ALTERATIONS OF MULLER (GLIAL) CELLS IN DYSTROPHIC RETINAE OF RCS RATS

We have carried out a light microscopical study of Muller cells in the retinae of rats with inherited retinal dystrophy (Royal College of Surgeons rats). Isolated retinae of both control and Royal College of Surgeons rats were exposed to a Procion Yellow solution which is taken up selectively into Muller cells. The shape of the cells was then studied by confocal microscopy. Enzymatically isolated Muller cells were studied immunocytochemically with antibodies against glial fibrillary acidic protein, cathepsin D, beta-amyloid precursor protein, bcl-2 protooncogene product, and glutamine synthetase. Muller cells from RCS retinae were shorter than those from control retinae, and showed a coarse hypertrophy of their distal (sclerad) processes. In Muller cells isolated from the retinae of Royal College of Surgeon's rats, the expression of glial fibrilliary acidic protein, cathepsin D, beta-amyloid precursor protein and bcl-2 protooncogene product was increased, and the expression of glutamine synthetase was reduced. Obviously, loss of neighbouring neurons leads to major alterations of both the shape and metabolism of Muller cells. The expression of enzymes that serve functional glio-neuronal interactions, such as glutamine synthetase, seems to be down-regulated, whereas proteins involved in cell reconstruction (cathepsin D), cell repair (possibly beta-amyloid precursor protein), and protection against apoptotic cell death (bcl-2 protooncogene product), are up-regulated, together with the 'pathological marker' glial fibrilliary acidic protein.