EPC‐derived exosomes promote osteoclastogenesis through LncRNA‐MALAT1

Bone repair involves bone resorption through osteoclastogenesis and the stimulation of neovascularization and osteogenesis by endothelial progenitor cells (EPCs). However, the role of EPCs in osteoclastogenesis is unclear. In this study, we assess the effects of EPC‐derived exosomes on the migration and osteoclastic differentiation of primary mouse bone marrow‐derived macrophages (BMMs) in vitro using immunofluorescence, western blotting, RT‐PCR and Transwell assays. We also evaluated the effects of EPC‐derived exosomes on the homing and osteoclastic differentiation of transplanted BMMs in a mouse bone fracture model in vivo. We found that EPCs cultured with BMMs secreted exosomes into the medium and, compared with EPCs, exosomes had a higher expression level of LncRNA‐MALAT1. We confirmed that LncRNA‐MALAT1 directly binds to miR‐124 to negatively control miR‐124 activity. Moreover, overexpression of miR‐124 could reverse the migration and osteoclastic differentiation of BMMs induced by EPC‐derived exosomes. A dual‐luciferase reporter assay indicated that the integrin ITGB1 is the target of miR‐124. Mice treated with EPC‐derived exosome‐BMM co‐transplantations exhibited increased neovascularization at the fracture site and enhanced fracture healing compared with those treated with BMMs alone. Overall, our results suggest that EPC‐derived exosomes can promote bone repair by enhancing recruitment and differentiation of osteoclast precursors through LncRNA‐MALAT1.     

Zoledronate Attenuates Angiogenic Effects of Angiotensin II-Stimulated Endothelial Progenitor Cells via RhoA and MAPK Signaling

Background

New vessel formation plays a pivotal role in the pathogenesis of neovascular-related diseases. Endothelial progenitor cells (EPCs) were found to contribute to neovascular-related diseases and interference with EPC neovascularization may be a novel target for these diseases. Zoledronate (Zol) was reported to exhibit anti-angiogenic effect. Basing on these evidences, we proposed that Zol may affect EPC function to exert novel anti-angiogenic effect. In this study, we therefore investigated the effects of Zol on multiple aspects of EPC function and explored the underlying mechanisms involved.

Methodology/Principal Findings

EPCs were cultured from bone marrow derived mononuclear cells. The potential effects of Zol on Angiotensin II (Ang II)-stimulated EPC proliferation, migration, adhesion, in vitro tube formation were investigated. The results showed that Ang II (1 µM) enhanced EPC migration, adhesion, in vitro tube formation but had no effect on cell proliferation. Zol (75 and 100 µM) inhibited proliferation of EPCs and 50 µM geranylgeranyol (GGOH) could reverse the decrease of EPC proliferation. We found for the first time that Zol (50–100 µM) dose dependently attenuated migration, adhesion, and in vitro tube formation of EPCs stimulated by Ang II. GGOH could reverse the attenuation of EPC function induced by Zol. However, Zol did not induce EPC apoptosis. In addition, the underlying mechanisms were determined. The results revealed that Zol markedly down-regulated active RhoA stimulated by Ang II and inhibited the phosphorylation of Erk1/2 and JNK. Moreover, RhoA silencing resulted in a notable inhibition of EPC in vitro tube formation, suggesting that RhoA suppression played a pivotal role in Zol antiangiogenic effect.

Conclusions/Significance

These findings suggested that Zol attenuated the promotion of EPC function stimulated by Ang II and exhibited novel antiangiogenic effect via RhoA and MAPK signaling. Thus, Zol may be served as a novel therapeutic agent for neovascular-related diseases treatment.     

