Ex vivo enrichment of mesenchymal cell progenitors by fibroblast growth factor 2

Bone marrow stromal cells, obtained from postnatal bone marrow, contain progenitors able to differentiate into several mesenchymal lineages. Their use in gene and cell therapy requires their in vitro expansion and calls for the investigation of the culture conditions required to preserve these cells as a stem compartment with high differentiative potential during their life span. Here we report that fibroblast growth factor 2 (FGF-2)-supplemented bone marrow stromal cell primary cultures display an early increase in telomere size followed by a gradual decrease, whereas in control cultures telomere length steadily decreases with increasing population doublings. Together with clonogenic culture conditions, FGF-2 supplementation prolongs the life span of bone marrow stromal cells to more than 70 doublings and maintains their differentiation potential until 50 doublings. These results suggest that FGF-2 in vitro selects for the survival of a particular subset of cells enriched in pluripotent mesenchymal precursors and is useful in obtaining a large number of cells with preserved differentiation potential for mesenchymal tissue repair.     

A new technique to expand human mesenchymal stem cells using basement membrane extracellular matrix

Mesenchymal stem cells (MSC) show a very short proliferative life span and readily lose the differentiation potential in culture. However, the growth rate and the proliferative life span of the stem cells markedly increased using tissue culture dishes coated with a basement membrane-like extracellular matrix, which was produced by PYS-2 cells or primary endothelial cells. Furthermore, the stem cells expanded on the extracellular matrix, but not those on plastic tissue culture dishes, retained the osteogenic, chondrogenic, and adipogenic potential throughout many mitotic divisions. The extracellular matrix had greater effects on the proliferation of MSC and the maintenance of the multi-lineage differentiation potential than basic fibroblast growth factor. Mesenchymal stem cells expanded on the extracellular matrix should be useful for regeneration of large tissue defects and repeated cell therapies, which require a large number of stem or progenitor cells.     

Impaired differentiation potential of human trabecular bone mesenchymal stromal cells from elderly patients

Background aimsAdvances in bone tissue engineering with mesenchymal stromal cells (MSC) as an alternative to conventional orthopedic procedures has opened new horizons for the treatment of large bone defects. Bone marrow (BM) and trabecular bone are both sources of MSC. Regarding clinical use, we tested the potency of MSC from different sources.MethodsWe obtained MSC from 17 donors (mean age 64.6 years) by extensive washing of trabecular bone from the femoral head and trochanter, as well as BM aspirates of the iliac crest and trochanter. The starting material was evaluated by histologic analysis and assessment of colony-forming unit–fibroblasts (CFU-F). The MSC populations were compared for proliferation and differentiation potential, at RNA and morphologic levels.ResultsMSC proliferation potential and immunophenotype (expression of CD49a, CD73, CD90, CD105, CD146 and Stro-1) were similar whatever the starting material. However, the differentiation potential of MSC obtained by bone washing was impaired compared with aspiration; culture-amplified cells showed few Oil Red O-positive adipocytes and few mineralized areas and formed inconsistent Alcian blue-positive high-density micropellets after growth under adipogenic, osteogenic and chondrogenic conditions, respectively. MSC cultured with 1 ng/mL fibroblast growth factor 2 (FGF-2) showed better differentiation potential.ConclusionsTrabecular bone MSC from elderly patients is not good starting material for use in cell therapy for bone repair and regeneration, unless cultured in the presence of FGF-2.     

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.     

Proteomic analysis of the impact of static culturing on the expansion of rat bone marrow mesenchymal stem cells

The clinical potential of mesenchymal stem cells (MSC) in tissue engineering and regenerative medicine is due to their self-renewal, proliferation and multi-lineage differentiation potential. Clinical use requires large cell numbers; which can, theoretically, be generated by ex vivo expansion of plastic adherent, MSC subpopulation, of bone marrow cells (BMC). Effects of serial culture on MSC phenotype were investigated using non-gel based quantitative proteomic methodology for static monolayer cultures of rat BMC. In total, 382 proteins were relatively quantified (≥ 2 peptides). Nine proteins were up-regulated and seven down-regulated at passage 4 relative to passage 2 (p ≤ 0.05). We propose that serial culture impacts on MSC expansion (observed decline in colony forming potential and colony size) is through a combination of osteogenic differentiation and ageing/senescence and propose six novel protein biomarkers as candidates for quality control purposes in bioprocessing.     

