Therapeutic Potential of Human-Derived Endothelial Colony-Forming Cells in Animal Models

Endothelial colony forming cells from human umbilical cord blood improved severe erectile dysfunction in obese type II diabetic rats

AIM

To investigate the effect of intracavernous injection of human umbilical cord blood derived endothelial colony forming cells (HUCB ECFCs) on erectile dysfunction (ED) in Zucker Diabetic Fatty (ZDF) rat model.

METHODS

Erectile function was assessed by cavernous nerve electrostimulation in ZDF rats aged 20-28 weeks. Following confirmation of severe ED at the age of 28 weeks, 21 ZDF rats were randomly assigned to three experimental groups: 1 million ECFCs, 2 million ECFCs, and phosphate buffered saline (PBS). Four weeks after intracavernous injection, the efficacy of ECFCs was quantified by intracavernous pressure (ICP) measurement, Masson's trichrome staining, immunohistologic and immunoblot analyses and TUNEL assay.

KEY FINDINGS

Intracavernous ECFC administration improved ICP in a dose-dependent manner in comparison to the age-matched PBS group. Functional improvement in ICP was accompanied by a significant restoration of the cavernosal endothelial and smooth muscle cell content and cavernosal nerve function. The percentage eNOS and nNOS positive cavernosal cells, and their respective protein expression levels and nNOS positive cells in the dorsal penile nerve in 2 million ECFCs treated groups were significantly higher than the PBS group. TUNEL stain quantification showed a significant decrease in cavernosal apoptosis following ECFC treatment.

SIGNIFICANCE

The results are expected to provide a scientific basis to further study the clinical application of HUCB ECFCs in ameliorating ED in human.

CONCLUSIONS

HUCB ECFCs significantly improved severe ED in ZDF rats through improvement of the nerve and endothelium function and restoration of smooth muscle in the cavernosum by overcoming the cavernosal apoptosis.

Acidic preconditioning of endothelial colony-forming cells (ECFC) promote vasculogenesis under proinflammatory and high glucose conditions in vitro and in vivo

Background

We have previously demonstrated that acidic preconditioning of human endothelial colony-forming cells (ECFC) increased proliferation, migration, and tubulogenesis in vitro, and increased their regenerative potential in a murine model of hind limb ischemia without baseline disease. We now analyze whether this strategy is also effective under adverse conditions for vasculogenesis, such as the presence of ischemia-related toxic molecules or diabetes, one of the main target diseases for cell therapy due to their well-known healing impairments.

Methods

Cord blood-derived CD34⁺ cells were seeded in endothelial growth culture medium (EGM2) and ECFC colonies were obtained after 14–21 days. ECFC were exposed at pH 6.6 (preconditioned) or pH 7.4 (nonpreconditioned) for 6 h, and then pH was restored at 7.4. A model of type 2 diabetes induced by a high-fat and high-sucrose diet was developed in nude mice and hind limb ischemia was induced in these animals by femoral artery ligation. A P value < 0.05 was considered statistically significant (by one-way analysis of variance).

Results

We found that acidic preconditioning increased ECFC adhesion and the release of pro-angiogenic molecules, and protected ECFC from the cytotoxic effects of monosodium urate crystals, histones, and tumor necrosis factor (TNF)α, which induced necrosis, pyroptosis, and apoptosis, respectively. Noncytotoxic concentrations of high glucose, TNFα, or their combination reduced ECFC proliferation, stromal cell-derived factor (SDF)1-driven migration, and tubule formation on a basement membrane matrix, whereas almost no inhibition was observed in preconditioned ECFC. In type 2 diabetic mice, intravenous administration of preconditioned ECFC significantly induced blood flow recovery at the ischemic limb as measured by Doppler, compared with the phosphate-buffered saline (PBS) and nonpreconditioned ECFC groups. Moreover, the histologic analysis of gastrocnemius muscles showed an increased vascular density and reduced signs of inflammation in the animals receiving preconditioned ECFC.

