Age and topographic variation of insulin-like growth factor-binding protein 2 in the human rpe.
OBJECTIVE
Previous studies have shown that insulin-like growth factor-binding protein (IGFBP)-2 is markedly upregulated in senescent RPE cells in vitro, and might therefore be a marker of senescent cells in vivo. This study was conducted to determine whether IGFBP-2 expression in human RPE cells from the macula and periphery varies with age in vivo.


METHODS
Paraformaldehyde (4%)-fixed and optimal cutting temperature (OCT) compound-embedded human eyes from 17 patients were cryosectioned and subjected to high-sensitivity digoxigenin (DIG)-labeled cRNA in situ hybridization to determine the expression of IGFBP-2. Complementary immunohistochemistry experiments using a polyclonal anti-IGFBP-2 antibody were performed to confirm IGFBP-2 protein expression. Specimens were examined by light microscopy, and images were captured with a digital camera. The total numbers of RPE cells and IGFBP-2 mRNA expression-positive RPE cells were counted for each section, and the ratio of labeled RPE cells to total RPE cells counted was calculated for both macular and peripheral regions of each donor.


RESULTS
IGFBP-2 mRNA expression was detected in the ganglion cell layer, inner and outer nuclear layers, and inner segments of photoreceptor cells in all 17 eyes. In 16 of 17 eyes, IGFBP-2 mRNA expression was detected in the RPE. In 11, the ratio of labeled cells to total RPE cells counted per section in the macula was 1.2 times greater than the ratio in the periphery (P = 0.008). The ratio of labeled RPE cells in the macula decreased with age (P = 0.0064). Immunohistochemistry studies for IGFBP-2 confirmed the expression pattern found by in situ hybridization.


CONCLUSIONS
There is a topographical and age-related change in IGFBP-2 expression in RPE cells from human donor eyes. This distribution is likely not to represent senescent RPE cells in vivo.
Miyamura
N
N
Departments of Ophthalmology and. Molecular and Cellular Biology, University of California, Davis 95616-8794, USA.
Mishima
K
K
Honda
S
S
Aotaki-Keen
A E
AE
Morse
L S
LS
Handa
J T
JT
Hjelmeland
L M
LM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014019:Tissue Donors; D016707:Tissue Fixation
D018971:Insulin-Like Growth Factor Binding Protein 2; D012333:RNA, Messenger