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J. Chen, F.A. Concepcion, J. Chen; The Rhodopsin–arrestin Complex: A Pathway to Retinal Degeneration in Vertebrates . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3624.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In Drosophila, specific genetic mutations that lead to excessive levels of rhodopsin–arrestin (R–Arr) complex were found to cause photoreceptor cell death in a transducin–independent manner (Alloway et al., 2000; Kiselev et al., 2000). The purpose of this study was to investigate whether this novel cell death pathway initiated by R–Arr complex is conserved in vertebrates. Methods: K296E is a naturally occurring rhodopsin mutation in humans that causes retinitis pigmentosa. Previous studies have shown that K296E is constitutively active in stimulating transducin in vitro. When expressed in transgenic mouse rods, however, K296E does not appear to activate transducin, but is persistently bound to Arr (Li et al., 1995). To test whether R–Arr complex is the stimulus for photoreceptor cell death in this disease model, K296E transgenic mice were bred into Arr–/–, transducin–/–, or Arr–transducin double knockout backgrounds. Retinal sections were prepared from these mice at different ages, and retinal morphology was assessed. Results: Retinal morphology did not improve when K296E was expressed in the transducin–/– background, supporting the previous observation that constitutive signaling was not the cause of retinal degeneration in these mice. A similar rate of photoreceptor cell death was observed when K296E was expressed in the Arr–/– background, although R–Arr complex formation was precluded in this genetic background. This suggests that, in the absence of Arr, K296E signals constitutively through transducin and causes photoreceptor cell death. To prevent transducin signaling as well as R–Arr complex formation, K296E was expressed in the Arr–transducin double knockout background. Remarkably, in the double knockout background, retinal morphology of mice expressing K296E improved significantly when compared to transgene negative littermate controls. Conclusions: Our results provide strong in vivo evidence that the photoreceptor cell death pathway initiated by R–Arr complex is conserved from invertebrates to vertebrates. Blocking the formation of R–Arr complex may lend significantly toward the development of therapeutic treatments for retinitis pigmentosa.
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