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1.  Endothelial Progenitor Cells Derived from Wharton's Jelly of the Umbilical Cord Reduces Ischemia-Induced Hind Limb Injury in Diabetic Mice by Inducing HIF-1α/IL-8 Expression 
Stem Cells and Development  2012;22(9):1408-1418.
Peripheral arterial diseases, the major complication of diabetes, can result in lower limb amputation. Since endothelial progenitor cells (EPCs) are involved in neovascularization, the aim of this study was to examine whether EPCs isolated from Wharton's jelly (WJ-EPCs) of the umbilical cord, a rich source of mesenchymal stem cells, could reduce ischemia-induced hind limb injury in diabetic mice. We evaluated the effects of WJ-EPC transplantation on hind limb injury caused by femoral artery ligation in mice with streptozotocin (STZ)-induced diabetes. We found that the ischemic hind limb in mice with STZ-induced diabetes showed decreased blood flow and capillary density and increased cell apoptosis and that these effects were significantly inhibited by an injection of WJ-EPCs. In addition, hypoxia-inducible factor-1α (HIF-1α) and interleukin-8 (IL-8) were highly expressed in transplanted WJ-EPCs in the ischemic skeletal tissues and were present at high levels in hypoxia-treated cultured WJ-EPCs. Moreover, incubation of the NOR skeletal muscle cell line under hypoxic conditions in conditioned medium from EPCs cultured for 16 h under hypoxic conditions resulted in decreased expression of pro-apoptotic proteins and increased expression of anti-apoptotic proteins. The inhibition of HIF-1α or IL-8 expression by EPCs using HIF-1α siRNA or IL-8 siRNA, respectively, prevented this change in expression of apoptotic-related proteins. Wharton's jelly in the umbilical cord is a valuable source of EPCs, and transplantation of these EPCs represents an innovative therapeutic strategy for treating diabetic ischemic tissues. The HIF-1α/IL-8 signaling pathway plays a critical role in the protective effects of EPCs in the ischemic hind limb of diabetic mice.
PMCID: PMC3629854  PMID: 23252631
2.  Novel Cell-Free Strategy for Therapeutic Angiogenesis: In Vitro Generated Conditioned Medium Can Replace Progenitor Cell Transplantation 
PLoS ONE  2009;4(5):e5643.
Current evidence suggests that endothelial progenitor cells (EPC) contribute to ischemic tissue repair by both secretion of paracrine factors and incorporation into developing vessels. We tested the hypothesis that cell-free administration of paracrine factors secreted by cultured EPC may achieve an angiogenic effect equivalent to cell therapy.
Methodology/Principal Findings
EPC-derived conditioned medium (EPC-CM) was obtained from culture expanded EPC subjected to 72 hours of hypoxia. In vitro, EPC-CM significantly inhibited apoptosis of mature endothelial cells and promoted angiogenesis in a rat aortic ring assay. The therapeutic potential of EPC-CM as compared to EPC transplantation was evaluated in a rat model of chronic hindlimb ischemia. Serial intramuscular injections of EPC-CM and EPC both significantly increased hindlimb blood flow assessed by laser Doppler (81.2±2.9% and 83.7±3.0% vs. 53.5±2.4% of normal, P<0.01) and improved muscle performance. A significantly increased capillary density (1.62±0.03 and 1.68±0.05/muscle fiber, P<0.05), enhanced vascular maturation (8.6±0.3 and 8.1±0.4/HPF, P<0.05) and muscle viability corroborated the findings of improved hindlimb perfusion and muscle function. Furthermore, EPC-CM transplantation stimulated the mobilization of bone marrow (BM)-derived EPC compared to control (678.7±44.1 vs. 340.0±29.1 CD34+/CD45− cells/1×105 mononuclear cells, P<0.05) and their recruitment to the ischemic muscles (5.9±0.7 vs. 2.6±0.4 CD34+ cells/HPF, P<0.001) 3 days after the last injection.
Intramuscular injection of EPC-CM is as effective as cell transplantation for promoting tissue revascularization and functional recovery. Owing to the technical and practical limitations of cell therapy, cell free conditioned media may represent a potent alternative for therapeutic angiogenesis in ischemic cardiovascular diseases.
PMCID: PMC2682571  PMID: 19479066
3.  Recovery from hindlimb ischemia is less effective in type 2 than in type 1 diabetic mice: Roles of eNOS and endothelial progenitor cells 
We sought to directly compare the effects of type 1 and type 2 diabetes on post-ischemic neovascularization and evaluate the mechanisms underlying differences between these groups. We tested the hypothesis that type 2 diabetic mice have a greater reduction in eNOS expression, greater increase in oxidative stress, and reduced arteriogenesis and angiogenesis resulting is less complete blood flow recovery than type 1 diabetic mice after induction of hindlimb ischemia.
Hindlimb ischemia was generated by femoral artery excision in streptozotocin-treated mice (model of type 1 diabetes), in db/db mice (model of type 2 diabetes), and in control (C57BL/6) mice. Dependent variables included markers of arteriogenesis and angiogenesis, as well as eNOS and markers of oxidative stress.
Post-ischemia recovery of hindlimb perfusion was significantly less in type 2 than in type 1 diabetic mice; however, neither diabetic group demonstrated a significant increase in collateral artery diameter or collateral artery angioscore in the ischemic hindlimb. The capillary/myofiber ratio in the gastrocnemius muscle decreased in response to ischemia in control or type 1 diabetic mice, but remained the same in type 2 diabetic mice. Gastrocnemius muscle eNOS expression was lower in type 1 and 2 diabetic mice than in control mice; this expression decreased after induction of ischemia in type 2, but not type 1 diabetic mice. The percentage of endothelial progenitor cells (EPC) in peripheral blood failed to increase in either diabetic group after induction of ischemia, whereas this variable significantly increased in the control group in response to ischemia. EPC eNOS expression decreased after induction of ischemia in type 1, but not type 2 diabetic mice. EPC nitrotyrosine accumulation increased after induction of ischemia in type 2, but not type 1 diabetic mice. EPC migration in response to VEGF was reduced in type 1 and type 2 diabetic mice than in control mice. EPC incorporation into tubular structures was less effective in type 2 diabetic mice. Extensive fatty infiltration was present in ischemic muscle of type 2, but not type 1 diabetic mice.
