Obesity is the most common nutritional disorder in Western society. Uncoupling protein-2 (UCP2) is a recently identified member of the mitochondrial transporter superfamily that is expressed in many tissues, including adipose tissue. Like its close relatives UCP1 and UCP3, UCP2 uncouples proton entry in the mitochondrial matrix from ATP synthesis and is therefore a candidate gene for obesity. We show here that a common G/A polymorphism in the UCP2 promoter region is associated with enhanced adipose tissue mRNA expression in vivo and results in increased transcription of a reporter gene in the human adipocyte cell line PAZ-6. In analyzing 340 obese and 256 never-obese middle-aged subjects, we found a modest but significant reduction in obesity prevalence associated with the less-common allele. We confirmed this association in a population-based sample of 791 middle-aged subjects from the same geographic area. Despite its modest effect, but because of its high frequency (approximately 63%), the more-common risk allele conferred a relatively large population-attributable risk accounting for 15% of the obesity in the population studied.

SUMMARY Obesity and diabetes affect more than half a billion individuals worldwide. Interestingly, the two conditions do not always coincide and the molecular determinants of “healthy” versus “unhealthy” obesity remain ill-defined. Chronic metabolic inflammation (metaflammation) is believed to be pivotal. Here, we tested a hypothesized anti-inflammatory role for heme oxygenase-1 (HO-1) in the development of metabolic disease. Surprisingly, in matched biopsies from “healthy” versus insulin-resistant obese subjects we find HO-1 to be among the strongest positive predictors of metabolic disease in humans. We find that hepatocyte and macrophage conditional HO-1 deletion in mice evokes resistance to diet-induced insulin resistance and inflammation, dramatically reducing secondary disease such as steatosis and liver toxicity. Intriguingly, cellular assays show that HO-1 defines prestimulation thresholds for inflammatory skewing and NF-κB amplification in macrophages and for insulin signaling in hepatocytes. These findings identify HO-1 inhibition as a potential therapeutic strategy for metabolic disease.

Obesity is frequently associated with type 2 diabetes. We previously observed an association of a functional G/A polymorphism in the uncoupling protein 2 (UCP2) promoter with obesity. The wild-type G allele was associated with reduced adipose tissue mRNA expression in vivo, reduced transcriptional activity in vitro, and increased risk of obesity. On the other hand, studies in animal and cell culture models identified pancreatic beta-cell UCP2 expression as a main determinant of the insulin secretory response to glucose. We therefore ascertained associations of the -866G/A polymorphism with beta-cell function and diabetes risk in obesity. We show here that the pancreatic transcription factor PAX6 preferentially binds to and more effectively trans activates the variant than the wild-type UCP2 promoter allele in the beta-cell line INS1-E. By studying 39 obese nondiabetic humans, we observed genotype differences in beta-cell function; wild-type subjects displayed a greater disposition index (the product of insulin sensitivity and acute insulin response to glucose) than subjects with the variant allele (P < 0.03). By comparing obese subjects with and without type 2 diabetes, we observed genotype-associated differences in diabetes prevalence that translated into a twofold age-adjusted risk reduction in wild-type subjects. Thus, the more common UCP2 promoter G allele, while being conducive for obesity, affords relative protection against type 2 diabetes.

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PGC-1α has been implicated in the pathogenesis of neurodegenerative disorders. Several single-nucleotide polymorphisms (SNPs) located in two separate haplotype blocks of PPARGC1A have shown associations with Huntington's disease (HD) and Parkinson's disease, but causative SNPs have not been identified. One SNP (rs7665116) was located in a highly conserved 233 bp region of intron 2. To determine whether rs7665116 is located in an alternative exon, we performed 5'-RLM-RACE from exon 3 and discovered multiple new transcripts that initiated from a common novel promoter located 587 kb upstream of exon 2, but did not contain the conserved region harboring rs7665116. Using real-time polymerase chain reaction, RNase protection assays and northern blotting, we show that the majority of these transcripts are brain specific and are at least equally or perhaps more abundant than the reference sequence PPARGC1A transcripts in whole brain. Two main transcripts containing independent methionine start codons encode full-length brain-specific PGC-1α proteins that differ only at their N-termini (NTs) from PGC-1α, encoded by the reference sequence. Additional truncated isoforms containing these NTs that are similar to NT-PGC-1α exist. Other transcripts may encode potential dominant negative forms, as they are predicted to lack the second LXXLL motif that serves as an interaction site for several nuclear receptors. Furthermore, we show that the new promoter is active in neuronal cell lines and describe haplotypes encompassing this region that are associated with HD age of onset. The discovery of such a large PPARGC1A genomic locus and multiple isoforms in brain warrants further functional studies and may provide new tissue-specific targets for treating neurodegenerative diseases.

