Biomedical subjects

D T Graves

Publications and source records attributed to D T Graves.

At least 55 records · Page 3Linked to original sources

PubMed1997

Monocyte recruitment and expression of monocyte chemoattractant protein-1 are developmentally regulated in remodeling bone in the mouse.

Tooth eruption is defined as the movement of a tooth from its site of development within the alveolar bone to its position of function in the oral cavity. It represents an excellent model to examine osseous metabolism as bone resorption and bone formation occur simultaneously and are spatially separated. Bone resorption occurs in the coronal (occlusal) area, whereas bone formation occurs in the basal area. Monocytes are thought to have a significant role in the regulation of osseous metabolism. The goal of this study was to examine the recruitment of monocytes to bone in C57BL/6J mice that are undergoing developmentally regulated bone remodeling. Monocytes were detected by immunohistochemistry and osteoclasts were counted as bone-associated multi-nucleated, tartrate-resistant acid phosphatase (TRAP)-positive cells. Cell numbers were obtained from histological sections of animals sacrificed daily for 14 days after birth; an image analysis system was used for quantification. The results demonstrated that, immediately after birth, there were relatively few monocytic cells. In the area of bone resorption, the number of monocytes increased with time, reaching peaks at 5 and 9 days, and decreased thereafter. A similar pattern was observed for osteoclasts. In the area of bone formation, there was a time-dependent increase in the number of monocytes. In contrast, the number of osteoclasts in this area was highest at the earliest time points and decreased after day 3. To investigate potential mechanisms for the recruitment of monocytes, expression of monocyte chemoattractant protein (MCP)-1 was assessed. The number of MCP-1-positive cells increased with time and was generally proportional to the recruitment of mononuclear phagocytes. Osteoblasts were the principal bone cell type expressing MCP-1. The results demonstrate that the recruitment of mononuclear cells in the occlusal area is associated with bone resorption. In contrast, recruitment of monocytes in the basal area is associated with bone formation and a decrease in the number of osteoclasts. These results suggest that monocytes have different functional roles in areas of bone formation compared with bone resorption. Furthermore, the expression of MCP-1 is developmentally regulated and may provide a mechanistic basis to explain the recruitment of monocytic cells.

Animals↗

PubMed1996

Pro-inflammatory cytokines downregulate platelet derived growth factor-alpha receptor gene expression in human osteoblastic cells.

Platelet derived growth factor (PDGF) is thought to play a significant role in bone repair and regeneration. We previously demonstrated that PDGF-AA binding can be modulated by interleukin-1 (IL-1). We now report that TNF-alpha significantly reduces PDGF-AA binding by decreasing the number of PDGF-alpha receptor subunits on the surface of normal human osteoblastic cells. This inhibition is likely due to a decrease in synthesis of PDGF-alpha receptors since TNF-alpha causes a relatively rapid decrease in PDGF-alpha receptor mRNA levels as determined by Northern blot analysis. The physiologic importance of this inhibition is demonstrated by a TNF-alpha induced decrease in PDGF-AA stimulated tyrosine kinase activity. When saturating concentrations of TNF-alpha were used, the addition of IL-1 further inhibited PDGF-AA binding and further decreased surface expression of PDGF-alpha receptors. In contrast, other mediators such as IL-6, PTH, 1,25(OH)2 vit D3, hydrocortisone, PGE2, bFGF, and IGF-1 had no effect. These results suggest that binding to the PDGF-alpha receptor is decreased by the strong pro-inflammatory cytokines such as IL-1 beta and TNF-alpha rather than as a general response to mediators important in bone resorption or bone formation. TNF-alpha and IL-1 are often co-expressed during destructive inflammatory processes. Thus, TNF-alpha and IL-1 may work in concert to limit the response of osteoblastic cells to PDGF-AA during periods of osseous inflammation.

Cell Line↗

PubMed1996

Monocyte chemoattractant protein 1 and interleukin-8 production in mononuclear cells stimulated by oral microorganisms.

