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

Maintenance of high proliferation and multipotent potential of human hair follicle-derived mesenchymal stem cells by growth factors

Cell therapy and cell-based tissue engineering is becoming increasingly important in regenerative medicine. Stem cells that are characterized by self-renewal, high proliferation and multiple differentiation potentials have attracted attention in cell-based regenerative medicine. Maintaining the aforementioned characteristics of stem cells is the first key step in cell-based regenerative medicine. Basic fibroblast growth factor (bFGF) is a well-known growth factor that efficiently maintains the self-renewal, high proliferation and multilineage differentiation potential of stem cells. Whether or not other growth factors, such as acidic fibroblast growth factor (aFGF) and epidermal growth factor (EGF) have similar effects has yet to be fully elucidated. Human hair follicle-derived mesenchymal stem cells (HF-MSCs) were obtained by organ culture. They exhibited surface markers of bone marrow mesenchymal stem cells as shown by positive staining for CD44, CD73, CD90 and CD105, and they also displayed trilineage differentiation potentials into adipocytes, chondrocytes and osteoblasts by cytochemistry and qRT-PCR. Flow cytometry analysis showed that up to 70% of HF-MSCs cultured in the presence of aFGF, bFGF or EGF stayed at the G0/G1 phase. Proliferation analysis showed that both bFGF and EGF at as low as 1 ng/ml and aFGF at above 5 ng/ml levels significantly increased the proliferation of HF-MSCs by cell counting. Consistent with proliferation analysis, immunofluorescence staining showed that more than 95% of HF-MSCs cultured in the presence of aFGF, bFGF and EGF were positively stained for proliferating cell nuclear antigen. HF-MSCs cultured in the presence of aFGF, bFGF or EGF retained marked trilineage differentiation potentials. By contrast, HF-MSCs cultured in the absence of bFGF, aFGF and EGF lost multipotency.

Mesenchymal stem cells and their use in therapy: what has been achieved?

The considerable therapeutic potential of human multipotent mesenchymal stromal cells or mesenchymal stem cells (MSCs) has generated increasing interest in a wide variety of biomedical disciplines. Nevertheless, researchers report studies on MSCs using different methods of isolation and expansion, as well as different approaches to characterize them; therefore, it is increasingly difficult to compare and contrast study outcomes. To begin to address this issue, the Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy proposed minimal criteria to define human MSCs. First, MSCs must be plastic-adherent when maintained in standard culture conditions (α minimal essential medium plus 20% fetal bovine serum). Second, MSCs must express CD105, CD73 and CD90, and MSCs must lack expression of CD45, CD34, CD14 or CD11b, CD79α or CD19 and HLA-DR surface molecules. Third, MSCs must differentiate into osteoblasts, adipocytes and chondroblasts in vitro. MSCs are isolated from many adult tissues, in particular from bone marrow and adipose tissue. Along with their capacity to differentiate and transdifferentiate into cells of different lineages, these cells have also generated great interest for their ability to display immunomodulatory capacities. Indeed, a major breakthrough was the finding that MSCs are able to induce peripheral tolerance, suggesting that they may be used as therapeutic tools in immune-mediated disorders. Although no significant adverse events have been reported in clinical trials to date, all interventional therapies have some inherent risks. Potential risks for undesirable events, such as tumor development, that might occur while using these stem cells for therapy must be taken into account and contrasted against the potential benefits to patients.

Amphiregulin-EGFR signaling mediates the migration of bone marrow mesenchymal progenitors toward PTH-stimulated osteoblasts and osteocytes

Intermittent administration of parathyroid hormone (PTH) dramatically increases bone mass and currently is one of the most effective treatments for osteoporosis. However, the detailed mechanisms are still largely unknown. Here we demonstrate that conditioned media from PTH-treated osteoblastic and osteocytic cells contain soluble chemotactic factors for bone marrow mesenchymal progenitors, which express a low amount of PTH receptor (PTH1R) and do not respond to PTH stimulation by increasing cAMP production or migrating toward PTH alone. Conditioned media from PTH-treated osteoblasts elevated phosphorylated Akt and p38MAPK amounts in mesenchymal progenitors and inhibition of these pathways blocked the migration of these progenitors toward conditioned media. Our previous and current studies revealed that PTH stimulates the expression of amphiregulin, an epidermal growth factor (EGF)-like ligand that signals through the EGF receptor (EGFR), in both osteoblasts and osteocytes. Interestingly, conditioned media from PTH-treated osteoblasts increased EGFR phosphorylation in mesenchymal progenitors. Using several different approaches, including inhibitor, neutralizing antibody, and siRNA, we demonstrate that PTH increases the release of amphiregulin from osteoblastic cells, which acts on the EGFRs expressed on mesenchymal progenitors to stimulate the Akt and p38MAPK pathways and subsequently promote their migration in vitro. Furthermore, inactivation of EGFR signaling specifically in osteoprogenitors/osteoblasts attenuated the anabolic actions of PTH on bone formation. Taken together, these results suggest a novel mechanism for the therapeutic effect of PTH on osteoporosis and an important role of EGFR signaling in mediating PTH's anabolic actions on bone.

Early growth response genes signaling supports strong paracrine capability of mesenchymal stem cells

MSCs provide a promising method for cell therapy through their wound healing and tissue regenerative properties. Originally, MSCs' role in wound healing was thought to be tied to their multipotency, but it is now accepted that MSCs mediate the healing process through their strong paracrine capability. EGF was shown to facilitate in vitro expansion of MSCs without altering multipotency. Our previous data suggest that the molecular machinery underlying MSCs' strong paracrine capability lies downstream of EGFR signaling, and we focus on transcription factors EGR1 and EGR2. Evidence suggests that EGR1 regulates angiogenic and fibrogenic factor production in MSCs, and an EGFR-EGR1-EGFR ligands autocrine loop is one of the underlying mechanisms supporting their strong paracrine machinery through EGR1. EGR2 appears to regulate the expression of immunomodulatory molecules. Chronic nonhealing wounds are ischemic, inflammatory, and often fibrotic, and the hypoxic micro-environment of these wounds may compromise MSCs' wound healing properties in vivo by upregulating the EGR1's fibrogenic effects and downregulating the EGR2's immuno-modulatory effects. Thus, these transcription factors can be potential targets in the optimization of cell-based therapies. Further study in vitro is required to understand MSCs' paracrine machinery and to optimize it as a tool for effective cell-based therapies.

Effects of medium supplements on proliferation, differentiation potential, and in vitro expansion of mesenchymal stem cells

Mesenchymal stem cells (MSCs) possess great potential for use in regenerative medicine. However, their clinical application may be limited by the ability to expand their cell numbers in vitro while maintaining their differential potentials and stem cell properties. Thus the aim of this study was to test the effect of a range of medium supplements on MSC self-renewal and differentiation potential. Cells were cultured until confluent and subcultured continuously until reaching senescence. Medium supplementation with fibroblast growth factor (FGF)-2, platelet-derived growth factor (PDGF)-BB, ascorbic acid (AA), and epidermal growth factor (EGF) both increased proliferation rate and markedly increased number of cell doublings before reaching senescence, with a greater than 1,000-fold increase in total cell numbers for AA, FGF-2, and PDGF-BB compared with control cultures. Long-term culture was associated with loss of osteogenic/adipocytic differentiation potential, particularly with FGF-2 supplementation but also with AA, EGF, and PDGF-BB. In addition FGF-2 resulted in reduction in expression of CD146 and alkaline phosphatase, but this was partially reversible on removal of the supplement. Cells expressed surface markers including CD146, CD105, CD44, CD90, and CD71 by flow cytometry throughout, and expression of these putative stem cell markers persisted even after loss of differentiation potentials. Overall, medium supplementation with FGF-2, AA, EGF, and PDGF-BB greatly enhanced the total in vitro expansion capacity of MSC cultures, although differentiation potentials were lost prior to reaching senescence. Loss of differentiation potential was not reflected by changes in stem cell surface marker expression.

