Age and topographic variation of insulin-like growth factor-binding protein 2 in the human RPE

PURPOSE. Previous studies have shown that insulin-like growth factor-bindin g 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 wa s 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) c ompound-embedded human eyes from 17 patients were cryosectioned and subject ed 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 con firm IGFBP-2 protein expression. Specimens were examined by light microscop y, 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, i nner 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 sect ion 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 stud ies for IGFBP-2 confirmed the expres sion pattern found by in situ hybridization. CONCLUSIONS. There is a topographical and age-related change in IGFBP-2 exp ression in RPE cells from human donor eyes. This distribution is likely not to represent senescent RPE cells in vivo.