Epidermal Growth Factor as a Candidate for Ex Vivo Expansion of Bone Marrow-Derived Mesenchymal Stem Cells

Growth Hormone-Releasing Hormone and Its Analogues: Significance for MSCs-Mediated Angiogenesis

Mesenchymal stromal cells (MSCs) are promising candidates for regenerative medicine because of their multipotency, immune-privilege, and paracrine properties including the potential to promote angiogenesis. Accumulating evidence suggests that the inherent properties of cytoprotection and tissue repair by native MSCs can be enhanced by various preconditioning stimuli implemented prior to cell transplantation. Growth hormone-releasing hormone (GHRH), a stimulator in extrahypothalamus systems including tumors, has attracted great attentions in recent years because GHRH and its agonists could promote angiogenesis in various tissues. GHRH and its agonists are proangiogenic in responsive tissues including tumors, and GHRH antagonists have been tested as antitumor agents through their ability to suppress angiogenesis and cell growth. GHRH-R is expressed by MSCs and evolving work from our laboratory indicates that treatment of MSCs with GHRH agonists prior to cell transplantation markedly enhanced the angiogenic potential and tissue reparative properties of MSCs through a STAT3 signaling pathway. In this review we summarized the possible effects of GHRH analogues on cell growth and development, as well as on the proangiogenic properties of MSCs. We also discussed the relationship between GHRH analogues and MSC-mediated angiogenesis. The analyses provide new insights into molecular pathways of MSCs-based therapies and their augmentation by GHRH analogues.

Improved Transplanted Stem Cell Survival in a Polymer Gel Supplemented With Tenascin C Accelerates Healing and Reduces Scarring of Murine Skin Wounds

Mesenchymal stem cells (MSCs) remain of great interest in regenerative medicine because of their ability to home to sites of injury, differentiate into a variety of relevant lineages, and modulate inflammation and angiogenesis through paracrine activity. Many studies have found that despite the promise of MSC therapy, cell survival upon implant is highly limited and greatly reduces the therapeutic utility of MSCs. The matrikine tenascin C, a protein expressed often at the edges of a healing wound, contains unique EGF-like repeats that are able to bind EGFR at low affinities and induce downstream prosurvival signaling without inducing receptor internalization. In this study, we utilized tenascin C in a collagen/GAG-based polymer (TPolymer) that has been shown to be beneficial for skin wound healing, incorporating human MSCs into the polymer prior to application to mouse punch biopsy wound beds. We found that the TPolymer was able to promote MSC survival for 21 days in vivo, leading to associated improvements in wound healing such as dermal maturation and collagen content. This was most marked in a model of hypertrophic scarring, in which the scar formation was limited. This approach also reduced the inflammatory response in the wound bed, limiting CD3e+ cell invasion by approximately 50% in the early wound-healing process, while increasing the numbers of endothelial cells during the first week of wound healing as well. Ultimately, this matrikine-based approach to improving MSC survival may be of great use across a variety of cell therapies utilizing matrices as delivery vehicles for cells.

Mesenchymal Stem/Stromal Cells in Regenerative Medicine: Can Preconditioning Strategies Improve Therapeutic Efficacy?

Mesenchymal stem/stromal cells (MSCs) are becoming increasingly important for the development of cell therapeutics in regenerative medicine. Featuring immunomodulatory potential as well as secreting a variety of trophic factors, MSCs showed remarkable therapeutic effects in numerous preclinical disease models. However, sustainable translation of MSC therapies to the clinic is hampered by heterogeneity of MSCs and non-standardized in vitro culture technologies. Moreover, potent MSC therapeutics require MSCs with maximum regenerative capacity. There is growing evidence that in vitro preconditioning strategies of MSCs can optimize their therapeutic potential. In the following we will discuss achievements and challenges of the development of MSC therapies in regenerative medicine highlighting specific in vitro preconditioning strategies prior to cell transplantation to increase their therapeutic efficacy.

Transcriptional profiling reveals intrinsic mRNA alterations in multipotent mesenchymal stromal cells isolated from bone marrow of newly-diagnosed type 1 diabetes patients

Background

Bone marrow multipotent mesenchymal stromal cells (MSCs) are a diverse subset of precursors that contribute to the homeostasis of the hematopoietic niche. MSCs can be isolated and expanded in vitro and have unique immunomodulatory and regenerative properties that make them attractive for the treatment of autoimmune diseases, including type 1 diabetes (T1D). Whether autologous or allogeneic MSCs are more suitable for therapeutic purposes has not yet been established. While autologous MSCs may present abnormal function, allogeneic cells may be recognized and rejected by the host immune system. Thus, studies that investigate biological characteristics of MSCs isolated from T1D patients are essential to guide future clinical applications.

Methods

Bone marrow-derived MSCs from recently diagnosed type 1 diabetes patients (T1D-MSCs) were compared with those from healthy individuals (C-MSCs) for morphological and immunophenotypic characteristics and for differentiation potential. Bioinformatics approaches allowed us to match absolute and differential gene expression of several adhesion molecules, immune mediators, growth factors, and their receptors involved with hematopoietic support and immunomodulatory properties of MSCs. Finally, the differentially expressed genes were collated for functional pathway enrichment analysis.

Results

T1D-MSCs and C-MSCs were similar for morphology, immunophenotype, and differentiation potential. Our absolute gene expression results supported previous literature reports, while also detecting new potential molecules related to bone marrow-derived MSC functions. T1D-MSCs showed intrinsic abnormalities in mRNA expression, including the immunomodulatory molecules VCAM-1, CXCL12, HGF, and CCL2. Pathway analyses revealed activation of sympathetic nervous system and JAK STAT signaling in T1D-MSCs.

Conclusions

Collectively, our results indicate that MSCs isolated from T1D patients present intrinsic transcriptional alterations that may affect their therapeutic potential. However, the implications of these abnormalities in T1D development as well as in the therapeutic efficacy of autologous MSCs require further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0351-y) contains supplementary material, which is available to authorized users.

Liver-derived human mesenchymal stem cells: a novel therapeutic source for liver diseases

Mesenchymal stem cells (MSCs) represent an attractive cell type for research and therapy due to their ability to proliferate, differentiate, modulate immune reactions, and secrete trophic factors. MSCs exist in a multitude of tissues, including bone marrow, umbilical cord, and adipose tissues. Moreover, MSCs have recently been isolated from the liver. Compared with other MSC types, liver-derived human MSCs (LHMSCs) possess general morphologies, immune functions, and differentiation capacities. Interestingly, LHMCSs produce higher levels of pro-angiogenic, anti-inflammatory, and anti-apoptotic cytokines than those of bone marrow-derived MSCs. Thus, these cells may be a promising therapeutic source for liver diseases. This paper summarizes the biological characteristics of LHMSCs and their potential benefits and risks for the treatment of liver diseases.

Soft Elasticity-Associated Signaling and Bone Morphogenic Protein 2 Are Key Regulators of Mesenchymal Stem Cell Spheroidal Aggregates

Cell therapy with adult mesenchymal stem cells (MSCs) is a promising approach to regenerative medicine and autoimmune diseases. There are various approaches to improve the efficacy of MSC-based therapeutics, and MSC preparation as spheroidal aggregates, or MSC spheroids, is a novel preparatory and delivery method. Spheroid formation induces a dramatic change in the gene expression profile of MSCs. Self-activation of interleukin-1 (IL1) signaling was shown to be upstream of both pro- and anti-inflammatory genes in MSC spheroids, but the molecular pathways that initiate IL1 signaling remain unknown. As bone morphogenic protein (BMP)2 upregulation precedes that of IL1B expression during spheroid formation, we hypothesized that BMP2 signaling triggers IL1 signaling in MSC spheroids. Contrary to expectations, BMP2 signaling decreased expression of IL1B and downstream genes in a SMAD6-dependent manner. Conversely, IL1B signaling enhanced BMP2 expression. Another major difference between two-dimensional (2D) monolayer culture and three-dimensional (3D) spheroid culture is the Young's elasticity modulus, or stiffness, of the materials surrounding the cells, as there is a million-fold difference between a plastic surface for standard 2D culture (GPa) and 3D spheroidal aggregates (0.1 kPa). We tested another hypothesis that soft elasticity-associated mechano-signaling initiates the gene expression change during spheroid formation. Results showed that both BMP2 expression and inflammatory signaling are upregulated in an elasticity-associated signaling-dependent manner in MSCs. Lastly, BMP2 signaling enhanced cell survival and cell spreading of MSC spheroids. In summary, our study suggests that soft elasticity and BMP2 signaling are critical for MSC spheroids.

