Human very Small Embryonic-like Cells Support Vascular Maturation and Therapeutic Revascularization Induced by Endothelial Progenitor Cells

Systematic review and meta-analysis of the effect of bone marrow-derived cell therapies on hind limb perfusion

Preclinical and clinical studies on the administration of bone marrow-derived cells to restore perfusion show conflicting results. We conducted a systematic review and meta-analysis on preclinical studies to assess the efficacy of bone marrow-derived cells in the hind limb ischemia model and identify possible determinants of therapeutic efficacy. In vivo animal studies were identified using a systematic search in PubMed and EMBASE on 10 January 2022. 85 studies were included for systematic review and meta-analysis. Study characteristics and outcome data on relative perfusion were extracted. The pooled mean difference was estimated using a random effects model. Risk of bias was assessed for all included studies. We found a significant increase in perfusion in the affected limb after administration of bone marrow-derived cells compared to that in the control groups. However, there was a high heterogeneity between studies, which could not be explained. There was a high degree of incomplete reporting across studies. We therefore conclude that the current quality of preclinical research is insufficient (low certainty level as per GRADE assessment) to identify specific factors that might improve human clinical trials.

A Combination of Distinct Vascular Stem/Progenitor Cells for Neovascularization and Ischemic Rescue

BACKGROUND

Peripheral vascular disease remains a leading cause of vascular morbidity and mortality worldwide despite advances in medical and surgical therapy. Besides traditional approaches, which can only restore blood flow to native arteries, an alternative approach is to enhance the growth of new vessels, thereby facilitating the physiological response to ischemia.

METHODS

The ActinCreER/R26VT2/GK3 Rainbow reporter mouse was used for unbiased in vivo survey of injury-responsive vasculogenic clonal formation. Prospective isolation and transplantation were used to determine vessel-forming capacity of different populations. Single-cell RNA-sequencing was used to characterize distinct vessel-forming populations and their interactions.

RESULTS

Two populations of distinct vascular stem/progenitor cells (VSPCs) were identified from adipose-derived mesenchymal stromal cells: VSPC1 is CD45-Ter119-Tie2+PDGFRa-CD31+CD105highSca1low, which gives rise to stunted vessels (incomplete tubular structures) in a transplant setting, and VSPC2 which is CD45-Ter119-Tie2+PDGFRa+CD31-CD105lowSca1high and forms stunted vessels and fat. Interestingly, cotransplantation of VSPC1 and VSPC2 is required to form functional vessels that improve perfusion in the mouse hindlimb ischemia model. Similarly, VSPC1 and VSPC2 populations isolated from human adipose tissue could rescue the ischemic condition in mice.

CONCLUSIONS

These findings suggest that autologous cotransplantation of synergistic VSPCs from nonessential adipose tissue can promote neovascularization and represents a promising treatment for ischemic disease.

Deciphering the Cardiovascular Potential of Human CD34+ Stem Cells

Ex vivo monitored human CD34⁺ stem cells (SCs) injected into myocardium scar tissue have shown real benefits for the recovery of patients with myocardial infarctions. They have been used previously in clinical trials with hopeful results and are expected to be promising for cardiac regenerative medicine following severe acute myocardial infarctions. However, some debates on their potential efficacy in cardiac regenerative therapies remain to be clarified. To elucidate the levels of CD34⁺ SC implication and contribution in cardiac regeneration, better identification of the main regulators, pathways, and genes involved in their potential cardiovascular differentiation and paracrine secretion needs to be determined. We first developed a protocol thought to commit human CD34⁺ SCs purified from cord blood toward an early cardiovascular lineage. Then, by using a microarray-based approach, we followed their gene expression during differentiation. We compared the transcriptome of undifferentiated CD34⁺ cells to those induced at two stages of differentiation (i.e., day three and day fourteen), with human cardiomyocyte progenitor cells (CMPCs), as well as cardiomyocytes as controls. Interestingly, in the treated cells, we observed an increase in the expressions of the main regulators usually present in cardiovascular cells. We identified cell surface markers of the cardiac mesoderm, such as kinase insert domain receptor (KDR) and the cardiogenic surface receptor Frizzled 4 (FZD4), induced in the differentiated cells in comparison to undifferentiated CD34⁺ cells. The Wnt and TGF-β pathways appeared to be involved in this activation. This study underlined the real capacity of effectively stimulated CD34⁺ SCs to express cardiac markers and, once induced, allowed the identification of markers that are known to be involved in vascular and early cardiogenesis, demonstrating their potential priming towards cardiovascular cells. These findings could complement their paracrine positive effects known in cell therapy for heart disease and may help improve the efficacy and safety of using ex vivo expanded CD34⁺ SCs.

Gonadotropins as novel active partners in vascular diseases: Insight from angiogenic properties and thrombotic potential of endothelial colony-forming cells

BACKGROUND

The impact of estrogen and testosterone on atherosclerotic cardiovascular disease is well known, but the role of the gonadotropins follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) to some extent remain less studied.

OBJECTIVES

To explore the angiogenic potential of gonadotropins on endothelial colony-forming cells (ECFCs).

METHODS

We examined the effects of various doses of gonadotropins on ECFCs obtained from cord blood by assessing colony number, proliferation, migration, and sprouting ability. Moreover, we studied thrombin generation in ECFCs exposed to gonadotropins by performing a thrombin generation assay. Finally, we determined the levels of circulating gonadotropins in 30 men, to exclude the effect of estrogen, with lower extremity arterial disease (LEAD), in comparison with age- and sex-matched controls.

