BMP-2, BMP-4, and PDGF-bb stimulate chemotactic migration of primary human mesenchymal progenitor cells

Potential roles of growth factor PDGF-BB in the bony repair of injured growth plate

Injured growth plate cartilage is often repaired by bony tissue resulting in impaired bone growth in children. Using a rat injury model, our previous studies show that following the injury-induced initial inflammatory response, an influx of mesenchymal-like cells occurs within the growth plate injury site prior to formation of bony tissue. As platelet-derived growth factor (PDGF-BB) is a potent chemotactic factor of mesenchymal cells during skeletal tissue repair, we examined its role during the early fibrogenic response and the subsequent bony repair of injured growth plate. Following growth plate injury, rats received daily injection of the PDGF receptor (PDGFR) inhibitor, Imatinib, for 7 days. Immunohistochemical analysis of injured growth plate at day 1 showed the presence of PDGF-BB expression in some inflammatory cells, while at day 4 PDGFR was expressed by a proportion of the infiltrating mesenchymal cells at the injury site. By day 4, PDGFR inhibition reduced mesenchymal infiltrate (P<0.05); by day 14, Imatinib-treated rats exhibited less bony trabeculae and cartilaginous repair tissues, fewer osteoclasts and less bone marrow (BM) at the injury site, compared to vehicle controls (P<0.01). In vitro "scratch" migration assays with rat BM mesenchymal cells revealed that recombinant PDGF-BB increased cell migration into the "wound" (P<0.05), while Imatinib inhibited this chemotactic response. Quantitative RT-PCR analysis showed that Imatinib treatment decreased expression of the cartilage and bone related genes, Col2a1 and osteocalcin, respectively. These results suggest that PDGF-BB contributes to growth plate injury repair by promoting mesenchymal progenitor cell infiltration, the chondrogenic and osteogenic responses, and remodelling of the repair tissues.

Tissue engineering in the rheumatic diseases

Diseases such as degenerative or rheumatoid arthritis are accompanied by joint destruction. Clinically applied tissue engineering technologies like autologous chondrocyte implantation, matrix-assisted chondrocyte implantation, or in situ recruitment of bone marrow mesenchymal stem cells target the treatment of traumatic defects or of early osteoarthritis. Inflammatory conditions in the joint hamper the application of tissue engineering during chronic joint diseases. Here, most likely, cartilage formation is impaired and engineered neocartilage will be degraded. Based on the observations that mesenchymal stem cells (a) develop into joint tissues and (b) in vitro and in vivo show immunosuppressive and anti-inflammatory qualities indicating a transplant-protecting activity, these cells are prominent candidates for future tissue engineering approaches for the treatment of rheumatic diseases. Tissue engineering also provides highly organized three-dimensional in vitro culture models of human cells and their extracellular matrix for arthritis research.

Mesenchymal stem cells for vascular regeneration

Mesenchymal stem cells (MSCs) have tremendous potential for regenerative medicine, and have been researched for the treatment of cardiovascular diseases. MSCs are a promising cell type because of their ease of isolation and expansion, their multipotency and their low immunogenicity. However, in order to fully utilize the therapeutic potential of MSCs, it is important to understand the intrinsic property of MSCs and the role of the microenvironment in modulating MSC behavior and function. Microenvironmental factors such as mechanical cues, soluble factors and matrix properties not only regulate MSC differentiation, but also modulate MSC signaling to the surrounding environment. Understanding the properties of MSCs and the role of the microenvironment will be beneficial for developing in vivo therapies for the construction of tissue-engineered vascular grafts and the treatment of ischemic cardiac tissues.

Curative effect of autologous platelet-rich plasma on a large cutaneous lesion in a dog

A dorsal tail mass (1 x 1.2 cm) was observed on a 10-year-old castrated male, Shih-tzu dog. A biopsy of the mass was performed and diagnosed histopathologically as a follicular cyst. A necrotic lesion (2.5 x 3 cm) developed at the biopsy site 1 week after sampling and failed to respond to 2 weeks of normal saline cleansing and systemic antibiotic administration. Autologous platelet-rich plasma was applied to the lesion which gradually improved over a 4-week period possibly by a contribution to the secretion of growth hormone, which can accelerate tissue regeneration. This case report suggests that autologous PRP may be beneficial in the management of large skin defects or in delayed wound healing.

Migration potential and gene expression profile of human mesenchymal stem cells induced by CCL25

Recruitment of mesenchymal stem cells (MSC) to tissue damages is a promising approach for in situ tissue regeneration. The physiological mechanisms and regulatory processes of MSC trafficking to injured tissue remain poorly understood. However, the pivotal role of chemokines in MSC recruitment has already been shown. The aim of this study was to determine the migratory potential and the gene expression profile of MSC stimulated with the CC chemokine CCL25 (TECK). Bone marrow derived human MSC were exposed to different doses of CCL25 in a standardized chemotaxis assay. Microarray gene expression profiling and pathway analysis were performed for CCL25 stimulated MSC. Maximum migration of MSC towards CCL25 was observed at 10(3) nM. Microarray analysis revealed an induction of molecules directly involved in chemotaxis and homing of bone marrow cells (CXCL1-3, CXCL8, PDE4B), cytoskeletal and membrane reorganisation (CXCL8, PLD1, IGFBP1), cellular polarity (PLD1), and cell movement (CXCL1-3, CXCL6, CXCL8, PTGS2, PDE4B, TGM2). Respective chemokine secretion was confirmed by protein membrane-array analysis. The activation of CXCR2 ligands (CXCL1-3, CXCL5-6, CXCL8) and a LIF-receptor/gp130 ligand (LIF) indicated an involvement of the respective signaling pathways during initiation of chemotaxis and migration. These results suggest CCL25 as a new potential candidate for further in situ regeneration approaches.

Transplanted abdominal granulation tissue induced bone formation--an in vivo study in sheep

Many wounds to both soft and hard tissues heal via the formation of a granulation tissue bed. This bed is supportive of neoangiogenesis and releases proangiogenic, migratory, and proliferative growth factors and cytokines. In this study granulation tissue was grown on an intraperitoneal implant (4 mm diameter, 20 mm length) in a sheep. After 2 weeks, this implant was removed and transplanted into a femoral bone defect (4 mm diameter, 20 mm length). The sheep were sacrificed after 3 months, and the implant site examined using micro-CT and histology. A bone plaque formed adjacent to the implant, only in the presence of the peritoneal granulation tissue. This suggests that the formation of granulation tissue is a relatively conserved response at various locations in the body and its transplantation from one location to another can be used to induce tissue healing. This technique may prove useful as a method of improving physiological response to biomaterials.

BMP2 induction of actin cytoskeleton reorganization and cell migration requires PI3-kinase and Cdc42 activity

Bone morphogenetic proteins (BMPs) are potent regulators of several cellular events. We report that exposure of C2C12 cells to BMP2 leads to an increase in cell migration and a rapid rearrangement of the actin filaments into cortical protrusions. These effects required independent and parallel activation of the Cdc42 small GTPase and the alpha-isoform of the phosphoinositide 3-kinase (PI3Kalpha), because ectopic expression of a dominant-negative form of Cdc42 or distinct pharmacological PI3K inhibitors abrogated these responses. Furthermore, we demonstrate that BMP2 activates different group I and group II PAK isoforms as well as LIMK1 with similar kinetics to Cdc42 or PI3K activation. BMP2 activation of PAK and LIMK1, measured by either kinase activity or with antibodies raised against phosphorylated residues at their activation loops, were abolished by blocking PI3K-signaling pathways. Together, these findings suggest that Cdc42 and PI3K signals emanating from BMP receptors are involved in specific regulation of actin assembly and cell migration.

