碱性成纤维细胞生长因子基因转染骨髓间充质干细胞在失神经肌肉萎缩中的应用

BACKGROUND: How to avoid denervated muscular atrophy is a key factor to improve the therapeutic efficacy on peripheral nerve injuries.OBJECTIVE: To study the effect of basic fibroblast growth factor (bFGF) gene-transfected bone marrow mesenchymal stem cells against denervated muscle atrophy.METHODS:bFGF genes were transfected into rat bone marrow mesenchymal stem cells using viral transfection method, and then MTT, immunohistochemical staining, hematoxylin-eosin staining, RT-PCR, western blot, and ELISA methods were used to detect the transfection efficiency and product expression. Thirty-two Sprague-Dawley rats were selected to make animal models of sciatic nerve injury, and subjected to multi-point intramuscular injection of bFGF-transfected bone marrow mesenchymal stem cells (experimental group) or cell culture fluid (control group). At 2, 4, 6, 8 weeks after transfection, the gastrocnemius muscle tissues were harvested to detect action potential, residual wet weight, and cross-sectional area of muscle fibers.RESULTS AND CONCLUSION: The bFGF gene was successfully transfected into bone marrow mesenchymal stem cells using the viral transfection method. The residual wet weight, cross-sectional area and residual action potential of the gastrocnemius muscle were significantly better in the experimental group than the control group (P < 0.05). These findings indicate that bFGF gene-transfected bone marrow mesenchymal stem cells transplanted into the denervated muscle can retard the development of muscle atrophy.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

细胞因子诱导杀伤细胞分泌因子影响人肝癌干细胞的凋亡

BACKGROUND: Immunotherapy with autologous immune cells has been developed as a major adjuvant therapy for malignant tumors, but its mechanism of action has not been elucidated. OBJECTIVE: To investigate the relationship between cytokine-induced killer cell secretion and apoptosis in human liver cancer stem cells. METHODS: Human liver cancer stem cells, HepG2 cells, were isolated and enriched using serum-free suspension method. The peripheral blood mononuclear cells from patients with liver cancer were induced by γ-interferon, CD3 monoclonal antibody and recombinant human interleukin-2 to form killer cells. Passage 1 liver cancer stem cells were divided into control group (culture alone) and experimental group (co-culture of cytokines-induced killer cells and human liver cancer stem cells). At 48 hours after culture, apoptosis in human liver cancer stem cells was detected using flow cytometry, and expression of caspase-3 mRNA and protein was detected using RT-PCR and western blot, respectively. RESULTS AND CONCLUSION: The apoptotic rate in the control group was significantly lower than that in the experimental group (P < 0.05). The expressions of caspase-3 at mRNA and protein levels were both higher in the experimental group than the control group (P < 0.05). Experimental findings show that cytokines-induced killer cells can significantly promote apoptosis in human liver cancer stem cells, and up-regulate the caspase-3 mRNA and protein expressions dramatically.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程      

中药诱导骨髓间充质干细胞的定向分化：研究与进展

BACKGROUND: In recent years, in-depth studies that single Chinese herbs or extracts, compound traditional Chinese medicine and medicated serum are used to regulate the directional differentiation of bone marrow mesenchymal stem cells into myofibroblasts, chondrocytes, osteoblasts, myocardial cells and nerve cells, which have become a highlight in the tissue engineering research.OBJECTIVE: To review the latest progress in the directional differentiation of bone marrow mesenchymal stem cells induced by Chinese herbs or their extracts.METHODS: The first author searched the CNKI, Wanfang and PubMed databases using the keywords of “Chinese herb, directional differentiation, mesenchymal stem cells” in Chinese and English, respectively, to retrieve relevant articles published from January 2010 to January 2016. Repetitive articles or those with no originality were eliminated. Totally 99 articles were searched initially, and then 43 articles were included in result analysis.RESULTS AND CONCLUSION: As the strongest seed cells in the bone differentiation system, bone marrow mesenchymal stem cells have a wide range of directional differentiation potential, and highlight the important value in combination with Chinese herbs for clinical treatment of various refractory diseases, especially for treatment of metabolic bone diseases, bone defects, nonunion and delayed union, which is not only conducive to in-depth, multi-angle studies on effects and mechanisms of Chinese herbs, but also to clinical treatment of various refractory diseases using bone marrow mesenchymal stem cells.   中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

