Localization of acidic fibroblast growth factor (aFGF) mRNA in mouse and bovine retina by in situ hybridization

The retinal pigment epithelium in visual function

Located between vessels of the choriocapillaris and light-sensitive outer segments of the photoreceptors, the retinal pigment epithelium (RPE) closely interacts with photoreceptors in the maintenance of visual function. Increasing knowledge of the multiple functions performed by the RPE improved the understanding of many diseases leading to blindness. This review summarizes the current knowledge of RPE functions and describes how failure of these functions causes loss of visual function. Mutations in genes that are expressed in the RPE can lead to photoreceptor degeneration. On the other hand, mutations in genes expressed in photoreceptors can lead to degenerations of the RPE. Thus both tissues can be regarded as a functional unit where both interacting partners depend on each other.

Endogenous and exogenous fibroblast growth factor 2 support survival of chick retinal neurons by control of neuronal neuronal bcl-x(L) and bcl-2 expression through a fibroblast berowth factor receptor 1- and ERK-dependent pathway

Fibroblast growth factor (FGF) 2 is a survival factor for various cell types, including retinal neurons. However, little is understood about the molecular bases of the neuroprotective role of FGF2 in the retina. In this report, FGF2 survival activity was studied in chick retinal neurons subjected to apoptosis by serum deprivation. Exogenous FGF2 supported neuronal survival after serum deprivation and increased neuronal bcl-x(L) and bcl-2 expression, through binding to its receptor R1 (FGF-R1), and subsequent extracellular signal-regulated kinase (ERK) activation. Endogenous FGF2 was transiently overexpressed after serum deprivation. Its down-regulation by antisense oligonucleotides and blockade of its signaling pathway (binding to FGF-R1, tyrosine phosphorylation, and ERK inhibition) decreased bcl-x(L) and bcl-2 levels and and enhanced apoptosis, suggesting that endogenous FGF2 supported neuronal survival through a pathway similar to that of exogenous FGF2. This pathway may serve to up-regulate, or maintain, bcl-x(L) and bcl-2 levels that normally decrease during the onset of apoptosis. Indeed, long-term ERK activation and high bcl-x(L) levels are necessary for the survival activity of both exogenous and endogenous FGF2. Because FGF2 is upregulated following retinal injury in vivo, we suggest that an injury-stimulated autocrine/paracrine FGF2 loop may serve to maintain high levels of survival proteins, such as Bcl-x(L), through ERK activation in retinal neurons.

Paracrine effects of phosphorylated and excreted FGF1 by retinal pigmented epithelial cells

We have recently shown that both inhibition of endogenous Fibroblast growth factor (FGF) synthesis in non dividing lens epithelial cells (Renaud et al. J. Biol. Chem 1996, 271: 2801-2811) and inhibition of secreted FGF1 in confluent quiescent retinal pigmented epithelial (RPE) cells (Guillonneau et al., Exp. Cell. Res. 1997, in press) induce rapid cell apoptosis. In addition, FGF2-stimulated release of endogenous FGF1 is associated with reduced apoptosis in RPE cells. We now show that a single addition of exogenous FGF2 to RPE cells induces after 4 days of culture, a great accumulation of FGF1 within the cells. Concomitantly we observe that FGF1 was released into the extracellular medium. Secreted FGF1 from RPE cells, purified from culture medium and added to either Go-arrested RPE or RMG cells at low plating density induced cell proliferation, whereas when it is added once to serum-depleted confluent RPE and RMG cells it prevented apoptosis. Both endogenous and secreted FGF1 are phosphorylated. In addition, FGF2 stimulated the production and release of phosphorylated FGF1 by RPE cells. We show that this secreted form of phosphorylated FGF1 binds to the high affinity tyrosine kinase receptors of RPE and RMG cells on retinal sections and to heparan sulfate proteoglycan in RPE cell extracellular matrix. In contrast to non-phosphorylated FGF1, phosphorylated secreted FGF1 was not degraded after internalization but accumulated within RPE and RMG cells, and is rapidly translocated to the nucleus suggesting a role in signal transduction and gene expression pathways. These results show that exogenous FGF2 activities might be mediated indirectly by phosphorylation and that secretion of FGF1 may function as a paracrine trophic factor for retinal cells.

