Responsiveness of human bone marrow stromal cells to shear stress

We examined the hypothesis that human mesenchymal stem cells detect physiological mechanical signals. Human bone marrow stromal cells (HBMSCs) were exposed to fluid shear stress of 12 dynes/cm(2) and analysed for their ability to express osteoblast-specific markers and associated signalling pathways. HBMSCs showed a significant increase in alkaline phosphatase (ALP) gene expression and a marked decrease in type I collagen, while no effect on Cbfa1/Runx2 was detected. This regulation is related to p38 and ERK1/2 activation, although the use of specific inhibitors to these two MAP kinases suggests that ALP mRNA induction is especially dependent on p38 activity, while type I collagen downregulation is ERK1/2-dependent. Interestingly, the expression of connexin43, which is involved in cell-to-cell communication of osteoblastic cells through gap junction formation, and its distribution through the cells, were modified by fluid flow (FF). HBMSCs are sensitive to shear stress and it appears essential to take their responsiveness into consideration before associating these regenerative cells with a bioactive biomaterial in a new bone tissue-engineering strategy.

Signal Transduction and Procoagulant State of Human Cord Blood—Progenitor-Derived Endothelial Cells after Interleukin-1α Stimulation

Isolation of endothelial progenitors from human umbilical cord blood generated great hope in vascular tissue engineering. However, before clinical use, progenitor derived endothelial cells (PDECs) have to be compared with mature endothelial cells (ECs). The aim of this study was to explore the behavior of PDECs exposed to a proinflammatory cytokine (interleukin-1alpha; IL-1alpha) according to the mitogen-activated protein (MAP) kinase and nuclear factor (NF)-kappaB signal transduction pathways as well as procoagulant activity (PCA). CD34(+) mononuclear cells were isolated using magnetic beads, cultured, and compared with human saphenous vein ECs (HSVECs). PDECs express endothelial markers: CD31, VE-cadherin, von Willebrand factor, KDR, and incorporate acetylated low-density lipoprotein (Dil-Ac-LDL). IL-1alpha similarly activates c-Jun N-terminal protein kinase (JNK) and p38 pathways in HSVECs and PDECs, whereas extracellular signal-related kinase (ERK)1/2 phosphorylation is lower in PDECs than in HSVECs. Low ERK1/2 phosphorylation in PDECs was specific to IL-1alpha as vascular endothelial growth factor (VEGF) similarly stimulated ERK1/2 pathway. With respect to inhibitor of NF-kappa B (Ikappa B) degradation, NF-kappa B translocation and phosphorylation, the NF-kappa B pathway is comparable in HSVECs and PDECs after stimulation. PCA and tissue factor level induced by IL-1alpha are lower in PDECs than in HSVECs. Thus, our data show that PDECs display the characteristics of functional mature ECs under IL-1alpha stimulation. However, we observed significant differences between PDECs and HSVECs related to both ERK1/2 pathway activation and tissue factor production.

Capability of human umbilical cord blood progenitor-derived endothelial cells to form an efficient lining on a polyester vascular graft in vitro

One of the goals of vascular tissue engineering is to create functional conduits for small-diameter bypass grafting. The present biocompatibility study was undertaken to check the ability of cord blood progenitor-derived endothelial cells (PDECs) to take the place of endothelial cells in vascular tissue engineering. After isolation, culture and characterization of endothelial progenitor cells, the following parameters were explored, with a commercial knitted polyester prosthesis (Polymaille C, Laboratoires Pérouse, France) impregnated with collagen: cell adhesion and proliferation, colonization, cell retention on exposure to flow, and the ability of PDECs to be regulated by arterial shear stress via mRNA levels. PDECs were able to adhere to commercial collagen-coated vascular grafts in serum-free conditions, and were maintained but did not proliferate when seeded at 2.0 x 10(5) cm(-2). Cellularized conduits were analyzed by histology and histochemical staining, demonstrating collagen impregnation and the endothelial characteristics of the colonizing cells. Thirty-six hours after cell seeding the grafts were maintained for 6 h of either static conditions (controls) or application of pulsatile laminar shear stress, which restored the integrity of the monolayer. Finally, quantitative real-time RT-PCR analysis performed at 4 and 8 h from cells lining grafts showed that MMP1 mRNA only was increased at 4h whereas vWF, VE-cadherin and KDR were not significantly modified at 4 and 8 h. Our results show that human cord blood PDECs are capable of forming an efficient lining and to withstand shear stress.

