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To examine the mechanisms by which insulin regulates VEGF expression , human retinal pigment epithelial ( RPE ) cells were exposed to insulin , and VEGF mRNA levels were quantified with RNase protection assays ( RPAs ) .
 retinal pigment epithelial ( RPE ) cells
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Anatomy 
Text: {0} 
Answer:
 retinal pigment epithelial ( RPE ) cells