Acidic and basic fibroblast growth factor messenger RNA and protein show increased expression in adult compared to developing normal and dystrophic rat retina

To further elucidate the possible roles of fibroblast growth factors (FGFs) in retinal pathophysiology, messenger RNA levels of acidic and basic FGF (aFGF and bFGF, respectively) were measured throughout embryonic and postnatal development until adulthood in normal and dystrophic (Royal College of Surgeons, RCS) rat retinas using sensitive reverse transcription-coupled polymerase chain reaction (PCR) techniques. In normal rats, both aFGF and bFGF transcript levels remained steadily low throughout embryogenesis and up until 7 d of postnatal age. By 13 d bFGF mRNA had increased 30-fold, and by adulthood (4 mo) levels were 150 times greater than in newborn retina. Dystrophic RCS retinas followed the same basic pattern, except that bFGF expression levels were increased relative to normal rats: By 4 d postnatal RCS retinas contained three times more bFGF mRNA than normal, by 7 d they contained six times more, and by 10 d they contained eight times more. In contrast, aFGF mRNA levels rose only threefold between embryonic and adult stages, and did not show any differences between normal and RCS rats. In parallel, staining of lightly fixed frozen sections of young (< 20 d) normal rat retina with antibodies to bFGF revealed only faint labeling of neural cells, whereas adult retinal sections were labeled strongly, especially within the photoreceptor layer. Twenty-day RCS rat retina showed detectable bFGF-like immunoreactivity. Hence, these data indicate that major aFGF and bFGF expression occurs only late in retinal maturation, suggesting these factors act principally as survival factors, especially for photoreceptors. In addition, the increased expression in a degenerative mutant strain may indicate the early onset of general cellular stress.

Expression of FGF5 in choroidal neovascular membranes associated with ARMD

PURPOSE

The fibroblast growth factors (FGFs) are a family of 9 heparin binding proteins which have been proposed to play key roles in angiogenesis. Basic FGF (bFGF), acidic FGF (aFGF) and FGF5 have previously been demonstrated to be expressed in the normal retina and RPE. In this study, the expression of FGF5 was explored in choroidal neovascular membranes removed from patients with age-related macular degeneration (ARMD).

METHOD

Three membranes were surgically removed from patients with ARMD, and were fixed, embedded and sectioned for immunohistochemistry. The membranes were immunostained with an affinity purified rabbit polyclonal antibody raised against the amino acid sequence for residues 175 to 185 of human FGF5 and visualized with the silver enhanced colloidal gold method for light microscopy.

RESULTS

FGF5 was expressed in membranes arising from ARMD, and was found primarily in blood vessels and the surrounding extracellular matrix.

CONCLUSIONS

These results suggest that FGF5 may have a functional role in the pathophysiology of ARMD.

Expression of FGF-1 and FGF-2 mRNA during lens morphogenesis, differentiation and growth

PURPOSE

There is now considerable evidence that FGF is involved in lens differentiation and growth throughout life. The aim of this study was to determine potential sites of FGF production in and near the lens during morphogenesis, differentiation and growth.

METHODS

The distribution of FGF-1 and FGF-2 mRNAs was analysed in embryonic, weanling and adult rat eyes by in situ hybridization.

RESULTS

During lens morphogenesis, there was distinct expression of FGF-1, but not FGF-2, in the lens placode and retinal disc cells. Subsequently, both forms of FGF showed similar expression patterns. During lens differentiation, distinct expression of FGFs was associated with elongating primary fiber cells. From embryonic day 20 onwards, lenses showed strongest expression of FGF mRNAs in the transitional zone, where epithelial cells differentiate into fibers, with weaker expression in the anterior epithelium. Messenger RNAs for both FGFs were also localised in ocular tissues near the lens and bordering the ocular media, particularly the cornea, ciliary body, iris and neural retina.

