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.     

The effect of pro-inflammatory cytokines on immunophenotype,differentiation capacity and immunomodulatory functions of human mesenchymal stem cells

Mesenchymal stem cells (MSCs), as cells with potential clinical utilities, have demonstrated preferential incorporation into inflammation sites. Immunophenotype and immunomodulatory functions of MSCs could alter by inflamed-microenvironments due to the local pro-inflammatory cytokine milieu. A major cellular mediator with specific function in promoting inflammation and pathogenicity of autoimmunity are IL-17-producing T helper 17 (Th17) cells that polarize in inflamed sites in the presence of pro-inflammatory cytokines such as Interleukin-1β (IL-1β), IL-6 and IL-23. Since MSCs are promising candidate for cell-based therapeutic strategies in inflammatory and autoimmune diseases, Th17 cell polarizing factors may alter MSCs phenotype and function. In this study, human bone-marrow-derived MSCs (BM-MSC) and adipose tissue-derived MSCs (AD-MSC) were cultured with or without IL-1β, IL-6 and IL-23 as pro-inflammatory cytokines. The surface markers and their differentiation capacity were measured in cytokine-untreated and cytokine-treated MSCs. MSCs-mediated immunomodulation was analyzed by their regulatory effects on mixed lymphocyte reaction (MLR) and the level of IL-10, TGF-β, IL-4, IFN-γ and TNF-α production as immunomodulatory cytokines. Pro-inflammatory cytokines showed no effect on MSCs morphology, immunophenotype and co-stimulatory molecules except up-regulation of CD45. Adipogenic and osteogenic differentiation capacity increased in CD45+ MSCs. Moreover, cytokine-treated MSCs preserved the suppressive ability of allogeneic T cell proliferation and produced higher level of TGF-β and lower level of IL-4. We concluded pro-inflammatory cytokines up-regulate the efficacy of MSCs in cell-based therapy of degenerative, inflammatory and autoimmune disorders.     

Potential surrogate quantitative immunomodulatory potency assay for monitoring human umbilical cord-derived mesenchymal stem cells production

Mesenchymal stem cells (MSCs) play an important role as immune modulator through interaction with several immune cells, including macrophages. In this study, the immunomodulatory potency of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) was demonstrated in the in vivo middle cerebral artery occlusion (MCAo)-induced brain injury rat model and in vitro THP-1-derived macrophages model. At 24 h after induction of MCAo, hUC-MSCs was administered via tail vein as a single dose. Remarkably, hUC-MSCs could inhibit M1 polarization and promote M2 polarization of microglia in vivo after 14 days induction of MCAo. Compared with THP-1-derived macrophages which had been stimulated by lipopolysaccharide, the secretion of proinflammatory cytokines, tumor necrosis factor-α (TNF-α) and interferon-γ inducible protein (IP-10), were significantly reduced in the presence of hUC-MSCs. Moreover, the secretion of anti-inflammatory cytokine, interleukin-10 (IL-10), was significantly increased after cocultured with hUC-MSCs. Prostaglandins E2 (PGE2), secreted by hUC-MSCs, is one of the crucial immunomodulatory factors and could be inhibited in the presence of COX2 inhibitor, NS-398. PGE2 inhibition suppressed hUC-MSCs immunomodulatory capability, which was restored after addition of synthetic PGE2, establishing the minimum amount of PGE2 required for immunomodulation. In conclusion, our data suggested that PGE2 is a crucial potency marker involved in the therapeutic activity of hUC-MSCs through macrophages immune response modulation and cytokines regulation. This study provides the model for the development of a surrogate quantitative potency assay of immunomodulation in stem cells production.     

