The concept of mesenchymal stem cells

Roles of Mesenchymal Cells in the Lung: From Lung Development to Chronic Obstructive Pulmonary Disease

Mesenchymal cells are an essential cell type because of their role in tissue support, their multilineage differentiation capacities and their potential clinical applications. They play a crucial role during lung development by interacting with airway epithelium, and also during lung regeneration and remodeling after injury. However, much less is known about their function in lung disease. In this review, we discuss the origins of mesenchymal cells during lung development, their crosstalk with the epithelium, and their role in lung diseases, particularly in chronic obstructive pulmonary disease.

Cell encapsulated and microenvironment modulating microbeads containing alginate hydrogel system for bone tissue engineering

Functional tissue regeneration using synthetic biomaterials requires proliferation and heterotypic differentiation of stem/progenitor cells within a specialized heterogeneous (biophysical-biochemical) microenvironment. The current techniques have limitations to develop synthetic hydrogels, mimicking native extracellular matrix porosity along with heterogeneous microenvironmental cues of matrix mechanics, degradability, microstructure and cell-cell interactions. Here, we have developed a microenvironment modulating system to fabricate in situ porous hydrogel matrix with two or more distinct tailored microenvironmental niches within microbeads and the hydrogel matrix for multicellular tissue regeneration. Electrosprayed pectin-gelatin blended microbeads and crosslinked alginate hydrogel system help to tailor microenvironmental niches of encapsulated cells where two different cells are surrounded by a specific microenvironment. The effect of different microenvironmental parameters associated with the microbead/hydrogel matrix was evaluated using human umbilical-cord mesenchymal stem cells (hUCMSCs). The osteogenic differentiation of hUCMSCs in the hydrogel matrix was evaluated for bone tissue regeneration. This will be the first report on microenvironment modulating microbead-hydrogel system to encapsulate two/more types of cells in a hydrogel, where each cell is surrounded with distinct niches for heterogeneous tissue regeneration.

Stem cells and COVID-19: are the human amniotic cells a new hope for therapies against the SARS-CoV-2 virus?

A new coronavirus respiratory disease (COVID-19) caused by the SARS-CoV-2 virus, surprised the entire world, producing social, economic, and health problems. The COVID-19 triggers a lung infection with a multiple proinflammatory cytokine storm in severe patients. Without effective and safe treatments, COVID-19 has killed thousands of people, becoming a pandemic. Stem cells have been suggested as a therapy for lung-related diseases. In particular, mesenchymal stem cells (MSCs) have been successfully tested in some clinical trials in patients with COVID-19. The encouraging results positioned MSCs as a possible cell therapy for COVID-19. The amniotic membrane from the human placenta at term is a valuable stem cell source, including human amniotic epithelial cells (hAECs) and human mesenchymal stromal cells (hAMSCs). Interestingly, amnion cells have immunoregulatory, regenerative, and anti-inflammatory properties. Moreover, hAECs and hAMSCs have been used both in preclinical studies and in clinical trials against respiratory diseases. They have reduced the inflammatory response and restored the pulmonary tissue architecture in lung injury in vivo models. Here, we review the existing data about the stem cells use for COVID-19 treatment, including the ongoing clinical trials. We also consider the non-cellular therapies that are being applied. Finally, we discuss the human amniotic membrane cells use in patients who suffer from immune/inflammatory lung diseases and hypothesize their possible use as a successful treatment against COVID-19.

Comparative separation methods and biological characteristics of human placental and umbilical cord mesenchymal stem cells in serum-free culture conditions

Background

Mesenchymal stem cells (MSCs) are considered to be an effective tool for regenerative medicine with promising applications for clinical therapy. However, incongruent data has been reported partially owing to their functional heterogeneity. To provide sufficient and suitable clinical seed cells derived from the placenta for MSC therapy, we compared the various current isolation methods, as well as the biological characteristics, of different human placenta mesenchymal stem cells (hPMSCs).

Methods

We selected placentas from 35 informed donors and exploited three commonly used methods. MSCs were isolated from different parts of placental tissue including umbilical cord (UC), amniotic membrane (AM), chorionic membrane (CM), chorionic villi (CV), and deciduae (DC). The appropriate isolation methods for each type of hPMSCs were first assessed. The resulting five MSC types from the same individuals were identified based on their surface marker expression, proliferation capacity, transcriptome, differentiation, multipotency and karyotype.

Results

All three methods successfully isolated the five hPMSC types from placental tissues. However, the UC-MSCs were most effectively separated via the tissue explant method, while the enzymatic digestion method was found to be more suitable for separating CV-MSCs, owing to its higher output efficiency compared to the other methods. Alternatively, the perfusion method was complicated and exhibited the lowest efficiency for cell isolation and uniformity. Furthermore, we determined that UC-MSCs and CV-MSCs express a higher level of paracrine cytokines and display much stronger proliferative capacity as well as superior extraction efficiency. Finally, karyotype analysis revealed that DC-MSCs are derived from the mother, while the other cell types are derived from the fetus. Moreover, the different hPMSCs exhibited unique gene expression profiles, which may prove advantageous in treatment of a broad range of diseases.

Conclusions

hPMSCs from different sources are similar yet also unique. Our results describe the biological characteristics of five hPMSCs and provide insights to aide in the selection process of candidates for MSCs treatment. Overall, UC- and CV-MSCs appear to be ideal sources of primary MSCs for clinical treatment and future research.

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.

A Review on the Effect of Plant Extract on Mesenchymal Stem Cell Proliferation and Differentiation

Stem cell has immense potential in regenerative cellular therapy. Mesenchymal stem cells (MSCs) can become a potential attractive candidate for therapy due to its remarkable ability of self-renewal and differentiation into three lineages, i.e., ectoderm, mesoderm, and endoderm. Stem cell holds tremendous promises in the field of tissue regeneration and transplantation for disease treatments. Globally, medicinal plants are being used for the treatment and prevention of a variety of diseases. Phytochemicals like naringin, icariin, genistein, and resveratrol obtained from plants have been extensively used in traditional medicine for centuries. Certain bioactive compounds from plants increase the rate of tissue regeneration, differentiation, and immunomodulation. Several studies show that bioactive compounds from plants have a specific role (bioactive mediator) in regulating the rate of cell division and differentiation through complex signal pathways like BMP2, Runx2, and Wnt. The use of plant bioactive phytochemicals may also become promising in treating diseases like osteoporosis, neurodegenerative disorders, and other tissue degenerative disorders. Thus, the present review article is aimed at highlighting the roles and consequences of plant extracts on MSCs proliferation and desired lineage differentiations.

A highly standardized and characterized human platelet lysate for efficient and reproducible expansion of human bone marrow mesenchymal stromal cells

BACKGROUND

Human platelet lysate (hPL) represents a powerful alternative to fetal bovine serum (FBS) for human mesenchymal stromal cell (hMSC) expansion. However, the large variability in hPL sources and production protocols gives rise to discrepancies in product quality, characterization and poor batch-to-batch standardization.

METHODS

hPL prepared with more than 200 donors (200+DhPL) or with five donors (5DhPL) were compared in terms of growth factor (GF) contents and biochemical analysis. A multiple protein assay and proteomic analysis were performed to further characterize 200+DhPL batches. We also compared the phenotypic and functional characteristics of bone marrow (BM)-hMSCs grown in 200+DhPL versus FBS+basic fibroblast growth factor (bFGF).