CONCLUSIONS

These findings are consistent with the known distribution of FGF protein in the eye and implicate various ocular tissues as potential sources of FGF that may influence lens cells. Furthermore, the fact that lens cells have the potential for synthesizing FGF, together with evidence from previous studies that lens cells express FGF receptors and respond to lens-derived FGF, raises the possibility that some aspects of lens cell behaviour in situ may be influenced by autocrine mechanism(s) of FGF stimulation.

The neurotrophic activity of fibroblast growth factor 1 (FGF1) depends on endogenous FGF1 expression and is independent of the mitogen-activated protein kinase cascade pathway

The expression of fibroblast growth factor (FGF) 1, a potent neurotrophic factor, increases during differentiation and remains high in adult neuronal tissues. To examine the importance of this expression on the neuronal phenotype, we have used PC12 cells, a model to study FGF-induced neuronal differentiation. After demonstrating that FGF1 and FGF2 are synthesized by PC12 cells, we investigated if FGF1 expression could be a key element in differentiation. Using the cell signaling pathway to determine the effects of FGF1 alone, FGF1 plus heparin, or a mutated FGF1, we showed an activation to the same extent of mitogen-activated protein (MAP) kinase kinase and MAP kinase (extracellular regulated kinase 1). However, only FGF1 plus heparin could promote PC12 cell differentiation. Thus, the MAP kinase pathway is insufficient to promote differentiation. Analysis of the PC12 cells after the addition of FGF1 plus heparin or FGF2 demonstrated a significant increase in the level of FGF1 expression with the same time course as the appearance of the neuritic extensions. Transfection experiments were performed to enhance constitutivly or after dexamethasone induction the level of FGF1 expression. The degree of differentiation achieved by the cells correlated directly with the amount of FGF1 expressed. The MAP kinase pathway did not appear to be involved. Interestingly, a 5-fold increase in FGF1 in constitutive transfected cells extended dramatically their survival in serum-free medium, suggesting that the rise of FGF1 synthesis during neuronal differentiation is probably linked to their ability to survive in the adult. All of these data demonstrate that, in contrast to the MAP kinase cascade. FGF1 expression is sufficient to induce in PC12 cells both differentiation and survival. It also shows that auto- and trans-activation of FGF1 expression is involved in the differentiation process stimulated by exogenous FGFs through a new pathway which remains to be characterized.

Survival factors in retinal degenerations

Recent experiments on the retina have examined the effectiveness of various factors (e.g. growth factors, neurotrophins and cytokines) for enhancing survival and reducing injury of retinal neurons, such as photoreceptors and ganglion cells, whose death leads to blindness in degenerative retinal diseases. It has also been shown that retinal injury stimulates intrinsic survival mechanisms that promote survival of these neurons.

Growth factor effects on the proliferation of different retinal glial cells in vitro

Vascularized mammalian retinae contain two distinct neuroglial cells types, radially oriented Müller cells and astrocytes, which are located in the nerve fiber layer. These cell types derive from different precursor cells and proliferate during ontogenesis at distinct schedules. The aim of the present study was to disclose whether growth factors, which are known to interfere with the development of neuroglial cells in the central nervous system, like basic and acidic fibroblast growth factor (aFGF and bFGF), epidermal growth factor (EGF) and platelet-derived growth factor, have similar or distinct effects on the proliferative capacity of retinal astrocytes and Müller cells. These questions were tested by applying growth factors to cultured astrocytes and Müller cells from early postnatal rabbit retina. Proliferating cells were identified by double labeling experiments combining cell type specific markers with bromodeoxyuridine immunocytochemistry and [3H]thymidine incorporation experiments, respectively. In addition, we used the anatomical advantage of the rabbit retina. Its peripheral part is astroglial cell-free. Cultures prepared from this part of the retina (P-cultures) contain Müller cells, microglial cells and neurons, while cultures from the 'central part', the medullary rays (MR) region contain, in addition, astrocytes and oligodendrocytes. Our studies show that Müller cell proliferation is stimulated by EGF in a dose dependent manner, while astrocyte proliferation is stimulated by aFGF and bFGF. The proliferation of O4-positive glial precursor cells is stimulated by aFGF, bFGF and platelet-derived growth factor, but not by EGF. Microglial cells, which are a minor population in these cultures, do not respond to either of these factors.