Determine exogenous human DDAH2 gene function in rabbit bone marrow–derived endothelial progenitor cells in vitro

The in vitro amplification of endothelial progenitor cells (EPCs) is an important method because of its role in gene transferring and regenerative medicine. In this study, we isolated rabbit bone marrow–derived EPCs to further manipulation and overexpression of dimethylarginine dimethylaminohydrolase (DDAH) in EPCs. Isolated EPCs were cultured, expanded in endothelial basal medium. Morphology of EPCs and expression levels of surface markers detected using immunocytochemistry staining and through the use of flow cytometery. Endothelial progenitor cells were transfected with plasmid vectors expressing human DDAH2 (DDAH2‐EPCs). Three days after gene transfer, positive transfected‐EPCs proliferation and DDAH activity were assayed. We observed colonies conformation and endothelium‐like morphology gradually in the third week of culture. Characterization results revealed positive expression of EPC surface markers CD106, Flk‐1, vWF, and CD34 using few identification techniques. Overexpression of DDAH2 increased citrulline production after 96 hours of transfection, 235.34 ± 0.69 vs 95.26 ± 5.76 ng/mL; P = .023. These results suggest that cell population with EPC characteristics can be simply isolated from rabbit bone marrow and successfully engineered to overexpress exogenous gene. In this study, we offer a feasible method to isolate and identify EPCs from bone marrow. In addition, an efficient transfection with a plasmid vector (without risk of interference) can be constructed a hybrid structure with EPC and DDAH2 gene to examine their function in vitro.     

In vivo enhancement of angiogenesis by adenoviral transfer of HIF-1alpha-modified endothelial progenitor cells (Ad-HIF-1alpha-modified EPC for angiogenesis)

Hypoxia inducible factor (HIF)-1alpha over-expression may have beneficial effects in cell therapy of hypoxia-induced pathophysiological processes, such as ischemic disease. Our previous study showed the feasibility of ex vivo modification of endothelial progenitor cells (EPCs) by HIF-1alpha transfection. In this study, we sought to determine if such ex vivo modified EPCs facilitated functional therapeutic neovascularization. Ad-HIF-1alpha was transduced in human EPC in vitro. HIF-1alpha-transduced EPCs were administered to nude mice with hindlimb ischemia. BrdU-labeling of these EPCs showed that they enhanced neovascularization in vivo. Limb and toe necrosis was significantly reduced in HIF-1alpha-EPC group compared to GFP-EPC group and medium control group at 14 days after transplantation (both P<0.05). A statistically significant difference was still observed in the HIF-1alpha group until 1 and 2 months of follow-up. Neovascularization was improved by both histological and physiological assessments. Exogenous EPC homing was observed. HIF-1alpha over-expression enhanced its mRNA and protein expression in the ischemia zone. The expression of genes downstream of HIF-1alpha was examined to explore the possible mechanism of EPC homing. In conclusion, HIF-1alpha-EPC gene transfer augments impaired neovascularization in experimentally induced mouse hindlimb ischemia in vivo.     

Period 2 is essential to maintain early endothelial progenitor cell function in vitro and angiogenesis after myocardial infarction in mice

Cellular therapeutic neovascularization has been successfully performed in clinical trials for patients with ischaemia diseases. Despite the vast knowledge of cardiovascular disease and circadian biology, the role of the circadian clock in regulating angiogenesis in myocardial infarction (MI) remains poorly understood. In this study, we aimed to investigate the role and underlying mechanisms of Period 2 (Per2) in endothelial progenitor cell (EPC) function. Flow cytometry revealed lower circulating EPC proportion in per2^−/− than in wild-type (WT) mice. PER2 was abundantly expressed in early EPCs in mice. In vitro, EPCs from per2^−/− mice showed impaired proliferation, migration, tube formation and adhesion. Western blot analysis demonstrated inhibited PI3k/Akt/FoxO signalling and reduced C-X-C chemokine receptor type 4 (CXCR4) protein level in EPCs of per2^−/− mice. The impaired proliferation was blocked by activated PI3K/Akt/FoxO signalling. Direct interaction of CXCR4 and PER2 was detected in WT EPCs. To further study the effect of per2 on in vivo EPC survival and angiogenesis, we injected saline or DiI-labelled WT or per2^−/− EPC intramyocardially into mice with induced MI. Per2^−/− reduced the retention of transplanted EPCs in the myocardium, which was associated with significantly reduced DiI expression in the myocardium of MI mice. Decreased angiogenesis in the myocardium of per2^−/− EPC-treated mice coincided with decreased LV function and increased infarct size in the myocardium. Per2 may be a key factor in maintaining EPC function in vitro and in therapeutic angiogenesis in vivo.     

