Platelet-derived growth factor (PDGF)

Ohne Zusammenfassung     

Platelet-derived growth factor promotes polymorphonuclear leukocyte activation

The platelet-derived growth factor (PDGF) has several well defined important biologic activities. Platelet-derived growth factor is the major mitogen in human serum for cells of mesenchymal origins; it is a potent chemoattractant protein for human monocytes, neutrophils, fibroblasts, and smooth muscle cells; and has been implicated in transformation by simian sarcoma virus and perhaps in transformation by other agents as well. In this article, PDGF has been shown to stimulate activation of human peripheral blood neutrophils defined by loss of membrane associated calcium as reflected by loss of chlortetracycline fluorescence, release of superoxide anion and specific granule enzymes, and enhanced neutrophil adherence and aggregation. These responses occurred in a dose-dependent fashion at concentrations of PDGF between 10 ng/mL (0.4 nmol/L) and 40 ng/mL (1.5 nmol/L) and were comparable to effects obtained with optimal concentrations of fMLP and C5a. Degranulation induced by PDGF was selective for secondary (specific) granules and not primary (azurophil) granules. Platelet-derived growth factor thus is ideally suited for a pivotal role in attracting inflammatory cells locally and initiating neutrophil activation at sites of blood vessel injury. Platelet-derived growth factor or a closely related protein also may play an important role in attracting and activating neutrophils in association with inflammatory tumors.     

Platelet-derived growth factor promotes human peripheral monocyte activation

Like in the polymorphonuclear leukocyte (PMN), the platelet-derived growth factor (PDGF) purified to homogeneity is capable of inducing monocyte activation responses as evaluated by generation of superoxide anion (O-.2) from membrane-associated oxidase system, release of granule enzymes, and enhanced cell adherence and cell aggregation. Superoxide anion release was maximized at 10 ng/mL PDGF and was comparable to that induced by 10(-7) mol/L formyl-methionyl-leucyl- phenylalanine. The potency of PDGF to induce this response in monocytes was of the same magnitude as that observed in PMNs. Similarly, lysozyme release and monocyte adherence were also increased in a dose-dependent manner and achieved maximal responses at 40 ng/mL concentration of PDGF. The PDGF concentration required to achieve maximal monocyte aggregation was two-fold (60 ng/mL) of that found for PMNs. In contrast to PMNs, a positive correlation (gamma = .93; P less than .01) was observed between the increases of PDGF concentration and beta- glucuronidase release. These findings indicate that PDGF can induce the full sequence of cell activation events in human monocytes similar to human PMNs.     

Platelet-derived growth factor: purification and partial characterization.

A cationic protein that stimulates DNA synthesis in human cultured cells was isolated from human platelets by ion exchange chromatography, hydrophobic chromatography, gel chromatography, and gel electrophoresis in sodium dodecyl sulfate. The electrophoretic behavior of biologically active or radioiodinated and reduced growth factor indicated that the native protein (approximately 30,000 daltons) was composed of two different polypeptides (approximately 13,000-14,000 and 16,000-17,000 daltons, respectively) linked via reduction-susceptible bonds. The stimulatory activity on human glial cells of the purified product at a concentration of approximately 4 ng/ml (0.13 nM) was equal to that of 1% human serum.     

Platelet-derived growth factor stimulates growth of highly enriched multipotent haemopoietic progenitors

Platelet-derived growth factor (PDGF) has been shown to stimulate growth of normal and malignant fibroblasts, glial cells and smooth muscle cells. A growth promoting effect on human haemopoietic precursors has also been described, but the interpretation of this haemopoietic proliferative response to PDGF has been hampered by the lack of purity of the target population. In this study we show that PDGF promotes growth of early bone marrow haemopoietic progenitors depleted of either monocytes or T lymphocytes which are known to influence haemopoiesis. Moreover, the action of PDGF is even increased on a highly enriched BI-3C5 early bone marrow population. BI-3C5 is a novel monoclonal antibody which recognizes an antigen present on all multilineage colony-forming cells (CFU-mix) (Tindle et al. 1985). BI-3C5 positively and negatively sorted fractions were obtained by fluorescence activated cell sorting (FACS) and PDGF was found to stimulate growth of CFU-mix in the BI-3C5-positive fraction (consisting of only 4-6% of the marrow population), the effect being more marked than that on unsorted bone marrow. The results suggest that the product of the cellular proto-oncogene c-sis (the putative structural gene for the beta chain of PDGF) may play a regulatory role in the in vivo proliferation of multipotent haemopoietic progenitors.     