Comparison of immunomodulatory properties of mesenchymal stem cells derived from adult human tissues

Mesenchymal stem cells (MSCs), which evoke only minimal immune reactivity, may have anti-inflammatory and immunomodulatory effects. In this study, we conducted a comparative analysis of the immunomodulatory properties of MSCs derived from adult human tissues including bone marrow (BM), adipose tissues (AT), umbilical cord blood (CB), and cord Wharton’s jelly (WJ). Using a multiple cytokine detection assay, we showed that there were no significant differences in levels of secreted factors from non-stimulated MSCs. We compared the immunosuppressive effect of BM-MSCs, AT-MSCs, CB-MSCs, and WJ-MSCs on phytohemagglutinin-induced T-cell proliferation. AT-MSCs, CB-MSCs, and WJ-MSCs effectively suppressed mitogen-induced T-cell proliferation as effectively as did BM-MSCs. Levels of interferon (IFN)-γ and tumor necrosis factor (TNF)-α secreted from activated T-cells increased over time, but these levels were significantly reduced when cocultured with each type of MSCs. In addition, the expression of hepatocyte growth factor, IL-10, transforming growth factor-β₁, cyclooxygenase (COX)-1, and COX-2 were unchanged in MSCs treated with IFN-γ and/or TNF-α, while indoleamine 2,3-dioxygenase (IDO) expression increased. IFN-γ and/or TNF-α produced by activated T-cells were correlated with induction of IDO expression by MSCs, which, in turn, suppressed T-cell proliferation. These findings suggest that MSCs derived from AT, CB, or WJ could be substituted for BM-MSCs for treatment of allogeneic conflicts.     

Cloned, CD117 selected human amniotic fluid stem cells are capable of modulating the immune response

Amniotic fluid stem (AFS) cells are broadly multipotent, can be expanded extensively in culture, are not tumorigenic and can be readily cryopreserved for cell banking. Mesenchymal stem cells (MSC) show immunomodulatory activity and secrete a wide spectrum of cytokines and chemokines that suppress inflammatory responses, block mixed lymphocyte reactions (MLR) and other immune reactions, and have proven therapeutic against conditions such as graft-versus-host disease. AFS cells resemble MSCs in many respects including surface marker expression and differentiation potential. We therefore hypothesized that AFS cells may exhibit similar immunomodulatory capabilities. We present data to demonstrate that direct contact with AFS cells inhibits lymphocyte activation. In addition, we show that cell-free supernatants derived from AFS cells primed with total blood monocytes or IL-1β, a cytokine released by monocytes and essential in mediation of the inflammatory response, also inhibited lymphocyte activation. Further investigation of AFS cell-free supernatants by protein array revealed secretion of multiple factors in common with MSCs that are known to be involved in immune regulation including growth related oncogene (GRO) and monocyte chemotactic protein (MCP) family members as well as interleukin-6 (IL-6). AFS cells activated by PBMCs released several additional cytokines as compared to BM-MSCs, including macrophage inflammatory protein-3α (MIP-3α), MIP-1α and Activin. AFS cells also released higher levels of MCP-1 and lower levels of MCP-2 compared to BM-MSCs in response to IL-1β activation. This suggests that there may be some AFS-specific mechanisms of inhibition of lymphocyte activation. Our results indicate that AFS cells are able to suppress inflammatory responses in vitro and that soluble factors are an essential component in the communication between lymphocytes and AFS cells. Their extensive self-renewal capacity, possibility for banking and absence of tumorigenicity may make AFS cells a superior source of stable, well characterized "off the shelf" immunomodulatory cells for a variety of immunotherapies.     

间充质干细胞旁分泌作用的研究进展

间充质干细胞（MSCs）通常利用多分化特性在组织损伤时起到修复功能。然而,近期研究表明,MSCs大多数治疗作用都是通过旁分泌来发挥作用的,其中最受关注的是可溶性蛋白分泌和细胞外膜泡（EVS）。MSCs释放的EVS可反映细胞的来源,能够影响局部微环境中其他细胞的活动。越来越多人提出利用MSCs分泌的各种因子（称为分泌体）替代MSCs细胞治疗的观点。现就MSCs旁分泌特性、分泌体发生和释放机制以及细胞来源对旁分泌影响等方面的研究进展进行综述。     