A new source of endothelial progenitor cells--vascular biology redefined?

The initial discovery of endothelial progenitor cells (EPCs) in tandem with emerging concepts in stem cell biology has generated enormous interest and excitement in fields as diverse as tissue engineering, regenerative medicine, and tumor and vascular biology. A recent paper by Ingram et al. identifies a complete hierarchy of EPCs in the vessel wall, providing a new framework for classification of cells supporting endopoiesis akin to that previously established for hematopoiesis. This could have fundamental implications for our understanding of the role of the endothelium and, more specifically, the role of EPC interfacing with the vessel wall in health and disease.     

Kaposi’s sarcoma-associated herpesvirus infection of endothelial progenitor cells impairs angiogenic activity <Emphasis Type="Italic">in vitro</Emphasis>

A recent study reported that endothelial progenitor cells (EPCs0 are one of the reservoirs of Kaposi’s sarcoma associated herpesvirus (KSHV). Although EPCs are closely linked to angiogenesis and vasculogenesis, little is known about the angiogenic potential of KSHV in EPCs. In this study, we used EPCs isolated from human umbilical cord blood to show that early infection by KSHV in vitro impaired the neovascularization of EPCs in matrigel. Our results suggest that KSHV may disrupt the angiogenic potential of EPCs and that the disseminated infection of KSHV could be associated with EPC dysfunction.     

PPARα Is Essential for Microparticle-Induced Differentiation of Mouse Bone Marrow-Derived Endothelial Progenitor Cells and Angiogenesis

Background

Bone marrow-derived endothelial progenitor cells (EPCs) are critical for neovascularization. We hypothesized that microparticles (MPs), small fragments generated from the plasma membrane, can activate angiogenic programming of EPCs.

Methodology/Principal Findings

We studied the effects of MPs obtained from wild type (MPs^PPARα+/+) and knock-out (MPs^{PPARα−/−}) mice on EPC differentiation and angiogenesis. Bone marrow-derived cells were isolated from WT or KO mice and were cultured in the presence of MPs^PPARα+/+ or MPs^{PPARα−/−} obtained from blood of mice. Only MPs^PPARα+/+ harboring PPAR^α significantly increased EPC, but not monocytic, differentiation. Bone marrow-derived cells treated with MPs^PPARα+/+ displayed increased expression of pro-angiogenic genes and increased in vivo angiogenesis. MPs^PPARα+/+ increased capillary-like tube formation of endothelial cells that was associated with enhanced expressions of endothelial cell-specific markers. Finally, the effects of MPs^PPARα+/+ were mediated by NF-κB-dependent mechanisms.

Conclusions/Significance

Our results underscore the obligatory role of PPARα carried by MPs for EPC differentiation and angiogenesis. PPARα-NF-κB-Akt pathways may play a pivotal stimulatory role for neovascularization, which may, at least in part, be mediated by bone marrow-derived EPCs. Improvement of EPC differentiation may represent a useful strategy during reparative neovascularization.     

Estrogen and progesterone play pivotal roles in endothelial progenitor cell proliferation

Background  

It has been previously suggested that angiogenesis occurs during the menstrual cycle. Moreover, a rise in uterine blood flow is largely maintained by vasodilatation and substantial increases in angiogenesis. It is known that estradiol (E2) and progesterone (P4) are involved in angiogenesis. Recently, endothelial progenitor cells (EPCs) were found to be involved in neovascularization; however, their roles in uterine neovascularization have not been well characterized. We hypothesized that E2- or P4-mediated EPC proliferation plays important roles in uterine neovascularization during the menstrual cycle.     

