Analysis of the contribution to type 2 diabetes susceptibility of sequence variation in the gene encoding stearoyl-CoA desaturase, a key regulator of lipid and carbohydrate metabolism

Antidiabetic Effect of Rehmanniae Radix Based on Regulation of TRPV1 and SCD1

Purpose: This study aimed to disclose the antidiabetic mechanisms of Rehmanniae Radix (RR).

Methods: The antidiabetic effect of RR was studied in Streptozocin (STZ)–induced diabetes mellitus (DM) rats and HepG2 cells with insulin resistance (IR). Antidiabetic targets and signaling pathways of RR were confirmed by the network pharmacology and transcriptome analysis as well as HK2 cells induced by high glucose (HG).

Results: After the DM rats were administrated RR extract (RRE) for 4 weeks, their body weight was 10.70 ± 2.00% higher than those in the model group, and the fasting blood glucose (FBG), AUC of the oral glucose tolerance test, and insulin sensitivity test values were 73.23 ± 3.33%, 12.31 ± 2.29%, and 13.61 ± 5.60% lower in the RRE group, respectively. When compared with the model group, an increase of 45.76 ± 3.03% in the glucose uptake of HepG2 cells with IR was seen in the RRE group. The drug (RR)–components–disease (DM)–targets network with 18 components and 58 targets was established. 331 differentially expressed genes (DEGs) were identified. TRPV1 and SCD1 were important DEGs by the intersectional analysis of network pharmacology and renal transcriptome. The TRPV1 overexpression significantly inhibited apoptosis and oxidative stress of the HK2 cells induced by HG, while SCD1 overexpression induced apoptosis and oxidative stress of the HK2 cells induced by low and high glucose. When compared to the HG group, the mRNA and protein expressions of TRPV1 in the presence of RRE (100 μg/ml) increased by 3.94 ± 0.08 and 2.83 ± 0.40 folds, respectively.

Conclusion: In summary, RR displayed an inspiring antidiabetic effect by reducing FBG and IR, upregulating the mRNA and protein expressions of TRPV1, and downregulating mRNA expression of SCD1. Induction of TRPV1 and inhibition of SCD1 by RR was possibly one of its antidiabetic mechanisms.

Positive association of SCD1 genetic variation and metabolic syndrome in dialysis patients in China

Aim: Metabolic syndrome (MetS) diagnosed in the dialysis patients is increasingly reported which worsens the prognosis of the renal diseases. The relationship of SCD1 with MetS is largely unknown. The purpose of this study was to investigate the relationship between SCD1 polymorphism and MetS in dialysis patients. Methods: A cross-sectional study was conducted on 323 Chinese dialysis patients, and the correlation between the seven SNPs of SCD1 gene (rs10883465, rs2060792, rs1502593, rs522951, rs3071, rs3978768 and rs1393492) and MetS was analyzed. Results: One tag-SNP (rs1393492) has significantly associated with the prevalence of MetS. Dialysis patients with rs1393492 AA genotype of SCD1 are more prone to MetS (p = 0.021). Conclusion: This study shows that the rs1393492 variations of SCD1 gene are related with the development of MetS in Chinese dialysis patients.

SCD rs41290540 single-nucleotide polymorphism modifies miR-498 binding and is associated with a decreased risk of coronary artery disease

Background

Atherosclerosis is the primary cause of coronary artery disease (CAD), and stearoyl‐CoA desaturase (SCD) is associated with atherosclerosis. However, the associations between variants of SCD and CAD have not yet been decided.

Methods

This study analyzed SCD rs41290540 single‐nucleotide polymorphism (SNP) in the 3′‐untranslated region for an association with a risk of CAD among the Chinese Han population. CAD patients and controls were genotyped for SNP rs41290540 in SCD by SNaPshot. The binding affinity of miR‐498 to rs41290540 was determined by a luciferase assay, and SCD expression was assessed using Western blot.

Results

A total of 969 CAD patients and 1,095 control subjects were involved in this study. The SCD rs41290540CC genotype is associated with a decreased risk of CAD compared with the AA genotype. Furthermore, the CC genotype is associated with lower serum total cholesterol (TC). Western blot analysis demonstrated that miR‐498 suppressed the expression of SCD. A luciferase assay confirmed that rs41290540 A>C variation in the SCD 3′UTR inhibits miR‐498 binding.

