Long-Term Protection of Cones by CNTF Secreting Implants in Transgenic Rats Carrying the Rhodopsin Mutation S334ter

Abstract

Purpose: : We studied cone photoreceptor degeneration in a rat model of retinitis pigmentosa, transgenic rats carrying the rhodopsin mutation S334ter. The present work investigates long-term preservation of cone photoreceptors and their outer segments by CNTF delivered via Encapsulated Cell Technology (ECT) microimplants.

Methods: : The CNTF secreting ECT microimplant is 2.0 x 0.45 mm and contains genetically engineered human retinal cells. It can be placed in the rat eye. At post-natal day 20 (PD 20), the right eye of an animal was implanted with a CNTF secreting microdevice and the left eye with a microdevice that contained parental cells that had no CNTF secreting capability. Some eyes were implanted with empty devices as controls. Eyes were harvested 70 days and 140 days after implantation. Cone outer segments were identified by PNA (peanut agglutinin lectin) staining and opsin staining in whole-mount retinas and examined by fluorescence confocal microscopy.

Results: : Loss of cone outer segments was evident as early as postnatal day 12 (PD12), characterized by complete lack of PNA staining in small areas which formed round or irregularly shaped non-staining patches. The loss of PNA staining was progressive. In the patches, however, cone cells were still present, as demonstrated by the positive staining of cone arrestin. In eyes implanted with CNTF secreting microdevices, PNA staining was evenly distributed 70 or 140 days after implantation without patches that lacked PNA staining. The densities of PNA positive cells were significantly higher in CNTF device implanted retinas than in parental cell or empty devices implanted ones.

Conclusions: : Sustained delivery of CNTF using CNTF secreting implants protects cones and helps them to maintain their outer segments.

Keywords: neuroprotection • retinal degenerations: cell biology • age-related macular degeneration