Purpose: To characterize molecular and cellular changes induced by sustained expression of ciliary neurotrophic factor (CNTF) in the rds mutant mouse retina.
Methods: Recombinant adeno-associated virus (rAAV) expressing CNTF was injected subretinally, for transduction of peripherin/rds(+/)(-) transgenic mice that carry the P216L mutation found in human retinitis pigmentosa. Characterization of retinal neurons and glia was performed by immunocytochemistry with cell-type-specific markers. Activation of signaling molecules was examined by Western blot and immunostaining. Alterations of gene transcription profiles were studied by microarray analyses.
Results: CNTF viral transduction maintained rhodopsin expression in surviving rod photoreceptors, but greatly reduced both S- and M-opsin normally expressed in cones. In addition, CNTF treatment resulted in increased numbers and dispersion of Müller glia and Chx10-positive bipolar cells within the inner nuclear layer. Persistent CNTF signaling also caused enhanced phosphorylation of STAT1, STAT3, and p42/44 ERK, as well as their levels of expression. Moreover, altered transcription profiles were detected for a large number of genes. Among these, Crx and Nrl involved in photoreceptor differentiation and several genes involved in phototransduction were suppressed.
Conclusions: Despite the rescue from cell death, continuous exposure to CNTF changed photoreceptor cell profiles, especially resulting in the loss of cone immunoreactivity. In addition, the Müller glia and bipolar cells became disorganized, and the number of cells expressing Müller and bipolar cell markers increased. Constitutive CNTF production resulted in sustained activation of cytokine signal transduction and altered the expression of a large number of genes. Therefore, stringent regulation of CNTF may be necessary for its therapeutic application in preventing retinal degeneration.