Jinrui Cui

Genome-Wide Association Study Identifies Variants Associated With Histologic Features of Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS Little data are available from genome-wide association studies (GWASs) of liver histology in patients with nonalcoholic fatty liver disease (NAFLD). We conducted a pilot GWAS in patients with NAFLD, characterized by histology, who were enrolled in the NASH Clinical Research Network (CRN) Database Study. METHODS We studied clinical, laboratory, and histologic data from 236 non-Hispanic white women with NAFLD. We analyzed 324,623 single nucleotide polymorphisms (SNPs) from the 22 autosomal chromosomes. Multivariate-adjusted logistic regression analyses were conducted for binary outcomes, and linear regression analysis was applied for quantitative traits. A P value < 1 × 10(-6) was considered to be significant. RESULTS In multivariate models adjusted for age, body mass index, diabetes, waist/hip ratios, and levels of glycated hemoglobin, the NAFLD activity score was associated with the SNP rs2645424 on chromosome 8 in farnesyl diphosphate farnesyl transferase 1 (FDFT1) (P = 6.8 × 10(-7)). The degree of fibrosis was associated with the SNP rs343062 on chromosome 7 (P = 2.7 × 10(-8)). SNPs associated with lobular inflammation included SNP rs1227756 on chromosome 10 in COL13A1 (P = 2.0 × 10(-7)), rs6591182 on chromosome 11 (P = 8.6 × 10(-7)), and rs887304 on chromosome 12 in EFCAB4B (P = 7.7 × 10(-7)). SNPs associated with serum levels of alanine aminotransferase included rs2499604 on chromosome 1 (P = 2.2 × 10(-6)), rs6487679 on chromosome 12 in PZP (P = 1.3 × 10(-6)), rs1421201 on chromosome 18 (P = 1.0 × 10(-5)), and rs2710833 on chromosome 4 (P = 6.3 × 10(-7)). No significant associations were observed between genotypes and steatosis, ballooning degeneration, portal inflammation, or other features of NAFLD. CONCLUSIONS A GWAS significantly associated genetic variants with features of hepatic histology in patients with NAFLD. These findings should be validated in larger and more diverse cohorts.

CRTC3 links catecholamine signalling to energy balance

The adipose-derived hormone leptin maintains energy balance in part through central nervous system-mediated increases in sympathetic outflow that enhance fat burning. Triggering of β-adrenergic receptors in adipocytes stimulates energy expenditure by cyclic AMP (cAMP)-dependent increases in lipolysis and fatty-acid oxidation. Although the mechanism is unclear, catecholamine signalling is thought to be disrupted in obesity, leading to the development of insulin resistance. Here we show that the cAMP response element binding (CREB) coactivator Crtc3 promotes obesity by attenuating β-adrenergic receptor signalling in adipose tissue. Crtc3 was activated in response to catecholamine signals, when it reduced adenyl cyclase activity by upregulating the expression of Rgs2, a GTPase-activating protein that also inhibits adenyl cyclase activity. As a common human CRTC3 variant with increased transcriptional activity is associated with adiposity in two distinct Mexican-American cohorts, these results suggest that adipocyte CRTC3 may play a role in the development of obesity in humans.

SORCS1: A Novel Human Type 2 Diabetes Susceptibility Gene Suggested by the Mouse

OBJECTIVE—A small number of susceptibility genes for human type 2 diabetes have been identified by candidate gene analysis or positional cloning. Genes found to influence diabetes or related traits in mice are likely to be susceptibility genes in humans. SorCS1 is the gene identified as responsible for the mouse chromosome 19 T2dm2 quantitative trait locus for fasting insulin levels, acting via impaired insulin secretion and increased islet disruption in obese females. Genes that impair compensatory insulin secretion in response to obesity-induced insulin resistance may be particularly relevant to human diabetes. Thus, we sought to determine whether variation in the human SORCS1 gene was associated with diabetes-related traits. RESEARCH DESIGN AND METHODS—We assessed the contribution of variation in SORCS1 to human insulin–related traits in two distinct Mexican-American cohorts. One cohort (the Mexican-American Coronary Artery Disease [MACAD] cohort) consisted of nondiabetic individuals, allowing assessment of genetic association with subclinical intermediate insulin-related traits; the second cohort (the San Antonio Family Diabetes Study [SAFADS]) contained individuals with diabetes, allowing association analyses with overt disease. RESULTS—We first found association of SORCS1 single nucleotide polymorphisms and haplotypes with fasting insulin levels and insulin secretion in the MACAD cohort. Similar to our results in the mice, the genetic association was strongest in overweight women. We then observed association with diabetes risk and age at diagnosis in women of the SAFADS cohort. CONCLUSIONS—Identification of SORCS1 as a novel gene affecting insulin secretion and diabetes risk is likely to provide important insight into the biology of obesity-induced type 2 diabetes.

