Modulation of PDGF-C and PDGF-D expression during bleomycin-induced lung fibrosis

PDGF isoforms are a family of polypeptides that bind to cell surface receptors and induce fibroblast proliferation and chemotaxis. The PDGF-A and -B chain isoforms have been implicated in fibroproliferative lung injury in animal models and in human disease. Two recently recognized PDGF polypeptides, PDGF-C and -D, differ from the PDGF-A and -B isoforms in that they require proteolytic cleavage before they can bind and activate the PDGF receptors. Our findings demonstrate that administration of bleomycin to murine lungs leads to a significant increase in PDGF-C mRNA expression and a significant decrease in PDGF-D mRNA expression. PDGF-C expression was localized to areas of lung injury by in situ hybridization, and PDGF-C expression was not upregulated in the lungs of BALB/c mice that are resistant to bleomycin-induced lung fibrosis. Moreover, there is in vivo phosphorylation of the PDGF-receptor that binds PDGF-C in response to bleomycin administration. These observations strongly suggest a role for PDGF-C in bleomycin-induced pulmonary fibrosis.     

PDGF-D is a specific, protease-activated ligand for the PDGF beta-receptor

The term 'platelet-derived growth factor' (PDGF) refers to a family of disulphide-bonded dimeric isoforms that are important for growth, survival and function in several types of connective tissue cell. So far, three different PDGF chains have been identified - the classical PDGF-A and PDGF-B and the recently identified PDGF-C. PDGF isoforms (PDGF-AA, AB, BB and CC) exert their cellular effects by differential binding to two receptor tyrosine kinases. The PDGF alpha-receptor (PDGFR-alpha) binds to all three PDGF chains, whereas the beta-receptor (PDGFR-beta) binds only to PDGF-B. Gene-targeting studies using mice have shown that the genes for PDGF-A and PDGF-B, as well as the two PDGFR genes, are essential for normal development. Furthermore, overexpression of PDGFs is linked to different pathological conditions, including malignancies, atherosclerosis and fibroproliferative diseases. Here we have identify and characterize a fourth member of the PDGF family, PDGF-D. PDGF-D has a two-domain structure similar to PDGF-C and is secreted as a disulphide-linked homodimer, PDGF-DD. Upon limited proteolysis, PDGF-DD is activated and becomes a specific agonistic ligand for PDGFR-beta. PDGF-DD is the first known PDGFR-beta-specific ligand, and its unique receptor specificity indicates that it may be important for development and pathophysiology in several organs.     

Cognitive and socio-emotional deficits in platelet-derived growth factor receptor-β gene knockout mice

Platelet-derived growth factor (PDGF) is a potent mitogen. Extensive in vivo studies of PDGF and its receptor (PDGFR) genes have reported that PDGF plays an important role in embryogenesis and development of the central nervous system (CNS). Furthermore, PDGF and the β subunit of the PDGF receptor (PDGFR-β) have been reported to be associated with schizophrenia and autism. However, no study has reported on the effects of PDGF deletion on mice behavior. Here we generated novel mutant mice (PDGFR-β KO) in which PDGFR-β was conditionally deleted in CNS neurons using the Cre/loxP system. Mice without the Cre transgene but with floxed PDGFR-β were used as controls. Both groups of mice reached adulthood without any apparent anatomical defects. These mice were further examined by conducting several behavioral tests for spatial memory, social interaction, conditioning, prepulse inhibition, and forced swimming. The test results indicated that the PDGFR-β KO mice show deficits in all of these areas. Furthermore, an immunohistochemical study of the PDGFR-β KO mice brain indicated that the number of parvalbumin (calcium-binding protein)-positive (i.e., putatively γ-aminobutyric acid-ergic) neurons was low in the amygdala, hippocampus, and medial prefrontal cortex. Neurophysiological studies indicated that sensory-evoked gamma oscillation was low in the PDGFR-β KO mice, consistent with the observed reduction in the number of parvalbumin-positive neurons. These results suggest that PDGFR-β plays an important role in cognitive and socioemotional functions, and that deficits in this receptor may partly underlie the cognitive and socioemotional deficits observed in schizophrenic and autistic patients.     