Endothelial progenitor cells for regeneration

Endothelial progenitor cells (EPCs) have been recently isolated from peripheral blood and bone marrow (BM), and shown to be incorporated into sites of physiological and pathological neovascularization in vivo. In contrast to differentiated endothelial cells (ECs), transplantation of EPCs successfully enhanced vascular development by in situ differentiation and proliferation within ischemic organs. Based on such a novel concept of closed up function on EPCs in postnatal neovascularization, the beneficial property of EPC is attractive for cell therapy as well as cell-mediated gene therapy applications targeting regeneration of ischemic tissue.     

The Biphasic Effects of Oxidized-Low Density Lipoprotein on the Vasculogenic Function of Endothelial Progenitor Cells

Late-outgrowth endothelial progenitor cells (EPCs) are stress-resistant and responsible for reparative functions in the cardiovascular system. Oxidized-LDL (oxLDL) plays a critical role in cardiovascular disease pathogenesis. However, it is largely unknown what the impacts of oxLDL are on late-outgrowth EPCs. This study aimed to investigate the concentration-related effects of oxLDL on EPC functions and related angiogenesis, in vitro and in vivo. In this study, early and late-outgrowth EPCs were generated from circulating human mononuclear cells. oxLDL may regulate EPC vasculogenic function via the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1). Lower concentrations (5 μg/mL) of oxLDL can potentiate EPC tube formation in vitro and in vivo by activating eNOS mechanisms, which are mediated by p38 MAPK- and SAPK/JNK-related pathways. Higher concentrations of oxLDL (10-50 μg/mL) impaired EPC function via the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase pathways and consequent inhibition of eNOS activity, which could be reversed by anti-oxidants (diphenylene iodonium and apocynin) and gp91^phox siRNA. In conclusion, oxLDL has concentration-dependent biphasic effects on human late-outgrowth EPC tube formation in vitro and in vivo.     

VEGF contributes to postnatal neovascularization by mobilizing bone marrow-derived endothelial progenitor cells.

Vascular endothelial growth factor (VEGF) has been shown to promote neovascularization in animal models and, more recently, in human subjects. This feature has been assumed to result exclusively from its direct effects on fully differentiated endothelial cells, i.e. angiogenesis. Given its regulatory role in both angiogenesis and vasculogenesis during fetal development, we investigated the hypothesis that VEGF may modulate endothelial progenitor cell (EPC) kinetics for postnatal neovascularization. Indeed, we observed an increase in circulating EPCs following VEGF administration in vivo. VEGF-induced mobilization of bone marrow-derived EPCs resulted in increased differentiated EPCs in vitro and augmented corneal neovascularization in vivo. These findings thus establish a novel role for VEGF in postnatal neovascularization which complements its known impact on angiogenesis.     

Impaired therapeutic vasculogenesis by transplantation of OxLDL-treated endothelial progenitor cells

Previous in vitro studies have revealed that oxidized low density lipoprotein (OxLDL) has negative effects on the proliferation and activity of endothelial progenitor cells (EPCs). Here, we evaluated the effect of OxLDL on the therapeutic potential of EPCs in ischemia-induced neovascularization. EPCs derived from mobilized human peripheral blood mononuclear cells were cultured without or with OxLDL before transplantation. Hindlimb ischemia models were surgically induced in athymic nude mice, which then received an intracardiac injection of 3 x 10(5) EPCs. By laser Doppler perfusion image and ischemia damage score, we found that blood perfusion and ischemia damage were less well recovered in the OxLDL-treated EPC transplantation group than in controls. Histological examination showed fewer transplanted EPCs and lower capillary density in ischemic tissue. Local delivery of Stromal cell-derived factor (SDF-1) restored this defect and improved blood perfusion by recruiting OxLDL-treated EPCs to the ischemic area and increasing host capillary density. These results provide for the first time direct evidence that OxLDL impaired the therapeutic potential of EPCs in ischemia-induced neovascularization through an inhibitory effect on the migration, adhesion, and incorporation of EPCs into vasculature and/or entrapment in the perivascular region in vivo. A therapeutic strategy based on SDF-1 administration ameliorated such defects and improved postischemic neovascularization.     

