Abstract

Age-related progressive glomerular sclerosis in the rat is associated with increased expression of tumor necrosis factor-β₁ and increased protein content in the renal cortex, enhanced production of H₂O₂, in both renal glomeruli and mesangial cells (MCs) cultured from them, as well as augmented glomerular oxidative damage. We have previously shown that tretinoin-treated old male Fischer 344 rats have 30% lower protein content in the renal cortex than control old rats. Here, we report that this effect may depend on the inhibition of the expression of tumor necrosis factor-β₁, a matrigenic cytokine, and osteopontin, a protein with cell adhesive and chemotactic properties. In addition, we show that tretinoin prevents the cytotoxicity of H₂O₂ in cultured human MCs by increasing both the catalase activity and the reduced glutathione content, which are dose- and time-dependent changes. These increases were not dependent on each other: when these effects were previously inhibited with 3-amino-1,2,4-atriazole orl-buthionine-(S,R)-sulfoximine, respectively, tretinoin still induced the increase of the other noninhibited antioxidant defense. An enhanced gene transcription is the most likely mechanism involved in the tretinoin-induced stimulation of MC antioxidant defense systems because 1) preincubation of MCs with actinomycin D or cycloheximide fully abolished it; 2) tretinoin-incubated MCs showed increased levels of catalase mRNA and γ-glutamyl-cysteine synthetase (catalytic subunit) mRNA, the latter being the rate-limiting step in de novo reduced glutathione synthesis; and 3) the stability of both mRNA was unchanged by tretinoin. These results show one strategy of protecting renal cells from H₂O₂-mediated injury based on increasing their antioxidant defenses.