Downregulation of ErbB3 by Wnt3a contributes to wnt-induced osteoblast differentiation in mesenchymal cells

Mesenchymal stem cells (MSC) can differentiate into osteoblasts upon activation of Wnt signaling. Identifying targets of Wnt signaling in MSC may help promote MSC osteoblast differentiation for bone regeneration. In this study, using microarray analysis we found that Wnt3a upregulates neuregulin 1 (NRG-1) during Wnt3a-induced osteoblast differentiation in primary human MSC and murine C3H10T1/2 mesenchymal cells. Western blot and qPCR analyses confirmed that NRG-1 is upregulated by Wnt3a, and that this effect was counterbalanced by decreased expression of the NRG-1 receptor ErbB3. Consistently, exogenous NRG-1 had no effect on alkaline phosphatase (ALP) activity, an early marker of osteoblast differentiation. In contrast, small interfering RNA-mediated silencing of endogenous NRG-1 increased basal and Wnt3a-induced ALP activity in MSC. We showed that short hairpin (sh) ErbB3 and Wnt3a additively increased β-catenin transcriptional activity and ALP activity in MSC. These effects were abrogated by DKK1, indicating that cross-talk between Wnt3a and ErbB3 control MSC osteoblast differentiation via Wnt/β-catenin signaling. Furthermore, ErbB3 silencing decreased Src expression. Pharmacological inhibition of Src signaling promoted ErbB3- and Wnt-induced ALP activity, suggestive of a role of Src signaling in the modulation of osteoblast differentiation by ErbB3 and Wnt3a. The results indicate that downregulation of ErbB3 induced by Wnt3a contributes to Wnt3a-induced early osteoblast differentiation of MSCs through increased canonical Wnt/β-catenin signaling and decreased Src signaling.

Stable changes in mesenchymal stromal cells from multiple myeloma patients revealed through their responses to Toll-like receptor ligands and epidermal growth factor

In human multiple myeloma (MM), the tumor cells exhibit strict dependence on bone marrow (BM) stromal elements. It has been suggested that, in turn, MM cells modify multipotent stromal cells (MSCs), diverting them to support the myeloma. We investigated MM-derived MSCs by comparing their toll-like receptor (TLR) responses to those of MSCs derived from healthy controls. We now report that MM-derived MSCs manifested intact proliferation responses and IL-6 secretion and their adipose and osteogenic differentiation responses to TLR ligands were also similar to those of healthy controls, ranging from augmentation to inhibition. However, MM-derived MSCs were found to be defective in IL-8 secretion and ERK1/2 phosphorylation following TLR-2 activation. Moreover, MM-derived MSCs failed to respond to EGF by elevation of ERK1/2 phosphorylation. The persistence of these changes in extensively cultured MM-derived MSCs, suggests that these cells are stably, if not irreversibly modified.

Platelet-derived growth factor promotes the proliferation of human umbilical cord-derived mesenchymal stem cells

This study was designed to investigate the effect of platelet-derived growth factor (PDGF) on the proliferation of human umbilical cord mesenchymal stem cells (UC-MSCs) and further explore the mechanism of PDGF in promoting the proliferation of UC-MSCs. The human UC-MSCs were treated with different concentrations of PDGF, and the effects were evaluated by counting the cell number, the cell viability, the expression of PDGF receptors analyzed by RT-PCR, and the detection of the gene expression of cell proliferation, cell cycle and pluripotency, and Brdu assay by immunofluorescent staining and Quantitative real-time (QRT-PCR). The results showed that PDGF could promote the proliferation of UC-MSCs in vitro in a dose-dependent way, and 10 to 50 ng/ml PDGF had a significant proliferation effect on UC-MSCs; the most obvious concentration was 50 ng/ml. Significant inhibition on the proliferation of UC-MSCs was observed when the concentration of PDGF was higher than 100 ng/ml, and all cells died when the concentration reached 200 ng/ml PDGF. The PDGF-treated cells had stronger proliferation and antiapoptotic capacity than the control group by Brdu staining. The expression of the proliferation-related genes C-MYC, PCNA and TERT and cell cycle-related genes cyclin A, cyclin 1 and CDK2 were up-regulated in PDGF medium compared with control. However, pluripotent gene OCT4 was not significantly different between cells cultured in PDGF and cells analyzed by immunofluorescence and QRT-PCR. The PDGF could promote the proliferation of human UC-MSCs in vitro.

EGFR ligands drive multipotential stromal cells to produce multiple growth factors and cytokines via early growth response-1

Cell therapy with adult bone marrow multipotential stromal cells/mesenchymal stem cells (MSCs) presents a promising approach to promote wound healing and tissue regeneration. The strong paracrine capability of various growth factors and cytokines is a key mechanism of MSC-mediated wound healing and tissue regeneration, and the goal of this study is to understand the underlying mechanism that supports the strong paracrine machineries in MSCs. Microarray database analyses revealed that early growth response-1 (EGR1) is highly expressed in MSCs. Our previous studies showed that epidermal growth factor (EGF) treatment induces growth factor production in MSCs in vitro. Since EGF strongly upregulates EGR1, we hypothesized that EGF receptor (EGFR)-EGR1 signaling plays a pivotal role in MSC paracrine activity. EGF treatment upregulated the gene expression of growth factors and cytokines, including EGFR ligands in a protein kinase C (PKC)- and/or mitogen-activated protein kinase-extracellular-signal-regulated kinase-dependent manner, and it was reversed by shRNA against EGR1. PKC activator phorbol 12-myristate 13-acetate enhanced EGFR tyrosyl phosphorylation and upregulated the gene expression of growth factors and cytokines in a heparin-binding EGF-like growth factor (HBEGF) inhibitor CRM197 sensitive manner, indicating an involvement of autocrined HBEGF in the downstream of PKC signaling. Moreover, stimulation with growth factors and cytokines induced the expression of EGFR ligands, presumably via EGR1 upregulation. These data indicate EGR1 as a convergence point of multiple signaling pathways, which in turn augments the production of multiple growth factors and cytokines by enhancing the autocrine signaling with EGFR ligands.

The stimulation of adipose-derived stem cell differentiation and mineralization by ordered rod-like fluorapatite coatings

In this study, the effect of ordered rod-like FA coatings of metal discs on adipose-derived stem cell (ASC)'s growth, differentiation and mineralization was studied in vitro; and their mineral inductive effects in vivo. After 3 and 7 days, the cell number on the metal surfaces was significantly higher than those on the ordered and disordered FA surfaces. However, after 4 weeks much greater amounts of mineral formation was induced on the two FA surfaces with and even without osteogenesis induction. The osteogenic profiles showed the up regulation of a set of pro-osteogenic transcripts and bone mineralization phenotypic markers when the ASCs were grown on FA surfaces compared to metal surfaces at 7 and 21 days. In addition to BMP and TGFβ signaling pathways, EGF and FGF pathways also appeared to be involved in ASC differentiation and mineralization. In vivo studies showed accelerated and enhanced mineralized tissue formation integrated within ordered FA coatings. After 5 weeks, over 80% of the ordered FA coating was integrated with a mineralized tissue layer covering the implants. Both the intrinsic properties of the FA crystals and the topography of the FA coating appeared to dominate the cell differentiation and mineralization process.

