A combination of CNTF and BDNF rescues rd photoreceptors but changes rod differentiation in the presence of RPE in retinal explants

PURPOSE. To gather information regarding the combination of ciliary neurotr ophic factor (CNTF) and brain-derived neurotrophic factor (BDNF), compared with the individual factors when used as a treatment to retard photorecepto r cell loss in rd mouse retina explants and to investigate the observation that the retinal pigment epithelium (RPE) influences rod differentiation by this treatment. METHODs. Postnatal day (PN)2 or PN7 control and rd mouse retinas were grown with attached retinal pigment epithelium (RPE). The explants were kept in culture up to PN28. During this culture period CNTF, BDNF, CNTF+BDNF, or ve hicle were continuously administered to the culture medium. The nontrophic factors cyclosporin A and N-CBZ-aspartic acid-glutamic acid-valine-aspartic acid-fluoromethyl ketone (z-DEVD-fmk) were also used. The number of photor eceptor nuclei remaining in the outer nuclear layer (ONL) was analyzed in h ematoxylin and eosin-stained sections. Rod- and cone-specific antibodies we re used to determine identity and state of differentiation of the photorece ptors. RESULTS. Compared with vehicle treatment, BDNF or CNTF resulted in 1.4 or 2 -fold more surviving cell roars in the ONL, respectively. However, when CNT F and BDNF were applied together, surviving ONL cell counts in the rd expla nts were approximately 3 times those in vehicle-treated explants. In the pr esence of CNTF or CNTF+BDNF, opsin and arrestin expression in rods was decr eased compared with rods without attached RPE. Cyclosporin A and z-DEVD-fmk did not show rescue of rd photoreceptor cells. CONCLUSIONS. CNTF or BDNF treatment of rd retinal explants delays photorece ptor cell loss to some extent. However, when these agents are combined, pho toreceptor rescue is much more effective. The quenching of opsin and arrest in expression caused by treatment suggests that simultaneous with rod rescu e, rod differentiation is depressed. Regarding retinal degeneration, the re sults from the selective inhibitors of apoptosis rank the CNTF+BDNF combina tion treatment as the most consistent and effective experimental pharmacolo gic intervention currently available.