NOX4 is a major regulator of cord blood-derived endothelial colony-forming cells which promotes post-ischaemic revascularization

AIMS

Cord blood-derived endothelial colony-forming cells (CB-ECFCs) are a defined progenitor population with established roles in vascular homeostasis and angiogenesis, which possess low immunogenicity and high potential for allogeneic therapy and are highly sensitive to regulation by reactive oxygen species (ROS). The aim of this study was to define the precise role of the major ROS-producing enzyme, NOX4 NADPH oxidase, in CB-ECFC vasoreparative function.

METHODS AND RESULTS

In vitro CB-ECFC migration (scratch-wound assay) and tubulogenesis (tube length, branch number) was enhanced by phorbol 12-myristate 13-acetate (PMA)-induced superoxide in a NOX-dependent manner. CB-ECFCs highly-expressed NOX4, which was further induced by PMA, whilst NOX4 siRNA and plasmid overexpression reduced and potentiated in vitro function, respectively. Increased ROS generation in NOX4-overexpressing CB-ECFCs (DCF fluorescence, flow cytometry) was specifically reduced by superoxide dismutase, highlighting induction of ROS-specific signalling. Laser Doppler imaging of mouse ischaemic hindlimbs at 7 days indicated that NOX4-knockdown CB-ECFCs inhibited blood flow recovery, which was enhanced by NOX4-overexpressing CB-ECFCs. Tissue analysis at 14 days revealed consistent alterations in vascular density (lectin expression) and eNOS protein despite clearance of injected CB-ECFCs, suggesting NOX4-mediated modulation of host tissue. Indeed, proteome array analysis indicated that NOX4-knockdown CB-ECFCs largely suppressed tissue angiogenesis, whilst NOX4-overexpressing CB-ECFCs up-regulated a number of pro-angiogenic factors specifically-linked with eNOS signalling, in parallel with equivalent modulation of NOX-dependent ROS generation, suggesting that CB-ECFC NOX4 signalling may promote host vascular repair.

CONCLUSION

Taken together, these findings indicate a key role for NOX4 in CB-ECFCs, thereby highlighting its potential as a target for enhancing their reparative function through therapeutic priming to support creation of a pro-reparative microenvironment and effective post-ischaemic revascularization.

No evidence of Gremlin1-mediated activation of VEGFR2 signaling in endothelial cells

Canonical Gremlin1 (GREM1) signaling involves binding to and sequestering bone morphogenetic proteins (BMPs) in the extracellular matrix, preventing the activation of cognate BMP receptor. Exquisite temporospatial control of the GREM1-BMP interaction is required during development, and perturbation of this balance leads to abnormal limb formation and defective kidney development. In addition to inhibition of BMP signaling, several other noncanonical signaling modalities of GREM1 have been postulated. Some literature reports have suggested that GREM1 can bind to and activate vascular endothelial growth factor receptor-2 (VEGFR2) in endothelial cells, human kidney epithelial cells, and others. These reports suggest that the GREM1 → VEGFR2 signaling can drive angiogenesis both in vitro and in vivo We report here that, despite exhaustive attempts, we did not observe GREM1 activation of VEGFR2 in any of the cell lines reported by the above-mentioned studies. Incubation of endothelial colony-forming cells (ECFCs) or human umbilical vein endothelial cells (HUVECs) with recombinant VEGF triggered a robust increase in VEGFR2 tyrosine phosphorylation. In contrast, no VEGFR2 phosphorylation was detected when cells were incubated with recombinant GREM1 over a range of time points and concentrations. We also show that GREM1 does not interfere with VEGF-mediated VEGFR2 activation, suggesting that GREM1 does not bind with any great affinity to VEGFR2. Measurements of ECFC barrier integrity revealed that VEGF induces barrier function disruption, but recombinant human GREM1 had no effect in this assay. We believe that these results provide an important clarification of the potential interaction between GREM1 and VEGFR2 in mammalian cells.

Therapies for Type 1 Diabetes: Current Scenario and Future Perspectives

Type 1 diabetes (T1D) is caused by autoimmune destruction of insulin-producing β cells located in the endocrine pancreas in areas known as islets of Langerhans. The current standard-of-care for T1D is exogenous insulin replacement therapy. Recent developments in this field include the hybrid closed-loop system for regulated insulin delivery and long-acting insulins. Clinical studies on prediction and prevention of diabetes-associated complications have demonstrated the importance of early treatment and glucose control for reducing the risk of developing diabetic complications. Transplantation of primary islets offers an effective approach for treating patients with T1D. However, this strategy is hampered by challenges such as the limited availability of islets, extensive death of islet cells, and poor vascular engraftment of islets post-transplantation. Accordingly, there are considerable efforts currently underway for enhancing islet transplantation efficiency by harnessing the beneficial actions of stem cells. This review will provide an overview of currently available therapeutic options for T1D, and discuss the growing evidence that supports the use of stem cell approaches to enhance therapeutic outcomes.

