Intravitreal CNTF Injection Leads to Reversible Photoreceptor Deconstruction in the Normal Canine Retina

Abstract

Purpose: : To evaluate the short-term effects of a single intravitreal CNTF injection on the structure, function, and gene expression pattern in normal canine retinas.

Methods: : Normal, adult dogs were injected intravitreally with 12 µg of human recombinant CNTF; contralateral eyes served as controls and were injected with a similar volume of PBS. Retinal function (flash ERG), morphology (LM, EM), gene (qRT-PCR) and protein expression (immunohistochemistry and western blotting) were evaluated at 1, 2, and 5 weeks post injection.

Results: : One week after CNTF injection both scotopic and photopic ERG responses were almost completely extinguished. The ERG amplitudes partially recovered by 2 weeks, and completely restored by 5 weeks post injection. The transient functional loss at 1 week was associated with a drastic but reversible shortening and disorganization of photoreceptor inner and outer segments. Expression of photoreceptor-specific genes, e.g. opsins and cyclic nucleotide-gated channel subunits, was significantly reduced at 1 week, but subsequently recovered. While most of these mRNA reductions were between 68 - 84%, S-opsin expression was more severely affected with a 99.99% decrease. There was a marked increase in phosphor-STAT3 at 1 week in the outer nuclear, inner nuclear, and ganglion cell layers. This increase was more moderate for phosphor-STAT1. The amounts of both phosphor-STAT1 and phosphor-STAT3 gradually declined and returned to the control levels by 5 weeks post injection.

Conclusions: : Intravitreal injection of CNTF protein leads to reversible biochemical and structural changes, as well as decreases in photo-responsiveness of rods and cones in the normal canine retina. This process is likely mediated by activation of the Jak/STATs pathways.

Keywords: cytokines/chemokines • drug toxicity/drug effects • photoreceptors