Mesenchymal stem cells: biology, pathophysiology, translational findings, and therapeutic implications for cardiac disease

Mesenchymal stem cells (MSCs) are a prototypical adult stem cell with capacity for self-renewal and differentiation with a broad tissue distribution. Initially described in bone marrow, MSCs have the capacity to differentiate into mesoderm- and nonmesoderm-derived tissues. The endogenous role for MSCs is maintenance of stem cell niches (classically the hematopoietic), and as such, MSCs participate in organ homeostasis, wound healing, and successful aging. From a therapeutic perspective, and facilitated by the ease of preparation and immunologic privilege, MSCs are emerging as an extremely promising therapeutic agent for tissue regeneration. Studies in animal models of myocardial infarction have demonstrated the ability of transplanted MSCs to engraft and differentiate into cardiomyocytes and vasculature cells, recruit endogenous cardiac stem cells, and secrete a wide array of paracrine factors. Together, these properties can be harnessed to both prevent and reverse remodeling in the ischemically injured ventricle. In proof-of-concept and phase I clinical trials, MSC therapy improved left ventricular function, induced reverse remodeling, and decreased scar size. This article reviews the current understanding of MSC biology, mechanism of action in cardiac repair, translational findings, and early clinical trial data of MSC therapy for cardiac disease.     

大鼠骨髓间充质干细胞条件培养液对心脏成纤维细胞胶原合成的影响

目的体外模拟机体缺血环境,研究骨髓间充质干细胞(MSCs)旁分泌对心脏成纤维细胞胶原合成的影响,为MSCs移植机制提供实验依据。方法分离培养SD大鼠的MSCs,换以无血清培养液同时缺氧处理不同时间,然后收集MSCs的条件培养液,以此条件培养液作为刺激因子孵育 SD大鼠的心脏成纤维细胞,用MTT和3H-脯氨酸掺入观察心脏成纤维细胞的增殖及胶原合成。结果用MSCs条件培养液培养心脏成纤维细胞,3H-脯氨酸掺入明显高于对照组,缺氧6 h组的3H-脯氨酸掺入高于对照组约100％,提示MSCs条件培养液刺激心脏成纤维细胞胶原合成增加;MTT结果无显著差异,提示:MSCs条件培养液没有影响心脏成纤维细胞的增殖。结论大鼠骨髓间充质干细胞的缺氧和无血清条件培养液能够通过旁分泌刺激心脏成纤维细胞自身合成胶原能力的增强,提示移植到缺血心肌缺血区的骨髓间充质干细胞可能通过旁分泌作用影响心脏成纤维细胞的胶原合成,从而参与损伤心肌的修复。     

Improved graft mesenchymal stem cell survival in ischemic heart with a hypoxia-regulated heme oxygenase-1 vector.

OBJECTIVES: The goal of this study was to modify mesenchymal stem cells (MSCs) cells with a hypoxia-regulated heme oxygenase-1 (HO-1) plasmid to enhance the survival of MSCs in acute myocardial infarction (MI) heart. BACKGROUND: Although stem cells are being tested clinically for cardiac repair, graft cells die in the ischemic heart because of the effects of hypoxia/reoxygenation, inflammatory cytokines, and proapoptotic factors. Heme oxygenase-1 is a key component in inhibiting most of these factors. METHODS: Mesenchymal stem cells from bone marrow were transfected with either HO-1 or LacZ plasmids. Cell apoptosis was assayed in vitro after hypoxia-reoxygen treatment. In vivo, 1 x 10(6) of male MSC(HO-1), MSC(LacZ), MSCs, or medium was injected into mouse hearts 1 h after MI (n = 16/group). Cell survival was assessed in a gender-mismatched transplantation model. Apoptosis, left ventricular remodeling, and cardiac function were tested in a gender-matched model. RESULTS: In the ischemic myocardium, the MSC(HO-1) group had greater expression of HO-1 and a 2-fold reduction in the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling-positive cells compared with the MSC(LacZ) group. At seven days after implantation, the survival MSC(HO-1) was five-fold greater than the MSC(LacZ) group; MSC(HO-1) also attenuated left ventricular remodeling and enhanced the functional recovery of infarcted hearts two weeks after MI. CONCLUSIONS: A hypoxia-regulated HO-1 vector modification of MSCs enhances the tolerance of engrafted MSCs to hypoxia-reoxygen injury in vitro and improves their viability in ischemic hearts. This demonstration is the first showing that a physiologically inducible vector expressing of HO-1 genes improves the survival of stem cells in myocardial ischemia.     