卵巢癌CD90+肿瘤干细胞的生物学特性

BACKGROUND: Thinking from ovarian cancer stem cell theory shows that: in the tumor cells, there are a fraction of stem cells with self-renewing ability and multipotent differentiation, which are the root causes of ovarian cancer recurrence and drug resistance. Studies have shown that CD90 can be used as a surface marker of mesenchymal stem cells and stem cells of other cancers.OBJECTIVE: To explore the biological features of CD90⁺ tumor cells from ovarian cancer tissues.METHODS:Primary ovarian cancer cells were isolated from the abdominal dropsy of ovarian cancer patients to sort CD90⁺ and CD90^- cells using flow cytometry. RT-PCR was used to detect expressions of stem cell-related genes and epithelial to mesenchymal transition-related genes. Cell invasion was observed by Transwell invasion assay, cell proliferation and differentiation observed by clone formation assay, stem cell potential observed by suspension sphere-forming assay, and tumor formation rate observed by in vivo tumorigenicity experiment.RESULTS AND CONCLUSION: Compared with the CD90^- cells, the expressions of CD44, CD133, ALDH1, N-cad and Vimentine were significantly higher in the CD90⁺ cells (P < 0.05), but the expression of E-cad was significantly decreased in the CD90⁺ cells (P < 0.05). Tumor formation rates of CD90^- and CD90⁺ cells were increased significantly with the increase of seeded cell number, which was more obvious in CD90⁺ cells. The number of transmembrane cells, the number of cell clones and the number of suspended spheres were significantly higher in the CD90⁺ cells than the CD90^- cells (P < 0.05). Experimental findings from this study show that CD90⁺ cells highly express epithelial to mesenchymal transition-related genes and stem cell-related genes, with higher invasion, proliferation and differentiation, in vivo tumorigenicity and potential of stem cells. CD90⁺ cell separation may be a new method to separate ovarian cancer stem cells.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

脐带间充质干细胞在颅脑损伤模型鼠体内的迁徙与定位

BACKGROUND: Choosing an effective means to label and trace the distribution, differentiation and migration of cells in vivo help to further explore the specific mechanism of cells that exert a therapeutic effect.OBJECTIVE: To understand the migration and localization of BrdU-labeled human umbilical cord mesenchymal stem cells in brain injury model rats.METHODS: Human umbilical cord blood samples were obtained, and the isolation of human umbilical cord mesenchymal stem cells was carried out. The primary and passage culture were performed. The phenotype of cells was detected by flow cytometry. Passage 3 human umbilical cord mesenchymal stem cells were labeled using BrdU, and the cell proliferation was detected using MTT method. BrdU-labeled cells were injected into brain injury rats via the tail vein. At 14 days after transplantation, brain tissues in the injury region were cut into sections and the migration and location of the umbilical cord mesenchymal stem cells were observed under inverted fluorescence microscope.RESULTS AND CONCLUSION:Cell surface specific markers CD45 and CD34 were detected by flow cytometry, but the cells could not express CD44, CD105 and CD29. Based on the cell growth curve, the cells came into a conditioning period at 1-3 days of seeding and came into a logarithmic phase at 3-5 days. BrdU-positive cells were visible at the injury region after 14 days, indicating that in the rats, transplanted human umbilical cord mesenchymal stem cells migrated from the peripheral blood to the site of brain injury to achieve the effective repair of injured parts.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

