC). The "homing" specificity of endothelial progenitor cells (EPC) by establishing an orthotopic implantation model in nude mice. EPCs harvested from the marrow cells were separated by density gradient centrifugation. Fluorescence microscope, flow cytometry (FCM) and double fluorescence staining with FITC-UEA-I and DiI-ac-LDL, were employed to identify the cells. 4',6-diamidino-2-phenylindole (DAPI) labelling and real-time PCR were used for detecting the expression of CD133 and chemokines to trace and observe the distribution of EPCs. Our results showed that the distribution rate of EPCs was obviously higher than that in other important organs and the negative control group. Detection of CD133 and chemokines yielded similar results in difference tissues. Our experiment confirmed that the chemotaxis of EPCs does exist in HCC. Moreover, HIF-1α, SDF-1 and VEGF might play important roles in the "homing" of EPCs in HCC. EPCs might be a potential candidate for targeting vector of HCC for gene therapy.

Aging-related decrease of human ASC angiogenic potential is reversed by hypoxia preconditioning through ROS production

Adipose stroma/stem cells (ASC) represent an ideal source of autologous cells for cell-based therapy. Their transplantation enhances neovascularization after experimental ischemic injury. Aging is associated with a progressive decrease in the regenerative potential of mesenchymal stem cells (MSCs) from bone marrow. This work aims to determine the aging effect on human ASC capacities. First, we show that aging impairs angiogenic capacities of human ASC (hASC) in a mouse ischemic hindlimb model. Although no change in hASC number, phenotype, and proliferation was observed with aging, several mechanisms involved in the adverse effects of aging have been identified in vitro combining a concomitant decrease in (i) ASC ability to differentiate towards endothelial cells, (ii) secretion of proangiogenic and pro-survival factors, and (iii) oxidative stress. These effects were counteracted by a hypoxic preconditioning that improved in vivo angiogenic capacities of hASC from older donors, while hASC from young donors that have a strong ability to manage hypoxic stress were not. Finally, we identified reactive oxygen species (ROS) generation as a key signal of hypoxia on hASC angiogenic capacities. This study demonstrates for the first time that age of donor impaired angiogenic capacities of hASC in ischemic muscle and change in ROS generation by hypoxic preconditioning reverse the adverse effect of aging.

Understanding vascular development

The vasculature of an organism has the daunting task of connecting all the organ systems to nourish tissue and sustain life. This complex network of vessels and associated cells must maintain blood flow, but constantly adapt to acute and chronic changes within tissues. While the vasculature has been studied for over a century, we are just beginning to understand the processes that regulate its formation and how genetic hierarchies are influenced by mechanical and metabolic cues to refine vessel structure and optimize efficiency. As we gain insights into the developmental mechanisms, it is clear that the processes that regulate blood vessel development can also enable the adult to adapt to changes in tissues that can be elicited by exercise, aging, injury, or pathology. Thus, research in vessel development has provided tremendous insights into therapies for vascular diseases and disorders, cancer interventions, wound repair and tissue engineering, and in turn, these models have clearly impacted our understanding of development. Here we provide an overview of the development of the vascular system, highlighting several areas of active investigation and key questions that remain to be answered.

Genetic module and miRNome trait analyses reflect the distinct biological features of endothelial progenitor cells from different anatomic locations

Background

Endothelial progenitor cells (EPCs) play a fundamental role in post-natal vascular repair, yet EPCs from different anatomic locations possess unique biological properties. The underlying mechanisms are unclear.

Results

EPCs from CB expressed abundant genes involved in cell cycle, hypoxia signalling and blood vessel development, correlating with the phenotypes that CB-EPCs proliferated more rapidly, migrated faster, and formed tubule structure more efficiently. smRNA-seq further deciphered miRNome patterns in EPCs isolated from CB or PB: 54 miRNAs were enriched in CB-EPCs, while another 50 in PB-EPCs. Specifically, CB-EPCs expressed more angiogenic miRNAs such as miR-31, while PB-EPCs possessed more tumor suppressive miRNAs including miR-10a. Knocking down miR-31 levels in CB-EPCs suppressed cell migration and microtubule formation, while overexpressing miR-31 in PB-EPCs helped to recapitulate some of CB-EPC functions.

Conclusions

Our results show the foundation for a more detailed understanding of EPCs from different anatomic sources. Stimulating the expression of angiogenic microRNAs or genes in EPCs of low activity (such as those from patients with cardiovascular diseases) might allow the development of novel therapeutic strategies.

A novel tissue engineering approach using an endothelial progenitor cell–seeded biopolymer to treat intracranial saccular aneurysms

Object

Recurrence after endovascular coiling of intracranial aneurysms is reported in up to 42% of cases and is attributed to the lack of endothelialization across the neck. In this study the authors used a novel tissue engineering approach to promote endothelialization by seeding endothelial progenitor cells (EPCs) within a fibrin polymer injected endovascularly into the aneurysm.

Methods

Experimental aneurysms were created in New Zealand White rabbits and were left untreated, surgically clipped, or embolized with platinum coils, fibrin biopolymer alone, or fibrin combined with autologous cultured EPCs.

Results

In aneurysms treated with EPCs, a confluent monolayer of endothelial cells with underlying neointima was demonstrated across the neck at 16 weeks posttreatment, which was not observed with aneurysms treated using the other methods.

Conclusions

This novel technique may address reasons for the limited durability of standard coil embolization and provides further avenues for the development of improved devices for the care of patients with aneurysms.