Role of vascular endothelial growth factor in the communication between human osteoprogenitors and endothelial cells

Proper bone remodeling requires an active process of angiogenesis which in turn supplies the necessary growth factors and stem cells. This tissue cooperation suggests a cross-talk between osteoblasts and endothelial cells. This work aims to identify the role of paracrine communication through vascular endothelial growth factor (VEGF) in co-culture between osteoblastic and endothelial cells. Through a well defined direct contact co-culture model between human osteoprogenitors (HOPs) and human umbilical vein endothelial cells (HUVECs), we observed that HUVECs were able to migrate along HOPs, inducing the formation of specific tubular-like structures. VEGF(165) gene expression was detected in the HOPs, was up-regulated in the co-cultured HOPs and both Flt-1 and KDR gene expression increased in co-cultured HUVECs. However, the cell rearrangement observed in co-culture was promoted by a combination of soluble chemoattractive factors and not by VEGF(165) alone. Despite having no observable effect on endothelial cell tubular-like formation, VEGF appeared to have a crucial role in osteoblastic differentiation since the inhibition of its receptors reduced the co-culture-stimulated osteoblastic phenotype. This co-culture system appears to enhance both primary angiogenesis events and osteoblastic differentiation, thus allowing for the development of new strategies in vascularized bone tissue engineering.

Subcutaneous-induced membranes have no osteoinductive effect on macroporous HA-TCP in vivo

Induced Membranes Technique was first described to enhance bone reconstruction of large osseous defects. Previous in vitro studies established their osteoinductive potential, due to the presence of opteoblasts precursors and to high amounts of growth factors contained within. The purpose of this study was to test in vivo the osteoinductive properties of induced membranes on a macroporous HA-TCP in a nonosseous subcutaneous site. Subcutaneous-induced membranes were obtained in 21 rabbits; 1 month later, the membranes were filled with a biphasic calcium phosphate material composed of 75% hydroxyapatite (HA) and 25% beta-tricalcium phosphate associated or not with autograft. Histological and immunohistochemical studies were performed on membrane biopsies. Undecalcified and decalcified sections were qualitatively and quantitatively analyzed. (45)Ca uptake was observed and quantified on the sections using microimager analysis. Dense vascularity was found in the induced membranes. New bone formation was detected in the HA-TCP + autograft samples and increased significantly from 3 to 6 months (p < 0.05). No bone was detected in the biomaterial graft alone in the induced membranes at any time. This study showed that induced membranes placed in a nonosseous site have no osteoinductive properties on a macroporous biphasic calcium phosphate biomaterial.

Additive effect of RGD coating to functionalized titanium surfaces on human osteoprogenitor cell adhesion and spreading

Titanium-based biomaterials for endosseous implants have found widespread applications in the orthopedic, maxillofacial, and dental domains. Indeed, the surface characteristics such as their chemical modification control considerably the cellular response and, subsequently, the quality and the quantity of new-formed bone around the implant. In this study, human osteoprogenitor (HOP) cell adhesion on different titanium surfaces functionalized with hydroxyapatite (HA), type I collagen, or Arg-Gly-Asp (RGD)-containing peptides is investigated by the quartz crystal resonators and by confocal laser scanning microscopy (CLSM) for the imaging of focal contact formation. Data obtained by quartz crystal resonator technique revealed that RGD-containing peptides alone increase HOP cell adhesion in early time period of culture. Moreover, association of RGD-containing peptides with either type I collagen or with HA layers induces an additive effect on HOP cell adhesion compared to Ti-Coll or Ti-HA. CLSM shows both the area of focal contact by cell unit and the cytoskeleton network organization to differ according to the surfaces. Interestingly, association of RGD-containing peptides with HA layers induces an additive effect on focal contact formation on HOP cells compared to Ti-HA alone. These data confirm that an RGD peptide effect occurs in the early time of culture, which is beneficial for osteoblast to spreading, differentiation, and survival.