The Vasoreparative Potential of Endothelial Colony Forming Cells: A Journey Through Pre-clinical Studies

For over a decade various cell populations have been investigated for their vasoreparative potential. Cells with the capacity to promote blood vessel regeneration are commonly known as endothelial progenitor cells (EPCs); although such a definition is currently considered too simple for the complexity of cell populations involved in the reparative angiogenic process. A subset of EPCs called endothelial colony forming cells (ECFCs) have emerged as a suitable candidate for cytotherapy, primarily due to their clonogenic progenitor characteristics, unequivocal endothelial phenotype, and inherent ability to promote vasculogenesis. ECFCs can be readily isolated from human peripheral and cord blood, expanded ex vivo and used to revascularize ischemic tissues. These cells have demonstrated efficacy in several in vivo preclinical models such as the ischemic heart, retina, brain, limb, lung and kidney. This review will summarize the current pre-clinical evidence for ECFC cytotherapy and discuss their potential for clinical application.

A treatment algorithm for couples with unexplained infertility based on sperm chromatin assessment

OBJECTIVE

To design a reproductive treatment algorithm based on the sperm DNA fragmentation (SDF) for couples with unexplained infertility following a poor intrauterine insemination (IUI) outcome.

DESIGN

Couples that failed IUI with no apparent reproductive issue in both partners were allocated to diverse reproductive treatments on the basis of SDF.

SETTING

Reproductive medical center in an academic setting.

PATIENT(S)

Over 4 years, couples with an unexpected poor IUI outcome and no apparent female or male partner reproductive issues were recruited.

INTERVENTION(S)

IUI, IVF, and ICSI were performed in the standard fashion following sperm SDF assays.

MAIN OUTCOMES MEASURE(S)

Fertilization rate, implantation rate, pregnancy characteristics, and delivery rates.

RESULT(S)

A total of 354 couples with unexplained infertility and normal semen parameters underwent 1133 IUI cycles. Clinical pregnancy rate (CPR) with IUI at our center in an age-matched cohort is 23.9% while the study cohort had 1.8%. Following SDF assessment, couples with failed IUI attempts but normal SDF (SCSA 9.8 ± 4.6%; TUNEL 11.8 ± 6.2%) underwent IVF with a CPR of 12.7%; those with abnormal SDF underwent ICSI with ejaculated spermatozoa, resulting in a CPR of 18.7%. This group included couples with normal SDF that had failed IVF. Couples with abnormal SDF that failed ICSI with ejaculated spermatozoa achieved a CPR of 31.0% with surgically retrieved spermatozoa.

CONCLUSION(S)

Couples with unexplained infertility that present with unexpectedly poor IUI outcomes can be funneled into a treatment algorithm guided by the integrity of the sperm genome for higher chances of pregnancy using an alternate method of insemination.

Abstract 7: Platinum resistance in epithelial ovarian cancer is dependent on a PDGFR alpha-VEGF-A signalling mechanism that activates downstream angiogenesis pathways

Introduction:

40-45% of patients with High Grade Serous Ovarian Cancer (HGSOC) will eventually relapse with platinum resistant disease. Tothill et al and TCGA are two independent gene expression datasets which have demonstrated the presence of a mesenchymal molecular subgroup, characterised by upregulation of angiogenesis regulating genes. Angiogenesis is known to be an integral pathological feature of HGSOC and anti-angiogenics have dominated the field of drug development in EOC. However, despite this, anti-angiogenic agents have failed to demonstrate a significant impact on overall survival (OS) benefit. In this study, we asked if platinum resistance could be associated with an improved response to anti-angiogenic agents and what the underlying biological rationale for this could be.

Methods:

A meta-analysis of 14 phase II and III clinical trials in EOC were used to investigate the association between platinum resistance and response to anti-angiogenic agents. In addition, we analysed gene expression in 12 matched pre- and post-chemotherapy EOC samples. Novel isogenic cisplatin-resistant HGSOC cell lines were established to study the development of an angiogenic phenotype. Further studies were performed in novel ascites-derived primary cell lines from HGSOC patients with known outcomes following platinum-based chemotherapy.

Result:

In the clinical trial meta-analysis, an OS benefit for antiangiogenics was observed in platinum-resistant disease (p=0.029), whilst platinum-sensitive EOC only derived progression free survival (PFS) (p=<0.0001) benefit and not OS (p=0.125). In the 12 matched pairs of patient samples, post-platinum samples had a higher micro-vessel density (MVD) relative to their paired treatment-naïve sample (p= 0.0001). Additionally, an in vivo angiogenesis matrigel plug assay demonstrated that cisplatin-resistant EOC cell lines were associated with an increase in MVD (p=<0.0001). MVD was reduced in the platinum-resistant cells following treatment with bevacizumab (p=0.001). Ascites-derived primary cells established from platinum-resistant patients demonstrated overexpression of VEGF-A, consistent with stimulating angiogenesis. Gene expression analysis of pre- and post-platinum paired samples identified that PDGFRα (p=0.007) and PDGFRβ (p=0.005) were differentially expressed in the post-platinum therapy samples. In vitro validation in the platinum-resistant cell lines demonstrated that VEGF-A expression was regulated by PDGFRα.

