The Effects of Flap Ischemia on Normal and Diabetic Progenitor Cell Function

Novel cell therapy with ex vivo cultured peripheral blood mononuclear cells significantly impacts angiogenesis in the murine ischemic limb model

Introduction

Autologous mononuclear cells (MNCs) have been used in vascular regenerative therapy since the identification of endothelial progenitor cells (EPCs). However, the efficacy of autologous EPC therapy for diseases such as diabetes and connective tissue disorders is limited due to deficiencies in the number and function of EPCs. To address this, we developed a novel RE-01 cells that enriches pro-angiogenic cells from peripheral blood MNCs (PBMNCs).

Methods

PBMNCs were collected from healthy volunteers following ethical guidelines. RE-01 cells were cultured in the presence of specific growth factors for 5 days without media change. Flow cytometry was used to analyze cell surface markers. Tube formation assays, EPC culture assays, and mRNA analysis were performed to evaluate angiogenic potential. The efficacy of RE-01 cells upon transplantation into ischemic hind limbs of mice was evaluated.

Results

RE-01 cells exhibited a significant increase in pro-angiogenic cells such as M2 macrophages and angiogenic T cells, in contrast to PBMNCs, while the number of inflammatory cells reduced. In vitro assays demonstrated the enhanced angiogenic abilities of RE-01 cells, supported by increased mRNA expression of angiogenesis-related cytokines. In vivo studies using mouse ischemic hind limb models have shown that blood flow and angiogenesis improved following RE-01 cell transplantation. Transplantations for 3 consecutive days significantly improved the number of pericyte-recruited vessels in the severely ischemic hind limbs of mice.

Conclusions

RE-01 cells showed promising results in enhancing angiogenesis and arteriogenesis, possibly owing to the presence of M2 macrophages and angiogenic T cells. These cells also demonstrated anti-fibrotic effects. The efficacy of RE-01 cells has been confirmed in mouse models, suggesting their potential for treating ischemic vascular diseases. Clinical trials are planned to validate the safety and efficacy of RE-01 cell therapy in patients with connective tissue disease and unhealed ulcers. We hope that this new RE-01 cell therapy will prevent many patients from undergoing amputation.

Dihydromyricetin regulates KEAP1-Nrf2 pathways to enhance the survival of ischemic flap

In clinical flap practice, there are a lot of studies being done on how to promote the survival of distal random flap necrosis in the hypoxic and ischemic state. As a traditional Chinese medicine, dihydromyricetin (DHM) is crucial in preventing oxidative stress and apoptosis in a number of disorders. In this work, we examined the impact of DHM on the ability to survive of ischemia flaps and looked into its fundamental mechanism. Our results showed that DHM significantly increased the ischemic flaps' survival area, encouraged angiogenesis and blood flow, reduced oxidative stress and apoptosis, and stimulated KEAP1-Nrf2 (Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor) signaling pathways. Adeno-associated virus (AAV) upregulation of KEAP1 expression also negated the favorable effects of DHM on flap survival. By activating KEAP1-Nrf2 signaling pathways, DHM therapy promotes angiogenesis while reducing oxidative stress and apoptosis.

Effect of MNCQQ Cells on Migration of Human Dermal Fibroblast in Diabetic Condition

A major symptom of diabetes mellitus (DM) is unfit hyperglycemia, which leads to impaired wound healing. It has been reported that the migration of fibroblasts can be suppressed under high glucose (HG) conditions. In our previous study, we introduced a serum-free culture method for mononuclear cells (MNCs) called quantity and quality control culture (QQc), which could improve the vasculogenic and tissue regeneration ability of MNCs. In this study, we described a culture model in which we applied a high glucose condition in human dermal fibroblasts to simulate the hyperglycemia condition in diabetic patients. MNC-QQ cells were cocultured with fibroblasts in this model to evaluate its role in improving fibroblasts dysfunction induced by HG and investigate its molecular mechanism. It was proven in this study that the impaired migration of fibroblasts induced by high glucose could be remarkably enhanced by coculture with MNC-QQ cells. PDGF B is known to play important roles in fibroblasts migration. Quantitative PCR revealed that MNC-QQ cells enhanced the gene expressions of PDGF B in fibroblasts under HG. Taken with these results, our data suggested a possibility that MNC-QQ cells accelerate wound healing via improving the fibroblasts migration and promote the gene expressions of PDGF B under diabetic conditions.

The Effect of Adipose Derived Stromal Vascular Fraction on Flap Viability in Experimental Diabetes Mellitus and Chronic Renal Disease

BACKGROUND

The presence of chronic renal disease(CRD) concurrently with diabetes mellitus(DM) increases the flap failure. Adipose derived stromal vascular fraction (SVF) is known to enhance skin flap viability in both healthy and diabetic individuals. The aim of this experimental study was to investigate the effect of SVF on skin flap viability in rats with DM and CRD.

METHODS

48 Sprague-Dawley rats were separated into four groups as follows: group I (control), group II (diabetes mellitus), group III (chronic renal disease), and group IV (diabetes with chronic renal disease).Two dorsal flaps were elevated. Flaps on left side of all groups received 0.5 cc of SVF, while same amount of plasma-buffered saline (PBS) was injected into right side. On postoperative day 7, flaps were harvested for macroscopic, histopathologic and biochemical assessments. Areas of flap survival were measured macroscopically. Blood level of vascular endothelial growth factor (VEGF) was measured after injection of SVF.

RESULTS

Macroscopically, SVF has significantly improved flap viability (p < 0.05). Flap viability percentage was lower in DM and CRD groups when compared with healthy control group. In respect of new capillary formation, there was a statistically significant difference between SVF injected flaps and PBS injected sides (p < 0.05). Similarly, VEGF levels were higher in all study groups and there was a significant difference in comparison to control group (p < 0.05).

CONCLUSIONS

The study showed that injection of SVF increased flap viability via endothelial differentiation and neovascularization. In vivo function of stem cells might be impaired due to uremia and diabetes-related microenviromental changes.

MMP9 secreted from mononuclear cell quality and quantity culture mediates STAT3 phosphorylation and fibroblast migration in wounds

Introduction

Intractable ulcers may ultimately lead to amputation. To promote wound healing, researchers developed a serum-free ex vivo peripheral blood mononuclear cell quality and quantity culture (MNC-QQc) as a source for cell therapy. In mice, pigs, and even humans, cell therapy with MNC-QQc reportedly yields a high regenerative efficacy. However, the mechanism of wound healing by MNC-QQc cells remains largely unknown. Hence, using an in vitro wound healing model, this study aimed to investigate MNC-QQc cells and the migratory potential of dermal fibroblasts.

Methods

After separation from a 50 mL blood sample from healthy individuals, mononuclear cells were cultured for 7 days in a serum-free ex vivo expansion system with five different cytokines (MNC-QQc method). The effects of MNC-QQc cells on human dermal fibroblast migration were observed by scratch assay. An angiogenesis array screened the MNC-QQc cell supernatant for proteins related to wound healing. Finally, fibroblast migration was confirmed by observing the intracellular signal transduction pathways via Western blot.