RESULTS

By contrast to 5DhPL, industrial 200+DhPL displayed a strong standardization of GF contents and biochemical characteristics. We identified specific plasmatic components and platelet-released factors as the most relevant markers for the evaluation of the standardization of hPL batches. We used a multiplex assay and proteomic analysis of 200+DhPL to establish a proteomic signature and demonstrated the robust standardization of batches. 200+DhPL was shown to improve and standardize BM-hMSC expansion compared with FBS+bFGF. The levels of expression of BM-hMSC membrane markers were found to be much more homogeneous between batches when cells were cultured in 200+DhPL. BM-hMSCs cultured in parallel under both conditions displayed similar adipogenic and osteogenic differentiation potential and immunosuppressive properties.

CONCLUSIONS

We report a standardization of hPL and the importance of such standardization for the efficient amplification of more homogeneous and reproducible cell therapy products.

Viral inactivation of human platelet lysate by gamma irradiation preserves its optimal efficiency in the expansion of human bone marrow mesenchymal stromal cells

BACKGROUND

Human platelet lysate (hPL) represents a powerful medium supplement for human mesenchymal stromal cell (hMSC) expansion. The recently published general chapters of the Pharmacopeia require the addition of a step of viral inactivation during the production process of such raw biological material used for cell-based medicinal products.

STUDY DESIGN AND METHODS

The ability of gamma irradiation to inactivate viruses from a panel representative of the virus diversity was evaluated. The impact of gamma irradiation on hPL composition and efficiency as a supplement for hMSC culture was evaluated.

RESULTS

An efficient inactivation of all the viruses tested was demonstrated, with the minimum reduction factors obtained being superior to 4.5 log₁₀ for human immunodeficiency virus (HIV) and hepatitis A virus (HAV) and superior to 5 log₁₀ for bovine viral diarrhea virus (BVDV), pseudorabies virus (PRV) and porcine parvovirus (PPV). The gamma irradiation did not affect the content in interesting biochemical factors for cell culture or in growth factors (GF), except to basic fibroblast GF (bFGF) whereas it highly impacted the contents in the factors involved in the coagulation cascade. Finally, gamma irradiated hPL remained as efficient as non-irradiated hPL for the proliferation, clonogenic potential, differentiation potential, and immunosuppressive properties of hMSCs.

CONCLUSION

The feasibility of using gamma irradiation to efficiently inactivate viruses in hPL while maintaining its optimal efficacy as a supplement for hMSC expansion was demonstrated. Such an inactivated hPL represents a very attractive raw material for the efficient production of safe cellular therapy products.

Preclinical Studies of the Biosafety and Efficacy of Human Bone Marrow Mesenchymal Stem Cells Pre-Seeded into β-TCP Scaffolds after Transplantation

Background: Cell-Based Therapies (CBT) constitute a valid procedure for increasing the quantity and quality of bone in areas with an inadequate bone volume. However, safety and efficacy should be investigated prior to clinical application. The objective of this study was to evaluate the biodistribution, safety and osteogenic capacity of bone marrow-derived human mesenchymal stem cells (hBMMSCs) pre-seeded into β-tricalcium phosphate (TCP) and implanted into NOD/SCID mice at subcutaneous and intramuscular sites. Methods: hBMMSCs were isolated, characterized and then cultured in vitro on a porous β-TCP scaffold. Cell viability and attachment were analyzed and then hBMMSCs seeded constructs were surgically placed at subcutaneous and intramuscular dorsal sites into NOD/SCID mice. Acute and subchronic toxicity, cell biodistribution and efficacy were investigated. Results: There were no deaths or adverse events in treated mice during the 48-hour observation period, and no toxic response was observed in mice. In the 12-week subchronic toxicity study, no mortalities, abnormal behavioral symptoms or clinical signs were observed in the saline control mice or the hBMMSCs/β-TCP groups. Finally, our results showed the bone-forming capacity of hBMMSCs/β-TCP since immunohistochemical expression of human osteocalcin was detected from week 7. Conclusions: These results show that transplantation of hBMMSCs/β-TCP in NOD/SCID mice are safe and effective, and might be applied to human bone diseases in future clinical trials.

The Effect of Bone Marrow Mesenchymal Stem Cells on the Granulocytic Differentiation of HL-60 Cells

Objective:

Mesenchymal stem cells (MSCs) are multipotent stromal cells that can differentiate into a variety of cell types. They control the process of hematopoiesis by secreting regulatory cytokines and growth factors and by the expression of important cell adhesion molecules for cell-to-cell interactions. This investigation was intended to examine the effect of bone marrow (BM)-derived MSCs on the differentiation of HL-60 cells according to morphological evaluation, flow cytometry analysis, and gene expression profile.

Materials and Methods:

The BM-MSCs were cultured in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum (FBS). After the third passage, the BM-MSCs were irradiated at 30 Gy. To compare how the HL-60 cells differentiated in groups treated differently, HL-60 cells were cultured in RPMI-1640 and supplemented with 10% FBS. The HL-60 cells were seeded into six-well culture plates and treated with all-trans-retinoic acid (ATRA), BM-MSCs, or BM-MSCs in combination with ATRA, while one well remained as untreated HL-60 cells. The expression levels of the granulocyte subset-specific genes in the HL-60 cells were assayed by real-time polymerase chain reaction.

Results:

Our results revealed that BM-MSCs support the granulocytic differentiation of the human promyelocytic leukemia cell line HL-60.

Conclusion:

Based on the results of this study, we concluded that BM-MSCs may be an effective resource in reducing or even preventing ATRA’s side effects and may promote differentiation for short medication periods. Though BM-MSCs are effective resources, more complementary studies are necessary to improve this differentiation mechanism in clinical cases.

Pathogen reduction through additive-free short-wave UV light irradiation retains the optimal efficacy of human platelet lysate for the expansion of human bone marrow mesenchymal stem cells

Background

We recently developed and characterized a standardized and clinical grade human Platelet Lysate (hPL) that constitutes an advantageous substitute for fetal bovine serum (FBS) for human mesenchymal stem cell (hMSC) expansion required in cell therapy procedures, avoiding xenogenic risks (virological and immunological) and ethical issues. Because of the progressive use of pathogen-reduced (PR) labile blood components, and the requirement of ensuring the viral safety of raw materials for cell therapy products, we evaluated the impact of the novel procedure known as THERAFLEX UV-Platelets for pathogen reduction on hPL quality (growth factors content) and efficacy (as a medium supplement for hMSC expansion). This technology is based on short-wave ultraviolet light (UV-C) that induces non-reversible damages in DNA and RNA of pathogens while preserving protein structures and functions, and has the main advantage of not needing the addition of any photosensitizing additives (that might secondarily interfere with hMSCs).

Methodology / Principal findings

We applied the THERAFLEX UV-Platelets procedure on fresh platelet concentrates (PCs) suspended in platelet additive solution and prepared hPL from these treated PCs. We compared the quality and efficacy of PR-hPL with the corresponding non-PR ones. We found no impact on the content of five cytokines tested (EGF, bFGF, PDGF-AB, VEGF and IGF-1) but a significant decrease in TGF-ß1 (-21%, n = 11, p<0.01). We performed large-scale culture of hMSCs from bone marrow (BM) during three passages and showed that hPL or PR-hPL at 8% triggered comparable BM-hMSC proliferation as FBS at 10% plus bFGF. Moreover, after proliferation of hMSCs in an hPL- or PR-hPL-containing medium, their profile of membrane marker expression, their clonogenic potential and immunosuppressive properties were maintained, in comparison with BM-hMSCs cultured under FBS conditions. The potential to differentiate towards the adipogenic and osteogenic lineages of hMSCs cultured in parallel in the three conditions also remained identical.

