Stephan Hoffmann

VEGF release by retinal glia depends on both oxygen and glucose supply

Isolated retinae or isolated Müller cells were cultured in vitro, and vascular endothelial growth factor (VEGF) was assayed as protein (by ELISA) and as mRNA (by semi-quantitative RTPCR). In both types of cultures, hypoxia (5% O2) resulted in an upregulated VEGF release. While the unstimulated VEGF secretion was virtually independent of glucose (0.125–25 mM), elevated glucose concentrations (10–25 mM) blocked most of the stimulatory effect of hypoxia on VEGF mRNA synthesis (determined in Müller cell cultures) as well as on VEGF release (in both retina and Müller cell cultures). It is concluded that in retinal glial (Müller) cells, being responsible for retinal VEGF synthesis (and, thus, for undesirable neovascularization), the metabolic effects of hypoxia can be compensated by a surplus of glucose.

Rapid isolation of choriocapillary endothelial cells by Lycopersicon esculentum-coated Dynabeads.

Abstract In vitro studies of choroidal endothelial cells may be critical for understanding the pathogenesis of neovascularization in age-related macular degeneration, since endothelial cells from different sites are highly heterogeneous in their morphology and behavior. Isolation of choroidal endothelial cells is complicated and labor intensive because of the small size of the choroid and the difficulty of excluding contaminating cells. We describe a rapid, simplified method for the isolation of bovine choroidal endothelial cells using microdissection followed by the use of superparamagnetic beads (Dynabeads) coated with the endothelial cell-specific lectin Lycopersicon esculentum, which selectively binds to fucose residues on the endothelial cell surface. Cells bound to beads are isolated using a magnetic particle concentrator. Isolated cells grew to confluence in a monolayer with a cobblestone morphology and were shown to be endothelial cells by their greater than 95% immunoreactivity to von Willebrand factor and phagocytosis of dil-acetylated LDL. Isolated cells grew as tubes in three-dimensional cultures. This method markedly reduces the time needed for pure culture of cells and makes the in vitro study of choroidal endothelial cells practical and reproducible.

MMP-2 and MMP-9 secretion by rpe is stimulated by angiogenic molecules found in choroidal neovascular membranes.

Purpose: Matrix metalloproteinases (MMP)-2 and -9 play an important role in the pathogenesis of choroidal neovascularization (CNV). Retinal pigment epithelial cells (RPE) are an important source of MMPs in the outer retinal environment, however little is known about the local factors that modulate MMP secretion in these cells. The purpose of this study was to determine the effects of CNV involved growth factors and the extracellular matrix molecule fibronectin on MMP-2 and -9 secretion by cultured human RPE. Methods: MMP-2 and -9 secretion was studied using gelatin zymography, Western blot, and ELISA assay of RPE culture supernatants. The effects of stimulating the cells for 36 hours with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bGFG), tumor necrosis factor-alpha (TNF-α), or fibronectin (FN), all angiogenic factors found in CNV membranes, was determined. Results: Resting RPE cells secreted MMP-2 but not MMP-9. Stimulation with TNF-α induced secretion of MMP-9 and increased the secretion of MMP-2. MMP-2 secretion was also increased by stimulation with FN and VEGF, but not bFGF. Conclusion: The results indicated that the angiogenic molecules VEGF, FN, and TNF-α stimulate MMP-2 and -9 secretion from RPE and thus further promote CNV.

Hypoxia: modulation of endothelial cell proliferation by soluble factors released by retinal cells.

A devastating complication of ischemic retinopathies is retinal neovascularization. We studied the impact on retinal endothelial cell proliferation of soluble factors released from cultured retinal glial (Müller) cells and from retinal explant cultures. Hypoxia strongly stimulated VEGF release by all types of cultures but endothelial cell growth was not further increased by the corresponding conditioned media if compared to supernatants obtained under normoxia. When the final concentration of the hypoxia-conditioned media was adjusted to the VEGF level of normoxia-conditioned media, they even inhibited endothelial cell proliferation. Inhibition may be exerted by TGF-β2 but TGF-β2 mRNA and protein expression in Müller cells were found to be down-regulated under hypoxia. We conclude that retinal endothelial cell proliferation is controlled by the balance of the amount and/or efficacy of several stimulatory and inhibitory factors.

Impact of endostatin on bFGF-induced proliferation, migration, and matrix metalloproteinase-2 expression/secretion of bovine choroidal endothelial cells.

Purpose: To investigate the potential role of endostatin, an endogenous angiogenesis inhibitor, in the prevention of choroidal angiogenesis-related disorders. Methods: Bovine choroidal endothelial cells (CEC) were cultured and treated with basic fibroblast growth factor (bFGF) alone or combined with endostatin at concentrations ranging from 0.1 to 10 μg/ml. The proliferation and migration of CECs were evaluated by using 3, (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay and modified Boyden chamber assay, respectively. For evaluating expression and secretion of matrix metalloproteinase-2 (MMP-2), CEC-conditioned media were subjected to zymography and/or Western blot analysis, and the cells were used for semiquantitative reverse transcription polymerase chain reaction (RT-PCR) analysis. Results: Endostatin did not inhibit bFGF-induced or nonstimulated CEC proliferation (p > 0.05). The bFGF-induced migration was significantly inhibited by endostatin at concentrations of 1 and 10 μg/ml (p < 0.05). The bFGF-upregulated expression of mRNA in CECs and the secretion of MMP-2 protein of CECs were both suppressed by endostatin. Conclusions: Inhibitory effect of endostatin on expression and secretion of MMP-2 and cell migration, but not on proliferation of CECs, could respond to its therapeutic action for choroidal neovascularization-dependent disorders.

Carboxyamido-Triazole Modulates Retinal Pigment Epithelial and Choroidal Endothelial Cell Attachment, Migration, Proliferation, and MMP-2 Secretion of Choroidal Endothelial Cells

Purpose: To determine the effect of the calcium signaling modulating drug carboxyamido-triazole (CAI) on substeps of exudative age-related macular degeneration (AMD) in vitro. Materials and Methods: Zymography and ELISA determined the effect of CAI on MMP-2 production of choroidal endothelial cells (CECs) stimulated by bFGF and VEGF. The effects of CAI on attachment of retinal pigment endothelial (RPE) cells/CECs onto fibronectin, laminin, collagen IV, and migration toward fibronectin were investigated. Proliferation induced by serum and bFGF (10 μ g/ml) with and without CAI (0.1–10 μ M) was measured by cell counting and 3H-uptake. Viability and apoptosis of the exposed cells was assessed by an MTT and an apoptosis assay. Results: CAI inhibited serum- and bFGF-induced proliferation, cell attachment onto fibronectin and collagen IV, but only CEC attachment onto laminin. Inhibition of MMP-2 production was observed (10 μ M CAI). CAI reduced the cellular viability by apoptosis induction. Conclusions: CAI inhibits substeps of exudative macular degeneration and may be of value for the treatment of the disease.