当归补血汤对体外造血微环境中小鼠肌卫星细胞增殖及c-kit表达的影响

目的观察当归补血汤对体外造血微环境中小鼠肌卫星细胞增殖及c-kit表达的影响。方法分离培养小鼠卫星细胞并鉴定。制备含有不同剂量当归补血汤的大鼠载药血清及对应剂量的骨髓基质细胞条件培养基。将肌卫星细胞随机分为8组:正常大鼠血清组、当归补血汤载药血清1～3组、正常大鼠血清条件培养基组、条件培养基1～3组,MTT法检测细胞增殖活性,免疫组化法检测细胞c-kit的表达情况,荧光实时定量PCR检测细胞c-kit mRNA的表达。结果培养的肌卫星细胞呈Desmin免疫阳性;与正常大鼠血清组相比,载药血清各组及条件培养基各组细胞增殖显著,载药血清3组、条件培养基各组阳性细胞c-kit蛋白及mRNA表达量有显著性差异,随当归补血汤载药血清浓度增大c-kit表达量增多,条件培养基也呈同样的变化趋势。结论当归补血汤载药血清及含载药血清的条件培养基可促进肌卫星细胞增殖及c-kit的表达。     

Equal modulation of endothelial cell function by four distinct tissue-specific mesenchymal stem cells

Mesenchymal stem cells (MSCs) can generate multiple end-stage mesenchymal cell types and constitute a promising population of cells for regenerative therapies. Additionally, there is increasing evidence supporting other trophic activities of MSCs, including the ability to enable formation of vasculature in vivo. Although MSCs were originally isolated from the bone marrow, the presence of these cells in the stromal vascular fraction of multiple adult tissues has been recently recognized. However, it is unknown whether the capacity to modulate vasculogenesis is ubiquitous to all MSCs regardless of their tissue of origin. Here, we demonstrated that tissue-resident MSCs isolated from four distinct tissues have equal capacity to modulate endothelial cell function, including formation of vascular networks in vivo. MSCs were isolated from four murine tissues, including bone marrow, white adipose tissue, skeletal muscle, and myocardium. In culture, all four MSC populations secreted a plethora of pro-angiogenic factors that unequivocally induced proliferation, migration, and tube formation of endothelial colony-forming cells (ECFCs). In vivo, co-implantation of MSCs with ECFCs into mice generated an extensive network of blood vessels with ECFCs specifically lining the lumens and MSCs occupying perivascular positions. Importantly, there were no differences among all four MSCs evaluated. Our studies suggest that the capacity to modulate the formation of vasculature is a ubiquitous property of all MSCs, irrespective of their original anatomical location. These results validate multiple tissues as potential sources of MSCs for future cell-based vascular therapies.     

The interactions between brain microvascular endothelial cells and mesenchymal stem cells under hypoxic conditions

The purpose of the present study was to investigate the interactions between brain microvascular endothelial cells (BMEC) and mesenchymal stem cells (MSC) under hypoxic conditions. Primary cultured human bone marrow MSC and rat BMEC were isolated, cultured and identified. Vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) were detected in the conditioned media of BMEC and MSC under normal and hypoxic conditions using ELISA. MSC differentiation was analyzed using flow cytometry and fluorescence immunocytochemistry. Transendothelial electrical resistance (TEER) techniques were employed to measure changes in permeability across the BMEC monolayer. Under hypoxic conditions, the concentration of VEGF and MMP-9 in the conditioned media increased significantly, with greater levels in the MSC than the BMEC media. Primary MSC did not express vWF and Flk-1. MSC were co-cultured with BMEC under hypoxic conditions 5 days later. MSC expressing Flk-1 accounted for 23.64+/-2.50% (n=6, P<0.001) of the total number of cells. Interestingly, some Flk-1 positive cells began to coexpress vWF simultaneously. Under hypoxic conditions, MSC conditioned media significantly enhanced the proliferation and migration of BMEC. In addition, MSC decreased the TEER of the BMEC monolayer (lowest values: 50.5+/-2.6% of the original), which could partially be inhibited by both anti-VEGF antibody and MMP-9 inhibitor. These data indicate that under hypoxic conditions BMEC induce MSC to differentiate into endothelial cells, and MSC enhance the proliferation and migration of BMEC through paracrine functions, while simultaneously increasing the permeability of the BMEC monolayer.     