Discussion:

We have demonstrated that previous platinum therapy for EOC is associated with an increase in tumor PDGFα and VEGF-A expression, correlating with a response to anti-angiogenic therapies. This data suggests that platinum therapy resistance may inform the selection of EOC patients for novel antiangiogenic therapies in future clinical trials.

Citation Format: Aya El Helali, Nuala McCabe, Christopher Steele, Lara Dura Perez, Christina L. O'Neill, Naomi Dickson, Niamh McGivern, Caolan Harkin, Andrena McCavigan, Reinhold J. Medina, Laura A. Knight, Stephen McQuaid, Jacqueline A. James, Caroline O. Michie, Charlie Gourley, W Glenn McCluggage, Denis P. Harkin, Richard H. Wilson, Alan W. Stitt, Richard D. Kennedy. Platinum resistance in epithelial ovarian cancer is dependent on a PDGFR alpha-VEGF-A signalling mechanism that activates downstream angiogenesis pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 7.

Development of ICSI

The first conception outside of the human body that led to the birth of Louise Brown was a tremendous accomplishment, which opened the door to the utilization of assisted reproductive techniques globally. This brought the understanding that accomplishing life in a dish required several steps, the most obvious being the timing and characteristics of fertilization. It soon became obvious in the 1980s that the most disappointing phenomenon was unexpected and complete fertilization failure. Among the approaches that were attempted to treat male factor infertility, ICSI surfaced as the technique that brought the ratio of the gametes to 1:1 and was also able to grant consistent fertilization and a higher pregnancy rate. ICSI has now been implemented for a quarter of a century, proving itself as the ultimate technique utilizing ejaculated spermatozoa independent of the semen parameters and is the sole insemination method to be used with surgically retrieved spermatozoa. There are currently various indications for ICSI that are widely adopted, rendering it the most popular insemination method worldwide. The reliability of ICSI ensures its employment in upcoming techniques involving in vitro spermatogenesis and neogametogenesis.

The Vasoreparative Function of Myeloid Angiogenic Cells Is Impaired in Diabetes Through the Induction of IL1β

Myeloid angiogenic cells (MACs) promote revascularization through the paracrine release of angiogenic factors and have been harnessed as therapeutic cells for many ischemic diseases. However, their proangiogenic properties have been suggested to be diminished in diabetes. This study investigates how the diabetic milieu affects the immunophenotype and function of MACs. Both MACs isolated from diabetic conditions and healthy cells exposed to a diabetic environment were used to determine the potential of MACs as a cell therapy for diabetic‐related ischemia. MACs were isolated from human peripheral blood and characterized alongside proinflammatory macrophages M (LPS + IFNγ) and proangiogenic macrophages M (IL4). Functional changes in MACs in response to high‐d‐glucose were assessed using an in vitro 3D‐tubulogenesis assay. Phenotypic changes were determined by gene and protein expression analysis. Additionally, MACs from type 1 diabetic (T1D) patients and corresponding controls were isolated and characterized. Our evidence demonstrates MACs identity as a distinct macrophage subtype that shares M2 proangiogenic characteristics, but can be distinguished by CD163^hi expression. High‐d‐glucose treatment significantly reduced MACs proangiogenic capacity, which was associated with a significant increase in IL1β mRNA and protein expression. Inhibition of IL1β abrogated the antiangiogenic effect induced by high‐d‐glucose. IL1β was also significantly upregulated in MACs isolated from T1D patients with microvascular complications compared to T1D patients without microvascular complications or nondiabetic volunteers. This study demonstrates that Type 1 diabetes and diabetic‐like conditions impair the proangiogenic and regenerative capacity of MACs, and this response is mediated by IL‐1β. Stem Cells2018;36:834–843

Intracytoplasmic sperm injection: state of the art in humans

Among infertile couples, 25% involve both male and female factors, while male factor alone accounts for another 25% due to oligo-, astheno-, teratozoospermia, a combination of the three, or even a complete absence of sperm cells in the ejaculate and can lead to a poor prognosis even with the help of assisted reproductive technology (ART). Intracytoplasmic sperm injection (ICSI) has been with us now for a quarter of a century and in spite of the controversy generated since its inception, it remains in the forefront of the techniques utilized in ART. The development of ICSI in 1992 has drastically decreased the impact of male factor, resulting in millions of pregnancies worldwide for couples who, without ICSI, would have had little chance of having their own biological child. This review focuses on the state of the art of ICSI regarding utility of bioassays that evaluate male factor infertility beyond the standard semen analysis and describes the current application and advances in regard to ICSI, particularly the genetic and epigenetic characteristics of spermatozoa and their impact on reproductive outcome.

