Ischemia- and cytokine-induced mobilization of bone marrow-derived endothelial progenitor cells for neovascularization

MSCs Become Collagen-Type I Producing Cells with Different Phenotype in Allogeneic and Syngeneic Bone Marrow Transplantation

Mesenchymal stem cells (MSCs) have been widely used in therapeutic applications for many decades. However, more and more evidence suggests that factors such as the site of origin and pre-implantation treatment have a crucial impact on the result. This study investigates the role of freshly isolated MSCs in the lacrimal gland after allogeneic transplantation. For this purpose, MSCs from transgenic GFP mice were isolated and transplanted into allogeneic and syngeneic recipients. While the syngeneic MSCs maintained a spherical shape, allogeneic MSCs engrafted into the tissue as spindle-shaped cells in the interstitial stroma. Furthermore, the MSCs produced collagen type I in more than 85% to 95% of the detected GFP+ MSCs in the recipients of both models, supposedly contributing to pathogenic fibrosis in allogeneic recipients compared to syngeneic models. These findings indicate that allogeneic MSCs act completely differently from syngeneic MSCs, highlighting the importance of understanding the exact mechanisms behind MSCs.

Advances and Perspectives in Dental Pulp Stem Cell Based Neuroregeneration Therapies

Human dental pulp stem cells (hDPSCs) are some of the most promising stem cell types for regenerative therapies given their ability to grow in the absence of serum and their realistic possibility to be used in autologous grafts. In this review, we describe the particular advantages of hDPSCs for neuroregenerative cell therapies. We thoroughly discuss the knowledge about their embryonic origin and characteristics of their postnatal niche, as well as the current status of cell culture protocols to maximize their multilineage differentiation potential, highlighting some common issues when assessing neuronal differentiation fates of hDPSCs. We also review the recent progress on neuroprotective and immunomodulatory capacity of hDPSCs and their secreted extracellular vesicles, as well as their combination with scaffold materials to improve their functional integration on the injured central nervous system (CNS) and peripheral nervous system (PNS). Finally, we offer some perspectives on the current and possible future applications of hDPSCs in neuroregenerative cell therapies.

Systemic Administration of G-CSF Accelerates Bone Regeneration and Modulates Mobilization of Progenitor Cells in a Rat Model of Distraction Osteogenesis

Granulocyte colony-stimulating factor (G-CSF) was shown to promote bone regeneration and mobilization of vascular and osteogenic progenitor cells. In this study, we investigated the effects of a systemic low dose of G-CSF on both bone consolidation and mobilization of hematopoietic stem/progenitor cells (HSPCs), endothelial progenitor cells (EPCs) and mesenchymal stromal cells (MSCs) in a rat model of distraction osteogenesis (DO). Neovascularization and mineralization were longitudinally monitored using positron emission tomography and planar scintigraphy. Histological analysis was performed and the number of circulating HSPCs, EPCs and MSCs was studied by flow cytometry. Contrary to control group, in the early phase of consolidation, a bony bridge with lower osteoclast activity and a trend of an increase in osteoblast activity were observed in the distracted callus in the G-CSF group, whereas, at the late phase of consolidation, a significantly lower neovascularization was observed. While no difference was observed in the number of circulating EPCs between control and G-CSF groups, the number of MSCs was significantly lower at the end of the latency phase and that of HSPCs was significantly higher 4 days after the bone lengthening. Our results indicate that G-CSF accelerates bone regeneration and modulates mobilization of progenitor cells during DO.

An oral absorbent, AST-120, restores vascular growth and blood flow in ischemic muscles in diabetic mice via modulation of macrophage transition

Background Diabetes has a pronounced effect on the peripheral vasculature. The accumulation of advanced glycation end products (AGEs) is regarded as the crucial mechanism responsible for vascular damage in diabetes, but it is not easy to be avoided from food. In this study, we aimed to investigate the effects of an oral absorbent, AST-120, on the accumulation of AGEs and changes in blood flow recovery in diabetic mice. Methods The mice were divided into four groups, wild-type (WT) mice without treatment, WT mice treated with 5% AST-120 mixed into pulverized chow, streptozotocin-induced diabetes mellitus (DM) mice, and DM mice treated with 5% AST-120. Six weeks after hind-limb ischemia surgery, blood flow reperfusion, histology, plasma AGE, and cytokine were examined. Bone marrow cells were cultured and derived into macrophages to evaluate the effects of AGEs on macrophage polarization. Results Plasma AGEs were significantly increased in diabetic mice. AST-120 could bind to AGEs and reduced their plasma concentrations. Histological analysis revealed fewer collateral vessels with corresponding impairment of blood flow recovery in diabetic mice. In these mice, AGE-positive and AGE receptor-positive macrophages were numerous in ischemic limbs compared with non- diabetic mice. In diabetic mice, macrophages in ischemic tissues demonstrated greater M1 polarization than M2 polarization; this pattern was reversed in the AST-120 treatment group. The change in macrophage polarization was associated with the corresponding expression of pro-inflammatory cytokines in the ischemic tissues. In cell cultures, AGEs triggered the transformation of bone marrow-derived macrophages into the M1 phenotype. The alterations in the polarization of macrophages were reversed after treatment with AST-120. Conclusions Oral administration of AST-120 decreased the serum levels of AGEs in diabetic mice and improved neovascularization of ischemic limbs. This benefit may be due to, at least partially, the alterations in macrophage polarization and the associated changes in inflammatory cytokines.

The Effect of Platelet-Rich Plasma on Endothelial Progenitor Cell Functionality

Platelets mediate circulating endothelial progenitor cell (EPC) recruitment and maturation, participating in vascular repair, however the underlying mechanism(s) remain unclear. We investigated the effect of platelet-rich plasma (PRP) on the functionality of CD34⁺-derived late-outgrowth endothelial cells (OECs) in culture. Confluent OECs were coincubated with PRP under platelet aggregation (with adenosine diphosphate; ADP) and nonaggregation conditions, in the presence/absence of the reversible P2Y12 platelet receptor antagonist ticagrelor. Outgrowth endothelial cell activation was evaluated by determining prostacyclin (PGI₂) and monocyte chemoattractant protein-1 (MCP-1) release and intercellular adhesion molecule-1 (ICAM-1) membrane expression. Similar experiments were performed using human umbilical vein endothelial cells (HUVECs). Platelet-rich plasma increased ICAM-1 expression and PGI₂ and MCP-1 secretion compared with autologous platelet-poor plasma, whereas ADP-aggregated platelets in PRP did not exhibit any effect. Platelet-rich plasma pretreated with ticagrelor prior to activation with ADP increased all markers to a similar extent as PRP. Similar results were obtained using HUVECs. In conclusion, PRP induces OEC activation, a phenomenon not observed when platelets are aggregated with ADP. Platelet inhibition with ticagrelor restores the PRP capability to activate OECs. Since EPC activation is important for endothelial regeneration and angiogenesis, we suggest that agents inhibiting platelet aggregation, such as ticagrelor, may promote platelet-EPC interaction and EPC function.

Molecular Profiling and Gene Banking of Rabbit EPCs Derived from Two Biological Sources

Endothelial progenitor cells (EPCs) have been broadly studied for several years due to their outstanding regenerative potential. Moreover, these cells might be a valuable source of genetic information for the preservation of endangered animal species. However, a controversy regarding their characterization still exists. The aim of this study was to isolate and compare the rabbit peripheral blood- and bone marrow-derived EPCs with human umbilical vein endothelial cells (HUVECs) in terms of their phenotype and morphology that could be affected by the passage number or cryopreservation as well as to assess their possible neuro-differentiation potential. Briefly, cells were isolated and cultured under standard endothelial conditions until passage 3. The morphological changes during the culture were monitored and each passage was analyzed for the typical phenotype using flow cytometry, quantitative real–time polymerase chain reaction (qPCR) and novel digital droplet PCR (ddPCR), and compared to HUVECs. The neurogenic differentiation was induced using a commercial kit. Rabbit cells were also cryopreserved for at least 3 months and then analyzed after thawing. According to the obtained results, both rabbit EPCs exhibit a spindle-shaped morphology and high proliferation rate. The both cell lines possess same stable phenotype: CD14⁻CD29⁺CD31⁻CD34⁻CD44⁺CD45⁻CD49f⁺CD73⁺CD90⁺CD105⁺CD133⁻CD146⁻CD166⁺VE-cadherin⁺VEGFR-2⁺SSEA-4⁺MSCA-1⁻vWF⁺eNOS⁺AcLDL⁺ALDH⁺vimentin⁺desmin⁺α-SMA⁺, slightly different from HUVECs. Moreover, both induced rabbit EPCs exhibit neuron-like morphological changes and expression of neuronal markers ENO2 and MAP2. In addition, cryopreserved rabbit cells maintained high viability (>85%) and endothelial phenotype after thawing. In conclusion, our findings suggest that cells expanded from the rabbit peripheral blood and bone marrow are of the endothelial origin with a stable marker expression and interesting proliferation and differentiation capacity.