Immunochemical evidence for a fibroblast growth factor receptor in adult retinal optic fiber and synaptic layers

Evidence for fibroblast growth factor receptors in the central nervous system has only been obtained using autoradiographic localization of fibroblast growth factor binding sites and messenger RNA. To clarify those neuronal functions that are regulated by fibroblast growth factor receptors, we have localized immunocytochemically the fibroblast growth factor receptor protein in bovine retina, a neural tissue of well-defined structure and function. The extracellular domain of the gene product referred to as fibroblast growth factor receptor 2 was expressed genetically in bacteria to obtain a polyclonal antibody. Positive staining was confined almost exclusively to the synaptic and optic fiber layers. Such a specific association suggests a role for this receptor in modulation of synaptic terminals and ganglion cell axons of the optic nerve, especially with respect to glutamate release.

Regulation of cell division and rod differentiation in the teleost retina

We tested the effects of several growth factors on the proliferation and differentiation of cells in the teleost retina which typically become rod photoreceptors to understand their regulation. Using organotypic slice cultures of differentiated teleost fish retinal tissue, we found that insulin and insulin-like growth factor I (IGF-I) stimulate proliferation of rod precursor cells whereas basic fibroblast growth factor (bFGF) does not. In the presence of bFGF, however, a greater proportion of the cells that had divided expressed a rod photoreceptor-specific phenotype than did control slices. This suggests insulin and the related IGF-I can influence the regulation of neuronal cell division whereas bFGF promotes the differentiation of neuronal stem cells into rod photoreceptors in retinal slice culture. These results support the idea that cell division and differentiation are differentially regulated and diffusible factors play a role in this process.

Acidic fibroblast growth factor is expressed abundantly by photoreceptors within the developing and mature rat retina

In order to further understand the role(s) of fibroblast growth factors (FGFs) in the development, differentiation and function of the central nervous system, we analysed the expression of the mRNA, and the presence and tissue distribution of the translated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Firstly, the relative abundance of aFGF mRNA was assayed in embryonic (between 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcription-coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throughout the embryonic period and until postnatal day 7. Therefore the quantity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three-fold higher than at early developmental times. In situ hybridization of adult rat retina using specific antisense aFGF riboprobes revealed labelling in all cellular layers. Antisera raised against recombinant human aFGF revealed very little labelling of 4-day postnatal retina, but by postnatal days 8 and 17 immunoreactive aFGF was localized mainly within the photoreceptor cell bodies. Western blots of retinal extracts derived from 17-day embryonic, 4-day postnatal and adult retina probed with the same antibody revealed a single immunoreactive band of the expected molecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribed and translated within the retina subsequent to the major steps of cell birth, migration and differentiation, and seems to be abundantly expressed by maturing photoreceptor cells.