Tenogenic induction of equine mesenchymal stem cells by means of growth factors and low-level laser technology

Tendons regenerate poorly due to a dense extracellular matrix and low cellularity. Cellular therapies aim to improve tendon repair using mesenchymal stem cells and tenocytes; however, a current limitation is the low proliferative potential of tenocytes in cases of severe trauma. The purpose of this study was to develop a method useful in veterinary medicine to improve the differentiation of Peripheral Blood equine mesenchymal stem cells (PB-MSCs) into tenocytes. PB-MSCs were used to study the effects of the addition of some growth factors (GFs) as TGFβ3 (transforming growth factor), EGF2 (Epidermal growth factor), bFGF2 (Fibroblast growth factor) and IGF-1 (insulin-like growth factor) in presence or without Low Level Laser Technology (LLLT) on the mRNA expression levels of genes important in the tenogenic induction as Early Growth Response Protein-1 (EGR1), Tenascin (TNC) and Decorin (DCN). The singular addition of GFs did not show any influence on the mRNA expression of tenogenic genes whereas the specific combinations that arrested cell proliferation in favour of differentiation were the following: bFGF2 + TGFβ3 and bFGF2 + TGFβ3 + LLLT. Indeed, the supplement of bFGF2 and TGFβ3 significantly upregulated the expression of Early Growth Response Protein-1 and Decorin, while the use of LLLT induced a significant increase of Tenascin C levels. In conclusion, the present study might furnish significant suggestions for developing an efficient approach for tenocyte induction since the external administration of bFGF2 and TGFβ3, along with LLLT, influences the differentiation of PB-MSCs towards the tenogenic fate.

Tenascin-C Signaling in melanoma

Tenascin-C (TNC), a multifunctional matricellular glyco-protein, is highly expressed in the majority of melanoma cell lines and has been implicated in the progression of melanoma. A growing body of evidence has implicated the role of TNC in the process of invasion and metastasis for melanoma. However, the mechanism and individual signaling pathways by which TNC drives melanoma progression have not been illuminated. Herein we provide perspectives from the investigation of TNC in other settings that may hint at the mechanistic role of TNC in this disease.

Comparative Study on the Differentiation of Mesenchymal Stem Cells Between Fetal and Postnatal Rat Spinal Cord Niche

In a previous study, we established a prenatal surgical approach and transplanted mesenchymal stem cells (MSCs) into the fetal rat spinal column to treat neural tube defects (NTDs). We found that the transplanted MSCs survived and differentiated into neural lineage cells. Various cytokines and extracellular signaling systems in the spinal cord niche play an important role in cell differentiation. In this study, we observed the differentiation of transplanted MSCs in different spinal cord niches and further observed the expression of neurotrophic factors and growth factors in the spinal cord at different developmental stages to explore the mechanism of MSC differentiation in different spinal cord niches. The results showed that transplanted MSCs expressed markers of neural precursor cells (nestin), neurogliocytes (GFAP), and neurons (β-tubulin). The percentages of GFP(+)/nestin(+) double-positive cells in transplanted MSCs in E16, P1, and P21 rats were 18.31%, 12.18%, and 5.06%, respectively. The percentages of GFP(+)/GFAP(+) double-positive cells in E16, P1, and P21 rats were 32.01%, 15.35%, and 12.56%, respectively. The percentages of GFP(+)/β-tubulin(+) double-positive cells in E16, P1, and P21 were 11.76%, 7.62%, and 4.88%, respectively. The differentiation rates of MSCs in embryonic spinal cords were significantly higher than in postnatal spinal cords (p < 0.05). We found that the transplanted MSCs expressed synapsin-1 at different developmental stages. After MSC transplantation, we observed that neurotrophic factor-3 (NT-3), fibroblast growth factor-2 (FGF-2), FGF-8, transforming growth factor-α (TGF-α), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) significantly increased in the MSC transplantation group compared with the blank injection group. Furthermore, FGF-2 and VEGF expression were positively correlated with the number of surviving MSCs. In addition, we found that the expression of brain-derived neurotrophic factor (BDNF), NT-3, FGF-8, TGF-β, epidermal growth factor (EGF), and insulin-like growth factor (IGF) decreased with age, and the expression of FGF-2, FGF-10, FGF-20, TGF-α, and PDGF increased with age. Our data suggest that the embryonic spinal cord niche is more conducive to MSC differentiation after transplantation.

Spheroid Culture of Mesenchymal Stem Cells

Compared with traditional 2D adherent cell culture, 3D spheroidal cell aggregates, or spheroids, are regarded as more physiological, and this technique has been exploited in the field of oncology, stem cell biology, and tissue engineering. Mesenchymal stem cells (MSCs) cultured in spheroids have enhanced anti-inflammatory, angiogenic, and tissue reparative/regenerative effects with improved cell survival after transplantation. Cytoskeletal reorganization and drastic changes in cell morphology in MSC spheroids indicate a major difference in mechanophysical properties compared with 2D culture. Enhanced multidifferentiation potential, upregulated expression of pluripotency marker genes, and delayed replicative senescence indicate enhanced stemness in MSC spheroids. Furthermore, spheroid formation causes drastic changes in the gene expression profile of MSC in microarray analyses. In spite of these significant changes, underlying molecular mechanisms and signaling pathways triggering and sustaining these changes are largely unknown.

The EGFR-HER2 module: a stem cell approach to understanding a prime target and driver of solid tumors

The epidermal growth factor receptor (EGFR) and a coreceptor denoted HER2/ERBB2 are frequently overexpressed or mutated in solid tumors, such as carcinomas and gliomas. In line with driver roles, cancer drugs intercepting EGFR or HER2 currently outnumber therapies targeting other hubs of signal transduction. To explain the roles for EGFR and HER2 as prime drivers and targets, we take lessons from invertebrates and refer to homeostatic regulation of several mammalian tissues. The model we infer ascribes to the EGFR-HER2 module pivotal functions in rapid clonal expansion of progenitors called transient amplifying cells (TACs). Accordingly, TACs of tumors suffer from replication stress, and hence accumulate mutations. In addition, several lines of evidence propose that in response to EGF and related mitogens, TACs might undergo dedifferentiation into tissue stem cells, which might enable entry of oncogenic mutations into the stem cell compartment. According to this view, antibodies or kinase inhibitors targeting EGFR-HER2 effectively retard some solid tumors because they arrest mutation-enriched TACs and possibly inhibit their dedifferentiation. Deeper understanding of the EGFR-HER2 module and relations between cancer stem cells and TACs will enhance our ability to control a broad spectrum of human malignancies.

Epidermal growth factor enhances osteogenic differentiation of dental pulp stem cells in vitro

Introduction

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) play an important role in extracellular matrix mineralization, a complex process required for proper bone regeneration, one of the biggest challenges in dentistry. The purpose of this study was to evaluate the osteogenic potential of EGF and bFGF on dental pulp stem cells (DPSCs).

Material and methods

Human DPSCs were isolated using CD105 magnetic microbeads and characterized by flow cytometry. To induce osteoblast differentiation, the cells were cultured in osteogenic medium supplemented with EGF or bFGF at a low concentration. Cell morphology and expression of CD146 and CD10 surface markers were analyzed using fluorescence microscopy. To measure mineralization, an alizarin red S assay was performed and typical markers of osteoblastic phenotype were evaluated by RT-PCR.

Results

EGF treatment induced morphological changes and suppression of CD146 and CD10 markers. Additionally, the cells were capable of producing calcium deposits and increasing the mRNA expression to alkaline phosphatase (ALP) and osteocalcin (OCN) in relation to control groups (p < 0.001). However, bFGF treatment showed an inhibitory effect.

Conclusion

These data suggests that DPSCs in combination with EGF could be an effective stem cell-based therapy for bone tissue engineering applications in periodontics and oral implantology.

Tethering of Epidermal Growth Factor (EGF) to Beta Tricalcium Phosphate (βTCP) via Fusion to a High Affinity, Multimeric βTCP-Binding Peptide: Effects on Human Multipotent Stromal Cells/Connective Tissue Progenitors

Transplantation of freshly-aspirated autologous bone marrow, together with a scaffold, is a promising clinical alternative to harvest and transplantation of autologous bone for treatment of large defects. However, survival proliferation, and osteogenic differentiation of the marrow-resident stem and progenitor cells with osteogenic potential can be limited in large defects by the inflammatory microenvironment. Previous studies using EGF tethered to synthetic polymer substrates have demonstrated that surface-tethered EGF can protect human bone marrow-derived osteogenic stem and progenitor cells from pro-death inflammatory cues and enhance their proliferation without detriment to subsequent osteogenic differentiation. The objective of this study was to identify a facile means of tethering EGF to clinically-relevant βTCP scaffolds and to demonstrate the bioactivity of EGF tethered to βTCP using stimulation of the proliferative response of human bone-marrow derived mesenchymal stem cells (hBMSC) as a phenotypic metric. We used a phage display library and panned against βTCP and composites of βTCP with a degradable polyester biomaterial, together with orthogonal blocking schemes, to identify a 12-amino acid consensus binding peptide sequence, LLADTTHHRPWT, with high affinity for βTCP. When a single copy of this βTCP-binding peptide sequence was fused to EGF via a flexible peptide tether domain and expressed recombinantly in E. coli together with a maltose-binding domain to aid purification, the resulting fusion protein exhibited modest affinity for βTCP. However, a fusion protein containing a linear concatamer containing 10 repeats of the binding motif the resulting fusion protein showed high affinity stable binding to βTCP, with only 25% of the protein released after 7 days at 37oC. The fusion protein was bioactive, as assessed by its abilities to activate kinase signaling pathways downstream of the EGF receptor when presented in soluble form, and to enhance the proliferation of hBMSC when presented in tethered form on commercial βTCP bone regeneration scaffolds.