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.

Promise of autologous CD34+ stem/progenitor cell therapy for treatment of cardiovascular disease

CD34+ cells are haematopoietic stem cells used therapeutically in patients undergoing radiation or chemotherapy due to their regenerative potential and ability to restore the haematopoietic system. In animal models, CD34+ cells have been associated with therapeutic angiogenesis in response to ischaemia. Several trials have shown the potential safety and efficacy of CD34+ cell delivery in various cardiovascular diseases. Moreover, Phase III trials have now begun to explore the potential role of CD34+ cells in treatment of both myocardial and peripheral ischaemia. CD34+ cells have been shown to be safe and well-tolerated in the acute myocardial infarction (AMI), heart failure, and angina models. Several studies have suggested potential benefit of CD34+ cell therapy in patients with coronary microvascular disease as well. In this review, we will discuss the therapeutic potential of CD34+ cells, and describe the pertinent trials that have used autologous CD34+ cells in no-options refractory angina, AMI, and heart failure. Lastly, we will review the potential utility of autologous CD34+ cells in coronary endothelial and microvascular dysfunction.

Beneficial Effects of Astragaloside IV-Treated and 3-Dimensional-Cultured Endothelial Progenitor Cells on Angiogenesis and Wound Healing

INTRODUCTION

Astragaloside IV (AS-IV) is a natural herb extract and a popular compound used in traditional Chinese medicine because of its effect on multiple biological processes, such as promotion of cell proliferation, improvement in cardiopulmonary and vascular function, and promotion of angiogenesis around wounds, leading to accelerated wound healing. Vascular regeneration primarily results from the differentiation of endothelial progenitor cells (EPCs). Biomedical acceleration of angiogenesis and differentiation of EPCs around the wound remain challenging.

MATERIALS AND METHODS

In this study, we treated human umbilical cord blood-derived EPCs with AS-IV and cultured them on 2-dimensional (tissue culture polystyrene) and 3-dimensional culture plates (3DPs). These cultured cells were then combined with human blood plasma gel and applied on the skin of nude mice in an attempt to repair full-thickness skin defects.

RESULTS

The results show that using 3DP culture could increase vascular-related gene expression in EPCs. Furthermore, 12.5 μg/mL AS-IV-treaded EPCs were combined with plasma gels (P-3DP-EPC12.5) and showed enhanced vascular-related protein expression levels after 3 days of culture. Finally, P-3DP-EPC12.5s were used to repair full-thickness skin defects in nude mice, and we could register a wound healing rate greater than 90% by day 14.

CONCLUSIONS

Based on these results, we concluded that we have developed a potential therapeutic approach for wound healing using plasma gel containing 3-dimensional surface-cultured AS-IV-treated EPCs.

Endothelial Cells as Tools to Model Tissue Microenvironment in Hypoxia-Dependent Pathologies

Endothelial cells (ECs) lining the blood vessels are important players in many biological phenomena but are crucial in hypoxia-dependent diseases where their deregulation contributes to pathology. On the other hand, processes mediated by ECs, such as angiogenesis, vessel permeability, interactions with cells and factors circulating in the blood, maintain homeostasis of the organism. Understanding the diversity and heterogeneity of ECs in different tissues and during various biological processes is crucial in biomedical research to properly develop our knowledge on many diseases, including cancer. Here, we review the most important aspects related to ECs’ heterogeneity and list the available in vitro tools to study different angiogenesis-related pathologies. We focus on the relationship between functions of ECs and their organo-specificity but also point to how the microenvironment, mainly hypoxia, shapes their activity. We believe that taking into account the specific features of ECs that are relevant to the object of the study (organ or disease state), especially in a simplified in vitro setting, is important to truly depict the biology of endothelium and its consequences. This is possible in many instances with the use of proper in vitro tools as alternative methods to animal testing.

Pravastatin Promotes Endothelial Colony-Forming Cell Function, Angiogenic Signaling and Protein Expression In Vitro

Endothelial dysfunction is a primary feature of several cardiovascular diseases. Endothelial colony-forming cells (ECFCs) represent a highly proliferative subtype of endothelial progenitor cells (EPCs), which are involved in neovascularization and vascular repair. Statins are known to improve the outcome of cardiovascular diseases via pleiotropic effects. We hypothesized that treatment with the 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitor pravastatin increases ECFCs' functional capacities and regulates the expression of proteins which modulate endothelial health in a favourable manner. Umbilical cord blood derived ECFCs were incubated with different concentrations of pravastatin with or without mevalonate, a key intermediate in cholesterol synthesis. Functional capacities such as migration, proliferation and tube formation were addressed in corresponding in vitro assays. mRNA and protein levels or phosphorylation of protein kinase B (AKT), endothelial nitric oxide synthase (eNOS), heme oxygenase-1 (HO-1), vascular endothelial growth factor A (VEGF-A), placental growth factor (PlGF), soluble fms-like tyrosine kinase-1 (sFlt-1) and endoglin (Eng) were analyzed by real time PCR or immunoblot, respectively. Proliferation, migration and tube formation of ECFCs were enhanced after pravastatin treatment, and AKT- and eNOS-phosphorylation were augmented. Further, expression levels of HO-1, VEGF-A and PlGF were increased, whereas expression levels of sFlt-1 and Eng were decreased. Pravastatin induced effects were reversible by the addition of mevalonate. Pravastatin induces beneficial effects on ECFC function, angiogenic signaling and protein expression. These effects may contribute to understand the pleiotropic function of statins as well as to provide a promising option to improve ECFCs' condition in cell therapy in order to ameliorate endothelial dysfunction.

TNFα priming through its interaction with TNFR2 enhances endothelial progenitor cell immunosuppressive effect: new hope for their widespread clinical application

Background

Bone marrow derived endothelial progenitor cells (EPCs) are immature endothelial cells (ECs) involved in neo-angiogenesis and endothelial homeostasis and are considered as a circulating reservoir for endothelial repair. Many studies showed that EPCs from patients with cardiovascular pathologies are impaired and insufficient; hence, allogenic sources of EPCs from adult or cord blood are considered as good choices for cell therapy applications. However, allogenic condition increases the chance of immune rejection, especially by T cells, before exerting the desired regenerative functions. TNFα is one of the main mediators of EPC activation that recognizes two distinct receptors, TNFR1 and TNFR2. We have recently reported that human EPCs are immunosuppressive and this effect was TNFα-TNFR2 dependent. Here, we aimed to investigate if an adequate TNFα pre-conditioning could increase TNFR2 expression and prime EPCs towards more immunoregulatory functions.

Methods

EPCs were pre-treated with several doses of TNFα to find the proper dose to up-regulate TNFR2 while keeping the TNFR1 expression stable. Then, co-cultures of human EPCs and human T cells were performed to assess whether TNFα priming would increase EPC immunosuppressive and immunomodulatory effect.

Results

Treating EPCs with 1 ng/ml TNFα significantly up-regulated TNFR2 expression without unrestrained increase of TNFR1 and other endothelial injury markers. Moreover, TNFα priming through its interaction with TNFR2 remarkably enhanced EPC immunosuppressive and anti-inflammatory effects. Conversely, blocking TNFR2 using anti-TNFR2 mAb followed by 1 ng/ml of TNFα treatment led to the TNFα-TNFR1 interaction and polarized EPCs towards pro-inflammatory and immunogenic functions.

Conclusions

We report for the first time the crucial impact of inflammation notably the TNFα-TNFR signaling pathway on EPC immunological function. Our work unveils the pro-inflammatory role of the TNFα-TNFR1 axis and, inversely the anti-inflammatory implication of the TNFα-TNFR2 axis in EPC immunoregulatory functions. Priming EPCs with 1 ng/ml of TNFα prior to their administration could boost them toward a more immunosuppressive phenotype. This could potentially lead to EPCs’ longer presence in vivo after their allogenic administration resulting in their better contribution to angiogenesis and vascular regeneration.

