CD200 expression in human cultured bone marrow mesenchymal stem cells is induced by pro-osteogenic and pro-inflammatory cues

Phenotypic changes associated with continuous long term in vitro expansion of bone marrow-derived mesenchymal stem cells

In vitro expansion of mesenchymal stem cells is necessary to obtain a higher cell number for clinical applications. However, long-term expansion can produce significant phenotypic changes on these cells, decreasing their therapeutic utility. Therefore, understanding the phenotypic changes that long-term expansion triggers in mesenchymal stem cells will allow for better and more consistent cell therapy results. Here, we evaluate the phenotypic changes caused by continuous passaging through colony forming unit-fibroblast assay, senescence beta-galactosidase staining, morphology examination, secretome analysis, surface marker expression, protein quantification, osteogenic and adipogenic differentiation, and CD4+ T lymphocyte immunosuppressive potential. Long-term in vitro culture decreases mesenchymal stem cell osteogenic potential and self-renewal, increases cell size, and senescence, but does not consistently affect adipogenic differentiation. Surface marker expression remains similar for positive and negative markers, while secretory phenotype shifts with decreased p14ARF, MMP-3, p21 Waf1/Cip1,ENA-78, GCP-2, GROα, IL-3, IL-7, IL-8, RANTES, TNFβ, and VEGF-A expression, and increased p53, p16 INK4a, MCP-1, and SDF-1 expression. Immunomodulatory potential remains unchanged. These findings can help better understand the phenotypic changes that mesenchymal stem cells undergo while expanded in vitro.

Dual-Functional Peptide DPI-VTK Promotes Mesenchymal Stem Cell Migration for Bone Regeneration

Targeting specific populations of host cells with chemotactic and adhesion factors is a promising strategy for inducing bone regeneration without the use of exogenous cells. Two peptide sequences have been derived from phage display: the mesenchymal stem cell (MSC) binding DPI (DPIYALSWSGMA) sequence and the apatite binding VTK (VTKHLNQISQSY) sequence. When combined into the dual-functional sequence, DPI-VTK increases the adhesion strength of MSCs to apatite surfaces and the amount of bone formation with transplanted MSCs. Because many adhesion molecules can stimulate chemotaxis, and cell adhesion to peptide DPI-VTK is mediated by integrins also critical to migration, we hypothesized that DPI-VTK serves as an MSC-specific chemotactic factor and can increase bone regeneration by promoting the osteogenesis of the migrated host MSCs in vivo. In transwell assays, induced pluripotent stem cell-derived human MSCs (p < 0.0001) and primary mouse calvarial cells (p < 0.0001) showed significantly increased migration in vitro when DPI-VTK was used as a chemoattractant. Further characterization of DPI-VTK binding cells from mouse calvaria using flow cytometry showed specificity toward cells expressing MSC markers (CD29, CD73, CD90, CD105, CD106, Sca-1, CD44, and CD200). When conjugated to a mineralized scaffold in vivo, DPI-VTK increased the migration of CD90 and CD200 positive cells (p < 0.05) and increased bone formation versus no-peptide controls (p < 0.05). These results demonstrate the utility of phage display in creating multifunctional peptides that can increase migration, adhesion, and bone formation in vivo, a strategy that could be applied to numerous different cell types and systems. Results advance biomaterials-based bone regeneration in two ways-demonstrating the ability of the phage-derived peptides to increase the migration of MSCs in vivo and increase host-mediated bone regeneration-potentially bypassing cell transplantation.

State-of the-art and future perspective in co-culture systems for tendon engineering

Tendon is a connective tissue that links bone to muscle, allowing for maintenance of skeleton posture, joint movement, energy storage and transmission of muscle force to bone. Tendon is a hypocellular and hypovascular tissue of poor self-regeneration capacity. Current surgical treatments are of limited success, frequently resulting in reinjury. Upcoming cell therapies are primarily based on tenocytes, a cell population of limited self-renewal capacity in vitro or mesenchymal stromal cells, a cell population prone to ectopic bone formation in vivo. Over the years mono- or multi- factorial cell culture technologies have failed to effectively maintain tenocyte phenotype in culture during expansion or to prime mesenchymal stromal cells towards tenogenic lineage prior to implantation. Upon these limitations the concept of co-culture was conceived. Here, we comprehensively review and discuss tenogenic differentiation of mesenchymal stromal cells through direct or indirect culture with tenocytes in an attempt to generate a tenocyte or a tendon-like cell population for regenerative medicine purposes.

The therapeutic effects of induced pluripotent stem cell-derived mesenchymal stem cells on Parkinson's disease

Parkinson's disease (PD), characterized by progressive degeneration of dopaminergic neurons in substantia nigra, has no disease-modifying therapy. Mesenchymal stem cell (MSC) therapy has shown great promise as a disease-modifying solution for PD. Induced pluripotent stem cell-derived MSC (iMSC) not only has stronger neural repair function, but also helps solve the problem of MSC heterogeneity. So we evaluated the therapeutic effects of iMSCs on PD. iMSCs were administered by tail vein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD models of C57BL/6 mice. The results showed iMSCs increased body weights, inhibited the prolongation of latencies to descend in pole tests, the decrease of grip strength in grip strength tests and increase of open arm entries in elevated plus maze test, and showed a trend to alleviate striatal dopamine loss. They indicate iMSCs might improve functions partially by preserving striatal dopamine in PD. We for the first time (1) found that iMSC has therapeutic effects on PD; (2) tested specifically muscle strength in cell therapy for PD and found it increases muscle strength; (3) found cell therapy alleviated the increase of entries into the open arms in PD. It suggests iMSC is a promising candidate for clinical investigations and drug development for PD.

Immunophenotypical Characterization of Limbal Mesenchymal Stromal Cell Subsets during In Vitro Expansion

Limbal mesenchymal stromal cells (LMSCs) reside in the limbal niche, supporting corneal integrity and facilitating regeneration. While mesenchymal stem/stromal cells (MSCs) are used in regenerative therapies, there is limited knowledge about LMSC subpopulations and their characteristics. This study characterized human LMSC subpopulations through the flow cytometric assessment of fifteen cell surface markers, including MSC, wound healing, immune regulation, ASC, endothelial, and differentiation markers. Primary LMSCs were established from remnant human corneal transplant specimens and passaged eight times to observe changes during subculture. The results showed the consistent expression of typical MSC markers and distinct subpopulations with the passage-dependent expression of wound healing, immune regulation, and differentiation markers. High CD166 and CD248 expressions indicated a crucial role in ocular surface repair. CD29 expression suggested an immunoregulatory role. Comparable pigment-epithelial-derived factor (PEDF) expression supported anti-inflammatory and anti-angiogenic roles. Sustained CD201 expression indicated maintained differentiation capability, while VEGFR2 expression suggested potential endothelial differentiation. LMSCs showed higher VEGF expression than fibroblasts and endothelial cells, suggesting a potential contribution to ocular surface regeneration through the modulation of angiogenesis and inflammation. These findings highlight the heterogeneity and multipotent potential of LMSC subpopulations during in vitro expansion, informing the development of standardized protocols for regenerative therapies and improving treatments for ocular surface disorders.