Conclusion

This study demonstrates that the SCD rs41290540 may be associated with a decreased risk of CAD, lower serum TC, and decreased miR‐498 binding.

Key genes and co-expression network analysis in the livers of type 2 diabetes patients

AIMS/INTRODUCTION

The incidence of type 2 diabetes is increasing worldwide. Hepatic insulin resistance and liver lipid accumulation contributes to type 2 diabetes development. The aim of the present study was to investigate the key gene pathways and co-expression networks in the livers of type 2 diabetes patients.

MATERIALS AND METHODS

Dataset GSE15653 containing nine healthy individuals and nine type 2 diabetes patients was downloaded from the National Center for Biotechnology Information Gene Expression Omnibus database. Differentially expressed genes were obtained from the livers of type 2 diabetes patients, annotated pathway enrichment and protein-protein interaction network analysis. Next, functional modules and transcription factor networks were constructed. Gene co-expression networks were analyzed by weighted correlation network analysis to identify key modules related to clinical traits, and the candidate key genes were validated in hepatic insulin resistance models in vitro.

RESULTS

A total of 778 differentially expressed genes were filtered in the livers of type 2 diabetes patients, pathway enrichment analysis identified ke y pathways, such as the mitogen-activated protein kinase signaling pathway, Hippo signaling pathway and hypoxia-inducible factor-1 signaling pathway, that were associated with type 2 diabetes. Several transcription factors of three functional modules identified from protein-protein interaction networks are likely to be implicated in type 2 diabetes. Furthermore, weighted correlation network analysis identified five modules that were shown to be highly correlated with type 2 diabetes and other clinical traits. Functional annotation showed that these modules were mainly enriched in pathways such as metabolic pathways, phosphoinositide 3-kinase-protein kinase B signaling pathway and natural killer cell-mediated cytotoxicity. UBE2M and GPER were upregulated in L02 and HepG2 models, whereas P2RY11 only upregulated in L02 model, and UBE2N only downregulated in HepG2 model at a significant level.

CONCLUSIONS

These results would offer new insights into hepatic insulin resistance, type 2 diabetes pathogenesis, development and drug discovery.

Polymorphisms in stearoyl coa desaturase and sterol regulatory element binding protein interact with N-3 polyunsaturated fatty acid intake to modify associations with anthropometric variables and metabolic phenotypes in Yup'ik people

SCOPE

n-3 polyunsaturated fatty acid (n-3 PUFA) intake is associated with protection from obesity; however, the mechanisms of protection remain poorly characterized. The stearoyl CoA desaturase (SCD), insulin-sensitive glucose transporter (SLC2A4), and sterol regulatory element binding protein (SREBF1) genes are transcriptionally regulated by n-3 PUFA intake and harbor polymorphisms associated with obesity. The present study investigated how consumption of n-3 PUFA modifies associations between SCD, SLC2A4, and SREBF1 polymorphisms and anthropometric variables and metabolic phenotypes.

MATERIALS AND METHODS

Anthropometric variables and metabolic phenotypes were measured in a cross-sectional sample of Yup'ik individuals (n = 1135) and 33 polymorphisms were tested for main effects and interactions using linear models that account for familial correlations. n-3 PUFA intake was estimated using red blood cell nitrogen stable isotope ratios. SCD polymorphisms were associated with ApoA1 concentration and n-3 PUFA interactions with SCD polymorphisms were associated with reduced fasting cholesterol levels and waist-to-hip ratio. SLC2A4 polymorphisms were associated with hip circumference, high-density lipoprotein and ApoA1 concentrations. SREBF1 polymorphisms were associated with low-density lipoprotein and HOMA-IR and n-3 PUFA interactions were associated with reduced fasting insulin and HOMA-IR levels.

CONCLUSION

The results suggest that an individual's genotype may interact with dietary n-3 PUFAs in ways that are associated with protection from obesity-related diseases in Yup'ik people.

