Functional and genetic analysis in type 2 diabetes of Liver X receptor alleles – a cohort study

<p>Abstract</p> <p>Background</p> <p>Liver X receptor alpha <it>(LXRA</it>) and beta (<it>LXRB</it>) regulate glucose and lipid homeostasis in model systems but their importance in human physiology is poorly understood. This project aimed to determine whether common genetic variations in <it>LXRA </it>and <it>LXRB </it>associate with type 2 diabetes (T2D) and quantitative measures of glucose homeostasis, and, if so, reveal the underlying mechanisms.</p> <p>Methods</p> <p>Eight common single nucleotide polymorphisms in <it>LXRA </it>and <it>LXRB </it>were analyzed for association with T2D in one French cohort (N = 988 cases and 941 controls), and for association with quantitative measures reflecting glucose homeostasis in two non-diabetic population-based samples comprising N = 697 and N = 1344 adults. Investigated quantitative phenotypes included fasting plasma glucose, serum insulin, and HOMA_IRas measure of overall insulin resistance. An oral glucose tolerance test was performed in N = 1344 of adults. The two alleles of the proximal <it>LXRB </it>promoter, differing only at the SNP rs17373080, were cloned into reporter vectors and transiently transfected, whereupon allele-specific luciferase activity was measured. rs17373080 overlapped, according to <it>in silico </it>analysis, with a binding site for Nuclear factor 1 (NF1). Promoter alleles were tested for interaction with NF1 using direct DNA binding and transactivation assays.</p> <p>Results</p> <p>Genotypes at two <it>LXRB </it>promoter SNPs, rs35463555 and rs17373080, associated nominally with T2D (P values 0.047 and 0.026). No <it>LXRA </it>or <it>LXRB </it>SNP associated with quantitative measures reflecting glucose homeostasis. The rs17373080 C allele displayed higher basal transcription activity (P value < 0.05). The DNA-mobility shift assay indicated that oligonucleotides corresponding to either rs17373080 allele bound NF1 transcription factors in whole cell extracts to the same extent. Different NF1 family members showed different capacity to transactivate the <it>LXRB </it>gene promoter, but there was no difference between promoter alleles in NF1 induced transactivation activity.</p> <p>Conclusion</p> <p>Variations in the <it>LXRB </it>gene promoter may be part of the aetiology of T2D. However, the association between <it>LXRB </it>rs35463555 and rs17373080, and T2D are preliminary and needs to be investigated in additional larger cohorts. Common genetic variation in <it>LXRA </it>is unlikely to affect the risk of developing T2D or quantitative phenotypes related to glucose homeostasis.</p

A common polymorphism in NR1H2 (LXRbeta) is associated with preeclampsia

<p>Abstract</p> <p>Background</p> <p>Preeclampsia is a frequent complication of pregnancy and a leading cause of perinatal mortality. Both genetic and environmental risk factors have been identified. Lipid metabolism, particularly cholesterol metabolism, is associated with this disease. Liver X receptors alpha (NR1H3, also known as LXRalpha) and beta (NR1H2, also known as LXRbeta) play a key role in lipid metabolism. They belong to the nuclear receptor superfamily and are activated by cholesterol derivatives. They have been implicated in preeclampsia because they modulate trophoblast invasion and regulate the expression of the endoglin (CD105) gene, a marker of preeclampsia. The aim of this study was to investigate associations between the <it>NR1H3 </it>and <it>NR1H2 </it>genes and preeclampsia.</p> <p>Methods</p> <p>We assessed associations between single nucleotide polymorphisms of <it>NR1H3 </it>(rs2279238 and rs7120118) and <it>NR1H2 </it>(rs35463555 and rs2695121) and the disease in 155 individuals with preeclampsia and 305 controls. Genotypes were determined by high-resolution melting analysis. We then used a logistic regression model to analyze the different alleles and genotypes for those polymorphisms as a function of case/control status.</p> <p>Results</p> <p>We found no association between <it>NR1H3 </it>SNPs and the disease, but the <it>NR1H2 </it>polymorphism rs2695121 was found to be strongly associated with preeclampsia (genotype C/C: adjusted odds ratio, 2.05; 95% CI, 1.04-4.05; <it>p </it>= 0.039 and genotype T/C: adjusted odds ratio, 1.85; 95% CI, 1.01-3.42; <it>p </it>= 0.049).</p> <p>Conclusions</p> <p>This study provides the first evidence of an association between the <it>NR1H2 </it>gene and preeclampsia, adding to our understanding of the links between cholesterol metabolism and this disease.</p