Age-related decline in reendothelialization capacity of human endothelial progenitor cells is restored by shear stress

Aging is associated with dysfunction of endothelial progenitor cells (EPCs), and shear stress has a beneficial impact on EPC function; however, the effects of aging and shear stress on the endothelial repair capacity of EPCs after arterial injury have not been reported. Here we investigated the influence of aging and shear stress on the reendothelialization capacity of human EPCs and the related molecular mechanism. Compared with EPCs isolated from young subjects, EPCs from the elderly displayed an impaired migration and adhesion in vitro and demonstrated a significantly reduced reendothelialization capacity in vivo after transplantation into nude mice with carotid artery denudation injury. Shear stress pretreatment enhances the migration, adhesion, and reendothelialization capacity in both young and elderly EPCs; however, it was to a greater extent in EPCs from the elderly. Although basal CXC chemokine receptor 4 (CXCR4) expression was similar in EPCs from the 2 age groups, the stromal cell derived factor 1-induced CXCR4 and Janus kinase 2 phosphorylations were much lower in the elderly than in young EPCs. Shear stress treatment upregulated CXCR4 expression and phosphorylation and, importantly, restored the stromal cell-derived factor 1/CXCR4-dependent Janus kinase 2 phosphorylation in the elderly EPCs. Furthermore, short hairpin RNA-mediated knockdown of CXCR4 expression or pretreatment with Janus kinase 2 inhibitor diminished the enhancement in the migration, adhesion, and reendothelialization capacity of the elderly EPCs from shear stress treatments. Thus, our study demonstrates that upregulation of the CXCR4/Janus kinase 2 pathway by shear stress contributes to the enhanced reendothelialization capacity of EPCs from elderly men.

A potent soluble epoxide hydrolase inhibitor, t-AUCB, acts through PPARγ to modulate the function of endothelial progenitor cells from patients with acute myocardial infarction

BACKGROUND

Epoxyeicosatrienoic acids (EETs) are natural angiogenic mediators regulated by soluble epoxide hydrolase (sEH). Inhibitors of sEH can stabilize EETs levels and were reported to reduce atherosclerosis and inhibit myocardial infarction in animal models. In this work, we investigated whether increasing EETs with the sEH inhibitor t-AUCB would increase angiogenesis related function in endothelial progenitor cells (EPCs) from patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

EPCs were isolated from 50 AMI patients and 50 healthy subjects (control). EPCs were treated with different concentrations of t-AUCB for 24h with or without peroxisome proliferator activated receptor γ (PPARγ) inhibitor GW9662. Migration of EPCs was assayed in trans-well chambers. Angiogenesis assays were performed using a Matrigel-Matrix in vitro model. The expression of vascular endothelial growth factor (VEGF), hypoxia-inducible factor 1α (HIF-1α) mRNA and protein in EPCs was measured by real-time PCR or Western blot, respectively. Also, the concentration of EETs in the culture supernatant was detected by ELISA. The activity of EPCs in the AMI patient group was reduced compared to healthy controls. Whereas increasing EET levels with t-AUCB promoted a dose dependent angiogenesis and migration in EPCs from AMI patients. Additionally, the t-AUCB dose dependently increased the expression of the angiogenic factors VEGF and HIF-α. Lastly, we provide evidence that these effects were PPARγ dependent.

CONCLUSION

The results demonstrate that the sEH inhibitor positively modulated the functions of EPCs in patients with AMI through the EETs-PPARγ pathway. The present study suggests the potential utility of sEHi in the therapy of ischemic heart disease.

The effect of endothelial progenitor cells on angiotensin II-induced proliferation of cultured rat vascular smooth muscle cells

Previous studies have demonstrated that endothelial progenitor cells (EPCs) could delay the progress of vascular remodeling in blood vessel-proliferating diseases. The proliferation of vascular smooth muscle cells (VSMCs) is a pivotal factor in cardiovascular diseases. In this study, we investigated whether EPCs could inhibit the Angiotensin II (Ang II)-induced proliferation of VSMCs. The effect of early EPC-conditioned medium (E-EPC-CM), late EPCs-CM (L-EPC-CM), and HUVEC-CM on Ang II-induced proliferation of VSMCs was assessed by BrdU incorporation, total protein content, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, and flow cytometry. Reverse transcriptase-polymerase chain reaction and Western blot were performed to analyze the effect of different CMs on Ang II-induced phosphorylations of ERK, JNK, p38, and NF-κB subunit p65 and the expressions of c-myc and c-fos. E-EPC-CM, L-EPC-CM, and HUVEC-CM significantly inhibited the Ang II-induced DNA synthesis, total protein expression, cell survival, and cell cycle progress of VSMCs. Furthermore, E-EPC-CM significantly inhibited the Ang II-induced phosphorylation of ERK, JNK, p38, and p65 (nuclear translocation of p65) and the expressions of c-myc and c-fos. Taken together, these data suggested that EPCs may delay the progress of vascular remodeling in blood vessel-proliferating diseases by inhibiting Ang II-induced proliferation of VSMCs through inactivating MAPKs and NF-κB signaling pathways and by reducing the expressions of c-myc and c-fos.

Inhaled NO contributes to lung repair in piglets with acute respiratory distress syndrome via increasing circulating endothelial progenitor cells

Background

Nitric oxide (NO) plays an important role in mobilization of endothelial progenitor cells (EPCs). We hypothesized that inhaled NO (iNO) would induce EPC mobilization and therefore promote lung repair in acute respiratory distress syndrome (ARDS).

Methodology/Principal Findings

Healthy piglets were randomized into four groups (n = 6): Control (Con; mechanical ventilation only); ARDS (established by oleic acid infusion and mechanical ventilation); ARDS plus granulocyte-colony stimulating factor (G-CSF; 10 µg/kg/d subcutaneously); ARDS plus NO inhalation (iNO; 10 ppm). EPCs and mobilizing cytokines were assayed at different time points (baseline, 0, 24, 72 and 168 h) and injury reparation was assessed at 168 h. Compared to the Con group, the levels of EPCs were increased in bone marrow but not in blood in the ARDS group at 24 h. Compared to the ARDS group, inhaled NO induced a rapid elevation in the number of CD34⁺KDR⁺, KDR⁺CD133⁺ and CD34⁺KDR⁺CD133⁺ EPCs in blood (2163±454 vs. 1094±416, 1302±413 vs. 429±244, 1140±494 vs. 453±273 cells/ml, respectively, P<0.05), and a reduction in the percentage of KDR⁺CD133⁺ cells in bone marrow. Lung CD34, CD133, VEGF, VEGF receptor 2, endothelial NO synthase mRNA, and VEGF and VEGF receptor 2 protein expression levels were augmented in the iNO group, but not in the G-CSF group, compared to ARDS. Furthermore, iNO treatment reduced vascular permeability, increased pulmonary vessel density, and alleviated pulmonary edema and inflammation compared to ARDS treatment. Plasma VEGF, stromal cell-derived factor-1 (SDF-1) and bone marrow NO₂⁻/NO₃⁻ were significantly higher in the iNO group compared to the ARDS group at 72 h.