Unusual transduction response of progenitor-derived and mature endothelial cells exposed to laminar pulsatile shear stress

Progenitor-derived endothelial cells (PDECs) isolated from human umbilical cord blood generate a great hope in the fields of vascular tissue engineering. Endothelial cells subjected to shear stress convert mechanical stimuli into intracellular signals that affect cellular functions. It is essential to ensure that PDECs are able to sense shear stress as mature endothelial cells from human saphenous veins (HSVECs) do with mitogen-activated protein (MAP) kinase and nuclear factor (NF)-kappaB signal transduction pathways. HSVECs and PDECs were seeded on glass slides coated with gelatin and exposed to 12 dyn/cm2 in a parallel-plate flow chamber. In both cell types, shear stress activated extracellular signal-related kinase (ERK)1/2 with a rapid time course (maximum 5 min) followed by a reduced phosphorylation, and p38 pathway. c-Jun N-terminal protein kinase (JNK) phosphorylation is observed only in PDECs. With respect to NF-kappaB translocation to the nucleus, the NF-kappaB pathway is not activated by flow in HSVECs and PDECs although interleukin-1alpha (IL-1alpha) activates this pathway in both cell types. In our experimental conditions, shear stress does not modify the nuclear translocation of NF-kappaB in HSVECs after IL-1alpha stimulation. It can be stated that PDECs are shear stress sensitive and capable of signal transduction as mature HSVECs are, despite the unusual transduction response of both cell types.

Interaction between human umbilical vein endothelial cells and human osteoprogenitors triggers pleiotropic effect that may support osteoblastic function

Osteogenesis occurs in striking interaction with angiogenesis. There is growing evidence that endothelial cells are involved in the modulation of osteoblast differentiation. We hypothesized that primary human umbilical vein endothelial cells (HUVEC) should be able to modulate primary human osteoprogenitors (HOP) function in an in vitro co-culture model. In a previous study we demonstrated that a 3 day to 3 week co-culture stimulates HOP differentiation markers such as Alkaline Phosphatase (ALP) activity and mineralization. In the present study we addressed the effects induced by the co-culture on HOP within the first 48 hours. As a prerequisite, we validated a method based on immuno-magnetic beads to separate HOP from HUVEC after co-culture. Reverse transcription-real time quantitative PCR studies demonstrated up-regulation of the ALP expression in the co-cultured HOP, confirming previous results. Surprisingly, down-regulation of runx2 and osteocalcin was also shown. Western blot analysis revealed co-culture induced down-regulation of Connexin43 expression in both cell types. Connexin43 function may be altered in co-cultured HOP as well. Stimulation of the cAMP pathway was able to counterbalance the effect of the co-culture on the ALP activity, but was not able to rescue runx2 mRNA level. Co-culture effect on HOP transcriptome was analyzed with GEArray cDNA microarray showing endothelial cells may also modulate HOP extracellular matrix production. In accordance with previous work, we propose endothelial cells may support initial osteoblastic proliferation but do not alter the ability of the osteoblasts to produce extracellular mineralizing matrix.

Gene response in endothelial cells cultured on engineered surfaces is regulated by shear stress

