Retinoid processing in dark– and light–adapted abcr–/– mice

Abstract

Abstract: : Purpose: In a recent study of Rpe65–/– mice and wildtype controls, Qtaishat et al. employed an in vivo radiolabeling technique to determine the kinetics of RPE processing of visual cycle retinoids (1). The present study was undertaken to examine the fate of similarly radiolabeled RPE retinoids in the abcr knockout mouse, a strain that lacks the ABCR transporter and exhibits an impaired movement of all–trans retinol photoproduct from the disk lumen to the rod cytosol (2). Methods: abcr–/– mice and wildtype controls that had been dark–adapted overnight received an intraperitoneal injection of 3 µCi of all–trans (³H)retinol and were then either maintained in darkness for defined period (1.5, 4.5, 24 or 48 hr) (1) or exposed to bleaching light (both eyes) for 2 min and then dark–adapted for 1.5 or 4.5 hr. Following sacrifice of the animal, (³H)retinoids extracted from the RPE, retina, serum and liver were quantified by HPLC and flow scintillation analysis. Results: In dark–adapted abcr–/– as well as control mice, serum all–trans (³H)retinol was elevated at 1.5 and 4.5 hr post–injection and subsequently decreased to near–baseline levels. RPE (³H)retinyl ester in abcr–/–’s and controls exhibited peak levels at 4.5 and 24 hr, respectively. (³H)retinaldehydes in the retina of dark–maintained mice increased with post–injection period up to 48 hr. As observed previously (1), liver (³H)retinoids accounted for >90% of total (³H)retinoids recovered from all tissues. In both abcr–/–’s and controls, rhodopsin bleaching produced a transient reduction in the molar level of 11–cis retinal in the retina and a transient increase in that of RPE retinyl ester; apparent peak changes in both were at 1.5 hr. Conclusions: The available data indicate that in dark–maintained abcr–/–’s, the distribution of (³H)retinoids resembles that previously observed in wildtype mice (1), and suggest that the investigated illumination conditions are workable for determining bleach–induced changes in (³H)retinoid distributions in abcr–/– eye tissues. (1) Qtaishat, Redmond and Pepperberg (2003) IOVS 44:1435–1446. (2) Weng, Mata, Azarian, Tzekov, Birch and Travis (1999) Cell 98:13–23.

Keywords: retinoids/retinoid binding proteins • transgenics/knock–outs