Conclusions

Acidic preconditioning improved ECFC survival and angiogenic activity in the presence of proinflammatory and damage signals present in the ischemic milieu, even under high glucose conditions, and increased their therapeutic potential for postischemia tissue regeneration in a murine model of type 2 diabetes. Collectively, our data suggest that acidic preconditioning of ECFC is a simple and inexpensive strategy to improve the effectiveness of cell transplantation in diabetes, where tissue repair is highly compromised.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0872-7) contains supplementary material, which is available to authorized users.

Mycophenolic acid induces senescence of vascular precursor cells

OBJECTIVE

Endothelial dysfunction is central to the pathogenesis of many rheumatic diseases, typified by vascular inflammation and damage. Immunosuppressive drugs induce disease remission and lead to improved patient survival. However, there remains a higher incidence of cardiovascular disease in these patients even after adequate disease control. The purpose of this study was to determine the effect of mycophenolic acid (MPA), a commonly used immunosuppressive drug in rheumatology, on blood vessel or circulating endothelial colony forming cell number and function.

METHODS

We tested whether mycophenolic acid exerts an inhibitory effect on proliferation, clonogenic potential and vasculogenic function of endothelial colony forming cell. We also studied potential mechanisms involved in the observed effects.

RESULTS

Treatment with MPA decreased endothelial colony forming cell proliferation, clonogenic potential and vasculogenic function in a dose-dependent fashion. MPA increased senescence-associated β-galactosidase expression, p21 gene expression and p53 phosphorylation, indicative of activation of cellular senescence. Exogenous guanosine supplementation rescued diminished endothelial colony forming cell proliferation and indices of senescence, consistent with the known mechanism of action of MPA.

CONCLUSION

Our findings show that clinically relevant doses of MPA have potent anti-angiogenic and pro-senescent effects on vascular precursor cells in vitro, thus indicating that treatment with MPA can potentially affect vascular repair and regeneration. This warrants further studies in vivo to determine how MPA therapy contributes to vascular dysfunction and increased cardiovascular disease seen in patients with inflammatory rheumatic disease.

Endothelial Progenitor Cells as Shuttle of Anticancer Agents

Cell therapies are treatments in which stem or progenitor cells are stimulated to differentiate into specialized cells able to home to and repair damaged tissues. After their discovery, endothelial progenitor cells (EPCs) stimulated worldwide interest as possible vehicles to perform autologous cell therapy of tumors. Taking into account the tumor-homing properties of EPCs, two different approaches to control cancer progression have been pursued by combining cell-based therapy with gene therapy or with nanomedicine. The first approach is based on the possibility of engineering EPCs to express different transgenes, and the second is based on the capacity of EPCs to take up nanomaterials. Here we review the most important progress covering the following issues: the characterization of bona fide endothelial progenitor cells, their role in tumor vascularization and metastasis, and preclinical data about their use in cell-based tumor therapy, considering antiangiogenic, suicide, immune-stimulating, and oncolytic virus gene therapy. The mixed approach of EPC cell therapy and nanomedicine is discussed in terms of plasmonic-dependent thermoablation and molecular imaging.

Tissue regeneration using endothelial colony-forming cells: promising cells for vascular repair

Repairing and rebuilding damaged tissue in diseased human subjects remains a daunting challenge for clinical medicine. Proper vascular formation that serves to deliver blood-borne nutrients and adequate levels of oxygen and to remove wastes is critical for successful tissue regeneration. Endothelial colony-forming cells (ECFC) represent a promising cell source for revascularization of damaged tissue. ECFCs are identified by displaying a hierarchy of clonal proliferative potential and by pronounced postnatal vascularization ability in vivo. In this review, we provide a brief overview of human ECFC isolation and characterization, a survey of a number of animal models of human disease in which ECFCs have been shown to have prominent roles in tissue repair, and a summary of current challenges that must be overcome before moving ECFC into human subjects as a cell therapy.

