Expression of HB-EGF by retinal pigment epithelial cells in vitreoretinal proliferative disease

The heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been implicated in wound-healing processes of various tissues. However, it is not known whether HB-EGF may represent a factor implicated in overstimulated wound-healing processes of the retina during proliferative retinopathies. Therefore, we investigated whether human retinal pigment epithelial (RPE) cells, which are crucially involved in proliferative retinopathies, express and respond to HB-EGF. RPE cells express mRNAs for various members of the EGF-related growth factor family, among them for HB-EGF, as well as for the EGF receptors ErbB1, -2, -3, and -4. The gene expression of HB-EGF is stimulated in the presence of transforming and basic fibroblast growth factors and by oxidative stress and is suppressed during chemical hypoxia. Exogenous HB-EGF stimulates proliferation and migration of RPE cells and the gene and protein expression of the vascular endothelial growth factor (VEGF). HB-EGF activates at least three signal transduction pathways in RPE cells including the extracellular signal-regulated kinases (involved in the proliferation-stimulating action of HB-EGF), p38 (mediates the effects on chemotaxis and secretion of VEGF), and the phosphatidylinositol-3 kinase (necessary for the stimulation of chemotaxis). In epiretinal membranes of patients with proliferative retinopathies, HB-EGF immunoreactivity was partially colocalized with the RPE cell marker, cytokeratins; this observation suggests that RPE cell-derived HB-EGF may represent one factor that drives the uncontrolled wound-healing process of the retina. The stimulating effect on the secretion of VEGF may suggest that HB-EGF is also implicated in the pathological angiogenesis of the retina

Increased immunostaining of bFGF is a hallmark of ischemia-reperfusion in the rat retina.

<p>The images display representative slices of a control retina (<i>upper panel</i>) and a retina obtained 3 d after reperfusion (<i>lower panel</i>). Specimens were labeled with antibodies against bFGF (<i>red</i>) and vimentin (<i>green</i>). Co-labeling yielded a <i>yellow</i> merge signal, and cell nuclei were labeled with Hoechst 33258 (<i>blue</i>, scale bar, 20 µm). Note increasing vimentin and bFGF labeling in the outer nuclear layer (ONL) after ischemia as compared to the control tissue. <i>Unfilled arrowhead</i>, ganglion cell soma; <i>arrow</i>, Müller cell soma; <i>filled arrowhead</i>, Müller cell process. GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; OPL, outer plexiform layer; PRS, photoreceptor segments.</p

Localization of glial aquaporin-4 and Kir4.1 in the light-injured murine retina

Excessive light causes damage to photoreceptor and pigment epithelial cells, and a local edema in the outer retina. Since Müller glial cells normally mediate the osmohomeostasis in the inner retina (mainly via channel-mediated transport of potassium and water), we determined whether retinal light injury causes an alteration in the retinal localization of glial water (aquaporin-4) and potassium (Kir4.1) channels, and in the potassium conductance of Müller cells. Mice were treated with bright white light (intensity, 15,000 lux) for two hours. Light treatment results in Müller cell gliosis as indicated by the enhanced staining of the glial fibrillary acidic protein and an increase in the cell membrane area reflecting cellular hypertrophy. In light-injured retinas, the immunostaining of the photoreceptor water channel aquaporin-1 disappeared along with the degeneration of the outer retina, and the outer nuclear layer contained large spherical bodies representing photoreceptor nuclei which were fused together. The immunostainings of the aquaporin-4 and Kir4.1 proteins were increased in the outer retina after light treatment. Since the amplitude of the potassium currents of Müller cells remained largely unaltered, the increase in the Kir4.1 immunostaining is supposed to be caused by a redistribution of the channel protein. The data indicate that Müller glial cells respond to excessive light with an alteration in the localization of Kir4.1 and aquaporin-4 proteins; this alteration is thought to be a response to the edema in the outer retina and may support the resolution of edema

Müller cells express bFGF in retinal tissue.

<p>Panel <b>A</b> demonstrates glial localization of bFGF (<i>green</i> immunostaining) in a surgically excised fibrovascular membrane from a subject with non-hypoxic pathologic myopia and a patient with PDR (scale bar, 25 µm). <b>B</b>: Freshly dissociated human Müller cells express bFGF (<i>red</i>) and GFAP (<i>green;</i> scale bar, 50 µm). Co-staining of GFAP in panel <b>A</b> yielded a <i>yellow</i> merge signal. Parallel tissue samples or cells stained with nonimmune IgG did not fluoresce (not shown).</p