Paracrine Fibroblast Growth Factor Research Articles

Structural basis for FGF hormone signalling

α/βKlotho coreceptors simultaneously engage fibroblast growth factor (FGF) hormones (FGF19, FGF21 and FGF23)1,2 and their cognate cell-surface FGF receptors (FGFR1–4) thereby stabilizing the endocrine FGF–FGFR complex3–6. However, these hormones still require heparan sulfate (HS) proteoglycan as an additional coreceptor to induce FGFR dimerization/activation and hence elicit their essential metabolic activities6. To reveal the molecular mechanism underpinning the coreceptor role of HS, we solved cryo-electron microscopy structures of three distinct 1:2:1:1 FGF23–FGFR–αKlotho–HS quaternary complexes featuring the ‘c’ splice isoforms of FGFR1 (FGFR1c), FGFR3 (FGFR3c) or FGFR4 as the receptor component. These structures, supported by cell-based receptor complementation and heterodimerization experiments, reveal that a single HS chain enables FGF23 and its primary FGFR within a 1:1:1 FGF23–FGFR–αKlotho ternary complex to jointly recruit a lone secondary FGFR molecule leading to asymmetric receptor dimerization and activation. However, αKlotho does not directly participate in recruiting the secondary receptor/dimerization. We also show that the asymmetric mode of receptor dimerization is applicable to paracrine FGFs that signal solely in an HS-dependent fashion. Our structural and biochemical data overturn the current symmetric FGFR dimerization paradigm and provide blueprints for rational discovery of modulators of FGF signalling2 as therapeutics for human metabolic diseases and cancer.

FGF1 ameliorates obesity-associated hepatic steatosis by reversing IGFBP2 hypermethylation.

Obesity is a major contributing factor for metabolic-associated fatty liver disease (MAFLD). Fibroblast growth factor (FGF) 1 is the first paracrine FGF family member identified to exhibit promising metabolic regulatory properties capable of conferring glucose-lowering and insulin-sensitizing effect. This study explores the role and molecular underpinnings of FGF1 in obesity-associated hepatic steatosis. In a mouse high-fat diet (HFD)-induced MAFLD model, chronic treatment with recombinant FGF1(rFGF1) was found to effectively reduce the severity of insulin resistance, hyperlipidemia, and inflammation. FGF1 treatment decreased lipid accumulation in the mouse liver and palmitic acid-treated AML12 cells. These effects were associated with decreased mature form SREBF1 expression and its target genes FASN and SCD1. Interestingly, we uncovered that rFGF1 significantly induced IGFBP2 expression at both mRNA and protein levels in HFD-fed mouse livers and cultured hepatocytes treated with palmitic acid. Adeno-associated virus-mediated IGFBP2 suppression significantly diminished the therapeutic benefit of rFGF1 on MAFLD-associated phenotypes, indicating that IGFBP2 plays a crucial role in the FGF1-mediated reduction of hepatic steatosis. Further analysis revealed that rFGF1 treatment reduces the recruitment of DNA methyltransferase 3 alpha to the IGFBP2 genomic locus, leading to decreased IGFBP2 gene methylation and increased mRNA and protein expression. Collectively, our findings reveal FGF1 modulation of lipid metabolism via epigenetic regulation of IGFBP2 expression, and unravel the therapeutic potential of the FGF1-IGFBP2 axis in metabolic diseases associated with obesity.

Fibroblast growth factor 10 protects against particulate matter-induced lung injury by inhibiting oxidative stress-mediated pyroptosis via the PI3K/Akt/Nrf2 signaling pathway.

Particulate matter (PM) is a major environmental contaminant that causes and worsens respiratory diseases. Fibroblast growth factor 10 (FGF10), a paracrine fibroblast growth factor that specifically stimulates repair and regeneration after injury, has been shown to protect against PM-induced lung injury. However, the underlying mechanisms are still unclear. In this study, the protective effects of FGF10 were investigated using a PM-induced lung injury mouse model in vivo and BEAS-2B cells in vitro. According to the findings, FGF10 treatment alleviated PM-induced oxidative damage and pyroptosis in vivo and in vitro. Mechanistically, FGF10 activated antioxidative Nrf2 signaling. Inhibition of PI3K signaling with LY294002 or Nrf2 signaling with ML385 revealed that FGF10-mediated lung protection was mediated by the PI3K/Akt/Nrf2 pathway. These results collectively indicate that FGF10 inhibits oxidative stress-mediated pyroptosis via the PI3K/Akt/Nrf2 pathway, suggesting a possible therapy for PM-induced lung injury.