We conclude that type 2 diabetic mice displayed a significantly less effective response to hindlimb ischemia than type 1 diabetic mice.
PMCID: PMC2797079  PMID: 19837544
collateral artery; arteriogenesis; angiogenesis; nitrotyrosine; nitric oxide
4.  Transfusion of CXCR4-Primed Endothelial Progenitor Cells Reduces Cerebral Ischemic Damage and Promotes Repair in db/db Diabetic Mice 
PLoS ONE  2012;7(11):e50105.
This study investigated the role of stromal cell-derived factor-1α (SDF-1α)/CXC chemokine receptor 4 (CXCR4) axis in brain and endothelial progenitor cells (EPCs), and explored the efficacy of CXCR4 primed EPCs in treating ischemic stroke in diabetes. The db/db diabetic and db/+ mice were used in this study. Levels of plasma SDF-1α and circulating CD34+CXCR4+ cells were measured. Brain SDF-1α and CXCR4 expression were quantified at basal and after middle cerebral artery occlusion (MCAO). In in vitro study, EPCs were transfected with adenovirus carrying null (Ad-null) or CXCR4 (Ad-CXCR4) followed with high glucose (HG) treatment for 4 days. For pathway block experiments, cells were pre-incubated with PI3K inhibitor or nitric oxide synthase (NOS) inhibitor for two hours. The CXCR4 expression, function and apoptosis of EPCs were determined. The p-Akt/Akt and p-eNOS/eNOS expression in EPCs were also measured. In in vivo study, EPCs transfected with Ad-null or Ad-CXCR4 were infused into mice via tail vein. On day 2 and 7, the cerebral blood flow, neurologic deficit score, infarct volume, cerebral microvascular density, angiogenesis and neurogenesis were determined. We found: 1) The levels of plasma SDF-1α and circulating CD34+CXCR4+ cells were decreased in db/db mice; 2) The basal level of SDF-1α and MCAO-induced up-regulation of SDF-1α/CXCR4 axis were reduced in the brain of db/db mice; 3) Ad-CXCR4 transfection increased CXCR4 expression in EPCs and enhanced EPC colonic forming capacity; 4) Ad-CXCR4 transfection prevented EPCs from HG-induced dysfunction (migration and tube formation) and apoptosis via activation of PI3K/Akt/eNOS signal pathway; 4) Ad-CXCR4 transfection enhanced the efficacy of EPC infusion in attenuating infarct volume and promoting angiogenesis and neurogenesis. Our data suggest that Ad-CXCR4 primed EPCs have better therapeutic effects for ischemia stroke in diabetes than unmodified EPCs do.
PMCID: PMC3503762  PMID: 23185548
5.  Rosuvastatin Enhances Angiogenesis via eNOS-Dependent Mobilization of Endothelial Progenitor Cells 
PLoS ONE  2013;8(5):e63126.
Circulating endothelial progenitor cells (circEPCs) of bone marrow (BM) origin contribute to postnatal neovascularization and represent a potential therapeutic target for ischemic disease. Statins are beneficial for ischemia disease and have been implicated to increase neovascularization via mechanisms independent of lipid lowering. However, the effect of Statins on EPC function is not completely understood. Here we sought to investigate the effects of Rosuvastatin (Ros) on EPC mobilization and EPC-mediated neovascularization during ischemic injury. In a mouse model of surgically-induced hindlimb ischemia (HLI), treatment of mice with low dose (0.1 mg/kg) but not high dose (5 mg/kg) significantly increased capillary density and accelerated blood flow recovery, as compared to saline-treated group. When HLI was induced in mice that had received Tie2/LacZ BM transplantation, Ros treatment led a significantly larger amount of endothelial cells (ECs) of BM origin incorporated at ischemic sites than saline. After treatment of mice with a single low dose of Ros, circEPCs significantly increased from 2 h, peaked at 4 h, declined until 8 h. In a growth-factor reduced Matrigel plug-in assay, Ros treatment for 5 d induced endothelial lineage differentiation in vivo. Interestingly, the enhanced circEPCs and post-HLI neovascularization stimulated by Ros were blunted in mice deficient in endothelial nitric oxide synthase (eNOS), and Ros increased p-Akt/p-eNOS levels in EPCs in vitro, indicating these effects of Ros are dependent on eNOS activity. We conclude that Ros increases circEPCs and promotes their de novo differentiation through eNOS pathway.
PMCID: PMC3660394  PMID: 23704894
6.  Apolipoprotein (a) Impairs Endothelial Progenitor Cell-Mediated Angiogenesis 
DNA and Cell Biology  2013;32(5):243-251.
Improvement of blood flow and promotion of angiogenesis are important therapeutic measures for the treatment of ischemic peripheral vascular diseases. Since apolipoprotein (a) (apo (a)) is a glycoprotein with repetitive kringle domains exhibiting 75% to 98% structural homology with plasminogen (Plg), apo (a) may also have a negative effect on endothelial progenitor cell (EPC)-induced angiogenesis through Plg-like inhibitory effects on EPC proliferation, adhesion, migration, and angiogenesis. To evaluate the effect of apo (a) on EPCs-induced angiogenesis, EPCs were isolated from the bone marrow of apo (a) transgenic mice, wild-type litter mates, and normal mice. These cells were cultured without or with apo (a) before transplantation. Hindlimb ischemia models were surgically induced in mice, which then received an intravenous injection of 3×105 EPCs. At 3, 7, and 14 days post EPC transplantation, the adhesion, migration abilities, and capillary density in calf muscles were assessed. Results indicate that apo (a) significantly reduced the adhesion and migration abilities of EPCs. Furthermore, the tubule-like formation of EPCs on Matrigel gels was damaged. In vivo experiments showed the homing of EPCs to ischemic peripheral vascular, and the number of capillary vessels decreased significantly in apo(a) transgenic mice. This study demonstrated that apo (a) could attenuate the adhesion, migration, and homing abilities of EPCs and could impair the angiogenesis ability of EPCs.