Decursin inhibits vasculogenesis in early tumor progression by suppression of endothelial progenitor cell differentiation and function

Endothelial progenitor cells (EPCs) contribute to the tumor vasculature during tumor progression. Decursin isolated from the herb Angelica gigas is known to possess potent anti‐inflammatory activities. Recently, we reported that decursin is a novel candidate for an angiogenesis inhibitor [Jung et al., 2009 ]. In this study, we investigated whether decursin regulates EPC differentiation and function to inhibit tumor vasculogenesis. We isolated AC133+ cells from human cord blood and decursin significantly decreased the number of EPC colony forming units of human cord blood‐derived AC133+ cells that produce functional EPC progenies. Decursin dose‐dependently decreased the cell number of EPC committing cells as demonstrated by EPC expansion studies. Decursin inhibited EPC differentiation from progenitor cells into spindle‐shaped EPC colonies. Additionally, decursin inhibited proliferation and migration of early EPCs isolated from mouse bone marrow. Furthermore, decursin suppressed expression of angiopoietin‐2, angiopoietin receptor Tie‐2, Flk‐1 (vascular endothelial growth factor receptor‐2), and endothelial nitric oxide synthase in mouse BM derived EPCs in a dose‐dependent manner. Decursin suppressed tube formation ability of EPCs in collaboration with HUVEC. Decursin (4 mg/kg) inhibited tumor‐induced mobilization of circulating EPCs (CD34 + /VEGFR‐2+ cells) from bone marrow and early incorporation of Dil‐Ac‐LDL‐labeled or green fluorescent protein (GFP)+ EPCs into neovessels of xenograft Lewis lung carcinoma tumors in wild‐type‐ or bone‐marrow‐transplanted mice. Accordingly, decursin attenuated EPC‐derived endothelial cells in neovessels of Lewis lung carcinoma tumor masses grown in mice. Together, decursin likely affects EPC differentiation and function, thereby inhibiting tumor vasculogenesis in early tumorigenesis. J. Cell. Biochem. 113: 1478–1487, 2012. © 2012 Wiley Periodicals, Inc.     

Hepatocyte growth factor induces angiogenesis in injured lungs through mobilizing endothelial progenitor cells

Circulating endothelial progenitor cells (EPCs) play a pivotal role in angiogenesis. Hepatocyte growth factor (HGF) is known to induce proliferation and motility in endothelial cells, and to play a role in mitogenic and morphogenic actions. However, the role of HGF in EPC mobilization has not been clearly described yet. We investigated the effect of HGF on mobilizing EPCs and on angiogenesis in elastase-induced lung injury. HGF significantly increased the triple-positive (Sca-1(+), Flk-1(+), and c-kit(+)) fraction in peripheral mononuclear cells in mice. The bone marrow-derived cells were recruited into the injured lungs, where they differentiated to capillary endothelial cells. HGF induced proliferation of both bone marrow-derived and resident endothelial cells in the alveolar wall. In conclusion, the present study suggests that HGF induces EPC mobilization from the bone marrow and enhances the proliferation of endothelial cells in vivo. These complex effects induced by HGF orchestrate pulmonary regeneration in emphysematous lung parenchyma.     

