Dietary fat interacts with QTLs controlling induction of Pgc-1α and Ucp1 during conversion of white to brown fat

To identify novel regulatory factors controlling induction of the brown adipocyte-specific mitochondrial uncoupling protein (Ucp1) mRNA in the retroperitoneal white fat depot, we previously mapped quantitative trait loci (QTLs) that control this trait to chromosomes 2, 3, 8, and 19. Since the peroxisome proliferator activator receptor-gamma coactivator-1alpha (PGC-1) regulates Ucp1 and other genes of energy metabolism, we have evaluated whether the QTLs controlling Ucp1 mRNA levels also modulate Pgc-1alpha mRNA levels by analysis of backcross progeny from the A/J and C57BL/6J strains of mice. The results indicate that a locus on chromosome 3 orchestrates expression of Pgc-1alpha and Ucp1 in retroperitoneal fat of mice fed a low-fat diet; however, the effect of this locus on Pgc-1alpha is lost, and a significant correlation between Ucp1 and Pgc-1alpha is severely reduced in mice fed a high-fat diet. An additional QTL located on chromosome 5 has also been identified for the selective regulation of Ucp1 mRNA levels. Similar to the effects of a high-fat diet on the chromosome 3 QTL, linkage of the chromosome 5 QTL is also lost in mice on a high-fat diet. Thus dietary fat has a profound influence on PGC-1alpha-regulated pathways controlling energy metabolism in white fat. The allelic variation observed in the regulation of Ucp1 and Pgc-1alpha expression in brown adipocytes of white fat but not interscapular brown fat suggests that fundamentally different regulatory mechanisms exist to control the thermogenic capacities of these tissues.