Preclinical Evaluation and Optimization of a Cell Therapy Using Human Cord Blood-Derived Endothelial Colony-Forming Cells for Ischemic Retinopathies

Cell therapy using endothelial progenitors holds promise for vascular repair in ischemic retinopathies. Using a well-defined subpopulation of human cord blood-derived endothelial progenitors known as endothelial colony-forming cells (ECFCs), we have evaluated essential requirements for further development of this cell therapy targeting the ischemic retina, including dose response, delivery route, and toxicity. First, to evaluate therapeutic efficacy relating to cell dose, ECFCs were injected into the vitreous of mice with oxygen-induced retinopathy. Using angiography and histology, we found that intravitreal delivery of low dose (1 × 10³ ) ECFCs was as effective as higher cell doses (1 × 10⁴ , 1 × 10⁵ ) in promoting vascular repair. Second, injection into the common carotid artery was tested as an alternative, systemic delivery route. Intracarotid ECFC delivery conferred therapeutic benefit which was comparable to intravitreal delivery using the same ECFC dose (1 × 10⁵ ), although there were fewer human cells observed in the retinal vasculature following systemic delivery. Third, cell immunogenicity was evaluated by injecting ECFCs into the vitreous of healthy adult mice. Assessment of murine ocular tissues identified injected cells in the vitreous, while demonstrating integrity of the host retina. In addition, ECFCs did not invade into the retina, but remained in the vitreous, where they eventually underwent cell death within 3 days of delivery without evoking an inflammatory response. Human specific Alu sequences were not found in healthy mouse retinas after 3 days of ECFC delivery. These findings provide supportive preclinical evidence for the development of ECFCs as an efficacious cell product for ischemic retinopathies. Stem Cells Translational Medicine 2018;7:59-67.

Hypoxia-induced responses by endothelial colony-forming cells are modulated by placental growth factor

Background

Endothelial colony-forming cells (ECFCs), also termed late outgrowth endothelial cells, are a well-defined circulating endothelial progenitor cell type with an established role in vascular repair. ECFCs have clear potential for cell therapy to treat ischaemic disease, although the precise mechanism(s) underlying their response to hypoxia remains ill-defined.

Methods

In this study, we isolated ECFCs from umbilical cord blood and cultured them on collagen. We defined the response of ECFCs to 1% O₂ exposure at acute and chronic time points.

Results

In response to low oxygen, changes in ECFC cell shape, proliferation, size and cytoskeleton phenotype were detected. An increase in the number of senescent ECFCs also occurred as a result of long-term culture in 1% O₂. Low oxygen exposure altered ECFC migration and tube formation in Matrigel®. Increases in angiogenic factors secreted from ECFCs exposed to hypoxia were also detected, in particular, after treatment with placental growth factor (PlGF). Exposure of cells to agents that stabilise hypoxia-inducible factors such as dimethyloxalylglycine (DMOG) also increased PlGF levels. Conditioned medium from both hypoxia-treated and DMOG-treated cells inhibited ECFC tube formation. This effect was reversed by the addition of PlGF neutralising antibody to the conditioned medium, confirming the direct role of PlGF in this effect.

Conclusions

This study deepens our understanding of the response of ECFCs to hypoxia and also identifies a novel and important role for PlGF in regulating the vasculogenic potential of ECFCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0430-0) contains supplementary material, which is available to authorized users.

Endothelial cell-derived pentraxin 3 limits the vasoreparative therapeutic potential of circulating angiogenic cells

Aims

Circulating angiogenic cells (CACs) promote revascularization of ischaemic tissues although their underlying mechanism of action and the consequences of delivering varying number of these cells for therapy remain unknown. This study investigates molecular mechanisms underpinning CAC modulation of blood vessel formation.

Methods and results

CACs at low (2 × 10⁵ cells/mL) and mid (2 × 10⁶ cells/mL) cellular densities significantly enhanced endothelial cell tube formation in vitro, while high density (HD) CACs (2 × 10⁷ cells/mL) significantly inhibited this angiogenic process. In vivo, Matrigel-based angiogenesis assays confirmed mid-density CACs as pro-angiogenic and HD CACs as anti-angiogenic. Secretome characterization of CAC-EC conditioned media identified pentraxin 3 (PTX3) as only present in the HD CAC-EC co-culture. Recombinant PTX3 inhibited endothelial tube formation in vitro and in vivo. Importantly, our data revealed that the anti-angiogenic effect observed in HD CAC-EC co-cultures was significantly abrogated when PTX3 bioactivity was blocked using neutralizing antibodies or PTX3 siRNA in endothelial cells. We show evidence for an endothelial source of PTX3, triggered by exposure to HD CACs. In addition, we confirmed that PTX3 inhibits fibroblast growth factor (FGF) 2-mediated angiogenesis, and that the PTX3 N-terminus, containing the FGF-binding site, is responsible for such anti-angiogenic effects.

Conclusion

Endothelium, when exposed to HD CACs, releases PTX3 which markedly impairs the vascular regenerative response in an autocrine manner. Therefore, CAC density and accompanying release of angiocrine PTX3 are critical considerations when using these cells as a cell therapy for ischaemic disease.

