Erythropoietin, a hypoxia-regulated factor, elicits a pro-angiogenic program in human mesenchymal stem cells

Thermosensitive Hydrogels for Periodontal Regeneration: A Systematic Review of the Evidence

OBJECTIVES

Thermosensitive hydrogels are now among the most commonly used biomaterials in tissue engineering. Due to their unique characteristics, this review aimed to evaluate the suitability of thermosensitive hydrogels in periodontal regeneration.

MATERIAL AND METHODS

PubMed, Scopus, and Web of Science databases were searched until March 25, 2024, to retrieve relevant articles. The eligibility criteria for the included studies were determined by the designed PICO elements. Results from each included study were extracted, focusing on the three main areas: thermosensitivity, cellular characteristics, and in vivo characteristics.

RESULTS

Nineteen studies were included in our study. The thermosensitivity assessment of the hydrogels indicated a range of sol-gel transition times from 40 s to 20 min based on the type of polymers and the fabrication process. The cellular characterization was assessed based on three main cellular behaviors: cellular viability/proliferation, differentiation, and migration. The in vivo characterization was performed based on two main approaches: radiographic and histologic evaluation.

CONCLUSIONS

The results indicated that the addition of bioactive agents could enhance the in vivo efficacy of thermosensitive hydrogels in periodontal regeneration through three main areas: antimicrobial, anti-inflammatory, and regenerative effects.

Effect of erythropoietin on angiogenic potential of dental pulp cells

Erythropoietin (EPO) is a 34-kDa glycoprotein that possesses the potential for angiogenesis, as well as anti-inflammatory and anti-apoptotic properties. The present study aimed to examine the effect of EPO on the angiogenesis of dental pulp cells (DPCs) and to explore the underlying mechanisms of these effects. It was demonstrated that EPO not only promoted DPCs proliferation but also induced angiogenesis of DPCs in a paracrine fashion. EPO enhanced the angiogenic capacity by stimulating DPCs to secrete a series of angiogenic cytokines. ELISA confirmed that high concentrations of EPO increased the production of MMP-3 and angiopoietin-1 but decreased the secretion of IL-6. Furthermore, EPO activated the ERK1/2 and p38 signaling pathways in DPCs, while inhibition of these pathways diminished the angiogenesis capacity of DPCs. The present study suggested that EPO may have an important role in the repair and regeneration of dental pulp.

Hematopoietic Stem Cells: Nature and Niche Nurture

Like all cells, hematopoietic stem cells (HSCs) and their offspring, the hematopoietic progenitor cells (HPCs), are highly sociable. Their capacity to interact with bone marrow niche cells and respond to environmental cytokines orchestrates the generation of the different types of blood and immune cells. The starting point for engineering hematopoiesis ex vivo is the nature of HSCs, and a longstanding premise is that they are a homogeneous population of cells. However, recent findings have shown that adult bone marrow HSCs are really a mixture of cells, with many having lineage affiliations. A second key consideration is: Do HSCs "choose" a lineage in a random and cell-intrinsic manner, or are they instructed by cytokines? Since their discovery, the hematopoietic cytokines have been viewed as survival and proliferation factors for lineage committed HPCs. Some are now known to also instruct cell lineage choice. These fundamental changes to our understanding of hematopoiesis are important for placing niche support in the right context and for fabricating an ex vivo environment to support HSC development.

Angiogenesis: A Cellular Response to Traumatic Injury

ABSTRACT

The development of new vasculature plays a significant role in a number of chronic disease states, including neoplasm growth, peripheral arterial disease, and coronary artery disease, among many others. Traumatic injury and hemorrhage, however, is an immediate, often dramatic pathophysiologic insult that can also necessitate neovascularization to promote healing. Traditional understanding of angiogenesis involved resident endothelial cells branching outward from localized niches in the periphery. Additionally, there are a small number of circulating endothelial progenitor cells that participate directly in the process of neovessel formation. The bone marrow stores a relatively small number of so-called pro-angiogenic hematopoietic progenitor cells-that is, progenitor cells of a hematopoietic potential that differentiate into key structural cells and stimulate or otherwise support local cell growth/differentiation at the site of angiogenesis. Following injury, a number of cytokines and intercellular processes are activated or modulated to promote development of new vasculature. These processes initiate and maintain a robust response to vascular insult, allowing new vessels to canalize and anastomose and provide timely oxygen delivering to healing tissue. Ultimately as we better understand the key players in the process of angiogenesis we can look to develop novel techniques to promote healing following injury.

Establishment and Characterization of a Stromal Cell Line Derived From a Patient With Thoracic Endometriosis

Thoracic endometriosis (TE) syndrome is a clinical condition known as an extrapelvic form of endometriosis with the presence of functioning endometrial tissue involving lung parenchyma, pleura, chest wall, or diaphragm. In an effort to obtain an endometriosis ex vivo model, we established the spontaneously growing TH-EM1 cell line from endometriotic implants in lung parenchyma from a woman with TE. Maintained in long-term culture, the cells grew as large mesenchymal-like cells with a doubling time between 5 and 6 days. Treatment with medroxyprogesterone acetate (10^-7 mol/L) inhibited the TH-EM1 cells growth and induced morphological changes to an epithelial-like cells. Strong expression of the nuclear estrogen receptors, progesterone receptors, and erytropoietin receptors were found in both the pulmonary implant and the TH-EM1 cells by immunohistochemical analysis. Consistent immunoreactivity of TH-EM1 cells for CD9, CD13, CD73, CD90, CD105, and CD157 was revealed by flow cytometry. Likewise, the embryonic markers, SRY-box 2 (SOX-2) and the Nanog molecules, were detected in 76% and 52% of the cells, while fetal hemoglobin and a-globin were detected in 76% and 65% of TH-EM1 cells, respectively. By RHG banding, normal metaphases were observed, while the microarray chromosomal analysis showed gains of DNA sequences located on the segments 8p23.1, 11p15.5, and 12p11.23. The described in vitro cellular model can serve as a useful tool to study the pathogenesis of endometriosis and to improve the knowledge of molecular mechanisms controlling the endometriotic cell dissemination potential.

Effects of Oxygen and Glucose on Bone Marrow Mesenchymal Stem Cell Culture

This study determines whether the viability of mesenchymal stem cell (MSC) in vitro is most sensitive to oxygen supply, energetic substrate supply, or accumulation of lactate. Mouse unmodified (wild type (WT)) and erythropoietin (EPO) gene-modified MSC is cultured for 7 days in normoxic (21%) and anoxic conditions. WT-MSC is cultured in anoxia for 45 days in high and regular glucose media and both have similar viability when compared to their normoxic controls at 7 days. Protein production of EPO-MSC is unaffected by the absence of oxygen. MSC doubling time and post-anoxic exposure is increased (WT: 32.3-73.3 h; EPO: 27.2-115 h). High glucose leads to a 37% increase in cell viability at 13 days and 17% at 30 days, indicating that MSC anoxic survival is affected by supply of metabolic substrate. However, after 30 days, little difference in viability is found, and at 45 days, complete cell death occurs in both the conditions. This death cannot be attributed to lack of glucose or lactate levels. MSC stemness is retained for both osteogenic and adipogenic differentiations. The absence of oxygen increases the doubling time of MSC but does not affect their viability, protein production, or differentiation capacity.

Injectable thermosensitive chitosan/gelatin-based hydrogel carried erythropoietin to effectively enhance maxillary sinus floor augmentation in vivo

OBJECTIVE

Maxillary sinus floor augmentation (MSFA) is commonly used to increase the alveolar bone height in the posterior maxilla before implant placement. In the present study, we evaluated if the injectable thermosensitive chitosan/β-sodium glycerophosphate disodium salt hydrate/gelatin (CS/GP/GA) hydrogel carried erythropoietin (EPO) could enhance the new bone formation for MSFA in vivo.