Results

The migration of fibroblasts co-cultured with MNC-QQc cells increased by matrix metallopeptidase-9 (MMP9) secretion, as suggested by the angiogenesis array. Furthermore, the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in fibroblast/MNC-QQc cell co-culture and fibroblast culture with added recombinant human MMP9 protein increased. When fibroblasts were cultured with either an MMP9 inhibitor or a STAT3 inhibitor, both fibroblast migration and STAT3 phosphorylation were significantly suppressed.

Conclusions

MNC-QQc cells promote wound healing by the secretion of MMP9, which induces fibroblast migration via the STAT3 signaling pathway.

Quality and Quantity-Cultured Human Mononuclear Cells Improve Human Fat Graft Vascularization and Survival in an In Vivo Murine Experimental Model

BACKGROUND

Fat graft ischemia impedes us from having satisfying long-term results. The quality and quantity culture is a 1-week cell culture that increases the vasculogenic potential of peripheral blood mononuclear cells (PBMNC). This in vivo murine model investigates whether enrichment with quality and quantity-cultured human mononuclear cells (MNC-QQ) improves the vascularization in the human fat graft and whether this decreases the tissue loss.

METHODS

Human adipose tissue, PBMNC, MNC-QQ, and stromal vascular fraction were prepared. First, PBMNC, MNC-QQ, and stromal vascular fraction were compared in vitro for vasculogenic potential by endothelial progenitor cell colony-forming and culture assays. Second, 0.25-g fat grafts were created with 1 × 106 PBMNC (n = 16), 1 × 106 MNC-QQ (n = 16), 1 × 106 stromal vascular fraction (n = 16), or phosphate-buffered saline as control (n = 16) before grafting in BALB/c nude mice. Grafts were analyzed for weight persistence, vessel formation by CD31 immunohistochemistry, and angiogenic markers by quantitative polymerase chain reaction.

RESULTS

MNC-QQ develop more definitive endothelial progenitor cell colonies and more functional endothelial progenitor cells compared to PBMNC and stromal vascular fraction. Weight persistence after 7 weeks was significantly higher in grafts with MNC-QQ (89.8 ± 3.5 percent) or stromal vascular fraction (90.1 ± 4.2 percent) compared with control (70.4 ± 6.3 percent; p < 0.05). MNC-QQ-enriched grafts had the highest vessel density (96.6 ± 6.5 vessels/mm2; control, 70.4 ± 5.6 vessels/mm2; p < 0.05). MNC-QQ exerted a direct vasculogenic effect through vascular integration and a potential paracrine vascular endothelial growth factor-mediated effect.

CONCLUSION

Quality and quantity-cultured human mononuclear cells containing endothelial progenitor cells stimulate fat graft vascularization and enhance graft survival in a rodent recipient.

Ex vivo conditioning of peripheral blood mononuclear cells of diabetic patients promotes vasculogenic wound healing

The quality and quantity of endothelial progenitor cells (EPCs) are impaired in patients with diabetes mellitus patients, leading to reduced tissue repair during autologous EPC therapy. This study aimed to address the limitations of the previously described serum-free Quantity and Quality Control Culture System (QQc) using CD34+ cells by investigating the therapeutic potential of a novel mononuclear cell (MNC)-QQ. MNCs were isolated from 50 mL of peripheral blood of patients with diabetes mellitus and healthy volunteers (n = 13 each) and subjected to QQc for 7 days in serum-free expansion media with VEGF, Flt-3 ligand, TPO, IL-6, and SCF. The vascular regeneration capability of MNC-QQ cells pre- or post-QQc was evaluated with an EPC colony-forming assay, FACS, EPC culture, tube formation assay, and quantitative real time PCR. For in vivo assessment, 1 × 10⁴ pre- and post-MNC-QQc cells from diabetic donors were injected into a murine wound-healing model using Balb/c nude mice. The percentage of wound closure and angio-vasculogenesis was then assessed. This study revealed vasculogenic, anti-inflammatory, and wound-healing effects of MNC-QQ therapy in both in vitro and in vivo models. This system addresses the low efficiency and efficacy of the current naïve MNC therapy for wound-healing in diabetic patients. As this technique requires a simple blood draw, isolation, and peripheral blood MNC suspension culture for only a week, it can be used as a simple and effective outpatient-based vascular and regenerative therapy for patients with diabetes mellitus.

Biomaterials for Bioprinting Microvasculature

Microvasculature functions at the tissue and cell level, regulating local mass exchange of oxygen and nutrient-rich blood. While there has been considerable success in the biofabrication of large- and small-vessel replacements, functional microvasculature has been particularly challenging to engineer due to its size and complexity. Recently, three-dimensional bioprinting has expanded the possibilities of fabricating sophisticated microvascular systems by enabling precise spatiotemporal placement of cells and biomaterials based on computer-aided design. However, there are still significant challenges facing the development of printable biomaterials that promote robust formation and controlled 3D organization of microvascular networks. This review provides a thorough examination and critical evaluation of contemporary biomaterials and their specific roles in bioprinting microvasculature. We first provide an overview of bioprinting methods and techniques that enable the fabrication of microvessels. We then offer an in-depth critical analysis on the use of hydrogel bioinks for printing microvascularized constructs within the framework of current bioprinting modalities. We end with a review of recent applications of bioprinted microvasculature for disease modeling, drug testing, and tissue engineering, and conclude with an outlook on the challenges facing the evolution of biomaterials design for bioprinting microvasculature with physiological complexity.

Mesenchymal stem cells improve survival in ischemic diabetic random skin flap via increased angiogenesis and VEGF expression

Random skin flaps (RSFs) are cutaneous flaps. Despite the negative impact of diabetes mellitus (DM) on RSF viability, they are commonly used in diabetic patients. In this study, we have assessed bone marrow mesenchymal stem cell (BMMSC) treatment on RSF survival, tensiometrical parameters, angiogenesis, and mast cells (MCs) count in an ischemic RSF model in rats with type 1 DM (T1DM). We induced T1DM in 30 Wistar adult male rats. The animals were assigned to three groups of 10 rats per group as follows: group 1 (control); group 2 (placebo), and group 3 (BMMSCs). A 30  ×  80  mm RSF was created in each rat. On day 7, we measured the viable portion of each RSF. A sample was taken for histological and immunohistochemistry studies, fibroblasts, MCs, angiogenesis, collagen bundle density, and the presence of vascular endothelial growth factor (VEGF)+ cells. An additional sample was taken to evaluate the flap's incision strength. Treatment with BMMSCs (17.8  ±  0.37) significantly increased RSF survival compared with the control (13.3  ±  0.35) and placebo (16.1  ±  0.27) groups (one-way analysis of variance, P  =  .000; least significant difference, P  =  .000, P  =  .002). There was a significant improvement in angiogenesis, as confirmed by stereologic examination. Assessment of VEGF+ cells showed prominent neovascularization in BMMSC-treated RSFs compared with the control and placebo groups. Subdermal injection of BMMSC significantly increased ischemic RSF survival as a result of stimulated neovascularization in T1DM rats. Treatment of diabetic RSF with BMMSCs showed no beneficial effects in the fibroblast number and biomechanical parameters for the repair of ischemic wounds in the rat model. Treatment with BMMSCs significantly increased collagen bundle density.

