馬渕 洋

Mesenchymal stem/stromal cells (MSCs) are distributed in various tissues and are used in clinical applications as a source of transplanted cells because of their easy harvestability. Although MSCs express numerous cell-surface antigens, single-cell analyses have revealed a highly heterogeneous cell population depending on the original tissue and donor conditions, including age and interindividual differences. This heterogeneity leads to differences in their functions, such as multipotency and immunomodulatory effects, making it challenging to effectively treat targeted diseases. The therapeutic efficacy of MSCs is controversial and depends on the implantation site. Thus, there is no established recipe for the transplantation of MSCs (including the type of disease, type of origin, method of cell culture, form of transplanted cells, and site of delivery). Our recent preclinical study identified appropriate MSCs and their suitable transplantation routes in a mouse model of inflammatory bowel disease (IBD). Three-dimensional (3D) cultures of MSCs have been demonstrated to enhance their properties and sustain engraftment at the lesion site. In this note, we explore the methods of MSC transplantation for treating IBDs, especially Crohn's disease, from clinical trials published over the past decade. Given the functional changes in MSCs in 3D culture, we also investigate the clinical trials using 3D constructs of MSCs and explore suitable diseases that might benefit from this approach. Furthermore, we discuss the advantages of the prospective isolation of MSCs in terms of interindividual variability. This note highlights the need to define the method of MSC transplantation, including interindividual variability, the culture period, and the transplantation route.

Myeloid cells, which originate from hematopoietic stem/progenitor cells (HSPCs), play a crucial role in mitigating infections. This study aimed to explore the impact of mesenchymal stem/stromal cells (MSCs) on the differentiation of HSPCs and progenitors through the C-C motif chemokine CCL2/CCR2 signaling pathway. Murine MSCs, identified as PDGFRα+Sca-1+ cells (PαS cells), were found to secrete CCL2, particularly in response to lipopolysaccharide stimulation. MSC-secreted CCL2 promoted the differentiation of granulocyte/macrophage progenitors into the myeloid lineage. MSC-derived CCL2 plays an important role in the early phase of myeloid cell differentiation in vivo. Single-cell RNA sequencing analysis confirmed that CCL2-mediated cell fate determination was also observed in human bone marrow cells. These findings provide valuable insights for investigating the in vivo effects of MSC transplantation.

BACKGROUND: Severe peripheral nerve damage always requires surgical treatment. Autologous nerve transplantation is a standard treatment, but it is not sufficient due to length limitations and extended surgical time. Even with the available artificial nerves, there is still large room for improvement in their therapeutic effects. Novel treatments for peripheral nerve injury are greatly expected. METHODS: Using a specialized microfluidic device, we generated artificial neurite bundles from human iPSC-derived motor and sensory nerve organoids. We developed a new technology to isolate cell-free neurite bundles from spheroids. Transplantation therapy was carried out for large nerve defects in rat sciatic nerve with novel artificial nerve conduit filled with lineally assembled sets of human neurite bundles. Quantitative comparisons were performed over time to search for the artificial nerve with the therapeutic effect, evaluating the recovery of motor and sensory functions and histological regeneration. In addition, a multidimensional unbiased gene expression profiling was carried out by using next-generation sequencing. RESULT: After transplantation, the neurite bundle-derived artificial nerves exerted significant therapeutic effects, both functionally and histologically. Remarkably, therapeutic efficacy was achieved without immunosuppression, even in xenotransplantation. Transplanted neurite bundles fully dissolved after several weeks, with no tumor formation or cell proliferation, confirming their biosafety. Posttransplant gene expression analysis highlighted the immune system's role in recovery. CONCLUSION: The combination of newly developed microfluidic devices and iPSC technology enables the preparation of artificial nerves from organoid-derived neurite bundles in advance for future treatment of peripheral nerve injury patients. A promising, safe, and effective peripheral nerve treatment is now ready for clinical application.

The demand for stem cell-based cultured meat as an alternative protein source is increasing in response to global food scarcity. However, the definition of quality controls, including appropriate growth factors and cell characteristics, remains incomplete. Cluster of differentiation (CD) 29 is ubiquitously expressed in bovine muscle tissue and is a marker of progenitor cells in cultured meat. However, CD29+ cells are naturally heterogeneous, and this quality control issue must be resolved. In this study, the aim was to identify the subpopulation of the CD29+ cell population with potential utility in cultured meat production. The CD29+ cell population exhibited heterogeneity, discernible through the CD44 and CD344 markers. CD29+CD44-CD344- cells displayed the ability for long-term culture, demonstrating high adipogenic potential and substantial lipid droplet accumulation, even within 3D cultures. Conversely, CD29+CD44+ cells exhibited rapid proliferation but were not viable for prolonged culture. Using cells suitable for adipocyte and muscle differentiation, we successfully designed meat buds, especially those rich in fat. Collectively, the identification and comprehension of distinct cell populations within bovine tissues contribute to quality control predictions in meat production. They also aid in establishing a stable and reliable cultured meat production technique.

Abstract Cancer cells inevitably interact with neighboring host tissue-resident cells during the process of metastatic colonization, establishing a metastatic niche to fuel their survival, growth, and invasion. However, the underlying mechanisms in the metastatic niche are yet to be fully elucidated owing to the lack of methodologies for comprehensively studying the mechanisms of cell–cell interactions in the niche. Here, we improve a split green fluorescent protein (GFP)-based genetically encoded system to develop secretory glycosylphosphatidylinositol-anchored reconstitution-activated proteins to highlight intercellular connections (sGRAPHIC) for efficient fluorescent labeling of tissue-resident cells that neighbor on and putatively interact with cancer cells in deep tissues. The sGRAPHIC system enables the isolation of metastatic niche-associated tissue-resident cells for their characterization using a single-cell RNA sequencing platform. We use this sGRAPHIC-leveraged transcriptomic platform to uncover gene expression patterns in metastatic niche-associated hepatocytes in a murine model of liver metastasis. Among the marker genes of metastatic niche-associated hepatocytes, we identify Lgals3, encoding galectin-3, as a potential pro-metastatic factor that accelerates metastatic growth and invasion.