Optimization of pre-transplantation conditions to enhance the efficacy of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are considered a potential tool for cell based regenerative therapy due to their immunomodulatory property, differentiation potentials, trophic activity as well as large donor pool. Poor engraftment and short term survival of transplanted MSCs are recognized as major limitations which were linked to early cellular ageing, loss of chemokine markers during ex vivo expansion, and hyper-immunogenicity to xeno-contaminated MSCs. These problems can be minimized by ex vivo expansion of MSCs in hypoxic culture condition using well defined or xeno-free media i.e., media supplemented with growth factors, human serum or platelet lysate. In addition to ex vivo expansion in hypoxic culture condition using well defined media, this review article describes the potentials of transient adaptation of expanded MSCs in autologous serum supplemented medium prior to transplantation for long term regenerative benefits. Such transient adaptation in autologous serum supplemented medium may help to increase chemokine receptor expression and tissue specific differentiation of ex vivo expanded MSCs, thus would provide long term regenerative benefits.

Enhanced osteoinductivity of recombinant human bone morphogenetic protein-2 in combination with epidermal growth factor in a rabbit tibial defect model

This study aims to explore the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on bone formation when treated with epidermal growth factor (EGF) using human mesenchymal stem cells (hMSCs) and a rabbit tibial defect model. The rhBMP-2 (250 ng/ml)+EGF (10 ng/ml) group showed higher alkaline phosphatase (ALP) activity, ALP expression, increased calcium amount than rhBMP-2 group. In micro-CT and histology results of animal experiments, the rhBMP-2+EGF group showed more amount of bone bridging compared to the rhBMP-2 group. Among the 8-week groups, the rhBMP-2+EGF group showed significantly higher percent bone volume and trabecular number compared to the rhBMP-2 group. The combined treatment with EGF and rhBMP-2 induced significantly higher bone formation compared to that of rhBMP-2 only in both hMSCs and a rabbit tibial defect model. Therefore, EGF is expected to facilitate bone formation effect of rhBMP-2 when both factors are treated in combination.

Klf2 contributes to the stemness and self-renewal of human bone marrow stromal cells

Mesenchymal stem cells (MSCs) have shown great therapeutic potential in clinical trials; however, loss of pluripotency due to culture senescence is a major factor limiting their application. Understanding the physiology of stem cell self-renewal and stemness, and identifying the molecules that regulate these processes, are critical to future advances in tissue and organ regeneration. The Krüppel-like factor (Klf) family are key transcription factors implicated in self-renewal of embryonic stem cells. Here we identify Klf2 as a crucial transcription factor in undifferentiated human bone marrow stromal cells (hBMSCs), as indicated by gene expression in three culture media. To investigate the role of Klf2 in detail, an overexpression study using a lentiviral system in hBMSCs was performed. After Klf2 overexpression, cell proliferation was increased. The expression of pluripotency-associated genes, including Oct4, Nanog, and Rex1, was also upregulated by Klf2 overexpression. In addition, quantitative RT-PCR indicated a lower level of expression of differentiation related genes in Klf2 overexpressing cells as compared to control cells. Our results identify a functionally conserved role for Klf2 in hBMSCs, in which its expression is biologically important for stemness and self-renewal. These results are the first to show a role for Klf2 in the proliferation and pluripotency of hBMSCs.

Human mesenchymal stem cells possess different biological characteristics but do not change their therapeutic potential when cultured in serum free medium

Introduction

Mesenchymal stem cells (MSCs) are widely investigated in clinical researches to treat various diseases. Classic culture medium for MSCs, even for clinical use, contains fetal bovine serum. The serum-containing medium (SCM) seems a major obstacle for MSCs-related therapies due to the risk of contamination of infectious pathogens. Some studies showed that MSCs could be expanded in serum free medium (SFM); however, whether SFM would change the biological characteristics and safety issues of MSCs has not been well answered.

Methods

Human umbilical cord mesenchymal stem cells (hUC-MSCs) were cultured in a chemical defined serum free medium. Growth, multipotency, surface antigen expression, telomerase, immunosuppressive ability, gene expression profile and genomic stability of hUC-MSCs cultured in SFM and SCM were analyzed and compared side by side.

Results

hUC-MSCs propagated more slowly and senesce ultimately in SFM. SFM-expanded hUC-MSCs were different from SCM-expanded hUC-MSCs in growth rate, telomerase, gene expression profile. However, SFM-expanded hUC-MSCs maintained multipotency and the profile of surface antigen which were used to define human MSCs. Both SFM- and SCM-expanded hUC-MSCs gained copy number variation (CNV) in long-term in vitro culture.

Conclusion

hUC-MCSs could be expanded in SFM safely to obtain enough cells for clinical application, meeting the basic criteria for human mesenchymal stem cells. hUC-MSCs cultured in SFM were distinct from hUC-MSCs cultured in SCM, yet they remained therapeutic potentials for future regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/scrt522) contains supplementary material, which is available to authorized users.

Epidermal growth factor attenuates tubular necrosis following mercuric chloride damage by regeneration of indigenous, not bone marrow-derived cells

To assess effects of epidermal growth factor (EGF) and pegylated granulocyte colony-stimulating factor (P-GCSF; pegfilgrastim) administration on the cellular origin of renal tubular epithelium regenerating after acute kidney injury initiated by mercuric chloride (HgCl2 ). Female mice were irradiated and male whole bone marrow (BM) was transplanted into them. Six weeks later recipient mice were assigned to one of eight groups: control, P-GCSF+, EGF+, P-GCSF+EGF+, HgCl2 , HgCl2 +P-GCSF+, HgCl2 +EGF+ and HgCl2 +P-GCSF+EGF+. Following HgCl2 , injection tubular injury scores increased and serum urea nitrogen levels reached uraemia after 3 days, but EGF-treated groups were resistant to this acute kidney injury. A four-in-one analytical technique for identification of cellular origin, tubular phenotype, basement membrane and S-phase status revealed that BM contributed 1% of proximal tubular epithelium in undamaged kidneys and 3% after HgCl2 damage, with no effects of exogenous EGF or P-GCSF. Only 0.5% proximal tubular cells were seen in S-phase in the undamaged group kidneys; this increased to 7-8% after HgCl2 damage and to 15% after addition of EGF. Most of the regenerating tubular epithelium originated from the indigenous pool. BM contributed up to 6.6% of the proximal tubular cells in S-phase after HgCl2 damage, but only to 3.3% after additional EGF. EGF administration attenuated tubular necrosis following HgCl2 damage, and the major cause of this protective effect was division of indigenous cells, whereas BM-derived cells were less responsive. P-GCSF did not influence damage or regeneration.

Optimization of growth inducing factors for colony forming and attachment of bone marrow-derived mesenchymal stem cells regarding bioengineering application

PURPOSE

These days, mesenchymal stem cells (MSCs) have received worldwide attention because of their potentiality in tissue engineering for implant dentistry. The purpose of this study was to evaluate various growth inducing factors in media for improvement of acquisition of bone marrow mesenchymal stem cells (BMMSCs) and colony forming unit-fibroblast (CFU-F).

MATERIALS AND METHODS

The mouse BMMSCs were freshly obtained from female C3H mouse femur and tibia. The cells seeded at the density of 10⁶/dish in media supplemented with different density of fetal bovine serum (FBS), 1α, 25-dihydroxyvitamin (VD3) and recombinant human epidermal growth factor (rhEGF). After 14 days, CFU-F assay was conducted to analyze the cell attachment and proliferation, and moreover for VD3, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay was additionally conducted.

RESULTS

The cell proliferation was increased with the increase of FBS concentration (P<.05). The cell proliferation was highest at the density of 20 ng/mL rhEGF compared with 0 ng/mL and 200 ng/mL rhEGF (P<.05). For VD3, although the colony number was increased with the increase of its concentration, the difference was not statistically significant (P>.05).

