G-CSF-mobilized peripheral blood mononuclear cells from diabetic patients augment neovascularization in ischemic limbs but with impaired capability

Association between Cerebrovascular Risk Factors and Collateral Compensation in Chronic Symptomatic Intracranial Vertebrobasilar Stenosis

INTRODUCTION

The level of collateral compensation plays a pivotal role in chronic symptomatic intracranial vertebrobasilar stenosis (IVBS). This study aimed to evaluate the association between cerebrovascular risk factors and collateral compensation in chronic symptomatic IVBS.

METHODS

This single-center cross-sectional study retrospectively reviewed 238 patients with angiographically demonstrated IVBS and divided them into good collateral compensation (GCC) group (collateral grade: 3-4, n = 110) and poor collateral compensation (PCC) group (collateral grade: 0-2, n = 128). The demographic information, laboratory tests, and clinical data of the two groups were compared and assessed using univariate logistic regression. Multivariate logistic regression was employed to analyze the independent related factors of collateral compensation.

RESULTS

Hyperlipidemia, high-density lipoprotein (HDL), and fasting blood glucose (FBG) were significantly different between the two groups. Multivariate logistic regression analysis revealed that HDL (odds ratio [OR]: 1.134, 95% confidence interval [CI]: 1.081-1.190), FBG (OR: 0.945, 95% CI: 0.925-0.964), and hyperlipidemia (OR: 0.261, 95% CI: 0.129-0.527) were statistically independent related factors of collateral compensation. The receiver-operating characteristic (ROC) analysis provided cutoff values of 34 mg/dL and 135 mg/dL for HDL and FBG associated with GCC and PCC.

CONCLUSION

Higher HDL levels are associated with higher incidence of GCC, whereas higher FBG levels and hyperlipidemia are associated with higher incidence of PCC.

Novel topical allogeneic bone-marrow-derived mesenchymal stem cell treatment of hard-to-heal diabetic foot ulcers: a proof of concept study

Aim

The aim of this study was to investigate safety of treating diabetic foot ulcers with a topically administered mesenchymal stem cell product.

Method

Individuals with diabetes, peripheral neuropathy, toe blood pressure > 39 mmHg and non-infected foot ulcers with duration of four to fifty-two weeks were screened. Participants were treated with a one-time application of a topically applied allogeneic cellular product containing CD362 enriched mesenchymal stem cells suspended in a collagen solution. Participants were subsequently followed for seven months to gather information on adverse event and serious adverse events.

Results/discussion

A total of sixteen individuals were screened, of whom two were included. The included participants incurred a total of seven adverse events and one serious adverse event. Increased exudation from the treated diabetic foot ulcer was observed for both participants and a connection to investigational medicinal product was suspected. The increased exudation was resolved within one week after application of investigational medicinal product, without any further complications. The serious adverse event consisted of a hospital admission due to neurological symptoms, which were assumed to be caused by hypoglycemia, with no suspected correlation to the investigational medicinal product. None of the other observed adverse events were suspected to be associated with the investigational medicinal product.

Conclusion

This study presents data from two individuals with a diabetic foot ulcer treated with a novel topical mesenchymal stem cell product. An adverse event observed for both participants was suspected to be associated to the investigational medicinal product, i.e., increased exudation, which was resolved within one week, did not lead to further complications and can easily be remedied by choosing bandages with higher absorption capacity or increasing frequency of bandage changes. This study lays the groundwork for further large scale randomized clinical studies.

Trial registration: EudraCT number 2015-005580-16. Registered 12/06-2018.

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

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

A Molecular and Clinical Review of Stem Cell Therapy in Critical Limb Ischemia

Peripheral artery disease (PAD) is one of the major vascular complications in individuals suffering from diabetes and in the elderly that can progress to critical limb ischemia (CLI), portending significant burden in terms of patient morbidity and mortality. Over the last two decades, stem cell therapy (SCT) has risen as an attractive alternative to traditional surgical and/or endovascular revascularization to treat this disorder. The primary benefit of SCT is to induce therapeutic neovascularization and promote collateral vessel formation to increase blood flow in the ischemic limb and soft tissue. Existing evidence provides a solid rationale for ongoing in-depth studies aimed at advancing current SCT that may change the way PAD/CLI patients are treated.

Modulating putative endothelial progenitor cells for the treatment of endothelial dysfunction and cardiovascular complications in diabetes

Diabetes induces a decrease in the number and function of different pro-angiogenic cell types generically designated as putative endothelial progenitor cells (EPC), which encompasses cells from myeloid origin that act in a paracrine fashion to promote angiogenesis and putative "true" EPC that contribute to endothelial replacement. This not only compromises neovasculogenesis in ischemic tissues but also impairs, at an early stage, the reendotheliziation process at sites of injury, contributing to the development of endothelial dysfunction and cardiovascular complications. Hyperglycemia, insulin resistance and dyslipidemia promote putative EPC dysregulation by affecting the SDF-1/CXCR-4 and NO pathways and the p53/SIRT1/p66Shc axis that contribute to their mobilization, migration, homing and vasculogenic properties. To optimize the clinical management of patients with hypoglycemic agents, statins and renin-angiotensin system inhibitors, which display pleiotropic effects on putative EPC, is a first step to improve their number and angiogenic potential but specific strategies are needed. Among them, mobilizing therapies based on G-CSF, erythropoietin or CXCR-4 antagonism have been developed to increase putative EPC number to treat ischemic diseases with or without prior cell isolation and transplantation. Growth factors, genetic and pharmacological strategies are also evaluated to improve ex vivo cultured EPC function before transplantation. Moreover, pharmacological agents increasing in vivo the bioavailability of NO and other endothelial factors demonstrated beneficial effects on neovascularization in diabetic ischemic models but their effects on endothelial dysfunction remain poorly evaluated. More experiments are warranted to develop orally available drugs and specific agents targeting p66Shc to reverse putative EPC dysfunction in the expected goal of preventing endothelial dysfunction and diabetic cardiovascular complications.