红景天多糖对精原干细胞体外增殖的影响

BACKGROUND: To establish a rapid and effective method to obtain sufficient spermatogonial stem cells that can meet the clinical need is urgent to be solved in the spermatogonial stem cell transplantation. OBJECTIVE: To study the effect of rhodiola polysaccharide on the proliferation of spermatogonial stem cells in vitro. METHODS: Under sterile conditions, spermatogonial stem cells and Sertoli cells were isolated from the testis of mice, and spermatogonial stem cells were seeded onto the feed layer of Sertoli cells. Then, the co-cultured cells were assigned into experimental group 1 (simple cell culture medium), experimental group 2 (cell culture medium containing 150 mg/L rhodiola polysaccharide) and experimental group 3 (cell culture medium containing 150 mg/L rhodiola polysaccharide, 1 U/L leukemia inhibitory factor and 10 μg/L glial cell line-derived neurotrophic factor). After 7 days of co-culture, flow cytometry was used to detect cell proliferation in vitro, and cell viability and positive expression of GFRa-1, Thy-1 and C-kit were calculated. RESULTS AND CONCLUSION: After 7 days of co-culture, the cells grew rapidly and presented with colony and thyrsiform growth, and the number of cell masses increased significantly, all of which were in line with the proliferative features of spermatogonial stem cells. The GFRa-1, Thy-1 and C-kit proteins were expressed in the cell membrane and cytoplasm, mainly in the cell membrane. The viability of spermatogonial stem cells and positive expression of GFRa-1 and Thy-1 were ranked as follows: experimental group 3 > experimental group 2 > experimental group 1, and there were significant differences between groups (P < 0.05). The positive expression of C-kit had no difference between experimental groups 1 and 2, but it was significantly higher in the experimental group 3 than the other two groups (P < 0.05). These findings indicate that rhodiola polysaccharide used alone or combined with leukemia inhibitory factor and glial cell line-derived neurotrophic factor can enhance the proliferative ability of spermatogonial stem cells in vitro.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

Application of Stem Cells in Tissue Engineering

Stem cells have become an important source of seed cells for tissue engineering because they are relatively easy to expand in vitro and can be induced to differentiate into various cell types in vitro or in vivo. In the current stage, most stem cell researches focus on in vitro studies, including in vitro induction and phenotype characterization. Our center has made a great deal of effort in the in vivo study by using stem cells as seed cells for tissue construction. We have used bone marrow s…     

双氢青蒿素抑制胶质瘤干细胞侵袭迁移的机制

BACKGROUND: Dihydroartmisinin can promote apoptosis of glioma cells GL261, but its effect on glioma stem cells is still unknown.OBJECTIVE: To investigate the preliminary mechanism that dihydroartemisinin inhibits migration and invasion of glioma stem cells.METHODS:Glioma stem cells were isolated from mouse malignant glioma cell lines GL261. Immunofluorescence analysis was conducted to identify the characteristics of glioma stem cells. Migration and invasion abilities of glioma stem cells were analyzed by Transwell assay. The mRNA expressions of Toll-like receptor 2, matrix metalloproteinase-2 and matrix metalloproteinase-9 were examined by real-time fluorescence quantitative PCR.RESULTS AND CONCLUSION: The characteristics of glioma stem cells were identified by CD133 and Nestin staining. The migration and invasion of glioma stem cells were attenuated by dihydroartemisinin dose-dependently. Moreover, the mRNA expression of Toll-like receptor 2, matrix metalloproteinase-2 and matrix metalloproteinase-9 was also decreased by dihydroartemisinin in a dose dependent manner. These results suggest that dihydroartemisinin inhibits the migration and invasion of glioma stem cells probably through attenuation of Toll-like receptor signaling pathway.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