PDGF—D和VEGF在宫颈鳞癌中的表达及其意义

目的：检测宫颈鳞癌组织中血小板源性生长因子D（PDGF—D）和血管内皮生长因子（VEGF）的表达,探讨二者在宫颈癌变过程中的作用及意义,为探讨宫颈鳞癌的发病机制和宫颈鳞癌的早期治疗提供理论依据。方法：采用免疫组织化学（sP法）检测40例宫颈鳞癌和10例正常宫颈组织中PDGF—D和VEGF蛋白的表达,分析两者之间的相关性及其与临床病理特征之间的关系。结果：宫颈鳞癌组织中PDGF—D和VEGF蛋白的表达显著高于正常宫颈组织（P〈0．05）;PDGF—D和VEGF的表达与宫颈鳞癌的分化程度及淋巴结转移有关（P〈0．05）;与年龄及临床分期无关（P〉0．05）。Spearman相关分析发现PDGF—D与VEGF表达程度呈正相关（r=0．346,P〈0．05）。结论：1．PDGF—D和VEGF在宫颈鳞癌组织中特异性高表达,可能在宫颈鳞癌的发生、发展与转移中起着重要作用。2．PDGF-D和VEGF表达与宫颈鳞癌的分化程度及淋巴结转移有关,与年龄及临床分期无关,提示它们可能在宫颈鳞癌的浸润和转移及预后方面有重要的监测意义。3．PDGF-D和VEGF在宫颈鳞癌组织中的表达呈正相关,提示两者起着相互促进的作用,对PDGF—D和VEGF的联合检查,为临床实际应用提供了参考。     

Platelet-derived growth factor D, tissue-specific expression in the eye, and a key role in control of lens epithelial cell proliferation

Platelet-derived growth factor D (PDGF-D), also known as Iris-expressed growth factor, is a member of the PDGF/vascular endothelial growth factor family. The expression of PDGF-D in the eye is tissue-specific. In the anterior segment, it is localized to iris and ciliary body, whereas in the retina, PDGF-D is restricted to the outer plexiform layer. PDGF-D is present in aqueous humor but is not detectable in mature lens or in mouse lens-derived alphaTN4-1 cells. However, it is expressed in rabbit lens-derived N/N1003A cells. N/N1003A cell-conditioned medium stimulates proliferation in rat lens explants, and this is blocked by immunodepletion of PDGF-D. Immunopurified PDGF-D also stimulates cell proliferation in rat lens explants and in NIH 3T3 cells. In organ culture of rat eye anterior segments, anti-PDGF-D strongly inhibits lens epithelial cell proliferation. This finding suggests a major in vivo role for PDGF-D in the mechanisms of coordinated growth of eye tissues. Intervention in the PDGF-D pathway in the eye, perhaps by antibody or blocking peptide, could be useful in the treatment of certain cataracts, including post-operative secondary cataract.     

Interleukin-1 promotes proliferation of vascular smooth muscle cells in coordination with PDGF or a monocyte derived growth factor

