Retinal Degeneration in a Rodent Model of Smith-Lemli-Opitz Syndrome

Abstract

Objective: To assess the electrophysiologic, histologic, and biochemical features of an animal model of Smith-Lemli-Opitz syndrome (SLOS).Methods: Sprague-Dawley rats were treated with AY9944, a selective inhibitor of 3␤-hydroxysterol-⌬ 7reductase (the affected enzyme in SLOS). Dark-and lightadapted electroretinograms were obtained from treated and control animals. From each animal, 1 retina was analyzed by microscopy, and the contralateral retina plus serum samples were analyzed for sterol composition. The main outcome measures were rod and cone electroretinographic amplitudes and implicit times, outer nuclear layer (ONL) thickness, rod outer segment length, pyknotic ONL nucleus counts, and the 7-dehydrocholesterol/ cholesterol mole ratio in the retina and serum.Results: By 10 weeks' postnatal age, rod and cone electroretinographic wave amplitudes in AY9944-treated animals were significantly reduced and implicit times were significantly increased relative to controls. Maximal rod photoresponse and gain values were reduced approximately 2-fold in treated animals relative to controls. The ONL thickness and average rod outer segment length were reduced by approximately 18% and 33%, respectively, and ONL pyknotic nucleus counts were approximately 4.5-fold greater in treated animals relative to controls. The retinal pigment epithelium of treated animals contained massive amounts of membranous/lipid inclusions not routinely observed in controls. The 7-dehydrocholesterol/cholesterol mole ratios in treated retinas and serum samples were approximately 5:1 and 9:1, respectively, whereas the ratios in control tissues were essentially zero.Conclusions: This rodent model exhibits the key biochemical hallmarks associated with SLOS and displays electrophysiologic deficits comparable to or greater than those observed in the human disease.Clinical Relevance: These results predict retinal degeneration in patients with SLOS, particularly those with the more severe (type II) form of the disease, and may be more broadly relevant to other inborn errors of cholesterol biosynthesis. This animal model may also be of use in evaluating therapeutic treatments for SLOS and in understanding the slow phototransduction kinetics observed in patients with SLOS.

Partial Rescue of Retinal Function and Sterol Steady-State in a Rat Model of Smith-Lemli-Opitz Syndrome

“…At 10 wk of age, dark-adapted (rod) and lightadapted (cone) ERG were recorded from anesthetized animals, as described in detail elsewhere (11).…”

“…Brains and livers were harvested, quickly rinsed in ice-chilled PBS, blotted dry, and frozen in liquid nitrogen. One retina was harvested and frozen; the contralateral eye was enucleated and fixed with buffered mixed aldehydes for histologic and morphometric analyses (11). All tissues were stored in darkness at -85ºC until ready for further processing.…”

“…The SLOS rat model (11)(12)(13) is induced by treatment of pregnant rats and their progeny with AY9944, a selective inhibitor of 3␤-hydroxysterol-⌬ 7 -reductase (14,15), the enzyme defective in SLOS. The clinical relevance of the SLOS rat model is highlighted by the fact that pediatric SLOS patients exhibit markedly abnormal darkadapted (rod) ERG (16), similar to those observed in the SLOS rat model.…”

“…Herein, we demonstrate that dietary Chol supplementation can dramatically alter the steady-state sterol composition of the retina, restoring near-normal Chol levels and reducing 7-DHC levels, with concomitant improvement of retina electrophysiological function and reduced photoreceptor pyknosis. Pups from AY9944-treated dams were injected subcutaneously with AY9944 (30 mg/kg, in PBS) three times per week on alternating days, starting at postnatal d 1 (P1) and continuing throughout life, as previously described (11,13). These animals also were injected concomitantly with vitamins A, D, and E (Vital-A, DϩE; Schering-Plough, Kenilworth, NJ) as described previously (11,13), which dramatically improves postnatal viability (13).…”

“…Pups from AY9944-treated dams were injected subcutaneously with AY9944 (30 mg/kg, in PBS) three times per week on alternating days, starting at postnatal d 1 (P1) and continuing throughout life, as previously described (11,13). These animals also were injected concomitantly with vitamins A, D, and E (Vital-A, DϩE; Schering-Plough, Kenilworth, NJ) as described previously (11,13), which dramatically improves postnatal viability (13). Control pups received no vitamin injections, as this did not affect survival, retinal histology or function, or sterol levels in normal rats (unpublished results).…”