Mesenchymal stem cells use integrin beta1 not CXC chemokine receptor 4 for myocardial migration and engraftment

WITHDRAWN: Molecular Characteristics of Bone Marrow Mesenchymal Stem Cells: An Appealing Source for Regenerative Medicine

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.hlc.2012.04.021. The duplicate article has therefore been withdrawn.

Adenoviral transduction of mesenchymal stem cells: in vitro responses and in vivo immune responses after cell transplantation

Adult mesenchymal stem cells (MSCs) are non-hematopoietic cells with multi-lineage potential which makes them attractive targets for regenerative medicine applications. However, to date, therapeutic success of MSC-therapy is limited and the genetic modification of MSCs using viral vectors is one option to improve their therapeutic potential. Ex-vivo genetic modification of MSCs using recombinant adenovirus (Ad) could be promising to reduce undesired immune responses as Ad will be removed before cell/tissue transplantation. In this regard, we investigated whether Ad-modification of MSCs alters their immunological properties in vitro and in vivo. We found that Ad-transduction of MSCs does not lead to up-regulation of major histocompatibility complex class I and II and co-stimulatory molecules CD80 and CD86. Moreover, Ad-transduction caused no significant changes in terms of pro-inflammatory cytokine expression, chemokine and chemokine receptor and Toll-like receptor expression. In addition, Ad-modification of MSCs had no affect on their ability to suppress T cell proliferation in vitro. In vivo injection of Ad-transduced MSCs did not change the frequency of various immune cell populations (antigen presenting cells, T helper and cytotoxic T cells, natural killer and natural killer T cells) neither in the blood nor in tissues. Our results indicate that Ad-modification has no major influence on the immunological properties of MSCs and therefore can be considered as a suitable gene vector for therapeutic applications of MSCs.

Harnessing the mesenchymal stem cell secretome for the treatment of cardiovascular disease

The broad repertoire of secreted trophic and immunomodulatory cytokines produced by mesenchymal stem cells (MSCs), generally referred to as the MSC secretome, has considerable potential for the treatment of cardiovascular disease. However, harnessing this MSC secretome for meaningful therapeutic outcomes is challenging due to the limited control of cytokine production following their transplantation. This review outlines the current understanding of the MSC secretome as a therapeutic for treatment of ischemic heart disease. We discuss ongoing investigative directions aimed at improving cellular activity and characterizing the secretome and its regulation in greater detail. Finally, we provide insights on and perspectives for future development of the MSC secretome as a therapeutic tool.

Activation of Toll-like receptor 3 amplifies mesenchymal stem cell trophic factors and enhances therapeutic potency

Clinical trials of bone marrow mesenchymal stem cell (MSC) therapy have thus far demonstrated moderate and inconsistent benefits, indicating an urgent need to improve therapeutic efficacy. Although administration of sufficient cells is necessary to achieve maximal therapeutic benefits, documented MSC clinical trials have largely relied on injections of ∼1 × 10(6) cells/kg, which appears too low to elicit a robust therapeutic response according to published preclinical studies. However, repeated cell passaging necessary for large-scale expansion of MSC causes cellular senescence and reduces stem cell potency. Using the RNA mimetic polyinosinic-polycytidylic acid [poly(I:C)] to engage MSC Toll-like receptor 3 (TLR3), we found that poly(I:C), signaling through multiple mitogen-activated protein kinase pathways, induced therapeutically relevant trophic factors such as interleukin-6-type cytokines, stromal-derived factor 1, hepatocyte growth factor, and vascular endothelial growth factor while slightly inhibiting the proliferation and migration potentials of MSC. At the suboptimal injection dose of 1 × 10(6) cells/kg, poly(I:C)-treated MSC, but not untreated MSC, effectively stimulated regeneration of the failing hamster heart 1 mo after cell administration. The regenerating heart exhibited increased CD34(+)/Ki67(+) and CD34(+)/GATA4(+) progenitor cells in the presence of decreased inflammatory cells and cytokines. Cardiac functional improvement was associated with a ∼50% reduction in fibrosis, a ∼40% reduction in apoptosis, and a ∼55% increase in angiogenesis, culminating in prominent cardiomyogenesis evidenced by abundant distribution of small myocytes and a ∼90% increase in wall thickening. These functional, histological, and molecular characterizations thus establish the utility of TLR3 engagement for enabling the low-dose MSC therapy that may be translated to more efficacious clinical applications.

The role of chemokines in mesenchymal stem cell homing to myocardium

A growing body of preclinical evidence suggests that mesenchymal stem cells (MSCs) are effective for the structural and functional recovery of the infracted heart. Accordingly, clinical trials are underway to determine the benefit of MSC-based therapies. While systemic administration of MSCs is an attractive strategy, and is the route currently used for the administration of MSCs in clinical studies for myocardial infarction, the majority of infused cells do not appear to localize to infracted myocardium in animal studies. Recently, important progress has been made in identifying chemokine receptors critical for the migration and homing of MSCs. Here, we review recent literature regarding mechanisms of MSC homing and recruitment to the ischemic myocardium, and discuss potential influences of low engraftment rates of systemically administered MSCs to the infracted heart tissue on the effects of MSC-based therapies on myocardial infarction.

GMP-adapted overexpression of CXCR4 in human mesenchymal stem cells for cardiac repair

BACKGROUND

Human mesenchymal stem cells (MSC) have been utilized for cardiac regeneration after myocardial damage. Their clinical effects are marginal and only a minority of administered cells could make their way into the myocardium. The chemokine receptor CXCR4 has been identified as crucial for migration and homing of stem cells. In this study we overexpressed CXCR4 on human MSC to improve cell trafficking and tissue repair.

METHODS

Human MSC were isolated from the spongiosa of tibia and femur as well as from pelvic bone marrow. MSC were characterized by differentiation assays and FACS analysis. CXCR4 was overexpressed by mRNA-nucleofection. Intracellular signaling was analyzed to demonstrate functionality of CXCR4. The modified Boyden chamber, wounding assays and time lapse microscopy were utilized to investigate MSC migration.

RESULTS

MSC did not express relevant amounts of CXCR4 spontaneously. CXCR4 could be overexpressed in 93% of MSC with a cell viability of 62%. Functionality of the overexpressed CXCR4 was demonstrated by a significant cytosolic Ca(2+) increase and activation of different MAP kinases followed by SDF-1α stimulation. In contrast no improvement of cell migration could be observed. There was a strong basal MSC chemokinesis independent from CXCR4 expression.

CONCLUSIONS

CXCR4 could be effectively overexpressed in human MSC by mRNA-nucleofection. Despite functionality of CXCR4 MSC were characterized by a strong basal chemokinesis that could not be further enhanced by CXCR4 overexpression. As isolation, culture and nucleofection of pelvic bone marrow-derived MSC basically fulfill the GMP-requirements our approach seems suited for an in vivo application in patients.