In vitro endothelialization of small-diameter synthetic vascular prostheses confluently lined with cultured autologous endothelial cells (ECs) before implantation has been shown to increase their patency. Many authors have studied the effects of shear stress on EC gene response seeded on various substrates showing different gene expression profiles according to cell type, flow times, or shear type with different molecular biology techniques, but few studies have reported any EC gene response to shear stress when cells are seeded on vascular grafts. The purpose of this in vitro study was to investigate whether ECs were able to transduce shear stress at the level of the nucleus. Human saphenous vein ECs were seeded on glass slides coated with gelatin or fibrin glue or on 6-mm fibrin-glue-coated grafts. Then cells were exposed to 12 dyn/cm(2) for 4 h and ribonucleic acid (RNA) were extracted. The relative messenger RNA (mRNA) expression was studied using real-time quantitative polymerase chain reaction for the following mRNAs: von Willebrand Factor, tissue-plasminogen activator, CD31, vascular endothelial (VE)-cadherin, beta(1) integrin, and vascular endothelial growth factor receptor type 2. From parallel flow chambers, results have shown similar EC gene response on gelatin and fibrin glue under laminar shear stress with downregulation of prothrombotic genes, as well as upregulation of nonthrombotic genes and upregulation of adhesion molecules such as VE-cadherin, but some discrepancies are noted, with a downregulation of CD31 and kinase insert domain receptor (KDR) for the former, without significant variation for the latter. In comparison, results show upregulation of tissue type plasminogen activator gene and downregulation of KDR, VE-cadherin, and beta(1) integrin genes in ECs lining grafts. To conclude, the major finding of our study is to show that human saphenous vein ECs seeded on fibrin glue (in planar flow chambers or in tubular grafts) can be regulated using shear stress via gene expression changes in a nonthrombotic way.

Human endothelial progenitor cell attachment to polysaccharide-based hydrogels: a pre-requisite for vascular tissue engineering

A hydrogel was prepared from polysaccharides (pullulan/dextran/fucoidan) and evaluated as a novel biomaterial for Endothelial Progenitor Cell (EPC) culture. Using a cross-linking process with sodium trimetaphosphate in aqueous solution, homogeneous, transparent and easy to handle gels were obtained with a water content higher than 90%. Circular scaffolds (6 mm diameter and 2 mm thickness discs) were used for cell culture. Different types of EPCs were used: CD34+ derived ECs from cord blood and two sorts of CD133+ derived ECs from human bone marrow, old (30 days) and young (4 days) cells. EPCs were characterised as endothelial cells by immunofluorescent stainings for CD31 and Dil-Ac-LDL. CD133+ derived ECs from bone marrow were characterized by RT-PCR for CD31, VE-cadherin and KDR. HSVECs (Human Saphenous Vein Endothelial Cells) were used as control cells. We evaluated whether different kinds of EPCs could adhere on this novel hydrogel 4 h and 24 h after seeding, by a colorimetric quantitative test. EPCs adhered to hydrogels in serum- free conditions with values being over than 80% for young CD133+ cells at 4 h and 24 h. This pullulan-based hydrogel could constitute a suitable support for vascular cell adhesion as a pre-requisite for vascular tissue engineering.

Calcium carbonate–calcium phosphate mixed cement compositions for bone reconstruction

The feasibility of making calcium carbonate-calcium phosphate (CaCO(3)-CaP) mixed cements, comprising at least 40% (w/w) CaCO(3) in the dry powder ingredients, has been demonstrated. Several original cement compositions were obtained by mixing metastable crystalline CaCO(3) phases with metastable amorphous or crystalline CaP powders in aqueous medium. The cements set within at most 1 h at 37 degrees C in atmosphere saturated with water. The hardened cement is microporous and exhibits weak compressive strength. The setting reaction appeared to be essentially related to the formation of a highly carbonated nanocrystalline apatite phase by reaction of the metastable CaP phase with part or almost all of the metastable CaCO(3) phase. The recrystallization of metastable CaP varieties led to a final cement consisting of a highly carbonated poorly crystalline apatite analogous to bone mineral associated with various amounts of vaterite and/or aragonite. The presence of controlled amounts of CaCO(3) with a higher solubility than that of the apatite formed in the well-developed CaP cements might be of interest to increase resorption rates in biomedical cement and favors its replacement by bone tissue. Cytotoxicity testing revealed excellent cytocompatibility of CaCO(3)-CaP mixed cement compositions.

