Glutathione-S-transferase A4-4 (GSTA4-4) controlled the 4-hydroxynonenal (HNE) cytotoxicity. Chondrocytes were transfected with (a) small interfering RNA (siRNA) GSTA4-4 or with (c) wild-type or mutant GSTA4-4 expression plasmids, and then cell viability was determined by MTT assay. (b) and (d) GSTA4-4 protein expression was evaluated respectively in cellular extracts of transfected chondrocytes with siRNA or expression plasmids of GSTA4-4 by Western blotting. Data are mean ± standard error of the mean and expressed as a percentage of untreated cells. Statistics: Student unpaired t test; *P < 0.05, **P < 0.01, ***P < 0.001. CTL, control; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; mut, mutant; wt, wild-type.