FGF10 mediates protective anti-oxidative effects in particulate matter-induced lung injury through Nrf2 and NF-κB signaling

Particulate matter (PM), a well-known environmental pollutant, is an independent risk factor associated with the morbidity of various respiratory diseases. Oxidative stress is an important pathophysiological mechanism related to PM exposure, which mediates redox-sensitive inflammatory signaling, leading to lung injury. Fibroblast growth factor 10 (FGF10), a paracrine fibroblast growth factor that mediates mesenchymal to epithelial signaling, participates in epithelial repair during lung injury. However, whether FGF10-mediated repair in PM-induced lung injury is related to the regulation of oxidative stress remains to be elucidated. In vivo, the C57BL/6 mice were randomly divided, with intratracheal instillation of 5 mg/kg FGF10 1 h before 4 mg/kg PM for 2 consecutive days. In vitro, the BEAS-2B cells were pretreated with 10 ng/mL FGF10 before exposed to 200 µg/mL PM. Besides, the specific Nrf2 inhibitor ML385 was adopted in vitro. The harvested lung tissues were pathologic grading scored. The state of oxidative stress was assessed with dihydroethidium (DHE) staining, malondialdehyde (MDA) activity, hydrogen peroxide (H2O2) assays and reactive oxygen species (ROS). The contents of IL-6 and IL-8 in bronchoalveolar lavage (BAL) as well as culture supernatant were quantified by ELISA. The protein levels of nuclear factor erythroid 2 related factor 2 (Nrf2) and nuclear factor-κB (NF-κB) signaling from lung tissue as well as cell lysate were determined by Western blot. In this study, recombinant FGF10 administration relieved the degree of lung injury, which is characterized by bronchitis, in a mouse model of PM exposure. In addition, reduced ROS levels, which are indicative of restrained oxidative stress, were also observed. Moreover, two redox-sensitive signaling pathways, Nrf2 and NF-κB, were found to be differentially regulated by FGF10. Using a cellular model of PM exposure, we found that the anti-inflammatory effect of FGF10 on NF-κB signaling was mediated through the regulation of oxidative stress. The anti-oxidative effect relied on the stimulation of Nrf2 signaling. Blockade of Nrf2 signaling with ML385 significantly compromised the anti-inflammatory effect of FGF10. These results underscore that the protective anti-oxidative effects of FGF10 in lung injury are mediated by the stimulation of Nrf2 signaling and inhibition of the NF-κB pathway.

Role of Fibroblast Growth Factors in the Crosstalk of Hepatic Stellate Cells and Uveal Melanoma Cells in the Liver Metastatic Niche.

Hepatic metastasis is the critical factor determining tumor-associated mortality in different types of cancer. This is particularly true for uveal melanoma (UM), which almost exclusively metastasizes to the liver. Hepatic stellate cells (HSCs) are the precursors of tumor-associated fibroblasts and support the growth of metastases. However, the underlying mechanisms are widely unknown. Fibroblast growth factor (FGF) signaling is dysregulated in many types of cancer. The aim of this study was to analyze the pro-tumorigenic effects of HSCs on UM cells and the role of FGFs in this crosstalk. Conditioned medium (CM) from activated human HSCs significantly induced proliferation together with enhanced ERK and JNK activation in UM cells. An in silico database analysis revealed that there are almost no mutations of FGF receptors (FGFR) in UM. However, a high FGFR expression was found to be associated with poor survival for UM patients. In vitro, the pro-tumorigenic effects of HSC-CM on UM cells were abrogated by a pharmacological inhibitor (BGJ398) of FGFR1/2/3. The expression analysis revealed that the majority of paracrine FGFs are expressed by HSCs, but not by UM cells, including FGF9. Furthermore, the immunofluorescence analysis indicated HSCs as a cellular source of FGF9 in hepatic metastases of UM patients. Treatment with recombinant FGF9 significantly enhanced the proliferation of UM cells, and this effect was efficiently blocked by the FGFR1/2/3 inhibitor BGJ398. Our study indicates that FGF9 released by HSCs promotes the tumorigenicity of UM cells, and thus suggests FGF9 as a promising therapeutic target in hepatic metastasis.

