Role Of Platelet-derived Growth Factor Research Articles

Abstract 4420: Matriptase-mediated proteolytic regulation of biological activity and spatial distribution of PDGF-D

Abstract The oncogenic roles of platelet-derived growth factor D (PDGF-D) and its proteolytic activator, matriptase, have been strongly implicated in human prostate cancer. The latent full-length PDGF-D consists of N-terminal CUB domain, C-terminal growth factor domain, and hinge region in between. Matriptase processes the full-length PDGF-D dimer (FL-D) into PDGF-D growth factor domain dimer (GFD-D) in a step-wise manner, involving generation of hemidimer (HD), which is an intermediate product containing one full-length PDGF-D subunit and one growth factor domain subunit. In this study, we showed that HD acts as a dominant-negative ligand of PDGF/PDGFR signaling in fibroblasts whereas it has its own unique function in pre-osteoclasts. The regulation of PDGF-D's activity by matriptase is biphasic as demonstrated by the event that active PDGF-D GFD-D can be further cleaved into a smaller and yet inactive form if the enzymatic action of matriptase persists. By mutagenesis analyses, we identified amino acid residues R340R341GR343A at the C-terminus of PDGF-D growth factor domain to be the matriptase cleavage site through which PDGF-D is inactivated. Based on the sequence analysis in comparison with the published crystal structure of PDGF-B, we suggest that R340R341GR343A is within the loop III of PDGF-D growth factor domain, a critical domain for its binding to the PDGF receptor. When the positively charged arginine residues of R340R341GR343A were mutated to alanine residues, PDGF-D GFD-D lost its biological activity in activating β-PDGFR. Further, we found that proteolytic processing of latent PDGF-D to remove CUB domain and hinge region is tightly linked with the storage of PDGF-D GFD-D within extracellular matrix (ECM) in vitro. These results indicate the increased affinity to the ECM from FL-D, HD, to GFD-D and also suggest that CUB domain and hinge region of PDGF-D prevent the sequestration of PDGF-D in ECM. Interestingly, the matriptase cleavage site R340R341GR343A within the growth factor domain is also critical for PDGF-D association with ECM. Taken together, the present study reports structural elements crucial to the biologically function of PDGF-D and its association with ECM, suggesting that proteolytic processing is a crucial mechanism for PDGF-D to establish its tissue gradient. Citation Format: Wei Huang, Hyeong-Reh C. Kim. Matriptase-mediated proteolytic regulation of biological activity and spatial distribution of PDGF-D. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4420. doi:10.1158/1538-7445.AM2014-4420

Abstract 28: The influence of PDGF and VEGF on tumor proliferation in colon cancer

Abstract Background: The platelet derived growth factor (PDGF) and Vascular Endothelial Growth Factor (VEGF) are known to play a crucial role in different tumor entities. Involved in cell migration and proliferation of stromal cells and tumor cells they represent key targets in cancer therapy. The aim of the study was to analyse the specific role of PDGF and VEGF stimulation on tumor cell proliferation and metabolism in colorectal cancer (CRC). Methods: The human colon cancer cell line HT-29 and Caco-2 were cultured and stimulated with PDGF and VEGF in a time-dependent manner. Whole cell extracts and RNA extracts were analyzed by Western Blot and RT-q-PCR for PDGF- and VEGF receptors and for components of cellular metabolism. To discover effects of PDGF and VEGF on proliferation MTS proliferation assays were performed. Results: Western Blot analysis and RT-qPCR showed no relevant PDGF-receptor α and β expression in HT-29 cells but varying expression in Caco-2 cells. Stimulation with PDGF or VEGF resulted in increased proliferation compared to untreated controls while simultaneous stimulation with both growth factors did not result in intensified proliferation. Additionally, under stimulation altered expression of various metabolic components was detected. Conclusion: Our results demonstrate a promoting effect on tumor cell proliferation of both growth factors VEGF and PDGF. Simultaneous stimulation did not show synergistic effects. PDGF in HT-29 cells resulted in proliferation in the absence of PDGF receptors with changes in tumor cell metabolism after stimulation. Moreover in HT-29 cells glucose metabolism changed during stimulation. In conclusion, our data give evidence for direct receptor/ligand signalling of PDGF not only on stromal cells but also on colon cancer cells even in the absence of the PDGF receptor. Citation Format: Romana Mönch, Tanja Grimmig, Vinicius Kannen, Christoph T. Germer, Ana Maria Waaga-Gasser, Martin Gasser. The influence of PDGF and VEGF on tumor proliferation in colon cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 28. doi:10.1158/1538-7445.AM2014-28

