title: Uric acid promotes apoptosis in human proximal tubule cells by oxidative stress and the activation of NADPH oxidase NOX 4.
abstract: Mild hyperuricemia has been linked to the development and progression of tubulointerstitial renal damage. However the mechanisms by which uric acid may cause these effects are poorly explored. We investigated the effect of uric acid on apoptosis and the underlying mechanisms in a human proximal tubule cell line (HK-2). Increased uric acid concentration decreased tubule cell viability and increased apoptotic cells in a dose dependent manner (up to a 7-fold increase, p<0.0001). Uric acid up-regulated Bax (+60% with respect to Ctrl; p<0.05) and down regulated X-linked inhibitor of apoptosis protein. Apoptosis was blunted by Caspase-9 but not Caspase-8 inhibition. Uric acid induced changes in the mitochondrial membrane, elevations in reactive oxygen species and a pronounced up-regulation of NOX 4 mRNA and protein (p<0.05). In addition, both reactive oxygen species production and apoptosis was prevented by the NADPH oxidase inhibitor DPI as well as by Nox 4 knockdown. URAT 1 transport inhibition by probenecid and losartan and its knock down by specific siRNA, blunted apoptosis, suggesting a URAT 1 dependent cell death. In summary, our data show that uric acid increases the permissiveness of proximal tubule kidney cells to apoptosis by triggering a pathway involving NADPH oxidase signalling and URAT 1 transport. These results might explain the chronic tubulointerstitial damage observed in hyperuricaemic states and suggest that uric acid transport in tubular cells is necessary for urate-induced effects.
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Verzola
authors.affiliation: I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Clinica Nefrologica, Dialisi e Trapianto, Genoa, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Ratto
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Villaggio
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Emanuele Luigi
authors.initials: EL
authors.lastname: Parodi
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Pontremoli
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Garibotto
authors.affiliation: University of Genoa and I.R.C.C.S. Azienda Ospedaliera Universitaria San Martino-IST, Istituto Nazionale per la Ricerca sul Cancro, Department of Internal Medicine, Genoa, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Viazzi
mesh_terms: D000704:Analysis of Variance; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D008297:Male; D051336:Mitochondrial Membranes / Q000187:drug effects; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013778:Tetrazolium Salts; D013844:Thiazoles; D014527:Uric Acid / Q000494:pharmacology*
chemical_list: D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D013844:Thiazoles; D014527:Uric Acid; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; C022616:thiazolyl blue