Apolipoprotein localization in isolated drusen and retinal apolipoprotein gene expression.

PURPOSE. To evaluate apolipoprotein ( Apo) gene expression in native human retinal pigment epithelium ( RPE) and neurosensory retina and to detect apolipoproteins within age- related, extramacular drusen. METHOD. Drusen were isolated manually from 10 eyes of 10 donors ( age range, 58 - 93 years) with grossly normal maculas that were preserved in 4% paraformaldehyde within 6 hours of death. In cryosections of druse- enriched pellets ( 6 - 57 drusen per eye), the Apos A- I, A- II, B, C- I, C- II, C- III, E, and J were detected by indirect immunofluorescence. Two graders assessed the prevalence and pattern of immunoreactivity. mRNA transcripts were detected by reverse- transcription polymerase chain reaction ( RT- PCR), with human hepatoma HepG2 cells as the positive control. RESULTS. Extramacular drusen were classified in two groups on gross appearance: transparent with a reflective shell and cloudy. The proportion of the latter increased significantly with age. All Apos examined were detectable, in descending order of prevalence: ApoE ( 99.5%), J ( 99.5%), C- I ( 93.1%), B ( 80.4%), A- I ( 61.0%), A- II ( 59.2%), C- II ( 57.7%), and C- III ( 16.6%). Immunoreactivity was either diffusely distributed throughout the drusen ( 56.7%), confined to the druse rim ( 16.0%), or both ( 21.2%). Six percent displayed evidence of organized substructure reminiscent of active remodeling. The proportion of diffusely labeled drusen decreased significantly with age for ApoE ( P = 0.034) and ApoE/ C- I combined ( P = 0.027). RT- PCR products for Apos C- I, C- II, E, and J were found in retina and RPE; for ApoA- II in the retina only. The ApoC- III message was undetectable. CONCLUSIONS. To an emerging model of an RPE- secreted large lipoprotein particle implied by previous work, this study adds ApoC- I and ApoC- II, major modulators of lipoprotein lipase activity, and confirms previously demonstrated Apos A- I, B- 100, and E. It is possible that a neutral lipid- rich druse shell containing Apos will be visible in the living fundus.