Is there a role for endothelin-1 in light-induced retinal degeneration?

SUBURO AM; TORBIDONI V; IRIBARNE M

Park City, Utah

Congreso; Ninth International Conference on Endothelin; 2005

University of Utah, EEUU

Exposure to excessive light induces degeneration of photoreceptors that is accompanied by reactive gliosis. We have described the presence of endothelin-1 (ET-1) and its receptors (ETA and ETB) in different sites of the mouse retina, including the retinal pigment epithelium, the outer plexiform layer (OPL), astrocytes, the ganglion cell layer and endothelium. After light induced degeneration ET-1 and ETB are overexpressed in astrocytes, and endothelinergic structures disappear from the OPL. Therefore, we asked whether blocking endothelinergic receptors would modify the course of light induced degeneration. BALB-c mice were kept under basal illumination conditions (60 lux:darkness, 12:12 hours), or exposed to constant illumination (1,500 lux) during 4 days. Animals from both groups received Tezosentan (10 mg/kg SC) or saline. Retinas from the four experimental groups were studied by immunohistochemistry and Western blots using antibodies against ET-1, receptors ETA and ETB, glial fibrillary acidic protein (GFAP) or cleaved caspase 3 (CC3). Changes in retinal astrocytes were evaluated in retinal wholemounts immunostained for ET-1, ETB or GFAP. Quantitative image analysis showed a large increase of these markers after 4 days of constant illumination. Tezosentan treatment significantly reduced the GFAP increase, both in wholemounts and Western blots. Dying photoreceptor cells were estimated by the amount of CC3 positive nuclei within the outer nuclear layer (ONL). The number of CC3-labeled nuclei significantly decreased after Tezosentan treatment. Our observations show that Tezosentan decreases the GFAP response of retinal glia to photoreceptor degeneration. Immunohistochemical and Western blot evidence indicates that both the astrocytic and the Müller cell responses are quenched by blockade of endothelinergic receptors. Decrease of the glial response is probably the sum of at least two different mechanisms: (a) the inhibition of ETB receptors in astrocytes, which are upregulated in the degenerating retina and (b) the reduction of photoreceptor death shown by CC3 labeling. These results provide experimental evidence that ET-1 may modulate photoreceptor survival and the gliotic response to photoreceptor degeneration.