NEURON-SPECIFIC ENOLASE - A NEURONAL SURVIVAL FACTOR IN THE RETINAL EXTRACELLULAR-MATRIX

To identify soluble proteins of the retinal interphotoreceptor matrix (IPM), we isolated IPM from the bovine eye by gentle ravage and subjec ted it to SDS-PAGE, In the resultant gel, a 46 kDa band was particular ly prominent and appeared to be a single protein, This protein was ele ctroblotted to nitrocellulose membrane, digested with trypsin, and sel ected peptides were isolated by HPLC and subjected to Edman microseque ncing. The amino acid sequences of the peptides were found to be virtu ally identical to that of human neuron-specific enolase (NSE), A monoc lonal antibody specific for human NSE confirmed the presence of this e nzyme in the bovine IPM by both Western blotting and immunocytochemica l analysis, Immunofluorescence microscopy demonstrated that NSE is mai nly localized to the basal domain of the IPM surrounding photoreceptor cells but is also prominent in the inner segments of the cone photore ceptor neurons, When NSE was added to cultures of human retinoblastoma cells, no effect on morphology was observed, However, a positive effe ct on cell growth and/or survival was readily apparent, It thus seems that not only is NSE a significant component of the retinal extracellu lar matrix, but that it could function as a survival (neuronotrophic) factor for photoreceptor neurons.