Transplantation of Human Placenta-Derived Mesenchymal Stem Cells Alleviates Critical Limb Ischemia in Diabetic Nude Rats

Neovasculogenesis induced by stem cell therapy is an innovative approach to improve critical limb ischemia (CLI) in diabetes. Mesenchymal stem cells (MSCs) are ideal candidates due to their angiogenic and immunomodulatory features. The aim of this study is to determine the therapeutic effects of human placenta-derived MSCs (P-MSCs) on diabetic CLI, with or without exogenous insulin administration, and the underlying mechanism of any effect. A series of in vitro experiments were performed to assess the stemness and vasculogenic activity of P-MSCs. P-MSCs were intramuscularly injected at two different doses with and without the administration of insulin. The efficacy of P-MSC transplantation was evaluated by ischemia damage score, ambulatory score, laser Doppler perfusion image (LDPI), capillary, and vascular density. In vivo imaging was applied to track the implanted P-MSCs. In vivo differentiation and in situ secretion of angiogenic cytokines were determined. In vitro experimental outcomes showed the differentiation potential and potent paracrine effect of P-MSCs. P-MSCs survived in vivo for at least 3 weeks and led to the acceleration of ischemia recovery, due to newly formed capillaries, increased arterioles, and secretion of various proangiogenic factors. P-MSCs participate in angiogenesis and vascularization directly through differentiation and cytokine expression.

VCAM-1+ placenta chorionic villi-derived mesenchymal stem cells display potent pro-angiogenic activity

Introduction

Mesenchymal stem cells (MSCs) represent a heterogeneous cell population that is promising for regenerative medicine. The present study was designed to assess whether VCAM-1 can be used as a marker of MSC subpopulation with superior angiogenic potential.

Methods

MSCs were isolated from placenta chorionic villi (CV). The VCAM-1^+/− CV-MSCs population were separated by Flow Cytometry and subjected to a comparative analysis for their angiogenic properties including angiogenic genes expression, vasculo-angiogenic abilities on Matrigel in vitro and in vivo, angiogenic paracrine activities, cytokine array, and therapeutic angiogenesis in vascular ischemic diseases.

Results

Angiogenic genes, including HGF, ANG, IL8, IL6, VEGF-A, TGFβ, MMP₂ and bFGF, were up-regulated in VCAM-1⁺CV-MSCs. Consistently, angiogenic cytokines especially HGF, IL8, angiogenin, angiopoitin-2, μPAR, CXCL1, IL-1β, IL-1α, CSF2, CSF3, MCP-3, CTACK, and OPG were found to be significantly increased in VCAM-1⁺ CV-MSCs. Moreover, VCAM-1⁺CV-MSCs showed remarkable vasculo-angiogenic abilities by angiogenesis analysis with Matrigel in vitro and in vivo and the conditioned medium of VCAM-1⁺ CV-MSCs exerted markedly pro-proliferative and pro-migratory effects on endothelial cells compared to VCAM-1⁻CV-MSCs. Finally, transplantation of VCAM-1⁺CV-MSCs into the ischemic hind limb of BALB/c nude mice resulted in a significantly functional improvement in comparison with VCAM-1⁻CV-MSCs transplantation.

Conclusions

VCAM-1⁺CV-MSCs possessed a favorable angiogenic paracrine activity and displayed therapeutic efficacy on hindlimb ischemia. Our results suggested that VCAM-1⁺CV-MSCs may represent an important subpopulation of MSC for efficient therapeutic angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0297-0) contains supplementary material, which is available to authorized users.

Genetic targeting of sprouting angiogenesis using Apln-CreER

Under pathophysiological conditions in adults, endothelial cells (ECs) sprout from pre-existing blood vessels to form new ones by a process termed angiogenesis. During embryonic development, Apelin (APLN) is robustly expressed in vascular ECs. In adult mice, however, APLN expression in the vasculature is significantly reduced. Here we show that APLN expression is reactivated in adult ECs after ischaemia insults. In models of both injury ischaemia and tumor angiogenesis, we find that Apln-CreER genetically labels sprouting but not quiescent vasculature. By leveraging this specific activity, we demonstrate that abolishment of the VEGF-VEGFR2 signalling pathway as well as ablation of sprouting ECs diminished tumour vascularization and growth without compromising vascular homeostasis in other organs. Collectively, we show that Apln-CreER distinguishes sprouting vessels from stabilized vessels in multiple pathological settings. The Apln-CreER line described here will greatly aid future mechanistic studies in both vascular developmental biology and adult vascular diseases.

A novel molecule Me6TREN promotes angiogenesis via enhancing endothelial progenitor cell mobilization and recruitment

Critical limb ischaemia is the most severe clinical manifestation of peripheral arterial disease. The circulating endothelial progenitor cells (EPCs) play important roles in angiogenesis and ischemic tissue repair. The increase of circulating EPC numbers by using mobilization agents is critical for obtaining a better therapeutic outcome in patients with ischemic disease. Here, we firstly report a novel small molecule, Me6TREN (Me6), can efficiently mobilize EPCs into the blood circulation. Single injection of Me6 induced a long-lasting increase in circulating Flk-1⁺ Sca-1⁺ EPC numbers. In a mouse hind limb ischemia (HLI) model, local intramuscular transplantation of these Me6-mobilized cells accelerated the blood flow restoration in the ischemic muscles. More importantly, systemic administration of Me6 notably increased the capillary density, arteriole density and regenerative muscle weight in the ischemic tissue of HLI. Mechanistically, we found Me6 reduced stromal cell-derived factor-1α level in bone marrow by up-regulation of matrix metallopeptidase-9 expression, which allowed the dissemination of EPCs into peripheral blood. These data indicate that Me6 may represent a potentially useful therapy for ischemic disease via enhancing autologous EPC recruitment and promote angiogenesis.