CD200 is overexpressed in the pancreatic tumor microenvironment and predictive of overall survival

Pancreatic cancer is an aggressive disease with a 5 year survival rate of 13%. This poor survival is attributed, in part, to limited and ineffective treatments for patients with metastatic disease, highlighting a need to identify molecular drivers of pancreatic cancer to target for more effective treatment. CD200 is a glycoprotein that interacts with the receptor CD200R and elicits an immunosuppressive response. Overexpression of CD200 has been associated with differential outcomes, depending on the tumor type. In the context of pancreatic cancer, we have previously reported that CD200 is expressed in the pancreatic tumor microenvironment (TME), and that targeting CD200 in murine tumor models reduces tumor burden. We hypothesized that CD200 is overexpressed on tumor and stromal populations in the pancreatic TME and that circulating levels of soluble CD200 (sCD200) have prognostic value for overall survival. We discovered that CD200 was overexpressed on immune, stromal, and tumor populations in the pancreatic TME. Particularly, single-cell RNA-sequencing indicated that CD200 was upregulated on inflammatory cancer-associated fibroblasts. Cytometry by time of flight analysis of PBMCs indicated that CD200 was overexpressed on innate immune populations, including monocytes, dendritic cells, and monocytic myeloid-derived suppressor cells. High sCD200 levels in plasma correlated with significantly worse overall and progression-free survival. Additionally, sCD200 correlated with the ratio of circulating matrix metalloproteinase (MMP) 3: tissue inhibitor of metalloproteinase (TIMP) 3 and MMP11/TIMP3. This study highlights the importance of CD200 expression in pancreatic cancer and provides the rationale for designing novel therapeutic strategies that target this protein.

Effect of High BMI on Human Bone Marrow-Derived Mesenchymal Stromal Cells

Bone marrow-derived mesenchymal stromal cells (BMSCs) are attractive candidates in tissue engineering and regenerative medicine. Growing evidence has suggested that a high body mass index (BMI) can affect the properties of BMSCs, resulting in a reduced quality of the cells. However, the results are not consistent. Therefore, this study aimed to investigate the influences of high BMI on human BMSCs (hBMSCs). To avoid gender bias, BMSCs from females and males were studied independently. Finally, hBMSCs from 89 females and 152 males were separately divided into the normal BMI group (18.5 kg/m2 ≤ BMI < 25 kg/m2) and the high BMI group (BMI > 25 kg/m2). The cells were analyzed for the colony-forming potential; proliferation capacity; in vitro adipogenic, osteogenic, and chondrogenic differentiation potentials; and the expression of 32 common surface antigens. The results showed that high BMI did not change the number of colonies at passage 1 in females and males. In contrast, significantly reduced colony numbers at passage 4 (P4) were found in both female and male donors with high BMI. The doubling time of hBMSCs was comparable between the normal and the high BMI groups of females and males. Furthermore, the results of trilineage differentiation did not differ between the different BMI groups of males. In females, the high and the normal BMI groups also showed similar adipogenic and chondrogenic differentiation, while osteogenic differentiation was significantly enhanced in the high-BMI group. Regarding the expression of surface antigens, the expressions of CD200 and SSEA4 on hBMSCs were reduced in the high-BMI group of females and males, respectively. In conclusion, high BMI suppressed the clonogenicity of female and male hBMSCs at P4, improved the in vitro osteogenesis of female hBMSCs, and decreased the expressions of CD200 on hBMSCs in females and SSEA4 in males.

Promising Markers in the Context of Mesenchymal Stem/Stromal Cells Subpopulations with Unique Properties

The heterogeneity of the mesenchymal stem/stromal cells (MSCs) population poses a challenge to researchers and clinicians, especially those observed at the population level. What is more, the lack of precise evidences regarding MSCs developmental origin even further complicate this issue. As the available evidences indicate several possible pathways of MSCs formation, this diverse origin may be reflected in the unique subsets of cells found within the MSCs population. Such populations differ in specialization degree, proliferation, and immunomodulatory properties or exhibit other additional properties such as increased angiogenesis capacity. In this review article, we attempted to identify such outstanding populations according to the specific surface antigens or intracellular markers. Described groups were characterized depending on their specialization and potential therapeutic application. The reports presented here cover a wide variety of properties found in the recent literature, which is quite scarce for many candidates mentioned in this article. Even though the collected information would allow for better targeting of specific subpopulations in regenerative medicine to increase the effectiveness of MSC-based therapies.

Single-cell RNA sequencing of human non-hematopoietic bone marrow cells reveals a unique set of inter-species conserved biomarkers for native mesenchymal stromal cells

BACKGROUND

Native bone marrow (BM) mesenchymal stem/stromal cells (BM-MSCs) participate in generating and shaping the skeleton and BM throughout the lifespan. Moreover, BM-MSCs regulate hematopoiesis by contributing to the hematopoietic stem cell niche in providing critical cytokines, chemokines and extracellular matrix components. However, BM-MSCs contain a heterogeneous cell population that remains ill-defined. Although studies on the taxonomy of native BM-MSCs in mice have just started to emerge, the taxonomy of native human BM-MSCs remains unelucidated.

METHODS

By using single-cell RNA sequencing (scRNA-seq), we aimed to define a proper taxonomy for native human BM non-hematopoietic subsets including endothelial cells (ECs) and mural cells (MCs) but with a focal point on MSCs. To this end, transcriptomic scRNA-seq data were generated from 5 distinct BM donors and were analyzed together with other transcriptomic data and with computational biology analyses at different levels to identify, characterize and classify distinct native cell subsets with relevant biomarkers.

RESULTS

We could ascribe novel specific biomarkers to ECs, MCs and MSCs. Unlike ECs and MCs, MSCs exhibited an adipogenic transcriptomic pattern while co-expressing genes related to hematopoiesis support and multilineage commitment potential. Furthermore, by a comparative analysis of scRNA-seq of BM cells from humans and mice, we identified core genes conserved in both species. Notably, we identified MARCKS, CXCL12, PDGFRA, and LEPR together with adipogenic factors as archetypal biomarkers of native MSCs within BM. In addition, our data suggest some complex gene nodes regulating critical biological functions of native BM-MSCs together with a preferential commitment toward an adipocyte lineage.

CONCLUSIONS

Overall, our taxonomy for native BM non-hematopoietic compartment provides an explicit depiction of gene expression in human ECs, MCs and MSCs at single-cell resolution. This analysis helps enhance our understanding of the phenotype and the complexity of biological functions of native human BM-MSCs.

