Abstract
Study question
Could Nrf2 polymorphism (-617C>A; rs6721961) and oxidative stress (OS)-induced changes of signature seminal plasma (SP) miRNAs related to Nrf2 provide possible biomarkers of male infertility?
Summary answer
-617C>A SNP is associated with infertility through sperm OS DNA damage and miR-582-5p and miR-20a-5p, differentially represented between spermatozoa of smokers-non-smokers, might regulate Nrf2/ARE axis.
What is known already
As an extrinsic factor causing OS, smoking decreases male infertility by causing sperm membrane damage and DNA fragmentation. Expression of proteins related to the antioxidant defense system and phase 2 detoxifying enzymes controlled mainly by Nrf2/ARE pathway components is vital in managing OS-induced DNA damage. miRNAs, which multiple of are produced abundantly in male germ cells throughout spermatogenesis, have been detected in SP and contribute to multiple biological processes related to male reproductive events. miRNA-expression alterations may be induced in response to OS and without involving DNA sequence changes, miRNAs can provide additional mechanism of regulating the Nrf2 gene expression.
Study design, size, duration
Wild-type (WT) and SNP (-617) alleles in the Nrf2 gene were studied in 100 infertile cases and 100 controls and their associations with seminal parameters in relation to smoking status were assessed. In infertile cases, sperm DNA damage level was determined and compared among Nrf2 genotypes. Interactions between differentially expressed miRNAs (DEMIs) in response to smoking and Nrf2/ARE pathway components were visualized on a miRNA-mRNA regulatory network using CluePedia (v1.5.7) plugin of Cytoscape software (v3.8.2).
Participants/materials, setting, methods
Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was utilized to genotype the Nrf2 SNP (-617). DNA damages were analyzed by Comet assay. DEMIs were identified by a comprehensive bioinformatics analysis using the miRNA expression dataset GSE44134 downloaded from the GEO database. Predicted targets of DEMIs in smokers were identified by mirDIP portal. Known interactions between Nrf2 and its first neighbors were visualized after selecting STRING-actions, miRTarBase and miRecords validated miRNA source files from CluePedia panel.
Main results and the role of chance
There was significant difference for Nrf2 polymorphism between fertile and infertile males. The A allele was detected more frequently in the patient group; (P = 0.001). The frequencies of the C and A alleles of the Nrf2 were 62% and 38% in patients, and 78% and 44% in control group. The AA genotype was higher in the infertiles; 14% vs. 3% (P = 0.001). In smokers, sperm quality decreased significantly in AA genotype. The risk of DNA damage was highest with 224.58 AU in the AA genotype group, whereas it is the lowest with 164.56 AU in those carrying the CC genotype (P < 0.005). 21 differentially expressed miRNAs (including 7 downregulated and 14 upregulated in smokers) were identified. Among the upregulated DEMIs, miR-582-5p, miR-20a-5p, miR-573, miR-186-5p, miR-499a-5p were found to target the Nrf2 mRNA, suggesting their usage as biomarkers capable of indicating the antioxidant ability of the male reproductive system. The interrelations between Nrf2/Nrf2 direct interactors and DEMIs revealed the regulatory role of hsa-miR-20a-5p in SQSTM1/p62-Keap1-Nrf2 axis linked to selective autophagy. hsa-miR-582-5p was found to regulate the JNK/Jun/caspase-3 pathway, previously shown to be activated in response to OS, in which JUN can activate or suppress the Nrf2 expression.
Limitations, reasons for caution
Small number of cases while evaluating the effect of smoking weakens our ability to generalize the results. Including other coexisting factors and larger patient groups carrying other functional variants of Nrf2 as well as confirming the results at the protein level would further strengthen the results of the study.
Wider implications of the findings
This study is the first to report -617C>A polymorphism in the Nrf2 gene in the Turkish population and such a SNP may cause impaired fertility in men, especially in smokers, through oxidative metabolism. Considering these data may be valuable in determining risk groups.
Trial registration number
N/A
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