Homing of endothelial progenitor cells to ischemic peripheral vascular sites and the number of capillaries were decreased in mice transgenic for Apo (a). This gene attenuated adhesion, migration, and homing abilities of EPCs and impaired angiogenesis.
PMCID: PMC3651684  PMID: 23581552
7.  Identification of E-Selectin as a Novel Target for the Regulation of Post-Natal Neovascularization: Implications for Diabetic Wound Healing 
Annals of Surgery  2010;252(4):625-634.
We previously reported that stromal cell-derived factor-1α (SDF-1α, a homing signal for recruiting endothelial progenitor cells (EPC) to areas of neovascularization), is down-regulated in diabetic wounds 1. We now investigate signals whereby mature endothelial cells (EC) and circulating EPC achieve SDF-1α-mediated EPC homing.
SDF-1α in diabetic wounds were therapeutically increased by injection of SDF-1α–engineered bone marrow-derived fibroblasts versus control cells (N= 48 (20, NOD), (28, STZ-C57)). PCR-array gene expression differences were validated by Western blotting and immunohistochemistry. The role of adhesion molecule(s) in mediating SDF-1α-induced EPC homing and wound healing was furthered studied using antagonists in vitro and in vivo.
Increasing wound SDF-1α via cell-base therapy promotes healing in diabetic mice (~20% increase in healing rates by day 3, p=0.006). SDF-1α increased EC-EPC adhesion and specifically upregulated E-selectin expression in human microvascular EC (2.3-fold increase, p<0.01). This effect was also significant in blood vessels of the experimental mice and resulted in increased wound neovascularization. The regulatory effects of SDF-1α on EC-EPC adhesion and EPC homing were specifically mediated by E-selectin, as the application of E-selectin antagonists significantly inhibited SDF-1α-induced EC-EPC adhesion, EPC homing, wound neovascularization, and wound healing.
SDF-1α–engineered cell-based therapy promotes diabetic wound healing in mice by specifically upregulating E-selectin expression in mature EC leading to increase EC-EPC adhesion, EPC homing and increased wound neovascularization. These findings provide novel insight into the signals underlying the biological effect of SDF-1α on EPC homing and point to E-selectin as a new potential target for therapeutic manipulation of EPC trafficking in diabetic wound healing.
PMCID: PMC3391745  PMID: 20881769
8.  Identification of mouse colony-forming endothelial progenitor cells for postnatal neovascularization: a novel insight highlighted by new mouse colony-forming assay 
Endothelial progenitor cells (EPCs) play a critical role in restoration of ischemic diseases. However, the actual status of EPC development and the mechanisms of EPC dysfunctions in patients with various ischemic diseases remain unknown.
To investigate the detailed function of EPCs in experimental murine models, we have established an EPC colony forming assay (EPC-CFA) in murine EPCs. The abilities of murine EPCs in differentiation, adhesive capacity, proliferative potency, and transplantation in vitro and in vivo were then examined.
Peripheral blood mononuclear cells (PB-MNCs), bone marrow mononuclear cells (BM-MNCs) or bone marrow c-Kit+/Sca-1+ lineage negative (BM-KSL) cells differentiated into two types of EPC colony forming units (EPC-CFUs), large sized EPC (large-EPC)-CFUs and small sized EPC (small-EPC)-CFUs. Gene expression analysis demonstrated that both EPC-CFU-derived cells expressed eNOS, Flk-1 and VE-cadherin, markers of endothelial cells (ECs), although the small-EPCs derived from small-EPC-CFU were higher in number and showed more immature features (higher population of KSL cells). Functionally, the large-EPCs derived from large-EPC-CFU had higher adhesive capacity but lower proliferative potency than small-EPCs, showing improved tubular forming capacity and incorporation potency into primary EC-derived tube formation. Importantly, hindlimb ischemia increased the frequencies of large-EPC-CFUs differentiated from PB-MNCs and bone marrow. Actually, transplantation of large-EPCs into ischemic hindlimb enhanced neovascularization in hindlimb ischemia model, although small-EPCs or murine ECs did not, suggesting that large-EPC-CFUs might play an important role in restoration of ischemic diseases.
We demonstrated, using a murine ischemia model, that the EPC-CFA could be a useful way to investigate the differentiation levels of murine EPCs, further providing a crucial clue that large-EPC-CFU status may be more functional or effective EPCs to promote neovascularization.
PMCID: PMC3706928  PMID: 23448126
9.  Zoledronate Inhibits Ischemia-Induced Neovascularization by Impairing the Mobilization and Function of Endothelial Progenitor Cells 
PLoS ONE  2012;7(7):e41065.
Bisphosphonates are a class of pharmacologic compounds that are commonly used to treat postmenopausal osteoporosis and malignant osteolytic processes. Studies have shown that bone marrow-derived endothelial progenitor cells (EPCs) play a significant role in postnatal neovascularization. Whether the nitrogen-containing bisphosphonate zoledronate inhibits ischemia-induced neovascularization by modulating EPC functions remains unclear.
Methodology/Principal Findings
Unilateral hindlimb ischemia was surgically induced in wild-type mice after 2 weeks of treatment with vehicle or zoledronate (low-dose: 30 μg/kg; high-dose: 100 μg/kg). Doppler perfusion imaging demonstrated that the ischemic limb/normal side blood perfusion ratio was significantly lower in wild-type mice treated with low-dose zoledronate and in mice treated with high-dose zoledronate than in controls 4 weeks after ischemic surgery (control vs. low-dose vs. high-dose: 87±7% vs. *61±18% vs. **49±17%, *p<0.01, **p<0.005 compared to control). Capillary densities were also significantly lower in mice treated with low-dose zoledronate and in mice treated with high-dose zoledronate than in control mice. Flow cytometry analysis showed impaired mobilization of EPC-like cells (Sca-1+/Flk-1+) after surgical induction of ischemia in mice treated with zoledronate but normal levels of mobilization in mice treated with vehicle. In addition, ischemic tissue from mice that received zoledronate treatment exhibited significantly lower levels of the active form of MMP-9, lower levels of VEGF, and lower levels of phosphorylated eNOS and phosphorylated Akt than ischemic tissue from mice that received vehicle. Results of the in vitro studies showed that incubation with zoledronate inhibited the viability, migration, and tube-forming capacities of EPC.