Overexpression of fibroblast growth factor receptor 2 in bone marrow mesenchymal stem cells enhances osteogenesis and promotes critical cranial bone defect regeneration

Background: Reconstruction of cranial bone defects is one of the most challenging problems in reconstructive surgery, and several biological tissue engineering methods have been used to promote bone repair, such as genetic engineering of bone marrow mesenchymal stem cells (BMSCs). Fibroblast growth factor receptor 2 (Fgfr2) is an important regulator of bone construction and can be used as a potential gene editing site. However, its role in the osteogenesis process of BMSCs remains unclear. This article clarifies the function of Fgfr2 in BMSCs and explores the role of Fgfr2-overexpressed BMSCs carried by light-induced porous hydrogel (GelMA) in the repair of cranial bone defects. Methods: Lenti-virus was used to overexpress Fgfr2 in BMSCs, and cell counting kit-8, transwell, and flow cytometry assays were conducted to investigate the proliferation, migration, and characteristics. After 0, 3, 7, and 10 days of osteogenic or chondrogenic induction, the changes in osteogenic and chondrogenic ability were detected by real-time PCR, western blot, alkaline phosphatase staining, alizarin Red staining, and alcian blue staining. To investigate the viability of BMSCs carried by GelMA, calcein and propyl iodide staining were carried out as well. Finally, a critical cranial bone defect model was established in 6-week-old male mice and micro-computerized tomography, masson staining, and immunohistochemistry of OCN were conducted to test the bone regeneration properties of implanting Fgfr2-overexpressed BMSCs with GelMA in cranial bone defects over 6 weeks. Results: Overexpression of Fgfr2 in BMSCs significantly promoted cell proliferation and migration and increased the percentage of CD200+CD105+ cells. After osteogenic and chondrogenic induction, Fgfr2 overexpression enhanced both osteogenic and chondrogenic ability. Furthermore, in cranial bone defect regeneration, BMSCs carried by light-induced GelMA showed favorable biocompatibility, and Fgfr2-overexpressed BMSCs induced superior cranial bone regeneration compared to a normal BMSCs group and an untreated blank group. Conclusion: In vitro, Fgfr2 enhanced the proliferation, migration, and stemness of BMSCs and promoted osteogenesis and chondrogenesis after parallel induction. In vivo, BMSCs with Fgfr2 overexpression carried by GelMA showed favorable performance in treating critical cranial bone defects. This study clarifies the multiple functions of Fgfr2 in BMSCs and provides a new method for future tissue engineering.

Progress and emerging techniques for biomaterial-based derivation of mesenchymal stem cells (MSCs) from pluripotent stem cells (PSCs)

The use of mesenchymal stem cells (MSCs) for clinical purposes has skyrocketed in the past decade. Their multilineage differentiation potentials and immunomodulatory properties have facilitated the discovery of therapies for various illnesses. MSCs can be isolated from infant and adult tissue sources, which means they are easily available. However, this raises concerns because of the heterogeneity among the various MSC sources, which limits their effective use. Variabilities arise from donor- and tissue-specific differences, such as age, sex, and tissue source. Moreover, adult-sourced MSCs have limited proliferation potentials, which hinders their long-term therapeutic efficacy. These limitations of adult MSCs have prompted researchers to develop a new method for generating MSCs. Pluripotent stem cells (PSCs), such as embryonic stem cells and induced PSCs (iPSCs), can differentiate into various types of cells. Herein, a thorough review of the characteristics, functions, and clinical importance of MSCs is presented. The existing sources of MSCs, including adult- and infant-based sources, are compared. The most recent techniques for deriving MSCs from iPSCs, with a focus on biomaterial-assisted methods in both two- and three-dimensional culture systems, are listed and elaborated. Finally, several opportunities to develop improved methods for efficiently producing MSCs with the aim of advancing their various clinical applications are described.

The immunoregulatory protein CD200 as a potentially lucrative yet elusive target for cancer therapy

CD200 is an immunoregulatory cell surface ligand with proven pro-tumorigenic credentials via its ability to suppress CD200 receptor (CD200R)-expressing anti-tumor immune function. This definitive role for the CD200-CD200R axis in regulating an immunosuppressive tumor microenvironment has garnered increasing interest in CD200 as a candidate target for immune checkpoint inhibition therapy. However, while the CD200 blocking antibody samalizumab is still in the early stages of clinical testing, alternative mechanisms for the pro-tumorigenic role of CD200 have recently emerged that extend beyond direct suppression of anti-tumor T cell responses and, as such, may not be susceptible to CD200 antibody blockade. Herein, we will summarize the current understanding of CD200 expression and function in the tumor microenvironment as well as alternative strategies for potential neutralization of multiple CD200 mechanisms in human cancers.

CD200 as a Potential New Player in Inflammation during Rotator Cuff Tendon Injury/Repair: An In Vitro Model

Rotator cuff tendon (RCT) disease results from multifactorial mechanisms, in which inflammation plays a key role. Pro-inflammatory cytokines and tendon stem cell/progenitor cells (TSPCs) have been shown to participate in the inflammatory response. However, the underlying molecular mechanism is still not clear. In this study, flow cytometry analyses of different subpopulations of RCT-derived TSPCs demonstrate that after three days of administration, TNFα alone or in combination with IFNγ significantly decreases the percentage of CD146+CD49d+ and CD146+CD49f+ but not CD146+CD109+ TSPCs populations. In parallel, the same pro-inflammatory cytokines upregulate the expression of CD200 in the CD146+ TSPCs population. Additionally, the TNFα/IFNγ combination modulates the protein expression of STAT1, STAT3, and MMP9, but not fibromodulin. At the gene level, IRF1, CAAT (CAAT/EBPbeta), and DOK2 but not NF-κb, TGRF2 (TGFBR2), and RAS-GAP are modulated. In conclusion, although our study has several important limitations, the results highlight a new potential role of CD200 in regulating inflammation during tendon injuries. In addition, the genes analyzed here might be new potential players in the inflammatory response of TSPCs.

Autophagy inhibition restores CD200 expression under IL-1β microenvironment in placental mesenchymal stem cells of fetal origin and improves its pulmonary fibrosis therapeutic potential

BACKGROUND

Mesenchymal stem cells (MSCs) are promising remedies for various inflammatory disease including pulmonary fibrosis (PF). However, the properties of MSCs in PF pathological microenvironment remain unclear. In this study, the efficacy of autophagy in placental mesenchymal stem cells of fetal origin (fPMSCs) in either IL-1β treatment or BLM induced pulmonary fibrosis mice model was examined.

METHODS

The characteristic of fPMSCs was identified by morphological observation, flow cytometry and differentiation potential. In vitro experiments, fPMSCs were stimulated with IL-1β, to mimic inflammatory microenvironment of pulmonary fibrosis. The immunosuppressive properties and autophagic function in fPMSCs treated with IL-1β were evaluated by both macrophage cells THP-1 activation and the expression of CD200 situation, autophagy marker and MAPK signaling pathway. The in vivo anti-fibrotic activity of fPMSCs interfering autophagy was evaluated by using BLM induced pulmonary fibrosis mice model.