Differentiation of hESCs into Mesodermal Subtypes: Vascular-, Hematopoietic- and Mesenchymal-lineage Cells

To date, studies on the application of mesodermally derived mesenchymal-, hematopoietic- and vascular-lineage cells for cell therapy have provided either poor or insufficient data. The results are equivocal with regard to therapeutic efficiency and yield. Since the establishment of human embryonic stem cells (hESCs) in 1998, the capacity of hESCs to differentiate into various mesodermal lineages has sparked considerable interest in the regenerative medicine community, a group interested in generating specialized cells to treat patients suffering from degenerative diseases. Even though hESCs are sensitive, effective methods for guiding the differentiation of hESCs into specific mesodermal cell types are still being developed. In addition, to understand the functional properties of hESC derivatives, numerous animal model studies have been performed by many research groups over the last decade. In this review, we describe and summarize the protocols currently used for differentiation of hESCs into multiple mesodermal lineages and their therapeutic efficiency in different animal models. Furthermore, we discuss the technical hurdles associated with each protocol and the safety of hESC derivatives for therapeutic applications. Technical improvement of the methods used to produce hESC derivatives for therapeutic use in patients with degenerative diseases should remain an objective of future studies, as should the development of effective and stable induction systems.

Restoring stem cell mobilization to promote vascular repair in diabetes

Diabetes triggers endothelial dysfunction, which is linked to increased risk of cardiovascular diseases. Stem and progenitor cells from the bone marrow are involved in the maintenance of vascular integrity. Diabetic patients show a dysfunction of these cells, which might represent a novel pathophysiological mechanism of vascular disease. Specifically, stem and progenitor cells fail to egress from the bone marrow (BM) due to BM pathological alterations and unresponsiveness to mobilizing stimuli. In this review, we describe impaired stem cell mobilization in diabetes as a mechanism of failed vascular repair and we provide evidence that pharmacological strategies can restore mobilization. We discuss recent advances in the knowledge of aberrant organization of the diabetic BM and its implications for impaired mobilization. Finally, we describe in detail the pharmacological exploitation of the G-CSF/DPP-4(CD26)/SDF-1α axis as a novel strategy to improve mobilization and attain vascular repair in diabetes.

Five-year results of intracoronary infusion of the mobilized peripheral blood stem cells by granulocyte colony-stimulating factor in patients with myocardial infarction

AIM

To evaluate the long-term effects of peripheral blood stem cell therapy in myocardial infarction (MI) patients.

METHODS AND RESULTS

A total of 163 patients with MI who were successfully revascularized with drug-eluting stents were enrolled and randomly assigned to four groups: acute MI (AMI) cell infusion, AMI control, old MI (OMI) cell infusion, and OMI control. We compared 5 years' clinical outcomes between the cell infusion group (57 and 22 patients with AMI and OMI, respectively) and the control (60 and 24 patients with AMI and OMI, respectively). In the time-sequence comparison from baseline to 6 and 24 months follow-up after AMI, left ventricular ejection fraction (LVEF) by cardiac magnetic resonance imaging was significantly improved in the cell infusion group (n = 57), but not in the control group (n = 60). In the between-group comparison, the difference in improvement of LVEF for 2 years after AMI did not reach statistical significance between cell infusion and control groups. Intriguingly, the major adverse cardiac events for 5 years were significantly reduced in the cell infusion group (n = 79) compared with the control (n = 84; composite of cardiac death, non-fatal MI, hospitalization for heart failure and angina, and target vessel revascularization; 22.8 vs. 39.3%, P = 0.015).

CONCLUSIONS

Peripheral blood stem cell therapy has potential to improve long-term cardiovascular outcomes in MI patients.

Why is coronary collateral growth impaired in type II diabetes and the metabolic syndrome?

Type II diabetes and the metabolic syndrome are strong predictors of severity of occlusive coronary disease and poorer outcomes of coronary revascularization therapies. Coronary collateral growth can provide an alternative or accessory pathway of revascularization. However, collateral growth is impaired in type II diabetes and the metabolic syndrome. Although many factors necessary for collateral growth are known and many interventions have shown promising results in animal studies, not a single attempt to induce coronary collateral growth in human clinical trials has led to satisfactory results. Accordingly, the first part of this review outlines the known deleterious effects of diabetes and the metabolic syndrome on factors necessary for collateral growth, including pro-angiogenic growth factors, endothelial function, the redox state of the coronary circulation, intracellular signaling, leukocytes and bone marrow-derived progenitors cells. The second section highlights the gaps in our current knowledge of how these factors interact with the radically altered environment of the coronary circulation in diabetes and the metabolic syndrome. The interplay between these pathologies and inadequately explored areas related to the temporal regulation of collateral remodeling and the roles of the extracellular matrix, vascular cell phenotype and pro-inflammatory cytokines are emphasized with implications to development of efficient therapies.

Early and Long-term Effects of the Autologous Peripheral Stem Cell Implantation for Critical Limb Ischemia

OBJECTIVE

Therapeutic angiogenesis by peripheral blood mononuclear cells (PB-MNCs) implantation has been shown to be a safe and effective treating for critical limb ischemia (CLI). We herein report our investigation of the long-term efficacy of implantation of granulocyte-colony stimulating factor (G-CSF)-induced PB-MNCs to treat patients with CLI for which surgical bypass and/or percutaneous transluminal angioplasty are not possible. Methods and Methods : Eleven cases were enrolled in this study. Following an injection of G-CSF (250 ug/day) for 3 days, PB-MNCs (1.1 ± 0.5 × 10(10) including 1.5 ± 0.2 × 10(7) CD34-positive cells) were harvested by apheresis and then injected into 13 ischemic limbs.

RESULTS

Resting pain either diminished or improved in 10 cases (91%) at 4 weeks, and ulcer formation was cured in 6 out of 10 limbs (60%) after treatment. The time required to enhance the arteries at the level of foot-joint by angiography which was performed in the abdominal aorta was shortened by 1 month (10 ± 4 seconds) and 6 months (12 ± 1) compared with the pretreatment time (15 ± 5). Three patients died after treatment, and the actuarial survival rate at 3 years was 73%. Freedom from major amputation at 3 years was 92%.

CONCLUSION

The local injection of G-CSF-induced PB-MNCs showed striking early and long-term effects.