Platelet-derived Growth Factor Primes Cancer-associated Fibroblasts for Apoptosis

Desmoplastic malignancies such as cholangiocarcinoma (CCA) are characterized by a dense stroma containing an abundance of myofibroblasts termed cancer-associated fibroblasts (CAF). The CAF phenotype represents an "activated state" in which cells are primed for cell death triggered by BH3 mimetics. Accordingly, this primed state may be therapeutically exploited. To elucidate the mechanisms underlying this poorly understood apoptotic priming, we examined the role of platelet-derived growth factor (PDGF) in CAF priming for cell death given its prominent role in CAF activation. PDGF isomers PDGF-B and PDGF-D are abundantly expressed in CCA cells derived from human specimens. Either isomer sensitizes myofibroblasts to cell death triggered by BH3 mimetics. Similar apoptotic sensitization was observed with co-culture of myofibroblasts and CCA cells. Profiling of Bcl-2 proteins expressed by PDGF-primed myofibroblasts demonstrated an increase in cellular levels of Puma. PDGF-mediated increases in cellular Puma levels induced proapoptotic changes in Bak, which resulted in its binding to Bcl-2. Short hairpin RNA-mediated down-regulation of Puma conferred resistance to PDGF-mediated apoptotic priming. Conversely, the BH3 mimetic navitoclax disrupted Bcl-2/Bak heterodimers, allowing Bak to execute the cell death program. Treatment with a Bcl-2-specific BH3 mimetic, ABT-199, reduced tumor formation and tumor burden in a murine model of cholangiocarcinoma. Collectively, these findings indicate that apoptotic priming of CAF by PDGF occurs via Puma-mediated Bak activation, which can be converted to active full-blown apoptosis by navitoclax or ABT-199 for therapeutic benefit.

Research advances of platelet derived growth factor family and its significance in neovascular eye diseases

Platelet derived growth factor (PDGF) is a family of peliotropic growth factors that regulate cell proliferation and differentiation in an autocrine or paracrine manner through receptor mediated signal transduction pathways. Recent studies have demonstrated that PDGF plays an important role in ocular neovascularization, and the application of PDGF has a broad prospect in treatment of ocular neovascularization. Here, we summarize the current understanding of structure, function and expression of PDGF in the eye; the effects of PDGF on the blood vessel forming cells, as well as the interaction between PDGF and other pro-angiogenic factors. In addition, the role of PDGF in neovascular eye diseases, including retinopathy of prematurity, diabetic retinopathy, age-related macular degeneration, corneal neovascularization, and neovascular glaucoma, is also discussed.

Expression of PDGF-B and methylation levels of its gene promoter in human gliomas

Objective To investigate the role of platelet-derived growth factor B (PDGF-B) expression levels and the methylation levels of its gene promoter on proliferation of human gliomas.Methods The expressions of PDGF-B,p-Smad2 and Ki-67 were determined by immunohistochemistry in 54 human glioma specimens.And the methylation levels of PDGF-B gene promoter were determined using pyrosequencing.Results (1) The expression levels of PDGF-B increased with the pathologic grades elevated (P ＜0.05).(2) There was a positive and significant correlation between the expression levels of PDGF-Band Ki-67 as well as p-Smad2 (r =0.839,P ＜0.001) (r =0.802,P ＜0.001),respectively.And an inverse and significant correlation was found between the expression levels of PDGF-B and its gene promoter methylation (r =-0.817,P ＜0.001).(3) The methylation levels of PDGF-B gene promoter were significantly higher in low grade gliomas (WHO Ⅰ Ⅱ) than those in high grade gliomas (WHO Ⅲ Ⅳ) (P =0.001).Conclusions The expression levels of PDGF-B and its gene promoter methylation play an important role in predicting the malignancy and proliferation of human gliomas. Key words: Glioma; Gene Methylation; Pyrosequencing; Platelet-derived growth factov B