RESULTS

fPMSCs belonged to CD73⁺CD90⁺CD105⁺/CD14^- CD34^-CD45^-HLA-DR^- cells, and capable differentiation to adipogenic, osteogenic and chondrogenic cells. In addition, immunoinhibitory activity of fPMSCs for macrophage was restrained by IL-1β treatment in CD200 dependent manner. Suppression of autophagy by sh-Atg5 lentivirus increased the expression of CD200 and ratio of CD200 positive fPMSCs, and enhanced fPMSCs immunosuppression for THP-1 activation. Mechanistically, IL-1β induced autophagy regulated by p38 signaling cascade. In vivo, autophagy inhibition induced by Atg5 knockdown in fPMSCs resulted in strengthening antifibrotic effects on PF mice model.

CONCLUSIONS

Collectively, autophagy derived from inflammatory microenvironment hampered the immunoinhibitory properties of MSCs. Based on this, adjustment of autophagy may be a valid approach to facilitate their immunomodulatory and anti-fibrotic efficacy.

The Role of CD200-CD200 Receptor in Human Blood and Lymphatic Endothelial Cells in the Regulation of Skin Tissue Inflammation

CD200 is a cell membrane glycoprotein that interacts with its structurally related receptor (CD200R) expressed on immune cells. We characterized CD200–CD200R interactions in human adult/juvenile (j/a) and fetal (f) skin and in in vivo prevascularized skin substitutes (vascDESS) prepared by co-culturing human dermal microvascular endothelial cells (HDMEC), containing both blood (BEC) and lymphatic (LEC) EC. We detected the highest expression of CD200 on lymphatic capillaries in j/a and f skin as well as in vascDESS in vivo, whereas it was only weakly expressed on blood capillaries. Notably, the highest CD200 levels were detected on LEC with enhanced Podoplanin expression, while reduced expression was observed on Podoplanin-low LEC. Further, qRT-PCR analysis revealed upregulated expression of some chemokines, including CC-chemokine ligand 21 (CCL21) in j/aCD200⁺ LEC, as compared to j/aCD200⁻ LEC. The expression of CD200R was mainly detected on myeloid cells such as granulocytes, monocytes/macrophages, T cells in human peripheral blood, and human and rat skin. Functional immunoassays demonstrated specific binding of skin-derived CD200⁺ HDMEC to myeloid CD200R⁺ cells in vitro. Importantly, we confirmed enhanced CD200–CD200R interaction in vascDESS in vivo. We concluded that the CD200–CD200R axis plays a crucial role in regulating tissue inflammation during skin wound healing.

Targeting pediatric leukemia-propagating cells with anti-CD200 antibody therapy

Treating refractory pediatric acute lymphoblastic leukemia (ALL) remains a challenge despite impressive remission rates (>90%) achieved in the last decade. The use of innovative immunotherapeutic approaches such as anti-CD19 chimeric antigen receptor T cells does not ensure durable remissions, because leukemia-propagating cells (LPCs) that lack expression of CD19 can cause relapse, which signifies the need to identify new markers of ALL. Here we investigated expression of CD58, CD97, and CD200, which were previously shown to be overexpressed in B-cell precursor ALL (BCP-ALL) in CD34+/CD19+, CD34+/CD19-, CD34-/CD19+, and CD34-/CD19- LPCs, to assess their potential as therapeutic targets. Whole-genome microarray and flow cytometric analyses showed significant overexpression of these molecules compared with normal controls. CD58 and CD97 were mainly co-expressed with CD19 and were not a prerequisite for leukemia engraftment in immune deficient mice. In contrast, expression of CD200 was essential for engraftment and serial transplantation of cells in measurable residual disease (MRD) low-risk patients. Moreover, these CD200+ LPCs could be targeted by using the monoclonal antibody TTI-CD200 in vitro and in vivo. Treating mice with established disease significantly reduced disease burden and extended survival. These findings demonstrate that CD200 could be an attractive target for treating low-risk ALL, with minimal off-tumor effects that beset current immunotherapeutic approaches.

The CD200/CD200R mechanism in mesenchymal stem cells' regulation of dendritic cells

OBJECTIVE

To investigate the CD200/CD200R pathway mechanism in mesenchymal stem cells' (MSC) regulation of dendritic cells (DC) (MSc).

METHODS

We collected marrow samples from 40 patients admitted to our hospital from January 2018 to December 2019. The bone marrow MSCs were cultivated, and the peripheral blood mononuclear cells (PBMC) and peripheral blood DC were isolated to establish an in vitro immune response model. The expressions of the CD200 molecule on the surface of MSC were measured. Anti-CD200 blocking antibodies were added to the culture system to observe the effect of the PBMC differentiation and the immature DC (imDC) to mature DC (mDC). Then the impact of the different positive rates of CD200 in the same MSC on imDC maturity was measured.

RESULTS

After adding mitogen pHA, the IL-4, IL-10, and TNF-α secretions were increased (all P<0.05), and the OD value of the PBMC+pHA group was higher than it was in the PBMC group. After stimulated by pHA, the CD200 of the MSC group was higher than it was in the MSC+PBMC group (P<0.05). The MSC+PBMC group co-culture inhibited the development of imDC to mDC. Adding anti-CD200 antibodies to the MSC+PBMC co-culture system, MSC could still inhibit the differentiation of PBMC to imDC, and MSC had a significant inhibition effect on imDC to mDC maturation (P=0.006). The addition of MSC reduces the maturation markers on the surface of mDC (P<0.05). The addition of MSC inhibited the ability of mDC to stimulate PBMC (P_OD<0.05) and decreased the IL-12 (P_IL-12<0.05) levels. The addition of the anti-CD200 antibody increased the proliferation ability of mDC to stimulate PBMC (P_OD<0.05), and it also increased the IL-12 levels in mDC (P_IL-12<0.05). The expression of the DC mature immune phenotype in the CD200 high expression group was weak (P_{CD83, CD86}<0.05).

CONCLUSION

The mechanism by which MSC inhibits DC may be achieved through the CD200/CD200R pathway, and the CD200/CD200R pathway mainly acts on the process from imDC to mDC.

The developing mouse coronal suture at single-cell resolution

Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.