CONCLUSION

FBS played the main role in cell attachment and growth, and the growth factor like rhEGF played the additional effect. However, VD3 did not have much efficacy compare with the other two factors. Improvement of the conditions could be adopted to acquire more functional MSCs to apply into bony defect around implants easily.

Neuronal-like cell differentiation of non-adherent bone marrow cell-derived mesenchymal stem cells

Non-adherent bone marrow cell-derived mesenchymal stem cells from C57BL/6J mice were separated and cultured using the “pour-off” method. Non-adherent bone marrow cell-derived mesenchymal stem cells developed colony-forming unit-fibroblasts, and could be expanded by supplementation with epidermal growth factor. Immunocytochemistry showed that the non-adherent bone marrow cell-derived mesenchymal stem cells exposed to basic fibroblast growth factor/epidermal growth factor/nerve growth factor expressed the neuron specific markers, neurofilament-200 and NeuN, in vitro. Non-adherent bone marrow cell-derived mesenchymal stem cells from β-galactosidase transgenic mice were also transplanted into focal ischemic brain (right corpus striatum) of C57BL/6J mice. At 8 weeks, cells positive for LacZ and β-galactosidase staining were observed in the ischemic tissues, and cells co-labeled with both β-galactosidase and NeuN were seen by double immunohistochemical staining. These findings suggest that the non-adherent bone marrow cell-derived mesenchymal stem cells could differentiate into neuronal-like cells in vitro and in vivo.

Autologous platelet-rich plasma: a biological supplement to enhance adipose-derived mesenchymal stem cell expansion

Currently the use of non-autologous cell culture media (e.g., animal-derived or allogeneic serum) for clinical applications of mesenchymal stem cells (MSCs) is criticized by regulatory agencies. Autologous platelet-rich plasma (PRP) is proposed as a safer alternative medium supplement for adipose-derived mesenchymal stem cells (AT-MSC) culture. To study its efficiency on cell proliferation, AT-MSCs were cultured for 10 days in media supplemented with different concentrations of autologous non-activated PRP (nPRP) or thrombin-activated PRP (tPRP) (1-60%). AT-MSC proliferation, cell phenotype, multipotency capacity, and chromosome stability were assessed and compared to AT-MSCs expanded in a classical medium supplemented with 10% of fetal bovine serum (FBS). Culture media supplemented with nPRP showed dose-dependent higher AT-MSC proliferation than did FBS or tPRP. Twenty percent nPRP was the most effective concentration to promote cell proliferation. This condition increased 13.9 times greater AT-MSC number in comparison to culture with FBS, without changing the AT-MSC phenotype, differentiation capacity, and chromosome status. We concluded that 20% autologous nPRP is a safe, efficient, and cost-effective supplement for AT-MSC expansion. It should be considered as an alternative to FBS or other nonautologous blood derivatives. It could serve as a potent substitute for the validation of future clinical protocols as it respects good manufacturing practices and regulatory agencies' standards.

EGF-induced adipose tissue mesothelial cells undergo functional vascular smooth muscle differentiation

Recent studies suggested that the post-natal mesothelium retain differentiative potential of the embryonic mesothelium, which generates fibroblasts and vascular smooth muscle cells (VSMCs), in developing coelomic organs via epithelial-to-mesenchymal transition (EMT). Whether adult mesothelial cells (MCs) are able to give rise to functional VSMCs in vitro and which are the factors and mechanisms directing this process remain largely unknown. Here, we isolated adipose tissue MCs (ATMCs) from adult mice, and demonstrated that ATMCs cultured in a serum-containing media supplemented with epidermal growth factor (EGF) efficiently increased both their proliferation and EMT above levels found in only serum-containing media cultures. EGF-induced ATMCs gained phosphorylation of the EGF receptor and activated simultaneously ILK/Erk1/2, PI3K/Akt and Smad2/3-dependent pathways. Sequential subculture onto collagen-I surface efficiently improved their vasculogenic EMT towards cells featuring VSMCs (α-SMA, calponin, caldesmon, SM22α, desmin, SM-MHC, smoothelin-B and PDGFR-β) that could actively contract in response to receptor and non-receptor-mediated vasoactive agonists. Overall, our results indentify EGF signalling as a robust vasculogenic inductive pathway for ATMCs, leading to their transdifferentiation into functional VSMC-like cells.

Optimization of culture condition of human bone marrow stromal cells in terms of purification, proliferation, and pluripotency

Human bone marrow stromal cells (hBMSCs) possess multilineage differentiation potential and play an important role in modern tissue engineering. However, the development of culture media to maintain hBMSCs in an undifferentiated, self-renewing state during their robust proliferation remains a challenge. We developed and tested modified growth medium [medium 1: epidermal growth factor (EGF), platelet-derived growth factor (PDGF), low glucose, 2% fetal calf serum (FCS)] on hBMSCs by comparing primary cell isolation, multipassage expansion, culture morphology, proliferation, and cellular phenotype, and performing an expression analysis of intrinsic-regulated genes to other two media. Cell morphology, proliferation, and phenotype varied among the media, while cells cultured in medium 1 displayed small, spindle-shaped morphology with the highest rate of growth capacities and the expected phenotype. RT-PCR analysis showed that medium 1 displayed the lowest expression levels of osteogenic genes, chondrogenic genes (osteonectin, runt-related transcription factor 2, cartilage oligo matrix protein, and SOX9), and adipogenic genes (lipoprotein lipase). The expression of another adipogenic gene, peroxisome proliferator-activator receptor-γ2, was higher in medium 1 but did not reach significance. In addition, hBMSCs expanded in medium 1 showed the highest expression ratio of self-renewing-related genes Krüppel-like factor 2 (KLF2) and KLF5. In conclusion, medium 1 allows for better expansion and pluripotency maintenance of hBMSCs and serves as a preferred alternative to traditional serum-containing media for research applications and future clinical use.

Mechanical unloading of bone in microgravity reduces mesenchymal and hematopoietic stem cell-mediated tissue regeneration

Mechanical loading of mammalian tissues is a potent promoter of tissue growth and regeneration, whilst unloading in microgravity can cause reduced tissue regeneration, possibly through effects on stem cell tissue progenitors. To test the specific hypothesis that mechanical unloading alters differentiation of bone marrow mesenchymal and hematopoietic stem cell lineages, we studied cellular and molecular aspects of how bone marrow in the mouse proximal femur responds to unloading in microgravity. Trabecular and cortical endosteal bone surfaces in the femoral head underwent significant bone resorption in microgravity, enlarging the marrow cavity. Cells isolated from the femoral head marrow compartment showed significant down-regulation of gene expression markers for early mesenchymal and hematopoietic differentiation, including FUT1(-6.72), CSF2(-3.30), CD90(-3.33), PTPRC(-2.79), and GDF15(-2.45), but not stem cell markers, such as SOX2. At the cellular level, in situ histological analysis revealed decreased megakaryocyte numbers whilst erythrocytes were increased 2.33 fold. Furthermore, erythrocytes displayed elevated fucosylation and clustering adjacent to sinuses forming the marrow-blood barrier, possibly providing a mechanistic basis for explaining spaceflight anemia. Culture of isolated bone marrow cells immediately after microgravity exposure increased the marrow progenitor's potential for mesenchymal differentiation into in-vitro mineralized bone nodules, and hematopoietic differentiation into osteoclasts, suggesting an accumulation of undifferentiated progenitors during exposure to microgravity. These results support the idea that mechanical unloading of mammalian tissues in microgravity is a strong inhibitor of tissue growth and regeneration mechanisms, acting at the level of early mesenchymal and hematopoietic stem cell differentiation.

Enhanced proliferation of bone marrow mesenchymal stem cells by co-culture with TM4 mouse Sertoli cells: involvement of the EGF/PI3K/AKT pathway

Bone marrow mesenchymal stem cells (BM-MSCs) are considered as a promising option in the field of regenerative medicine and tissue engineering. However, little is known about how TM4 mouse Sertoli cells, which are known to enhance stem cells proliferation in co-culture, may influence the proliferation of BM-MSCs and which signaling pathways are involved in. To address these questions, an in vitro transwell system was used. We found that TM4 cells could produce soluble factors which enhanced the growth of BM-MSCs without inhibiting the multipotency. Furthermore, cell cycle analysis showed that co-culture with the TM4 cells accelerated the progress of BM-MSCs from the G1 to the S phase. The expression of the phospho-akt, mdm2, as well as pho-CDC2, and cyclin D1 were markedly upregulated in co-cultured BM-MSCs. The observed promoting effect was significantly inhibited by the administration of the PI3K/AKT inhibitor, LY294002. Among the various growth factors produced by TM4 cells, the epithelial growth factor (EGF) stimulated the proliferation of the BM-MSCs more significantly compared with the other growth factors examined in this study. Neutralization of EGF via a blocking antibody significantly limited the promoting growth effect in BM-MSCs. These results suggest that TM4 cells provide a favorable in vitro environment for BM-MSCs growth and imply the involvement of the EGF/PI3K/AKT pathway.