Inhibition of HMGB1 Might Enhance the Protective Effect of Taxifolin in Cardiomyocytes via PI3K/AKT Signaling Pathway

Cardiovascular diseases (CVD) affect millions of people and spend a lot of medical costs around the world each year. Taxifolin is a natural anti-oxidative reagent obtained from multiple plants and exhibits a wide range of pharmacological effects. High mobility group box protein 1 (HMGB1) is expressed in multiple types of cells in the extracellular environment, regulating the pro-inflammatory process. Here, we detected the viability of cells using MTT assay, and the expression of each target protein was detected using western blotting analysis. The expression of each target mRNA was detected using the qPCR method, and the concentration of each cytokine in serum samples was detected using the ELISA method. In this study, we found that taxifolin could decrease the expression of hypoxia-inducible factor-1α (HIF-1α) while increasing the expression of endothelial nitric oxide synthase (eNOS), presented a protective role. Besides, taxifolin could also increase the expression of vascular endothelial growth factor-α (VEGF-α), transforming growth factor-β (TGF-β) and fibroblast growth factor21 (FGF21), resulting in viability rate increasing. And these effects were mediated by phosphatidylinositol 3-hydroxy kinase (PI3K)/AKT/mTOR signaling pathway; a similar trend was also observed in HMGB1 knockdown mice. We also found that inhibition of HMGB1 could enhance the cardioprotective effect of taxifolin and might be a new therapeutic strategy for cardiovascular disease.

The secretome of endothelial progenitor cells: a potential therapeutic strategy for ischemic stroke

Ischemic stroke continues to be a leading cause of mortality and morbidity in the world. Despite recent advances in the field of stroke medicine, thrombolysis with recombinant tissue plasminogen activator remains as the only pharmacological therapy for stroke patients. However, due to short therapeutic window (4.5 hours of stroke onset) and increased risk of hemorrhage beyond this point, each year globally less than 1% of stroke patients receive this therapy which necessitate the discovery of safe and efficacious therapeutics that can be used beyond the acute phase of stroke. Accumulating evidence indicates that endothelial progenitor cells (EPCs), equipped with an inherent capacity to migrate, proliferate and differentiate, may be one such therapeutics. However, the limited availability of EPCs in peripheral blood and early senescence of few isolated cells in culture conditions adversely affect their application as effective therapeutics. Given that much of the EPC-mediated reparative effects on neurovasculature is realized by a wide range of biologically active substances released by these cells, it is possible that EPC-secretome may serve as an important therapeutic after an ischemic stroke. In light of this assumption, this review paper firstly discusses the main constituents of EPC-secretome that may exert the beneficial effects of EPCs on neurovasculature, and then reviews the currently scant literature that focuses on its therapeutic capacity.

The Role of Bone Marrow Aspirate in Osseous and Soft Tissue Pathology

Bone marrow aspirate (BMA) is an emerging therapy that is gaining popularity for orthoplastic reconstruction. The stem cells collected are multipotent and regenerative in nature. In addition to stem cells, other biological components collected augment the mitogen of local cells, proliferation, and angiogenesis, and inhibit proinflammatory cytokine and bacteria to optimize an environment to heal. The most common site for harvest is the iliac crest. Techniques for harvesting BMA are simple to perform, financially modest, and associated with low morbidity. Additional research is needed to evolve and standardize the technology; however, BMA is proven to be advantageous for tissue repair.

The detrimental qualitative and quantitative alterations of circulating endothelial progenitor cells in patients with bronchiectasis

BACKGROUND

Bronchiectasis is an independent risk factor for cardiovascular disease（CVD）and cardiac dysfunction. Endothelial progenitor cells (EPCs) play a crucial role in maintaining endothelial function, and is inversely correlated with cardiovascular risk factors or cardiac dysfunction. However, the relationship between EPCs and bronchiectasis is unknown.

METHODS

Twenty-nine patients with stable bronchiectasis and 15 healthy controls were recruited. Fasting venous blood were collected for determining circulating EPC number and activity as well as systemic inflammatory cytokines.

RESULTS

The number and migratory or proliferative activity of circulating EPCs in bronchiectasis patients were significantly reduced (p < 0.001). In high E-FACED group, the number of circulating EPCs evaluated by cell culture assay and EPC proliferation were decreased (p < 0.05). Similarly, the number and function of circulating EPCs were both reduced in low forced expiratory volume in 1 s (FEV1) or high mMRC group (p < 0.05). There was a significant correlation between circulating EPCs and bronchiectasis disease severity, according to the E-FACED score (p < 0.05), particularly to FEV1 (p < 0.05) and mMRC dyspnea score (p < 0.05). The count and activity of EPCs inversely correlated with hsCRP levels and IL-6 levels (p < 0.01).

CONCLUSIONS

Deficiencies in the number and function of circulating EPCs are present in patients with bronchiectasis. The changes are related to disease severity and may be partly attributed to systemic inflammation. The current findings may provide novel surrogate evaluation biomarkers and potential therapeutic target for bronchiectasis.

Gangrene, revascularization, and limb function improved with E-selectin/adeno-associated virus gene therapy

OBJECTIVE

Novel therapeutic angiogenic concepts for critical limb ischemia are still needed for limb salvage. E-selectin, a cell-adhesion molecule, is vital for recruitment of the stem/progenitor cells necessary for neovascularization in ischemic tissues. We hypothesized that priming ischemic limb tissue with E-selectin/adeno-associated virus (AAV) gene therapy, in a murine hindlimb ischemia and gangrene model, would increase therapeutic angiogenesis and improve gangrene.

METHODS

FVB/NJ mice were given intramuscular hindlimb injections of either E-selectin/AAV or LacZ/AAV and then underwent induction of gangrene via femoral artery ligation and concomitant systemic injections of the nitric oxide synthesis inhibitor L-NAME (L-NG-Nitro arginine methyl ester; 40 mg/kg). Gangrene was evaluated via the Faber hindlimb appearance score. The rate of ischemic limb reperfusion and ischemic tissue angiogenesis were evaluated using laser Doppler perfusion imaging and DiI perfusion with confocal laser scanning microscopy of the ischemic footpads, respectively. The treadmill exhaustion test was performed on postoperative day (POD) 8 to determine hindlimb functionality.

RESULTS

The E-selectin/AAV-treated mice (n = 10) had decreased Faber ischemia scores compared with those of the LacZ/AAV-treated mice (n = 7) at both PODs 7 and 14 (P < .05 and P < .01, respectively), improved laser Doppler perfusion imaging reperfusion indexes by POD 14 (P < .01), and greater gangrene footpad capillary density (P < .001). E-selectin/AAV-treated mice also had improved exercise tolerance (P < .05) and lower relative muscular atrophy (P < .01).

CONCLUSION

We surmised that E-selectin/AAV gene therapy would significantly promote hindlimb angiogenesis, reperfusion, and limb functionality in mice with hindlimb ischemia and gangrene. Our findings highlight the reported novel gene therapy approach to critical limb ischemia as a potential therapeutic option for future clinical studies.

Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF

Background

After traumatic skeletal muscle injury, muscle healing is often incomplete and produces extensive fibrosis. The sequence of M1 and M2 macrophage accumulation and the duration of each subtype in the injured area may help to direct the relative extent of fibrogenesis and myogenesis during healing. We hypothesized that increasing the number of M1 macrophages early after traumatic muscle injury would produce more cellular and molecular substrates for myogenesis and fewer substrates for fibrosis, leading to better muscle healing.

Methods

To test this hypothesis, we transfected skeletal muscle with a plasmid vector to transiently express GM-CSF shortly after injury to drive the polarization of macrophages towards the M1 subset. C57BL/6 mouse tibialis anterior (TA) muscles were injured by contusion and electroporated with uP-mGM, which is a plasmid vector that transiently expresses GM-CSF. Myogenesis, angiogenesis, and fibrosis were evaluated by histology, immunohistochemistry, and RT-qPCR; subpopulations of macrophages by flow cytometry; and muscle functioning by the maximum running speed on the treadmill and the recovery of muscle mass.

Results

Muscle injury increased the number of local M1-like macrophages and decreased the number of M2-like macrophages on day 4, and uP-mGM treatment enhanced this variation. uP-mGM treatment decreased TGF-β1 protein expression on day 4, and the Sirius Red-positive area decreased from 35.93 ± 15.45% (no treatment) to 2.9% ± 6.5% (p < 0.01) on day 30. uP-mGM electroporation also increased Hgf, Hif1α, and Mtor gene expression; arteriole density; and muscle fiber number during regeneration. The improvement in the quality of the muscle tissue after treatment with uP-mGM affected the increase in the TA muscle mass and the maximum running speed on a treadmill.

Conclusion

Collectively, our data show that increasing the number of M1-like macrophages immediately after traumatic muscle injury promotes muscle recovery with less fibrosis, and this can be achieved by the transient expression of GM-CSF.