Enhanced regeneration of critical bone defects using a biodegradable gelatin sponge and beta-tricalcium phosphate with bone morphogenetic protein-2

We examine the osteogenicity of a sponge biomaterial consisting of a biodegradable mixture of gelatin and beta-tricalcium phosphate (betaTCP) that bound bone morphogenetic protein 2 (BMP-2) in critical-sized bone defects in rats. Gelatin-betaTCP sponges containing either phosphate buffered saline or incorporating BMP-2 are implanted into 5 mm diameter bone defects created in rat mandibles. We assess the defects biweekly for 8 weeks following implantation. There is significantly higher osteoinductive activity and significantly more Gla-osteocalcin content at bone-defect healing sites treated with gelatin-betaTCP sponges incorporating BMP-2 than there is in those treated with sponges that did not contain BMP-2. Histologically, new bone that contains bone marrow and that is connected to the original bone almost entirely replaces the regenerated bone. These results show that biodegradable gelatin-betaTCP incorporating BMP-2 is osteogenic enough to promote healing in large bone defects.

Chemotaxis of human articular chondrocytes and mesenchymal stem cells

Migration of chondrocytes and mesenchymal stem cells (MSCs) may be important in cartilage development, tissue response to injury, and in tissue engineering. This study analyzed growth factors and cytokines for their ability to induce migration of human articular chondrocytes and bone marrow-derived mesenchymal stem cells in Boyden chamber assays. In human articular chondrocytes serum induced dose- and time-dependent increases in cell migration. Among a series of growth factors and cytokines tested only PDGF induced a significant increase in cell migration. The PDGF isoforms AB and BB were more potent than AA. There was an aging-related decline in the ability of chondrocytes to migrate in response to serum and PDGF. Human bone marrow MSC showed significant chemotaxis responses to several factors, including FBS, PDGF, VEGF, IGF-1, IL-8, BMP-4, and BMP-7. In summary, these results demonstrate that directed cell migration is inducible in human articular chondrocytes and MSC. PDGF is the most potent factor analyzed, and may be useful to promote tissue integration during cartilage repair or tissue engineering.

PDGF receptor beta is a potent regulator of mesenchymal stromal cell function

Mesenchymal stromal cells (MSCs) in bone marrow are important for bone homeostasis. Although platelet-derived growth factor (PDGF) has been reported to be involved in osteogenic differentiation of MSCs, the role remains controversial and the network of PDGF signaling for MSCs has not been clarified. To clarify the underlying regulatory mechanism of MSC functions mediated by PDGF, we deleted the PDGF receptor (PDGFR)beta gene by Cre-loxP strategy and examined the role of PDGF in osteogenic differentiation of MSCs and fracture repair. In cultured MSCs, the mRNA expression of PDGF-A, -B, -C, and -D as well as PDGFRalpha and beta was detected. Depletion of PDGFRbeta in MSCs decreased the mitogenic and migratory responses and enhanced osteogenic differentiation as evaluated by increased alkaline phosphatase (ALP) activity and mRNA levels of ALP, osteocalcin (OCN), bone morphogenetic protein (BMP) 2, Runx2, and osterix in quantitative RT-PCR. PDGF-BB, but not PDGF-AA, inhibited osteogenic differentiation accompanied by decreased ALP activity and mRNA levels, except for BMP2. These effects of PDGF-BB were eliminated by depletion of PDGFRbeta in MSCs except that PDGF-BB still suppressed osterix expression in PDGFRbeta-depleted MSCs. Depletion of PDGFRbeta significantly increased the ratio of woven bone to callus after fracture. From the combined analyses of PDGF stimulation and specific PDGFRbeta gene deletion, we showed that PDGFRbeta signaling distinctively induces proliferative and migratory responses but strongly inhibits osteogenic differentiation of MSCs. The effects of PDGFRalpha on the osteogenic differentiation were very subtle. PDGFRbeta could represent an important target for guided tissue regeneration or tissue engineering of bone.

Differential proteome of bone marrow mesenchymal stem cells from osteoarthritis patients

OBJECTIVE

Adult mesenchymal stem cells (MSCs) are multipotent cells whose primary reservoir is bone marrow (BM). Following situations of extensive tissue damage, MSCs are mobilized and migrate to the site of injury. Osteoarthritis (OA) is a condition that involves extensive cartilage and bone damage. To gain insight into the pathogenesis of OA, we have analyzed the differential BM-MSCs proteome of OA patients.

METHODS

MSCs protein extracts were prepared from BM aspirates from six patients with OA and from six hip fracture subjects without OA, and analyzed by Two-dimensional gels, using the differential in-gel electrophoresis approach. Differentially expressed proteins were identified by mass spectrometry. In addition, the chemotactic responses of OA and control MSCs were assessed.

RESULTS

The majority of proteins that changed at least 1.5-fold (P<0.05) belonged to the following three categories: metabolic enzymes (14 proteins, 36%), cytoskeleton/motility (12 proteins, 32%), and transporters (three proteins, 8%). In OA MSCs, a high percentage of metabolic enzymes (n=8, 57%) were up-regulated and most of the proteins related to cytoskeleton/motility (n=9, 75%) were down-regulated. There was a significant increase in the migration response of OA MSCs to platelet-derived growth factor-BB (chemotaxis index CI: 5.13+/-1.19 vs 3.35+/-0.42, P=0.043).

CONCLUSIONS

In this study, we have described the differential proteome of BM-MSCs from OA patients together with an increased chemotactic response of these cells in the context of OA. These results could indicate an activation of OA BM-MSCs in response to chemotactic signals sent by the altered subchondral bone in an attempt to heal damaged tissue.

Gene expression profile of adult human bone marrow-derived mesenchymal stem cells stimulated by the chemokine CXCL7

A variety of chemokines has been shown to recruit human bone marrow-derived mesenchymal stem cells (MSC) and may be potential candidates for chemokine-based tissue regeneration approaches. The aim of our study was to determine whether the chemokine CXCL7 stimulates migration of human bone marrow-derived MSC and to analyze the effect of CXCL7 on the recruitment of MSC on the broad molecular level. Chemotaxis assays documented that high doses of CXCL7 significantly recruited MSC. Gene expression profiling using oligonucleotide microarrays showed that MSC treated with CXCL7 differentially expressed genes related to cell migration, cell adhesion and extracellular matrix remodeling. Pathway analysis showed that CXCL7 induced the expression of all chemokines binding the interleukin (IL) receptors A and B, CXCR1 and CXCR2, as well as the IL6 signal transducer (gp130) and its ligands IL6 and leukemia inhibitory factor (LIF). Induction of differentially expressed chemokines CXCL1-3, CXCL5, and CXCL6 as well as LIF and gp130 in MSC by CXCL7 was verified by real-time polymerase chain reaction. Immunoassay of cell culture supernatants confirmed elevated levels of the interleukins 6 and 8 in MSC upon treatment with CXCL7. Chemotaxis assays showed that interleukin 6 did not recruit MSC. In conclusion, CXCL7 significantly stimulates the migration of human MSC in vitro. Pathway analysis suggests that recruitment of human MSC by CXCL7 is supported by the induction of ligands of the interleukin 8 receptors, synergistically activating the respective signaling pathways.

