title: Urinary proteins induce lysosomal membrane permeabilization and lysosomal dysfunction in renal tubular epithelial cells.
abstract: Lysosomal membrane permeabilization (LMP) has been shown to cause the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol and initiate a cell death pathway. Whether proteinuria triggers LMP in renal tubular epithelial cells (TECs) to accelerate the progression of renal tubulointerstitial injury remains unclear. In the present study, we evaluated TEC injury as well as changes in lysosomal number, volume, activity, and membrane integrity after urinary protein overload in vivo and in vitro. Our results revealed that neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels were significantly increased in the urine of patients with minimal change nephrotic syndrome (MCNS) and the culture supernatant of HK-2 cells treated by urinary proteins extracted from MCNS patients. Urinary protein overload also induced apoptotic cell death in HK-2 cells. Importantly, we found that lysosomal volume and number were markedly increased in TECs of patients with MCNS and HK-2 cells overloaded with urinary proteins. However, lysosome function, as assessed by proteolytic degradation of DQ-ovalbumin and cathepsin-B and cathepsin-L activities, was decreased in HK-2 cells overloaded with urinary proteins. Furthermore, urinary protein overload led to a diffuse cytoplasmic immunostaining pattern of cathepsin-B and irregular immunostaining of lysosome-associated membrane protein-1, accompanying a reduction in intracellular acidic components, which could be improved by pretreatment with antioxidant. Taken together, our results indicate that overloading of urinary proteins caused LMP and lysosomal dysfunction at least partly via oxidative stress in TECs.
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China hf-liu@263.net.
authors.forename: Wei Jing
authors.initials: WJ
authors.lastname: Liu
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Bi-Hua
authors.initials: BH
authors.lastname: Xu
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Ye
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Dong
authors.initials: D
authors.lastname: Liang
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Hong-Luan
authors.initials: HL
authors.lastname: Wu
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Yuan-Yuan
authors.initials: YY
authors.lastname: Zheng
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Jian Kun
authors.initials: JK
authors.lastname: Deng
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Benyi
authors.initials: B
authors.lastname: Li
authors.affiliation: Institute of Nephrology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Hua-feng
authors.initials: HF
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D000328:Adult; D002403:Cathepsins / Q000378:metabolism; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007684:Kidney Tubules / Q000473:pathology / Q000503:physiopathology*; D008247:Lysosomes / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D010047:Ovalbumin; D018384:Oxidative Stress; D010539:Permeability; D011507:Proteinuria / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D055815:Young Adult
chemical_list: D010047:Ovalbumin; D002403:Cathepsins
keywords: lysosomal dysfunction; lysosomal membrane permeabilization; tubular epithelial cells; urinary proteins