Interleukin-27 enhances the production of tumour necrosis factor-α and interferon-γ by bone marrow T lymphocytes in aplastic anaemia

Aplastic anaemia (AA) is considered as an immune-mediated bone marrow failure syndrome. The mechanism is involved with a variety of immune molecules including interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α) and interleukins (ILs). IL-27 is a novel member of the IL-12 family, which mediates T cell response and enhances the production of IFN-γ. However, little is known about the role of IL-27 in the development of AA. This study investigated the role of IL-27 and its receptor IL-27R in the pathogenesis of AA. Both the mRNA expression of IL-27/IL-27R subunits in the bone marrow mononuclear cells (BMMNCs) and the levels of IL-27 in the marrow plasma in AA were found to be higher than in controls. Increased IL-27 correlated with the disease severity of AA. Subsequently, we stimulated marrow T lymphocytes with recombinant human (rh)IL-27 and found that rhIL-27 enhanced the production of TNF-α and IFN-γ in both CD4(+) and CD8(+) T lymphocytes from AA patients. We also detected increased TNF-α and IFN-γ in the supernatants of BMMNCs from AA patients after IL-27 stimulation. In conclusion, our data suggest that elevated IL-27 and IL-27-induced TNF-α and IFN-γ overproduction might be involved in the pathogenesis of AA.

Adult mouse epicardium modulates myocardial injury by secreting paracrine factors

The epicardium makes essential cellular and paracrine contributions to the growth of the fetal myocardium and the formation of the coronary vasculature. However, whether the epicardium has similar roles postnatally in the normal and injured heart remains enigmatic. Here, we have investigated this question using genetic fate-mapping approaches in mice. In uninjured postnatal heart, epicardial cells were quiescent. Myocardial infarction increased epicardial cell proliferation and stimulated formation of epicardium-derived cells (EPDCs), which remained in a thickened layer on the surface of the heart. EPDCs did not adopt cardiomyocyte or coronary EC fates, but rather differentiated into mesenchymal cells expressing fibroblast and smooth muscle cell markers. In vitro and in vivo assays demonstrated that EPDCs secreted paracrine factors that strongly promoted angiogenesis. In a myocardial infarction model, EPDC-conditioned medium reduced infarct size and improved heart function. Our findings indicate that epicardium modulates the cardiac injury response by conditioning the subepicardial environment, potentially offering a new therapeutic strategy for cardiac protection.

Single dose granulocyte colony-stimulating factor markedly enhances shear-dependent platelet function in humans

Granulocyte colony-stimulating factor (G-CSF) has been associated with the induction of a hypercoagulable state in patients as well as peripheral blood stem donors. Interestingly, sparse data exist on the kinetics of platelet and coagulation activation in response to G-CSF and it is unknown if G-CSF augments shear-dependent platelet function. These two issues are addressed in the current trial. Thirty-six healthy volunteers were enrolled into this study. All subjects received a single-dose of 5 microg/kg filgrastim intravenously. The effects of recombinant G-CSF on platelet and coagulation function were assessed by the platelet function analyzer PFA-100 (collagen/epinephrine (CEPI-CT), collagen/ADP (CADP-CT) closure times), von Willebrand factor activity (vWF : RiCO) ELISA, tissue factor (TF)-mRNA expression on circulating leukocytes and rotation thrombelastography (ROTEM). G-CSF time-dependently enhanced shear dependent platelet function measured by the PFA-100: CEPI-CT declined by 48% and CADP-CT by 31% with nadir values after 24 h (p < 0.001 as compared to baseline) and returned to near-baseline values after 72 hours. In accordance, VWF : RiCO increased by 59% after 24 h (p < 0.001) and returned to baseline 48 h later. TF-mRNA peaked after 4 hours (>6 fold increase p < 0.001) and reached near-baseline values after 24 hours. Nadir closure times were seen after 24 hours (-15%; p < 0.001). Single-dose administration of 5 microg/kg G-CSF significantly enhances shear-dependent platelet function and strongly induces leukocyte TF-mRNA, which translates into shortened clotting times ex vivo.

Improved function of circulating angiogenic cells is evident in type 1 diabetic islet-transplanted patients

Circulating angiogenic cells (CACs) are vascular-committed bone marrow-derived cells that are dysfunctional in type 1 diabetes (T1D). Here we studied whether restoration of normoglycemia following islet transplantation is associated with better CAC function. We carried out a cross-sectional study of 18 T1D patients, 14 insulin-independent islet-transplanted patients (ITA) and 14 healthy controls (C) evaluating in vivo and in vitro CACs viability and function. We found that the percentage of CACs in vivo did not differ among the three groups while the number of CAC colonies obtained from T1D, but not from ITA, was reduced compared to C (C = 7.3 ± 1.9, T1D = 0.9 ± 0.4 and ITA = 4.7 ± 1.9; p < 0.05 T1D vs. all). In vitro CAC migration/differentiation were similar, while in vivo an improved angiogenic ability of ITA compared to T1D was shown (capillary density: C = 93.5 ± 22.1, T1D = 19.2 ± 2.8 and ITA = 44.0 ± 10.5, p < 0.05 T1D vs. all). Increased apoptosis and lesser IL-8 secretion were evident in CACs obtained from T1D compared to C and ITA. in vitro addition of anti-hIL-8 reduced the number of colonies obtained from C. Finally, T1D, but not ITA, had a lower endothelial-dependent dilatation (EDD) compared with C. These data suggest that CAC function is altered in T1D and may be improved after islet transplantation.

Transcriptional regulation of survivin by c-Myc in BCR/ABL-transformed cells: implications in anti-leukaemic strategy

BCR/ABL can cause chronic myelogenous leukaemia (CML) in part by altering the transcription of specific genes with growth- and/or survival-promoting functions. Recently, BCR/ABL has been shown to activate survivin, an important regulator of cell growth and survival, but the precise molecular mechanisms behind its expression and consequences thereof in CML cells remain unclear. Here, we reported that BCR/ABL promotes survivin expression and its cytoplasmic accumulation. The increase of survivin was largely controlled at the transcriptional level through a mechanism mediated by JAK2/PI3K signal pathways that activated c-Myc, leading to transactivation of survivin promoter. Dynamic down-regulation of survivin was a key event involved in imatinib-induced cell death while forced expression of survivin partially counteracted imatinib's effect on cell survival. Additionally, shRNA-mediated silencing of survivin or c-Myc eradicated colony formation of K562 cells in semi-solid culture system, implying an essential role for this transcriptional network in BCR/ABL-mediated cell transformation and survival. Finally, interruption of c-Myc activity by 10058-F4 exerted an anti-leukaemia effect with a synergistic interaction with imatinib and overcame the anti-apoptosis rescued by IL-3 supplement. In conclusion, we have identified JAK2/PI3K-mediated and c-Myc-dependent transactivation of survivin as a novel pathway in the transcriptional network orchestrated by BCR/ABL. These results suggest that the interference with this circuitry might be a potential utility for CML treatment.