Platelet-derived growth factor is increased in pulmonary capillary hemangiomatosis

Background:Pulmonary capillary hemangiomatosis (PCH) is a rare cause of pulmonary arterial hypertension with no effective medical therapy and a high risk of mortality. The pathogenesis of PCH is unknown.Methods:We used gene expression analysis to compare lung tissue samples from two patients with PCH to those from seven control subjects. The nodules of proliferating capillaries in PCH patients were needle microdissected from cryostat sections. RNA extraction and labeling were followed by hybridization to U95Av2 oligonucleotide arrays (Affymetrix; Santa Clara, CA).In situhybridization and immunohistochemistry were also performed.Results:The gene expression profile of PCH allowed for unsupervised clustering from the profile of the lung tissue samples of control subjects. Platelet-derived growth factor (PDGF)-B gene (PDGFB), PDGF receptor (PDGFR)-β gene (PDGFR-β), mast cell-related genes, and type 2 pneumocyte-related genes were found to be overexpressed in PCH lesions.In situhybridization as well as immunohistochemistry for PDGFB showed expression by type 2 pneumocytes and endothelial cells. Immunohistochemical staining for PDGFR-β localized to pericytic/vascular smooth muscle cells surrounding the proliferating capillaries. CD117 staining confirmed an abundance of mast cells in the lesions, which also stained heavily for PDGFR-β.Conclusions:The expression of thePDGFBandPDGFR-β genes characterizes the nodular proliferations of PCH. Increased numbers of mast cells, pericytes, and type II pneumocytes accompany the endothelial proliferation. The up-regulation of these important angiogenic and antiapoptotic genes suggests a mechanism and potential therapeutic approaches for PCH.     

Platelet-derived growth factor involvement in myocardial remodeling following infarction

Cardiac remodeling occurs in the infarcted heart (MI). The underlying regulatory mechanisms are under investigation. Platelet-derived growth factor (PDGF) is a family of growth factors that stimulates cell growth, differentiation and migration. Herein, we sought to determine whether PDGF is involved in cardiac repair/remodeling following MI. The temporal and spatial expressions of PDGF isoforms (A, B, C and D) and PDGF receptor (PDGFR)-α and β as well as cell types expressing PDGF were examined in the infarcted rat heart. Sham-operated rats served as controls. We found that the normal myocardium expressed all PDGF isoforms, and cell types expressing PDGF were primarily interstitial cells. Following MI, PDGF-A and D were significantly increased in the infarcted myocardium during 6 weeks of the observation period and cells expressing PDGF-A and D were primarily endothelial cells, macrophages and myofibroblasts (myoFb). PDGF-B and C expressions were, however, reduced in the infarcted heart. In the noninfarcted myocardium, PDGF-D expression was increased in the late stage of MI and cells expressing PDGF-D were predominantly fibroblasts. Both PDGFR-α and β were significantly increased in the infarcted myocardium in the early and late stages of MI and in the noninfarcted myocardium in the late stage of MI. Enhanced PDGF-A, PDGF-D and PDGFR are coincident with angiogenesis, and inflammatory and fibrogenic responses in the infarcted myocardium, suggesting their regulation on cardiac repair. Elevated PDGF-D in the noninfarcted myocardium suggests its involvement in the development of interstitial fibrosis that appears in the late stage of MI.     

Platelet-derived growth factor stimulates bone resorption by monocyte monolayers

Resorption of devitalized bone particles by monocytes grown in culture was stimulated by platelet-derived growth factor (PDGF) in a dose-dependent manner. Bone resorption in response to PDGF was time-dependent with a significant increase over control cultures evident by 72 hours. These data are the first to demonstrate stimulation of bone resorption by PDGF in a specific cell type known to resorb bone in vivo and in vitro.     

Platelet-derived growth factor receptor-beta promotes early endothelial cell differentiation

Platelet-derived growth factor BB (PDGF-BB) has been assigned a critical role in vascular stability by promoting the recruitment of PDGF receptor-beta-expressing perivascular cells. Here we present data indicating that early hematopoietic/endothelial (hemangio) precursors express PDGFR-beta based on coexpression with CD31, vascular endothelial growth factor receptor-2, and CD41 in 2 models: mouse yolk sac (embryonic day 8 [E8]) and differentiating mouse embryonic stem cells (embryoid bodies). Expression of PDGFR-beta on hemangioprecursor cells in the embryoid bodies gradually disappeared, and, at E14, expression appeared on perivascular cells. Activation of the PDGFR-beta on the hemangioprecursors accelerated the differentiation of endothelial cells, whereas differentiation of the hematopoietic lineage was suppressed. In E9.5 yolk sacs derived from recombinant mice expressing kinase-active PDGFR-beta with an aspartic acid to asparagine (D894N) replacement in the kinase activating loop and from mice with ubiquitous expression of PDGF-BB driven by the Rosa26 locus, the number of CD41-expressing early hematopoietic cells decreased by 36% and 34%, respectively, compared with staged wild-type littermates. Moreover, enhanced vascular remodeling was evident in the Rosa26-PDGF-BB yolk sacs. We conclude that PDGFR-beta is expressed on early hemangioprecursor cells, regulating vascular/hematopoietic development.     

