Correlation of regenerable opsin with rod ERG signal in Rpe65-/- mice during development and aging.
OBJECTIVE
RPE65 has been shown to be essential for the production of 11-cis retinal by the retinal pigment epithelium. Mutations in RPE65 are known to be associated with severe forms of early-onset retinal dystrophy. This project was designed to determine the amount of regenerable opsin in Rpe65-/- mice during development and aging, and to examine the function of this rhodopsin by electroretinography (ERG).


METHODS
Young and aged Rpe65-/- and wild-type (WT) mice were dark adapted. Endogenous rhodopsin and regenerable opsin were measured using absorption-difference spectrophotometry. Photoreceptor function was assessed with scotopic single-flash ERGs and photoreceptors were counted in histologic sections. Opsin's primary structure was analyzed by mass-spectrometric mapping.


RESULTS
Unlike WT mice, amounts of regenerable opsin in Rpe65-/- mice decreased significantly with age, which correlated with a decrease in the number of photoreceptors and a decline in ERG amplitudes. Opsin structure, however, did not change. No endogenous levels of rhodopsin were measurable in the Rpe65-/- mice (detection limit: 0.225 pmol). 11-cis Retinal injections resulted in the regeneration of similar amounts of rhodopsin and improved rod function in a comparable way, irrespective of age.


CONCLUSIONS
In the aged Rpe65-/- mouse, opsin levels decrease because of the loss of photoreceptors. The remaining opsin is structurally intact, and the components of the phototransduction cascade and the retinal circuitry remain functional, despite the absence of normal photoreceptor activity.
Rohrer
Baerbel
B
Department of Ophthalmology Medical University of South Carolina, 167 Ashley Avenue, Charleston, SC 29425, USA. rohrer@musc.edu
Goletz
Patrice
P
Znoiko
Sergei
S
Ablonczy
Zsolt
Z
Ma
Jian-xing
JX
Redmond
T Michael
TM
Crouch
Rosalie K
RK
D000375:Aging / Q000502:physiology*; D000818:Animals; D002352:Carrier Proteins; D003623:Dark Adaptation; D004596:Electroretinography; D005136:Eye Proteins / Q000502:physiology*; D007267:Injections; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015591:Microspectrophotometry; D011506:Proteins / Q000502:physiology*; D012038:Regeneration; D017948:Retinal Rod Photoreceptor Cells / Q000254:growth & development* / Q000502:physiology*; D012172:Retinaldehyde / Q000494:pharmacology; D017299:Rod Opsins / Q000096:biosynthesis*; D014785:Vision, Ocular / Q000502:physiology; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D002352:Carrier Proteins; D005136:Eye Proteins; D011506:Proteins; D012172:Retinaldehyde; D017299:Rod Opsins; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase