Modulation of 3-hydroxy-3-methylglutaryl-CoA reductase gene expression by CuZn superoxide dismutase in human fibroblasts and HepG2 cells

The homeostasis of intracellular cholesterol in animal cells is highly regulated by a complex system in which the microsomal rate-limiting enzyme 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase plays a key role in cholesterol synthesis. Substantial evidence has demonstrated that the cytosolic antioxidant enzyme CuZn superoxide dismutase (SOD1) inhibits the HMG-CoA reductase activity in rat hepatocytes and in human fibroblasts by decreasing cholesterol synthesis. Although these data suggest that SOD1 exerts a physiological role in cholesterol metabolism, it is still unclear whether the decrease of HMG-CoA reductase activity is mediated by transcriptional or by posttranscriptional events. The results of the present study, obtained by one-step RT-PCR assay, demonstrated that both SOD1 and the metal-free form of enzyme (Apo SOD1) inhibit HMG-CoA reductase gene expression in hepatocarcinoma HepG2 cells, in normal human fibroblasts, and in fibroblasts of subjects affected by familiar hypercholesterolemia. Accordingly, SOD1 could be used as a potential agent in the treatment of hypercholesterolemia, even in subjects lacking a functional LDL receptor pathway.