Combined Influence of LDLR and HMGCR Sequence Variation on Lipid-Lowering Response to Simvastatin

Objective—Although statins are efficacious for lowering low-density lipoprotein cholesterol, there is wide interindividual variation in response. We tested the extent to which combined effects of common alleles of LDLR and HMGCR can contribute to this variability. Methods and Results—Haplotypes in the LDLR 3′-untranslated region (3-UTR) were tested for association with lipid-lowering response to simvastatin treatment in the Cholesterol and Pharmacogenetics trial (335 blacks and 609 whites). LDLR haplotype 5 (LDLR L5) was associated with smaller simvastatin-induced reductions in low-density lipoprotein cholesterol, total cholesterol, non-high-density lipoprotein cholesterol, and apolipoprotein B (P=0.0002 to 0.03) in blacks but not whites. The combined presence of LDLR L5 and previously described HMGCR haplotypes in blacks was associated with significantly attenuated apolipoprotein B reduction (−22.4±1.5%, N=89) compared with both noncarriers (−30.6±1.5%, N=78, P=0.0001) and carriers of either individual haplotype (−28.2±1.1%, N=158, P=0.001). We observed similar differences when measuring simvastatin-mediated induction of low-density lipoprotein receptor surface expression using lymphoblast cell lines (P=0.03). Conclusion—We have identified a common LDLR 3-UTR haplotype that is associated with attenuated lipid-lowering response to simvastatin treatment. Response was further reduced in individuals with both LDLR and previously described HMGCR haplotypes. Previously identified racial differences in statin efficacy were partially explained by the greater prevalence of these combined haplotypes in blacks.

Hypertension genes are genetic markers for insulin sensitivity and resistance.

Insulin resistance is a determinant of blood pressure variation and risk factor for hypertension. Because insulin resistance and blood pressure cosegregate in Mexican American families, we thus investigated the association between variations in 9 previously reported hypertension genes (ACE, AGT, AGTRI, ADDI, NPPA, ADDRB2, SCNN1A, GNB3, and NOS3) and insulin resistance. Families were ascertained via a coronary artery disease proband in the Mexican American Coronary Artery Disease Project. Individuals from 100 Mexican American families (n=656) were genotyped for 14 polymorphisms in the 9 genes and all adult offspring and offspring spouses were phenotyped for insulin sensitivity by hyperinsulinemic euglycemic clamp (n=449). AGT M235T and NOS3 A(−922)G and E298D polymorphisms were significantly associated with insulin sensitivity (P=0.018, 0.036, 0.039) but were not significant after adjusting for body mass index. ADD1 G460W was associated with insulin sensitivity only after adjusting for body mass index. The NPPA T2238C and SCNN1A A663T were associated with decreased fasting insulin levels after adjusting for body mass index (P=0.015 and 0.028). In conclusion, AGT, NOS3, NPPA, ADRB2, ADD1, and SCNN1A may well be genetic markers for insulin resistance, and adiposity was a potential modifier for only some gene/trait combinations. Our data support the hypothesis that genes in the blood pressure pathway may play a role in insulin resistance in Mexican Americans.