Chemokines are a family of low-molecular-weight proinflammatory cytokines that stimulate recruitment of leukocytes. The chemokines interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) are relatively specific chemoattractants for neutrophils and monocytes, respectively. Chemokine expression contributes to the presence of different leukocyte populations observed in normal and pathologic states. In the present studies, peripheral blood mononuclear cells (PBMC) were stimulated by microbes (Candida albicans, Streptococcus mutans, Porphyromonas gingivalis, and Actinobacillus actinomycetemcomitans) selected based upon their importance as oral pathogens. IL-8 and MCP-1 gene expression and protein release were determined by Northern blot (RNA blot) analysis and enzyme-linked immunosorbent assay. C. albicans, P. gingivalis, and A. actinomycetemcomitans induced high levels of production of both MCP-1 and IL-8. S. mutans was a strong inducer of MCP-1, but it did not stimulate significant production of IL-8. C. albicans, S. mutans, and A. actinomycetemcomitans were 500 to 5,000 times more potent than P. gingivalis in terms of MCP-1 production. In general, the microbe-to-PBMC ratios required for maximum gene expression of MCP-1 were lower than those for IL-8. However, for actual protein release of MCP-1 versus IL-8, differences in the effects of various microbe concentrations were observed only for A. actinomycetemcomitans. These results demonstrate that different oral pathogens induce specific dose-dependent patterns of chemokine gene expression and release. Such patterns may help explain the immunopathology of oral infections, particularly with regard to inflammatory leukocyte recruitment.

Aggregatibacter actinomycetemcomitans↗

PubMed1996

Quantitative analysis of periodontal defects in a skull model by subtraction radiography using a digital imaging device.

This paper describes a quantitative study of periodontal defects produced in a skull model using subtraction images obtained with a digital imaging device, radiovisiography (RVG). Analysis using radiovisiography was compared to changes in weight and volume determined by physical measurements. Four types of periodontal defects were studied: 2-wall, 3-wall, crater, and furcation. All defects were fabricated on posterior teeth in alveolar bone and done with triplicate samples. Defects were made progressively larger in approximately 1 mm steps allowing examination of defects ranging from 1 mm to 5 mm. Radiographic images before and after each step were obtained with a radiovisiography system and subtracted. Changes in weight and defect volume were also recorded and compared to the results obtained after each step from the digital subtraction. For each defect type, a regression analysis was performed to compare changes in bone mass determined by weight with calculated bone loss determined by subtraction radiography or by volume measurements. When the calculated bone losses were compared to the true bone losses it was evident that the subtraction method frequently, but not always, underestimated the lesion sizes. For all lesions the average underestimation was 22%. The largest underestimation occurred with furcation lesions where the measured bone loss was underestimated on average by 67%. Two-walled lesions were underestimated by 30%, 3-wall lesions by 3%, and crater lesions were overestimated by 10%. Furthermore, the accuracy of each 1 mm step in bone loss varied considerably. At present, the imaging system is not sufficiently accurate to establish absolute determinations of the bone loss, but would be clinically useful in determining relative changes in bone loss or gain after treatment. In addition, caution must be taken in interpreting a given change in calculated bone loss, since considerable variation may result in either underestimation or overestimation of bone loss.

Alveolar Bone Loss↗

PubMed1995

Interleukin-1 modulates phosphorylation of proteins in human osteoblastic cells.