Hematopoietic Stem Cell Transcription Factors in Cardiovascular Pathology

Transcription factors as multifaceted modulators of gene expression that play a central role in cell proliferation, differentiation, lineage commitment, and disease progression. They interact among themselves and create complex spatiotemporal gene regulatory networks that modulate hematopoiesis, cardiogenesis, and conditional differentiation of hematopoietic stem cells into cells of cardiovascular lineage. Additionally, bone marrow-derived stem cells potentially contribute to the cardiovascular cell population and have shown potential as a therapeutic approach to treat cardiovascular diseases. However, the underlying regulatory mechanisms are currently debatable. This review focuses on some key transcription factors and associated epigenetic modifications that modulate the maintenance and differentiation of hematopoietic stem cells and cardiac progenitor cells. In addition to this, we aim to summarize different potential clinical therapeutic approaches in cardiac regeneration therapy and recent discoveries in stem cell-based transplantation.

Vagal α7nAChR signaling regulates α7nAChR+Sca1+ cells during lung injury repair

Background

The distal airways of the lung and bone marrow are innervated by the vagus nerve. Vagal α7nAChR signaling plays a key role in regulating lung infection and inflammation; however, whether this pathway regulates α7nAChR⁺Sca1⁺ cells during lung injury repair remains unknown. We hypothesized that vagal α7nAChR signaling controls α7nAChR⁺Sca1⁺ cells, which contribute to the resolution of lung injury.

Methods

Pneumonia was induced by intratracheal challenge with E. coli. The bone marrow mononuclear cells (BM-MNCs) were isolated from the bone marrow of pneumonia mice for immunofluorescence. The bone marrow, blood, BAL, and lung cells were isolated for flow cytometric analysis by labeling with anti-Sca1, VE-cadherin, p-Akt1, or Flk1 antibodies. Immunofluorescence was also used to examine the coexpression of α7nAChR, VE-cadherin, and p-Akt1. Sham, vagotomized, α7nAChR knockout, and Akt1 knockout mice were infected with E. coli to study the regulatory role of vagal α7nAChR signaling and Akt1 in Sca1⁺ cells.

Results

During pneumonia, BM-MNCs were enriched with α7nAChR⁺Sca1⁺ cells, and this cell population proliferated. Transplantation of pneumonia BM-MNCs could mitigate lung injury and increase engraftment in recipient pneumonia lungs. Activation of α7nAChR by its agonist could boost α7nAChR⁺Sca1⁺ cells in the bone marrow, peripheral blood, and bronchoalveolar lavage (BAL) in pneumonia. Immunofluorescence revealed that α7nAChR, VE-cadherin, and p-Akt1 were coexpressed in the bone marrow cells. Vagotomy could reduce α7nAChR⁺VE-cadherin⁺ and VE-cadherin⁺p-Akt1⁺ cells in the bone marrow in pneumonia. Knockout of α7nAChR reduced VE-cadherin⁺ cells and p-Akt1⁺ cells in the bone marrow. Deletion of Akt1 reduced Sca1⁺ cells in the bone marrow and BAL. More importantly, 91.3 ± 4.9% bone marrow and 77.8 ± 4.9% lung α7nAChR⁺Sca1⁺VE-cadherin⁺ cells expressed Flk1, which is a key marker of endothelial progenitor cells (EPCs). Vagotomy reduced α7nAChR⁺Sca1⁺VE-cadherin⁺p-Akt1⁺ cells in the bone marrow and lung from pneumonia mice. Treatment with cultured EPCs reduced ELW compared to PBS treatment in E. coli pneumonia mice at 48 h. The ELW was further reduced by treatment with EPCs combining with α7nAChR agonist-PHA568487 compared to EPC treatments only.

Conclusions

Vagal α7nAChR signaling regulates α7nAChR⁺Sca1⁺VE-cadherin⁺ EPCs via phosphorylation of Akt1 during lung injury repair in pneumonia.

Potential mechanisms underlying the association between single nucleotide polymorphism (BRAP and ALDH2) and hypertension among elderly Japanese population

Minor allele frequency (MAF) of rs3782886 (BRAP) and rs671 (ALDH2) are reported to be inversely associated with blood pressure. Another study revealed that hematopoietic activity which is evaluated by reticulocytes could influenced on hypertension status partly by indicating activity of endothelial maintenance. Therefore, to evaluate the association between genetic factor and hypertension, influence of hematopoietic activity should be considered. A multi-faced analysis was performed in a simple general elderly population model (1,313 older Japanese aged 60–98 years). Participants were stratified by median values of reticulocytes (5.21 × 10⁴ cells/μL for men and 4.65 × 10⁴ cells/μL for women). Independent of known cardiovascular risk factors, MAF of rs3782886 and rs671 are significantly inversely associated with hypertension for participants with high hematopoietic activity (high reticulocytes level) (fully adjusted odds ratio (ORs) were 0.72 (0.55, 0.96) for rs3782886 and 0.72 (0.54, 0.96) for rs671) but not for low reticulocytes count (the corresponding values were 1.05 (0.79, 1.39) and 1.08 (0.81, 1.45), respectively). Hematopoietic activity evaluated by reticulocytes levels could influence on the association between single nucleotide polymorphism (rs3782886 and rs671) and hypertension. Those results were efficient tool to clarify the part of the mechanism that underlying the association between genetic factor and hypertension.

Circulating exosomal miR-144-3p inhibits the mobilization of endothelial progenitor cells post myocardial infarction via regulating the MMP9 pathway

Background: The angiogenesis post myocardial infarction (MI) is compromised in diabetes. MiR-144-3p is reported to be highly expressed in circulating exosomes of diabetic patients, implying its role in diabetic complications. However, whether circulating exosomes and enriched miR-144-3p are involved in the impaired neovascularization in diabetes and the underlying mechanism is unclear.

Results: DMexo and miR-144-3p mimic-treated MSCs had elevated miR-144-3p levels and decreased MMP9, Ets1 and PLG expression. The percentage of EPCs were relatively lower in DMexo-treated or agomir-treated MI mice compared with MI mice. Finally, the luciferase assay confirmed the direct binding between miR-144-3p and Ets1.

Conclusion: Exosomal miR-144-3p could impair the mobilization ability of EPCs, which was associated with impaired ischemia-induced neovascularization.

Methods: Circulating exosomes were isolated from Streptozotocin (STZ)-induced mice. In vitro, mesenchymal stem cells (MSCs) were incubated with exosomes from diabetic mice (DMexo), and miR-144-3p mimic or inhibitor. miR-144-3p, and MMP9 pathway were measured using qPCR and immunoblotting. In vivo, MI mice induced by left anterior descending ligation were treated with DMexo, as well as miR-144-3p agomir. Flow cytometry was used to profile endothelial progenitor cells (EPCs) in peripheral blood and bone marrow post 24 hours respectively.

Abnormal DNA Methylation Induced by Hyperglycemia Reduces CXCR 4 Gene Expression in CD 34+ Stem Cells

Background CD 34⁺ stem/progenitor cells are involved in vascular homeostasis and in neovascularization of ischemic tissues. The number of circulating CD 34⁺ stem cells is a predictive biomarker of adverse cardiovascular outcomes in diabetic patients. Here, we provide evidence that hyperglycemia can be "memorized" by the stem cells through epigenetic changes that contribute to onset and maintenance of their dysfunction in diabetes mellitus. Methods and Results Cord-blood-derived CD 34⁺ stem cells exposed to high glucose displayed increased reactive oxygen species production, overexpression of p66^shc gene, and downregulation of antioxidant genes catalase and manganese superoxide dismutase when compared with normoglycemic cells. This altered oxidative state was associated with impaired migration ability toward stromal-cell-derived factor 1 alpha and reduced protein and mRNA expression of the C-X-C chemokine receptor type 4 ( CXCR 4) receptor. The methylation analysis by bisulfite Sanger sequencing of the CXCR 4 promoter revealed a significant increase in DNA methylation density in high-glucose CD 34⁺ stem cells that negatively correlated with mRNA expression (Pearson r=-0.76; P=0.004). Consistently, we found, by chromatin immunoprecipitation assay, a more transcriptionally inactive chromatin conformation and reduced RNA polymerase II engagement on the CXCR 4 promoter. Notably, alteration of CXCR 4 DNA methylation, as well as transcriptional and functional defects, persisted in high-glucose CD 34⁺ stem cells despite recovery in normoglycemic conditions. Importantly, such an epigenetic modification was thoroughly confirmed in bone marrow CD 34⁺ stem cells isolated from sternal biopsies of diabetic patients undergoing coronary bypass surgery. Conclusions CD 34⁺ stem cells "memorize" the hyperglycemic environment in the form of epigenetic modifications that collude to alter CXCR 4 receptor expression and migration.