Genome-Wide Linkage of Plasma Adiponectin Reveals a Major Locus on Chromosome 3q Distinct From the Adiponectin Structural Gene The IRAS Family Study

Adiponectin (APM1) is an adipocyte-derived peptide that contributes to glucose, lipid, and energy homeostasis. We assessed the genetic basis of plasma adiponectin in Hispanic-American and African-American families enrolled through the Insulin Resistance Atherosclerosis Study Family Study. A 10-cM genome scan was performed in two batches: an original set (set 1) consisting of 66 families (45 Hispanic American and 21 African American) and a replication set (set 2) consisting of 66 families (45 Hispanic American and 21 African American). Adiponectin levels were measured by radioimmunoassay in 1,727 individuals from 131 of 132 families. Linkage analysis was carried out in Hispanic Americans and African Americans separately in set 1, set 2, and the pooled set (set 1 plus set 2), with and without diabetic subjects. A major gene was mapped to 3q27 with a logarithm of odds (LOD) score of 8.21 in the Hispanic-American sample. Ninety-six unrelated individuals were screened for polymorphisms in the APM1 gene, and 18 single nucleotide polyporphisms (SNPs) were genotyped in the Hispanic-American sample. Plasma adiponectin level was modestly associated with two SNPs and their accompaning haplotypes. Incorporating each or both SNPs in the linkage analysis, however, did not significantly reduce the LOD score. Therefore, a quantitative trait locus at 3q27, likely distinct from the APM1 gene, contributes to the variation of plasma adiponectin levels in the Hispanic-American population.

Body Adiposity Index versus Body Mass Index and Other Anthropometric Traits as Correlates of Cardiometabolic Risk Factors

Objective The worldwide prevalence of obesity mandates a widely accessible tool to categorize adiposity that can best predict associated health risks. The body adiposity index (BAI) was designed as a single equation to predict body adiposity in pooled analysis of both genders. We compared body adiposity index (BAI), body mass index (BMI), and other anthropometric measures, including percent body fat (PBF), in their correlations with cardiometabolic risk factors. We also compared BAI with BMI to determine which index is a better predictor of PBF. Methods The cohort consisted of 698 Mexican Americans. We calculated correlations of BAI, BMI, and other anthropometric measurements (PBF measured by dual energy X-ray absorptiometry, waist and hip circumference, height, weight) with glucose homeostasis indices (including insulin sensitivity and insulin clearance from euglycemic clamp), lipid parameters, cardiovascular traits (including carotid intima-media thickness), and biomarkers (C-reactive protein, plasminogen activator inhibitor-1 and adiponectin). Correlations between each anthropometric measure and cardiometabolic trait were compared in both sex-pooled and sex-stratified groups. Results BMI was associated with all but two measured traits (carotid intima-media thickness and fasting glucose in men), while BAI lacked association with several variables. BAI did not outperform BMI in its associations with any cardiometabolic trait. BAI was correlated more strongly than BMI with PBF in sex-pooled analyses (r = 0.78 versus r = 0.51), but not in sex-stratified analyses (men, r = 0.63 versus r = 0.79; women, r = 0.69 versus r = 0.77). Additionally, PBF showed fewer correlations with cardiometabolic risk factors than BMI. Weight was more strongly correlated than hip with many of the cardiometabolic risk factors examined. Conclusions BAI is inferior to the widely used BMI as a correlate of the cardiometabolic risk factors studied. Additionally, BMI’s relationship with total adiposity may not be the sole determinate of its association with cardiometabolic risk.

Fasting insulin reflects heterogeneous physiological processes: role of insulin clearance

Several processes contribute to variation in fasting insulin concentration, including fasting glucose, insulin resistance, insulin secretion, and insulin clearance. Our goal was to determine the relative contribution of each of these insulin-related traits, plus anthropometric parameters, to fasting insulin among 470 Mexican Americans. The euglycemic hyperinsulinemic clamp yielded insulin sensitivity (M value) and metabolic clearance rate of insulin (MCRI). Acute insulin secretion was estimated by the insulinogenic index (IGI30) from the oral glucose tolerance test. Regression (univariate) and generalized estimating equations (multivariate) were used to describe the relationship of insulin-related traits to fasting insulin. Univarate analyses were used to select which traits to include in the multivariate model. In multivariate analysis, MCRI, M, BMI, waist circumference, and fasting glucose were independently associated with fasting insulin. Decreasing M and MCRI were associated with increasing fasting insulin, whereas increasing BMI, waist circumference, and fasting glucose were associated with increasing fasting insulin. Standardized coefficients allowed determination of the relative strength of each traits association with fasting insulin in the entire cohort (strongest to weakest): MCRI (-0.35, P < 0.0001), M (-0.24, P < 0.0001), BMI (0.20, P = 0.0011), waist circumference (0.16, P = 0.021), and fasting glucose (0.11, P = 0.014). Fasting insulin is a complex phenotype influenced by several independent processes, each of which might have its own environmental and genetic determinants. One of the most associated traits was insulin clearance, which has implications for studies that have used fasting insulin as a surrogate for insulin resistance.