Adipose stem and progenitor cells (ASPCs) have been isolated from humans and animals for use in regenerative medicine and therapy. However, knowledge of ASPCs in other species is limited. Particularly, ASPCs in livestock are expected to enhance the fat content and meat composition. In this study, we isolated bovine ASPCs using cell surface markers. Specifically, we focused on ASPC markers in humans and experimental animals, namely CD26, CD146, and CD54. Stromal vascular fraction cells from bovine fat were separated using flow cytometry before primary culture. We evaluated the self-renewal and adipogenic potential of each fraction. We identified four cell populations: CD26-CD146+CD54+, CD26-CD146+CD54-, CD26-CD146-, and CD26+CD146-. Among them, the CD26-CD146+ fraction, particularly CD54+, demonstrated the properties of preadipocytes (PreAs), characterized by slow proliferation and a high adipogenic capacity. In conclusion, we could collect and characterize possible PreAs as CD26-CD146+CD54+ or CD26-CD146+CD54-, which are expected for in vitro bovine adipogenic assays in the future.

Although neural stem/progenitor cells derived from human induced pluripotent stem cells (hiPSC-NS/PCs) are expected to be a cell source for cell-based therapy, tumorigenesis of hiPSC-NS/PCs is a potential problem for clinical applications. Therefore, to understand the mechanisms of tumorigenicity in NS/PCs, we clarified the cell populations of NS/PCs. We established single cell-derived NS/PC clones (scNS/PCs) from hiPSC-NS/PCs that generated undesired grafts. Additionally, we performed bioassays on scNS/PCs, which classified cell types within parental hiPSC-NS/PCs. Interestingly, we found unique subsets of scNS/PCs, which exhibited the transcriptome signature of mesenchymal lineages. Furthermore, these scNS/PCs expressed both neural (PSA-NCAM) and mesenchymal (CD73 and CD105) markers, and had an osteogenic differentiation capacity. Notably, eliminating CD73+ CD105+ cells from among parental hiPSC-NS/PCs ensured the quality of hiPSC-NS/PCs. Taken together, the existence of unexpected cell populations among NS/PCs may explain their tumorigenicity leading to potential safety issues of hiPSC-NS/PCs for future regenerative medicine.

Schwartz-Jampel syndrome (SJS) is an autosomal recessive disorder caused by loss-of-function mutations in heparan sulfate proteoglycan 2 (HSPG2), which encodes the core basement membrane protein perlecan. Myotonia is a major criterion for the diagnosis of SJS; however, its evaluation is based solely on physical examination and can be challenging in neonates and young children. Furthermore, the pathomechanism underlying SJS-related myotonia is not fully understood, and effective treatments for SJS are limited. Here, we established a cellular model of SJS using patient-derived human-induced pluripotent stem cells. This model exhibited hyper-responsiveness to acetylcholine as a result of abnormalities in the perlecan molecule, which were confirmed via comparison of their calcium imaging with calcium imaging of satellite cells derived from Hspg2-/--Tg mice, which exhibit myotonic symptoms similar to SJS symptoms. Therefore, our results confirm the utility of creating cellular models for investigating SJS and their application in evaluating myotonia in clinical cases, while also providing a useful tool for the future screening of SJS therapies.

The incidence of inflammatory bowel diseases (IBD) is increasing worldwide. Mesenchymal stem/stromal cells (MSCs) have immunomodulatory functions and are a promising source for cell transplantation therapy for IBD. However, owing to their heterogeneous nature, their therapeutic efficacy in colitis is controversial and depends on the delivery route and form of transplanted cells. Cluster of differentiation (CD) 73 is widely expressed in MSCs and used to obtain a homogeneous MSC population. Herein, we determined the optimal method for MSC transplantation using CD73+ cells in a colitis model. mRNA sequencing analysis showed that CD73+ cells exhibited a downregulation of inflammatory gene expression and an upregulation of extracellular matrix-related gene expression. Furthermore, three-dimensional CD73+ cell spheroids showed enhanced engraftment at the injured site through the enteral route, facilitated extracellular matrix remodeling, and downregulated inflammatory gene expression in fibroblasts, leading to the attenuation of colonic atrophy. Therefore, the interaction between intestinal fibroblasts and exogenous MSCs via tissue remodeling is one mechanism that can be exploited for colitis prevention. Our results highlight that the transplantation of homogeneous cell populations with well-characterized properties is beneficial for IBD treatment.

Salivary glands act as virus reservoirs in various infectious diseases and have been reported to be targeted by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the mechanisms underlying infection and replication in salivary glands are still enigmatic due to the lack of proper in vitro models. Here, we show that human induced salivary glands (hiSGs) generated from human induced pluripotent stem cells can be infected with SARS-CoV-2. The hiSGs exhibit properties similar to those of embryonic salivary glands and are a valuable tool for the functional analysis of genes during development. Orthotopically transplanted hiSGs can be engrafted at a recipient site in mice and show a mature phenotype. In addition, we confirm SARS-CoV-2 infection and replication in hiSGs. SARS-CoV-2 derived from saliva in asymptomatic individuals may participate in the spread of the virus. hiSGs may be a promising model for investigating the role of salivary glands as a virus reservoir.

Myoepithelial (ME) cells in exocrine glands exhibit both epithelial and mesenchymal features, contributing to fluid secretion through contraction. However, the regulation mechanism of behind this unique phenotype in salivary glands remains unclear. We established a flow cytometry-based purification method using cell surface molecules, epithelial cell adhesion molecule (EpCAM) and alpha 6 integrin (CD49f), to characterize ME cells. EpCAM+CD49fhigh cells showed relatively high expression of ME cell-marker genes, such as alpha-smooth muscle actin (α-SMA). For lineage tracing and strict isolation, tdTomato+EpCAM+CD49fhigh-ME cells were obtained from myosin heavy chain 11 (Myh11) -CreERT2/tdTomato mice. Transcriptome analysis revealed that expression of genes involved in the epithelial-mesenchymal transition, including Snai2, were upregulated in the ME cell-enriched subset. Snai2 suppression in stable ME cells decreased α-SMA and increased Krt14 expression, suggesting that ME cell features may be controlled by the epithelial-mesenchymal balance regulated by Snai2. In contrast, ME cells showed reduced ME properties and expressed the ductal markers Krt18/19 under sphere culture conditions. Notch signaling was activated under sphere culture conditions; excessive activation of Notch signaling accelerated Krt18/19 expression, but reduced α-SMA and Snai2 expression, suggesting that the behavior of Snai2-expressing ME cells may be controlled by Notch signaling.