FGF-2对人骨髓间充质干细胞增殖和向成骨细胞分化的影响

探讨体外培养条件下,成纤维细胞生长因子-2（FGF-2）和地塞米松（Dex）对第7代人骨髓间充质干细胞（MSCs）增殖和向成骨细胞分化的作用以及两者联合使用的效应。MSCs经含FGF-2或／和Dex的培养液作用后,于不同时间采用MTT法测定细胞增殖情况;对硝基苯磷酸（pNPP）法测定碱性磷酸酶（ALP）活性;ELISA法测定骨钙蛋白（OC）含量;茜素红S染色法对沉积的钙盐进行染色。发现：（1）FGF-2组细胞的生长速度为对照组的1．31倍,Dex／FGF-2组细胞的生长速度为FGF-2组的1．12倍。（2）Dex组的ALP活性、OC含量和细胞外基质钙盐沉积分别为对照组的17．0倍、2．12倍和10．56倍,并能形成成熟的羟基磷灰石（HA）结晶和骨结节;FGF-2组的ALP活性比对照组降低了76．7％,虽然OC含量、钙盐沉积增加,但不能形成成熟的HA结晶和骨结节;FGF-2对Dex诱导的ALP活性增加和HA结晶形成有拮抗作用。由此证明：（1）FGF-2可促进MSCs的增殖,Dex对MSCs的增殖无明显作用;Dex能增强FGF-2对MSCs的促增殖效应。（2）Dex可使MSCs分化为成熟的成骨细胞,是一个有效的成骨细胞分化诱导剂;FGF-2可使MSCs分化为未成熟的成骨细胞;FGF-2拮抗Dex诱导MSCs分化为成熟的成骨细胞。     

The role of growth factors in maintenance of stemness in bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are an active topic of research in regenerative medicine due to their ability to secrete a variety of growth factors and cytokines that promote healing of damaged tissues and organs. In addition, these secreted growth factors and cytokines have been shown to exert an autocrine effect by regulating MSC proliferation and differentiation. We found that expression of EGF, FGF-4 and HGF were down-regulated during serial passage of bone marrow-derived mesenchymal stem cells (BMSCs). Proliferation and differentiation potentials of BMSCs treated with these growth factors for 2 months were evaluated and compared to BMSCs treated with FGF-2, which increased proliferation of BMSCs. FGF-2 and -4 increased proliferation potentials at high levels, about 76- and 26-fold, respectively, for 2 months, while EGF and HGF increased proliferation of BMSCs by less than 2.8-fold. Interestingly, differentiation potential, especially adipogenesis, was maintained only by HGF treatment. Treatment with FGF-2 rapidly induced activation of AKT and later induced ERK activation. The basal level of phosphorylated ERK increased during serial passage of BMSCs treated with FGF-2. The expression of LC3-II, an autophagy marker, was gradually increased and the population of senescent cells was increased dramatically at passage 7 in non-treated controls. But FGF-2 and FGF-4 suppressed LC3-II expression and down-regulated senescent cells during long-term (i.e. 2 month) cultures. Taken together, depletion of growth factors during serial passage could induce autophagy, senescence and down-regulation of stemness (proliferation via FGF-2/-4 and differentiation via HGF) through suppression of AKT and ERK signaling.     

Modulating osteogenesis of mesenchymal stem cells by modifying growth factor availability

Growth factors control the proliferation and differentiation of osteoprogenitor cells. This study explores the effects of modulating growth factors (VEGF, IGF-1, FGF-2 and BMP-2) on osteogenesis of mesenchymal stem cells (MSCs) in vitro. Constant and profiled delivery protocols, in accordance with protein expression in vitro, were applied to deliver or neutralize growth factors. Cell number, alkaline phosphatase (ALP-2) and osteocalcin (OC) expression, and mineralization were measured as outcome variables. Profiled addition of VEGF increased MSC proliferation. Constant and profiled application of FGF-2 and neutralization of IGF-1 and BMP-2 decreased ALP-2 levels. Profiled addition of BMP-2 vastly increased OC release from MSCs, but constant addition of IGF-1, constant and profiled neutralization of IGF-1 and FGF-2 reduced OC levels. Constant addition of IGF-1 and FGF-2, as well as profiled loading of FGF-2 decreased mineralization of MSCs. This study indicated that endogenous IGF-1 and FGF-2 are essential to osteogenesis; excess IGF-1 and FGF-2 were inhibitory to bone formation. Selective, temporally specific addition of growth factors, such as BMP-2 and VEGF appears to be an important strategy to enhance osteogenesis.     