RESULTS

Exposure to FSH, LH, or PRL resulted in an increase in ECFC migration but showed no effect on proliferation or ECFC commitment from cord blood mononuclear cells. Using a three-dimensional fibrin gel assay, we showed that ECFC sprouting was significantly enhanced by gonadotropins. Exposure to FSH also increased the thrombin generation of ECFCs exposed to FSH. Finally, FSH and LH levels in men with LEAD were higher than those in controls.

CONCLUSION

Gonadotropins increase ECFC-related angiogenesis and may be involved in thrombin generation in cardiovascular disease. Gonadotropins may act as biomarkers; moreover, we hypothesize that gonadotropin-blocking strategies may be a novel interesting therapeutic approach in atherosclerotic cardiovascular disease.

Elevated Circulating Stem Cells Level is Observed One Month After Implantation of Carmat Bioprosthetic Total Artificial Heart

The Aeson® total artificial heart (A-TAH) has been developed as a total heart replacement for patients at risk of death from biventricular failure. We previously described endothelialization of the hybrid membrane inside A-TAH probably at the origin of acquired hemocompatibility. We aimed to quantify vasculogenic stem cells in peripheral blood of patients with long-term A-TAH implantation. Four male adult patients were included in this study. Peripheral blood mononuclear cells were collected before A-TAH implantation (T0) and after implantation at one month (T1), between two and five months (T2), and then between six and twelve months (T3). Supervised analysis of flow cytometry data confirmed the presence of the previously identified Lin^-CD133⁺CD45^- and Lin^-CD34⁺ with different CD45 level intensities. Lin^-CD133⁺CD45^-, Lin^-CD34⁺CD45^- and Lin^-CD34⁺CD45⁺ were not modulated after A-TAH implantation. However, we demonstrated a significant mobilization of Lin^-CD34⁺CD45^dim (p = 0.01) one month after A-TAH implantation regardless of the expression of CD133 or c-Kit. We then visualized data for the resulting clusters on a uniform manifold approximation and projection (UMAP) plot showing all single cells of the live Lin^- and CD34⁺ events selected from down sampled files concatenated at T0 and T1. The three clusters upregulated at T1 are CD45^dim clusters, confirming our results. In conclusion, using a flow cytometry approach, we demonstrated in A-TAH-transplanted patients a significant mobilization of Lin^-CD34⁺CD45^dim in peripheral blood one month after A-TAH implantation. Using a flow cytometry approach, we demonstrated in A-TAH transplanted patients a significant mobilization of Lin^-CD34⁺CD45^dim in peripheral blood one month after A-TAH implantation. This cell population could be at the origin of newly formed endothelial cells on top of hybrid membrane in Carmat bioprosthetic total artificial heart.

Isolation Methods for Human CD34 Subsets Using Fluorescent and Magnetic Activated Cell Sorting: an In Vivo Comparative Study

INTRODUCTION

Acute myocardial infarction (AMI) and resulting cardiac damage and heart failure are leading causes of morbidity and mortality worldwide. Multiple studies have examined the utility of CD34⁺ cells for the treatment of acute and ischemic heart disease. However, the optimal strategy to enrich CD34 cells from clinical sources is not known. We examined the efficacy of fluorescence activated cell sorting (FACS) and magnetic beads cell sorting (MACS) methods for CD34 cell isolation from mobilized human mononuclear peripheral blood cells (mhPBMNCs).

METHODS

mhPBCs were processed following acquisition using FACS or MACS according to clinically established protocols. Cell viability, CD34 cell purity and characterization of surface marker expression were assessed using a flow cytometer. For in vivo characterization of cardiac repair, we conducted LAD ligation surgery on 8-10 weeks female NOD/SCID mice followed by intramyocardial transplantation of unselected mhPBMNCs, FACS or MACS enriched CD34⁺ cells.

RESULTS

Both MACS and FACS isolation methods achieved high purity rates, viability, and enrichment of CD34⁺ cells. In vivo studies following myocardial infarction demonstrated retention of CD34⁺ in the peri-infarct region for up to 30 days after transplantation. Retained CD34⁺ cells were associated with enhanced angiogenesis and reduced inflammation compared to unselected mhPBMNCs or PBS treatment arms. Cardiac scar and fibrosis as assessed by immunohistochemistry were reduced in FACS and MACS CD34⁺ treatment groups. Finally, reduced scar and augmented angiogenesis resulted in improved cardiac functional recovery, both on the global and regional function and remodeling assessments by echocardiography.

CONCLUSION

Cell based therapy using enriched CD34⁺ cells sorted by FACS or MACS result in better cardiac recovery after ischemic injury compared to unselected mhPBMNCs. Both enrichment techniques offer excellent recovery and purity and can be equally used for clinical applications.

