Jagged-1 Signaling in the Bone Marrow Microenvironment Promotes Endothelial Progenitor Cell Expansion and Commitment of CD133+ Human Cord Blood Cells for Postnatal Vasculogenesis

HOX genes in stem cells: Maintaining cellular identity and regulation of differentiation

Stem cells display a unique cell type within the body that has the capacity to self-renew and differentiate into specialized cell types. Compared to pluripotent stem cells, adult stem cells (ASC) such as mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) exhibit restricted differentiation capabilities that are limited to cell types typically found in the tissue of origin, which implicates that there must be a certain code or priming determined by the tissue of origin. HOX genes, a subset of homeobox genes encoding transcription factors that are generally repressed in undifferentiated pluripotent stem cells, emerged here as master regulators of cell identity and cell fate during embryogenesis, and in maintaining this positional identity throughout life as well as specifying various regional properties of respective tissues. Concurrently, intricate molecular circuits regulated by diverse stem cell-typical signaling pathways, balance stem cell maintenance, proliferation and differentiation. However, it still needs to be unraveled how stem cell-related signaling pathways establish and regulate ASC-specific HOX expression pattern with different temporal-spatial topography, known as the HOX code. This comprehensive review therefore summarizes the current knowledge of specific ASC-related HOX expression patterns and how these were integrated into stem cell-related signaling pathways. Understanding the mechanism of HOX gene regulation in stem cells may provide new ways to manipulate stem cell fate and function leading to improved and new approaches in the field of regenerative medicine.

Regulation of Endothelial Progenitor Cell Functions in Ischemic Heart Disease: New Therapeutic Targets for Cardiac Remodeling and Repair

Ischemic heart disease (IHD) is the leading cause of morbidity and mortality worldwide. Ischemia and hypoxia following myocardial infarction (MI) cause subsequent cardiomyocyte (CM) loss, cardiac remodeling, and heart failure. Endothelial progenitor cells (EPCs) are involved in vasculogenesis, angiogenesis and paracrine effects and thus have important clinical value in alternative processes for repairing damaged hearts. In fact, this study showed that the endogenous repair of EPCs may not be limited to a single cell type. EPC interactions with cardiac cell populations and mesenchymal stem cells (MSCs) in ischemic heart disease can attenuate cardiac inflammation and oxidative stress in a microenvironment, regulate cell survival and apoptosis, nourish CMs, enhance mature neovascularization, alleviate adverse ventricular remodeling after infarction and enhance ventricular function. In this review, we introduce the definition and discuss the origin and biological characteristics of EPCs and summarize the mechanisms of EPC recruitment in ischemic heart disease. We focus on the crosstalk between EPCs and endothelial cells (ECs), smooth muscle cells (SMCs), CMs, cardiac fibroblasts (CFs), cardiac progenitor cells (CPCs), and MSCs during cardiac remodeling and repair. Finally, we discuss the translation of EPC therapy to the clinic and treatment strategies.

Extracellular Vesicles Derived from Endothelial Progenitor Cells Protect Human Glomerular Endothelial Cells and Podocytes from Complement- and Cytokine-Mediated Injury

Glomerulonephritis are renal inflammatory processes characterized by increased permeability of the Glomerular Filtration Barrier (GFB) with consequent hematuria and proteinuria. Glomerular endothelial cells (GEC) and podocytes are part of the GFB and contribute to the maintenance of its structural and functional integrity through the release of paracrine mediators. Activation of the complement cascade and pro-inflammatory cytokines (CK) such as Tumor Necrosis Factor α (TNF-α) and Interleukin-6 (IL-6) can alter GFB function, causing acute glomerular injury and progression toward chronic kidney disease. Endothelial Progenitor Cells (EPC) are bone-marrow-derived hematopoietic stem cells circulating in peripheral blood and able to induce angiogenesis and to repair injured endothelium by releasing paracrine mediators including Extracellular Vesicles (EVs), microparticles involved in intercellular communication by transferring proteins, lipids, and genetic material (mRNA, microRNA, lncRNA) to target cells. We have previously demonstrated that EPC-derived EVs activate an angiogenic program in quiescent endothelial cells and renoprotection in different experimental models. The aim of the present study was to evaluate in vitro the protective effect of EPC-derived EVs on GECs and podocytes cultured in detrimental conditions with CKs (TNF-α/IL-6) and the complement protein C5a. EVs were internalized in both GECs and podocytes mainly through a L-selectin-based mechanism. In GECs, EVs enhanced the formation of capillary-like structures and cell migration by modulating gene expression and inducing the release of growth factors such as VEGF-A and HGF. In the presence of CKs, and C5a, EPC-derived EVs protected GECs from apoptosis by decreasing oxidative stress and prevented leukocyte adhesion by inhibiting the expression of adhesion molecules (ICAM-1, VCAM-1, E-selectin). On podocytes, EVs inhibited apoptosis and prevented nephrin shedding induced by CKs and C5a. In a co-culture model of GECs/podocytes that mimicked GFB, EPC-derived EVs protected cell function and permeselectivity from inflammatory-mediated damage. Moreover, RNase pre-treatment of EVs abrogated their protective effects, suggesting the crucial role of RNA transfer from EVs to damaged glomerular cells. In conclusion, EPC-derived EVs preserved GFB integrity from complement- and cytokine-induced damage, suggesting their potential role as therapeutic agents for drug-resistant glomerulonephritis.

