Endothelins Inhibit Osmotic Swelling of Rat Retinal Glial and Bipolar Cells by Activation of Growth Factor Signaling

Abstract

Water accumulation in retinal glial (Müller) and neuronal cells resulting in cellular swelling contributes to the development of retinal edema and neurodegeneration. Here, we show that endothelin-1 (ET-1) dose-dependently inhibits the hypoosmotic swelling of Müller cells in freshly isolated retinal slices of control and diabetic rats, with a maximal inhibition at 100 nM. Osmotic Müller cell swelling was also inhibited by ET-2. The effect of ET-1 was mediated by activation of ET and ET receptors resulting in transactivation of metabotropic glutamate receptors, purinergic P2Y, and adenosine A receptors. ET-1 (but not ET-2) also inhibited the osmotic swelling of bipolar cells in retinal slices, but failed to inhibit the swelling of freshly isolated bipolar cells. The inhibitory effect of ET-1 on the bipolar cell swelling in retinal slices was abrogated by inhibitors of the FGF receptor kinase (PD173074) and of TGF-β1 superfamily activin receptor-like kinase receptors (SB431542), respectively. Both Müller and bipolar cells displayed immunoreactivities of ET and ET receptor proteins. The data may suggest that neuroprotective effects of ETs in the retina are in part mediated by prevention of the cytotoxic swelling of retinal glial and bipolar cells. ET-1 acts directly on Müller cells, while the inhibitory effect of ET-1 on bipolar cell swelling is indirectly mediated, via stimulation of the release of growth factors like bFGF and TGF-β1 from Müller cells.

Interplay between renal endothelin and purinergic signaling systems

“…Visual system. Similar findings were reported in the visual system, where Vogler et al (35) found that ET-1 inhibits osmotic swelling of rat retinal glial and bipolar cells by activation of growth factors and that this effect was associated with release of ATP and activation of P2Y 1 receptor. Collectively, these findings suggest a potential cooperative interaction between P2 and ET-1 signaling in different physiological functions.…”

Implication of VEGF and aquaporin 4 mediating Müller cell swelling to diabetic retinal edema

“…These cells were collected from transgenic rats carrying a temperature-sensitive SV40 large T-antigen gene [21,22]. The TR-MUL5 cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) at 33°C in a humidified atmosphere of 5% CO 2 /air.…”