We report that interleukin-1 (IL-1) potentiates the proliferation of vascular smooth muscle cells. Growth of early passage smooth muscle cells was not significantly affected by IL-1 alone. Treatment with IL-1 together with the platelet derived growth factor (PDGF) or another polypeptide growth factor derived from mitogen activated human monocytes (MDGF) resulted in a significant enhancement of cell growth over either PDGF or MDGF alone. DNA synthesis was enhanced only marginally (30-40%) in quiescent cultures treated with an optimal concentration of IL-1 alone. In the presence of 5 units/ml of PDGF or MDGF, IL-1 produced about six- to eightfold higher DNA synthesis than the untreated cultures. Induction of DNA synthesis was linear between 0.1 and 1.0 pM IL-1, dependent on PDGF concentration, and was effectively neutralized by monoclonal antibodies against IL-1 beta. The growth promoting activity of IL-1 was extremely potent producing half-maximum stimulation at a concentration of 0.5 pM. These results suggest that IL-1 may play an important role in the modulation of growth and other activities of vascular smooth muscle cells. These observations are especially important with regard to defining the potential macrophage derived mediators contributing to vascular cell proliferation during inflammation and the pathogenesis of atherosclerosis. It is shown here that elicitation of IL-1 induced growth response requires a coordinated action with another priming growth factor such as PDGF. In this regard, IL-1 mediated proliferation of smooth muscle cells may have analogy with the IL-1 mediated T-cell activation and IL-2 production where concerted actions of antigen/mitogen and IL-1 are required.     

PDGF-D, a new protease-activated growth factor

Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer, fibrotic diseases and arteriosclerosis. The PDGF family currently consists of at least three gene products, PDGF-A, PDGF-B and PDGF-C, which selectively signal through two PDGF receptors (PDGFRs) to regulate diverse cellular functions. After two decades of searching, PDGF-A and B were the only ligands identified for PDGFRs. Recently, however, database mining has resulted in the discovery of a third member of the PDGF family, PDGF-C, a functional analogue of PDGF-A that requires proteolytic activation. PDGF-A and PDGF-C selectively activate PDGFR-alpha, whereas PDGF-B activates both PDGFR-alpha and PDGFR-beta. Here we identify and characterize a new member of the PDGF family, PDGF D, which also requires proteolytic activation. Recombinant, purified PDGF-D induces DNA synthesis and growth in cells expressing PDGFRs. In cells expressing individual PDGFRs, PDGF-D binds to and activates PDGFR-beta but not PDGFR-alpha. However, in cells expressing both PDGFRs, PDGF-D activates both receptors. This indicates that PDGFR-alpha activation may result from PDGFR-alpha/beta heterodimerization.     

Mice Lacking Platelet-Derived Growth Factor D Display a Mild Vascular Phenotype

Platelet-derived growth factor D (PDGF-D) is the most recently discovered member of the PDGF family. PDGF-D signals through PDGF receptor β, but its biological role remains largely unknown. In contrast to other members of the PDGF family of growth factors, which have been extensively investigated using different knockout approaches in mice, PDGF-D has until now not been characterized by gene inactivation in mice. Here, we present the phenotype of a constitutive Pdgfd knockout mouse model (Pdgfd^-/-), carrying a LacZ reporter used to visualize Pdgfd promoter activity. Inactivation of the Pdgfd gene resulted in a mild phenotype in C57BL/6 mice, and the offspring was viable, fertile and generally in good health. We show that Pdgfd reporter gene activity was consistently localized to vascular structures in both postnatal and adult tissues. The expression was predominantly arterial, often localizing to vascular bifurcations. Endothelial cells appeared to be the dominating source for Pdgfd, but reporter gene activity was occasionally also found in subpopulations of mural cells. Tissue-specific analyses of vascular structures revealed that NG2-expressing pericytes of the cardiac vasculature were disorganized in Pdgfd^-/- mice. Furthermore, Pdgfd^-/- mice also had a slightly elevated blood pressure. In summary, the vascular expression pattern together with morphological changes in NG2-expressing cells, and the increase in blood pressure, support a function for PDGF-D in regulating systemic arterial blood pressure, and suggests a role in maintaining vascular homeostasis.     