Zoledronate inhibited ischemia-induced neovascularization by impairing EPC mobilization and angiogenic functions. These findings suggest that administration of zoledronate should be withheld in patients with ischemic events such as acute limb ischemia.
PMCID: PMC3405104  PMID: 22848429
10.  Dual Angiogenic and Neurotrophic Effects of Bone Marrow–Derived Endothelial Progenitor Cells on Diabetic Neuropathy 
Circulation  2009;119(5):699-708.
Endothelial progenitor cells (EPCs) are known to promote neovascularization in ischemic diseases. Recent evidence suggested that diabetic neuropathy is causally related to impaired angiogenesis and deficient growth factors. Accordingly, we investigated whether diabetic neuropathy could be reversed by local transplantation of EPCs.
Methods and Results
We found that motor and sensory nerve conduction velocities, blood flow, and capillary density were reduced in sciatic nerves of streptozotocin-induced diabetic mice but recovered to normal levels after hind-limb injection of bone marrow–derived EPCs. Injected EPCs were preferentially and durably engrafted in the sciatic nerves. A portion of engrafted EPCs were uniquely localized in close proximity to vasa nervorum, and a smaller portion of these EPCs were colocalized with endothelial cells. Multiple angiogenic and neurotrophic factors were significantly increased in the EPC-injected nerves. These dual angiogenic and neurotrophic effects of EPCs were confirmed by higher proliferation of Schwann cells and endothelial cells cultured in EPC-conditioned media.
We demonstrate for the first time that bone marrow-derived EPCs could reverse various manifestations of diabetic neuropathy. These therapeutic effects were mediated by direct augmentation of neovascularization in peripheral nerves through long-term and preferential engraftment of EPCs in nerves and particularly vasa nervorum and their paracrine effects. These findings suggest that EPC transplantation could represent an innovative therapeutic option for treating diabetic neuropathy.
PMCID: PMC2746559  PMID: 19171856
angiogenesis; diabetes mellitus; progenitor cells; diabetic neuropathy
11.  Endothelial progenitor cell transplantation improves long-term outcome in mice 
Annals of neurology  2010;67(4):488-497.
Endothelial progenitor cells (EPCs) have been implicated in playing an important role in vascular repair and revascularization in ischemic organs including brain tissue. However, the cause of EPC migration and the function of EPC playing following post-ischemia are unclear. Here, we reported EPC therapy in a mouse model of transient middle cerebral artery occlusion (tMCAO) to explore the roles of EPC following ischemic brain injury.
Human EPCs were cultured, characterized, and confirmed with flow cytometry. Ex vivo expanded EPCs (1×106) were injected via jugular vein after 1 hour of tMCAO. Histological and behavioral analyses were performed from day 1 to 28 days after tMCAO.
EPCs were detected in ischemic brain region 24 hours after MCAO. EPC transplantation significantly reduced ischemic infarct volume at 3 days following MCAO compared to the control (p<0.05). CXCR4 was expressed on majority of EPCs and SDF-1-induced EPC migration was blocked by AMD3100 in vitro. SDF-1 was up-regulated in ischemic brain and AMD3100 could reduce EPCs migration to the ischemic region in vivo, suggesting that SDF-1/CXCR4 was involved in EPC-mediated neuroprotection. Compared to the control, EPC therapy reduced mouse cortex atrophy 4 weeks after tMCAO, which was accompanied by improved neurobehavioral outcomes (p<0.05). In addition, EPC injection potently increased angiogenesis in the peri-infarction area (p<0.05).
We conclude that systemic delivery of EPC protect against cerebral ischemic injury, promote neurovascular repair, and improve long-term neurobehavioral outcomes. Our data suggests that SDF-1/CXCR4 plays a critical role in EPC-mediated neuroprotection.
PMCID: PMC3026588  PMID: 20437584
angiogenesis; EPCs; ischemia; mice; neuroprotection
12.  Local Injection of Deferoxamine Improves Neovascularization in Ischemic Diabetic Random Flap by Increasing HIF-1α and VEGF Expression 
PLoS ONE  2014;9(6):e100818.
Although the systemic administration of deferoxamine (DFO) is protective in experimental models of normal ischemic flap and diabetic wound, its effect on diabetic flap ischemia using a local injection remains unknown.
To explore the feasibility of local injection of DFO to improve the survival of ischemic random skin flaps in streptozotocin (STZ)-induced diabetic mice.
Ischemic random skin flaps were made in 125 mice. Animals were divided into the DFO-treated (n = 20), PBS-treated (n = 16) and untreated (n = 16) groups. Surviving area, vessel density, and expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) were evaluated on the seventh day after local injection.
The viability of DFO-treated flap was significantly enhanced, with increased regional blood perfusion and capillary density compared with those in the two control groups. Fluorescence-activated cell sorting (FACS) analysis demonstrated a marked increase in systemic Flk-1+/CD11b− endothelial progenitor cells (EPCs) in DFO-treated mice. Furthermore, the expression of VEGF and HIF-1α was increased not only in diabetic flap tissue, but also in dermal fibroblasts cultured under hyperglycemic and hypoxic conditions.
Local injection of DFO could exert preventive effects against skin flap necrosis in STZ-induced diabetic mice by elevating the expression of HIF-1α and VEGF, increased EPC mobilization, which all contributed to promote ischemic diabetic flap survival.
