Differential regulation of acidic and basic fibroblast growth factor gene expression in fibroblast growth factor-treated rat aortic smooth muscle cells

Identification and functional characterisation of a Schistosoma japonicum insulin-like peptide

Background

Previous studies have shown that insulin receptors in schistosomes, triggered by host insulin, play an important role in parasite growth, development and fecundity by regulating glucose metabolism. However, limited information is available on the recently identified endogenous insulin-like peptide (ILP) in blood flukes.

Results

We isolated ILPs from Schistosoma japonicum (SjILP) and S. recognised (SmILP) and present results of their molecular and structural analysis. SjILP shares 63% amino acid identity with SmILP, but only 18% identity with human insulin. There is high cross immunological reactivity between the S. japonicum and S. mansoni ILPs as observed in western blots using an anti-SjILP polyclonal antibody. ADP binding/hydrolysis ability was observed in both SjILP and SmILP, but not in human insulin, suggesting a parasite-specific role for ILP compared with host insulin. Protein binding assays using the Octet-RED system showed SjILP binds S. japonicum IRs (SjIR1 and SjIR2) strongly. An anti-phospho antibody against extracellular signal-regulated kinase (Erk) recognised a 44-kDa target band in an extract of adult worms after stimulation by rSjILP in vitro, suggesting an important role for SjILP in activating SjIRs and in regulating downstream signal transduction. Immunolocalisation showed SjILP is located on the tegument and the underlying musculature, similar to that observed for SjIR1, but it is also present throughout the parenchyma of males and in the vitelline cells of females, the same locations as SjIR2 described in an earlier published study of ours. The same localisation of SjILP and the SjIRs is suggestive of an interaction between the insulin-like peptide and the IRs. In addition to binding host insulin, schistosomes also can express their own endogenous ILPs, which can activate the parasite insulin signal pathway, thereby playing a critical role in worm growth, development and fertility.

Conclusions

These findings shed new light on ILPs in schistosomes, providing further insight into the distinct and specialised functions of SjIR1 and 2 in S. japonicum and their interaction with host insulin.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2095-7) contains supplementary material, which is available to authorized users.

Cloning and characterisation of Schistosoma japonicum insulin receptors

Background

Schistosomes depend for growth and development on host hormonal signals, which may include the insulin signalling pathway. We cloned and assessed the function of two insulin receptors from Schistosoma japonicum in order to shed light on their role in schistosome biology.

Methodology/Principal Findings

We isolated, from S. japonicum, insulin receptors 1 (SjIR-1) and 2 (SjIR-2) sharing close sequence identity to their S. mansoni homologues (SmIR-1 and SmIR-2). SjIR-1 is located on the tegument basal membrane and the internal epithelium of adult worms, whereas SjIR-2 is located in the parenchyma of males and the vitelline tissue of females. Phylogenetic analysis showed that SjIR-2 and SmIR-2 are close to Echinococcus multilocularis insulin receptor (EmIR), suggesting that SjIR-2, SmIR-2 and EmIR share similar roles in growth and development in the three taxa. Structure homology modelling recovered the conserved structure between the SjIRs and Homo sapiens IR (HIR) implying a common predicted binding mechanism in the ligand domain and the same downstream signal transduction processing in the tyrosine kinase domain as in HIR. Two-hybrid analysis was used to confirm that the ligand domains of SjIR-1 and SjIR-2 contain the insulin binding site. Incubation of adult worms in vitro, both with a specific insulin receptor inhibitor and anti-SjIRs antibodies, resulted in a significant decrease in worm glucose levels, suggesting again the same function for SjIRs in regulating glucose uptake as described for mammalian cells.

Conclusions

Adult worms of S. japonicum possess insulin receptors that can specifically bind to insulin, indicating that the parasite can utilize host insulin for development and growth by sharing the same pathway as mammalian cells in regulating glucose uptake. A complete understanding of the role of SjIRs in the biology of S. japonicum may result in their use as new targets for drug and vaccine development against schistosomiasis.