Aldehyde Dehydrogenase-2 Is a Host Factor Required for Effective Bone Marrow Mesenchymal Stem Cell Therapy

Objective—

Mesenchymal stem cell (MSC) therapy is a promising treatment for ischemic injury. However, the environmental regulatory mechanism is essentially unclear and thus greatly limits its application in clinical setting. Accumulating evidence suggests a vital role of aldehyde dehydrogenase-2 (ALDH2) in microenvironment homeostasis after ischemia. About 540 million people or 8% of population worldwide carry a loss-of-function allele of ALDH2. It is unknown whether ALDH2 functions as a host factor regulating the therapeutic potential of donor MSCs. Therefore, this study was designed to determine whether and how host ALDH2 regulates MSC retention and therapeutic efficacy after transplantation into ischemic tissues.

Approach and Results—

Mice limb ischemia was performed by femoral artery ligation. A total of 10 6 MSCs were injected into the ischemic thigh muscles. One, 2, and 4 weeks after transplantation, MSC retention, blood perfusion recovery, limb necrosis, and fibrosis were analyzed. Compared with wild-type tissue, ALDH2 deficiency tissue significantly limited MSC retention and its perfusion recovery and limb salvage effects after ischemia. Importantly, local overexpression of ALDH2 optimized tissue microenvironment and significantly magnified all these MSC-induced improvement. Further study indicated that host ALDH2 regulated transplanted MSC survival and therapy as a microenvironment homeostasis mediator via local capillary density, energy supply, and oxidative stress regulating after ischemia.

Conclusions—

Our study establishes ALDH2 as a key mediator of host stem cell niche for optimal MSC therapy and suggests that ALDH2 deficiency present in the general population is a limiting host factor to be considered for MSC therapy.

Concise review: optimizing expansion of bone marrow mesenchymal stem/stromal cells for clinical applications

Bone marrow-derived mesenchymal stem/stromal cells (MSCs) have demonstrated success in the clinical treatment of hematopoietic pathologies and cardiovascular disease and are the focus of treating other diseases of the musculoskeletal, digestive, integumentary, and nervous systems. However, during the requisite two-dimensional (2D) expansion to achieve a clinically relevant number of cells, MSCs exhibit profound degeneration in progenitor potency. Proliferation, multilineage potential, and colony-forming efficiency are fundamental progenitor properties that are abrogated by extensive monolayer culture. To harness the robust therapeutic potential of MSCs, a consistent, rapid, and minimally detrimental expansion method is necessary. Alternative expansion efforts have exhibited promise in the ability to preserve MSC progenitor potency better than the 2D paradigm by mimicking features of the native bone marrow niche. MSCs have been successfully expanded when stimulated by growth factors, under reduced oxygen tension, and in three-dimensional bioreactors. MSC therapeutic value can be optimized for clinical applications by combining system inputs to tailor culture parameters for recapitulating the niche with probes that nondestructively monitor progenitor potency. The purpose of this review is to explore how modulations in the 2D paradigm affect MSC progenitor properties and to highlight recent efforts in alternative expansion techniques.

Application of stem cell/growth factor system, as a multimodal therapy approach in regenerative medicine to improve cell therapy yields

Stem cells hold a great promise for regenerative medicine, especially for replacing cells in infarcted organ that hardly have any intrinsic renewal capacity, including heart and brain. Signaling pathways that regulate pluripotency or lineage-specific gene and protein expression have been the major focus of stem cell research. Between them, there are some well known signaling pathways such as GF/GFR systems, SDF-1α/CXC4 ligand receptor interaction and PI3K/Akt signaling, and cytokines may regulate cell fate decisions, and can be utilized to positively influence cell therapy outcomes or accentuate synergistic compliance. For example, contributing factors in the progression of heart failure are both the loss of cardiomyocytes after myocardial infarction, and the absence of an adequate endogenous repair signaling. Combining cell engraftment with therapeutic signaling factor delivery is more exciting in terms of host progenitor/donor stem cell survival and proliferation. Thus stem cell-based therapy, besides triggering signaling pathways through GF/GFR systems can become a realistic option in regenerative processes for replacing lost cells and reconstituting the damaged organ, as before.

Conditioned mesenchymal stem cells attenuate progression of chronic kidney disease through inhibition of epithelial-to-mesenchymal transition and immune modulation

Mesenchymal stem cells (MSCs) have been shown to improve the outcome of acute renal injury models; but whether MSCs can delay renal failure in chronic kidney disease (CKD) remains unclear. In the present study, the were cultured in media containing various concentrations of basic fibroblast growth factor, epidermal growth factor and ascorbic acid 2-phosphate to investigate whether hepatocyte growth factor (HGF) secretion could be increased by the stimulation of these growth factors. Then, TGF-β1-treated renal interstitial fibroblast (NRK-49F), renal proximal tubular cells (NRK-52E) and podocytes were co-cultured with conditioned MSCs in the absence or presence of ascorbic acid 2-phosphate to quantify the protective effects of conditioned MSCs on renal cells. Moreover, male Sprague-Dawley rats were treated with 1 × 10⁶ conditioned MSCs immediately after 5/6 nephrectomy and every other week through the tail vein for 14 weeks. It was found that basic fibroblast growth factor, epidermal growth factor and ascorbic acid 2-phosphate promoted HGF secretion in MSCs. Besides, conditioned MSCs were found to be protective against TGF-β1 induced epithelial-to-mesenchymal transition of NRK-52E and activation of NRK-49F cells. Furthermore, conditioned MSCs protected podocytes from TGF-β1-induced loss of synaptopodin, fibronectin induction, cell death and apoptosis. Rats transplanted with conditioned human MSCs had a significantly increase in creatinine clearance rate, decrease in glomerulosclerosis, interstitial fibrosis and increase in CD4⁺CD25⁺Foxp3⁺ regulatory T cells counts in splenocytes. Together, our studies indicated that conditioned MSCs preserve renal function by their anti-fibrotic and anti-inflammatory effects. Transplantation of conditioned MSCs may be useful in treating CKD.

Effects of human epidermal growth factor gene-transfected mesenchymal stem cells on fibroblast migration and proliferation

OBJECTIVES

We were interested in determining whether epidermal growth factor gene-transfected mesenchymal stem cells (EGF-MSC) would accelerate fibroblast migration and proliferation.

MATERIALS AND METHODS

Fibroblasts were cultured in serum-free conditioned media from EGF-MSC; RT-PCR was performed to detect expression of EGF gene in EGF-MSCs. EGF protein levels in cell culture supernatants from EGF-MSC were assayed by ELISA and proliferation of EGF-MSC-treated fibroblasts was performed using MTT assay. Effects of EGF-MSC on fibroblast migration were evaluated using scratch wound and transmigration assays. Cell adhesion molecules, cell dynamics molecules and phospho-(Ser) kinase substrate expressions of EGF-MSC-treated fibroblasts were evaluated by western blotting.

RESULTS

EGF gene expression increased in EGF-MSCs and viability of EGF-MSC-treated fibroblasts was elevated. EGF-MSC-treated fibroblasts showed increased migration compared to controls. Expressions of cell adhesion molecules (β-catenin, N-cadherin), cell dynamics molecules (cofilin, ezrin) and phospho-(Ser) kinase substrates (phospho-MAPK/CDK substrate, phospho-Arg-(Ser)-X-Tyr/Phe-X-pSer motif) increased in EGF-MSC-treated fibroblasts. These results imply that EGF-MSCs contributed to enhancing the wound healing process by increased cell adhesion, dynamic effects, fibroblast migration, and proliferation.

CONCLUSIONS

This study indicates that EGF-MSCs had a positive influence on fibroblast migration and proliferation and EGF-MSC may provide a useful strategy for wound healing.