Effects of multiple agents on epithelial differentiation of rabbit adipose-derived stem cells in 3D culture

Mesenchymal stem cells have been given particular attention in tissue regeneration research due to their multipotency and proliferative activity. In this study, we investigated the possibility of epithelial differentiation of rabbit adipose-derived stem cells (rASCs) in an in vitro 3D culture system. The experimental procedure was performed with different contributing factors including all-trans retinoic acid (ATRA), epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), and hydrocortisone in air-liquid interface culture, for modulating proliferation and providing a synergistic effect on epithelial differentiation of rASCs. After induction, immunofluorescence staining, western blot analysis, flow cytometry analysis, and quantitative real-time polymerase chain reaction assay have been performed to detect the expression of epithelial-specific markers and mesenchymal marker alpha-smooth muscle actin (α-SMA). The growth pattern and viability of cells were evaluated by transmission electron microscopy and Hoechst 33258 assay, respectively. After treated with optimized induction medium (including 2.5 μM ATRA, 20 ng/mL EGF, 10 ng/mL KGF, 10 ng/mL HGF, and 0.5 μg/mL hydrocortisone), rASCs were observed to display a stratified epithelial-like morphology, with the expression of cytokeratin 19 and cytokeratin 13 in 63.69%±2.63% and 22.17%±1.51%, respectively, and the relative expression level of cytokeratin 19 increased to 3.152 compared with 0.151 before induction. The expression of α-SMA decreased to 19.40%±1.45% after induction, but almost no expression of involucrin was detected. The results showed that the establishment of an epithelial-specific microenvironment may be a feasible way for epithelial differentiation of ASCs in vitro, and provided an alternative for research on epithelium regeneration.

Neural cell adhesion molecule modulates mesenchymal stromal cell migration via activation of MAPK/ERK signaling

Mesenchymal Stromal Cells (MSCs) represent promising tools for cellular therapy owing to their multipotentiality and ability to localize to injured, inflamed sites and tumor. Various approaches to manipulate expression of MSC surface markers, including adhesion molecules and chemokine receptors, have been explored to enhance homing of MSCs. Recently, Neural Cell Adhesion Molecule (NCAM) has been found to be expressed on MSCs yet its function remains largely elusive. Herein, we show that bone marrow-derived MSCs from NCAM deficient mice exhibit defective migratory ability and significantly impaired adipogenic and osteogenic differentiation potential. We further explore the mechanism governing NCAM mediated migration of MSCs by showing the interplay between NCAM and Fibroblast Growth Factor Receptor (FGFR) induces activation of MAPK/ERK signaling, thereby the migration of MSCs. In addition, re-expression of NCAM180, but not NCAM140, could restore the defective MAPK/ERK signaling thereby the migration of NCAM deficient MSCs. Finally, we demonstrate that NCAM180 expression level could be manipulated by pro-inflammatory cytokine Tumor Necrosis Factor (TNF)-α treatment. Overall, our data reveal the vital function of NCAM in MSCs migration and differentiation thus raising the possibility of manipulating NCAM expression to enhance homing and therapeutic potential of MSCs in cellular therapy.

Migration of human mesenchymal stem cells under low shear stress mediated by mitogen-activated protein kinase signaling

Human mesenchymal stem cells (hMSCs) are attractive candidates for cell-based tissue repair approaches and have been used as vectors for delivering therapeutic genes to sites of injury. It is believed that hMSCs are able to detect and respond to shear stress due to blood and interstitial fluid flow through mechanotransduction pathways after transplantation. However, information regarding hMSC migration under shear stress and its mechanism is still limited. In this study, we examined the effect of shear stress on hMSC migration and the role of mitogen-activated protein kinases (MAPKs) in their migration. Shear stress between 0.2 and 10 Pa, which was produced by the flow medium, was exerted on fluorescently labeled hMSCs. Cell migration was evaluated using the scratch wound assay, and images were captured using a microscope equipped with a digital 3CCD camera. The results showed that hMSCs subjected to a shear stress of 0.2 Pa caused notably faster wound closure than statically cultured hMSCs, while migration in the 0.5- and 1-Pa shear stress group did not differ significantly from that in the control group. Shear stress >2 Pa markedly inhibited hMSC migration. hMSCs subjected to a shear stress of 0.2 Pa displayed an increase in extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), and p38 MAPK activation for up to 60 min, while a shear stress of 2 Pa abrogated the activation. JNK and p38 MAPK inhibitors completely abolished the effect of shear stress on hMSC migration, while significant differences were observed between the ERK1/2 inhibitor-treated static control and shear stress groups. Taken together, these results demonstrate that low shear stress effectively induces hMSC migration and that JNK and p38 MAPK play more prominent roles in shear stress-induced migration than ERK1/2.

Production of reactive oxygen species by multipotent stromal cells/mesenchymal stem cells upon exposure to fas ligand

Multipotent stromal cells (MSCs) can be differentiated into osteoblasts and chondrocytes, making these cells candidates to regenerate cranio-facial injuries and lesions in long bones. A major problem with cell replacement therapy, however, is the loss of transplanted MSCs at the site of graft. Reactive oxygen species (ROS) and nonspecific inflammation generated at the ischemic site have been hypothesized to lead to MSCs loss; studies in vitro show MSCs dying both in the presence of ROS or cytokines like FasL. We questioned whether MSCs themselves may be the source of these death inducers, specifically whether MSCs produce ROS under cytokine challenge. On treating MSCs with FasL, we observed increased ROS production within 2 h, leading to apoptotic death after 6 h of exposure to the cytokine. N-acetyl cysteine, an antioxidant, is able to protect MSCs from FasL-induced ROS production and subsequent ROS-dependent apoptosis, though the MSCs eventually succumb to ROS-independent death signaling. Epidermal growth factor (EGF), a cell survival factor, is able to protect cells from FasL-induced ROS production initially; however, the protective effect wanes with continued FasL exposure. In parallel, FasL induces upregulation of the uncoupling protein UCP2, the main uncoupling protein in MSCs, which is not abrogated by EGF; however, the production of ROS is followed by a delayed apoptotic cell death despite moderation by UCP2. FasL-induced ROS activates the stress-induced MAPK pathways JNK and p38MAPK as well as ERK, along with the activation of Bad, a proapoptotic protein, and suppression of survivin, an antiapoptotic protein; the latter two key modulators of the mitochondrial death pathway. FasL by itself also activates its canonical extrinsic death pathway noted by a time-dependent degradation of c-FLIP and activation of caspase 8. These data suggest that MSCs participate in their own demise due to nonspecific inflammation, holding implications for replacement therapies.

VEGF(165) expressing bone marrow mesenchymal stem cells differentiate into hepatocytes under HGF and EGF induction in vitro

A short half-life and low levels of growth factors in an injured microenvironment necessitates the sustainable delivery of growth factors and stem cells to augment the regeneration of injured tissues. Our aim was to investigate the ability of VEGF(165) expressing bone marrow mesenchymal stem cells (BMMSCs) to differentiate into hepatocytes when cultured with hepatocyte growth factor (HGF) and epidermal growth factor (EGF) in vitro. We isolated, cultured and identified rabbit BMMSCs, then electroporated the BMMSCs with VEGF(165)-pCMV6-AC-GFP plasmid. G418 was used to select transfected cells and the efficiency was up to 70%. The groups were then divided as follows: Group A was electroporated with pCMV6-AC-GFP plasmid + HGF + EGF and Group B was electroporated with VEGF(165)-pCMV6-AC-GFP plasmid +HGF + EGF. After 14 days, BMMSCs were induced into short spindle and polygonal cells. Alpha-fetoprotein (AFP) was positive and albumin (ALB) was negative in Group A, while both AFP and ALB were positive in group B on day 10. AFP and ALB in both groups were positive on day 20, but the quantity of AFP in group B decreased with prolonged time and was about 43.5% less than group A. The quantity of the ALB gene was increased with prolonged time in both groups. However, there was no significant difference between group A and B on day 10 and 20. Our results demonstrated that VEGF(165)-pCMV6-AC-GFP plasmid modified BMMSCs still had the ability to differentiate into hepatocytes. The VEGF(165) gene promoted BMMSCs to differentiate into hepatocyte-like cells under the induction of HGF and EGF, and reduced the differentiation time. These results have implications for cell therapies.

