Retinal pigment epithelium defects accelerate photoreceptor degeneration in cell type-specific knockout mouse models of choroideremia.
OBJECTIVE
Choroideremia (CHM) is a progressive X-linked degeneration of three ocular layers (photoreceptors, retinal pigment epithelium, and choroid), with a complex and still largely unclear pathogenesis. To investigate the pathophysiology of CHM, the authors engineered mice with a cell type-specific Chm/Rep1 knockout (KO).


METHODS
A mouse line carrying a conditional allele Chm(Flox) was crossed with the transgenic line IRBP-Cre to achieve Chm KO, specifically in the photoreceptor layer, and Tyr-Cre to produce Chm KO, specifically in the retinal pigment epithelial and other pigmented cells. Chm(Flox), Tyr-Cre+ and Chm(Flox), IRBP-Cre+ mice were mated to produce mice with Chm KO in both layers. All mouse lines were studied by histology, electron microscopy, electroretinography (ERG), scanning laser ophthalmoscopy (SLO), and biochemical


METHODS



RESULTS
In Chm(Flox), IRBP-Cre+ mice the authors observed the progressive degeneration of photoreceptors in the presence of normal retinal pigment epithelium (RPE). Chm(Flox), Tyr-Cre+ mice exhibited coat color dilution and pigment abnormalities of the RPE in the presence of an intact outer nuclear layer. In 6- to 8-month-old Chm(Flox), Tyr-Cre+, IRBP-Cre+ mice, the degeneration of photoreceptors was accelerated compared with Chm(Flox), IRBP-Cre+ mice but became leveled with age, such that it was comparable at 12 to 14 months. Detailed ERG and SLO analysis supported the histopathologic findings.


CONCLUSIONS
Defects in photoreceptors and RPE can arise because of intrinsic defects caused cell autonomously by the Chm KO. However, when both photoreceptors and RPE are diseased, the dynamics of the degenerative process are altered. Photoreceptor functional deficit and cell death manifest much earlier, suggesting that the diseased RPE accelerates photoreceptor degeneration.
Tolmachova
Tanya
T
Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK.
Wavre-Shapton
Silene T
ST
Barnard
Alun R
AR
MacLaren
Robert E
RE
Futter
Clare E
CE
Seabra
Miguel C
MC
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D000818:Animals; D015794:Choroideremia / Q000235:genetics / Q000503:physiopathology*; D004195:Disease Models, Animal; D004596:Electroretinography; D005136:Eye Proteins / Q000235:genetics; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D009887:Ophthalmoscopy; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology*; D012162:Retinal Degeneration / Q000503:physiopathology*; D055213:Retinal Pigment Epithelium / Q000473:pathology*; D012177:Retinol-Binding Proteins / Q000235:genetics; D000099214:Retinol-Binding Proteins, Interstitial
D048868:Adaptor Proteins, Signal Transducing; D005136:Eye Proteins; D012177:Retinol-Binding Proteins; D000099214:Retinol-Binding Proteins, Interstitial; C081787:CHM protein, human
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