Role of basic fibroblast growth factor (FGF-2) in diabetic nephropathy and mechanisms of its induction by hyperglycemia in human renal fibroblasts

Basic fibroblast growth factor (FGF-2) plays a role in renal fibrogenesis, although its potential implications for tubulointerstitial involvement in diabetic nephropathy are unknown. We evaluated the expression of FGF-2 in kidney biopsies from patients with diabetic nephropathy and studied the mechanisms of its induction in human renal fibroblasts under hyperglycemia. Tubulointerstitial expression of FGF-2 was significantly upregulated in diabetic nephropathy compared with control kidneys with a good correlation to the degree of the injury. Fibroblasts cultivated in high glucose displayed increased FGF-2 mRNA as well as protein synthesis and secretion compared with normal glucose. Proliferation rates under hyperglycemia were significantly higher and could be almost completely inhibited by addition of a neutralizing FGF-2 antibody. Alterations in proliferation were associated with changes in p27(kip1) expression. Hyperglycemia induced the expression of PKC-beta1 and PKC-beta2; however, only inhibition of PKC-beta1 but not PKC-beta2 led to a significant decrease of FGF-2 levels. Relevance of the culture findings and functional association was corroborated by colocalization of FGF-2 and PKC-beta in human diabetic kidneys in vivo. High glucose stimulated fibronectin synthesis and secretion, which could be substantially prevented by inhibition of PKC-beta1 and to a lesser extent by inhibiting the FGF-2. Expression of active phosphorylated form of p38 mitogen-activated protein kinase was upregulated under hyperglycemia; however, its inhibition had no effects on FGF-2 synthesis. Our results implicate a role of FGF-2 in high glucose-altered molecular signaling in pathogenesis of diabetic renal disease.

Loading of collagen-heparan sulfate matrices with bFGF promotes angiogenesis and tissue generation in rats

The loading of biocompatible matrices with growth factors offers the opportunity to induce specific cell behavior. The attachment of heparan sulfate (HS) to these matrices may promote the binding, modulation, and sustained release of signaling molecules. In this study, basic fibroblast growth factor (bFGF) was bound to crosslinked collagenous matrices with and without covalently attached HS. The tissue response to these matrices was evaluated after subcutaneous implantation in rats. Attachment of HS to collagen matrices increased the bFGF binding capacity threefold and resulted in a more gradual and sustained release of the growth factor in vitro. bFGF primarily was located at the matrix margins. In vivo, the presence of HS without bFGF resulted in a transient vascularization, predominantly at the matrix periphery. Angiogenesis was further enhanced by combining HS with bFGF. In contrast to collagen-HS and collagen/bFGF matrices, collagen-HS/bFGF matrices remained highly vascularized throughout the matrix during the 10-week implantation period. In addition, these latter matrices revealed an intense and prolonged tissue response and considerably promoted the generation of new tissue. Foreign body reactions were only observed sporadically at this time interval. It is concluded that bFGF loading of collagen-HS matrices has additional value for those tissue-engineering applications that require enhanced angiogenesis and generation of new tissue.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Sequential cytokine therapy for pressure ulcers: clinical and mechanistic response

OBJECTIVE

To compare the healing response of sequential topically applied cytokines to that of each cytokine alone and to a placebo in pressure ulcers, and to evaluate the molecular and cellular responses.

SUMMARY BACKGROUND DATA

Because of a deficiency of cytokine growth factors in chronic wounds and the reversal of impaired healing in animal models, pressure ulcer trials have been performed with several exogenously applied growth factors. Because single-factor therapy has not been uniformly successful, combination or sequential cytokine therapy has been proposed. Laboratory data have suggested that sequential treatment with granulocyte-macrophage/colony-stimulating factor (GM-CSF)/basic fibroblast growth factor (bFGF) might augment the previously reported effect of bFGF alone.