Epidermal growth factor receptor signalling contributes to osteoblastic stromal cell proliferation, osteoclastogenesis and disease progression in giant cell tumour of bone

AIMS

Epidermal growth factor receptor (EGFR) is implicated in bone remodelling. The aim was to determine whether EGFR protein expression contributes to the aggressiveness and recurrence potential of giant cell tumour of bone (GCTB), an osteolytic primary bone tumour that can exhibit markedly variable clinical behaviour.

METHODS AND RESULTS

Immunohistochemical analysis on tissue microarrays (TMA) of 231 primary, 97 recurrent, 17 metastatic and 26 malignant GCTBs was performed using TMA analysis software and whole digital slides allowing validated scoring. EGFR expression was restricted to neoplastic stromal cells and was significantly more frequent in recurrent (71 of 92; 77%) than in non-recurrent GCTBs (86 of 162; 53%) (P = 0.002); and in clinicoradiologically aggressive (31 of 43; 72%) than latent (27 of 54; 50%) cases (P = 0.034). Detecting phosphotyrosine epitopes pY1068 and -pY1173 indicated active EGFR signalling, and finding EGFR ligands EGF and transforming growth factor-α restricted to cells of the monocytic lineage suggested paracrine EGFR activation in stromal cells. In functional studies EGF supported proliferation of GCTB stromal cells, and the addition of EGF and macrophage-colony stimulating factor promoted osteoclastogenesis.

CONCLUSION

In GCTB, EGFR signalling in neoplastic stromal cells may contribute to disease progression through promoting stromal cell proliferation and osteoclastogenesis.

Heparan sulfate enhances the self-renewal and therapeutic potential of mesenchymal stem cells from human adult bone marrow

Insufficient cell number hampers therapies utilizing adult human mesenchymal stem cells (hMSCs) and current ex vivo expansion strategies lead to a loss of multipotentiality. Here we show that supplementation with an embryonic form of heparan sulfate (HS-2) can both increase the initial recovery of hMSCs from bone marrow aspirates and increase their ex vivo expansion by up to 13-fold. HS-2 acts to amplify a subpopulation of hMSCs harboring longer telomeres and increased expression of the MSC surface marker stromal precursor antigen-1. Gene expression profiling revealed that hMSCs cultured in HS-2 possess a distinct signature that reflects their enhanced multipotentiality and improved bone-forming ability when transplanted into critical-sized bone defects. Thus, HS-2 offers a novel means for decreasing the expansion time necessary for obtaining therapeutic numbers of multipotent hMSCs without the addition of exogenous growth factors that compromise stem cell fate.

Controlling multipotent stromal cell migration by integrating "course-graining" materials and "fine-tuning" small molecules via decision tree signal-response modeling

Biomimetic scaffolds have been proposed as a means to facilitate tissue regeneration by multi-potent stromal cells (MSCs). Effective scaffold colonization requires a control of multiple MSC responses including survival, proliferation, differentiation, and migration. As MSC migration is relatively unstudied in this context, we present here a multi-level approach to its understanding and control, integratively tuning cell speed and directional persistence to achieve maximal mean free path (MFP) of migration. This approach employs data-driven computational modeling to ascertain small molecule drug treatments that can enhance MFP on a given materials substratum. Using poly(methyl methacrylate)-graft-poly(ethylene oxide) polymer surfaces tethered with epidermal growth factor (tEGF) and systematically adsorbed with fibronectin, vitronectin, or collagen-I to present hTERT-immortalized human MSCs with growth factor and extracellular matrix cues, we measured cell motility properties along with signaling activities of EGFR, ERK, Akt, and FAK on 19 different substrate conditions. Speed was consistent on collagen/tEGF substrates, but low associated directional persistence limited MFP. Decision tree modeling successfully predicted that ERK inhibition should enhance MFP on collagen/tEGF substrates by increasing persistence. Thus, we demonstrated a two-tiered approach to control MSC migration: materials-based "coarse-graining" complemented by small molecule "fine-tuning".

Isolation and characterization of equine amnion mesenchymal stem cells

The amnion is a particular tissue whose cells show features of multipotent stem cells proposed for use in cellular therapy and regenerative medicine. From equine amnion collected after the foal birth we have isolated MSCs (mesenchymal stem cells), namely EAMSCs (equine amnion mesenchymal stem cells), from the mesoblastic layer. The cells were grown in α-MEM (α-modified minimum essential medium) and the effect of EGF (epidermal growth factor) supplementation was evaluated. To assess the growth kinetic of EAMSCs we have taken into account some parameters [PD (population doubling), fold increase and DT (doubling time)]. The differentiation in chondrogenic, adipogenic and osteogenic types of cells and their epitope expression by a cytofluorimetric study have been reported. EGF supplementation of the culture medium resulted in a significant increase in PD growth parameter and in the formation of bone nodules for the osteogenic differentiation. By immunohistochemistry the amnion tissue shows a positivity for the c-Kit (cluster tyrosine-protein kinase), CD105 and Oct-4 (octamer-binding transcription factor 4) antigens that confirmed the presence of MSCs with embryonic phenotype.

Mesenchymal stromal cell migration: possibilities to improve cellular therapy

Mesenchymal stromal cells (MSC) represent a type of multipotent cells that can be isolated from several human tissues and that can be expanded ex vivo for clinical application. The regenerative and immune modulatory capacities of MSC have raised hopes for clinical applications of MSC. At the moment, many clinical trials applying MSC for treatment of multiple diseases are being set up. Currently, extensive expansion (3-6 weeks) is required to obtain enough cells for transplantation. However, culture-expanded MSC have almost completely lost their engraftment potential. MSC expansion cultures are initiated with a heterogeneous, poorly defined cell population. It is unknown which MSC populations are expanded and how this affects homing capacity. Thus, understanding MSC migration will offer perspectives to modulate the expansion protocols to obtain cells that maintain migration and homing capacities. This review highlights our current understanding of MSC migration with particular emphasis on the possibilities to improve MSC-based therapy.

Differential roles of hypoxia inducible factor subunits in multipotential stromal cells under hypoxic condition

Cell therapy with bone marrow multipotential stromal cells (MSCs) represents a promising approach to promote wound healing and tissue regeneration. MSCs expanded in vitro lose early progenitors with differentiation and therapeutic potentials under normoxic condition, whereas hypoxic condition promotes MSC self-renewal through preserving colony forming early progenitors and maintaining undifferentiated phenotypes. Hypoxia inducible factor (HIF) pathway is a crucial signaling pathway activated in hypoxic condition. We evaluated the roles of HIFs in MSC differentiation, colony formation, and paracrine activity under hypoxic condition. Hypoxic condition reversibly decreased osteogenic and adipogenic differentiation. Decrease of osteogenic differentiation depended on HIF pathway; whereas decrease of adipogenic differentiation depended on the activation of unfolded protein response (UPR), but not HIFs. Hypoxia-mediated increase of MSC colony formation was not HIF-dependent also. Hypoxic exposure increased secretion of VEGF, HGF, and basic FGF in a HIF-dependent manner. These findings suggest that HIF has a limited, but pivotal role in enhancing MSC self-renewal and growth factor secretions under hypoxic condition.

Upregulation of Adipogenesis and Chondrogenesis in MSC Serum-Free Culture

Serum-free media have been shown to be effective in the expansion of mesenchymal stem cells (MSCs). However, the effects may go beyond cell expansion as the differentiation potentials of the cells may be modified, thus influencing their efficacy for downstream applications. The latter is poorly understood, and this has prompted an evaluation of the influence of a serum-free formulation on the chondrogenic, adipogenic, and osteogenic potential of MSCs. The media consisted of Knockout™ Serum Replacement (KSR) with a cocktail of growth factors coupled with either collagen or fibronectin coatings. Collagen coating was selected as it promoted consistent cellular attachment. When compared against fetal bovine serum (FBS) controls, cell proliferation in the serum-free media was enhanced at passage 1. Similar levels of surface markers were observed in the two groups with a slight reduction in CD90 and CD73 in the serum-free culture at passage 3. The cultures were screened under differentiation conditions and a better maintenance of the chondrogenic potential was noted in the serum-free media with higher expressions of glycoaminoglycans (GAGs) and collagen II. Chondrogenesis was deficient in the FBS group and this was attributed to the inherent inconsistency of animal serum. Adipogenesis was enhanced in the serum-free group with a higher PPARG expression and lipid accumulation. Similar levels of osteogenic mineralization was noted in the FBS and serum-free groups but collagen I gene expression was suppressed in the latter. This was initially observed during expansion. These observations were attributed to the signaling cascades triggered by the cytokines presented in the serum-free formulation and the interaction with the collagen substrate. The serum-free media helps to maintain and enhance the chondrogenic and adipogenic potentials of the MSCs, respectively. This advantage can be exploited for therapeutic applications in cartilage and adipose tissue engineering.