In vitro effects of RU486 on proliferation and differentiation capabilities of human bone marrow mesenchymal stromal cells

Although exogenous glucocorticoids (GC) play a role in the regulation of bone marrow mesenchymal stem/stromal cells (MSCs) proliferation and differentiation, the function of endogenous GC is not well understood. The purpose of this study was to investigate the effect of the blockage of endogenous GC using RU486, an antagonist of the glucocorticoid receptor, on the in vitro proliferation and differentiation capabilities of human MSCs. We quantitatively measured cell proliferation of human MSCs after treatment with increasing concentrations of RU486. We also evaluated multiple MSC differentiation capabilities, as well as the expression of stemness and senescence genes after proliferation of these human cells in vitro in the presence of RU486 at 10(-8)M. It was observed that RU486 treatment significantly increases the proliferation of human MSCs, although the optimal dose of RU486 for this increase in proliferation differs depending on the gender of the MSC donor. This improvement in MSC proliferation with RU486 treatment was higher in MSCs from male donors than that from females. No effect of RU486 on MSC proliferation was observed in a steroid-free medium. RU486 pretreatment significantly increased the expression of mRNA for alkaline phosphatase in human MSCs and the mRNA expression of osteocalcin of these cells up-regulated earlier after their exposure to osteogenic differentiation medium. Although no statistical significance in terms of chondrogenic differentiation markers was detected, mRNA expression for aggrecan and collagen type 2 were higher in a majority of the RU486-pretreated donor MSCs than their untreated controls. No significant difference in terms of MSC adipogenic differentiation capabilities were observed after RU486 treatment. RU486 treatment up-regulated the expressions of FGF-2 and Sox-11 in human MSCs. These results indicate that blockage of endogenous GCs may be developed as a novel approach to effectively improve the proliferation and osteochondral differentiation capabilities of human MSCs for potential clinical applications. Additional studies will be required to determine the potential long-term effects of RU486 treatment on these bone marrow cells.     

3D mesenchymal stem/stromal cell osteogenesis and autocrine signalling

Mesenchymal stem/stromal cells (MSC) are rapidly becoming a leading candidate for use in tissue regeneration, with first generation of therapies being approved for use in orthopaedic repair applications. Capturing the full potential of MSC will likely require the development of novel in vitro culture techniques and devices. Herein we describe the development of a straightforward surface modification of an existing commercial product to enable the efficient study of three dimensional (3D) human bone marrow-derived MSC osteogenic differentiation. Hundreds of 3D microaggregates, of either 42 or 168 cells each, were cultured in osteogenic induction medium and their differentiation was compared with that occurring in traditional two dimensional (2D) monolayer cultures. Osteogenic gene expression and matrix composition was significantly enhanced in the 3D microaggregate cultures. Additionally, BMP-2 gene expression was significantly up-regulated in 3D cultures at day 3 and 7 by approximately 25- and 30-fold, respectively. The difference in BMP-2 gene expression between 2D and 3D cultures was negligible in the more mature day 14 osteogenic cultures. These data support the notion that BMP-2 autocrine signalling is up-regulated in 3D MSC cultures, enhancing osteogenic differentiation. This study provides both mechanistic insight into MSC differentiation, as well as a platform for the efficient generation of microtissue units for further investigation or use in tissue engineering applications.     