Design and characterization of a FGF1‐FGF21 chimeric protein with increased stability and enhanced antidiabetic activities

Fibroblast growth factor (FGF) family is consisted of 22 proteins that regulate a wide variety of biological functions such as wound healing, tissue repairs, and angiogenesis. FGF family follows three main modes of action: paracrine, intracrine or endocrine. One member of the paracrine FGFs is FGF1, which works locally through interaction with heparin or heparin sulfate (HS). With its mitogenic and cell survival activities, FGF1 participates in many developmental processes, cell growth and differentiation, tissue repairs, and tumor growth and invasion. A representative of endocrine FGFs is FGF21, which is often used in long range physiological processes, but does not require HS. FGF21 engages in many functions across various organs like liver, pancreas, adipose tissues. One of FGF21’s abilities is the regulation of glucose uptake in adipocytes through upregulating the transcription of glucose transporter‐1. Thus, FGF21 is a potential treatment for metabolic diseases such as Type‐2 Diabetes. However, FGF21 has been reported to possess an inherently unstable core with low thermal stability and receptor affinity. Herein, we designed a structure‐based chimera protein by replacing the core of FGF21 with a thermally stable paracrine FGF1 (sFGF1). Using techniques such as fluorescence spectroscopy, and circular dichroism, we show that the chimera protein sFGF1‐FGF21 adopts a β‐trefoil core. Intrinsic fluorescence spectra of the chimera protein shows an emission maximum centered at 307 nm indicating that the emission of the conserved tryptophan is quenched similar to wildtype FGF1. Differential calorimetry data suggests that chimera sFGF1‐FGF21 is significantly more stable than wild type FGF21. The findings of this study provide valuable clues for the rational design of FGF21‐based therapeutic against hyperglycemia and obesity.

Lactic acid induces fibroblast growth factor 23 (FGF23) production in UMR106 osteoblast-like cells

Endocrine and paracrine fibroblast growth factor 23 (FGF23) is a protein predominantly produced by bone cells with strong impact on phosphate and vitamin D metabolism by targeting the kidney. Plasma FGF23 concentration early rises in kidney and cardiovascular diseases correlating with progression and outcome. Lactic acid is generated in anaerobic glycolysis. Lactic acidosis is the consequence of various physiological and pathological conditions and may be fatal. Since FGF23 production is stimulated by inflammation and lactic acid induces pro-inflammatory signaling, we investigated whether and how lactic acid influences FGF23. Experiments were performed in UMR106 osteoblast-like cells, Fgf23 mRNA levels estimated from quantitative real-time polymerase chain reaction, and FGF23 protein determined by enzyme-linked immunosorbent assay. Lactic acid dose-dependently induced Fgf23 gene expression and up-regulated FGF23 synthesis. Also, Na+-lactate as well as formic acid and acetic acid up-regulated Fgf23. The lactic acid effect was significantly attenuated by nuclear factor kappa-light-chain enhancer of activated B-cells (NFκB) inhibitors wogonin and withaferin A. Lactic acid induces FGF23 production, an effect at least in part mediated by NFκB. Lactic acidosis may, therefore, be paralleled by a surge in plasma FGF23.

Fibroblast growth factor induced Ucp1 expression in preadipocytes requires PGE2 biosynthesis and glycolytic flux.

High uncoupling protein 1 (Ucp1) expression is a characteristic of differentiated brown adipocytes and is linked to adipogenic differentiation. Paracrine fibroblast growth factor 8b (FGF8b) strongly induces Ucp1 transcription in white adipocytes independent of adipogenesis. Here, we report that FGF8b and other paracrine FGFs act on brown and white preadipocytes to upregulate Ucp1 expression via a FGFR1-MEK1/2-ERK1/2 axis, independent of adipogenesis. Transcriptomic analysis revealed an upregulation of prostaglandin biosynthesis and glycolysis upon Fgf8b treatment of preadipocytes. Oxylipin measurement by LC-MS/MS in FGF8b conditioned media identified prostaglandin E2 as a putative mediator of FGF8b induced Ucp1 transcription. RNA interference and pharmacological inhibition of the prostaglandin E2 biosynthetic pathway confirmed that PGE2 is causally involved in the control over Ucp1 transcription. Importantly, impairment of or failure to induce glycolytic flux blunted the induction of Ucp1, even in the presence of PGE2 . Lastly, a screening of transcription factors identified Nrf1 and Hes1 as required regulators of FGF8b induced Ucp1 expression. Thus, we conclude that paracrine FGFs co-regulate prostaglandin and glucose metabolism to induce Ucp1 expression in a Nrf1/Hes1-dependent manner in preadipocytes, revealing a novel regulatory network in control of Ucp1 expression in a formerly unrecognized cell type.