METHODS

A masked, randomized pressure ulcer trial was performed comparing sequential GM-CSF/bFGF therapy with that of each cytokine alone and with placebo during a 35-day period. The primary measure was wound volume decrease over time. Cytokine wound levels and mRNA levels were serially determined. Fibroblast-populated collagen lattices (FPCLs) were constructed from serial fibroblast biopsies. Cellular ultrastructure was evaluated by electron microscopy. Changes in ease of surgical closure and its relative cost were determined.

RESULTS

Ulcers treated with cytokines had greater closure than those in placebo-treated patients. Patients treated with bFGF alone did the best, followed by the GM-CSF/bFGF group. Patients treated with GM-CSF or bFGF had higher levels of their respective cytokine after treatment. Patients with the greatest amount of healing showed higher levels of platelet-derived growth factor (PDGF) on day 10 and transforming growth factor beta (TGFbeta1) on day 36. Message for the bFGF gene was upregulated after treatment with exogenous bFGF, suggesting autoinduction of the cytokine. FPCLs did not mimic the wound responses. Ultrastructure of wound biopsies showed response to bFGF. Treatment with any of the cytokines improved the wound by allowing easier wound closure. This was most marked for the bFGF-alone treatment, with a cost savings of $9,000 to $9,200.

CONCLUSIONS

Treatment with bFGF resulted in significantly greater healing than the other treatments in this trial. The clinical response appeared to be related to upregulation of the bFGF message and to increased levels of PDGF-AB, bFGF, and TGFbeta1 in the wounds and changes in ultrastructure. The resultant improvements could be correlated with cost savings.

Nitric oxide--cyclic GMP pathway regulates vascular smooth muscle cell phenotypic modulation: implications in vascular diseases

The role of cGMP-dependent protein kinase (PKG) in the regulation of rat aortic vascular smooth muscle cells (VSMC) phenotype was examined using a transfected cell culture system. Repetitively passaged VSMC do not express PKG and exist in the synthetic phenotype. Transfection of PKG-l alpha cDNA, or the active catalytic domain of PKG-l alpha, resulted in the appearance of VSMC having a morphology consistent with the contractile phenotype. PKG-expressing cells also contained markers for the contractile phenotype (for example, smooth muscle specific myosin heavy chain, calponin, alpha-actin) and reduced levels of synthetic phenotype markers (osteopontin, thrombospondin). PKG-transfected VSMC have also reduced the levels of fibroblast growth factor receptors 1 and 2, consistent with the establishment of a more contractile phenotype. The regulation of PKG expression in VSMC is largely undefined; however, continuous exposure of cultured bovine aortic smooth muscle cells with nitric oxide (NO)-donor drugs or cyclic nucleotide analogues reduced the expression of PKG. These results suggest that PKG occupies a critical role in VSMC phenotype and that suppression of PKG expression during inflammation or injury promotes a more synthetic state of the VSMC.

Angiotensin II and endothelin-1 increase fibroblast growth factor-2 mRNA expression in vascular smooth muscle cells

The vasoactive hormone angiotensin II (Ang II) can stimulate vascular smooth muscle cell (SMC) hypertrophy and proliferation; thus, it may have an important role in the pathogenesis of hypertension, atherosclerosis and restenosis. Several studies have indicated that Ang II bioactivity on SMC may depend, at least in part, on its ability to induce the expression of polypeptide growth factors that can function in an autocrine manner. Here we report that Ang II treatment of rat aortic SMC increases fibroblast growth factor-2 (FGF-2) but not FGF-1 mRNA levels. Increased FGF-2 mRNA expression is first detectable at 30 min after Ang II addition and maximal levels are present at 8 hr. Ang II induction of FGF-2 mRNA levels is dependent on de novo RNA and protein synthesis. The Ang II effect can be blocked by treatment with either the Ang II type 1 receptor-selective antagonist CI-996 or the tyrosine kinase inhibitor genistein. The potent vasoconstrictor and SMC mitogen endothelin-1 can also induce FGF-2 mRNA levels in rat aortic SMC. These results indicate that FGF-2 gene expression is up-regulated by two distinct vasoactive peptides implicated in vascular SMC growth control in vivo.