Mesenchymal stromal cells lose their immunosuppressive potential after allotransplantation

OBJECTIVE

The stem cell fraction of mesenchymal stromal cells (MSCs) is capable of self-renewal and under inductive conditions differentiates into bone, cartilage, hematopoietic stroma, and other mesenchymal tissues. Therefore, MSCs represent a promising source for hard tissue repair therapies. MSCs are also immunosuppressive and prevent activation of allogeneic lymphocytes in vitro. Thus it has been suggested that they might be able to engraft in allogeneic recipients and downregulate recipients' immunity. In this study we examined whether MSCs retain their immunomodulating properties in vivo after allotransplantation.

MATERIALS AND METHODS

MSCs were propagated from bone marrow (BM), placenta, or umbilical cord tissues. Using a murine parental-into-F1 model of graft-vs-host disease (GVHD) we tried to control GVHD by intravenous transplanting parental or recipient MSCs together with parental lymphocytes (day 0) and on days +7 and +14. MSCs' immunosuppressive potential in vivo was also examined by comparing their ability to construct ectopic bone after local transplantation with osteogenic inductor (demineralized bone matrix) under the kidney capsule of syngeneic and allogeneic recipients.

RESULTS

Repeated IV MSC injections failed to reduce GVHD-related recipient mortality. Local implantation of MSCs propagated from BM, placenta or umbilical cord resulted in ectopic bone formation in syngeneic recipients and in transplant rejection by allogeneic mice.

CONCLUSION

MSCs lose their immunosuppressive potential in mismatched setting.

Human periosteum-derived progenitor cells express distinct chemokine receptors and migrate upon stimulation with CCL2, CCL25, CXCL8, CXCL12, and CXCL13

For bone repair, transplantation of periosteal progenitor cells (PCs), which had been amplified within supportive scaffolds, is applied clinically. More innovative bone tissue engineering approaches focus on the in situ recruitment of stem and progenitor cells to defective sites and their subsequent use for guided tissue repair. Chemokines are known to induce the directed migration of bone marrow CD34(-) mesenchymal stem cells (MSCs). The aim of our study was to determine the chemokine receptor expression profile of human CD34(-) PCs and to demonstrate that these cells migrate upon stimulation with selected chemokines. PCs were isolated from periosteum of the mastoid bone and displayed a homogenous cell population presenting an MSC-related cell-surface antigen profile (ALCAM(+), SH2(+), SH3(+), CD14(-), CD34(-), CD44(+), CD45(-), CD90(+)). The expression profile of chemokine receptors was determined by real-time PCR and immunohistochemistry. Both methods consistently demonstrated that PCs express receptors of all four chemokine subfamilies CC, CXC, CX(3)C, and C. Migration of PCs and a dose-dependent migratory effect of the chemokines CCL2 (MCP1), CCL25 (TECK), CXCL8 (IL8), CXCL12 (SDF1alpha), and CXCL13 (BCA1), but not CCL22 (MDC) were demonstrated using a 96-multiwell chemotaxis assay. In conclusion, for the first time, here we report that human PCs express chemokine receptors, present their profile, and demonstrate a dose-dependent migratory effect of distinct chemokines on these cells. These results are promising towards in situ bone repair therapies based on guiding PCs to bone defects, and encourage further in vivo studies.

Inflammation and tumor microenvironments: defining the migratory itinerary of mesenchymal stem cells

Mesenchymal stem cells (MSC) exhibit tropism for sites of tissue damage as well as the tumor microenvironment. Many of the same inflammatory mediators that are secreted by wounds are found in the tumor microenvironment and are thought to be involved in attracting MSC to these sites. Cell migration is dependent on a multitude of signals ranging from growth factors to chemokines secreted by injured cells and/or respondent immune cells. MSC are likely to have chemotactic properties similar to other immune cells that respond to injury and sites of inflammation. Thus, the well-described model of leukocyte migration can serve as a reasonable example to facilitate the identification of factors involved in MSC migration. Understanding the factors involved in regulating MSC migration to tumors is essential to ultimately develop novel clinical strategies aimed at using MSC as vehicles to deliver antitumor proteins or suppress MSC migration to reduce tumor growth. For example, radiation enhances inflammatory signaling in the tumor microenvironment and may be used to potentiate site-specific MSC migration. Alternatively, restricting the migration of the MSC to the tumor microenvironment may prevent competent tumor-stroma formation, thereby hindering the growth of the tumor. In this review, we will discuss the role of inflammatory signaling in attracting MSC to tumors.

Rotation and asymmetric development of the zebrafish heart requires directed migration of cardiac progenitor cells

We have used high-resolution 4D imaging of cardiac progenitor cells (CPCs) in zebrafish to investigate the earliest left-right asymmetric movements during cardiac morphogenesis. Differential migratory behavior within the heart field was observed, resulting in a rotation of the heart tube. The leftward displacement and rotation of the tube requires hyaluronan synthase 2 expression within the CPCs. Furthermore, by reducing or ectopically activating BMP signaling or by implantation of BMP beads we could demonstrate that BMP signaling, which is asymmetrically activated in the lateral plate mesoderm and regulated by early left-right signals, is required to direct CPC migration and cardiac rotation. Together, these results support a model in which CPCs migrate toward a BMP source during development of the linear heart tube, providing a mechanism by which the left-right axis drives asymmetric development of the vertebrate heart.

Growth factor release following femoral nailing

The aim of this study was to investigate whether growth factors essential for fracture healing are substantially increased in the immediate aftermath following reaming of the intramedullary cavity for stabilisation of femoral shaft fractures. Consecutive adult patients whose femoral shaft fractures stabilised with either reamed (10 patients) or unreamed (10 patients) intramedullary nailing were studied. Peripheral blood samples and samples from the femoral canal before and after reaming and nail insertion were collected. Serum was extracted and using Elisa colorimetric assays the concentration of Platelet Derived Growth Factor-BetaBeta (PDGF), Vascular Endothelial Growth Factor (VEGF), Insulin-like Growth Factor-I (IGF-I), Transforming Growth Factor beta 1 (TGF-beta1) and Bone Morphogenetic Protein-2 (BMP-2) was measured. The mean age of the twenty patients who participated in the study was 38 years (range 20-63). Reaming substantially increased all studied growth factors (p<0.05) locally in the femoral canal. VEGF and PDGF were increased after reaming by 111.2% and 115.6% respectively. IGF-I was increased by 31.5% and TGF-beta1 was increased by 54.2%. In the unreamed group the levels of PDGF-BB, VEGF, TGF-beta1 remained unchanged while the levels of IGF-I decreased by 10%. The levels of these mediators in the peripheral circulation were not altered irrespectively of the nail insertion technique used. BMP-2 levels during all time points were below the detection limit of the immunoassay. This study indicates that reaming of the intramedullary cavity is associated with increased liberation of growth factors. The osteogenic effect of reaming could be secondary not only to grafting debris but also to the increased liberation of these molecules.