The State of Art of Regenerative Therapy in Cardiovascular Ischemic Disease: Biology, Signaling Pathways, and Epigenetics of Endothelial Progenitor Cells

Ischemic heart disease is currently a major cause of mortality and morbidity worldwide. Nevertheless, the actual therapeutic scenario does not target myocardial cell regeneration and consequently, the progression toward the late stage of chronic heart failure is common. Endothelial progenitor cells (EPCs) are bone marrow-derived stem cells that contribute to the homeostasis of the endothelial wall in acute and chronic ischemic disease. Calcium modulation and other molecular pathways (NOTCH, VEGFR, and CXCR4) contribute to EPC proliferation and differentiation. The present review provides a summary of EPC biology with a particular focus on the regulatory pathways of EPCs and describes promising applications for cardiovascular cell therapy.

Vascular Remodeling in Moyamoya Angiopathy: From Peripheral Blood Mononuclear Cells to Endothelial Cells

The pathophysiological mechanisms of Moyamoya angiopathy (MA), which is a rare cerebrovascular condition characterized by recurrent ischemic/hemorrhagic strokes, are still largely unknown. An imbalance of vasculogenic/angiogenic mechanisms has been proposed as one possible disease aspect. Circulating endothelial progenitor cells (cEPCs) have been hypothesized to contribute to vascular remodeling of MA, but it remains unclear whether they might be considered a disease effect or have a role in disease pathogenesis. The aim of the present study was to provide a morphological, phenotypical, and functional characterization of the cEPCs from MA patients to uncover their role in the disease pathophysiology. cEPCs were identified from whole blood as CD45^dimCD34⁺CD133⁺ mononuclear cells. Morphological, biochemical, and functional assays were performed to characterize cEPCs. A significant reduced level of cEPCs was found in blood samples collected from a homogeneous group of adult (mean age 46.86 ± 11.7; 86.36% females), Caucasian, non-operated MA patients with respect to healthy donors (HD; p = 0.032). Since no difference in cEPC characteristics and functionality was observed between MA patients and HD, a defective recruitment mechanism could be involved in the disease pathophysiology. Collectively, our results suggest that cEPC level more than endothelial progenitor cell (EPC) functionality seems to be a potential marker of MA. The validation of our results on a larger population and the correlation with clinical data as well as the use of more complex cellular model could help our understanding of EPC role in MA pathophysiology.

Endothelial Overexpression of Metallothionein Prevents Diabetes-Induced Impairment in Ischemia Angiogenesis Through Preservation of HIF-1α/SDF-1/VEGF Signaling in Endothelial Progenitor Cells

Diabetes-induced oxidative stress is one of the major contributors to dysfunction of endothelial progenitor cells (EPCs) and impaired endothelial regeneration. Thus, we tested whether increasing antioxidant protein metallothionein (MT) in EPCs promotes angiogenesis in a hind limb ischemia (HLI) model in endothelial MT transgenic (JTMT) mice with high-fat diet- and streptozocin-induced diabetes. Compared with littermate wild-type (WT) diabetic mice, JTMT diabetic mice had improved blood flow recovery and angiogenesis after HLI. Similarly, transplantation of JTMT bone marrow-derived mononuclear cells (BM-MNCs) stimulated greater blood flow recovery in db/db mice with HLI than did WT BM-MNCs. The improved recovery was associated with augmented EPC mobilization and angiogenic function. Further, cultured EPCs from patients with diabetes exhibited decreased MT expression, increased cell apoptosis, and impaired tube formation, while cultured JTMT EPCs had enhanced cell survival, migration, and tube formation in hypoxic/hyperglycemic conditions compared with WT EPCs. Mechanistically, MT overexpression enhanced hypoxia-inducible factor 1α (HIF-1α), stromal cell-derived factor (SDF-1), and vascular endothelial growth factor (VEGF) expression and reduced oxidative stress in ischemic tissues. MT's pro-EPC effects were abrogated by siRNA knockdown of HIF-1α without affecting its antioxidant action. These results indicate that endothelial MT overexpression is sufficient to protect against diabetes-induced impairment of angiogenesis by promoting EPC function, most likely through upregulation of HIF-1α/SDF-1/VEGF signaling and reducing oxidative stress.

Atherosclerotic Pre-Conditioning Affects the Paracrine Role of Circulating Angiogenic Cells Ex-Vivo

In atherosclerosis, circulating angiogenic cells (CAC), also known as early endothelial progenitor cells (eEPC), are thought to participate mainly in a paracrine fashion by promoting the recruitment of other cell populations such as late EPC, or endothelial colony-forming cells (ECFC), to the injured areas. There, ECFC replace the damaged endothelium, promoting neovascularization. However, despite their regenerative role, the number and function of EPC are severely affected under pathological conditions, being essential to further understand how these cells react to such environments in order to implement their use in regenerative cell therapies. Herein, we evaluated the effect of direct incubation ex vivo of healthy CAC with the secretome of atherosclerotic arteries. By using a quantitative proteomics approach, 194 altered proteins were identified in the secretome of pre-conditioned CAC, many of them related to inhibition of angiogenesis (e.g., endostatin, thrombospondin-1, fibulins) and cell migration. Functional assays corroborated that healthy CAC released factors enhanced ECFC angiogenesis, but, after atherosclerotic pre-conditioning, the secretome of pre-stimulated CAC negatively affected ECFC migration, as well as their ability to form tubules on a basement membrane matrix assay. Overall, we have shown here, for the first time, the effect of atherosclerotic factors over the paracrine role of CAC ex vivo. The increased release of angiogenic inhibitors by CAC in response to atherosclerotic factors induced an angiogenic switch, by blocking ECFC ability to form tubules in response to pre-conditioned CAC. Thus, we confirmed here that the angiogenic role of CAC is highly affected by the atherosclerotic environment.

Intrinsic Vascular Repair by Endothelial Progenitor Cells in Acute Coronary Syndromes: an Update Overview

Bone marrow-derived endothelial progenitor cells (EPCs) play a key role in the maintenance of endothelial homeostasis and endothelial repair at areas of vascular damage. The quantification of EPCs in peripheral blood by flow cytometry is a strategy to assess this reparative capacity. The number of circulating EPCs is inversely correlated with the number of cardiovascular risk factors and to the occurrence of cardiovascular events. Therefore, monitoring EPCs levels may provide an accurate assessment of susceptibility to cardiovascular injury, greatly improving risk stratification of patients with high cardiovascular risk, such as those with an acute myocardial infarction. However, there are many issues in the field of EPC identification and quantification that remain unsolved. In fact, there have been conflicting protocols used to the phenotypic identification of EPCs and there is still no consensual immunophenotypical profile that corresponds exactly to EPCs. In this paper we aim to give an overview on EPCs-mediated vascular repair with special focus on acute coronary syndromes and to discuss the different phenotypic profiles that have been used to identify and quantify circulating EPCs in several clinical studies. Finally, we will synthesize evidence on the prognostic role of EPCs in patients with high cardiovascular risk.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

High expression of endothelial progenitor cell-induced angiogenic markers is associated with bile acid levels in HCC

Endothelial progenitor cell (EPC)-induced angiogenesis activity is enhanced in hepatocellular carcinoma (HCC); however, the contributing factors remain unknown. The present study aimed to investigate the factors influencing the number of EPCs and circulating progenitor cells (CPCs), as well as the expression levels of vascular endothelial growth factor receptor 2 (VEGFR-2) and CD34, in patients with HCC. The expression levels of VEGFR-2 and CD34 were assessed in 72 HCC tumor and matched adjacent tissue microarrays by immunohistochemistry. The associations between VEGFR-2 or CD34 expression in tumors, clinicopathological characteristics and overall survival rates were analyzed. The number of EPCs and CPCs were analyzed in the peripheral blood of patients with HCC. In this study, high expression levels of VEGFR-2 and CD34 were detected in the tumor tissues of 41 (56.9%) and 44 (61.1%) patients, respectively. VEGFR-2 expression was significantly associated with tumor size (P<0.001), bile acid level (P=0.014) and α-fetoprotein level (P=0.011). However, CD34 expression was associated with tumor size (P=0.009), recrudescence (P<0.001) and bile acid (P=0.009). Next, the expression levels of VEGFR-2 and CD34 in tumor and adjacent tissues were compared according to the bile acid level. VEGFR-2 and CD34 expression levels were both higher in the high bile acid group, whereas expression levels of the markers were higher in adjacent tissues compared with tumor tissues. Kaplan-Meier curve analysis identified that patients with low CD34 expression had a longer overall survival compared with patients with high CD34 expression (P=0.029). Multivariate analysis also indicated that both VEGFR-2 (P=0.020) and CD34 (P=0.035) were independent prognostic risk factors. Moreover, flow cytometry demonstrated that the number of EPCs and CPCs was negatively related with the bile acid levels in patients with HCC. In conclusion, in patients with HCC, bile acid promotes EPC-induced angiogenesis. Furthermore, EPCs and CPCs may be activated by bile acid in tumors but are more so in adjacent tissues.