Epigenetic Changes in Endothelial Progenitors as a Possible Cellular Basis for Glycemic Memory in Diabetic Vascular Complications

The vascular complications of diabetes significantly impact the quality of life and mortality in diabetic patients. Extensive evidence from various human clinical trials has clearly established that a period of poor glycemic control early in the disease process carries negative consequences, such as an increase in the development and progression of vascular complications that becomes evident many years later. Importantly, intensive glycemic control established later in the disease process cannot reverse or slow down the onset or progression of diabetic vasculopathy. This has been named the glycemic memory phenomenon. Scientists have successfully modelled glycemic memory using various in vitro and in vivo systems. This review emphasizes that oxidative stress and accumulation of advanced glycation end products are key factors driving glycemic memory in endothelial cells. Furthermore, various epigenetic marks have been proposed to closely associate with vascular glycemic memory. In addition, we comment on the importance of endothelial progenitors and their role as endogenous vasoreparative cells that are negatively impacted by the diabetic milieu and may constitute a "carrier" of glycemic memory. Considering the potential of endothelial progenitor-based cytotherapies, future studies on their glycemic memory are warranted to develop epigenetics-based therapeutics targeting diabetic vascular complications.

Ex vivo expansion of human outgrowth endothelial cells leads to IL-8-mediated replicative senescence and impaired vasoreparative function

Harnessing outgrowth endothelial cells (OECs) for vasoreparative therapy and tissue engineering requires efficient ex vivo expansion. How such expansion impacts on OEC function is largely unknown. In this study, we show that OECs become permanently cell-cycle arrested after ex vivo expansion, which is associated with enlarged cell size, β-galactosidase activity, DNA damage, tumor suppressor pathway activation, and significant transcriptome changes. These senescence hallmarks were coupled with low telomerase activity and telomere shortening, indicating replicative senescence. OEC senescence limited their regenerative potential by impairing vasoreparative properties in vitro and in vivo. Integrated transcriptome-proteome analysis identified inflammatory signaling pathways as major mechanistic components of the OEC senescence program. In particular, IL8 was an important facilitator of this senescence; depletion of IL8 in OECs significantly extended ex vivo lifespan, delayed replicative senescence, and enhanced function. While the ability to expand OEC numbers prior to autologous or allogeneic therapy remains a useful property, their replicative senescence and associated impairment of vasorepair needs to be considered. This study also suggests that modulation of the senescence-associated secretory phenotype could be used to optimize OEC therapy.

The role of immune-related myeloid cells in angiogenesis

Macrophage function is not restricted to the innate and adaptive immune responses, but also includes host defence, wound healing, angiogenesis and homeostatic processes. Within the spectrum of macrophage activation there are two extremes: M1 classically activated macrophages which have a pro-inflammatory phenotype, and M2 alternatively activated macrophages which are pro-angiogenic and anti-inflammatory. An important property of macrophages is their plasticity to switch from one phenotype to the other and they can be defined in their polarisation state at any point between the two extremes. In order to determine what stage of activation macrophages are in, it is essential to profile various phenotypic markers for their identification. This review describes the angiogenic role for myeloid cells: circulating monocytes, Tie-2 expressing monocytes (TEMs), myeloid-derived suppressor cells (MDSCs), tumour associated macrophages (TAMs), and neutrophils. Each cell type is discussed by phenotype, roles within angiogenesis and possible targets as a cell therapy. In addition, we also refer to our own research on myeloid angiogenic cells (MACs), outlining their ability to induce angiogenesis and their similarities to alternatively activated M2 macrophages. MACs significantly contribute to vascular repair through paracrine mechanisms as they lack the capacity to differentiate into endothelial cells. Since MACs also retain plasticity, phenotypic changes can occur according to disease states and the surrounding microenvironment. This pro-angiogenic potential of MACs could be harnessed as a novel cellular therapy for the treatment of ischaemic diseases, such as diabetic retinopathy, hind limb ischaemia and myocardial infarction; however, caution needs to be taken when MACs are delivered into an inflammatory milieu.

Deep sequencing reveals predominant expression of miR-21 amongst the small non-coding RNAs in retinal microvascular endothelial cells