Myelodysplastic syndrome (MDS) is a clonal disorder of hematopoietic stem cells (HSCs), characterized by ineffective hematopoiesis and frequent progression to leukemia. It has long remained unresolved how MDS cells, which are less proliferative, inhibit normal hematopoiesis and eventually dominate the bone marrow space. Despite several studies implicating mesenchymal stromal or stem cells (MSCs), a principal component of the HSC niche, in the inhibition of normal hematopoiesis, the molecular mechanisms underlying this process remain unclear. Here, we demonstrate that both human and mouse MDS cells perturb bone metabolism by suppressing the osteolineage differentiation of MSCs, which impairs the ability of MSCs to support normal HSCs. Enforced MSC differentiation rescues the suppressed normal hematopoiesis in both in vivo and in vitro MDS models. Intriguingly, the suppression effect is reversible and mediated by extracellular vesicles (EVs) derived from MDS cells. These findings shed light on the novel MDS EV-MSC axis in ineffective hematopoiesis.

Mesenchymal stem cells (MSCs) exhibit self-renewal, multi-lineage differentiation potential and immunomodulatory properties, and are promising candidates for cellular therapy of various tissues. Despite the effective function of MSCs, the gradual loss of stem cell characteristics that occurs with repeated passages may significantly limit their therapeutic potential. A novel 3D shaking method was previously established to generate MSC spheroids in growth medium (GM-spheroids) and successfully maintain the multipotency of expanded MSCs, yet the expression of MSC-related genes was still low. In this study, we used a neurosphere culture technique to optimize the shaking culture method using human bone marrow-derived MSCs (BM-MSCs). MSC spheroids generated in neurosphere medium (NM-spheroids) maintained high expression of MSC-related genes during 3 weeks of prolonged shaking culture. Moreover, NM-spheroids generated from expanded MSCs showed high viability, upregulation of MSC-related and immune-related genes, and recovery of differentiation potential in vitro. Expanded adherent MSCs, GM-spheroids, and NM-spheroids were transplanted into a rat femur bone defect model to investigate their therapeutic potential in bone repair. Adherent MSCs and GM-spheroids showed delayed bone healing. In contrast, NM-spheroids showed high transplantation efficiency and enhanced bone regeneration. These data suggest that NM-spheroids generated using modified neurosphere culture conditions under continuous shaking recovered their stem cell characteristics in vitro and enhanced bone regeneration in vivo. Therefore, NM-spheroids should have great clinical potential for bone and tissue regenerative therapies as a stem cell-based biomaterial therapy.

Microglial activation followed by recruitment of blood-borne macrophages into the central nervous system (CNS) aggravates neuroinflammation. Specifically, in multiple sclerosis (MS) as well as in experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, activated microglia and macrophages (Mg/Mφ) promote proinflammatory responses and expand demyelination in the CNS. However, a potent therapeutic approach through the systemic route for regulating their functions has not yet been developed. Here, we demonstrate that a systemically injected DNA/RNA heteroduplex oligonucleotide (HDO), composed of an antisense oligonucleotide (ASO) and its complementary RNA, conjugated to cholesterol (Chol-HDO) distributed more efficiently to demyelinating lesions of the spinal cord in EAE mice with significant gene silencing than the parent ASO. Importantly, systemic administration of Cd40-targeting Chol-HDO improved clinical signs of EAE with significant downregulation of Cd40 in Mg/Mφ. Furthermore, we successfully identify that macrophage scavenger receptor 1 (MSR1) is responsible for the uptake of Chol-HDO by Mg/Mφ of EAE mice. Overall, our findings demonstrate the therapeutic potency of systemically administered Chol-HDO to regulate activated Mg/Mφ in neuroinflammation.

Manipulating lymphocyte functions with gene silencing approaches is promising for treating autoimmunity, inflammation, and cancer. Although oligonucleotide therapy has been proven to be successful in treating several conditions, efficient in vivo delivery of oligonucleotide to lymphocyte populations remains a challenge. Here, we demonstrate that intravenous injection of a heteroduplex oligonucleotide (HDO), comprised of an antisense oligonucleotide (ASO) and its complementary RNA conjugated to α-tocopherol, silences lymphocyte endogenous gene expression with higher potency, efficacy, and longer retention time than ASOs. Importantly, reduction of Itga4 by HDO ameliorates symptoms in both adoptive transfer and active experimental autoimmune encephalomyelitis models. Our findings reveal the advantages of HDO with enhanced gene knockdown effect and different delivery mechanisms compared with ASO. Thus, regulation of lymphocyte functions by HDO is a potential therapeutic option for immune-mediated diseases.

Junctional adhesion molecules (JAMs) are expressed in diverse types of stem and progenitor cells, but their physiological significance has yet to be established. Here, we report that JAMs exhibit a novel mode of interaction and biological activity in adipose-derived stromal/stem cells (ADSCs). Among the JAM family members, JAM-B and JAM-C were concentrated along the cell membranes of mouse ADSCs. JAM-C but not JAM-B was broadly distributed in the interstitial spaces of mouse adipose tissue. Interestingly, the JAM-C ectodomain was cleaved and secreted as a soluble form (sJAM-C) in vitro and in vivo, leading to deposition in the fat interstitial tissue. When ADSCs were grown in culture plates coated with sJAM-C, cell adhesion, cell proliferation and the expression of five mesenchymal stem cell markers, Cd44, Cd105, Cd140a, Cd166 and Sca-1, were significantly elevated. Moreover, immunoprecipitation assay showed that sJAM-C formed a complex with JAM-B. Using CRISPR/Cas9-based genome editing, we also demonstrated that sJAM-C was coupled with JAM-B to stimulate ADSC adhesion and maintenance. Together, these findings provide insight into the unique function of sJAM-C in ADSCs. We propose that JAMs contribute not only to cell-cell adhesion, but also to cell-matrix adhesion, by excising their ectodomain and functioning as a niche-like microenvironment for stem and progenitor cells.

The current process of meat production using livestock has significant effects on the global environment, including high emissions of greenhouse gases. In recent years, cultured meat has attracted attention as a way to acquire animal proteins. However, the lack of markers that isolate proliferating cells from bovine tissues and the complex structure of the meat make it difficult to culture meat in a dish. In this study, we screened 246 cell-surface antibodies by fluorescence-activated cell sorting for their capacity to form colonies and their suitability to construct spheroid “meat buds”. CD29+ cells (Ha2/5 clone) have a high potency to form colonies and efficiently proliferate on fibronectin-coated dishes. Furthermore, the meat buds created from CD29+ cells could differentiate into muscle and adipose cells in a three-dimensional structure. The meat buds embedded in the collagen gel proliferated in the matrix and formed large aggregates. Approximately 10 trillion cells can theoretically be obtained from 100 g of bovine tissue by culturing and amplifying them using these methods. The CD29+ cell characteristics of bovine tissue provide insights into the production of meat alternatives in vitro.