Recombinant human platelet-derived growth factor: biology and clinical applications

The abilities of bone to remodel, fractures to repair, and bone grafts to incorporate are all fundamental reflections of the bone remodeling cycle. This process is characterized by the recruitment and differentiation of osteoblastic and osteoclastic cell populations, whose cellular activities are coordinated and regulated by an elaborate system of growth factors and cytokines. One of the crucial biological factors responsible for reparative osseous activity is platelet-derived growth factor (PDGF). The potent stimulatory effects of PDGF as a chemoattractant and mitogen for mesenchymal cells (including osteogenic cells), along with its ability to promote angiogenesis, have been demonstrated in a variety of preclinical models predicting maxillofacial, spine and appendicular skeletal, and soft-tissue applications. The biological profile of PDGF, including its ability to recruit osteoprogenitor cells, makes it particularly suited to address the skeletal defects that are seen with comorbid conditions such as osteoporosis, diabetes, and the effects of smoking. The clinical success and safety that have been demonstrated with use of recombinant human PDGF (rhPDGF) in the repair of periodontal defects have led to U.S. Food and Drug Administration (FDA) approval of rhPDGF for this indication. Ongoing pilot and pivotal trials in the United States and internationally will continue to clarify the promising role of PDGF in the treatment of challenging skeletal disorders.

Accelerated fracture healing in the geriatric, osteoporotic rat with recombinant human platelet-derived growth factor-BB and an injectable beta-tricalcium phosphate/collagen matrix

Aging and osteoporosis contribute to decreased bone mass and bone mineral density as well as compromised fracture healing rates and bone repair quality. Consequently, the purpose of this study was to determine if recombinant human platelet-derived growth factor-BB (rhPDGF-BB) delivered in an injectable beta-tricalcium phosphate/collagen matrix would enhance tibial fracture healing in geriatric (>2 years of age), osteoporotic rats. A total of 80 rats were divided equally among four groups: Fracture alone; Fracture plus matrix; Fracture plus matrix and either 0.3 mg/mL or 1.0 mg/mL rhPDGF-BB. At 3 and 5 weeks, rats were euthanized and treatment outcome was assessed histologically, radiographically, biomechanically, and by micro-CT. Results indicated rhPDGF-BB-treated fractures in osteoporotic, geriatric rats caused a statistically significant time-dependent increase in torsional strength 5 weeks after treatment. The healed fractures were equivalent in torsional strength to the contralateral, unoperated tibiae. Data from the study are the first, to our knowledge, to underscore rhPDGF-BB efficacy in an injectable beta-tricalcium phosphate/collagen matrix accelerated fracture repair in a geriatric, osteoporotic rat model.

Fibronectin, vitronectin, and collagen I induce chemotaxis and haptotaxis of human and rabbit mesenchymal stem cells in a standardized transmembrane assay

The mesenchymal stem cell (MSC) is a critical element in tissue repair and regeneration. Its ability to differentiate into multiple connective tissue cell types and to self-renew has made it a prime candidate in regenerative medicine strategies. Currently, the environmental cues responsible for in situ recruitment and control of MSC distribution at repair sites are not entirely revealed and in particular the role of extracellular matrix (ECM) proteins as motogenic factors has not been studied. Here we have used a standardized transmembrane chemotaxis assay to assess the chemotactic and haptotactic potential of fibronectin, vitronectin, and collagen type 1 on MSCs from both rabbit and human origin. The use of both cell types was based in part on the widespread use of rabbit models for musculoskeletal-related tissue engineering and repair models and their unknown correspondence to human in terms of MSC migration. The optimized assay yielded a greatly increased chemotactic response toward known factors such as platelet-derived growth factor-BB (PDGF)-BB compared to previous studies. Our primary finding was that all three ECM proteins tested (fibronectin, vitronectin, and collagen I) induced significant motogenic activity, in both soluble and insoluble forms, for both rabbit and human MSCs. These results suggest that ECM proteins could play roles as significant as cytokines in the recruitment of pluripotential repair cells wound and tissue repair sites. Furthermore, designed ECM coatings of scaffolds or implants could provide a new tool to control both cell influx and outflux from the scaffold post-implantation. Finally, the similarity of motogenic behavior of both rabbit and human cells suggests the rabbit is a reliable model for assessing MSC recruitment in repair and regeneration strategies.

Regeneration of ovine articular cartilage defects by cell-free polymer-based implants

The aim of our study was the evaluation of a cell-free cartilage implant that allows the recruitment of mesenchymal stem and progenitor cells by chemo-attractants and subsequent guidance of the progenitors to form cartilage repair tissue after microfracture. Chemotactic activity of human serum on human mesenchymal progenitors was tested in 96-well chemotaxis assays and chondrogenic differentiation was assessed by gene expression profiling after stimulating progenitors with hyaluronan in high-density cultures. Autologous serum and hyaluronan were combined with polyglycolic acid (PGA) scaffolds and were implanted into full-thickness articular cartilage defects of the sheep pre-treated with microfracture. Defects treated with microfracture served as controls. Human serum was a potent chemo-attractant and efficiently recruited mesenchymal progenitors. Chondrogenic differentiation of progenitors upon stimulation with hyaluronan was shown by the induction of typical chondrogenic marker genes like type II collagen and aggrecan. Three months after implantation of the cell-free implant, histological analysis documented the formation of a cartilaginous repair tissue. Controls treated with microfracture showed no formation of repair tissue. The cell-free cartilage implant consisting of autologous serum, hyaluronan and PGA utilizes the migration and differentiation potential of mesenchymal progenitors for cartilage regeneration and is well suited for the treatment of cartilage defects after microfracture.

CYR61/CCN1 and WISP3/CCN6 are chemoattractive ligands for human multipotent mesenchymal stroma cells

BACKGROUND

CCN-proteins are known to be involved in development, homeostasis and repair of mesenchymal tissues. Since these processes implicate recruitment of cells with the potential to be committed to various phenotypes, we studied the effect of CYR61/CCN1 and WISP3/CCN6 on migration of human bone marrow derived mesenchymal stroma cells (MSCs) in comparison to in vitro osteogenic differentiated MSCs using a modified Boyden chamber assay.

RESULTS

CYR61 and WISP3 were purified as fusion proteins with a C-terminal Fc-tag from baculovirus infected SF21 cells using protein G sepharose columns. CYR61 and WISP3 stimulated cell migration of undifferentiated MSCs in a dose-dependent manner. CYR61 and WISP3 had similar effects on committed osteogenic precursor cells. Checkerboard analysis revealed that CYR61 and WISP3 stimulated true directed cell migration (chemotaxis) of MSCs and committed osteogenic precursors. In MSCs the chemotactic activity of WISP3 but not CYR61 was mediated through integrin alphanuss5.