Mesenchymal stem/stromal cells enhance engraftment, vasculogenic and pro-angiogenic activities of endothelial colony forming cells in immunocompetent hosts

The clinical use of endothelial colony forming cells (ECFC) is hampered by their restricted engraftment. We aimed to assess engraftment, vasculogenic and pro-angiogenic activities of ECFC in immunocompetent (C57BL/6: WT) or immunodeficient (rag1 -/- C57BL/6: Rag1) mice. In addition, the impact of host immune system was investigated where ECFC were co-implanted with mesenchymal stem/stromal cells (MSC) from adult bone marrow (AdBM-MSC), fetal bone marrow (fBM-MSC), fetal placental (fPL-MSC), or maternal placental (MPL-MSC). Transplantation of ECFCs in Matrigel plugs resulted in less cell engraftment in WT mice compared to Rag1 mice. Co-implantation with different MSCs resulted in a significant increase in cell engraftment up to 9 fold in WT mice reaching levels of engraftment observed when using ECFCs alone in Rag1 mice but well below levels of engraftment with MSC-ECFC combination in Rag1 recipients. Furthermore, MSCs did not reduce murine splenic T cell proliferation in response to ECFCs in vitro. ECFCs enhanced the murine neo-vascularization through paracrine effect, but with no difference between Rag1 and WT mice. In conclusions, the host adaptive immune system affects the engraftment of ECFCs. MSC co-implantation improves ECFC engraftment and function even in immunocompetent hosts mostly through non-immune mechanisms.

TRPC3-mediated Ca2+ signals as a promising strategy to boost therapeutic angiogenesis in failing hearts: The role of autologous endothelial colony forming cells

Endothelial progenitor cells (EPCs) are a sub-population of bone marrow-derived mononuclear cells that are released in circulation to restore damaged endothelium during its physiological turnover or rescue blood perfusion after an ischemic insult. Additionally, they may be mobilized from perivascular niches located within larger arteries' wall in response to hypoxic conditions. For this reason, EPCs have been regarded as an effective tool to promote revascularization and functional recovery of ischemic hearts, but clinical application failed to exploit the full potential of patients-derived cells. Indeed, the frequency and biological activity of EPCs are compromised in aging individuals or in subjects suffering from severe cardiovascular risk factors. Rejuvenating the reparative phenotype of autologous EPCs through a gene transfer approach has, therefore, been put forward as an alternative approach to enhance their therapeutic potential in cardiovascular patients. An increase in intracellular Ca²⁺ concentration constitutes a pivotal signal for the activation of the so-called endothelial colony forming cells (ECFCs), the only known truly endothelial EPC subset. Studies from our group showed that the Ca²⁺ toolkit differs between peripheral blood- and umbilical cord blood (UCB)-derived ECFCs. In the present article, we first discuss how VEGF uses repetitive Ca²⁺ spikes to regulate angiogenesis in ECFCs and outline how VEGF-induced intracellular Ca²⁺ oscillations differ between the two ECFC subtypes. We then hypothesize about the possibility to rejuvenate the biological activity of autologous ECFCs by transfecting the cell with the Ca²⁺ -permeable channel Transient Receptor Potential Canonical 3, which selectively drives the Ca²⁺ response to VEGF in UCB-derived ECFCs.

VEGF-induced intracellular Ca2+ oscillations are down-regulated and do not stimulate angiogenesis in breast cancer-derived endothelial colony forming cells

