[High glucose stimulates synthesis of fibronectin in human mesangial cells via serum and glucocorticoid induced protein kinase-1 signaling pathway]

Abstract

Objective: To investigate the role of serum and glucocorticoid induced kinase-1 (SGK(1)) pathways in fibronectin (FN) synthesis in human mesangial cell (HMC) under high glucose condition and the mechanism by which SGK(1) contributes to glomerulosclerosis in diabetic nephropathy (DN).

Methods: HMCs were cultured and transfected with (P)IRES2-EGFP-(S422D) SGK(1) mutant (SD), plasmid containing SGK(1) dominant activation mutant, or blank plasmid. Non-transfected HMCs were used as control group. Then the HMCs were divided into 6 groups: transfected with SD + high glucose (SD-HG, 25 mmol/L D-glucose), transfected with FP + high glues (FP + HG), non-transfected + high glucose (NT-HG), transfeted with SD + normal glucose (SD-NG, 5.5 mmol/L D-glucose), transfected with FP + normal glues (FP + NG), and non-transfected + normal glucose (NT-NG). Eight hours after the glucose stimulation, RT-PCR was used to examine the SGK(1) mRNA expression and fibronectin (FN). Western blotting was used to detect the fibronectin (FN) protein expression.

Results: The SGK(1) mRNA expression of the SD + HG group was 0.709, significantly higher than those of the FP + HG and NT + HP groups (0.497 and 0.491, both P < 0.01). The SGK(1) protein expression of the SD + HG group was 1,178,497, significantly higher than those of the FP + HG and NT + HP groups (193,875 and 195,597 respectively, both P < 0.01). The FN mRNA expression of the SD + HG group was 0.749, significantly higher than those of the FP + HG and NT + HP groups (0.463 and 0.475 respectively, both P < 0.01). The FN protein expression of the SD + HG group was 659,550, significantly higher than those of the FP + HG and NT + HG groups (342,354 and 340,428 respectively, both P < 0.01). There were not significant differences in the expressions of FN mRNA and protein among different NG groups.

Conclusion: SGK(1) may be involved in the signal transduction leading to the increase of fibronectin production in DN and therefore may play an active part in glomerulosclerosis in DN.