Overexpression of stearoyl-CoA desaturase 1 in bone marrow mesenchymal stem cells enhance the expression of induced endothelial cells

Background

Bone marrow mesenchymal stem cells (BM-MSCs) are capable of differentiating into endothelial cells in vitro and acquire major characteristics of mature endothelial-like expression of vWF and CD31. SFAs and lipid oxidation products have been linked with postprandial endothelial dysfunction. Consumption of SFAs impairs arterial endothelial function, while a Mediterranean-type MUFA-diet has a beneficial effect on endothelial function by producing a decrease in levels of vWF, TFPI and PAI-1. Stearoyl-CoA desaturase 1 (SCD1), which converts SFA to MUFA, is involved in the cellular biosynthesis of MUFAs from SFA substrates. High expression of SCD1 is corresponded with low rates of fatty acid oxidation, therefore it might reduce inflammatory responses and be beneficial for the growth of induced endothelial cells. Overexpression of SCD1 in BM-MSCs might increase the growth of induced endothelial cells. The goal of this research is to study the relationship between overexpression of SCD1 and the expression of induced endothelial cells in BM-MSCs in vitro.

Methods

The gene SCD1 was integrated into a lentiviral vector, and then 293 T cells were transfected by the connected product to produce a packaged virus. BM-MSCs were infected by the packaged virus. Cell culture and endothelial induction were performed. Fluorescent quantitative PCR of CD31, vWF and VE-cad was performed after 1 week and 2 weeks to test the growth of induced endothelial cells.

Results

The mRNA amount of CD31, vWF and VE-cad of the SCD1 overexpressed group was statistically higher than that of the empty vector (EV) group and that of the normal group after 1 week and 2 weeks, respectively (p < 0.05). Immunocytochemical staining of CD31 or vWF was detected by visualizing red color.

Conclusions

This study suggested that overexpression of SCD1 in BM-MSCs could increase the expression of induced endothelial cells in vitro.

Unsaturated fatty acids, desaturases, and human health

With the increasing concern for health and nutrition, dietary fat has attracted considerable attention. The composition of fatty acids in a diet is important since they are associated with major diseases, such as cancers, diabetes, and cardiovascular disease. The biosynthesis of unsaturated fatty acids (UFA) requires the expression of dietary fat-associated genes, such as SCD, FADS1, FADS2, and FADS3, which encode a variety of desaturases, to catalyze the addition of a double bond in a fatty acid chain. Recent studies using new molecular techniques and genomics, as well as clinical trials have shown that these genes and UFA are closely related to physiological conditions and chronic diseases; it was found that the existence of alternative transcripts of the desaturase genes and desaturase isoforms might affect human health and lipid metabolism in different ways. In this review, we provide an overview of UFA and desaturases associated with human health and nutrition. Moreover, recent findings of UFA, desaturases, and their associated genes in human systems are discussed. Consequently, this review may help elucidate the complicated physiology of UFA in human health and diseases.

Polymorphisms in the SCD1 gene are associated with indices of stearoyl CoA desaturase activity and obesity: a prospective study

SCOPE

The serum fatty acid (FA) composition is influenced by dietary fat and the endogenous production of FAs. Stearoyl CoA desaturase 1 (SCD1) is the rate-limiting enzyme catalyzing the synthesis of MUFAs from saturated FAs. Variations in SCD1 activity have been associated with obesity, diabetes, or inflammation. We evaluated the associations between genetic variation of the SCD1 gene, SCD1 activity, intake of oil, and obesity in a population-based prospective study in southern Spain.

METHODS AND RESULTS

We collected phenotypic, metabolic, nutritional, and genetic information. The type of dietary fat was assessed from samples of cooking oil taken from the participants' kitchens and analyzed by GC. A total of nine single nucleotide polymorphisms (SNPs) of the SCD1 gene were analyzed by SNPlex technology. We found a significant association between SCD1 genetic variation and enzyme activity in four of nine polymorphisms studied. An interaction between rs10883463 and olive oil intake on the [18:1/18:0] desaturase index was found (p = 0.009). We also showed that genetic variations in the SCD1 gene were associated with obesity.

CONCLUSION

Our results show a relationship between genetic variation of the SCD1 gene, enzyme activity, and the risk of obesity, an association that is not independent of the type of oil consumed.