Diabetes impairs arteriogenesis in the peripheral circulation: review of molecular mechanisms. Clin Sci (Lond). 2010;119:225-238. [PMID: 20545627 DOI: 10.1042/cs20100082]

Patients suffering from both diabetes and PAD (peripheral arterial disease) are at risk of developing critical limb ischaemia and ulceration, and potentially requiring limb amputation. In addition, diabetes complicates surgical treatment of PAD and impairs arteriogenesis. Arteriogenesis is defined as the remodelling of pre-existing arterioles into conductance vessels to restore the perfusion distal to the occluded artery. Several strategies to promote arteriogenesis in the peripheral circulation have been devised, but the mechanisms through which diabetes impairs arteriogenesis are poorly understood. The present review provides an overview of the current literature on the deteriorating effects of diabetes on the key players in the arteriogenesis process. Diabetes affects arteriogenesis at a number of levels. First, it elevates vasomotor tone and attenuates sensing of shear stress and the response to vasodilatory stimuli, reducing the recruitment and dilatation of collateral arteries. Secondly, diabetes impairs the downstream signalling of monocytes, without decreasing monocyte attraction. In addition, EPC (endothelial progenitor cell) function is attenuated in diabetes. There is ample evidence that growth factor signalling is impaired in diabetic arteriogenesis. Although these defects could be restored in animal experiments, clinical results have been disappointing. Furthermore, the diabetes-induced impairment of eNOS (endothelial NO synthase) strongly affects outward remodelling, as NO signalling plays a key role in several remodelling processes. Finally, in the structural phase of arteriogenesis, diabetes impairs matrix turnover, smooth muscle cell proliferation and fibroblast migration. The review concludes with suggestions for new and more sophisticated therapeutic approaches for the diabetic population.

Inducible cardiomyocyte-specific gene disruption directed by the rat Tnnt2 promoter in the mouse

We developed a conditional and inducible gene knockout methodology that allows effective gene deletion in mouse cardiomyocytes. This transgenic mouse line was generated by coinjection of two transgenes, a "reverse" tetracycline-controlled transactivator (rtTA) directed by a rat cardiac troponin T (Tnnt2) promoter and a Cre recombinase driven by a tetracycline-responsive promoter (TetO). Here, Tnnt2-rtTA activated TetO-Cre expression takes place in cardiomyocytes following doxycycline treatment. Using two different mouse Cre reporter lines, we demonstrated that expression of Cre recombinase was specifically and robustly induced in the cardiomyocytes of embryonic or adult hearts following doxycycline induction, thus, allowing cardiomyocyte-specific gene disruption and lineage tracing. We also showed that rtTA expression and doxycycline treatment did not compromise cardiac function. These features make the Tnnt2-rtTA;TetO-Cre transgenic line a valuable genetic tool for analysis of spatiotemporal gene function and cardiomyocyte lineage tracing during developmental and postnatal periods.

Role of endothelial progenitor cells during ischemia-induced vasculogenesis and collateral formation

Cell-based therapy has emerged as a promising therapeutic tool for treatment of ischemic cardiovascular disease. Both unselected bone marrow-derived mononuclear cells (BMNCs), which include stem/progenitor cells and several other cell types, and endothelial progenitor cells (EPCs), a subpopulation of BMNCs, display regenerative potential in ischemic tissue. Abundant evidence supports the involvement of EPCs in capillary growth, and EPCs also appear to participate in the formation of collateral vessels. Collectively, these effects have led to improved perfusion and functional recovery in animal models of myocardial and peripheral ischemia, and in early clinical trials, the therapeutic administration of EPCs to patients with myocardial infarction or chronic angina has been associated with positive trends in perfusion. EPCs also contribute to endothelial repair and may, consequently, impede the development or progression of arteriosclerosis. This review provides a brief summary of the preclinical and clinical evidence for the role of EPCs in blood-vessel formation and repair during ischemic cardiovascular disease.

Neovascularization in diabetes

Diabetes and its complications are a major public health burden in the developed world. The major cause of diabetic complications is abnormal growth of new blood vessels. This dysfunctional neovascularization results in significant morbidity and mortality in patients with diabetes and, as such, is a major focus of basic and clinical investigation. It has become clear that hyperglycemia disrupts tissue-level signaling in response to hypoxia and ischemia, impairs the vasculogenic potential of circulating stem cells and fundamentally alters the structure and function of key neovascularization proteins, including hypoxia-inducible factor-1. These mechanistic and pathophysiologic studies have revealed new therapeutic targets to restore normal neovascularization and to ameliorate and prevent diabetic vascular complications.

Cardiovascular risk factors and collateral artery formation

Arterial lumen narrowing and vascular occlusion is the actual cause of morbidity and mortality in atherosclerotic disease. Collateral artery formation (arteriogenesis) refers to an active remodelling of non-functional vascular anastomoses to functional collateral arteries, capable to bypass the site of obstruction and preserve the tissue that is jeopardized by ischaemia. Hemodynamic forces such as shear stress and wall stress play a pivotal role in collateral artery formation, accompanied by the expression of various cytokines and invasion of circulating leucocytes. Arteriogenesis hence represents an important compensatory mechanism for atherosclerotic vessel occlusion. As arteriogenesis mostly occurs when lumen narrowing by atherosclerotic plaques takes place, presence of cardiovascular risk factors (e.g. hypertension, hypercholesterolaemia and diabetes) is highly likely. Risk factors for atherosclerotic disease affect collateral artery growth directly and indirectly by altering hemodynamic forces or influencing cellular function and proliferation. Adequate collateralization varies significantly among atherosclerotic patients, some profit from the presence of extensive collateral networks, whereas others do not. Cardiovascular risk factors could increase the risk of adverse cardiovascular events in certain patients because of the reduced protection through an alternative vascular network. Likewise, drugs primarily thought to control cardiovascular risk factors might contribute or counteract collateral artery growth. This review summarizes current knowledge on the influence of cardiovascular risk factors and the effects of cardiovascular medication on the development of collateral vessels in experimental and clinical studies.