Epidermal growth factor, basic fibroblast growth factor and platelet-derived growth factor-bb can substitute for fetal bovine serum and compete with human platelet-rich plasma in the ex vivo expansion of mesenchymal stromal cells derived from adipose tissue

BACKGROUND AIMS

Human mesenchymal stromal cells (MSC) are multipotent cells possessing self-renewal capacity, long-term viability and multilineage potential. We analyzed the effect of four different medium supplements on the expansion and differentiation of adipose tissue-derived MSC (ADSC) in order to avoid the use of xenogeneic serum.

METHODS

We compared fetal bovine serum (FBS) with 10% human platelet-rich plasma (hPRP), 3% human platelet-poor plasma (hPPP) and with a cytokine cocktail composed of epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) and platelet-derived growth factor-bb (PDGFbb) added to 3% hPPP. This mixture was developed testing EGF, bFGF, granulocyte-colony-stimulating factor (G-CSF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF-I), PDGFbb and transforming growth factor (TGF)-β1 added alone or in combination with hPPP.

RESULTS

Our data demonstrate that the addition of EGF, bFGF and PDGFbb, in a medium supplemented with hPPP, obtainable from 150-200 mL whole autologous blood, supports ADSC expansion better than FBS, as confirmed by cumulative population doublings (cPD; 15.0 ± 0.5 versus 9.4 ± 2.8). The addition of human platelet-rich plasma (hPRP) further improved ADSC proliferation (cPD 20.0 ± 1.2), but the achievement of hPRP presented a major drawback, requiring 1000-1200 mL autologous or donor whole blood. The medium supplements did not influence ADSC phenotype: they expressed CD105, CD90 and CD44 lacking hematopoietic antigens. The exposure to the proposed cocktail or to hPRP increased adipogenic and osteogenic differentiation.

CONCLUSIONS

The addition of EGF, bFGF and PDGFbb to hPPP could ensure a sufficient number of ADSC for clinical applications, avoiding the use of animal serum and representing a novel approach in regenerative medicine.

Engineered bivalent ligands to bias ErbB receptor-mediated signaling and phenotypes

The ErbB receptor family is dysregulated in many cancers, and its therapeutic manipulation by targeted antibodies and kinase inhibitors has resulted in effective chemotherapies. However, many malignancies remain refractory to current interventions. We describe a new approach that directs ErbB receptor interactions, resulting in biased signaling and phenotypes. Due to known receptor-ligand affinities and the necessity of ErbB receptors to dimerize to signal, bivalent ligands, formed by the synthetic linkage of two neuregulin-1β (NRG) moieties, two epidermal growth factor (EGF) moieties, or an EGF and a NRG moiety, can potentially drive homotypic receptor interactions and diminish formation of HER2-containing heterodimers, which are implicated in many malignancies and are a prevalent outcome of stimulation by native, monovalent EGF, or NRG. We demonstrate the therapeutic potential of this approach by showing that bivalent NRG (NN) can bias signaling in HER3-expressing cancer cells, resulting in some cases in decreased migration, inhibited proliferation, and increased apoptosis, whereas native NRG stimulation increased the malignant potential of the same cells. Hence, this new approach may have therapeutic relevance in ovarian, breast, lung, and other cancers in which HER3 has been implicated.

Epidermal growth factor receptor plays an anabolic role in bone metabolism in vivo

While the epidermal growth factor receptor (EGFR)-mediated signaling pathway has been shown to have vital roles in many developmental and pathologic processes, its functions in the development and homeostasis of the skeletal system has been poorly defined. To address its in vivo role, we constructed transgenic and pharmacologic mouse models and used peripheral quantitative computed tomography (pQCT), micro-computed tomography (µCT) and histomorphometry to analyze their trabecular and cortical bone phenotypes. We initially deleted the EGFR in preosteoblasts/osteoblasts using a Cre/loxP system (Col-Cre Egfr(f/f)), but no bone phenotype was observed because of incomplete deletion of the Egfr genomic locus. To further reduce the remaining osteoblastic EGFR activity, we introduced an EGFR dominant-negative allele, Wa5, and generated Col-Cre Egfr(Wa5/f) mice. At 3 and 7 months of age, both male and female mice exhibited a remarkable decrease in tibial trabecular bone mass with abnormalities in trabecular number and thickness. Histologic analyses revealed decreases in osteoblast number and mineralization activity and an increase in osteoclast number. Significant increases in trabecular pattern factor and structural model index indicate that trabecular microarchitecture was altered. The femurs of these mice were shorter and smaller with reduced cortical area and periosteal perimeter. Moreover, colony-forming unit-fibroblast (CFU-F) assay indicates that these mice had fewer bone marrow mesenchymal stem cells and committed progenitors. Similarly, administration of an EGFR inhibitor into wild-type mice caused a significant reduction in trabecular bone volume. In contrast, Egfr(Dsk5/+) mice with a constitutively active EGFR allele displayed increases in trabecular and cortical bone content. Taken together, these data demonstrate that the EGFR signaling pathway is an important bone regulator and that it primarily plays an anabolic role in bone metabolism.

The regulation of differentiation in mesenchymal stem cells

Mesenchymal stromal/stem cells (MSCs) are a population of stromal cells present in the bone marrow and most connective tissues, capable of differentiation into mesenchymal tissues such as bone and cartilage. MSCs are attractive candidates for biological cell-based tissue repair approaches because of their extensive proliferative ability in culture while retaining their mesenchymal multilineage differentiation potential. In addition to its undoubted scientific interest, the prospect of monitoring and controlling MSC differentiation is a crucial regulatory and clinical requirement. Hence, the molecular regulation of MSC differentiation has been extensively studied. Most of the studies are in vitro, because the identity of MSCs in their tissues of origin in vivo remains undefined. This review addresses the current knowledge of the molecular basis of differentiation of cultured MSCs, with a particular focus on chondrogenesis and osteogenesis. Building on the information coming from developmental biology studies of embryonic skeletogenesis, several signaling pathways and transcription factors have been investigated and shown to play critical roles in MSC differentiation. In particular, the Wnt and transforming growth factor-β/bone morphogenetic protein signaling pathways are well known to modulate in MSCs the molecular differentiation into cartilage and bone. Relevant to the emerging concept of stem cell niches is the demonstration that physical factors can also participate in the regulation of MSC differentiation. Knowledge of the regulation of MSC differentiation will be critical in the design of three-dimensional culture systems and bioreactors for automated bioprocessing through mathematical models applied to systems biology and network science.