Fibroblast growth factor induces proliferating cell nuclear antigen-immunoreactive cells in goldfish retina

New rod photoreceptors are added to mature teleost retinas throughout life by regulated proliferation of rod precursor cells (RPCs). In this study, candidate regulators of RPC proliferation, acidic and basic fibroblast growth factors (aFGF and bFGF; 0.1 microgram/eye), interleukin-6 (IL-6; 0.1 microgram) and phytohaemagglutinin (HA15; 1.0 microgram), were injected intravitreally into one eye of goldfish (body length 5-6 cm), and mitotic RPCs in both retinas were detected and counted 3-50 days later by immunohistochemistry for proliferating cell nuclear antigen (PCNA). Retinal integrity after treatment was assessed by immunohistochemistry for tyrosine hydroxylase (TH) and other retinal antigens. All the agents applied altered the density of PCNA-immunoreactive (ir) cells in the outer and inner nuclear layers (ONL and INL) in both retinas as soon as 2-3 days after unilateral injection. Initially (2-20 days after injection), particularly in the treated retina, PCNA-ir cells appeared in clusters accompanied by various numbers of scattered individual cells, but subsequently the clusters of PCNA-ir cells disappeared while the density of singly distributed cells increased until 30 days after injection. At the doses given, these effects were most striking with aFGF and bFGF and less with IL-6 and HA15. In radial cryosections, other cellular elements immunoreactive to markers such as TH, serotonin, neuropeptide Y, substance P, glutamine synthetase, glial fibrillary acidic protein and protein kinase C, were found normal in terms of morphology. In addition, a monoclonal antibody (NN-2) was found to label some non-neuronal structures (macrophages, microglia and blood vessels) inside and outside the retina intoxicated with 6-hydroxydopamine, a few NN-2-ir cells being PCNA-positive. However, clustered PCNA-ir and marginal neuroblast cells were NN-2-negative. These results indicate that FGFs may play an important role in stimulating the proliferation of RPCs, for example, in the regeneration of fish retinas following neurotoxic destruction.

Increasing cell density down-regulates the expression of acidic FGF by human RPE cells in vitro

Previous studies have reported the expression of acidic fibroblast growth factor (aFGF) by rat, bovine, and human retinal pigment epithelium (RPE) in vivo. To critically examine the expression of aFGF by RPE cells, we studied the density dependence of steady-state levels of mRNA and protein expression in vitro. Northern blot analysis demonstrated 5 transcripts ranging from 4.5 kB to 1 kB. Steady-state levels of all the transcripts decreased as a function of culture density. A polyclonal antibody was raised against recombinant human aFGF and affinity purified on aFGF coupled to AffiGel-10. The resulting antibody crossreacted with bFGF but not FGF-5, but this crossreactivity could be eliminated by absorption of the antibody on bFGF coupled to AffiGel-10. The final antibody preparation recognized only a single band at approximately 18.5 kD in lysates of RPE. Immunohistochemical staining with this antibody preparation demonstrated a marked dependence on cell density after 3 days in culture. Low culture density yielded cells staining moderately for aFGF, while confluent cells exhibited little or no staining. The reduction of aFGF from RPE cells in culture in a density-dependent fashion could also be demonstrated by Western blot analysis.

Fibroblast growth factor receptor deficiency in dystrophic retinal pigmented epithelium

The retinal pigmented epithelium (RPE) is known to be the site of the primary lesion in inherited retinal dystrophy in the Royal College of Surgeons (RCS) rat, a model for retinitis pigmentosa. Although the only functional defect so far detected in these cells is their failure to efficiently phagocytose shed photoreceptor outer segment debris, the actual cause of photoreceptor cell death is still unknown. Recently the possibility of "trophic factors" important in photoreceptor survival produced by normal RPE but not by dystrophic RPE has been suggested. Hence we decided to investigate the presence and abundance of two candidate diffusible factors, the acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), as well as their high affinity cell surface receptors (FGF-R). mRNA was isolated from primary cultures of purified normal and dystrophic RPE and analyzed by PCR amplification using specific oligonucleotide primers for aFGF and bFGF: the size and abundance of amplified fragments was similar for both cell types. Also, aFGF protein, detected by immunocytochemistry using specific antisera, appeared to be present in approximately equal amounts and distributed in a similar pattern. However, scatchard analysis of radio-labelled bFGF binding to primary cultures of normal and dystrophic rat RPE revealed that dystrophic RPE possess only 29% the number of surface receptors compared to congenic normal cells. Furthermore, the level of expression of FGF-R2 mRNA, but not that of FGF-R1, was significantly different. Other parameters measured (receptor affinity, profile of ligand internalization and degradation, receptor molecular weight and mitogenic activity) did not show any significant differences between normal and dystrophic RPE. The precise role of FGF-R deficiency in the etiology of the disease hence remains to be determined, but it indicates the importance of trophic factors in the normal functioning of the retina.