Tomorrow's skeleton staff: mesenchymal stem cells and the repair of bone and cartilage

Stem cells are regenerating medicine. Advances in stem cell biology, and bone marrow-derived mesenchymal stem cells in particular, are demonstrating that many clinical options once thought to be science fiction may be attainable as fact. The extra- and intra-cellular signalling used by stem cells as they differentiate into lineages appropriate to their destination are becoming understood. Thus, the growth stimuli afforded by LIF, FGF-2 and HGF, as well as the complementary roles of Wnt and Dickkopf-1 in stem cell proliferation are evident. The ability to direct multi-lineage mesenchymal stem sell (MSC) potential towards an osteogenic phenotype by stimulation with Menin and Shh are important, as are the modulatory roles of Notch-1 and PPARgamma. Control of chondrocytic differentiation is effected by interplay of Brachyury, BMP-4 and TGFbeta3. Smads 1, 4 and 5 also play a role in these phenotypic expressions. The ability to culture MSC has led to their use in tissue repair, both as precursor and differentiated cell substitutes, and with successful animal models of bone and cartilage repair using MSC, their clinical use is accelerating. However, MSC also suppress some T-cell functions in transplanted hosts, and could facilitate tumour growth, so a cautious approach is needed.     

Glycosaminoglycans mimetics potentiate the clonogenicity, proliferation, migration and differentiation properties of rat mesenchymal stem cells

Successful use of stem cell-based therapeutic products is conditioned by transplantation of optimized cells in permissive microenvironment. Mesenchymal stem cell (MSC) fates are tightly regulated by humoral factors, cellular interactions and extracellular matrix (ECM) components, such as glycosaminoglycans (GAG), which are complex polysaccharides with structural heterogeneity. During osteogenesis, a temporally controlled expression of particular GAG species is required to interact with specific growth promoting and differentiating factors to regulate their biological activities. As a comparative tool to study natural GAG, we used structurally and functionally related synthetic GAG mimetics. One of these compounds [OTR₄₁₂₀] was previously shown to stimulate bone repair in rat models. Here, we demonstrate that structurally distinct GAG mimetics stimulate differentially clonogenicity, proliferation, migration and osteogenic phenotype of MSC in vitro, according to their specific chemical signature, underlying the role of sulfate and acetyl groups in specific interactions with heparin binding factors (HBF). These effects are dependent on FGF-2 interactions since they are inhibited by a FGF receptor 1 signaling pathway blocker. These data suggest that the in vivo [OTR₄₁₂₀] bone regenerative effect could be due to its ability to induce MSC migration and osteogenic differentiation. To conclude, we provide evidences showing that GAG mimetics may have great interest for bone regeneration therapy and represent an alternative to exogenous growth factor treatments to optimize potential therapeutic properties of MSC.     

Repair of injured articular and growth plate cartilage using mesenchymal stem cells and chondrogenic gene therapy

Injuries to the articular cartilage and growth plate are significant clinical problems due to their limited ability to regenerate themselves. Despite progress in orthopedic surgery and some success in development of chondrocyte transplantation treatment and in early tissue-engineering work, cartilage regeneration using a biological approach still remains a great challenge. In the last 15 years, researchers have made significant advances and tremendous progress in exploring the potentials of mesenchymal stem cells (MSCs) in cartilage repair. These include (a) identifying readily available sources of and devising appropriate techniques for isolation and culture expansion of MSCs that have good chondrogenic differentiation capability, (b) discovering appropriate growth factors (such as TGF-beta, IGF-I, BMPs, and FGF-2) that promote MSC chondrogenic differentiation, (c) identifying or engineering biological or artificial matrix scaffolds as carriers for MSCs and growth factors for their transplantation and defect filling. In addition, representing another new perspective for cartilage repair is the successful demonstration of gene therapy with chondrogenic growth factors or inflammatory inhibitors (either individually or in combination), either directly to the cartilage tissue or mediated through transducing and transplanting cultured chondrocytes, MSCs or other mesenchymal cells. However, despite these rapid pre-clinical advances and some success in engineering cartilage-like tissue and in repairing articular and growth plate cartilage, challenges of their clinical translation remain. To achieve clinical effectiveness, safety, and practicality of using MSCs for cartilage repair, one critical investigation will be to examine the optimal combination of MSC sources, growth factor cocktails, and supporting carrier matrixes. As more insights are acquired into the critical factors regulating MSC migration, proliferation and chondrogenic differentiation both ex vivo and in vivo, it will be possible clinically to orchestrate desirable repair of injured articular and growth plate cartilage, either by transplanting ex vivo expanded MSCs or MSCs with genetic modifications, or by mobilising endogenous MSCs from adjacent source tissues such as synovium, bone marrow, or trabecular bone.     