The roles of platelet-derived growth factors and their receptors in brain radiation necrosis

BackgroundBrain radiation necrosis (RN) occurring after radiotherapy is a serious complication. We and others have performed several treatments for RN, using anticoagulants, corticosteroids, surgical resection and bevacizumab. However, the mechanisms underlying RN have not yet been completely elucidated. For more than a decade, platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have been extensively studied in many biological processes. These proteins influence a wide range of biological responses and participate in many normal and pathological conditions. In this study, we demonstrated that PDGF isoforms (PDGF-A, B, C, and D) and PDGFRs (PDGFR-α and β) are involved in the pathogenesis of human brain RN. We speculated on their roles, with a focus on their potential involvement in angiogenesis and inflammation in RN.MethodsSeven surgical specimens of RN, obtained from 2006 to 2013 at our department, were subjected to histopathological analyses and stained with hematoxylin and eosin. We qualitatively analyzed the protein expression of each isoform of PDGF by immunohistochemistry. We also examined their expression with double immunofluorescence.ResultsAll PDGFs were expressed in macrophages, microglia, and endothelial cells in the boundary of the core of RN, namely, the perinecrotic area (PN), as well as in undamaged brain tissue (UB). PDGF-C, D and PDGFR-α were also expressed in reactive astrocytes in PN. PDGFs and PDGFR-α were scarcely detected in UB, but PDGFR-β was specifically expressed in endothelial cells not only in PN but also in UB.ConclusionsPDGFs/PDGFRs play critical roles in angiogenesis and possibly in inflammation, and they contribute to the pathogenesis of RN, irrespective of the original tumor pathology and applied radiation modality. Treatments for the inhibition of PDGF-C, PDGF-D, and PDGFR-α may provide new approaches for the treatment of RN induced by common radiation therapies.

Downregulation of angiogenesis factors, VEGF and PDGF, after rapid IgE desensitization and oral immunotherapy in children with food allergy.

Background. Angiogenesis has a key role in several conditions and is regulated by several factors such as the platelet-derived growth factor (PDGF) or the vascular endothelial growth factor (VEGF). The goal of this study was to investigate the possible role of PDGF and VEGF in a group of patients with severe food allergy. Methods. We design a prospective longitudinal study (n = 30) with patients with persistent cow's milk proteins (CMP) allergy. After achieving a CMP rush desensitization protocol, a clinical followup including SPT and blood samples to determine sIgE, protein levels, PDGF, and VEGF-A and a panel of the most representative Th1, Th2, Treg, and Th17 cytokines were also monitored. Results. Baseline levels of PDGF and VEGF in the CMP allergic patients (1170 pg/mL and 253 pg/mL) were different compared to those nonallergic CMP control subjects (501 pg/mL and 108 pg/mL). Both PDGF and VEGF were significantly downregulated (P < 0.05) 6 months after completion of the CMP desensitization process and remained significantly decreased 12 months later. Conclusion. The present study shows a significant increase of PDGF and VEGF in anaphylaxis suffering children compared to a control group. Interestingly, both VEGF and PDGF were significantly downregulated after completing a full CMP rush IgE desensitization.

Integral role of platelet-derived growth factor in mediating transforming growth factor-β1-dependent mesenchymal stem cell stiffening.