Endothelial Progenitor Cells Induce Angiogenesis: a Potential Mechanism Underlying Neovascularization in Encephaloduroarteriosynangiosis

Encephaloduroarteriosynangiosis (EDAS) is one of the most commonly used indirect vascular reconstruction methods. EDAS aids in the formation of collateral vessels from the extracranial to the intracranial circulation in patients with moyamoya disease (MMD). However, the underlying mechanism of collateral vessel formation is not well understood. Endothelial progenitor cells (EPCs) differentiate to form the vascular endothelial cells and play a very important role in angiogenesis. We designed this prospective clinical trial to investigate the presence of EPCs in patients with MMD and to explore the neovascularization mechanism mediated by the EPCs in EDAS. The patients who were diagnosed with MMD were recruited between February 5, 2017, and January 7, 2018. The blood samples were obtained from an antecubital vein and were analyzed using flow cytometry. EPCs were defined as CD34^brCD133⁺CD45^dimKDR⁺. All the patients enrolled in the study underwent EDAS. Cerebral arteriography was performed 6 months post-EDAS to assess the efficacy of synangiosis. The correlation between EPC count and good collateral circulation was evaluated. Among the 116 patients with MMD enrolled in this study, 73 were women and 43 were men. The average age of the patients was 33.8 ± 15.2 years. The EPC count of the patients with MMD was 0.071% ± 0.050% (expressed as percentage of the peripheral blood mononuclear cells). The EPC count in the good postoperative collateral circulation group was significantly higher (0.085% ± 0.054%) than that in the poor collateral circulation group (0.048% ± 0.034%) (P = 0.000). The age, modified Suzuki-Mugikura grade, and EPC count were significantly correlated with the good collateral circulation post-EDAS in the multivariate analysis (P = 0.018, P = 0.007, and P = 0.003, respectively). The formation of collateral vessels by EDAS is primarily driven by angiogenesis. The EPC count may be the most critical factor for collateral circulation. The therapeutic effect of EDAS is more likely to benefit younger or severe ischemic patients with MMD.

Effects of nicotine on the translation of stem cell therapy

Although stem cell therapy has tremendous therapeutic potential, clinical translation of stem cell therapy has yet to be fully realized. Recently, patient comorbidities and lifestyle choices have emerged to be important factors in the efficacy of stem cell therapy. Tobacco usage is an important risk factor for numerous diseases, and nicotine exposure specifically has become increasing more prevalent with the rising use of electronic cigarettes. This review describes the effects of nicotine exposure on the function of various stem cells. We place emphasis on the differential effects of nicotine exposure in vitro and as well as in preclinical models. Further research on the effects of nicotine on stem cells will deepen our understanding of how lifestyle choices can impact the outcome of stem cell therapies.

The TNF/TNFR2 signaling pathway is a key regulatory factor in endothelial progenitor cell immunosuppressive effect

Background

Endothelial progenitor cells (EPCs) are non-differentiated endothelial cells (ECs) present in blood circulation that are involved in neo-vascularization and correction of damaged endothelial sites. Since EPCs from patients with vascular disorders are impaired and inefficient, allogenic sources from adult or cord blood are considered as good alternatives. However, due to the reaction of immune system against allogenic cells which usually lead to their elimination, we focused on the exact role of EPCs on immune cells, particularly, T cells which are the most important cells applied in immune rejection. TNFα is one of the main activators of EPCs that recognizes two distinct receptors. TNFR1 is expressed ubiquitously and its interaction with TNFα leads to differentiation and apoptosis, whereas, TNFR2 is expressed predominantly on ECs, immune cells and neural cells and is involved in cell survival and proliferation. Interestingly, it has been shown that different immunosuppressive cells express TNFR2 and this is directly related to their immunosuppressive efficiency. However, little is known about immunological profile and function of TNFR2 in EPCs.

Methods

Using different in-vitro combinations, we performed co-cultures of ECs and T cells to investigate the immunological effect of EPCs on T cells. We interrupted in the TNFα/TNFR2 axis either by blocking the receptor using TNFR2 antagonist or blocking the ligand using T cells derived from TNFα KO mice.

Results

We demonstrated that EPCs are able to suppress T cell proliferation and modulate them towards less pro-inflammatory and active phenotypes. Moreover, we showed that TNFα/TNFR2 immune-checkpoint pathway is critical in EPC immunomodulatory effect.

Conclusions

Our results reveal for the first time a mechanism that EPCs use to suppress immune cells, therefore, enabling them to form new immunosuppressive vessels. Furthermore, we have shown the importance of TNFα/TNFR2 axis in EPCs as an immune checkpoint pathway. We believe that targeting TNFR2 is especially crucial in cancer immune therapy since it controls two crucial aspects of tumor microenvironment: 1) Immunosuppression and 2) Angiogenesis.

Video Abstract. (MP4 46355 kb)

Cirrhotic Endothelial Progenitor Cells Enhance Liver Angiogenesis and Fibrosis and Aggravate Portal Hypertension in Bile Duct-Ligated Cirrhotic Rats

Background

Circulating cirrhotic endothelial progenitor cells (EPC) interact with both liver sinusoidal endothelial cells (LSEC) and hepatic stellate cells (HSC) and promote angiogenesis in vitro. This study evaluated the effect of cirrhotic and control EPCs on hepatic angiogenesis, microcirculation, and fibrosis in vivo in rat models of cirrhosis.

Methodology

Animal models of cirrhosis were prepared by bile duct ligation (BDL). Circulating EPCs isolated from healthy human and cirrhotic blood were characterized by flow cytometry, cultured and administered through the tail vein in BDL rats after 2 weeks of ligation. The cells were given thrice a week for 2 weeks. The untreated group of BDL rats received only saline. Fibrosis was evaluated by Masson’s trichrome staining. Dedifferentiated LSECs were identified by the expression of CD31, and activated HSCs were marked as alpha-SMA-positive cells and were studied by immunohistochemistry and western blotting in saline-, healthy EPC-, and cirrhotic EPC-treated rats. In vivo, hepatic and systemic hemodynamic parameters were evaluated. Liver functions were evaluated.

Results

In comparison to controls, BDL rats revealed an increase of fibrosis and angiogenesis. Among the treated rats, cirrhotic EPC-treated rats had increased fibrosis grade as compared to healthy EPC-treated and saline-treated rats. There was an increase of both fibrosis and angiogenesis markers, alpha-SMA and CD31 in cirrhotic EPC-treated rats as compared to healthy EPC-treated and saline-treated rats in immunohistochemistry and western blot studies. Cirrhotic EPC-treated BDL rats had high portal pressure and portal blood flow with significantly elevated hepatic vascular resistance in comparison with healthy EPC- and saline-treated BDL animals, without significant differences in mean arterial pressure. Cirrhotic EPC-treated BDL rats also showed a substantial increase in the hepatic expression of angiogenic receptors, VEGFR2 and CXCR4 in comparison with saline-treated rats.

Conclusion

The study suggests that transplantation of cirrhotic EPCs enhances LSEC differentiation and angiogenesis, activates HSCs and worsens fibrosis, thus resulting in hepatic hemodynamic derangements in BDL-induced cirrhosis.

N-acetylcysteine differentially regulates the populations of bone marrow and circulating endothelial progenitor cells in mice with limb ischemia

Endothelial progenitor cells (EPCs) are important to tissue repair and regeneration especially after ischemic injury, and very heterogeneous in phenotypes and biological features. Reactive oxygen species are involved in regulating EPC number and function. N-acetylcysteine (NAC) inhibits ischemia-induced reactive oxygen species formation and promotes ischemic limb recovery. This study was to evaluate the effect of NAC on EPC subpopulations in bone marrow (BM) and blood in mice with limb ischemia. Limb ischemia was induced by femoral artery ligation in male C57BL/6 mice with or without NAC treatment. EPC subpopulations, intracellular reactive oxygen species production, cell proliferation and apoptosis in BM and blood cells were analyzed at baseline, day 3 (acute ischemia) and 21 (chronic) after ligation. c-Kit+/CD31+, Sca-1+/Flk-1+, CD34+/CD133+, and CD34+/Flk-1+ were used to define EPC subpopulations. Limb blood flow, function, muscle structure, and capillary density were evaluated with laser Doppler perfusion imaging, treadmill test, and immunohistochemistry, respectively, at day 3, 7, 14 and 21 post ischemia. Reactive oxygen species production in circulating and BM mononuclear cells and EPCs populations were significantly increased in BM and blood in mice with acute and chronic ischemia. NAC treatment effectively blocked ischemia-induced reactive oxygen species production in circulating and BM mononuclear cells, and selectively increased EPC population in circulation, not BM, with preserved proliferation in mice with chronic ischemia, and enhanced limb blood flow and function recovery, while preventing acute ischemia-induced increase in BM and circulating EPCs. These data demonstrated that NAC selectively enhanced circulating EPC population in mice with chronic limb ischemia.