瘀胆血清诱导骨髓间充质干细胞向肝细胞的分化

BACKGROUND: Under certain conditions, bone marrow mesenchymal stem cells can be differentiated into hepatocytes, which are an important source of liver cells. Moreover, multiple factors can be involved in this induced differentiation process.OBJECTIVE: To investigate the inducible effect of cholestatic serum on the differentiation of bone marrow mesenchymal stem cells into hepatocytes.METHODS: Cholestatic animal model was prepared in rats to extract cholestatic serum. Bone marrow mesenchymal stem cells isolated from rats were divided into three groups and cultured in serum-free hepatocyte medium, serum-free hepatocyte medium plus cholestatic serum, serum-free hepatocyte medium plus normal serum, respectively.RESULTS AND CONCLUSION: The positive expression of alpha fetoprotein and keratin 18 and mass concentration of albumin were significantly higher in the serum-free hepatocyte medium plus cholestatic serum group than the other two groups (P < 0.05). These findings indicate that cholestatic serum has a certain inducible role in the differentiation of bone marrow mesenchymal stem cells into hepatocytes.  中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

CD133+细胞联合人脐血干细胞在心力衰竭小鼠中的作用

BACKGROUND: Currently, conventional treatment methods for heart failure are all ineffective. OBJECTIVE: To explore the combined effects of human umbilical cord stem cells and CD133+ cells in mice with heart failure, providing a new insight into the treatment of heart failure. METHODS: Full-term newborn umbilical cord from vaginal delivery was collected to isolate CD133+ cells and human umbilical cord stem cells using lymphocyte separation medium method. Twenty Balb/C nude mice were randomly subjected to mononuclear cell injection (mononuclear cell group) or injection of CD133+ cells combined with human umbilical cord stem cells (combined group) via the tail vein after establishing heart failure models. RESULTS AND CONCLUSION: Fourteen days after injection, the body weight and liver, heart and lung mass of mice were significantly larger in the combined group than the mononuclear cell group (P < 0.05). After 30 days, myocardial cells arranged regularly in the combined group, but disorderly in the mononuclear cell group; compared with the mononuclear cell group, the average area of myocardial collagen fibers was significantly decreased in the combined group (P < 0.05), and the level of serum matrix metalloproteinase-9 was also significantly lower in the combined group (P < 0.05). Masson staining showed that blue-stained collagen fibers in the combined group were less but arranged neatly; however, in the mononuclear cell group, the number of collagen fibers that arranged irregularly was increased to different extents. To conclude, the combined use of CD133+ cells and human umbilical cord stem cells has desired outcomes in the treatment of heart failure in mice, indicating a higher clinical value. 中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

Assessment of the myogenic stem cell compartment following transplantation of Pax3/Pax7-induced embryonic stem cell-derived progenitors

An effective long-term cell therapy for skeletal muscle regeneration requires donor contribution to both muscle fibers and the muscle stem cell pool. Although satellite cells have these abilities, their therapeutic potential so far has been limited due to their scarcity in adult muscle. Myogenic progenitors obtained from Pax3-engineered mouse embryonic stem (ES) cells have the ability to generate myofibers and to improve the contractility of transplanted muscles in vivo, however, whether these cells contribute to the muscle stem cell pool and are able to self-renew in vivo are still unknown. Here, we addressed this question by investigating the ability of Pax3, which plays a critical role in embryonic muscle formation, and Pax7, which is important for maintenance of the muscle satellite cell pool, to promote the derivation of self-renewing functional myogenic progenitors from ES cells. We show that Pax7, like Pax3, can drive the expansion of an ES-derived myogenic progenitor with significant muscle regenerative potential. We further demonstrate that a fraction of transplanted cells remains mononuclear, and displays key features of skeletal muscle stem cells, including satellite cell localization, response to reinjury, and contribution to muscle regeneration in secondary transplantation assays. The ability to engraft, self-renew, and respond to injury provide foundation for the future therapeutic application of ES-derived myogenic progenitors in muscle disorders.     