Quality and Quantity-Cultured Murine Endothelial Progenitor Cells Increase Vascularization and Decrease Fibrosis in the Fat Graft

BACKGROUND

Fat grafting has become a valuable technique for soft-tissue reconstruction; however, long-lasting success depends on several determinants. An early blood supply to the transplanted adipocytes is important to prevent ischemia. The recently developed quality and quantity (QQ) culture increases the vasculogenic potential of endothelial progenitor cells. The authors used a murine fat grafting model to address the hypothesis that QQ-cultured endothelial progenitor cells stimulate the establishment of a blood vessel network and increase graft success.

METHODS

c-KitSca-1Lin (KSL) cells were isolated as endothelial progenitor cell precursors from C57BL/6 mice. Adipose tissue was grafted with QQ-cultured KSL cells (QQKSL group), uncultured KSL cells (KSL group), adipose-derived stem cells (ASC group), and a combination (QQKSL+ASC group), and compared to a control group. Five and 10 weeks later, grafts were weighed, histologic and immunohistochemical parameters were evaluated, and gene expression was quantified by quantitative polymerase chain reaction.

RESULTS

The highest vessel density was observed in the combined QQKSL+ASC group (68.0 ± 4.3/mm; p < 0.001) and the QQKSL group (53.9 ± 3.0/mm; p < 0.001). QQKSL cells were engrafted in proximity to the graft vasculature. QQKSL cells decreased the fibrosis percentage (13.8 ± 1.8 percent; p < 0.05). The combined QQKSL+ASC group (22.4 ± 1.8/mm; p < 0.001) showed the fewest local inflammation units. A significant up-regulation of platelet-derived growth factor and adiponectin expression was observed in the QQKSL group and QQKSL+ASC group. Graft weight persistence was not significantly different between groups.

CONCLUSIONS

Supplementing fat grafts with quality and quantity-cultured endothelial progenitor cells improves graft quality by stimulating vascularization. The increased vessel density is associated with less fibrosis, less inflammation, and better adipose tissue integrity. Enriching fat grafts with QQ-cultured endothelial progenitor cells is a potential solution to their clinical shortcomings.

Runx3 inhibits endothelial progenitor cell differentiation and function via suppression of HIF-1α activity

Endothelial progenitor cells (EPCs) are bone marrow (BM)‑derived progenitor cells that can differentiate into mature endothelial cells, contributing to vasculogenesis in the blood vessel formation process. Runt‑related transcription factor 3 (RUNX3) belongs to the Runt domain family and is required for the differentiation of specific immune cells and neurons. The tumor suppressive role of RUNX3, via the induction of apoptosis and cell cycle arrest in a variety of cancers, and its deletion or frequent silencing by epigenetic mechanisms have been studied extensively; however, its role in the differentiation of EPCs is yet to be investigated. Therefore, in the present study, adult BM‑derived hematopoietic stem cells (HSCs) were isolated from Runx3 heterozygous (Rx3+/‑) or wild‑type (WT) mice. The differentiation of EPCs from the BM‑derived HSCs of Rx3+/‑ mice was found to be significantly increased compared with those of the WT mice, as determined by the number of small or large colony‑forming units. The migration and tube formation abilities of Rx3+/‑ EPCs were also observed to be significantly increased compared with those of WT EPCs. Furthermore, the number of circulating EPCs, defined as CD34+/vascular endothelial growth factor receptor 2 (VEGFR2)+ cells, was also significantly increased in Rx3+/‑ mice. Hypoxia‑inducible factor (HIF)‑1α was upregulated in Rx3+/‑ EPCs compared with WT EPCs, even under normoxic conditions. Furthermore, in a hindlimb ischemic mouse models, the recovery of blood flow was observed to be highly stimulated in Rx3+/‑ mice compared with WT mice. Also, in a Lewis lung carcinoma cell allograft model, the tumor size in Rx3+/‑ mice was significantly larger than that in WT mice, and the EPC cell population (CD34+/VEGFR2+ cells) recruited to the tumor was greater in the Rx3+/‑ mice compared with the WT mice. In conclusion, the present study revealed that Runx3 inhibits vasculogenesis via the inhibition of EPC differentiation and functions via the suppression of HIF‑1α activity.

Quality-Quantity Control Culture Enhances Vasculogenesis and Wound Healing Efficacy of Human Diabetic Peripheral Blood CD34+ Cells

Autologous endothelial progenitor cell (EPC) therapy is commonly used to stimulate angiogenesis in ischemic repair and wound healing. However, low total numbers and functional deficits of EPCs make autologous EPC therapy ineffective in diabetes. Currently, no known ex vivo culture techniques can expand and/or ameliorate the functional deficits of EPCs for clinical usage. Recently, we showed that a quality‐quantity culture (QQc) system restores the vasculogenic and wound‐healing efficacy of murine diabetic EPCs. To validate these results and elucidate the mechanism in a translational study, we evaluated the efficacy of this QQc system to restore the vasculogenic potential of diabetic human peripheral blood (PB) CD34+ cells. CD34+ cells purified from PB of diabetic and healthy patients were subjected to QQc. Gene expression, vascular regeneration, and expression of cytokines and paracrine mediators were analyzed. Pre‐ or post‐QQc diabetic human PB‐CD34+ cells were transplanted into wounded BALB/c nude mice and streptozotocin‐induced diabetic mice to assess functional efficacy. Post‐QQc diabetic human PB‐CD34+ cell therapy significantly accelerated wound closure, re‐epithelialization, and angiogenesis. The higher therapeutic efficacy of post‐QQc diabetic human PB‐CD34+ cells was attributed to increased differentiation ability of diabetic CD34+ cells, direct vasculogenesis, and enhanced expression of angiogenic factors and wound‐healing genes. Thus, QQc can significantly enhance the therapeutic efficacy of human PB‐CD34+ cells in diabetic wounds, overcoming the inherent limitation of autologous cell therapy in diabetic patients, and could be useful for treatment of not only wounds but also other ischemic diseases. Stem Cells Translational Medicine2018;7:428–438

The Effect of Atorvastatin on the Viability of Ischemic Skin Flaps in Diabetic Rats

BACKGROUND

Endothelial progenitor cells play a critical role in neovascularization. However, the mobilization, recruitment, and functional capacity of endothelial progenitor cells are significantly impaired in diabetes. Statins have been shown to augment the number and improve the function of endothelial progenitor cells. This study investigated the effects of statins on the viability of ischemic skin flaps in diabetic rats.

METHODS

Twenty normal and 40 diabetic Sprague-Dawley rats were included in this study. Atorvastatin (10 mg/kg/day) was administered orally in 20 diabetic rats at 2 weeks before flap surgery for 21 consecutive days. Other rats received equal vehicle. Two weeks after first gavage, a 3 × 10-cm skin flap was established on the backs of rats. The necrotic area of each skin flap was measured at 7 days postoperatively. Capillary density and endothelial progenitor cells recruited to the flaps were analyzed using immunofluorescence staining. Circulating endothelial progenitor cell number was determined by flow cytometry. In vitro migration and tube formation experiments were used to analyze the function of endothelial progenitor cells.

