Molecular Epidemiological Study On Association Between Leptin And Rheumatoid Arthritis

ObjectiveRheumatoid arthritis（RA）is a connective tissue diseases featured by joint inflammation,which can generate musculoskeletal deformities and dysfunctions.Leptin,one of the most abundant adipokines secreted by adipose tissue,plays a crucial role in regulating energy metabolism and immune system.In recent years,plenty of studies clarified that leptin is related to autoimmunity and inflammation.There is evidence that leptin might be involved in the pathogenesis and progress of RA,but the association between leptin gene single nucleotide polymorphisms（SNPs）and genetic susceptibility of RA had not been studied in Chinese population.Our study aimed to investigate the association between leptin SNPs and RA susceptibility and compare the plasma leptin levels between RA patients and health controls.Moreover,we performed a two-sample mendelian randomization（TSMR）study to explore the causal relationship between the genetical predicted circulating leptin levels and the risk of RA.Methods（1）A case-control design was applied in the present study.At genotyping stage,a total of 595 RA patients and 599 health controls were included.RA patients,all met the criteria of the American College of Rheumatology（ACR）/European League Against Rheumatism collaborative initiative（EULAR）revised in 2010,were collected from the Rheumatology department of the First Affiliated Hospital of University of Science and Technology of China（USTC）and the First Affiliated Hospital of Anhui Medical University（AHMU）.Health controls were collected from the health center of the first affiliated Hospital of AHMU.The improved multiple ligase detection reaction（i MLDR）was performed to investigate the association of three SNPs of leptin（rs2167270,rs2071045,rs10244329）with susceptibility and main laboratory parameters of RA patients.Then the plasma leptin concentrations in 103 RA patients and 95 health controls was accessed by the enzyme linked immunosorbent assay（ELISA）.（2）Two-sample mendelian randomization study was performed to explore the causal relationship between the genetical predicted circulating leptin levels and the risk of RA.The dataset of circulating leptin levels was obtained from the published genome-wide association study（GWAS）,including 33987 subjects of European ancestry.Six SNPs were selected as instrumental variables（IVs）,which strongly associated with circulating leptin levels(P<5*10^-6)and independent（R²<0.01）.While,the corresponding effects between IVs and the risk of rheumatoid arthritis was abstracted from a GWAS meta-analysis,including 14361 RA patients and 43923controls of European ancestry.TSMR analyses with inverse-variance weighted（IVW）,MR-Egger regression,weighted mode and weighted median methods were performed to estimate the causal effects.The intercept of MR-Egger regression was used to detect the horizontal pleiotropy between IVs and outcome.Leave-one-out method was used in the sensitivity analyses and estimated by IVW.The heterogeneity among SNPs were tested by Cochran’s Q statistics.Results（1）There was no significant difference in the genotypes,allele frequencies,dominant models and recessive models of rs2167270,rs2071045,rs10244329between RA patients and health controls（all p>0.05）.Subgroup analyses of association between gene polymorphisms and main laboratory parameters of RA patients showed no significant difference in genotypes and allele frequencies of three SNPs between anti-cyclic citrullinated peptide（anti-CCP）-/rheumatoid factor（RF）-positive and anti-CCP-/RF-negative RA patients（all p>0.05）.In addition,the results of ELISA illustrated no significant difference in plasma leptin levels between RA patients and health controls（p=0.17）,also between anti-CCP-/RF-positive and anti-CCP-/RF-negative RA patients（all p>0.05）.（2）No causal relationship was showed between the genetical predicted circulating leptin levels and the risk of RA by the results of IVW（OR=1.506,95%CI=0.857-2.646,P=0.154）,MR-Egger（OR=2.360,95%CI=0.180-30.866,P=0.548）,weighted mode（OR=1.404,95%CI=0.679-2.905,P=0.402）and weighted median methods（OR=1.496,95%CI=0.750-2.984,P=0.271）.No significant horizontal pleiotropy was found between IVs and outcome（intercept=-0.016,SE=0.046,P=0.743）.Sensitivity analyses demonstrated the stability of our results.And no significant heterogeneity among SNPs was tested（Cochran’s Q=1.514,P=0.911）.ConclusionsIn the present study,our findings indicate that the polymorphisms of rs2167270,rs 2071045,rs10244329 are not related to the susceptibility and main laboratory parameters of RA.And no causal relationship exists between the genetical predicted circulating leptin levels and the risk of RA.