Albumin stimulates interleukin-8 expression in proximal tubular epithelial cells in vitro and in vivo

Abstract

Renal tubulointerstitial injury is characterized by inflammatory cell infiltrate; however, the stimuli for leukocyte recruitment are not fully understood. IL-8 is a potent chemokine produced by proximal tubular epithelial cells (PTECs). Whether nephrotic proteins stimulate tubular IL-8 expression remains unknown. Acute exposure of human PTECs to albumin induced IL-8 gene and protein expression time-and dose-dependently. Apical albumin predominantly stimulated basolateral IL-8 secretion. Electrophoretic mobility shift assay demonstrated nuclear translocation of NF-κB, and the p65/p50 subunits were activated. NF-κB activation and IL-8 secretion were attenuated by the NF-κB inhibitors pyrrolidine dithiocarbamate and cell-permeable peptide. Albumin upregulated intracellular reactive oxygen species (ROS) generation, while exogenous H 2 O 2 stimulated NF-κB translocation and IL-8 secretion. Albumin-induced ROS generation, NF-κB activation, and IL-8 secretion were endocytosis-and PKC-dependent as these downstream events were abrogated by the PI3K inhibitors LY294002 and wortmannin, and the PKC inhibitors GF109203X and staurosporin, respectively. In vivo, IL-8 mRNA expression was localized by in situ hybridization to the proximal tubules in nephrotic kidney tissues. The intensity of IL-8 immunostaining was higher in nephrotic than non-nephrotic subjects. In conclusion, albumin is a strong stimulus for tubular IL-8 expression, which occurs via NF-κB-dependent pathways through PKC activation and ROS generation.

Activation of the Signal Transducer and Activator of Transcription Signaling Pathway in Renal Proximal Tubular Cells by Albumin

“…ROS generation was found to be upregulated compared with the control within 15 min after either albumin or apoTf had been added to the medium ( Figure 5). Dose-dependent upregulation of intracellular ROS generation was observed, as previously reported (37). The result was not changed by addition of DMSO, which was used as the solvent for AG490, rotenone, and DPI (data not shown).…”

“…Recently, it was reported that albumin upregulated ROS generation in proximal tubular cells (37,38). Therefore, to directly assess whether albumin could induce oxidative stress in mProx24 cells, we used the CM-H 2 DCFDA method and fluorescence-activated cell sorter (FACS) analysis.…”

Luminal Alkalinization Attenuates Proteinuria-Induced Oxidative Damage in Proximal Tubular Cells

“…4 -6 ROS are abundantly generated in the proximal tubular cells through the reabsorption of urinary albumin. 4,5 Urinary albumin is reabsorbed by endocytosis that is mediated by the proximal tubular scavenger receptors megalin, cubilin, and CD36. 4 -9 Subsequently, these receptor-albumin complexes activate protein kinase C (PKC) signaling pathways, which lead to NA-D(P)H oxidase-mediated (NOX-mediated) ROS generation.…”

Mitochondria Are the Major Targets in Albumin-Induced Apoptosis in Proximal Tubule Cells

“…In this study, we investigated the apoptotic response and the responsible pathways that resulted from albumin exposure in human proximal tubule cells. In previous studies, incubation of human proximal tubule cells with albumin resulted in the increased production of reactive oxygen species (ROS) and activation of NF-B in relation to free radicals (7,20). Oxidative stress and ROS-mediated tubule cell apoptosis have also been implicated in ischemic kidney injury, diabetic nephropathy, and oxalateassociated nephrotoxicity (21)(22)(23).…”