Effect of low doses of red wine and pure resveratrol on circulating endothelial progenitor cells

Circulating endothelial progenitor cells (EPCs) play a significant role in neovascularization of ischaemic tissues and in re-endothelization of injured blood vessels. Identification of compounds able to enhance EPC levels and improve their functional activity, noticeably compromised by risk factors for coronary heart disease, is of clinical interest. This study evaluates the effects of red wine on EPCs. After being isolated from total peripheral blood mononuclear cells, EPC phenotype was confirmed by the presence of double positive cells for DiLDL uptake and lectin binding and by expression of CD34, CD133 and VE-cadherin cell surface markers. Long-term culture in the presence of red wine (1 microl/ml), containing resveratrol (Resv) at physiological concentration (nM), determined a time-dependent amelioration of cell number (P < 0.05). The presence of red wine prevented the TNF-alpha-induced reduction of EPC number (P < 0.05) and this effect was accompanied by reduced p38-phosphorylation expression levels (P < 0.05) and increased NOx levels (P < 0.05) Indeed, pure Resv alone significantly improved the TNF-alpha reduced EPC number (P < 0.05). This evidence indicates novel beneficial effects of red wine and Resv in the positive modulation of EPCs levels.     

Transplantation of endothelial progenitor cells for therapeutic neovascularization

Endothelial progenitor cells (EPCs), which were first identified in adult peripheral blood mononuclear cells (MNCs), play an important role in postnatal neovascularization. Tissue ischemia augments mobilization of EPCs from bone marrow into the circulation and enhances incorporation of EPCs at sites of neovascularization. Two methods to obtain EPCs from bone marrow, peripheral blood or cord blood MNCs have been evaluated for therapeutic neovascularization: (1) fresh isolation using anti-CD34, anti-KDR or anti-AC133 antibody, and (2) ex vivo expansion of total MNCs. In an immunodeficient mouse model of hindlimb ischemia, systemic transplantation of human ex vivo expanded EPCs improves limb survival through the enhancement of blood flow in the ischemic tissue. A similar strategy also leads to histological and functional preservation of ischemic myocardium of nude rats. Recently, a preclinical study of catheter-based, intramyocardial transplantation ofautologous EPCs in a swine model of chronic myocardial ischemia demonstrated the therapeutic potential of cell-based therapy, with attenuation of myocardial ischemia and improvement in left ventricular function. These favorable outcomes strongly suggest a therapeutic impact of EPC transplantation in clinical settings. Further basic research, with improved understanding of the mechanisms governing homing and incorporation of EPCs, will be still necessary to optimize the methodology of the cell therapy.     

The Relationship between Endothelial Progenitor Cell Populations and Epicardial and Microvascular Coronary Disease—A Cellular,Angiographic and Physiologic Study

Background

Endothelial progenitor cells (EPCs) are implicated in protection against vascular disease. However, studies using angiography alone have reported conflicting results when relating EPCs to epicardial coronary artery disease (CAD) severity. Moreover, the relationship between different EPC types and the coronary microcirculation is unknown. We therefore investigated the relationship between EPC populations and coronary epicardial and microvascular disease.

Methods

Thirty-three patients with a spectrum of isolated left anterior descending artery disease were studied. The coronary epicardial and microcirculation were physiologically interrogated by measurement of fractional flow reserve (FFR), index of microvascular resistance (IMR) and coronary flow reserve (CFR). Two distinct EPC populations (early EPC and late outgrowth endothelial cells [OECs]) were isolated from these patients and studied ex vivo.

Results

There was a significant inverse relationship between circulating OEC levels and epicardial CAD severity, as assessed by FFR and angiography (r = 0.371, p = 0.04; r = -0.358, p = 0.04; respectively). More severe epicardial CAD was associated with impaired OEC migration and tubulogenesis (r = 0.59, p = 0.005; r = 0.589, p = 0.004; respectively). Patients with significant epicardial CAD (FFR<0.75) had lower OEC levels and function compared to those without hemodynamically significant stenoses (p<0.05). In contrast, no such relationship was seen for early EPC number and function, nor was there a relationship between IMR and EPCs. There was a significant relationship between CFR and OEC function.

Conclusions

EPC populations differ in regards to their associations with CAD severity. The number and function of OECs, but not early EPCs, correlated significantly with epicardial CAD severity. There was no relationship between EPCs and severity of coronary microvascular disease.