Endothelial colony forming cells (ECFCs) represent a population of truly endothelial precursors that promote the angiogenic switch in solid tumors, such as breast cancer (BC). The intracellular Ca²⁺ toolkit, which drives the pro-angiogenic response to VEGF, is remodelled in tumor-associated ECFCs such that they are seemingly insensitive to this growth factor. This feature could underlie the relative failure of anti-VEGF therapies in cancer patients. Herein, we investigated whether and how VEGF uses Ca²⁺ signalling to control angiogenesis in BC-derived ECFCs (BC-ECFCs). Although VEGFR-2 was normally expressed, VEGF failed to induce proliferation and in vitro tubulogenesis in BC-ECFCs. Likewise, VEGF did not trigger robust Ca²⁺ oscillations in these cells. Similar to normal cells, VEGF-induced intracellular Ca²⁺ oscillations were triggered by inositol-1,4,5-trisphosphate-dependent Ca²⁺ release from the endoplasmic reticulum (ER) and maintained by store-operated Ca²⁺ entry (SOCE). However, InsP₃-dependent Ca²⁺ release was significantly lower in BC-ECFCs due to the down-regulation of ER Ca²⁺ levels, while there was no remarkable difference in the amplitude, pharmacological profile and molecular composition of SOCE. Thus, the attenuation of the pro-angiogenic Ca²⁺ response to VEGF was seemingly due to the reduction in ER Ca²⁺ concentration, which prevents VEGF from triggering robust intracellular Ca²⁺ oscillations. However, the pharmacological inhibition of SOCE prevented BC-ECFC proliferation and in vitro tubulogenesis. These findings demonstrate for the first time that BC-ECFCs are insensitive to VEGF, which might explain at cellular and molecular levels the failure of anti-VEGF therapies in BC patients, and hint at SOCE as a novel molecular target for this disease.

Dysregulation of endothelial colony-forming cell function by a negative feedback loop of circulating miR-146a and -146b in cardiovascular disease patients

Functional impairment of endothelial colony-forming cells (ECFCs), a specific cell lineage of endothelial progenitor cells (EPCs) is highly associated with the severity of coronary artery disease (CAD), the most common type of cardiovascular disease (CVD). Emerging evidence show that circulating microRNAs (miRNAs) in CAD patients’ body fluid hold a great potential as biomarkers. However, our knowledge of the role of circulating miRNA in regulating the function of ECFCs and the progression of CAD is still in its infancy. We showed that when ECFCs from healthy volunteers were incubated with conditioned medium or purified exosomes of cultured CAD ECFCs, the secretory factors from CAD ECFCs dysregulated migration and tube formation ability of healthy ECFCs. It is known that exosomes influence the physiology of recipient cells by introducing RNAs including miRNAs. By using small RNA sequencing (smRNA-seq), we deciphered the circulating miRNome in the plasma of healthy individual and CAD patients, and found that the plasma miRNA spectrum from CAD patients was significantly different from that of healthy control. Interestingly, smRNA-seq of both healthy and CAD ECFCs showed that twelve miRNAs that had a higher expression in the plasma of CAD patients also showed higher expression in CAD ECFCs when compared with healthy control. This result suggests that these miRNAs may be involved in the regulation of ECFC functions. For identification of potential mRNA targets of the differentially expressed miRNA in CAD patients, cDNA microarray analysis was performed to identify the angiogenesis-related genes that were down-regulated in CAD ECFCs and Pearson’s correlation were used to identify miRNAs that were negatively correlated with the identified angiogenesis-related genes. RT-qPCR analysis of the five miRNAs that negatively correlated with the down-regulated angiogenesis-related genes in plasma and ECFC of CAD patients showed miR-146a-5p and miR-146b-5p up-regulation compared to healthy control. Knockdown of miR-146a-5p or miR-146b-5p in CAD ECFCs enhanced migration and tube formation activity in diseased ECFCs. Contrarily, overexpression of miR-146a-5p or miR-146b-5p in healthy ECFC repressed migration and tube formation in ECFCs. TargetScan analysis showed that miR-146a-5p and miR-146b-5p target many of the angiogenesis-related genes that were down-regulated in CAD ECFCs. Knockdown of miR-146a-5p or miR-146b-5p restores CAV1 and RHOJ levels in CAD ECFCs. Reporter assays confirmed the direct binding and repression of miR-146a-5p and miR-146b-5p to the 3’-UTR of mRNA of RHOJ, a positive regulator of angiogenic potential in endothelial cells. Consistently, RHOJ knockdown inhibited the migration and tube formation ability in ECFCs. Collectively, we discovered the dysregulation of miR-146a-5p/RHOJ and miR-146b-5p/RHOJ axis in the plasma and ECFCs of CAD patients that could be used as biomarkers or therapeutic targets for CAD and other angiogenesis-related diseases.