Growth factor-induced retinal regeneration in vivo

It is apparent from a number of studies that the RPE has a remarkable ability to regenerate neural retina. While retinal regeneration from the RPE has not been reported in adult vertebrates, with the exception of the newt, there is evidence that many vertebrate species have the ability to regenerate a new neural retina during the early development. Studies of retinal regeneration in the chicken embryo have provided some insight into the requirements for this process. Recent investigations using copolymer implants as an intraocular delivery system for growth factors have demonstrated that the state of differentiation of RPE cells in the stage 22-24 chicken embryo can be altered in vivo by specific growth factors, aFGF and bFGF. These results raise the distinct possibility that variations in the local production of FGFs and their receptors in the eye during development may, in part, regulate the pathway of differentiation of RPE and neural retina precursors. Further research on the role of FGFs and their receptors in retinal development and regeneration will not only contribute to our understanding of how the differentiated state is achieved and maintained but may provide a foundation for future attempts to develop methods of treatment for various degenerative and proliferative diseases of the eye.

Purification of an active receptor for acidic and basic fibroblast growth factor from bovine retina

Acidic and basic fibroblast growth factors (FGFs) influence cell division and differentiation in retina cells. Their effects are thought to be mainly mediated through stimulation of a specific membrane receptor and subsequent generation of an intracellular signal pathway. In this study, we purified a FGF receptor of 130 kDa from bovine neural retina using wheat germ agglutinin affinity chromatography followed by FGF-affinity chromatography. The isolated receptor showed ligand binding activity with dissociation constants of 0.8 nM and 2 nM for aFGF and bFGF, respectively. Furthermore, binding of aFGF and bFGF to purified receptor resulted in self-phosphorylation, demonstrating that the isolated receptor had an unaltered intrinsic kinase activity.

Endogenous aFGF expression and cellular changes after a demyelinating lesion in the spinal cord of adult normal mice: immunohistochemical study

Fibroblast growth factors (FGFs) are known to act on glial cells in vitro. At the present time, their involvement in the remyelinating process of the adult central nervous system (CNS) is still unknown. In the present study, using immunohistochemistry (IHC), we investigated the evolution in time and space of acidic FGF (aFGF) expression and CNS cell changes occurring after a chemically induced demyelinating lesion. In a first early period, aFGF immunostaining was shown to decrease around the demyelinated area. A dramatic increase was then observed and was accompanied by an increase of cell density around and inside the lesion. This was correlated with the beginning of remyelination. Late after demyelination, while remyelination was still in progress, aFGF immunostaining of the lesion and unlesioned spinal cord were comparable. A role of aFGF in remyelination is proposed.

Effects of acidic fibroblast growth factor on hippocampal long-term potentiation in fasted rats

Effects of human recombinant acidic fibroblast growth factor (haFGF) on long-term potentiation (LTP) and the increase of the spike amplitude induced by weak tetanic stimulation were investigated and compared with those of CS23 (modified human basic FGF) in the dentate gyrus of fasted and nonfasted rats. haFGF didn't influence the LTP induced by the tetanus of 100 pulses at 100 Hz in both 24 hr fasted and non-fasted rats. On the other hand, the tetanus of 20 pulses at 60 Hz significantly enhanced the amplitude of population spike and facilitated the generation of LTP by the i.c.v. injection of 10 microliters of 20-40 micrograms/ml haFGF in 24 hr fasted rats but not in non-fasted rats. However, 40 micrograms/ml CS23 induced LTP when the tetanus of 20 pulses at 60 Hz was applied in both fasted and non-fasted states. These results suggest that haFGF might be one of the regulating factors of feeding and memory.

