Albumin and advanced glycation endproducts activated KIM-1 release by proximal tubular epithelial cells through distinct kinetics and mechanism

Abstract

BACKGROUND: Tubulointerstitial injury in diabetic nephropathy (DN) is an important factor in disease progression. Kidney injury molecule-1 (KIM-1) is expressed by proximal tubular epithelial cell (PTEC) and released upon kidney injury. In this study, we examine the kinetics and mechanism of KIM-1 release in PTEC under the activation by different mediators of DN, including human serum albumin (HSA), advanced glycation endproducts (AGE) and glucose. METHODS: The kinetics of KIM-1 and MMP-3 release by PTEC under the activation with HSA, AGE and glucose; was determined by RT-PCR and ELISA. The activation profiles of major signaling pathways in PTEC cultured with HSA, AGE and glucose, were identified by PCR array. Based on these array data, blockade experiments with various signaling inhibitors were designed to examine their regulatory roles on KIM-1 release. RESULTS: We have shown that HSA induce KIM-1 shedding in PTEC by MMP-3. We further addressed the potency and kinetics of AGE- and glucose-mediated KIM-1 shedding in PTEC as compared to that of HSA. Prompt shedding of KIM-1 was observed in PTEC cultured 4 h with HSA and AGE, but not with glucose. Long term culturing PTEC for 3 days with AGE exhibited sustained release of KIM-1 and this is not observed for HSA. In all experiments, glucose did not induce KIM-1 release by PTEC. HSA and AGE activated the ERK and NF-kB pathways in PTEC. The Jak-Stat pathway was activated by AGE but not by HSA. Incubation of PTEC with diphenylene iodonium, but not pyrrolidine dithiocarbamate, P98059 or fludarabine, blocked the short term release of KIM-1 mediated by HSA or AGE. Interestingly, fludarabine but not diphenylene iodonium, pyrrolidine dithiocarbamate or PD98059, diminished the long term KIM-1 release by PTEC cultured with AGE. CONCLUSIONS: Our data suggest that KIM-1 release in PTEC was differentially upregulated by HSA and AGE. The short term KIM-1 release was mediated by the reactive oxygen species while Jak-Stat pathway controls the long-term KIM-1 release mediated by AGE.