Abstract
Purpose::
Hyperglycemia has been established as a major risk factor for diabetic retinopathy (DR).The progression of DR is mainly related to a local imbalance of pro- versus anti-angiogenic factors in the retina. We have hypothesized that angiogenic factors are released from retinal pigment epithelial (RPE) cells cultured under high glucose (HG) conditions.
Methods::
Cultured human retinal endothelial (RE) cells were exposed to culture medium of ARPE-19 cells grown in a HG medium to determine whether RPE cells released factors that promote tube formation. For transcriptome analysis, the expression profiles of ARPE-19 cells cultured under HG conditions were determined by GeneChip (Affymetrix). We investigated whether ANGPTL4 was a major angiogenic factor released from ARPE-19 cells under HG conditions by experiments of recombinant protein, conditioned medium (CM) from ARPE-19 cells and RNA interference (RNAi), using cultured human RE cells as the test system.
Results::
The CM from ARPE-19 cells cultured under HG conditions promoted tube formation of cultured human RE cells. GeneChip analysis showed that ANGPTL4 was one of the most up-regulated genes under HG conditions. In addition, recombinant ANGPTL4 promoted all of the elements of angiogenesis; cell invasion, migration, proliferation, and tube formation in human RE cells at the comparable effect to VEGF in vitro. The results of experiments using CM from ARPE-19 cells and RNAi combined demonstrated that ANGPTL4 was a major angiogenic factor released from ARPE-19 cells under HG conditions.
Conclusions::
Our results demonstrated that the induction of the angiogenic activity by HG in ARPE-19 cells was mainly mediated by an up-regulation of ANGPTL4 expression. Although in vivo validation is necessary in human diabetes patients, our data suggest that RPE cells might contribute to the pathogenesis of DR via up-regulated expression of ANGPTL4. These findings may have many novel implications in relation to clinical aspects of DR.
Keywords: diabetic retinopathy • retinal pigment epithelium • cell-cell communication