Protein overload induces renal proximal tubular epithelial cell apoptosis by down-regulating WNT/β-catenin signalling

Abstract

BACKGROUND: Numerous studies have demonstrated a tubulotoxic role of excess proteins on renal proximal tubular epithelial cell (PTECs) via various signalling pathways. However, the role of Wnt/β-catenin signalling in PTECs during protein overload remains unknown. METHODS: Wnt/β-catenin expressions were measured in control and human serum albumin (HSA)-treated human kidney 2 (HK-2) cells by real-time PCR and Western blotting. Genetic knockdown of β-catenin was achieved using siRNA transfection. Apoptotic phenotypes were evaluated by real-time PCR and TUNEL assay. RESULTS: Upon the 4-day-HSA stimulation, gene expression of β-catenin, frizzle-dreceptor 1 and Wnt-1 in PTECs declined by 26%±2 (p<0.05, t-test), 65%±2 (p<0.05) and 57%±6 (p<0.05) versus control, respectively. Western blots showed that protein expression of cytosolic and nuclear active β-catenin decreased by 57%±8 (p<0.05) and 66%±8 (p<0.05) after 4-day HAS treatment, respectively. Simultaneously, Bax/Bcl-2 gene expression ratio increased by 31%±8 (p<0.05). Transfection of β-catenin siRNA into HK-2 cells up-regulated Bax/Bcl-2 gene expression ratio by 23%±7 (p<0.05) relative to mock transfection. HAS treatment and β-catenin siRNA transfection increased the number of TUNEL-positive cells by 70%±10 (p<0.05) and 73%±8 (p<0.05), respectively. CONCLUSIONS: Protein-overload promotes tubular cell apoptosis via down-regulation of Wnt/β-catenin signalling in PTECs.