Molecular description of fibroblast growth factor and mechanisms by which fibroblast growth factor-21 mediating biological actions and acting as a biologic biomarker of cardiovascular diseases

Fibroblast growth factor (FGF) family members are mostly secreted as signaling proteins with diverse functions in development and metabolism. FGFs can be classified as intracellular, paracrine, and endocrine FGFs by their action mechanisms. FGF-21 is a novel member of endocrine FGF subfamily with pleotropic actions. Recent findings indicate that FGF-21 can act as a cardiomyokine; that is, it is produced by cardiac cells and acts in an autocrine manner on the heart itself. The heart is sensitive to the effects of FGF-21, both systemic and locally generated, owing to the expression in cardiomyocytes of β-Klotho, the key coreceptor known to confer specific responsiveness to FGF-21 action. It has been shown to exert cardioprotective effects in against cardiac hypertrophy, myocardial infarction, cardiac inflammation, cardiac ischemia-reperfusion injury, diabetic cardiomyopathy, and oxidative stress. It also promotes energy supply to the heart through fatty acid β-oxidation. Intracellular mechanisms involving peroxisome proliferator-activated receptor α and sirtunin 1 mediate transcriptional regulation of the FGF-21 gene in response to exogenous stimuli. This review explores the molecular mechanism by which FGF-21 provides cardioprotection.

Paracrine Fibroblast Growth Factor 1 Functions as Potent Therapeutic Agent for Intrahepatic Cholestasis by Downregulating Synthesis of Bile Acid.

Endocrine fibroblast growth factor (FGF) 19 has been shown to be capable of maintaining bile acid (BA) homeostasis and thus hold promise to be a potential therapeutic agent for cholestasis liver disease. However, whether paracrine FGFs possess this BA regulatory activity remains to be determined. In our study, we identified that paracrine fibroblast growth factor 1 (FGF1) was selectively downregulated in the liver of alpha naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis mice, suggesting a pathological relevance of this paracrine FGF with abnormal BA metabolism. Therefore, we evaluated the effects of engineered FGF1 mutant - FGF1ΔHBS on the metabolism of hepatic BA and found that this protein showed a more potent inhibitory effect of BA biosynthesis than FGF19 without any hepatic mitogenic activity. Moreover, the chronic administration of FGF1ΔHBS protected liver against ANIT-induced injury by reducing hepatic BA accumulation. Taken together, these data suggest that FGF1ΔHBS may function as a potent therapeutic agent for intrahepatic cholestasis liver disease.

HSV-1 triggers paracrine fibroblast growth factor response from cortical brain cells via immediate-early protein ICP0

BackgroundHerpes simplex virus-1 (HSV-1) infections of the central nervous system (CNS) can result in HSV-1 encephalitis (HSE) which is characterized by severe brain damage and long-term disabilities. Different cell types including neurons and astrocytes become infected in the course of an HSE which leads to an activation of glial cells. Activated glial cells change their neurotrophic factor profile and modulate inflammation and repair. The superfamily of fibroblast growth factors (FGFs) is one of the largest family of neurotrophic factors comprising 22 ligands. FGFs induce pro-survival signaling in neurons and an anti-inflammatory answer in glial cells thereby providing a coordinated tissue response which favors repair over inflammation. Here, we hypothesize that FGF expression is altered in HSV-1-infected CNS cells.MethodWe employed primary murine cortical cultures comprising a mixed cell population of astrocytes, neurons, microglia, and oligodendrocytes. Astrocyte reactivity was morphometrically monitored by an automated image analysis algorithm as well as by analyses of A1/A2 marker expression. Altered FGF expression was detected by quantitative real-time PCR and its paracrine FGF activity. In addition, HSV-1 mutants were employed to characterize viral factors important for FGF responses of infected host cells.ResultsAstrocytes in HSV-1-infected cortical cultures were transiently activated and became hypertrophic and expressed both A1- and A2-markers. Consistently, a number of FGFs were transiently upregulated inducing paracrine neurotrophic signaling in neighboring cells. Most prominently, FGF-4, FGF-8, FGF-9, and FGF-15 became upregulated in a switch-on like mechanism. This effect was specific for CNS cells and for a fully functional HSV-1. Moreover, the viral protein ICP0 critically mediated the FGF switch-on mechanism.ConclusionsHSV-1 uses the viral protein ICP0 for the induction of FGF-expression in CNS cells. Thus, we propose that HSV-1 triggers FGF activity in the CNS for a modulation of tissue response upon infection.