Regulatory factors of mesenchymal stem cell migration into injured tissues and their signal transduction mechanisms

Adult stem cells hold great promise for wound healing and tissue regeneration. Mesenchymal stem cells (MSCs), for example, have been shown to play a role in tissue repair. Research has shown that endogenous bone marrow MSCs or exogenously delivered MSCs migrate to the sites of injury and participate in the repair process. The precise mechanisms underlying migration of MSCs into the injured tissue are still not fully understood, although multiple signaling pathways and molecules were reported, including both chemoattractive factors and endogenous electric fields at wounds. This review will briefly summarize the regulatory facors and signaling transduction pathways involved in migration of MSCs. A better understanding of the molecular mechanisms involved in the migration of MSCs will help us to develop new stem cell-based therapeutic strategies in regenerative medicine.

p85alpha regulates osteoblast differentiation by cross-talking with the MAPK pathway

Class IA phosphoinositide 3-kinase (PI3K) is involved in regulating many cellular functions including cell growth, proliferation, cell survival, and differentiation. The p85 regulatory subunit is a critical component of the PI3K signaling pathway. Mesenchymal stem cells (MSC) are multipotent cells that can be differentiated into osteoblasts (OBs), adipocytes, and chondrocytes under defined culture conditions. To determine whether p85α subunit of PI3K affects biological functions of MSCs, bone marrow-derived wild type (WT) and p85α-deficient (p85α(-/-)) cells were employed in this study. Increased cell growth, higher proliferation rate and reduced number of senescent cells were observed in MSCs lacking p85α compare with WT MSCs as evaluated by CFU-F assay, thymidine incorporation assay, and β-galactosidase staining, respectively. These functional changes are associated with the increased cell cycle, increased expression of cyclin D, cyclin E, and reduced expression of p16 and p19 in p85α(-/-) MSCs. In addition, a time-dependent reduction in alkaline phosphatase (ALP) activity and osteocalcin mRNA expression was observed in p85α(-/-) MSCs compared with WT MSCs, suggesting impaired osteoblast differentiation due to p85α deficiency in MSCs. The impaired p85α(-/-) osteoblast differentiation was associated with increased activation of Akt and MAPK. Importantly, bone morphogenic protein 2 (BMP2) was able to intensify the differentiation of osteoblasts derived from WT MSCs, whereas this process was significantly impaired as a result of p85α deficiency. Addition of LY294002, a PI3K inhibitor, did not alter the differentiation of osteoblasts in either genotype. However, application of PD98059, a Mek/MAPK inhibitor, significantly enhanced osteoblast differentiation in WT and p85α(-/-) MSCs. These results suggest that p85α plays an essential role in osteoblast differentiation from MSCs by repressing the activation of MAPK pathway.

The lamina propria of adult human oral mucosa harbors a novel stem cell population

The highly regenerative capacity of the human adult oral mucosa suggests the existence of a robust stem cell (SC) population in its lamina propria (OMLP). The purpose of this study was to characterize the availability, growth, immunophenotype, and potency of this presumable SC population. Cells positive for the embryonic stem cell transcription factors Oct4 and Sox2 and for p75 formed distinct cord-like structure in the OMLP. Regardless of donor age, trillions of cells, termed human oral mucosa stem cells (hOMSC), 95% of which express mesenchymal stromal cell markers, were simply, and reproducibly produced from a biopsy of 3-4 x 2 x 1 mm(3). A total of 40-60% of these cells was positive for Oct4, Sox2, and Nanog and 60-80% expressed constitutively neural and neural crest SC markers. hOMSC differentiated in culture into mesodermal (osteoblastic, chondroblastic, and adipocytic), definitive endoderm and ectodermal (neuronal) lineages. Unexpectedly, hOMSC treated with dexamethasone formed tumors consisting of two germ layer-derived tissues when transplanted in severe combined immune deficiency mice. The tumors consisted of tissues produced by neural crest cells during embryogenesis-cartilage, bone, fat, striated muscle, and neural tissue. These results show that the adult OMLP harbors a primitive SC population with a distinct primitive neural-crest like phenotype and identifies the in vivo localization of putative ancestors for this population. This is the first report on ectodermal- and mesodermal-derived mixed tumors formation by a SC population derived from a nonmalignant somatic adult human tissue.

Growth factor regulation of proliferation and survival of multipotential stromal cells

Multipotential stromal cells (MSCs) have been touted to provide an alternative to conservative procedures of therapy, be it heart transplants, bone reconstruction, kidney grafts, or skin, neuronal and cartilage repair. A wide gap exists, however, between the number of MSCs that can be obtained from the donor site and the number of MSCs needed for implantation to regenerate tissue. Standard methods of MSC expansion being followed in laboratories are not fully suitable due to time and age-related constraints for autologous therapies, and transplant issues leave questions for allogenic therapies. Beyond these issues of sufficient numbers, there also exists a problem of MSC survival at the graft. Experiments in small animals have shown that MSCs do not persist well in the graft environment. Either there is no incorporation into the host tissue, or, if there is incorporation, most of the cells are lost within a month. The use of growth and other trophic factors may be helpful in counteracting these twin issues of MSC expansion and death. Growth factors are known to influence cell proliferation, motility, survival and morphogenesis. In the case of MSCs, it would be beneficial that the growth factor does not induce differentiation at an early stage since the number of early-differentiating progenitors would be very low. The present review looks at the effect of and downstream signaling of various growth factors on proliferation and survival in MSCs.

Plasticity of marrow mesenchymal stem cells from human first-trimester fetus: from single-cell clone to neuronal differentiation

Recent results have shown that bone marrow mesenchymal stem cells (BMSCs) from human first-trimester abortus (hfBMSCs) are closer to embryonic stem cells and perform greater telomerase activity and faster propagation than mid- and late-prophase fetal and adult BMSCs. However, no research has been done on the plasticity of hfBMSCs into neuronal cells using single-cell cloned strains without cell contamination. In this study, we isolated five single cells from hfBMSCs and obtained five single-cell cloned strains, and investigated their biological property and neuronal differentiation potential. We found that four of the five strains showed similar expression profile of surface antigen markers to hfBMSCs, and most of them differentiated into neuron-like cells expressing Nestin, Pax6, Sox1, β-III Tubulin, NF-L, and NSE under induction. One strain showed different expression profile of surface antigen markers from the four strains and hfBMSCs, and did not differentiate toward neuronal cells. We demonstrated for the first time that some of single-cell cloned strains from hfBMSCs can differentiate into nerve tissue-like cell clusters under induction in vitro, and that the plasticity of each single-cell cloned strain into neuronal cells is different.

Mesenchymal stromal cells, colony-forming unit fibroblasts, from bone marrow of untreated advanced breast and lung cancer patients suppress fibroblast colony formation from healthy marrow

We have shown that bone marrow (BM) from untreated advanced lung and breast cancer patients (LCP and BCP) have a reduced number of colony-forming unit fibroblasts (CFU-Fs) or mesenchymal stem cells (MSCs). Factors that regulate the proliferation and differentiation of CFU-F are produced by the patients' BM microenvironment. We have now examined whether conditioned media (CM) from patients' CFU-F-derived stromal cells also inhibits the colony-forming efficiency (CFE) of CFU-F in primary cultures from healthy volunteers (HV)-BM. Thus the number and proliferation potential of HV-CFU-F were also found to be decreased and similar to colony numbers and colony size of patients' CFU-F. Stromal cells from both of these types of colonies appeared relatively larger and lacked the characteristic spindle morphology typically seen in healthy stromal cells. We developed an arbitrary mesenchymal stromal cell maturational index by taking three measures consisting of stromal cell surface area, longitudinal and horizontal axis. All stromal indices derived from HV-CFU-F grown in patients' CM were similar to those from stromal elements derived from patients' CFU-F. These indices were markedly higher than stromal indices typical of HV-CFU-F cultured in healthy CM or standard medium [alpha-medium plus 20% heat-inactivated fetal bovine serum (FBS)]. Patients' CM had increased concentrations of the CFU-F inhibitor, GM-CSF, and low levels of bFGF and Dkk-1, strong promoters of self-renewal of MSCs, compared to the levels quantified in CM from HV-CFU-F. Moreover, the majority of patients' MSCs were unresponsive in standard medium and healthy CM to give CFU-F, indicating that the majority of mesenchymal stromal cells from patients' CFU-F are locked in maturational arrest. These results show that alterations of GM-CSF, bFGF, and Dkk-1 are associated with deficient cloning and maturation arrest of CFU-F. Defective autocrine and paracrine mechanisms may be involved in the BM microenvironments of LCP and BCP.