An In Vitro Study of the Effects of Crocin on the Modulation of DSPP, VEGF-A, HLA-G5, STAT3 and CD200 Expression in Human Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs) have been recommended as promising candidate for cell-based therapeutic applications due to high potentials in tissue repair/regeneration and modulation of immune responses. The gene expression change strategy by natural plant enhancers is an available opportunity to improve the stemness properties of these cells. The objective of this research was the evaluation of Crocin effects (saffron plant's bioactive compound) on immunoregulation and tissue regeneration-related biomarkers expression in human DPSCs. Based on the results of cell viability assay, application of 400 μM and lower concentrations of Crocin had no toxic effects on DPSCs; however, the time-dependent cytotoxic effects were observed at higher concentrations. This study, probably for the first time, detected the surface expression of CD200 in DPSCs with a slight time-dependent upward trend and reported that treatment with Crocin could increase expression of this macromolecule up to many times over. Also, it revealed that this carotenoid significantly led to the time-dependent upregulation of dentin sialophosphoprotein, vascular endothelial growth factor A, human leukocyte antigen-G5, and signal transducer and activator of transcription-3 messenger ribonucleic acids (mRNAs); however, this significant upregulation for STAT3 occurred, followed by a remarkable reduction. The results of this study indicated that cell treatment with Crocin may be effective in improving the stemness capacities of DPSCs. Therefore, the study provided basis for more insights into the biological effects of Crocin on DPSCs that it may aid in the future improvement of mesenchymal stem cell-based therapies.

Effect of the secretome of multipotent mesenchymal stromal cells induced by dexamethasone in vitro on the expression of phospho-NF-κB p65 and Ki-67 in mononuclear cells

Introduction: To investigate the influence of secretomes from native and dexamethasone-treated adipose-derived multipotent mesenchymal stromal cells (MMSC) on the proliferation of mononuclear cells (MNCs) and on their expression of phospho-NF-κB p65 in vitro.

Materials and Methods: MMSCs were isolated from the fat of 5 healthy donors. The cells were grown in culture up to passage four, then treated with dexamethasone for 3 hours, washed off the preparations, and incubated in a serum-free medium for 48 hours. Some of the cells were not treated with dexamethasone. Supernatants from cell cultures were concentrated by ultrafiltration, standardized by the content of galectin-1, sterilized, and added to MNCs from peripheral blood of 8 healthy donors. MNCs were isolated in a Ficoll density gradient according to a standard protocol. The expression of phospho-NF-κB p65 and Ki-67 in MNCs under the influence of MMSC secretomes in isotypic and negative controls was determined on a flow cytometer.

Results and Discussion: The expression of phospho-NF-kκB p65 and Ki-67 is decreased by the MMSC secretome. At the same time, a statistically significant decrease in phospho-NF-κB p65 by 36.2% (p &lt; 0.05) is observed when using a secretome from native cells. Ki-67 expression is reduced by 42.3% (p &lt; 0.05) under the influence of a secretome from dexamethasone-treated MMSCs.

Conclusion: The MMSC secretome, as well as MMSCs themselves, has an anti-inflammatory effect due to the effect on the expression of the active form of NF-κB and the proliferative activity of mononuclear cells. At the same time, pretreatment of cells with dexamethasone reduces the effect on phospho-NF-κB expression and increases the inhibitory effect on MNC proliferation.

The Role of Melanotransferrin (CD228) in the regulation of the differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells (hBM-MSC)

Melanotransferrin (CD228), firstly reported as a melanoma-associated antigen, is a membrane-bound glycoprotein of an iron-binding transferrin homolog. CD228 was found to be expressed significantly higher in human bone marrow-derived mesenchymal stem cells (hBM-MSC) than in human embryonic fibroblasts (FB) by RT-PCR, western blotting and flow cytometry. The expression of CD228 declined in aged hBM-MSC as osteogenesis-related genes did. We examined a possible role for CD228 in the regulation of osteogenesis and adipogenesis of hBM-MSC. Surprisingly, siRNA-mediated CD228 knockdown increased the expression of the transcription factor DLX5 and enhanced osteogenesis of hBM-MSC evidenced by an increased expression of the runt-related transcription factor 2 (RUNX2), osterix (Osx), and osteocalcin (OC), as well as higher alkaline phosphatase (ALP) activity and extracellular calcium deposition. Interestingly, hBM-MSC transfected with CD228 siRNA also showed an increase in intracellular lipid level during adipogenesis, indicated by oil red O staining of differentiated adipocytes. Overall, our study unveils CD228 as a cell surface molecule expressed by young hBM-MSC, but not by FB. It also provides evidence to suggest a role for CD228 as a negative regulator of osteogenesis and of lipid accumulation during adipogenesis in hBM-MSC in vitro.

Gingival-Derived Mesenchymal Stem Cell from Rabbit (Oryctolagus cuniculus): Isolation, Culture, and Characterization

OBJECTIVE

 This study aims to confirm whether the GDMSCs isolated from rabbit's (Oryctolagus cuniculus) gingiva are mesenchymal stem cells (MSCs).

MATERIALS AND METHODS

 This study design was partly quasi-experimental with an observational design. GDMSCs were isolated from the gingiva of healthy male rabbits (O. cuniculus) (n = 2), 6 months old, and 3 to 5 kg of body weight. The specific cell surface markers of MSCs; clusters of differentiation (CD), namely, CD44, CD73, CD90, CD105, and CD200 expressions; and hematopoietic stem cell surface markers CD34 and CD45 were examined using flow cytometry and immunohistochemistry with immunofluorescence. The osteogenic differentiation of isolated GDMSCs was examined using alizarin red staining.

RESULTS

 GDMSCs in the fourth passage showed a spindle-like formation and fibroblast-like cells that attached to the base of the culture plate. GDMSCs were MSCs that positively expressed CD44, CD73, CD90, CD105, and CD200 but did not express CD34 and CD45 when examined using flow cytometry and immunohistochemical analysis. GDMSCs had osteogenic differentiation confirmed by calcified deposits in vitro with a red-violet and brownish color after alizarin red staining.

CONCLUSION

 GDMSCs isolated from the rabbits (O. cuniculus) were confirmed as MSCs in vitro documented using immunohistochemistry and flow cytometry. GDMSCs can differentiate into osteogenic lineage in vitro that may be suitable for regenerative dentistry.

Immunosuppressive Property of MSCs Mediated by Cell Surface Receptors

In the past decade, mesenchymal stem cells (MSCs) tend to exhibit inherent tropism for refractory inflammatory diseases and engineered MSCs have appeared on the market as therapeutic agents. Recently, engineered MSCs target to cell surface molecules on immune cells has been a new strategy to improve MSC applications. In this review, we discuss the roles of multiple receptors (ICAM-1, Gal-9, PD-L1, TIGIT, CD200, and CXCR4) in the process of MSCs' immunosuppressive properties. Furthermore, we discuss the principles and strategies for developing receptor-regulated MSCs and their mechanisms of action and the challenges of using MSCs as immunosuppressive therapies.

