Muller cell response to laser-induced increase in intraocular pressure in rats

The goal of this study was to investigate the reaction of the Muller cells to elevated intraocular pressure (TOP). Elevated TOP is one of the risk factors in glaucomatous retinal ganglion cell (RGC) degeneration. Muller cells play an important role in retinal homeostasis. The reaction of Miller cells was examined by evaluating temporal changes in glutamate aspartate transporter (GLAST), glutamine synthase (GS), glial fibrillary acidic protein (GFAP), and the B-cell lymphoma (Bcl-2) using immunoblotting and immunohistochemical techniques. After TOP was elevated for 4-60 days, there was a time-related decrease in RGC ranging from 6% to 44%. There was also a time-related increase in GLAST protein reaching maximum after 3 weeks of elevated TOP. On the other hand, there was very little change in the expression of GS during the first 2 weeks followed by some increase between 21 and 60 days. An increase in Bcl-2 was biphasic with maximum increase after 4 days followed by decline after 15 and 21 days. GFAP, which is usually not expressed in normal Miller cells, was present at all time points. In all cases, the increase was most intense in the vicinity of the ganglion cells where the astrocytes and endfeet of the Muller cells are located. These results indicate that Muller cells react to the insult of elevated TOP by expressing GFAP and Bcl-2, proteins that are expressed in reactive gliosis and other pathological conditions. The increase in GLAST along with minimum change in GS indicates a disturbance in glutamate homeostasis. (C) 2004 Wiley-Liss, Inc.