RESULTS

Atorvastatin treatment increased flap survival rate and capillary density. In addition, more endothelial progenitor cells were identified in peripheral blood and skin flaps in diabetic rats receiving atorvastatin. Atorvastatin treatment also restored the impaired function of diabetic endothelial progenitor cells in migration and tube formation.

CONCLUSION

Atorvastatin notably promoted neovascularization and enhanced the viability of ischemic skin flaps in diabetic rats, which may be mediated at least partially by augmenting the number and restoring the functional capacity of endothelial progenitor cells.

Ex vivo expansion of circulating CD34(+) cells enhances the regenerative effect on rat liver cirrhosis

Ex vivo expansion of autologous cells is indispensable for cell transplantation therapy of patients with liver cirrhosis. The aim of this study was to investigate the efficacy of human ex vivo-expanded CD34⁺ cells for treatment of cirrhotic rat liver. Recipient rats were intraperitoneally injected with CCl₄ twice weekly for 3 weeks before administration of CD34⁺ cells. CCl₄ was then re-administered twice weekly for 3 more weeks, and the rats were sacrificed. Saline, nonexpanded or expanded CD34⁺ cells were injected via the spleen. After 7 days, CD34⁺ cells were effectively expanded in a serum-free culture medium. Expanded CD34⁺ cells were also increasingly positive for cell surface markers of VE-cadherin, VEGF receptor-2, and Tie-2. The expression of proangiogenic growth factors and adhesion molecules in expanded CD34⁺ cells increased compared with nonexpanded CD34⁺ cells. Expanded CD34⁺ cell transplantation reduced liver fibrosis, with a decrease of αSMA⁺ cells. Assessments of hepatocyte and sinusoidal endothelial cell proliferative activity indicated the superior potency of expanded CD34⁺ cells over non-expanded CD34⁺ cells. The inhibition of integrin αvβ3 and αvβ5 disturbed the engraftment of transplanted CD34⁺ cells and aggravated liver fibrosis. These findings suggest that expanded CD34⁺ cells enhanced the preventive efficacy of cell transplantation in a cirrhotic model.

Recent Progress in Endothelial Progenitor Cell Culture Systems: Potential for Stroke Therapy

Endothelial progenitor cells (EPCs) participate in endothelial repair and angiogenesis due to their abilities to differentiate into endothelial cells and to secrete protective cytokines and growth factors. Consequently, there is considerable interest in cell therapy with EPCs isolated from peripheral blood to treat various ischemic injuries. Quality and quantity-controlled culture systems to obtain mononuclear cells enriched in EPCs with well-defined angiogenic and anti-inflammatory phenotypes have recently been developed, and increasing evidence from animal models and clinical trials supports the idea that transplantation of EPCs contributes to the regenerative process in ischemic organs and is effective for the therapy of ischemic cerebral injury. Here, we briefly describe the general characteristics of EPCs, and we review recent developments in culture systems and applications of EPCs and EPC-enriched cell populations to treat ischemic stroke.

The role of Notch signaling in diabetic endothelial progenitor cells dysfunction

AIMS

To investigate the role of Notch signaling pathway in vasculogenic dysfunction of diabetic EPCs (DM-EPCs).

METHODS

The study was performed in mice and diabetes was induced with Streptozotocin. The functional consequences of Notch pathway modulation were studied by assessment of colony forming capacity (EPC colony forming assay), EPC differentiation capacity (% of definitive EPC-CFU (dEPC-CFU)), circulating EPCs (EPC culture assay) and migrated cells (migration assay); in the presence of Notch inhibitor (γ-secretase inhibitors (GSI)) compared to control. Notch pathway and VEGF involvement in DM- EPCs were assessed by gene expression (RT-qPCR).

RESULTS

DM demonstrated to increase Notch pathway expression in bone marrow (BM) EPCs followed by lower EPC-CFU number, EPCs differentiation capacity, number of circulating EPCs, migrated cells and VEGF expression compared to control (p<0.05). Inhibition of Notch pathway by GSI rescued vasculogenic dysfunction in DM-EPCs as represented by increase in EPC-CFU number, differentiation capacity and number of circulating EPCs (p<0.05).

CONCLUSION

Our findings indicate the involvement of Notch pathway in mediating DM-EPCs dysfunction including less number of EPC-CFU, circulating EPCs and migrated cell number compared to control. Further in vitro inhibition of Notch pathway by GSI rescued DM-EPC dysfunction. Therefore targeting Notch pathway in DM may provide a target to restore DM-EPC dysfunction.

Endogenous cell therapy improves bone healing

BACKGROUND

Although bone repair is often a relatively rapid and efficient process, many bone defects do not heal. Because an adequate blood supply is essential for new bone formation, we hypothesized that augmenting new blood vessel formation by increasing the number of circulating vasculogenic progenitor cells (PCs) with AMD3100 and enhancing their trafficking to the site of injury with recombinant human parathyroid hormone (rhPTH) will improve healing.

METHODS

Critical-sized 3-mm cranial defects were trephined into the right parietal bone of C57BLKS/J 6 mice (N = 120). The mice were divided into 4 equal groups (n = 30 for each). The first group received daily subcutaneous injections of AMD3100 (5 mg/kg). The second group received daily subcutaneous injections of rhPTH (5 mg/kg). The third group received both AMD3100 and rhPTH. The fourth group received subcutaneous injections of saline. Circulating vasculogenic PC numbers, new blood vessel formation, and bony regeneration were assessed. Progenitor cell adhesion, migration, and tubule formation were assessed in the presence of rhPTH and AMD3100.

RESULTS

Flow cytometry demonstrated that combination therapy significantly increased the number of circulating PCs compared with all other groups. In vitro, AMD3100-treated PCs had significantly increased adhesion migration, and tubule formation was assessed in the presence of rhPTH. Combination therapy significantly improved new blood vessel formation in those with cranial defect compared with all other groups. Finally, bony regeneration was significantly increased in the combination therapy group compared with all other groups.

CONCLUSIONS

The combination of a PC-mobilizing and traffic-enhancing agent improved bony regeneration of calvarial defects in mice.

Oxidative stress tolerance of early stage diabetic endothelial progenitor cell

Introduction

One of the causes for poor vasculogenesis of diabetes mellitus (DM) is known to rise from the dysfunction of bone marrow-derived endothelial progenitor cells (BM EPCs). However, the origin of its cause is less understood. We aimed to investigate the effect of oxidative stress in early stage of diabetic BM-EPC and whether its vasculogenic dysfunction is caused by oxidative stress.

Methods

Bone marrow c-Kit+Sca-1+Lin− (BM-KSL) cells were sorted from control and streptozotocin-induced diabetic C57BL6J mice by flow cytometry. BM-KSLs were then assessed for vasculogenic potential (colony forming assay; EPC-CFA), accumulation of intracellular ROS (CM-H2DCFDA), carbonylated protein (ELISA), anti-oxidative enzymes expression (RT-qPCR) and catalase activity (Amplex Red).