Mesenchymal stem/stromal cells (MSCs) are present in various body tissues and help in maintaining homeostasis. The stemness of MSCs has been evaluated in vitro. In addition, analyses of cell surface antigens and gene expression patterns have shown that MSCs comprise a heterogeneous population, and the diverse and complex nature of MSCs makes it difficult to identify the specific roles in diseases. There is a lack of understanding regarding the classification of MSC properties. In this review, we explore the characteristics of heterogeneous MSC populations based on their markers and gene expression profiles. We integrated the contents of previously reported single-cell analysis data to better understand the properties of mesenchymal cell populations. In addition, the cell populations involved in the development of myeloproliferative neoplasms (MPNs) are outlined. Owing to the diversity of terms used to describe MSCs, we used the text mining technology to extract topics from MSC research articles. Recent advances in technology could improve our understanding of the diversity of MSCs and help us evaluate cell populations.

Human mesenchymal stem/stromal cells (hMSCs) have garnered enormous interest as a potential resource for cell-based therapies. However, the molecular mechanisms regulating senescence in hMSCs remain unclear. To elucidate these mechanisms, we performed gene expression profiling to compare clonal immature MSCs exhibiting multipotency with less potent MSCs. We found that the transcription factor Frizzled 5 (FZD5) is expressed specifically in immature hMSCs. The FZD5 cell surface antigen was also highly expressed in the primary MSC fraction (LNGFR+ THY-1+ ) and cultured MSCs. Treatment of cells with the FZD5 ligand WNT5A promoted their proliferation. Upon FZD5 knockdown, hMSCs exhibited markedly attenuated proliferation and differentiation ability. The observed increase in the levels of senescence markers suggested that FZD5 knockdown promotes cellular senescence by regulating the noncanonical Wnt pathway. Conversely, FZD5 overexpression delayed cell cycle arrest during the continued culture of hMSCs. These results indicated that the intrinsic activation of FZD5 plays an essential role in negatively regulating senescence in hMSCs and suggested that controlling FZD5 signaling offers the potential to regulate hMSC quality and improve the efficacy of cell-replacement therapies using hMSCs.

Somatic stem cells have been isolated from multiple human tissues for their potential usefulness in cell therapy. Currently, mesenchymal stromal cells (MSCs) are prepared after several passages requiring a few months of cell culture. In this study, we used a prospective isolation method of somatic stem cells from gestational or fat tissues, which were identified using CD73 antibody. CD73-positive population from various tissues existed individually in flowcytometric pattern, especially subcutaneous fat- and amniotic-derived cells showed the highest enrichment of CD73-positive cells. Moreover, the cell populations isolated with the prospective method showed higher proliferative capacity and stem cell marker expression, compared to the cell populations which isolated through several passages of culturing whole living cells: which we named "conventional method" in this paper. Furthermore, the therapeutic potential of CD73-positive cells was evaluated in vivo using a mouse model of pulmonary fibrosis. After intranasal administration, murine CD73-positive cells reduced macrophage infiltration and inhibited fibrosis development. These results suggest that further testing using CD73-positive cells may be beneficial to help establish the place in regenerative medicine use.

Cell adhesion between oligodendrocytes and neuronal axons is a critical step for myelination that enables the rapid propagation of action potential in the central nervous system. Here, we show that the transmembrane protein teneurin-4 plays a role in the cell adhesion required for the differentiation of oligodendrocytes. We found that teneurin-4 formed molecular complexes with all of the four teneurin family members and promoted cell-cell adhesion. Oligodendrocyte lineage cells attached to the recombinant extracellular domain of all the teneurins and formed well-branched cell processes. In an axon-mimicking nanofibers assay, nanofibers coated with the recombinant teneurin-4 extracellular domain increased the differentiation of oligodendrocytes. Our results show that teneurin-4 binds to all teneurins through their extracellular domain, which facilitates the oligodendrocyte-axon adhesion, and promotes oligodendrocyte differentiation via its homophilic interaction.

Mesenchymal stromal/stem cells (MSCs), which generally expand into adherent monolayers, readily lose their proliferative and multilineage potential following repeated passages. Floating culture systems can be used to generate MSC spheroids, which are expected to overcome limitations associated with conventional adherent cultures while facilitating scaffold-free cell transplantation. However, the phenotypic characteristics of spheroids after long-term culture are unknown. In addition, regenerative therapies require new culture systems to maintain their undifferentiated state. In this study, we established a novel culture method employing three-dimensional (3D) "shaking" to generate MSC spheroids using bone marrow derived MSCs. Floating 3D cultures of mouse or human MSCs formed spheroids after shaking (85-95 rpm), within 1 month. These spheroids maintained their osteogenic-, adipogenic-, and chondrogenic-differentiation capacity. The adipogenic-differentiation capacity of adherent cultured mouse and human MSCs, which is lost following several passages, was remarkedly restored by shaking-culture. Notably, human MSC spheroids exhibited a renewable "undifferentiated MSC-pool" property, wherein undifferentiated MSCs grew from spheroids seeded repeatedly on a plastic culture dish. These data suggest that the shaking-culture method maintains and restores multipotency that is lost following monolayer expansion and thereby shows potential as a promising strategy for regenerative therapies with mesenchymal tissues.

The spleen is comprised of spatially distinct compartments whose functions, such as immune responses and removal of aged red blood cells, are tightly controlled by the non-hematopoietic stromal cells that provide regionally-restricted signals to properly activate hematopoietic cells residing in each area. However, information regarding the ontogeny and relationships of the different stromal cell types remains limited. Here we have used in vivo lineage tracing analysis and in vitro mesenchymal stromal cell assays and found that Tlx1, a transcription factor essential for embryonic spleen organogenesis, marks neonatal stromal cells that are selectively localized in the spleen and retain mesenchymal progenitor potential to differentiate into mature follicular dendritic cells, fibroblastic reticular cells and marginal reticular cells. Furthermore, by establishing a novel three-dimensional cell culture system that enables maintenance of Tlx1-expressing cells in vitro, we discovered that signals from the lymphotoxin β receptor and TNF receptor promote differentiation of these cells to express MAdCAM-1, CCL19 and CXCL13, representative functional molecules expressed by different subsets of mature stromal cells in the spleen. Taken together, these findings indicate that mesenchymal progenitor cells expressing Tlx1 are a subset of lymphoid tissue organizer-like cells selectively found in the neonatal spleen.