METHODS

EPO-CS/GP/GA hydrogel was prepared by ionic crosslinking. Then, characteristics of EPO-CS/GP/GA were evaluated by morphology, injectable property and pH on the gelling time (GT). The release profile of EPO was evaluated by enzyme linked immunosorbent assay (ELISA), and effects of EPO on proliferation and osteoblastic differentiation of bone marrow stromal cells (BMSC) were analyzed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and reverse transcription quantitative real-time PCR (RT-qPCR), respectively. Finally, EPO-CS/GP/GA was injected into the maxillary sinus floor of the rabbit to test the potential application for MSFA.

RESULTS

Results showed that GT was decreased with the increase of pH value. The GT was 110±15s at pH 7.0. SEM images showed that the CS/GP/GA hydrogel had a sponge network structure. Results from ELISA assay revealed that the cumulative release of EPO from the EPO-CS/GP/GA hydrogel reached 67% at 4h, and 94% at 15 days. MTT assay showed that EPO within EPO-CS/GP/GA hydrogel could significantly promote proliferation of BMSCs compared to control group (p<0.001) . Results of RT-qPCR assays demonstrated that the expression of Sp7, Runx2, Col I and Alp were significantly increased from EPO-CS/GP/GA group compared to control group on day 14 (p<0.001). Importantly, EPO-CS/GP/GA hydrogel could significantly induce bone formation (81.98mm³) compared with control group (43.11mm³) after 12 weeks post-implantation in vivo. The calculation of thickness of mesenchymal condensation indicated that thickness of mesenchymal condensation was significantly increased from EPO-CS/GP/GA group (∼121.4μm) compared to control group (∼37μm) resulting in enhancing intramembranous ossification.

SIGNIFICANCE

The EPO-CS/GP/GA hydrogel provides a novel strategy for MSFA with a minimally invasive way.

Towards a New Understanding of Decision-Making by Hematopoietic Stem Cells

Cells within the hematopoietic stem cell compartment selectively express receptors for cytokines that have a lineage(s) specific role; they include erythropoietin, macrophage colony-stimulating factor, granulocyte colony-stimulating factor, granulocyte/macrophage colony-stimulating factor and the ligand for the fms-like tyrosine kinase 3. These hematopoietic cytokines can instruct the lineage fate of hematopoietic stem and progenitor cells in addition to ensuring the survival and proliferation of cells that belong to a particular cell lineage(s). Expression of the receptors for macrophage colony-stimulating factor and granulocyte colony-stimulating factor is positively autoregulated and the presence of the cytokine is therefore likely to enforce a lineage bias within hematopoietic stem cells that express these receptors. In addition to the above roles, macrophage colony-stimulating factor and granulocyte/macrophage colony-stimulating factor are powerful chemoattractants. The multiple roles of some hematopoietic cytokines leads us towards modelling hematopoietic stem cell decision-making whereby these cells can 'choose' just one lineage fate and migrate to a niche that both reinforces the fate and guarantees the survival and expansion of cells as they develop.

Biological functions of mesenchymal stem cells and clinical implications

Mesenchymal stem cells (MSCs) are isolated from multiple biological tissues-adult bone marrow and adipose tissues and neonatal tissues such as umbilical cord and placenta. In vitro, MSCs show biological features of extensive proliferation ability and multipotency. Moreover, MSCs have trophic, homing/migration and immunosuppression functions that have been demonstrated both in vitro and in vivo. A number of clinical trials are using MSCs for therapeutic interventions in severe degenerative and/or inflammatory diseases, including Crohn's disease and graft-versus-host disease, alone or in combination with other drugs. MSCs are promising for therapeutic applications given the ease in obtaining them, their genetic stability, their poor immunogenicity and their curative properties for tissue repair and immunomodulation. The success of MSC therapy in degenerative and/or inflammatory diseases might depend on the robustness of the biological functions of MSCs, which should be linked to their therapeutic potency. Here, we outline the fundamental and advanced concepts of MSC biological features and underline the biological functions of MSCs in their basic and translational aspects in therapy for degenerative and/or inflammatory diseases.

Pleiotropic effects of Erythropoietin. Influence of Erythropoietin on processes of mesenchymal stem cells differentiation

Structure and synthesis of Erythropoietin: Erythropoietin (EPO) is a glycoprotein hormone.

Recombinant Erythropoietin (Epoetin): Human recombinant erythropoietin is characterised as a factor which stimulates differentiation and proliferation of erythroid precursor cells, and as a tissue protective factor.

Anti-ischemic effects of recombinant Erythropoietin: Erythropoietin is one of the most perspective humoral agents which are involved in the preconditioning phenomenon.

Erythropoietin receptors and signal transduction pathways: Erythropoietin effects on cells through their interconnection with erythropoietin receptors, which triggers complex intracellular signal cascades, such as JAK2/STAT signaling pathway, phosphatidylinositol 3-kinase (PI3K), protein kinase C, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB signaling pathways.

Mechanisms of the effect of Erythropoietin on hematopoietic and non-hematopoietic cells and tissues: In addition to regulation of haemopoiesis, erythropoietin mediates bone formation as it has an effect on hematopoietic stem cells and osteoblastic niche, and this illustrates connection between the processes of haematopoiesis and osteopoiesis which take place in the red bone marrow.

The effect of Erythropoietin on mesenchymal stem cells and process of bone tissue formation: Erythropoietin promotes mesenchymal stem cells proliferation, migration and differentiation in osteogenic direction. The evidence of which is expression of bone phenotype by cells under the influence of EPO, including activation of bone specific transcription factors Runx2, osteocalcin and bone sialoprotein.

Conclusion: Erythropoietin has a pleiotropic effect on various types of cells and tissues. But the mechanisms which are involved in the process of bone tissue restoration via erythropoietin are still poorly understood.

An injectable and thermosensitive hydrogel: Promoting periodontal regeneration by controlled-release of aspirin and erythropoietin

Periodontitis is an inflammatory disease induced by complex interactions between host immune system and plaque microorganism. Alveolar bone resorption caused by periodontitis is considered to be one of the main reasons for tooth loss in adults. To terminate the alveolar bone resorption, simultaneous anti-inflammation and periodontium regeneration is required, which has not appeared in the existing methods. In this study, chitosan (CS), β-sodium glycerophosphate (β-GP), and gelatin were used to prepare an injectable and thermosensitive hydrogel, which could continuously release aspirin and erythropoietin (EPO) to exert pharmacological effects of anti-inflammation and tissue regeneration, respectively. The releasing profile showed that aspirin and EPO could be continuously released from the hydrogels, which exhibited no toxicity both in vitro and in vivo, for at least 21 days. Immunohistochemistry staining and micro-CT analyses indicated that administration of CS/β-GP/gelatin hydrogels loaded with aspirin/EPO could terminate the inflammation and recover the height of the alveolar bone, which is further confirmed by histological observations. Our results suggested that CS/β-GP/gelatin hydrogels are easily prepared as drug-loading vectors with excellent biocompatibility, and the CS/β-GP/gelatin hydrogels loaded with aspirin/EPO are quite effective in anti-inflammation and periodontium regeneration, which provides a great potential candidate for periodontitis treatment in the dental clinic. Statement of Significance To terminate the alveolar bone resorption caused by periodontitis, simultaneous anti-inflammation and periodontium regeneration is required, which has not appeared in the existing methods. Here, (1) the chitosan (CS)/β-sodium glycerophosphate/gelatin hydrogels loaded with aspirin/erythropoietin (EPO) can form at body temperature in 5 min with excellent biocompatibility in vitro and in vivo; (2) The faster release of aspirin than EPO in the early stage is beneficial for anti-inflammation and provides a microenvironment for ensuring the regeneration function of EPO in the following step. In vivo experiments revealed that the hydrogels are effective in the control of inflammation and regeneration of the periodontium. These results indicate that our synthesized hydrogels have a great potential in the future clinical application.

