Endothelins and its receptors in light-injured retina. International Congress of Eye Research

TORBIDONI V; IRIBARNE M; SUBURO AM

Sydney, Australia

Congreso; International Congress of Eye Research; 2004

Internationational Society of Eye Research

Purpose: Endothelins are powerful vasoconstrictor peptides, that also act as astrocytic growth factors, regulators of gap junctions conductance and blood-retinal barrier permeability. Furthermore they would play a role in cell death. Thus, we studied expression of endothelin-1 and 3 (ET-1 and ET-3) and its receptors in mouse retinas submitted to constant illumination from 3 to 18 days. We also tested whether tezosentan, an antagonist of endothelin receptors,could revert some of the constant light effects. Methods:BALB-c mice were bred under cyclic low level illumination. Experimental animals were kept under 1,500 lux during 6, 9 or 8 days. Tezosentan (1 mg/kg, i.p.) was injected daily. Retinas obtained from perfusion-fixed mice were incubated with antibodies against glial fibrillary acidic protein (GFAP), ET-1, ET-3, their receptors ET-A, ET-B and cleaved caspase-3 (CC-3). Differences in immunoreactivity (ir)were measured in retinal wholemounts using Kontron 400. Results:Almost half of the outer nuclear layer disappeared after 6 days of constant illumination, whereas only a single layer of cell nuclei remained after 18 days. GFAP-ir area increased after 3 days of illumination. In normal retinas, ET-1-ir was only detected in astrocytes, as shown by colocalization with GFAP. ET-3-ir could not be observed. ET-A-ir and ET-B-ir appeared on endothelial cells. ET-A-ir was also present in ganglion cells and outer plexiform layer (OPL). Astrocytes exhibited very low levels of ET-B-ir. CC-3-ir was not detected in normal retinas. In light-injured retinas, astrocytic ET-1-ir area steadily increased during the experimental period. Significant changes were detected at the 18-day stage. Astrocytic ET-B-ir increased early, significant differences being detected after 6 days. No changes in endothelial or ganglion cell immunoreactivities were observed, but ET-A-ir disappeared from OPL. Tesozentan did not change light-induced decrease of the outer nuclear layer (ONL), neither the increase of astrocytic GFAP-ir. After six days of constant illumination, the density of ONL nuclei expressing CC-3 was similar both in treated and untreated retinas. Conclusions:Our observations indicate that ET-1 is the major endothelin in the retina. Distribution of this peptide and its receptors suggest that the endothelinergic system could have a role in astrocytic and photoreceptor functions. Astrocytes seem to be a rich source of ET-1 that could interact with receptors in nearby endothelial and ganglion cells, and also in the same astrocytes. Astrocytes reacted to light injury with an increase in ET-1- and ET-B-ir. However, neither theseresponses, nor the associated GFAP-ir increase, were blocked by tesozentan. Although further experiments are required, present observations suggest that, under these experimental conditions, blockade of ET would not improve photoreceptor survival.