Exocrine glands share a common morphology consisting of ductal, acinar, and basal/myoepithelial cells, but their functions and mechanisms of homeostasis differ among tissues. Salivary glands are an example of exocrine glands, and they have been reported to contain multipotent stem cells that differentiate into other tissues. In this study, we purified the salivary gland stem/progenitor cells of adult mouse salivary glands using the cell surface marker CD133 by flow cytometry. CD133+ cells possessed stem cell capacity, and the transplantation of CD133+ cells into the submandibular gland reconstituted gland structures, including functional acinar. CD133+ cells were sparsely distributed in the intercalated and exocrine ducts and expressed Sox9 at higher levels than CD133- cells. Moreover, we demonstrated that Sox9 was required for the stem cell properties CD133+ cells, including colony and sphere formation. Thus, the Sox9-related signaling may control the regeneration salivary glands.

Human organoid systems recapitulate in vivo organ architecture yet fail to capture complex pathologies such as inflammation and fibrosis. Here, using 11 different healthy and diseased pluripotent stem cell lines, we developed a reproducible method to derive multi-cellular human liver organoids composed of hepatocyte-, stellate-, and Kupffer-like cells that exhibit transcriptomic resemblance to in vivo-derived tissues. Under free fatty acid treatment, organoids, but not reaggregated cocultured spheroids, recapitulated key features of steatohepatitis, including steatosis, inflammation, and fibrosis phenotypes in a successive manner. Interestingly, an organoid-level biophysical readout with atomic force microscopy demonstrated that organoid stiffening reflects the fibrosis severity. Furthermore, organoids from patients with genetic dysfunction of lysosomal acid lipase phenocopied severe steatohepatitis, rescued by FXR agonism-mediated reactive oxygen species suppression. The presented key methodology and preliminary results offer a new approach for studying a personalized basis for inflammation and fibrosis in humans, thus facilitating the discovery of effective treatments.

Pericytes are mesenchymal cells that surround the endothelial cells of small vessels in various organs. These cells express several markers, such as NG2, CD146, and PDGFRβ, and play an important role in the stabilization and maturation of blood vessels. It was also recently revealed that like mesenchymal stem cells (MSCs), pericytes possess multilineage differentiation capacity, especially myogenic, adipogenic, and fibrogenic differentiation capacities. Although some previous studies have reported that pericytes also have osteogenic potential, the osteogenesis of pericytes can still be further elucidated. In the present study, we established novel methods for isolating and culturing primary murine pericytes. An immortalized pericyte line was also established. Multilineage induction of the pericyte line induced osteogenesis, adipogenesis, and chondrogenesis of the cells in vitro. In addition, pericytes that were injected into the fracture site of a bone fracture mouse model contributed to callus formation. Furthermore, in vivo pericyte-lineage-tracing studies demonstrated that endogenous pericytes also differentiate into osteoblasts and osteocytes and contribute to bone fracture healing as a cellular source of osteogenic cells. Pericytes can be a promising therapeutic candidate for treating bone fractures with a delayed union or nonunion as well as bone diseases causing bone defects.

Introduction The anterior cruciate ligament (ACL) consists of various components, such as collagen, elastin fibres, and fibroblasts. Because ACL has a poor regenerative ability, ACL reconstruction need require the use of autologous tendons. In recent years, tissue-resident stem cells have been studied to promote ACL regeneration as an alternatively method. However, the existence of stem cells in ligaments has not been clearly defined. Here, we prospectively isolated stem cells from ACLs and characterized their properties. Methods ACLs from 11 donors and bone marrows (BM) from 8 donors were obtained with total knee arthroplasty. We used flow cytometry to screen the cell surface markers on ACL cells. Frozen sections were prepared from patient ACL tissues and stained with specific antibodies. Cultured ACL-derived and BM-derived cells at passage 3 were differentiated into adipocytes, osteoblasts and tendon/ligament cells. Results ACL-derived mesenchymal stem/stromal cells (ACL-MSCs) expressed high levels of CD73 and CD90. Immunohistochemical analyses revealed that ACL-MSCs were located on the inner surface of ACL sinusoids. Furthermore, the expression of cell surface antigens was clearly different between ACL-MSCs and bone marrow (BM)-derived MSCs (BM-MSCs) at the time of isolation, but the two cell populations became indistinguishable after long-term culture. Interestingly, ACL-MSCs are markedly different from BM-MSCs in their differentiation ability and have a high propensity to differentiate into ligament-committed cells. Conclusions Our findings suggest that ACL-MSCs express CD90 and CD73 markers, and their differentiation capacity is maintained even through culture. The cell population having tissue-specific properties is an important research target for investigating the ligament therapies.

Background: Synovial mesenchymal stem cells (MSCs) are an attractive cell source for cartilage and meniscus regeneration. Synovial tissue can be histologically classified into three regions surface, stromal and perivascular region, but the localization of synovial MSCs has not been fully investigated. We identified markers specific for each region, and compared properties of MSCs derived from each region in the synovium. Methods: The intensity of immunostaining with 19 antibodies was examined for surface, stromal, and perivascular regions of human synovium from six osteoarthritis patients. Specific markers were identified and synovial cells derived from each region were sorted. Proliferation, surface marker expression, chondrogenesis, calcification and adipogenesis potentials were compared in synovial MSCs derived from the three regions. Results: We selected CD55+ CD271- for synovial cells in the surface region, CD55- CD271- in the stromal region, and CD55- CD271+ in the perivascular region. The ratio of the sorted cells to non-hematopoietic lineage cells was 5% in the surface region, 70% in the stromal region and 15% in the perivascular region. Synovial cells in the perivascular fraction had the greatest proliferation potential. After expansion, surface marker expression profiles and adipogenesis potentials were similar but chondrogenic and calcification potentials were higher in synovial MSCs derived from the perivascular region than in those derived from the surface and stromal regions. Conclusions: We identified specific markers to isolate synovial cells from the surface, stromal, and perivascular regions of the synovium. Synovial MSCs in the perivascular region had the highest proliferative and chondrogenic potentials among the three regions.