Conclusions

These results suggest that iNO induces mobilization of EPCs from bone marrow into circulation, contributes to vascular repair, and thereby alleviates lung damage.

Endothelin 1 activation of endothelin A receptor/NADPH oxidase pathway and diminished antioxidants critically contribute to endothelial progenitor cell reduction and dysfunction in salt-sensitive hypertension

Circulating endothelial progenitor cells (EPCs) are reduced in hypertension, which inversely correlates with its mortality. Deoxycorticosterone acetate (DOCA)-salt hypertension features elevated endothelin (ET) 1 and oxidative stress. We tested the hypothesis that ET-1 induces EPC dysfunction by elevating oxidative stress through the ET(A)/NADPH oxidase pathway in salt-sensitive hypertension. Both ET(A) and ET(B) receptors were expressed in EPCs, but only ET(A) receptors were significantly increased in EPCs of DOCA-salt rats. EPC number and function were reduced in DOCA-salt rats compared with sham controls, and both were reversed by in vivo blockade of ET(A) receptors or NADPH oxidase. The enzymatic activities of NAPDH oxidase and its subunits gp91(phox), p22(phox), and Rac1 were augmented in EPCs of DOCA-salt rats, with concomitantly decreased antioxidant enzymes manganese superoxide dismutase, copper-zinc superoxide dismutase, and glutathione peroxidase 1. Reactive oxygen species level was elevated in EPCs from DOCA-salt rats, accompanied by increased EPC telomerase inactivation, senescence, and apoptosis, which were rescued by ET(A) or NADPH oxidase blockade. Cell therapy of normal or treated DOCA EPCs, but not untreated DOCA EPCs, significantly increased capillary density and blood perfusion in ischemic hindlimbs of DOCA-salt rats. p53 and Bax/Bcl-2 ratios were increased in EPCs of DOCA-salt rats, which were reversed by ET(A) antagonist, NADPH oxidase inhibitor, or polyethylene glycol-superoxide dismutase. Finally, in ET(B)-deficient rats, plasma ET-1 was elevated, and EPC number and telomerase activity were diminished. These results demonstrate, for the first time, that both ET-1 activation of ET(A)/NADPH oxidase pathway and diminished antioxidants critically contribute to EPC reduction and dysfunction via increased oxidative stress in salt-sensitive hypertension.

Purification and long-term expansion of multipotent endothelial-like cells with potential cardiovascular regeneration

Endothelial progenitor cells (EPC) represent a relatively rare cell population, and expansion of sufficient cell numbers remains a challenge. Nevertheless, human adipose-derived stem cells (hASC) can be easily isolated and possess the ability to differentiate into endothelial cells. Here, we propose the isolation and characterization of multipotent endothelial-like cells (ME-LC) with the capacity to maintain their vascular progenitor properties for long periods. hASC were isolated from lipoaspirates and cultured through distinct consecutive culture stages for 2 months to enrich ME-LC: first in Dulbecco's modified Eagle's medium-fetal bovine serum (stage I), followed by a stage of culture in absent of fetal bovine serum (stage II), a culture in SFO3 medium (stage III), and, finally, the culture of ME-LC into collagen IV-coated flasks in endothelial growth medium (EGM-2) (stage IV). ME-LC display increased expression levels of endothelial and hematopoietic lineage markers (CD45, KDR, and CXCR4) and EPC markers (CD34 and CD133), whereas the expression of CD31 was barely detectable. Reverse transcription (RT)-polymerase chain reaction assays showed expression of genes involved in early stages of EPC differentiation and decreased expression of genes associated to differentiated EPC (TIE-2, DLL4, and FLT-1). ME-LC formed capillary-like structures when grown on Matrigel, secreted increased levels of stromal cell-derived factor-1 (SDF-1), and showed the ability to migrate attracted by SDF-1, vascular endothelial growth factor, and hematopoietic growth factor cytokines. Importantly, ME-LC retained the capacity to differentiate into cardiomyocyte-like cells. We present a simplified and efficient method to generate large numbers of autologous ME-LC from lipoaspirates-derived hASC, opening up potential cell-based therapies for cardiovascular regenerative medicine.

Role of heat shock proteins in stem cell behavior

Stress response is well appreciated to induce the expression of heat shock proteins (Hsps) in the cell. Numerous studies have demonstrated that Hsps function as molecular chaperones in the stabilization of intracellular proteins, repairing damaged proteins, and assisting in protein translocation. Various kinds of stem cells (embryonic stem cells, adult stem cells, or induced pluripotent stem cells) have to maintain their stemness and, under certain circumstances, undergo stress. Therefore, Hsps should have an important influence on stem cells. Actually, numerous studies have indicated that some Hsps physically interact with a number of transcription factors as well as intrinsic and extrinsic signaling pathways. Importantly, alterations in Hsp expression have been demonstrated to affect stem cell behavior including self-renewal, differentiation, sensitivity to environmental stress, and aging. This chapter summarizes recent findings related to (1) the roles of Hsps in maintenance of stem cell dormancy, proliferation, and differentiation; (2) the expression signature of Hsps in embryonic/adult stem cells and differentiated stem cells; (3) the protective roles of Hsps in transplanted stem cells; and (4) the possible roles of Hsps in stem cell aging.