Heterogeneity of the Stearoyl-CoA desaturase-1 (SCD1) gene and metabolic risk factors in the EPIC-Potsdam study

BACKGROUND

Stearoyl-CoA desaturase-1 (SCD1) is an enzyme involved in lipid metabolism. In mice and humans its activity has been associated with traits of the metabolic syndrome, but also with the prevention of saturated fatty acids accumulation and subsequent inflammation, whereas for liver fat content inconsistent results have been reported. Thus, variants of the gene encoding SCD1 (SCD1) could potentially modify metabolic risk factors, but few human studies have addressed this question.

METHODS

In a sample of 2157 middle-aged men and women randomly drawn from the Potsdam cohort of the European Prospective Investigation into Cancer and Nutrition, we investigated the impact of 7 SCD1 tagging-single nucleotide polymorphisms (rs1502593, rs522951, rs11190480, rs3071, rs3793767, rs10883463 and rs508384) and 5 inferred haplotypes with frequency >5% describing 90.9% of the genotype combinations in our population, on triglycerides, body mass index (BMI), waist circumference (WC), glycated haemoglobin (HbA1c), high-sensitivity C-reactive protein (hs-CRP), gamma-glutamyltransferase (GGT), alanine aminotransferase (ALT) and fetuin-A.

RESULTS

No significant associations between any of the SNPs or haplotypes and BMI, WC, fetuin-A and hs-CRP were observed. Associations of rs10883463 with triglycerides, GGT and HbA1c as well as of rs11190480 with ALT activity, were weak and became non-significant after multiple-testing correction. Also associations of the haplotype harbouring the minor allele of rs1502593 with HbA1c levels, the haplotype harbouring the minor alleles of rs11190480 and rs508384 with activity of ALT, and the haplotype harbouring the minor alleles of rs522951, rs10883463 and rs508384 with triglyceride and HbA1C levels and GGT activities did not withstand multiple-testing correction.

CONCLUSION

These findings suggest that there are no associations between common variants of SCD1 or its inferred haplotypes and the investigated metabolic risk factors. However, given the results from animal models, heterogeneity of human SCD1 warrants further investigation, in particular with regard to rare variants.

Enzymatic activity and genetic variation in SCD1 modulate the relationship between fatty acids and inflammation

Fatty acids (FA) represent a diverse class of molecules known to regulate inflammatory pathways. Therefore enzymes that regulate FA metabolism are attractive candidates to better understand the relationship between FA and inflammation. Stearoyl-CoA desaturase 1 (SCD1) is rate limiting for the conversion of saturated FA (SFA) to monounsaturated FA (MUFA). Evidence suggests that SCD1 activity may be positively associated with inflammation. Moreover, genetic variation in SCD1 may alter enzyme activity; however, it is unknown whether this affects inflammatory status. The goal of this study was to examine the relationships between plasma FA, SCD1 activity, and SCD1 polymorphisms with C-reactive protein (CRP) levels in young adults. SFA, MUFA, and CRP were measured in fasted plasma samples from European (n=279, 198 female and 81 male) and Asian (n=249, 179 female and 70 male) subjects, 20-29 years old. Circulating levels of palmitic (16:0), palmitoleic (16:1), stearic (18:0), and oleic acids (18:1) were measured by gas chromatography and SCD1 activity was estimated by the ratio of product to precursor (16:1/16:0; 18:1/18:0). Positive associations were identified between CRP levels and 16:0 (p<2.0×10(-4)), 16:1 (p<0.05), and the SCD1 index (18:1/18:0; p<6.0×10(-3)) in European and Asian females, while 18:0 was inversely associated with CRP (p<2.0×10(-4)) in both groups. Ten single nucleotide polymorphisms (SNPs) in SCD1 were genotyped in all subjects. One SNP (rs2060792) was associated (p<0.05) with 16:0 and 18:0 levels in females of European descent. This same SNP was also associated with CRP levels in both groups of females (p<0.05). Overall, SCD1 activity and genetic variation have an important role in modulating the relationship between FA and inflammation in young adults.