Mesenchymal Stromal Cells from Fetal and Maternal Placenta Possess Key Similarities and Differences: Potential Implications for Their Applications in Regenerative Medicine

Placenta-derived mesenchymal stromal cells (MSC) have attracted more attention for their immune modulatory properties and poor immunogenicity, which makes them suitable for allogeneic transplantation. Although MSC isolated from different areas of the placenta share several features, they also present significant biological differences, which might point to distinct clinical applications. Hence, we compared cells from full term placenta distinguishing them on the basis of their origin, either maternal or fetal. We used cells developed by Pluristem LTD: PLacenta expanded mesenchymal-like adherent stromal cells (PLX), maternal-derived cells (PLX-PAD), fetal-derived cells (PLX-R18), and amniotic membrane-derived MSC (hAMSC). We compared immune modulatory properties evaluating effects on T-lymphocyte proliferation, expression of cytotoxicity markers, T-helper and T-regulatory cell polarization, and monocyte differentiation toward antigen presenting cells (APC). Furthermore, we investigated cell immunogenicity. We show that MSCs and MSC-like cells from both fetal and maternal sources present immune modulatory properties versus lymphoid (T cells) and myeloid (APC) cells, whereby fetal-derived cells (PLX-R18 and hAMSC) have a stronger capacity to modulate immune cell proliferation and differentiation. Our results emphasize the importance of understanding the cell origin and characteristics in order to obtain a desired result, such as modulation of the inflammatory response that is critical in fostering regenerative processes.

Mesenchymal Stem Cells in the Adult Human Liver: Hype or Hope?

Chronic liver diseases constitute a significant economic, social, and biomedical burden. Among commonly adopted approaches, only organ transplantation can radically help patients with end-stage liver pathologies. Cell therapy with hepatocytes as a treatment for chronic liver disease has demonstrated promising results. However, quality human hepatocytes are in short supply. Stem/progenitor cells capable of differentiating into functionally active hepatocytes provide an attractive alternative approach to cell therapy for liver diseases, as well as to liver-tissue engineering, drug screening, and basic research. The application of methods generally used to isolate mesenchymal stem cells (MSCs) and maintain them in culture to human liver tissue provides cells, designated here as liver MSCs. They have much in common with MSCs from other tissues, but differ in two aspects-expression of a range of hepatocyte-specific genes and, possibly, inherent commitment to hepatogenic differentiation. The aim of this review is to analyze data regarding liver MSCs, probably another type of liver stem/progenitor cells different from hepatic stellate cells or so-called hepatic progenitor cells. The review presents an analysis of the phenotypic characteristics of liver MSCs, their differentiation and therapeutic potential, methods for isolating these cells from human liver, and discusses issues of their origin and heterogeneity. Human liver MSCs are a fascinating object of fundamental research with a potential for important practical applications.

Infrapatellar fat pad-derived MSC response to inflammation and fibrosis induces an immunomodulatory phenotype involving CD10-mediated Substance P degradation

The infrapatellar fat pad (IFP) serves as a reservoir of Mesenchymal Stem Cells (MSC), and with adjacent synovium plays key roles in joint disease including the production of Substance P (SP) affecting local inflammatory responses and transmitting nociceptive signals. Here, we interrogate human IFP-derived MSC (IFP-MSC) reaction to inflammatory and pro-fibrotic environments (cell priming by TNFα/IFNγ and TNFα/IFNγ/CTGF exposure respectively), compared with bone marrow-derived MSC (BM-MSC). Naïve IFP-MSC exhibit increased clonogenicity and chondrogenic potential compared with BM-MSC. Primed cells experienced dramatic phenotypic changes, including a sharp increase in CD10, upregulation of key immunomodulatory transcripts, and secreted growth factors/cytokines affecting key pathways (IL-10, TNF-α, MAPK, Ras and PI3K-Akt). Naïve, and more so primed MSC (both) induced SP degradation in vitro, reproduced with their supernatants and abrogated with thiorphan, a CD10 inhibitor. These findings were reproduced in vivo in a rat model of acute synovitis, where transiently engrafted human IFP-MSC induced local SP reduction. Functionally, primed IFP-MSC demonstrated sustained antagonism of activated human peripheral blood mononuclear cells (PBMC) proliferation, significantly outperforming a declining dose-dependent effect with naïve cohorts. Collectively, our in vitro and in vivo data supports cell priming as a way to enhance the immunoregulatory properties of IFP-MSC, which selectively engraft in areas of active synovitis/IFP fibrosis inducing SP degradation, resulting in a cell-based product alternative to BM-MSC to potentially treat degenerative/inflammatory joint diseases.

Aldehyde dehydrogenase activity of Wharton jelly mesenchymal stromal cells: isolation and characterization

Mesenchymal stromal cells (MSCs) are promising tools in regenerative medicine and targeted therapies. Although different origins have been described, there is still huge need to find a valuable source harboring specific subpopulations of MSCs with precise therapeutic functions. Here, we isolated by fluorescence activated cell sorting technique, two populations of Wharton's jelly (WJ)-MSCs based on their aldehyde dehydrogenase (ALDH) activity. Two different ALDH activities (low vs. high) were thus observed. We then analyzed their gene expression profile for stemness, phenotype, response to hypoxia, angiogenesis, hematopoietic support, immunomodulation and multilineage differentiation abilities (osteogenesis, adipogenesis, and chondrogenesis). According to ALDH activity, many differences in the mRNA expression of these populations were noticed. In conclusion, we provide evidences that WJ harbors two distinct populations of MSCs with different ALDH activity. These populations seem to display specific functional competences that may be interesting for concise therapeutic applications.

Aldehyde Dehydrogenase Activity in Adipose Tissue: Isolation and Gene Expression Profile of Distinct Sub-population of Mesenchymal Stromal Cells

Thanks to their relative abundance and easier collection, adipose tissue (AT) is considered an alternative source for the isolation of mesenchymal stromal cells (MSCs). MSCs have great therapeutic values and are thus under investigations for several clinical indications such as regenerative medicine and immunomodulation. In this work, we aimed to identify, isolate and characterize AT-MSCs based on their aldehyde dehydrogenase (ALDH) activity known to be a classical feature of stem cells. FACS technology allowed to isolate two different populations of AT-MSCs according to their ALDH activity (referred as ALDH⁺ and ALDH^-). Depending on their ALDH activity, the transcriptome analysis of both cell populations demonstrated a differential pattern of genes related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis, immunomodulation). Based on these profiling, both AT-MSC populations could differ in terms of biological responses and functionalities. Collectively, the use of ALDH for isolating and identifying sub-populations of MSCs with specific gene profile may represent an alternative method to provide solutions for targeted therapeutic applications.