The retinal vascular endothelium is essential for angiogenesis and is involved in maintaining barrier selectivity and vascular tone. The aim of this study was to identify and quantify microRNAs and other small regulatory non-coding RNAs (ncRNAs) which may regulate these crucial functions. Primary bovine retinal microvascular endothelial cells (RMECs) provide a well-characterized in vitro system for studying angiogenesis. RNA extracted from RMECs was used to prepare a small RNA library for deep sequencing (Illumina Genome Analyzer). A total of 6.8 million reads were mapped to 250 known microRNAs in miRBase (release 16). In many cases, the most frequent isomiR differed from the sequence reported in miRBase. In addition, five novel microRNAs, 13 novel bovine orthologs of known human microRNAs and multiple new members of the miR-2284/2285 family were detected. Several ∼30 nucleotide sno-miRNAs were identified, with the most highly expressed being derived from snoRNA U78. Highly expressed microRNAs previously associated with endothelial cells included miR-126 and miR-378, but the most highly expressed was miR-21, comprising more than one-third of all mapped reads. Inhibition of miR-21 with an LNA inhibitor significantly reduced proliferation, migration, and tube-forming capacity of RMECs. The independence from prior sequence knowledge provided by deep sequencing facilitates analysis of novel microRNAs and other small RNAs. This approach also enables quantitative evaluation of microRNA expression, which has highlighted the predominance of a small number of microRNAs in RMECs. Knockdown of miR-21 suggests a role for this microRNA in regulation of angiogenesis in the retinal microvasculature. J. Cell. Biochem. 113: 2098–2111, 2012. © 2012 Wiley Periodicals, Inc.

Therapeutic revascularisation of ischaemic tissue: the opportunities and challenges for therapy using vascular stem/progenitor cells

Ischaemia-related diseases such as peripheral artery disease and coronary heart disease constitute a major issue in medicine as they affect millions of individuals each year and represent a considerable economic burden to healthcare systems. If the underlying ischaemia is not sufficiently resolved it can lead to tissue damage, with subsequent cell death. Treating such diseases remains difficult and several strategies have been used to stimulate the growth of blood vessels and promote regeneration of ischaemic tissues, such as the use of recombinant proteins and gene therapy. Although these approaches remain promising, they have limitations and results from clinical trials using these methods have had limited success. Recently, there has been growing interest in the therapeutic potential of using a cell-based approach to treat vasodegenerative disorders. In vascular medicine, various stem cells and adult progenitors have been highlighted as having a vasoreparative role in ischaemic tissues. This review will examine the clinical potential of several stem and progenitor cells that may be utilised to regenerate defunct or damaged vasculature and restore blood flow to the ischaemic tissue. In particular, we focus on the therapeutic potential of endothelial progenitor cells as an exciting new option for the treatment of ischaemic diseases.

Selective extracellular vesicle-mediated export of an overlapping set of microRNAs from multiple cell types

BACKGROUND

MicroRNAs (miRNAs) are a class of small RNA molecules that regulate expression of specific mRNA targets. They can be released from cells, often encapsulated within extracellular vesicles (EVs), and therefore have the potential to mediate intercellular communication. It has been suggested that certain miRNAs may be selectively exported, although the mechanism has yet to be identified. Manipulation of the miRNA content of EVs will be important for future therapeutic applications. We therefore wished to assess which endogenous miRNAs are enriched in EVs and how effectively an overexpressed miRNA would be exported.

RESULTS

Small RNA libraries from HEK293T cells and vesicles before or after transfection with a vector for miR-146a overexpression were analysed by deep sequencing. A subset of miRNAs was found to be enriched in EVs; pathway analysis of their predicted target genes suggests a potential role in regulation of endocytosis. RT-qPCR in additional cell types and analysis of publicly available data revealed that many of these miRNAs tend to be widely preferentially exported. Whilst overexpressed miR-146a was highly enriched both in transfected cells and their EVs, the cellular:EV ratios of endogenous miRNAs were not grossly altered. MiR-451 was consistently the most highly exported miRNA in many different cell types. Intriguingly, Argonaute2 (Ago2) is required for miR-451 maturation and knock out of Ago2 has been shown to decrease expression of other preferentially exported miRNAs (eg miR-150 and miR-142-3p).

CONCLUSION

The global expression data provided by deep sequencing confirms that specific miRNAs are enriched in EVs released by HEK293T cells. Observation of similar patterns in a range of cell types suggests that a common mechanism for selective miRNA export may exist.

Myeloid angiogenic cells act as alternative M2 macrophages and modulate angiogenesis through interleukin-8

Endothelial progenitor cells (EPCs) promote angiogenesis, and clinical trials have shown such cell therapy to be feasible for treating ischemic disease. However, clinical outcomes have been contradictory owing to the diverse range of EPC types used. We recently characterized two EPC subtypes, and identified outgrowth endothelial cells as the only EPC type with true progenitor and endothelial characteristics. By contrast, myeloid angiogenic cells (MACs) were shown to be monocytic cells without endothelial characteristics despite being widely described as "EPCs." In the current study we demonstrated that although MACs do not become endothelial cells or directly incorporate into a microvascular network, they can significantly induce endothelial tube formation in vitro and vascular repair in vivo. MAC-derived interleukin-8 (IL-8) was identified as a key paracrine factor, and blockade of IL-8 but not vascular endothelial growth factor (VEGF) prevented MAC-induced angiogenesis. Extracellular IL-8 transactivates VEGFR2 and induces phosphorylation of extracellular signal-regulated kinases. Further transcriptomic and immunophenotypic analysis indicates that MACs represent alternative activated M2 macrophages. Our findings demonstrate an unequivocal role for MACs in angiogenesis, which is linked to paracrine release of cytokines such as IL-8. We also show, for the first time, the true identity of these cells as alternative M2 macrophages with proangiogenic, antiinflammatory and pro-tissue-repair properties.