Mesenchymal stem cells (MSCs) play an important role in matrix remodeling, fibroblast activation, angiogenesis, and immunomodulation and are an integral part of fibrovascular networks that form in developing tissues and tumors. The engraftment and function of MSCs in tissue niches is regulated by a multitude of soluble proteins. Transforming growth factor-β1 (TGF-β1) and platelet-derived growth factor-BB (PDGF) have previously been recognized for their role in MSC biology; thus, we sought to investigate their function in mediating MSC mechanics and matrix interactions. Cytoskeletal organization, characterized by cell elongation, stress fiber formation, and condensation of actin and microtubules, was dramatically affected by TGF-β1, individually and in combination with PDGF. The intracellular mechanical response to these stimuli was measured with particle tracking microrheology. MSCs stiffened in response to TGF-β1 (their elastic moduli was ninefold higher than control cells), a result that was enhanced by the addition of PDGF (100-fold change). Blocking TGF-β1 or PDGF signaling with inhibitors SB-505124 or JNJ-10198409, respectively, reversed soluble-factor-induced stiffening, indicating that crosstalk between these two pathways is essential for stiffening response. A genome-wide microarray analysis revealed TGF-β1-dependent regulation of cytoskeletal actin-binding protein genes. Actin crosslinking and bundling protein genes, which regulate cytosolic rheology through changes in semiflexible actin polymer meshwork, were upregulated with TGF-β1 treatment. TGF-β1 alone and in combination with PDGF also amplified surface integrin expression and adhesivity of MSCs with extracellular matrix proteins. These findings will provide a more mechanistic insight for modeling tissue-level rigidity in fibrotic tissues and tumors.

Molecular mechanisms of PDGF-AA expression induced by the dsRNA-mimetic poly (I:C) and IL-18

Several animal studies suggest a role of platelet-derived growth factors (PDGFs) particularly A and B in atherosclerosis. Previously, it has been shown that viral infections have the ability to initiate and accelerate atherosclerosis in animal models. Recently, it has been reported that IL-18 has a pro-atherogenic character. Moreover, viral infections have been shown to be associated with induction of IL-18 bioactivity. By using human predendritic KG1 cells, we sought to assess PDGF-AA production under the influence of IL-18 and the byproduct of viral replication, dsRNA-mimetic poly (I:C). Here we demonstrate that poly (I:C) and IL-18 have the ability to induce PDGF-AA expression. In addition, costimulation of KG-1 cells with both IL-18 plus poly (I:C) shows an additive effect on PDGF-AA production. Furthermore, we demonstrate that neither p38 nor SAPK/JNK is required for PDGF-AA production by both PIC and IL-18. However, the expression of PDGF-AA has been found to be associated with increased activation of NF-κB and enhancement of DNA-binding capacity of NF-κB as shown by electrophoretic mobility shift assay (EMSA) and supershift analysis. Collectively, this study demonstrates that the byproduct of viral replication, dsRNA [poly (I:C)], and IL-18 have the ability to induce PDGF-AA in NF-κB-dependent manner. Furthermore, dsRNA act in an additive way with IL-18 to induce PDGF-AA which plays a major role in atherosclerosis. These data might help to understand the pro-atherogenic character of IL-18 and molecular mechanisms of viral infection-induced atherosclerosis.

The Role of Platelet-Derived Growth Factor in the Pathogenesis of Sinonasal Polyps: Immunohistochemical Assessment in Epithelial, Subepithelial and Deep Layers of the Mucosa