High NESTIN Expression Marks the Endosteal Capillary Network in Human Bone Marrow

Hematopoiesis is hosted, supported and regulated by a special bone marrow (BM) microenvironment known as "niche." BM niches have been classified based on micro-anatomic distance from the bone surface into "endosteal" and "central" niches. Whilst different blood vessels have been found in both BM niches in mice, our knowledge of the human BM architecture is much more limited. Here, we have used a combination of markers including NESTIN, CD146, and αSMA labeling different blood vessels in benign human BM. Applying immunohistochemical/immunofluorescence techniques on BM trephines and performing image analysis on almost 300 microphotographs, we detected high NESTIN expression in BM endothelial cells (BMECs) of small arteries (A) and endosteal arterioles (EA), and also in very small vessels we named NESTIN+ capillary-like tubes (NCLTs), not surrounded by sub-endothelial perivascular cells that occasionally reported low levels of NESTIN expression. Statistically, NCLTs were detected within 40 μm from bone trabecula, frequently found in direct contact to the bone line and spatially correlated with hematopoietic stem/progenitor cells. Our results support the expression of NESTIN in human BMECs of EA and A in accordance with the updated classification of murine BM micro-vessels. NCLTs for their peculiar characteristics and micro-anatomical localization have been here proposed as transitional vessels possibly involved in regulating human hematopoiesis.

Endothelial Progenitors in the Tumor Microenvironment

Tumor vascularization refers to the formation of new blood vessels within a tumor and is considered one of the hallmarks of cancer. Tumor vessels supply the tumor with oxygen and nutrients, required to sustain tumor growth and progression, and provide a gateway for tumor metastasis through the blood or lymphatic vasculature. Blood vessels display an angiocrine capacity of supporting the survival and proliferation of tumor cells through the production of growth factors and cytokines. Although tumor vasculature plays an essential role in sustaining tumor growth, it represents at the same time an essential way to deliver drugs and immune cells to the tumor. However, tumor vasculature exhibits many morphological and functional abnormalities, thus resulting in the formation of hypoxic areas within tumors, believed to represent a mechanism to maintain tumor cells in an invasive state.Tumors are vascularized through a variety of modalities, mainly represented by angiogenesis, where VEGF and other members of the VEGF family play a key role. This has represented the basis for the development of anti-VEGF blocking agents and their use in cancer therapy: however, these agents failed to induce significant therapeutic effects.Much less is known about the cellular origin of vessel network in tumors. Various cell types may contribute to tumor vasculature in different tumors or in the same tumor, such as mature endothelial cells, endothelial progenitor cells (EPCs), or the same tumor cells through a process of transdifferentiation. Early studies have suggested a role for bone marrow-derived EPCs; these cells do not are true EPCs but myeloid progenitors differentiating into monocytic cells, exerting a proangiogenic effect through a paracrine mechanism. More recent studies have shown the existence of tissue-resident endothelial vascular progenitors (EVPs) present at the level of vessel endothelium and their possible involvement as cells of origin of tumor vasculature.

Contextual Regulation of Skeletal Physiology by Notch Signaling

PURPOSE OF REVIEW

This article reviews the past 2 years of research on Notch signaling as it relates to bone physiology, with the goal of reconciling seemingly discrepant findings and identifying fruitful areas of potential future research.