In vitro and in vivo study of human amniotic fluid-derived stem cell differentiation into myogenic lineage

Recent findings have shown that amniotic fluid (AF) could be a putative new source of multipotent stem cells (SC). We investigated whether these human SC could efficiently differentiate into myogenic lineage in vitro and integrate in vivo skeletal muscle in severe combined immunodeficiency (SCID) mice. C/kit immunomagnetic-sorted AF (AF c/kit+) SC were characterized by immunocytochemistry and Southern blotting for myogenic markers (desmin, MyoD). In vitro, AF c/kit+ SC phenotypic conversion into myogenic cells was assayed by myogenic-specific induction media. AF c/kit+ SC without ex vivo manipulation were transplanted into the tibialis anterior (TA) of (SCID) mice. Acquisition of a myogenic-like phenotype (desmin, MyoD) in AF c/kit+ SC was observed after culture in myogenic-specific induction media. In vivo, transplanted AF c/kit+ SC showed an engraftment in the skeletal muscle of SCID mice, but with unexpected tubular glandular tissue-like differentiation. Importantly, no immuno-rejection, inflammatory response or tumorigenicity of these cells was found. Within these experimental conditions, AF c/kit+ SC were able to differentiate into myogenic cells in vitro, but not in vivo after their transplantation into the skeletal muscle of SCID mice. Because AF c/kit+ SC survived and differentiated into tubular gland-like cells after their transplantation in the TA, an ex vivo engagement in myogenic pathway prior their transplantation could favor their differentiation into myogenic cells in vivo.     

The origin, molecular regulation and therapeutic potential of myogenic stem cell populations

Satellite cells, originating in the embryonic dermamyotome, reside beneath the myofibre of mature adult skeletal muscle and constitute the tissue-specific stem cell population. Recent advances following the identification of markers for these cells (including Pax7, Myf5, c-Met and CD34) (CD, cluster of differentiation; c-Met, mesenchymal epithelial transition factor) have led to a greater understanding of the role played by satellite cells in the regeneration of new skeletal muscle during growth and following injury. In response to muscle damage, satellite cells harbour the ability both to form myogenic precursors and to self-renew to repopulate the stem cell niche following myofibre damage. More recently, other stem cell populations including bone marrow stem cells, skeletal muscle side population cells and mesoangioblasts have also been shown to have myogenic potential in culture, and to be able to form skeletal muscle myofibres in vivo and engraft into the satellite cell niche. These cell types, along with satellite cells, have shown potential when used as a therapy for skeletal muscle wasting disorders where the intrinsic stem cell population is genetically unable to repair non-functioning muscle tissue. Accurate understanding of the mechanisms controlling satellite cell lineage progression and self-renewal as well as the recruitment of other stem cell types towards the myogenic lineage is crucial if we are to exploit the power of these cells in combating myopathic conditions. Here we highlight the origin, molecular regulation and therapeutic potential of all the major cell types capable of undergoing myogenic differentiation and discuss their potential therapeutic application.     

Human fetal skeletal muscle contains a myogenic side population that expresses the melanoma cell-adhesion molecule

Muscle side population (SP) cells are rare myogenic progenitors distinct from satellite cells, the known tissue-specific stem cells of skeletal muscle. Studies in mice demonstrated that muscle SP cells give rise to satellite cells in vivo. Given that muscle SP cells are heterogeneous, it has been difficult to prospectively enrich for myogenic progenitors within the SP fraction, particularly from human tissue. Further, conditions that favor the expansion of human muscle SP cells while retaining their myogenic potential have yet to be reported. In this study, human fetal muscle SP and main population (MP) cells were purified based on the expression of melanoma cell adhesion molecule (MCAM), a marker we previously reported to enrich for cells with myogenic potential. To define the relationship between MCAM expression and the degree of myogenic commitment, single cells were analyzed for the expression of myogenic-specific markers. Myogenic factors strongly associated with MCAM expression in single cells, particularly Myf5. Different MCAM+ populations, including SP cells, were expanded and assayed for fusion potential in vitro and engraftment potential in vivo. All MCAM+ subpopulations fused robustly into myotubes in vitro, whereas the MCAM- subpopulations did not. Further, MCAM+ SP cells exhibited the highest fusion potential in vitro and were the only fraction to engraft in vivo, although at low levels, following propagation. Thus, MCAM can be used to prospectively enrich for myogenic muscle SP cells in human fetal muscle. Moreover, we provide evidence that human MCAM+ SP cells have intrinsic myogenic activity that is retained after propagation.     

