BACKGROUND

Podocyte injury with loss of cells into the urine seems to be an early factor in diabetic nephropathy. Advanced glycation end-products (AGEs) are important mediators of structural and functional renal abnormalities in diabetic nephropathy. We and others have previously described that mice with a deletion in the gene for the cell cycle regulatory p27(Kip1) are protected from some features of diabetic nephropathy.

METHODS

The present study investigates a potential influence of AGE-modified bovine serum albumin (AGE-BSA) on podocyte growth and p27(Kip1) expression in culture. The p27(Kip1) expression was measured by western blots and real-time PCR. Cell cycle analysis, cell hypertrophy, proliferation and various markers of apoptosis and necrosis were assessed. The p27(Kip) expression was inhibited by siRNA or was overexpressed in podocytes with an inducible expression system.

RESULTS

AGE-BSA was actively taken up into the cell as determined by immunohistochemistry, western blots and HPLC. Incubation with AGE-BSA induced in differentiated podocytes, but not in tubular cells, p27(Kip1) mRNA and protein expression. This induction was associated with cell cycle arrest of podocytes, cell hypertrophy (as measured by increases in cell size and protein/cell number ratios) and an increase in necrotic, but not apoptotic cells. Inhibition of p27(Kip1) expression with siRNA halted the AGE-BSA-mediated cell cycle arrest and hypertrophy, but did not interfere with AGE uptake into podocytes. In contrast, overexpression of p27(Kip1) using an inducible expression system stimulated hypertrophy and cell cycle arrest of podocytes.

CONCLUSION

Our data demonstrate that AGE-BSA-induced hypertrophy and damage of cultured podocytes occurs by a mechanism involving p27(Kip1). This effect can contribute to the loss of podocytes in diabetic nephropathy.