An essential role for the Id1/PI3K/Akt/NFkB/survivin signalling pathway in promoting the proliferation of endothelial progenitor cells in vitro

The enhancement of re-endothelialisation is a critical therapeutic option for repairing injured blood vessels. Endothelial progenitor cells (EPCs) are the major source of cells that participate in endothelium repair and contribute to re-endothelialisation by reducing neointima formation after vascular injury. The over-expression of the inhibitor of differentiation or DNA binding 1 (Id1) significantly improved EPC proliferation. This study aimed to investigate the effects of Id1 on the phosphatidylinositol-3-kinase (PI3K)/Akt/nuclear factor kappa B (NFκB)/survivin signalling pathway and its significance in promoting EPC proliferation in vitro. Spleen-derived EPCs were cultured as previously described. Id1 was presented at low levels in EPCs, and was rapidly up-regulated by stimulation with vascular endothelial growth factor. We demonstrated that transient transfection of Id1 into EPCs activated the PI3K/Akt/NFκB/survivin signalling pathway and promoted EPC proliferation. The proliferation of EPCs was extensively inhibited by silencing of endogenous Id1, and knockdown of Id1 expression led to suppression of PI3K/Akt/NFκB/survivin signalling pathway in EPCs. In addition, blockade by the PI3K-specific inhibitor LY294002, Akt inhibitor, the NFκB inhibitor BAY 11-7082, the survivin inhibitor Curcumin, or the survivin inhibitor YM155 reduced the effects of Id1 transfection. These results suggest that the Id1/PI3K/Akt/NFκB/survivin signalling pathway plays a critical role in EPC proliferation. The Id1/PI3K/Akt/NFκB/survivin signalling pathway may represent a novel therapeutic target in the prevention of restenosis after vascular injury.

Molecular imaging of mesenchymal stem cell: mechanistic insight into cardiac repair after experimental myocardial infarction

BACKGROUND

Mesenchymal stem cells (MSCs) can differentiate into endothelial cells in vivo. However, it is unknown if the differentiated MSCs persist in vivo and if this potential persistence contributes to functional improvement after experimental myocardial infarction.

METHODS AND RESULTS

We generated a lentivector encoding 2 distinct reporter genes, one driven by a constitutive murine stem cell virus promoter and the other driven by an endothelial-specific Tie-2 promoter. The endothelial specificity of the lentivector was validated by its expression in endothelial cells but not in human MSCs (hMSCs). The lentivirus-transduced hMSCs were injected into peri-infarct areas of the hearts of severe combined immune-deficient mice. Persistence of injected cells was tracked by bioluminescence imaging (BLI) and verified by immunohistochemical staining. The BLI signal from the endothelial-specific reporter revealed that hMSCs differentiated into endothelial cells 48 hours after injection. However, both the constitutive and endothelial-specific BLI signals disappeared by day 50. Nonetheless, the improvement in left ventricle ejection fraction with hMSC therapy persisted for up to 6 months. Immunohistochemical staining showed that hMSC-derived endothelial cells integrated into endogenous CD31(+) vessels. Furthermore, hMSC-transplanted hearts had more CD31(+) vessels and a lesser degree of cardiac fibrosis compared with the controls at 6 months.

CONCLUSIONS

hMSCs differentiated into endothelial cells and integrated into blood vessels after experimental myocardial infarction. The differentiated hMSCs only lasted for up to 50 days in vivo, but improvement in cardiac function persisted for up to 6 months. Increased angiogenesis and decreased fibrosis were associated with cardiac functional improvement after hMSC transplantation.

The functional expression of TLR3 in EPCs impairs cell proliferation by induction of cell apoptosis and cell cycle progress inhibition

Toll-like receptor 3 (TLR3), a member of the TLR family that recognizes double-stranded RNA (dsRNA), plays an important role in antiviral immunity. TLR3 is widely expressed in various cells and the activation of TLR3 induces cell apoptosis in some cells. However, the effect of TLR3 on cell proliferation in endothelial progenitor cells (EPCs) is unclear. In this study, we found that EPCs expressed high levels of TLR1, 3, 4, and 6 and low levels of TLR2, 5, 7, 8, and 10. The treatment of EPCs with TLR3 agonist Poly I:C up-regulated the expression of cytokines IL-1β, IL-6, IL-8, TNF-α, IFN-α, and IFN-β, indicating that EPCs expressed functional TLR3. Moreover, Poly I:C treatment induced cell cycle progress inhibition and cell apoptosis, leading to the inhibition of cell proliferation. Further studies indicated that IL-1β was involved in TLR3-induced cell proliferation inhibition, as IL-1β inhibited cell proliferation in a dose-dependent manner, and the IL-1β receptor type I (IL-1R1)-neutralizing antibody ameliorated Poly I:C-induced cell proliferation inhibition. Taken together, these results suggest that Poly I:C impairs cell proliferation by inducing cell cycle progress inhibition and cell apoptosis via TLR3 in EPCs.

Cilostazol activates function of bone marrow-derived endothelial progenitor cell for re-endothelialization in a carotid balloon injury model

BACKGROUND

Cilostazol(CLZ) has been used as a vasodilating anti-platelet drug clinically and demonstrated to inhibit proliferation of smooth muscle cells and effect on endothelial cells. However, the effect of CLZ on re-endothelialization including bone marrow (BM)-derived endothelial progenitor cell (EPC) contribution is unclear. We have investigated the hypothesis that CLZ might accelerate re-endothelialization with EPCs.

METHODOLOGY/PRINCIPAL FINDINGS

Balloon carotid denudation was performed in male Sprague-Dawley rats. CLZ group was given CLZ mixed feed from 2 weeks before carotid injury. Control group was fed normal diet. CLZ accelerated re-endothelialization at 2 weeks after surgery and resulted in a significant reduction of neointima formation 4 weeks after surgery compared with that in control group. CLZ also increased the number of circulating EPCs throughout the time course. We examined the contribution of BM-derived EPCs to re-endothelialization by BM transplantation from Tie2/lacZ mice to nude rats. The number of Tie2-regulated X-gal positive cells on injured arterial luminal surface was increased at 2 weeks after surgery in CLZ group compared with that in control group. In vitro, CLZ enhanced proliferation, adhesion and migration activity, and differentiation with mRNA upregulation of adhesion molecule integrin αvβ3, chemokine receptor CXCR4 and growth factor VEGF assessed by real-time RT-PCR in rat BM-derived cultured EPCs. In addition, CLZ markedly increased the expression of SDF-1α that is a ligand of CXCR4 receptor in EPCs, in the media following vascular injury.

