Emma Carlsson

PGC-1alpha-responsive genes involved in oxidative phosphorylation are coordinately downregulated in human diabetes.

DNA microarrays can be used to identify gene expression changes characteristic of human disease. This is challenging, however, when relevant differences are subtle at the level of individual genes. We introduce an analytical strategy, Gene Set Enrichment Analysis, designed to detect modest but coordinate changes in the expression of groups of functionally related genes. Using this approach, we identify a set of genes involved in oxidative phosphorylation whose expression is coordinately decreased in human diabetic muscle. Expression of these genes is high at sites of insulin-mediated glucose disposal, activated by PGC-1α and correlated with total-body aerobic capacity. Our results associate this gene set with clinically important variation in human metabolism and illustrate the value of pathway relationships in the analysis of genomic profiling experiments.

A polymorphism in the adiponectin gene influences adiponectin expression levels in visceral fat in obese subjects

Objective:Reduced serum adiponectin levels have been found in obesity and type 2 diabetes and variations in the adiponectin gene (APM1) have been associated with type 2 diabetes and features of the metabolic syndrome in different populations.Study Design:Here, we investigated the expression of APM1 in adipose tissue and studied the relationship between variation in APM1 expression, the APM1 G276T polymorphism, the common PPARG Pro12Ala polymorphism and clinical features of 36 morbidly obese (body mass index (BMI) 41.5±4.9 kg/m2) nondiabetic subjects.Results:APM1 mRNA expression in visceral fat was correlated with serum adiponectin levels (r=0.54, P=0.012). In visceral, but not in subcutaneous, adipose tissue APM1 mRNA level was 38% higher among carriers of the APM1 G276T T allele (G/T and T/T) than among carriers of the G/G genotype (0.91±0.06 for G/T and T/T carriers vs 0.66±0.09 for G/G carriers, P=0.013). Carriers of the T allele also had significantly higher body fat percent compared to G/G carriers (65±6 vs 56±10%, P=0.011).Conclusion:Our results indicate that genetic variation in APM1 influences the expression of the gene in visceral adipose tissue and suggest a potential role for such variation in regulation of body fat accumulation in obese subjects.

Role of the FOXC2 -512C>T polymorphism in type 2 diabetes: possible association with the dysmetabolic syndrome.

OBJECTIVE:Overexpression of the human transcription factor FOXC2 gene (FOXC2) protects against insulin resistance in mice and a common FOXC2 polymorphism (–512C>T) has been suggested to be associated with insulin resistance in humans. Here, we addressed the potential role for FOXC2 as a candidate gene for type 2 diabetes and associated phenotypes.MATERIALS AND METHODS:A case–control study was performed in 390 type 2 diabetic patients and 307 control subjects. The number of patients was increased to a total of 768 subjects for further study of phenotypic differences relating to the dysmetabolic syndrome relative to genetic variation. The FOXC2 –512C>T polymorphism was genotyped by a restriction fragment length polymorphism PCR assay.RESULTS:FOXC2 –512C>T allele and genotype distribution did not differ between patients with type 2 diabetes and control subjects, but the C/C genotype was associated with increased body mass index (BMI, kg/m2) (Pa=0.03) among type 2 diabetic patients. The FOXC2 –512C>T polymorphism was a significant independent predictor of BMI (P=0.001) in a multiple regression model including age, gender and affection status. We found no significant association with type 2 diabetes-related metabolic parameters but that the C-allele (P=0.01) and C/C and C/T genotypes (P=0.03) were significantly over-represented in type 2 diabetic males with a concomitant diagnosis of dysmetabolic syndrome.CONCLUSION:We conclude that FOXC2 is associated with obesity and metabolic deterioration but does not contribute to an increased risk for type 2 diabetes.

Pro-opiomelanocortin gene is associated with serum leptin levels in lean but not in obese individuals.