Markers for characterization of bone marrow multipotential stromal cells

Given the observed efficacy of culture-expanded multipotential stromal cells, also termed mesenchymal stem cells (MSCs), in the treatment of graft-versus host and cardiac disease, it remains surprising that purity and potency characterization of manufactured cell batches remains rather basic. In this paper, we will initially discuss surface and molecular markers that were proposed to serve as the indicators of the MSC potency, in terms of their proliferative potential or the ability to differentiate into desired lineages. The second part of this paper will be dedicated to a critical discussion of surface markers of uncultured (i.e., native) bone marrow (BM) MSCs. Although no formal consensus has yet been reached on which markers may be best suited for prospective BM MSC isolation, markers that cross-react with MSCs of animal models (such as CD271 and W8-B2/MSCA-1) may have the strongest translational value. Whereas small animal models are needed to discover the in vivo function on these markers, large animal models are required for safety and efficacy testing of isolated MSCs, particularly in the field of bone and cartilage tissue engineering.

Perspectives on mesenchymal stem cells: tissue repair, immune modulation, and tumor homing

Mesenchymal stem cells (MSCs) or MSC-like cells have been identified in a variety of different tissues that share molecular expression profiles and biological functions but also retain a unique differentiation preference depending on their tissue origins. MSCs play beneficial roles in the healing of damaged tissue by directly differentiating to many different resident cell types and/or by secreting several trophic factors that aid tissue repair. Aside from MSCs' reparative stem cell function, they drive immune responses toward immunosuppression and anti-inflammation. This novel function of MSCs opens up new avenues for clinical development of MSC immune-therapeutics to treat uncontrollable, life threatening, severe, chronic inflammation and autoimmune disease. Unexpectedly high rates of MSCs' tumor homing capacity and their tumor supporting capability have also been noted in tumor-bearing animal models. In this review, we will discuss MSCs' basic cell biology and perspectives on MSCs in terms of tissue repair, immune modulation, and tumor homing.

Challenges for heart disease stem cell therapy

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The use of stem cells to improve recovery of the injured heart after myocardial infarction (MI) is an important emerging therapeutic strategy. However, recent reviews of clinical trials of stem cell therapy for MI and ischemic heart disease recovery report that less than half of the trials found only small improvements in cardiac function. In clinical trials, bone marrow, peripheral blood, or umbilical cord blood cells were used as the source of stem cells delivered by intracoronary infusion. Some trials administered only a stem cell mobilizing agent that recruits endogenous sources of stem cells. Important challenges to improve the effectiveness of stem cell therapy for CVD include: (1) improved identification, recruitment, and expansion of autologous stem cells; (2) identification of mobilizing and homing agents that increase recruitment; and (3) development of strategies to improve stem cell survival and engraftment of both endogenous and exogenous sources of stem cells. This review is an overview of stem cell therapy for CVD and discusses the challenges these three areas present for maximum optimization of the efficacy of stem cell therapy for heart disease, and new strategies in progress.

Empowering adult stem cells for myocardial regeneration

Treatment strategies for heart failure remain a high priority for ongoing research due to the profound unmet need in clinical disease coupled with lack of significant translational progress. The underlying issue is the same whether the cause is acute damage, chronic stress from disease, or aging: progressive loss of functional cardiomyocytes and diminished hemodynamic output. To stave off cardiomyocyte losses, a number of strategic approaches have been embraced in recent years involving both molecular and cellular approaches to augment myocardial structure and performance. Resultant excitement surrounding regenerative medicine in the heart has been tempered by realizations that reparative processes in the heart are insufficient to restore damaged myocardium to normal functional capacity and that cellular cardiomyoplasty is hampered by poor survival, proliferation, engraftment, and differentiation of the donated population. To overcome these limitations, a combination of molecular and cellular approaches must be adopted involving use of genetic engineering to enhance resistance to cell death and increase regenerative capacity. This review highlights biological properties of approached to potentiate stem cell-mediated regeneration to promote enhanced myocardial regeneration, persistence of donated cells, and long-lasting tissue repair. Optimizing cell delivery and harnessing the power of survival signaling cascades for ex vivo genetic modification of stem cells before reintroduction into the patient will be critical to enhance the efficacy of cellular cardiomyoplasty. Once this goal is achieved, then cell-based therapy has great promise for treatment of heart failure to combat the loss of cardiac structure and function associated with acute damage, chronic disease, or aging.

Platelet lysate from whole blood-derived pooled platelet concentrates and apheresis-derived platelet concentrates for the isolation and expansion of human bone marrow mesenchymal stromal cells: production process, content and identification of active components

Background aims

The clinical use of human mesenchymal stromal cells (MSC) requires ex vivo expansion in media containing supplements such as fetal bovine serum or, alternatively, human platelet lysate (PL).

Methods

Platelet concentrates were frozen, quarantine stored, thawed and sterile filtered to obtain PL. PL content and its effect on fibroblast-colony-forming unit (CFU-F) formation, MSC proliferation and large-scale expansion were studied.

Results

PL contained high levels of basic fibroblast growth factor (bFGF), soluble CD40L (sCD40L), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), platelet-derived growth factor AA (PDGF-AA), platelet-derived growth factor AB/BB (PDGF-AB/BB), chemokine (C-C) ligand 5 (CCL5; RANTES) transforming growth factor-β1 (TGF-β1) and chemokine (C-X-C) ligand 1/2/3 (GRO), with low batch-to-batch variability, and most were stable for up to 14 days. Inhibition of PDGF-BB and bFGF decreased MSC proliferation by about 20% and 50%, respectively. The strongest inhibition (about 75%) was observed with a combination of anti-bFGF + anti-PDGF-BB and anti-bFGF + anti-TGF-β1 + anti-PDGF-BB. Interestingly, various combinations of recombinant PDGF-BB, bFGF and TGF-β1 were not sufficient to promote cell proliferation. PL from whole blood-derived pooled platelet concentrates and apheresis platelet concentrates did not differ significantly in their growth-promoting activity on MSC.

Conclusions

PL enhances MSC proliferation and can be regarded as a safe tool for MSC expansion for clinical purposes. \in particular, PDGF-BB and bFGF are essential components for the growth-promoting effect of PL, but are not sufficient for MSC proliferation.