Preparation, physical–chemical characterisation and cytocompatibility of calcium carbonate cements

The feasibility of calcium carbonate cements involving the recrystallisation of metastable calcium carbonate varieties has been demonstrated. Calcium carbonate cement compositions presented in this paper can be prepared straightforwardly by simply mixing water (liquid phase) with two calcium carbonate phases (solid phase) which can be easily obtained by precipitation. An original cement composition was obtained by mixing amorphous calcium carbonate and vaterite with an aqueous medium. The cement set and hardened within 2h at 37 degrees C in an atmosphere saturated with water and the final composition of the cement consisted mostly of aragonite. The hardened cement was microporous and showed poor mechanical properties. Cytotoxicity tests revealed excellent cytocompatibility of calcium carbonate cement compositions. Calcium carbonates with a higher solubility than the apatite formed for most of the marketed calcium phosphate cements might be of interest to increase biomedical cement resorption rates and to favour its replacement by bone tissue.

Functionalization of biomaterials and cell to cell communication

In the field of osseous substitution, the possibilities being offered to the surgeons prove sometimes difficult to apply in particular in the case of great losses of osseous substance. For these reasons, it is necessary to develop innovative techniques to satisfy the request increasing for substitutes and to see appearing on the market solutions combining availability, perenniality and biosecurity of the implants. The implantation of stem cells in a biomaterial opens a way of development of therapeutic substitute. Moreover, in order to optimize the rehabitation of the biomaterials by the cells and the host tissues, the second approach consists in modifying the surface of materials by the coating or the grafting of adhesive factors in order to stimulate their colonization. At least, one cannot consider a tissue mechanism of repair without a better knowledge of the respective role of the various cell populations implied in the rebuilding of this tissue and their cell to cell communication processes.

Review: Endothelial Cells Cultured on Engineered Vascular Grafts Are Able to Transduce Shear Stress

In vitro endothelialization of small-diameter vascular prostheses confluently lined with cultured autologous endothelial cells (ECs) before clinical implantation improves their patency. Many authors have studied the effects of shear stress on ECs seeded on various substrates showing activation of mitogen-activated protein (MAP) kinases. Very few studies have reported any functional EC response to shear stress when they are seeded on vascular grafts. The purpose of this in vitro study was to investigate whether ECs were able to transduce shear stress. Human saphenous vein ECs were seeded on 6 mm fibrin-glue-coated grafts, then submitted to 15 dyn/cm(2) for 10, 30, and 120 min. Cell lysates were submitted to Western blot analysis to detect phosphorylated ERK 1/2 and p38. ERK 1/2 activation was observed at 10 min (1.6 fold) followed by a lower activation than under static conditions at 30 and 120 min. Shear stress induced a significant increase in p38 phosphorylation (2.5 fold) at 10 and 30 min, decreasing at 120 min. Thus, ECs are able to transduce shear stress in an in vitro model in closed clinical conditions, but the ERK 1/2 and p38 temporal activation profile is different. We provide new insights into the validity of the vascular tissue engineering approach.

The effect of cyclo-DfKRG peptide immobilization on titanium on the adhesion and differentiation of human osteoprogenitor cells

This study takes place in the field of development of a bioactive surface of titanium alloys. In this paper, titanium was functionalized with cyclo-DfKRG peptide by coating or grafting using different anchors (thiol or phosphonate) as spacers between the surface and the peptide. Cell adhesion, and differentiation of human osteoprogenitor (HOP) cells arising from human bone marrow were investigated. Our results seem to demonstrate that cyclo-DfKRG peptide coating with a phosphonate anchor and grafting procedure contributes to higher cell adhesion and a strong ALP and Cbfa1 mRNA expression, after 10 days of cell seeding. At the contrary, this peptide coated with a thiol anchor stimulates differentiation of HOP within 3 days of culture.