Results

Compared to control, DM BM-KSL had significantly lower EPC-CFUs in both definitive EPC-CFU and total EPC-CFU (p < 0.05). Interestingly, the oxidative stress level of DM BM-KSL was comparable and was not significantly different to control followed by increased in anti-oxidative enzymes expression and catalase activity.

Conclusions

Primitive BM-EPCs showed vasculogenic dysfunction in early diabetes. However the oxidative stress is not denoted as the major initiating factor of its cause. Our results suggest that primitive BM-KSL cell has the ability to compensate oxidative stress levels in early diabetes by increasing the expression of anti-oxidative enzymes.

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Primitive BM-EPC showed EPC-CFU dysfunction in early diabetes.

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Primitive BM-EPC has the ability to withstand oxidative stress in early diabetes.

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Early diabetic BM-EPC increased anti-oxidative expression to compensate oxidative stress.

CD34(+) cell therapy is safe and effective in slowing the decline of hepatic reserve function in patients with decompensated liver cirrhosis

BACKGROUND AND AIM

Preclinical studies in rodent models of chronic liver fibrosis have shown that transplantation of peripheral blood (PB) CD34(+) cells leads to hepatic regeneration and a reduction of liver fibrosis by suppressing hepatic stellate cell activity and increasing matrix metalloproteinase activity. The aim of this study was to examine the safety and clinical efficacy of intrahepatic transplantation of autologous granulocyte colony-stimulating factor (G-CSF)-mobilized PB-CD34(+) cells in patients with decompensated liver cirrhosis.

METHODS

PB-CD34(+) cells were isolated from G-CSF-mobilized apheresis products. Ten patients were treated with G-CSF-mobilized PB-CD34(+) cells (treatment group) and seven patients were treated with standard medical therapy. For mobilization, patients in the treatment group received subcutaneous injections of 10 μg G-CSF/kg/day for 5 days. The cells were then injected at three different doses (5 × 10(5) , 1 × 10(6) and 2 × 10(6) cells/kg) through the hepatic artery. Thereafter, all patients were followed up for 24 months.

RESULTS

G-CSF treatment and leukapheresis were well tolerated, and no serious adverse events were observed. Patients in the treatment group had a significant but transient splenomegaly. After 24 weeks, serum albumin was significantly increased in patients who had received middle or high doses of CD34(+) cells compared with baseline. Doppler ultrasound showed a significant increase in hepatic blood flow velocity and blood flow volume after CD34(+) cell therapy. The hepatic vein pressure gradient decreased in two patients who received high-dose CD34(+) cells at week 16.

CONCLUSIONS

CD34(+) cell therapy is feasible, safe and effective in slowing the decline of hepatic reserve function.

Role of formyl peptide receptor 2 in homing of endothelial progenitor cells and therapeutic angiogenesis

Endothelial progenitor cells (EPCs) hold a great promise as a therapeutic mediator in treatment of ischemic disease conditions. The discovery of EPCs in adult blood has been a cause of significant enthusiasm in the field of endothelial cell research and numerous clinical trials have been expedited. After more than a decade of research in basic science and clinical applications, limitations and new strategies of EPC therapeutics have emerged. With various phenotypes, vague definitions, and uncertain distinction from hematopoietic cells, understanding EPC biology remains challenging. However, EPCs, still hold great hope for treatment of critical ischemic injury as low concern regarding safety can accelerate the clinical applications from basic findings. This review provides an introduction to EPC as cellular therapeutics, which highlights a recent finding that EPC homing was promoted through FPR2 signaling.

Local injection of deferoxamine improves neovascularization in ischemic diabetic random flap by increasing HIF-1α and VEGF expression

BACKGROUND

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.

OBJECTIVE

To explore the feasibility of local injection of DFO to improve the survival of ischemic random skin flaps in streptozotocin (STZ)-induced diabetic mice.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Inhibitory effect of glyceollins on vasculogenesis through suppression of endothelial progenitor cell function

SCOPE

Endothelial progenitor cells (EPCs) are derived from hematopoietic stem cells, and have the ability to differentiate into mature endothelial cells and contribute to neovascularization. Glyceollins are a type of phytoalexin produced in soybeans under stress conditions. The aim of this study is to determine the effect of glyceollin treatment on EPCs during early tumor vasculogenesis.

METHODS AND RESULTS

We found that glyceollin treatment significantly decreased the number of EPC colony-forming units in human cord blood-derived AC133⁺ cells and mouse bone-marrow-derived c-Kit⁺/Sca-1⁺/Lin⁻ cells. Glyceollin treatment diminished the number of lineage-committed EPC cells in a dose-dependent manner (1-20 μM). Glyceollin treatment inhibited EPC migration, tube formation and the mRNA expression of angiopoietin-1 (Ang-1), Tie-2, stromal-derived factor-1 (SDF-1), C-X-C-chemokine receptor-4 (CXCR4), and endothelial nitric oxide synthase (eNOS) in cultured EPCs. Glyceollin treatment suppressed activation of Akt, Erk, and eNOS induced by SDF-1α or vascular endothelial growth factor (VEGF). Treatment with 10 mg/kg glyceollins significantly reduced the number of tumor-induced circulating EPCs and the incorporation of EPCs into neovessels in bone marrow transplanted mice.

CONCLUSION

These results suggest that glyceollins inhibit the function of EPCs in tumor neovascularization. Glyceollins from soybean elicitation could be beneficial in prevention of cancer development via vasculogenesis.

Quality-control culture system restores diabetic endothelial progenitor cell vasculogenesis and accelerates wound closure

Delayed diabetic wound healing is, in part, the result of inadequate endothelial progenitor cell (EPC) proliferation, mobilization, and trafficking. Recently, we developed a serum-free functional culture system called the quality and quantity culture (QQc) system that enhances the number and vasculogenic potential of EPCs. We hypothesize that QQc restoration of diabetic EPC function will improve wound closure. To test this hypothesis, we measured diabetic c-kit(+)Sca-1(+)lin(-) (KSL) cell activity in vitro as well as the effect of KSL cell-adoptive transfer on the rate of euglycemic wound closure before and after QQc. KSL cells were magnetically sorted from control and streptozotocin-induced type I diabetic C57BL6J bone marrow. Freshly isolated control and diabetic KSL cells were cultured in QQc for 7 days and pre-QQc and post-QQc KSL function testing. The number of KSL cells significantly increased after QQc for both diabetic subjects and controls, and diabetic KSL increased vasculogenic potential above the fresh control KSL level. Similarly, fresh diabetic cells form fewer tubules, but QQc increases diabetic tubule formation to levels greater than that of fresh control cells (P < 0.05). Adoptive transfer of post-QQc diabetic KSL cells significantly enhances wound closure compared with fresh diabetic KSL cells and equaled wound closure of post-QQc control KSL cells. Post-QQc diabetic KSL enhancement of wound closure is mediated, in part, via a vasculogenic mechanism. This study demonstrates that QQc can reverse diabetic EPC dysfunction and achieve control levels of EPC function. Finally, post-QQc diabetic EPC therapy effectively improved euglycemic wound closure and may improve diabetic wound healing.

