Association Of TLR2 And AKT1 Gene Polymorphisms With Sporadic Parkinson’s Disease In Chinese Han Population

Objective: Parkinson’s disease(PD)is characterized by neuropsychiatric symptoms such as depression and anxiety preceding the onset of motor symptoms.Major features of PD include the loss of dopaminergic neurons in the substantia nigra and Lewy body depositions.It has been suggested that mitochondrial dysfunction,oxidative stress and oxidative damage underlie the pathogenesis of PD.Activity of substantia nigra dopaminergic neurons is critical for striatal synaptic plasticity and associative learning.The degeneration of dopaminergic neurons leads to a disinhibition of the subthalamic nucleus thus increasing excitatory projections to the substantia nigra.In consequence,excessive activity causes excitotoxicity and oxidative stress.Consequently,intracellular accumulation of filamentous α-synuclein(α-syn)aggregates to form Lewy bodies,a pathologic hallmark of PD.Lewy body disease is also a group of neurodegenerative disorders characterized by α-syn accumulation that includes Lewy body dementia and PD symptoms.Genetic defects,aging,and environmental toxicants have been recognized as risk factors for the development of these diseases.Inflammatory process is implicated in PD incidence and progression,which leads to the damage and subsequent loss of DA neurons.Among the most important components of the innate immunity pathway,Toll-like receptors(TLRs)play a key role in the pathophysiology of a range of human diseases.Given that TLR2 forms heterodimers it is clear that defects in this gene could influence ligand recognition of multiple receptors,which could affect the immune response and thus alter susceptibility to PD disease.AKT1 is a serine/threonine protein kinase,which is critical for cell survival,and influences survival of both neuronal and non-neuronal cells.AKT1 is involved in intracellular signaling pathways postulated as of etiological importance in Parkinson’s disease of the dopamine system.Stimulation of TLR2 results in the recruitment of active PI3 K to the TLR2 cytosolic domain,leading to activation of the PI3K/AKT pathway.Therefore,it is possible that activation of TLR2 will activate the AKT signaling pathway during Parkinson’s disease.The effects of polymorphism on PD risk depend on ethnicity,highlighting the need for further study of these polymorphisms in other populations.In view of the population-specific heterogeneity,we accomplished the study to explore the role of three identified genetic variants of rs3804099,rs3804100,rs2498799,rs2494732 and rs1130214 in risk of sporadic PD in a Han Chinese population.Methods: This study included cases meeting the UK PD Brain Bank criteria(UKPD-BB)for sporadic PD with an emphasis on sporadic cases with no family history for this disease.In addition,healthy controls were selected randomly.Patients with early-onset PD(EOPD,diagnosed <50 years of age)and late-onset PD(LOPD,diagnosed≥50 years of age)matched with the same-age control subgroups.DNA was obtained from blood samples using standard protocols.We isolated genomic DNA from peripheral blood lymphocytes using a Genomic DNA extraction kit(Tiangen,Beijing)following the manufacturer’s instructions.Polymorphisms were detected in all subjects by PCR–RFLP.The PCR products were digested with restriction endonuclease.All the digestion products were resolved on a 2% agarose gel stained with ethidium bromide and visualized in ultraviolet light.To validate genotyping results,we performed sequencing analysis in randomly-selected 10% of the samples.All statistical tests were carried out using SPSS version 17.0.The allelic and genotypic frequencies of each polymorphism were compared between the patients and the controls using Chi-square test and conditional logistic regression.Results:(1)We identified SNP rs3804099 in TLR2 as being significantly associated with sporadic PD risk in the northern Chinese population.The combination of the two alleles “TC+CC” had higher risk association(OR=1.376,95%CI=1.043-1.814,p=024 for TT vs.TC/CC).In allele analysis,the phenotypes were distributed at 72.9% T and 27.1% C in sporadic PDs and 67.6% T and 32.4% C in controls(OR= 1.293,95% CI = 1.044–1.601,p=0.019).From the subgroup analysis based on gender and age at onset,the variant allele T carrier of rs3804099 was higher in cases(73.1%)than in controls(67.4%)in the late-onset cohort(OR= 1.319,95% CI = 1.047–1.663,p=0.019).Also,in rs3804099 TT / TC+CC showed statistically significant risk(LOPD OR=1.417,95%CI=1.051-1.911,p=022).(2)We identified a significant difference in the frequency of genotype(p=0.019)and in the G allele(OR=0.764,95%CI=0.587-0.995,p=0.045)at rs2498799 of AKT1 gene between sporadic PD in Han Chinese female and the female healthy controls.Furthermore,this association of GG/GA+AA genotype remained significant in female cohort(OR=0.538,95%CI=0.345-0.841,p=006).Besides,the association of subjects with GG/GA+AA genotype show significant in female of late-onset cohort(OR=0.521,95%CI= 0.309-0.877,95%CI=0.012)Conclusion: We explored here the interaction between immune genetic variations and sporadic PD patients.Examination of our data leads to our conclusion that rs3804099 of TLR2 is a susceptibility gene for sporadic PD in Chinese Han population.Furthermore,the northern Chinese population showed bias for the dominant model in rs3804099 in the late-onset cohort.We observed a combined effect of a genetic variant of TLR2,a major trigger of peripheral and central inflammatory responses,older age at onset sporadic PD.Also,we demonstrate that the studied genetic variants in AKT1 are associated with sporadic PD in Chinese Han Parkinson patients.Our results do strengthen the hypothesis that AKT1 is a candidate gene for sporadic PD,through the analysis identified the G allele of rs2498799 as protecting Han Chinese females from developing PD.Finally,the sporadic PD cases are under the assumption that TLR2 and AKT1 genetic variation that causes effects,whose specific pathogenesis remains to be elucidated.We propose that the risk factors,genetic polymorphism of TLR2 and AKT1,act in immune-related pathways contributing to increase the progression of PD.We hypothesized that damage to dopaminergic neurons is mediated by the dysregulation of TLR2 through the AKT1 pathway under conditions of protein level and could contribute a decrease in the cell innate immunity of sporadic Parkinson’s disease.