Emerging Roles of Fibroblast Growth Factor 10 in Cancer.

Whilst cross-talk between stroma and epithelium is critical for tissue development and homeostasis, aberrant paracrine stimulation can result in neoplastic transformation. Chronic stimulation of epithelial cells with paracrine Fibroblast Growth Factor 10 (FGF10) has been implicated in multiple cancers, including breast, prostate and pancreatic ductal adenocarcinoma. Here, we examine the mechanisms underlying FGF10-induced tumourigenesis and explore novel approaches to target FGF10 signaling in cancer.

Paracrine Fibroblast Growth Factor Initiates Oncogenic Synergy with Epithelial FGFR/Src Transformation in Prostate Tumor Progression

Cross talk of stromal-epithelial cells plays an essential role in both normal development and tumor initiation and progression. Fibroblast growth factor (FGF)-FGF receptor (FGFR)-Src kinase axis is one of the major signal transduction pathways to mediate this cross talk. Numerous genomic studies have demonstrated that expression levels of FGFR/Src are deregulated in a variety of cancers including prostate cancer; however, the role that paracrine FGF (from stromal cells) plays in dysregulated expression of epithelial FGFRs/Src and tumor progression in vivo is not well evaluated. In this study, we demonstrate that ectopic expression of wild-type FGFR1/2 or Src kinase in epithelial cells was not sufficient to initiate prostate tumorigenesis under a normal stromal microenvironment in vivo. However, paracrine FGF10 synergized with ectopic expression of epithelial FGFR1 or FGFR2 to induce epithelial-mesenchymal transition. Additionally, paracrine FGF10 sensitized FGFR2-transformed epithelial cells to initiate prostate tumorigenesis. Next, paracrine FGF10 also synergized with overexpression of epithelial Src kinase to high-grade tumors. But loss of the myristoylation site in Src kinase inhibited paracrine FGF10-induced prostate tumorigenesis. Loss of myristoylation alters Src levels in the cell membrane and inhibited FGF-mediated signaling including inhibition of the phosphotyrosine pattern and FAK phosphorylation. Our study demonstrates the potential tumor progression by simultaneous deregulation of proteins in the FGF/FGFRs/Src signal axis and provides a therapeutic strategy of targeting myristoylation of Src kinase to interfere with the tumorigenic process.

FGFR inhibitors: Effects on cancer cells, tumor microenvironment and whole-body homeostasis (Review).

Fibroblast growth factor (FGF)2, FGF4, FGF7 and FGF20 are representative paracrine FGFs binding to heparan-sulfate proteoglycan and fibroblast growth factor receptors (FGFRs), whereas FGF19, FGF21 and FGF23 are endocrine FGFs binding to Klotho and FGFRs. FGFR1 is relatively frequently amplified and overexpressed in breast and lung cancer, and FGFR2 in gastric cancer. BCR-FGFR1, CNTRL-FGFR1, CUX1-FGFR1, FGFR1OP-FGFR1, MYO18A-FGFR1 and ZMYM2-FGFR1 fusions in myeloproliferative neoplasms are non-receptor-type FGFR kinases, whereas FGFR1-TACC1, FGFR2-AFF3, FGFR2-BICC1, FGFR2-PPHLN1, FGFR3-BAIAP2L1 and FGFR3-TACC3 fusions in solid tumors are transmembrane-type FGFRs with C-terminal alterations. AZD4547, BGJ398 (infigratinib), Debio-1347 and dovitinib are FGFR1/2/3 inhibitors; BLU9931 is a selective FGFR4 inhibitor; FIIN-2, JNJ-42756493, LY2874455 and ponatinib are pan-FGFR inhibitors. AZD4547, dovitinib and ponatinib are multi-kinase inhibitors targeting FGFRs, colony stimulating factor 1 receptor (CSF1R), vascular endothelial growth factor (VEGF)R2, and others. The tumor microenvironment consists of cancer cells and stromal/immune cells, such as cancer-associated fibroblasts (CAFs), endothelial cells, M2-type tumor-associating macrophages (M2-TAMs), myeloid-derived suppressor cells (MDSCs) and regulatory T cells. FGFR inhibitors elicit antitumor effects directly on cancer cells, as well as indirectly through the blockade of paracrine signaling. The dual inhibition of FGF and CSF1 or VEGF signaling is expected to enhance the antitumor effects through the targeting of immune evasion and angiogenesis in the tumor microenvironment. Combination therapy using tyrosine kinase inhibitors (FGFR or CSF1R inhibitors) and immune checkpoint blockers (anti-PD-1 or anti-CTLA-4 monoclonal antibodies) may be a promising choice for cancer patients. The inhibition of FGF19-FGFR4 signaling is associated with a risk of liver toxicity, whereas the activation of FGF23-FGFR4 signaling is associated with a risk of heart toxicity. Endocrine FGF signaling affects the pathophysiology of cancer patients who are prescribed FGFR inhibitors. Whole-genome sequencing is necessary for the detection of promoter/enhancer alterations of FGFR genes and rare alterations of other genes causing FGFR overexpression. To sustain the health care system in an aging society, a benefit-cost analysis should be performed with a focus on disease-free survival and the total medical cost before implementing genome-based precision medicine for cancer patients.