Secretion of immunoregulatory cytokines by mesenchymal stem cells

According to the minimal criteria of the International Society of Cellular Therapy, mesenchymal stem cells (MSCs) are a population of undifferentiated cells defined by their ability to adhere to plastic surfaces when cultured under standard conditions, express a certain panel of phenotypic markers and can differentiate into osteogenic, chondrogenic and adipogenic lineages when cultured in specific inducing media. In parallel with their major role as undifferentiated cell reserves, MSCs have immunomodulatory functions which are exerted by direct cell-to-cell contacts, secretion of cytokines and/or by a combination of both mechanisms. There are no convincing data about a principal difference in the profile of cytokines secreted by MSCs isolated from different tissue sources, although some papers report some quantitative but not qualitative differences in cytokine secretion. The present review focuses on the basic cytokines secreted by MSCs as described in the literature by which the MSCs exert immunodulatory effects. It should be pointed out that MSCs themselves are objects of cytokine regulation. Hypothetical mechanisms by which the MSCs exert their immunoregulatory effects are also discussed in this review. These mechanisms may either influence the target immune cells directly or indirectly by affecting the activities of predominantly dendritic cells. Chemokines are also discussed as participants in this process by recruiting cells of the immune systems and thus making them targets of immunosuppression. This review aims to present and discuss the published data and the personal experience of the authors regarding cytokines secreted by MSCs and their effects on the cells of the immune system.     

Injection of synthetic mesenchymal stem cell mitigates osteoporosis in rats after ovariectomy

Osteoporosis is a severe skeletal disorder. Patients have a low bone mineral density and bone structural deterioration. Mounting lines of evidence suggest that inappropriate apoptosis of osteoblasts/osteocytes leads to maladaptive bone remodelling in osteoporosis. It has been suggested that transplantation of stem cells, including mesenchymal stem cells, may alter the trajectory of bone remoulding and mitigate osteoporosis in animal models. However, stem cells needed to be carefully stored and characterized before usage. In addition, there is great batch‐to‐batch variation in stem cell production. Here, we fabricated therapeutic polymer microparticles from the secretome and membranes of mesenchymal stem cells (MSCs). These synthetic MSCs contain growth factors secreted by MSCs. In addition, these particles display MSC surface molecules. In vitro, co‐culture with synthetic MSCs increases the viability of osteoblast cells. In a rat model of ovariectomy‐induced osteoporosis, injection of synthetic MSCs mitigated osteoporosis by reducing cell apoptosis and systemic inflammation, but increasing osteoblast numbers. Synthetic MSC offers a promising therapy to manage osteoporosis.     

Immunophenotypic characteristics of multipotent mesenchymal stromal cells that affect the efficacy of their use in the prevention of acute graft vs host disease

BACKGROUNDMultipotent mesenchymal stromal cells (MSCs) are widely used in the clinic due to their unique properties, namely, their ability to differentiate in all mesenchymal directions and their immunomodulatory activity. Healthy donor MSCs were used to prevent the development of acute graft vs host disease (GVHD) after allogeneic bone marrow transplantation (allo-BMT). The administration of MSCs to patients was not always effective. The MSCs obtained from different donors have individual characteristics. The differences between MSC samples may affect their clinical efficacy.AIMTo study the differences between effective and ineffective MSCs.METHODSMSCs derived from the bone marrow of a hematopoietic stem cells donor were injected intravenously into allo-BMT recipients for GVHD prophylaxis at the moment of blood cell reconstitution. Aliquots of 52 MSC samples that were administered to patients were examined, and the same cells were cultured in the presence of peripheral blood mononuclear cells (PBMCs) from a third-party donor or treated with the pro-inflammatory cytokines IL-1β, IFN and TNF. Flow cytometry revealed the immunophenotype of the nontreated MSCs, the MSCs cocultured with PBMCs for 4 d and the MSCs exposed to cytokines. The proportions of CD25-, CD146-, CD69-, HLA-DR- and PD-1-positive CD4+ and CD8+ cells and the distribution of various effector and memory cell subpopulations in the PBMCs cocultured with the MSCs were also determined.RESULTSDifferences in the immunophenotypes of effective and ineffective MSCs were observed. In the effective samples, the mean fluorescence intensity (MFI) of HLA-ABC, HLA-DR, CD105, and CD146 was significantly higher. After MSCs were treated with IFN or cocultured with PBMCs, the HLA-ABC, HLA-DR, CD90 and CD54 MFI showed a stronger increase in the effective MSCs, which indicated an increase in the immunomodulatory activity of these cells. When PBMCs were cocultured with effective MSCs, the proportions of CD4+ and CD8+central memory cells significantly decreased, and the proportion of CD8+CD146+ lymphocytes increased more than in the subpopulations of lymphocytes cocultured with MSC samples that were ineffective in the prevention of GVHD; in addition, the proportion of CD8+effector memory lymphocytes decreased in the PBMCs cocultured with the effective MSC samples but increased in the PBMCs cocultured with the ineffective MSC samples. The proportion of CD4+CD146+ lymphocytes increased only when cocultured with the inefficient samples.CONCLUSIONFor the first time, differences were observed between MSC samples that were effective for GVHD prophylaxis and those that were ineffective. Thus, it was shown that the immunomodulatory activity of MSCs depends on the individual characteristics of the MSC population.     