Conclusion / Significance

We demonstrated the feasibility of using UV-C-treated platelets to subsequently obtain pathogen-reduced hPL, while preserving its optimal quality and efficacy for hMSC expansion in cell therapy applications.

Mesenchymal Stem and Progenitor Cells in Regeneration: Tissue Specificity and Regenerative Potential

It has always been an ambitious goal in medicine to repair or replace morbid tissues for regaining the organ functionality. This challenge has recently gained momentum through considerable progress in understanding the biological concept of the regenerative potential of stem cells. Routine therapeutic procedures are about to shift towards the use of biological and molecular armamentarium. The potential use of embryonic stem cells and invention of induced pluripotent stem cells raised hope for clinical regenerative purposes; however, the use of these interventions for regenerative therapy showed its dark side, as many health concerns and ethical issues arose in terms of using these cells in clinical applications. In this regard, adult stem cells climbed up to the top list of regenerative tools and mesenchymal stem cells (MSC) showed promise for regenerative cell therapy with a rather limited level of risk. MSC have been successfully isolated from various human tissues and they have been shown to offer the possibility to establish novel therapeutic interventions for a variety of hard-to-noncurable diseases. There have been many elegant studies investigating the impact of MSC in regenerative medicine. This review provides compact information on the role of stem cells, in particular, MSC in regeneration.

Villous Chorion: A Potential Source for Pluripotent-like Stromal Cells

Context:

Multipotent stromal cells are isolated from various fetal sources and studied for their phenotypic characterization and ability to differentiate into different lineages.

Aims:

In this study, we aimed to isolate mesenchymal stem or stromal cells (MSCs) from villous chorion, expand under clinical scale level, compared the potency with other source of fetal-derived MSCs and studied their differentiation capabilities to form all three germ layers.

Subjects and Methods:

Placenta obtained from C-section was used to isolate villous chorion-MSCs (VC-MSCs) were expanded up to tenth passage and their characteristics were assessed by proliferation rate and phenotypic characterization using fluorescence-activated cell sorting and also expanded MSCs were analyzed for differentiated into all three germ layers by cytochemical staining.

Results:

Stem cell isolated from VC yielded up to 2.16 × 10⁹ cells at second passage and 3.06–4.23 × 10⁴ cells/cm² at tenth passage. The total yield of cells with all three sources analysis showed that VC has a low yield at second passage compared to amniotic membrane and Wharton's jelly, but the VC-MSCs yield significant amount in lesser days. The phenotypic characterization revealed positive for CD73, CD90, and CD105 and negative for CD79, CD34, CD45, human leukocyte antigen-DR proving their stemness even at tenth passage. They can able to differentiate into ectodermic neural cells, endodermic hepatocytes, and mesodermal differentiation of chondrocytes, adipocytes, and osteogenic cells proving their ability to differentiate into all three germ layers.

Conclusions:

This result suggests that the VC-MSCs are ideal source of stem cells with similar characteristics such as other adult stem cells. Thus, VC-derived MSCs can be potential clinical source in regenerative medicine.

Mesenchymal stem cells attenuate hydrogen peroxide-induced oxidative stress and enhance neuroprotective effects in retinal ganglion cells

The apoptosis of retinal ganglion cells leads to visual impairment and blindness in ocular neurodegenerative diseases, especially in diabetic retinopathy (DR). Mounting evidence suggests that oxidative stress contributes to the pathogenesis of DR. In the present study, we investigated whether bone mesenchymal stem cells (BMSCs) have protective ability to relieve hydrogen peroxide (H₂O₂)-induced injury on retinal ganglion cells in vitro. An immortalized retinal ganglion cells, RGC-5 cells, were exposed to an indicated concentration of H₂O₂ for 24 h. Cell viability was analyzed by CCK-8 assay to find out a certain concentration to build H₂O₂ oxidative damage model. Morphological changes in RGC-5 cells were observed under optical microscope, and cell apoptosis was detected with Hoechst fluorescence staining. Then, BMSCs were co-cultured with RGC-5 cells in a transwell culture system for 24 h and 48 h. Flow cytometry was performed to qualify the apoptosis rate of RGC-5 cells. Conditioned medium was collected for evaluation the inflammatory cytokines by ELISA. The content of intracellular malondialdehyde (MDA) and superoxide dismutase (SOD) was assayed by thiobarbituric acid and xanthine oxidase method, respectively. qRT-PCR and ELISA were conducted for analysis of the expression changes in brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), respectively. After H₂O₂ exposure, the morphological varieties were observed as cytoplasm shrinking and paramorphia together with nuclear gathering. Meanwhile, the apoptotic cells had hyperfluorescence with Hoechst 33258 staining. Co-culture with BMSCs significantly inhibited retinal cell death. It was found that BMSCs reduced H₂O₂-induced inflammatory factors IL-1β and TNF-α, down-regulated intracellular oxidant factor MDA, up-regulated intracellular antioxidant factor SOD, and increased neurotrophins BDNF and CNTF expression. BMSCs may enhance protective effect of RGC-5 cells in H₂O₂-induced damage through improving antioxidant capacity, inhibiting pro-inflammatory cytokine secretion, and promoting neurotrophin expression.

Proliferation and osteogenic differentiation of mesenchymal stromal cells in a novel porous hydroxyapatite scaffold

AIM

To compare the effect of bovine bone derived porous hydroxyapatite (BDHA) scaffold on proliferation and osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells (hMSCs) compared with commercial hydroxyapatite (CHA) scaffold.

MATERIALS AND METHODS

The porosity and pore size were analyzed using micro-CT. The biocompatibility was demonstrated by alamar blue assay, and cell attachment through SEM and Hoechst staining. The osteogenic differentiation was demonstrated using biochemical assay and osteogenic gene expression.

RESULTS

BDHA and CHA scaffolds showed porosity of 76.6 ± 0.6 and 64.3 ± 0.3% and pore size diameter of 0.04-0.25 and 0.1-2.6 mm, respectively. hMSCs proliferation, ALP activity, osteocalcin secretion and osteogenic gene expression are comparable in both the scaffolds.

CONCLUSION

These results demonstrated that BDHA is biocompatible, supports cell adhesion and promotes proliferation and osteogenic differentiation.

The mesenchymal transcription factor SNAI-1 instructs human liver specification

Epithelial-mesenchymal transition (EMT) and the mesenchymal-epithelial transition (MET) are processes required for embryo organogenesis. Liver develops from the epithelial foregut endoderm from which the liver progenitors, hepatoblasts, are specified. The migrating hepatoblasts acquire a mesenchymal phenotype to form the liver bud. In mid-gestation, hepatoblasts mature into epithelial structures: the hepatocyte cords and biliary ducts. While EMT has been associated with liver bud formation, nothing is known about its contribution to hepatic specification. We previously established an efficient protocol from human embryonic stem cells (hESC) to generate hepatic cells (Hep cells) resembling the hepatoblasts expressing alpha-fetoprotein (AFP) and albumin (ALB). Here we show that Hep cells express both epithelial (EpCAM and E-cadherin) and mesenchymal (vimentin and SNAI-1) markers. Similar epithelial and mesenchymal hepatoblasts were identified in human and mouse fetal livers, suggesting a conserved interspecies phenotype. Knock-down experiments demonstrated the importance of SNAI-1 in Hep cell hepatic specification. Moreover, ChIP assays revealed direct binding of SNAI-1 in the promoters of AFP and ALB genes consistent with its transcriptional activator function in hepatic specification. Altogether, our hESC-derived Hep cell cultures reveal the dual mesenchymal and epithelial phenotype of hepatoblast-like cells and support the unexpected transcriptional activator role of SNAI-1 in hepatic specification.