CONCLUSION

Our results indicate that CYR61 and WISP3 can function as soluble ligands transmitting chemotactic signals to human MSCs but differ in the involvement of integrin alphanuss5. This may be relevant for their possible role in connective tissue repair.

Synovial fluid recruits human mesenchymal progenitors from subchondral spongious bone marrow

Microfracture is a frequently used reparative technique that induces a healing response in articular cartilage defects. Penetration of the subchondral bone leads to blood clot formation, allows multipotent mesenchymal cells to access the defect and, subsequently, leads to cartilaginous repair tissue. The aim of our study was to analyze the chemotactic recruitment of human subchondral spongious bone marrow-derived cells by synovial fluid (SF) from normal donors (ND), patients with osteoarthritis (OA) and rheumatoid arthritis (RA). Subchondral spongious bone marrow-derived mesenchymal progenitors were isolated from bone cylinders after high tibial osteotomy and analyzed for the presence of stem cell-related cell surface antigens by flow cytometry. Recruitment of subchondral progenitors by normal SF and SF from donors with degenerated joint diseases was documented by using a modified Boyden chamber chemotaxis assay. The chemotaxis assay demonstrated that synovial fluid has the potential to recruit mesenchymal progenitors in vitro. SF from normal donors and patients with OA showed no difference in the potential to stimulate cell migration. SF obtained from RA donors showed significantly reduced cell recruitment compared to SF derived from OA patients (p = 0.0054) and normal donors (p < 0.0001). The chemotactic activity of SF obtained from normal donors and from patients with degenerative joint diseases suggests that SF may be actively involved in the migration of progenitors in cartilage defects after microfracture.

Comparison of the cytokine-induced migratory response between primary and subcultured populations of rat mesenchymal bone marrow cells

BACKGROUND

The aim of this study was to investigate the phenotypic differences of primary rat mesenchymal bone marrow cells (MBMCs) and subcultured cells, the influence of subculture and cell density on the cellular phenotypes, and the difference in the migratory responses of these cells to cytokines.

METHODS

MBMCs were isolated from 8-week-old Wistar rats, and the cells were cultured for 1 week (passage 0, P0) or 3 weeks (P0-3W). P0 cells were subcultured for 1 week (P1). P1 cells were subcultured at several cell densities for 1 week (P2). Cell size and granularity were analyzed by flow cytometry. The gene expression characteristics of these cells were analyzed by reverse transcription polymerase chain reaction. Cell migration to bone morphogenetic protein-2 (BMP-2), fibroblast growth factor-2 (FGF-2), and platelet-derived growth factor-bb (PDGF-bb) was evaluated using a Boyden chamber.

RESULTS

Three morphologically distinct populations in P0 and two in P2 were detected. The levels of human rapidly self-renewing cell-related marker genes in P0 were more highly expressed than in P2. Mesenchymal stem cell-associated markers were expressed at the same level in P0 and P2. The gene expression levels of immature oligodendrocyte precursor cell markers in P0 were higher than those in P2, whereas those of smooth muscle cell markers and osteoblastic cell markers in P0 were lower than those in P2. Subculture decreased the gene expression levels of human rapidly self-renewing cell-associated markers. Cell migration of P0 cells was stimulated by PDGF-bb but not by BMP-2 or FGF-2. In contrast, PDGF-bb, BMP-2, and FGF-2 all stimulated cell migration of P2.

CONCLUSION

The types of cells in populations of primary and subcultured rat MBMCs were different, and the distribution of each cell population appeared to be changed by the culture conditions. The cell migration effect by PDGF-bb, BMP-2, and FGF-2 differed between the primary and subcultured MBMCs.

Towards in situ tissue repair: human mesenchymal stem cells express chemokine receptors CXCR1, CXCR2 and CCR2, and migrate upon stimulation with CXCL8 but not CCL2

The recruitment of bone marrow CD34- mesenchymal stem- and progenitor cells (MSC) and their subsequent differentiation into distinct tissues is the precondition for in situ tissue engineering. The objective of this study was to determine the entire chemokine receptor expression profile of human MSC and to investigate their chemotactic response to the selected chemokines CCL2, CXCL8 and CXCL12. Human MSC were isolated from iliac crest bone marrow aspirates and showed a homogeneous population presenting a typical MSC-related cell surface antigen profile (CD14-, CD34-, CD44+, CD45-, CD166+, SH-2+). The expression profile of all 18 chemokine receptors was determined by real-time PCR and immunohistochemistry. Both methods consistently demonstrated that MSC express CC, CXC, C and CX(3)C receptors. Gene expression and immunohistochemical analysis documented that MSC express chemokine receptors CCR2, CCR8, CXCR1, CXCR2 and CXCR3. A dose-dependent chemotactic activity of CXCR4 and CXCR1/CXCR2 ligands CXCL12 and CXCL8 (interleukin-8) was demonstrated using a 96-well chemotaxis assay. In contrast, the CCR2 ligand CCL2 (monocyte chemoattractant protein-1, MCP-1) did not recruited human MSC. In conclusion, we report that the chemokine receptor expression profile of human MSC is much broader than known before. Furthermore, for the first time, we demonstrate that human MSC migrate upon stimulation with CXCL8 but not CCL2. In combination with already known data on MSC recruitment and differentiation these are promising results towards in situ regenerative medicine approaches based on guiding of MSC to sites of degenerated tissues.

Starch-Based Microparticles as Vehicles for the Delivery of Active Platelet-Derived Growth Factor

In a previous work, we described the use of starch-based microparticles as vehicles for the controlled release of corticosteroids. The goal of the present work is to evaluate the potential of these microparticles to incorporate and release platelet-derived growth factor (PDGF). The loading efficiency and release profile were evaluated, and PDGF was incorporated into and released from the matrix of starch-based microparticles. The release profile shows rapid release of PDGF in the first 24 h, after which there was a slow but constant release for up to 8 weeks. The maintenance of the PDGF biological activity after incorporation and release was evaluated by its mitogenic effect over osteoblastic cells, and it was shown to be comparable to that of PDGF supplemented to the culture medium. This proves that the incorporation and release did not affect the biological activity of the growth factor (GF). The results clearly demonstrate that starch-based microparticles are suitable vehicles for the incorporation and release of GFs. When combined with previous results, these materials also suggest their ability to enhance the regenerating potential of tissue engineering hybrid constructs.

Bone morphogenetic protein-2/4 signalling pathway components are expressed in the human thymus and inhibit early T-cell development

T-cell differentiation is driven by a complex network of signals mainly derived from the thymic epithelium. In this study we demonstrate in the human thymus that cortical epithelial cells produce bone morphogenetic protein 2 (BMP2) and BMP4 and that both thymocytes and thymic epithelium express all the molecular machinery required for a response to these proteins. BMP receptors, BMPRIA and BMPRII, are mainly expressed by cortical thymocytes while BMPRIB is expressed in the majority of the human thymocytes. Some thymic epithelial cells from cortical and medullary areas express BMP receptors, being also cell targets for in vivo BMP2/4 signalling. The treatment with BMP4 of chimeric human-mouse fetal thymic organ cultures seeded with CD34+ human thymic progenitors results in reduced cell recovery and inhibition of the differentiation of human thymocytes from CD4- CD8- to CD4+ CD8+ cell stages. These results support a role for BMP2/4 signalling in human T-cell differentiation.