FTO gene polymorphisms and obesity risk: a meta-analysis

<p>Abstract</p> <p>Background</p> <p>The pathogenesis of obesity is reportedly related to variations in the fat mass and an obesity-associated gene (<it>FTO</it>); however, as the number of reports increases, particularly with respect to varying ethnicities, there is a need to determine more precisely the effect sizes in each ethnic group. In addition, some reports have claimed ethnic-specific associations with alternative SNPs, and to that end there has been a degree of confusion.</p> <p>Methods</p> <p>We searched PubMed, MEDLINE, Web of Science, EMBASE, and BIOSIS Preview to identify studies investigating the associations between the five polymorphisms and obesity risk. Individual study odds ratios (OR) and their 95% confidence intervals (CI) were estimated using per-allele comparison. Summary ORs were estimated using a random effects model.</p> <p>Results</p> <p>We identified 59 eligible case-control studies in 27 articles, investigating 41,734 obesity cases and 69,837 healthy controls. Significant associations were detected between obesity risk and the five polymorphisms: rs9939609 (OR: 1.31, 95% CI: 1.26 to 1.36), rs1421085 (OR: 1.43, 95% CI: 1.33 to 1.53), rs8050136 (OR: 1.25, 95% CI: 1.13 to 1.38), rs17817449 (OR: 1.54, 95% CI: 1.41 to 1.68), and rs1121980 (OR: 1.34, 95% CI: 1.10 to 1.62). Begg's and Egger's tests provided no evidence of publication bias for the polymorphisms except rs1121980. There is evidence of higher heterogeneity, with <it>I</it>²test values ranging from 38.1% to 84.5%.</p> <p>Conclusions</p> <p>This meta-analysis suggests that <it>FTO </it>may represent a low-penetrance susceptible gene for obesity risk. Individual studies with large sample size are needed to further evaluate the associations between the polymorphisms and obesity risk in various ethnic populations.</p

Hepatic PPARα is critical in the metabolic adaptation to sepsis.

Although the role of inflammation to combat infection is known, the contribution of metabolic changes in response to sepsis is poorly understood. Sepsis induces the release of lipid mediators, many of which activate nuclear receptors such as the peroxisome proliferator-activated receptor (PPAR)α, which controls both lipid metabolism and inflammation. We aimed to elucidate the previously unknown role of hepatic PPARα in the response to sepsis. Sepsis was induced by intraperitoneal injection of Escherichia coli in different models of cell-specific Ppara-deficiency and their controls. The systemic and hepatic metabolic response was analyzed using biochemical, transcriptomic and functional assays. PPARα expression was analyzed in livers from elective surgery and critically ill patients and correlated with hepatic gene expression and blood parameters. Both whole body and non-hematopoietic Ppara-deficiency in mice decreased survival upon bacterial infection. Livers of septic Ppara-deficient mice displayed an impaired metabolic shift from glucose to lipid utilization resulting in more severe hypoglycemia, impaired induction of hyperketonemia and increased steatosis due to lower expression of genes involved in fatty acid catabolism and ketogenesis. Hepatocyte-specific deletion of PPARα impaired the metabolic response to sepsis and was sufficient to decrease survival upon bacterial infection. Hepatic PPARA expression was lower in critically ill patients and correlated positively with expression of lipid metabolism genes, but not with systemic inflammatory markers. During sepsis, Ppara-deficiency in hepatocytes is deleterious as it impairs the adaptive metabolic shift from glucose to FA utilization. Metabolic control by PPARα in hepatocytes plays a key role in the host defense against infection. As the main cause of death in critically ill patients, sepsis remains a major health issue lacking efficacious therapies. While current clinical literature suggests an important role for inflammation, metabolic aspects of sepsis have mostly been overlooked. Here, we show that mice with an impaired metabolic response, due to deficiency of the nuclear receptor PPARα in the liver, exhibit enhanced mortality upon bacterial infection despite a similar inflammatory response, suggesting that metabolic interventions may be a viable strategy for improving sepsis outcomes

Association between liver X receptor α gene polymorphisms and risk of metabolic syndrome in French populations

CONTEXT: The metabolic syndrome is a complex and multifactorial disorder often associated with type 2 diabetes mellitus and cardiovascular diseases. The liver X receptor alpha (NR1H3) plays numerous roles in metabolic pathways involved in metabolic syndrome. OBJECTIVE: In the search for susceptibility genes to metabolic syndrome, we hypothesized that common genetic variation in NR1H3 gene influences metabolic syndrome susceptibility. DESIGN: Two large French population-based studies (n=1130 and 1160) including overall 664 individuals with and 1626 individuals without metabolic syndrome were genotyped for three polymorphisms (rs12221497, rs11039155 and rs2279239) of NR1H3. RESULTS: We found that the -6A allele of rs11039155 was consistently associated with a 30% reduction in risk of metabolic syndrome in the two independent population samples (adjusted OR (95% CI)=0.68 (0.53-0.86), P=0.001 for the combined sample). Moreover, it was associated with an increase in plasma HDL-cholesterol concentrations (P=0.02 for the combined sample). Neither rs12221497 nor rs11039155, both polymorphisms located in the 5' region of NR1H3, had significant influence on NR1H3 and ATP-binding cassette transporter A1 (ABCA1) gene expression in primary human macrophages. CONCLUSIONS: These results suggest that NR1H3 plays an important role in the HDL-cholesterol metabolism and in the genetic susceptibility to metabolic syndrom