The influence of chitosan hydrogel on stem cell engraftment, survival and homing in the ischemic myocardial microenvironment

One challenge of cellular cardiomyoplasty for myocardial infarction (MI) is how to improve MI microenvironment to facilitate stem cell engraftment, survival and homing for myocardial repair. The application of injectable hydrogels is an effective strategy. However, it has not been thoroughly investigated on the role of the injectable scaffolds, in improving MI microenvironment, providing space and guidance for cell survival, engraftment and homing. We explored an injectable chitosan hydrogel for stem cell delivery into ischemic heart and investigated the beneficial effects and mechanisms of the hydrogel. In vitro, H(2)O(2)-treatment was used to mimic reactive oxygen species (ROS) microenvironment. The influence of ROS and protection of chitosan components on adipose-derived mesenchymal stem cells (ADSCs) was analyzed too. In vivo, MI was induced by the left anterior descending artery ligation in SD rats. PBS, chitosan hydrogel, ADSC/PBS and ADSC/chitosan hydrogel were injected into the border of infracted hearts respectively. Multi-techniques were used to assess the beneficial effects of chitosan hydrogel after transplantation. We observed that ROS generated by ischemia would impair ADSC adhesion molecules, including integrin-related adhesion molecules integrin αV and β1, focal adhesion-related molecules p-FAK and p-Src, and corresponding ligands of host myocardium ICAM1 and VCAM1. Chitosan hydrogel could rescue these molecules through ROS scavenging and recruit key chemokine for stem cell homing, such as SDF-1. The results suggest that chitosan hydrogel could improve MI microenvironment, enhance stem cell engraftment, survival and homing in ischemic heart through ROS scavenging and chemokine recruitment, contributing to myocardial repair.

Recent concepts for the roles of progenitor/stem cell niche in heart repair

Progenitor/stem cell (PSC) has shown great promise for generation in failing heart. Advances in PSC biology have greatly enhanced our understanding of how PSC self-renewal, migration, maintenance of stemness, and cell-fate commitment depend on the balance of complex signals in their microenvironment. Endogenous PSC exists within structural and functional units known as PSC niches, which play important roles in directing PSC behavior. Recent years have witnessed great progress in our understanding of the PSC niche in cardiovascular biology. PSC based therapy could lead to successful cardiac regeneration or repair. Realizing the potential of therapeutic strategies is based on 1) differentiation of the PSC into all of the cellular constituents of the heart; 2) release of paracrine/ autocrine factors from the PSC; 3) fusion of the PSC with the existing constituents of the heart; and 4) stimulation of endogenous repair (regeneration of PSC niches). Importantly, cardiac PSC niches contain supporting cells and these cell-cell interactions have crucial regulatory roles in PSC based therapy. These findings have important implications for heart development, bioengineering, and furthermore elucidate a broader dimension of PSC control within the niche toward cardiomyocyte phenotype.

Mesenchymal stem cells exhibit firm adhesion, crawling, spreading and transmigration across aortic endothelial cells: effects of chemokines and shear

Mesenchymal stem cells (MSCs) have anti-inflammatory and immunosuppressive properties and may be useful in the therapy of diseases such as arteriosclerosis. MSCs have some ability to traffic into inflamed tissues, however to exploit this therapeutically their migratory mechanisms need to be elucidated. This study examines the interaction of murine MSCs (mMSCs) with, and their migration across, murine aortic endothelial cells (MAECs), and the effects of chemokines and shear stress. The interaction of mMSCs with MAECs was examined under physiological flow conditions. mMSCs showed lack of interaction with MAECs under continuous flow. However, when the flow was stopped (for 10min) and then started, mMSCs adhered and crawled on the endothelial surface, extending fine microvillous processes (filopodia). They then spread extending pseudopodia in multiple directions. CXCL9 significantly enhanced the percentage of mMSCs adhering, crawling and spreading and shear forces markedly stimulated crawling and spreading. CXCL9, CXCL16, CCL20 and CCL25 significantly enhanced transendothelial migration across MAECs. The transmigrated mMSCs had down-regulated receptors CXCR3, CXCR6, CCR6 and CCR9. This study furthers the knowledge of MSC transendothelial migration and the effects of chemokines and shear stress which is of relevance to inflammatory diseases such as arteriosclerosis.

Damage-associated molecular patterns (DAMPs) and mesenchymal stem cells: a matter of attraction and excitement

Necrotic cell death is a typical feature of solid tumors leading to the release of necrotic products, also known as damage-associated molecular patterns (DAMPs), that enhance angiogenesis and prime the immune response. Among the DAMPs, particular attention has been focused on the DNA-binding molecule high-mobility group box 1 (HMGB-1) that can act as a chemoattractant and activator of granulocytes. Here, we discuss an article in this issue of the European Journal of Immunology that demonstrates that DAMPs promote both proliferation and trafficking of mesenchymal stem cells (MSCs), identifying HMGB-1 as a key factor in the regulation of these processes. Moreover, the study shows that DAMPs interfere with the expression of the immunosuppressive molecule indoleamine-2,3-dioxygenase in MSCs, and that the biological activity of HMGB-1 toward MSCs is abolished when HMGB-1 is oxidized. Based on the data from this, and other studies, we depict a model in which DAMPs released from necrotic tumor cells attract and stimulate local proliferation of MSCs that differentiate into tumor-associated fibroblasts promoting tumor growth and angiogenesis. Importantly, the hypoxic conditions of the tumor microenvironment may protect DAMPs from oxidation and thereby preserve their functionality.

Variability in chemokine-induced adhesion of human mesenchymal stromal cells

BACKGROUND AIMS. Intravenously applied mesenchymal stromal cells (MSC) are under investigation for numerous clinical indications. However, their capacity to activate shear stress-dependent adhesion to endothelial ligands is incompletely characterized. METHODS. Parallel-plate flow chambers were used to induce firm adhesion of MSC to integrin ligand vascular cell adhesion molecule (VCAM)-1. Human MSC were stimulated by chemokine (C-C motif) ligand (CCL15)/macrophage inflammatory protein (MIP-5), CCL19/MIP-3β chemokine (C-X-C motif) ligand (CXCL8)/interleukin (IL)-8, CXCL12/ stromal derived factor (SDF-1) or CXCL13/B lymphocyte chemoattractant (BLC). RESULTS. Two MSC isolates responded to three chemokines (either to CCL15, CCL19 and CXCL13, or to CCL19, CXCL12 and CXCL13), two isolates responded to two chemokines (to CCL15 and CCL19, or to CCL19 and CXCL13), and one isolate responded to CCL19 only. In contrast, all tested MSC isolates responded to selectins (P-selectin and E-selectin) or integrin ligand VCAM-1, as visualized by a velocity reduction under flow. CONCLUSIONS. Inter-individual variability of chemokine-induced integrin activation should be considered when evaluating human MSC as cellular therapies.

