Chemotactic response of mesenchymal cells, fibroblasts and osteoblast-like cells to bone Gla protein

The use of mesenchymal stem cells in tissue engineering: A global assessment

Mesenchymal stem cells (MSCs) are of great interest to both clinicians and researchers for their great potential to enhance tissue engineering. Their ease of isolation, manipulability and potential for differentiation are specifically what have made them so attractive. These multipotent cells have been found to differentiate into cartilage, bone, fat, muscle, tendon, skin, hematopoietic-supporting stroma and neural tissue. Their diverse in vivo distribution includes bone marrow, adipose, periosteum, synovial membrane, skeletal muscle, dermis, pericytes, blood, trabecular bone, human umbilical cord, lung, dental pulp and periodontal ligament. Despite their frequent use in research, no standardized criteria exist for the identification of mesenchymal stem cells; The International Society for Cellular Therapy has sought to change this with a set of guidelines elucidating the major surface markers found on these cells. While many studies have shown MSCs to be just as effective as unipotent cells for certain types of tissue regeneration, limitations do exist due to their immunosuppressive properties. This paper serves as a review pertaining to these issues, as well as others related to the use of MSCs in tissue engineering.

Induction and detection of human mesenchymal stem cell migration in the 48-well reusable transwell assay

The induction and detection of chemotactic migration in mesenchymal stem cells (MSC) are complicated by their adherent nature. We describe here the experimental details for inducing the transmigration of MSC seeded in microchemotaxis chambers and reliably identifying the translocated cells. A combination of 8-microm pore-sized membranes and a two-step staining procedure resulted in the detection of MSC migration against a gradient of human plasma which plateaued after 4 h. Microscopic enumeration of the transmigrated cells clearly distinguished contaminating nonmigrated cells from transmigrated cells. Chemokinetic and chemotactic effects could be separated and were influenced by precoated fibronectin or vitronectin. Thus, the technique described allows rapid and reliable induction and determination of migration in adherent MSC.

Platelet-derived growth factor beta-receptors can both promote and inhibit chemotaxis in human vascular smooth muscle cells

The effect of the three platelet-derived growth factor (PDGF) isoforms AA, AB, and BB on migration was investigated in cultured human saphenous vein smooth muscle cells. The modified Boyden chamber technique yielded efficacies BB >> AB, AA = 0. However, the BB concentration-response relationship displayed a pronounced peak, occurring between 1 and 10 ng/mL, with no response above this range. Checkerboard analysis showed that the promotion of migration at low concentrations was chemotactic in nature but that the downturn was independent of gradient. Furthermore, at high concentrations BB was able to prevent chemotaxis induced by fetal calf serum and epidermal growth factor (EGF). Experiments using low concentrations of BB in combination with high concentrations of AA to saturate PDGF alpha-receptors in the presence and absence of a neutralizing antibody to alpha-receptors revealed that alpha-receptor activation induced partial inhibition of chemotaxis but this did not account for the inhibition of migration by high concentrations of BB. Despite possessing no significant chemotactic action itself, high concentrations of the AB isoform completely inhibited BB induced chemotaxis. Taken together these results suggest that the chemotactic signal induced by PDGF is dominated by PDGF beta-receptors and switches from positive at low concentrations to negative at higher concentrations. Stimulation of DNA synthesis by the three isoforms (as measured by [3H] thymidine incorporation) yielded saturable responses for the AB and BB isoforms, with similar efficacy and weak or no response for the AA isoform. Concentration-dependent patterns of tyrosine phosphorylation of certain proteins mirrored the form of the chemotactic response and suggest one possible underlying regulatory mechanism to account for the disparity between PDGF-induced chemotaxis and DNA synthesis.