Valproic Acid Decreases Endothelial Colony Forming Cells Differentiation and Induces Endothelial-to-Mesenchymal Transition-like Process

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor is a widely used anticonvulsant drug. VPA is also under clinical evaluation to be employed in anticancer therapy, as an antithrombotic agent or a molecule to be used in the stem cells expansion protocols. Since endothelial colony forming cells (ECFC) has been identified as the human postnatal vasculogenic cells involved in thrombotic disorders and serve as a promising source of immature cell for vascular repair, objectives of the present study were to determine how VPA contributes to ECFC commitment and their angiogenic properties. We examined the effect of VPA on ECFC obtained from cord blood by evaluating colony number, proliferation, migration and their sprouting ability in vitro, as well as their in vivo vasculogenic properties. VPA inhibited endothelial differentiation potential from of cord blood derived stem cells associated with decreased proliferation and sprouting activity of cultured ECFC. VPA treatment significantly decreased the vessel-forming ability of ECFC transplanted together with mesenchymal stem cells (MSC) in Matrigel implants in nude mice model. Surprisingly, a microscopic evaluation revealed that VPA induces marked morphological changes from a cobblestone-like EC morphology to enlarged spindle shaped morphology of ECFC. RT-qPCR and a CD31/CD90 flow cytometry analysis confirmed a phenotypic switch of VPA-treated ECFC to mesenchymal-like phenotype. In conclusion, the pan-HDAC inhibitor VPA described for expansion of hematopoietic stem cells and very small embryonic like stem cells cannot be successfully employed for differentiation of endothelial lineage committed ECFC into functional endothelial cells. Our data also suggest that VPA based therapeutics may induce endothelial dysfunction associated with fibrosis that might induce thrombosis recurrence or venous insufficiency.

Diverse cellular origins of adult blood vascular endothelial cells

During embryonic stages, vascular endothelial cells (ECs) originate from the mesoderm, at specific extraembryonic and embryonic regions, through a process called vasculogenesis. In the adult, EC renewal/replacement mostly depend on local resident ECs or endothelial progenitor cells (EPCs). Nevertheless, contribution from circulating ECs/EPCs was also reported. In addition, cells lacking from EC/EPC markers with in vitro extended plasticity were shown to originate endothelial-like cells (ELCs). Most of these cells consist of mesenchymal stromal progenitors, which would eventually get mobilized from the bone marrow after injury. Based on that, current knowledge on different mouse and human bone marrow stromal cell (BM-SC) subpopulations, able to contribute with mesenchymal stromal/stem cells (MSCs), is herein reviewed. Such analyses underline an unexpected heterogeneity among sinusoidal LepR⁺ stromal/CAR cells. For instance, in a recent report a subgroup of LepR⁺ stromal/CAR progenitors, which express GLAST and is traced in Wnt1^Cre;R26R^Tom mice, was found to contribute with ELCs in vivo. These GLAST ​⁺ ​Wnt1⁺ BM-SCs were shown to get mobilized to the peripheral blood and to contribute with liver regeneration. Other sources of ELCs, such as adipose, neural and dental pulp tissues, were also published. Finally, mechanisms likely involved in the enhanced cellular plasticity properties of bone marrow/adipose tissue stromal cells, able to originate ELCs, are assessed. In the future, strategies to analyze the in vivo expression profile of stromal cells, with MSC properties, in combination with screening of active genomic regions at the single cell-level, during early postnatal development and/or after injury, will likely help understanding properties of these ELC sources.

Differential Expression of the Tetraspanin CD9 in Normal and Leukemic Stem Cells

Simple Summary

Before their use in regenerative medicine, stem cells need to be expanded to obtain sufficient cells for the efficient reparation of the injured tissues. This expansion must not affect their integrity. Regarding the role played by different receptors, we observed that, during their expansion, the number of promising pluripotent stem cells found in adult tissues, i.e., very small embryonic-like stem cells (VSELs), which express the CD9 receptor, decreased. This is due to their higher mortality rate compared to that of those not expressing CD9, which can lead to low regenerative efficiency for injured tissues. Interestingly, this could be overcome by the addition of a specific growth factor, allowing the re-establishment of their function. Finally, we found that the expression of this receptor is also deregulated in cells phenotypically identical to VSELs isolated from leukemic patients, which attests to the instability of its expression and may explain disease progression.

Abstract

CD9 plays a crucial role in cellular growth, mobility, and signal transduction, as well as in hematological malignancy. In myeloid neoplasms, CD9 is involved in the altered interactions between leukemic and stromal cells. However, apart from its role in CD34⁺ progenitors and myeloid and megakaryocytic differentiation, its function in normal and leukemic pluripotent cells has not yet been determined. Very small embryonic-like stem cells (VSELs) are promising pluripotent stem cells found in adult tissues that can be developed for safe and efficient regenerative medicine. VSELs express different surface receptors of the highest importance in cell functioning, including CD9, and can be effectively mobilized after organ injury or in leukemic patients. In the present study, we observed that CD9 is among the most expressed receptors in VSELs under steady-state conditions; however, once the VSELs are expanded, CD9⁺ VSELs decrease and are more apoptotic. CD9^– VSELs had no proliferative improvement in vitro compared to those that were CD9⁺. Interestingly, the addition of SDF-1 induced CD9 expression on the surface of VSELs, as observed by flow cytometry, and improved their migration. In addition, we observed, in the phenotypically identical VSELs present in the peripheral blood of patients with myeloproliferative neoplasms, compared to healthy subjects, a significantly higher number of CD9⁺ cells. However, in their hematopoietic stem cell (HSC) counterparts, the expression remained comparable. These results indicate that, likewise, in progenitors and mature cells, CD9 may play an important function in normal and malignant VSELs. This could explain the refractoriness observed by some groups of expanded stem cells to repairing efficiently damaged tissue when used as a source in cell therapies. Understanding the function of the CD9 receptor in normal and malignant CD34⁺ and VSELs, along with its relationship with the CXCR4/SDF-1 pathway, will enable advances in the field of adult pluripotent cell usage in regenerative medicine and in their role in leukemia.

