Iris-derived melanocytes contain a growth factor that resembles basic fibroblast growth factor

Direct FGF receptor 1 activation through an anti-idiotypic strategy mimicks the biological activity of FGF-2 and inhibits the progression of the bladder carcinoma derived from NBT-II cells

The hypothesis that tumor growth is angiogenesis-dependent has been documented by a considerable body of direct and indirect experimental data. Since the discovery of the vascular endothelial growth factor (VEGF), most attention has been focused on the VEGF system. Although fibroblast growth factors 1 and 2 (FGF-1 and FGF-2) can exert a strong angiogenic activity when they are supplied as a single pharmacological agent, their role in pathological angiogenesis in preclinical models remains controversial. To decipher the contribution of FGF receptors in various models of angiogenesis, we took advantage of the anti-idiotypic strategy to obtain circulating agonists specific for FGFR-1 and FGFR-2 (AIdF-1 and AIdF-2). They mimicked FGF-1 and FGF-2 for receptor binding, signal transduction, proliferation of endothelial cells and differentiation of the bladder carcinoma cell NBT-II which expresses FGFR-2b but not FGFR-1. The constitutive expression of FGFR-1 allowed binding of FGF-2 and AIdF-2 and inhibition of the proliferation of NBT-II cells. AIdF-1 and AIdF-2 induced angiogenesis in the corneal pocket assay. Although FGFR-1 dimerization achieved by AIdF-2 injection led to highly differentiated and smaller NBT-II tumors, no sign of reduction of tumor angiogenesis was observed, thus suggesting that endothelial cells are resistant to FGF.

A Hidden Retinal Regenerative Capacity from the Chick Ciliary Margin is Reactivated In Vitro, that is Accompanied by Down-regulation of Butyrylcholinesterase

The chicken retina has a capacity to regenerate in vivo, which is restricted up to embryonic day 4 (E4). Here we test the proliferative patterns of dissociated chicken cells from the centre retina or the ciliary margin, including pigmented cells, after their transfer into rotation culture. For central cells in culture, the uptake of [3H]thymidine after a short initial rise decreases similarly to their in ovo counterparts. In contrast, marginal cells that have been shown to regenerate up to E9 into retinotypic stratospheroids re-enter a novel and long-lasting phase of in vitro cell division. We have shown previously that cell types of all nuclear layers are produced. Both observations taken together indicate a pronounced self-renewal of multipotent stem cells. Molecularly, the enzyme butyrylcholinesterase, which in other systems has been shown to mark transitory neuronal cells between proliferation and differentiation, is strongly expressed at the ciliary margin over most of the embryonic period. After these cells are transferred into rotation culture, butyrylcholinesterase is down-regulated. Concomitantly, the neuronal differentiation marker acetylcholinesterase increases. We conclude that the regenerative capacity of the chick retina is not lost at E4, but rather remains hidden in the chicken ciliary margin, since it can be reactivated in vitro at least up to E9. We suggest that butyrylcholinesterase may be linked to the regulation of stem cell activity.

Cell release of bioactive fibroblast growth factor 2 by exon 6-encoded sequence of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor which is synthesized and secreted by many differentiated cells in response to various stimuli including hypoxia and growth factor exposure. Alternative splicing of vascular endothelial growth factor mRNA results in three distinct molecular forms: V189 and V165 or V121 which lack the exons 6 or 6 and 7, respectively. To clarify the functions of the 24-amino acid insertion, the biological activity of V165 was compared with that exerted by purified recombinant V189 and a synthetic peptide designed on the sequence encoded by exon 6 (Ex6P). V189 and Ex6P, but not V165, induced cell proliferation on corneal endothelial cells cultured in vitro. These effects were due to the release of fibroblast growth factor 2 (FGF2) stored in the extracellular matrix but not to direct interactions with FGF receptors since V189 was inefficient on heparan sulfate-deficient cells expressing constitutively FGF-R1. Moreover corneas incubated ex vivo with Ex6P solubilized 10-fold more FGF2 than a isocationic peptide containing a scrambled sequence. Ex6P elicited an angiogenic response in a corneal pocket assay which was totally inhibited by addition of anti-FGF2 IgG. Moreover the angiogenic response to V189, but not to V165, was inhibited by FGF2 immunoneutralization. These findings demonstrate that the presence of the exon 6-encoded sequence confers VEGF with the ability to exert its biological effects through FGF2 signaling pathways.

