Retinoid processing in cone and Müller cell lines

Abstract

To determine whether cones and Müller cells in the rod dominated retina, cooperate to regenerate the 11-cis retinal chromophore via the retinoid cycle, two cell lines from the rod dominated retinas of Murine were used for this study, 661W a mouse cell line derived from cones and rMC-1, a rat Müller cell line. Retinoid cycle enzymes were analyzed by RT-PCR and their catalytic activity were detected by incubation with retinoids and analyzed by HPLC. We found that, 661W cells are capable of reducing all-trans retinal to all-trans retinol due to the presence of multiple dehydrogenases and generate minor amounts of retinyl-ester. The rMC-1 cells take up all-trans retinol and oxidizes it to all-trans retinal or esterify it to retinyl-ester, but are incapable of isomerizing all-trans retinoids to 11-cis retinoids. This could be a reflection of lack of necessary activities in Müller cells in vivo which suggests that Müller cells do not contribute to retinoid cycling by regenerating 11-cis retinoids. Alternatively, this could be due to the potential that rMC-1, as a transformed cell line, has stopped expressing the proteins needed for the regeneration of 11-cis retinoids.

RDH13L, an Enzyme Responsible for the Aldehyde-Alcohol Redox Coupling Reaction (AL-OL Coupling Reaction) to Supply 11-cis Retinal in the Carp Cone Retinoid Cycle

“…8A, mouse RDH14 showed the coupling activity. Expression level of mouse RDH14 mRNA is significant in a culture cell line (661W) established from mouse cones, and the level is higher in the all-cone Nrl knock-out retina compared with the wild-type retina (28), which suggests its expression in wild-type mouse cones. In our study, carp RDH14 did not show the coupling activity appreciably.…”

Protein tyrosine-O-sulfation in the retina

“…Amplified samples were separated on 1% agarose gels in the presence of ethidium bromide and alongside the 1 Kb plus DNA ladder (Invitrogen). Amplification of the house-keeping gene hypoxanthine-guanine phosphoribosyltransferase (HPRT) was used as a control as described before (Kanan et al, 2008). …”

Retinoids and Retinal Diseases

“…However, such an activity may not be required because cones can directly take up 11- cis -ROL and oxidize it to 11- cis -RAL. Retinas from Nrl −/− mice, which have only S-cone photoreceptors, express RDH13 and RDH14 at high levels compared with rod-dominant, wild-type retinas, indicating that these candidate enzymes may be responsible for the cone RDH activity (Kanan et al 2008). Carp RDH13L, which clusters with the mammalian RDH14 group (Figure 6), has been identified as a major 11- cis -RDH in cone photoreceptors.…”