Ciliary Neurotrophic Factor (CNTF) Delivered by Adeno-associated Viruses (AAV) Leads to Photoreceptor Loss and Impairs Retinal Function in Wild-type Rats

Abstract

Abstract: : Purpose:Our recent studies have demonstrated that intravitreal administration of AAV.CNTF led to morphological but not functional protection of photoreceptors in rhodopsin transgenic rats (Mol. Ther. 4:461-472, 2001). The present study determines the effect of long-term delivery of CNTF on retinal morphology and function in wild-type rats. Methods:AAV.CNTF was made to express a secretable form of CNTF in tandem with a marker GFP. In Sprague-Dawley rats, the vector was administered intravitreally in one eye and AAV.GFP or sham injection into the contralateral eye within the first week of life (Group1, n=6) or at 7 weeks of age (Group 2, n=5). ERGs were performed at 4 weeks post-injection in Group 1 and at 10 weeks in Group 2. Retinal histology and rhodopsin immunostaining were examined at 23 weeks post-injection in Group 1 (n=4) and at 10 weeks in Group 2 (n=5). Results:Light microscopy showed decreased thickness of the outer nuclear layer (ONL) in AAV.CNTF injected eyes in 3/4 animals (1-5 rows) in Group 1 and 2/5 animals (3-6 rows) in Group 2, while AAV.GFP or sham injected eyes had 9-11 rows in the ONL. In the other 4 animals, AAV.CNTF-injected eyes showed swelling and disorganization of outer segments. Photoreceptor abnormalities occurred primarily in the temporal hemisphere of the retina (corresponding to the injection site as indicated by GFP expression). Immunohistochemistry showed weaker rhodopsin staining in the temporal retinas of AAV.CNTF eyes relative to the same regions of control eyes, but no obvious differences in cellular specificity of staining between the nasal retinas. ERGs showed major asymmetries in rod and cone amplitudes with the AAV.CNTF injected eyes reduced in 4/6 animals in Group 1 and 3/5 animals in Group 2, relative to control eyes. Both photoreceptor and post-receptoral components of the rod ERGs were affected. Conclusions:Long-term delivery of CNTF with AAV in the normal rat retina may have deleterious effects on retinal structure and function.

Keywords: gene transfer/gene therapy • growth factors/growth factor receptors • photoreceptors