Hepatocellular carcinoma cells and their fibrotic microenvironment modulate bone marrow-derived mesenchymal stromal cell migration in vitro and in vivo

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the third cause of cancer-related death. Fibrogenesis is an active process characterized by the production of several proinflammatory cytokines, chemokines and growth factors. It involves the activation of hepatic stellate cells (HSCs) which accumulate at the site of injury and are the main source of the extracellular matrix deposits. There are no curative treatments for advanced HCC, thus, new therapies are urgently needed. Mesenchymal stromal cells (MSCs) have the ability to migrate to sites of injury or to remodeling tissues after in vivo administration; however, in several cancer models they demonstrated limited efficacy to eradicate experimental tumors partially due to poor engraftment. Thus, the aim of this work was to analyze the capacity of human MSCs (hMSCs) to migrate and anchor to HCC tumors. We observed that HCC and HSCs, but not nontumoral stroma, produce factors that induce hMSC migration in vitro. Conditioned media (CM) generated from established HCC cell lines were found to induce higher levels of hMSC migration than CM derived from fresh patient tumor samples. In addition, after exposure to CM from HCC cells or HSCs, hMSCs demonstrated adhesion and invasion capability to endothelial cells, type IV collagen and fibrinogen. Consistently, these cells were found to increase metalloproteinase-2 activity. In vivo studies with subcutaneous and orthotopic HCC models indicated that intravenously infused hMSCs migrated to lungs, spleen and liver. Seven days post-hMSC infusion cells were located also in the tumor in both models, but the signal intensity was significantly higher in orthotopic than in subcutaneous model. Interestingly, when orthotopic HCC tumors where established in noncirrhotic or cirrhotic livers, the amount of hMSCs localized in the liver was higher in comparison with healthy animals. A very low signal was found in lungs and spleens, indicating that liver tumors are able to recruit them at high efficiency. Taken together our results indicate that HCC and HSC cells produce factors that efficiently induce hMSC migration toward tumor microenvironment in vitro and in vivo and make MSCs candidates for cell-based therapeutic strategies to hepatocellular carcinoma associated with fibrosis.

Identification of chemoattractive factors involved in the migration of bone marrow-derived mesenchymal stem cells to brain lesions caused by prions

Bone marrow-derived mesenchymal stem cells (MSCs) have been reported to migrate to brain lesions of neurodegenerative diseases; however, the precise mechanisms by which MSCs migrate remain to be elucidated. In this study, we carried out an in vitro migration assay to investigate the chemoattractive factors for MSCs in the brains of prion-infected mice. The migration of immortalized human MSCs (hMSCs) was reduced by their pretreatment with antibodies against the chemokine receptors, CCR3, CCR5, CXCR3, and CXCR4 and by pretreatment of brain extracts of prion-infected mice with antibodies against the corresponding ligands, suggesting the involvement of these receptors, and their ligands in the migration of hMSCs. In agreement with the results of an in vitro migration assay, hMSCs in the corpus callosum, which are considered to be migrating from the transplanted area toward brain lesions of prion-infected mice, expressed CCR3, CCR5, CXCR3, and CXCR4. The combined in vitro and in vivo analyses suggest that CCR3, CCR5, CXCR3, and CXCR4, and their corresponding ligands are involved in the migration of hMSCs to the brain lesions caused by prion propagation. In addition, hMSCs that had migrated to the right hippocampus of prion-infected mice expressed CCR1, CX3CR1, and CXCR4, implying the involvement of these chemokine receptors in hMSC functions after chemotactic migration. Further elucidation of the mechanisms that underlie the migration of MSCs may provide useful information regarding application of MSCs to the treatment of prion diseases.

Integrin activation and internalization on soft ECM as a mechanism of induction of stem cell differentiation by ECM elasticity

The mechanism by which ECM elasticity induces lineage specification of stem cells has not been clearly understood. Integrins are well-documented mechanosensors that are positioned at the beginning of the sensing pathway. By using an antibody specifically recognizing the active conformation of β1 integrin, we observed that β1 integrin activation in bone marrow mesenchymal stem cells (BMMSCs) was induced by soft substrate to a significantly greater degree than by stiff substrate. In contrast, however, the level of cell surface integrin on soft substrate was significantly lower than that on stiff substrate. Soft substrate markedly enhanced the internalization of integrin, and this internalization was mediated mainly through caveolae/raft-dependent endocytosis. The inhibition of integrin internalization blocked the neural lineage specification of BMMSCs on soft substrate. Furthermore, soft substrate also repressed the bone morphogenetic protein (BMP)/Smad pathway at least partially through integrin-regulated BMP receptor endocytosis. A theoretical analysis based on atomic force microscopy (AFM) data indicated that integrin-ligand complexes are more easily ruptured on soft substrate; this outcome may contribute to the enhancement of integrin internalization on soft substrate. Taken together, our results suggest that ECM elasticity affects integrin activity and trafficking to modulate integrin BMP receptor internalization, thus contributing to stem cell lineage specification.

Hox transcription factor regulation of adult bone-marrow-derived cell behaviour during tissue repair and regeneration

INTRODUCTION

Bone marrow offers a valuable source of stem/progenitor cells that contribute to the repair of injured tissues. Failure in the function of these cells results in delayed or reduced tissue repair. Identification of factors that can correct these defects is critical to treating the underlying dysfunction. Notably, homeobox (Hox) transcription factors have been identified as having significant effects on BMDC behaviour, including differentiation, migration and adhesion in injured tissue, and may provide a basis for future therapies.

AREAS COVERED

Hox protein regulation of bone-marrow-derived cell (BMDC) differentiation, factors that influence BMDC behaviour in response to injury, the effects of the diabetic environment on BMDCs, methods that can be used to reprogramme BMDCs, and the use of Hox transcription factors to correct BMDC behaviour.

EXPERT OPINION

Hox gene therapy has been successfully employed to change cell behaviour using ex vivo 'reprogramming' strategies overexpressing selected Hox genes in BMDCs to direct the fate of these cells to the desired cell type, promoting tissue repair.

Regulatory factors of mesenchymal stem cell migration into injured tissues and their signal transduction mechanisms

Adult stem cells hold great promise for wound healing and tissue regeneration. Mesenchymal stem cells (MSCs), for example, have been shown to play a role in tissue repair. Research has shown that endogenous bone marrow MSCs or exogenously delivered MSCs migrate to the sites of injury and participate in the repair process. The precise mechanisms underlying migration of MSCs into the injured tissue are still not fully understood, although multiple signaling pathways and molecules were reported, including both chemoattractive factors and endogenous electric fields at wounds. This review will briefly summarize the regulatory facors and signaling transduction pathways involved in migration of MSCs. A better understanding of the molecular mechanisms involved in the migration of MSCs will help us to develop new stem cell-based therapeutic strategies in regenerative medicine.

Homing pathways of mesenchymal stromal cells (MSCs) and their role in clinical applications

Mesenchymal stromal cells (MSCs) have come into focus for an increasing number of cellular therapies. Since most clinical protocols use intravenous application of MSCs, it has become important to understand their trafficking in the bloodstream. Moreover, since relatively little is known where the transplanted MSCs might locate, a better understanding of involved homing mechanisms will likely shed light on how MSCs exert their therapeutic effects. This review focuses on the current knowledge of homing pathways of transplanted MSCs. We describe regulatory signalling molecules and receptors involved. An outlook is given on significance of these findings for the future use of MSCs as a cellular therapeutic.