ObjectivesThe aim of this study is to investigate the role of platelet-derived growth factor (PDGF) in the pathogenesis of sinonasal polyps.MethodsStudy group (groups 1-3) consisted of nasal polyp samples of patients with sinonasal polyps and the control group consisted of inferior turbinate samples of patients without nasal polyp. In group 1, 14 specimens from ethmoid sinus; in group 2, 10 specimens from nasal cavity; in group 3, 10 specimens from maxillary sinus; and in group 4 (control), 9 specimens from inferior turbinate were included. By immunohistochemical staining technique, the PDGF positivity index (PI) in mucosal layers and in the inflammatory cells were assessed at the epithelium (EP), subepithelial layer of lamina propria (SE), and deep paraglandular layer of the mucosa (D).ResultsPolymorphonuclear cell (PMNC)-percentage (%) values of ethmoid and maxillary sinus, and the PDGF PI from all cells of ethmoid sinus and nasal cavity were significantly higher than those of the control group. As mononuclear cell-% (MNC-%) increased, the PDGF_EP_basal PI, PDGF_SE_endothelial PI, and PDGF_D_endothelial PI decreased. As PMNC-PDGF PI increased, the PDGF_D_perivascular PI decreased and PDGF_D_endothelial PI increased. As PDGF-MNC PI increased, the PDGF_EP_apical PI, PDGF_SE_endothelial PI, and PDGF_D_endothelial PI decreased. As PDGF-all cells (PMNCs, MNCs, and fibroblasts) PI increased, the PDGF_EP_basal PI and PDGF_D_endothelial PI decreased, and the PDGF_D_perivascular PI increased.ConclusionWe concluded that the PDGF systems play important roles in polyp pathogenesis. Fibroblast-derived PDGF may be more important than MNC-derived PDGF in polyp developing process. Increased perivascular-PDGF-PI in deep layers of the mucosa may result in sinonasal polyp formation by causing an increase in vascular permeability and extracellular edema, and thus promoting migration of inflammatory cells to extracellular area. Tissue oxygenization may be important for the initiation of PDGF release system. Because of this reason, nasal obstruction should be medically treated earlier, and, if necessary, by surgical approaches.

Platelet-derived growth factor signaling in mesenchymal cells

Platelet-derived growth factors (PDGFs) and their receptors are major mitogens for many cell types of mensenchymal origin, including fibroblasts and vascular smooth muscle cells (VSMCs). Their role in enhancing migratory and proliferative responses and extracellular matrix synthesis in these cells, make them key regulators of critical biological functions and in tissue diseases including tissue remodeling, scarring and fibrosis. The activities of the PDGFs have been extensively characterized at the molecular and cellular level and inin vivomodel systems. This, in turn, has lead to an increasing number of PDGF-based therapies designed to accelerate or combat defects in tissue repair. This review aims to summarize recent developments in the role of PDGF in key mesenchymal cell functions. Many of the current developments in this field have primarily focused on advancements in understanding cell differentiation, migration, proliferation and the development of emerging PDGF-based therapies and hence will be primary focus of this review.

PDGF and PDGF receptors in glioma

The family of platelet-derived growth factors (PDGFs) plays a number of critical roles in normal embryonic development, cellular differentiation, and response to tissue damage. Not surprisingly, as it is a multi-faceted regulatory system, numerous pathological conditions are associated with aberrant activity of the PDGFs and their receptors. As we and others have shown, human gliomas, especially glioblastoma, express all PDGF ligands and both the two cell surface receptors, PDGFR-α and -β. The cellular distribution of these proteins in tumors indicates that glial tumor cells are stimulated via PDGF/PDGFR-α autocrine and paracrine loops, while tumor vessels are stimulated via the PDGFR-β. Here we summarize the initial discoveries on the role of PDGF and PDGF receptors in gliomas and provide a brief overview of what is known in this field.

Abstract 4367: Contribution of malignant thrombocytosis to ovarian cancer proliferation and resistance to chemotherapy-induced-apoptosis through Platelet Derived Growth Factor Receptor-Alpha (PDGFRA) signaling