Pulp Revascularization on Permanent Teeth with Open Apices in a Middle-aged Patient

Pulp revascularization is a promising procedure for the treatment of adolescents' immature permanent teeth with necrotic pulp and/or apical periodontitis. However, the ability to successfully perform pulp revascularization in a middle-aged patient remains unclear. A 39-year-old woman was referred for treatment of teeth #20 and #29 with necrotic pulp, extensive periapical radiolucencies, and incomplete apices. Pulp revascularization procedures were attempted, including root canal debridement, triple antibiotic paste medication, and platelet-rich plasma transplantation to act as a scaffold. Periapical radiographic and cone-beam computed tomographic examinations were used to review the changes in the apical lesions and root apex configuration. The patient remained asymptomatic throughout the 30-month follow-up. Periapical radiographic examination revealed no change in the apical lesions of either tooth at 8 months. The periapical radiolucency disappeared on tooth #20 and significantly decreased on tooth #29 by the 30-month follow-up, findings that were also confirmed by cone-beam computed tomographic imaging. No evidence of root lengthening or thickening was observed. Successful revascularization was achieved in a middle-aged patient's teeth.

The Effect of Hypoxia on Mesenchymal Stem Cell Biology

Although physiological and pathological role of hypoxia have been appreciated in mammalians for decades however the cellular biology of hypoxia more clarified in the past 20 years. Discovery of the transcription factor hypoxia-inducible factor (HIF)-1, in the 1990s opened a new window to investigate the mechanisms behind hypoxia. In different cellular contexts HIF-1 activation show variable results by impacting various aspects of cell biology such as cell cycle, apoptosis, differentiation and etc. Mesenchymal stem cells (MSC) are unique cells which take important role in tissue regeneration. They are characterized by self-renewal capacity, multilineage potential, and immunosuppressive property. Like so many kind of cells, hypoxia induces different responses in MSCs by HIF- 1 activation. The activation of this molecule changes the growth, multiplication, differentiation and gene expression profile of MSCs in their niche by a complex of signals. This article briefly discusses the most important effects of hypoxia in growth kinetics, signalling pathways, cytokine secretion profile and expression of chemokine receptors in different conditions.

“Ins” and “Outs” of mesenchymal stem cell osteogenesis in regenerative medicine

Repair and regeneration of bone requires mesenchymal stem cells that by self-renewal, are able to generate a critical mass of cells with the ability to differentiate into osteoblasts that can produce bone protein matrix (osteoid) and enable its mineralization. The number of human mesenchymal stem cells (hMSCs) diminishes with age and ex vivo replication of hMSCs has limited potential. While propagating hMSCs under hypoxic conditions may maintain their ability to self-renew, the strategy of using human telomerase reverse transcriptase (hTERT) to allow for hMSCs to prolong their replicative lifespan is an attractive means of ensuring a critical mass of cells with the potential to differentiate into various mesodermal structural tissues including bone. However, this strategy must be tempered by the oncogenic potential of TERT-transformed cells, or their ability to enhance already established cancers, the unknown differentiating potential of high population doubling hMSCs and the source of hMSCs (e.g., bone marrow, adipose-derived, muscle-derived, umbilical cord blood, etc.) that may provide peculiarities to self-renewal, differentiation, and physiologic function that may differ from non-transformed native cells. Tissue engineering approaches to use hMSCs to repair bone defects utilize the growth of hMSCs on three-dimensional scaffolds that can either be a base on which hMSCs can attach and grow or as a means of sequestering growth factors to assist in the chemoattraction and differentiation of native hMSCs. The use of whole native extracellular matrix (ECM) produced by hMSCs, rather than individual ECM components, appear to be advantageous in not only being utilized as a three-dimensional attachment base but also in appropriate orientation of cells and their differentiation through the growth factors that native ECM harbor or in simulating growth factor motifs. The origin of native ECM, whether from hMSCs from young or old individuals is a critical factor in “rejuvenating” hMSCs from older individuals grown on ECM from younger individuals.

Stromal cell-derived factor-1 receptor CXCR4-overexpressing bone marrow mesenchymal stem cells accelerate wound healing by migrating into skin injury areas

Stromal cell-derived factor-1 (SDF-1) and its membrane receptor C-X-C chemokine receptor type 4 (CXCR4) are involved in the homing and migration of multiple stem cell types, neovascularization, and cell proliferation. This study investigated the hypothesis that bone marrow-derived mesenchymal stem cells (BMSCs) accelerate skin wound healing in the mouse model by overexpression of CXCR4 in BMSCs. We compared SDF-1 expression and skin wound healing times of BALB/c mice, severe combined immunodeficiency (SCID) mice, and immune system-deficient nude mice after (60)Co radiation-induced injury of their bone marrow. The occurrence of transplanted adenovirus-transfected CXCR4-overexpressing male BMSCs in the wound area was compared with the occurrence of untransfected male BALB/c BMSCs in (60)Co-irradiated female mice skin wound healing areas by Y chromosome marker analyses. The wound healing time of BALB/c mice was 14.00±1.41 days, whereas for the nude and SCID mice it was 17.16±1.17 days and 19.83±0.76 days, respectively. Male BMSCs could be detected in the surrounding areas of (60)Co-irradiated female BALB/c mice wounds, and CXCR4-overexpressing BMSCs accelerated the wound healing time. CXCR4-overexpressing BMSCs migrate in an enhanced manner to skin wounds in a SDF-1-expression-dependent manner, thereby reducing the skin wound healing time.

S100A16 inhibits osteogenesis but stimulates adipogenesis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have the capacity to differentiate into osteoblasts and adipocytes. Bone marrow adipogenesis exerts an inhibitory effect on osteogenesis, which leads to osteoporosis. S100A16, a novel member of the S100 family, is ubiquitously expressed, and markedly enhances adipogenesis. The aim of this study was to demonstrate, in the mouse BM-MSC model, whether S100A16 significantly stimulates adipogenic, rather than osteogenic differentiation. The overexpression of S100A16 led to a significant increase in Oil Red O staining (a marker of adipocyte differentiation) but a decrease in Alizarin Red S staining (a marker of osteoblast differentiation). In contrast, reducing the expression of S100A16 resulted in minimal Oil Red O staining but increased Alizarin Red S staining. During differentiation into osteoblasts, RUNX2 expression increased fourfold in the S100A16(KO+/-) BM-MSCs, but only increased by approximately 1.5-fold in the S100A16(TG+/+) BM-MSCs. And BMP2 occurred in the same changes. Upon induction of BM-MSC differentiation into adipocytes, peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer binding protein-α expression were significantly higher in the cells overexpressing S100A16 protein but lower in the cells with reduced expression of S100A16 protein, compared with the control cells, which were BM-MSCs derived from C57/BL6. S100A16 increased PPARγ promoter luciferase activity and decreased RUNX2 promoter luciferase activity. ERK1/2 phosphorylation was stimulated during osteogenesis, whereas p-JNK phosphorylation was increased by stimulation of adipogenesis. Our results suggest that S100A16 inhibits osteogenesis but stimulates adipogenesis by increasing the transcription of PPARγ and decreasing the transcription of RUNX2. The ERK1/2 pathway is involved in the regulation of osteogenesis whereas the JNK pathway is involved in adipogenesis.