Interleukin-1 (IL-1) is a potent bone resorbing cytokine with diverse biological effects. We previously reported that IL-1 inhibits PDGF-AA-induced biological activities including PDGF-AA-induced tyrosyl phosphorylation. In the present studies, we first investigated and compared the tyrosyl phosphorylation pattern induced by EGF, IGF-1, PDGF-AA, and bFGF in human osteoblastic cells. We then examined the effect of IL-1 on the tyrosyl phosphoproteins induced by each ligand. Immunoblot analyses show that EGF, IGF-1, and PDGF-AA each elicit a different pattern of tyrosyl phosphorylated proteins in normal human osteoblastic cells. IL-1 beta inhibits PDGF-AA induced autophosphorylation by down-regulation of the PDGF-alpha receptor, as demonstrated by immunoprecipitation experiments. For other ligand-induced tyrosyl phosphoproteins, IL-1 beta reduced the intensity of EGF-induced pp55,000, and IGF-1 induced pp185,000 and pp175,000. These experiments indicate that IL-1 inhibits phosphorylation of specific proteins induced by growth factors. By using inhibitors of secondary message pathways, we determined that the inhibitory effect of IL-1 beta on PDGF-AA receptor binding and receptor tyrosyl autophosphorylation was not dependent on protein kinase A, protein kinase C, or the formation of prostaglandins. These data suggest the existence of an alternative pathway that may participate in IL-1 beta signaling.

Bone Neoplasms↗

PubMed1995

Receptor binding of PDGF-AA and PDGF-BB, and the modulation of PDGF receptors by TGF-beta, in human periodontal ligament cells.

The growth factors PDGF-AA and PDGF-BB have previously been shown to be potent mitogens for human periodontal ligament (hPDL) cells in vitro. Additionally, the mitogenic response to PDGF-AA has been shown to be specifically inhibited by TGF-beta. The purpose of the present investigation was to examine the binding of PDGF-AA and PDGF-BB, and the modulation of PDGF binding by TGF-beta, in hPDL cells. Scatchard analysis identified an average of 32,000 PDGF-AA high-affinity binding sites per cell with a dissociation constant (Kd) of 0.66 nM and an average of 36,000 PDGF-BB binding sites per cell with a dissociation constant (kd) of 0.44 nM. After treatment with TGF-beta, the receptor number for PDGF-AA was found to specifically decrease by approximately 50%, with no change in binding affinity. This reduced number of binding sites was shown to correlate with both a decrease in levels of receptor tyrosine phosphorylation and a decreased number of alpha receptor subunits. Northern blot analysis identified the TGF-beta-mediated decrease in PDGF alpha receptor subunit mRNA levels. PDGF-BB showed little change in the number of binding sites or in the binding affinity with TGF-beta treatment, and the data were consistent with an increase in the number of beta receptor subunits. These results demonstrate nearly equivalent numbers of receptors for both PDGF-AA and PDGF-BB in hPDL cells. Also, modulation of PDGF binding, by TGF-beta, was shown to result in a reduced number of alpha receptor subunits with an increase in the number of beta receptor subunits.

Cells, Cultured↗

PubMed1995

MCP-1-stimulated monocytes preferentially utilize beta 2-integrins to migrate on laminin and fibronectin.

Recruitment of monocytes to inflammatory sites involves a series of sequential attachments and detachments to extracellular matrix proteins in response to a chemoattractant gradient. In this study we compared the migration of human peripheral blood monocytes on different extracellular matrix proteins in response to monocyte chemoattractant protein-1 (MCP-1) and N-formylmethionyl-leucyl-phenylalanine. Monocytes migrated more effectively on laminin compared with other extracellular matrix proteins. In contrast, this preference was not observed with neutrophils, suggesting that the monocytes and neutrophils may have differences in their migration on extracellular matrix proteins. To study this further, function-blocking monoclonal antibodies were used to examine mechanistically whether beta 1- and beta 2-integrins were involved in monocyte migration on fibronectin or laminin in response to MCP-1. Monocyte migration on both laminin and fibronectin was blocked 100% (P < 0.05) by intact monoclonal antibody, F(ab') fragments, and F(ab')2 fragments to beta 2-integrins. We also determined that antibodies to beta 2-integrins block monocyte migration that has already been initiated. In contrast, antibody to the beta 1-integrins inhibited monocyte migration by approximately 40% (P < 0.05). Thus monocytes that express both beta 1- and beta 2-integrins require utilization of beta 2-integrins in migration on extracellular matrix proteins. The results also suggest that beta 1-integrins facilitate monocyte migration but that monocyte migration is not absolutely dependent on the interaction of beta 1-integrins with extracellular matrix proteins. In contrast, neutrophil migration is beta 2-integrin dependent and is not facilitated by beta 1-integrins.