Platelet-derived endothelial cell growth factor: structure and function.

Platelet-derived endothelial cell growth factor (PD-ECGF) is a 45-kDa single chain polypeptide, which stimulates the growth and chemotaxis of endothelial cells in vitro and angiogenesis in vivo. Purification from human platelets and cDNA cloning of PD-ECGF disclosed that it is a novel type of angiogenic factor without sequence similarity to hitherto known proteins. PD-ECGF is present in human platelets as well as in placenta. Amino acid sequencing of PD-ECGF from human placenta revealed that the placental form has an additional 5 amino acids at the N-terminus. In cultured cells, it is produced by normal fibroblasts as well as some transformed cell lines. PD-ECGF lacks a hydrophobic signal sequence and remains inside the producer cells. PD-ECGF may act at sites of injury as a wound hormone and thus play an important role under several physiological and pathological conditions.     

Platelet-derived growth factors

Blood platelets are a rich source of growth factors, including platelet-derived growth factor, platelet-derived endothelial cell growth factor, and transforming growth factor beta. Platelet-derived growth factor stimulates the growth of mesenchymal cells such as fibroblasts and vascular smooth muscle cells, whereas platelet-derived endothelial cell growth factor is a mitogen for vascular endothelial cells. Transforming growth factor beta is a bifunctional regulator of cellular growth, but acts as a potent inhibitor for most cell types. Most of the growth regulatory substances in platelets have been reported to reside in platelet alpha-granules, but platelet-derived endothelial cell growth factor appears to be present in platelet cytoplasm. These growth factors may act at sites of injury as wound hormones. Moreover, they play important roles for some pathological conditions such as atherosclerosis, myelofibrosis, connective tissue diseases, and neoplastic disorders.     

Platelet-derived growth factor induces apoptosis in growth-arrested murine fibroblasts.

The platelet-derived growth factor (PDGF) is a potent mitogen for murine fibroblasts. PDGF-stimulated cells express a set of immediate-early-response genes but require additional (progression) factors in serum to progress through the cell cycle. Serum-deprived cells are reversibly arrested in G0 phase and fail to fully traverse the G1 phase of the cell cycle when stimulated by PDGF alone. We now report that serum-deprived normal rat kidney fibroblast (NRK) cells stimulated by either PDGF AA or PDGF BB homodimers undergo apoptotic cell death. Furthermore, we show that epidermal growth factor also induces apoptotic cell death in serum-deprived NRK cells, epidermal growth factor enhances the rate of apoptosis in PDGF-treated cells, and a progression factor (insulin) but not endogenously expressed Bc1-2 fully protects NRK cells from PDGF-stimulated apoptosis. The results indicate that PDGF induces apoptosis in growth-arrested NRK cells and that the inability of NRK cells to transit the G1/S checkpoint is the critical determinant in establishing the genetic program(s) to direct the PDGF signal to apoptosis. The results suggest that polypeptide growth factors in vivo may signal cell fate positively or negatively in settings that limit the potential of cells to completely transit the cell cycle.     

Platelet-derived growth factor is decreased in patients with myeloproliferative disorders

Platelet-derived growth factor (PDGF) has been suggested to play some role in the pathogenesis of myelofibrosis frequently encountered in patients with myeloproliferative disorders (MPD). In this study we measured PDGF activity and PF4 content in circulating platelets of patients with MPD. Both factors were lower than those of normal controls. PDGF activity in patients with myelofibrosis was slightly lower than in those without fibrosis. However, when adjusted to whole blood volume, there was a positive correlation between platelet count and PDGF activity per ml whole blood. Nevertheless, no correlation was found between activity and grade of bone marrow fibrosis. These results may support the idea that an abnormal release of PDGF occurs from platelets or megakaryocytes in the bone marrow environment, resulting in the stimulation of fibroblast proliferation, and hence, the occurrence of myelofibrosis in patients with MPD.     