The Paracrine Role of Endothelial Cells in Bone Formation via CXCR4/SDF-1 Pathway

Vascularization is a prerequisite for bone formation. Endothelial progenitor cells (EPCs) stimulate bone formation by creating a vascular network. Moreover, EPCs secrete various bioactive molecules that may regulate bone formation. The aim of this research was to shed light on the pathways of EPCs in bone formation. In a subcutaneous nude mouse ectopic bone model, the transplantation of human EPCs onto β-TCP scaffold increased angiogenesis (p < 0.001) and mineralization (p < 0.01), compared to human neonatal dermal fibroblasts (HNDF group) and a-cellular scaffold transplantation (β-TCP group). Human EPCs were lining blood vessels lumen; however, the majority of the vessels originated from endogenous mouse endothelial cells at a higher level in the EPC group (p < 01). Ectopic mineralization was mostly found in the EPCs group, and can be attributed to the recruitment of endogenous mesenchymal cells ten days after transplantation (p < 0.0001). Stromal derived factor-1 gene was expressed at high levels in EPCs and controlled the migration of mesenchymal and endothelial cells towards EPC conditioned medium in vitro. Blocking SDF-1 receptors on both cells abolished cell migration. In conclusion, EPCs contribute to osteogenesis mainly by the secretion of SDF-1, that stimulates homing of endothelial and mesenchymal cells. This data may be used to accelerate bone formation in the future.

Vascular Regeneration in Peripheral Artery Disease

Peripheral artery disease is a common disorder and a major cause of morbidity and mortality worldwide. Therapy is directed at reducing the risk of major adverse cardiovascular events and at ameliorating symptoms. Medical therapy is effective at reducing the incidence of myocardial infarction and stroke to which these patients are prone but is inadequate in relieving limb-related symptoms, such as intermittent claudication, rest pain, and ischemic ulceration. Limb-related morbidity is best addressed with surgical and endovascular interventions that restore perfusion. Current medical therapies have only modest effects on limb blood flow. Accordingly, there is an opportunity to develop medical approaches to restore limb perfusion. Vascular regeneration to enhance limb blood flow includes methods to enhance angiogenesis, arteriogenesis, and vasculogenesis using angiogenic cytokines and cell therapies. We review the molecular mechanisms of these processes; briefly discuss what we have learned from the clinical trials of angiogenic and cell therapies; and conclude with an overview of a potential new approach based upon transdifferentiation to enhance vascular regeneration in peripheral artery disease.

The Formation of Coronary Vessels in Cardiac Development and Disease

Understanding how coronary blood vessels form and regenerate during development and progression of cardiac diseases will shed light on the development of new treatment options targeting coronary artery diseases. Recent studies with the state-of-the-art technologies have identified novel origins of, as well as new, cellular and molecular mechanisms underlying the formation of coronary vessels in the postnatal heart, including collateral artery formation, endocardial-to-endothelial differentiation and mesenchymal-to-endothelial transition. These new mechanisms of coronary vessel formation and regeneration open up new possibilities targeting neovascularization for promoting cardiac repair and regeneration. Here, we highlight some recent studies on cellular mechanisms of coronary vessel formation, and discuss the potential impact and significance of the findings on basic research and clinical application for treating ischemic heart disease.

Targeting Angiotensin-Converting Enzyme-2/Angiotensin-(1-7)/Mas Receptor Axis in the Vascular Progenitor Cells for Cardiovascular Diseases

Bone marrow-derived hematopoietic stem/progenitor cells are vasculogenic and play an important role in endothelial health and vascular homeostasis by participating in postnatal vasculogenesis. Progenitor cells are mobilized from bone marrow niches in response to remote ischemic injury and migrate to the areas of damage and stimulate revascularization largely by paracrine activation of angiogenic functions in the peri-ischemic vasculature. This innate vasoprotective mechanism is impaired in certain chronic clinical conditions, which leads to the development of cardiovascular complications. Members of the renin-angiotensin system-angiotensin-converting enzymes (ACEs) ACE and ACE2, angiotensin II (Ang II), Ang-(1-7), and receptors AT1 and Mas-are expressed in vasculogenic progenitor cells derived from humans and rodents. Ang-(1-7), generated by ACE2, is known to produce cardiovascular protective effects by acting on Mas receptor and is considered as a counter-regulatory mechanism to the detrimental effects of Ang II. Evidence has now been accumulating in support of the activation of the ACE2/Ang-(1-7)/Mas receptor pathway by pharmacologic or molecular maneuvers, which stimulates mobilization of progenitor cells from bone marrow, migration to areas of vascular damage, and revascularization of ischemic areas in pathologic conditions. This minireview summarizes recent studies that have enhanced our understanding of the physiology and pharmacology of vasoprotective axis in bone marrow-derived progenitor cells in health and disease. SIGNIFICANCE STATEMENT: Hematopoietic stem progenitor cells (HSPCs) stimulate revascularization of ischemic areas. However, the reparative potential is diminished in certain chronic clinical conditions, leading to the development of cardiovascular diseases. ACE2 and Mas receptor are key members of the alternative axis of the renin-angiotensin system and are expressed in HSPCs. Accumulating evidence points to activation of ACE2 or Mas receptor as a promising approach for restoring the reparative potential, thereby preventing the development of ischemic vascular diseases.

Association between height and circulating CD34-positive cells taken into account for the influence of enhanced production among elderly Japanese men: a cross-sectional study

Recent studies have revealed an inverse association between height and cardiovascular disease and that endothelial progenitor cells (CD34-positive cells) contribute to vascular maintenance, which is associated with cardiovascular disease. However, evidence of the association between height and CD34-positive positive cells among elderly participants is limited. To assess this association, we conducted a cross-sectional study of 231 elderly Japanese men aged 65–69. Since enhanced production of circulating CD34-positive cells in response to endothelial injury might act have a strong confounding effect on the association between height and circulating CD34-positive cells, the median value for the levels of these cells (0.93 cells/μL) was used to stratify the participants. Multivariable linear regression analysis demonstrated that height was significantly positively associated with circulating CD34-positive cells for those participants with low levels of circulating CD34-positive cells (n=114) but not for those with higher levels (n=117), with a multi-adjusted standardized parameter estimate (β) of 0.27 (p=0.008) for low and 0.11 (0.275) for higher circulating CD34-positive cell levels. The positive association is limited to participants with relatively low circulating CD34-positive cell levels, whose productivity of these cells is not activated. Our findings indicate that height is an indicator of vascular maintenance capability in elderly Japanese men.

Rationale and design of the granulocyte-macrophage colony stimulating factor in peripheral arterial disease (GPAD-3) study

BACKGROUND

Lower extremity peripheral arterial disease (PAD) is a public health problem and many patients with PAD experience claudication despite adequate medical and/or surgical management. Mobilization of endogenous progenitor cells using Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) is a novel therapeutic option that has shown promising results in experimental models and phase I/IIA clinical trials. The GPAD-3 trial will study the effect of two successive administrations of GM-CSF at 3-month interval for improving claudication among patients with lower extremity PAD.

METHODS

We plan to recruit 176 patients in this ongoing randomized, double-blind, placebo-controlled Phase IIB trial. After screening for inclusion and exclusion criteria, eligible subjects undergo a 4-week screening phase where they perform subcutaneous placebo injections thrice weekly and walk at least three times a day until they develop claudication. After the screening phase, eligible subjects undergo baseline testing and are randomized 2:1 to receive 500 μg/day of GM-CSF subcutaneously thrice weekly for three weeks or placebo injections. After 3 months, follow-up endpoint testing is performed and subjects in the GM-CSF group receive the second administration of the drug for three weeks while subjects in placebo group receive matching placebo injections. All participants undergo endpoint testing at six-month and nine-month follow-up. The primary endpoint is change in 6-min walk distance between baseline and 6-month follow-up.

CONCLUSION

GPAD-3 explores a novel approach to address the need for alternative therapies that can alleviate symptoms among patients with lower extremity PAD. If successful, this study will pave the way for a pivotal Phase III trial.