Inhibition of platelet-derived growth factor receptorbeta by imatinib mesylate suppresses proliferation and alters differentiation of human mesenchymal stem cells in vitro

OBJECTIVES: Recent data show that Imatinib mesylate (IM) also affects haematopoietic stem cells (HSC), T lymphocytes and dendritic cells that do not harbour constitutively active tyrosine kinases. MATERIALS AND METHODS: We evaluated possible effects of IM on human bone marrow-derived mesenchymal stem cells (MSC) in vitro. RESULTS: Screening the activity of 42 receptor tyrosine kinases revealed an exclusive inhibition of platelet-derived growth factor receptorbeta (PDGFRbeta). Analysis of downstream targets of PDGFRbeta demonstrated IM-mediated reduction of Akt and Erk1/2 phosphorylation. Culture of MSC with IM led to the reversible development of perinuclear multi-vesicular bodies. The proliferation and clonogenicity of MSC were significantly reduced compared to control cultures. IM favoured adipogenic differentiation of MSC whereas osteogenesis was suppressed. The functional deficits described led to a 50% reduction in the support of clonogenic haematopoietic stem cells, cultured for 1 month on a monolayer of MSC with IM. CONCLUSION: In summary, inhibition of PDGFRbeta and downstream Akt and Erk signalling by IM has a significant impact on proliferation and differentiation of human MSC in vitro.     

Effect of different growth factors on human osteoblasts activities: a possible application in bone regeneration for tissue engineering

Cultured human primary osteoblasts reproduce the phenotypic differentiation and maturation of cells in vivo. We have investigated the influence of three isoforms of transforming growth factor beta (TGF-beta1, TGF-beta2 and TGF-beta3), three fibroblast growth factors (FGF-2, FGF-4 and FGF-6) and the active metabolite of Vitamin D [1,25-(OH)(2)D3] on proliferation, alkaline phosphatase activity and mineralization of human osteoblasts during a period of 24 days of culture. TGF-beta isoforms and three FGFs examined have been proved to be inducers of osteoblasts proliferation (higher extent for TGF-beta and FGF-2) and inhibitors of alkaline phosphatase activity and osteoblasts mineralization. Combination of these growth factors with the active form of Vitamin D induced osteodifferentiation. In fact Vitamin D showed an additive effect on alkaline phosphatase activity and calcium content, induced by FGF-2 and TGF-beta in human osteoblast. These results highlight the potential of proliferating cytokines' combination with mineralizing agents for in vitro bone growth induction in bone tissue engineering.     

Impact of oxygen environment on mesenchymal stem cell expansion and chondrogenic differentiation

Introduction:  In vitro expansion and differentiation of mesenchymal stem cells (MSC) rely on specific environmental conditions, and investigations have demonstrated that one crucial factor is oxygen environment.
Objectives:  In order to understand the impact of oxygen tension on MSC culture and chondrogenic differentiation in vitro , we developed a mathematical model of these processes and applied it in predicting optimal assays.
Methods and results:  We compared ovine MSCs under physiologically low and atmospheric oxygen tension. Low oxygen tension improved their in vitro population growth as demonstrated by monoclonal expansion and colony forming assays. Moreover, it accelerated induction of the chondrogenic phenotype in subsequent three-dimensional differentiation cultures. We introduced a hybrid stochastic multiscale model of MSC organization in vitro . The model assumes that cell adaptation to non-physiological high oxygen tension reversibly changes the structure of MSC populations with respect to differentiation. In simulation series, we demonstrated that these changes profoundly affect chondrogenic potential of the populations. Our mathematical model provides a consistent explanation of our experimental findings.
Conclusions:  Our approach provides new insights into organization of MSC populations in vitro. The results suggest that MSC differentiation is largely reversible and that lineage plasticity is restricted to stem cells and early progenitors. The model predicts a significant impact of short-term low oxygen treatment on MSC differentiation and optimal chondrogenic differentiation at 10–11% pO₂.