Abstract Background: Thrombocytosis at the time of ovarian cancer diagnosis is correlated with decreased interval to progression and decreased overall survival, but the mechanisms for these outcomes are poorly understood. We considered the possible role of Platelet-Derived Growth Factor (PDGF) signaling through PDGFRA as a mechanism for platelet-driven increases in tumor cell growth and progression. Methods: In vitro (co-culture experiments with multiple ovarian cancer cell lines and platelets) and in vivo (orthotopic mouse model of ovarian cancer) experiments were performed to assess the functional and biological effects of platelets on ovarian cancer with regard to invasion, proliferation, and apoptotic response to chemotherapy. In vitro assays queried whether PDGFRA may be implicated in the observed effects. Results: Co-culture assays of ovarian cancer cells with and without platelets showed increased ovarian cancer cell migration (p&amp;lt;0.05 for all cell lines) and proliferation (p&amp;lt;0.05 for all cell lines) in the presence of platelets. Co-culture assays including docetaxel showed ovarian cancer cells had a decreased apoptotic response in the presence of platelets (p&amp;lt;0.05 for all lines). Proliferative and anti-apoptotic effects did not require direct platelet-to-cell contact. Blocking PDGFRA using a monoclonal antibody and/or siRNA reversed, in part, the protective effects that platelets had in decreasing docetaxel-mediated apoptosis (p&amp;lt;0.05). In an orthotopic mouse model of ovarian cancer, platelet transfusions resulted in increased mean tumor weight (4.1g v 2.1g, p=0.03) and increased mean number of tumor nodules (62 v 20, p=0.004). These effects were abrogated by platelet pre-treatment with aspirin and by mouse treatment with aspirin. Immunohistochemistry of tumor specimens showed increased proliferation in the platelet transfused-mice compared to control (82.5% v 66.3%, p&amp;lt;0.001) and decreased apoptosis in transfused-mice compared to control (37.5% decrease, p=0.009). CD31 suggested greater blood vessel maturation in platelet-transfused mice; the ratio of lumen-containing to total vessels was greater in the platelet transfused mice (1.23 v 0.679, p=0.03). Immunofluorescence studies demonstrated platelet extravasation into tumor, confirming the potential for direct platelet-tumor cell interaction. Conclusions: Adverse cancer outcomes correlated to thrombocytosis are partially explained by PDGF-mediated taxane resistance in vitro. We confirmed in vivo that thrombocytosis contributes to increased aggressiveness of malignancy, suggesting that the clinical and mechanistic implications of malignant thrombocytosis warrant further study in order to identify clinically relevant biomarkers and therapeutic targets. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4367. doi:1538-7445.AM2012-4367

Role of Platelet-derived Growth Factor in Hindfoot Fusion

Bone healing that is orchestrated by osteoblasts and osteoclasts is regulated by a complex interaction between biochemical factors such as cytokines and growth factors. One of the critical early growth factors that have an influence on healing is platelet-derived growth factor (PDGF). PDGF is a family of polypeptides that has the ability to attract and stimulate the metabolic activity of mesenchymal cells, stimulating a repair process that includes increased bone formation. Recently, a fully synthetic bone graft material composed of recombinant human platelet-derived growth factor and a β-tricalcium phosphate matrix under the name Augment Bone Graft was shown to be a safe alternative to autogenous bone graft for hindfoot fusion operations. This review provides an overview of the role of PDGF in the biology of bone healing and examines the clinical utility and most recent literature regarding efficacy of the use of PDGF as a safe alternative to autogenous bone graft for hindfoot fusion operations. Finally, the surgical procedure of ankle arthrodesis is described as an example of how PDGF may be used for surgical treatment of end-stage hindfoot arthritis.

Platelet-derived growth factor and renal disease

This review focuses on the recent advances in our understanding of the role of platelet-derived growth factor (PDGF) in glomerular disease. Accumulating evidence indicates a critical involvement of PDGF receptor-β (PDGFR-β) signaling in glomerular disease. Augmented signaling via PDGFR-β is involved in the pathogenesis of IgA nephropathy. Therefore, targeting PDGFR-β signaling is a viable therapeutic strategy for glomerular diseases. However, current PDGFR-β antagonists are nonspecific, and their long-term effects remain to be elucidated. To develop effective intervention therapies targeting PDGF signaling, it is necessary to clarify the specific involvement of PDGF in the pathogenesis of glomerular disease. A novel PDGFR-β targeting mouse model has provided new insight into the postnatal role of PDGFR-β in aging-related mesangial sclerosis and the glomerular remodeling after nephrectomy. Furthermore, the same study indicated the redundancy of growth factor signals underlying glomerular remodeling. In this context, other studies have suggested a role for PDGFR-α signaling and collaborating growth factors to compensate for PDGFR-β in the kidney glomerulus. Intervention in growth factor signaling could be a valuable therapeutic strategy for kidney glomerular diseases. Further studies are required to characterize the pathogenesis of these diseases for the successful development of such a therapy.

