Effects of overexpressed SGK1 on the secretion of fibronectin in human podocytes

AIM: To investigate the effects of high concentration of glucose on the expressions of serum and glucocorticoid induced protein kinase 1 (SGK1) and fibronectin in human podocytes and detect the production of fibronectin in human podocytes transfected with active and mutant forms of SGK1.METHODS: The expressions of SGK1 and fibronectin in human podocytes exposed in high glucose for 24 h were detected by using Western blotting.Human podocytes were transfected with three kinds of plasmid: pIRES2-EGFP-SGK1SD (SGK1-active plasmid),pIRES2-EGFP-SGK1KN (SGK1-mutant plasmid) and pIRES2-EGFP (empty vector plasmide).The synthesis levels of fibronectin were detected by immunofluorescence.RESULTS: The expression of SGK1 in normal human podocytes was observed and the expression level was up-regulated in podocytes exposed to high glucose for 24 h (50±4 vs 35±3),parallelly with the high expression of fibronectin (19±4 vs 12±2).The secretion of fibronectin was increased obviously in SGK1-active plasmid (SGK1SD) transfected podocytes compared with the vector transfected podocytes.Whereas,the fibronectin level was decreased significantly but not completely abolished in SGK1-mutant plasmid (SGK1KN) transfected podocytes,compared with SGK1SD transfected podocytes.CONCLUSION: SGK1 may be involved in the synthesis of fibronectin in human podocytes induced by high glucose and play a critical role in the activation of human podocytes during early stage of diabetic nephropathy.