Anagliptin, a DPP-4 inhibitor, suppresses proliferation of vascular smooth muscles and monocyte inflammatory reaction and attenuates atherosclerosis in male apo E-deficient mice

Dipeptyl peptidase-4 (DPP-4) inhibitors modulate the progression of atherosclerosis. To gain insights into their mechanism of action, 9-wk-old male apolipoprotein E (apoE)-deficient mice were fed a DPP-4 inhibitor, anagliptin-containing diet. The effects of anagliptin were investigated in, a monocyte cell line, human THP-1 cells, and rat smooth muscle cells (SMCs). Treatment with anagliptin for 16 wk significantly reduced accumulation of monocytes and macrophages in the vascular wall, SMC content in plaque areas, and oil red O-stained area around the aortic valve without affecting glucose tolerance or body weight. Serum DPP-4 concentrations were significantly higher in apoE-deficient mice than control mice, and the levels increased with aging, suggesting the involvement of DPP-4 in the progression of atherosclerosis. Indeed, soluble DPP-4 augmented cultured SMC proliferation, and anagliptin suppressed the proliferation by inhibiting ERK phosphorylation. In THP-1 cells, anagliptin reduced lipopolysaccharide-induced TNF-α production with inhibiting ERK phosphorylation and nuclear translocation of nuclear factor-κB. Quantitative analysis also showed that anagliptin reduced the area of atherosclerotic lesion in apoE-deficient mice. These results indicated that the anti-atherosclerotic effect of anagliptin is mediated, at least in part, through its direct inhibition of SMC proliferation and inflammatory reaction of monocytes.

Autologous G-CSF-mobilized peripheral blood CD34+ cell therapy for diabetic patients with chronic nonhealing ulcer

Recently, animal studies have demonstrated the efficacy of endothelial progenitor cell (EPC) therapy for diabetic wound healing. Based on these preclinical studies, we performed a prospective clinical trial phase I/IIa study of autologous G-CSF-mobilized peripheral blood (PB) CD34(+) cell transplantation for nonhealing diabetic foot patients. Diabetic patients with nonhealing foot ulcers were treated with 2 × 10(7) cells of G-CSF-mobilized PB CD34(+) cells as EPC-enriched population. Safety and efficacy (wound closure and vascular perfusion) were evaluated 12 weeks posttherapy and further followed for complete wound closure and recurrence. A total of five patients were enrolled. Although minor amputation and recurrence were seen in three out of five patients, no death, other serious adverse events, or major amputation was seen following transplantation. Complete wound closure was observed at an average of 18 weeks with increased vascular perfusion in all patients. The outcomes of this prospective clinical study indicate the safety and feasibility of CD34(+) cell therapy in patients with diabetic nonhealing wounds.

Obesity impairs wound closure through a vasculogenic mechanism

Since obesity impairs wound healing and bone marrow (BM)-derived vasculogenic progenitor cells (PCs) are important for tissue repair, we hypothesize that obesity-impaired wound healing is due, in part, to impaired PC mobilization, trafficking, and function. Peripheral blood was obtained from nondiabetic, obese (BMI > 30, n = 25), and nonobese (BMI < 30, n = 17) subjects. Peripheral blood human (h)PCs were isolated, quantified, and functionally assessed. To corroborate the human experiments, 6-mm stented wounds were created on nondiabetic obese mice (TALLYHO/JngJ, n = 15) and nonobese mice (SWR/J, n = 15). Peripheral blood mouse (m)PCs were quantified and wounds were analyzed. There was no difference in the number of baseline circulating hPCs in nondiabetic, obese (hPC-ob), and nonobese (hPC-nl) subjects, but hPC-ob had impaired adhesion (p < 0.05), migration (p < 0.01), and proliferation (p < 0.001). Nondiabetic obese mice had a significant decrease in the number of circulating PCs (mPC-ob) at 7 (p = 0.008) and 14 days (p = 0.003) after wounding. The impaired circulating mPC-ob response correlated with significantly impaired wound closure at days 14 (p < 0.001) and 21 (p < 0.001) as well as significantly fewer new blood vessels in the wounds (p < 0.001). Our results suggest that obesity impairs the BM-derived vasculogenic PC response to peripheral injury and this, in turn, impairs wound closure.

Development of serum-free quality and quantity control culture of colony-forming endothelial progenitor cell for vasculogenesis

Quantitative and qualitative impairment of endothelial progenitor cells (EPCs) limits the efficacy of autologous cell therapy in patients with cardiovascular diseases. Here, we developed a serum-free quality and quantity control culture system for colony-forming EPCs to enhance their regenerative potential. A culture with serum-free medium containing stem cell factor, thrombopoietin, vascular endothelial growth factor, interleukin-6, and Flt-3 ligand was determined as optimal quality and quantity culture (QQc) in terms of the most vasculogenic colony-forming EPC expansion, evaluated by the newly established EPC colony formation assay. The QQc of umbilical cord blood-CD133(+) cells for 7 days produced a 52.9-fold increase in total cell number and 3.28-fold frequency in definitive EPC colony development, resulting in a 203.9-fold increase in estimated total definitive EPC colony number in vitro. Pre- or post-QQc cells were intramyocardially transplanted into nude rats with myocardial infarction (MI). Echocardiographic and micromanometer-tipped conductance catheter examinations 28 days post-MI revealed significant preservation of left ventricular (LV) function in rats receiving pre- or post-QQc cells compared with those receiving phosphate-buffered saline. Assessments of global LV contractility indicated a dose-dependent effect of pre- or post-QQc cells and the superior potency of post-QQc cells over pre-QQc cells. Furthermore, immunohistochemistry showed more abundant formation of both human and rat endothelial cells and cardiomyocytes in the infarcted myocardium following transplantation of post-QQc cells compared with pre-QQc cells. Our optimal serum-free quality and quantity culture may enhance the therapeutic potential of EPCs in both quantitative and qualitative aspects for cardiovascular regeneration.

Improved culture-based isolation of differentiating endothelial progenitor cells from mouse bone marrow mononuclear cells

Numerous endothelial progenitor cell (EPC)-related investigations have been performed in mouse experiments. However, defined characteristics of mouse cultured EPC have not been examined. We focused on fast versus slow adherent cell population in bone marrow mononuclear cells (BMMNCs) in culture and examined their characteristics. After 24 h-culture of BMMNCs, attached (AT) cells and floating (FL) cells were further cultured in endothelial differentiation medium separately. Immunological and molecular analyses exhibited more endothelial-like and less monocyte/macrophage-like characteristics in FL cells compared with AT cells. FL cells formed thick/stable tube and hypoxia or shear stress overload further enhanced these endothelial-like features with increased angiogenic cytokine/growth factor mRNA expressions. Finally, FL cells exhibited therapeutic potential in a mouse myocardial infarction model showing the specific local recruitment to ischemic border zone and tissue preservation. These findings suggest that slow adherent (FL) but not fast attached (AT) BMMNCs in culture are EPC-rich population in mouse.

