Clusterin protects renal tubular epithelial cells from gentamicin-mediated cytotoxicity

Clusterin is a heterodimeric secreted glycoprotein that is upregulated after acute renal injury. In aminoglycoside nephrotoxicity, clusterin is induced in the tubular epithelium and increased levels are found in the urine. In this study, we developed an in vitro model of gentamicin-induced cytotoxicity in renal proximal tubule cells and tested whether clusterin protected these cells from injury. LLC-PK(1) cells were incubated with varying concentrations of gentamicin in serum-free media, and cytotoxicity was quantified by lactate dehydrogenase release and confirmed by vital dye exclusion. A dose-dependent increase in cytotoxicity occurred with gentamicin concentrations up to 27 mg/ml. Clusterin decreased cytotoxicity in a dose- and time-dependent manner at 6, 12, and 24 h, whereas albumin, used as a control protein, had no effect. In contrast to the aminoglycoside model, when cells were injured by depletion of ATP, clusterin had only a minimally protective effect. LLC-PK(1) cells did not express megalin, a receptor that can mediate the uptake of both clusterin and aminoglycosides into proximal tubule cells. Uptake of gentamicin into LLC-PK(1) cells was observed despite the absence of megalin. In conclusion, clusterin specifically protects against gentamicin-induced renal tubular cell injury by a megalin-independent mechanism.