Establishment and Characterization of a Stromal Cell Line Derived From a Patient With Thoracic Endometriosis

Thoracic endometriosis (TE) syndrome is a clinical condition known as an extrapelvic form of endometriosis with the presence of functioning endometrial tissue involving lung parenchyma, pleura, chest wall, or diaphragm. In an effort to obtain an endometriosis ex vivo model, we established the spontaneously growing TH-EM1 cell line from endometriotic implants in lung parenchyma from a woman with TE. Maintained in long-term culture, the cells grew as large mesenchymal-like cells with a doubling time between 5 and 6 days. Treatment with medroxyprogesterone acetate (10-7 mol/L) inhibited the TH-EM1 cells growth and induced morphological changes to an epithelial-like cells. Strong expression of the nuclear estrogen receptors, progesterone receptors, and erytropoietin receptors were found in both the pulmonary implant and the TH-EM1 cells by immunohistochemical analysis. Consistent immunoreactivity of TH-EM1 cells for CD9, CD13, CD73, CD90, CD105, and CD157 was revealed by flow cytometry. Likewise, the embryonic markers, SRY-box 2 (SOX-2) and the Nanog molecules, were detected in 76% and 52% of the cells, while fetal hemoglobin and α-globin were detected in 76% and 65% of TH-EM1 cells, respectively. By RHG banding, normal metaphases were observed, while the microarray chromosomal analysis showed gains of DNA sequences located on the segments 8p23.1, 11p15.5, and 12p11.23. The described in vitro cellular model can serve as a useful tool to study the pathogenesis of endometriosis and to improve the knowledge of molecular mechanisms controlling the endometriotic cell dissemination potential.

Mechanical Stretch Promotes the Osteogenic Differentiation of Bone Mesenchymal Stem Cells Induced by Erythropoietin

INTRODUCTION

The effects of erythropoietin (EPO) on the behaviors of bone marrow mesenchymal stem cells (BMSCs) subjected to mechanical stretch remain unclear. This study was therefore aimed at establishing the dose-response effect of EPO stimulation on rat BMSCs and investigating the effects of mechanical stretch combined with EPO on the proliferation and osteogenic differentiation of BMSCs.

MATERIAL AND METHODS

The proliferation and osteogenic differentiation of rat BMSCs were examined and compared using EPO with different concentrations. Thereafter, BMSCs were subjected to 10% elongation using a Flexcell strain unit, combined with 20 IU/ml EPO. The proliferation of BMSCs was detected by Cell Counting Kit-8, colony formation assay, and cell cycle assay; meanwhile, the mRNA expression levels of Ets-1, C-myc, Ccnd1, and C-fos were detected by reverse transcription and real-time quantitative PCR (qPCR). The osteogenic differentiation of BMSCs was detected by alkaline phosphatase (ALP) staining, and the mRNA expression levels of ALP, OCN, COL, and Runx2 were detected by qPCR. The role of the extracellular signal-regulated kinases 1/2 (ERK1/2) in the osteogenesis of BMSCs stimulated by mechanical stretch combined with 20 IU/ml EPO was examined by Western blot.

RESULTS

Our results showed that effects of EPO on BMSCs included a dose-response relationship, with the 20 IU/ml EPO yielding the largest. Mechanical stretch combined with 20 IU/ml EPO promoted proliferation and osteogenic differentiation of BMSCs. The increase in ALP, mineral deposition, and osteoblastic genes induced by the mechanical stretch-EPO combination was inhibited by U0126, an ERK1/2 inhibitor.

CONCLUSION

EPO was able to promote the proliferation and osteogenic differentiation of BMSCs, and these effects were enhanced when combined with mechanical stretch. The underlying mechanism may be related to the activation of the ERK1/2 signaling pathway.

Erythropoietin (rhEPOa) promotes endothelial transdifferentiation of stem cells of the apical papilla (SCAP)

OBJECTIVE

Mesenchymal stem cells (MSCs) have attracted worldwide attention for their capacity to repair damaged tissue, immunosuppression, ability to differentiate into several cell types and their secretome. Earlier studies have demonstrated their angiogenic potential in vitro and in vivo. However, little is known regarding pro-angiogenic inducers of stable endothelial transdifferentiation of MSCs. Here, we employed human MSCs from the Apical Papilla (SCAP) and investigated whether recombinant human erythropoietin-alpha (rhEPOa) could act as such inducer.

DESIGN

Cultured SCAP cells were exposed to rhEPOa and assessed for cell growth kinetics, viability and morphology, as well as their capacity to form capillary tubule structures in selected microenvironments. RT-PCR was used to monitor endothelial markers and activation of EPO/EPOR pathway signaling components; while gelatin zymographies to assess activation of MMP-2.

RESULTS

rhEPOa treatment initially (48 h) accelerated cell proliferation and allowed SCAP to sprout micro-tubular structures. Morphological and biochemical differentiation was accompanied by activation of MMP-2 and upregulation of PECAM-1, VEGFR2, vWF and VE-cadherin/CDH5. SCAP expressed the cognate EPO-R, while rhEPOa-treated SCAP exhibited higher expression of molecules involved in EPO/EPOR pathway (EPOR and JAK2).

CONCLUSION

rhEPOa is capable of promoting endothelial transdifferentiation of SCAP which may be of clinical value in treating of ischemic disorders.

Intramyocardial angiogenetic stem cells and epicardial erythropoietin save the acute ischemic heart

Ischemic heart failure is the leading cause of mortality worldwide. An early boost of intracardiac regenerative key mechanisms and angiogenetic niche signaling in cardiac mesenchymal stem cells (MSCs) could improve myocardial infarction (MI) healing. Epicardial erythropoietin (EPO; 300 U kg^-1) was compared with intraperitoneal and intramyocardial EPO treatments after acute MI in rats (n=156). Real-time PCR and confocal microscopy revealed that epicardial EPO treatment enhanced levels of intracardiac regenerative key indicators (SDF-1, CXCR4, CD34, Bcl-2, cyclin D1, Cdc2 and MMP2), induced transforming growth factor β (TGF-β)/WNT signaling in intramyocardial MSC niches through the direct activation of AKT and upregulation of upstream signals FOS and Fzd7, and augmented intracardiac mesenchymal proliferation 24 h after MI. Cardiac catheterization and tissue analysis showed superior cardiac functions, beneficial remodeling and increased capillary density 6 weeks after MI. Concomitant fluorescence-activated cell sorting, co-cultures with neonatal cardiomyocytes, angiogenesis assays, ELISA, western blotting and RAMAN spectroscopy demonstrated that EPO could promote cardiomyogenic differentiation that was specific of tissue origin and enhance paracrine angiogenetic activity in cardiac CD45^-CD44⁺DDR2⁺ MSCs. Epicardial EPO delivery might be the optimal route for efficient upregulation of regenerative key signals after acute MI. Early EPO-mediated stimulation of mesenchymal proliferation, synergistic angiogenesis with cardiac MSCs and direct induction of TGF-β/WNT signaling in intramyocardial cardiac MSCs could initiate an accelerated healing process that enhances cardiac recovery.

The impact of hypoxic-ischemic brain injury on stem cell mobilization, migration, adhesion, and proliferation

Neonatal hypoxic-ischemic encephalopathy continues to be a significant cause of death or neurodevelopmental delays despite standard use of therapeutic hypothermia. The use of stem cell transplantation has recently emerged as a promising supplemental therapy to further improve the outcomes of infants with hypoxic-ischemic encephalopathy. After the injury, the brain releases several chemical mediators, many of which communicate directly with stem cells to encourage mobilization, migration, cell adhesion and differentiation. This manuscript reviews the biomarkers that are released from the injured brain and their interactions with stem cells, providing insight regarding how their upregulation could improve stem cell therapy by maximizing cell delivery to the injured tissue.

