pcDNA3.1(+)-CTGF真核表达质粒构建及其在人成骨样细胞SaOS-2细胞中的表达*

目的:构建结缔组织生长因子(CTGF)的pcDNA3.1(+)真核表达质粒(pcDNA3.1(+)-CTGF),并检测其在人成骨样细胞SaOS-2中的表达,为进一步研究CTGF基因在骨发育和骨修复中的机制提供技术支撑。方法:采用PCR方法体外克隆CTGF基因全序列,将其用同源重组技术连接到线性pcDNA3.1(+)载体上,构建pcDNA3.1(+)-CTGF真核表达质粒,并对该质粒进行测序鉴定;鉴定无误后转染至SaOS-2细胞中,观察其48 h的表达情况。结果:基因测序证实pcDNA3.1(+)-CTGF真核表达重组质粒构建成功,与对照组相比,转染SaOS-2细胞48 h后的CTGF表达水平显著上调,达到对照组的4.8×10⁵倍(P＜0.01)。结论:成功构建了pcDNA3.1(+)-CTGF真核表达质粒,并能在人成骨样细胞SaOS-2中稳定表达,为深入研究CTGF基因对骨生成的调控机制奠定了基础。     

Calcium from LactoCalcium milk mineral after digestion with pepsin stimulates mineralized bone nodule formation in human osteoblast-like SaOS-2 cells in vitro and may be rendered bioavailable in vivo

Many individuals cannot obtain the optimum calcium requirement from food for a variety of reasons. Therefore, calcium supplements are important sources of dietary calcium. One of the calcium sources commercially available is LactoCalcium (milk minerals) that has 28% calcium, and a 2:1 ratio of calcium to phosphorus. The objectives of this study were (a) to examine whether calcium can be released from LactoCalcium by using digestive enzymes and (b) to determine its biological activity by examining its ability to stimulate bone formation. LactoCalcium was treated in vitro by using simulated gastric and intestinal fluids or porcine gastric, pancreatic and intestinal extracts. Our results indicate the role of enzymes or bile extract in the digestion of the product. We show that, by increasing the concentration of pepsin at a fixed concentration of LactoCalcium (substrate), the percentage of released calcium increased in a dose-dependent manner, showing that, at the right enzyme concentration, as much as 100% of the calcium present in LactoCalcium can be made available. The biological activity of the digested calcium was demonstrated by the stimulation of mineralized bone nodules in SaOS-2 cells in a dose-dependent manner. Thus, 1 mM and 3 mM calcium released from LactoCalcium increased the nodule area by 23.17 mm(2) (p<0.0001) and 77.78 mm(2) (p<0.0001), respectively, as compared to a value of 0.99 mm(2) at 0.5 mM calcium from LactoCalcium. These results demonstrate the in vitro bioavailability and bioactivity of calcium from LactoCalcium and serve as a basis for carrying out in vivo analyses to determine the suitability of using LactoCalcium as a source of calcium for individuals at risk of developing osteoporosis.     

Interactions between cells and titanium surfaces

The interaction between cells and implant materials is determined by the surface structure and/or surface composition of the material. In the past years, titanium and titanium alloys have proved their superiority over other implant materials in many clinical applications. This predominant behaviour is caused by a dense passive oxide layer which forms within milliseconds in oxidizing media. Titanium dioxide layers of 100 nm thickness were produced on the surface of cp-titanium grade 2, and on an experimental alloy of high vanadium content (Ti1.5Al25V) as a harmful control. The layers were produced by thermal and anodic oxidation and by coating by means of the sol-gel process. The resulting oxide layers were characterized with respect of their structure and chemical composition. In cell tests (proliferation, MTT, morphology, actin staining), the reaction of the cells was examined. It was shown that the sol-gel-produced titanium oxide layer is able to shield the cells from toxic alloying elements, with the result that the cell reaction is influenced only by the thin titanium oxide surface layer and not by the composition of the bulk material.     