Mathematical modelling of the distribution of newly formed bone in bone tissue engineering

New bone formation in bone substitutes is usually investigated by histomorphometric global analysis. This study provides a novel mathematical modelling approach of new bone formation in the use of osteoinductive and functionalized biomaterials for bone tissue engineering. We discuss here the repartition and the probability to get new bone formation inside Biphasic Calcium Phosphate (BCP) loaded with autologous osteogenic cells, functionalized with a cyclo RGD peptide, after implantation in rabbits for 2 and 4 weeks. This local analysis allowed us to complement classical global findings and to demonstrate that after 2 weeks of implantation, the probability of new bone formation was significantly higher in RGD-grafted BCP and that new formed bone was largely distributed from the edge to the centre of the implant. While no significant differences were obtained after 4 weeks of implantation between RGD-grafted and non-grafted materials, distribution of new bone formation inside RGD-grafted materials was significantly more homogeneous as demonstrated by our mathematical modelling approach. In conclusion, local analysis of new bone formation inside macroporous substitutes coupled with mathematical modelling constitutes a potential quantitative approach for the evaluation of the osteoconductive and osteoinductive characteristics of such biomaterials.

Mineralization of regenerated cellulose hydrogels induced by human bone marrow stromal cells

The proliferation of cultured human bone marrow stromal cells (HBMSC) on regenerated cellulose hydrogels was assessed. Regenerated cellulose hydrogels showed good rates of HBMSC proliferation, the cells exhibiting a flattened morphology, and after 22 days in culture, the cells had homogeneously colonized the surface of the materials. Moreover, since the early days in culture, between the surface of the materials and attached cells a continuous granulated hydroxyapatite layer was formed. It has been previously demonstrated in vitro, but without cells, that these materials did not mineralize. Hence, it seems that HBMSC promoted the mineralization of the surface.

Effect of several sterilisation techniques on homogeneous self assembled monolayers

Understanding how cells sense their environment and are able to regulate their metabolism is of great importance for the success of biomaterials implantation. Self assembled monolayers (SAMs) are in use nowadays to model the surface of such materials. They permit the control of different surface parameters (like chemistry, surface energy and topography) enabling to get a greater insight in cells behaviour when interacting with surfaces and thus, in the future, to enhance surface properties of biomaterials. As sterilisation is the compulsory step for in vitro and in vivo assays with living biological materials, it is important to know how SAMs react under sterilisation techniques in use on biomaterials. In this work, the effect of three types of sterilisation techniques: gamma-irradiation, mostly used on biomaterials, dry heat and steam autoclaving, have been investigated on NH2 and CH3 terminated SAMs. Gamma-irradiation destructs drastically the NH2 and partially the CH3 monolayers by producing oxidative compounds (COOH, C=O, C-OH). The main product induced by gamma-irradiation on NH2 monolayers is carboxylic acid, whereas CH3 shows an important increase in the amount of alcoholic groups. This difference in deterioration is assumed to be due to the higher stability of the CH3 monolayer. Steam autoclaving to a lesser extent gives the same results on NH2 monolayers. Dry heat seems to be the most reliable technique, which can be used on such surfaces as it removes physically adsorbed organic contaminants without affecting the integrity of the surface.

Development of a resorbable macroporous cellulosic material used as hemostatic in an osseous environment

The control of bleeding is a frequently encountered therapeutic problem, particularly during dental surgery. The most efficient substances used to resolve this problem are not risk-free because of their animal or human origins, so cellulosic materials are potentially of interest. The aim of this study was to develop a resorbable macroporous cellulosic material for use as a resorbable hemostatic agent in bone sites. The degradation and the cytocompatibility of the cellulosic material versus controls were evaluated and its behaviour in vivo was studied. An original process using calcium carbonate powder as inverse matrix was used to develop a macroporous material. In order to predegrade the cellulosic material for hemostatic use, oxidation was performed with periodate. A dialdehyde component unstable at physiological pH was thus obtained. The material was found to have cytotoxicity, biocompatibility, and resorption properties similar to control but its hemostatic power was higher.

