Abstract
Purpose:
The pathogenic mutation S163R in the gC1q domain of the complement C1q tumor necrosis factor-related protein-5 (C1QTNF5/CTRP5) causes autosomal dominant late-onset retinal degeneration (L-ORD) in humans. Here, our goal was to test the effects of mutant S163R C1QTNF5 protein overexpression in RPE cells following AAV-mediated delivery to wild-type mouse eyes.
Methods:
We generated scAAV vectors (AAV2 or AAV8Y733F) containing either human wild-type C1QTNF5 or mutant S163R C1QTNF5, driven by an RPE-specific BEST1 promoter, and delivered them subretinally into one eye of adult C57BL/6 mice, while the contralateral eyes remained untreated and served as controls. Retinal function was assessed by full-field electroretinography (ERG) under scotopic (dark-adapted) and photopic conditions at 1 month post-injection. Digital fundus imaging, evaluation of retinal morphology by hematoxylin and eosin staining of paraffin sections, and immunohistochemistry were also performed.
Results:
RPE targeted overexpression of S163R C1QTNF5 mutant leads to widespread photoreceptor degeneration, thinning and loss of RPE cells. In contrast, abnormally high levels of wild-type C1QTNF5 causes dramatically enlarged RPE cells, loss of RPE intercellular integrity and depigmentation, consistent with our previous findings. Treatment with either wild-type or mutant C1QTNF5 leads to significantly reduced a- and b-wave ERG amplitudes when examined at 1 month post-injection, and loss of cells from both the outer and inner retina. Interestingly, treated retinas retain an organized laminar structure, as they become rapidly thinner in only 4 months post-injection.
Conclusions:
Overexpression of the S163R mutant C1QTNF5 in the RPE of normal mice exerts pathological effects similar to some of those found in patients with autosomal dominant late-onset retinal degeneration, such as RPE thinning, RPE cell loss, and retinal degeneration. These results support the hypothesis that L-ORD caused by the S163R mutation may result from a toxic gain of function of the mutant C1QTNF5 protein. Results of wild-type C1QTNF5 overexpression suggest that simple gene augmentation of L-ORD with wild-type C1QTNF5 may not be therapeutic.
Keywords: 412 age-related macular degeneration •
701 retinal pigment epithelium •
648 photoreceptors