Engineering micropatterned surfaces to modulate the function of vascular stem cells

Multipotent vascular stem cells have been implicated in vascular disease and in tissue remodeling post therapeutic intervention. Hyper-proliferation and calcified extracellular matrix deposition of VSC cause blood vessel narrowing and plaque hardening thereby increasing the risk of myocardial infarct. In this study, to optimize the surface design of vascular implants, we determined whether micropatterned polymer surfaces can modulate VSC differentiation and calcified matrix deposition. Undifferentiated rat VSC were cultured on microgrooved surfaces of varied groove widths, and on micropost surfaces. 10 μm microgrooved surfaces elongated VSC and decreased cell proliferation. However, microgrooved surfaces did not attenuate calcified extracellular matrix deposition by VSC cultured in osteogenic media conditions. In contrast, VSC cultured on micropost surfaces assumed a dendritic morphology, were significantly less proliferative, and deposited minimal calcified extracellular matrix. These results have significant implications for optimizing the design of cardiovascular implant surfaces.     

Effects of zinc on the mineralization of bone nodules from human osteoblast-like cells

Zinc is an important mineral that is required for normal bone development. However, the direct effects of zinc on the mineralization of bone cells of human origin are not clear. The objective of this study was to determine the effects of zinc on the differentiation of SaOS-2 human osteoblast-like cells and the formation of mineralized bone nodules. Cells were cultured for 8 d and then transferred to zinc-free medium and treated with varying concentrations (0–50 μM) of zinc. Alkaline phosphatase (ALP) activity was used as a measure of osteoblast differentiation, and bone nodules were detected by von Kossa staining. After 4, 6, and 8 d of treatment, zinc increased ALP activity at 1 and 10 μM, but decreased activity at 50 μM. After 9 d of treatment, zinc increased both the number and area of mineralized bone nodules at low concentrations (1 and 10 μM), but decreased both at higher concentrations (25 and 50 μM). These findings demonstrate that zinc has biphasic effects on the differentiation and mineralization of human osteoblast-like cells.     

Separation of osteoblast-like cells from bone marrow by fluorescence-activated cell sorting

The purification of the osteoblast-like cells (2-3%) among the bone marrow cells (BMC) of C57BL/6 mice using a specific anti-osteoblast serum and a fluorescence-activated cell sorter is described. The antiserum was raised against osteoblast cells isolated from calvaria from neonatal mice. The majority of the cells of the osteoblast-enriched fraction from bone marrow showed a parathormone-induced increase in cyclic adenine monophosphate but no response to calcitonin. This is similar to the response of osteoblast cells obtained from the calvaria. Electron microscopic studies of the extracellular matrix of cultured osteoblast-like cells purified from bone marrow showed the deposition of apatite crystals within and in close apposition to the vesicles. These findings suggest that the isolated cell population was enriched in osteoblasts. Such a cell system from bone marrow might provide an experimental system for investigating the mechanism of bone formation.     

Inflammatory microcrystals alter the functional phenotype of human osteoblast-like cells in vitro: synergism with IL-1 to overexpress cyclooxygenase-2

Chronic crystal-associated arthropathies such as gout and pseudogout can lead to local bone destruction. Because osteoblasts, which orchestrate bone remodeling via soluble factors and cell-to-cell interactions, have been described in contact with microcrystals, particularly in uratic foci of gout, we hypothesized that microcrystals of monosodium urate monohydrate (MSUM) and of calcium pyrophosphate dihydrate (CPPD) could alter osteoblastic functions. MSUM and CPPD adhered to human osteoblastic cells (hOB) in vitro and were partly phagocytized as shown by scanning electron microscopy. MSUM and CPPD dose-dependently stimulated the production of PGE(2) in hOB as assessed by enzyme immunoassay, a response that was synergistically enhanced in the presence of IL-1. The mechanism of this synergism was, at least in part, at the level of the expression of cyclooxygenase-2 as evaluated by immunoblot analysis. MSUM and CPPD also stimulated the expression of IL-6 and IL-8 and reduced the 1,25-dihydroxyvitamin D(3)-induced activity of alkaline phosphatase and osteocalcin in hOB (with no synergism with IL-1). MSUM- or CPPD-stimulated expression of IL-6 in hOB pretreated with the selective cyclooxygenase-2 inhibitor NS-398 was increased, unlike that induced by IL-1 alone which was partially reduced. MSUM-, CPPD- or IL-1-induced expression of IL-8 was unchanged by pretreating hOB with NS-398. These results suggest that inflammatory microcrystals alter the normal phenotype of hOB, redirecting them toward reduced bone formation and amplified osteoblast-mediated bone resorption, abnormalities that could play a role in the bone destruction associated with chronic crystal-induced arthritis.     