Genetic variation in stearoyl-CoA desaturase 1 is associated with metabolic syndrome prevalence in Costa Rican adults

Stearoyl-CoA desaturase 1 (SCD1) activity, a key regulator of lipid metabolism, may be associated with the development of metabolic syndrome (MetS). We examined the association of genetic variation in the SCD1 gene with the occurrence of MetS and its five components in a population of Costa Rican adults (n = 2152; mean age, 58 y; range, 18-86 y). Associations of tag single nucleotide polymorphisms (tagSNP) of the SCD1 gene with prevalence of MetS and its five components were analyzed by use of log-Poisson models with robust variance estimates and linear regression models, respectively. The likelihood ratio was used to test potential gene-fatty acid interactive effects with adipose tissue α-linolenic acid. One tagSNP (rs1502593) was significantly associated with an increased prevalence of MetS in the total study sample. Compared with the common homozygous CC genotype, the CT and TT genotypes for rs1502593 were associated with higher prevalence ratios (PR) of MetS for CT vs. CC: [PR = 1.22 (95% CI = 1.03, 1.44)] and for TT vs. CC [PR = 1.24 (95% CI = 1.01, 1.52)]. Among women, we observed borderline positive associations between systolic blood pressure and fasting blood sugar levels and rs1502593 (P = 0.05 and 0.06). Compared to the common haplotype (frequency ≥ 5%) with no minor alleles of SCD1 tagSNP, the other two observed common haplotypes carrying the rs1502593 minor allele were significantly associated with elevated prevalence of MetS. No gene-fatty acid interactive effects were observed. Our results suggest that genetic variation in the SCD1 gene may play a role in the development of MetS.

Erythrocyte membrane phospholipid fatty acids, desaturase activity, and dietary fatty acids in relation to risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study

BACKGROUND

The long-term role of fatty acids (FAs) in the cause of diabetes remains largely unclear.

OBJECTIVE

We aimed to investigate erythrocyte membrane FAs, desaturase activity, and dietary FAs in relation to the incidence of type 2 diabetes.

DESIGN

We applied a nested case-cohort design (n = 2724, including 673 incident diabetes cases) within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study, which involves 27,548 middle-aged subjects. Thirty erythrocyte membrane FAs (percentage of total FAs) and FA intake (percentage of total fat) were measured at baseline, and physician-confirmed incident diabetes was assessed during a mean follow-up of 7.0 y. We evaluated Δ⁵ desaturase (D5D) and Δ⁶ desaturase (D6D) activity by using FA product-to-precursor ratios (traditional approach) and by investigating variants in FADS1 and FADS2 genes that encode these desaturases (Mendelian randomization approach).

RESULTS

As a main finding, erythrocyte 16:1n-7 and 18:3n-6 and FA ratios, which reflect stearoyl coenzyme A desaturase (SCD) and D6D activity, were directly related to diabetes risk in multivariable-adjusted models [relative risks (95% CIs) comparing extreme quintiles: 16:1n-7, 2.11 (1.46, 3.05); 18:3n-6, 2.00 (1.38, 2.88); SCD, 2.61 (1.75, 3.89); and D6D, 2.46 (1.67, 3.63)], whereas the FA ratio that reflects D5D activity was inversely associated with risk [0.46 (0.31, 0.70)]. The Mendelian randomization approach corroborated the direct relation for D6D activity and tended to support the inverse relation for D5D activity. Proportions of dietary FAs showed only modest to low correlations with erythrocyte FAs and were not significantly associated with risk.

CONCLUSION

The FA profile of erythrocyte membrane phospholipids and activity of desaturase enzymes are strongly linked to the incidence of type 2 diabetes.

Genetic variation in lipid desaturases and its impact on the development of human disease

Perturbations in lipid metabolism characterize many of the chronic diseases currently plaguing our society, such as obesity, diabetes, and cardiovascular disease. Thus interventions that target plasma lipid levels remain a primary goal to manage these diseases. The determinants of plasma lipid levels are multi-factorial, consisting of both genetic and lifestyle components. Recent evidence indicates that fatty acid desaturases have an important role in defining plasma and tissue lipid profiles. This review will highlight the current state-of-knowledge regarding three desaturases (Scd-1, Fads1 and Fads2) and their potential roles in disease onset and development. Although research in rodent models has provided invaluable insight into the regulation and functions of these desaturases, the extent to which murine research can be translated to humans remains unclear. Evidence emerging from human-based research demonstrates that genetic variation in human desaturase genes affects enzyme activity and, consequently, disease risk factors. Moreover, this genetic variation may have a trans-generational effect via breastfeeding. Therefore inter-individual variation in desaturase function is attributed to both genetic and lifestyle components. As such, population-based research regarding the role of desaturases on disease risk is challenged by this complex gene-lifestyle paradigm. Unravelling the contribution of each component is paramount for understanding the inter-individual variation that exists in plasma lipid profiles, and will provide crucial information to develop personalized strategies to improve health management.