CONCLUSIONS/SIGNIFICANCE

CLZ promotes EPC mobilization from BM and EPC recruitment to sites of arterial injury, and thereby inhibited neointima formation with acceleration of re-endothelialization with EPCs as well as pre-existing endothelial cells in a rat carotid balloon injury model. CLZ could be not only an anti-platelet agent but also a promising tool for endothelial regeneration, which is a key event for preventing atherosclerosis or restenosis after vascular intervention.

Differential adhesion molecule expression during murine embryonic stem cell commitment to the hematopoietic and endothelial lineages

Mouse embryonic stem cells (ESC) make cell fate decisions based on intrinsic and extrinsic factors. The decision of ESC to differentiate to multiple lineages in vitro occurs during the formation of embryoid bodies (EB) and is influenced by cell-environment interactions. However, molecular mechanisms underlying cell-environmental modulation of ESC fate decisions are incompletely understood. Since adhesion molecules (AM) influence proliferation and differentiation in developing and adult tissues, we hypothesized that specific AM interactions influence ESC commitment toward hematopoietic and endothelial lineages. Expression of AM in the adherens, tight and gap junction pathways in ESC subpopulations were quantified. E-cadherin (E-cad), Claudin-4 (Cldn4), Connexin-43 (Cx43), Zona Occludens-1 (ZO-1) and Zona Occludens-2 (ZO-2) transcript levels were differentially expressed during early stages of hematopoietic/endothelial commitment. Stable ESC lines were generated with reduced expression of E-cad, Cldn4, Cx43, ZO-1 and ZO-2 using shRNA technology. Functional and phenotypic consequences of modulating AM expression were assessed using hematopoietic colony forming assays, endothelial sprouting assays and surface protein expression. A decrease in E-cad, Cldn4, Cx43 and ZO-1 expression was associated with less commitment to the hematopoietic lineage and increased endothelial differentiation as evidenced by functional and phenotypic analysis. A reduction in ZO-2 expression did not influence endothelial differentiation, but decreased hematopoietic commitment two-fold. These data indicate that a subset of AM influence ESC decisions to commit to endothelial and hematopoietic lineages. Furthermore, differentially expressed AM may provide novel markers to delineate early stages of ESC commitment to hematopoietic/endothelial lineages.

Relationships between vascular dysfunction, circulating endothelial progenitor cells, and psychological status in healthy subjects

BACKGROUND

Although the mechanisms remain unclear, depression and mental stress are associated with endothelial dysfunction and increases risk of cardiovascular disease (CVD). Recent studies suggest that circulating endothelial progenitor cells (EPC) play an important role in endothelial repair and correlate with endothelial function.

METHODS

We studied the relationship between the level of circulating CD34/KDR(+) EPCs and CD133/KDR(+) EPCs, brachial artery flow-mediated dilation (FMD), Depression Anxiety Stress Scales in 129 normal individuals (54 ± 10 years, 54 men) without prior CVD or diabetes.

RESULTS

Their median depression score (DS) and stress score (SS) was 4 (range 0-34) and 6 (range 0-32), respectively. As defined by the ≥75th percentile, 41 subjects (32%) had high DS (≥8) and 31 (24%) had high SS (≥14). Subjects with high DS had significantly lower FMD (5.4 ± 2.7 versus 8.0 ± 4.0%, P<0.001) and percentage of CD34/KDR(+) EPC (1.2 ± 1.3 versus 2.0 ± 2.4%, P = 0.037), but not CD133/KDR(+) EPC (0.56 ± 0.42 versus 0.68 ± 0.76%, P = 0.44), than those with normal DS. In contrast, there were no significant difference in FMD (6.8 ± 3.5 versus 7.3 ± 3.9%, P = 0.46), percentages of circulating CD34/KDR(+) EPC (1.20 ± 1.28 versus 1.95 ± 2.34%, P = 0.052) and CD133/KDR(+) EPC (0.55 ± 0.41 versus 0.67 ± 0.73%, P = 0.52) between subjects with high and normal SS. Multivariate regression analysis revealed that high DS (OR 1.08, 95% CI: 1.02-1.15, P = 0.010) and old age (OR 1.05, 95% CI: 1.01-1.10, P = 0.019), but not SS or percentage of circulating EPC, were independent predictors for decreased FMD.

CONCLUSIONS

Our results demonstrated that, in subjects without significant CVD, a high DS was associated with impaired brachial FMD and depletion of circulating EPC. However, only DS, but not SS or EPC count, was an independent predictor for impaired brachial FMD.

Differentiation of adult stem cells into smooth muscle for vascular tissue engineering

BACKGROUND

Herein we evaluate the potential of adipose-derived stem cells (ASC) to differentiate into smooth muscle cells (SMC) and their potential for use in a tissue-engineered vascular graft.

MATERIALS AND METHODS

We isolated ASC (CD13+29+90+) from the peri-umbilical adipose tissue of patients undergoing vascular surgery, and cultured them in media containing angiotensin II (AngII), sphingosylphosphorylcholine (SPC), or transforming growth factor-beta 1 (TGFβ1) for up to 3 weeks. SMC differentiation was assessed by (1) expression of early (calponin, caldesmon) and late (myosin heavy chain, MHC) SMC markers by RT-PCR, qPCR and Western blot, and (2) contraction upon plating on collagen gel. Differentiated ASCs were seeded onto a vascular graft (decellularized saphenous vein) within a bioreactor, and cell attachment was determined using confocal microscopy.