Photodynamic therapy inactivates extracellular matrix-basic fibroblast growth factor: insights to its effect on the vascular wall

PURPOSE

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of oxygen and other free radical moieties without the generation of heat, has been shown to inhibit the development of experimentally induced intimal hyperplasia. The host response to PDT, a form of vascular injury that results in complete vascular wall cell eradication, is devoid of inflammation and proliferation and promotes favorable vascular wall healing. These effects do not result in intimal hyperplasia and are suggestive of PDT-induced changes in the extracellular matrix (ECM). As a model to better understand the biologic consequences of PDT on the vascular wall matrix proteins, the effect of PDT was studied on the powerful matrix-resident mitogen basic fibroblast factor (bFGF) in vitro.

METHODS

PDT (5 to 200 J/cm2, 100 mW/cm2, 675 nm) was used with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 micrograms/ml) to inactivate bFGF in vitro while 100 J/cm2 of irradiation was administered 24 hours after 5 mg/ml of the photosensitizer was used in vivo. PDT was used on bFGF in solution and on endothelial cell-derived ECM. Enzyme-linked immunosorbent assay was used to quantitate bFGF in solution after PDT treatment or after extraction from the ECM by collagenase and heparin. Functional activity of matrix-associated bFGF was assessed by smooth muscle cell mitogenesis by 3H-thymidine incorporation. To demonstrate the in vivo relevance of these observations, immunohistochemical analysis of PDT-treated rat carotid arteries was undertaken.

RESULTS

PDT eliminated detectable levels of bFGF in solution. PDT of ECM significantly reduced matrix-bound bFGF (1.0 +/- 0.6 vs 27.5 +/- 1.3 pg/ml; p < 0.0001). This reduction in bFGF after PDT of the ECM was associated with a decrease in vascular smooth muscle cell mitogenesis (52.4% +/- 4.6%; p < 0.0001) when plated on PDT-treated matrix compared with nontreated matrix. Quantitative replenishment of exogenous bFGF to PDT-treated matrix restored proliferation to baseline levels. PDT of rat carotid arteries demonstrated a loss of bFGF staining compared with control nontreated arteries.

CONCLUSIONS

PDT inactivation of matrix-resident bFGF and possibly other bioactive molecules can provide a mechanism by which PDT suppresses smooth muscle cell proliferation in the vessel wall. This free radical-mediated alteration of matrix may contribute to favorable vascular healing when PDT is used for the inhibition of injury-induced intimal hyperplasia.

Oncostatin M induces basic fibroblast growth factor expression in endothelial cells and promotes endothelial cell proliferation, migration and spindle morphology

Oncostatin M (OSM), a pleiotropic cytokine originally isolated from supernatants of the U937 histiocytic lymphoma cell line, has been shown to have regulatory effects on a wide variety of cultured and tumor cells. We investigated the effects of OSM on basic fibroblast growth factor (bFGF) gene expression in bovine arterial endothelial (BAE) cells. Levels of bFGF mRNA transcripts were low in uninduced BAE cells, were maximal at 8 hours of exposure to OSM, and returned to control levels by 24 hours. Induction of bFGF mRNA transcripts by OSM was dose-dependent. Nuclear transcriptional run-on analysis demonstrated that exposure of BAE cells to OSM stimulated bFGF gene transcription. OSM treatment of BAE cells enhanced the synthesis of bFGF protein as determined by ELISA assays. Immunocytochemistry studies demonstrated the presence of low levels of bFGF protein within the cytoplasm in uninduced cells. After stimulation for 8 hours with OSM there was significant staining for bFGF in the cytoplasm. However, 24 hours after exposure to OSM, bFGF antigen was located only within the nuclei. Western blot analysis demonstrated that OSM stimulated predominantly the synthesis of a 22 kDa form of bFGF. In addition, OSM stimulated endothelial cell proliferation and migration as well as acquisition of a spindle shape. Phosphorothioate antisense oligonucleotide directed against bFGF inhibited OSM induced BAE cell proliferation and spindle shape formation but had only a minimal effect on migration. The levels of the 22 kDa form of bFGF were reduced by antisense treatment indicating that OSM induced proliferation and morphology change is likely to be regulated by intracellular bFGF. Our studies suggest that OSM released at sites of vascular injury could stimulate angiogenesis by inducing bFGF synthesis, endothelial cell proliferation and migration.