Significant associations of stearoyl-CoA desaturase (SCD1) gene with fat deposition and composition in skeletal muscle

Gene expression studies in humans and animals have shown that elevated stearoyl-CoA desaturase (SCD1) activity is associated with increased fat accumulation and monounsaturation of saturated fatty acids in skeletal muscle. However, results of the two reported association studies in humans are inconsistent. In the present study, we annotated the bovine SCD1 gene and identified 3 single nucleotide polymorphisms (SNPs) in its 3'untranslated region (UTR). Genotyping these SNPs on a Wagyu x Limousin reference population revealed that the SCD1 gene was significantly associated with six fat deposition and fatty acid composition traits in skeletal muscle, but not with subcutaneous fat depth and percent kidney-pelvic-heart fat. In particular, we confirmed that the high stearoyl-CoA desaturase activities/alleles were positively correlated with beef marbling score, amount of monounsaturated fatty acids and conjugated linoleic acid content, but negatively with amount of saturated fatty acids. The inconsistent associations between human studies might be caused by using different sets of markers because we observed that most associated markers are located near the end of 3'UTR. We found that the proximity of the polyadenylation signal site is highly conserved among human, cattle and pig, indicating that the region might contain functional elements involved in posttranscriptional control of SCD1 activity. In conclusion, our cross species study provided solid evidence to support SCD1 gene as a critical player in skeletal muscle fat metabolism.

A high activity index of stearoyl-CoA desaturase is associated with increased risk of fracture in men

The activity index of stearoyl-CoA desaturase (SCD), a key enzyme in lipogenesis, was associated with increased risk of fracture in a longitudinal population-based cohort of men. This indicates that elevated levels of endogenous lipogenesis increase the risk of fracture and suggest a role for saturated fat in the pathogenesis of osteoporosis.

INTRODUCTION

Osteoblasts and marrow adipocytes are derived from a common mesenchymal progenitor, and experimental studies have indicated that increased adipogenesis can occur at the expense of osteoblasts, leading to bone loss. Stearoyl-CoA desaturase (SCD) converts saturated to monounsaturated fatty acids and is a key enzyme in lipogenesis.

METHODS

Analysis was performed in a population-based, longitudinal cohort study of men (n = 2009). A product-to-precursor index (palmitoleic acid/palmitic acid) was used to estimate SCD activity in fasting serum analyzed in samples obtained at enrollment at age 50 years. Fractures were documented in 422 men during 35 years of follow-up. Cox regression analysis was used to determine the risk of fracture according to SCD activity index.

RESULTS

The risk of fracture was highest among men with the highest levels of SCD activity index. Multivariable analysis of the risk of fracture in the highest quintile as compared to the lowest one showed that the rate ratio was 1.71 (95% CI 1.26-2.33) for any fracture, with an estimated population attributable risk of 15%. The risk was further increased within the highest quintile.

CONCLUSIONS

Our results indicate that elevated levels of endogenous lipogenesis increase the risk of fracture and suggest a role for saturated fat in the pathogenesis of osteoporosis.

Polymorphisms in the SCD1 gene: associations with body fat distribution and insulin sensitivity

OBJECTIVE

Obesity and insulin resistance are major risk factors for metabolic diseases and are influenced by lifestyle and genetics. The lipogenic enzyme, stearoyl-coenzyme A-desaturase (SCD), is related to obesity. Further, SCD1-deficent mice are protected against obesity and insulin resistance. We hypothesized that genetic polymorphisms in the SCD1 gene would be associated with obesity, insulin sensitivity, and estimated SCD activity in humans.

RESEARCH METHODS AND PROCEDURES

The study population was 1143 elderly Swedish men taking part of a population-based cohort study, the Uppsala Longitudinal Study of Adult Men. Associations between single nucleotide polymorphisms and obesity (waist circumference and BMI), insulin sensitivity (assessed by hyperinsulinemic euglycemic clamp), and estimated SCD activity (fatty acid ratios) were analyzed using linear regression analysis.

