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S. Panjala, J. J. Steinle; Regulation of IGF-1 Receptor Signaling by Beta-Adrenergic Receptors and Insulin in Human Retinal Endothelial Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):34.
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. To determine whether beta-adrenergic receptor activities can regulate IGF-1 receptor signaling in human retinal endothelial cells cultured in high glucose conditions.
. Human retinal endothelial cells were grown in high glucose medium and treated with xamoterol or the combination of insulin and xamoterol. The treated and non-treated cell lysates were used to examine the role of xamoterol and the combination of insulin and xamoterol in the regulation of total and phosphorylated IGF-1 receptor, IRS-1, IRS-2, Akt and cleavage of caspase-3. To verify which regions of the retina were undergoing apoptosis, TUNEL labeling was completed.
. IGF-1 receptor phosphorylation is significantly decreased in retinal cells treated with xamoterol and in the cells treated with the combination of insulin and xamoterol. Tyrosine phosphorylation of IRS-1 is significantly increased in the cells treated with xamoterol, but significantly decreased in cells treated with combination of insulin and xamoterol, suggesting that insulin and xamoterol may have antagonistic effects on IRS-1 phosphorylation. IRS-2 phosphorylation was not changed following xamoterol treatment alone, but was increased following insulin and xamoterol co-treatment. Akt phosphorylation is increased at 30-minute time point in cells treated with both insulin and xamoterol, whereas xamoterol alone produced no change in phosphorylation of Akt. While no change is observed in the cleavage of caspase-3 in the cells treated with combination of insulin and xamoterol, caspase-3 cleavage increased significantly at the 15- and 30-minute time point in the cells treated with xamoterol alone. One explanation for the lack of protection from apoptosis via insulin may be the acute time course investigated for insulin.
. Our results suggest that IGF-1 receptor signaling is reduced in retinal endothelial cells following treatment with xamoterol and the combination of xamoterol and insulin. The reduction in phosphorylation of IGF-1 receptor signaling could explain the increase in caspase-3 levels following xamoterol. While no change was observed in the cleavage of caspase-3 levels in the retinal cells treated with combination of insulin and xamoterol, the acute time course of insulin used may have prevented the protective effects of insulin from being observed. The data suggest that beta-adrenergic receptors regulate IGF-1 receptor signaling in retinal endothelial cells cultured in high glucose. This regulation may be countered by insulin signaling in specific cases. Overall, these results further support the idea that beta-adrenergic receptors can modulate key signaling pathways in the retina.
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