CD18 Antigens↗

PubMed1995

Chemokines, a family of chemotactic cytokines.

Chemokines are low-molecular-weight proteins that stimulate recruitment of leukocytes. They are secondary pro-inflammatory mediators that are induced by primary pro-inflammatory mediators such as interleukin-1 (IL-1) or tumor necrosis factor (TNF). The physiologic importance of this family of mediators is derived from their specificity. Unlike the classic leukocyte chemo-attractants, which have little specificity, members of the chemokine family induce recruitment of well-defined leukocyte subsets. Thus, chemokine expression can account for the presence of different types of leukocytes observed in various normal or pathologic states. There are two major chemokine sub-families based upon the position of cysteine residues, i.e., CXC and CC. All members of the CXC chemokine sub-family have an intervening amino acid between the first two cysteines; members of the CC chemokine sub-family have two adjacent cysteines. As a general rule (with some notable exceptions), members of the CXC chemokines are chemotactic for neutrophils, and CC chemokines are chemotactic for monocytes and a small sub-set of lymphocytes. This review discusses the potential role of chemokines in inflammation and focuses on the two best-characterized chemokines, monocyte chemoattractant protein-1 (MCP-1), a CC chemokine, and interleukin-8 (IL-8), a member of the CXC chemokine sub-family.

Chemokine CCL2↗

PubMed1995

Monocyte chemoattractant protein-1 expression and monocyte recruitment in osseous inflammation in the mouse.

In bone, early events in inflammation involve the production and release of primary proinflammatory cytokines, such as interleukin-1 beta. By activation of target cells, these cytokines are thought to induce a second wave of cytokines, including monocyte chemoattractant protein-1 (MCP-1). MCP-1 is a cytokine that stimulates chemotaxis of monocytes. Experiments were undertaken to examine the expression of MCP-1 in bone-associated cells in vivo. To observe in vivo expression of MCP-1, an inflammatory lesion was created in the murine mandible. Immunohistochemistry experiments using specific antibodies to MCP-1 were conducted to identify MCP-1-expressing cells in inflamed and noninflamed bone. We found that osteoblasts were the principal cells expressing MCP-1 in inflamed bone. There was little or no MCP-1 expression in noninflamed bone. Immunohistochemistry experiments were carried out to assess monocyte recruitment during osseous inflammation. The number of MCP-1-positive cells was significantly correlated to the number of monocytes/macrophages present (n = 15; r = 0.69; P < = 0.01). These in vivo results strongly suggest that MCP-1 is an important mediator involved in the recruitment of monocytes/macrophages in inflamed bone.

Animals↗

PubMed1995

Fibroblasts, mononuclear phagocytes, and endothelial cells express monocyte chemoattractant protein-1 (MCP-1) in inflamed human gingiva.

Gingival inflammation is initiated by bacterial colonization of the tooth surface. It is characterized by infiltration of mononuclear cells, a feature of many forms of chronic inflammation. Monocyte chemoattractant protein-1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of cells in vitro. We examined MCP-1 expression in chronic gingival inflammation by double antibody immunohistochemistry that utilized rabbit anti-MCP-1 antibody simultaneously with mouse monoclonal antibodies to specific cellular markers. MCP-1 mRNA expression by fibroblasts in inflamed gingival tissues was examined by in situ hybridization. We report here that in human chronic gingival inflammation the principal cell type expressing MCP-1 in dense inflammatory infiltrates is the mononuclear phagocyte. The cells expressing MCP-1 in moderately inflamed areas and in adjacent areas to inflammatory infiltrates are mononuclear phagocytes and fibroblasts, while in areas of fibroblastic hyperplasia, MCP-1 positive cells are predominantly fibroblasts. We also demonstrate that in moderately and highly inflamed areas, the extent of MCP-1 expression is greater than that in adjacent normal/mildly inflamed areas. As the degree of inflammation increased, there is also a concomitant increase in the number of mononuclear phagocytes. Furthermore, it is apparent that most of the infiltrating monocytes/macrophages are positive for MCP-1 in vivo. Our finding that MCP-1 expression is unambiguously identified in fibroblasts suggests that they can play a role in host defense by initiating the recruitment of monocytes. In addition, the expression of chemokines such as MCP-1 may represent a mechanism for amplification of inflammatory signals in gingival inflammation.