Is COVID-19 a New Hematologic Disease?

SARS-CoV-2 viruses are positive single-stranded RNA viruses, whose infection can be asymptomatic or lead to the coronavirus disease 2019 (Covid-19). Covid-19 is a respiratory infection with a significant impact on the hematopoietic system and hemostasis leading to several cardiovascular complications. Hematologic consequences of this new infection allowed medical community to start new treatment approaches concerning infection going from targeted anti-inflammatory drugs to anticoagulation or stem cell therapies. A better understanding of Covid-19 pathophysiology, in particular hematological disorders, will help to choose appropriate treatment strategies.

Human Aortic Valve Interstitial Cells Display Proangiogenic Properties During Calcific Aortic Valve Disease

OBJECTIVE

The study's aim was to analyze the capacity of human valve interstitial cells (VICs) to participate in aortic valve angiogenesis. Approach and Results: VICs were isolated from human aortic valves obtained after surgery for calcific aortic valve disease and from normal aortic valves unsuitable for grafting (control VICs). We examined VIC in vitro and in vivo potential to differentiate in endothelial and perivascular lineages. VIC paracrine effect was also examined on human endothelial colony-forming cells. A pathological VIC (VICp) mesenchymal-like phenotype was confirmed by CD90+/CD73+/CD44+ expression and multipotent-like differentiation ability. When VICp were cocultured with endothelial colony-forming cells, they formed microvessels by differentiating into perivascular cells both in vivo and in vitro. VICp and control VIC conditioned media were compared using serial ELISA regarding quantification of endothelial and angiogenic factors. Higher expression of VEGF (vascular endothelial growth factor)-A was observed at the protein level in VICp-conditioned media and confirmed at the mRNA level in VICp compared with control VIC. Conditioned media from VICp induced in vitro a significant increase in endothelial colony-forming cell proliferation, migration, and sprouting compared with conditioned media from control VIC. These effects were inhibited by blocking VEGF-A with blocking antibody or siRNA approach, confirming VICp involvement in angiogenesis by a VEGF-A dependent mechanism.

CONCLUSIONS

We provide here the first proof of an angiogenic potential of human VICs isolated from patients with calcific aortic valve disease. These results point to a novel function of VICp in valve vascularization during calcific aortic valve disease, with a perivascular differentiation ability and a VEGF-A paracrine effect. Targeting perivascular differentiation and VEGF-A to slow calcific aortic valve disease progression warrants further investigation.

ATP-Nlrp3 Inflammasome-Complement Cascade Axis in Sterile Brain Inflammation in Psychiatric Patients and its Impact on Stem Cell Trafficking

Recent evidence indicates that the occurrence of psychiatric disorders in patients is linked to a local “sterile” inflammation of brain or due to a systemic inflammation process that affects the central nervous system. This is supported by the observation that in peripheral blood of psychotic patients are detectable several mediators and markers of inflammation as well as clinical data on correlations between systemic chronic inflammatory processes and psychiatric disorders. This may explain why some reported anti-inflammatory treatment strategies have beneficial effects on ameliorating psychotic events. In this review we will present a concept that aberrant purinergic signaling and increases in extracellular level of adenosine triphosphate (ATP) in the brain parenchyma may lead to activation of Nlrp3 inflammasome in microglia cells and as a consequence microglia released danger associated molecular pattern (DAMP) proteins activate complement cascade (ComC) in mannan binding lectin (MBL) – dependent manner. Activation of ATP-Nlrp3 inflammasome-ComC axis may also orchestrate trafficking of stem cells released from bone marrow into peripheral blood observed in psychotic patients. Based on this, the ATP-Nlrp3 inflammasome-ComC axis may become a target for new therapeutic approaches, which justifies the development and clinical application of efficient anti-inflammatory treatment strategies targeting this axis in psychiatry.

Gelatin Based Polymer Cell Coating Improves Bone Marrow-Derived Cell Retention in the Heart after Myocardial Infarction

BACKGROUND

Acute myocardial infarction (AMI) and the ensuing ischemic heart disease are approaching an epidemic state. Limited stem cell retention following intracoronary administration has reduced the clinical efficacy of this novel therapy. Polymer based cell coating is biocompatible and has been shown to be safe. Here, we assessed the therapeutic utility of gelatin-based biodegradable cell coatings on bone marrow derived cell retention in ischemic heart.

METHODS

Gelatin based cell coatings were formed from the surface-mediated photopolymerization of 3% gelatin methacrylamide and 1% PEG diacrylate. Cell coating was confirmed using a multimodality approach including flow cytometry, imaging flow cytometry (ImageStream System) and immunohistochemistry. Biocompatibility of cell coating, metabolic activity of coated cells, and the effect of cell coating on the susceptibility of cells for engulfment were assessed using in vitro models. Following myocardial infarction and GFP+ BM-derived mesenchymal stem cell transplantation, flow cytometric and immunohistochemical assessment of retained cells was performed.

RESULTS

Coated cells are viable and metabolically active with coating degrading within 72 h in vitro. Importantly, cell coating does not predispose bone marrow cells to aggregation or increase their susceptibility to phagocytosis. In vitro and in vivo studies demonstrated no evidence of heightened immune response or increased phagocytosis of coated cells. Cell transplantation studies following myocardial infarction proved the improved retention of coated bone marrow cells compared to uncoated cells.