Transplantation of Endothelial Progenitor Cells as Therapeutics for Cardiovascular Diseases

With better understanding of endothelial progenitor cells (EPCs), many therapeutic approaches to cardiovascular diseases have been developed. This article will review novel research of EPCs in promoting angiogenesis, vasculogenesis, and endothelialization, as a design for future clinical treatment. Cell therapy has the potential to supply stem/progenitor cells and multiple angiogenic factors to the region of ischemia. The efficacy of EPC transplantation may be impaired by low survival rate, insufficient cell number, and impaired function in aging and diseases. Combination of EPCs or cells primed with growth factors or genetic modification may improve the therapeutic efficacy. The molecular mechanism involved in EPC repairing processes is essential. Thus, we have also addressed the molecular mechanism of mobilization, homing, and differentiation of EPCs. The potential of therapeutic neovascularization, angiogenic factor therapy, and cell transplantation have been elucidated. Based on past experience and actual knowledge, future strategies for EPC therapy will be proposed in order to fully exploit the potential of EPC transplantation with clinical relevance for cardiovascular disease applications.

Fog2 is critical for cardiac function and maintenance of coronary vasculature in the adult mouse heart

Aberrant transcriptional regulation contributes to the pathogenesis of both congenital and adult forms of heart disease. While the transcriptional regulator friend of Gata 2 (FOG2) is known to be essential for heart morphogenesis and coronary development, its tissue-specific function has not been previously investigated. Additionally, little is known about the role of FOG2 in the adult heart. Here we used spatiotemporally regulated inactivation of Fog2 to delineate its function in both the embryonic and adult mouse heart. Early cardiomyocyte- restricted loss of Fog2 recapitulated the cardiac and coronary defects of the Fog2 germline murine knockouts. Later cardiomyocyte-restricted loss of Fog2 (Fog2MC) did not result in defects in cardiac structure or coronary vessel formation. However, Fog2MC adult mice had severely depressed ventricular function and died at 8-14 weeks. Fog2MC adult hearts displayed a paucity of coronary vessels, associated with myocardial hypoxia, increased cardiomyocyte apoptosis, and cardiac fibrosis. Induced inactivation of Fog2 in the adult mouse heart resulted in similar phenotypes, as did ablation of the FOG2 interaction with the transcription factor GATA4. Loss of the FOG2 or FOG2-GATA4 interaction altered the expression of a panel of angiogenesis-related genes. Collectively, our data indicate that FOG2 regulates adult heart function and coronary angiogenesis.

Endothelial progenitor cell therapy in atherosclerosis: a double-edged sword?

Atherosclerosis, an inflammatory process that selectively affects arteries, is highly prevalent in human. Thrombo-occlusive complications of atherosclerosis, including stroke and myocardial infarction, are becoming major causes of morbidity and mortality in the industrialized world. Atherosclerosis develops in response to local endothelial injuries. Endothelial dysfunction and cell loss are prominent features in atherosclerosis. Restoring the endothelial lining to normal is critical for slowing or reversing the progression of atherosclerosis. Increasing data suggest that endothelial progenitor cells (EPCs) play a significant role in reendothelialization of the injured blood vessels. This review focuses on the effects of EPC mobilization and transfusion in the condition of atherosclerosis. The aim of the review is to provide an update on the progress in this research field, highlight the role of EPCs in atherosclerosis and discuss the possible mechanisms and potential risks of progenitor cell-based therapy in atherosclerosis.

Transplantation of human embryonic stem cell-derived endothelial cells for vascular diseases

Using endothelial cells for therapeutic angiogenesis/vasculogenesis of ischemia diseases has led to exploring human embryonic stem cells (hESCs) as a potentially unlimited source for endothelial progenitor cells. With their capacity for self-renewal and pluripotency, hESCs and their derived endothelial cells (hESC-ECs) may be more advantageous than other endothelial cells obtained from diseased populations. However, hESC-ECs' poor differentiation efficiency and poorly characterized in vivo function after transplantation present significant challenges for their future clinical application. This review will focus on the differentiation pathways of hESCs and their therapeutic potential for vascular diseases, as well as the monitoring of transplanted cells' fate via molecular imaging. Finally, cell enhancement strategies to improve the engraftment efficiency of hESC-ECs will be discussed.

Human peripheral blood endothelial progenitor cells synthesize and express functionally active tissue factor

INTRODUCTION

Endothelial progenitor cells are circulating cells able to home to sites of vascular damage and to contribute to the revascularization of ischemic areas. We evaluated whether endothelial progenitor cells synthesize tissue factor, a procoagulant protein also involved in angiogenesis.

MATERIALS AND METHODS

Endothelial progenitor cells were obtained from the peripheral blood mononuclear fraction of normal donors and cultured in endothelial medium supplemented with specific growth factors. The procoagulant activity expressed by cells disrupted by freeze-thaw cycles was assessed by a one stage clotting assay. Tissue factor mRNA expression was evaluated by RT-PCR.

RESULTS

Endothelial progenitor cells do not express procoagulant activity in baseline conditions. However, lipopolysaccharide induces the expression of procoagulant activity. The effect is dose-dependent and reaches statistical significance at 100 ng/mL lipopolysaccharide. Inhibition with an anti-tissue factor antibody and amplification of cDNA with primers based on the tissue factor sequence confirm the identity of this activity with tissue factor. The kinetics of tissue factor expression by endothelial progenitor cells is identical to that of human umbilical vein endothelial cells showing maximal activity within 4 hours, and then decreasing; in contrast, tissue factor expression by mononuclear cells lasts for longer times. Both 5,6-dichloro-beta D-ribofuranosyl-benzimidazole and cycloheximide prevented the expression of procoagulant activity. Stimulation of endothelial progenitor cells with tumor necrosis factor-alpha did not elicit any detectable procoagulant activity.

