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Danielle M. Robertson, Yu-Chieh Wu, Benjamin R. Buckner, Meifang Zhu; Increased Extracellular IGFBP3 In Human Diabetic Tears And Corneal Epithelial Cells Following Hyperglycemic Challenge In Vitro. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1857.
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The insulin-like growth factor binding protein-3 (IGFBP3) is a glycosylated secretory protein that functions to sequester insulin-like growth factor (IGF-1) and prevent IGF-1 activation of the IGF-1 receptor (IGF-1R). The purpose of this study was to characterize IGFBP3 and IGF-1 expression in normal and diabetic human tears and in telomerase-immortalized human corneal epithelial cells (hTCEpi) cultured under hyperglycemic challenge and to correlate these changes with total and phosphorylated levels of IGF-1R.
Tear samples were collected non-invasively from the inferior tear meniscus of moderately controlled diabetics and non-diabetic controls; a Cochet-Bonnet Aesthesiometer was used to determine corneal sensitivity. mRNA and protein levels for IGFBP3, IGF-1 and IGF-1R in hTCEpi cells cultured in normal (5 mM) and elevated (25 mM) glucose were assessed by real time PCR and western blot. IGFBP3 and IGF-1 in tear samples and conditioned media were assessed by ELISA. For all assays, mannitol was used as an osmotic control. Phosphorylated IGF-1R levels were assessed by western blot and ELISA following treatment with IGF-1 and IGFBP3.
In tear samples, IGFBP3 was increased 2.8 fold in diabetic tears compared to non-diabetic controls (p=0.006); IGF-1 levels were slightly decreased in diabetic tears, although not significant. No difference in corneal sensitivity was detected between groups. Consistent with the in vivo findings, IGFBP3 in conditioned media was increased 2.2 fold (p<0.001) in response to high glucose in vitro; however, IGFBP3 mRNA levels were reduced (p<0.001). mRNA and protein expression for IGF-1R were unchanged. When tested in vitro, the increase in the IGFBP3:IGF-1 ratio detected in diabetic tears compared to normal controls blocked phosphorylation of the IGF-1R by IGF-1 (p<0.001).
Taken together, these findings demonstrate that IGFBP3 is increased in response to hyperglycemia and may function to attenuate IGF-1R signaling in the diabetic cornea. A long-term increase in IGFBP3 may contribute to epithelial compromise and the pathogenesis of ocular surface complications reported in diabetes.
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