Different protein kinase C isozymes could modulate bradykinin-induced extracellular calcium-dependent and -independent increases in osteoblast-like MC3T3-E1 cells.

Effects of protein kinase C (PKC) on bradykinin (BK)-induced intracellular calcium mobilization, consisting of rapid Ca2+ release from internal stores and a subsequent sustained Ca2+ inflow, were examined in Fura-2-loaded osteoblast-like MC3T3-E1 cells. The sustained Ca2+ inflow as inferred with Mn2+ quench method was blocked by Ni2+ and a receptor-operated Ca2+ channel blocker SK&F 96365, but not by nifedipine. The short-term pretreatment with phorbol 12-myristate 13-acetate (PMA), inhibited BK-stimulated Ca2+ inflow, and the prior treatment with PKC inhibitors, H-7 or staurosporine, enhanced the initial internal release and reversed the PMA effect. Moreover, 6 h pretreatment with PMA caused similar effect on the BK-induced inflow to that obtained with PKC inhibitors, whereas 24 h pretreatment was necessary to affect the internal release. On the other hand, the translocation and down-regulation of PKC isozymes were examined after PMA treatment of MC3T3-E1 cells by immunoblot analyses of PKCs with the isozyme-specific antibodies. 6 h treatment with PMA induced down-regulation of PKC beta, whereas longer treatment was needed for down-regulation of PKC alpha. Taken together, it was suggested that the BK-induced initial Ca2+ peak and the sustained Ca2+ inflow through the activation of a receptor-operated Ca2+ channel, are differentially regulated by PKC isozymes alpha and beta, respectively, in osteoblast-like MC3T3-E1 cells.     

The effects of pulsed electromagnetic fields on the cellular activity of SaOS-2 cells

Although pulsed electromagnetic fields (PEMFs) have been used for treatments of nonunion bone fracture healing for more than three decades, the underlying cellular mechanism of bone formation promoted by PEMFs is still unclear. It has been observed that a series of parameters such as pulse shape and frequency should be carefully controlled to achieve effective treatments. In this article, the effects of PEMFs with repetitive pulse burst waveform on the cellular activity of SaOS-2 osteoblast-like cells were investigated. In particular, cell proliferation and mineralization due to the imposed PEMFs were assessed through direct cell counts, the MTT assay, tissue nonspecific alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining. PEMF stimulation with repetitive pulse burst waveform did not affect metabolic activity and cell number. However, the ALP activity of SaOS-2 cells and mineral nodule formation increased significantly after PEMF stimulation. These observations suggest that repetitive pulse burst PEMF does not affect cellular metabolism; however, it may play a role in the enhancement of SaOS-2 cell mineralization. We are currently investigating cellular responses under different PEMF waveforms and Western blots for protein expression of bone mineralization specific proteins.     

Hepatic stellate cells modulate the differentiation of bone marrow mesenchymal stem cells into hepatocyte-like cells

Differentiation of stem cells is tightly regulated by the microenvironment which is mainly composed of nonparenchymal cells. Herein, we investigated effect of hepatic stellate cells (HSCs) in different states on mesenchymal stem cells (MSCs) differentiation. Rat HSCs were isolated and stayed quiescent within 5 days. Primary HSCs were activated by being in vitro cultured for 7 days or cocultured with Kupffer cells for 5 days. MSCs were cocultured with HSCs of different states. Expression of hepatic lineage markers was analyzed by RT-PCR and immunofluorescence. Glycogen deposition was detected by periodic acid-schiff staining. MSCs cocultured with HSC-T6 or Kupffer cell activated HSCs were morphologically transformed into hepatocyte-like cells. Hepatic-specific marker albumin was expressed in 78.3% of the differentiated MSCs 2 weeks after initiation of coculture. In addition, the differentiated MSCs also expressed alpha-fetoprotein, cytokeratin-18, glutamine synthetase and phosphoenolpyruvate carboxykinase. Glycogen deposition was detectable in 55.4% of the differentiated MSCs 6 weeks after initiation of coculture. However, the quiescent HSCs or culture activated HSCs did not exert the ability to modulate the differentiation of MSCs. Moreover, Kupffer cell activated HSCs rather than culture activated HSCs expressed hepatocyte growth factor mRNA. We draw the conclusion that fully activated HSCs could modulate MSCs differentiation into hepatocyte-like cells.     