CONCLUSIONS

Endothelial progenitor cells can be stimulated by lipopolysaccharide to synthesize tissue factor. This protein might be involved in thrombotic phenomena and might contribute to endothelial progenitor cells related neovascularization.

Nkx2-5- and Isl1-expressing cardiac progenitors contribute to proepicardium

Correct delineation of the hierarchy of cardiac progenitors is a key step to understanding heart development, and will pave the way for future use of cardiac progenitors in the treatment of heart disease. Multipotent Nkx2-5 and Isl1 cardiac progenitors contribute to cardiomyocyte, smooth muscle, and endothelial lineages, which constitute the major lineages of the heart. Recently, progenitors located within the proepicardium and epicardium were reported to differentiate into cardiomyocytes, as well as smooth muscle and endothelial cells. However, the relationship of these proepicardial progenitors to the previously described Nkx2-5 and Isl1 cardiac progenitors is incompletely understood. To address this question, we performed in vivo Cre-loxP-based lineage tracing. Both Nkx2-5- and Isl1-expressing progenitors contributed to the proepicardium and expressed Wt1 and Tbx18, markers of proepicardial progenitor cells. Interestingly, Nkx2-5 knockout resulted in abnormal proepicardial development and decreased expression of Wt1, suggesting a functional role for Nkx2-5 in proepicardium formation. Taken together, these results suggest that Nkx2-5 and/or Isl1 cardiac progenitors contribute to proepicardium during heart development.

Degradation of BM SDF-1 by MMP-9: the role in G-CSF-induced hematopoietic stem/progenitor cell mobilization

The major involvement of chemokines and proteolytic enzymes has recently been discovered in the mobilization process. Here, we report that the degradation of BM stromal cell-derived factor (SDF-1) by matrix metalloproteinase (MMP)-9 is important in G-CSF-mediated hematopoietic stem/progenitor cells (HSPCs) mobilization. In this study, the SDF-1 concentration in healthy donors BM plasma decreased significantly after 5 days of G-CSF administration, with no obvious change of SDF-1 in the peripheral blood. We also observed a similar result by immunohistochemical staining on the BM biopsy slides. In vitro, mobilized BM plasma exhibited decreased chemotactic effect on CD34(+) cells, compared with steady-state BM plasma. MMP-9 protein and mRNA increased dramatically in the BM plasma in accordance with SDF-1 decrease. MMP-9 enriched supernatant from HT1080 cell-conditioned medium upregulated CXCR4 expression and the migration of BM CD34(+) cells toward SDF-1. SDF-1 was a substrate for MMP-9, furthermore, SDF-1 also stimulated MMP-9 proteolytic enzyme activity of BM CD34(+) cells, which facilitate HSPCs migration. In BALB/c mice, HSPCs mobilization was significantly inhibited by anti-SDF-1 antibodies or MMP inhibitor, o-phenanthroline. In conclusion, the degradation of BM SDF-1 by MMP-9 is a vital step in mobilization.

Epicardial progenitors contribute to the cardiomyocyte lineage in the developing heart

The heart is formed from cardiogenic progenitors expressing the transcription factors Nkx2-5 and Isl1 (refs 1 and 2). These multipotent progenitors give rise to cardiomyocyte, smooth muscle and endothelial cells, the major lineages of the mature heart. Here we identify a novel cardiogenic precursor marked by expression of the transcription factor Wt1 and located within the epicardium-an epithelial sheet overlying the heart. During normal murine heart development, a subset of these Wt1(+) precursors differentiated into fully functional cardiomyocytes. Wt1(+) proepicardial cells arose from progenitors that express Nkx2-5 and Isl1, suggesting that they share a developmental origin with multipotent Nkx2-5(+) and Isl1(+) progenitors. These results identify Wt1(+) epicardial cells as previously unrecognized cardiomyocyte progenitors, and lay the foundation for future efforts to harness the cardiogenic potential of these progenitors for cardiac regeneration and repair.

Endothelial progenitor cells for the treatment of diabetic vasculopathy: panacea or Pandora's box?

The discovery of endothelial progenitor cell (EPC) a decade ago has refuted the previous belief that vasculogenesis only occurs during embryogenesis. The reduced circulating concentration of EPCs is a surrogate marker of endothelial function and has been implicated in the pathogenesis of many vascular diseases. To date, the therapeutic benefit of neovascularization in ischaemic conditions in a non-diabetic setting has been demonstrated. This article aims to review the biology of EPCs in the diabetic setting with special emphasis on the effects of cardiovascular risk factor modification on EPC phenotype and methods to reverse or augment EPC dysfunction. The potential of the use of EPCs in the treatment of the diabetic vascular dysfunction will also be discussed.

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro, MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro. On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.

The effect of the controlled release of basic fibroblast growth factor from ionic gelatin-based hydrogels on angiogenesis in a murine critical limb ischemic model

The localized delivery of exogenous, angiogenic growth factors has become a promising alternative treatment of peripheral artery disease (PAD) and critical limb ischemia. In the present study, we describe the development of a novel controlled release vehicle to promote angiogenesis in a murine critical limb ischemic model. Ionic, gelatin-based hydrogels were prepared by the carbodiimide-mediated amidation reaction between the carboxyl groups of gelatin or poly-L-glutamic acid molecules and the amine groups of poly-L-lysine or gelatin molecules, respectively. The degree of swelling of the synthesized hydrogels was assessed as a function of EDC/NHS ratios and the pH of the equilibrating medium, while the release kinetic profile of basic fibroblast growth factor (FGF-2) was evaluated in human fibroblast cultures. The degree of swelling (DS) decreased from 26.5+/-1.7 to 18.5+/-2.4 as the EDC concentration varied from 0.75 to 2.5 mg/ml. Eighty percent of the FGF-2 was released at controlled rates from gelatin-polylysine (gelatin-PLL) and gelatin-polyglutamic acid (gelatin-PLG) hydrogel scaffolds over a period of 28 days. Cell adhesion studies revealed that the negatively charged surface of the gelatin-PLG hydrogels exhibited superior adhesion capabilities in comparison to gelatin-PLL and control gelatin surfaces. Laser Doppler perfusion imaging as well as CD31(+) capillary immunostaining demonstrated that the controlled release of FGF-2 from ionic gelatin-based hydrogels is superior in promoting angiogenesis in comparison to the bolus administration of the growth factor. Over 4 weeks, FGF-2 releasing gelatin-PLG hydrogels exhibited marked reperfusion with a Doppler ratio of 0.889 (+/-0.04) which was 69.3% higher than in the control groups.