Endocrine FGFs: Evolution, Physiology, Pathophysiology, and Pharmacotherapy.

The human fibroblast growth factor (FGF) family comprises 22 structurally related polypeptides that play crucial roles in neuronal functions, development, and metabolism. FGFs are classified as intracrine, paracrine, and endocrine FGFs based on their action mechanisms. Paracrine and endocrine FGFs are secreted signaling molecules by acting via cell-surface FGF receptors (FGFRs). Paracrine FGFs require heparan sulfate as a cofactor for FGFRs. In contrast, endocrine FGFs, comprising FGF19, FGF21, and FGF23, require α-Klotho or β-Klotho as a cofactor for FGFRs. Endocrine FGFs, which are specific to vertebrates, lost heparan sulfate-binding affinity and acquired a systemic signaling system with α-Klotho or β-Klotho during early vertebrate evolution. The phenotypes of endocrine FGF knockout mice indicate that they play roles in metabolism including bile acid, energy, and phosphate/active vitamin D metabolism. Accumulated evidence for the involvement of endocrine FGFs in human genetic and metabolic diseases also indicates their pathophysiological roles in metabolic diseases, potential risk factors for metabolic diseases, and useful biomarkers for metabolic diseases. The therapeutic utility of endocrine FGFs is currently being developed. These findings provide new insights into the physiological and pathophysiological roles of endocrine FGFs and potential diagnostic and therapeutic strategies for metabolic diseases.

Myogenic-specific ablation of Fgfr1 impairs FGF2-mediated proliferation of satellite cells at the myofiber niche but does not abolish the capacity for muscle regeneration

Skeletal muscle satellite cells (SCs) are Pax7+ myogenic stem cells that reside between the basal lamina and the plasmalemma of the myofiber. In mature muscles, SCs are typically quiescent, but can be activated in response to muscle injury. Depending on the magnitude of tissue trauma, SCs may divide minimally to repair subtle damage within individual myofibers or produce a larger progeny pool that forms new myofibers in cases of overt muscle injury. SC transition through proliferation, differentiation and renewal is governed by the molecular blueprint of the cells as well as by the extracellular milieu at the SC niche. In particular, the role of the fibroblast growth factor (FGF) family in regulating SCs during growth and aging is well recognized. Of the several FGFs shown to affect SCs, FGF1, FGF2, and FGF6 proteins have been documented in adult skeletal muscle. These prototypic paracrine FGFs transmit their mitogenic effect through the FGFRs, which are transmembrane tyrosine kinase receptors. Using the mouse model, we show here that of the four Fgfr genes, only Fgfr1 and Fgfr4 are expressed at relatively high levels in quiescent SCs and their proliferating progeny. To further investigate the role of FGFR1 in adult myogenesis, we have employed a genetic (Cre/loxP) approach for myogenic-specific (MyoDCre-driven) ablation of Fgfr1. Neither muscle histology nor muscle regeneration following cardiotoxin-induced injury were overtly affected in Fgfr1-ablated mice. This suggests that FGFR1 is not obligatory for SC performance in this acute muscle trauma model, where compensatory growth factor/cytokine regulatory cascades may exist. However, the SC mitogenic response to FGF2 is drastically repressed in isolated myofibers prepared from Fgfr1-ablated mice. Collectively, our study indicates that FGFR1 is important for FGF-mediated proliferation of SCs and its mitogenic role is not compensated by FGFR4 that is also highly expressed in SCs.

