Reduced adiposity and liver steatosis by stearoyl-CoA desaturase deficiency are independent of peroxisome proliferator-activated receptor-α

Stearoyl-CoA desaturase catalyzes the rate-limiting step in the biosynthesis of monounsaturated fatty acids, which are required for normal rates of synthesis of triglycerides, cholesterol esters, and phospholipids. Mice with a targeted disruption of the stearoyl-CoA desaturase 1 (SCD1) isoform are protected against diet and leptin deficiency-induced adiposity, have increased energy expenditure, and have up-regulated expression of hepatic genes encoding enzymes of fatty acid β-oxidation. Because peroxisome proliferator- activated receptor-α (PPARα) is a key transcription factor that induces the transcription of fatty acid β-oxidation and thermogenic genes, we hypothesized that the increased fatty acid oxidation observed in SCD1 deficiency is dependent on activation of the PPARa pathway. Here we show that mice nullizygous for SCD1 and PPARα are still protected against adiposity, have increased energy expenditure, and maintain high expression of PPARα target genes in the liver and brown adipose tissue. The SCD1 deficiency rescued hepatic steatosis of the PPARα^-/- mice. The SCD1 mutation increased the phosphorylation of both AMP-activated protein kinase and acetyl-CoA carboxylase, thereby increasing CPT activity and stimulating the oxidation of liver palmitoyl-CoA in the PPARa null mice. The findings indicate that the reduced adiposity, reduced liver steatosis, increased energy expenditure, and increased expression of PPARα target genes associated with SCD1 deficiency are independent of activation of the PPARα pathway.