Increased Mitochondrial Common Deletion in Oligo-Astheno-Teratozoospermia Samples Is Not Correlated with Increased Global DNA Methylation: Unexpected Results for ATP Levels.

Abstract

Background: mtDNA4977 deletion, linked to impaired mitochondrial function, is reportedly elevated in the spermatozoa of infertile males. We hypothesized that increased deletion load could lead to reduced ATP and S-adenosylmethionine (SAM) levels, thereby disrupting the balance between DNA methylation and demethylation. This study aimed to investigate the relationship between mtDNA4977 deletion, ATP levels, SAM concentration, and global DNA methylation in sperm samples of infertile men.

Materials and methods: In this experimental study, semen samples were collected from 22 men with oligoasthenoteratozoospermia (OAT) and 22 controls. Sperm analysis was performed according to the World Health Organization criteria. Spermatozoa were isolated, and mtDNA4977 deletion was assessed using quantitative polymerase chain reaction (PCR). ATP levels were measured by bioluminescence, SAM levels were measured by ELISA, and global DNA methylation was measured by 5-methylcytosine (5-mC) quantification. Data were analyzed using the Mann-Whitney U test. Correlation values were calculated using Spearman's correlation.

Results: mtDNA4977 deletion was detected in all samples. The OAT group exhibiting a significantly higher deletion load comparing the control group (P<0.001). Surprisingly, ATP levels were significantly higher in the OAT group (P<0.001). Similarly, SAM levels were significantly elevated in the OAT group compared to the control group (P<0.001). No significant difference in global DNA methylation was observed between the two groups (P=0.052). Furthermore, Spearman's correlation analysis revealed no significant association between deletion load, ATP, SAM, and global methylation levels in men with OAT.

Conclusion: While we could not definitively determine the exact mechanism underlying the elevated ATP levels, we propose potential explanations, such as an increased mitochondrial copy number or the accumulation of unconsumed ATP due to motility defects. A possible reason for the lack of significant methylation differences may be the limitation of examining global methylation without assessing gene-specific methylation profiles in spermatozoa. Further research is needed to explore these findings and their implications for male infertility.