Periodontal-ligament-derived stem cells exhibit the capacity for long-term survival, self-renewal, and regeneration of multiple tissue types in vivo

Primary periodontal ligament stem cells (PDLSCs) are known to possess multidifferentiation potential and exhibit an immunophenotype similar to that described for bone-marrow-derived mesenchymal stem cells. In the present study, bromo-deoxyuridine (BrdU)-labeled ovine PDLSCs implanted into immunodeficient mice survived after 8 weeks post-transplantation and exhibited the capacity to form bone/cementum-like mineralized tissue, ligament structures similar to Sharpey's fibers with an associated vasculature. To evaluate self-renewal potential, PDLSCs were recovered from harvested primary transplants 8 weeks post-transplantation that exhibit an immunophenotype and multipotential capacity comparable to primary PDLSCs. The re-derived PDLSCs isolated from primary transplants were implanted into secondary ectopic xenogeneic transplants. Histomorphological analysis demonstrated that four out of six donor re-derived PDLSC populations displayed a capacity to survive and form fibrous ligament structures and mineralized tissues associated with vasculature in vivo, although at diminished levels in comparison to primary PDLSCs. Further, the capacity for long-term survival and the potential role of PDLSCs in dental tissue regeneration were determined using an ovine preclinical periodontal defect model. Autologous ex vivo-expanded PDLSCs that were prelabeled with BrdU were seeded onto Gelfoam(®) scaffolds and then transplanted into fenestration defects surgically created in the periodontium of the second premolars. Histological assessment at 8 weeks post-implantation revealed surviving BrdU-positive PDLSCs associated with regenerated periodontium-related tissues, including cementum and bone-like structures. This is the first report to demonstrate the self-renewal capacity of PDLSCs using serial xenogeneic transplants and provides evidence of the long-term survival and tissue contribution of autologous PDLSCs in a preclinical periodontal defect model.

Akt- and Erk-mediated regulation of proliferation and differentiation during PDGFRβ-induced MSC self-renewal

Understanding the mechanisms that direct mesenchymal stem cell (MSC) self-renewal fate decisions is a key to most tissue regenerative approaches. The aim of this study here was to investigate the mechanisms of action of platelet-derived growth factor receptor β (PDGFRβ) signalling on MSC proliferation and differentiation. MSC were cultured and stimulated with PDGF-BB together with inhibitors of second messenger pathways. Cell proliferation was assessed using ethynyl-2′-deoxyuridine and phosphorylation status of signalling molecules assessed by Western Blots. To assess differentiation potentials, cells were transferred to adipogenic or osteogenic media, and differentiation assessed by expression of differentiation association genes by qRT-PCR, and by long-term culture assays. Our results showed that distinct pathways with opposing actions were activated by PDGF. PI3K/Akt signalling was the main contributor to MSC proliferation in response to activation of PDGFRβ. We also demonstrate a negative feedback mechanism between PI3K/Akt and PDGFR-β expression. In addition, PI3K/Akt downstream signal cascades, mTOR and its associated proteins p70S6K and 4E-BP1 were involved. These pathways induced the expression of cyclin D1, cyclin D3 and CDK6 to promote cell cycle progression and MSC proliferation. In contrast, activation of Erk by PDGFRβ signalling potently inhibited the adipocytic differentiation of MSCs by blocking PPARγ and CEBPα expression. The data suggest that PDGFRβ-induced Akt and Erk pathways regulate opposing fate decisions of proliferation and differentiation to promote MSC self-renewal. Thus, activation of multiple intracellular cascades is required for successful and sustainable MSC self-renewal strategies.

Different expression patterns of growth factors in rat fetuses with spina bifida aperta after in utero mesenchymal stromal cell transplantation

BACKGROUND AIMS

In a previous study, we successfully devised a prenatal surgical approach and transplanted mesenchymal stromal cells (MSCs) to fetal rat spinal column to treat retinoic acid-induced neural tube defects in rat. Our results show that MSCs survived, migrated and differentiated into neural lineage cells. We intended to study various growth factor expressions in rat fetal spinal cords with spina bifida aperta after in utero MSC transplantation and the effect of in vivo growth factor introduction for prenatal spina bifida treatment.

METHODS

Pregnant rats were treated with retinoic acid on embryonic day 10 and then received fetal surgery for MSC transplantation and/or lentiviral epidermal growth factor (EGF) injection on embryonic day 16; various growth factor expression in spinal cords from embryonic day 20 fetuses were analyzed by means of quantitative reverse transcriptase-polymerase chain reaction. Terminal deoxynucleotidyl transferase dUTP nick end labeling analysis was performed to observe spinal tissue apoptosis.

RESULTS

Growth factor expression was dysregulated in spinal cords with spina bifida. After MSC transplantation, we observed significantly increased expression of EGF, fibroblast growth factor (FGF)-8, FGF-2 and FGF-20 in the MSC transplantation group compared with blank injection; Furthermore, EGF expression positively correlated with surviving MSC amounts. Expression of other growth factors was not significantly different. In vivo EGF introduction reduced spinal tissue apoptosis.

CONCLUSIONS

Our results suggest that intrinsic EGF and FGF-2, FGF-8 and FGF-20 might affect the in vivo fate of transplanted MSCs in a fetal rat spina bifida model. In vivo EGF introduction together with MSC transplantation might serve as a new strategy for prenatal spina bifida treatment.

Stem cell-based tissue engineering approaches for musculoskeletal regeneration

The field of regenerative medicine and tissue engineering is an ever evolving field that holds promise in treating numerous musculoskeletal diseases and injuries. An important impetus in the development of the field was the discovery and implementation of stem cells. The utilization of mesenchymal stem cells, and later embryonic and induced pluripotent stem cells, opens new arenas for tissue engineering and presents the potential of developing stem cell-based therapies for disease treatment. Multipotent and pluripotent stem cells can produce various lineage tissues, and allow for derivation of a tissue that may be comprised of multiple cell types. As the field grows, the combination of biomaterial scaffolds and bioreactors provides methods to create an environment for stem cells that better represent their microenvironment for new tissue formation. As technologies for the fabrication of biomaterial scaffolds advance, the ability of scaffolds to modulate stem cell behavior advances as well. The composition of scaffolds could be of natural or synthetic materials and could be tailored to enhance cell self-renewal and/or direct cell fates. In addition to biomaterial scaffolds, studies of tissue development and cellular microenvironments have determined other factors, such as growth factors and oxygen tension, that are crucial to the regulation of stem cell activity. The overarching goal of stem cell-based tissue engineering research is to precisely control differentiation of stem cells in culture. In this article, we review current developments in tissue engineering, focusing on several stem cell sources, induction factors including growth factors, oxygen tension, biomaterials, and mechanical stimulation, and the internal and external regulatory mechanisms that govern proliferation and differentiation.

Early growth response-2 signaling mediates immunomodulatory effects of human multipotential stromal cells

While most studies have suggested multipotential stromal cell or mesenchymal stem cell (MSC) therapies are useful for immune-mediated diseases, MSCs' immunomodulatory effects were not entirely reproduced in some studies, indicating the necessity to determine the underlying mechanism of MSCs' effects on immune response regulation to maximize their immunomodulatory effects. We have identified the transcription factor early growth response gene-2 (EGR2) as a novel molecular switch regulating known immunomodulatory molecules in human MSCs. EGR2 binds to the promoter regions of these genes, interleukin-6 (IL6), leukemia inhibitory factor (LIF), indoleamine dioxygenase-1 (IDO1), and cyclooxygenase-2/prostaglandin-endoperoxide synthase 2 (COX2/PTGS2), and siRNA against EGR2 was shown to downregulate these genes and reduce the production of prostaglandin E2, an immunomodulatory mediator produced downstream of COX2/PTGS2. Moreover, EGR2 knockdown restores T-lymphocyte proliferation reduced by MSC coculture. Therefore, EGR2 is a potential target for the optimization of immunomodulatory properties of MSC-based therapies.

The osteogenic differentiation of PDLSCs is mediated through MEK/ERK and p38 MAPK signalling under hypoxia

PURPOSE

During orthodontic treatment and chronic periodontitis, the periodontal vasculature is severely impaired by overloaded mechanical force or chronic inflammation. This leads to the hypoxic milieu of the periodontal stem cell niche and ultimately affects periodontal tissue remodelling. However, the role of hypoxia in the regulation of periodontal ligament stem cell (PDLSC) behaviours still remains to be elucidated. The present study was aimed at investigating the effects of hypoxia on osteogenic differentiation, mineralisation and paracrine release of PDLSCs and further demonstrating the involvement of mitogen-activated protein kinase (MAPK) signalling in the process.

METHODS

First, PDLSCs were isolated and characterised. Second, the effects of different periods of hypoxia on PDLSC osteogenic potential, mineralisation and paracrine release were investigated. Third, extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase activities under hypoxia were measured. Finally, specific MAPK inhibitors PD98059 and SB203580 were employed to investigate the involvement of two kinases in PDLSC osteogenesis under hypoxia.

RESULTS

Immunocytochemical staining and multilineage differentiation assays verified that the isolated cells were PDLSCs. Cell viability, alkaline phosphatase (ALP) activity, messenger RNA (mRNA) and protein levels of runt-related transcription factor 2 (Runx2) and Sp7, mineralisation and prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) release were significantly increased by hypoxia. ERK1/2 and p38 were activated in different ways under hypoxia. Furthermore, hypoxia-stimulated transcription and expression of the above-mentioned osteogenic regulators were also reversed by PD98059 and SB203580 to different degrees.