Mesenchymal stem cells at the intersection of cell and gene therapy

IMPORTANCE OF THE FIELD

Mesenchymal stem cells have the ability to differentiate into osteoblasts, chondrocytes and adipocytes. Along with differentiation, MSCs can modulate inflammation, home to damaged tissues and secrete bioactive molecules. These properties can be enhanced through genetic-modification that would combine the best of both cell and gene therapy fields to treat monogenic and multigenic diseases.

AREAS COVERED IN THIS REVIEW

Findings demonstrating the immunomodulation, homing and paracrine activities of MSCs followed by a summary of the current research utilizing MSCs as a vector for gene therapy, focusing on skeletal disorders, but also cardiovascular disease, ischemic damage and cancer.

WHAT THE READER WILL GAIN

MSCs are a possible therapy for many diseases, especially those related to the musculoskeletal system, as a standalone treatment, or in combination with factors that enhance the abilities of these cells to migrate, survive or promote healing through anti-inflammatory and immunomodulatory effects, differentiation, angiogenesis or delivery of cytolytic or anabolic agents.

TAKE HOME MESSAGE

Genetically-modified MSCs are a promising area of research that would be improved by focusing on the biology of MSCs that could lead to identification of the natural and engrafting MSC-niche and a consensus on how to isolate and expand MSCs for therapeutic purposes.

Ablation of TNF-alpha receptors influences mesenchymal stem cell-mediated cardiac protection against ischemia

Mesenchymal stem cell (MSC) infusion may reduce myocardial ischemic injury. TNF-alpha is a proinflammatory cytokine produced in large quantities during myocardial ischemia that can exert beneficial or detrimental effects on MSC function by binding to a 55-kd receptor (TNFR1) or a 75-kd receptor (TNFR2) on MSCs. We investigated whether genetic modification with ablation of TNFR1 and/or TNFR2 affects MSC-mediated protection against myocardial ischemic injury. The MSCs were harvested from wild-type mice (WT-MSCs) and knockout mice with ablation of TNFR1 and/or TNFR2 (TNFR1KO, TNFR2KO, and TNFR1/R2KO MSCs). After anesthesia was initiated via inhalation of isoflurane, myocardial ischemia was induced in rats via coronary artery ligation. Hearts were then injected with vehicle or MSCs (1 x 10 cells/mL). Myocardial function was assessed 28 days postsurgery with 2-dimensional echocardiograms and isolated heart perfusion. Myocardial tissue was collected for cytokine analysis and infarct measurements. We found that MSC treatment offered significant protection against myocardial ischemia, namely by decreasing infarct size, improving heart function, and decreasing ventricular remodeling compared with vehicle. Compared with WT-MSCs, TNFR1KO MSCs conferred increased cardiac protection, although TNFR2KO and TNFR1/R2KO MSCs conferred less cardiac protection. In addition, treatment with TNFR1KO MSCs was associated with decreased levels of proinflammatory cytokines and an increased level of vascular endothelial growth factor in the myocardium, whereas treatment with TNFR2KO or TNFR1/R2KO MSCs was associated with increased levels of proinflammatory cytokines and a decreased level of vascular endothelial growth factor compared with treatment with WT-MSCs. We conclude that MSC TNFR1 and TNFR2 play important roles in MSC-mediated cardiac protection after myocardial ischemia.

Magnetic resonance imaging of stem cell migration

Noninvasive cellular imaging allows the real-time tracking of grafted cells as well as the monitoring of their migration. In this review, we will focus on cell tracking using MRI, since MRI is noninvasive, clinically transferable, and displays good resolution, ranging from 50 μm in animal experiments up to 300 μm using whole body clinical scanners. In addition to information about grafted cells, MRI provides information about the surrounding tissue (i.e., lesion size, edema, inflammation), which may negatively affect graft survival or the functional recovery of the tissue. Transplanted cells are labeled with MR contrast agents in vitro prior to transplantation in order to visualize them in the host tissue. The chapter will focus on the use of superparamagnetic iron oxide nanoparticles (SPIO), because they have strong effects on T2 relaxation yet do not affect cell viability, and will provide an overview of different modifications of SPIO and their use in MR tracking in living organisms.

CXCR4 and matrix metalloproteinase-2 are involved in mesenchymal stromal cell homing and engraftment to tumors

BACKGROUND AIMS

Bone marrow-derived mesenchymal stromal cells (BMSC) have been shown to migrate to injury, ischemia and tumor microenvironments. The mechanisms by which mesenchymal stromal cells (MSC) migrate across endothelium and home to the target tissues are not yet fully understood.

METHODS

We used rat BMSC to investigate the molecular mechanisms involved in their tropism to tumors in vitro and in vivo.

RESULTS

BMSC were shown to migrate toward four different tumor cells in vitro, and home to both subcutaneous and lung metastatic prostate tumor models in vivo. Gene expression profiles of MSC exposed to conditioned medium (CM) of various tumor cells were compared and revealed that matrix metalloproteinase-2 (MMP-2) expression in BMSC was downregulated after 24 h exposure to tumor CM. Chemokine (C-X-C motif) Receptor 4 (CXCR4) upregulation was also found in BMSC after 24 h exposure to tumor CM. Exposure to tumor cell CM enhanced migration of BMSC toward tumor cells. Stromal Cell-Derived Factor (SDF-1) inhibitor AMD3100 and MMP-2 inhibitor partly abolished the BMSC migration toward tumor cells in vitro.

CONCLUSIONS

These results suggest that the CXCR4 and MMP-2 are involved in the multistep migration processes of BMSC tropism to tumors.

Mesenchymal stem cells require integrin β1 for directed migration induced by osteopontin in vitro

Mesenchymal stem cells (MSCs) are characterized by their ability of self-renewal paired with the capacity to differentiate into multiple mesenchymal cell lineages. Numerous studies have reported beneficial effects of MSCs in tissue repair and regeneration. After in vivo administration, MSCs home to and engraft to injured tissues. However, the molecular mechanisms are not clear. Osteopontin (OPN) has been found to be elevated in response to injury and inflammation and its role on cell mobilization has been studied. Therefore, the facts imply that OPN may contribute to the recruitment of MSCs to the sites of injury. In this study, using transwell assay, we found that rat bone marrow-derived mesenchymal stem cells (rMSCs) migrated towards OPN in a concentration-dependent manner. To further examine the involved molecular mechanisms for OPN-induced rMSCs migration, RT-PCR, and Western blot were used to detect the expressions of integrin β1 and CD44v6, the two receptors of OPN. OPN promoted integrin β1 mRNA and protein expression while CD44v6 mRNA level was not altered. Blockade of integrin β1 also inhibited OPN-induced rMSCs migration, indicating the possible involvement of integrin β1 in OPN-induced migration in rMSCs. Our data have shown for the first time that OPN increases integrin β1 expression in rMSCs and promotes rMSCs migration through the ligation to integrin β1.

