Role Of FGF-2 Research Articles

Cytosolic Low Molecular Weight FGF2 Orchestrates RIG-I-Mediated Innate Immune Response.

Fibroblast growth factor (FGF)2,which is one of the 22 members of the FGF family, functions as an extracellular molecule involved in canonical receptor tyrosine kinase signaling. It has been implicated in angiogenesis and the development of the CNS. In this article, we reveal that cytosolic low m.w. isoform (LMW) FGF2 (18 kDa), not its secreted form, plays an unexpected role in the innate immune response. Cytosolic LMW FGF2 directly associated with inactivated RIG-I under physiological conditions, which enhanced RIG-I protein stability, thereby maintaining basal RIG-I levels. However, during RIG-I activation induced by viral RNA, cytosolic FGF2 bound to the caspase recruitment domains of activated RIG-I, which blocked RIG-I-MAVS complex formation. LMW FGF2 deficiency increased type I IFN production, whereas the overexpression of LMW FGF2 exerted the opposite effect. Cytosolic LMW FGF2 functions as a negative regulator in RIG-I-mediated antiviral signaling. This work provides insight into the role of FGF2 in innate immune response.

Fibroblast Growth Factor 2 Mediates Isoproterenol-induced Cardiac Hypertrophy through Activation of the Extracellular Regulated Kinase.

Fibroblast growth factor 2 (basic FGF or FGF2) has been shown to affect growth and differentiation in some tissues and to be required for cardiac hypertrophy in vivo. FGF2 has been shown in vitro to signal through the mitogen-activated protein kinase (MAPK) to affect cell survival and growth. To ascertain the role of FGF2 in cardiac hypertrophy, wildtype, Fgf2 knockout, non-transgenic, and FGF2 transgenic mice were treated with isoproterenol or saline via subcutaneous mini-osmotic pump implants to induce a hypertrophic response to β-adrenergic stimulation. Fgf2 knockout hearts are protected from isoproterenol-induced cardiac hypertrophy; whereas, FGF2 transgenic hearts show exacerbated cardiac hypertrophy as assessed by heart weight-to-body weight ratios and myocyte cross-sectional area. Echocardiography reveals significantly decreased fractional shortening in isoproterenol-treated FGF2 transgenic mice but not in Fgf2 knockout mice suggesting that FGF2 mediates the maladaptive cardiac dysfunction seen in cardiac hypertrophy induced by isoproterenol. Western blot analysis also reveals alterations in MAPK signaling in Fgf2 knockout and FGF2 transgenic hearts subjected to isoproterenol treatment, suggesting that this cascade mediates FGF2's pro-hypertrophic effect. Pharmacologic inhibition of extracellular signal-regulated kinase (ERK) signaling results in an attenuated hypertrophic response in isoproterenol-treated FGF2 transgenic mice, but this response is not seen with p38 mitogen-activated protein kinase (p38) pathway inhibition, suggesting that FGF2 activation of ERK but not p38 is necessary for FGF2's role in the mediation of cardiac hypertrophy.

Stage-Specific Effects of Fibroblast Growth Factor 2 on the Differentiation of Dental Pulp Cells

Dentinogenesis is a complex and multistep process, which is regulated by various growth factors, including members of the fibroblast growth factor (FGF) family. Both positive and negative effects of FGFs on dentinogenesis have been reported, but the underlying mechanisms of these conflicting results are still unclear. To gain a better insight into the role of FGF2 in dentinogenesis, we used dental pulp cells from various transgenic mice, in which fluorescent protein expression identifies cells at different stages of odontoblast differentiation. Our results showed that the continuous exposure of pulp cells to FGF2 inhibited mineralization and revealed both the stimulatory and inhibitory effects of FGF2 on the expression of markers of dentinogenesis and various transgenes. During the proliferation phase of in vitro growth, FGF2 increased the expression of markers of dentinogenesis and the percentages of dentin matrix protein 1/green fluorescent protein (DMP1-GFP)-positive functional odontoblasts and dentin sialophosphoprotein (DSPP)-Cerulean-positive odontoblasts. Additional exposure to FGF2 during the differentiation/mineralization phase of in vitro growth decreased the extent of mineralization and the expression of markers of dentinogenesis and of the DMP1-GFP and DSPP-Cerulean transgenes. Recovery experiments showed that the inhibitory effects of FGF2 on dentinogenesis were related to the blocking of the differentiation of cells into mature odontoblasts. These observations together showed the stage-specific effects of FGF2 on dentinogenesis by dental pulp cells, and they provide critical information for the development of improved treatments for vital pulp therapy and dentin regeneration.