Hepatocyte growth factor and other fibroblast secretions modulate the phenotype of human bronchial epithelial cells

The luminal airway surface is lined with epithelial cells that provide a protective barrier from the external environment and clear inhaled pathogens from the lung. To accomplish this important function, human bronchial epithelial (HBE) cells must be able to rapidly regenerate a mucociliary layer of cells following epithelial injury. Whereas epithelial-fibroblast interactions are known to modulate the airway architecture during lung development and repair, little is known about how these two cells interact. Using a primary HBE and lung fibroblast coculture system, we demonstrate that 1) subepithelial fibroblasts provide a suitable environment for differentiation of HBE cells into a polarized ciliated phenotype despite being cultured in media that induces terminal squamous differentiation and growth arrest in the absence of fibroblasts, 2) HBE cells cocultured with subepithelial fibroblasts exhibit augmented ciliogenesis, accelerated wound repair, and diminished polarized ion transport compared with cells grown in control conditions, and 3) hepatocyte growth factor (HGF) is important for subepithelial fibroblast modulation of HBE cell differentiation. These results provide a model to study fibroblast modulation of epithelial phenotype and indicate that HGF secreted by subepithelial fibroblasts contributes to HBE cell differentiation.     

Modulation of phenotype and cytoskeleton architecture by interleukin-1 alpha in human osteoblast-like cells in vitro.

Interleukin-1 alpha, a growth factor produced by macrophages as well as many other types of cells, is able to modulate biosynthetic activities in bone cells. In this work, the authors show that the administration of interleukin-1 alpha to osteoblast-like cells in vitro induces a marked change in cell morphology, which becomes dendritic, with a smaller cellular body and numerous prolongations. The morphological changes are also accompanied by an altered expression in the pattern of cytoskeleton proteins.     

Effect of TNF-alpha on human osteosarcoma cell line Saos2--TNF-alpha regulation of bone sialoprotein gene expression in Saos2 osteoblast-like cells

Tumor necrosis factor-alpha (TNF-alpha) is a major mediator of inflammatory response in many diseases. It inhibits bone formation and stimulates bone resorption. To determine the molecular mechanisms involved in the regulation of gene expression of osteoblast-like cells, we analyzed the effects of TNF-alpha on the human osteosarcoma cell line Saos2. We used RT-PCR to examine the effects of TNF-alpha on bone sialoprotein (BSP), core binding factor a1 (Cbfa1), osterix, alpha 1 (I) collagen, cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), cathepsin B, cathepsin L and tissue inhibitors of metalloproteinase-1 (TIMP-1). TNF-alpha (10ng/ml) increased BSP, IL-6 and COX-2 mRNA levels after 3h, reaching maximal levels at 12 h. Cbfa1 mRNA levels increased after 3 h, but decreased by 24 h. Osterix, cathepsin B, cathepsin L and TIMP-1 mRNA levels did not change after stimulation with TNF-alpha. On the other hand, alpha 1 (I) collagen mRNA expression was suppressed by TNF-alpha at 24 h. Transient transfection analyses were performed using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene. TNF-alpha (10 ng/ml) had no effect on the promoter activities of BSP transfected into Saos2 cells. The results of gel mobility shift assays using radiolabeled double-stranded cAMP response element (CRE) and FGF2 response element (FRE) oligonucleotides in the proximal promoter of the rat BSP gene showed increased binding of nuclear proteins at 6 h. Gel mobility shift assays with radiolabelled COX-2-CRE and COX-2-NF kappa B oligonucleotides revealed an increase in the binding of nuclear proteins from TNF-alpha-stimulated Saos2 cells. These studies, therefore, showed that TNF-alpha indirectly increased BSP expression, and that it could be mediated through COX-2 and Cbfa1 expression in Saos2 osteoblast-like cells.     