Stem Cell Therapy for Arterial Restenosis: Potential Parameters Contributing to the Success of Bone Marrow-Derived Mesenchymal Stromal Cells

Purpose

Restenosis is a complex and heterogeneous pathophysiological phenomenon occurring in patients submitted to revascularization procedures. Previous studies proved the antirestenotic properties of injected allogenic mesenchymal stromal cells (MSCs) in an experimental model of rat carotid (re)stenosis induced through arteriotomy. In this study we describe some of the effects subsequent to MSC treatment of rats submitted to carotid arteriotomy and possibly responsible for their antirestenotic effect.

Methods

Rat MSCs were isolated from bone marrow, expanded in vitro and characterized. Subsequently, we evaluated the effects of MSC administration via tail vein at 3 and 7?days after carotid arteriotomy both in rat serum and in injured carotids, focusing on DNA oxidative damage (8-oxo-dG detection), cell proliferation index (BrdU incorporation assay), apoptotic index (TUNEL assay), the expression of inflammation- and proliferation-related genes (RT-PCR), the release of growth factors and of inflammation-related cytokines (antibody arrays and ELISA).

Results

MSC administration induced a greater cell proliferation in carotids after arteriotomy, together with an increased level of VEGF in the serum and with the higher expression of VEGF mRNA in injured carotids. Serum analysis also revealed a decreased level of the pro-inflammatory cytokines CXCL1, CXCL5, L-Selectin, ICAM-1 and LIX, and of TIMP1 and SDF-1alpha in MSC-treated rats. The MSC immunomodulatory activity was confirmed by the decreased expression of TLR2 and TLR4 in injured carotids.

Conclusions

MSCs play an immunomodulatory paracrine role when injected in rats submitted to carotid arteriotomy, accompanied by the release of VEGF, possibly contributing to the accelerated repair of the injured vascular wall.     

Mesenchymal stromal cells from Shwachman‐Diamond syndrome patients fail to recreate a bone marrow niche in vivo and exhibit impaired angiogenesis

Shwachman‐Diamond syndrome (SDS) is a rare multi‐organ recessive disease mainly characterised by pancreatic insufficiency, skeletal defects, short stature and bone marrow failure (BMF). As in many other BMF syndromes, SDS patients are predisposed to develop a number of haematopoietic malignancies, particularly myelodysplastic syndrome and acute myeloid leukaemia. However, the mechanism of cancer predisposition in SDS patients is only partially understood. In light of the emerging role of mesenchymal stromal cells (MSCs) in the regulation of bone marrow homeostasis, we assessed the ability of MSCs derived from SDS patients (SDS‐MSCs) to recreate a functional bone marrow niche, taking advantage of a murine heterotopic MSC transplant model. We show that the ability of semi‐cartilaginous pellets (SCPs) derived from SDS‐MSCs to generate complete heterotopic ossicles in vivo is severely impaired in comparison with HD‐MSC‐derived SCPs. Specifically, after in vitro angiogenic stimuli, SDS‐MSCs showed a defective ability to form correct networks, capillary tubes and vessels and displayed a marked decrease in VEGFA expression. Altogether, these findings unveil a novel mechanism of SDS‐mediated haematopoietic dysfunction based on hampered ability of SDS‐MSCs to support angiogenesis. Overall, MSCs could represent a new appealing therapeutic target to treat dysfunctional haematopoiesis in paediatric SDS patients.     