Intrathecal application of neuroectodermally converted stem cells into a mouse model of ALS: limited intraparenchymal migration and survival narrows therapeutic effects

Stem and progenitor cells provide a promising therapeutic strategy for amyotrophic lateral sclerosis (ALS). To comparatively evaluate the therapeutic potentials of human bone marrow-derived mesodermal stromal cells (hMSCs) and umbilical cord blood cells (hUBCs) in ALS, we transplanted hMSCs and hUBCs and their neuroectodermal derivatives (hMSC-NSCs and hUBC-NSCs) into the ALS mouse model over-expressing the G93A mutant of the human SOD1 gene. We used a standardized protocol similar to clinical studies by performing a power calculation to estimate sample size prior to transplantation, matching the treatment groups for gender and hSOD-G93A gene content, and applying a novel method for directly injecting 100,000 cells into the CSF (the cisterna magna). Ten days after transplantation we found many cells within the subarachnoidal space ranging from frontal basal cisterns back to the cisterna magna, but only a few cells around the spinal cord. hMSCs and hMSC-NSCs were also located within the Purkinje cell layer. Intrathecal cell application did not affect survival times of mice compared to controls. Consistently, time of disease onset and first pareses, death weight, and motor neuron count in lumbar spinal cord did not vary between treatment groups. Interestingly, transplantation of hMSCs led to an increase of pre-symptomatic motor performance compared to controls in female animals. The negative outcome of the present study is most likely due to insufficient cell numbers within the affected brain regions (mainly the spinal cord). Further experiments defining the optimal cell dose, time point and route of application and particularly strategies to improve the homing of transplanted cells towards the CNS region of interest are warranted to define the therapeutic potential of mesodermal stem cells for the treatment of ALS.

The in vitro migration capacity of human bone marrow mesenchymal stem cells: comparison of chemokine and growth factor chemotactic activities

Adult bone marrow (BM)-derived stem cells, including hematopoietic stem cells (HSCs) and MSCs, represent an important source of cells for the repair of a number of damaged tissues. In contrast to HSCs, the soluble factors able to induce MSC migration have not been extensively studied. In the present work, we compared the in vitro migration capacity of human BM-derived MSCs, preincubated or not with the inflammatory cytokines interleukin 1beta (IL1beta) and tumor necrosis factor alpha (TNFalpha), in response to 16 growth factors (GFs) and chemokines. We show that BM MSCs migrate in response to many chemotactic factors. The GFs platelet-derived growth factor-AB (PDGF-AB) and insulin-like growth factor 1 (IGF-1) are the most potent, whereas the chemokines RANTES, macrophage-derived chemokine (MDC), and stromal-derived factor-1 (SDF-1) have limited effect. Remarkably, preincubation with TNFalpha leads to increased MSC migration toward chemokines, whereas migration toward most GFs is unchanged. Consistent with these results, BM MSCs express the tyrosine kinase receptors PDGF-receptor (R) alpha, PDGF-Rbeta, and IGF-R, as well as the RANTES and MDC receptors CCR2, CCR3, and CCR4 and the SDF-1 receptor CXCR4. TNFalpha increases CCR2, CCR3, and CCR4 expression (as opposed to that of CXCR4), together with RANTES membrane binding. These data indicate that the migration capacity of BM MSCs is under the control of a large range of receptor tyrosine kinase GFs and CC and CXC chemokines. Most chemokines are more effective on TNFalpha-primed cells. Our results suggest that the mobilization of MSCs and their subsequent homing to injured tissues may depend on the systemic and local inflammatory state. Disclosure of potential conflicts of interest is found at the end of this article.

BMP-7 and CBFA1 in allograft bone in vivo bone formation and the influence of gamma-irradiation

An initial study showed that morselized human bone grafts were osteoconductive and osteoinductive when implanted in nude rat tibial window defects, and 25 kGy of gamma-irradiation significantly reduced those properties. The mechanism of the osteoinductivity and the influence of gamma-irradiation required further investigation. In this study we assessed the paraffin sections of seven morselized human bone grafts implanted into rat tibial defects for 3 weeks after being treated with 0, 15, or 25 kGy gamma-radiation respectively. Osteoclast-like cell counting and protein expressions of bone morphogenetic protein-7 (BMP-7), core binding factor alpha1 (CBFA1), and proliferating cell nuclear antigen (PCNA) were investigated and the positive signals were quantitatively analyzed. More new bone formation was observed in the 0 and 15 kGy groups compared with 25 kGy groups. The newly formed bones were found mainly from the intact cortex into the defects bridged by the implanted grafts. A dense staining of BMP-7 and CBFA1 was noted in the osteoblast-like cells in those areas. The BMP-7 and CBFA1 staining was also seen in the cells surrounding the implanted grafts in the centre areas of the defects in distance from the intact cortex. Quantitative analysis of immunohistochemical staining of the centre areas of the defects showed that gamma-irradiation (15 and 25 kGy) significantly reduced the expression of CBFA1 and BMP-7. In conclusion, morselized human bone grafts may contain some factors, which induced osteoblast lineage differentiation and bone formation and gamma-irradiation damages those bone inducing factors.

BMP7 promotes adipogenic but not osteo-/chondrogenic differentiation of adult human bone marrow-derived stem cells in high-density micro-mass culture

The objective of our study was to elucidate the potential of bone morphogenetic protein-7 (BMP7) to initiate distinct mesenchymal lineage development of human adult mesenchymal stem cells (MSC) in three-dimensional micro-mass culture. Expanded MSC were cultured in high-density micro-masses under serum-free conditions that favor chondrogenic differentiation and were stimulated with 50-200 ng/ml BMP7 or 10 ng/ml transforming growth factor-beta3 (TGFbeta3) as control. Histological staining of proteoglycan with alcian blue, mineralized matrix according to von Kossa, and lipids with Oil Red O, immunostaining of type II collagen as well as real-time gene expression analysis of typical chondrogenic, adipogenic, and osteogenic marker genes showed that BMP7 promoted adipogenic differentiation of MSC. Micro-masses stimulated with BMP7 developed adipocytic cells filled with lipid droplets and showed an enhanced expression of the adipocyte marker genes fatty acid binding protein 4 (FABP4) and the adipose most abundant transcript 1 (apM1). Development along the chondrogenic lineage or stimulation of osteogenic differentiation were not evident upon stimulation with BMP7 in different concentrations. In contrast, TGFbeta3 directed MSC to form a cartilaginous matrix that is rich in proteoglycan and type II collagen. Gene expression analysis of typical chondrocyte marker genes like cartilage oligomeric matrix protein (COMP), link protein, aggrecan, and types IIalpha1 and IXalpha3 collagen confirmed chondrogenic differentiation of MSC treated with TGFbeta3. These results suggest that BMP7 promotes the adipogenic and not the osteogenic or chondrogenic lineage development of human stem cells when assembled three-dimensionally in micro-masses.