The homing of human cord blood stem cells to sites of inflammation

Efficient homing of human umbilical cord blood mesenchymal stem cells (hUCBSC) to inflammation sites is crucial for therapeutic use. In glioblastoma multiforme, soluble factors released by the tumor facilitate the migratory capacity of mesenchymal stem cells toward glioma cells. These factors include chemokines and growth inducers. Nonetheless, the mechanistic details of these factors involved in hUCBSC homing have not been clearly delineated. The present study is aimed to deduce specific factors involved in hUCBSC homing by utilizing a glioma stem cell-induced inflammatory lesion model in the mouse brain. Our results show that hUCBSC do not form tumors in athymic nude mice brains and do not elicit immune responses in immunocompetent SKH1 mice. Further, hUCBSC spheroids migrate and invade glioma spheroids, while no effect was observed on rat fetal brain aggregates. Several cytokines, including GRO, MCP-1, IL-8, IL-3, IL-10, Osteopontin and TGF-β2, were constitutively secreted in the naive hUCBSC-conditioned medium, while significant increases of IL-8, GRO, GRO-α, MCP-1 and MCP-2 were observed in glioma stem cell-challenged hUCBSC culture filtrates. Furthermore, hUCBSC showed a stronger migration capacity toward glioma stem cells in vitro and exhibited enhanced migration to glioma stem cells in an intracranial human malignant glioma xenograft model. Our results indicate that multiple cytokines are involved in recruitment of hUCBSC toward glioma stem cells, and that hUCBSC are a potential candidate for glioma therapy.     

Gene expression,protein profiling,and chemotactic activity of infrapatellar fat pad mesenchymal stem cells in pathologies of the knee joint

The infrapatellar fat pad (IPFP) is a periarticular adipose knee tissue. This tissue contains a large number of mesenchymal stem cells (MSCs). In the present work, we wanted to study the IPFP MSCs and their relationship and differences in two groups, anterior cruciate ligament (ACL) ruptures knees and ostheoarthrosis (OA). The IPFP of 42 patients with OA or ACL rupture were analyzed. Isolation, primary culture, and a genetic and proteomic study of MSCs from IPFP were performed. Gene expression of IL-6, tumor necrosis factor (TNF), IL-8, HSPA1A (Hsp70), CXCL10, RANTES, MMP1, MMP3, TIMP1, and BMP7 was analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). We analyzed MSCs from from 12 diferents patients in two cellular pools (6 from AO disease and 6 from ALC rupture to form two cell pool), for the iTRAQ Proteomic Assay. The conditional media were used in quantitative analysis of MSC soluble factors by Luminex and for de migration assay. A higher gene expression of IL-6, TNF, CXCL10, RANTES, and MMP1 and OPG in MSCs from OA versus ACL (p < 0.05) was observed. Conversely HSPA1A, TIMP1, and RANKL showed a significant lower expression in OA-MSCs (p < 0.05). In the secretome analysis, adipsin and visfantin levels in the supernatants from OA-MSCs were lower (p < 0.05) respect to ACL-MSCs. Also, the monocytic cells migrated two-folds in the presence of conditioned media from OA-MSCs patients versus patients with ACL-MSC. The infrapatellar pad should be considered as an adipose tissue capable of producing and excreting inflammatory mediators directly in the knee joint, influencing the development and progression of knee joint pathologies.     