RESULTS

Subjects homozygous for the rare alleles of rs10883463, rs7849, rs2167444, and rs508384 had decreased BMI and waist circumference and improved insulin sensitivity. The rare allele of rs7849 demonstrated the strongest effect on both insulin sensitivity [regression coefficient (beta)=1.19, p=0.007] and waist circumference (beta=-4.4, p=0.028), corresponding to 23% higher insulin sensitivity and 4 cm less waist circumference.

CONCLUSION

This study indicates that genetic variations in the SCD1 gene are associated with body fat distribution and insulin sensitivity, results that accord well with animal data. These results need confirmation in other populations with a larger sample size.

Dietary fat, genes and insulin sensitivity

Both insulin resistance and dyslipidaemia are determined by genetic and environmental factors. Depending on their expression and their function, gene variants may influence either insulin action or dyslipidaemia. The purpose of this review was to give some examples from recent studies of gene variants that influence insulin signalling and the interaction between gene and diet to predispose insulin resistance. Recent findings indicate a major role for genetic susceptibility to the insulin resistance syndrome. Nutrition also plays an important role in the development and progression of the condition. Genetic background may interact with habitual dietary fat composition, affecting predisposition to the insulin resistance syndrome and individual responsiveness to changes in dietary fat intake. Due to the complex nature of gene-environment interactions, therefore, therapeutic dietary therapy may require a 'personalized' nutrition approach in the future. Although results have not always been consistent, gene variants that affect primary insulin action or dyslipidaemia, and particularly their interaction with the environment, are important modulators of glucose metabolism and insulin resistance syndrome.

Regulation of lipid metabolism by soy protein and its implication in diseases mediated by lipid disorders

Soybeans have a high-quality protein that has been consumed for approximately 5000 years in Oriental countries. The awareness that soy products are healthy has increased their consumption in Western countries. Substantial data from epidemiological surveys and nutritional interventions in humans and animals indicate that soy protein reduces serum total and low-density lipoprotein (LDL) cholesterol and triglycerides as well as hepatic cholesterol and triglycerides. This review examines the evidence on the possible mechanisms for which soy protein has beneficial effects in diabetes, obesity and some forms of chronic renal disease. Consumption of soy protein due to low methionine content reduces serum homocysteine concentration, decreasing the risk of acquiring a cardiovascular disease. On the other hand, soy protein reduces the insulin/glucagon ratio, which in turn down-regulates the expression of the hepatic transcription factor sterol regulatory element binding protein (SREBP)-1. The reduction of this factor decreases the expression of several lipogenic enzymes, decreasing in this way serum and hepatic triglycerides as well as LDL cholesterol and very LDL triglycerides in diabetes and obesity, reducing lipotoxicity in the liver. Soy protein intake also reduces hepatic lipotoxicity by maintaining the number of functional adipocytes, preventing the transfer of fatty acids to extra adipose tissues. Furthermore, soy protein isoflavones stimulate the transcription factor SREBP-2, increasing serum cholesterol clearance. The reduction of serum cholesterol and triglyceride concentrations by soy protein intake produces beneficial effects in the kidney preventing the inflammatory response, increasing the renal flow by releasing endothelial nitric oxide (NO) synthase from the caveolae, facilitating the synthesis of NO. Thus, soy protein consumption may reduce the clinical and biochemical abnormalities in diseases mediated by lipid disorders.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Role of the mitochondrial DNA 16184-16193 poly-C tract in type 2 diabetes

Recent evidence suggests that polymorphic genetic variation in the non-coding region of mitochondrial DNA (the 16184-16193 polycytosine [poly-C] tract) contributes to the cause of type 2 diabetes, but previous studies only just reached significance. We aimed to investigate this association. We compared patients with type 2 diabetes (n=992) with two independent control groups (n=536, n=1029) from the UK, and saw no difference in the frequency of the 16184-16193 poly-C tract. This finding was confirmed by a meta-analysis of European studies of 1455 patients and 3132 controls (odds ratio 1.16, 95% CI 0.94-1.44). Genetic variation of the 16184-16193 poly-C tract is unlikely to have a major role in the cause of type 2 diabetes.