RESULTS

Prior to differentiation, ASC expressed low levels of all three molecular markers. After culture in each differentiating medium, the extent of up-regulation of calponin, caldesmon, and MHC was variable across all cell lines. After seeding onto collagen gel, ASCs differentiated in SPC and TGFβ1 exhibit contractile properties, similar to smooth muscle cell controls. Differentiated stem cells adhered and proliferated on the vascular graft.

CONCLUSION

These data suggest that human adipose-derived stem cells (1) exhibit variable expression of SMC molecular markers after differentiation, (2) exhibit a contractile phenotype after differentiation with SPC and TGFβ1, and (3) proliferate on a vascular graft scaffold. Thus, ASCs are potentially useful in the construction of autologous arteries.

Cerebral microvascular endothelium and the pathogenesis of neurodegenerative diseases

Diseases of the central nervous system (CNS) pose a significant health challenge, but despite their diversity, they share many common features and mechanisms. For example, endothelial dysfunction has been implicated as a crucial event in the development of several CNS disorders, such as Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, multiple sclerosis, human immunodeficiency virus (HIV)-1-associated neurocognitive disorder and traumatic brain injury. Breakdown of the blood–brain barrier (BBB) as a result of disruption of tight junctions and transporters, leads to increased leukocyte transmigration and is an early event in the pathology of these disorders. The brain endothelium is highly reactive because it serves as both a source of, and a target for, inflammatory proteins and reactive oxygen species. BBB breakdown thus leads to neuroinflammation and oxidative stress, which are implicated in the pathogenesis of CNS disease. Furthermore, the physiology and pathophysiology of endothelial cells are closely linked to the functioning of their mitochondria, and mitochondrial dysfunction is another important mediator of disease pathology in the brain. The high concentration of mitochondria in cerebrovascular endothelial cells might account for the sensitivity of the BBB to oxidant stressors. Here, we discuss how greater understanding of the role of BBB function could lead to new therapeutic approaches for diseases of the CNS that target the dynamic properties of brain endothelial cells.

Aging is associated with a proapoptotic endothelial progenitor cell phenotype

The aim of this study was to determine if aging is associated with enhanced endothelial progenitor cell (EPC) sensitivity to apoptosis. Cells with phenotypic EPC characteristics were isolated from healthy, nonobese young (age 25 ± 1 years) and older (61 ± 1 years) men. Intracellular active caspase-3 concentrations in response to staurosporine stimulation were approximately 35% higher (p < 0.05) in EPCs from older (3.15 ± 0.29 pg/ml) compared with young (2.33 ± 0.24 pg/ml) men. Protein expression of Akt, p70 S6-kinase and Bcl-2 was markedly lower (approx. 35, 75 and 60%, respectively, all p < 0.05) in EPCs from older compared with young men, whereas there were no age-related differences in either 14-3-3ε or Bax expression. Additionally, EPC telomerase activity was 57% lower (p < 0.05) in older (0.18 ± 0.11 AU) versus young (0.43 ± 0.11 AU) men. These results indicate that aging is associated with a proapoptotic EPC phenotype characterized by decreased expression of key antiapoptotic proteins associated with the PI-3-kinase signaling pathway and reduced telomerase activity. These age-related changes likely contribute, in part, to the diminished ability of EPCs to resist an apoptotic stimulus in older men. Increased susceptibility to apoptosis may contribute to the numerical and functional impairments observed in EPCs with aging.

Calcitonin gene-related peptide released from endothelial progenitor cells inhibits the proliferation of rat vascular smooth muscle cells induced by angiotensin II

We have recently demonstrated that endothelial progenitor cells (EPCs) inhibit AngII-induced proliferation of vascular smooth muscle cells (VSMCs) by inactivating MAPKs and NF-κB signaling pathway and reducing expression of oncogene c-myc and c-fos. The inhibitory effect of EPCs on VSMCs is associated with paracrine mechanism. However, the potential mechanism of EPCs on the regulation of AngII-induced proliferation of VSMCs was unknown. Calcitonin gene-related peptide (CGRP) could inhibit AngII-induced proliferation and transformation of VSMCs. However, it has not been known whether CGRP released from EPCs is a potential regulator in regulation of AngII-induced proliferation of VSMCs. Early endothelial progenitor cell-conditioned medium(E-EPC-CM) was pre-incubated with functional blocking antibodies against CGRP for 1 h or VSMCs was preteated with CGRP(837)(CGRP receptor antagonist) for 1 h before VSMCs were pretreated with CM for 30 min. DNA synthesis ability, total protein levels, cell survival, signal transduction, and expressions of c-myc and c-fos of VSMCs induced by AngII (10(-6)mol/l) were detected to assess the role of CGRP in AngII-induced proliferation of VSMCs. E-EPC-CM could significantly inhibit AngII-induced DNA synthesis ability, total protein levels, cell survival, phosphorylation of ERK, JNK, p38, p65, and expressions of c-myc and c-fos compared with the control group(P < 0.05). However, Pretreatment with anti-CGRP antibody and CGRP(837) could significantly weaken the inhibitory effect of E-EPC-CM on proliferation of VSMCs induced by AngII (P < 0.05). EPCs exert anti-proliferative effects on VSMCs mediated by the release of CGRP.

Novel therapy for myocardial infarction: can HGF/Met be beneficial?

Myocardial infarction (MI) is a leading cause of hospitalization worldwide. A recently developed strategy to improve the management of MI is based on the use of growth factors which are able to enhance the intrinsic capacity of the heart to repair itself or regenerate after damage. Among others, hepatocyte growth factor (HGF) has been proposed as a modulator of cardiac repair of damage due to the pleiotropic effects elicited by Met receptor stimulation. In this review we describe the mechanistic basis for autocrine and paracrine protection of HGF in the injured heart. We also analyse the role of HGF/Met in stem cell maintenance and in stem cell therapies for MI. Finally, we summarize the most significant results on the use of HGF in experimental models of heart injury and discuss the potential of the molecule for treating ischaemic heart disease in humans.