Human mesenchymal progenitor cell responses to a novel textured poly(L-lactide) scaffold for ligament tissue engineering

Biocompatibility and cell seeding capability of a new cell scaffold made of textured polylactic acid (PLA) fibers was investigated as a new material for tissue engineering of anterior cruciate ligaments (ACL). Adhesion and proliferation of human mesenchymal progenitor cells (MPC) was investigated after 15 days by scanning electron microscopy and standard histology. Expression of collagen type I and III, fibronectin, tenascin C, decorin, smooth muscle actin, and the matrix metalloproteinases MMP-1 and MMP-2, as well as their tissue inhibitors TIMP-1 and TIMP-2 was analyzed using real-time PCR. Protein expression of collagen I and III, tenascin C, and proliferating nuclear antigen (PCNA) was determined by immunohistology. Apoptosis was analyzed by detection of p53 expression and TUNEL staining. MPC seeded the scaffold homogeneously and showed good cell growth and no increased rate of apoptosis. After 15 days, the matrix forming genes collagen type I, tenascin C, and decorin were upregulated, indicating the formation of a ligament-like matrix. MMP-1 and TIMP-1 were also significantly increased, suggesting initial matrix remodeling. It was concluded that the new porous PLA scaffold allowed homogeneous cell seeding, a fibroblastic phenotype and the production of a ligament-like matrix and, therefore, might be a suitable cell carrier for ACL tissue engineering.

Effect of platelet-rich plasma on migration and proliferation of SaOS-2 osteoblasts: role of platelet-derived growth factor and transforming growth factor-beta

Platelet-enriched plasma (PRP) is used in therapy as a source of growth factors in bone fracture and wound healing; however, few data exist on its role in the different aspects of the healing process. The effect of PRP and of the two main growth factors present in this preparation (platelet-derived growth factor [PDGF] and transforming growth factor-beta [TGF-beta]) was evaluated in vitro using the human osteoblastic cell line SaOS-2, which was shown by reverse transcription-polymerase chain reaction to express both PDGF-alpha and -beta receptors. Batroxobine-activated PRP was added in different concentrations to SaOS-2 cells to assess cell migration (by a microchemotaxis assay) and cell proliferation (by [3H]-thymidine incorporation into the DNA). Immunoneutralization with anti-PDGF-beta or anti-TGF-beta antibodies allowed the assessment of the specific role of these growth factors. The overall results obtained indicate that PRP dose-dependently stimulates both chemotaxis and cell proliferation. PDGF and TGF-beta appear to exert distinct effects on the two parameters, the former involved in stimulating cell migration and the latter in inhibiting cell proliferation. It is concluded that the different growth factors present in activated PRP can specifically contribute to the main processes of tissue regeneration.

BMP signaling regulates PGC numbers and motility in organ culture

Members of the bone morphogenetic protein (BMP) family play diverse roles in multiple developmental processes. However, in the mouse, mutations in many BMPs, BMP receptors and signaling components result in early embryonic lethality making it difficult to analyze the role of these factors during organogenesis or tissue homeostasis in the adult. To bypass this early lethality, we used an organ culture system to study the role of BMPs during primordial germ cell (PGC) migration. PGCs are the embryonic precursors of the sperm and eggs. BMPs induce formation of primordial germ cells within the proximal epiblast of embryonic day 7.5 (E7.5) mouse embryos. PGCs then migrate via the gut to arrive at the developing gonads by E10.5. Addition of BMP4 or the BMP-antagonist Noggin to transverse slices dissected from E9.5 embryos elevated PGC numbers or reduced PGC numbers, respectively. Noggin treatment also slowed and randomized PGC movements, resulting in a failure of PGCs to colonize the urogenital ridges (UGRs). Based on p-Smad1/5/8 staining, migratory PGCs do not respond to endogenous BMPs. Instead, the somatic cells of the urogenital ridges exhibit elevated p-Smad1/5/8 staining revealing active BMP signaling within the UGRs. Noggin treatment abrogated p-Smad staining within the UGRs and blocked localized expression of Kitl, a cytokine known to regulate the survival and motility of PGCs and Id1, a transcription factor expressed within the UGRs. We propose that BMP signaling regulates PGC migration by controlling gene expression within the somatic cells along the migration route and within the genital ridges.

Mesenchymal progenitor cells communicate via alpha and beta integrins with a three-dimensional collagen type I matrix

BACKGROUND/AIMS

The aim of our study was to investigate interactions of mesenchymal progenitor cells (MPCs) with collagen matrices.

METHODS

Human bone-marrow-derived MPCs were cultivated in collagen type I gels with and without inhibition of beta(1)-integrin by a specific antibody. Collagen gel contraction, cell morphology, expression of integrin subunits and several genes related to matrix synthesis and turnover as well as MPC differentiation were analyzed over 14 days.

RESULTS

Human MPCs markedly contracted free-floating collagen gels. Contraction was nearly completely inhibited by blocking beta(1)-integrin. Cellular morphology was elongated in the absence and mostly round in the presence of the antibody. Expression of integrin alpha(1), alpha(2) and beta(1) subunits showed several changes partly dependent on beta(1)-integrin blocking. Expression of matrix metalloproteinase-1 was elevated irrespective of beta(1)-integrin blocking and tenascin-C was subsequently induced during gel contraction. Spontaneous induction of chondrogenic, osteogenic or adipogenic differentiation was observed neither in the presence nor in the absence of the beta(1)-integrin antibody.

CONCLUSION

Our results indicate that the interaction of human MPCs with fibrillar collagen type I involves beta(1)- and alpha-integrin subunits and induces changes in gene expression related to extracellular matrix synthesis and turnover but not differentiation to the chondrogenic, osteogenic or adipogenic phenotype.

Elevated extracellular calcium stimulates secretion of bone morphogenetic protein 2 by a macrophage cell line

It has been suggested that macrophages and multinucleated giant cells are responsible for phagocytosis of resorbable calcium phosphate (CaP) compounds implanted in bone defects. However, function of macrophages around the CaP, if continuously exposed to various concentration of extracellular calcium ions ([Ca(2+)](o)), is still unknown. The present study showed that when resorbable octacalcium phosphate was implanted in mouse calvaria, macrophage-like cells were observed around the implant during bone formation. Then, experiments were designed to investigate whether secretion of bone morphogenetic protein 2 (BMP-2) is enhanced by [Ca(2+)](o) in a macrophage cell line (J774A.1) in vitro. The mRNA expression and the secretion of BMP-2 in J774A.1 cells were significantly increased when incubated in the medium with [Ca(2+)](o) up to 14mM. The promotion of mRNA expression was maintained even when incubated with a small amount of minute CaP crystals. The present results suggest that [Ca(2+)](o) above physiological concentration may stimulate macrophages to induce osteogenic cytokine, such as BMP-2, for bone formation by osteoblast.