OBJECTIVE: Mutations in the pro-opiomelanocortin and melanocortin 4 receptor genes (POMC and MC4R) cause monogenic obesity, and the POMC locus (2p21) has been linked to leptin levels and body mass index (BMI). We searched for monogenic obesity due to mutations in POMC and MC4R among morbidly obese Swedes and studied the association of POMC variants with BMI and serum leptin levels.DESIGN: MC4R and POMC were screened for mutations in 102 obese Swedish subjects (40±11 y, 41.3±5.0 kg/m2) using the single-strand conformation polymorphism technique. The detected polymorphisms were genotyped in 118 lean control subjects (56±11 y, 22.6±1.3 kg/m2) and studied for association with BMI and serum leptin levels.RESULTS: No cases of monogenic obesity due to mutations in POMC or MC4R were identified and none of the four common POMC polymorphisms (RsaI, ins56, Glu188Gly and C8246T) were associated with obesity. Lean carriers of the C8246T CC-genotype had higher serum leptin levels compared to CT or TT carriers (9.7±6.6 vs 6.7±4.4 μg/l, P=0.003 for leptin levels adjusted for age, sex and BMI in regression analysis), especially lean females (P=0.004) and lean female carriers with the C8246T(CC)/RsaI(−−or +−) genotype combinations (P<0.0005). Neither the C8246T CC-genotype nor the C8246T(CC)/RsaI(−−or +−) were associated with serum leptin levels in obese subjects.CONCLUSIONS: Monogenic forms of obesity due to mutations in POMC and MC4R are rare in Swedish obese patients. Polymorphisms in POMC are associated with variation in serum leptin levels within the normal range in healthy lean but not in obese individuals.

The hormone-sensitive lipase C–60G promoter polymorphism is associated with increased waist circumference in normal-weight subjects

Objective:Hormone-sensitive lipase (HSL) is a key enzyme in the mobilization of fatty acids from triglyceride stores in adipocytes. The aim of the present study was to investigate the role of the HSL gene promoter variant C-60G, a polymorphism which previously has been associated with reduced promoter activity in vitro, in obesity and type 2 diabetes.Design:We genotyped two materials consisting of obese subjects and non-obese controls, one material with offspring-parents trios, where the offspring was abdominally obese and one material with trios, where the offspring had type 2 diabetes or impaired glucose homeostasis. HSL promoter containing the HSL C-60G G-allele was generated and tested against a construct with the C-allele in HeLa cells and primary rat adipocytes. HSL mRNA levels were quantified in subcutaneous and visceral fat from 33 obese subjects.Results:We found that the common C-allele was associated with increased waist circumference and WHR in lean controls, but there was no difference in genotype frequency between obese and non-obese subjects. There was a significant increased transmission of C-alleles to the abdominally obese offspring but no increased transmission of C-alleles was observed to offspring with impaired glucose homeostasis. The G-allele showed reduced transcription in HeLa cells and primary rat adipocytes. HSL mRNA levels were significantly higher in subcutaneous compared to visceral fat from obese subjects.Conclusion:The HSL C-60G polymorphism is associated with increased waist circumference in non-obese subjects.

Gastric Regulatory Peptides in Rats with Reduced Acid Secretion

Gastric acid secretion is known to be controlled by a complex system of interacting factors. Amongst these, regulatory peptides make a significant contribution. In the present study, immunocytochemistry and radioimmunoassay were used to investigate gastric regulatory peptides in animals with pharmacologically reduced gastric acid secretion. Increased numbers of densely immunostained antral gastrin-immunoreactive (G) cells were seen in rats which had been rendered virtually achlorhydric by administration of high-dose (400 mumol/kg daily) omeprazole over a 10-week period. These morphological changes were accompanied by increases in the plasma, antral and fundic concentrations of gastrin, as measured by radioimmunoassay. In contrast, antral somatostatin-containing cells were reduced, and there was a corresponding fall in the tissue content of the peptide. Ten weeks after treatment had ceased, the peptide profiles had returned to normal. No other regulatory peptide, whether endocrine or neural, appeared to alter during treatment with high-dose omeprazole. Treatment with high-dose (700 mumol/kg daily) ranitidine also caused an elevation in the G cell population and the antral and plasma content of gastrin, but to a lesser extent than that observed during omeprazole treatment. Somatostatin cells and tissue levels did not alter in these animals, and no other morphological changes could be detected. Radioimmunoassay, however, measured reduced quantities of vasoactive intestinal peptide, peptide histidine isoleucine and calcitonin gene-related peptide. Achlorhydria, induced by omeprazole at a dosage of 250-500 times that required for effective acid inhibition in man and animals, therefore resulted in reciprocal changes in gastrin and somatostatin cells. These changes are support for the postulated roles of these peptides in the control of gastric acid secretion.