Hematopoietic Stem Cells and Their Roles in Tissue Regeneration

Hematopoietic stem cells (HSCs) are regarded as one of essential cell sources for treating regenerative diseases. Among many stem cells, the feasibility of using adult-derived hematopoietic stem cells in therapeutic approaches is very diverse, and is unarguably regarded as an important cell source in stem cell biology. So far, many investigators are exploring HSCs and modified HSCs for use in clinical and basic science. In the present review, we briefly summarized HSCs and their application in pathophysiologic conditions, including non-hematopoietic tissue regeneration as well as blood disorders. HSCs and HSCs-derived progenitors are promising cell sources in regenerative medicine and their contributions can be properly applied to treat pathophysiologic conditions. Among many adult stem cells, HSCs are a powerful tool to treat patients with diseases such as hematologic malignancies and liver disease. Since HSCs can be differentiated into diverse progenitors including endothelial progenitors, they may be useful for constructing strategies for effective therapy.

5F peptide promotes endothelial differentiation of bone marrow stem cells through activation of ERK1/2 signaling

Synthetic apolipoprotein A-I (apoA-I) mimetic peptide 5F exhibits anti-atherosclerotic ability with largely unknown mechanism(s). Bone marrow (BM)-derived endothelial progenitor cells (EPCs) play a critical role in vascular integrity and function. The objective of the present study was to evaluate the effect of 5F on endothelial differentiation of BM stem cells and related mechanisms. Murine BM multipotent adult progenitor cells (MAPCs) were induced to differentiate into endothelial cells in vitro with or without 5F. The expression of endothelial markers vWF, Flk-1 and CD31 was significantly increased in the cells treated with 5F with enhanced in vitro vascular tube formation and LDL uptake without significant changes on proliferation and stem cell maker Oct-4 expression. Phosphorylated ERK1/2, not Akt, was significantly increased in 5F-treated cells. Treatment of MAPCs with PD98059 or small interfering RNA against ERK2 substantially attenuated ERK1/2 phosphorylation, and effectively prevented 5F-induced enhancement of endothelial differentiation of MAPCs. In vivo studies revealed that 5F increased EPCs number in the BM in mice after acute hindlimb ischemia that was effectively prevented with PD98059 treatment. These data supported the conclusion that 5F promoted endothelial differentiation of MAPCs through activation of ERK1/2 signaling.

Defining the role of pulmonary endothelial cell heterogeneity in the response to acute lung injury

Pulmonary endothelial cells (ECs) are an essential component of the gas exchange machinery of the lung alveolus. Despite this, the extent and function of lung EC heterogeneity remains incompletely understood. Using single-cell analytics, we identify multiple EC populations in the mouse lung, including macrovascular endothelium (maEC), microvascular endothelium (miECs), and a new population we have termed Car4-high ECs. Car4-high ECs express a unique gene signature, and ligand-receptor analysis indicates they are primed to receive reparative signals from alveolar type I cells. After acute lung injury, they are preferentially localized in regenerating regions of the alveolus. Influenza infection reveals the emergence of a population of highly proliferative ECs that likely arise from multiple miEC populations and contribute to alveolar revascularization after injury. These studies map EC heterogeneity in the adult lung and characterize the response of novel EC subpopulations required for tissue regeneration after acute lung injury.

Dual-Peptide-Functionalized Nanofibrous Scaffolds Recruit Host Endothelial Progenitor Cells for Vasculogenesis to Repair Calvarial Defects

Vasculogenesis (de novo formation of vessels) induced by endothelial progenitor cells (EPCs) is requisite for vascularized bone regeneration. However, there exist few available options for promoting vasculogenesis within artificial bone grafts except for exogenous EPC transplantation, which suffers from the source of EPC, safety, cost, and time concerns in clinical applications. This study aimed at endogenous EPC recruitment for vascularized bone regeneration by using a bioinspired EPC-induced graft. The EPC-induced graft was created by immobilizing two bioactive peptides, WKYMVm and YIGSR, on the surface of poly(ε-caprolactone) (PCL)/poliglecaprone (PGC) nanofibrous scaffolds via a polyglycolic acid (PGA)-binding peptide sequence. Remarkable immobilization efficacy of WKYMVm and YIGSR peptides and their sustained release (over 14 days) from scaffolds were observed. In vivo and in vitro studies showed robust recruitment of EPCs, which subsequently contributed to early vasculogenesis and ultimate bone regeneration. The dual-peptide-functionalized nanofibrous scaffolds proposed in this study provide a promising therapeutic strategy for vasculogenesis in bone defect repair.

Harnessing the anti-inflammatory properties of stem cells for transplant therapy in hemorrhagic stroke

Hemorrhagic stroke is a global health crisis plagued by neuroinflammation in the acute and chronic phases. Neuroinflammation approximates secondary cell death, which in turn robustly contributes to stroke pathology. Both the physiological and behavioral symptoms of stroke correlate with various inflammatory responses in animal and human studies. That slowing the secondary cell death mediated by this inflammation may attenuate stroke pathology presents a novel treatment strategy. To this end, experimental therapies employing stem cell transplants support their potential for neuroprotection and neuroregeneration after hemorrhagic stroke. In this review, we evaluate experiments using different types of stem cell transplants as treatments for stroke-induced neuroinflammation. We also update this emerging area by examining recent preclinical and clinical trials that have deployed these therapies. While further investigations are warranted to solidify their therapeutic profile, the reviewed studies largely posit stem cells as safe and potent biologics for stroke, specifically owing to their mode of action for sequestering neuroinflammation and promoting neuroregenerative processes.

Targeting endothelial thioredoxin-interacting protein (TXNIP) protects from metabolic disorder-related impairment of vascular function and post-ischemic revascularisation

INTRODUCTION

Although thioredoxin-interacting protein (TXNIP) is involved in a variety of biological functions, the contribution of endothelial TXNIP has not been well-defined in regards to endothelial and vascular function or in post-ischemic revascularisation. We postulated that inhibition of endothelial TXNIP with siRNA or in a Cre-LoxP system could be involved in protection from high fat, high protein, low carbohydrate (HFHPLC) diet-induced oxidative stress and endothelial dysfunction, leading to vascular damage and impaired revascularisation in vivo.

METHODS AND RESULTS

To investigate the role of endothelial TXNIP, the TXNIP gene was deleted in endothelial cells using anti-TXNIP siRNA treatment or the Cre-LoxP system. Murine models were fed a HFHPLC diet, known to induce metabolic disorders. Endothelial TXNIP targeting resulted in protection against metabolic disorder-related endothelial oxidative stress and endothelial dysfunction. This protective effect mitigates media cell loss induced by metabolic disorders and hampered metabolic disorder-related vascular dysfunction assessed by aortic reactivity and distensibility. In aortic ring cultures, metabolic disorders impaired vessel sprouting and this alteration was alleviated by deletion of endothelial TXNIP. When subjected to ischemia, mice fed a HFHPLC diet exhibited defective post-ischemic angiogenesis and impaired blood flow recovery in hind limb ischemia. However, reducing endothelial TXNIP rescued metabolic disorder-related impairment of ischemia-induced revascularisation.

CONCLUSION

Collectively, these results show that targeting endothelial TXNIP in metabolic disorders is essential to maintaining endothelial function, vascular function and improving ischemia-induced revascularisation, making TXNIP a potential therapeutic target for therapy of vascular complications related to metabolic disorders.

Therapeutic Angiogenesis with Somatic Stem Cell Transplantation

Therapeutic angiogenesis is an important strategy to rescue ischemic tissues in patients with critical limb ischemia having no other treatment option such as endovascular angioplasty or bypass surgery. Studies indicated so far possibilities of therapeutic angiogenesis using autologous bone marrow mononuclear cells, CD34⁺ cells, peripheral blood mononuclear cells, adipose-derived stem/progenitor cells, and etc. Recent studies indicated that subcutaneous adipose tissue contains stem/progenitor cells that can give rise to several mesenchymal lineage cells. Moreover, these mesenchymal progenitor cells release a variety of angiogenic growth factors including vascular endothelial growth factor, fibroblast growth factor, hepatocyte growth factor and chemokine stromal cell-derived factor-1. Subcutaneous adipose tissues can be harvested by less invasive technique. These biological properties of adipose-derived regenerative cells (ADRCs) implicate that autologous subcutaneous adipose tissue would be a useful cell source for therapeutic angiogenesis in humans. In this review, I would like to discuss biological properties and future perspective of ADRCs-mediated therapeutic angiogenesis.

Therapeutic Angiogenesis

Myocardial ischemia and peripheral vascular disease persist as significant clinical problems despite improved medical, surgical, and endovascular therapies. Advances in our understanding of the biological mechanisms that govern capillary neovascularization and collateral artery growth have enabled molecular therapies for revascularizing ischemic tissues. Generally known as therapeutic angiogenesis, this review summarizes the essential pre-clinical research and the major clinical trials of molecular therapies for ischemic disease. Early clinical experience has established the proof of principle, however, inconsistent and modest improvements in clinical outcomes have exposed the complexity of neovascularization and problems with transitioning basic science to clinical applicability.