OS062. Oxidative stress mediates podocyte injury in preeclampsia.

INTRODUCTION: Emerging evidence has shown that other than glomerular endotheliosis, podocyte injury plays a key role in kidney dysfunction in preeclampsia (PE). Podocyte shedding has been demonstrated in patients with PE, and proteinuria is signature of podocyte injury. We previously found altered distribution and reduced expression of podocyte protein nephrin and podoplanin in shed podocytes in PE. However, the mechanism of podocyte shedding and altered podocyte functional protein expression in shed podocytes in PE is not known.

OBJECTIVES: To investigate if oxidative stress could induce podocyte injury in PE.

METHODS: Kidney podocytes were isolated from urinary specimen from women with PE. Urinary podocytes were cultured with RPMI 1640 supplemented with 10% FBS and ITS liquid media. Podocyte expression and distribution of nephrin and superoxide dismutase-1 (CuZn-SOD) were determined by immunofluorescent staining. Images were captured by Apotome Observer and were reconstructed with Axiovision software. CuZn-SOD expression was used as an indicator of podocyte oxidative stress. Immortalized human podocytes (AB 8/13 cells) were used as control. Effects of oxidative stress on podocyte nephrin and CuZn-SOD expressions were induced by treating AB 8/13 cells with or without exposure to the hypoxic mimetic agent cobalt chloride. Protein expressions and distributions for nephrin and CuZn-SOD were determined by immunofluorescent staining and by Western blot.

RESULTS: In differentiated podocytes (AB 8/13 cells), nephrin and CuZn-SOD were co-localized and expressed in the peripheral region of the foot process area. In contrast, nephrin and CuZn-SOD expressions were markedly reduced or lost in the foot process area in shed podocytes from PE patients. When AB 8/13 cells were treated with cobalt chloride, the patterns of nephrin and CuZn-SOD expressions and distributions were similar to that seen in shed podocytes from PE. Nephrin and CuZn-SOD expression and distribution were time-dependently decreased in AB 8/13 cells treated with cobalt chloride. We further found that after prolonged culture, shed podocytes differentiated into mature podocytes in vitro evidenced by the expression of nephrin and CuZn-SOD at the foot process area of the cells.

CONCLUSION: Nephrin is a specific podocyte slit diaphragm protein. The findings of the co-localization of nephrin and CuZn-SOD in differentiated podocytes and a lack of nephrin and CuZn-SOD expressions in shed podocytes from PE suggest that sufficient antioxidant activity is required for maintaining the functional integrity of glomerular podocytes. The differentiation process was associated with functional protein rejuvenation including nephrin, podoplanin, and CuZn-SOD in shed podocytes from PE. The phenomenon of oxidative stress-induced reduced and altered nephrin and CuZn-SOD expression and distribution further suggests that increased oxidative stress contributes to podocyte injury in PE.