Extracellular cleavage of the vascular endothelial growth factor 189-amino acid form by urokinase is required for its mitogenic effect

Alternative splicing of vascular endothelial growth factor (VEGF) mRNA results in three distinct molecular forms of 121 or 165 (V165) amino acids that are released in the conditioned medium of cultured cells and one longer isoform of 189 amino acids (V189) that remains cell-associated. V189 has been expressed in wild type CHO-K1 cells and in glycosaminoglycan-deficient pgsA-745 Chinese hamster ovary (CHO) mutant cells. It could be released from CHO-K1 cell membranes by heparin or a synthetic peptide designed on the sequence encoded by exon 6 but was freely released from CHO mutant cells. In both cases, the immunoreactive V189 was mainly released as a 40-kDa cleaved form, provided that the serine protease urokinase, but not plasmin, was active. Recombinant V189 was purified from insect cells infected with a recombinant baculovirus as a nonmitogenic 50-kDa precursor that binds to the receptor Flt-1 but not to Flk-1. It could be matured by urokinase as a 38-kDa fragment able to bind to Flk-1 and to trigger cell proliferation. V165 and V189, however, could be cleaved by plasmin as 34-kDa fragments that exhibit a decreased mitogenic activity. These findings indicate that the carboxyl-terminal domain of V189 masks its binding domain to Flk-1.

Vascular endothelial growth factor is an autocrine growth factor for hair dermal papilla cells

The transition of the late anagen to the catagen phase is concomitant with the disappearance of perifollicular capillaries, and therefore cyclical hair growth might depend on the ability of the dermal papilla to synthesize and release soluble growth and differentiation factors toward pre-existing capillaries. We characterized an angiogenic growth factor in the conditioned medium of dermal papilla cells indistinguishable from vascular endothelial growth factor as judged by biochemical and immunologic criteria. In addition, these cells bind vascular endothelial, growth factor on two binding sites and proliferate or migrate in the presence of this growth factor. Moreover, neutralizing antibodies inhibit these biologic effects, confirming that vascular endothelial growth factor might contribute to hair growth either by acting directly on papilla cells or by stimulating the local vascularization.

Immunolocalization of growth factors in the human ciliary body epithelium

Although various growth factors have been identified in the human aqueous humor, their sources have not been fully established so far. To determine, whether the ciliary body epithelium is capable of producing growth factors in vivo, we studied the immunolocalization of EGF, bFGF, IGF-I, TGF-alpha, TGF-beta and PDGF-AB in human ciliary body tissue obtained from 20 autopsy eyes (12 to 88 years; fixed within 6 hours post mortem) and 1 surgically enucleated melanoma eye using light and electron microscopic immunohistochemistry. Antibody binding was visualized by indirect immunofluorescence and immunogold labeling on differently fixed frozen and resin-embedded sections. The immunohistochemical findings indicate the production of EGF, bFGF, IGF-I, and TGF-alpha, to a minor degree also TGF-beta, particularly TGF-beta 2, by the ciliary epithelial cells, predominantly the nonpigmented cells. Ultrastructural evidence for an endogenous production included the distinct and specific labeling of secretory organelles (rough endoplasmic reticulum, Golgi complex), cytoplasmic vesicles, and the basolateral membrane infoldings. The ciliary epithelium failed to stain significantly with antibodies to TGF-beta 1 and PDGF-AB. Labeling for bFGF was found to depend on the specific antibodies and fixation conditions employed. Sequestration of bFGF and PDGF-AB in the basement membranes of the ciliary epithelium could be demonstrated under certain conditions. Peaks of labeling intensity were consistently observed at the crests of the ciliary processes and in the pars plana, suggesting regional variations in activity and secretion of growth factors into the aqueous humor and vitreous. While only PDGF-AB may be derived from the serum, it appears likely that most growth factors demonstrated are not circulating hormones but rather act as autocrine and/or paracrine factors.

Detection, quantification, and significance of basic fibroblast growth factor in the aqueous humor of man, cat, dog and pig

By using a highly specific and sensitive heterologous radioimmunoassay, we determined the content of basic fibroblast growth factor (bFGF) in fresh samples of aqueous humor obtained from human (n = 18), feline (n = 8), canine (n = 12), and porcine (n = 10) eyes by paracentesis. The content of bFGF in human aqueous humor ranged from 0.480 to 1.44 ng ml-1 (mean +/- S.D. = 1.074 +/- 0.297 ng ml-1); in feline samples, from 0.672 to 1.152 ng ml-1 (1.016 +/- 0.158 ng ml-1); in canine samples, from 0.640 to 1.232 ng ml-1 (1.026 +/- 0.171 ng ml-1); and in porcine samples, from 0.627 to 0.957 ng ml-1 (0.728 +/- 0.115 ng ml-1). These values were confirmed by means of a dot/slot-blot technique. For all species, the aqueous samples had normal protein levels that ranged from 5 to 19 mg dl-1. There was no correlation of the content of bFGF with the level of protein or with age of the human subjects. The similarity in the concentrations of bFGF in the aqueous humor as well as the stability of the blood-aqueous barriers of all four species indicate that cats, dogs, and pigs can serve as suitable animal models for the study of the role of bFGF in health and disease. We suggest the possible involvement of bFGF in the pathogenesis of anterior-segment disorders, such as neovascular glaucoma, and in the wound-healing response of limbal tissues after glaucoma filtration surgery.