Mesenchymal autologous stem cells

The use of cell-based therapies for spinal cord injuries has recently gained prominence as a potential therapy or component of a combination strategy. Experimental and clinical studies have been performed using mesenchymal stem cell therapy to treat spinal cord injuries with encouraging results. However, there have been reports on the adverse effects of these stem cell-based therapies, especially in the context of tumor modulation. This article surveys the literature relevant to the potential of mesenchymal autologous stem cells for spinal cord injuries and their clinical implications.

Isolation and characterization of the environmental bacterial and fungi contamination in a pharmaceutical unit of mesenchymal stem cell for clinical use

Design and implementation of an environmental monitoring program is vital to assure the maintenance of acceptable quality conditions in a pharmaceutical manufacturing unit of human mesenchymal stem cells. Since sterility testing methods require 14 days and these cells are only viable for several hours, they are currently administered without the result of this test. Consequently environmental monitoring is a key element in stem cell banks for assuring low levels of potential introduction of contaminants into the cell products. The aim of this study was to qualitatively and quantitatively analyze the environmental microbiological quality in a pharmaceutical manufacturing unit of human mesenchymal stem cells production for use in advanced therapies. Two hundred and sixty one points were tested monthly during one year, 156 from air and 105 from surfaces. Among the 6264 samples tested, 231 showed contamination, 76.6% for bacteria and 23.4% for fungi. Microbial genuses isolated were Staphylococcus (89.7%), Microccocus (4.5%), Kocuria (3.2%) and Bacillus (2.6%). In the identification of fungi, three genuses were detected: Aspergillus (56%), Penicillium (26%) and Cladosporium (18%). The origin of the contamination was found to be due to personnel manipulation and air microbiota. For all sampling methods, alert limits were set and corrective measures suggested.

Fibrin glue as the cell-delivery vehicle for mesenchymal stromal cells in regenerative medicine

The use of tissue-engineering techniques such as stem-cell therapy to renew injured tissues is a promising strategy in regenerative medicine. As a cell-delivery vehicle, fibrin glues (FG) facilitate cell attachment, growth and differentiation and, ultimately, tissue formation and organization by its three-dimensional structure. Numerous studies have provided evidence that stromal cells derived from bone marrow (bone marrow stromal cells; BMSC) and adipose tissue (adipose-derived stromal cells; ADSC) contain a population of adult multipotent mesenchymal stromal cells (MSC) and endothelial progenitor cells that can differentiate into several lineages. By combining MSC with FG, the implantation could take advantage of the mutual benefits. Researchers and physicians have pinned their hopes on stem cells for developing novel approaches in regenerative medicine. This review focuses on the therapeutic potential of MSC with FG in bone defect reconstruction, cartilage and tendon injury repair, ligament, heart and nerve regeneration, and, furthermore, wound healing.

Epigenetic regulation of mesenchymal stem cells: a focus on osteogenic and adipogenic differentiation

Stem cells are characterized by their capability to self-renew and terminally differentiate into multiple cell types. Somatic or adult stem cells have a finite self-renewal capacity and are lineage-restricted. The use of adult stem cells for therapeutic purposes has been a topic of recent interest given the ethical considerations associated with embryonic stem (ES) cells. Mesenchymal stem cells (MSCs) are adult stem cells that can differentiate into osteogenic, adipogenic, chondrogenic, or myogenic lineages. Owing to their ease of isolation and unique characteristics, MSCs have been widely regarded as potential candidates for tissue engineering and repair. While various signaling molecules important to MSC differentiation have been identified, our complete understanding of this process is lacking. Recent investigations focused on the role of epigenetic regulation in lineage-specific differentiation of MSCs have shown that unique patterns of DNA methylation and histone modifications play an important role in the induction of MSC differentiation toward specific lineages. Nevertheless, MSC epigenetic profiles reflect a more restricted differentiation potential as compared to ES cells. Here we review the effect of epigenetic modifications on MSC multipotency and differentiation, with a focus on osteogenic and adipogenic differentiation. We also highlight clinical applications of MSC epigenetics and nuclear reprogramming.

Endothelial origin of mesenchymal stem cells

Mesenchymal stem/stromal cells (MSCs) are fibroblastoid cells capable of long-term expansion and skeletogenic differentiation. While MSCs are known to originate from neural crest and mesoderm, immediate mesodermal precursors that give rise to MSCs have not been characterized. Recently, using human embryonic stem cells (hESCs), we demonstrated that mesodermal MSCs arise from APLNR+ precursors with angiogenic potential, mesenchymoangioblasts, which can be identified by FGF2-dependent colony-forming assay in serum-free semisolid medium. In this overview we provide additional insights on cellular pathways leading to MSC establishment from mesoderm, with special emphasis on endothelial-mesenchymal transition as a critical step in MSC formation. In addition, we highlight an essential role of FGF2 in induction of angiogenic cells with potential to transform into MSCs (mesenchymoangioblasts) or hematopoietic cells (hemangioblasts) from mesoderm, and discuss correlations of our in vitro findings with the course of angioblast development during embryogenesis.

Long term culture of mesenchymal stem cells in hypoxia promotes a genetic program maintaining their undifferentiated and multipotent status

Background

In the bone marrow, hematopietic and mesenchymal stem cells form a unique niche in which the oxygen tension is low. Hypoxia may have a role in maintaining stem cell fate, self renewal and multipotency. However, whereas most studies addressed the effect of transient in vitro exposure of MSC to hypoxia, permanent culture under hypoxia should reflect the better physiological conditions.

Results

Morphologic studies, differentiation and transcriptional profiling experiments were performed on MSC cultured in normoxia (21% O₂) versus hypoxia (5% O₂) for up to passage 2. Cells at passage 0 and at passage 2 were compared, and those at passage 0 in hypoxia generated fewer and smaller colonies than in normoxia. In parallel, MSC displayed (>4 fold) inhibition of genes involved in DNA metabolism, cell cycle progression and chromosome cohesion whereas transcripts involved in adhesion and metabolism (CD93, ESAM, VWF, PLVAP, ANGPT2, LEP, TCF1) were stimulated. Compared to normoxic cells, hypoxic cells were morphologically undifferentiated and contained less mitochondrias. After this lag phase, cells at passage 2 in hypoxia outgrew the cells cultured in normoxia and displayed an enhanced expression of genes (4-60 fold) involved in extracellular matrix assembly (SMOC2), neural and muscle development (NOG, GPR56, SNTG2, LAMA) and epithelial development (DMKN). This group described herein for the first time was assigned by the Gene Ontology program to "plasticity".

Conclusion

The duration of hypoxemia is a critical parameter in the differentiation capacity of MSC. Even in growth promoting conditions, hypoxia enhanced a genetic program that maintained the cells undifferentiated and multipotent. This condition may better reflect the in vivo gene signature of MSC, with potential implications in regenerative medicine.

