Expression of Endothelin and its Receptors in Light-Injured Retina

SUBURO AM; TORBIDONI V; IRIBARNE M; PRASANNA G

Ft. Lauderdale, Florida

Congreso; Association for Research in Vision and Ophthalmology 2004; 2004

ARVO

Purpose: Endothelins are powerful vasoconstrictor peptides,that also act as astrocytic growth factors, regulators of gapjunctions conductance and blood retinal barrier permeability.Since they could be involved in the glial response to retinalinjury, we have studied the expression of endothelins and theirreceptors in mouse retinas submitted to constant light inducedphotoreceptor degeneration.Methods:BALB c mice were bred under cyclic low level illumination.Experimental animals were kept under 1,500 lux for periods of3, 6, 9 and 18 days. Retinas obtained from perfusion fixed mice were incubated with antibodies against glial fibrillaryacidic protein (GFAP), endothelins 1 and 3 (ET 1 and ET 3)or their receptors ET A, ET B. Areas of astrocyteimmunoreactivity (ir) were measured in retinal wholemounts using Kontron 400. For RT PCR, RNA was extracted from non fixedretinas.Results: Almost half of the outer nuclear layer disappeared after6 days of constant illumination, whereas only a single layerof cell nuclei remained after 18 days. Gliosis, as evidencedby the area of GFAP immunoreactivity, increased after 3 days of illumination. In normal retinas, ET 1 ir wasonly detected in astrocytes, as shown by co localizationwith GFAP. ET 3 ir could not be observed. ET A irand ET B ir appeared on endothelial cells. ET A irwas also present in ganglion cells and outer plexiform layer (OPL). Astrocytes exhibited very low levels of ET B ir.In light injured retinas, astrocytic ET 1 irarea steadily increased during the experimental period. Significantchanges, however, were only present at the 18 day stage. The ratio ET 1/actin mRNA increased in a similar fashion.By contrast, area of astrocytic ET B ir showed anearly increase, significant differences being detected by the6 day stage. No changes in endothelial and ganglion cell immunoreactivitiescould be detected, but ET A ir disappeared fromOPL.Conclusions:Gliosis, affecting both Müller cells and astrocytes,was an early event in our experimental model. The endothelinergic system seemed to be specifically associated to astrocytes, sinceneither the ligands nor the receptors could be detected in Müller cells. The early increase in astrocytic ET B immunoreactivitysuggests that this receptor might probably be nvolved in the gliotic response.