Erythropoietin and a nonerythropoietic peptide analog promote aortic endothelial cell repair under hypoxic conditions: role of nitric oxide

The cytoprotective effects of erythropoietin (EPO) and an EPO-related nonerythropoietic analog, pyroglutamate helix B surface peptide (pHBSP), were investigated in an in vitro model of bovine aortic endothelial cell injury under normoxic (21% O₂) and hypoxic (1% O₂) conditions. The potential molecular mechanisms of these effects were also explored. Using a model of endothelial injury (the scratch assay), we found that, under hypoxic conditions, EPO and pHBSP enhanced scratch closure by promoting cell migration and proliferation, but did not show any effect under normoxic conditions. Furthermore, EPO protected bovine aortic endothelial cells from staurosporine-induced apoptosis under hypoxic conditions. The priming effect of hypoxia was associated with stabilization of hypoxia inducible factor-1α, EPO receptor upregulation, and decreased Ser-1177 phosphorylation of endothelial nitric oxide synthase (NOS); the effect of hypoxia on the latter was rescued by EPO. Hypoxia was associated with a reduction in nitric oxide (NO) production as assessed by its oxidation products, nitrite and nitrate, consistent with the oxygen requirement for endogenous production of NO by endothelial NOS. However, while EPO did not affect NO formation in normoxia, it markedly increased NO production, in a manner sensitive to NOS inhibition, under hypoxic conditions. These data are consistent with the notion that the tissue-protective actions of EPO-related cytokines in pathophysiological settings associated with poor oxygenation are mediated by NO. These findings may be particularly relevant to atherogenesis and postangioplasty restenosis.

Effect of SDF-1/CXCR4 axis on the migration of transplanted bone mesenchymal stem cells mobilized by erythropoietin toward lesion sites following spinal cord injury

Accumulating evidence has indicated that the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis plays a crucial role in the recruitment of bone marrow-derived mesenchymal stem cells (BMSCs) into lesion sites in animal models. The aim of this study was to investigate the effects of the SDF-1/CXCR4 axis on the migration of transplanted BMSCs mobilized by erythropoietin (EPO) toward the lesion site following spinal cord injury (SCI). A model of SCI was established in rats using the modified Allen's test. In the EPO group, EPO was administered at a distance of 2 mm cranially and then 2 mm caudally from the site of injury. In the BMSC group, 10 μl of BMSC suspension was administered in the same manner. In the BMSC + EPO group, both BMSCs and EPO were administered as described above. In the BMSC + EPO + AMD3100 group, in addition to the injection of BMSCs and EPO, AMD3100 (a chemokine receptor antagonist) was administered. The Basso-Beattie-Bresnahan (BBB) Locomotor Rating Scale and a grid walk test were used to estimate the neurological recovery following SCI. Enzyme-linked immunosorbent assay (ELISA) was performed to assess the tumor necrosis factor-α (TNF-α) and SDF-1 expression levels. An immunofluorescence assay was performed to identify the distribution of the BMSCs in the injured spinal cord. A Transwell migration assay was performed to examine BMSC migration. A terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was performed to detect the apoptotic index (AI). Western blot analysis was performed to measure the expression levels of erythropoietin receptor (EPOR) and CXCR4. Significant improvements in locomotor function were detected in the BMSC + EPO group compared with the BMSC group (P<0.05). GFP-labeled BMSCs were observed and were located at the lesion sites. Additionally, EPO significantly decreased the TNF-α levels and increased the SDF-1 levels in the injured spinal cord (P<0.05). The AI in the BMSC + EPO group was significantly lower compared with that in the other groups (P<0.05). Furthermore, EPO significantly upregulated the protein expression of CXCR4 in the BMSCs and promoted the migration of the BMSCs, whereas these effects were markedly inhibited when the BMSCs were co-transplanted with AMD3100. The findings of the present study confirm that EPO mobilizes BMSCs to the lesion site following SCI and enhances the anti-apoptotic effects of the BMSCs by upregulating the expression of SDF-1/CXCR4 axis.

Low Oxygen Tension Primes Aortic Endothelial Cells to the Reparative Effect of Tissue-Protective Cytokines

Erythropoietin (EPO) has both erythropoietic and tissue-protective properties. The EPO analogues carbamylated EPO (CEPO) and pyroglutamate helix B surface peptide (pHBSP) lack the erythropoietic activity of EPO but retain the tissue-protective properties that are mediated by a heterocomplex of EPO receptor (EPOR) and the β common receptor (βCR). We studied the action of EPO and its analogues in a model of wound healing where a bovine aortic endothelial cells (BAECs) monolayer was scratched and the scratch closure was assessed over 24 h under different oxygen concentrations. We related the effects of EPO and its analogues on repair to their effect on BAECs proliferation and migration (evaluated using a micro-Boyden chamber). EPO, CEPO and pHBSP enhanced scratch closure only at lower oxygen (5%), while their effect at atmospheric oxygen (21%) was not significant. The mRNA expression of EPOR was doubled in 5% compared with 21% oxygen, and this was associated with increased EPOR assessed by immunofluorescence and Western blot. By contrast, βCR mRNA levels were similar in 5% and 21% oxygen. EPO and its analogues increased both BAECs proliferation and migration, suggesting that both may be involved in the reparative process. The priming effect of low oxygen tension on the action of tissue-protective cytokines may be of relevance to vascular disease, including atherogenesis and restenosis.

Platelet-Rich Plasma Promotes Axon Regeneration, Wound Healing, and Pain Reduction: Fact or Fiction

Platelet-rich plasma (PRP) has been tested in vitro, in animal models, and clinically for its efficacy in enhancing the rate of wound healing, reducing pain associated with injuries, and promoting axon regeneration. Although extensive data indicate that PRP-released factors induce these effects, the claims are often weakened because many studies were not rigorous or controlled, the data were limited, and other studies yielded contrary results. Critical to assessing whether PRP is effective are the large number of variables in these studies, including the method of PRP preparation, which influences the composition of PRP; type of application; type of wounds; target tissues; and diverse animal models and clinical studies. All these variables raise the question of whether one can anticipate consistent influences and raise the possibility that most of the results are correct under the circumstances where PRP was tested. This review examines evidence on the potential influences of PRP and whether PRP-released factors could induce the reported influences and concludes that the preponderance of evidence suggests that PRP has the capacity to induce all the claimed influences, although this position cannot be definitively argued. Well-defined and rigorously controlled studies of the potential influences of PRP are required in which PRP is isolated and applied using consistent techniques, protocols, and models. Finally, it is concluded that, because of the purported benefits of PRP administration and the lack of adverse events, further animal and clinical studies should be performed to explore the potential influences of PRP.

The osteogenic effect of erythropoietin on human mesenchymal stromal cells is dose-dependent and involves non-hematopoietic receptors and multiple intracellular signaling pathways

Erythropoietin (EPO) is a pleiotropic growth factor. Of interest for skeletal tissue engineering, the non-hematopoietic capabilities of EPO include its osteogenic and angiogenic potencies. The main aim of this study was to investigate the dose-response relationship and determine the lowest effective dose of EPO that reliably increases the osteogenic differentiation of human mesenchymal stromal cells (hMSCs). Additional aims were to elucidate the surface receptors and to investigate the role of the intracellular signaling pathways by blocking the mammalian target of rapamycin (mTOR), Jak-2 protein tyrosine kinase (JAK2), and phosphoinositide 3-kinases (PI3K). The primary outcome measures were two mineralization assays, Arsenazo III and alizarin red, applied after 10, 14, and 21 days. Moreover, alkaline phosphatase activity, cell number, and cell viability were determined after 2 and 7 days. A proportional dose-response relationship was observed. In vivo, the lowest effective dose of 20 IU/ml should be used for further research to accommodate safety concerns about adverse effects. Ex vivo, the most effective dose of 100 IU/ml could facilitate vascularization and bone ingrowth in cell-based scaffolds. The expression of non-hematopoietic receptors EPOR and CD131 was documented, and EPO triggered all three examined intracellular pathways. Future studies of the efficacy of EPO in cell-based tissue engineering can benefit from our findings.