In vitro endothelial cell susceptibility to xenobiotics: Comparison of three cell types

In three different endothelial cell (EC) cultures (primary human umbilical cord vein, so-called HUVEC; and immortalized cell lines HBMEC and EA-hy-926), the effects of different xenobiotics were studied in order to standardize vascular EC models for in vitro pharmacotoxicological studies. Cell characteristics were first investigated by the production and the mRNA levels of known endothelial markers in the three EC culture models. EC secretory products, tissue plasminogen activator (tPA) and von Willebrand factor (vWF), were present in the supernatant of the immortalized cell lines. The mRNA levels of vWF, tPA, platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), and beta -integrin subunit, which are involved in the control of platelet function, coagulation, and fibrinolysis as well as in cell-matrix interactions, were investigated in all EC types. For at least three parameters, cultured cells provided marked characteristics of EC phenotype, in HUVEC and in immortalized cell lines, regardless of their origin from the macro- or microcirculation. Toxicity experiments were assessed after 24 h exposure to cadmium, cyclosporin A and cisplatin by MTT assay. These experiments show nonsignificant difference in susceptibility to cyclosporin A and cadmium on HUVEC, HBMEC, and EA-hy-926. However, HBMEC, seems to be highly susceptible to cisplatin compared to HUVEC, the latter being more sensitive than EA-hy-926. For experiments conducted with cyclosporin and cadmium, cell lines could constitute an alternative material for routine cytotoxicity studies.

Human primary endothelial cells stimulate human osteoprogenitor cell differentiation

Bone development and remodeling depend on complex interactions between bone-forming osteoblasts and other cells present within the bone microenvironment, particularly endothelial cells that may be pivotal members of a complex interactive communication network in bone. While cell cooperation was previously established between Human OsteoProgenitor cells (HOP) and Human Umbilical Vein Endothelial Cells (HUVEC) the aim of our study was to investigate if this interaction is specific to Human Endothelial cell types (ECs) from different sources. Osteoblastic cell differentiation analysis performed using different co-culture models with direct contact revealed that Alkaline Phosphatase (Al-P) activity was only increased by the direct contact of HOP with human primary vascular endothelial cell types including endothelial precursor cells (EPCs) isolated from blood cord, endothelial cells from Human Saphen Vein (HSV) while a transformed cell line, the Human Bone Marrow Endothelial Cell Line (HBMEC) did not modify osteoblastic differentiation of HOP. Because connexin 43, a specific gap junction protein, seemed to be involved in HUVEC/HOP cell cooperation, expression by RT-PCR and immunocytochemistry of this gap junctional protein was investigated in EPCs, HSV and HBMEC. Both endothelial cells are positive to this protein and the disruption of gap junction communication using 18alpha-glycyrrhetinic acid treatment decreased the positive effect of these endothelial co-cultures on HOP differentiation as was previously demonstrated for HUVEC and HOP co-cultures. These data seem to indicate that this cross talk between HOP and ECs, through gap junction communication constitutes an additional concept in cell differentiation control.

Cyclo-(DfKRG) peptide grafting onto Ti–6Al–4V: physical characterization and interest towards human osteoprogenitor cells adhesion

In the present paper, specific interest has been devoted to the design of new hybrid materials associating Ti-6Al-4V alloy and osteoprogenitor cells through the grafting of two RGD containing peptides displaying a different conformation (linear RGD and cyclo-DfKRG) onto titanium surface. Biomimetic modification was performed by means of a three-step reaction procedure: silanization with APTES, cross-linking with SMP and finally immobilization of peptides thanks to thiol bonding. The whole process was performed in anhydrous conditions to ensure homogeneous biomolecules layout as well as to guarantee a sufficient amount of biomolecules grafted onto surfaces. The efficiency of this new route for biomimetic modification of titanium surface was demonstrated by measuring the adhesion between 1 and 24 h of osteoprogenitor cells isolated from HBMSC. Benefits of the as-proposed method were related to the high concentration of peptides grafted onto the surface (around 20 pmol/mm(2)) as well as to the capacity of cyclo-DfKRG peptide to interact with integrin receptors. Moreover, High Resolution beta-imager (using [(35)S]-Cys) has exhibited the stability of peptides grafted onto the surface when treated in harsh conditions.