Bone metastatic lesions are classified as osteoblastic or osteolytic lesions. Prostate and breast cancer patients frequently exhibit osteoblastic-type and osteolytic-type bone metastasis, respectively. In metastatic lesions, tumor cells interact with many different cell types, including osteoblasts, osteoclasts, and mesenchymal stem cells, resulting in an osteoblastic or osteolytic phenotype. However, the mechanisms responsible for the modification of bone remodeling have not been fully elucidated. MicroRNAs (miRNAs) are transferred between cells via exosomes and serve as intercellular communication tools, and numerous studies have demonstrated that cancer-secreted miRNAs are capable of modifying the tumor microenvironment. Thus, cancer-secreted miRNAs can induce an osteoblastic or osteolytic phenotype in the bone metastatic microenvironment. In this study, we performed a comprehensive expression analysis of exosomal miRNAs secreted by several human cancer cell lines and identified eight types of human miRNAs that were highly expressed in exosomes from osteoblastic phenotype-inducing prostate cancer cell lines. One of these miRNAs, hsa-miR-940, significantly promoted the osteogenic differentiation of human mesenchymal stem cells in vitro by targeting ARHGAP1 and FAM134A Interestingly, although MDA-MB-231 breast cancer cells are commonly known as an osteolytic phenotype-inducing cancer cell line, the implantation of miR-940-overexpressing MDA-MB-231 cells induced extensive osteoblastic lesions in the resulting tumors by facilitating the osteogenic differentiation of host mesenchymal cells. Our results suggest that the phenotypes of bone metastases can be induced by miRNAs secreted by cancer cells in the bone microenvironment.

Background: Muscle satellite cells are resident skeletal muscle stem cells responsible for muscle regeneration. Isolation of satellite cells is a critical process for clinical application such as drug screening and cell transplantation. Fluorescence-activated cell sorting (FACS) enables the direct isolation of satellite cells from muscle tissue. During the process used to isolate satellite cells from skeletal muscle, enzymatic digestion is the first step. Therefore, the evaluation and standardization of enzymes is important not only for reproducibility of cellular yield and viability, but also for traceability of material used in protocols. Methods: The comparison of muscle digestion was performed either by a mixture of recombinant collagenase G (ColG) and collagenase H (ColH) or by a conventional collagenase II. The degree of cell damage and surface antigen expression upon collagenase treatment were analyzed by FACS. To investigate whether satellite cells isolated using recombinant collagenase can regenerate injured muscle, satellite cells were cultured, transplanted into injured muscles, and analyzed by immunostaining. Results: We show that ColG and ColH were efficient to isolate satellite cells from mouse skeletal muscle tissue. Digestion with a combination of ColG and ColH enriched satellite cells with intact surface antigens such as alpha 7 and beta 1 integrins. Furthermore, satellite cells isolated using ColG and ColH dramatically proliferated and remained undifferentiated in vitro. When transplanted, satellite cells isolated using ColG and ColH enhanced the therapeutic efficacy in vivo. Conclusions: Our results provide an efficient method of satellite cell preparation using recombinant collagenases with a high cell yield, viability of cells, and regeneration potency to fit the biological raw material criteria. (C) 2017, The Japanese Society for Regenerative Medicine. Production and hosting by Elsevier B.V.

Oligodendrocytes are well known as myelin-forming cells in the central nervous system (CNS). However, detailed mechanisms of oligodendrocyte differentiation and myelination are poorly understood, particularly due to the difficulty of the purification of murine oligodendrocyte precursor cells (OPCs). We have recently established a transgenic mouse line that expresses a fluorescent protein Venus under the promoter of Sox10, whose expression is restricted to OPCs and oligodendrocytes in the CNS. Here, we have characterized Venus-positive cells from the Sox10-Venus mouse brain for analyzing oligodendrocyte differentiation. We first purified Venus-positive cells from the postnatal day 0-2 brain by flow cytometry. Most of the Venus-positive cells expressed NG2, an OPC marker. After induction of differentiation, an increased population of galactocerebroside-positive oligodendrocytes and decrease of OPCs were observed in the Venus-positive culture. Furthermore, a time-lapse analysis showed that Venus-positive oligodendrocytes dynamically changed their morphology with highly branched cell processes during differentiation. In addition, we found that Venus-positive OPCs were able to differentiate to type II astrocytes. In vivo, OPCs and oligodendrocytes express Venus, and some of astrocytes were positive for Venus in the ventral cortex. Taken together, the Sox10-Venus mouse system is useful for analyzing differentiation and multipotency of murine OPCs.

Mesenchymal stem/stromal cells (MSCs), which reside in the bone marrow (BM) and various other tissues, can self-renew and differentiate into mesenchymal lineages. Many groups have harvested rat MSCs (rMSCs) from rat BM (rBM) by using a flush-out procedure and have evaluated surface marker expression after long-term culture. However, MSCs gradually differentiate during expansion and exhibit altered proliferation rates, morphological features and functions in vitro. Variations in MSC isolation methods may alter the effectiveness of therapeutic applications. Here, on the basis of CD29 (Itgb1) and CD54 (Icam1) expression, we prospectively isolated a population with a high colony-forming ability and multi-lineage potential from the rBM, and we demonstrated that most of these cells expressed CD73. Successful engraftment of rMSCs was achieved by using a fluorescence-conjugated anti-CD73 antibody. In humans and mice, MSCs were also purified by CD73, thus suggesting that CD73 may serve as a universal marker for prospective isolation of MSCs. Our results may facilitate investigations of MSC properties and function.

The dermal papilla (DP) is a specialised mesenchymal component of the hair follicle (HF) that plays key roles in HF morphogenesis and regeneration. Current technical difficulties in preparing trichogenic human DP cells could be overcome by the use of highly proliferative and plastic human induced pluripotent stem cells (hiPSCs). In this study, hiPSCs were differentiated into induced mesenchymal cells (iMCs) with a bone marrow stromal cell phenotype. A highly proliferative and plastic LNGFR(+) THY-1(+) subset of iMCs was subsequently programmed using retinoic acid and DP cell activating culture medium to acquire DP properties. The resultant cells (induced DP-substituting cells [iDPSCs]) exhibited up-regulated DP markers, interacted with human keratinocytes to up-regulate HF related genes, and when co-grafted with human keratinocytes in vivo gave rise to fibre structures with a hair cuticle-like coat resembling the hair shaft, as confirmed by scanning electron microscope analysis. Furthermore, iDPSCs responded to the clinically used hair growth reagent, minoxidil sulfate, to up-regulate DP genes, further supporting that they were capable of, at least in part, reproducing DP properties. Thus, LNGFR(+) THY-1(+) iMCs may provide material for HF bioengineering and drug screening for hair diseases.