Characterization of FGF family growth factors concerning branching morphogenesis of mouse lung epithelium.

Mouse lung rudiments express eight members of fibroblast growth factor (FGF) family genes from embryonic day 10 (E10) to E13. Some of these are expressed in either the epithelium or mesenchyme, while others are expressed in both. Incorporating the results of our previous study, we characterized the branch-inducing activities of all of FGFs expressed in the early lung rudiment. Of these, FGF1, FGF2, FGF7, FGF9 and FGF10 induced branching morphogenesis in Matrigel-embedded E11 epithelium, and their effective concentrations varied (10 nM, 10 nM, 3 nM, 1 nM, and 100 nM, respectively). Whereas shaking culture dishes containing medium supplemented with FGF7 or FGF10 showed reduced branching morphogenesis, those supplemented with FGF1, FGF2, or FGF9 did not, suggesting the involvement of autocrine growth factor(s) in branching morphogenesis induced by FGF7 or FGF10. In the presence of heparin, a well-known activator of FGF signaling, cystic morphology with lumen expansion was observed in cultures containing FGF1, FGF7, or FGF10, but growth arrest was observed in cultures containing FGF2 or FGF9. These results indicate that several paracrine and autocrine FGFs function during branching morphogenesis of lung epithelium.

Physiological functions and underlying mechanisms of fibroblast growth factor (FGF) family members: recent findings and implications for their pharmacological application.

Despite their name, fibroblast growth factors (FGFs) are multifunctional regulators affecting a wide variety of physiological events. This review summarizes our recent studies on FGFs from mechanistic, physiological and application-oriented viewpoints. These include studies on the importance of βKlotho and glycosaminoglycans for the signaling of hormonal FGFs (FGF21 and FGF19); the physiological role of a paracrine FGF (FGF18) in hair cycle regulation; and the development of a stable, chimeric FGF protein composed of FGF1 and FGF2 domains suitable for radioprotection.

Fibroblast Growth Factor 2 Causes G2/M Cell Cycle Arrest in Ras-Driven Tumor Cells through a Src-Dependent Pathway

We recently reported that paracrine Fibroblast Growth Factor 2 (FGF2) triggers senescence in Ras-driven Y1 and 3T3Ras mouse malignant cell lines. Here, we show that although FGF2 activates mitogenic pathways in these Ras-dependent malignant cells, it can block cell proliferation and cause a G2/M arrest. These cytostatic effects of FGF2 are inhibited by PD173074, an FGF receptor (FGFR) inhibitor. To determine which downstream pathways are induced by FGF2, we tested specific inhibitors targeting mitogen-activated protein kinase (MEK), phosphatidylinositol 3 kinase (PI3K) and protein kinase C (PKC). We show that these classical mitogenic pathways do not mediate the cytostatic activity of FGF2. On the other hand, the inhibition of Src family kinases rescued Ras-dependent malignant cells from the G2/M irreversible arrest induced by FGF2. Taken together, these data indicate a growth factor-sensitive point in G2/M that likely involves FGFR/Ras/Src pathway activation in a MEK, PI3K and PKC independent manner.

Conversion of a Paracrine Fibroblast Growth Factor into an Endocrine Fibroblast Growth Factor

FGFs 19, 21, and 23 are hormones that regulate in a Klotho co-receptor-dependent fashion major metabolic processes such as glucose and lipid metabolism (FGF21) and phosphate and vitamin D homeostasis (FGF23). The role of heparan sulfate glycosaminoglycan in the formation of the cell surface signaling complex of endocrine FGFs has remained unclear. Here we show that heparan sulfate is not a component of the signal transduction unit of FGF19 and FGF23. In support of our model, we convert a paracrine FGF into an endocrine ligand by diminishing heparan sulfate-binding affinity of the paracrine FGF and substituting its C-terminal tail for that of an endocrine FGF containing the Klotho co-receptor-binding site to home the ligand into the target tissue. In addition to serving as a proof of concept, the ligand conversion provides a novel strategy for engineering endocrine FGF-like molecules for the treatment of metabolic disorders, including global epidemics such as type 2 diabetes and obesity.