Mechanistic and therapeutic implications of PDGF-b activation during liver fibrogenesis

The role of platelet-derived growth factor (PDGF) family for the perpetuation of liver fibrogenesis and stellate cell activation is well documented. Increasing PDGF-b levels are observed in patients with severe liver fibrosis. We have recently demonstrated that forced expression of PDGF-b in hepatocytes results in spontaneous liver fibrosis, but the exact molecular mechanisms and signaling pathways remain unknown. The goal of this study was to dissect the role of PDGF-b by using whole transcriptomic time-course analysis to identify potential therapeutic targets for liver fibrosis. PDGF-b transgenic (Tg) and Alb-Cre-Ctl mice were investigated over a period of 32 weeks. Macroscopic and microscopic changes were monitored by IHC, RT-PCR and Western blotting. Time-dependent transcriptomic changes were examined using microarrays.PDFG-b transgenic animals developed spontaneous and severe liver fibrosis. Phenotypically, changes were accompanied by progressive accumulation of HSC and increased collagen deposit. Transcriptomic analysis revealed time-dependent activation of gene sets important for extracellular matrix remodeling, cell cycle as well as PDGF-b signaling and involved upregulation of known HSC markers (Thy–1) and key-fibrogenic molecules such as collagens, Timp2 and Ctgf in PDGF-b-Tg animals. Further, downregulation of Cebp-a and Ppar-a both associated with liver fibrogenesis was observed. Importantly, significant elevation of PDGF-b levels was also observed in human patients with cirrhosis and liver cancer.In conclusion, forced PDGF-b expression lead to spontaneous and progressive liver fibrosis in both human and rodents by upregulation of key fibrogenic molecules and inhibition of protective signaling such as PPAR-a and CEBP-a. Our results indicate the potential of modulating molecules embedded in PDGF-b signaling as an attractive anti-fibrogenic strategy for human liver fibrosis highlighting the translational significance of the PDGF-b transgenic model.

PTEN Regulates PDGF Ligand Switch for β-PDGFR Signaling in Prostate Cancer

Platelet-derived growth factor (PDGF) family members are potent growth factors that regulate cell proliferation, migration, and transformation. Clinical studies have shown that both PDGF receptor β (β-PDGFR) and its ligand PDGF D are up-regulated in primary prostate cancers and bone metastases, whereas PDGF B, a classic ligand for β-PDGFR, is not frequently detected in clinical samples. In this study, we examined the role of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in the regulation of PDGF expression levels using both a prostate-specific, conditional PTEN-knockout mouse model and mouse prostate epithelial cell lines established from these mice. We found an increase in PDGF D and β-PDGFR expression levels in PTEN-null tumor cells, accompanied by a decrease in PDGF B expression. Among Akt isoforms, increased Akt3 expression was most prominent in mouse PTEN-null cells, and phosphatidylinositol 3-kinase/Akt activity was essential for the maintenance of increased PDGF D and β-PDGFR expression. In vitro deletion of PTEN resulted in a PDGF ligand switch from PDGF B to PDGF D in normal mouse prostate epithelial cells, further demonstrating that PTEN regulates this ligand switch. Similar associations between PTEN status and PDGF isoforms were noted in human prostate cancer cell lines. Taken together, these results suggest a mechanism by which loss of PTEN may promote prostate cancer progression via PDGF D/β-PDGFR signal transduction.

