Glucose-induced serum- and glucocorticoid-regulated kinase activation in oncofetal fibronectin expression

Preferential expression of oncofetal extra domain-B fibronectin (EDB+ FN), a proposed angiogenic marker, has been shown in proliferative diabetic retinopathy. High levels of glucose also increase EDB+ FN expression in endothelial cells (ECs) via transforming growth factor-β1 (TGF-β1) and endothelin-1 (ET-1). The present study was aimed at elucidating the role of serum- and glucocorticoid-regulated kinase (SGK-1) in glucose-induced EDB+ FN expression. Using human macro- and microvascular ECs, we show that high levels of glucose, TGF-β1, and ET-1 increase the EDB+ FN expression via SGK-1 alteration at the mRNA, protein, and activity levels. Inhibition of TGF-β1 and ET-1 prevented glucose-induced SGK-1 activation and the EDB+ FN expression. Furthermore, using siRNA-mediated SGK-1 gene silencing, we show that glucose-induced EDB+ FN expression can be completely prevented. These findings provide first evidence of glucose-induced SGK-1 activation in altered EDB+ FN expression and provide novel avenues for therapeutic modalities.