Plasmin-mediated proteolysis of osteocalcin

Plasmin cleaves osteocalcin at a site within its carboxyl end, thus creating an N-midterminal 1-43 and a short C-terminal 44-49 peptides. The products of the cleavage were identified by matrix assisted laser desorption ionization time of flight mass spectrophotometry and by reversed phase high performance liquid chromatography followed by N-terminal sequence determination. When separated by sodium dodecyl sulfide-polyacrylamide gel electrophoresis in the presence of reducing agents, large (LF; N-midterminal) and a small molecular weight (SF; C-terminal) fragments can be identified. The major cleavage site involves arg43-arg44 amino acid residues, and the resulting 44-49 C-terminal fragment appears as a slow migrating band on native gels (SFnat). Elevated levels of calcium ion inhibit the plasmin-mediated lysis of osteocalcin. Plasmin-mediated cleavage of osteocalcin occurs both in solution and when bound to hydroxyapatite. Both osteocalcin cleavage products detach from the hydroxyapatite substrate. Diisopropyl fluorophosphate-inhibited plasmin does not displace osteocalcin from the hydroxyapatite surface. Previously, the C-terminal pentapeptide has been shown to be chemotactic for bone cells while bone particles lacking osteocalcin were resistant to bone resorption. We therefore hypothesize that the plasmin-mediated digestion of free and hydroxyapatite-bound osteocalcin could play a role in the regulation of bone remodeling.

Chemotaxis of skeletal muscle satellite cells

Migration of myogenic cells occurs extensively during both embryogenesis and regeneration of skeletal muscle and is important in myoblast gene therapy, but little is known about factors that promote chemotaxis of these cells. We have used satellite cells from adult rats purified by Percoll density gradient centrifugation to test growth factors and wound fluids for chemotactic activity in blind-well Boyden chambers. Of a variety of growth factors tested only hepatocyte growth factor (HGF) and transforming growth factor-beta (TGF-beta) exhibited significant chemotactic activity. The dose-response curves for both of these factors was bell-shaped with maximum activity in the 1-10 ng/ml range. Checkerboard analysis of TGF-beta showed that chemotaxis occurred only in response to a positive concentration gradient. An extract of rat platelets also exhibited chemotactic activity for satellite cells. Half-maximal activity of this material was about 3 micrograms/ml, and there was no evidence of inhibition of migration at high concentrations. Checkerboard analysis of platelet extract exhibited evidence of both chemotaxis and chemokinesis, or increase in random motility of cells. Inhibition experiments showed that most, but not all, of the chemotactic activity in platelet extract could be blocked with a neutralizing antibody to TGF-beta. A saline extract of crushed muscle was found to contain both mitogenic and motogenic factors for satellite cells. The two activities were present in different fractions after heparin affinity chromatography. We propose that the proliferation and migration of satellite cells during regeneration is regulated by overlapping gradients of several effector molecules released at the site of muscle injury. These molecules may also be useful for enhancing the dispersion of injected myoblasts during gene therapy.

Bone marrow interface: preferential attachment of an osteoblastic marrow stromal cell line

In this study, we report on the cell adhesion properties of marrow stromal cells to extracellular matrix components such as collagen and noncollagenous proteins. The osteoblastic cells and their non-osteoblastic counter-parts (MBA series) from the marrow stroma differentially recognized a spectrum of extracellular matrix proteins. The osteoblastic cells, MBA-15, preferentially attached to bone matrix proteins, whereas fibroendothelial MBA-2.1 and adipocytic 14F1.1 cells did not. The MBA-15 cells demonstrated a preference in their attachment to fibronectin > mixture of collagens > bone matrix extracts > collagen type I > noncollagenous proteins. Clonal subpopulations derived from the MBA-15 cell line representing various stages along the osteogenic lineage expressed differential attachment preference. MBA-15.4, a less differentiated clonal line, was compared to MBA-15.6, a mature cell line.