In vitro assays for adhesion and migration of osteoblastic cells (Saos-2) on titanium surfaces

The first event occurring at the boundary between a metal implant and living tissue is the attachment of cells onto the metal surface of the implant. The attachment characteristics of the metal in this situation are critical in determining its biocompatibility and usefulness as artificial bone and tooth implants. Using the human osteosarcoma cell line Saos-2, we attempted to establish simple and reliable methods for evaluating the attachment of cultured osteoblastic cells onto titanium samples that had been subjected to various surface treatments. Fluorescence actin imaging showed that cells cultured on titanium with hydrofluoric acid etching (HF-Ti) exhibited delayed spreading of their cytoplasm, as compared to cells cultured for the same length of time on nitrided titanium or physically polished titanium. The HF-Ti-cultured cells also exhibited poor assembly of focal contacts, as visualized by vinculin immunofluorescence. Furthermore, in motility assays based on an in vitro wound model, cells cultured on HF-Ti migrated more slowly than cells cultured on other titanium surfaces. These data suggest that Saos-2 cells attach less effectively to the HF-Ti surface. The methods described in this study should be useful for assessing the initial interactions of cultured cells with various materials, including metals.S.G. is the recipient of a grant awarded to foreign students by the government of Japan. This study was supported by the Integrated Center for Science (INCS) at Ehime University.     

Topographical cues of direct metal laser sintering titanium surfaces facilitate osteogenic differentiation of bone marrow mesenchymal stem cells through epigenetic regulation

Objectives

To investigate the role of hierarchical micro/nanoscale topography of direct metal laser sintering (DMLS) titanium surfaces in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), as well as the possible underlying epigenetic mechanism.

Materials and methods

Three groups of titanium specimens were prepared, including DMLS group, sandblasted, large‐grit, acid‐etched (SLA) group and smooth titanium (Ti) group. BMSCs were cultured on discs followed by surface characterization. Cell adhesion and proliferation were examined by SEM and CCK‐8 assay, while osteogenic‐related gene expression was detected by real‐time RT‐PCR. Immunofluorescence, western blotting and in vivo study were also performed to evaluate the potential for osteogenic induction of materials. In addition, to investigate the underlying epigenetic mechanisms, immunofluorescence and western blotting were performed to evaluate the global level of H3K4me3 during osteogenesis. The H3K4me3 and H3K27me3 levels at the promoter area of the osteogenic gene Runx2 were detected by ChIP assay.

Results

The DMLS surface exhibits greater protein adsorption ability and shows better cell adhesion performance than SLA and Ti surfaces. Moreover, both in vitro and in vivo studies demonstrated that the DMLS surface is more favourable for the osteogenic differentiation of BMSCs than SLA and Ti surfaces. Accordingly, osteogenesis‐associated gene expression in BMSCs is efficiently induced by a rapid H3K27 demethylation and increase in H3K4me3 levels at gene promoters upon osteogenic differentiation on DMLS titanium surface.

Conclusions

Topographical cues of DMLS surfaces have greater potential for the induction of osteogenic differentiation of BMSCs than SLA and Ti surfaces both in vitro and in vivo. A potential epigenetic mechanism is that the appropriate topography allows rapid H3K27 demethylation and an increased H3K4me3 level at the promoter region of osteogenesis‐associated genes during the osteogenic differentiation of BMSCs.

     

Human mature endothelial cells modulate peripheral blood mononuclear cell differentiation toward an endothelial phenotype

Circulating endothelial progenitor cells (EPCs) can contribute to neovascularization, even if the mechanisms by which they interact with mature endothelial cells remain unclear. The interactions between human coronary artery endothelial cells (HCAECs) and peripheral blood mononuclear cells (PBMCs) during their early differentiation towards an EPC phenotype were investigated. A co-culture model, in which the two cell types share the same culture medium in the absence of any exogenous angiogenic stimulus, was used. The role of hypoxia was assessed by pretreating HCAECs with 3% O₂ before co-culture setting. Since we have previously shown that both adherent and suspended PBMCs display a significant increase in endothelial marker expression within the 2nd day of culture in an angiogenic environment, the role of HCAECs on early PBMC differentiation was evaluated in both adherent and suspended cell fractions.A 3-day co-culture period increased the expression of VEGF-R2, VE-cadherin, α_vβ₃- and α₅-integrin in both the adherent and suspended PBMCs, assessed by cytofluorimetric analysis, and up-regulated VEGF-R1 mRNA assessed by real-time RT-PCR. HCAECs influenced PBMC adhesion, transendothelial migration and cell organization on Matrigel. Hypoxia modulated either PBMC differentiation or their functional properties. These data strongly suggest that endothelium may support the differentiation of PBMCs into EPCs.