PDGF-D contributes to neointimal hyperplasia in rat model of vessel injury

In this study, we determined the role of PDGF-D, a new member of the PDGF family, in a rat model of balloon injured artery made with a 2F catheter in Sprague-Dawley male rats. PDGF-D expression was studied in the injured and control segments of abdominal aorta. The function of PDGF-D was evaluated in rat vascular smooth muscle cells stably transfected with PDGF-D gene. We found that in normal abdominal aorta, PDGF-D was highly expressed in adventia, moderate in endothelia, and unidentified in media. Stable transfection of PDGF-D gene into vascular smooth muscle cells increased the cell migration by 2.2-fold, and the proliferation by 2.3-fold, respectively, and MMP-2 production and activity as well. These results support the fact that PDGF-D is involved in the formation of neointimal hyperplasia induced by balloon catheter injury and may serve as a target in preventing vascular restenosis after coronary angioplasty.     

Structural and functional specificities of PDGF-C and PDGF-D, the novel members of the platelet-derived growth factors family

The platelet-derived growth factor (PDGF) family was for more than 25 years assumed to consist of only PDGF-A and -B. The discovery of the novel family members PDGF-C and PDGF-D triggered a search for novel activities and complementary fine tuning between the members of this family of growth factors. Since the expansion of the PDGF family, more than 60 publications on the novel PDGF-C and PDGF-D have been presented, highlighting similarities and differences to the classical PDGFs. In this paper we review the published data on the PDGF family covering structural (gene and protein) similarities and differences among all four family members, with special focus on PDGF-C and PDGF-D expression and functions. Little information on the protein structures of PDGF-C and -D is currently available, but the PDGF-C protein may be structurally more similar to VEGF-A than to PDGF-B. PDGF-C contributes to normal development of the heart, ear, central nervous system (CNS), and kidney, while PDGF-D is active in the development of the kidney, eye and brain. In adults, PDGF-C is active in the kidney and the central nervous system. PDGF-D also plays a role in the lung and in periodontal mineralization. PDGF-C is expressed in Ewing family sarcoma and PDGF-D is linked to lung, prostate and ovarian cancers. Both PDGF-C and -D play a role in progressive renal disease, glioblastoma/medulloblastoma and fibrosis in several organs.     

Cultured primate aortic smooth muscle cells express both the PDGF-A and PDGF-B genes but do not secrete mitogenic activity or dimeric platelet-derived growth factor protein

Proliferation of smooth muscle cells (SMC) in the arterial intima of man and experimental animals is important in the pathogenesis of atherosclerosis. Vascular SMC proliferation in vitro is stimulated by a number of agents, including the potent protein mitogen, platelet-derived growth factor (PDGF). Recent studies on rat arterial SMC indicate that these cells may, under certain circumstances, synthesize PDGF protein mitogens, suggesting that the regulation of SMC proliferation in vivo may have an autocrine or paracrine component. In this study we demonstrate that cultured nonhuman primate (baboon) aortic SMC transcribe both the PDGF-A and PDGF-B genes but do not secrete detectable mitogenic activity characteristic of native PDGF. The absence of this activity was not due to the presence in the cell conditioned medium of factors inhibitory for PDGF-mediated mitogenic activity. Metabolic labeling of the cells and immunoprecipitation with specific antibodies to human PDGF did not detect a dimeric (30 kDa) PDGF protein in either the intracellular or extracellular compartments, but instead identified PDGF-related proteins of molecular weight 12 kDa and 100 kDa. These data suggest the presence in vascular SMC of a mechanism regulating the translation of PDGF mRNA that may play an important role in the control of SMC proliferation in vivo.     

Emerging roles of PDGF-D signaling pathway in tumor development and progression

Platelet-derived growth factor-D (PDGF-D) can regulate many cellular processes, including cell proliferation, apoptosis, transformation, migration, invasion, angiogenesis and metastasis. Therefore PDGF-D signaling has been considered to be important in human malignancies, and thus PDGF-D signaling may represent a novel therapeutic target, and as such suggests that the development of agents that will target PDGF-D signaling is likely to have a significant therapeutic impact on human cancers. This mini-review describes the mechanisms of signal transduction associated with PDGF-D signaling to support the role of PDGF-D in the carcinogenesis. Moreover, we summarize data on several PDGF-D inhibitors especially naturally occurring “chemopreventive agent” such an indole compound, which we believe could serve as a novel agent for the prevention of tumor progression and/or treatment of human malignancies by targeted inactivation of PDGF-D signaling.     