Numerical analysis of extracellular fluid flow and chemical species transport around and within porous bioactive glass

Modeling of the physical phenomena present at the biomaterial-tissue interface provides a valuable tool for examining the underlying mechanisms which influence the overall behavior of the implant-host system. Based on histological data from a previous implantation study (E. Schepers, M. De Clercq, P. Ducheyne, and R. Kempeneers, "Bioactive glass particulate materials as a filler for bone lesions," J. Oral Rehab.; 18, 439-452, 1991, Ref. 1) which documented the differentiation of mesenchymal cells to cells expressing the osteoblastic phenotype in porous bioactive glass, a finite element momentum and mass transport model was constructed. In this analysis, the extracellular compositional variations and fluid flow conditions around and within porous bioactive glass granules were determined. Numerical simulations demonstrated that the interstitial fluid flow around these granules (300-360 microns) is viscosity dominated (low Reynolds number flow) and that the fluid inside the granules remains stagnant. This velocity field results in shear stresses proportional to the velocity gradient at the granule-fluid interface outside the particles and no shear stresses inside the particles. A parametric study on the effect of interstitial fluid flow on chemical species (Na+, Ca+2, HPO(4)-2) transport outside the granules revealed three domains. At low velocities (0-0.1 micron/s), the transport of species is diffusion controlled. At intermediate velocities (1.0-10 microns/s), diffusion and convection contribute to the species transport. The concentration of chemical species is nearly uniform at high velocities (100-800 microns/s). For all three cases, the transport of chemical species within the granules is diffusion controlled. The differences in transport mechanisms and interstitial fluid flow conditions lead to variations in concentrations, reaction rates, and shear stresses between the inside and the outside of the glass granules. These differences may influence cellular migration, attachment, differentiation, and the overall response to these bioactive materials.

Effects of high calcium concentration on the functions and interactions of osteoblastic cells and monocytes and on the formation of osteoclast-like cells

The present study was performed to clarify the role of high calcium concentration and the appearance of mononuclear cells at the resorptive site in bone remodeling. Our recent study revealed that the high concentration of extracellular calcium ([Ca2+]e) stimulated DNA synthesis in osteoblastic MC3T3-E1 cells not only directly but also indirectly via monocytes. Human monocyte-conditioned medium (CM) significantly stimulated DNA synthesis and inhibited alkaline phosphatase (ALP) activity. In contrast, when monocytes were cultured at high [Ca2+]e concentrations (more than 3 mM), CM from these monocytes significantly stimulated ALP activity in MC3T3-E1 cells. Such stimulatory effect of CM was not observed at a high magnesium concentration (Mg2+, 5 mM). Treatment of monocytes with the calcium ionophore A23187 did not affect the CM-induced effect on DNA synthesis and ALP activity in these cells. To determine the migration potency of MC3T3-E1 cells and monocytes toward the high [Ca2+]e, chemotaxis assay was performed. The increasing [Ca2+]e (more than 3 mM) induced a chemotactic response of MC3T3-E1 cells as well as monocytes, but the high concentration of Mg2+ (5 mM) did not induce it. On the other hand, treatment with high [Ca2+]e (more than 3 mM) or CM significantly inhibited the 1,25-(OH)2D3-induced formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNC) from their precursors derived from mouse spleen cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and complete amino acid sequence of osteocalcin from canine bone

Osteocalcin was purified in high yield and to homogeneity from the diaphysis of dog femora by the following steps: (1) acid demineralization of bone powder, (2) solid-phase extraction of acid-soluble proteins on Sep-Pak C18 cartridges, (3) gel filtration on Sephadex G-50, and (4) fast protein liquid chromatography on an Accell-QMA anion-exchange column. Starting from 30 g washed bone powder, approximately 7-10 mg pure protein was obtained in 2 days. The key step is the initial solid-phase extraction of osteocalcin from a large volume of a demineralized bone solution. The primary structure was established by automated sequence analyses of two tryptic peptides, of two endoproteinase Glu-C carboxy-terminal peptides, and of the first 30 amino acid residues of the intact protein. Dog osteocalcin contains 49 amino acids, has a molecular mass of 5654 daltons, contains no Thr, Met, Hyp, or Trp, has a disulfide bond between Cys 23 and 29, and is fully gamma-carboxylated at residues 17, 21, and 24. Dog osteocalcin does not contain a pair of basic amino acids found at positions 43-44 in most other osteocalcins from mammals and birds. A computer search for homology indicated 88, 90, 84, 88, 66, and 57% sequence identity of dog osteocalcin with human, bovine, cat, monkey, chicken, and swordfish osteocalcin, respectively, and weaker homologies with the gamma-carboxylated domains of blood-clotting proteins and the Pro-rich N-terminal extensions of myosin light-chain A1 and beta-crystalline B1. The possible relevance of these homologies to the structure and potential functions of osteocalcin is discussed.