Effect of Recombinant Human Erythropoietin On the Stemness of Bone Marrow-derived Mesenchymal Stem Cells in vitro

The purpose of this study was to investigate the effects of the recombinant human erythropoietin (rhEPO) on proliferative and multi-differentiation potential of the bone marrow-derived mesenchymal stem cells (MSCs). The MSCs were isolated primarily from bone marrow of adult rat and purified at increasing passage. A purified population of MSCs can be obtained about 2 weeks after the initiation of culture. After three passages (P3-MSCs), bone marrow-derived adherent cells were identified, then different concentrations of rhEPO (0.1, 1, 5, 10, 100 U/ml) was added into the Passage-3 cells which had been identified. The expression of the surface markers in adherent cells was detected by the flow cytometry. The mRNA levels of transcription factors OCT4, SOX2, Nanog and TERT were measured by reverse transcription-polymerase chain reaction (RT-PCR). The results showed that CD29 and CD90 were positive in MSCs, but not CD33, CD44 and CD45, and the cells could differentiate into multiple lineages such as osteocytes and adipocytes. The expression of OCT4, SOX2, TERT, Nanog mRNA were up-regulated by the treatment of EPO. The effect of EPO was the most obvious when its concentration was 5U/mL after 12h. we conclude that MSCs can not only perserve characteristics of stem cells but also maintain its multi-lineage differentiation potential after appropriate treatment of EPO.

Mesenchymal stem cells: roles and relationships in vascularization

One of the primary challenges in translating tissue engineering to clinical applicability is adequate, functional vascularization of tissue constructs. Vascularization is necessary for the long-term viability of implanted tissue expanded and differentiated in vitro. Such tissues may be derived from various cell sources, including mesenchymal stem cells (MSCs). MSCs, able to differentiate down several lineages, have been extensively researched for their therapeutic capabilities. In addition, MSCs have a variety of roles in the vascularization of tissue, both through direct contact and indirect signaling. The studied relationships between MSCs and vascularization have been utilized to further the necessary advancement of vascularization in tissue engineering concepts. This review aims to provide a summary of relevant relationships between MSCs, vascularization, and other relevant cell types, along with an overview discussing applications and challenges related to the roles and relationships of MSCs and vascular tissues.

Erythropoietin and the vascular wall: the controversy continues

BACKGROUND AND AIMS

Erythropoietin (EPO) stimulates erythropoiesis through its specific receptor (EPO-R). Preclinical work has assigned a role for the EPO/EPO-R system in the heart and blood vessels. The potential use of erythropoiesis-stimulating agents (ESAs) for nonhematopoietic indications is a focus of current research. This article considers proven actions of EPO in the cardiovascular system, with emphasis on the human responses.

DATA SYNTHESIS

By use of specific anti-EPO-R antibody no EPO-R protein was detected by Western blotting in normal non-erythroid tissues. Clinical trials failed to demonstrate clear beneficial effects of high-dosed ESAs in patients with coronary syndrome or myocardial infarct. While ESA therapy may lead to an elevation in arterial blood pressure in previously anemic patients, several studies have reported no effects on vessels/blood pressure with ESAs. EPO has been reported to stimulate angiogenesis. EPO-R mRNA is detectable in human vascular endothelium. However, in most vitro studies very high concentrations of EPO were applied and well-designed studies have failed to show direct effects of ESAs on endothelial cells. Whether EPO promotes the mobilization of myeloid progenitor cells into the blood stream still needs to be studied in more detail, as this effect may prove useful for augmenting the neovascularization of ischemic tissues. With respect to the administration of ESAs to tumor patients, a deeper insight into the role of EPO for tumor angiogenesis is desirable.

CONCLUSIONS

The enthusiastic reports of the nonhematopoietic cytoprotective potential of EPO and its derivatives in the cardiovascular system have not yet been confirmed in placebo-controlled clinical trials.

Physiology and pharmacology of erythropoietin

Human erythropoietin (Epo) is a 30.4 kDa glycoprotein hormone composed of a single 165 amino acid residues chain to which four glycans are attached. The kidneys are the primary sources of Epo, its synthesis is controlled by hypoxia-inducible transcription factors (HIFs). Epo is an essential factor for the viability and proliferation of erythrocytic progenitors. Whether Epo exerts cytoprotection outside the bone marrow still needs to be clarified. Epo deficiency is the primary cause of the anemia in chronic kidney disease (CKD). Treatment with recombinant human Epo (rhEpo, epoetin) can be beneficial not only in CKD but also for other indications, primarily anemia in cancer patients receiving chemotherapy. Considering unwanted events, the administration of rhEpo or its analogs may increase the incidence of thromboembolism. The expiry of the patents for the original epoetins has initiated the production of similar biological medicinal products ('biosimilars'). Furthermore, analogs (darbepoetin alfa, methoxy PEG-epoetin beta) with prolonged survival in circulation have been developed ('biobetter'). New erythropoiesis-stimulating agents are in clinical trials. These include compounds that augment erythropoiesis directly (e.g. Epo mimetic peptides or activin A binding protein) and chemicals that act indirectly by stimulating endogenous Epo synthesis (HIF stabilizers).

Platelet-rich plasma and the elimination of neuropathic pain

Peripheral neuropathic pain typically results from trauma-induced nociceptive neuron hyperexcitability and their spontaneous ectopic activity. This pain persists until the trauma-induced cascade of events runs its full course, which results in complete tissue repair, including the nociceptive neurons recovering their normal biophysical properties, ceasing to be hyperexcitable, and stopping having spontaneous electrical activity. However, if a wound undergoes no, insufficient, or too much inflammation, or if a wound becomes stuck in an inflammatory state, chronic neuropathic pain persists. Although various drugs and techniques provide temporary relief from chronic neuropathic pain, many have serious side effects, are not effective, none promotes the completion of the wound healing process, and none provides permanent pain relief. This paper examines the hypothesis that chronic neuropathic pain can be permanently eliminated by applying platelet-rich plasma to the site at which the pain originates, thereby triggering the complete cascade of events involved in normal wound repair. Many published papers claim that the clinical application of platelet-rich plasma to painful sites, such as muscle injuries and joints, or to the ends of nerves evoking chronic neuropathic pain, a process often referred to as prolotherapy, eliminates pain initiated at such sites. However, there is no published explanation of a possible mechanism/s by which platelet-rich plasma may accomplish this effect. This paper discusses the normal physiological cascade of trauma-induced events that lead to chronic neuropathic pain and its eventual elimination, techniques being studied to reduce or eliminate neuropathic pain, and how the application of platelet-rich plasma may lead to the permanent elimination of neuropathic pain. It concludes that platelet-rich plasma eliminates neuropathic pain primarily by platelet- and stem cell-released factors initiating the complex cascade of wound healing events, starting with the induction of enhanced inflammation and its complete resolution, followed by all the subsequent steps of tissue remodeling, wound repair and axon regeneration that result in the elimination of neuropathic pain, and also by some of these same factors acting directly on neurons to promote axon regeneration thereby eliminating neuropathic pain.

The effect of erythropoietin on autologous stem cell-mediated bone regeneration

Mesenchymal stem cells (MSCs) although used for bone tissue engineering are limited by the requirement of isolation and culture prior to transplantation. Our recent studies have shown that biomaterial implants can be engineered to facilitate the recruitment of MSCs. In this study, we explore the ability of these implants to direct the recruitment and the differentiation of MSCs in the setting of a bone defect. We initially determined that both stromal derived factor-1alpha (SDF-1α) and erythropoietin (Epo) prompted different degrees of MSC recruitment. Additionally, we found that Epo and bone morphogenetic protein-2 (BMP-2), but not SDF-1α, triggered the osteogenic differentiation of MSCs in vitro. We then investigated the possibility of directing autologous MSC-mediated bone regeneration using a murine calvaria model. Consistent with our in vitro observations, Epo-releasing scaffolds were found to be more potent in bridging the defect than BMP-2 loaded scaffolds, as determined by computed tomography (CT) scanning, fluorescent imaging and histological analyses. These results demonstrate the tremendous potential, directing the recruitment and differentiation of autologous MSCs has in the field of tissue regeneration.