Proteomic techniques for characterisation of mesenchymal stem cell secretome

Mesenchymal stem cells (MSCs) are multipotent cells with a substantial potential in human regenerative medicine due to their ability to migrate to sites of injury, capability to suppress immune response and accessibility in large amount from patient's own bone marrow or fat tissue. It has been increasingly observed that the transplanted MSCs did not necessarily engraft and differentiate at the site of injury but might exert their therapeutic effects through secreted trophic signals. The MSCs secrete a variety of autocrine/paracrine factors, called secretome, that support regenerative processes in the damaged tissue, induce angiogenesis, protect cells from apoptotic cell death and modulate immune system. The cell culture medium conditioned by MSCs or osteogenic, chondrogenic as well as adipogenic precursors derived from MSCs has become a subject of intensive proteomic profiling in the search for and identification of released factors and microvesicles that might be applicable in regenerative medicine. Jointly with the methods for MSC isolation, expansion and differentiation, proteomic analysis of MSC secretome was enabled recently mainly due to the extensive development in protein separation techniques, mass spectrometry, immunological methods and bioinformatics. This review describes proteomic techniques currently applied or prospectively applicable in MSC secretomics, with a particular focus on preparation of the secretome sample, protein/peptide separation, mass spectrometry and protein quantification techniques, analysis of posttranslational modifications, immunological techniques, isolation and characterisation of secreted vesicles and exosomes, analysis of cytokine-encoding mRNAs and bioinformatics.     

Therapeutic potential of the immunomodulatory activities of adult mesenchymal stem cells

Adult mesenchymal stem cells (MSCs) include a select population of resident cells within adult tissues, which retain the ability to differentiate along several tissue‐specific lineages under defined media conditions and have finite expansion potential in vitro. These adult progenitor populations have been identified in various tissues, but it remains unclear exactly what role both transplanted and native MSCs play in processes of disease and regeneration. Interestingly, increasing evidence reveals a unique antiinflammatory immunomodulatory phenotype shared among this population, lending support to the idea that MSCs play a central role in early tissue remodeling responses where a controlled inflammatory response is required. However, additional evidence suggests that MSCs may not retain infinite immune privilege and that the context with which these cells are introduced in vivo may influence their immune phenotype. Therefore, understanding this dynamic microenvironment in which MSCs participate in complex feedback loops acting upon and being influenced by a plethora of secreted cytokines, extracellular matrix molecules, and fragments will be critical to elucidating the role of MSCs in the intertwined processes of immunomodulation and tissue repair. Birth Defects Research (Part C) 90:67–74, 2010. © 2010 Wiley‐Liss, Inc.     

Mesenchymal stem cells in regenerative medicine applied to rheumatic diseases: Role of secretome and exosomes

Over the last decades, mesenchymal stem cells (MSCs) have been extensively studied with regard to their potential applications in regenerative medicine. In rheumatic diseases, MSC-based therapy is the subject of great expectations for patients who are refractory to proposed treatments such as rheumatoid arthritis (RA), or display degenerative injuries without possible curative treatment, such as osteoarthritis (OA). The therapeutic potential of MSCs has been demonstrated in several pre-clinical models of OA or RA and both the safety and efficacy of MSC-based therapy is being evaluated in humans. The predominant mechanism by which MSCs participate to tissue repair is through a paracrine activity. Via the production of a multitude of trophic factors with various properties, MSCs can reduce tissue injury, protect tissue from further degradation and/or enhance tissue repair. However, a thorough in vivo examination of MSC-derived secretome and strategies to modulate it are still lacking. The present review discusses the current understanding of the MSC secretome as a therapeutic for treatment of inflammatory or degenerative pathologies focusing on rheumatic diseases. We provide insights on and perspectives for future development of the MSC secretome with respect to the release of extracellular vesicles that would have certain advantages over injection of living MSCs or administration of a single therapeutic factor or a combination of factors.     

