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Daniel Lipinski, Alun Barnard, Mandeep Singh, Edward Lee, Robert MacLaren; AAV-Mediated Expression of Secreted Human Ciliary Neurotropic Factor (hCNTF) Leads to Long-Term Preservation of Cone Photoreceptors in an Autosomal Recessive Model of Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2711. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Loss of cone photoreceptors secondary to advanced rod degeneration leads to a decline of central vision in retinitis pigmentosa (RP). hCNTF has previously been shown to preserve retinal neurons, but its long-term neuroprotective effect in vivo remains poorly characterised. Herein, we assess the effect of hCNTF in a rhodopsin knockout mouse model of RP with transgenic fluorescence in cone photoreceptors, allowing cone survival to be quantified longitudinally against a background of rod-specific degeneration by fundus imaging.
rAAV2/2 vector expressing secreted hCNTF was injected intravitreally (2µl) at high (1x10^10gp/µl), medium (1x10^9gp/µl) or low (1x10^8gp/µl) titre at postnatal week (W) 4 in Rho-/-TgOPN1-EGFP+/- mice (n=5-8 per group); the contralateral eye received 2µl PBS. Intrinsically fluorescent cones were quantified by in vivo scanning laser ophthalmoscopy (SLO) at W8, 10, 12, 15, 18, 21, 24 and 30. Function was assessed by electroretinography (ERG) at W8, 10, 12 and 15, and visual acuity determined at W30 by optomotor response (OMR) and laser speckle Doppler flowometry. Immunohistochemistry (IHC) and total RNA sequencing was performed at W30.
IHC showed transduction of ganglion cells and Müller glia after intravitreal injection of rAAV2/2.hCNTF vector. In vivo quantification of fluorescent cones demonstrated preservation for 30 weeks in high and medium titre groups (p<0.001, 2-way ANOVA, n=5-6); cones were absent by W18 in sham eyes. Histology confirmed preservation of cones and 1-2 outer nuclear rows. Photopic b-wave was suppressed by hCNTF and absent beyond W15 in all groups. Square-wave, high-contrast grating elicited OMR responses (head tracking) only in hCNTF treated eyes at W30.
AAV-mediated delivery of hCNTF anatomically preserved cone photoreceptors for the duration of the 7 month study. Despite suppression of the photopic ERG, other assessments (OMR, light-evoked cortical blood flow changes) showed maintenance of functional vision in treated eyes, indicating utility of hCNTF for the treatment of end-stage RP presenting with secondary cone loss. hCNTF secreted from inner retinal cells provides global trophic support, potentially allowing protection of central/foveal cones to be achieved without subfoveal gene delivery, thus limiting surgical risk.
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