PMCID: PMC4071063  PMID: 24963878
13.  Reduced levels of circulating endothelial progenitor cells in acute myocardial infarction patients with diabetes or pre-diabetes: accompanying the glycemic continuum 
Diabetic patients have a significantly worse prognosis after an acute myocardial infarction (AMI) than their counterparts. Previous studies have shown that the number of circulating endothelial progenitor cells (EPCs) significantly increase early after an AMI in normoglycemic patients. However, it is well known that type 2 diabetes mellitus (DM) is associated with impaired function and reduced circulating EPCs levels. Nonetheless, few studies have analyzed EPCs response of diabetics to an AMI and the EPC response of pre-diabetic patients has not been reported yet. Therefore, we hypothesized that in the acute phase of an AMI, diabetic and pre-diabetics have lower circulating EPCs levels than patients with normal glucose metabolism. We also evaluated the possible capacity of chronic antidiabetic treatment in the recovery of EPCs response to an AMI in diabetics.
One-hundred AMI patients were prospectively enrolled in the study. Using the high-performance flow cytometer FACSCanto II, circulating EPCs (CD45dimCD34+KDR+ and CD45dimCD133+KDR+ cells) were quantified, within the first 24 hours of admission. In addition, as an indirect functional parameter, we also analyzed the fraction of EPCs coexpressing the homing marker CXCR4.
We found that in the acute phase of an AMI, diabetic patients presented significantly lower levels of circulating CD45dimCD34+KDR+ and CD45dimCD133+KDR+ EPCs by comparison with nondiabetics, with a parallel decrease in the subpopulations CXCR4+ (p < 0.001). Indeed, this study suggests that the impaired response of EPCs to an AMI is an early event in the natural history of DM, being present even in pre-diabetes. Our results, also demonstrated that numbers of all EPCs populations were inversely correlated with HbA1c (r = -0.432, p < 0.001 for CD45dimCD34+KDR+ cells). Finally, this study suggests that previous chronic insulin therapy (but not oral antidiabetic drugs) attenuate the deficient response of diabetic EPCs to an AMI.
This study indicates that there is a progressive decrease in EPCs levels, from pre-diabetes to DM, in AMI patients. Moreover, glycemic control seems to be determinant for circulating EPCs levels presented in the acute phase of an AMI and chronic insulin therapy may probably attenuate the deficit in EPCs pool seen in diabetics.
PMCID: PMC4082424  PMID: 24934236
Endothelial progenitor cells; Diabetes; Pre-diabetes; Insulin; Oral antidiabetic drugs; Acute myocardial infarction; Homing
14.  Role of Nox2-Based NADPH Oxidase in Bone Marrow and Progenitor Cell Function Involved in Neovascularization Induced by Hindlimb Ischemia 
Circulation research  2008;103(2):212-220.
Bone marrow (BM) is the major reservoir for endothelial progenitor cells (EPCs). Postnatal neovascularization depends on not only angiogenesis but also vasculogenesis, which is mediated through mobilization of EPCs from BM and their recruitment to the ischemic sites. Reactive oxygen species (ROS) derived from Nox2-based NADPH oxidase play an important role in postnatal neovascularization; however, their role in BM and EPC function is unknown. Here we show that hindlimb ischemia of mice significantly increases Nox2 expression and ROS production in BM-mononuclear cells (BMCs), which is associated with an increase in circulating EPC-like cells. Mice lacking Nox2 show reduction of ischemia-induced flow recovery, ROS levels in BMCs, as well as EPC mobilization from BM. Transplantation of wild-type (WT)-BM into Nox2-deficient mice rescues the defective neovascularization, whereas WT mice transplanted with Nox2-deficient BM show reduced flow recovery and capillary density compared to WT-BM transplanted control. Intravenous infusion of WT- and Nox2-deficient BMCs into WT mice reveals that neovascularization and homing capacity are impaired in Nox2-deficient BMCs in vivo. In vitro, Nox2-deficient c-kit+Lin− BM stem/progenitor cells show impaired chemotaxis and invasion as well as polarization of actins in response to stromal derived factor (SDF), which is associated with blunted SDF-1–mediated phosphorylation of Akt. In conclusion, Nox2-derived ROS in BM play a critical role in mobilization, homing, and angiogenic capacity of EPCs and BM stem/progenitor cells, thereby promoting revascularization of ischemic tissue. Thus, NADPH oxidase in BM and EPCs is potential therapeutic targets for promoting neovascularization in ischemic cardiovascular diseases.
PMCID: PMC2711765  PMID: 18583711
NADPH oxidase; reactive oxygen species; angiogenesis; vasculogenesis; neovascularization; stromal derived factor; endothelial progenitor cells
15.  Kallikrein Gene-Modified EPCs Induce Angiogenesis in Rats with Ischemic Hindlimb and Correlate with Integrin αvβ3 Expression 
PLoS ONE  2013;8(9):e73035.
Human tissue kallikrein (hTK) plays an essential role in the physiological and pathological mechanisms of blood vessels. This study aimed to determine whether angiogenesis induced by endothelial progenitor cells (EPCs) transduced with the adenovirus-mediated hTK gene could improve blood flow in rat hindlimb ischemia in vivo and to establish a promising mechanism in vitro.
EPCs transduced with adenovirus encoding hTK-162 (i.e., Ad/hTK-transduced EPCs or Ad/GFP-transduced EPCs) were administered to Wister rats with hindlimb ischemia through therapeutic neovascularization. Muscular capillary density (MCD), blood flow (BF), and the number of myofibers were measured at days 7, 14, and 21 after treatment. Expressions of integrin αvβ3 and endothelial nitric oxide synthase (eNOS) were detected on the surface of EPCs.
MCD, BF, and the number of myofibers in rats with Ad/hTK-transduced EPCs remarkably increased at day 21 after treatment compared with rats with Ad/GFP-transduced EPCs or the control group (P<0.01). Expressions of integrin αvβ3 and eNOS protein on the surface of EPCs also increased in rats with Ad/hTK-transduced EPCs. The levels of integrin αvβ3 expression were reduced by PI3K and eNOS blockade, and the inhibitor of integrin αvβ3 abrogated the migration and adhesion of hTK-transduced EPCs (P<0.05).
hTK gene delivery in vivo improves the natural angiogenic response to ischemia. The ability of hTK gene-transduced EPCs can be enhanced in vitro, in which integrin αvβ3 plays a role in the process.