Disagreements in the therapeutic use of mesenchymal stem cell-derived secretome

In a recent article, the authors provide a detailed summary of the characteristics and biological functions of mesenchymal stem cells (MSCs), as well as a discussion on the potential mechanisms of action of MSC-based therapies. They describe the morphology, biogenesis, and current isolation techniques of exosomes, one of the most important fractions of the MSC-derived secretome. They also summarize the characteristics of MSC-derived exosomes and highlight their functions and therapeutic potential for tissue/organ regeneration and for kidney, liver, cardiovascular, neurological, and musculoskeletal diseases, as well as cutaneous wound healing. Despite the fact that MSCs are regarded as an important pillar of regenerative medicine, their regenerative potential has been demonstrated to be limited in a number of pathological conditions. The negative effects of MSC-based cell therapy have heightened interest in the therapeutic use of MSC-derived secretome. On the other hand, MSC-derived exosomes and microvesicles possess the potential to have a significant impact on disease development, including cancer. MSCs can interact with tumor cells and promote mutual exchange and induction of cellular markers by exchanging secretome. Furthermore, enzymes secreted into and activated within exosomes can result in tumor cells acquiring new properties. As a result, therapeutic applications of MSC-derived secretomes must be approached with extreme caution.     

Mesenchymal stem cells secretome: The cornerstone of cell-free regenerative medicine

Mesenchymal stem cells (MSCs) are the most frequently used stem cells in clinical trials due to their easy isolation from various adult tissues, their ability of homing to injury sites and their potential to differentiate into multiple cell types. However, the realization that the beneficial effect of MSCs relies mainly on their paracrine action, rather than on their engraftment in the recipient tissue and subsequent differentiation, has opened the way to cell-free therapeutic strategies in regenerative medicine. All the soluble factors and vesicles secreted by MSCs are commonly known as secretome. MSCs secretome has a key role in cell-to-cell communication and has been proven to be an active mediator of immune-modulation and regeneration both in vitro and in vivo. Moreover, the use of secretome has key advantages over cell-based therapies, such as a lower immunogenicity and easy production, handling and storage. Importantly, MSCs can be modulated to alter their secretome composition to better suit specific therapeutic goals, thus, opening a large number of possibilities. Altogether these advantages now place MSCs secretome at the center of an important number of investigations in different clinical contexts, enabling rapid scientific progress in this field.     

Cytokine interplay among the diseased retina,inflammatory cells and mesenchymal stem cells - a clue to stem cell-based therapy

Retinal degenerative disorders, such as diabetic retinopathy, retinitis pigmentosa, age-related macular degeneration or glaucoma, represent the most common causes of loss of vision and blindness. In spite of intensive research, treatment options to prevent, stop or cure these diseases are limited. Newer therapeutic approaches are offered by stem cell-based therapy. To date, various types of stem cells have been evaluated in a range of models. Among them, mesenchymal stem/stromal cells (MSCs) derived from bone marrow or adipose tissue and used as autologous cells have been proposed to have the potential to attenuate the negative manifestations of retinal diseases. MSCs delivered to the vicinity of the diseased retina can exert local anti-inflammatory and repair-promoting/regenerative effects on retinal cells. However, MSCs also produce numerous factors that could have negative impacts on retinal regeneration. The secretory activity of MSCs is strongly influenced by the cytokine environment. Therefore, the interactions among the molecules produced by the diseased retina, cytokines secreted by inflammatory cells and factors produced by MSCs will decide the development and propagation of retinal diseases. Here we discuss the interactions among cytokines and other factors in the environment of the diseased retina treated by MSCs, and we present results supporting immunoregulatory and trophic roles of molecules secreted in the vicinity of the retina during MSC-based therapy.     

Immunomodulatory properties of human adult and fetal multipotent mesenchymal stem cells

In recent years, a large number of studies have contributed to our understanding of the immunomodulatory mechanisms used by multipotent mesenchymal stem cells (MSCs). Initially isolated from the bone marrow (BM), MSCs have been found in many tissues but the strong immunomodulatory properties are best studied in BM MSCs. The immunomodulatory effects of BM MSCs are wide, extending to T lymphocytes and dendritic cells, and are therapeutically useful for treatment of immune-related diseases including graft-versus-host disease as well as possibly autoimmune diseases. However, BM MSCs are very rare cells and require an invasive procedure for procurement. Recently, MSCs have also been found in fetal-stage embryo-proper and extra-embryonic tissues, and these human fetal MSCs (F-MSCs) have a higher proliferative profile, and are capable of multilineage differentiation as well as exert strong immunomodulatory effects. As such, these F-MSCs can be viewed as alternative sources of MSCs. We review here the current understanding of the mechanisms behind the immunomodulatory properties of BM MSCs and F-MSCs. An increase in our understanding of MSC suppressor mechanisms will offer insights for prevalent clinical use of these versatile adult stem cells in the near future.     