Adipose tissue-derived progenitor cells and cancer

Recruitment of stem cells and partially differentiated progenitor cells is a process which accompanies and facilitates the progression of cancer. One of the factors complicating the clinical course of cancer is obesity, a progressively widespread medical condition resulting from overgrowth of white adipose tissue (WAT), commonly known as white fat. The mechanisms by which obesity influences cancer risk and progression are not completely understood. Cells of WAT secret soluble molecules (adipokines) that could stimulate tumor growth, although there is no consensus on which cell populations and which adipokines are important. Recent reports suggest that WAT-derived mesenchymal stem (stromal) cells, termed adipose stem cells (ASC), may represent a cell population linking obesity and cancer. Studies in animal models demonstrate that adipokines secreted by ASC can promote tumor growth by assisting in formation of new blood vessels, a process necessary for expansion of tumor mass. Importantly, migration of ASC from WAT to tumors has been demonstrated, indicating that the tumor microenvironment in cancer may be modulated by ASC-derived trophic factors in a paracrine rather than in an endocrine manner. Here, we review possible positive and adverse implications of progenitor cell recruitment into the diseased sites with a particular emphasis on the role in cancer progression of progenitors that are expanded in obesity.

Genetic engineering of mesenchymal stem cells and its application in human disease therapy

The use of stem cells for tissue regeneration and repair is advancing both at the bench and bedside. Stem cells isolated from bone marrow are currently being tested for their therapeutic potential in a variety of clinical conditions including cardiovascular injury, kidney failure, cancer, and neurological and bone disorders. Despite the advantages, stem cell therapy is still limited by low survival, engraftment, and homing to damage area as well as inefficiencies in differentiating into fully functional tissues. Genetic engineering of mesenchymal stem cells is being explored as a means to circumvent some of these problems. This review presents the current understanding of the use of genetically engineered mesenchymal stem cells in human disease therapy with emphasis on genetic modifications aimed to improve survival, homing, angiogenesis, and heart function after myocardial infarction. Advancements in other disease areas are also discussed.

TGF-beta enhances the integrin alpha2beta1-mediated attachment of mesenchymal stem cells to type I collagen

The heterodimeric integrins are important receptors for the attachment of cells to their extracellular matrix. Here, we studied the attachment of human mesenchymal stem cells (MSCs) to type I collagen (col-1), which is part of the extracellular matrix in bone, skin, and connective tissues. Furthermore, we examined how TGF-beta influences the integrin expression and attachment of MSC. Using flow cytometry, immunoblot, and RT-PCR, we report that MSC express several integrin subunits, including the alpha(2)beta(1) integrin (VLA-2, CD49b/CD29). TGF-beta increases the expression of integrin subunits alpha(2), alpha(6), and beta(1) in MSC, thereby enhancing the attachment of MSC to col-1. The TGF-beta-mediated up-regulation of the expression of the integrin subunits alpha(2) and alpha(6) is mainly mediated in MSC by Smad2.

Mesenchymal stem cells, used as bait, disclose tissue binding sites: a tool in the search for the niche?

We developed an ex vivo approach characterizing renal mesenchymal stem cell (MSC) adhesion to kidney sections. Specificity of MSC adhesion was confirmed by demonstrating a) 3T3 cells displayed 10-fold lower adhesion, and b) MSC adhesion was CXCR4/stromal-derived factor-1 (SDF-1)-dependent. MSC adhesion was asymmetrical, with postischemic sections exhibiting more than twofold higher adhesion than controls, and showed preference to perivascular areas. Pretreating kidney sections with cyclic arginine-glycine-aspartic acid peptide resulted in increased MSC adhesion (by displacing resident cells), whereas blockade of CXCR4 with AMD3100 and inhibition of alpha4beta1(VLA4) integrin or vascular cellular adhesion molecule-1, reduced adhesion. The difference between adhered cells under cyclic arginine-glycine-aspartic acid peptide-treated and control conditions reflected prior occupancy of binding sites with endogenous cells. The AMD3100-inhibitable fraction of adhesion reflected CXCR4-dependent adhesion, whereas maximal adhesion was interpreted as kidney MSC-lodging capacity. MSC obtained from mice overexpressing caveolin-1 exhibited more robust adhesion than those obtained from knockout animals, consistent with CXCR4 dimerization in caveolae. These data demonstrate a) CXCR4/SDF-1-dependent adhesion increases in ischemia; b) CXCR4/SDF-1 activation is dependent on MSC surface caveolin-1; and c) occupancy of MSC binding sites is decreased, while d) capacity of MSC binding sites is expanded in postischemic kidneys. In conclusion, we developed a cell-bait strategy to unmask renal stem cell binding sites, which may potentially shed light on the MSC niche(s) and its characteristics.

High-density lipoprotein exerts vasculoprotection via endothelial progenitor cells

Endothelial progenitor cells (EPC) enhance endothelial cell repair, improve endothelial dysfunction and are a predictor for cardiovascular mortality. High-density lipoprotein (HDL) cholesterol levels inversely correlate with cardiovascular events and have vasculoprotective effects. Here we postulate that HDL influences EPC biology. HDL and EPC were isolated according to standard procedures. Differentiation of mononuclear cells into DiLDL/lectin positive cells was enhanced after HDL treatment compared to vehicle. HDL was able to inhibit apoptosis (TUNEL assay, annexin V staining) while proliferation (BrdU incorporation) of early outgrowth colonies after extended cell cultivation (14 days) was increased. Flow chamber experiments revealed an improved adhesion of HDL pre-incubated EPC on human coronary artery endothelial cells (HCAEC) compared to vehicle while HDL treatment of HCAEC prevented adhesion of inflammatory cells. Flow cytometry demonstrated an up-regulation of beta2- and alpha4-integrins on HDL pre-incubated EPC. Blocking experiments revealed a unique role of beta2-integrin in EPC adhesion. Treatment of wild-type mice with recombinant HDL after endothelial denudation resulted in enhanced re-endothelialization compared to vehicle. Finally, in patients with coronary artery disease a correlation between circulating EPC and HDL concentrations was demonstrated. We provide evidence that HDL mediates important vasculoprotective action via the improvement of function of circulating EPC.