Enhanced vascularization in a microporous polyurethane graft impregnated with basic fibroblast growth factor and heparin

Rapid and controlled neoarterial regeneration via perianastomotic as well as transmural tissue ingrowth is critical to patency of implanted small-caliber artificial vascular grafts. Microporous polyurethane (PU) grafts (inner diameter, 1.5 mm; wall thickness, 100 microns; length, 20 mm; pore size, 100 microns), fabricated using an excimer laser ablation technique, were coated with a mixed solution of photoreactive gelatin, basic fibroblast factor (bFGF), and heparin, and were photocured by ultraviolet irradiation. Control grafts were treated with only photoreactive gelatin. An in vitro study showed that coimmobilization of bFGF and heparin (bFGF/heparin) in a crosslinked gelatin gel significantly enhances proliferation of endothelial cells. The bFGF/heparin-impregnated grafts (n = 6) and nonimpregnated (control) grafts (n = 9) were implanted in aortas of rats for 4 weeks. All the implanted grafts were patent, but there was a marked difference in the extent of neoarterial regeneration between the two groups. Irrespective of group, endothelialization proceeded from anastomotic sites and little occurrence of transmural capillary ingrowth was observed. The extent of endothelialization was much greater for bFGF/heparin-immobilized grafts than that for controls. In subendothelial tissues for the impregnated group, a significantly profound peripheral transmural tissue ingrowth including recruits of smooth muscle cells and fibroblasts from adjacent native tissue was observed near anastomotic sites; subendothelial tissue regeneration was noticed at the midportions of the grafts. However, only a fibrin layer was formed on control grafts. Thus, coimmobilization of bFGF and heparin significantly accelerated neoarterial regeneration via both perianastomotic and transmural tissue ingrowth. The former was more extensive than the latter.

Detection of keratinocyte growth factor (KGF) messenger ribonucleic acid and immunolocalization of KGF in the canine testis

Keratinocyte growth factor (KGF) was originally discovered in human embryonic lung fibroblasts and is a member of the fibroblast growth factor (FGF) family. Members of the FGF family have been shown to regulate testicular function. However, the recently discovered KGF has not been studied in the testis. KGF has been detected in many other tissues, including the prostate, an organ whose development and function have been associated with presence of the testis. In this study, KGF mRNA was detected in the whole testis using reverse transcription polymerase chain reaction (RT-PCR). The 575-bp KGF-specific product was detected along with a 594-bp β-actin-specific product. To identify the cell types in which KGF mRNA was predominantly expressed, interstitial cells were physically separated from seminiferous tubules. The interstitial cells were then sorted on a discontinuous Percoll gradient and total cellular mRNAs isolated. Using RT-PCR and Southern hybridization with specific cDNA probes, the KGF mRNA was detected in interstitial cells. KGF expression levels were then evaluated semiquantitatively with a competitive RT-PCR assay. KGF expression levels were highest in interstitial cells that equilibrated between 20 and 30% Percoll. Enriched Leydig cells and seminiferous tubules expressed low levels of KGF. Finally, immunohistochemical analysis was performed on canine testes using a rabbit anti-KGF polyclonal antibody. The KGF protein was localized predominantly to peritubular cells of the canine testis. These results suggest that KGF is synthesized in the canine testis.

Vascular remodelling and molecular biology: new concepts and therapeutic possibilities

1. Over the past decade major advances in molecular cell biology have greatly increased our understanding of the way in which many growth factor genes are expressed and regulated. This knowledge is currently being translated into investigations of the cardiovascular system. 2. Two growth factor families appear to play particularly important roles, the fibroblast growth factors and the transforming growth factors-beta. These are multifunctional growth factors capable of remodelling the vasculature through their effects on cell migration, proliferation and matrix formation. 3. An understanding of their regulation, properties and nature of their receptors is providing novel insights into the physiology and pathobiology of the vasculature. It is also providing highly specific targets for future therapy.