CONCLUSION

Gelation based polymer cell coating is biologically safe and biodegradable. Therapies employing these strategies may represent an attractive target for improving outcomes of cardiac regenerative therapies in human studies.

Human Endothelial Colony Forming Cells Express Intracellular CD133 that Modulates their Vasculogenic Properties

Stem cells at the origin of endothelial progenitor cells and in particular endothelial colony forming cells (ECFCs) subtype have been largely supposed to be positive for the CD133 antigen, even though no clear correlation has been established between its expression and function in ECFCs. We postulated that CD133 in ECFCs might be expressed intracellularly, and could participate to vasculogenic properties. ECFCs extracted from cord blood were used either fresh (n = 4) or frozen (n = 4), at culture days <30, to investigate the intracellular presence of CD133 by flow cytometry and confocal analysis. Comparison with HUVEC and HAEC mature endothelial cells was carried out. Then, CD133 was silenced in ECFCs using specific siRNA (siCD133-ECFCs) or scramble siRNA (siCtrl-ECFCs). siCD133-ECFCs (n = 12), siCtrl-ECFCs (n = 12) or PBS (n = 12) were injected in a hind-limb ischemia nude mouse model and vascularization was quantified at day 14 with H&E staining and immunohistochemistry for CD31. Results of flow cytometry and confocal microscopy evidenced the positivity of CD133 in ECFCs after permeabilization compared with not permeabilized ECFCs (p < 0.001) and mature endothelial cells (p < 0.03). In the model of mouse hind-limb ischemia, silencing of CD133 in ECFCs significantly abolished post-ischemic revascularization induced by siCtrl-ECFCs; indeed, a significant reduction in cutaneous blood flows (p = 0.03), capillary density (CD31) (p = 0.01) and myofiber regeneration (p = 0.04) was observed. Also, a significant necrosis (p = 0.02) was observed in mice receiving siCD133-ECFCs compared to those treated with siCtrl-ECFCs. In conclusion, our work describes for the first time the intracellular expression of the stemness marker CD133 in ECFCs. This feature could resume the discrepancies found in the literature concerning CD133 positivity and ontogeny in endothelial progenitors.

Role of Adult Tissue-Derived Pluripotent Stem Cells in Bone Regeneration

Background

Bone marrow-derived mononuclear cells (BM-MNC) consist of a heterogeneous mix of mesenchymal stem cells (MSC), hematopoietic progenitor cells (HPC), endothelial progenitor cells (EPC), monocytes, lymphocytes and pluripotent stem cells. Whereas the importance of MSC and EPC has been well documented in bone healing and regeneration studies, the role of pluripotent stem cells is still poorly understood. In the present study we evaluated if and how Very Small Embryonic Like cells (VSEL), isolated from rat BM-MNC, contribute to bone healing.

Methods

Large bone defects were made in the femurs of 38 Sprague Dawley female rats and treated with β-TCP scaffold granules seeded with male VSEL; BM-MNC, VSEL-depleted BM-MNC or scaffold alone, and bone healing was evaluated at 8 weeks post-surgery.

Results

Bone healing was significantly increased in defects treated with VSEL and BM-MNC, compared to defects treated with VSEL-depleted BM-MNC. Donor cells were detected in new bone tissue, in all the defects treated with cells, and in fibrous tissue only in defects treated with VSEL-depleted BM-MNC. The number of CD68+ cells was the highest in the VSEL-depleted group, whereas the number of TRAP positive cells was the lowest in this group.

Conclusions

Based on the results, we can conclude that VSEL play a role in BM-MNC induced bone formation. In our rat femur defect model, in defects treated with VSEL-depleted BM-MNC, osteoclastogenesis and bone formation were decreased, and foreign body reaction was increased.

Similar Population of CD133+ and DDX4+ VSEL-Like Stem Cells Sorted from Human Embryonic Stem Cell, Ovarian, and Ovarian Cancer Ascites Cell Cultures: The Real Embryonic Stem Cells?

A population of small stem cells with diameters of up to 5 μm resembling very small embryonic-like stem cells (VSELs) were sorted from human embryonic stem cell (hESC) cultures using magnetic-activated cell sorting (MACS) based on the expression of a stem-cell-related marker prominin-1 (CD133). These VSEL-like stem cells had nuclei that almost filled the whole cell volume and expressed stem-cell-related markers (CD133, SSEA-4) and markers of germinal lineage (DDX4/VASA, PRDM14). They were comparable to similar populations of small stem cells sorted from cell cultures of normal ovaries and were the predominant cells in ascites of recurrent ovarian cancer. The sorted populations of CD133+ VSEL-like stem cells were quiescent in vitro, except for ascites, and were highly activated after exposure to valproic acid and follicle-stimulating hormone (FSH), indicating a new tool to study these cells in vitro. These VSEL-like stem cells spontaneously formed clusters resembling tumour-like structures or grew into larger, oocyte-like cells and were differentiated in vitro into adipogenic, osteogenic and neural lineages after sorting. We propose the population of VSEL-like stem cells from hESC cultures as potential original embryonic stem cells, which are present in the human embryo, persist in adult human ovaries from the embryonic period of life and are involved in cancer manifestation.