Animals↗

PubMed1994

IL-1 down-regulates platelet-derived growth factor-alpha receptor gene expression at the transcriptional level in human osteoblastic cells.

Regulation of the platelet-derived growth factor (PDGF)-alpha receptor is thought to play an important role in pathophysiologic processes. Previously, we have reported that IL-1 has the potential to regulate PDGF-induced biologic activity in both normal human osteoblastic cells and the human osteoblastic cell line, MG-63, by decreasing the expression of PDGF-alpha receptor mRNA. In the present studies, we analyzed the effects of IL-1 on transcription rates and the stability of PDGF-alpha receptor mRNA in MG-63 cells. The data indicate that the t1/2 of PDGF-alpha receptor mRNA is approximately 3.3 h after incubation with the RNA II polymerase transcription inhibitor 5,6-dichloro-1 beta-D-ribofuranosylbenzimidazole (DRB). Approximately the same t1/2 (3.1 h) was obtained when osteoblastic cells were incubated with IL-1. The t1/2 for PDGF-alpha receptor mRNA for cells incubated with both IL-1 and DRB was 3 h. This finding suggests that the levels of PDGF-alpha receptor mRNA transcripts are not regulated by post-transcriptional mechanisms. Results of nuclear run-on analysis were consistent with this conclusion, demonstrating that IL-1 modulates PDGF-alpha receptor gene expression at the transcriptional level. Surprisingly, incubation of cells with cycloheximide also caused down-regulation of PDGF-alpha receptor mRNA, which suggests that synthesis of a labile factor is necessary for constitutive expression. The functional consequence of down-regulation of PDGF-alpha receptors by IL-1 was also assessed. By using chemotaxis assays, we demonstrated that IL-1 significantly inhibited PDGF-AA-mediated migration in human MG-63 osteoblastic sarcoma cells.

Chemotaxis↗

PubMed1994

Expression of monocyte chemoattractant protein 1 in human osteoblastic cells stimulated by proinflammatory mediators.

Monocyte chemoattractant protein 1 (MCP-1) is a member of the chemokine superfamily of genes that induces chemotaxis of monocytes in inflammatory processes. The effects of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), transforming growth factor beta (TGF-beta), platelet-derived growth factor (PDGF-BB), parathyroid hormone (PTH), and 1,25(OH)2D3 on MCP-1 expression in human osteoblastic cells were compared. Inflammatory or proinflammatory cytokines stimulated the production of MCP-1 in normal human osteoblastic cells as determined by RIA. The osteotrophic mediators PTH and 1,25(OH)2D3 and PDGF-BB had no effect on MCP-1 expression. In further studies, the steady-state mRNA and MCP-1 protein levels in two human osteoblastic cell lines, MG-63 and SaOS-2, were examined. MCP-1 expression at both the protein and mRNA levels was greatly increased by IL-1 beta and TNF-alpha. At the mRNA level, IL-1 beta and TNF-alpha strongly induced MCP-1 expression; TGF-beta and IL-6 induced MCP-1 but to a lesser extent. No significant changes in MCP-1 mRNA or MCP-1 protein secretion were observed when cells were treated with PDGF-BB, PTH, and 1,25(OH)2D3. When tested on preosteoclasts, MCP-1 was shown to have no effect on the formation of multinucleated, tartrate-resistant acid phosphatase (TRAP)-positive osteoclastic cells.

