Transferrin Receptor Levels are increased by Interleukin 1β in a Human Kidney Proximal Tubular Cell line

Abstract

BackgroundIron is required for several essential cellular processes such as DNA synthesis and energy metabolism, but when present in excess can cause cellular injury. Although kidney iron levels and urinary excretion of iron and iron transport proteins such as transferrin are increased in patients with kidney disease, it remains unclear how iron is handled by the kidneys during inflammation. We hypothesize that inflammation increases renal tubular iron uptake mechanisms, which in turn may promote cellular injury.Methods and ResultsTo understand how iron is handled by proximal tubule cells during inflammation, we turned to HK‐2 cells, a human proximal tubular cell line, and investigated the levels and distribution of transferrin receptor and divalent metal transporter 1 (DMT‐1) in response to interleukin 1β, a pro‐inflammatory cytokine. Transferrin receptor allows the uptake of iron after binding and internalization of iron‐loaded transferrin while DMT‐1 carries divalent metals like iron, zinc and copper inside the cells. Our data with HK‐2 cells indicated that transferrin receptor levels doubled upon treatment with 0.1 ng/mL interleukin 1β for 24 hours (P<0.005 by one‐way ANOVA, followed by Dunnett's test). Immunofluorescent staining of HK‐2 cells showed no apparent change in transferrin receptor distribution. In contrast, DMT‐1 levels in HK‐2 cells remained unchanged upon treatment with interleukin 1β for 24 hours at concentrations as high as 50 ng/mL. Increased intracellular levels of iron may lead to mitochondrial oxidative stress, which in turn may impact ATP production. After treating HK‐2 cells with 1 ng/mL interleukin 1β for 24 hours, intracellular ATP levels were measured and indicated no significant difference with untreated cells.ConclusionsThese data suggest that under inflammatory conditions, the uptake mechanism for the key iron transport protein transferrin is increased in the proximal tubule. This could have important implications in the setting of glomerular injury, which permits greater amounts of transferrin to be filtered, resulting in increased exposure of proximal tubular cells to transferrin and thus iron uptake.