BMP-IHH-mediated interplay between mesenchymal stem cells and osteoclasts supports calvarial bone homeostasis and repair

Calvarial bones are connected by fibrous sutures. These sutures provide a niche environment that includes mesenchymal stem cells (MSCs), osteoblasts, and osteoclasts, which help maintain calvarial bone homeostasis and repair. Abnormal function of osteogenic cells or diminished MSCs within the cranial suture can lead to skull defects, such as craniosynostosis. Despite the important function of each of these cell types within the cranial suture, we have limited knowledge about the role that crosstalk between them may play in regulating calvarial bone homeostasis and injury repair. Here we show that suture MSCs give rise to osteoprogenitors that show active bone morphogenetic protein (BMP) signalling and depend on BMP-mediated Indian hedgehog (IHH) signalling to balance osteogenesis and osteoclastogenesis activity. IHH signalling and receptor activator of nuclear factor kappa-Β ligand (RANKL) may function synergistically to promote the differentiation and resorption activity of osteoclasts. Loss of Bmpr1a in MSCs leads to downregulation of hedgehog (Hh) signalling and diminished cranial sutures. Significantly, activation of Hh signalling partially restores suture morphology in Bmpr1a mutant mice, suggesting the functional importance of BMP-mediated Hh signalling in regulating suture tissue homeostasis. Furthermore, there is an increased number of CD200+ cells in Bmpr1a mutant mice, which may also contribute to the inhibited osteoclast activity in the sutures of mutant mice. Finally, suture MSCs require BMP-mediated Hh signalling during the repair of calvarial bone defects after injury. Collectively, our studies reveal the molecular and cellular mechanisms governing cell–cell interactions within the cranial suture that regulate calvarial bone homeostasis and repair.

Understanding the signaling mechanisms regulating cells in cranial sutures could help develop strategies for repairing skull defects or fractures. Little is known about how osteoblasts, osteoclasts and mesenchymal stem cells (MSCs) in cranial sutures regulate the homeostasis and repair of skull bones. Yang Chai at the University of Southern California, United States, and colleagues show that preventing the expression of bone morphogenetic protein receptor type IA (Bmpr1a) in MSCs leads to defective cranial sutures in which osteogenic activity is increased and osteoclast activity is reduced. Stimulating the Hedgehog signaling pathway not only partially rescued the defective sutures but also promoted skull bone healing after injury in Bmpr1a mutant mice, highlighting the importance of BMP-mediated Hedgehog signaling for balancing skull bone formation and resorption.

Concise Review: Stem/Progenitor Cell Proteoglycans Decorated with 7-D-4, 4-C-3, and 3-B-3(-) Chondroitin Sulfate Motifs Are Morphogenetic Markers of Tissue Development

This study reviewed the occurrence of chondroitin sulfate (CS) motifs 4-C-3, 7-D-4, and 3-B-3(-), which are expressed by progenitor cells in tissues undergoing morphogenesis. These motifs have a transient early expression pattern during tissue development and also appear in mature tissues during pathological remodeling and attempted repair processes by activated adult stem cells. The CS motifs are information and recognition modules, which may regulate cellular behavior and delineate stem cell niches in developmental tissues. One of the difficulties in determining the precise role of stem cells in tissue development and repair processes is their short engraftment period and the lack of specific markers, which differentiate the activated stem cell lineages from the resident cells. The CS sulfation motifs 7-D-4, 4-C-3, and 3-B-3 (-) decorate cell surface proteoglycans on activated stem/progenitor cells and appear to identify these cells in transitional areas of tissue development and in tissue repair and may be applicable to determining a more precise role for stem cells in tissue morphogenesis. Stem Cells 2018;36:1475-1486.

Forced expression of CD200 improves the differentiation capability and immunoregulatory functions of mesenchymal stromal cells

OBJECTIVE

In order to identify specific mesenchymal stromal cell (MSC) populations with enhanced therapeutic efficacy, we evaluated the functional changes associated with the stable expression of CD200, which is associated with immune regulatory function and osteogenic differentiation, in human bone marrow-derived MSCs (CD200/MSCs).

RESULTS

We detected significantly greater osteogenesis and chondrogenesis in CD200/MSCs than in mock-transfected MSCs. In addition, the immune regulatory function of MSCs in mixed lymphocyte reactions was enhanced by CD200 gene transfection. In CD200/MSCs, the secretion of inflammatory cytokines, i.e., IL-6 and IL-8, was reduced, and levels of the anti-inflammatory factors IL-10, FOXP3, and indoleamine 2,3-dioxygenase 1 were elevated. Finally, CD200 transfection increased the stemness of MSCs, as evidenced by greater colony numbers in colony-forming unit fibroblast assays and analyses of NANOG and OCT-4 expression.

CONCLUSIONS

These results suggest that CD200/MSCs have therapeutic applications, and further in-depth research should focus on the development of a clinically applicable cell-based therapeutic strategy.

Foreskin-derived mesenchymal stromal cells with aldehyde dehydrogenase activity: isolation and gene profiling

Background

Mesenchymal stromal cells (MSCs) become an attractive research topic because of their crucial roles in tissue repair and regenerative medicine. Foreskin is considered as a valuable tissue source containing immunotherapeutic MSCs (FSK-MSCs).

Results

In this work, we used aldehyde dehydrogenase activity (ALDH) assay (ALDEFLUOR™) to isolate and therefore characterize subsets of FSK-MSCs. According to their ALDH activity, we were able to distinguish and sort by fluorescence activated cell sorting (FACS) two subsets of FSK-MSCs (referred as ALDH⁺ and ALDH⁻). Consequently, these subsets were characterized by profiling the gene expression related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis and immunomodulation). We thus demonstrated by Real Time PCR several relevant differences in gene expression based on their ALDH activity.

Conclusion

Taken together, this preliminary study suggests that distinct subsets of FSK-MSCs with differential gene expression profiles depending of ALDH activity could be identified. These populations could differ in terms of biological functionalities involving the selection by ALDH activity as useful tool for potent therapeutic applications. However, functional studies should be conducted to confirm their therapeutic relevance.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0157-0) contains supplementary material, which is available to authorized users.

The effects of conditioned media generated by polarized macrophages on the cellular behaviours of bone marrow mesenchymal stem cells

Macrophages (Mφs) are involved in a variety of physiological and pathological events including wound healing and tissue regeneration, in which they play both positive and negative roles depending on their polarization state. In this study, we investigated the cellular behaviours of bone marrow mesenchymal stem cells (BMMSCs) after incubation in different conditioned media (CMs) generated by unpolarized Mφs (M0) or polarized Mφs (M1 and M2). Mφ polarization was induced by stimulation with various cytokines, and CMs were obtained from in vitro Mφ cultures termed CM0, CM1 and CM2 based on each Mφ phenotype. We found that CM1 supported the proliferation and adipogenic differentiation of BMMSCs, whereas CM0 had a remarkable effect on cell osteogenic differentiation. To a certain degree, CM2 also facilitated BMMSC osteogenesis; in particular, cells incubated with CM2 exhibited an enhanced capacity to form robust stem cell sheets. Although incubation with CM1 also increased production of extracellular matrix components, such as fibronectin, COL-1 and integrin β1during sheet induction, the sheets generated by CM2-incubated cells were thicker than those generated by CM1-incubated cells (P < 0.001). Our data suggest that each Mφ phenotype has a unique effect on BMMSCs. Fine-tuning Mφ polarization following transplantation may serve as an effective method to modulate the therapeutic potential of BMMSCs.