Arteriogenesis: the development and growth of collateral arteries

In patients with atherosclerotic vascular diseases, collateral vessels bypassing major arterial obstructions have frequently been observed. This may explain why some patients remain without symptoms or signs of ischemia. The term "arteriogenesis" was introduced to differentiate the formation of collateral arteries from angiogenesis, which mainly occurs in the ischemic, collateral flow-dependent tissue. Many observations in various animal models and humans support that the remodeling of preexisting collateral vessels is the mechanism of collateral artery formation. This remodeling process seems to be mainly flow-mediated. It involves endothelial cell activation, basal membrane degradation, leukocyte invasion, proliferation of vascular cells, neointima formation (in most species studied), and changes of the extracellular matrix. The contribution of ischemia to arteriogenesis is still unclear, but arteriogenesis clearly can occur in the absence of any significant ischemia. It is questionable, whether collateral arteries also form de novo in ischemic vascular diseases. A better understanding of the mechanisms of arteriogenesis will be important for the design of more effective strategies for the treatment of patients with ischemic vascular diseases.     

Bone marrow mesenchymal stem cells inhibit the response of naive and memory antigen-specific T cells to their cognate peptide

Mesenchymal stem cells (MSCs) have been recently shown to inhibit T-cell proliferation to polyclonal stimuli. We characterized the effect of MSCs of bone marrow origin on the T-cell response of naive and memory T cells to their cognate antigenic epitopes. The immune response to murine male transplantation antigens, HY, was selected because the peptide identity and major histocompatibility complex (MHC) restriction of the immunodominant epitopes are known. C57BL/6 female mice immunized with male cells were the source of memory T cells, whereas C6 mice transgenic for HY-specific T-cell receptor provided naive T cells. Responder cells were stimulated in vitro with male spleen cells or HY peptides in the presence or absence of MSCs. MSCs inhibited HY-specific naive and memory T cells in a dose-dependent fashion and affected cell proliferation, cytotoxicity, and the number of interferon gamma (IFN-gamma)-producing HY peptide-specific T cells. However, the MSC inhibitory effect did not selectively target antigen-reactive T cells. When MSCs were added to the T-cell cultures in a Transwell system or MSCs were replaced by MSC culture supernatant, the inhibitory activity was abrogated. T-cell reactivity was also restored if MSCs were removed from the cultures. The expression of MHC molecules and the presence in culture of antigen-presenting cells (APCs) or of CD4(+)/CD25(+) regulatory T cells were not required for MSCs to inhibit. We conclude that MSCs inhibit naive and memory T-cell responses to their cognate antigens. Overall our data suggest that MSCs physically hinder T cells from the contact with APCs in a noncognate fashion.     

Alkylating chemotherapeutic agents cyclophosphamide and melphalan cause functional injury to human bone marrow-derived mesenchymal stem cells

The adverse effects of melphalan and cyclophosphamide on hematopoietic stem cells are well-known; however, the effects on the mesenchymal stem cells (MSCs) residing in the bone marrow are less well characterised. Examining the effects of chemotherapeutic agents on patient MSCs in vivo is difficult due to variability in patients and differences in the drug combinations used, both of which could have implications on MSC function. As drugs are not commonly used as single agents during high-dose chemotherapy (HDC) regimens, there is a lack of data comparing the short- or long-term effects these drugs have on patients post treatment. To help address these problems, the effects of the alkylating chemotherapeutic agents cyclophosphamide and melphalan on human bone marrow MSCs were evaluated in vitro. Within this study, the exposure of MSCs to the chemotherapeutic agents cyclophosphamide or melphalan had strong negative effects on MSC expansion and CD44 expression. In addition, changes were seen in the ability of MSCs to support hematopoietic cell migration and repopulation. These observations therefore highlight potential disadvantages in the use of autologous MSCs in chemotherapeutically pre-treated patients for future therapeutic strategies. Furthermore, this study suggests that if the damage caused by chemotherapeutic agents to marrow MSCs is substantial, it would be logical to use cultured allogeneic MSCs therapeutically to assist or repair the marrow microenvironment after HDC.     

