Association Of Polymorphisms Of KSR2 With Obesity And Lipid Metabolic Disorders In A Chinese Han Population

BackgroundThe high incidence of obesity and lipid disorders have severly threatened human’ health and have aroused global focus on the dangers. Obesity and lipid disorders are the leading risk factors of type 2 diabetes, cardiovascular disease, metabolic syndrome and cancer. In our country, with the improvement of living quality and the changes of life style, obesity and lipid metabolism disorders are increasing year by year. Obesity and lipid metabolism disorders can affect the quality of life, and even life-threatening. They have become a worldwide health concern because of their rapidly increased incidence. Closely related to the incidence of chronic diseases such as diabetes, ischemic heart and cerebrovascular disease, obesity and lipid metabolism disorders have become the focus of China’s public health prevention and control.Store-operated calcium entry (SOCE) plays the major role in Ca2+ entry mechanism of nonexcitable cells and manipulation of various physiological and pathological processes. Kinase suppressor of Ras 2 (KSR2) is directly relevant to SOCE. KSR2 is critical for the rise of cytosolic Ca2+concentration and optimal calcium entry. As a calcineurin substrate, KSR2-associated calcineurin is crucial for SOCE. KSR2 binds and interplays with the kinase components of MAPK/ERK pathway and simultaneously accelerates ERK cascade activation in response to calcium signals, the important energy sensor AMP-activated protein kinase (AMPK) which is interacted with ERK can also be regulated by KSR2. Solid evidences showed that KSR2 could potently regulate the MAP kinases ERK1/2 and in turn affect adipogenesis. Animal experiments showed that KSR2 knock-out mice were more obese and glucose intolerant than wild controls, which implicated the critical role of KSR2 in lipid and glucose metabolism. That function of KSR2 was supported by a study that showed KSR2 regulated cellular glucose uptake and fatty acid oxidation through AMPK-dependent mechanism. Further studies using targeted KSR2 knock-out mice showed that KSR2 deficiency lead to hyperphagia and obesity, which consolidated an indispensible role of KSR2 in energy homeostasis.A recent study suggested that chromosome 12q24 might harbor a new susceptibility locus for hypertension, type 2 diabetes mellitus, and dyslipidemia. Genome scanning showed that Kinase Suppressors of Ras 2 (KSR2) is located in human chromosome 12q24.22-q24.23, which indicated KSR2 might be involved in the former susceptibility.These years, researches have found that Kinase Suppressor of Ras 2 (KSR2) is involved in energy balance, insulin sensitivity and cellular fuel oxidation. Its variations might predispose the carriers to some risks of the obesity and metabolic diseases. Polymorphisms of KSR2 were assumed to be associated with metabolic disorders. Genome-wide association study in adult inhabitants of the island of Korcula found that two SNPs near KSR2, namely rs1044502 and rs4767631, were associated with total and LDL cholesterol levels. Another genome-wide association study find rs7964157 could reduce the risk of metabolic syndrome such as dyslipidemia in the African population. Heretofore, no reports had been published on the risk of obesity and metabolic disorders predisposed by the genetic variations of KSR2 in Aisan population.ObjectiveWe conducted this study to explore the potential impact of KSR2 genetic polymorphisms on risks of metabolic disorders in Chinese Han population. Gender stratification study was conducted at the same time to reveal the gender differences.Materials and Methods1. The subjects were randomly recruited from a cohort of 1722 unrelated ethnic Han Chinese (including 694 male and 1028 female) who received a physical examination program in Nanfang Hospital, Guangzhou, China. On account of the failure of some samples, we eventually obtain 1676 cases of rs7955803 (including 671 male and 1005 female) and 1703 cases of rs10774926 (including 683 male and female 1020). The metabolic indices and demographic characteristics were measured and collected by specialist in Nanfang Hospital. The diagnosis of lipid metabolic disorders was judged according to the updated National Cholesterol Education Program Adult Treatment Panel Ⅲ criteria (NCEP-ATP Ⅲ). The information of single nucleotide polymorphisms (SNPs) on rs7955803 and rs10774926 of KSR2 were acquired from NCBI (build 36, dbSNP b126) and HapMap Project database (release #27). The rs7955803 was a synonymous polymorphism while rs10774926 was in the 3’UTR.SNP genotyping was performed with the