Vascular stem cells and ischaemic retinopathies

Retinal ischaemic disorders such as diabetic retinopathy and retinal vein occlusion are common. The hypoxia-related stimuli from oxygen-deprived neural and glial networks can drive expression of growth factors and cytokines which induce leakage from the surviving vasculature and/or pre-retinal and papillary neovascularisation. If left untreated, retinal vascular stasis, hypoxia or ischaemia can lead to macular oedema or fibro-vascular scar formation which are associated with severe visual impairment, and even blindness. Current therapies for ischaemic retinopathies include laser photocoagulation, injection of corticosteroids or VEGF-antibodies and vitreoretinal surgery, however they carry significant side effects. As an alternative approach, we propose that if reparative intra-retinal angiogenesis can be harnessed at the appropriate stage, ischaemia could be contained or reversed. This review provides evidence that reperfusion of ischaemic retina and suppression of sight-threatening sequelae is possible in both experimental and clinical settings. In particular, there is emphasis on the clinical potential for endothelial progenitor cells (EPCs) to promote vascular repair and reversal of ischaemic injury in various tissues including retina. Gathering evidence from an extensive published literature, we outline the molecular and phenotypic nature of EPCs, how they are altered in disease and provide a rationale for harnessing the vascular reparative properties of various cell sub-types. When some of the remaining questions surrounding the clinical use of EPCs are addressed, they may provide an exciting new therapeutic option for treating ischaemic retinopathies.

Outgrowth endothelial cells: characterization and their potential for reversing ischemic retinopathy

PURPOSE

Endothelial progenitor cells (EPCs) have potential for promoting vascular repair and revascularization of ischemic retina. However, the highly heterogeneous nature of these cells causes confusion when assessing their biological functions. The purpose of this study was to provide a comprehensive comparison between the two main EPC subtypes, early EPCs (eEPCs) and outgrowth endothelial cells (OECs), and to establish the potential of OECs as a novel cell therapy for ischemic retinopathy.

METHODS

Two types of human blood-derived EPCs were isolated and compared using immunophenotyping and multiple in vitro functional assays to assess interaction with retinal capillary endothelial cells and angiogenic activity. OECs were delivered intravitreally in a mouse model of ischemic retinopathy, and flat mounted retinas were examined using confocal microscopy.

RESULTS

These data indicate that eEPCs are hematopoietic cells with minimal proliferative capacity that lack tube-forming capacity. By contrast, OECs are committed to an endothelial lineage and have significant proliferative and de novo tubulogenic potential. Furthermore, only OECs are able to closely interact with endothelial cells through adherens and tight junctions and to integrate into retinal vascular networks in vitro. The authors subsequently chose OECs to test a novel cell therapy approach for ischemic retinopathy. Using a murine model of retinal ischemia, they demonstrated that OECs directly incorporate into the resident vasculature, significantly decreasing avascular areas, concomitantly increasing normovascular areas, and preventing pathologic preretinal neovascularization.

CONCLUSIONS

As a distinct EPC population, OECs have potential as therapeutic cells to vascularize the ischemic retina.

Molecular analysis of endothelial progenitor cell (EPC) subtypes reveals two distinct cell populations with different identities

Background

The term endothelial progenitor cells (EPCs) is currently used to refer to cell populations which are quite dissimilar in terms of biological properties. This study provides a detailed molecular fingerprint for two EPC subtypes: early EPCs (eEPCs) and outgrowth endothelial cells (OECs).

Methods

Human blood-derived eEPCs and OECs were characterised by using genome-wide transcriptional profiling, 2D protein electrophoresis, and electron microscopy. Comparative analysis at the transcript and protein level included monocytes and mature endothelial cells as reference cell types.

Results

Our data show that eEPCs and OECs have strikingly different gene expression signatures. Many highly expressed transcripts in eEPCs are haematopoietic specific (RUNX1, WAS, LYN) with links to immunity and inflammation (TLRs, CD14, HLAs), whereas many transcripts involved in vascular development and angiogenesis-related signalling pathways (Tie2, eNOS, Ephrins) are highly expressed in OECs. Comparative analysis with monocytes and mature endothelial cells clusters eEPCs with monocytes, while OECs segment with endothelial cells. Similarly, proteomic analysis revealed that 90% of spots identified by 2-D gel analysis are common between OECs and endothelial cells while eEPCs share 77% with monocytes. In line with the expression pattern of caveolins and cadherins identified by microarray analysis, ultrastructural evaluation highlighted the presence of caveolae and adherens junctions only in OECs.

Conclusions

This study provides evidence that eEPCs are haematopoietic cells with a molecular phenotype linked to monocytes; whereas OECs exhibit commitment to the endothelial lineage. These findings indicate that OECs might be an attractive cell candidate for inducing therapeutic angiogenesis, while eEPC should be used with caution because of their monocytic nature.