Characterization of platelet lysate cultured mesenchymal stromal cells and their potential use in tissue-engineered osteogenic devices for the treatment of bone defects

Mesenchymal stromal cells (MSCs), seeded onto a scaffold and associated with platelet-gel, may represent an innovative treatment to improve bone repair. The preparation of MSCs for clinical use requires the fulfillment of Good Manufacturing Practice indications. The aim of this study was to validate a Good Manufacturing Practice-grade protocol of tissue engineering for bone regeneration, seeding platelet lysate (PL)-cultured MSCs onto an hydroxyapatite clinical-grade scaffold. Six large-scale experiments were performed. MSC expansions were performed comparing fetal bovine serum 10% and PL 5%. We demonstrated that PL lots contain high levels of growth factors possibly responsible of accelerated growth rate, since the number of colony-forming unit-fibroblast and population doublings were always significantly higher in PL cultures. MSCs were characterized for their phenotype and multilineage differentiation capacity, demonstrating appropriate features for both conditions. Gene expression analysis revealed higher expression of typical osteogenic genes of PL-cultured MSCs, when compared to fetal bovine serum MSCs. Cell transformation was excluded by analysis of karyotype, absence of growth without anchorage, and p53/c-myc gene expression. Scaffolds were precoated with retronectin before MSC seeding. MSC adhesion, distribution, and proliferation were demonstrated through the whole surface of the scaffold by scanning electron microscopy analysis or by immunofluorescence and MSC osteogenic differentiation through quantitative reverse transcriptase-polymerase chain reaction of typical osteogenic genes. The present report offers a model of an MSC-based bioengineered device, using an hydroxyapatite clinical-grade scaffold, and supports its potential use in tissue engineering to repair bone defects.

Non-resorbing osteoclasts induce migration and osteogenic differentiation of mesenchymal stem cells

Osteoclast activity has traditionally been regarded as restricted to bone resorption but there is some evidence that also non-resorbing osteoclasts might influence osteoblast activity. The aim of the present study was to further investigate the hypothesis of an anabolic function of non-resorbing osteoclasts by investigating their capability to recruit mesenchymal stem cells (MSC) and to provoke their differentiation toward the osteogenic lineage. Bone-marrow-derived human MSC were exposed to conditioned media (CM) derived from non-resorbing osteoclast cultures, which were generated from human peripheral blood monocytes. Osteogenic marker genes (transcription factor Runx2, bone sialoprotein, alkaline phosphatase (AP), and osteopontin) were significantly increased. Osteogenic differentiation (OD) was also proved by von Kossa and AP staining occurred in the same range as in MSC cultures stimulated with osteogenic supplements. Chemotactic responses of MSC were measured with a modified Boyden chamber assay. CM from osteoclast cultures induced a strong migratory response in MSC, which was greatly reduced in the presence of an anti-human platelet-derived growth factor (PDGF) receptor beta antibody. Correspondingly, significantly increased PDGF-BB concentrations were measured in the CM using a PDGF-BB immunoassay. CM derived from mononuclear cell cultures did not provoke MSC differentiation and had a significantly lower migratory effect on MSC suggesting that the effects were specifically mediated by osteoclasts. In conclusion, it can be suggested that human non-resorbing osteoclasts induce migration and OD of MSC. While effects on MSC migration might be mainly due to PDGF-BB, the factors inducing OD remain to be elucidated.

Biochemical and biomechanical gradients for directed bone marrow stromal cell differentiation toward tendon and bone

Substrates with mechanical property gradients and various extracellular matrix ligand loadings were evaluated for their ability to direct bone marrow stromal cell differentiation along osteogenic and tenogenic lineages. After verifying reproducible mechanical compliance characteristics of commercial hydrogel gradient substrates, substrates were functionalized with whole length fibronectin or collagen, both of which are found in skeletal structures and are relevant to cell-matrix signalling. Bone marrow stromal cells were seeded onto the substrates in growth media and cultured first to examine cell attachment and morphology, indicating higher levels of attachment on collagen substrates after 1h, and increased spreading and organization trends after 24h. Differentiation studies showed an increase in osteoblast differentiation on fibronectin substrates while collagen substrates lacked osteogenic differentiation. Osteogenic differentiation decreased on substrates of lower stiffness and lower ligand density. Molecular investigations revealed an increase in relevant signalling molecules for osteoblasts that were consistent with differentiation studies, but detected the presence of tenoblast markers on collagen substrates within a narrow range of stiffness. Our results indicate that mechanovariant substrates do hold promise as a culture platform for directed differentiation to tendon and bone by altering gene level expression of relevant signalling molecules. This study aids in understanding the molecular mechanisms that drive differentiation from substrate based cues, and could aid the design of therapeutic biomaterials at the transition from tendon to bone.

Epidermal growth factor (EGF) transfection of human bone marrow stromal cells in bone tissue engineering

A novel therapeutic approach for the treatment of bone defects is gene therapy assisted bone tissue engineering using bone marrow stromal cells (hBMSC). The aim of this study was to investigate the influence of human epidermal growth factor (hEGF) on proliferation and alkaline phosphatase (AP) activity of primary hBMSC in vitro. hBMSC cultures were achieved by explantation culture of bone chips. Following exposure to 0-10 ng recombinant hEGF (rhEGF)/ml cell numbers were determined by automated cell counting and cell bound AP activity was measured spectrophotometrically. hBMSC were transfected with hEGF plasmids and the proliferative effect was studied by cocultivation of transfected and untreated cells using porous cell culture inserts. The persistence of hEGF expression even after cell transfer was studied by the generation of possibly osteogenic constructs introducing transfected hBMSC in fibrin glue and bovine cancellous bone. The maximum increase in proliferation (156 +/- 7%) and AP activity (220 +/- 34%) was detected after exposition to 10 ng rhEGF/ml. In the separation chamber assay transfected cells produced hEGF concentrations up to 3.6 ng/ml, which induced a mean proliferation increase of 93% which could be significantly inhibited by a neutralizing hEGF antibody. Further, EGFsecretion of transfected hBMSC in 3D-culture was verified. Recombinant and transgenic hEGF stimulate proliferation of primary hBMSC in vitro. Lipotransfection of hBMSC with hEGF plasmids allows the transient and site directed delivery of biologically active transgenic hEGF. The introduction of mitogenic, angiogenic and chemoattractive factors in gene therapy assisted bone tissue engineering is discussed by the example of EGF.

Optimizing stem cell function for the treatment of ischemic heart disease

BACKGROUND

Stem cell-based therapies for myocardial ischemia have demonstrated promising early clinical results, but their benefits have been limited in duration due to impaired donor cell engraftment and function. Several strategies have emerged for enhancing stem cell function prior to their therapeutic use particularly with regard to stem cell homing, paracrine function, and survival. This review discusses current understandings of stem cell-mediated cardioprotection as well as methods of enhancing post-transplantation stem cell function and survival through hypoxic preconditioning, genetic manipulation, and pharmacologic pretreatment.

MATERIALS AND METHODS

A literature search was performed using the MEDLINE and PubMed databases using the keywords "stem cell therapy," "myocardial ischemia," "hypoxic preconditioning," "paracrine function," and "stem cell pretreatment." Studies published in English since January 1990 were selected. In addition, studies were identified from references cited in publications found using the search terms.

RESULTS

All included studies utilized animal studies and/or in vitro techniques. Stem cell modifications generally targeted stem cell homing (SDF-1, CXCR4), paracrine function (VEGF, angiogenin, Ang-1, HGF, IL-18 binding protein, TNFR1/2), or survival (Akt, Bcl-2, Hsp20, HO-1, FGF-2). However, individual modifications commonly exhibited pleiotropic effects involving some or all of these general categories.