Comparative analysis of neuroectodermal differentiation capacity of human bone marrow stromal cells using various conversion protocols

Human adult bone marrow-derived mesodermal stromal cells (hMSCs) are able to differentiate into multiple mesodermal tissues, including bone and cartilage. There is evidence that these cells are able to break germ layer commitment and differentiate into cells expressing neuroectodermal properties. There is still debate about whether this results from cell fusion, aberrant marker gene expression or real neuroectodermal differentiation. Here we extend our work on neuroectodermal conversion of adult hMSCs in vitro by evaluating various epigenetic conversion protocols using quantitative RT-PCR and immunocytochemistry. Undifferentiated hMSCs expressed high levels of fibronectin as well as several neuroectodermal genes commonly used to characterize neural cell types, such as nestin, beta-tubulin III, and GFAP, suggesting that hMSCs retain the ability to differentiate into neuroectodermal cell types. Protocols using a direct differentiation of hMSCs into a neural phenotype failed to induce significant changes in morphology and/or expression of markers of early and mature glial/neuronal cells types. In contrast, a multistep protocol with conversion of hMSCs into a neural stem cell-like population and subsequent terminal differentiation in mature glia and neurons generated relevant morphological changes as well as significant increase of expression levels of marker genes for early and late neural cell types, such as nestin, neurogenin2, MBP, and MAP2ab, accompanied by a loss of their mesenchymal properties. Our data provide an impetus for differentiating hMSCs in vitro into mature neuroectodermal cells. Neuroectodermally converted hMSCs may therefore ultimately help in treating acute and chronic neurodegenerative diseases. Analysis of marker gene expression for characterization of neural cells derived from MSCs has to take into account that several early and late neuroectodermal genes are already expressed in undifferentiated MSCs.

Chemotactic Migration of Human Mesenchymal Stem Cells and MC3T3-E1 Osteoblast-Like Cells Induced by COS-7 Cell Line Expressing rhBMP-7

During bone development, remodeling, and repair, bone morphogenetic proteins (BMPs) induce the differentiation of mesenchymal progenitor cells (MPCs) that enter into the osteoblastic lineage, and enhance the recruitment of MPCs and osteogenic cells. The process of migration is believed to be regulated, in part, by growth factors stored within the bone matrix, which are released by bone resorption. In this study, primary human mesenchymal stem cells (hMSCs) and MC3T3-E1 osteoblasts were examined for chemotaxis in response to recombinant human BMP-7 (rhBMP-7) produced in COS-7 cells (co-culture system). In order to produce BMP-7 transfected cells (BTCs), which serve as suppliers of rhBMP-7 under in vitro culture conditions, the encoding DNA was transferred into the pTARGET expression vector and introduced into COS-7 cells by conventional genetic engineering techniques. In cell culture studies, the rhBMP-7 produced in BTCs stimulated the specific activity of ALP, the production of cAMP in response to PTH, and the synthesis of osteocalcin. Migration assays were conducted with a computer-aided time-lapse video-microscopy system, to allow the rapid and precise analysis of cell migration and for the dynamic measurement of cell position and morphology. The migration distance and speed of the MC3T3-E1 cells, or hMSCs, co-cultured with BTCs, using a band-type seeding method, were significantly increased (p < 0.001), compared to those of the MC3T3-E1 cells (or hMSCs) only. In conclusion, these studies revealed that rhBMP-7 plays a role in the migration of bone-forming cells, and that the co-culture model (co-culture of bone-forming cells with BMP-7-producing cells) using a computer-aided, time-lapse video-microscopy system, is useful for the chemotactic migration assay of other chemotactic growth factors.

Platelet releasate increases the proliferation and migration of bone marrow-derived cells cultured under osteogenic conditions

Concentrated platelets and their products are currently being used as a clinical tool to accelerate endosseous wound healing. However, there is little understanding regarding the actions of platelets and platelet-released products on osteogenic cells. We show, herein, that releasate from thrombin-activated platelets increases the migration and proliferation of osteogenic cultures of bone marrow cells. Using a scratch wound assay, we demonstrated that platelet releasate (PR) stimulated up to a 2.4 +/- 0.5-fold increase in wound closure in serum-free medium, relative to a control containing thrombin. In the presence of serum, the addition of PR resulted in a 1.45 +/- 0.13-fold increase in scratch closure. To isolate cell migration from the effects of cell proliferation, cell monolayers were pre-incubated with 5, 10 and 20 microg/ml of Mitomycin C (MMC), which is a potent inhibitor of cell proliferation. This resulted in a large decrease in the leading front of scratch closure, which indicates that PR stimulated cell mitogenesis. However, irrespective of MMC pre-treatment, PR stimulated a motogenic response. These results provide evidence of possible mechanisms by which platelets could influence bone regeneration.

IGF-I and IGF-II stimulate directed cell migration of bone-marrow-derived human mesenchymal progenitor cells

Insulin-like growth factors (IGFs) are known to be key regulators of bone growth, remodeling, and repair. Since all these processes depend on the recruitment of cells with the potential to be committed to the osteoblastic lineage, we studied possible effects of IGF-I and -II on migration of human mesenchymal progenitor cells (MPC) using a modified Boyden chamber assay. The results were compared to those of primary osteoblasts and in vitro-osteogenic-differentiated MPC. IGF-I and -II stimulated cell migration of all these cell populations in a dose-dependent manner from 1 to 100ng/mL. The maximal chemotactic index (CI) was 4-5 for MPC and primary osteoblasts and about 3 for in vitro-differentiated MPC. Checkerboard analysis revealed that IGFs stimulated true directed cell migration (chemotaxis) and not simply chemokinesis. Addition of an antibody against the type I IGF receptor (alphaIR3) completely abolished (MPC) or markedly reduced (primary osteoblasts) the chemotactic effects of each of the IGFs. IGFBP-3 itself had no direct effect, while IGFBP-5 stimulated MPC migration at concentrations of 80 and 160ng/mL. Parallel application of IGFBP-3 had borderline inhibitory effects while the addition of 40ng/mL of IGFBP-5 enhanced the chemotactic effect of IGF-I on MPC. In conclusion, our results show that IGF-I and -II are chemotactic factors for MPC and indicate that IGFBP-5 both modulates the IGF-I effect and directly stimulates migration of human mesenchymal progenitor cells.

Oncostatin M induces proliferation of human adipose tissue-derived mesenchymal stem cells

Interleukin-6 (IL-6) subfamily of cytokines, including oncostatin M (OSM), leukemia inhibitory factor (LIF), and IL-6, has been implicated in a variety of physiological responses, such as cell growth, differentiation, and inflammation. In the present study, we demonstrated that both OSM and LIF stimulated the proliferation of human adipose tissue-derived mesenchymal stem cells (hATSCs), however, IL-6 had no effect on cell proliferation. OSM treatment induced phosphorylation of ERK, and pretreatment with U0126, a MEK inhibitor, prevented the OSM-stimulated proliferation of hATSCs, suggesting that the MEK/ERK pathway is involved in the OSM-induced proliferation. Treatment with OSM also induced phosphorylation of JAK2 and JAK3, and pretreatment of the cells with WHI-P131, a JAK3 inhibitor, but not with AG490, a JAK2 inhibitor, attenuated the OSM-induced proliferation of hATSCs. Furthermore, OSM treatment elicited phosphorylation of STAT1 and STAT3, and pretreatment with WHI-P131 specifically prevented the OSM-induced phosphorylation of STAT1, without affecting the OSM-induced phosphorylation of ERK and STAT3. These results suggest that two separate signaling pathways, such as MEK/ERK and JAK3/STAT1, are independently involved in the OSM-stimulated proliferation of hATSCs.