Erythropoietin increases circulating endothelial progenitor cells and reduces the formation and progression of cerebral aneurysm in rats

Endothelial dysfunction triggers early pathological changes in vessel walls, potentially leading to the formation of cerebral aneurysm (CA). Endothelial progenitor cells (EPCs) are critical in repairing damaged endothelium and could prevent or slow CA formation. We hypothesize that erythropoietin (EPO) stimulates EPCs mobilization, could alter the rate of CA formation and progression. The hypothesis was tested in a rat model of CA. CAs were induced in male Sprague-Dawley rats and treated with s.c. administration of EPO. Circulating EPCs and serum vascular endothelial grow factor (VEGF) were measured be flow cytometry and ELISA, respectively. mRNAs for inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS), matrix metalloproteinase-2 (MMP-2), and MMP-9 in aneurysm tissue were quantified by Real-time PCR. The size, internal elastic lamina (IEL), and media thickness of CAs were evaluated 1 and 3 months after aneurysm induction. Circulating EPCs were significantly lower in CA rats as compared to non-surgical controls. EPO increased levels of circulating EPCs and VEGF. It also decreased iNOS, MMP-2, and MMP-9 mRNA levels, while increased eNOS mRNA in aneurysm tissue. The changes in EPCs and biochemical markers are associated with suppression of new CA formation and prevention of preexisting CA progression. We have shown a close association among circulating EPCs, biochemical markers related to vascular remodeling, and the rate of CA formation and progression. Changes in patterns of cerebral blood flow and hypertension induced by surgical ligations of selected arteries exert significant hemodynamic stress to weaken vessel walls, primarily at sites of basilar bifurcation. The surgical stress also reduced circulating EPCs and slowed vascular repairs. EPO mobilizes EPCs from the bone marrow and promotes their homing. These results suggest that EPCs may serve as a marker for CA progression and EPO a promising candidate for the clinical management of CA.

Wnt1 is a proangiogenic molecule, enhances human endothelial progenitor function, and increases blood flow to ischemic limbs in a HGF-dependent manner

Human endothelial progenitor cells (hEPCs) participate in neovascularization of ischemic tissues. Function and number of hEPCs decline in patients with cardiovascular disease, and therapeutic strategies to enhance hEPC function remain an important field of investigation. The Wnt signaling system, comprising 19 lipophilic proteins, regulates vascular patterning in the developing embryo. However, the effects of Wnts on hEPCs and the adult vasculature remain unclear. We demonstrate here that Wnt1 is expressed in a subset of endothelial cells lining the murine embryonic dorsal aorta and is reactivated in malignant angiosarcoma, suggesting a strong association of Wnt1 with angiogenesis. We investigate the effects of Wnt1 in enhancing hEPC function and blood flow to ischemic tissues and show that Wnt1 enhances the proliferative and angiogenic functions of hEPCs in a hepatocyte growth factor (HGF)-dependent manner. Injection of Wnt1-expressing hEPCs increases blood flow and capillary density in murine ischemic hindlimbs. Furthermore, injection of Wnt1 protein alone similarly increases blood flow and capillary density in ischemic hindlimbs, and this effect is associated with increased HGF expression in ischemic muscle. These findings demonstrate that Wnt1, a marker of neural crest cells and hitherto unknown angiogenic function, is a novel angiogenic protein that is expressed in developing endothelial cells, exerts salutary effects on postnatal hEPCs, and can be therapeutically deployed to increase blood flow and angiogenesis in ischemic tissues.

In vivo serial MR imaging evaluates neointimal hyperplasia inhibited by intravenously transfused endothelial progenitor cells in carotid artery injured mice

PURPOSE

to study the feasibility of in vivo MR imaging in evaluation of endothelial progenitor cells (EPCs) on the progress of neointimal hyperplasia after carotid artery injury in mice.

METHODS

fifteen Kunming mice were injured in left carotid artery by removal of endothelium with a flexible wire 7 days after splenectomy. EPCs were collected by in vitro culture of spleen-derived mouse mononuclear cells (MNCs) in endothelial basal medium. After artery injury, the mice received EPCs (n= 6), phosphate buffered solution (PBS) (n= 6), and DiI-Ac-LDL labeled EPCs (n= 3) intravenously. In vivo serial MR imaging were performed at different time points after artery injury, and vessel-wall thickness and vessel-wall area at injury site were measured on MR imaging.

RESULTS

transfused Dil-Ac-LDL-labeled EPCs were found at the injury site by histopathological analyses. Vessel wall of injured artery was observed and quantitatively analyzed with MR imaging. Vessel-wall thickness was .487 ± .122 mm in the non-EPCs transfusion group and .294 ± .051 mm in the EPCs transfusion group 15 days after artery injury (P= .005). While vessel-wall area was .860 ± .182 mm(2) in the non-EPCs transfusion group and .468 ± .141 mm(2) in the EPCs transfusion group 15 days after artery injury (P= .002). Therefore, the neointimal hyperplasia of injured artery in the EPCs transfusion group was lesser than that in the non-EPCs transfusion group.

CONCLUSION

neointimal hyperplasia can be reduced by intravenous transfusion of EPCs and analyzed on in vivo MR imaging after vascular injury.

Effect of weight reduction on cardiovascular risk factors and CD34-positive cells in circulation

Being overweight or obese is associated with an increased risk for the development of non-insulin-dependent diabetes mellitus, hypertension, and cardiovascular disease. Dyslipidemia of obesity is characterized by elevated fasting triglycerides and decreased high-density lipoprotein-cholesterol concentrations. Endothelial damage and dysfunction is considered to be a major underlying mechanism for the elevated cardiovascular risk associated with increased adiposity. Alterations in endothelial cells and stem/endothelial progenitor cell function associated with overweight and obesity predispose to atherosclerosis and thrombosis. In our study, we analyzed the effect of a low calorie diet in combination with oral supplementation by vitamins, minerals, probiotics and human chorionic gonadotropin (hCG, 125-180 IUs) on the body composition, lipid profile and CD34-positive cells in circulation. During this dieting program, the following parameters were assessed weekly for all participants: fat free mass, body fat, BMI, extracellular/intracellular water, total body water and basal metabolic rate. For part of participants blood chemistry parameters and circulating CD34-positive cells were determined before and after dieting. The data indicated that the treatments not only reduced body fat mass and total mass but also improved the lipid profile. The changes in body composition correlated with the level of lipoproteins responsible for the increased cardiovascular risk factors. These changes in body composition and lipid profile parameters coincided with the improvement of circulatory progenitor cell numbers. As the result of our study, we concluded that the improvement of body composition affects the number of stem/progenitor cells in circulation.