Attachment to extracellular matrix molecules by cells differing in the expression of osteoblastic traits

Two sets of clonal cell populations differing in the expression of osteoblastic traits, the rat osteosarcoma cell lines ROS 17/2.8 and ROS 25/1 and the immortalized fetal rat calvarial cell lines RCT-1 and RCT-3, were compared for their ability to attach to a series of extracellular matrix (ECM) constituents in vitro. Both osteoblastic (ROS 17/2.8, RCT-3) and nonosteoblastic (ROS 25/1, RCT-1) cell lines attached in a time- and concentration-dependent manner to plates coated with fibronectin (FN), osteopontin (OP), type I collagen (Col I), type IV collagen (Col IV), and laminin (LN) but only weakly to osteocalcin (OC) and thrombospondin (TSP). In both systems, the osteoblastic and nonosteoblastic clones attached identically to FN. Both ROS 17/2.8 and ROS 25/1 attached to similar molar amounts of substrate with the same preference order: FN > LN > Col I > or = Col IV. Maximal ROS 17/2.8 attachment to OP was > or = Col I but required approximately 2.5 times more substrate. ROS 25/1 attached less effectively than ROS 17/2.8 to most non-FN substrates. RCT-3 cells attached similarly to ROS 17/2.8 except that the preference order for Col I and LN was reversed and attachment to OP was lower than for ROS 17/2.8 RCT-1 cells attached best to Col I rather than FN, and equaled or surpassed RCT-3 in attachment to other non-FN substrates. Thus in these experimental systems, cells expressing an osteoblast-like phenotype exhibited generally similar ECM attachment properties. Their nonosteoblastic counterparts recognized the same spectrum of ECM constituents but differed from the osteoblastic cells and from each other in the effectiveness of their attachment to substrates other than FN.

Differential chemotactic responses of different populations of fetal rat calvaria cells to platelet-derived growth factor and transforming growth factor beta

We tested the chemotactic response to platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF beta) of cells released enzymatically from fetal rat calvaria (RC). Both factors were chemotactic for RC cells, but the magnitude of the chemotactic response differed markedly between different populations and varied with time in culture of the cell populations. Cells released earlier from the calvaria showed a greater response than osteoblast-enriched populations released later. The optimal concentration of PDGF was the same for both alkaline phosphatase (AP)-positive and AP-negative cells within the populations. However AP-positive cells showed two peaks of response to TGF beta; one peak coincided with the TGF beta concentration also maximally affecting AP-negative cells, while the other occurred at a concentration 50-100 times higher. The results indicate that PDGF and TGF beta are chemotactic for both AP-positive and AP-negative cells in populations of cells derived from fetal calvariae, that chemotactic response declined with longer periods of time in culture, and that AP-positive osteoblast-like cells respond to a concentration of TGF beta that does not affect the AP-negative cells in the population.

The warfarin embryopathy: a rat model showing maxillonasal hypoplasia and other skeletal disturbances

Sprague-Dawley rats were given daily subcutaneous doses of sodium warfarin (100 mg/kg) and vitamin K1 (10 mg/kg) for up to 12 weeks, starting on the day after birth. This dosing regimen creates an extrahepatic vitamin K deficiency while preserving the vitamin K-dependent processes of the liver. Control rats received either vitamin K1 only or were untreated. All rats survived without any signs of hemorrhage. The warfarin-treated rats developed a marked maxillonasal hypoplasia associated with a 11-13% reduction in the length of the nasal bones compared with controls. The length of the posterior part of the skull was not significantly different from controls. In the warfarin-treated rats, the septal cartilage of the nasal septum showed large areas of calcification, not present in controls, and abnormal calcium bridges in the epiphyseal cartilages of the vertebrae and long bones. The ectopic calcification in the septal cartilage may have been the cause of the reduced longitudinal growth of the nasal septum and the associated maxillonasal hypoplasia. It is proposed that (1) the facial features of the human warfarin embryopathy are caused by reduced growth of the embryonic nasal septum, and (2) the septal growth retardation occurs because the warfarin-induced extrahepatic vitamin K deficiency prevents the normal formation of the vitamin K-dependent matrix gla protein in the embryo.