Variants of the Caveolin-1 Gene: A Translational Investigation Linking Insulin Resistance and Hypertension

CONTEXT The co-occurrence of insulin resistance (IR) and hypertension is a heritable condition leading to cardiovascular complications. Caveolin-1 (CAV1), a gene previously associated with metabolic dysfunction in animal and cellular models, may be a marker for these conditions in humans. OBJECTIVE The objective of the study was to examine the relationship between CAV1 variants and IR in two hypertensive cohorts and to corroborate the findings in a CAV1 knockout mouse. DESIGN, SETTING, AND PARTICIPANTS A candidate gene association study was conducted in two hypertensive cohorts: 1) Caucasian and 2) Hispanic. Multivariate associations between individual variants and insulin-resistant phenotypes were analyzed, accounting for age, gender, body mass index, and sibling relatedness. Intraperitoneal glucose tolerance tests were conducted in wild-type and CAV1 knockout mice. RESULTS In the Caucasian hypertensive cohort, minor allele carriers of two CAV1 single-nucleotide polymorphisms (rs926198, rs3807989) had significantly higher fasting insulin levels (P = 0.005, P = 0.007), increased homeostatic assessment model for insulin resistance (HOMA-IR) (P =0.005, P = 0.008), and decreased M value during hyperinsulinemic, euglycemic clamp procedure (P = 0.004, P = 0.05) than major allele homozygotes. Findings were replicated in the Hispanic hypertensive cohort cohort for fasting insulin levels (P = 0.005, P = 0.02) and HOMA-IR (P = 0.008 and P = 0.02). Meta-analysis demonstrated significant associations of both single-nucleotide polymorphisms with fasting insulin levels (P = 0.00008, P = 0.0004) and HOMA-IR (P = 0.0001, P = 0.0004). As compared with wild type, CAV1 knockout mice displayed higher blood pressure levels and higher fasting glucose, insulin, and HOMA-IR levels and an exaggerated glycemic response to a glucose challenge. CONCLUSION Variations in the CAV1 gene are associated with IR and hypertension. CAV1 gene polymorphisms may be a biomarker for IR and hypertension, enabling earlier detection and improved treatment strategies.

Genetic Variants Associated With Quantitative Glucose Homeostasis Traits Translate to Type 2 Diabetes in Mexican Americans: The GUARDIAN (Genetics Underlying Diabetes in Hispanics) Consortium

Insulin sensitivity, insulin secretion, insulin clearance, and glucose effectiveness exhibit strong genetic components, although few studies have examined their genetic architecture or influence on type 2 diabetes (T2D) risk. We hypothesized that loci affecting variation in these quantitative traits influence T2D. We completed a multicohort genome-wide association study to search for loci influencing T2D-related quantitative traits in 4,176 Mexican Americans. Quantitative traits were measured by the frequently sampled intravenous glucose tolerance test (four cohorts) or euglycemic clamp (three cohorts), and random-effects models were used to test the association between loci and quantitative traits, adjusting for age, sex, and admixture proportions (Discovery). Analysis revealed a significant (P < 5.00 × 10−8) association at 11q14.3 (MTNR1B) with acute insulin response. Loci with P < 0.0001 among the quantitative traits were examined for translation to T2D risk in 6,463 T2D case and 9,232 control subjects of Mexican ancestry (Translation). Nonparametric meta-analysis of the Discovery and Translation cohorts identified significant associations at 6p24 (SLC35B3/TFAP2A) with glucose effectiveness/T2D, 11p15 (KCNQ1) with disposition index/T2D, and 6p22 (CDKAL1) and 11q14 (MTNR1B) with acute insulin response/T2D. These results suggest that T2D and insulin secretion and sensitivity have both shared and distinct genetic factors, potentially delineating genomic components of these quantitative traits that drive the risk for T2D.