Nox5 mediates PDGF-induced proliferation in human aortic smooth muscle cells

The proliferation of vascular smooth muscle cells is important in the pathogenesis of many vascular diseases. Reactive oxygen species (ROS) produced by NADPH oxidases in smooth muscle cells have been shown to participate in signaling cascades regulating proliferation induced by platelet-derived growth factor (PDGF), a powerful smooth muscle mitogen. We sought to determine the role of Nox5 in the regulation of PDGF-stimulated human aortic smooth muscle cell (HASMC) proliferation. Cultured HASMC were found to express four isoforms of Nox5. When HASMC stimulated with PDGF were pretreated with N-acetyl cysteine (NAC), proliferation was significantly reduced. Proliferation induced by PDGF was also heavily dependent on JAK/STAT activation, as the JAK inhibitor, AG490, was able to completely abolish PDGF-stimulated HASMC growth. Specific knockdown of Nox5 with a siRNA strategy reduced PDGF-induced HASMC ROS production and proliferation. Additionally, siRNA to Nox5 inhibited PDGF-stimulated JAK2 and STAT3 phosphorylation. ROS produced by Nox5 play an important role in PDGF-induced JAK/STAT activation and HASMC proliferation.     

Characterization of a novel anti-peptide antibody that recognizes a specific conformation of the platelet-derived growth factor receptor.

Two site-specific anti-peptide antibodies (AbP1 and AbP2) were raised against the platelet-derived growth factor (PDGF) receptor. These two sites correspond to amino acid residues 977 through 988 (peptide 1) and 932 through 947 (peptide 2) of the murine PDGF receptor. Both antibodies recognized human and murine PDGF receptors in immunoprecipitation and immunoblotting analyses. None of the antibodies was directed to phosphotyrosine. One of the antibodies (AbP2) showed unusual antigen recognition specificity. This antibody specifically recognized the tyrosine-phosphorylated PDGF receptor and not the unphosphorylated native receptor, suggesting that recognition by this antibody requires a specific conformation that is induced by PDGF-stimulated autophosphorylation.     

PDGF A chain homodimers drive proliferation of bipotential (O-2A) glial progenitor cells in the developing rat optic nerve.

The bipotential glial progenitor cells (O-2A progenitors), which during development of the rat optic nerve give rise to oligodendrocytes and type 2 astrocytes, are stimulated to divide in culture by platelet-derived growth factor (PDGF), and there is evidence that PDGF is important for development of the O-2A cell lineage in vivo. We have visualized PDGF mRNA in the rat optic nerve by in situ hybridization, and its spatial distribution is compatible with the idea that type 1 astrocytes are the major source of PDGF in the nerve. We can detect mRNA encoding the A chain, but not the B chain of PDGF in the brain and optic nerve, suggesting that the major form of PDGF in the central nervous system is a homodimer of A chains (PDGF-AA). PDGF-AA is a more potent mitogen for O-2A progenitor cells than is PDGF-BB, while the reverse is true for human or rat fibroblasts. Fibroblasts display two types of PDGF receptors, type A receptors which bind to all three dimeric isoforms of PDGF, and type B receptors which bind PDGF-BB and PDGF-AB, but have low affinity for PDGF-AA. Our results suggest that O-2A progenitor cells possess predominantly type A receptors, and proliferate during development in response to PDGF-AA secreted by type 1 astrocytes.     