Mesenchymal stem cells

Bone and cartilage formation in the embryo and repair and turnover in the adult involve the progeny of a small number of cells called mesenchymal stem cells. These cells divide, and their progeny become committed to a specific and distinctive phenotypic pathway, a lineage with discrete steps and, finally, end-stage cells involved with fabrication of a unique tissue type, e.g., cartilage or bone. Local cuing (extrinsic factors) and the genomic potential (intrinsic factors) interact at each lineage step to control the rate and characteristic phenotype of the cells in the emerging tissue. The study of these mesenchymal stem cells, whether isolated from embryos or adults, provides the basis for the emergence of a new therapeutic technology of self-cell repair. The isolation, mitotic expansion, and site-directed delivery of autologous stem cells can govern the rapid and specific repair of skeletal tissues.

The concept of osseointegration and bone matrix expression

Osseointegration has been defined as the direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant. To date, this concept has been described by descriptive histological and ultrastructural criteria but not by biochemical means. This review evaluates the basic science work performed on this concept and then applies the concept to the principle of osseous healing. Specific studies are cited where alterations in the healing response are due to clinical management of implant placement and how studies of surface properties may lead to further insights on implant design and prognosis. In addition, a review of bone expression as a function of in vitro stress applications is given. This is followed by an indepth review of the collagens and noncollagenous proteins, described to date, within isolated bone matrix. It is this collagenous matrix (especially type I) that is described as being close to and oriented with a glycoprotein component next to the implant surface. In turn, the large family of noncollagenous proteins are important in mediating bone proliferation, matrix accumulation, orientation, mineralization, and turnover. This section is followed by a discussion of specific growth factors as they may relate to osseous healing around an implant.

Chemotactic response of osteoblastlike cells to transforming growth factor beta

Transforming growth factor beta (TGF-beta) has multiple effects on bone cell metabolism in vitro but its exact role in bone remodeling still needs to be defined. Here we demonstrate that TGF-beta is chemotactic for osteoblastlike cells from fetal rat calvariae and osteoblastlike ROS 17/2.8 osteosarcoma cells. Maximal chemotaxis occurred at 5-15 pg/ml of TGF-beta and was observed with TGF-beta 1 and TGF-beta 2 at equivalent concentrations. Conditioned medium from osteoblastlike cells containing latent TGF-beta failed to stimulate chemotactic migration. However, chemotactic activity was observed in conditioned medium that had been transiently acidified. Since acidification is known to activate TGF-beta, these results suggest that only active TGF-beta is capable of inducing a chemotactic response. Preincubation of osteoblastlike cells with TGF-beta in concentrations from 10 pg/ml to 1 ng/ml for 48 h abolished a subsequent chemotactic response of these cells to TGF-beta, indicating that TGF-beta-induced chemotaxis is a transient phenomenon. Since TGF-beta may be released from the bone matrix and/or activated during bone resorption, the chemotactic activity of TGF-beta for osteoblastlike cells may be important for the recruitment of osteoblastlike cells to sites of bone remodeling.

Chemotactic response of osteoblast-like cells to transforming growth factor beta

Transforming growth factor beta (TGF-beta) was tested for its ability to stimulate a chemotactic response in two clonal rat osteosarcoma (ROS) cell lines, 17/2 and 25/1. TGF-beta stimulated dose-dependent chemotaxis in both cell lines. In serum-containing media, maximal response was seen at a concentration of 500 fg (10(-15)g)/mL for the ROS 17/2 cells and 25 fg/mL for the ROS 25/1 cells. In serum-free media, the maximal chemotactic response to TGF-beta occurred at 5 fg/mL for both the ROS 17/2 and 25/1 cells. TGF-beta was not mitogenic at these dosages. The results indicate that TGF-beta could act as a chemoattractant for osteogenic cells in both demineralized bone matrix induced osteogenesis and in normal bone remodeling.