A population of myogenic stem cells that survives skeletal muscle aging

Age-related decline in integrity and function of differentiated adult tissues is widely attributed to reduction in number or regenerative potential of resident stem cells. The satellite cell, resident beneath the basal lamina of skeletal muscle myofibers, is the principal myogenic stem cell. Here we have explored the capacity of satellite cells within aged mouse muscle to regenerate skeletal muscle and to self-renew using isolated myofibers in tissue culture and in vivo. Satellite cells expressing Pax7 were depleted from aged muscles, and when aged myofibers were placed in culture, satellite cell myogenic progression resulted in apoptosis and fewer total differentiated progeny. However, a minority of cultured aged satellite cells generated large clusters of progeny containing both differentiated cells and new cells of a quiescent satellite-cell-like phenotype characteristic of self-renewal. Parallel in vivo engraftment assays showed that, despite the reduction in Pax7(+) cells, the satellite cell population associated with individual aged myofibers could regenerate muscle and self-renew as effectively as the larger population of satellite cells associated with young myofibers. We conclude that a minority of satellite cells is responsible for adult muscle regeneration, and that these stem cells survive the effects of aging to retain their intrinsic potential throughout life. Thus, the effectiveness of stem-cell-mediated muscle regeneration is determined by both extrinsic environmental influences and diversity in intrinsic potential of the stem cells themselves.     

Fusion-independent expression of functional ACh receptors in mouse mesoangioblast stem cells contacting muscle cells

Mesoangioblasts are vessel-associated fetal stem cells that can be induced to differentiate into skeletal muscle, both in vitro and in vivo . Whether this is due to fusion or to transdifferentiation into bona fide satellite cells is still an open question, for mesoangioblasts as well as for other types of stem cells. The early steps of satellite cell myogenic differentiation involve MyoD activation, membrane hyperpolarization and the appearance of ACh sensitivity and gap junctional communication. If mesoangioblasts differentiate into satellite cells, these characteristics should be observed in stem cells prior to fusion into multinucleated myotubes. We have investigated the functional properties acquired by mononucleated green fluorescent protein (GFP)-positive mesoangioblasts co-cultured with differentiating C2C12 myogenic cells, using the patch-clamp technique. Mesoangioblasts whose membrane contacted myogenic cells developed a hyperpolarized membrane resting potential and ACh-evoked current responses. Dye and electrical coupling was observed among mesoangioblasts but not between mesoangioblasts and myotubes. Mouse MyoD was detected by RT-PCR both in single, mononucleated mesoangioblasts co-cultured with C2C12 myotubes and in the total mRNA from mouse mesoangioblasts co-cultured with human myotubes, but not in human myotubes or stem cells cultured in isolation. In conclusion, when co-cultured with muscle cells, mesoangioblasts acquire many of the functional characteristics of differentiating satellite cells in the absence of cell fusion, strongly indicating that these stem cells undergo transdifferentiation into satellite cells, when exposed to a myogenic environment.     