CD34+ Hematopoietic Stem Cell Count Is Predictive of Vascular Event Occurrence in Children with Sickle Cell Disease

BACKGROUND/OBJECTIVES

Sickle cell disease (SCD) complications mostly result from vascular dysfunction, concerning systemic microvasculature and cerebral large vessels. The aim of this cohort study was to identify potential circulating biomarkers predictive for further vascular event occurrence in pediatric SCD.

METHODS

We consecutively enrolled 108 children with SCD at steady state, aged 3-18 years old (median 9.8 years). Hematology, coagulation, hemolysis, endothelial, platelet and vascular activation parameters were recorded at inclusion. Neurovascular and systemic vascular events were prospectively recorded during a mean follow-up period of 27 months.

RESULTS

Patients at steady state displayed significantly higher hemolysis and platelet activation markers, higher leukocyte, CD34+ hematopoietic stem cell and microvesicle counts, and a pro-coagulant profile compared to controls matched for age and ethnicity. Circulating endothelial cell or nucleosome level did not differ. During the follow-up period, 36 patients had at least one neurovascular (n = 12) or systemic vascular event (n = 25). In a multivariate model, high CD34+ cell count was the best predictor for the occurrence of a vascular event (OR 1.2 for 1000 cell/mL increase, 95% CI [1.049-1.4], p = 0.013, sensitivity 53%, specificity 84% for a threshold of 8675 cells/mL).

CONCLUSION

CD34+ cell count at steady state is a promising biomarker of further vascular event in children with SCD.

VSELs Maintain their Pluripotency and Competence to Differentiate after Enhanced Ex Vivo Expansion

The very small embryonic-like stem cells (VSELs) are known as a subset of adult pluripotent stem cells able to differentiate to all three germ layers. However, their small number and quiescence restrict the possibility of their use in cell therapy. In the present study, we first delineate different subpopulation of VSELs from human cord blood CD34+ cells to define their purity. We next determine genes expression levels in the whole transcriptome of VSELs expressing the pluripotent marker NANOG and control cells under the steady state condition. We found that more than a thousand of genes are downregulated in VSELs, as well as many membrane receptors, cells signaling molecules and CDKs mRNAs. In addition, we observed discordance in some pluripotent genes expression levels with embryonic stem cells (ESCs), which could explain VSELs quiescence. We then evaluate VSELs capacity to expand and differentiate in vitro in specific and appropriate media. After 12 days culture in specific medium containing a pyrimidoindole derivative (UM171), VSELs were significantly expanded for the first time without feeder cells and importantly preserve their capacities to differentiate into hematopoietic and endothelial cells. Interestingly, this stimulation of VSELs self-renewal restores the expression of some downregulated genes known as key regulators of cell proliferation and differentiation. The properties of such pluripotent expanded cells make them a potential candidate in regenerative medicine.

Endoglin as an Adhesion Molecule in Mature and Progenitor Endothelial Cells: A Function Beyond TGF-β

Endoglin (ENG) is a transmembrane glycoprotein expressed on endothelial cells that functions as a co-receptor for several ligands of the transforming growth factor beta (TGF-β) family. ENG is also a recognized marker of angiogenesis and mutations in the endoglin gene are responsible for Hereditary Hemorrhagic Telangiectasia (HHT) type 1, a vascular disease characterized by defective angiogenesis, arteriovenous malformations, telangiectasia, and epistaxis. In addition to its involvement in the TGF-β family signaling pathways, several lines of evidence suggest that the extracellular domain of ENG has a role in integrin-mediated cell adhesion via its RGD motif. Indeed, we have described a role for endothelial ENG in leukocyte trafficking and extravasation via its binding to leukocyte integrins. We have also found that ENG is involved in vasculogenic properties of endothelial progenitor cells known as endothelial colony forming cells (ECFCs). Moreover, the binding of endothelial ENG to platelet integrins regulate the resistance to shear during platelet-endothelium interactions under inflammatory conditions. Because of the need for more effective treatments in HHT and the involvement of ENG in angiogenesis, current studies are aimed at identifying novel biological functions of ENG which could serve as a therapeutic target. This review focuses on the interaction between ENG and integrins with the aim to better understand the role of this protein in blood vessel formation driven by progenitor and mature endothelial cells.

Potential Clinical Applications of Stem Cells in Regenerative Medicine

The field of regenerative medicine is looking for a pluripotent/multipotent stem cell able to differentiate across germ layers and be safely employed in therapy. Unfortunately, with the exception of hematopoietic stem/progenitor cells (HSPCs) for hematological applications, the current clinical results with stem cells are somewhat disappointing. The potential clinical applications of the more primitive embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have so far been discouraging, as both have exhibited several problems, including genomic instability, a risk of teratoma formation, and the possibility of rejection. Therefore, the only safe stem cells that have so far been employed in regenerative medicine are monopotent stem cells, such as the abovementioned HSPCs or mesenchymal stem cells (MSCs) isolated from postnatal tissues. However, their monopotency, and therefore limited differentiation potential, is a barrier to their broader application in the clinic. Interestingly, results have accumulated indicating that adult tissues contain rare, early-development stem cells known as very small embryonic-like stem cells (VSELs), which can differentiate into cells from more than one germ layer. This chapter addresses different sources of stem cells for potential clinical application and their advantages and problems to be solved.