A mesoderm-derived precursor for mesenchymal stem and endothelial cells

Among the three embryonic germ layers, the mesoderm is a major source of the mesenchymal precursors giving rise to skeletal and connective tissues, but these precursors have not previously been identified and characterized. Using human embryonic stem cells directed toward mesendodermal differentiation, we show that mesenchymal stem/stromal cells (MSCs) originate from a population of mesodermal cells identified by expression of apelin receptor. In semisolid medium, these precursors form FGF2-dependent compact spheroid colonies containing mesenchymal cells with a transcriptional profile representative of mesoderm-derived embryonic mesenchyme. When transferred to adherent cultures, individual colonies give rise to MSC lines with chondro-, osteo-, and adipogenic differentiation potentials. Although the MSC lines lacked endothelial potential, endothelial cells could be derived from the mesenchymal colonies, suggesting that, similar to hematopoietic cells, MSCs arise from precursors with angiogenic potential. Together, these studies identified a common precursor of mesenchymal and endothelial cells, mesenchymoangioblast, as the source of mesoderm-derived MSCs.

Lineage-specific promoter DNA methylation patterns segregate adult progenitor cell types

Mesenchymal stem cells (MSCs) can differentiate into multiple mesodermal cell types in vitro; however, their differentiation capacity is influenced by their tissue of origin. To what extent epigenetic information on promoters of lineage-specification genes in human progenitors influences transcriptional activation and differentiation potential remains unclear. We produced bisulfite sequencing maps of DNA methylation in adipogenic, myogenic, and endothelial promoters in relation to gene expression and differentiation capacity, and unravel a similarity in DNA methylation profiles between MSCs isolated from human adipose tissue, bone marrow (BM), and muscle. This similarity is irrespective of promoter CpG content. Methylation patterns of MSCs are distinct from those of hematopoietic progenitor cells (HPCs), pluripotent human embryonic stem cells (hESCs), and multipotent hESC-derived mesenchymal cells (MCs). Moreover, in vitro MSC differentiation does not affect lineage-specific promoter methylation states, arguing that these methylation patterns in differentiated cells are already established at the progenitor stage. Further, we find a correlation between lineage-specific promoter hypermethylation and lack of differentiation capacity toward that lineage, but no relationship between weak promoter methylation and capacity of transcriptional activation or differentiation. Thus, only part of the restriction in differentiation capacity of tissue-specific stem cells is programmed by promoter DNA methylation: hypermethylation seems to constitute a barrier to differentiation, however, no or weak methylation has no predictive value for differentiation potential.

Defining human mesenchymal stem cell efficacy in vivo

Allogeneic human mesenchymal stem cells (hMSCs) can suppress graft versus host disease (GvHD) and have profound anti-inflammatory and regenerative capacity in stroke, infarct, spinal cord injury, meniscus regeneration, tendinitis, acute renal failure, and heart disease in human and animal models of disease. There is significant clinical hMSC variability in efficacy and the ultimate response in vivo. The challenge in hMSC based therapy is defining the efficacy of hMSC in vivo. Models which may provide insight into hMSC bioactivity in vivo would provide a means to distinguish hMSCs for clinical utility. hMSC function has been described as both regenerative and trophic through the production of bioactive factors. The regenerative component involves the multi-potentiality of hMSC progenitor differentiation. The secreted factors generated by the hMSCs are milieu and injury specific providing unique niches for responses in vivo. These bioactive factors are anti-scarring, angiogenic, anti-apoptotic as well as regenerative. Further, from an immunological standpoint, hMSC's can avoid host immune response, providing xenographic applications. To study the in vivo immuno-regulatory effectiveness of hMSCs, we used the ovalbumin challenge model of acute asthma. This is a quick 3 week in vivo pulmonary inflammation model with readily accessible ways of measuring effectiveness of hMSCs. Our data show that there is a direct correlation between the traditional ceramic cube score to hMSCs attenuation of cellular recruitment due to ovalbumin challenge. The results from these studies verify the in vivo immuno-modulator effectiveness of hMSCs and support the potential use of the ovalbumin model as an in vivo model of hMSC potency and efficacy. Our data also support future directions toward exploring hMSCs as an alternative therapeutic for the treatment of airway inflammation associated with asthma.

The human nose harbors a niche of olfactory ectomesenchymal stem cells displaying neurogenic and osteogenic properties

We previously identified multipotent stem cells within the lamina propria of the human olfactory mucosa, located in the nasal cavity. We also demonstrated that this cell type differentiates into neural cells and improves locomotor behavior after transplantation in a rat model of Parkinson's disease. Yet, next to nothing is known about their specific stemness characteristics. We therefore devised a study aiming to compare olfactory lamina propria stem cells from 4 individuals to bone marrow mesenchymal stem cells from 4 age- and gender-matched individuals. Using pangenomic microarrays and immunostaining with 34 cell surface marker antibodies, we show here that olfactory stem cells are closely related to bone marrow stem cells. However, olfactory stem cells also exhibit singular traits. By means of techniques such as proliferation assay, cDNA microarrays, RT-PCR, in vitro and in vivo differentiation, we report that when compared to bone marrow stem cells, olfactory stem cells display (1) a high proliferation rate; (2) a propensity to differentiate into osseous cells; and (3) a disinclination to give rise to chondrocytes and adipocytes. Since peripheral olfactory stem cells originate from a neural crest-derived tissue and, as shown here, exhibit an increased expression of neural cell-related genes, we propose to name them olfactory ectomesenchymal stem cells (OE-MSC). Further studies are now required to corroborate the therapeutic potential of OE-MSCs in animal models of bone and brain diseases.

Human mesenchymal stem cells suppress chronic airway inflammation in the murine ovalbumin asthma model

Allogeneic human mesenchymal stem cells (hMSCs) introduced intravenously can have profound anti-inflammatory activity resulting in suppression of graft vs. host disease as well as regenerative events in the case of stroke, infarct, spinal cord injury, meniscus regeneration, tendinitis, acute renal failure, and heart disease in human and animal models of these diseases. hMSCs produce bioactive factors that provide molecular cuing for: 1) immunosuppression of T cells; 2) antiscarring; 3) angiogenesis; 4) antiapoptosis; and 5) regeneration (i.e., mitotic for host-derived progenitor cells). Studies have shown that hMSCs have profound effects on the immune system and are well-tolerated and therapeutically active in immunocompetent rodent models of multiple sclerosis and stroke. Furthermore, intravenous administration of MSCs results in pulmonary localization. Asthma is a major debilitating pulmonary disease that impacts in excess of 150 million people in the world with uncontrolled asthma potentially leading to death. In addition, the socioeconomic impact of asthma-associated illnesses at the pediatric and adult level are in the millions of dollars in healthcare costs and lost days of work. hMSCs may provide a viable multiaction therapeutic for this inflammatory lung disease by secreting bioactive factors or directing cellular activity. Our studies show the effectiveness and specificity of the hMSCs on decreasing chronic airway inflammation associated with the murine ovalbumin model of asthma. In addition, the results from these studies verify the in vivo immunoeffectiveness of hMSCs in rodents and support the potential therapeutic use of hMSCs for the treatment of airway inflammation associated with chronic asthma.