Endothelial progenitor cells as therapeutic agents in the microcirculation: an update

This review evaluates novel beneficial effects of circulating endothelial progenitor cells (EPCs) as shown by several preclinical studies and clinical trials carried out to test the safety and feasibility of using EPCs. There are 31 registered clinical trials (and many others still ongoing) and 19 published studies. EPCs originate in the bone marrow and migrate into the bloodstream where they undergo a differentiation program leading to major changes in their antigenic characteristics. EPCs lose typical progenitor markers and acquire endothelial markers, and two important receptors, (VEGFR and CXCR-4), which recruit circulating EPCs to damaged or ischemic microcirculatory (homing to damaged tissues) beds. Overall, therapeutic angiogenesis will likely change the face of regenerative medicine in the next decade with many patients worldwide predicted to benefit from these treatments.

Smoking is associated with depletion of circulating endothelial progenitor cells and elevated pulmonary artery systolic pressure in patients with coronary artery disease

Smoking is associated with depletion of endothelial progenitor cells (EPCs) and may subsequently contribute to the development of vascular dysfunction. The aim of this study was to investigate the relation between circulating EPCs and pulmonary artery systolic pressure (PASP) as determined by flow cytometry and echocardiography in 174 patients (mean age 69 ± 9 years, 95 smokers) with established coronary artery disease. Smokers had significantly lower circulating log CD34/KDR(+) (0.86 ± 0.03 vs 0.96 ± 0.03 × 10⁻³/ml, p = 0.032) and log CD133/KDR(+) (0.68 ± 0.03 vs 0.82 ± 0.03 × 10⁻³/ml, p = 0.002) EPCs and a higher prevalence of elevated PASP >30 mm Hg (52% vs 30%, p = 0.001) than nonsmokers. Smokers with elevated PASP also had significantly lower circulating log CD34/KDR(+) (0.74 ± 0.04 vs 0.88 ± 0.06 × 10⁻³/ml, p <0.001) and log CD133/KDR(+) (0.61 ± 0.04 vs 0.78 ± 0.05 × 10⁻³/ml, p <0.001) EPCs, higher pulmonary vascular resistance, and larger right ventricular dimensions with impaired function (all p values <0.05). Log CD34/KDR(+) and log CD133/KDR(+) EPC counts were significantly and negatively correlated with PASP (r = -0.30, p <0.001, and r = -0.34, p <0.001, respectively) and pulmonary vascular resistance (r = -0.29, p = 0.002, and r = -0.18, p = 0.013, respectively). In conclusion, this study demonstrated that in patients with coronary artery disease, smoking was associated with a reduced number of EPCs and elevated PASP. This suggests that in smokers, depletion of circulating EPCs might be linked to the occurrence of pulmonary vascular dysfunction.

Endothelial differentiation of adipose-derived stem cells from elderly patients with cardiovascular disease

Adipose-derived stem cells (ASCs) possess significant therapeutic potential for tissue engineering and regeneration. This study investigates the endothelial differentiation and functional capacity of ASCs isolated from elderly patients. Isolation of ASCs from 53 patients (50-89 years) revealed that advanced age or comorbidity did not negatively impact stem cell harvest; rather, higher numbers were observed in older donors (>70 years) than in younger. ASCs cultured in endothelial growth medium-2 for up to 3 weeks formed cords upon Matrigel and demonstrated acetylated-low-density lipoprotein and lectin uptake. Further stimulation with vascular endothelial growth factor and shear stress upregulated endothelial cell-specific markers (CD31, von Willebrand factor, endothelial nitric oxide synthase, and VE-cadherin). Inhibition of the PI(3)K but not mitogen-activated protein kinase pathway blocked the observed endothelial differentiation. Shear stress promoted an anti-thrombogenic phenotype as demonstrated by production of tissue-plasminogen activator and nitric oxide, and inhibition of plasminogen activator inhibitor-1. Shear stress augmented integrin α(5)β(1) expression and subsequently increased attachment of differentiated ASCs to basement membrane components. Finally, ASCs seeded onto a decellularized vein graft resisted detachment despite application of shear force up to 9 dynes. These results suggest that (1) advanced age and comorbidity do not negatively impact isolation of ASCs, and (2) these stem cells retain significant capacity to acquire key endothelial cell traits throughout life. As such, adipose tissue is a practical source of autologous stem cells for vascular tissue engineering.

Paracrine mechanisms of stem cell reparative and regenerative actions in the heart

Stem cells play an important role in restoring cardiac function in the damaged heart. In order to mediate repair, stem cells need to replace injured tissue by differentiating into specialized cardiac cell lineages and/or manipulating the cell and molecular mechanisms governing repair. Despite early reports describing engraftment and successful regeneration of cardiac tissue in animal models of heart failure, these events appear to be infrequent and yield too few new cardiomyocytes to account for the degree of improved cardiac function observed. Instead, mounting evidence suggests that stem cell mediated repair takes place via the release of paracrine factors into the surrounding tissue that subsequently direct a number of restorative processes including myocardial protection, neovascularization, cardiac remodeling, and differentiation. The potential for diverse stem cell populations to moderate many of the same processes as well as key paracrine factors and molecular pathways involved in stem cell-mediated cardiac repair will be discussed in this review. This article is part of a special issue entitled, "Cardiovascular Stem Cells Revisited".