Regulation of fibroblast growth factor 2 expression in oxygen-induced retinopathy.

Fibroblast growth factor (FGF) 2 is a potent endothelial cell mitogen and survival factor that is postulated to participate in the pathogenesis of retinopathy of prematurity (ROP). The purpose of the current study was to determine the transcriptional and translational regulation of FGF2 expression in oxygen-induced retinopathy (OIR), the animal model of ROP. We examined FGF2 protein and mRNA expression and optokinetic visual responses in transgenic mice possessing a dual-luciferase bicistronic transgene containing a 5'-internal ribosome entry site (IRES) of FGF2. We found that retinal FGF2 protein isoform expression varies with age but not in response to OIR. Analysis of luciferase, protein, and mRNA data indicate that FGF2 protein expression is translationally repressed during the vaso-obliterative phase of OIR, possibly by inhibiting elongation. At the transition from vaso-obliteration to neovascularization, heightened FGF2 protein expression corresponds to maintenance of IRES activity and diminished cap-dependent translational activity. During neovascularization, FGF2 expression is primarily regulated by transcription. Mice recovering from OIR display alterations in visual optokinetic responses and increased FGF2 protein expression at 6 weeks of age. In total, these findings illustrate the complexity of translational and transcriptional regulation of FGF2 protein expression in OIR. The augmentation of FGF2 expression and reduced optokinetic responses during the resolution of surface vasculopathy may indicate a role for FGF2 in the maintenance of neuroretinal function in OIR/ROP.

Roles of FGF-2 and TGF-beta/FGF-2 on differentiation of human mesenchymal stem cells towards nucleus pulposus-like phenotype

Human mesenchymal stem cells (MSCs) are reported to have the capability of differentiating towards nucleus pulposus (NP)-like phenotype under specific culture conditions. So far, the effects of fibroblast growth factor (FGF)-2 and the cocktail effects of transforming growth factor (TGF)-beta and FGF-2 on MSCs remain unclear. Therefore, we designed this study to clarify these effects. MSCs were cultured in conditioned medium containing FGF-2 or TGF-beta/FGF-2, and compared with basal or TGF-beta medium. The groups with FGF-2 showed the increase of cell proliferation. Functional gene markers and novel NP markers decreased in FGF-2 group, together with functional protein expression. Pho-ERK1/2 and pho-Smad3 differed significantly in the two conditioned groups. All these results suggest FGF-2 promotes MSCs’ proliferation, synergistically with TGF-beta. However, FGF-2 plays a negative role in cartilage homeostasis. We also demonstrate that FGF-2 has no positive effect in differentiating MSCs into NP-like cells, but hinders the acceleration effect of TGF-beta.

Stochastic specification of primordial germ cells from mesoderm precursors in axolotl embryos.

A common feature of development in most vertebrate models is the early segregation of the germ line from the soma. For example, in Xenopus and zebrafish embryos primordial germ cells (PGCs) are specified by germ plasm that is inherited from the egg; in mice, Blimp1 expression in the epiblast mediates the commitment of cells to the germ line. How these disparate mechanisms of PGC specification evolved is unknown. Here, in order to identify the ancestral mechanism of PGC specification in vertebrates, we studied PGC specification in embryos from the axolotl (Mexican salamander), a model for the tetrapod ancestor. In the axolotl, PGCs develop within mesoderm, and classic studies have reported their induction from primitive ectoderm (animal cap). We used an axolotl animal cap system to demonstrate that signalling through FGF and BMP4 induces PGCs. The role of FGF was then confirmed in vivo. We also showed PGC induction by Brachyury, in the presence of BMP4. These conditions induced pluripotent mesodermal precursors that give rise to a variety of somatic cell types, in addition to PGCs. Irreversible restriction of the germ line did not occur until the mid-tailbud stage, days after the somatic germ layers are established. Before this, germline potential was maintained by MAP kinase signalling. We propose that this stochastic mechanism of PGC specification, from mesodermal precursors, is conserved in vertebrates.

Walking along the Fibroblast Growth Factor 10 Route: A Key Pathway to Understand the Control and Regulation of Epithelial and Mesenchymal Cell-Lineage Formation during Lung Development and Repair after Injury.