Mesenchymal stromal cells: current understanding and clinical status

Multipotent mesenchymal stromal cells (MSCs) represent a rare heterogeneous subset of pluripotent stromal cells that can be isolated from many different adult tissues that exhibit the potential to give rise to cells of diverse lineages. Numerous studies have reported beneficial effects of MSCs in tissue repair and regeneration. After culture expansion and in vivo administration, MSCs home to and engraft to injured tissues and modulate the inflammatory response through synergistic downregulation of proinflammatory cytokines and upregulation of both prosurvival and antiinflammatory factors. In addition, MSCs possess remarkable immunosuppressive properties, suppressing T-cell, NK cell functions, and also modulating dentritic cell activities. Tremendous progress has been made in preclinical studies using MSCs, including the ability to use allogeneic cells, which has driven the application of MSCs toward the clinical setting. This review highlights our current understanding into the biology of MSCs with particular emphasis on the cardiovascular and renal applications, and provides a brief update on the clinical status of MSC-based therapy.

Mesenchymal stem cells: Mechanisms of immunomodulation and homing

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissue. A growing corpus of studies have highlighted two important aspects of MSC therapy: 1) MSCs can modulate T-cell-mediated immunological responses, and (2) systemically administered MSCs home to sites of ischemia or injury. In this review, we describe the known mechanisms of immunomodulation and homing of MSCs. First, we examine the low immunogenicity of MSCs and their antigen presentation capabilities. Next, we discuss the paracrine interactions between MSCs and innate [dendritic cells (DC)] and adaptive immune cells (T lymphocytes) with a focus on prostaglandin E(2) (PGE(2)), indoleamine 2,3-dioxygenase (IDO), and toll-like receptor (TLR) signaling pathways. We transition to outline the steps of activation, rolling/adhesion, and transmigration of MSCs into target tissues during inflammatory or ischemic conditions. These aspects of MSC grafts--immunomodulation and homing--are contextualized to understand a reported side effect of MSC therapy, cancer development.

Stem cells as vectors for antitumour therapy

Recent research suggests that mesenchymal stem cells (MSCs) are able to migrate specifically to tumours and their metastases throughout the body. This has led to considerable excitement about the possibility of modifying these cells to express anticancer molecules and using them as specific targeted anticancer agents. However, there are concerns that systemically delivered MSCs may have non-desirable effects, and there are also many unanswered questions including the mechanism of tumour homing. This review investigates the different MSC-delivered anticancer agents, addresses the questions and concerns, and tries to place this potential therapy in future cancer management.

Genetic modification of mesenchymal stem cells overexpressing CCR1 increases cell viability, migration, engraftment, and capillary density in the injured myocardium

RATIONALE

Although mesenchymal stem cell (MSC) transplantation has been shown to promote cardiac repair in acute myocardial injury in vivo, its overall restorative capacity appears to be restricted mainly because of poor cell viability and low engraftment in the ischemic myocardium. Specific chemokines are upregulated in the infarcted myocardium. However the expression levels of the corresponding chemokine receptors (eg, CCR1, CXCR2) in MSCs are very low. We hypothesized that this discordance may account for the poor MSC engraftment and survival.

OBJECTIVE

To determine whether overexpression of CCR1 or CXCR2 chemokine receptors in MSCs augments their cell survival, migration and engraftment after injection in the infarcted myocardium.

METHODS AND RESULTS

Overexpression of CCR1, but not CXCR2, dramatically increased chemokine-induced murine MSC migration and protected MSC from apoptosis in vitro. Moreover, when MSCs were injected intramyocardially one hour after coronary artery ligation, CCR1-MSCs accumulated in the infarcted myocardium at significantly higher levels than control-MSCs or CXCR2-MSCs 3 days postmyocardial infarction (MI). CCR1-MSC-injected hearts exhibited a significant reduction in infarct size, reduced cardiomyocytes apoptosis and increased capillary density in injured myocardium 3 days after MI. Furthermore, intramyocardial injection of CCR1-MSCs prevented cardiac remodeling and restored cardiac function 4 weeks after MI.

CONCLUSIONS

Our results demonstrate the in vitro and in vivo salutary effects of genetic modification of stem cells. Specifically, overexpression of chemokine receptor enhances the migration, survival and engraftment of MSCs, and may provide a new therapeutic strategy for the injured myocardium.

Mesenchymal stem cells: a new strategy for immunosuppression and tissue repair

Mesenchymal stem cells (MSCs) have great potential for treating various diseases, especially those related to tissue damage involving immune reactions. Various studies have demonstrated that MSCs are strongly immunosuppressive in vitro and in vivo. Our recent studies have shown that un-stimulated MSCs are indeed incapable of immunosuppression; they become potently immunosuppressive upon stimulation with the supernatant of activated lymphocytes, or with combinations of IFN-gamma with TNF-alpha, IL-1alpha or IL-1beta. This observation revealed that under certain circumstances, inflammatory cytokines can actually become immunosuppressive. We showed that there is a species variation in the mechanisms of MSC-mediated immunosuppression: immunosuppression by cytokine-primed mouse MSCs is mediated by nitric oxide (NO), whereas immunosuppression by cytokine-primed human MSCs is executed through indoleamine 2, 3-dioxygenase (IDO). Additionally, upon stimulation with the inflammatory cytokines, both mouse and human MSCs secrete several leukocyte chemokines that apparently serve to attract immune cells into the proximity with MSCs, where NO or IDO is predicted to be most active. Therefore, immunosuppression by inflammatory cytokine-stimulated MSCs occurs via the concerted action of chemokines and immune-inhibitory NO or IDO produced by MSCs. Thus, our results provide novel information about the mechanisms of MSC-mediated immunosuppression and for better application of MSCs in treating tissue injuries induced by immune responses.

Selection of highly osteogenic and chondrogenic cells from bone marrow stromal cells in biocompatible polymer-coated plates

To enrich the subpopulation that preserves self-renewal and multipotentiality from conventionally prepared bone marrow stromal cells (MSCs), we attempted to use 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer-coated plates that selected the MSCs with strong adhesion ability and evaluated the proliferation ability or osteogenic/chondrogenic potential of the MPC polymer-selected MSCs. The number of MSCs that were attached to the MPC polymer-coated plates decreased with an increase in the density of MPC unit (0-10%), whereas no significant difference in the proliferation ability was seen among these cells. The surface epitopes of CD29, CD44, CD105, and CD166, and not CD34 or CD45, were detectable in the cells of all MPC polymer-coated plates, implying that they belong to the MSC category. In the osteogenic and chondrogenic induction, the MSCs selected by the 2-5% MPC unit composition showed higher expression levels of osteoblastic and chondrocytic markers (COL1A1/ALP, or COL2A1/COL10A1/Sox9) at passage 2, compared with those of 0-1% or even 10% MPC unit composition, while the enhanced effects continued by passage 5. The selection based on the adequate cell adhesiveness by the MPC polymer-coated plates could improve the osteogenic and chondrogenic potential of MSCs, which would provide cell sources that can be used to treat the more severe and various bone/cartilage diseases.