The pleiotropic effects of simvastatin on retinal microvascular endothelium has important implications for ischaemic retinopathies

Background

Current guidelines encourage the use of statins to reduce the risk of cardiovascular disease in diabetic patients; however the impact of these drugs on diabetic retinopathy is not well defined. Moreover, pleiotropic effects of statins on the highly specialised retinal microvascular endothelium remain largely unknown. The objective of this study was to investigate the effects of clinically relevant concentrations of simvastatin on retinal endothelium in vitro and in vivo.

Methods and Findings

Retinal microvascular endothelial cells (RMECs) were treated with 0.01–10 µM simvastatin and a biphasic dose-related response was observed. Low concentrations enhanced microvascular repair with 0.1 µM simvastatin significantly increasing proliferation (p<0.05), and 0.01 µM simvastatin significantly promoting migration (p<0.05), sprouting (p<0.001), and tubulogenesis (p<0.001). High concentration of simvastatin (10 µM) had the opposite effect, significantly inhibiting proliferation (p<0.01), migration (p<0.01), sprouting (p<0.001), and tubulogenesis (p<0.05). Furthermore, simvastatin concentrations higher than 1 µM induced cell death. The mouse model of oxygen-induced retinopathy was used to investigate the possible effects of simvastatin treatment on ischaemic retinopathy. Low dose simvastatin(0.2 mg/Kg) promoted retinal microvascular repair in response to ischaemia by promoting intra-retinal re-vascularisation (p<0.01). By contrast, high dose simvastatin(20 mg/Kg) significantly prevented re-vascularisation (p<0.01) and concomitantly increased pathological neovascularisation (p<0.01). We also demonstrated that the pro-vascular repair mechanism of simvastatin involves VEGF stimulation, Akt phosphorylation, and nitric oxide production; and the anti-vascular repair mechanism is driven by marked intracellular cholesterol depletion and related disorganisation of key intracellular structures.

Conclusions

A beneficial effect of low-dose simvastatin on ischaemic retinopathy is linked to angiogenic repair reducing ischaemia, thereby preventing pathological neovascularisation. High-dose simvastatin may be harmful by inhibiting reparative processes and inducing premature death of retinal microvascular endothelium which increases ischaemia-induced neovascular pathology. Statin dosage should be judiciously monitored in patients who are diabetic or are at risk of developing other forms of proliferative retinopathy.

Lamin B methylation and assembly into the nuclear envelope

Lamin B is reversibly methyl-esterified and phosphorylated during the mammalian cell cycle. In order to study the role of methylation in lamin B function, we isolated mitotic cells in the presence of the microtubule inhibitor, nocodazole. Following removal of nocodazole, methylation of mitotic lamin B was found to precede its assembly into the nuclear envelope as cells exited mitosis. Very little additional methylation took place on assembled lamins. We were able to slow the rate of lamin B methylation with methylthioadenosine (MTA). A delay in lamin B methylation was accompanied by a corresponding delay in assembly of lamin B into the envelope. The delay was approximately 20-30 min beyond the typical 60-70 min usually required. Assembly of lamins A and C, which are not methylated, was also delayed by MTA, although to a lesser degree, suggesting that an interaction between the lamins is necessary for formation of the nuclear envelope. Chromatin decondensation was also slowed in the presence of MTA. Other inhibitors of methylation which had no inhibitory effect on the methyl esterification of lamin B were tested and found to have no effect on envelope assembly or chromatin decondensation. These results were obtained with Chinese hamster ovary cells as well as with the stem cell line, PC 13. Dephosphorylation of lamin B normally follows a time course similar to that of nuclear envelope assembly. In the presence of MTA, however, lamin B assembly was slowed with little effect on dephosphorylation. This resulted in a large population of dephosphorylated, but unassembled, lamin B protein, demonstrating that dephosphorylation is not sufficient for envelope assembly. The lack of effect on the time course of dephosphorylation also suggests that MTA is not acting upstream of the methylation event.

Visitors: a smouldering issue for burn unit personnel

Recent acknowledgement by medical care providers of the psychosocial role in health restoration has brought the issue of patient visiting to the forefront. The intense environment characteristic in critical care areas such as burn units has necessitated a carefully balanced 'compromise' between scientifically sound medical care and psychosocially oriented interventions. This is a current area of attention in the development of policy for burn unit operations. However, the 'compromise' seems to have been individually interpreted by professionals. This study investigated visitor policy components involved in shaping the staff-visitor-patient constellation. It also probes the consequences of this shaping process. Surveys were mailed to all 174 American burn units listed in the Directory of Burn Care Facilities (January, 1979). Our completed study reflected data reviewing the following characteristics: demographics (that is, age specification and bed distribution, bed allocation); visitor policy determination; visitor policy specifications (that is, who, when, how many); visitor policy, regulation and enforcement; and visitor integration (that is, rooming-in, programme involvement).