Platelet-derived growth factor receptor family mutations in gastrointestinal stromal tumours

OBJECTIVE: Activating mutations of either KIT or platelet-derived growth factor receptor alpha (PDGFRA) genes are present in the majority of gastrointestinal stromal tumours (GISTs). The type of gene mutation is associated with the aggressiveness of the disease, response to imatinib therapy, and the tumour site in the gastrointestinal tract. However, a subgroup of GISTs does not harbour these mutations. MATERIAL AND METHODS: Thirty-three GISTs were studied for mutations in exons encoding the juxtamembrane and the activation loop domains of KIT, PDGFRA, PDGFRB, CSF1R, and FLT3 genes using denaturing high-performance liquid chromatography and gene sequencing. RESULTS: Twenty-two (67%) GISTs had mutation in KIT and 3 (9%) in PDGFRA. The three PDGFRA mutations were all detected in exon 18 of the gene. Three of the 5 GISTs that had weak to moderate KIT expression had a PDGFRA mutation as compared to none of the 26 cases with strong KIT immunopositivity (p=0.022). No mutations were found in PDGFRB, CSF1R or FLT3 in the 8 cases that did not harbour KIT or PDGFRA mutations. CONCLUSIONS: KIT and PDGFRA are the most commonly mutated type III receptor tyrosine kinase genes in GIST. GISTs with PDGFRA mutations often have reduced expression of the KIT protein in immunohistochemistry, suggesting that immunohistochemistry may be potentially useful in identification of such GISTs.     

Platelet-derived growth factor receptor family mutations in gastrointestinal stromal tumours

Objective. Activating mutations of either KIT or platelet-derived growth factor receptor alpha (PDGFRA) genes are present in the majority of gastrointestinal stromal tumours (GISTs). The type of gene mutation is associated with the aggressiveness of the disease, response to imatinib therapy, and the tumour site in the gastrointestinal tract. However, a subgroup of GISTs does not harbour these mutations. Material and methods. Thirty-three GISTs were studied for mutations in exons encoding the juxtamembrane and the activation loop domains of KIT, PDGFRA, PDGFRB, CSF1R, and FLT3 genes using denaturing high-performance liquid chromatography and gene sequencing. Results. Twenty-two (67%) GISTs had mutation in KIT and 3 (9%) in PDGFRA. The three PDGFRA mutations were all detected in exon 18 of the gene. Three of the 5 GISTs that had weak to moderate KIT expression had a PDGFRA mutation as compared to none of the 26 cases with strong KIT immunopositivity (p=0.022). No mutations were found in PDGFRB, CSF1R or FLT3 in the 8 cases that did not harbour KIT or PDGFRA mutations. Conclusions.KIT and PDGFRA are the most commonly mutated type III receptor tyrosine kinase genes in GIST. GISTs with PDGFRA mutations often have reduced expression of the KIT protein in immunohistochemistry, suggesting that immunohistochemistry may be potentially useful in identification of such GISTs.     

Platelet-derived growth factor stimulates bone resorption via a prostaglandin-mediated mechanism

Platelet-derived growth factor (PDGF) stimulated up to 15-fold the production of prostaglandin E2 (PGE2) and bone resorption in neonatal mouse calvaria in organ culture. The action of PDGF on bone resorption occurred at low concentrations of the protein (ED50 = 10 ng/ml). All concentrations of PDGF which stimulated resorption also enhanced the production of PGE2 by bone; concentrations of PDGF which did not stimulate resorption did not enhance PGE2 production. PDGF-induced formation of PGE2 and bone resorption were inhibited completely by indomethacin (100 ng/ml) and hydrocortisone (1 microgram/ml). Indomethacin did not inhibit the bone resorption-stimulating activity of exogenous PGE2. In the continued presence of a maximum concentration of PDGF (100 ng/ml), an increase in bone resorption, as measured by an increase in medium calcium, was detected at 16 h (P less than 0.01), but not at 12 h; however, an increase in PGE2 production occurred within the first 2 h of treatment. A similar lag period for the onset of bone resorption was seen after the addition of exogenous PGE2 to the culture medium. On the other hand, exposure of bones to PDGF (50 ng/ml) for as brief a period as 5-15 min, followed by washout of PDGF, triggered bone resorption over the subsequent 48 h. PDGF increased cAMP production by bone within 30 min, and this effect of PDGF was blocked completely by indomethacin while the action of exogenous PGE2 on the production of cAMP was not blocked by indomethacin. The action of a low concentration of PDGF (1 ng/ml), which did not stimulate bone resorption alone, was potentiated by the phosphodiesterase inhibitor isobutylmethylxanthine (4 microM). We conclude that low concentrations of PDGF stimulate bone resorption via the enhanced local production of PGE2.