PMCID: PMC3760867  PMID: 24019890
16.  Magnetic Bionanoparticle Enhances Homing of Endothelial Progenitor Cells in Mouse Hindlimb Ischemia 
Korean Circulation Journal  2012;42(6):390-396.
Background and Objectives
Poor homing efficiency is one of the major limitations of current stem cell therapy. Magnetic bionanoparticles (MPs) obtained from Magnetospirillum sp. AMB-1 have a lipid bilayer membrane and ferromagnetic properties. We evaluated a novel priming strategy using MPs to enhance the homing of transplanted progenitor cells to target tissue.
Materials and Methods
Effects of MP on proliferation, viability, and migration of late human endothelial progenitor cells (EPCs) were examined in vitro. Additionally, effects of MP on gene and protein expression related to survival and adhesion were evaluated. Homing and angiogenic efficiency of MP transferred late EPCs was evaluated in nude mouse hindlimb ischemia model.
Below threshold concentration, MP transfer did not influence proliferation or survival of late EPCs, but enhanced migration and trans-endothelial migration of late EPCs toward magnet. Below threshold concentration, MP transfer did not influence gene and protein expression related to survival. In the mouse hindlimb ischemia model, late EPCs treated with high dose MP (5 ug/mL) showed enhanced homing of injected late EPCs in the ischemic limb by magnet, compared to low dose MP (1 ug/mL) treated late EPCs. In addition, high dose MP transferred EPC showed significantly better improvement of perfusion in ischemic limb compared to untreated EPC.
MP transfer with magnet application can be a promising novel strategy to enhance homing efficacy and outcomes of current stem cell therapy.
PMCID: PMC3390424  PMID: 22787469
Nanoparticles; Stem cells; Ischemia
17.  Functional disruption of α4 integrin mobilizes bone marrow–derived endothelial progenitors and augments ischemic neovascularization 
The cell surface receptor α4 integrin plays a critical role in the homing, engraftment, and maintenance of hematopoietic progenitor cells (HPCs) in the bone marrow (BM). Down-regulation or functional blockade of α4 integrin or its ligand vascular cell adhesion molecule-1 mobilizes long-term HPCs. We investigated the role of α4 integrin in the mobilization and homing of BM endothelial progenitor cells (EPCs). EPCs with endothelial colony-forming activity in the BM are exclusively α4 integrin–expressing cells. In vivo, a single dose of anti–α4 integrin antibody resulted in increased circulating EPC counts for 3 d. In hindlimb ischemia and myocardial infarction, systemically administered anti–α4 integrin antibody increased recruitment and incorporation of BM EPCs in newly formed vasculature and improved functional blood flow recovery and tissue preservation. Interestingly, BM EPCs that had been preblocked with anti–α4 integrin ex vivo or collected from α4 integrin–deficient mice incorporated as well as control cells into the neovasculature in ischemic sites, suggesting that α4 integrin may be dispensable or play a redundant role in EPC homing to ischemic tissue. These data indicate that functional disruption of α4 integrin may represent a potential angiogenic therapy for ischemic disease by increasing the available circulating supply of EPCs.
PMCID: PMC2118065  PMID: 16401693
18.  Effects of lycopene on number and function of human peripheral blood endothelial progenitor cells cultivated with high glucose 
Nutrition Research and Practice  2014;8(4):368-376.
The objectives of this study were to investigate the effects of lycopene on the migration, adhesion, tube formation capacity, and p38 mitogen-activated protein kinase (p38 MAPK) activity of endothelial progenitor cells (EPCs) cultivated with high glucose (HG) and as well as explore the mechanism behind the protective effects of lycopene on peripheral blood EPCs.
Mononuclear cells were isolated from human peripheral blood by Ficoll density gradient centrifugation. EPCs were identified after induction of cellular differentiation. Third generation EPCs were incubated with HG (33 mmol/L) or 10, 30, and 50 µg/mL of lycopene plus HG. MTT assay and flow cytometry were performed to assess proliferation and apoptosis of EPCs. EPC migration was assessed by MTT assay with a modified boyden chamber. Adhesion assay was performed by replating EPCs on fibronectin-coated dishes, after which adherent cells were counted. In vitro vasculogenesis activity was assayed by Madrigal network formation assay. Western blotting was performed to analyze protein expression of both phosphorylated and non-phosphorylated p38 MAPK.
The proliferation, migration, adhesion, and in vitro vasculogenesis capacity of EPCs treated with 10, 30, and 50 µg/mL of lycopene plus HG were all significantly higher comapred to the HG group (P < 0.05). Rates of apoptosis were also significantly lower than that of the HG group. Moreover, lycopene blocked phosphorylation of p38 MAPK in EPCs (P < 0.05). To confirm the causal relationship between MAPK inhibition and the protective effects of lycopene against HG-induced cellular injury, we treated cells with SB203580, a phosphorylation inhibitor. The inhibitor significantly inhibited HG-induced EPC injury.
Lycopene promotes proliferation, migration, adhesion, and in vitro vasculogenesis capacity as well as reduces apoptosis of EPCs. Further, the underlying molecular mechanism of the protective effects of lycopene against HG-induced EPC injury may involve the p38 MAPK signal transduction pathway. Specifically, lycopene was shown to inhibit HG-induced EPC injury by inhibiting p38 MAPKs.
PMCID: PMC4122707  PMID: 25110555
Lycopene; high glucose; endothelial progenitor cells; p38 MAPK; curve fitting
19.  GroEL1, a Heat Shock protein 60 of Chlamydia pneumoniae, Impairs Neovascularization by Decreasing Endothelial Progenitor Cell Function 
PLoS ONE  2013;8(12):e84731.
