Oxidised low density lipoprotein (LDL) contribute to endothelial and smooth muscle cell (SMC) dysfunction in atherosclerosis (Ross, 1999), induce the stress protein heme oxygenase-1 (HO-1) and elevate glutathione (GSH) as an adaptive antioxidant response against oxidative injury. HO-1 catabolises heme to carbon monoxide and the antioxidant biliverdin (Siow et al., 1999). We have shown moderately oxidized LDL (modLDL), a species high in lipid peroxides, enhances HO-1 and GSH levels to a greater extent than highly oxidized LDL (oxLDL) in human aortic SMC (HASMC) (Anwar et al., 2003). The transcription factor Nrf2 mediates HO-1 induction by LDL following transactivation of the antioxidant response element of antioxidant genes (Ishii et al., 2004). In this study we investigate whether mitogen activated protein kinases (MAPK) or protein kinase C (PKC) modulates HO-1 and GSH levels in HASMC. Cells were pretreated (30 min) in the absence or presence of MAPK inhibitors, U0126 (MEK), SB203580 (p38MAPK) and SP600125 (JNK) or PKC inhibitor GF109203 prior to treatment with native LDL (nLDL), modLDL or oxLDL (100 μg protein/ml, 2-24h). Combinations of the MAPK inhibitors were used to antagonise two or more pathways simultaneously. Phosphorylation of p42/p44MAPK (ERK), p38MAPK, JNK or CREB (cAMP-response element binding protein) and expression of HO-1 or Nrf2 in total and nuclear lysates were determined by western blot. Reduced GSH levels were assessed using a fluorescence assay. Nuclear translocation of Nrf2 was visualized by fluorescence immunohistochemistry. Treatment of cells (2 h) with oxidised LDL, but not nLDL, significantly (unpaired Student’s t test, p<0.01, n=3) enhanced levels of ERK, p38MAPK, JNK and CREB phosphorylation. Pretreatment with individual MAPK inhibitors[3] or PKC inhibitor significantly attenuated (47±12.2 %, p<0.01, n=3)HO-1 induction, but only inhibition of JNK significantly attenuated (34±2.2 %, p<0.01, n=7)elevation of GSH levels by modLDL(24h). Combined inhibition of JNK and p38MAPK inhibitors resulted in a further 47% attenuation in HO-1 induction by modLDL compared to either kinase individually, but did not alter GSH levels. Treatment of cells with oxidised LDL (2 h, 100 μg protein/ml) induced nuclear translocation of Nrf2. These novel findings suggest that PKC is involved in part in HO-1 induction by oxidized LDL through activation of CREB, however, MAPK modulate HO-1 expression via activation of Nrf2. In addition, elevation of GSH levels by oxidized LDL is mediated by JNK but not PKC, ERK, or p38MAPK.