Could we delay photoreceptor loss in retinal degeneration disease by gene therapy?

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In this study, we investigated if virus-mediated gene transfer could delay photoreceptor loss in retinal degeneration mouse retina. The vector we used is recombinant adeno-associated virus (rAAV), which is less immunogenic and is supposed to mediate stable gene transfection. We purified rAAV with target gene under CMV promoter, and injected into the eye of normal or retinal degeneration model mouse. The retinal degenerntion mouse is cGMP phosphodiesterase (PDE) gamma subunit knockout mouse, which shows photoreceptor degeneration within 21 days after birth. We studied rAAV injected eyes by light and electron microscopy and analyzed rAAV mediated gene transfer efficiency into the retina.1. reporter gene (GFP) expression in normal mouse retinaGFP is exprssed in ganglion cell, inner nuclear layer cell, and photoreceptors by intravitreal injection, and in RPE cells and photoreceptors by subretinal injection. GFP expression is detected around 7 days after injection and continued more than 1 … More momth.2. cGMP PDE gamma subunit gene expression in retinal degeneration mouse retinaWe injected 0.5 μl of 10^N infectious unit /μl rAAV with cGMP PDEgamma subunit cDNA into the subretinal space of knockout mouse around 5 days after birth. One month after injection, 3-5 layets of photoreceptors were observed to be present in rAAV injected area, compared with only 1 photoreceptor layer remained in control retina. Electron microscopy revealed that surviving photoreceptors possess moderate numbers of outer segments, which is little observed in control reina. Neither inflammation nor damage to the retinal structure was detected in rAAV injected retina.This study showed that the loss of photoreceptors in petinal degeneration mouse retina could be delayed by adeno-associated virus mediated gene transfer. This means the feasibility of gene therapy as the treatment for retinitis pigmentosa. More sudies, such as functional study of surviving photoreceptors, modification of rAAV to set more surviving cells and monitering the gene expression noninvasively, are necessary and we are now making efforts for them. Less