Vasculogenic Stem and Progenitor Cells in Human: Future Cell Therapy Product or Liquid Biopsy for Vascular Disease

New blood vessel formation in adults was considered to result exclusively from sprouting of preexisting endothelial cells, a process referred to angiogenesis. Vasculogenesis, the formation of new blood vessels from endothelial progenitor cells, was thought to occur only during embryonic life. Discovery of adult endothelial progenitor cells (EPCs) in 1997 opened the door for cell therapy in vascular disease. Endothelial progenitor cells contribute to vascular repair and are now well established as postnatal vasculogenic cells in humans. It is now admitted that endothelial colony-forming cells (ECFCs) are the vasculogenic subtype. ECFCs could be used as a cell therapy product and also as a liquid biopsy in several vascular diseases or as vector for gene therapy. However, despite a huge interest in these cells, their tissue and molecular origin is still unclear. We recently proposed that endothelial progenitor could come from very small embryonic-like stem cells (VSELs) isolated in human from CD133 positive cells. VSELs are small dormant stem cells related to migratory primordial germ cells. They have been described in bone marrow and other organs. This chapter discusses the reported findings from in vitro data and also preclinical studies that aimed to explore stem cells at the origin of vasculogenesis in human and then explore the potential use of ECFCs to promote newly formed vessels or serve as liquid biopsy to understand vascular pathophysiology and in particular pulmonary disease and haemostasis disorders.

Elevated Numbers of Circulating Very Small Embryonic-Like Stem Cells (VSELs) and Intermediate CD14++CD16+ Monocytes in IgA Nephropathy

IgA nephropathy (IgAN) is recognized as most frequent form of primary glomerulonephritis worldwide. IgAN is associated with renal degradation occurring due to irreversible pathological changes leading to glomerulosclerosis and interstitial fibrosis. It remains poorly understood whether and to what extent these changes are followed by the activation of regenerative mechanisms. Therefore, in this study we aimed to evaluate regenerative potential of IgAN patients by quantitating the frequencies of several stem cell types, namely circulating very small embryonic-like stem cells (VSELs), hematopoietic stem cells (HSCs), endothelial progenitor cells (EPCs) as well as different monocyte subsets with varying maturation and angiopoietic potential. Moreover, we analyzed whether changes in stem cell and monocyte frequencies were related to alterations of several chemotactic factors (stromal derived-factor (SDF-1), angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2)) and a marker of monocyte/macrophage activation, namely soluble form of CD163 receptor (sCD163). We showed that IgAN patients presented with enhanced levels of VSELs, but not other stem cell types. We also demonstrated significantly elevated numbers of intermediate monocytes known for their M2-like properties as well as high angiopoietic potential and CD163 expression. This finding was accompanied by detection of elevated sCD163 plasma levels in IgAN patients. Taking together, we demonstrated here that IgAN is associated with selective mobilization of VSELs and increased maturation of monocytes towards M2-like and angiopoietic phenotype. These findings contribute to better understanding of the role of regenerative mechanisms in the pathogenesis of chronic inflammation in the course of IgAN.

Osteoprotegerin Induces CD34+ Differentiation in Endothelial Progenitor Cells

Endothelial progenitor cells (EPCs) are the main hypothetical cells that could give rise to vessels and in particular one subtype isolated from peripheral or cord bloods: endothelial colony forming cells (ECFCs). These ECFCs are clonogenic precursors committed to endothelial lineage and have robust vasculogenic properties. However, their low number and poor expansion properties when isolated from human adult bloods, currently limit their use as an autologous cell therapy product. We previously reported that osteoprotegerin (OPG), a well-characterized regulator of bone metabolism, contributes to ischemic tissue revascularization, tumor growth in vivo, and potentiates ECFCs proangiogenic properties through the secretion of SDF-1. The current study investigated the role of OPG in ECFCs differentiation and expansion from cord blood CD34⁺ cells. OPG increased the number of ECFCs after endothelial differentiation of CD34⁺ cells, enhancing the time of EPCs colonies initial appearance and the growth kinetic of endothelial cell progeny. OPG-exposed ECFCs expressed higher levels of CD34⁺ compared to control ECFCs. In conclusion, our findings provide novel insights into OPG in regulation of CD34⁺ progenitor cells. These results give new opportunities for ex vivo expansion of human ECFCs using OPG as a cell culture component for future ECFC product manufacture according to GMP.

Egfl7 Represses the Vasculogenic Potential of Human Endothelial Progenitor Cells

Egfl7 (VE-statin) is a secreted protein mostly specific to the endothelial lineage during development and in the adult and which expression is enhanced during angiogenesis. Egfl7 involvement in human postnatal vasculogenesis remains unresolved yet. Our aim was to assess Egfl7 expression in several angiogenic cell types originating from human bone marrow, peripheral blood, or cord blood. We found that only endothelial colony forming cells (ECFC), which are currently considered as the genuine endothelial precursor cells, expressed large amounts of Egfl7. In order to assess its potential roles in ECFC, Egfl7 was repressed in ECFC by RNA interference and ECFC angiogenic capacities were tested in vitro and in vivo. Cell proliferation, differentiation, and migration were significantly improved when Egfl7 was repressed in ECFC in vitro, whereas miR-126-3p levels remained unchanged. In vivo, repression of Egfl7 in ECFC significantly improved post-ischemic revascularization in a model of mouse hind-limb ischemia. In conclusion, ECFC are the sole postnatal angiogenic cells which express large amounts of Egfl7 and whose angiogenic properties are repressed by this factor. Thus, Egfl7 inhibition may be considered as a therapeutic option to improve ECFC-mediated postnatal vasculogenesis and to optimize in vitro ECFC expansion in order to develop an optimized cell therapy approach.

