Apolipoprotein localization in isolated drusen and retinal apolipoprotein gene expression.
OBJECTIVE
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.


METHODS
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.
Li
Chuan-Ming
CM
Department of Ophthalmology, University of Alabama School of Medicine, Birmingham, Alabama 35294-0009, USA.
Clark
Mark E
ME
Chimento
Melissa F
MF
Curcio
Christine A
CA
D000368:Aged; D000369:Aged, 80 and over; D001053:Apolipoproteins / Q000235:genetics* / Q000378:metabolism*; D018929:Cell Culture Techniques; D017931:DNA Primers / Q000737:chemistry; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism*; D015593:Retinal Drusen / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D001053:Apolipoproteins; D017931:DNA Primers; D012333:RNA, Messenger