Morphological and immunocytochemical characteristics indicate the yield of early progenitors and represent a quality control for human mesenchymal stem cell culturing

Human mesenchymal stem cells (hMSC) are a heterogeneous cell population, which is reflected in varying morphological and biological properties. Three subpopulations with intrinsic characteristics can be distinguished: small rapidly self-renewing cells, spindle-shaped cells and large, flattened cells. Unfortunately, it has neither been possible to morphologically define these distinct cells consistently, nor to relate them to specific surface marker features. Here, the primary hMSC subpopulations of three donors are clearly defined by maximum cell diameter and area. Furthermore, these cells were stained for the putative hMSC surface markers CD105, CD90 as well as CD73, and evaluated by three-colour flow cytometry and simultaneous multicolour immunocytochemistry. Interestingly, cell cultures with a high rate of triple-positive hMSC featured a higher content of rapidly self-renewing cells. On the other hand, a higher fraction of flattened cells correlated with a loss of one or more hMSC surface markers. The expression of CD73 showed the highest heterogeneity. Immunocytochemistry further confirmed that flattened cells mainly lack CD73 expression, whereas rapidly self-renewing cells were steadily positive for all three hMSC markers. In the literature, hMSC properties are especially conceded to rapidly self-renewing cells, whereas flattened cells have been suggested to represent early stages of lineage-specific progenitors. We reveal that among the recently suggested surface markers, CD73 is the most sensitive, as it seems to be down-regulated in the early stages of differentiation. Our morphological and immunocytochemical characterization of hMSC subpopulations indicates the yield of early multipotent hMSC and thereby provides a quality control approach for hMSC culturing.

Promoter DNA methylation patterns of differentiated cells are largely programmed at the progenitor stage

The molecular background for the similarity of mesenchymal progenitor cells from various tissues is unknown. We characterize DNA methylation profiles of RefSeq promoters in relation to gene expression and differentiation in progenitors from adipose tissue, bone marrow, and muscle. Our data support the view of a common origin of mesenchymal progenitors.

Mesenchymal stem cells (MSCs) isolated from various tissues share common phenotypic and functional properties. However, intrinsic molecular evidence supporting these observations has been lacking. Here, we unravel overlapping genome-wide promoter DNA methylation patterns between MSCs from adipose tissue, bone marrow, and skeletal muscle, whereas hematopoietic progenitors are more epigenetically distant from MSCs as a whole. Commonly hypermethylated genes are enriched in signaling, metabolic, and developmental functions, whereas genes hypermethylated only in MSCs are associated with early development functions. We find that most lineage-specification promoters are DNA hypomethylated and harbor a combination of trimethylated H3K4 and H3K27, whereas early developmental genes are DNA hypermethylated with or without H3K27 methylation. Promoter DNA methylation patterns of differentiated cells are largely established at the progenitor stage; yet, differentiation segregates a minor fraction of the commonly hypermethylated promoters, generating greater epigenetic divergence between differentiated cell types than between their undifferentiated counterparts. We also show an effect of promoter CpG content on methylation dynamics upon differentiation and distinct methylation profiles on transcriptionally active and inactive promoters. We infer that methylation state of lineage-specific promoters in MSCs is not a primary determinant of differentiation capacity. Our results support the view of a common origin of mesenchymal progenitors.

Extensive adipogenic and osteogenic differentiation of patterned human mesenchymal stem cells in a microfluidic device

Microtechnology offers great prospects for cellular research by enabling controlled experimental conditions that cannot be achieved by traditional methods. This study demonstrates the use of a microfluidic platform for long-term cultivation (3 weeks) of human mesenchymal stem-like cells (MSCs), a cell population of high interest for tissue engineering. The typical high motility of the MSCs required a strategy for preventing cells from inhabiting the feeding channels and thus interfere with a steady perfusion of medium to the cell cultivation chamber. Hence, a straightforward and long-term patterning method was developed and implemented for reliable cell positioning within the device. This method was based on the modification of a polystyrene substrate into cell supportive and non-supportive regions by the use of selective oxygen plasma treatment and the triblock copolymer Pluronic. Also, a novel and size-effective "flip-chip" set-up for operating the devices was invented. Successful and reproducible adipogenic and osteogenic differentiation of MSCs in the device was demonstrated, verifying that an adequate long-term microfluidic cultivation environment was obtained. Strengths of the experimental protocol include ease of fabrication and maintenance (gravity driven), good cell performance (viability/differentiation), as well as the possibility of exposing the culture to heterogeneous laminar flow for experimental purposes.

Mesenchymal stem cell: present challenges and prospective cellular cardiomyoplasty approaches for myocardial regeneration

Myocardial ischemia and cardiac dysfunction have been known to follow ischemic heart diseases (IHDs). Despite a plethora of conventional treatment options, their efficacies are associated with skepticism. Cell therapies harbor a promising potential for vascular and cardiac repair, which is corroborated by adequate preclinical evidence. The underlying objectives behind cardiac regenerative therapies subsume enhancing angiomyogenesis in the ischemic myocardium, ameliorating cellular apoptosis, regenerating the damaged myocardium, repopulating the lost resident myocardial cells (smooth muscle, cardiomyocyte, and endothelial cells), and finally, decreasing fibrosis with a consequent reduction in ventricular remodeling. Although-cell based cardiomyoplasty approaches have an immense potential, their clinical utilization is limited owing to the increased need for better candidates for cellular cardiomyoplasty, better routes of delivery, appropriate dose for efficient engraftment, and better preconditioning or genetic-modification strategies for the progenitor and stem cells. Mesenchymal stem cells (MSCs) have emerged as powerful candidates in mediating myocardial repair owing to their unique properties of multipotency, transdifferentiation, intercellular connection with the resident cardiomyocytes via connexin 43 (Cx43)-positive gap junctions in the myocardium, and most important, immunomodulation. In this review, we present an in-depth discussion on the complexities associated with stem and progenitor cell therapies, the potential of preclinical approaches involving MSCs for myocardial repair, and an account of the past milestones and ongoing MSC-based trials in humans.

5-Azacytidine facilitates osteogenic gene expression and differentiation of mesenchymal stem cells by alteration in DNA methylation

Mesenchymal stem cells (MSCs) are considered to be one of the most promising therapeutic cell sources as they encompass a plasticity of multiple cell lineages. The challenge in using these cells lies in developing well-defined protocols for directing cellular differentiation to generate a desired lineage. In this study, we investigated the effect of 5-azacytidine, a DNA demethylating agent, on osteogenic differentiation of MSCs. The cells were exposed to 5-azacytidine in culture medium for 24 h prior to osteogenic induction. Osteogenic differentiation was determined by several the appearance of a number of osteogenesis characteristics, including gene expression, ALP activity, and calcium mineralization. Pretreatment of MSCs with 5-azacytidine significantly facilitated osteogenic differentiation and was accompanied by hypomethylation of genomic DNA and increased osteogenic gene expression. Taking dlx5 as a representative, methylation alterations of the "CpG island shore" in the promoter caused by 5-azacytidine appeared to contribute to osteogenic differentiation.

Rapid large-scale expansion of functional mesenchymal stem cells from unmanipulated bone marrow without animal serum

Adult mesenchymal stem cells (MSCs) are considered as valuable mediators for tissue regeneration and cellular therapy. This study was performed to develop conditions for regularly propagating a clinical quantity of > 2 x 10(8) MSCs without animal serum from small bone marrow (BM) aspiration volumes within short time. We established optimized culture conditions with pooled human platelet lysate (pHPL) replacing fetal bovine serum (FBS) for MSC propagation. MSC quality, identity, purity, and function were assessed accordingly. Biologic safety was determined by bacterial/fungal/mycoplasma/endotoxin testing and genomic stability by array comparative genomic hybridization (CGH). We demonstrate that unmanipulated BM can be used to efficiently initiate MSC cultures without the need for cell separation. Just diluting 1.5-5 mL heparinized BM per 500 mL minimum essential medium supplemented with L-glutamine, heparin, and 10% pHPL sufficiently supported the safe propagation of 7.8 +/- 1.5 x 10(8) MSCs within a single 11- to 16-day primary culture under defined conditions. This procedure also resulted in sustained MSC colony recovery. MSC purity, immune phenotype, and in vitro differentiation potential fully matched current criteria. Despite high proliferation rate, MSCs showed genomic stability in array CGH. This easy single-phase culture procedure can build the basis for standardized manufacturing of MSC-based therapeutics under animal serum-free conditions for dose-escalated cellular therapy and tissue engineering.