Basic research on embryonic lung development offers unique opportunities to make important discoveries that will impact human health. Developmental biologists interested in the molecular control of branching morphogenesis have intensively studied the developing lung, with its complex and seemingly stereotyped ramified structure. However, it is also an organ that is linked to a vast array of clinical problems in humans such as bronchopulmonary dysplasia in premature babies and emphysema, chronic obstructive pulmonary disease, fibrosis, and cancer in adults. Epithelial stem/progenitor cells reside in niches where they interact with specific extracellular matrices as well as with mesenchymal cells; the latter are still poorly characterized. Interactions of epithelial stem/progenitor cells with their microenvironments are usually instructive, controlling quiescence versus activation, proliferation, differentiation, and migration. During the past 18 years, Fgf10 has emerged not only as a marker for the distal lung mesenchyme during early lung development, but also as a key player in branching morphogenesis and a critical component of the niche for epithelial stem cells. In this paper, we will present the current knowledge regarding the lineage tree in the lung, with special emphasis on cell-lineage decisions in the lung mesenchyme and the role of Fgf10 in this context.

Role of FGF10 on tumorigenesis by MS‐K

Murine MS-K and NFSA cell lines formed tumor after inoculation into mouse and both cell lines expressed high level of vascular endothelial growth factor-A (vegf-A) and produced same level of VEGF-A. However, poor blood vessel formation, and necrosis was significantly observed in NFSA-tumor, contrary to well-developed blood vessel formation in MS-K tumor. The microarray analysis showed high expression of fibroblast growth factor-10 (fgf-10) in MS-K than NFSA. In this report, the role of fgf-10 on tumor growth was studied. MS-K enhanced more proliferation of endothelial cells by direct co-culture than NFSA, and rFGF10 supported the proliferation of HUVEC in combination with VEGF-A. fgf-10-knocked down MS-K, MS-K (fgf-10-KD), proliferated slower in vitro and the tumorigenicity of them was also slower than control. The blood vessel formation in these MS-K (fgf-10-KD) clones was reduced compared with the MS-K (normal). qPCR analysis showed the suppression of vegf-A, vegf-C and fgfr-1-expression in the MS-K (fgf-10-KD) clones. Taken together, these results indicated that FGF10, which was produced from tumor cells, was essential for the proliferation of tumor cell itself and also supports proliferation of endothelial cells. Thus, FGF10 plays an important role for tumor growth by both paracrine and autocrine manner.

Fibroblast growth factor control of cartilage homeostasis

Osteoarthritis (OA) and degenerative disc disease (DDD) are similar diseases involving the breakdown of cartilage tissue, and a better understanding of the underlying biochemical processes involved in cartilage degeneration may allow for the development of novel biologic therapies aimed at slowing the disease process. Three members of the fibroblast growth factor (FGF) family, FGF-2, FGF-18, and FGF-8, have been implicated as contributing factors in cartilage homeostasis. The role of FGF-2 is controversial in both articular and intervertebral disc (IVD) cartilage as it has been associated with species- and age-dependent anabolic or catabolic events. Recent evidence suggests that FGF-2 selectively activates FGF receptor 1 (FGFR1) to exert catabolic effects in human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme production, inhibition of extracellular matrix (ECM) accumulation and proteoglycan synthesis, and clustering of cells characteristic of arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating the FGFR3 pathway, inducing ECM formation and chondrogenic cell differentiation, and inhibiting cell proliferation. These changes result in dispersed chondrocytes or disc cells surrounded by abundant matrix. The role of FGF-8 has recently been identified as a catabolic mediator in rat and rabbit articular cartilage, but its precise biological impact on human adult articular cartilage or IVD tissue remains unknown. The available evidence reveals the promise of FGF-2/FGFR1 antagonists, FGF-18/FGFR3 agonists, and FGF-8 antagonists (i.e., anti-FGF-8 antibody) as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Fibroblast growth factor 2 induces the precocious development of endothelial cell networks in bovine luteinising follicular cells

The transition from follicle to corpus luteum represents a period of intense angiogenesis; however, the exact roles of angiogenic factors during this time remain to be elucidated. Thus, the roles of vascular endothelial growth factor (VEGF) A, fibroblast growth factor (FGF) 2 and LH in controlling angiogenesis were examined in the present study. A novel serum-free luteinising follicular angiogenesis culture system was developed in which progesterone production increased during the first 5 days and was increased by LH (P<0.01). Blockade of signalling from FGF receptors (SU5402; P<0.001) and, to a lesser extent, VEGF receptors (SU1498; P<0.001) decreased the development of endothelial cell (EC) networks. Conversely, FGF2 dose-dependently (P<0.001) induced the precocious transition of undeveloped EC islands into branched networks associated with a twofold increase in the number of branch points (P<0.001). In contrast, VEGFA had no effect on the area of EC networks or the number of branch points. LH had no effect on the area of EC networks, but it marginally increased the number of branch points (P<0.05) and FGF2 production (P<0.001). Surprisingly, progesterone production was decreased by FGF2 (P<0.01) but only on Day 5 of culture. Progesterone production was increased by SU5402 (P<0.001) and decreased by SU1498 (P<0.001). These results demonstrate that FGF and VEGF receptors play a fundamental role in the formation of luteal EC networks in vitro, which includes a novel role for FGF2 in induction of EC sprouting.

