Albumin overload induces apoptosis in LLC-PK1 cells

The degree of albuminuria is a well-known adverse prognostic indicator in h uman glomerular diseases. However, the mechanisms by which albuminuria by i tself contributes to tubulointerstitial injury and progression of renal dis ease remain unclear. We tested the hypothesis that apoptosis may represent one of the mechanisms by which tubule epithelial cells are damaged after al bumin overload in vitro. Cultured LLC-PK1 proximal tubule cells were incuba ted with varying concentrations of BSA. This resulted in a dose- and durati on-dependent induction of apoptosis, as evidenced by internucleosomal DNA c leavage (DNA laddering and nick-end labeling), externalization of plasma me mbrane phosphatidylserine (annexin labeling), and characteristic morphologi cal changes (cell shrinkage and nuclear condensation). Albumin overload als o resulted in a dose- dependent upregulation of Fas and Fas-associated prot ein with death domain (FADD), and activation of caspase 8. Incubation with the caspase 8 inhibitor IETD ameliorated the albumin-induced apoptosis. Col lectively, our results indicate that albumin overload induces apoptosis of cultured LLC-PK1 cells, mediated at least in part by the Fas-FADD-caspase 8 pathway.