Mechanism of Podocyte Injury in Diabetic Nephropathy

Lee, Eun Young; Song, Jae sook; Chung, Choon Hee; Hong, Sae Yong

Abstract

BACKGROUND: Since podocytes are involved in the maintenance of filtration barrier and normal structure in the kidney, podocyte injury can cause the disturbance of glomerular permselectivity and resultant proteinuria, and recent evidence shows that podocyte injury is associated with oxidative stress. However, the pathogenetic mechanism of podocyte injury in the development of diabetic nephropathy is not known. Thus, the present study examined the effect of high glucose level on cytoskeleton, slit diaphragm, podocyte-glomerular basement membrane interaction, and oxidative stress in cultured podocytes.
METHODS
Differentiated cultured podocytes were used in this study. Quiescent cells were incubated with culture media containing 30 mM glucose for 48 hours. The amounts of integrin alpha3, vinculin, zona occludens (ZO)-1 and fibronectin protein expressed by podocytes were measured by Western blot analysis. Dichlorofluorescein diacetate-sensitive intracellular reactive oxygen species (ROS) were observed by confocal microscope and quantified by quantification software. Thiobarbituric acid reactive substances were also measured. Podocytes incubated with culture media containing 5.6 mM glucose were used as control.
RESULTS
Integrin alpha3 expression was significantly decreased in podocytes cultured under high glucose level compared to control. However, vinculin and ZO-1 expressions were significantly increased in podocytes cultured under high glucose level compared to control. Fibronectin protein secreted by podocytes was also increased in podocytes cultured under high glucose level compared to control. ROS and thiobarbituric acid reactive substances in podocytes were also increased in high glucose medium compared to control.
CONCLUSION
High glucose-induced oxidative stress and the changes of integrin a3, ZO-1 and vinculin lead to the alterations of cytoskeleton, intercellular or cell-matrix interactions. This podocyte injury may play a major role in the disturbance of the urinary filtration barrier and the development of proteinuria. These results confirmed the important role of podocyte injury in the development of diabetic nephropathy.