A small proportion of mesenchymal stem cells strongly expresses functionally active CXCR4 receptor capable of promoting migration to bone marrow

Homing of bone marrow stromal cells (MSCs) to bone and bone marrow after transplantation, important for the correction of conditions such as metabolic storage disorders, can occur but with poor efficiency. Substantial improvements in engraftment will be required in order to derive a clinical benefit from MSC transplantation. Chemokines are the most important factors controlling cellular migration. Stromal-derived factor-1 (SDF-1) has been shown to be critical in promoting the migration of cells to the bone marrow, via its specific receptor CXCR4. The aim of our study was to investigate CXCR4 expression on MSCs and its role in mediating migration to bone marrow. We show that CXCR4, although present at the surface of a small subset of MSCs, is important for mediating specific migration of these cells to bone marrow.     

Transplantation of mesenchymal stem cells attenuates myocardial injury and dysfunction in a rat model of acute myocarditis

Acute myocarditis is a non-ischemic inflammatory disease of the myocardium for which there is currently no specific treatment. We have previously shown that mesenchymal stem cells (MSC) can ameliorate heart injury during acute ischemia and in dilated cardiomyopathy; however, the therapeutic potential in acute myocarditis is unclear. In this study, we investigated the ability of MSC to attenuate myocardial injury and dysfunction during the acute phase of experimental myocarditis. Ten-week-old male Lewis rats were injected with porcine myosin to induce myocarditis. Cultured MSC (3x10(6) cells/rat) were injected intravenously 7 days after myosin injection. At 3 weeks, myosin injection resulted in severe inflammation and significant deterioration of cardiac function. MSC transplantation attenuated increases in CD68-positive inflammatory cells and monocyte chemoattractant protein-1 (MCP-1) expression in myocardium, and improved cardiac function in this model. Furthermore, myocardial capillary density was higher in myocarditis tissue, and was further increased by MSC transplantation. In vitro, cultured adult rat cardiomyocytes were injured in response to MCP-1, whereas this effect was attenuated by MSC-derived conditioned medium, suggesting cardioprotective effects of MSC acting in a paracrine manner. MSC transplantation attenuated myocardial injury and dysfunction in a rat model of acute myocarditis, at least in part through paracrine effects of MSC.     

Chemokines in mesenchymal stem cell therapy for bone repair: a novel concept of recruiting mesenchymal stem cells and the possible cell sources

Skeletal injury is one of the most prevalent clinical problems that jeopardize the activities of daily life, especially in our aging society. Mesenchymal stem cells (MSCs) play pivotal roles in regenerating bones after bone injury. MSCs come from the surrounding tissues and/or circulation. Cell sources may be the bone marrow, periosteum, vessel walls, muscle, circulation, and elsewhere, and the migration of MSCs is necessary for bone healing. The mechanism(s) of recruitment and crucial molecules for cell migration are still unclear, but chemokines and their receptors seem to play critical roles. The induction of MSC recruitment from surrounding tissues or from the circulation can be a helpful modality to induce or to support cell-based therapy for bone regeneration.     

Mesenchymal stem cells for clinical application

Mesenchymal Stem Cells/Multipotent Marrow Stromal Cells (MSC) are multipotent adult stem cells present in all tissues, as part of the perivascular population. As multipotent cells, MSCs can differentiate into different tissues originating from mesoderm ranging from bone and cartilage, to cardiac muscle. Conflicting data show that MSCs could be pluripotent and able to differentiate into tissues and cells of non‐mesodermic origin as neurons or epithelial cells. Moreover, MSCs exhibit non‐HLA restricted immunosuppressive properties. This wide range of properties leads to increasing uses of MSC for immunomodulation or tissue repair. Based on their immunosuppressive properties MSC are used particularly in the treatment of graft versus host disease, For tissue repair, MSCs can work by different ways from cell replacement to paracrine effects through the release of cytokines and to regulation of immune/inflammatory responses. In regenerative medicine, trials are in progress or planed for healing/repair of different tissue or organs as bone, cartilage, vessels, myocardium, or epithelia. Although it has been demonstrated that ex‐vivo expansion processes using fetal bovine serum, recombinant growth factors (e.g. FGF2) or platelet lysate are feasible, definitive standards to produce clinical‐grade MSC are still lacking. MSCs have to be produced according GMP and regulation constraints. For answering to the numerous challenges in this fast developing field of biology and medicine, integrative networks linking together research teams, cell therapy laboratories and clinical teams are needed.     