Insights into inflammatory priming of mesenchymal stromal cells: functional biological impacts

Mesenchymal stromal cells (MSCs) are multipotent adult cells with relevant biological properties making them interesting tools for cell-based therapy. These cells have the ability to home to sites of injury and secrete bioactive factors as part of their therapeutic functions. However, depending on the local environment, diverse functions of MSCs can be modulated and thus can influence their therapeutic value. The specific cytokine milieu within the site of inflammation is vital in determining the fate and cell behaviors of MSCs. Indeed, inflammatory signals (called as inflammatory priming), may induce critical changes on the phenotype, multilineage potential, hematopoietic support and immunomodulatory capacity of MSCs. Thus, for appropriate clinical application of MSCs, it is important to well know and understand these effects. In summary, investigating MSC interactions with the inflammatory environment is necessary to empower the therapeutic value of MSCs.

Isolation and Characterization of Bone Marrow Mesenchymal Stromal Cell Subsets in Culture Based on Aldehyde Dehydrogenase Activity

Mesenchymal stromal cells (MSCs) have particular properties that allow their use as therapeutic strategies for several cell-based applications. Historically, bone marrow (BM)-MSCs are isolated by culture adherence since specific cell surface markers are yet to be developed. This original work aimed to identify and characterize isolating expanded BM-MSCs based on their aldehyde dehydrogenase (ALDH) activity known to be a hallmark of stem cells and relevant for their isolation. We thus isolated by fluorescence-activated cell sorting technology two functionally different populations of BM-MSCs depending on their ALDH activity (ALDH⁺ and ALDH^-). Transcriptome analysis and profiling clearly demonstrated that both populations of BM-MSCs present distinct pattern of genes related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis, immunomodulation) in an ALDH activity dependent manner. Both BM-MSC populations look to significantly differ in terms of biological responses and functionalities. More functional analyses are needed to understand and characterize the properties of these ALDH populations. Collectively, our results highlight ALDH activity as a potential feature for isolating and segregating functional and/or competent subset of BM-MSC populations, which may account for better and more efficient therapeutic issue.

On the origin and impact of mesenchymal stem cell heterogeneity: new insights and emerging tools for single cell analysis

Mesenchymal stem cells (MSCs) display substantial cell-to-cell variation. This heterogeneity manifests among donors, among tissue sources, and within cell populations. Such pervasive variability complicates the use of MSCs in regenerative applications and may limit their therapeutic efficacy. Most conventional assays measure MSC properties in bulk and, as a consequence, mask this cell-to-cell variation. Recent studies have identified extensive variability amongst and within clonal MSC populations, in dimensions including functional differentiation capacity, molecular state (e.g. epigenetic, transcriptomic, and proteomic status), and biophysical properties. While the origins of these variations remain to be elucidated, potential mechanisms include in vivo micro-anatomical heterogeneity, epigenetic bistability, and transcriptional fluctuations. Emerging tools for single cell analysis of MSC gene and protein expression may yield further insight into the mechanisms and implications of single cell variation amongst these cells, and ultimately improve the clinical utility of MSCs in tissue engineering and regenerative medicine applications. This review outlines the dimensions across which MSC heterogeneity is present, defines some of the known mechanisms that govern this heterogeneity, and highlights emerging technologies that may further refine our understanding and improve our clinical application of this unique cell type.

IL15RA is required for osteoblast function and bone mineralization

Interleukin-15 receptor alpha (IL15RA) is an important component of interleukin-15 (IL15) pro-inflammatory signaling. In addition, IL15 and IL15RA are present in the circulation and are detected in a variety of tissues where they influence physiological functions such as muscle contractility and overall metabolism. In the skeletal system, IL15RA was previously shown to be important for osteoclastogenesis. Little is known, however, about its role in osteoblast function and bone mineralization. In this study, we evaluated bone structural and mechanical properties of an Il15ra whole-body knockout mouse (Il15ra^-/-) and used in vitro and bioinformatic analyses to understand the role IL15/IL15RA signaling on osteoblast function. We show that lack of IL15RA decreased bone mineralization in vivo and in isolated primary osteogenic cultures, suggesting a cell-autonomous effect. Il15ra^-/- osteogenic cultures also had reduced Rankl/Opg mRNA ratio, indicating defective osteoblast/osteoclast coupling. We analyzed the transcriptome of primary pre-osteoblasts from normal and Il15ra^-/- mice and identified 1150 genes that were differentially expressed at a FDR of 5%. Of these, 844 transcripts were upregulated and 306 were downregulated in Il15ra^-/- cells. The largest functional clusters, highlighted using DAVID analysis, were related to metabolism, immune response, bone mineralization and morphogenesis. The transcriptome analysis was validated by qPCR of some of the most significant hits. Using bioinformatic approaches, we identified candidate genes, including Cd200 and Enpp1, that could contribute to the reduced mineralization. Silencing Il15ra using shRNA in the calvarial osteoblast MC3T3-E1 cell line decreased ENPP1 activity. Taken together, these data support that IL15RA plays a cell-autonomous role in osteoblast function and bone mineralization.

Distinctive expression pattern of cystathionine-β-synthase and cystathionine-γ-lyase identifies mesenchymal stromal cells transition to mineralizing osteoblasts

Mesenchymal stromal cells (MSCs) are key players in the repair or regeneration of the damaged bone tissue. However, heterogeneity exists between MSCs derived from different donors in their bone formation ability both in vitro and in vivo. The identification of markers defining MSCs with different functional phenotypes is fundamental to maximize their clinical potential. In our previous in vivo study, impaired expression in MSCs of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), the two key enzymes in the catabolic pathway of homocysteine, was associated to decreased bone formation and to the onset of osteoporosis in mice. Here, we investigated whether osteogenic differentiation of human MSCs (hMSCs) modulates the expression of CBS and CSE. The expression of CBS and CSE was also assessed during chondrogenesis to confirm the specificity of their expression during osteogenesis. hMSCs displayed a heterogeneous mineralizing capacity between donors (70% of the samples mineralized, while 30% did not mineralize). Inducible expression of CBS and CSE was found to be associated with a mineralizing phenotype in hMSCs. In particular, up-regulation of CSE was restricted to hMSCs undergoing mineralization. During chondrogenesis, CBS was significantly up-regulated while CSE expression was not affected. Ex-vivo findings confirmed that mature h-osteoblasts (hOBs) show consistently higher expression of CBS and CSE than hMSCs. Our data provide the first evidence that the expression of CBS and CSE in hMSCs closely correlates with the transition of hMSCs toward the osteoblastic phenotype and that CSE may constitute a novel marker of osteogenic differentiation.