Cytosine deaminase expressing human mesenchymal stem cells mediated tumour regression in melanoma bearing mice

BACKGROUND

Previously, we validated capability of human adipose tissue-derived mesenchymal stem cells (AT-MSC) to serve as cellular vehicles for gene-directed enzyme prodrug molecular chemotherapy. Yeast fusion cytosine deaminase : uracil phosphoribosyltransferase expressing AT-MSC (CD y-AT-MSC) combined with systemic 5-fluorocytosine (5FC) significantly inhibited growth of human colon cancer xenografts. We aimed to determine the cytotoxic efficiency to other tumour cells both in vitro and in vivo.

METHODS

CD y-AT-MSC/5FC-mediated proliferation inhibition against a panel of human tumour cells lines was evaluated in direct and indirect cocultures in vitro. Antitumour effect was tested on immunodeficient mouse model in vivo.

RESULTS

Although culture expansion of CD y-AT-MSC sensitized these cells to 5FC mediated suicide effect, expanded CD y-AT-MSC/5FC still exhibited strong bystander cytotoxic effect towards human melanoma, glioblastoma, colon, breast and bladder carcinoma in vitro. Most efficient inhibition (91%) was observed in melanoma A375 cell line when directly cocultured with 2% of therapeutic cells CD y-AT-MSC/5FC. The therapeutic paradigm of the CD y -AT-MSC/5FC system was further evaluated on melanoma A375 xenografts on nude mice in vivo. Complete regression in 89% of tumours was achieved when 20% CD y-AT-MSC/5FC were co-injected along with tumour cells. More importantly, systemic CD y-AT-MSC administration resulted in therapeutic cell homing into subcutaneous melanoma and mediated tumour growth inhibition.

CONCLUSIONS

CD y-AT-MSC capability of targeting subcutaneous melanoma offers a possibility to selectively produce cytotoxic agent in situ. Our data further demonstrate beneficial biological properties of AT-MSC as a cellular vehicle for enzyme/prodrug therapy approach to molecular chemotherapy.

Bovine endometrial stromal cells display osteogenic properties

The endometrium is central to mammalian fertility. The endometrial stromal cells are very dynamic, growing and differentiating throughout the estrous cycle and pregnancy. In humans, stromal cells appear to have progenitor or stem cell capabilities and the cells can even differentiate into bone. It is not clear whether bovine endometrial stromal cells exhibit a similar phenotypic plasticity. So, the present study tested the hypothesis that bovine endometrial stromal cells could be differentiated along an osteogenic lineage. Pure populations of bovine stromal cells were isolated from the endometrium. The endometrial stromal cell phenotype was confirmed by morphology, prostaglandin secretion, and susceptibility to viral infection. However, cultivation of the cells in standard endometrial cell culture medium lead to a mesenchymal phenotype similar to that of bovine bone marrow cells. Furthermore, the endometrial stromal cells developed signs of osteogenesis, such as alizarin positive nodules. When the stromal cells were cultured in a specific osteogenic medium the cells rapidly developed the characteristics of mineralized bone. In conclusion, the present study has identified that stromal cells from the bovine endometrium show a capability for phenotype plasticity similar to mesenchymal progenitor cells. These observations pave the way for further investigation of the mechanisms of stroma cell differentiation in the bovine reproductive tract.

Recent progress on tissue-resident adult stem cell biology and their therapeutic implications

Recent progress in the field of the stem cell research has given new hopes to treat and even cure diverse degenerative disorders and incurable diseases in human. Particularly, the identification of a rare population of adult stem cells in the most tissues/organs in human has emerged as an attractive source of multipotent stem/progenitor cells for cell replacement-based therapies and tissue engineering in regenerative medicine. The tissue-resident adult stem/progenitor cells offer the possibility to stimulate their in vivo differentiation or to use their ex vivo expanded progenies for cell replacement-based therapies with multiple applications in human. Among the human diseases that could be treated by the stem cell-based therapies, there are hematopoietic and immune disorders, multiple degenerative disorders, such as Parkinson's and Alzheimer's diseases, type 1 or 2 diabetes mellitus as well as eye, liver, lung, skin and cardiovascular disorders and aggressive and metastatic cancers. In addition, the genetically-modified adult stem/progenitor cells could also be used as delivery system for expressing the therapeutic molecules in specific damaged areas of different tissues. Recent advances in cancer stem/progenitor cell research also offer the possibility to targeting these undifferentiated and malignant cells that provide critical functions in cancer initiation and progression and disease relapse for treating the patients diagnosed with the advanced and metastatic cancers which remain incurable in the clinics with the current therapies.

Clinical Protocols for the Isolation and Expansion of Mesenchymal Stromal Cells

SUMMARY: Multipotent mesenchymal stromal cells (MSCs) are currently exploited in numerous clinical trials to investigate their potential in immune regulation, hematopoiesis, and tissue regeneration. The low frequency of MSCs necessitates cell expansion to achieve transplantable numbers. The challenge is to assure safe and high-quality cell production. GMP(Good Manufacturing Practice)-graded cell processing such as cell preparation, culture, and manipulation is mandatory for the progress of such advanced cell therapy. This review summarizes protocols to isolate MSCs from bone marrow and adipose tissue and to expand MSCs for clinical use focussing on culture media composition as well as culture devices and assays to ensure and control quality of the final product.

In vivo isolation and characterization of stem cells with diverse phenotypes using growth factor impregnated biomatrices

Background

The stimulation to differentiate into specific cell types for somatic stem cells is largely due to a series of internal and external signals coming from the microenvironment that surrounds the stem cell. Even though intensive research has been made, the basic mechanisms of plasticity and/or the molecules regulating stem cells proliferation and differentiation are not completely determined. Potential answers concerning the problems could be derived from the studies of stem cells in culture.

Methodology/Principle Findings

We combine a new procedure (using the matrigel biopolymer supplemented with a selected cytokine/growth factor) with classic techniques such as light, confocal and electron microscopy, immunohistochemistry and cell culture, to perform an analysis on stem cells involved in the leech (Hirudo medicinalis) repair tissues. The leech has a relative anatomical simplicity and is a reliable model for studying a variety of basic events, such as tissue repair, which has a striking similarity with vertebrate responses. Our data demonstrate that the injection of an appropriate combination of the matrigel biopolymer supplemented with a selected cytokine/growth factor in the leech Hirudo medicinalis is a remarkably effective tool for isolating a specific cell population in vivo. A comparative analysis of biopolymer in vivo sorted stem cells indicates that VEGF recruited cells of a hematopoietic/endothelial phenotype whereas MCP-1/CCL2 isolated cells that were of an early myeloid lineage.

Conclusion

Our paper describes, for the first time, a method allowing not only the isolation of a specific cell population in relation to the cytokine utilized but also the possibility to culture a precise cell type whose isolation is otherwise quite difficult. This approach could be broadly applied to isolate stem cells of diverse origins based on the recruitment stimuli employed.