Ischemic cerebral tissue and MCP-1 enhance rat bone marrow stromal cell migration in interface culture

OBJECTIVE: Intravascular administration of bone marrow stromal cells (MSCs) restores function in animal models of neural injury and neurodegeneration. Adult MSCs administered intravenously to rat migrate and express neural phenotypes in ischemic brain. The aim of the present study was to investigate the mechanisms targeting MSC migration into the ischemic brain. METHODS: Monocyte chemoattractant protein-1 (MCP-1), a chemoattractant factor, was measured in rat ischemic brain at various time points after middle cerebral artery occlusion (MCAo) using a specific enzyme-linked immunosorbent assay system (ELISA). In addition, using a microchemotaxis chamber, we measured whether ischemic brain tissue extracts induce migration of MSCs and whether brain tissue extracts incubated with antibodies against MCP-1 reduce MSC migration. RESULT: Our data indicate that ischemic brain MCP-1 levels significantly increase from 6 hours, peak at 48 hours after MCAo (p < 0.05), and thereafter gradually decrease. Brain tissue extract at 6 hours, 24 hours, and 48 hours after MCAo significantly increase MSC migration across the membrane of the microchemotaxis chamber compared to normal tissue (p < 0.05). However, when the ischemic brain tissue extracts are incubated with antibody against MCP-1, MSC migration is significantly reduced at 24 hours and 48 hours after MCAo compared to extracts without this antibody (p < 0.05). CONCLUSION: Our data suggest that MCP-1 contributes to MSC migration into the ischemic brain tissue environment.     

Human bone marrow mesenchymal stem cells in vivo

Great confusion still exists amongst cell biologists, musculoskeletal and other specialists interested in regenerative medicine regarding the in vivo identity of human bone marrow (BM) mesenchymal stem cells (MSCs). Contrary to views held in some quarters, methods for the robust identification and purification of BM MSCs are now well established. Human BM MSCs represent a phenotypically homogeneous cell population that share an identical phenotype with marrow adventitial reticular cells (ARCs), which are stromal cells similar in nature to pericytes. When an extensive panel of markers is used to characterize BM MSCs, it appears that the diverse MSC markers described in different laboratories are expressed on the same cell population. Rare cell phenotypical analysis and in vitro colony forming unit-fibroblast (CFU-F) assays produce no compelling evidence that BM MSCs circulate in healthy man. Furthermore, although investigators speak of a number of specific MSC markers, a true marker of MSC 'stemness' and multipotentiality has not yet been defined since culture-expanded MSCs may lose some of these markers, but remain multipotential. This knowledge provides a platform for understanding MSCs in vivo leading to novel approaches for therapy development, including in situ tissue engineering.     

Effect of aged bone marrow microenvironment on mesenchymal stem cell migration

Mesenchymal stem cells (MSCs) are known to have many notable features, especially their multiple differentiation ability and immunoregulatory capacity. MSCs are important stem cells in the bone marrow (BM), and their characteristics are affected by the BM microenvironment. However, effects of the BM microenvironment on the properties of MSCs are not well understood. In this study, we found that BM from aged mice decreased MSC colony formation. Flow cytometry data showed that the proportion of B220⁺ cells in BM from aged mice was significantly lower than that in BM from young mice, while the proportion of CD11b⁺, CD3⁺, Gr-1⁺, or F4/80⁺ cells are on the contrary. CD11b⁺, B220⁺, and Ter119⁺ cells from aged mice were not the subsets that decreased MSC colony formation. We further demonstrated that both BM from aged mice and young mice exhibited similar effects on the proliferation of murine MSC cell line C3H10T1/2. However, when cocultured with BM from aged mice, C3H10T1/2 showed slower migration ability. In addition, we found that phosphorylation of JNK (c-Jun N-terminal kinases) in C3H10T1/2 cocultured with BM from aged mice was lower than that in C3H10T1/2 cocultured with BM from young mice. Collectively, our data revealed that BM from aged mice could decrease the migration of MSCs from their niche through regulating the JNK pathway.