Effects of GPX3 and GSTA1 Polymorphisms on the Risk of Schizophrenia in Chinese Han Population

Background: Several lines of evidence support the fact that the presence of oxidative stress plays an important role in the pathophysiological mechanisms of schizophrenia (SCZ). The glutathione peroxidases (GPXs) and glutathione S-transferases (GSTs) are the major antioxidant enzymes. Polymorphic variants of GPX and GST can affect the antioxidant activities of their encoded enzymes. This study explored the possible associations of the GPX3 and GSTA1 gene polymorphisms and schizophrenia in the Chinese Han population. Methods: DNA from 316 healthy controls and 303 schizophrenic patients was genotyped for single nucleotide polymorphisms(SNPs) rs736775 in GPX3 and rs3957357 in GSTA1 using a PCR-LDR genotyping assay. The χ2 test compared differences in genetic distributions between the two groups in a case–control study. Results: No significant differences in allelic or genotypic frequencies of GPX3 rs736775 or GSTA1 rs3957357 were detected between cases and controls(GPX3 rs736775: χ2 =0.036, P=0.982 by genotype, χ2=0.020, P=0.888, odds ratio=1.017, 95% confidence interval=0.801-1.292 by allele; GSTA1 rs3957357: χ2 =1.100, P=0.577 by genotype, χ2=0.924, P=0.336, odds ratio=1.176, 95% confidence interval=0.845-1.637 by allele). Conclusions: Our results suggest that GPX3 rs736775 and GSTA1 rs3957357 SNPs are unlikely to be a candidate gene for susceptibility to SCZ in at least Chinese Han population. However, these results should be validated by replication in different populations. and a CC genotype frequency of 7.92% for patients with SCZ, compared with 44.30%, 47.79%, and 7.91%, respectively, in No significant differences in allelic or genotypic frequencies of observed between SCZ patients and controls in our study. This suggest that reaction-ligase detection reaction; ORs: Odds ratios; CIs: Confidence intervals.


