ADVANCED GLYCATED ALBUMIN IMPAIRS PROTEIN-DEGRADATION IN THE KIDNEY PROXIMAL TUBULES CELL-LINE LLC-PK1

Advanced glycation end-products (AGEs) are assumed to play a major rol e in the genesis of diabetic nephropathy and other diabetic complicati ons. We studied the potential effect of AGEs on protein turnover and l ysosomal proteinase activities in LLC-PK1 cells, a pig kidney proximal tubules cell Line. Advanced glycated bovine serum albumin (AGE-BSA) w as used as a model of AGEs and its action was compared to that of nong lycated BSA. AGE-BSA but not BSA (50 mu mol/l) induced a significant i ncrease in cell volume (BSA: 4870.6 +/- 74.8 fl, AGE-BSA: 5718.0 +/- 2 0.7 fl, p<0.01). Protein degradation rate was decreased by 13.8% after 48 bra. incubation with AGE-BSA (p<0.01) while protein synthesis incr eased by 19,1%, (p<0.01). After incubation with AGE-BSA but not BSA ac tivities of lysosomal cathepsins (B, L+B and Il) decreased in a time- and dose-dependent fashion. This decline was neither caused by a shift in lysosomal pH outside the optimal range for cathepsins, nor by a di rect inhibitory effect of AGEs modified proteins or peptides but most probably by inhibition of cathepsin B expression as measured by RT-PCR . It is supposed that impaired protease activities participated in dec reased protein breakdown and cell enlargement. For the first time our data provide the evidence that AGEs induce hypertrophy of LLC-PK1 cell s due to decreased protein breakdown resulting from reduced lysosomal proteinase activities with a concomitant stimulation of protein synthe sis.