Autoradiography↗

PubMed1994

MCP-1-stimulated monocyte attachment to laminin is mediated by beta 2-integrins.

Migration of monocytes to sites of inflammation involves a series of attachments and detachments to extracellular matrix proteins. We examined the capacity of a chemokine, monocyte chemoattractant protein-1 (MCP-1), to regulate attachment of human monocytes to laminin, collagen I, collagen IV, or fibronectin. MCP-1 increased monocyte attachment to laminin in a dose- and time-dependent manner and stimulated a lesser increase to the other matrix proteins. Function-blocking monoclonal antibodies (MAbs) to the integrin beta 2-subunit (CD18), including Fab' fragments and alpha M (CD11b) blocked > 70% of attachment, whereas MAbs to the beta 1-integrin subunit reduced attachment by < 30%. This suggests that the CD11b/CD18 integrin is the predominant molecule involved in adhesion of MCP-1-stimulated monocytes to laminin. The association of CD11b with F-actin illustrated by confocal microscopy further supports this concept. In contrast, when monocytes were stimulated with the beta 1-stimulatory MAb TS2/16, monocyte adhesion to laminin occurred through beta 1-integrins. Thus MCP-1 can stimulate monocyte attachment to laminin, and this process is mediated through beta 2-integrins, principally CD11b/CD18.

Antibodies, Monoclonal↗

PubMed1994

Periodontal regeneration with polypeptide growth factors.

Attempts at periodontal regeneration have been plagued by inconsistent results. The failures associated with these procedures are likely due to an insufficient number of cells themselves lacking sufficient activity to produce the supporting structures of the periodontium. Molecular studies have provided insight into the regenerative process by identifying locally acting mediators expressed during healing. These mediators, termed growth factors, may stimulate a wide variety of cellular events, including chemotaxis, proliferation, differentiation, and production of extracellular matrix proteins. Thus, the use of polypeptide hormones to enhance regeneration is based on the concept that the effect of the mediators that are naturally present can be enhanced by the addition of exogenous growth factors. Based on information originally obtained from in vitro studies, investigators have recently attempted to enhance bone formation and periodontal regeneration by using growth factors. This review focuses on five growth factor families that have potential for inducing periodontal regeneration based on their ability to stimulate osteoblasts and periodontal ligament cells in vitro or in vivo. These include platelet-derived growth factor, insulin-like growth factor, transforming growth factor-beta, fibroblast growth factor, and bone morphogenetic protein.

Animals↗

PubMed1994

Growth factors in periodontal regeneration.

Periodontal tissue repair and regeneration are regulated by the local production of growth factors. However, naturally produced growth factors may not be sufficient to optimally stimulate periodontal regeneration. Exogenous growth factors can be used to supplement natural growth factors in wound healing. The authors focus on describing the mechanisms of five growth factors in periodontal regeneration: platelet-derived growth factor; fibroblast growth factor; transforming growth factor-beta; insulinlike growth factor; and bone morphogenetic protein. The objective is to encourage strategies to exploit growth factors in the stimulation of cells in periodontal regeneration, which should result from continued in vivo animal studies.

Bone Morphogenetic Proteins↗

PubMed1994

Expression of monocyte chemoattractant protein-1 in delayed type hypersensitivity reactions in the skin.