RECENT FINDINGS

Conditional animal models and high-throughput omics have contributed to a greater understanding of the context-dependent role of Notch signaling in bone. However, significant gaps remain in our understanding of how spatiotemporal context and epigenetic state dictate downstream Notch phenotypes. Biphasic activation of Notch signaling orchestrates progression of mesenchymal progenitor cells through the osteoblast lineage, but there is a limited understanding of ligand- and receptor-specific functions. Paracrine Notch signaling through non-osteoblastic cell types contributes additional layers of complexity, and we anticipate impactful future work related to the integration of these cell types and signaling mechanisms.

Cellular and Molecular Heterogeneity Associated with Vessel Formation Processes

The microvasculature heterogeneity is a complex subject in vascular biology. The difficulty of building a dynamic and interactive view among the microenvironments, the cellular and molecular heterogeneities, and the basic aspects of the vessel formation processes make the available knowledge largely fragmented. The neovascularisation processes, termed vasculogenesis, angiogenesis, arteriogenesis, and lymphangiogenesis, are important to the formation and proper functioning of organs and tissues both in the embryo and the postnatal period. These processes are intrinsically related to microvascular cells, such as endothelial and mural cells. These cells are able to adjust their activities in response to the metabolic and physiological requirements of the tissues, by displaying a broad plasticity that results in a significant cellular and molecular heterogeneity. In this review, we intend to approach the microvasculature heterogeneity in an integrated view considering the diversity of neovascularisation processes and the cellular and molecular heterogeneity that contribute to microcirculatory homeostasis. For that, we will cover their interactions in the different blood-organ barriers and discuss how they cooperate in an integrated regulatory network that is controlled by specific molecular signatures.

Roles of circulating endothelial progenitor cells and endothelial cells in gastric carcinoma

The present study aimed to investigate the role of endothelial progenitor cells (EPCs) and endothelial cells (ECs) in the peripheral blood of patients with gastric cancer (GC), and to investigate vascular endothelial growth factor (VEGF) expression and microvessel density (MVD) in GC tissues. First, 6 ml peripheral blood with added anticoagulant was collected from each of the 42 patients with GC, followed by determination of the number of EPCs and ECs by flow cytometry using the surface markers cluster of differentiation (CD)34^brightCD133⁺CD31⁺CD45^dim and CD34^dimCD133⁻CD31^brightCD45⁻, respectively. VEGF expression in patients with GC was detected by the streptomycin avidin-peroxidase immunohistochemical method, and MVD was calculated using the marker CD34. EPC and EC levels were positively associated with VEGF expression level, as well as with MVD. VEGF expression was positive in 66.67% GC cases, and its level was significantly associated with tumor-node-metastasis (TNM) stage, invasion depth and lymph-node metastasis (P<0.05). VEGF expression level was also positively associated with MVD. MVD in GC was significantly larger than that in normal tissue (P<0.01), and it was significantly associated with TNM stage (P<0.05), invasion depth (P<0.01) and lymph-node metastasis (P<0.01). EPCs in the peripheral blood have an important role in GC development, and may be a promising indicator of GC diagnosis and prognosis.

Netrin-1 Promotes Inflammation Resolution to Achieve Endothelialization of Small-Diameter Tissue Engineering Blood Vessels by Improving Endothelial Progenitor Cells Function In Situ

The transplant of small-diameter tissue engineering blood vessels (small-diameter TEBVs) (<6 mm) in vascular replacement therapy often fails because of early onset thrombosis and long-standing chronic inflammation. The specific inflammation state involved in small-diameter TEBVs transplants remains unclear, and whether promoting inflammation resolution would be useful for small-diameter TEBVs therapy need study. The neural protuberant orientation factor 1 (Netrin-1) is found present in endothelial cells of natural blood vessels and has anti-inflammatory effects. This work generates netrin-1-modified small-diameter TEBVs by using layer-by-layer self-assembly to resolve the inflammation. The results show that netrin-1 reprograms macrophages (MΦ) to assume an anti-inflammatory phenotype and promotes the infiltration and subsequent efflux of MΦ from inflamed sites over time, which improves the local microenvironment and the function of early homing endothelial progenitor cells (EPCs). Small-diameter TEBVs modified by netrin-1 achieve endothelialization after 30 d and retain patency at 14 months. These findings suggest that promoting the resolution of inflammation in time is necessary to induce endothelialization of small-diameter TEBVs and prevent early thrombosis and problems associated with chronic inflammation. Furthermore, this work finds that the MΦ-derived exosomes can target and regulate EPCs, which may serve as a useful treatment for other inflammatory diseases.

Stem cells and heart disease - Brake or accelerator?