A Circadian Rhythm in both Complement Cascade (ComC) Activation and Sphingosine-1-Phosphate (S1P) Levels in Human Peripheral Blood Supports a Role for the ComC-S1P Axis in Circadian Changes in the Number of Stem Cells Circulating in Peripheral Blood

The number of hematopoietic stem/progenitor cells (HSPCs) circulating in peripheral blood (PB) is regulated by a circadian rhythm, and more HSPCs circulate in PB in the morning hours than at night. Different mechanisms have been proposed that might regulate this process, including changes in tonus of β-adrenergic innervation of bone marrow (BM) tissue. Our group reported that in mice circadian changes in the number of HSPCs circulating in PB correlates with diurnal activation of the complement cascade (ComC) and that the mice deficient in C5 component of ComC (C5-KO mice) do not show circadian changes in the number of circulating HSPCs in PB. We also reported the existence of a gradient between PB and BM of a bioactive phosphosphingolipid, sphingosine-1-phosphate (S1P), which is a major PB chemottractant for BM-residing HSPCs. Based on these observations, we investigated activation of the ComC and the level of S1P in the PB of 66 healthy volunteers. We found that both ComC activation and the S1P level undergo changes in a circadian cycle. While the ComC becomes highly activated during deep sleep at 2 am, S1P becomes activated later, and its highest level is observed at 8 am, which precedes circadian egress of HSPCs from BM into PB. In sum, circadian activation of the ComC-S1P axis releases HSPCs from BM into PB.

Novel View on Umbilical Cord Blood and Maternal Peripheral Blood-an Evidence for an Increase in the Number of Circulating Stem Cells on Both Sides of the Fetal-Maternal Circulation Barrier

Umbilical cord blood (UCB) is a rich source of stem cells, including hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitors cells (EPCs), and very small embryonic-like stem cells (VSELs). These cells most likely are mobilized into UCB in response to hypoxia and delivery stress. We have hypothesized that they may play a role in repairing certain tissue/organ injuries that occur in the newborn child after delivery. Here we asked whether delivery also mobilizes stem cells into maternal blood, as the mother also experiences hypoxia and several types of internal tissue injuries, particularly in the reproductive tract. We observed that the number of HSCs, MSCs, EPCs, and VSELs increases in maternal blood at 24 h after physiological delivery (n = 17). Based on this observation, we propose that delivery stress is associated with an increase in the number of circulating stem cells, not only on the fetal side but also on the maternal side of the fetal–maternal circulatory barrier.

Sterile Inflammation of Brain, due to Activation of Innate Immunity, as a Culprit in Psychiatric Disorders

Evidence has accumulated that the occurrence of psychiatric disorders is related to chronic inflammation. In support of this linkage, changes in the levels of circulating pro-inflammatory cytokines and chemokines in the peripheral blood (PB) of psychiatric patients as well as correlations between chronic inflammatory processes and psychiatric disorders have been described. Furthermore, an inflammatory process known as "sterile inflammation" when initiated directly in brain tissue may trigger the onset of psychoses. In this review, we will present the hypothesis that prolonged or chronic activation of the complement cascade (ComC) directly triggers inflammation in the brain and affects the proper function of this organ. Based on the current literature and our own work on mechanisms activating the ComC we hypothesize that inflammation in the brain is initiated by the mannan-binding lectin pathway of ComC activation. This activation is triggered by an increase in brain tissue of danger-associated molecular pattern (DAMP) mediators, including extracellular ATP and high-mobility group box 1 (HMGB1) protein, which are recognized by circulating pattern-recognition receptors, including mannan-binding lectin (MBL), that activate the ComC. On the other hand, this process is controlled by the anti-inflammatory action of heme oxygenase 1 (HO-1). In this review, we will try to connect changes in the release of DAMPs in the brain with inflammatory processes triggered by the innate immunity involving activation of the ComC as well as the inflammation-limiting effects of the anti-inflammatory HO-1 pathway. We will also discuss parallel observations that during ComC activation subsets of stem cells are mobilized into PB from bone marrow that are potentially involved in repair mechanisms.

Novel evidence that pituitary sex hormones regulate migration, adhesion, and proliferation of embryonic stem cells and teratocarcinoma cells

The pituitary sex hormones (SexHs): follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) regulate several functions crucial for reproduction, including oogenesis, spermatogenesis, and lactation. An important source of prolactin-like hormones, known as lactogens, is the placenta, and lactogens bind to the PRL receptor (PRLR) with high affinity and thereby mimic the actions of PRL. Recently, it has been demonstrated that pituitary SexHs were involved in metastatic lung cancer, certain sarcomas, and leukemia. In the present study we aimed to investigate whether FSH, LH, and PRL were able to stimulate stem cells involved in early development. To address this issue we employed a murine embryonic stem cell line (ES-D3) as well as two teratocarcinoma cell lines, P19 (murine) and NTera2 (human). We determined that all these cells expressed SexH receptors at the mRNA and protein levels and that stimulation of these receptors induced phosphorylation of p42/44 MAPK, p38 MAPK, and AKT. Moreover, ES-D3, P19, and NTera2 cells responded with increased migration and adhesion to physiological concentrations of pituitary SexHs. In view of these findings we proposed that maternal-derived pituitary SexHs regulate the biology of stem cells involved in early development.