Mesenchymal stem cells differentiate into renin-producing juxtaglomerular (JG)-like cells under the control of liver X receptor-alpha

Renin is a key enzyme for cardiovascular and renal homeostasis and is produced by highly specialized endocrine cells in the kidney, known as juxtaglomerular (JG) cells. The nature and origin of these cells remain as mysteries. Previously, we have shown that the nuclear hormone receptor liver X receptor-alpha (LXRalpha) is a major transcriptional regulator of the expression of renin, c-myc, and other genes involved with growth/differentiation. In this study we test the hypothesis that LXRalpha plays an important role not only in renin expression but also in renin-containing cell differentiation, specifically from the mesenchymal stem cell (MSC), which may be the origin of the JG cell. Indeed, our data demonstrated that LXRalpha activation by its ligands or cAMP stimulated renin gene expression in both murine and human MSCs. Furthermore, sustained cAMP stimulation of murine MSCs overexpressing LXRalpha led to their differentiation into JG-like cells expressing renin and alpha-smooth muscle actin. These MSC-derived JG-like cells contained renin in secretory granules and released active renin in response to cAMP. In conclusion, the activation of LXRalpha stimulates renin expression and induces MSCs differentiation into renin-secreting, JG-like cells. Our results suggest that the MSC may be the origin of the juxtaglomerular cell and provide insight into novel understanding of pathophysiology of the renin-angiotensin system.

Hepatocyte growth factor-mediated attraction of mesenchymal stem cells for apoptotic neuronal and cardiomyocytic cells

Human bone marrow-derived mesenchymal stem cells (MSC) home to injured tissues and have regenerative capacity. In this study, we have investigated in vitro the influence of apoptotic and necrotic cell death, thus distinct types of tissue damage, on MSC migration. Concordant with an increased overall motility, MSC migrated towards apoptotic, but not vital or necrotic neuronal and cardiac cells. Hepatocyte growth factor (HGF) was expressed by the apoptotic cells only. MSC, in contrast, revealed expression of the HGF-receptor, c-Met. Blocking HGF bioactivity resulted in significant reduction of MSC migration. Moreover, recombinant HGF attracted MSC in a dose-dependent manner. Thus, apoptosis initiates chemoattraction of MSC via the HGF/c-Met axis, thereby linking tissue damage to the recruitment of cells with regenerative potential.

Matrix metalloproteinase 1 is necessary for the migration of human bone marrow-derived mesenchymal stem cells toward human glioma

Human mesenchymal stem cells (MSCs) have increasingly been used as cellular vectors for the delivery of therapeutic genes to tumors. However, the precise mechanism of mobilization remains poorly defined. In this study, MSCs that expressed similar cell surface markers and exhibited multilineage differentiation potentials were isolated from various donors. Interestingly, different MSC isolates displayed differential migration ability toward human glioma cells. We hypothesized that distinct molecular signals may be involved in the varied tumor tropisms exhibited by different MSC isolates. To test this hypothesis, gene expression profiles of tumor-trophic MSCs were compared with those of non–tumor-trophic MSCs. Among the various differentially regulated genes, matrix metalloproteinase one (MMP1) gene expression and its protein activities were enhanced by 27-fold and 21-fold, respectively, in highly migrating MSCs compared with poorly migrating MSCs. By contrast, there was no change in the transcriptional levels of other MMPs. Functional inactivation of MMP1 abrogated the migratory potential of MSCs toward glioma-conditioned medium. Conversely, the nonmigratory phenotype of poorly migrating MSC could be rescued in the presence of either recombinant MMP1 or conditioned medium from the highly migrating MSCs. Ectopic expression of MMP1 in these poorly migrating cells also rendered the cells responsive to the signaling cues from the glioma cells in vivo. However, blocking the interaction of MMP1 and its cognate receptor PAR1 effectively diminished the migratory ability of MSCs. Taken together, this study provides, for the first time, supporting evidence that MMP1 is critically involved in the migration capacity of MSCs, acting through the MMP1/PAR1 axis. Stem Cells 2009;27:1366–1375

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.

Molecular mechanisms involved in mesenchymal stem cell migration to the site of acute myocardial infarction

Mesenchymal stem cells or multipotent mesenchymal stromal cells (both referred to as MSC) have been shown in some studies to have a beneficial effect on myocardial recovery after infarct. Current strategies for MSC delivery to heart involve intravenous, intraarterial, and intramuscular delivery. Different routes of MSC delivery and a lack of knowledge of the mechanisms that MSC utilise to migrate in vivo has most likely led to the marked variations in results that have been found. This review aims to summarise the current knowledge of MSC migratory mechanisms and looks to future methods of MSC manipulation prior to delivery in order to enhance MSC migration and engraftment.

Mesenchymal stem cell-based therapy: a new paradigm in regenerative medicine

Mesenchymal stem cells (MSCs), adherent fibroblastoid cells, present in bone marrow and many other tissues can be easily isolated and expanded in vitro. They are capable of differentiating into different cell types such as osteoblasts, chondrocytes, adipocytes, cardiomyocytes, hepatocytes, endothelial cells and neuronal cells. Such immense plasticity coupled with their ability to modulate the activity of immune cells makes them attractive for stem cell-based therapy aimed at treating previously incurable disorders. Preclinical studies have reported successful use of MSCs for delivering therapeutic proteins and repairing defects in a variety of disease models. These studies highlighted the in vivo potential of MSCs and their ability to home to injury sites and modify the microenvironment by secreting paracrine factors to augment tissue repair. Their therapeutic applicability has been widened by genetic modification to enhance differentiation and tissue targeting, and use in tissue engineering. Clinical trials for diseases such as osteogenesis imperfecta, graft-versus-host disease and myocardial infarction have shown some promise, demonstrating the safe use of both allogeneic and autologous cells. However, lack of knowledge of MSC behaviour and responses in vitro and in vivo force the need for basic and animal studies before heading to the clinic. Contrasting reports on immunomodulatory functions and tumorigenicity along with issues such as mode of cell delivery, lack of specific marker, low survival and engraftment require urgent attention to harness the potential of MSC-based therapy in the near future.

Coronary vessel development and insight towards neovascular therapy

Formation of the coronary arteries consists of a precisely orchestrated series of morphogenetic and molecular events which can be divided into three distinct processes: vasculogenesis, angiogenesis and arteriogenesis (Risau 1997; Carmeliet 2000). Even subtle perturbations in this process may lead to congenital coronary artery anomalies, as occur in 0.2-1.2% of the general population (von Kodolitsch et al. 2004). Contrary to the previously held dogma, the process of vasculogenesis is not limited to prenatal development. Both vasculogenesis and angiogenesis are now known to actively occur within the adult heart. When the need for regeneration arises, for example in the setting of coronary artery disease, a reactivation of embryonic processes ensues, redeploying many of the same molecular regulators. Thus, an understanding of the mechanisms of embryonic coronary vasculogenesis and angiogenesis may prove invaluable in developing novel strategies for cardiovascular regeneration and therapeutic coronary angiogenesis.