Abstract
Background: Several lines of evidence support the fact that the presence of oxidative stress plays an important role in the pathophysiological mechanisms of schizophrenia (SCZ). The glutathione peroxidases (GPXs) and glutathione S-transferases (GSTs) are the major antioxidant enzymes. Polymorphic variants of GPX and GST can affect the antioxidant activities of their encoded enzymes. This study explored the possible associations of the GPX3 and GSTA1 gene polymorphisms and schizophrenia in the Chinese Han population. Methods: DNA from 316 healthy controls and 303 schizophrenic patients was genotyped for single nucleotide polymorphisms(SNPs) rs736775 in GPX3 and rs3957357 in GSTA1 using a PCR-LDR genotyping assay. The χ2 test compared differences in genetic distributions between the two groups in a case-control study. Results: No significant differences in allelic or genotypic frequencies of GPX3 rs736775 or GSTA1 rs3957357 were detected between cases and controls(GPX3 rs736775: χ2 =0.036, P=0.982 by genotype, χ2=0.020, P=0.888, odds ratio=1.017, 95% confidence interval=0.801-1.292 by allele; GSTA1 rs3957357: χ2 =1.100, P=0.577 by genotype, χ2=0.924, P=0.336, odds ratio=1.176, 95% confidence interval=0.845-1.637 by allele).
Conclusions: Our results suggest that GPX3 rs736775 and GSTA1 rs3957357 SNPs are unlikely to be a candidate gene for susceptibility to SCZ in at least Chinese Han population. However, these results should be validated by replication in different populations.
Background Schizophrenia (SCZ) is a complex and severe mental disorder and is the most common among psychotic illness, with a prevalence of around 1% in the worldwide population [1][2][3].
Although the detailed mechanisms underlying the pathophysiology of SCZ is unknown for certain, multiple pieces of evidence illustrated that a complex interaction between genetic background and environmental factors was likely to be involved in the development of SCZ [4,5]. Dopamine (DA) is the principal neurotransmitter in the brain and play a significant role in the functions of neurons. However, the oxidative metabolites of dopamine are hydrogen peroxide (H 2 O 2 ) and DA quinones which is a principal source of reactive oxygen species (ROS) in the brain [6]. Oxidative stress arises when the balance between antioxidant activity and the formation of ROS is disrupted, and ROS can cause neuronal inflammation as a consequence of oxidative stress. Interestingly, several studies suggested that neuronal inflammation induced by oxidative stress play an important role in SCZ pathophysiological mechanisms [7][8][9].
Recently, glutathione (GSH) levels were reported to be decreased in the cerebrospinal fluid and in the prefrontal cortex of SCZ patients [10][11][12]. Furthermore, some studies showed changes in antioxidant enzyme activity in the plasma and postmortem brain of schizophrenia patients [7,13]. Taking all these factors into consideration, we had to focus our attention on the role of oxidative stress in the pathophysiology of SCZ through investigating two important antioxidant enzymes: glutathione peroxidases (GPXs) and glutathione S-transferases(GSTs).
GPX family belongs to selenium-dependent peroxidases and plays important role in protecting cells from oxidative damage by reducing free hydrogen peroxide to water. The GPX3, a member of GPX family, was found to be highly expressed in the prefrontal cortex suggests that GPX3 may be involved in antioxidant activity in brain [14]. Human GPX3 is located on chromosome 5q33.1 and has a common single nucleotide polymorphism(SNP), GPX3 rs736775 . Several studies have suggested the effect of this variant on GPX3 activity and many disorders [15][16][17][18].
GSTs consist of phase II detoxication enzyme and can catalyze the conjugation of the reduced form of glutathione (GSH) to xenobiotic substrates for the purpose of detoxification [19]. The GST alpha, a member of GSTs family, are located in chromosome 6 and shows an important detoxifying activity that protects the cell from ROS. GST alpha 1 (GSTA1) represents one of the most abundant alpha-class GST isoenzymes. Besides its through conjugation of reduced form glutathione GSH, GSTA1 can also inactivates quinones [20]. SNP rs3957357 in GSTA1 is just located in the promoter region of GSTA1 genes, and several studies suggested the pathogenic effects of this variant in many disorders [21,22].
Hence, the final reaction system containing 1 μl LDR product and 9 μl highly deionized formamide were performed under denaturation at 95°C for 3min and the genotypes were analyzed by ABI 3730XL sequencer and Genemapper software.   Furthermore, in order to ensure sufficient statistical power for the detection of disease susceptibility loci, additive, dominant and recessive genetic models were used to analyze genotype frequencies of GPX3 rs736775 and GSTA1 rs3957357. Table 4 shows that rs736775 and rs3957357 were not the risk factors for SCZ on the basis of these models (all P > 0.05) . Discussion It is well known that the oxygen consumption of brain is the highest in our body and hence generation of ROS increase. Moreover, the oxidative metabolites of dopamine are hydrogen peroxide (H 2 O 2 ) and DA quinones, which is a principal source of ROS in the brain [6]. Therefore, the brain is considered particularly vulnerable to ROS. Normally, ROS can be eliminated by the aantioxidant system. When the balance between the formation of ROS and intrinsic antioxidant capacity is upset, oxidative metabolite damage to neurons arises. Increasing evidence indicates that oxidative injury to neurons can play important roles in the pathophysiology of neuropsychiatric disorders including schizophrenia [7][8][9].
The Zhang et al. also suggested GPX3 rs736775 was a prognostic markers in patients with gastric cancer [17]. Another study showed that the increased risk for cardiovascular toxicity among patients was associated with GPX3 rs736775 [27]. Taking these results into consideration, GPX3 rs736775 might contribute to the altered antioxidant capacity in SCZ patients. In this study, we compared allelic and genotypic frequencies of rs736775 between 303 SCZ patients and 316 controls. However, we observed a TT genotype frequency of 43.56%, a CT genotype frequency of 48.51%, and a CC genotype frequency of 7.92% for patients with SCZ, compared with 44.30%, 47.79%, and 7.91%, respectively, in controls. No significant differences in allelic or genotypic frequencies of GPX3 rs736775 were observed between SCZ patients and controls in our study. This finding suggest that the GPX3 rs736775 polymorphism may not be the genetic risk factor for SCZ patients.
GSTs are encoded by the GST family of genes located on different chromosomes and the cytosolic GST can be classified into four major groups: Alpha, Mu, Pi, and Theta. The GST alpha(GSTA) family are located in chromosome 6 and shows an important detoxifying activity that protects the cell from ROS. The GSTA1 rs3957357 is one of five polymorphisms just located in the promoter region of GSTA1 genes, resulting in decreased enzyme activity. In recent years, GSTA1 rs3957357 has been reported to be associated with many disorders including bladder cancer, leukemia and gestational hypertension, as well as SCZ. For instance, Rossi et al. reported that GSTA1 rs3957357 may associate with event-free survival in patients with diffuse large B-cell lymphoma [21]. Iorio et al. suggested that the GSTA1 rs3957357 was significantly associated with gestational hypertension risk [28]. However, we are intrigued by the effects of GSTA1 polymorphisms on the risk of SCZ. Gravina   Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The study was approved by the Ethical Committees of Jining Medical University in accordance with the Code of Ethics of the Declaration of Helsinki. All participants gave written informed consent to participate in the study.

Consent for publication
Not applicable.