Putative Role Of Fgf 23 In The Development Of Hypophosphatemia And Bone Fructures In An Anemic Patient Treated By Intravenous Saccharated Ferric Oxide

A post-menopausal patient with normal kidney function was referred to our hospital because of severe lumber pain. She had been treated by initially oral, and then by intravenous iron for longer than five years for the treatment of iron deficiency anemia due to recurrent GI bleeding. On admission, multiple lumber bone fracture with low bone mineral density was confirmed. Laboratory tests revealed severe hypophosphatemia (1.6 mg/dl) with slight decrease of calcium ion level. Serum levels of 25D and 1,25D were low normal, while increase of intact PTH (83.9 pg/ml) and FGF23 (60 pg/ml) were observed. After terminating intravenous iron supplement, her symptoms and hypophsophatemia were gradually normalized with oral active vitamin D treatment. Although we could not completely exclude the contribution of disturbed iron absorption from the intestine, damages of proximal tubular cells by iron, and osteomalacia caused by the deposition of iron, increased FGF23 level may have played critical roles in the development of severe hypophosphatemia in this patient. Such hypophosphatemia due to high FGF23 has recently been reported in patients treated by intravenous sacharated ferric oxide.

Abstract 4979: Co-operative role for Notch and fibroblast growth factor FGF2 signaling pathways in maintaining malignant phenotype of neuroblastoma: Potential targets for neuroblastoma growth inhibition.

Abstract Neuroblastoma, an extracraniel tumor of childhood generally progresses to therapy resistant metastatic tumor. Increased expression and activities of mitogenic FGF and the Notch signaling have been extensively correlated with highly malignant behavior and poor prognosis of many cancers including neuroblastoma, making FGF2-Notch3 as rational targets for therapeutic intervention. We have previously shown that a cell surface protease called dipeptydyl peptidase IV (DPPIV) induces apoptotic cell death of neuroblastoma cells thereby inhibiting their tumorigenic potential. In this study, we further examined if tumor suppressor activity of DPPIV is linked to decreased FGF2 and notch signaling pathways. We utilized Affymetrix microarray gene expression analysis, RNA interference and pharmacological inhibitor approaches, western blot and immunofluorescence analysis in these studies. Our results show that either endogenous up-regulation of DPPIV or exogenous treatment of DPPIV leads to decreased FGF2 and Notch3 levels. Furthermore, inhibition of FGF2 expression using FGF2-targeted small interfering RNA decreased the levels of Notch3 and matrix metalloproteinases leading to down regulation of p-Akt, an important survival factor for tumor cells. Blocking of Notch3 function either through a pharmacological inhibitor gamma secretase, or through shRNA also resulted in decreased p-Akt levels, and increased p21/waf1 and cleaved caspase 3 that are apoptosis inducers. Decreased levels of FG2 and Notch3 were associated with induction of differentiation, apoptosis and growth inhibition of neuroblastoma cells (SK-N-AS). In summary, our studies suggest a cooperative role for FGF2 and Notch3 signaling pathways in maintaining tumor phenotype and blocking of these pathways can lead to neuroblastoma tumor cell death. Thus these studies identify FGF2-Nothch 3 signaling pathways as potential targets for inhibiting growth and survival of neuroblastoma cells. 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 4979. doi:1538-7445.AM2012-4979

The roles of FGF and MAP kinase signaling in the segregation of the epiblast and hypoblast cell lineages in bovine and human embryos

