Retinal Alterations in Mice With Endothelium-Restricted Overexpression of Endothelin-1

Abstract

Purpose:: In the retina, endothelin-1 (ET-1) is mainly present in neurons and glial cells; the highest ET-1-immunoreactivity being found in perivascular astrocytes. Because these glial cells possess endothelinergic receptors, they are thought to be the main target for ET-1 in neural tissues. Astrocytes, essential components of the blood-retinal barrier, are potentially receptive to ET-1 of neural and endothelium origin. To understand astrocyte response to endothelial-derived ET-1 we have studied the retina of mice with endothelium-restricted overexpression of ET-1.

Methods:: Transgenic C57BL6/J mice were constructed by inserting the human preproET-1 coding sequence cDNA under the endothelium-specific Tie-2 promoter/enhancer. Eyes from 12-month-old TG (n = 8) and WT (n = 9) mice were fixed and processed. Antibodies against ET-1 and glial fibrillary acidic protein (GFAP) were used to detect retinal astrocytes. Choroidal vascular profiles were also studied.

Results:: Wholemounts showed the same radial vascular pattern in WT and TG retinas and both genotypes exhibited typical GFAP and ET-1 immunostaining of astrocytes. However, TG retinas exhibited a larger amount of astrocyte cell bodies and processes than WT retinas. Image quantification demonstrated that areas occupied by GFAP and ET-1 immunoreactive cell bodies and processes were significantly higher in TG than in WT retinas. TG retinas had more astrocytes with more numerous and thicker processes. Besides, ET-1 immunoreactivity per astrocyte seemed higher in TG than in WT retinas. No GFAP immunoreacitivity was detected in Müller glial cells, suggesting a relatively low level of retinal damage. On the other hand, TG choroidal wholemounts suggested an alteration of vascular profiles.

Conclusions:: Endothelium-restricted overexpression of ET-1 leads to structural remodeling and endothelial dysfunction of resistance vessels. In the retina, no major structural changes were observed in the inner vascular plexus. However, retinal astrocytes showed substantial increases in the number of perivascular processes and their ET-1 content. Augmented endothelial ET-1 release could promote astrocyte proliferation and hypertrophy and, at the same time, astrocyte ET-B receptors would clear increased extracellular ET-1 levels. Astrocytic function probably explains differences in the response of retinal and peripheral vessels to endothelial increase in ET-1 release.

Keywords: astrocyte • blood supply • retina