Mesenchymal stem/stromal cells (MSCs) reside in the bone marrow and maintain their stemness under hypoxic conditions. However, the mechanism underlying the effects of hypoxia on MSCs remains to be elucidated. This study attempted to uncover the signaling pathway of MSC proliferation. Under low-oxygen culture conditions, MSCs maintained their proliferation and differentiation abilities for a long term. The Notch2 receptor was up-regulated in MSCs under hypoxic conditions. Notch2-knockdown (Notch2-KD) MSCs lost their cellular proliferation ability and showed reduced gene expression of hypoxia-inducible transcription factor (HIF)-1 alpha, HIF-2 alpha, and c-Myc. Overexpression of the c-Myc gene in Notch2-D MSCs allowed the cells to regain their proliferation capacity. These results suggested that Notch2 signaling is linked to c-Myc expression and plays a key role in the regulation of MSC proliferation. Our findings provide important knowledge for elucidating the self-replication competence of MSCs in the bone marrow microenvironment.

Objective: We investigated the effects of single or repetitive intra-articular injections of synovial mesenchymal stem cells (MSCs) on a rat osteoarthritis (OA) model, and elucidated the behaviors and underlying mechanisms of the stem cells after the injection. Design: One week after the transection of the anterior cruciate ligament (ACL) of wild type Lewis rats, one million synovial MSCs were injected into the knee joint every week. Cartilage degeneration was evaluated with safranin-o staining after the first injection. To analyze cell kinetics or MSC properties, luciferase, LacZ, and GFP expressing synovial MSCs were used. To confirm the role of MSCs, species-specific microarray and PCR analyses were performed using human synovial MSCs. Results: Histological analysis for femoral and tibial cartilage showed that a single injection was ineffective but weekly injections had significant chondroprotective effects for 12 weeks. Histological and flow-cytometric analyses of LacZ and GFP expressing synovial MSCs revealed that injected MSCs migrated mainly into the synovium and most of them retained their undifferentiated MSC properties though the migrated cells rapidly decreased. In vivo imaging analysis revealed that MSCs maintained in knees while weekly injection. Species-specific microarray and PCR analyses showed that the human mRNAs on day 1 for 21 genes increased over 50-fold, and increased the expressions of PRG-4, BMP-2, and BMP-6 genes encoding chondroprotective proteins, and TSG-6 encoding an anti-inflammatory one. Conclusion: Not single but periodic injections of synovial MSCs maintained viable cells without losing their MSC properties in knees and inhibited osteoarthritis (OA) progression by secretion of trophic factors. (C) 2016 The Authors. Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International.

Human dental pulp stem/progenitor cells (hDPSCs) are attractive candidates for regenerative therapy because they can be easily expanded to generate colony-forming unit-fibroblasts (CFU-Fs) on plastic and the large cell numbers required for transplantation. However, isolation based on adherence to plastic inevitably changes the surface marker expression and biological properties of the cells. Consequently, little is currently known about the original phenotypes of tissue precursor cells that give rise to plastic-adherent CFU-Fs. To better understand the in vivo functions and translational therapeutic potential of hDPSCs and other stem cells, selective cell markers must be identified in the progenitor cells. Here, we identified a dental pulp tissue-specific cell population based on the expression profiles of 2 cell-surface markers LNGFR (CD271) and THY-1 (CD90). Prospectively isolated, dental pulp-derived LNGFR(Low+)THY-1(High+) cells represent a highly enriched population of clonogenic cells-notably, the isolated cells exhibited long-term proliferation and multilineage differentiation potential in vitro. The cells also expressed known mesenchymal cell markers and promoted new bone formation to heal critical-size calvarial defects in vivo. These findings suggest that LNGFR(Low+)THY-1(High+) dental pulp-derived cells provide an excellent source of material for bone regenerative strategies.

Mesenchymal stem/stromal cells (MSCs) have the potential to form colonies in culture and reside in adult tissues. Because MSCs have been defined using cells cultured in vitro, discrepancies have arisen between studies concerning their properties. There are also differences between populations obtained using different isolation methods. This review article focuses on recent developments in the identification of novel MSC markers for the in vivo localization and prospective isolation of human MSCs. The prospective isolation method described in this study represents an important strategy for the isolation of MSCs in a short period of time, and may find applications for regenerative medicine. Purified MSCs can be tailored according to their intended clinical therapeutic applications. Lineage tracing methods define the MSC phenotype and can be used to investigate the physiological roles of MSCs in vivo. These findings may facilitate the development of effective stem cell treatments.

The senescence-associated secretory phenotype (SASP) has attracted attention as a mechanism that connects cellular senescence to tissue dysfunction, and specific SASP factors have been identified as systemic pro-aging factors. However, little is known about the age-dependent changes in the secretory properties of stem cells. Young, but not old, mesenchymal stem/stromal cells (MSCs) are a well-known source of critical regenerative factors, but the identity of these factors remains elusive. In this study, we identified growth differentiation factor 6 (Gdf6; also known as Bmp13 and CDMP- 2) as a regenerative factor secreted from young MSCs. The expression of specific secretory factors, including Gdf6, was regulated by the microRNA (miRNA) miR-17, whose expression declined with age. Upregulation of Gdf6 restored the osteogenic capacity of old MSCs in vitro and exerted positive effects in vivo on aging-associated pathologies such as reduced lymphopoiesis, insufficient muscle repair, reduced numbers of neural progenitors in the brain, and chronic inflammation. Our results suggest that manipulation of miRNA could enable control of the SASP, and that regenerative factors derived from certain types of young cells could be used to treat geriatric diseases.

Fibrosis of organs is observed in systemic autoimmune disease. Using a scleroderma mouse, we show that transplantation of MHC compatible, minor antigen mismatched bone marrow stromal/stem cells (BMSCs) play a role in the pathogenesis of fibrosis. Removal of donor BMSCs rescued mice from disease. Freshly isolated PDGFR(alpha)(+) Sca-1(+) BMSCs expressed MHC class II following transplantation and activated host T cells. A decrease in FOXP3(+) CD25(+) Treg population was observed. T cells proliferated and secreted IL -6 when stimulated with mismatched BMSCs in vitro. Donor T cells were not involved in fibrosis because transplanting T cell -deficient RAG2 knock out mice bone marrow still caused disease. Once initially triggered by mismatched BMSCs, the autoimmune phenotype was not donor BMSC dependent as the phenotype was observed after effector T cells were adoptively transferred into na ve syngeneic mice. Our data suggest that minor antigen mismatched BMSCs trigger systemic fibrosis in this autoimmune scleroderma model.