Differentiation of muscle-derived cells into myofibroblasts in injured skeletal muscle

Injured muscle can initiate regeneration promptly by activating myogenic cells that proliferate and differentiate into myotubes and myofibers. However, the recovery of the injured skeletal muscle often is hindered by the development of fibrosis. We hypothesized that the early-appearing myogenic cells in the injured area differentiate into myofibroblasts and eventually contribute to the development of fibrosis. To investigate this, we transplanted a genetically engineered clonal population of muscle-derived stem cells (MC13 cells) into the skeletal muscle of immunodeficient SCID mice, which were lacerated 4 weeks after transplantation. The MC13 cells regenerated numerous myofibers in the nonlacerated muscle and these myogenic cells were gradually replaced by myofibroblastic cells in the injured muscle. Our results suggest that the release of local environmental stimuli after muscle injury triggers the differentiation of myogenic cells (including MC13 cells) into fibrotic cells. These results demonstrate the potential of muscle-derived stem cells to differentiate into different lineages and illustrate the importance of controlling the local environment within the injured tissue to optimize tissue regeneration via the transplantation of stem cells.     

Muscle-derived stem cells for tissue engineering and regenerative therapy

Skeletal muscle has been recognized as an essential source of progenitor or satellite cells, which are primarily responsible for muscle regeneration. Recently, muscle has also been identified as a valuable source of postnatal stem cells that appear to be distinct from satellite cells and possess the ability to differentiate into other cell lineages. These cells, named muscle-derived stem cells, possess a high myogenic capacity and effectively regenerate both skeletal and cardiac muscle. Remarkably, when genetically modified ex vivo to express growth factors, these cells can differentiate into osteogenic and chondrogenic lineages and have been shown to promote the repair of bone and cartilage. Muscle stem cell-based regenerative therapy and tissue engineering using ex vivo gene therapy, are promising approaches for the treatment of various musculoskeletal, cardiovascular, and urological disorders.     

From pluripotency to myogenesis: a multistep process in the dish

Pluripotent stem cells (PSCs), such as embryonic stem cells or induced pluripotent stem cells are a promising source of cells for regenerative medicine as they can differentiate into all cell types building a mammalian body. However, protocols leading to efficient and safe in vitro generation of desired cell types must be perfected before PSCs can be used in cell therapies or tissue engineering. In vivo, i.e. in developing mouse embryo or teratoma, PSCs can differentiate into skeletal muscle, but in vitro their spontaneous differentiation into myogenic cells is inefficient. Numerous attempts have been undertaken to enhance this process. Many of them involved mimicking the interactions occurring during embryonic myogenesis. The key regulators of embryonic myogenesis, such as Wnts proteins, fibroblast growth factor 2, and retinoic acid, have been tested to improve the frequency of in vitro myogenic differentiation of PSCs. This review summarizes the current state of the art, comparing spontaneous and directed myogenic differentiation of PSCs as well as the protocols developed this far to facilitate this process.     

Reflections on lineage potential of skeletal muscle satellite cells: do they sometimes go MAD?

Postnatal muscle growth and repair is supported by satellite cells--myogenic progenitors positioned between the myofiber basal lamina and plasma membrane. In adult muscles, satellite cells are quiescent but become activated and contribute differentiated progeny when myofiber repair is needed. The development of cells expressing osteogenic and adipogenic genes alongside myoblasts in myofiber cultures raised the hypothesis that satellite cells possess mesenchymal plasticity. Clonal studies of myofiber-associated cells further suggest that satellite cell myogeneity and diversion into Mesenchymal Alternative Differentiation (MAD) occur in vitro by a stochastic mechanism. However, in vivo this potential may be executed only when myogenic signals are impaired and the muscle tissue is compromised. Such a mechanism may contribute to the increased adiposity of aging muscles. Alternatively, it is possible that mesenchymal interstitial cells (sometimes co-isolated with myofibers), rather than satellite cells, account for the nonmyogenic cells observed in myogenic cultures. Herein, we first elaborate on the myogenic potential of satellite cells. We then introduce definitions of adult stem-cell unipotency, multipotency, and plasticity, as well as elaborate on recent studies that established the status of satellite cells as myogenic stem cells. Last, we highlight evidence in favor of satellite cell plasticity and emerging hurdles restraining this hypothesis.