Fibroblast growth factor-1-inducible gene FR-17 encodes a nonmuscle alpha-actinin isoform

Polypeptide growth factor binding to cell surface receptors activates a cytoplasmic signaling cascade that ultimately promotes the expression of specific nuclear genes. As an approach to investigate the molecular mechanism of fibroblast growth factor (FGF)-1 mitogenic signaling, we have begun to identify and characterize FGF-1-inducible genes in murine NIH 3T3 cells. Here we report that one of these genes, termed FGF-regulated (FR)-17, is predicted to encode a nonmuscle isoform of alpha-actinin, an actin cross-linking protein found along microfilaments and in focal adhesion plaques. FGF-1 induction of alpha-actinin mRNA expression is first detectable at 2 h after mitogen addition and is dependent on the novo RNA and protein synthesis. Maximal alpha-actinin mRNA expression, corresponding to an approximately nineteenfold level of induction, is present after 12 h of FGF-1 stimulation. Western blot analysis indicated that FGF-1-stimulated cells also produce an increased amount of alpha-actinin protein. The FGF-1-related mitogen FGF-2, calf serum, several of the polypeptide growth factors present in serum, and the tumor promoter phorbol myristate acetate can also induce alpha-actinin mRNA expression. Finally, nonmuscle alpha-actinin mRNA is expressed in vivo in a tissue-specific manner, with relatively high levels detected in adult mouse intestine and kidney. These results indicate that nonmuscle alpha-actinin is a serum-, polypeptide growth factor-, and tumor promoter-inducible gene in mouse fibroblasts.

Regulation of polyamine synthesis and transport by fibroblast growth factor in aortic smooth muscle cells

Basic-FGF (FGF2) is implicated as a regulator of smooth muscle cell proliferation that develops after arterial injury. Polyamines are essential for cell growth and differentiation and may mediate some of the FGF2-elicited responses. To examine this possibility, the effect of FGF2 on polyamine synthesis and uptake was tested on rat arterial smooth muscle cells. Exposure of cells to FGF2 for 24 and 48 h resulted in increased intracellular polyamine content. Ornithine decarboxylase (ODC) activity increased in FGF2-treated cells after 6 h of treatment, whereas no increases were detected in ODC mRNA steady-state levels. Basic-FGF increased maximal polyamine transport rate without changes in Km. Treatment with actinomycin D decreased polyamine transport. The effect of cyclohexamide on polyamine uptake was dose dependent. These studies indicate that treatment of vascular smooth muscle cells with FGF2 results in increases in intracellular polyamine content, polyamine synthetic activity, and polyamine transport.

Intracellular signaling pathways required for rat vascular smooth muscle cell migration. Interactions between basic fibroblast growth factor and platelet-derived growth factor

Intracellular signaling pathways activated by both PDGF and basic fibroblast growth factor (bFGF) have been implicated in the migration of vascular smooth muscle cells (VSMC), a key step in the pathogenesis of many vascular diseases. We demonstrate here that, while bFGF is a weak chemoattractant for VSMCs, it is required for the PDGF-directed migration of VSMCs and the activation of calcium/calmodulin-dependent protein kinase II (CamKinase II), an intracellular event that we have previously shown to be important in the regulation of VSMC migration. Neutralizing antibodies to bFGF caused a dramatic reduction in the size of the intracellular calcium transient normally seen after PDGF stimulation and inhibited both PDGF-directed VSMC migration and CamKinase II activation. Partially restoring the calcium transient with ionomycin restored migration and CamKinase II activation as did the forced expression of a mutant CamKinase II that had been "locked" in the active state by site-directed mutagenesis. These results suggest that bFGF links PDGF receptor stimulation to changes in intracellular calcium and CamKinase II activation, reinforcing the central role played by CamKinase II in regulating VSMC migration.