[High glucose downregulates the expression of podocalyxin protein in glomerular podocytes of mice]

To examine the expression of podocalyxin protein in glomerular podocytes by long-term high glucose exposure in vitro and in vivo.

Immunohistochemical staining and computer image analysis were applied to detect the expression of podocalyxin protein in glomeruli from db/db mice and Wt mice. The effects of high glucose on the expression of podocalyxin protein were analyzed by Western blotting. The activation of MAPKS signaling pathway (ERK, p38 and JNK) by high glucose was also examined.

The expressions of podocalyxin protein in db/db mice were obviously less than that in Wt mice [(0.18+/-0.07) vs (0.25+/-0.05),P<0.05] assessed by immunostaining and semiquantitative analysis. Basal levels of podocalyxin protein were observed in cultured mouse podocytes. The level of podocalyxin protein declined at each time point by high glucose incubation, reached the lowest level on the 6th day (5.5% of control group, P<0.01), but no significant changes were observed in normal glucose and mannitol glucose incubation groups. High glucose medium induced phosphorylation of ERK1/2 as early as 30 minutes, reached the peak at hour 6; maintained the activation from hour 12 to 24, and declined to the basal level at hour 48. However, activation of ERK1/2 was not detected in normal glucose and mannitol glucose groups. Blockade of activation of ERK1/2 with PD98059, a specific ERK1/2 activation inhibitor, attenuated the high glucose-induced expression of podocalyxin protein on the 6th day.

High ambient glucose decreases the protein level of podocalyxin by podocyte in vitro and in vivo, and the decrease in podocalyxin protein is ERK1/2jdependent in cultured podocytes.