At the blastocyst stage of mammalian pre-implantation development, three distinct cell lineages have formed: trophectoderm, hypoblast (primitive endoderm) and epiblast. The inability to derive embryonic stem (ES) cell lines in a variety of species suggests divergence between species in the cell signaling pathways involved in early lineage specification. In mouse, segregation of the primitive endoderm lineage from the pluripotent epiblast lineage depends on FGF/MAP kinase signaling, but it is unknown whether this is conserved between species. Here we examined segregation of the hypoblast and epiblast lineages in bovine and human embryos through modulation of FGF/MAP kinase signaling pathways in cultured embryos. Bovine embryos stimulated with FGF4 and heparin form inner cell masses (ICMs) composed entirely of hypoblast cells and no epiblast cells. Inhibition of MEK in bovine embryos results in ICMs with increased epiblast precursors and decreased hypoblast precursors. The hypoblast precursor population was not fully ablated upon MEK inhibition, indicating that other factors are involved in hypoblast differentiation. Surprisingly, inhibition of FGF signaling upstream of MEK had no effects on epiblast and hypoblast precursor numbers in bovine development, suggesting that GATA6 expression is not dependent on FGF signaling. By contrast, in human embryos, inhibition of MEK did not significantly alter epiblast or hypoblast precursor numbers despite the ability of the MEK inhibitor to potently inhibit ERK phosphorylation in human ES cells. These findings demonstrate intrinsic differences in early mammalian development in the role of the FGF/MAP kinase signaling pathways in governing hypoblast versus epiblast lineage choices.

FGF signalling inhibits neural induction in human embryonic stem cells

Human embryonic stem cells (hESCs) can exit the self-renewal programme, through the action of signalling molecules, at any given time and differentiate along the three germ layer lineages. We have systematically investigated the specific roles of three signalling pathways, TGFβ/SMAD2, BMP/SMAD1, and FGF/ERK, in promoting the transition of hESCs into the neuroectoderm lineage. In this context, inhibition of SMAD2 and ERK signalling served to cooperatively promote exit from hESC self-renewal through the rapid downregulation of NANOG and OCT4. In contrast, inhibition of SMAD1 signalling acted to maintain SOX2 expression and prevent non-neural differentiation via HAND1. Inhibition of FGF/ERK upregulated OTX2 that subsequently induced the neuroectodermal fate determinant PAX6, revealing a novel role for FGF2 in indirectly repressing PAX6 in hESCs. Combined inhibition of the three pathways hence resulted in highly efficient neuroectoderm formation within 4 days, and subsequently, FGF/ERK inhibition promoted rapid differentiation into peripheral neurons. Our study assigns a novel, biphasic role to FGF/ERK signalling in the neural induction of hESCs, which may also have utility for applications requiring the rapid and efficient generation of peripheral neurons.

The roles of FGF and Wnt signaling during zebrafish maxillary barbel regeneration

The roles of FGF and Wnt signaling during zebrafish maxillary barbel regeneration

06-P007 Different functional roles of FGF2 and FGF10 signaling in S252W FGFR2 cells: Impact in the Apert phenotype?

06-P007 Different functional roles of FGF2 and FGF10 signaling in S252W FGFR2 cells: Impact in the Apert phenotype?

J021 Regulation of cardiac progenitor cells during development

Cardiac progenitor cells of the second heart field (SHF) contribute to the poles of the elongating embryonic heart. Failure or perturbation of SHF development leads to congenital heart defects. Recent studies have demonstrated the existence, in the postnatal heart, of resident cardiac progenitor cells that specifically express the transcription factor Islet1, a SHF marker, and that have the potential to differentiate into cardiomyocytes, smooth muscle and endothelial cells. Interestingly, several evidences suggest that these residual progenitor cells arise from the SHF. Through analysis of a transgene integration site position effect we have identified the transcriptional repressor Hes1 as a novel regulator of SHF development. Hes1, a target gene of the Notch signaling pathway, is expressed SHF progenitor cells. Analysis of E15.5 Hes1-/- embryos reveals outflow tract alignment defects (ventricular septal defects and overriding aorta). At earlier developmental stages, Hes1-/- embryos display SHF proliferation defects, cardiac neural crest cells reduction and fail to completely extend the outflow tract. Thus these data reveal a role for Hes1, and potentially Notch signaling, in SHF development. Given the importance of Isl1 as a marker of resident progenitor cells in the later heart we are analysing the role of known and novel regulators of the SHF (Hes1, Fgf10 and Tbx1) in the regulation of myocardial progenitor cell fate and in the definition of the critical niche occupied by residual cardiac progenitor cells in the forming and definitive heart. In Fgf10-/- mice, outflow tract alignment occurs normally. However, Fgf10-/- hearts are highly dysmorphic. We thus hypothesize that Fgf10 deletion may affect the proliferative capacities of SHF progenitors in order to maintain the residual progenitor cells pool in the fetal heart. Initial results have revealed that whereas Fgf10-/- hearts undergo heart tube extension normally, proliferation is impaired. Together, our results identify Hes1 as a novel regulator of SHF progenitor cell deployment and reveal a potential role of Fgf10 in regulating cardiac progenitor cell fate and cardiac growth during the fetal period. This study will increase our understanding of the molecular mechanisms governing the maintenance and differentiation of cardiac progenitor cells.