Impaired function of bone marrow-derived endothelial progenitor cells in murine liver fibrosis

Liver fibrosis (LF) caused by chronic liver damage has been considered as an irreversible disease. As alternative therapy for liver transplantation, there are high expectations for regenerative medicine of the liver. Bone marrow (BM)- or peripheral blood-derived stem cells, including endothelial progenitor cells (EPCs), have recently been used to treat liver cirrhosis. We investigated the biology of BM-derived EPC in a mouse model of LF. C57BL/6J mice were subcutaneously injected with carbon tetrachloride (CCl(4)) every 3 days for 90 days. Sacrificed 2 days after final injection, whole blood (WB) was collected for isolation of mononuclear cells (MNCs) and biochemical examination. Assessments of EPC in the peripheral blood and BM were performed by flow cytometry and EPC colony-forming assay, respectively, using purified MNCs and BM c-KIT(+), Sca-1(+), and Lin(-) (KSL) cells. Liver tissues underwent histological analysis with hematoxylin/eosin/Azan staining, and spleens were excised and weighed. CCl(4)-treated mice exhibited histologically bridging fibrosis, pseudolobular formation, and splenomegaly, indicating successful induction of LF. The frequency of definitive EPC-colony-forming-units (CFU) as well as total EPC-CFU at the equivalent cell number of 500 BM-KSL cells decreased significantly (p < 0.0001) in LF mice compared with control mice; no significant changes in primitive EPC-CFU occurred in LF mice. The frequency of WB-MNCs of definitive EPC-CFU decreased significantly (p < 0.01) in LF mice compared with control mice. Together, these findings indicated the existence of impaired EPC function and differentiation in BM-derived EPCs in LF mice and might be related to clinical LF.

Progenitor cell mobilization enhances bone healing by means of improved neovascularization and osteogenesis

BACKGROUND

Although bone repair is a relatively efficient process, a significant portion of patients fail to heal their fractures. Because adequate blood supply is essential to osteogenesis, the authors hypothesize that augmenting neovascularization by increasing the number of circulating progenitor cells will improve bony healing.

METHODS

Bilateral full-thickness defects were created in the parietal bones of C57 wild-type mice. Intraperitoneal AMD3100 (n = 33) or sterile saline (n = 33) was administered daily beginning on postoperative day 3 and continuing through day 18. Circulating progenitor cell number was quantified by fluorescence-activated cell sorting. Bone regeneration was assessed with micro-computed tomography. Immunofluorescent CD31 and osteocalcin staining was performed to assess for vascularity and osteoblast density.

RESULTS

AMD3100 treatment increased circulating progenitor cell levels and significantly improved bone regeneration. Calvarial defects of AMD3100-treated mice demonstrated increased vascularity and osteoblast density.

CONCLUSIONS

Improved bone regeneration in this model was associated with elevated circulating progenitor cell number and subsequently improved neovascularization and osteogenesis. These findings highlight the importance of circulating progenitor cells in bone healing and may provide a novel therapy for bone regeneration.

Aberrant kinetics of bone marrow-derived endothelial progenitor cells in the murine oxygen-induced retinopathy model

PURPOSE

Retinopathy of prematurity (ROP) causes serious blindness because of the vasculopathy that results from the abnormal oxygen dynamics. However, the systemic kinetics of bone marrow-derived endothelial progenitor cells (BM-derived EPCs) during the "postnatal vasculogenesis " of ROP has yet to be elucidated. Thus, the authors investigated the kinetics of BM-derived EPCs using a murine oxygen-induced retinopathy (OIR) model.

METHODS

OIR was induced in C57BL/6J mice by continual aeration with 75% oxygen from postnatal day (P) 7 to P12 that afterward returned to normal room air.

RESULTS

The frequency of circulating EPCs (Sca-1(+)/c-Kit(+) cells in blood) in an OIR model estimated by FACS decreased immediately after the hyperoxic phase (P12) and then increased at the hypoxic phase (P17) compared with control. Further, EPC colony-forming assay of BM-Lin(-)/Sca-1(+) (BM-LS) cells exhibited a conversion from the predominant primitive EPC colony production at P12 to the definitive EPC colony at P17. In the OIR retinas of BM-transplanted mice with BM-LS cells of EGFP transgenic mice, there was less incorporation of GFP(+) cells into vascular structures at P12, whereas there was a drastic recruitment into the "tufts " and for the intact vasculature at P17. Moreover, the definitive EPC colony cells intravitreally injected into OIR significantly abrogated pathologic versus primitive vascular growth.

CONCLUSIONS

Taken together, these findings propose that the deviation of functional bioactivities of BM-derived EPCs contributing to intact vascular development under the abnormal oxygen dynamics may provide important mechanistic insight into pathologic vascular development in ROP.

Endothelial progenitor cells: a novel tool for the therapy of ischemic diseases

Circulating endothelial progenitor cells (EPCs) are believed to home to sites of neovascularization, contributing to vascular regeneration either directly via incorporation into newly forming vascular structures or indirectly via the secretion of pro-angiogenic growth factors, thereby enhancing the overall vascular and hemodynamic recovery of ischemic tissues. The therapeutic application of EPCs has been shown to be effective in animal models of ischemia, and we as well as other groups involved in clinical trials have demonstrated that the use of EPCs was safe and feasible for the treatment of critical limb ischemia and cardiovascular diseases. However, many issues in the field of EPC biology, especially in regard to the proper and unambiguous molecular characterization of these cells, still remain unresolved, hampering not only basic research but also the effective therapeutic use and widespread application of these cells. Further, recent evidence suggests that several diseases and pathological conditions are correlated with a reduction in the number and biological activity of EPCs, making the development of novel strategies to overcome the current limitations and shortcomings of this promising but still limited therapeutic tool by refinement and improvement of EPC purification, expansion, and administration techniques, a rather pressing issue.

Methodological Development of a Clonogenic Assay to Determine Endothelial Progenitor Cell Potential

The precise and conceptual insight of circulating endothelial progenitor cell (EPC) kinetics is hampered by the absence of an assay system capable of evaluating the EPC differentiation cascade. An assay system for EPC colony formation was developed to delineate circulating EPC differentiation. EPC colony-forming assay using semisolid medium and single or bulk CD133 + cells from umbilical cord blood exhibited the formation of two types of attaching cell colonies made of small or large cells featuring endothelial lineage potential and properties, termed small EPC colony-forming units and large EPC colony-forming units, respectively. In vitro and in vivo assays of each EPC colony-forming unit cell revealed a differentiation hierarchy from small EPC to large EPC colonies, indicating a primitive EPC stage with highly proliferative activity and a definitive EPC stage with vasculogenic properties, respectively. Experimental comparison with a conventional EPC culture assay system disclosed EPC colony-forming unit cells differentiate into noncolony-forming early EPC. The fate analysis of single CD133 + cells into the endothelial and hematopoietic lineage was achieved by combining this assay system with a hematopoietic progenitor assay and demonstrated the development of colony-forming EPC and hematopoietic progenitor cells from a single hematopoietic stem cell. EPC colony-forming assay permits the determination of circulating EPC kinetics from single or bulk cells, based on the evaluation of hierarchical EPC colony formation. This assay further enables a proper exploration of possible links between the origin of EPC and hematopoietic stem cells, representing a novel and powerful tool to investigate the molecular signaling pathways involved in EPC biology.