A novel function for platelet-derived growth factor D: induction of osteoclastic differentiation for intraosseous tumor growth

Although increasing evidence suggests a critical role for platelet-derived growth factor (PDGF) receptor β (β-PDGFR) signaling in prostate cancer (PCa) progression, the precise roles of β-PDGFR and PDGF isoform-specific cell signaling have not been delineated. Recently, we identified the PDGF-D isoform as a ligand for β-PDGFR in PCa and showed that PDGF-D is activated by serine protease-mediated proteolytic removal of the CUB domain in a two-step process, yielding first a hemidimer (HD) and then a growth factor domain dimer. Herein, we demonstrate that the expression of PDGF-D in human PCa LNCaP cells leads to enhanced bone tumor growth and bone responses in immunodeficient mice. Histopathological analyses of bone tumors generated by PDGF-D-expressing LNCaP cells (LNCaP-PDGF-D) revealed osteolytic and osteoblastic responses similar to those observed in human PCa bone metastases. Importantly, we discovered a novel function of PDGF-D in the regulation of osteoclast differentiation, independent of the RANKL/RANK signaling axis. Although both PDGF-B and -D were able to activate β-PDGFR, only PDGF-D was able to induce osteoclastic differentiation in vitro, and upregulate the expression and nuclear translocation of nuclear factor of activated T cells 1, a master transcription factor for osteoclastogenesis. Taken together, these results reveal a new function of PDGF-D as a regulator of osteoclastic differentiation, an activity critical for the establishment of skeletal metastatic deposit in PCa patients.

Platelet-derived growth factor receptor signaling activates pericyte–myofibroblast transition in obstructive and post-ischemic kidney fibrosis

Pericytes are the major source of scar-producing myofibroblasts following kidney injury; however, the mechanisms of this transition are unclear. To clarify this, we examined Collagen 1 (α1)-green fluorescent protein (GFP) reporter mice (pericytes and myofibroblasts express GFP) following ureteral obstruction or ischemia-reperfusion injury and focused on the role of platelet-derived growth factor (PDGF)-receptor (PDGFR) signaling in these two different injury models. Pericyte proliferation was noted after injury with reactivation of α-smooth muscle actin expression, a marker of the myofibroblast phenotype. PDGF expression increased in injured tubules, endothelium, and macrophages after injury, whereas PDGFR subunits α and β were expressed exclusively in interstitial GFP-labeled pericytes and myofibroblasts. When PDGFRα or PDGFRβ activation was inhibited by receptor-specific antibody following injury, proliferation and differentiation of pericytes decreased. The antibodies also blunted the injury-induced transcription of PDGF, transforming growth factor β1, and chemokine CCL2. They also reduced macrophage infiltration and fibrosis. Imatinib, a PDGFR tyrosine kinase inhibitor, attenuated pericyte proliferation and kidney fibrosis in both fibrogenic models. Thus, PDGFR signaling is involved in pericyte activation, proliferation, and differentiation into myofibroblasts during progressive kidney injury. Hence, pericytes may be a novel target to prevent kidney fibrosis by means of PDGFR signaling blockade.

Aberrant hippocampal spine morphology and impaired memory formation in neuronal platelet‐derived growth factor beta‐receptor lacking mice

The physiological role of platelet-derived growth factor (PDGF) in the central nervous system (CNS) synaptic function remains uncharacterized. Here we identify physiological roles of PDGF receptor-β (PDGFR-β) in the CNS by conditional knockout of the gene encoding it. In the hippocampus, PDGFR-β colocalized immunohistochemically with both presynaptic synaptophysin and postsynaptic density-95 (PSD-95). In the hippocampal CA1 region, expression levels of postsynaptic proteins, including spinophilin, drebrin, and PSD-95, were significantly decreased in PDGFR-β knockout mice, although presynaptic synaptophysin levels remained comparable to controls. Interestingly, in hippocampal CA1 pyramidal neurons, dendritic spine density in PDGFR-β knockout mice was significantly decreased compared with that seen in wild-type mice, although spine length and number of dendritic branches remained unchanged. Consistent with these findings, impairment in hippocampal long-term potentiation (LTP) and in hippocampus-dependent memory formation were seen in PDGFR-β knockout mice. These results suggest PDGFR-β plays critical roles in spine morphology and memory formation in mouse brain.