Microvesicles derived from human umbilical cord mesenchymal stem cells stimulated by hypoxia promote angiogenesis both in vitro and in vivo

Although mesenchymal stem cells (MSCs) have been increasingly trialed to treat a variety of diseases, the underlying mechanisms remain still elusive. In this study, human umbilical cord (UC)-derived MSCs were stimulated by hypoxia, and the membrane microvesicles (MVs) in the supernatants were collected by ultracentrifugation, observed under an electron microscope, and the origin was identified with the flow cytometric technique. The results showed that upon hypoxic stimulus, MSCs released a large quantity of MVs of ~100 nm in diameter. The MVs were phenotypically similar to the parent MSCs, except that the majority of them were negative for the receptor of platelet-derived growth factor. DiI-labeling assay revealed that MSC-MVs could be internalized into human UC endothelial cells (UC-ECs) within 8 h after they were added into the culture medium. Carboxyfluorescein succinimidyl ester-labeling technique and MTT test showed that MSC-MVs promoted the proliferation of UC-ECs in a dose-dependent manner. Further, MVs could enhance in vitro capillary network formation of UC-ECs in a Matrigel matrix. In a rat hindlimb ischemia model, both MSCs and MSC-MVs were shown to improve significantly the blood flow recovery compared with the control medium (P<0.0001), as assessed by laser Doppler imaging analysis. These data indicate that MV releasing is one of the major mechanisms underlying the effectiveness of MSC therapy by promoting angiogenesis.

Mesenchymal stem cell 1 (MSC1)-based therapy attenuates tumor growth whereas MSC2-treatment promotes tumor growth and metastasis

BACKGROUND

Currently, there are many promising clinical trials using mesenchymal stem cells (MSCs) in cell-based therapies of numerous diseases. Increasingly, however, there is a concern over the use of MSCs because they home to tumors and can support tumor growth and metastasis. For instance, we established that MSCs in the ovarian tumor microenvironment promoted tumor growth and favored angiogenesis. In parallel studies, we also developed a new approach to induce the conventional mixed pool of MSCs into two uniform but distinct phenotypes we termed MSC1 and MSC2.

METHODOLOGY/PRINCIPAL FINDINGS

Here we tested the in vitro and in vivo stability of MSC1 and MSC2 phenotypes as well as their effects on tumor growth and spread. In vitro co-culture of MSC1 with various cancer cells diminished growth in colony forming units and tumor spheroid assays, while conventional MSCs or MSC2 co-culture had the opposite effect in these assays. Co-culture of MSC1 and cancer cells also distinctly affected their migration and invasion potential when compared to MSCs or MSC2 treated samples. The expression of bioactive molecules also differed dramatically among these samples. MSC1-based treatment of established tumors in an immune competent model attenuated tumor growth and metastasis in contrast to MSCs- and MSC2-treated animals in which tumor growth and spread was increased. Also, in contrast to these groups, MSC1-therapy led to less ascites accumulation, increased CD45+leukocytes, decreased collagen deposition, and mast cell degranulation.

CONCLUSION/SIGNIFICANCE

These observations indicate that the MSC1 and MSC2 phenotypes may be convenient tools for the discovery of critical components of the tumor stroma. The continued investigation of these cells may help ensure that cell based-therapy is used safely and effectively in human disease.

The effect of erythropoietin on normal and neoplastic cells

Erythropoietin (Epo) is an essential hormone that binds and activates the Epo receptor (EpoR) resident on the surface of erythroid progenitor cells, thereby promoting erythropoiesis. Recombinant human erythropoietin has been used successfully for over 20 years to treat anemia in millions of patients. In addition to erythropoiesis, Epo has also been reported to have other effects, such as tissue protection and promotion of tumor cell growth or survival. This became of significant concern in 2003, when some clinical trials in cancer patients reported increased tumor progression and worse survival outcomes in patients treated with erythropoiesis-stimulating agents (ESAs). One of the potential mechanisms proffered to explain the observed safety issues was that functional EpoR was expressed in tumors and/or endothelial cells, and that ESAs directly stimulated tumor growth and/or antagonized tumor ablative therapies. Since then, numerous groups have performed further research evaluating this potential mechanism with conflicting data and conclusions. Here, we review the biology of endogenous Epo and EpoR expression and function in erythropoiesis, and evaluate the evidence pertaining to the expression of EpoR on normal nonhematopoietic and tumor cells.

Migration of bone marrow-derived cells and improved perfusion after treatment with erythropoietin in a murine model of myocardial infarction

Erythropoietin (EPO) was shown to have protective effects after myocardial infarction (MI) by neovascularization and antiapoptotic mechanisms. Beside direct receptor-dependent mechanisms, mobilization and homing of bone marrow-derived cells (BMCs) may play a pivotal role in this regard. In this study, we intended to track different subpopulations of BMCs and to assess serially myocardial perfusion changes in EPO-treated mice after MI. To allow tracking of BMCs, we used a chimeric mouse model. Therefore, mice (C57BL/6J) were sublethally irradiated, and bone marrow (BM) from green fluorescent protein transgenic mice was transplanted. Ten weeks later coronary artery ligation was performed to induce MI. EPO was injected for 3 days with a total dose of 5000 IU/kg. Subpopulations (CD31, c-kit, CXCR-4 and Sca-1) of EGFP⁺ cells were studied in peripheral blood, bone marrow and hearts by flow cytometry. Myocardial perfusion was serially investigated in vivo by pinhole single-photon emission computed tomography (SPECT) at days 6 and 30 after MI. EPO-treated animals revealed an enhanced mobilization of BMCs into peripheral blood. The numbers of these cells in BM remained unchanged. Homing of all BMCs subpopulations to the ischaemic myocardium was significantly increased in EPO-treated mice. Among the investigated subpopulations, EPO predominantly affected migration of CXCR-4⁺ (4.3-fold increase). Repetitively SPECT analyses revealed a reduction of perfusion defects after EPO treatment over time. Our study shows that EPO treatment after MI enhances the migration capacity of BMCs into ischaemic tissue, which may attribute to an improved perfusion and reduced size of infarction, respectively.

Effects of erythropoietin receptors and erythropoiesis-stimulating agents on disease progression in cancer

Erythropoiesis-stimulating agents (ESAs) increase red blood cell (RBC) production in bone marrow by activating the erythropoietin receptor (EpoR) on erythrocytic-progenitor cells. Erythropoiesis-stimulating agents are approved in the United States and Europe for treating anaemia in cancer patients receiving chemotherapy based on randomised, placebo-controlled trials showing that ESAs reduce RBC transfusions. Erythropoiesis-stimulating agent-safety issues include thromboembolic events and concerns regarding whether ESAs increase disease progression and/or mortality in cancer patients. Several trials have reported an association between ESA use and increased disease progression and/or mortality, whereas other trials in the same tumour types have not provided similar findings. This review thoroughly examines available evidence regarding whether ESAs affect disease progression. Both clinical-trial data on ESAs and disease progression, and preclinical data on how ESAs could affect tumour growth are summarised. Preclinical topics include (i) whether tumour cells express EpoR and could be directly stimulated to grow by ESA exposure and (ii) whether endothelial cells express EpoR and could be stimulated by ESA exposure to undergo angiogenesis and indirectly promote tumour growth. Although assessment and definition of disease progression vary across studies, the current clinical data suggest that ESAs may have little effect on disease progression in chemotherapy patients, and preclinical data indicate a direct or indirect effect of ESAs on tumour growth is not strongly supported.