Therapeutic Potential of Human Umbilical Cord–Derived Stem Cells in Ischemic Diseases

Recent advances suggest human umbilical cord is a new source for stem cells. Our laboratory has established a method to readily isolate and expand stem cells from human umbilical cord tissues. The aim of this study was to investigate the therapeutic potential of human umbilical cord-derived stem (UCDS) cells in ischemic diseases. The UCDS cells were characterized by flow cytometry and differentiation into osteogenic and adipogenic cells. Unilateral hind limb ischemia was surgically induced by femoral artery ligation in nude mice. The animals were intramuscularly injected with 10(6) UCDS cells or control phosphate-buffered saline. Blood perfusion of ischemic limbs was detected by laser Doppler perfusion imaging. Transplantation of UCDS cells to the ischemic limbs of nude mice significantly improved the blood flow to the affected limbs. Thus, transplantation of UCDS cells may potentially be a promising treatment for human ischemic diseases.

Mesenchymal stem/stromal cells (MSC) transfected with stromal derived factor 1 (SDF-1) for therapeutic neovascularization: enhancement of cell recruitment and entrapment

Recruited bone marrow-derived circulating cells (RBCCs) play a key role in therapeutic neovascularization. Several important steps take place during this process, which include mobilization, migration, recruitment, adhesion and invasion, entrapment, differentiation, as well as paracrine functions. Recent study indicated that recruitment and entrapment of RBCCs are vital steps in vascular endothelial growth factor (VEGF)-induced angiogenesis. This entrapment is modulated by another important chemokine: stromal derived factor 1 (SDF-1). We reason that the enhancement of entrapment might be a novel target for therapeutic neovascularization. Therefore we hypothesize that mesenchymal stem/stromal cells that secrete VEGF in situ could be transfected with SDF-1 (MSC(SDF-1)). Their combination could augment mobilization, recruitment, survival, and above all the entrapment of RBCCs, all of which might greatly augment the angiogenesis pathway. For these reasons, we further hypothesize that MSC(SDF-1) might become a next generation cell/chemokine therapy for therapeutic neovascularization.

Prevention of diabetic microangiopathy by prophylactic transplant of mobilized peripheral blood mononuclear cells

AIM

To investigate whether the prophylactic local delivery of mobilized peripheral blood mononuclear cells (M-PBMNC) could prevent peripheral microangiopathy in diabetic nude mice.

METHODS

Diabetic nude mice were induced with intraperitoneal injections of streptozotocin. With the time course of diabetes, we detected the capillary and arteriole density of mice adductor muscles by immunohistopathy. In situ apoptosis was detected by using TdT-mediated dUTP nick end labeling (TUNEL) methods. M-PBMNC were labeled and locally delivered to the adductor muscles. Mononuclear cells were also isolated and cultured in vitro for the detection and counting of endothelial progenitor cells(EPC).

RESULTS

Rarefication of capillaries and arterioles, enhanced apoptosis in adductor muscles, and reduced circulating EPC in diabetic nude mice. Prophylactic local delivery of M-PBMNC halted the progression of microvascular rarefaction in hind-limb skeletal muscles by inhibiting apoptosis. We detected the survival, migration and incorporation of transplanted M-PBMNC into the murine vasculature in vivo. In addition, more EPC were available from M-PBMNC than non-mobilized cells.

CONCLUSION

These results suggested that the prophylactic local delivery of M-PBMNC may represent a novel approach for the treatment of microvascular complications in diabetics.

In vitro and in vivo differentiation of human umbilical cord derived stem cells into endothelial cells

The successful use of tissue-engineered transplants is hampered by the need for vascularization. Recent advances have made possible the using of stem cells as cell sources for therapeutic angiogenesis, including the vascularization of engineered tissue grafts. The goal of this study was to examine the endothelial potential of human umbilical cord-derived stem (UCDS) cells. UCDS cells were initially characterized and differentiated in an endothelial differentiation medium containing VEGF and bFGF. Differentiation into endothelial cells was determined by acetylated low-density lipoprotein incorporation and expression of endothelial-specific proteins, such as PECAM and CD34. In vivo, the transplanted UCDS cells were sprouting from local injection and differentiated into endothelial cells in a hindlimb ischemia mouse model. These findings indicate the presence of a cell population within the human umbilical cord that exhibits characteristics of endothelial progenitor cells. Therefore, human umbilical cord might represent a source of stem cells useful for therapeutic angiogenesis and re-endothelialization of engineered tissue grafts.

Endothelial progenitor cells transfected with PDGF: cellular and molecular targets for prevention of diabetic microangiopathy

Microvascular insufficiency represents a major cause of end-organ failure among diabetics. Prevention at early stage of disease is therefore necessary and is a focus of current investigations. Progression of diabetes is complicated by endothelial cell apoptosis as well as occlusion of arteriole and capillary leading to microvascular rarefaction. This favors the formation of non-healing limb ulcers and limits the benefit of revascularization. Recent study indicated that reduction of platelet derived growth factor (PDGF) expression was indeed critical, in causing functional and morphological vascular changes, namely the dissociation of pericytes from the capillaries in muscles. Diabetic microangiopathy is a result of pericytes dissociation from reduced PDGF as well as vessel rarefaction from reduced number of endothelial progenitor cells (EPCs) and EPC dysfunction. Since blood vessels develop through the assembly of these two principal cell types--endothelial cells and pericytes/smooth muscle cells, prevention of diabetic microangiopathy requires interventions targeting at both cell types in a complementary and synergistic manner. An improved recruitment of EPCs will help repair of injured endothelium while molecular targeting with PDGF will enhance pericytes recruitment. EPCs modified with PDGF therefore hold promise as the next generation of agents for prevention of microangiopathy.