method of PCR-based restriction fragment length polymorphism (PCR-RFLP). Primers were designed with the Primer Premier (Version 5.0). PCR products were digested by the restriction endonuclease over night. To ensure the accuracy of the method of PCR-RFLP, about 5% of total samples were then randomly selected to be sequenced. Statistical analysis was performed with the Statistical Package for Social Sciences (version 20.0; SPSS Inc., Chicago). The genotype distributions in control groups were tested for Hardy-Weinberg equilibrium. Adjusted for age and gender when appropriate, logistic regression model and covariance analysis are used to calculate the association between the polymorphisms and quantitative clinical indices in case-control study, respectively. The association study between alleles and metabolic disorders was using chi-square tests. The haplo.stats (Statistical Analysis of Haplotypes) package of R (version 3.0.1) was used to calculate the halpotype frequencies and their association with the risks of metabolic disorders.ResultsThe genetic polymorphisms of KSR2 were associated with the risks of general obesity, central obesity and lipid metabolic disorders.(1). rs7955803 was associated with high-density lipoprotein cholesterol and waist circumferenceThere were 1676 samples successfully genotyped, including 671 male and 1005 female. The polymorphism rs7955803 was associated with high-density lipoprotein cholesterol and waist circumference (P= 0.028; P= 0.016, respectively). Namely, in dominant model found that the T allele carriers had lower level waist circumference and high level high-density lipoprotein cholesterol compared with CC genotype.(2). rs7955803 was associated with the incidence of central obesity in femaleThere were 1676 samples successfully genotyped, including 671 male and 1005 female. The polymorphism rs7955803 was associated with waist circumference in female (P= 0.024). The dominant model found that the T allele carriers showed a 1.05cm smaller average waist circumference than the wild CC genotype. The female’s genotype distributions of rs7955803 met HWE in central obesity control groups (P> 0.05) and further case-control studies were analyzed, finding that the CT and CC genotype had a half risk of central obesity compared with CC genotype (OR = 0.50,95%CI:0.28-0.91, P= 0.023). However, it was not associated with male.(3). rs10774926 was associated with fasting blood glucose, total cholesterol and low-density lipoprotein cholesterol in femaleThere were 1703 samples successfully genotyped, including 683 male and 1020 female. The polymorphism rs10774926 was associated with fasting blood glucose, total cholesterol and low-density lipoprotein cholesterol in female (P= 0.028; P= 0.019; P= 0.028, respectively). GG genotype had a higher fasting blood glucose level compared with AA and AG genotype in female. Meanwhile, AA genotype had a lower total cholesterol and low-density lipoprotein cholesterol level compared with GG and AG genotype in female. The dominant model found that the G allele carriers of the male had a higher total cholesterol level compared with AA genotype (P= 0.049). However, in the female G allele carriers had lower total cholesterol and low-density lipoprotein cholesterol level compared with AA genotype (P= 0.006; P= 0.009).(4). rs 10774926 was associated with overweight and hypertriglyceridemia in maleThere were 1703 samples successfully genotyped, including 683 male and 1020 female. The genotype distributions of rs10774926 met HWE in overweight and hypertriglyceridemia control groups (P> 0.05) of the male and further case-control studies were analyzed. The mutant G allele of rs10774926 had higher risks of overweight and hypertriglyceridemia compared with A allele in the male (OR=1.37, 95%CI:0.99-1.89, P= 0.049; OR= 1.52,95%CI:1.14-2.02, P= 0.003). The analysis in dominant model found that the male G allele carriers (GG and AG) had higher risk of overweight and hypertriglyceridemia compared with AA genotype (OR= 4.41, 95%CI:1.26-15.37, P= 0.020; OR= 2.29,95%CI:1.03-5.11, P= 0.043).(5). Haplotypes of rs7955803 and rs10774926 was associated with the risks of hypertriglyceridemia in maleThe male carriers with halpotype CG had lower risk of hypertriglyceridemia compared with CA (OR= 1.52,95%CI:1.11-2.09, P=0.004).ConclusionsWe found KSR2 was associated with obesity and metabolic disorders in a Chinese Han population in a gender specific manner, which suggests KSR2 might be a target gene for prevention and therapy of such diseases. Our study might provide the deep understanding and theoretical basis of KSR2 gene involved in energy metabolism regulation mechanism.