CONCLUSIONS

Exposure of PDLSCs to hypoxia affected their osteogenic potential, mineralisation and paracrine release, and the process involved mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) and p38 MAPK signalling.

Epidermal growth factor can optimize a serum-free culture system for bone marrow stem cell proliferation in a miniature pig model

Bone marrow-derived mesenchymal stem cells have become an attractive cell source for periodontal ligament regeneration treatment because of their potential to engraft to several tissue types after injury. Most researchers have focused on the transplantation process, but few have paid attention to cell safety concerns and rapid proliferation before transplantation. Using serum-free medium to culture stem cells may be an effective method to avoid problems associated with exogenous serum and the addition of growth factors to promote cell proliferation. Here, we randomly divided our serum-free cultures and treated them with different levels of epidermal growth factor (EGF). We then evaluated changes in rates of cell adhesion, proliferation, apoptosis, and cell cycle ratio as well as their differentiation potential. The data showed that all of these parameters were significantly different when comparing serum-free cultures with and without 10 nM/L EGF (p < 0.05/0.01); however, cells with 10 nM/L EGF did not respond differently than cells grown in standard serum-containing media without EGF (p > 0.05). In summary, our results demonstrate that 10 nM/L EGF was the optimal dose for serum-free culture, which can replace traditional standard serum medium for in vitro expansion of miniature pig bone marrow-derived mesenchymal stem cells.

In situ tissue regeneration: chemoattractants for endogenous stem cell recruitment

Tissue engineering uses cells, signaling molecules, and/or biomaterials to regenerate injured or diseased tissues. Ex vivo expanded mesenchymal stem cells (MSC) have long been a cornerstone of regeneration therapies; however, drawbacks that include altered signaling responses and reduced homing capacity have prompted investigation of regeneration based on endogenous MSC recruitment. Recent successful proof-of-concept studies have further motivated endogenous MSC recruitment-based approaches. Stem cell migration is required for morphogenesis and organogenesis during development and for tissue maintenance and injury repair in adults. A biomimetic approach to in situ tissue regeneration by endogenous MSC requires the orchestration of three main stages: MSC recruitment, MSC differentiation, and neotissue maturation. The first stage must result in recruitment of a sufficient number of MSC, capable of effecting regeneration, to the injured or diseased tissue. One of the challenges for engineering endogenous MSC recruitment is the selection of effective chemoattractant(s). The objective of this review is to synthesize and evaluate evidence of recruitment efficacy by reported chemoattractants, including growth factors, chemokines, and other more recently appreciated MSC chemoattractants. The influence of MSC tissue sources, cell culture methods, and the in vitro and in vivo environments is discussed. This growing body of knowledge will serve as a basis for the rational design of regenerative therapies based on endogenous MSC recruitment. Successful endogenous MSC recruitment is the first step of successful tissue regeneration.

Cross-talk between EGF and BMP9 signalling pathways regulates the osteogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitors, which give rise to several lineages, including bone, cartilage and fat. Epidermal growth factor (EGF) stimulates cell growth, proliferation and differentiation. EGF acts by binding with high affinity to epidermal growth factor receptor (EGFR) on the cell surface and stimulating the intrinsic protein tyrosine kinase activity of its receptor, which initiates a signal transduction cascade causing a variety of biochemical changes within the cell and regulating cell proliferation and differentiation. We have identified BMP9 as one of the most osteogenic BMPs in MSCs. In this study, we investigate if EGF signalling cross-talks with BMP9 and regulates BMP9-induced osteogenic differentiation. We find that EGF potentiates BMP9-induced early and late osteogenic markers of MSCs in vitro, which can be effectively blunted by EGFR inhibitors Gefitinib and Erlotinib or receptor tyrosine kinase inhibitors AG-1478 and AG-494 in a dose- and time-dependent manner. Furthermore, EGF significantly augments BMP9-induced bone formation in the cultured mouse foetal limb explants. In vivo stem cell implantation experiment reveals that exogenous expression of EGF in MSCs can effectively potentiate BMP9-induced ectopic bone formation, yielding larger and more mature bone masses. Interestingly, we find that, while EGF can induce BMP9 expression in MSCs, EGFR expression is directly up-regulated by BMP9 through Smad1/5/8 signalling pathway. Thus, the cross-talk between EGF and BMP9 signalling pathways in MSCs may underline their important roles in regulating osteogenic differentiation. Harnessing the synergy between BMP9 and EGF should be beneficial for enhancing osteogenesis in regenerative medicine.

The key regulatory roles of the PI3K/Akt signaling pathway in the functionalities of mesenchymal stem cells and applications in tissue regeneration

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into various cell types and have been widely used in tissue engineering application. In tissue engineering, a scaffold, MSCs and growth factors are used as essential components and their interactions have been regarded to be important for regeneration of tissues. A critical problem for MSCs in tissue engineering is their low survival ability and functionality. Most MSCs are going to be apoptotic after transplantation. Therefore, increasing MSC survival ability and functionalities is the key for potential applications of MSCs. Several approaches have been studied to increase MSC tissue forming capacity including application of growth factors, overexpression of stem cell regulatory genes, and improvement of biomaterials for scaffolds. The effects of these approaches on MSCs have been associated with activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. The pathway plays central regulatory roles in MSC survival, proliferation, migration, angiogenesis, cytokine production, and differentiation. In this review, we summarize and discuss the literatures related to the roles of the PI3K/Akt pathway in the functionalities of MSCs and the involvement of the pathway in biomaterials-increased MSC functionalities. Biomaterials have been modified in their properties and surface structure and loaded with growth factors to increase MSC functionalities. Several studies demonstrated that the biomaterials-increased MSC functionalities are mediated by the activation of the PI3K/Akt pathway.

ARS-interacting multi-functional protein 1 induces proliferation of human bone marrow-derived mesenchymal stem cells by accumulation of β-catenin via fibroblast growth factor receptor 2-mediated activation of Akt

ARS-Interacting Multi-functional Protein 1 (AIMP1) is a cytokine that is involved in the regulation of angiogenesis, immune activation, and fibroblast proliferation. In this study, fibroblast growth factor receptor 2 (FGFR2) was isolated as a binding partner of AIMP peptide (amino acids 6-46) in affinity purification using human bone marrow-derived mesenchymal stem cells (BMMSCs). AIMP1 peptide induced the proliferation of adult BMMSCs by activating Akt, inhibiting glycogen synthase kinase-3β, and thereby increasing the level of β-catenin. In addition, AIMP1 peptide induced the translocation of β-catenin to the nucleus and increased the transcription of c-myc and cyclin D1 by activating the β-catenin/T-cell factor (TCF) complex. By contrast, transfection of dominant negative TCF abolished the effect of AIMP1. The inhibition of Akt, using LY294002, abolished the accumulation and nuclear translocation of β-catenin induced by AIMP1, leading to a decrease in c-myc and cyclin D1 expression, which decreased the proliferation of BMMSCs. An intraperitoneal injection of AIMP1 peptide into C57/BL6 mice increased the colony formation of fibroblast-like cells. Fluorescence activated cell sorting analysis showed that the colony-forming cells were CD29(+)/CD44(+)/CD90(+)/CD105(+)/CD34(-)/CD45(-), which is characteristic of MSCs. In addition, the fibroblast-like cells differentiated into adipocytes, chondrocytes, and osteocytes. Taken together, these data suggest that AIMP1 peptide promotes the proliferation of BMMSCs by activating the β-catenin/TCF complex via FGFR2-mediated activation of Akt, which leads to an increase in MSCs in peripheral blood.

Surface tethered epidermal growth factor protects proliferating and differentiating multipotential stromal cells from FasL-induced apoptosis

Multipotential stromal cells or mesenchymal stem cells (MSCs) have been proposed as aids in regenerating bone and adipose tissues, as these cells form osteoblasts and adipocytes. A major obstacle to this use of MSC is the initial loss of cells postimplantation. This cell death in part is due to ubiquitous nonspecific inflammatory cytokines such as FasL generated in the implant site. Our group previously found that soluble epidermal growth factor (sEGF) promotes MSC expansion. Furthermore, tethering EGF (tEGF) onto a two-dimensional surface altered MSC responses, by restricting epidermal growth factor receptor (EGFR) to the cell surface, causing sustained activation of EGFR, and promoting survival from FasL-induced death. sEGF by causing internalization of EGFR does not support MSC survival. However, for tEGF to be useful in bone regeneration, it needs to allow for MSC differentiation into osteoblasts while also protecting emerging osteoblasts from apoptosis. tEGF did not block induced differentiation of MSCs into osteoblasts, or adipocytes, a common default MSC-differentiation pathway. MSC-derived preosteoblasts showed increased Fas levels and became more susceptible to FasL-induced death, which tEGF prevented. Differentiating adipocytes underwent a reduction in Fas expression and became resistant to FasL-induced death, with tEGF having no further survival effect. tEGF protected undifferentiated MSC from combined insults of FasL, serum deprivation, and physiologic hypoxia. Additionally, tEGF was dominant in the face of sEGF to protect MSC from FasL-induced death. Our results suggest that MSCs and differentiating osteoblasts need protective signals to survive in the inflammatory wound milieu and that tEGF can serve this function.