New Cell-Based Therapy Paradigm: Induction of Bone Marrow-Derived Multipotent Mesenchymal Stromal Cells into Pro-Inflammatory MSC1 and Anti-inflammatory MSC2 Phenotypes

Cell-based therapies (CBTs) are quickly taking hold as a revolutionary new approach to treat many human diseases. Among the cells used in these treatments, multipotent mesenchymal stromal cells, also often and imprecisely termed mesenchymal stem cells (MSC), are widely used because they are considered clinically safe, unique in their immune-modulating capabilities, easily obtained from adult tissues, and quickly expanded as well as stored. However, despite these established advantages, there are limiting factors to employing MSCs in these therapeutic strategies. Foremost is the lack of a general consensus on a definition of these cells, marring efforts to prepare homogeneous lots and more importantly complicating their in vitro and in vivo investigation. Furthermore, although one of the most profound clinical effects of MSC intravenous administration is the modulation of host immune responses, no adequate ex vivo assays exist to consistently predict the therapeutic effect of each MSC lot in the treated patient. Until these issues are addressed, this very promising and safe new therapeutic approach cannot be used to its full advantage. However, these confounding issues do present exciting opportunities. The first is an opportunity to discover unknown aspects of host immune responses because the unique effect driven by MSC infusion on a patient's immunity has not yet been identified. In addition, there is an opportunity to develop methods, tests, and tools to better define MSCs and MSC-based therapy and provide consistency in preparation and effect. To this end, my laboratory recently developed a new approach to induce uniform pro-inflammatory MSC1 and anti-inflammatory MSC2 phenotypes from bone marrow-derived MSC preparations. I anticipate that MSC1 and MSC2 provide convenient tools with which to address some of these limitations and will help advance safe and effective CBTs for human disease.

Effect and mechanism of erythropoietin on mesenchymal stem cell proliferation in vitro under the acute kidney injury microenvironment

Erythropoietin (EPO) can stimulate the proliferation and protraction of endothelial progenitor cells, and plays an important role in the proliferation and differentiation of marrow-derived mesenchymal stem cells (mMSCs) under the acute kidney injury (AKI) microenvironment. In the present study, C57BL/6 mice mMSCs were isolated, and AKI mice models were prepared. The renal cortex was obtained to prepare the ischemia/reperfusion (I/R) kidney homogenate supernatant. P3-mMSCs were treated by different methods: one group was added only I/R kidney homogenate supernatant, and another contained different concentrations of EPO (1, 5, 10, 50 IU/mL) in I/R kidney homogenate supernatant. The proliferation and apoptosis of mMSCs were detected by CCK-8 and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling), respectively. Expression of erythropoietin receptor (EPOR) and protein of the signal pathway related to proliferation/apoptosis were also examined. The results showed that the proliferation ability of mMSCs treated with I/R kidney homogenate supernatant decreased significantly, while the apoptosis percentage was significantly higher than that of the control. After intervention of EPO, their proliferation enhanced and the apoptosis percentage decreased. EPOR expression was positive in P3-mMSCs. EPO decreased the expression of caspase-3 of mMSCs under the AKI microenvironment in a dose- and time-dependent manner, but increased the Bcl-2 expression. The expression of phosphor-Janus kinase 2, phosphor-signal transducer and activator of transcription (pSTAT-5) increased significantly in 10 IU/mL EPO cultured for five days. Our results show that EPO can promote proliferation of mMSCs in vitro under the AKI microenvironment, which is mediated by EPOR and related with the proliferation/apoptosis signal pathway.

Perivascular cells as mesenchymal stem cells

IMPORTANCE OF THE FIELD

Mesenchymal stem cells are multipotent adult stem cell populations that have broad differentiation plasticity and immunosuppressive potential that render them of great importance in cell-based therapies. They are identified by in vitro characteristics based on their differentiation potential for clinical approaches while their biological properties and in vivo identities are often less understood.

AREAS COVERED IN THIS REVIEW

Recent research carried out in the last decade on mesenchymal stem cell biology suggests that mesenchymal stem cells from various tissues reside in a perivascular location and these can be identified as pericytes that function as mural cells in microvessels.

WHAT THE READER WILL GAIN

This review covers recent progress on understanding the link between pericytes and mesenchymal stem cells discussing specific points such as response to injury and tissue-specific functions.

TAKE HOME MESSAGE

Despite a long and controversial history, there is a growing acceptance that perivascular cells are connected with mesenchymal stem cells, all that is really lacking is genetic evidence to show differentiation of pericytes into different cells types.

Recruitment of endogenous bone marrow mesenchymal stem cells towards injured liver

Recent studies suggest that mesenchymal stem cells (MSCs) possess a greater differentiation potential than once thought and that they have the capacity to regenerate damaged tissues/organs. However, the evidence is insufficient, and the mechanism governing the recruitment and homing of MSCs to these injured sites is not well understood. We first examined the MSCs circulating in peripheral blood and then performed chemotaxis, wound healing and tubule-formation assays to investigate the migration capability of mouse bone marrow MSCs (mBM-MSCs) in response to liver-injury signals. In addition, BM-MSCs from donor enhanced green fluorescent protein transgenic male mice were transplanted into liver-injured co-isogenic female recipients, either by intra-bone marrow injection or through the caudal vein, to allow in vivo tracking analysis of the cell fate after transplantation. Donor-derived cells were analysed by in vivo imaging analysis, PCR, flow cytometry and frozen sections. Microarray and real-time PCR were used for chemokine/cytokine and receptor analyses. We successfully isolated circulating MSCs in peripheral blood of liver-injured mice and provided direct evidence that mBM-MSCs could be mobilized into the circulation and recruited into the liver after stimulation of liver injury. CCR9, CXCR4 and c-MET were essential for directing cellular migration towards the injured liver. The recruited mBM-MSCs may play different roles, including hepatic fate specification and down-regulation of the activity of hepatic stellate cells which inhibits over-accumulation of collagen and development of liver fibrosis. Our results provide new insights into liver repair involving endogenous BM-MSCs and add new information for consideration when developing clinical protocols involving the MSCs.

A new mesenchymal stem cell (MSC) paradigm: polarization into a pro-inflammatory MSC1 or an Immunosuppressive MSC2 phenotype

Background

Our laboratory and others reported that the stimulation of specific Toll-like receptors (TLRs) affects the immune modulating responses of human multipotent mesenchymal stromal cells (hMSCs). Toll-like receptors recognize “danger” signals, and their activation leads to profound cellular and systemic responses that mobilize innate and adaptive host immune cells. The danger signals that trigger TLRs are released following most tissue pathologies. Since danger signals recruit immune cells to sites of injury, we reasoned that hMSCs might be recruited in a similar way. Indeed, we found that hMSCs express several TLRs (e.g., TLR3 and TLR4), and that their migration, invasion, and secretion of immune modulating factors is drastically affected by specific TLR-agonist engagement. In particular, we noted diverse consequences on the hMSCs following stimulation of TLR3 when compared to TLR4 by our low-level, short-term TLR-priming protocol.

Principal Findings

Here we extend our studies on the effect on immune modulation by specific TLR-priming of hMSCs, and based on our findings, propose a new paradigm for hMSCs that takes its cue from the monocyte literature. Specifically, that hMSCs can be polarized by downstream TLR signaling into two homogenously acting phenotypes we classify here as MSC1 and MSC2. This concept came from our observations that TLR4-primed hMSCs, or MSC1, mostly elaborate pro-inflammatory mediators, while TLR3-primed hMSCs, or MSC2, express mostly immunosuppressive ones. Additionally, allogeneic co-cultures of TLR-primed MSCs with peripheral blood mononuclear cells (PBMCs) predictably lead to suppressed T-lymphocyte activation following MSC2 co-culture, and permissive T-lymphocyte activation in co-culture with MSC1.

Significance

Our study provides an explanation to some of the conflicting reports on the net effect of TLR stimulation and its downstream consequences on the immune modulating properties of stem cells. We further suggest that MSC polarization provides a convenient way to render these heterogeneous preparations of cells more uniform while introducing a new facet to study, as well as provides an important aspect to consider for the improvement of current stem cell-based therapies.

