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P. Radreau, J. D. Rhodes, P. R. Kroon, J. Sanderson; Quercetin Activates the HIF-1 Signalling Pathway in Human Lens Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2084.
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A previous microarray study from our laboratory demonstrated that in lens epithelial cells treated with quercetin (10 µM), 65% of genes that showed significant increased expression (p≤0.01) were regulated by hypoxia inducible factor-1 (HIF-1). We have, therefore, investigated the effect of quercetin on the HIF-1 signalling pathway in human lens epithelial cells.
FHL-124 cells were grown to 90% confluency and exposed to quercetin (10 or 30 µM). Protein and mRNA levels were analyzed by Western blot and qRT-PCR respectively. Immunocytochemistry experiments were carried out for visualisation of HIF-1. VEGF was measured in cell medium using ELISA.
Quercetin (30 µM) induced an increase in HIF-1 protein levels after 4 and 24 hr, with a greater than 50-fold increase compared to untreated cells at 4 hr. At 10 µM quercetin, increases were seen after 24 hr. Visualisation of HIF-1 within the cell showed that quercetin caused its translocation to the nucleus and this persisted for at least 24 hr. To confirm the activation of HIF-1 signalling pathway by quercetin, we looked at the expression of four HIF-1 regulated genes: EPO, VEGF, PGK1 and BNIP3. mRNA levels of all four genes were significantly up-regulated after 24 and/or 48 hr quercetin treatment (10 µM). In addition, analysis of medium showed that quercetin induced an increase in secretion of VEGF from FHL-124 cells. For both quercetin concentrations (10 and 30 µM) and at all time points studied (24, 48 and 72 hr), there was a significant and dose-dependent increase of VEGF secretion in quercetin-treated compared to untreated cell media. The quercetin-induced accumulation and nuclear translocation of HIF-1 was reversed by addition of excess iron (100 µM).
Quercetin activates the HIF-1 signalling pathway in human lens epithelial cells, leading to increased expression of the downstream genes. This may be mediated by chelation of intracellular iron by quercetin which would inhibit the Fe2+-dependent prolyl hydroxylase which in turn would stabilize HIF-1. Activation of the HIF-1 pathway may play a role in cytoprotection by quercetin.
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