CONCLUSION

These strategies for optimizing stem cell-mediated cardioprotection present unique potential sets of advantages and disadvantages for clinical application. Additional questions remain including those that are most efficacious in terms of magnitude and duration of benefit as well as whether combinations may yield greater benefits in both the preclinical and clinical settings.

Hydrogen gas treatment prolongs replicative lifespan of bone marrow multipotential stromal cells in vitro while preserving differentiation and paracrine potentials

Cell therapy with bone marrow multipotential stromal cells/mesenchymal stem cells (MSCs) represents a promising approach in the field of regenerative medicine. Low frequency of MSCs in adult bone marrow necessitates ex vivo expansion of MSCs after harvest; however, such a manipulation causes cellular senescence with loss of differentiation, proliferative, and therapeutic potentials of MSCs. Hydrogen molecules have been shown to exert organ protective effects through selective reduction of hydroxyl radicals. As oxidative stress is one of the key insults promoting cell senescence in vivo as well as in vitro, we hypothesized that hydrogen molecules prevent senescent process during MSC expansion. Addition of 3% hydrogen gas enhanced preservation of colony forming early progenitor cells within MSC preparation and prolonged the in vitro replicative lifespan of MSCs without losing differentiation potentials and paracrine capabilities. Interestingly, 3% hydrogen gas treatment did not decrease hydroxyl radical, protein carbonyl, and 8-hydroxydeoxyguanosine, suggesting that scavenging hydroxyl radical might not be responsible for these effects of hydrogen gas in this study.

Postinfarct intramyocardial injection of mesenchymal stem cells pretreated with TGF-alpha improves acute myocardial function

Stem cell-based therapies offer promising potential for myocardial infarction (MI), but endogenous molecules released in response to injury likely impair posttransplantation stem cell function. Stem cell-mediated cardioprotection occurs in part via paracrine effects, and transforming growth factor-alpha (TGF-alpha) has been shown to enhance paracrine function. However, it is unknown whether pretreating stem cells with TGF-alpha increases stem cell-mediated cardioprotection after acute MI. Mesenchymal stem cells (MSCs) were treated with TGF-alpha (250 ng/ml) for 24 h. Adult male Sprague-Dawley rat hearts were isolated and perfused using the Langendorff method. MI was induced by ligating the left anterior descending coronary artery. Postligation (30 min), vehicle or 1 x 10(6) MSCs with or without pretreatment were injected in the infarct border zones, and the hearts were perfused for an additional 60 min. Left ventricular function was continuously measured, and infarct size was assessed with Evans blue dye and 2,3,5-triphenyltetrazolium chloride staining. Myocardial production of interleukin (IL)-1beta and IL-6 and caspase 3 activation was also measured. Left ventricular function decreased significantly following coronary artery ligation but improved following injection of untreated MSCs and to a greater extent after injection of pretreated MSCs. In addition, the infarct area, myocardial caspase 3 activation, and IL-6 production were lowest in hearts injected with pretreated cells. Intramyocardial injection of TGF-alpha-pretreated MSCs after acute MI is associated with increased myocardial function and decreased myocardial injury. This strategy may be useful for optimizing the therapeutic efficacy of stem cells for the treatment of acute MI.

Preconditioning mesenchymal stem cells with transforming growth factor-alpha improves mesenchymal stem cell-mediated cardioprotection

Mesenchymal stem cells (MSCs) are a promising therapy for acute organ ischemia in part due to their paracrine production of growth factors. However, transplanted cells encounter an inflammatory environment that mitigates their function and survival, and treating the cells with exogenous agents during ex vivo expansion before transplantation is one strategy for overcoming this limitation by enhancing paracrine function. We hypothesized that preconditioning bone marrow MSCs with TGF-alpha would 1) increase MSC production of the critical paracrine factor, vascular endothelial growth factor (VEGF), via a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism and 2) enhance myocardial functional recovery in a rat model of acute myocardial I/R injury. To study this, bone marrow MSCs were harvested from adult male mice (C57BL/6J) and treated in vitro for 24 h according to the following groups: 1) control, 2) TGF-alpha (250 ng mL (-1)), 3) TNF-alpha (50 ng mL (-1)), 4) TGF-alpha + TNF-alpha, 5) hypoxia, and 6) TGF-alpha + hypoxia. For the isolated heart perfusion experiments, adult male Sprague-Dawley rat hearts were isolated, perfused via the Langendorff model, and subjected to I/R. Vehicle or MSCs with or without TGF-alpha preconditioning were infused immediately before ischemia. Mesenchymal stem cells were also treated with TGF-alpha alone or in combination with a p38 MAPK inhibitor (SB202190). In vitro, TGF-alpha increased MSC VEGF production alone (157.9 +/- 1.11 - 291.0 +/- 3.74 pg 10 (-5); P < 0.05) and, to a greater extent, in combination with TNF-alpha or hypoxia (364.5 +/- 0.868 and 342.0 +/- 7.92 pg 10(-5) cells, respectively; P < 0.05 vs. TGF-alpha alone). Postischemic myocardial functional recovery was greater in hearts infused with TGF-alpha-preconditioned MSCs compared with untreated MSCs or vehicle. Myocardial IL-1beta and TNF-alpha production and activation of caspase 3 were significantly decreased after infusion of both cell groups. p38 MAPK inhibition suppressed TGF-alpha-stimulated MSC VEGF production and postischemic myocardial recovery. These results suggest that TGF-alpha stimulates MSC VEGF production in part via a p38 MAPK-dependent mechanism, and preconditioning MSCs with TGF-alpha may enhance their ability to protect myocardium during I/R injury.

Epidermal growth factor (EGF) treatment on multipotential stromal cells (MSCs). Possible enhancement of therapeutic potential of MSC

Adult bone marrow multipotential stromal cells (MSCs) hold great promise in regenerative medicine and tissue engineering. However, due to their low numbers upon harvesting, MSCs need to be expanded in vitro without biasing future differentiation for optimal utility. In this concept paper, we focus on the potential use of epidermal growth factor (EGF), prototypal growth factor for enhancing the harvesting and/or differentiation of MSCs. Soluble EGF was shown to augment MSC proliferation while preserving early progenitors within MSC population, and thus did not induce differentiation. However, tethered form of EGF was shown to promote osteogenic differentiation. Soluble EGF was also shown to increase paracrine secretions including VEGF and HGF from MSC. Thus, soluble EGF can be used not only to expand MSC in vitro, but also to enhance paracrine secretion through drug-releasing MSC-encapsulated scaffolds in vivo. Tethered EGF can also be utilized to direct MSC towards osteogenic lineage both in vitro and in vivo.

Culture effects of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) on cryopreserved human adipose-derived stromal/stem cell proliferation and adipogenesis

Previous studies have demonstrated that EGF and bFGF maintain the stem cell properties of proliferating human adipose-derived stromal/stem cells (hASCs) in vitro. While the expansion and cryogenic preservation of isolated hASCs are routine, these manipulations can impact their proliferative and differentiation potential. This study examined cryogenically preserved hASCs (n = 4 donors), with respect to these functions, after culture with basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) at varying concentrations (0-10 ng/ml). Relative to the control, cells supplemented with EGF and bFGF significantly increased proliferation by up to three-fold over 7-8 days. Furthermore, cryopreserved hASCs expanded in the presence of EGF and bFGF displayed increased oil red O staining following adipogenic induction. This was accompanied by significantly increased levels of several adipogenesis-related mRNAs: aP2, C/EBPalpha, lipoprotein lipase (LPL), PPARgamma and PPARgamma co-activator-1 (PGC1). Adipocytes derived from EGF- and bFGF-cultured hASCs exhibited more robust functionality based on insulin-stimulated glucose uptake and atrial natriuretic peptide (ANP)-stimulated lipolysis. These findings indicate that bFGF and EGF can be used as culture supplements to optimize the proliferative capacity of cryopreserved human ASCs and their adipogenic differentiation potential.