Hypoxia-preconditioned adipose tissue-derived mesenchymal stem cell increase the survival and gene expression of engineered neural stem cells in a spinal cord injury model

Hypoxic preconditioning (HP) is a novel strategy to make stem cells resistant to the ischemic environment they encounter after transplantation into injured tissue; this strategy improves survival of both the transplanted cells and the host cells at the injury site. Using both in vitro and in vivo injury models, we confirmed that HP-treated adipose tissue-derived mesenchymal stem cells (HP-AT-MSCs) increased cell survival and enhanced the expression of marker genes in DsRed-engineered neural stem cells (NSCs-DsRed). Similar to untreated AT-MSCs, HP-AT-MSCs had normal morphology and were positive for the cell surface markers CD90, CD105, and CD29, but not CD31. In three in vitro ischemic-mimicking injury models, HP-AT-MSCs significantly increased both the viability of NSCs-DsRed and the expression of DsRed and clearly reduced the number of annexin-V-positive apoptotic NSCs-DsRed and the expression of the apoptotic factor Bax. Consistent with the in vitro assay, co-transplantation of NSCs-DsRed with HP-AT-MSCs significantly improved the survival of the NSCs-DsRed, resulting in an increased expression of the DsRed reporter gene at the transplantation site in a rat spinal cord injury (SCI) model. These findings suggest that the co-transplantation of HP-AT-MSCs with engineered NSCs can improve both the cell survival and the gene expression of the engineered NSCs, indicating that this novel strategy can be used to augment the therapeutic efficacy of combined stem cell and gene therapies for SCI.

Survival, neuron-like differentiation and functionality of mesenchymal stem cells in neurotoxic environment: the critical role of erythropoietin

Mesenchymal stem cells (MSCs) can ameliorate symptoms in several neurodegenerative diseases. However, the toxic environment of a degenerating central nervous system (CNS) characterized by hypoxia, glutamate (Glu) excess and amyloid beta (Abeta) pathology may hamper the survival and regenerative/replacing capacities of engrafted stem cells. Indeed, human MSC (hMSC) exposed to hypoxia were disabled in (i) the capacity of their muscarinic receptors (mAChRs) to respond to acetylcholine (ACh) with a transient increase in intracellular [Ca(2+)], (ii) their capacity to metabolize Glu, reflected by a strong decrease in glutamine synthetase activity, and (iii) their survival on exposure to Glu. Cocultivation of MSC with PC12 cells expressing the amyloid precursor protein gene (APPsw-PC12) increased the release of IL-6 from MSC. HMSC exposed to erythropoietin (EPO) showed a cholinergic neuron-like phenotype reflected by increased cellular levels of choline acetyltransferase, ACh and mAChR. All their functional deficits observed under hypoxia, Glu exposure and APPsw-PC12 cocultivation were reversed by the application of EPO, which increased the expression of Wnt3a. EPO also enhanced the metabolism of Abeta in MSC by increasing their neprilysin content. Our data show that cholinergic neuron-like differentiation of MSC, their functionality and resistance to a neurotoxic environment is regulated and can be improved by EPO, highlighting its potential for optimizing cellular therapies of the CNS.

Intracardiac injection of erythropoietin induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Erythropoietin (EPO) protects the myocardium from ischaemic injury and promotes beneficial remodelling. We assessed the therapeutic efficacy of intracardiac EPO injection and EPO-mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, EPO (3000 U/kg) or saline was delivered by intracardiac injection. Compared to myocardial infarction control group (MIC), EPO significantly improved left ventricular function (n =11-14, P < 0.05) and decreased right ventricular wall stress (n = 8, P < 0.05) assessed by pressure-volume loops after 6 weeks. MI-EPO hearts exhibited smaller infarction size (20.1 +/- 1.1% versus 27.8 +/- 1.2%; n = 6-8, P < 0.001) and greater capillary density (338.5 +/- 14.7 versus 259.8 +/- 9.2 vessels per mm2; n = 6-8, P < 0.001) than MIC hearts. Direct EPO injection reduced post-MI myocardial apoptosis by approximately 41% (0.27 +/- 0.03% versus 0.42 +/- 0.03%; n = 6, P= 0.005). The chemoattractant SDF-1 was up-regulated significantly assessed by quantitative realtime PCR and immunohistology. c-Kit(+) and CD34(+) stem cells were significantly more numerous in MI-EPO than in MIC at 24 hrs in peripheral blood (n = 7, P < 0.05) and 48 hrs in the infarcted hearts (n = 6, P < 0.001). Further, the mRNAs of Akt, eNOS and EPO receptor were significantly enhanced in MI-EPO hearts (n = 7, P < 0.05). Intracardiac EPO injection restores myocardial functions following MI, which may attribute to the improved early recruitment of c-Kit(+) and CD34(+) stem cells via the enhanced expression of chemoattractant SDF-1.

Erythropoietin increases the motility of human bone marrow-multipotent stromal cells (hBM-MSCs) and enhances the production of neurotrophic factors from hBM-MSCs

Cell therapy has been extensively studied as an approach to repair damage in nervous system diseases. Multipotent stromal cells [MSCs] are well known to have neuroprotective effects and neural differentiation potential. The ability to induce migration of MSCs near nervous system damage via direct transplantation or via intravenous injections and increase the secretion of neurotrophic factors from MSCs might improve our ability to repair damage to the nervous system through cell therapy. In the present study, we investigated whether recombinant human erythropoietin [rhEPO], known to have a hematopoietic effect, could increase the motility of human bone marrow [hBM]-MSCs and enhance production of neurotrophic factors from hBM-MSCs. Based on the results of our MTT assay, trypan blue staining, and bromodeoxyuridine ELISA, rhEPO treatment increases the viability of MSCs but not their proliferation. With a migration assay kit, we demonstrated that the motility of hBM-MSCs was enhanced in rhEPO-treated cells. Immunoblotting assays revealed increased expression of phospho-Akt, phospho-GSK-3beta, phospho-extracellular signal-regulated kinase (ERK), beta PAK-interacting exchange factor (PIX), CXCR4, phospho tyrosine kinase B (TrkB), and vascular endothelial growth factor receptor-2 [VEGFR-2] in rhEPO-treated cells. Reverse transcription-polymerase chain reaction and gelatin zymography demonstrated that rhEPO treatment induces MMP-2 mRNA level and activity. In the studies using ELISAs, we found that rhEPO could increase levels of stromal cell-derived factor-1alpha, VEGF, and brain-derived neurotrophic factors. These findings suggest that rhEPO can increase the viability and motility of hBM-MSCs by affecting various intracellular signals including Akt, ERK, beta-PIX, CXCR4, TrkB, VEGFR-2, and MMP-2 and can enhance the production of neurotrophic factors from hBM-MSCs.

The pro-inflammatory peptide LL-37 promotes ovarian tumor progression through recruitment of multipotent mesenchymal stromal cells

Bone marrow-derived mesenchymal stem cells or multipotent mesenchymal stromal cells (MSCs) have been shown to engraft into the stroma of several tumor types, where they contribute to tumor progression and metastasis. However, the chemotactic signals mediating MSC migration to tumors remain poorly understood. Previous studies have shown that LL-37 (leucine, leucine-37), the C-terminal peptide of human cationic antimicrobial protein 18, stimulates the migration of various cell types and is overexpressed in ovarian, breast, and lung cancers. Although there is evidence to support a pro-tumorigenic role for LL-37, the function of the peptide in tumors remains unclear. Here, we demonstrate that neutralization of LL-37 in vivo significantly reduces the engraftment of MSCs into ovarian tumor xenografts, resulting in inhibition of tumor growth as well as disruption of the fibrovascular network. Migration and invasion experiments conducted in vitro indicated that the LL-37-mediated migration of MSCs to tumors likely occurs through formyl peptide receptor like-1. To assess the response of MSCs to the LL-37-rich tumor microenvironment, conditioned medium from LL-37-treated MSCs was assessed and found to contain increased levels of several cytokines and pro-angiogenic factors compared with controls, including IL-1 receptor antagonist, IL-6, IL-10, CCL5, VEGF, and matrix metalloproteinase-2. Similarly, Matrigel mixed with LL-37, MSCs, or the combination of the two resulted in a significant number of vascular channels in nude mice. These data indicate that LL-37 facilitates ovarian tumor progression through recruitment of progenitor cell populations to serve as pro-angiogenic factor-expressing tumor stromal cells.