Human mesenchymal stem cells (MSCs) are expected to have utility as a cell source in regenerative medicine. Because we previously reported that suppression of the Wnt/β-catenin signal enhances hepatic differentiation of human MSCs, we synthesized twenty-three derivatives of small molecule compounds originally reported to suppress the Wnt/β-catenin signal in human colorectal cancer cells. We then screened these compounds for their ability to induce hepatic differentiation of human UE7T-13 MSCs. After screening using WST assay, TCF reporter assay, and albumin mRNA expression, IC-2, a derivative of ICG-001, was identified as a potent inducer of hepatic differentiation of human MSCs. IC-2 potently induced the expression of albumin, complement C3, tryptophan 2,3-dioxygenase (TDO2), EpCAM, C/EBPα, glycogen storage, and urea production. Furthermore, we examined the effects of IC-2 on human bone marrow mononuclear cell fractions sorted according to CD90 and CD271 expression. Consequently, CD90+ CD271+ cells were found to induce the highest production of urea and glycogen, important hepatocyte functions, in response to IC-2 treatment. CD90+ CD271+ cells also highly expressed albumin mRNA. As the CD90+ CD271+ population has been reported to contain a rich fraction of MSCs, IC-2 apparently represents a potent inducer of hepatic differentiation of human MSCs.

Satellite cells are maintained in an undifferentiated quiescent state, but during muscle regeneration they acquire an activated stage, and initiate to proliferate and differentiate as myoblasts. The transmembrane protein teneurin-4 (Ten-4) is specifically expressed in the quiescent satellite cells; however, its cellular and molecular functions remain unknown. We therefore aimed to elucidate the function of Ten-4 in muscle satellite cells. In the tibialis anterior (TA) muscle of Ten-4-deficient mice, the number and the size of myofibers, as well as the population of satellite cells, were reduced with/without induction of muscle regeneration. Furthermore, we found an accelerated activation of satellite cells in the regenerated Ten-4-deficient TA muscle. The cell culture analysis using primary satellite cells showed that Ten-4 suppressed the progression of myogenic differentiation. Together, our findings revealed that Ten-4 functions as a crucial player in maintaining the quiescence of muscle satellite cells.

Repeated and dramatic pregnancy-induced uterine enlargement and remodeling throughout reproductive life suggests the existence of uterine smooth muscle stem/progenitor cells. The aim of this study was to isolate and characterize stem/progenitor-like cells from human myometrium through identification of specific surface markers. We here identify CD49f and CD34 as markers to permit selection of the stem/progenitor cell-like population from human myometrium and show that human CD45(-) CD31(-) glycophorin A(-) and CD49f(+) CD34(+) myometrial cells exhibit stem cell-like properties. These include side population phenotypes, an undifferentiated status, high colony-forming ability, multilineage differentiation into smooth muscle cells, osteoblasts, adipocytes, and chondrocytes, and in vivo myometrial tissue reconstitution following xenotransplantation. Furthermore, CD45(-) CD31(-) glycophorin A(-) and CD49f(+) CD34(+) myometrial cells proliferate under hypoxic conditions in vitro and, compared with the untreated nonpregnant myometrium, show greater expansion in the estrogen-treated nonpregnant myometrium and further in the pregnant myometrium in mice upon xenotransplantation. These results suggest that the newly identified myometrial stem/progenitor-like cells influenced by hypoxia and sex steroids may participate in pregnancy-induced uterine enlargement and remodeling, providing novel insights into human myometrial physiology.

Prep1, a TALE-family homeodomain transcription factor, has been demonstrated to play a critical role in embryonic hematopoiesis, as its insufficiency caused late embryonic lethality associated with defective hematopoiesis and angiogenesis. In the present study, we generated hematopoietic- and endothelial cell-specific Prep1-deficient mice and demonstrated that expression of Prep1 in the hematopoietic cell compartment is not essential for either embryonic or adult hematopoiesis, although its absence causes significant hematopoietic abnormalities in the adult bone marrow. Loss of Prep1 promotes cell cycling of hematopoietic stem/progenitor cells (HSPC), leading to the expansion of the HSPC pool. Prep1 deficiency also results in the accumulation of lineage-committed progenitors, increased monocyte/macrophage differentiation and arrested erythroid maturation. Maturation of T cells and B cells is also perturbed in Prep-deficient mice. These findings provide novel insight into the pleiotropic roles of Prep1 in adult hematopoiesis that were unrecognized in previous studies using germline Prep1 hypomorphic mice.

Although meniscus defects and degeneration are strongly correlated with the later development of osteoarthritis, the promise of regenerative medicine strategies is to prevent and/or delay the disease's progression. Meniscal reconstruction has been shown in animal models with tendon grafting and transplantation of mesenchymal stem cells (MSCs) however, these procedures have not shown the same efficacy in clinical studies. Here, our aim was to investigate the ability of tendon grafts pretreated with exogenous synovial-derived MSCs to prevent cartilage degeneration in a rat partial meniscus defect model. We removed the anterior half of the medial meniscus and grafted autologous Achilles tendons with or without a 10-minute pretreatment of the tendon with synovial MSCs. The meniscus and surrounding cartilage were evaluated at 2, 4, and 8 weeks (n = 5). Tendon grafts increased meniscus size irrespective of synovial MSCs. Histological scores for regenerated menisci were better in the tendon + MSC group than in the other two groups at 4 and 8 weeks. Both macroscopic and histological scores for articular cartilage were significantly better in the tendon + MSC group at 8 weeks. Implanted synovial MSCs survived around the grafted tendon and native meniscus integration site by cell tracking assays with luciferase+, LacZ+, DiI+, and/or GFP+ synovial MSCs and/or GFP+ tendons. Flow cytometric analysis showed that transplanted synovial MSCs retained their MSC properties at 7 days and host synovial tissue also contained cells with MSC characteristics. Synovial MSCs promoted meniscus regeneration augmented by autologous Achilles tendon grafts and prevented cartilage degeneration in rats.