Platelet-rich plasma promotes the proliferation of human muscle derived progenitor cells and maintains their stemness

Human muscle-derived progenitor cells (hMDPCs) offer great promise for muscle cell-based regenerative medicine; however, prolonged ex-vivo expansion using animal sera is necessary to acquire sufficient cells for transplantation. Due to the risks associated with the use of animal sera, the development of a strategy for the ex vivo expansion of hMDPCs is required. The purpose of this study was to investigate the efficacy of using platelet-rich plasma (PRP) for the ex-vivo expansion of hMDPCs. Pre-plated MDPCs, myoendothelial cells, and pericytes are three populations of hMDPCs that we isolated by the modified pre-plate technique and Fluorescence Activated Cell Sorting (FACS), respectively. Pooled allogeneic human PRP was obtained from a local blood bank, and the effect that thrombin-activated PRP-releasate supplemented media had on the ex-vivo expansion of the hMDPCs was tested against FBS supplemented media, both in vitro and in vivo. PRP significantly enhanced short and long-term cell proliferation, with or without FBS supplementation. Antibody-neutralization of PDGF significantly blocked the mitogenic/proliferative effects that PRP had on the hMDPCs. A more stable and sustained expression of markers associated with stemness, and a decreased expression of lineage specific markers was observed in the PRP-expanded cells when compared with the FBS-expanded cells. The in vitro osteogenic, chondrogenic, and myogenic differentiation capacities of the hMDPCs were not altered when expanded in media supplemented with PRP. All populations of hMDPCs that were expanded in PRP supplemented media retained their ability to regenerate myofibers in vivo. Our data demonstrated that PRP promoted the proliferation and maintained the multi-differentiation capacities of the hMDPCs during ex-vivo expansion by maintaining the cells in an undifferentiated state. Moreover, PDGF appears to be a key contributing factor to the beneficial effect that PRP has on the proliferation of hMDPCs.

Epidermal growth factor receptor (EGFR) signaling promotes proliferation and survival in osteoprogenitors by increasing early growth response 2 (EGR2) expression

Maintaining bone architecture requires continuous generation of osteoblasts from osteoprogenitor pools. Our previous study of mice with epidermal growth factor receptor (EGFR) specifically inactivated in osteoblast lineage cells revealed that EGFR stimulates bone formation by expanding the population of mesenchymal progenitors. EGFR ligands are potent regulators for the osteoprogenitor pool, but the underlying mechanisms are largely unknown. Here we demonstrate that activation of EGFR increases the number of osteoprogenitors by promoting cell proliferation and suppressing either serum depletion-induced or TNFα-induced apoptosis mainly through the MAPK/ERK pathway. Mouse calvarial organ culture revealed that EGF elevated the number of proliferative cells and decreased the number of apoptotic cells, which led to increased osteoblasts. Microarray analysis of MC3T3 cells, an osteoprogenitor cell line, revealed that EGFR signaling stimulates the expression of MCL1, an antiapoptotic protein, and a family of EGR transcription factors (EGR1, -2, and -3). The up-regulation of MCL1 and EGR2 by EGF was further confirmed in osteoprogenitors close to the calvarial bone surface. Overexpression of NAB2, a co-repressor for EGRs, attenuated the EGF-induced increase in osteoprogenitor number. Interestingly, knocking down the expression of EGR2, but not EGR1 or -3, resulted in a similar effect. Using inhibitor, adenovirus overexpression, and siRNA approaches, we demonstrate that EGFR signaling activates the MAPK/ERK pathway to stimulate the expression of EGR2, which in turn leads to cell growth and MCL1-mediated cell survival. Taken together, our data clearly demonstrate that EGFR-induced EGR2 expression is critical for osteoprogenitor maintenance and new bone formation.

The matrikine tenascin-C protects multipotential stromal cells/mesenchymal stem cells from death cytokines such as FasL

Multipotential stromal cells/mesenchymal stem cells (MSCs) are attractive candidates for regenerative therapy due to the ability of these cells to differentiate and positively influence neighboring cells. However, on implantation for wound reconstruction, these cells are lost as they are challenged by nonspecific inflammation signals generated in the wound environment and in response to any implanted foreign body. We have previously shown that sustained and surface-restricted epidermal growth factor receptor (EGFR) signaling by a tethered form of its prototypal ligand EGF enhances survival of MSC in the presence of death cytokines such as FasL, serum deprivation, and low oxygen in vitro. This was proposed to be due to the plasma membrane restriction of EGFR signaling. Interestingly, during wound repair, an extracellular matrix (ECM) component Tenascin-C (TNC) containing EGF-like repeats (EGFL) and fibronectin-like repeats (FNL) is upregulated. A few of the 14 EGFL on each of the 6 arms, especially the 14th, bind as low-affinity/high-avidity ligands to EGFR causing sustained surface-restricted EGFR signaling. We queried whether signaling by this physiologically relevant EGFR matrikine also protects MSCs from FasL-induced death. MSCs grown on TNC and Collagen I (as TNC by itself is antiadhesive) displayed a survival advantage in the presence of FasL. TNC neither sequestered nor neutralized FasL; rather, the effects of survival were via cell signaling. This survival was dependent on TNC activating EGFR and downstream pathways of Erk and Akt through EGFL; to a much lesser extent, the FNL of TNC also contributed to survival. Taken together, these results suggest that providing MSCs with a nonimmunogenic naturally occurring ECM moiety such as TNC enhances their survival in the presence of death factors, and this advantage occurs via signaling through EGFR primarily and integrins only to a minor extent. This matrix component is proposed to supplement MSC delivery on the scaffolds to provide a survival advantage against death upon in vivo implantation.

The simulated microgravity enhances multipotential differentiation capacity of bone marrow mesenchymal stem cells

Multi-differentiation capability is an essential characteristic of bone marrow mesenchymal stem cells (BMSCs). Method on obtaining higher-quality stem cells with an improved differentiation potential has gained significant attention for the treatment of clinical diseases and developmental biology. In our study, we investigated the multipotential differentiation capacity of BMSCs under simulated microgravity (SMG) condition. F-actin staining found that cytoskeleton took on a time-dependent change under SMG condition, which caused spindle to round morphological change of the cultured cells. Quantitative PCR and Western Blotting showed the pluripotency marker OCT4 was up-regulated in the SMG condition especially after SMG of 72 h, which we observed would be the most appropriate SMG duration for enhancing pluripotency of BMSCs. After dividing BMSCs into normal gravity (NG) group and SMG group, we induced them respectively in endothelium oriented, adipogenic and neuronal induction media. Immunostaining and Western Blotting found that endothelium oriented differentiated BMSCs expressed higher VWF and CD31 in the SMG group than in the NG group. The neuron-like cells derived from BMSCs in the SMG group also expressed higher level of MAP2 and NF-H. Furthermore, the quantity of induced adipocytes increased in the SMG group compared to the NG group shown by Oil Red O staining, The expression of PPARγ2 increased significantly under SMG condition. Therefore, we demonstrated that SMG could promote BMSCs to differentiate into many kinds of cells and predicted that enhanced multi-potential differentiation capacity response in BMSCs following SMG might be relevant to the changes of cytoskeleton and the stem cell marker OCT4.

Salient features of mesenchymal stem cells-implications for Ewing sarcoma modeling

Despite a heightened appreciation of the many defining molecular aberrations in Ewing sarcoma, the cooperative genetic environment and permissive cell of origin essential for EWS/ETS-mediated oncogenesis remain elusive. Consequently, inducible animal and in vitro models of Ewing sarcoma from a native cellular context are unable to fully recapitulate malignant transformation. Despite these shortcomings, human, and murine mesenchymal stem cells (MSCs) are the closest working in vitro systems available. MSCs are tolerant of ectopic EWS/FLI expression, which is accompanied by a molecular signature most similar to Ewing sarcoma. Whether MSCs are the elusive cell of origin or simply a tolerant platform of the EWS/FLI transcriptome, these cells have become an excellent molecular tool to investigate and manipulate oncogenesis in Ewing sarcoma. Our understanding of the biological complexity and heterogeneity of human MSCs (hMSCs) has increased substantially over time and as such, appreciation and utilization of these salient complexities may greatly enhance the efficient use of these cells as surrogate models for Ewing sarcoma tumorigenesis.