Urinary proteins induce lysosomal membrane permeabilization and lysosomaldysfunction in renal tubular epithelial cells

摘要

Lysosomal membranepermeabilization (LMP) has been shown to cause the release ofcathepsins and other hydrolases from the lysosomal lumen to thecytosol and initiate a cell death pathway. Whether proteinuria triggersLMP in renal tubular epithelial cells (TECs) to accelerate the progres-sion of renal tubulointerstitial injury remains unclear. In the presentstudy, we evaluated TEC injury as well as changes in lysosomalnumber, volume, activity, and membrane integrity after urinary pro-tein overload in vivo and in vitro. Our results revealed that neutrophilgelatinase-associated lipocalin and kidney injury molecule-1 levelswere significantly increased in the urine of patients with minimalchange nephrotic syndrome (MCNS) and the culture supernatant ofHK-2 cells treated by urinary proteins extracted from MCNS patients.Urinary protein overload also induced apoptotic cell death in FIK-2cells. Importantly, we found that lysosomal volume and number weremarkedly increased in TECs of patients with MCNS and HK-2 cellsoverloaded with urinary proteins. However, lysosome function, asassessed by proteolytic degradation of DQ-ovalbumin and cathep-sin-B and cathepsin-L activities, was decreased in HK-2 cells over-loaded with urinary proteins. Furthermore, urinary protein overloadled to a diffuse cytoplasmic immunostaining pattern of cathepsin-Band irregular immunostaining of lysosome-associated membrane pro-tein-1, accompanying a reduction in intracellular acidic components,which could be improved by pretreatment with antioxidant. Takentogether, our results indicate that overloading of urinary proteinscaused LMP and lysosomal dysfunction at least partly via oxidativestress in TECs.