UNCOUPLING PROTEIN-1 MESSENGER-RNA EXPRESSION IN OBESE HUMAN-SUBJECTS- THE ROLE OF SEQUENCE VARIATIONS AT THE UNCOUPLING PROTEIN-1 GENE LOCUS

Uncoupling protein-1 (UCP-1) activity in brown adipose tissue increase s thermogenesis, contributes to facultative energy expenditure in huma ns, and has been implicated in the pathogenesis of rodent obesity. To determine genetic factors controlling UCP-1 expression in humans, we m easured intra-and extraperitoneal UCP-1 mRNA abundance levels by a com petitive RT-PCR method and compared expression levels with common sequ ence variations in the beta 3-adrenergic receptor gene and the distal UCP-1 gene promoter in obese human subjects. While median and average UCP-1 mRNA levels in both the intra-and extraperitoneal tissue were lo wer in subjects heterozygous for the Trp64Arg mutation in the beta 3-a drenergic receptor gene, this difference was not statistically signifi cant. However, a strong association of intraperitoneal UCP-1 mRNA abun dance with the UCP-1 gene polymorphism at -3826 relative to the transc ription start site was observed that explained 19.3% of the interindiv idual variability. The minor allele imparted a dose-dependent reductio n on UCP gene expression. The importance of sequence variations at the UCP-1 gene locus as a common source of UCP-1 mRNA abundance variabili ty was supported by allele-specific expression studies utilizing a new ly identified polymorphism in exon 2 of the UCP-1 gene that predicts a substitution of alanine by threonine. In four subjects heterozygous f or the -3826 polymorphism, the mRNA species transcribed from the wild- type allele accounted for 63 +/- 6% percent of total intraperitoneal m RNA abundance. In one subject homozygous for the minor promoter allele , wild-type mRNA was also more abundant than variant mRNA. Thus, the U CP-1 polymorphism at -3826 is probably only a marker for a frequent mu tation causing reduced mRNA expression.