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PE Spoerri, S Caballero, SH Wilson, LC Shaw, MB Grant; Expression of IGFBP-3 by Human Retinal Endothelial Cell Cultures: IGFBP-3 Involvement in Growth Inhibition and Apoptosis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1339.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Growth hormone (GH)-insulin-like growth factor (IGF)-somatostatin (SST) axis has been implicated in the pathogenesis of proliferative diabetic retinopathy (PDR). GH, IGF and SST modulate each other’s action in vivo and have receptors on human retinal endothelial cells (HRECs). IGF-I is unique in that it is tightly regulated by six IGF binding proteins (IGFBPs). IGFBP-3 is the major carrier of IGF-I in circulation and has direct cell cycle inhibitory and apoptotic effects on various cell types. In this study, we examined the effect of IGFBP-3 on HREC proliferation and whether SST receptor (SSTR) agonists, known to inhibit HREC proliferation, mediate their effect by modulating local IGFBP-3 expression. Methods:To first determine whether IGFBP-3 is expressed endogenously by HRECs, we examined the expression and cellular localization of IGFBP-3 using anti-human IGFBP-3 (rabbit polyclonal antiserum) and fluorescein conjugated goat anti-rabbit IgG. HRECs were then exposed to varying concentrations of human recombinant IGFBP-3 and growth inhibition evaluated by MTT (thiazolyl blue) conversion. Apoptosis was examined using Alexa Fluor annexin V. Conditioned medium (CM) from SSTR agonist (L-363377, L-779976, L-796778)-treated HRECs was analyzed by ELISA for changes in IGFBP-3 concentration. Results:Immunostaining showed diffuse cellular staining corresponding to cell surface and nascent cytoplasmic IGFBP-3. HRECs exposed to 1, 10, 100, 500 and 1000 ng/ml showed a dose dependent inhibition of proliferation. HRECs treated with recombinant IGFBP-3 and stained with Alexa Fluor 488 annexin V showed numerous apoptotic green fluorescent cells. Exposure to SSTR agonists stimulated IGFBP-3 expression (p<0.05). Conclusion:HRECs express IGFBP-3. Exogenous administration of IGFBP-3 induced growth inhibition and apoptosis. SSTR agonists as therapeutic agents for treatment of proliferative retinopathies, mediate their growth inhibitory effect, in part, by increasing IGFBP-3 expression.
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