An insight into the role of magnesium in the immunomodulatory properties of mesenchymal stem cells

Magnesium (Mg²⁺) is a mineral with the ability to influence cell proliferation and to modulate inflammatory/immune responses, due to its anti-inflammatory properties. In addition, mesenchymal stem cells (MSCs) modulate the function of all major immune cell populations. Knowing that, the current work aimed to investigate the effects of Mg²⁺ enrichment, and its influence on the immunomodulatory capacity of MSCs. Murine C3H/10T1/2 MSCs were cultivated in media with different concentrations of Mg²⁺ (0, 1, 3 and 5 mM), in order to evaluate the effects of Mg²⁺ on MSC immunomodulatory properties, cell proliferation rates, expression of NFκB and STAT-3, production of IL-1β, IL-6, TGF-β, IL-10, PGE2 and NO, and TRPM7 expression. The results showed that TRPM7 is expressed in MSCs, but Mg²⁺, in the way that cells were cultivated, did not affect TRPM7 expression. Additionally, there was no difference in the intracellular concentration of Mg²⁺. Mg²⁺, especially at 5 mM, raised proliferation rates of MSCs, and modulated immune responses by decreasing levels of IL-1β and IL-6, and by increasing levels of IL-10 and PGE2 in cells stimulated with LPS or TNF-α. In addition, MSCs cultured in 5 mM Mg²⁺ expressed lower levels of pNFκB/NFκB and higher levels of pSTAT-3/STAT-3. Furthermore, conditioned media from MSCs reduced lymphocyte and macrophage proliferation, but Mg²⁺ did not affect this parameter. In addition, conditioned media from MSCs cultured at 5 mM of Mg²⁺ modulated the production profile of cytokines, especially of IL-1β and IL-6 in macrophages. In conclusion, Mg²⁺ is able to modulate some immunoregulatory properties of MSCs.     

Effect of heme oxygenase‐1 transduced bone marrow mesenchymal stem cells on damaged intestinal epithelial cells in vitro

In this study, we explored the effects of mesenchymal stem cells (MSCs) from bone marrow overexpressing heme oxygenase‐1 (HO‐1) on the damaged human intestinal epithelial barrier in vitro. Rat MSCs were isolated from bone marrow and transduced with rat HO‐1 recombinant adenovirus (HO‐MSCs) for stable expression of HO‐1. Colorectal adenocarinoma 2 (Caco2) cells were treated with tumor necrosis factor‐α (TNF‐α) to establish a damaged colon epithelial model. Damaged Caco2 were cocultured with MSCs, Ad‐MSCs, Ad‐HO + MSCs or HO‐MSCs. mRNA and protein expression of Zona occludens‐1 (ZO‐1) and human HO‐1 and the release of cytokines were measured. ZO‐1 and human HO‐1 in Caco2 were significantly decreased after treatment with TNF‐α; and this effect was reduced when coculture with MSCs from bone marrow. Expression of ZO‐1 was not significantly affected by Caco2 treatment with TNF‐α, Ad‐HO, and MSCs. In contrast, ZO‐1 and human HO‐1 increased significantly when the damaged Caco2 was treated with HO‐MSCs. HO‐MSCs showed the strongest effect on the expression of ZO‐1 in colon epithelial cells. Coculture with HO‐MSCs showed the most significant effects on reducing the expression of IL‐2, IL‐6, IFN‐γ and increasing the expression of IL‐10. HO‐MSCs protected the intestinal epithelial barrier, in which endogenous HO‐1 was involved. HO‐MSCs play an important role in the repair process by reducing the release of inflammatory cytokines and increasing the release of anti‐inflammatory factors. These results suggested that HO‐MSCs from bone marrow were more effective in repairing the damaged intestinal epithelial barrier, and the effectiveness of MSCs was improved by HO‐1 gene transduction, which provides favorable support for the application of stem cell therapy in the intestinal diseases.