Liposomes as a Putative Tool to Investigate NAADP Signaling in Vasculogenesis

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the newest discovered intracellular second messengers, which is able to release Ca²⁺ stored within endolysosomal (EL) vesicles. NAADP-induced Ca²⁺ signals mediate a growing number of cellular functions, ranging from proliferation to muscle contraction and differentiation. Recently, NAADP has recently been shown to regulate angiogenesis by promoting endothelial cell growth. It is, however, still unknown whether NAADP stimulates proliferation also in endothelial progenitor cells, which are mobilized in circulation after an ischemic insult to induce tissue revascularization. Herein, we described a novel approach to prepare NAADP-containing liposomes, which are highly cell membrane permeable and are therefore amenable for stimulating cell activity. Accordingly, NAADP-containing liposomes evoked an increase in intracellular Ca²⁺ concentration, which was inhibited by NED-19, a selective inhibitor of NAADP-induced Ca²⁺ release. Furthermore, NAADP-containing liposomes promoted EPC proliferation, a process which was inhibited by NED-19 and BAPTA, a membrane permeable intracellular Ca²⁺ buffer. Therefore, NAADP-containing liposomes stand out as a promising tool to promote revascularization of hypoxic/ischemic tissues by favoring EPC proliferation. J. Cell. Biochem. 118: 3722-3729, 2017. © 2017 Wiley Periodicals, Inc.

Endothelial Progenitors: A Consensus Statement on Nomenclature

Endothelial progenitor cell (EPC) nomenclature remains ambiguous and there is a general lack of concordance in the stem cell field with many distinct cell subtypes continually grouped under the term "EPC." It would be highly advantageous to agree on standards to confirm an endothelial progenitor phenotype and this should include detailed immunophenotyping, potency assays, and clear separation from hematopoietic angiogenic cells which are not endothelial progenitors. In this review, we seek to discourage the indiscriminate use of "EPCs," and instead propose precise terminology based on defining cellular phenotype and function. Endothelial colony forming cells and myeloid angiogenic cells are examples of two distinct and well-defined cell types that have been considered EPCs because they both promote vascular repair, albeit by completely different mechanisms of action. It is acknowledged that scientific nomenclature should be a dynamic process driven by technological and conceptual advances; ergo the ongoing "EPC" nomenclature ought not to be permanent and should become more precise in the light of strong scientific evidence. This is especially important as these cells become recognized for their role in vascular repair in health and disease and, in some cases, progress toward use in cell therapy. Stem Cells Translational Medicine 2017;6:1316-1320.

Priming of endothelial colony-forming cells in a mesenchymal niche improves engraftment and vasculogenic potential by initiating mesenchymal transition orchestrated by NOTCH signaling

The prospect of using endothelial progenitors is currently hampered by their low engraftment upon transplantation. We report that mesenchymal stem/stromal cells (MSCs), independent of source and age, improve the engraftment of endothelial colony forming cells (ECFCs). MSC coculture altered ECFC appearance to an elongated mesenchymal morphology with reduced proliferation. ECFC primed via MSC contact had reduced self-renewal potential, but improved capacity to form tube structures in vitro and engraftment in vivo Primed ECFCs displayed major differences in transcriptome compared to ECFCs never exposed to MSCs, affecting genes involved in the cell cycle, up-regulating of genes influencing mesenchymal transition, adhesion, extracellular matrix. Inhibition of NOTCH signaling, a potential upstream regulator of mesenchymal transition, in large part modulated this gene expression pattern and functionally reversed the mesenchymal morphology of ECFCs. The collective results showed that primed ECFCs survive better and undergo a mesenchymal transition that is dependent on NOTCH signaling, resulting in significantly increased vasculogenic potential.-Shafiee, A., Patel, J., Wong, H. Y., Donovan, P., Hutmacher, D. W., Fisk, N. M., Khosrotehrani, K. Priming of endothelial colony-forming cells in a mesenchymal niche improves engraftment and vasculogenic potential by initiating mesenchymal transition orchestrated by NOTCH signaling.