The role of FGF-2 in renal fibrogenesis

Basic fibroblast growth factor (FGF-2) is a pleiotropic cytokine which exerts its effects via four different high affinity receptors (FGFR-1 to -4) which function as protein tyrosine kinases. In the kidney, FGF-2 is expressed in epithelial cells already during fetal development. During later stages, expression of the cytokine can be found in distal tubular epithelial cells, glomerular cells and few interstitial cells. Expression in fibroblasts is robustly upregulated in chronic kidney scarring pointing to an important role in fibrogenesis. Functional studies have demonstrated that FGF-2 exerts mainly proliferative effects on a variety of renal cell types. In regard to fibrogenesis, the expression and induction of proliferation in interstitial fibroblasts may be the most important function. FGF-2 is one of the key factors contributing to autocrine fibroblast proliferation in post-inflammatory matrix synthesis. In addition, FGF-2 facilitates epithelial to mesenchymal transition of tubular epithelial cells contributing early to an increase of matrix producing cells. However, the cytokine does not contribute directly to extracellular matrix synthesis. Still, many aspects of FGF-2 in renal fibrogenesis remains to be evaluated.

The role of FGF-2 in renal fibrogenesis

Basic fibroblast growth factor (FGF-2) is a pleiotropic cytokine which exerts its effects via four different high affinity receptors (FGFR-1 to -4) which function as protein tyrosine kinases. In the kidney, FGF-2 is expressed in epithelial cells already during fetal development. During later stages, expression of the cytokine can be found in distal tubular epithelial cells, glomerular cells and few interstitial cells. Expression in fibroblasts is robustly upregulated in chronic kidney scarring pointing to an important role in fibrogenesis. Functional studies have demonstrated that FGF-2 exerts mainly proliferative effects on a variety of renal cell types. In regard to fibrogenesis, the expression and induction of proliferation in interstitial fibroblasts may be the most important function. FGF-2 is one of the key factors contributing to autocrine fibroblast proliferation in post-inflammatory matrix synthesis. In addition, FGF-2 facilitates epithelial to mesenchymal transition of tubular epithelial cells contributing early to an increase of matrix producing cells. However, the cytokine does not contribute directly to extracellular matrix synthesis. Still, many aspects of FGF-2 in renal fibrogenesis remains to be evaluated.

Growth factors involved in aqueous humour-induced lens cell proliferation

Lens epithelial cell proliferation is regulated by growth factors in the aqueous humour of the eye. Although the lens fibre cell-differentiating factors are well defined, the factors in aqueous that promote lens cell proliferation are not. Mitogens present in aqueous primarily signal through the MAPK/ERK and PI3-K/Akt pathways. By characterising the signalling pathways involved in lens cell proliferation, we aim to identify the factors in aqueous that regulate this process in vivo. Using rat lens epithelial explants, 5′-2′-bromo-deoxyuridine and H3-thymidine incorporation were used to compare the effects of aqueous, insulin-like growth factor (IGF-1), platelet-derived growth factor (PDGF-A), epidermal growth factor (EGF) and fibroblast growth factor (FGF-2) on lens cell proliferation. Western blotting was employed to characterise ERK1/2 and Akt signalling induced by these mitogens. The above assays were also repeated in the presence of selective receptor inhibitors. Similar to aqueous, FGF induced a sustained ERK1/2 signalling profile (up to 6 h), unlike IGF, PDGF and EGF that induced a transient activation of ERK1/2. In the presence of a FGF receptor (FGFR) inhibitor, the sustained aqueous-induced ERK1/2 signalling profile was perturbed, resembling the transient IGF-, PDGF- or EGF-induced profile. In the presence of other growth factor receptor inhibitors, aqueous maintained its sustained, 6 h, ERK1/2 signalling profile, although ERK1/2 phosphorylation at earlier time periods was reduced. No one-specific receptor inhibitor could block aqueous-induced lens cell proliferation; however, combinations of inhibitors could, providing FGFR signalling was blocked. Multiple growth factors are likely to regulate lens cell proliferation in vivo, with a key role for FGF in aqueous-induced signalling and lens cell proliferation.