After two decades of intensive research and attempts of clinical translation, stem cell based therapies for cardiac diseases are not getting closer to clinical success. This review tries to unravel the obstacles and focuses on underlying mechanisms as the target for regenerative therapies. At present, the principal outcome in clinical therapy does not reflect experimental evidence. It seems that the scientific obstacle is a lack of integration of knowledge from tissue repair and disease mechanisms. Recent insights from clinical trials delineate mechanisms of stem cell dysfunction and gene defects in repair mechanisms as cause of atherosclerosis and heart disease. These findings require a redirection of current practice of stem cell therapy and a reset using more detailed analysis of stem cell function interfering with disease mechanisms. To accelerate scientific development the authors suggest intensifying unified computational data analysis and shared data knowledge by using open-access data platforms.

Cardiac Function Improvement and Bone Marrow Response -: Outcome Analysis of the Randomized PERFECT Phase III Clinical Trial of Intramyocardial CD133+ Application After Myocardial Infarction

OBJECTIVE

The phase III clinical trial PERFECT was designed to assess clinical safety and efficacy of intramyocardial CD133⁺ bone marrow stem cell treatment combined with CABG for induction of cardiac repair.

DESIGN

Multicentre, double-blinded, randomised placebo controlled trial.

SETTING

The study was conducted across six centres in Germany October 2009 through March 2016 and stopped due slow recruitment after positive interim analysis in March 2015.

PARTICIPANTS

Post-infarction patients with chronic ischemia and reduced LVEF (25-50%).

INTERVENTIONS

Eighty-two patients were randomised to two groups receiving intramyocardial application of 5ml placebo or a suspension of 0.5-5×10⁶ CD133⁺.

OUTCOME

Primary endpoint was delta (∆) LVEF at 180days (d) compared to baseline measured in MRI.

FINDINGS (PRESPECIFIED)

Safety (n=77): 180d survival was 100%, MACE n=2, SAE n=49, without difference between placebo and CD133⁺. Efficacy (n=58): The LVEF improved from baseline LVEF 33.5% by +9.6% at 180d, p=0.001 (n=58). Treatment groups were not different in ∆LVEF (ANCOVA: Placebo +8.8% vs. CD133⁺ +10.4%, ∆CD133⁺vs placebo +2.6%, p=0.4).

FINDINGS (POST HOC)

Responders (R) classified by ∆LVEF≥5% after 180d were 60% of the patients (35/58) in both treatment groups. ∆LVEF in ANCOVA was +17.1% in (R) vs. non-responders (NR) (∆LVEF 0%, n=23). NR were characterized by a preoperative response signature in peripheral blood with reduced CD133⁺ EPC (RvsNR: p=0.005) and thrombocytes (p=0.004) in contrast to increased Erythropoeitin (p=0.02), and SH2B3 mRNA expression (p=0.073). Actuarial computed mean survival time was 76.9±3.32months (R) vs. +72.3±5.0months (NR), HR 0.3 [Cl 0.07-1.2]; p=0.067.Using a machine learning 20 biomarker response parameters were identified allowing preoperative discrimination with an accuracy of 80% (R) and 84% (NR) after 10-fold cross-validation.

INTERPRETATION

The PERFECT trial analysis demonstrates that the regulation of induced cardiac repair is linked to the circulating pool of CD133+ EPC and thrombocytes, associated with SH2B3 gene expression. Based on these findings, responders to cardiac functional improvement may be identified by a peripheral blood biomarker signature.

TRIAL REGISTRATION

ClinicalTrials.govNCT00950274.

Crosstalk between Stem and Progenitor Cellular Mediators with Special Emphasis on Vasculogenesis

The cellular components and molecular processes of signaling during vasculogenesis have been investigated for decades. Considerable efforts have been made to unravel regulatory mechanisms of vasculogenesis through crosstalk between vasculogenic playmakers located in the vascular niche, namely hematopoietic stem cells, endothelial progenitor cells, and mesenchymal stem and progenitor cells. Recent studies have increased the knowledge about signaling events within vascular microenvironment that leads to vasculogenesis. Findings from these recent studies indicate the impact of cellular crosstalk through signaling pathways such as vascular endothelial growth factor signaling, wingless and Notch signaling in vasculogenesis and vascular development. In this review, we highlight the signaling signature between stem and progenitor cellular mediators during vasculogenesis. We further focus on hematopoietic stem cell-endothelial progenitor cell crosstalk during vasculogenesis and discuss their potential implications and benefits for therapeutic interventions and regenerative therapy.