The number and function of endothelial progenitor cells (EPCs) are sensitive to hyperglycemia, hypertension, and smoking in humans, which are also associated with the development of atherosclerosis. GroEL1 from Chlamydia pneumoniae has been found in atherosclerotic lesions and is related to atherosclerotic pathogenesis. However, the actual effects of GroEL1 on EPC function are unclear. In this study, we investigate the EPC function in GroEL1-administered hind limb-ischemic C57BL/B6 and C57BL/10ScNJ (a toll-like receptor 4 (TLR4) mutation) mice and human EPCs. In mice, laser Doppler imaging, flow cytometry, and immunohistochemistry were used to evaluate the degree of neo-vasculogenesis, circulating level of EPCs, and expression of CD34, vWF, and endothelial nitric oxide synthase (eNOS) in vessels. Blood flow in the ischemic limb was significantly impaired in C57BL/B6 but not C57BL/10ScNJ mice treated with GroEL1. Circulating EPCs were also decreased after GroEL1 administration in C57BL/B6 mice. Additionally, GroEL1 inhibited the expression of CD34 and eNOS in C57BL/B6 ischemic muscle. In vitro, GroEL1 impaired the capacity of differentiation, mobilization, tube formation, and migration of EPCs. GroEL1 increased senescence, which was mediated by caspases, p38 MAPK, and ERK1/2 signaling in EPCs. Furthermore, GroEL1 decreased integrin and E-selectin expression and induced inflammatory responses in EPCs. In conclusion, these findings suggest that TLR4 and impaired NO-related mechanisms could contribute to the reduced number and functional activity of EPCs in the presence of GroEL1 from C. pneumoniae.
PMCID: PMC3871664  PMID: 24376840
20.  Endothelial Progenitor Cell Cotransplantation Enhances Islet Engraftment by Rapid Revascularization 
Diabetes  2012;61(4):866-876.
Impaired revascularization of transplanted islets is a critical problem that leads to progressive islet loss. Since endothelial progenitor cells (EPCs) are known to aid neovascularization, we aimed to enhance islet engraftment by cotransplanting EPCs with islets. Porcine islets, with (islet-EPC group) or without (islet-only group) human cord blood–derived EPCs, were transplanted into diabetic nude mice. The islet-EPC group reached euglycemia by ∼11 days posttransplantation, whereas the islet-only group did not. Also, the islet-EPC group had a higher serum porcine insulin level than the islet-only group. Islets from the islet-EPC group were more rapidly revascularized at the early period of transplantation without increment of final capillary density at the fully revascularized graft. Enhanced revascularization rate in the islet-EPC group was mainly attributed to stimulating vascular endothelial growth factor-A production from the graft. The rapid revascularization by EPC cotransplantation led to better graft perfusion and recovery from hypoxia. EPC cotransplantation was also associated with greater β-cell proliferation, probably by more basement membrane production and hepatocyte growth factor secretion. In conclusion, cotransplantation of EPCs and islets induces better islet engraftment by enhancing the rate of graft revascularization. These findings might provide a directly applicable tool to enhance the efficacy of islet transplantation in clinical practice.
PMCID: PMC3314353  PMID: 22362173
21.  Increased Vascular Senescence and Impaired Endothelial Progenitor Cell Function Mediated by Mutation of Circadian Gene Per2 
Circulation  2008;118(21):2166-2173.
Alteration of the circadian rhythm and increased vascular senescence are linked to cardiovascular disease. Per2, a circadian gene, is known to regulate endothelium-dependent vasomotion. However, the mechanism by which Per2 affects endothelial function is unknown. We hypothesize that endothelial dysfunction in Per2 mutant (Per2m/m) mice is mediated in part by increased vascular senescence and impaired endothelial progenitor cell (EPC) function.
Methods and Results
Endothelial cells from Per2m/m mice exhibit increased protein kinase Akt signaling, greater senescence, and impaired vascular network formation and proliferation. Indeed, Per2m/m mice have impaired blood flow recovery and developed autoamputation of the distal limb when subjected to hind-limb ischemia. Furthermore, matrigel implantation into Per2m/m mice resulted in less neovascularization. Because EPCs contribute to angiogenesis, we studied the role of Per2 in these cells using bone marrow transplantation. Basal EPC levels were similar between wild-type and Per2m/m mice. However, compared with wild-type bone marrow transplantation mice, EPC mobilization was impaired in Per2m/m bone marrow transplantation mice in response to ischemia or VEGF stimulation. Bone marrow transplantation or infusion of wild-type EPC restored blood flow recovery and prevented autoamputation in Per2m/m mice.
These findings indicate that mutation of Per2 causes Akt-dependent senescence and impairs ischemia-induced revascularization through the alteration of EPC function.
PMCID: PMC2656770  PMID: 18981300
angiogenesis; circadian rhythm; endothelium; ischemia; senescence
22.  Norepinephrine Stimulates Mobilization of Endothelial Progenitor Cells after Limb Ischemia 
PLoS ONE  2014;9(7):e101774.
During several pathological processes such as cancer progression, thermal injury, wound healing and hindlimb ischemia, the mobilization of endothelial progenitor cells (EPCs) mobilization was enhanced with an increase of sympathetic nerve activity and norepinephrine (NE) secretion, yet the cellular and molecular mechanisms involved in the effects of NE on EPCs has less been investigated.
Methods and Results
EPCs from BMs, peripheral circulation and spleens, the VEGF concentration in BM, skeletal muscle, peripheral circulation and spleen and angiogenesis in ischemic gastrocnemius were quantified in mice with hindlimbs ischemia. Systemic treatment of NE significantly increased EPCs number in BM, peripheral circulation and spleen, VEGF concentration in BM and skeletal muscle and angiogenesis in ischemic gastrocnemius in mice with hind limb ischemia, but did not affair VEGF concentration in peripheral circulation and spleen. EPCs isolated from healthy adults were cultured with NE in vitro to evaluate proliferation potential, migration capacity and phosphorylations of Akt and eNOS signal moleculars. Treatment of NE induced a significant increase in number of EPCs in the S-phase in a dose-dependent manner, as well as migrative activity of EPCs in vitro (p<0.05). The co-treatment of Phentolamine, I127, LY294002 and L-NAME with NE blocked the effects of NE on EPCs proliferation and migration. Treatment with NE significantly increased phosphorylation of Akt and eNOS of EPCs. Addition of phentolamine and I127 attenuated the activation of Akt/eNOS pathway, but metoprolol could not. Pretreatment of mice with either Phentolamine or I127 significantly attenuated the effects of NE on EPCs in vivo, VEGF concentration in BM, skeletal muscle and angiogenesis in ischemic gastrocnemius, but Metoprolol did not.