BACKGROUND: Monocyte chemoattractant Protein-1 (MCP-1) is a potent chemotactic factor for monocytes. Because many inflammatory dermatoses are characterized by mononuclear cell infiltrates, it is reasonable to postulate that MCP-1 might be involved in their pathogenesis. To date, no in vivo studies have been published concerning the expression of MCP-1 in this context. The aim of this study was to elucidate the expression of MCP-1 in human inflammatory skin diseases which are thought to involve delayed type hypersensitivity reactions. EXPERIMENTAL DESIGN: Expression of MCP-1 was examined in normal skin and three classes of inflammatory skin reactions by immunohistochemistry experiments utilizing a monospecific MCP-1 antiserum. The distribution of monocytes/macrophages and T lymphocytes was determined by immunohistochemistry using antibodies to specific cell surface markers. RESULTS: Immunostaining with MCP-1 antiserum demonstrated strong MCP-1 expression in lichenoid dermatitis, dermal hypersensitivity reactions, and spongiotic dermatitis. In contrast, normal skin showed minimal MCP-1 expression in the dermis. The cell types displaying MCP-1 expression were endothelial cells of dermal microvessels that were surrounded by lymphocytic infiltrates and monocytes/macrophages at the periphery of the perivascular infiltrates. Occasionally, MCP-1-positive mononuclear cells were present both in the infiltrates and in a diffuse pattern in the surrounding dermis. Keratinocytes were found to produce MCP-1 constitutively in normal skin and in inflamed conditions. The pattern of MCP-1 expression was similar to the pattern observed for monocyte/macrophage distribution, whereas the pattern of MCP-1 expression was different from the pattern of T lymphocyte distribution. CONCLUSIONS: We observed an enhanced expression of MCP-1 in inflammatory skin conditions. The expression of MCP-1 provides a mechanistic explanation for the increased recruitment of monocytes/macrophages in cell-mediated immune response such as delayed type hypersensitivity reactions in the skin.

Chemokine CCL2↗

PubMed1993

IL-1 and transforming growth factor-beta inhibit platelet-derived growth factor-AA binding to osteoblastic cells by reducing platelet-derived growth factor-alpha receptor expression.

Platelet-derived growth factor (PDGF) is thought to play a significant role in bone repair and regeneration. We previously demonstrated that PDGF-AA-induced chemotaxis and proliferation can be modulated by IL-1. We now report that IL-1 and transforming growth factor-beta (TGF-beta) significantly decrease the number of PDGF-AA binding sites in both normal and tumor-derived human osteoblastic cells, whereas PDGF-BB binding is minimally affected. The affinity of PDGF-AA binding remains unchanged in the presence of IL-1, but is slightly reduced by TGF-beta as demonstrated by Scatchard analysis. We also showed that tyrosyl kinase phosphorylation after PDGF-AA binding is decreased in the presence of both IL-1 and TGF-beta. Northern blot analysis indicates that both IL-1 and TGF-beta decrease the expression of PDGF-alpha receptor mRNA. These results suggest that IL-1 and TGF-beta have the potential to regulate PDGF-AA-induced biologic activity in normal human osteoblastic cells and in human osteoblastic sarcoma cells by decreasing the levels of the PDGF-alpha receptor.

Humans↗

PubMed1993

Effects of platelet-derived growth factor isoforms on calcium release from neonatal mouse calvariae.

Platelet-derived growth factor (PDGF) is the major growth factor in serum for cells of mesenchymal origin and induces many different activities, including bone resorption. Since the initial report that PDGF stimulated calcium release from bone organ cultures, it has been shown that PDGF is a dimeric protein consisting of two disulfide bonded polypeptides encoded by different genes. Three isoforms of the two gene products have been isolated. We compared the capacity of each isoform to stimulate calcium release from radiolabeled mouse calvariae. PDGF-AB from human platelets and recombinant PDGF-BB isoforms significantly stimulated calcium release at 5 ng/ml, but not in lower doses. Recombinant PDGF-AA did not induce calcium release. Indomethacin blocked the stimulated bone resorption, suggesting a prostaglandin-mediated mechanism of action. PDGF-induced calcium release was compared to TGF-beta 1 in the organ culture system. Approximately a 10-fold greater concentration of PDGF-AB and PDGF-BB was required to achieve a similar degree of calcium release as found in TGF-beta 1 treated calvariae. Thus, TGF-beta 1, PDGF-AB, and PDGF-BB significantly stimulated calcium release from mouse calvariae. This response is specific in that PDGF-AA did not stimulate calcium release.

Animals↗