Peroxisome proliferator-activated receptor-␥ coactivator-1 (PPARGC1) is a transcriptional coactivator that has been implicated in the regulation of genes involved in energy metabolism. We studied associations of two polymorphisms identified in PPARGC1 transcripts with obesity indices in 591 middle-aged men and 467 middle-aged women of a cross-sectional Austrian population. Because neither polymorphic site was likely to be a functional site, we analyzed sex-specific associations of two loci haplotype combinations with obesity indices. Significant associations with BMI (P ‫؍‬ 0.006), waist (P ‫؍‬ 0.01) and hip circumference (P ‫؍‬ 0.03), and total body fat (P ‫؍‬ 0.005) and borderline significant associations with abdominal visceral and subcutaneous fat were observed in women but not men. In women, plasma triglycerides, HDL cholesterol, and glucose significantly differed by haplotype combinations, but these associations were not maintained after statistical consideration of BMI. The haplotype combination of the double-variant allele with the double-wild-type allele was associated with the lowest obesity indices, whereas homozygosity for the double-variant allele was not discriminatory among haplotype combinations. These studies suggest functional differences of PPARGC1 haplotypes in human energy metabolism and support a role of PPARGC1 in obesity. Diabetes 51:1281-1286, 2002 P eroxisome proliferator-activated receptor-␥ coactivator-1 (PPARGC1) is a coactivator of PPAR-␥ and other nuclear hormone receptors and plays an essential role in energy homeostasis. Studies in rodents and cell culture models showed that Pgc1 stimulates mitochondrial biogenesis and activates genes of the oxidative phosphorylation pathway and thermogenesis (1-4). Human PPARGC1 exhibits 94% amino acid identity with the mouse ortholog and was mapped to chromosome 4p15.1 (5). This chromosomal region has been associated with basal insulin levels in Pima Indians (6) and abdominal subcutaneous fat in the Quebec Family Study (7). Because of these associations and PPARGC1's role in energy metabolism in animal models, we tested the hypothesis that markers at the PPARGC1 gene locus are associated with obesity indices.By sequencing eight cDNA alleles transcribed from muscle RNA, we identified four polymorphisms in PPARGC1 transcripts. Two polymorphisms, a G-to-A transition at position ϩ1,564 in exon 8 (that predicted a glycine to serine amino acid substitution at position 482, and therefore referred to as G482S) and an A-to-G substitution at position ϩ2,962 in the 3Ј-untranslated region (Genbank accession no. NM-013261) were selected because of their heterozygosity indices of 0.449 (95% CI 0.436 -0.462) and 0.499 (0.498 -0.501), respectively, to genotype 591 unrelated men and 467 unrelated women of the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR) (8). The two other polymorphisms, a silent G-to-A transition at ϩ1,302 in exon 8 and an A-to-T transversion at ϩ3,010 in exon 13 were not considered because heterozygo...

Obesity is a highly prevalent disorder in many western societies [1]. It is caused by an imbalance between energy intake and energy expenditure resulting in excess total body fat. Owing to its association with hypertension, hyperlipidaemia, and insulin resistance obesity increases the risk of cardiovascular disease and is an important predictor of morbidity and mortality [2,3]. Studies in stable populations, twins and adoptees have clearly established the importance of genetic factors in the aetiology of obesity [4±6]. Some pleiotropic genetic syndromes associated with obesity such as the Prader-Willi syndrome have been mapped to specific chromosomes [7] but the genes contributing to or causing the common forms of obesity have not yet been discovered. The recent discovery of several genes responsible for spontaneous obesity in mice has provided insight into the control of energy homeostasis in mammals. While the ob-, db-, tub, A y -and fat genes [8±12] may all play critical roles in human energy balance, only very few cases of obesity have been directly linked to defects in one of these genes [13,14].Small decreases in energy expenditure increase the risk for human obesity [15,16] and genetic factors determine, at least in part, the resting metabolic rate [17,18]. Regulated thermogenesis is thought to be Diabetologia (1998) Summary The mitochondrial uncoupling protein-2 (UCP-2) is a recently discovered homologue of the brown adipose tissue-specific uncoupling protein and could be involved in the regulation of energy balance. Since obesity is associated with disturbed energy homeostasis, we tested the hypothesis that UCP-2 gene expression is deficient in this disorder. We determined, by a competitive reverse transcription-polymerase chain reaction assay, UCP-2 mRNA expression in intra-and extraperitoneal adipose tissues of 107 morbidly obese subjects and 31 lean control subjects. In both obese and non-obese subjects, UCP-2 mRNA abundance was higher in the intraperitoneal than in the extraperitoneal tissue (p < 0.05), but no association was observed between intra-and extraperitoneal expression in either group. Compared with lean control subjects, both male and female obese subjects displayed significantly lower average UCP-2 mRNA expression in the intraperitoneal adipose tissue (p < 0.006), while UCP-2 mRNA abundance in extraperitoneal adipose tissue was not different between obese and non-obese men and women. Intraperitoneal UCP-2 mRNA remained low in nine obese subjects who lost 23 ± 12 kg of weight over a period of 10 ± 5 months subsequent to weight reducing surgery. These data support the concept that impaired adipose tissue expression of UCP-2 may play a role in the pathophysiology of obesity.[ Diabetologia (1998) 41: 940±946]

Data derived from several recent studies implicate peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in the pathogenesis of type 2 diabetes. Lacking DNA binding activity itself, PGC-1α is a potent, versatile regulator of gene expression that co-ordinates the activation and repression of transcription via proteinprotein interactions with specific, as well as more general, factors contained within the basal transcriptional machinery. PGC-1α is suggested to play a pivotal role in the control of genetic pathways that result in homeostatic glucose utilisation in liver and muscle, beta cell insulin secretion and mitochondrial biogenesis. This review focuses on the role of PGC-1α in glucose metabolism and considers how PGC-1α links cellular glucose metabolism, insulin sensitivity and mitochondrial function, and why defects in PGC-1α expression and regulation may contribute to the pathophysiology of type 2 diabetes in humans.