These results unravel that sympathetic nervous system regulate EPCs mobilization and their pro-angiogenic capacity via α adrenoceptor, β 2 adrenoceptor and meanwhile Akt/eNOS signaling pathway.
PMCID: PMC4090158  PMID: 25007164
23.  Impact of obesity control on circulating level of endothelial progenitor cells and angiogenesis in response to ischemic stimulation 
Background and aim
We tested the hypothesis that obesity reduced circulating number of endothelial progenitor cells (EPCs), angiogenic ability, and blood flow in ischemic tissue that could be reversed after obesity control.
8-week-old C57BL/6J mice (n = 27) were equally divided into group 1 (fed with 22-week control diet), group 2 (22-week high fat diet), and group 3 (14-week high fat diet, followed by 8-week control diet). Critical limb ischemia (CLI) was induced at week 20 in groups 2 and 3. The animals were sacrificed at the end of 22 weeks.
Heart weight, body weight, abdominal fat weight, serum total cholesterol level, and fasting blood sugar were highest in group 2 (all p < 0.001). The numbers of circulating EPCs (C-kit/CD31+, Sca-1/KDR + and CXCR4/CD34+) were lower in groups 1 and 2 than in group 3 at 18 h after CLI induction (p < 0.03). The numbers of differentiated EPCs (C-kit/CD31+, CXCR4/CD34+ and CD133+) from adipose tissue after 14-day cultivation were also lowest in group 2 (p < 0.001). Protein expressions of VCAM-1, oxidative index, Smad3, and TGF-β were higher, whereas the Smad1/5 and BMP-2, mitochondrial cytochrome-C SDF-1α and CXCR4 were lower in group 2 than in groups 1 and 3 (all p < 0.02). Immunofluorescent staining of CD31+ and vWF + cells, the number of small vessel (<15 μm), and blood flow through Laser Doppler scanning of ischemic area were lower in group 2 compared to groups 1 and 3 on day 14 after CLI induction (all p < 0.001).
Obesity suppressed abilities of angiogenesis and recovery from CLI that were reversed by obesity control.
PMCID: PMC3394222  PMID: 22568992
Obesity control; Endothelial progenitor cells; Angiogenesis; Critical limb ischemia
24.  Adiponectin Prevents Diabetic Premature Senescence of Endothelial Progenitor Cells and Promotes Endothelial Repair by Suppressing the p38 MAP Kinase/p16INK4A Signaling Pathway 
Diabetes  2010;59(11):2949-2959.
A reduced number of circulating endothelial progenitor cells (EPCs) are casually associated with the cardiovascular complication of diabetes. Adiponectin exerts multiple protective effects against cardiovascular disease, independent of its insulin-sensitizing activity. The objective of this study was to investigate whether adiponectin plays a role in modulating the bioavailability of circulating EPCs and endothelial repair.
Adiponectin knockout mice were crossed with db+/− mice to produce db/db diabetic mice without adiponectin. Circulating number of EPCs were analyzed by flow cytometry. Reendothelialization was evaluated by staining with Evans blue after wire-induced carotid injury.
In adiponectin knockout mice, the number of circulating EPCs decreased in an age-dependent manner compared with the wild-type controls, and this difference was reversed by the chronic infusion of recombinant adiponectin. In db/db diabetic mice, the lack of adiponectin aggravated the hyperglycemia-induced decrease in circulating EPCs and also diminished the stimulatory effects of the PPARγ agonist rosiglitazone on EPC production and reendothelialization. In EPCs isolated from both human peripheral blood and mouse bone marrow, treatment with adiponectin prevented high glucose–induced premature senescence. At the molecular level, adiponectin decreased high glucose–induced accumulation of intracellular reactive oxygen species and consequently suppressed activation of p38 MAP kinase (MAPK) and expression of the senescence marker p16INK4A.
Adiponectin prevents EPC senescence by inhibiting the ROS/p38 MAPK/p16INK4A signaling cascade. The protective effects of adiponectin against diabetes vascular complications are attributed in part to its ability to counteract hyperglycemia-mediated decrease in the number of circulating EPCs.
PMCID: PMC2963556  PMID: 20802255
25.  Cross Talk with Hematopoietic Cells Regulates the Endothelial Progenitor Cell Differentiation of CD34 Positive Cells 
PLoS ONE  2014;9(8):e106310.
Despite the crucial role of endothelial progenitor cells (EPCs) in vascular regeneration, the specific interactions between EPCs and hematopoietic cells remain unclear.
In EPC colony forming assays, we first demonstrated that the formation of EPC colonies was drastically increased in the coculture of CD34+ and CD34− cells, and determined the optimal concentrations of CD34+ cells and CD34− cells for spindle-shaped EPC differentiation.
Functionally, the coculture of CD34+ and CD34− cells resulted in a significant enhancement of adhesion, tube formation, and migration capacity compared with culture of CD34+ cells alone. Furthermore, blood flow recovery and capillary formation were remarkably increased by the coculture of CD34+ and CD34− cells in a murine hind-limb ischemia model. To elucidate further the role of hematopoietic cells in EPC differentiation, we isolated different populations of hematopoietic cells. T lymphocytes (CD3+) markedly accelerated the early EPC status of CD34+ cells, while macrophages (CD11b+) or megakaryocytes (CD41+) specifically promoted large EPC colonies.
Our results suggest that specific populations of hematopoietic cells play a role in the EPC differentiation of CD34+ cells, a finding that may aid in the development of a novel cell therapy strategy to overcome the quantitative and qualitative limitations of EPC therapy.
PMCID: PMC4148437  PMID: 25166961

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