The effect of peptide deletions on the glycosylation of murine immunoglobulin M heavy chains

The glycosylation and processing of the asparagine-linked oligosaccharides at individual glycosylation sites on the mu-chain of murine immunoglobulin M were investigated using variant cell lines that synthesize and secrete IgM heavy chains with known peptide deletions. Normal murine IgM has five N-linked oligosaccharides in the constant region of each heavy or mu-chain. Each mu-chain has four complex-type oligosaccharides as well as a single high mannose-type oligosaccharide near the carboxyl terminus of the molecule. The peptide deletion of the C mu 1 constant region domain in the heavy chains synthesized by one variant cell line did not prevent subsequent glycosylation at more distal glycosylation sites. In fact, the presence of this deletion resulted in more complete glycosylation at the C-terminal glycosylation site. Evaluation of glycopeptides containing individual glycosylation sites by Concanavalin A-Sepharose indicated that this deletion had no significant effect on the processing of structures from high mannose-type to complex-type oligosaccharide chains. In contrast, a deletion of the C-terminal peptide region of the heavy chain of IgM synthesized by a second variant cell line resulted in intracellular processing to more highly branched oligosaccharide structures at several of the glycosylation sites not involved in the deletion.     

PDGF-D Expression Is Down-Regulated by TGFβ in Fibroblasts

Transforming growth factor-β (TGFβ) is a key mediator of fibrogenesis. TGFβ is overexpressed and activated in fibrotic diseases, regulates fibroblast differentiation into myofibroblasts and induces extracellular matrix deposition. Platelet-derived growth factor (PDGF) is also a regulator of fibrogenesis. Some studies showed a link between TGFβ and PDGF in certain fibrotic diseases. TGFβ induces PDGF receptor alpha expression in scleroderma fibroblasts. PDGF-C and -D are the most recently discovered ligands and also play a role in fibrosis. In this study, we report the first link between TGFβ and PDGF-D and -C ligands. In normal fibroblasts, TGFβ down-regulated PDGF-D expression and up-regulated PDGF-C expression at the mRNA and protein levels. This phenomenon is not limited to TGFβ since other growth factors implicated in fibrosis, such as FGF, EGF and PDGF-B, also regulated PDGF-D and PDGF-C expression. Among different kinase inhibitors, only TGFβ receptor inhibitors and the IκB kinase (IKK) inhibitor BMS-345541 blocked the effect of TGFβ. However, activation of the classical NF-κB pathway was not involved. Interestingly, in a model of lung fibrosis induced by either bleomycin or silica, PDGF-D was down-regulated, which correlates with the production of TGFβ and other fibrotic growth factors. In conclusion, the down-regulation of PDGF-D by TGFβ and other growth factors may serve as a negative feedback in the network of cytokines that control fibrosis.     

Functional identification of a novel 14-3-3 epsilon splicing variant suggests dimerization is not necessary for 14-3-3 epsilon to inhibit UV-induced apoptosis

14-3-3 proteins function as a dimer and have been identified to involve in diverse signaling pathways. Here we reported the identification of a novel splicing variant of human 14-3-3 epsilon (14-3-3 epsilon sv), which is derived from a novel exon 1′ insertion. The insertion contains a stop codon and leads to a truncated splicing variant of 14-3-3 epsilon. The splicing variant is translated from the exon 2 and results in the deletion of an N-terminal α-helix which is crucial for the dimerization. Therefore, the 14-3-3 epsilon sv could not form a dimer with 14-3-3 zeta. However, after UV irradiation 14-3-3 epsilon sv could also support cell survival, suggesting monomer of 14-3-3 epsilon is sufficient to protect cell from apoptosis.     

Novel PDGF family members: PDGF-C and PDGF-D

Platelet-derived growth factors (PDGFs) were discovered almost two decades ago. The classical PDGF polypeptide chains, PDGF-A and PDGF-B, are well studied and they regulate a number of physiological and pathophysiological processes in many types of mesenchymal cells via two receptor tyrosine kinases, PDGF receptors alpha and beta. Recently, two additional PDGF polypeptide chains were discovered, namely PDGF-C and PDGF-D. The discovery of two additional ligands for the two PDGF receptors suggests that PDGF-mediated signaling is more complex than previously anticipated.