CD34+ cells represent highly functional endothelial progenitor cells in murine bone marrow

Background

Endothelial progenitor cells (EPCs) were shown to have angiogenic potential contributing to neovascularization. However, a clear definition of mouse EPCs by cell surface markers still remains elusive. We hypothesized that CD34 could be used for identification and isolation of functional EPCs from mouse bone marrow.

Methodology/Principal Findings

CD34⁺ cells, c-Kit⁺/Sca-1⁺/Lin⁻ (KSL) cells, c-Kit⁺/Lin⁻ (KL) cells and Sca-1⁺/Lin⁻ (SL) cells were isolated from mouse bone marrow mononuclear cells (BMMNCs) using fluorescent activated cell sorting. EPC colony forming capacity and differentiation capacity into endothelial lineage were examined in the cells. Although CD34⁺ cells showed the lowest EPC colony forming activity, CD34⁺ cells exhibited under endothelial culture conditions a more adherent phenotype compared with the others, demonstrating the highest mRNA expression levels of endothelial markers vWF, VE-cadherin, and Flk-1. Furthermore, a dramatic increase in immediate recruitment of cells to the myocardium following myocardial infarction and systemic cell injection was observed for CD34⁺ cells comparing with others, which could be explained by the highest mRNA expression levels of key homing-related molecules Integrin β2 and CXCR4 in CD34⁺ cells. Cell retention and incorporation into the vasculature of the ischemic myocardium was also markedly increased in the CD34⁺ cell-injected group, giving a possible explanation for significant reduction in fibrosis area, significant increase in neovascularization and the best cardiac functional recovery in this group in comparison with the others.

Conclusion

These findings suggest that mouse CD34⁺ cells may represent a functional EPC population in bone marrow, which could benefit the investigation of therapeutic EPC biology.

Differential activity of bone marrow hematopoietic stem cell subpopulations for EPC development and ischemic neovascularization

Although endothelial progenitor cells (EPCs) differentiate from minor populations of stem cells in bone marrow (BM), the differential role of hematopoietic stem cell (HSC) subpopulations in EPC development is largely unclear. Morphological characterization of EPC colonies has revealed that c-kit+/Sca-1+/lineage (Lin)-(KSL) cells mainly develop small EPC-colony forming units (CFUs) not large EPC-CFUs. In contrast, c-kit+/Sca-1-/Lin- (KL) cells develop large EPC-CFUs not small EPC-CFUs. Neither c-kit-/Sca-1+/Lin- (SL) cells nor c-kit-/Sca-1-/Lin- (L) cells develop EPC-CFUs to an appreciable extent. Hindlimb ischemia enhances formation of large EPC-CFUs from all HSC subpopulations, suggesting an important role for ischemia in functional EPC development. Real time RT-PCR analysis shows that KSL, KL and SL cells but not L cells express various factors at high levels, maintaining a BM-EPC pool. In hindlimb ischemia, transplanted KSL, KL and SL cells efficiently differentiate into endothelial lineage cells in situ and augment capillary density. The percentage of Ki-67+ cycling cells among transplanted cells in ischemic tissue was also greater for KSL, KL and SL cells than L cells. Moreover, the frequency of VEGF- or SDF-1-expressing cells was higher transplanted KSL, KL or SL cells than L cells. Thus, KSL, KL and SL cells are not different in their angiogenic competence under ischemic conditions. In conclusion, although KSL cells are clearly the most potent contributors to EPC development, KL and SL cells may also contribute to neovascularization via both autocrine and paracrine mechanisms in response to ischemic signals.

Hypoxia inducible microRNA 210 attenuates keratinocyte proliferation and impairs closure in a murine model of ischemic wounds

Ischemia complicates wound closure. Here, we are unique in presenting a murine ischemic wound model that is based on bipedicle flap approach. Using this model of ischemic wounds we have sought to elucidate how microRNAs may be implicated in limiting wound re-epithelialization under hypoxia, a major component of ischemia. Ischemia, evaluated by laser Doppler as well as hyperspectral imaging, limited blood flow and lowered tissue oxygen saturation. EPR oximetry demonstrated that the ischemic wound tissue had pO(2) <10 mm Hg. Ischemic wounds suffered from compromised macrophage recruitment and delayed wound epithelialization. Specifically, epithelial proliferation, as determined by Ki67 staining, was compromised. In vivo imaging showed massive hypoxia inducible factor-1alpha (HIF-1alpha) stabilization in ischemic wounds, where HIF-1alpha induced miR-210 expression that, in turn, silenced its target E2F3, which was markedly down-regulated in the wound-edge tissue of ischemic wounds. E2F3 was recognized as a key facilitator of cell proliferation. In keratinocytes, knock-down of E2F3 limited cell proliferation. Forced stabilization of HIF-1alpha using Ad-VP16- HIF-1alpha under normoxic conditions up-regulated miR-210 expression, down-regulated E2F3, and limited cell proliferation. Studies using cellular delivery of miR-210 antagomir and mimic demonstrated a key role of miR-210 in limiting keratinocyte proliferation. In summary, these results are unique in presenting evidence demonstrating that the hypoxia component of ischemia may limit wound re-epithelialization by stabilizing HIF-1alpha, which induces miR-210 expression, resulting in the down-regulation of the cell-cycle regulatory protein E2F3.

Characterization of a preclinical model of chronic ischemic wound

Chronic ischemic wounds presenting at wound clinics are heterogeneous with respect to etiology, age of the wound, and other factors complicating wound healing. In addition, there are ethical challenges associated with collecting repeated biopsies from a patient to develop an understanding of the temporal dynamics of the mechanisms underlying chronic wounds. The need for a preclinical model of ischemic wound is therefore compelling. The porcine model is widely accepted as an excellent preclinical model for human wounds. A full-thickness bipedicle flap approach was adopted to cause skin ischemia. Closure of excisional wounds placed on ischemic tissue was severely impaired resulting in chronic wounds. Histologically, ischemic wounds suffered from impaired re-epithelialization, delayed macrophage recruitment and poorer endothelial cell abundance and organization. Compared with the pair-matched nonischemic wound, unique aspects of the ischemic wound biology were examined on days 3, 7, 14, and 28 by systematic screening of the wound tissue transcriptome using high-density porcine GeneChips. Ischemia markedly potentiated the expression of arginase-1, a cytosolic enzyme that metabolizes the precursor of nitric oxide l-arginine. Ischemia also induced the SOD2 in the wound tissue perhaps as survival response of the challenged tissue. Human chronic wounds also demonstrated elevated expression of SOD2 and arginase-1. This study provides a thorough database that may serve as a valuable reference tool to develop novel hypotheses aiming to elucidate the biology of ischemic chronic wounds in a preclinical setting.