Induction of retinal regeneration in vivo by growth factors

We have previously reported that basic fibroblast growth factor (bFGF) can induce retinal regeneration in the stage 22-24 chicken embryo. The present study was undertaken to identify the cellular source of the regenerate and to determine whether other growth factors also elicit regeneration in this animal model. Polymer implants containing bFGF were inserted into eyes of chicken embryos immediately after extirpation of the neural retina. The retinal pigment epithelium (RPE) was left intact. Evaluation by light microscopy revealed that in bFGF-treated eyes the new neural retina arose by transdifferentiation of the entire RPE layer. Differentiation of the new neural retina occurred in a sequence similar to that of normal development but proceeded in a reverse (vitread) direction. All retinal laminae had differentiated by Day 15. However, the regenerate displayed reversed polarity, with photoreceptors closest to the lens. The RPE, pecten, and optic nerve were absent. Focal areas of degeneration in the retinal regenerate became evident for the first time on Day 10. Retinal regeneration was also observed after treatment with higher doses of acidic fibroblast growth factor, but not with nerve growth factor-beta, transforming growth factor-beta 1, insulin, or insulin-like growth factors I or II. These results raise the possibility that FGFs may play a role in retinal differentiation during development.

Prominent expression of acidic fibroblast growth factor in motor and sensory neurons

Several growth factors originally characterized and named for their action on a variety of cells have more recently been suggested to be importantly involved in the development and maintenance of the nervous system. Acidic fibroblast growth factor (aFGF) is a member of a family of seven structurally related polypeptide growth factors. The cells responsible for expression of aFGF in the nervous system of adult rats have been identified using an affinity-purified antibody to aFGF in immunohistochemical studies and synthetic oligonucleotide probes for in situ hybridization studies. High levels of aFGF expression were observed in motoneurons, primary sensory neurons, and retinal ganglion neurons. Glial cells did not express detectable amounts of aFGF. Confocal and electron microscopic analysis suggested that a large portion of aFGF immunoreactivity was associated with the cytoplasmic face of neuronal membranes, consistent with the hypothesis that aFGF is a sequestered growth factor.

Localization of acidic fibroblast growth factor in proliferative vitreoretinopathy membranes

The pathogenesis of proliferative vitreoretinopathy (PVR) membranes remains poorly understood. We have studied the presence of acidic fibroblast growth factor (aFGF), a potent mitogen for many cells, within these membranes. We have used affinity purified monospecific anti-aFGF polyclonal antibodies, in conjunction with highly sensitive immunofluorescence techniques. The labelling was exclusively localized to cell bodies and was absent from the extracellular matrix. Double labelling techniques revealed that all cytokeratin positive cells (probably pigmented epithelial cells) and macrophages contained aFGF-like immunoreactivity, whilst glial cells were unlabelled. Appropriate controls indicated the specificity of the antibodies. Hence, the presence of this mitogenic molecule within certain cell types constituting PVR membranes may contribute to the pathogenesis.

Acidic fibroblast growth factor (aFGF) is expressed in the neuronal and glial spinal cord cells of adult mice

Fibroblast growth factors (FGFs) are known to be synthesized in the central nervous system (CNS) and to act on CNS cells in vitro, but less is known about their synthesis, expression, and role in vivo. In this work, using specific anti-acidic fibroblast growth factor (aFGF) antibodies, we have shown for the first time, by immunohistochemistry, that aFGF is expressed in spinal cord cells of young adult normal mice. This expression is predominant in the cell nucleus. Using immunohistochemical double staining procedures, we identified the cell type expressing aFGF as neurons, astrocytes, and oligodendrocytes, but for each type, cells were not all positively immunostained.