Mitochondrial DNA 4977 Bp Deletion In Sperm And Male Infertility

Sperm motility is one of the major determinants of male fertility and isrequired for successful fertilization. To detect this deletion in patients ,sperm isa easy and exact method and maybe become a potential male infertility marker.In a previous study, Kao et al. demonstrated that the occurrence andaccumulation of the 4977 bp deletion of mitochondrial DNA (mtDNA) isassociated with diminished fertility and motility of human spermatozoa. Thisstudy is to detect the frequence of mtDNA 4977 bp deletion in sperm frominfertile males and to find a easy and exact molecule method to diagnose maleinfertility and for infertile males undergoing intracytoplasmic sperminjection(ICSI).Sperm dysfunction may be caused by a wide range of conditions, includingabnormalities of flagellar movement, failure in sperm–zona recognition, andinability to carry out sperm–oocyte fusion. In order to understand the aetiologyof the decreased motility and diminished fertility of the spermatozoa and todevelop an appropriate therapeutic strategy, the molecular basis of these defectsmust be elucidated.In this study, we have investigated 4977 bp deletions of sperm mtDNA in 104subfertile and infertile males. The nested PCR and the direct sequencing wereused in 104 infertile males for analysis of mtDNA 4977 bp deletion . The totalDNA was amplified to identify the 4977 bp deletion of mitochondrial DNA bypolymerase chain reaction (PCR),and products were verified by directsequencing. mtDNA 4977 bp deletion was detected in 31 of 104 , and thefrequence was 30% . On the basis of these findings, we suggest that the 4977-bpdeletion in sperm mtDNA is associated with a decline in male fertility, and thatit may play an important role in the pathophysiology of human spermdysfunction.the 4977-bp deletion and other types of mutations in sperm mtDNA willimpair the synthesis of mtDNA-encoded proteins that are essential formitochondrial respiratory function, and thereby cause a decline in motility andfertility of human sperm.Sperm motility is one of the major determinants of male fertility.Spermatozoa with poor motility cannot penetrate through mucus-filled cervicesand arrive at the site of fertilization. Poor sperm motility is an important causeof male infertility . The capability for active flagellar motion is essential for thefunctional competence of sperm and is crucial for their successful transportthrough the female reproductive tract to the oolemma. Enormous amounts ofenergy would be expended by sperm during their long, rapid swim in the maleand female genital tracts. Mitochondria play a pivotal role in the energymetabolism of animal and human cells. In addition to serving as the majorintracellular compartment of metabolic enzymes, mitochondria also contain theirown genetic materials. Mitochondrial DNA (mtDNA) is compact and lacks anefficient DNA repair mechanism. It replicates rapidly without proofreadingand with a mutation rate 10-100 times higher than that of nuclear DNA.Kitagawa et al. investigated accumulation of the 4977-bp mtDNA deletion inpostmenopausal ovaries.Deletions in mtDNA are `common' to many post-mitotic cell types. In particular,the 4977 bp deletion found in a number of tissues, e.g. brain, liver, heart andtestis has been described as the `common' deletion. This `common' deletion, likethe 7.4 kb deletion (another frequently analysed deletion) is flanked by directrepeats. It has been proposed that this characteristic of flanking direct repeatscould result in polymerase misreading, large scale deletion of the mitochondrialgenome and the loss of several vital genes from the ETC.Free radicals have been shown to have a severe affect on sperm function andsurvival. Furthermore, a strong link has been drawn between free radical activityand mtDNA in the testis .To this extent, free radicals have been proposed to bethe major cause of mtDNA damage and to initiate the vicious cycle resulting incell loss. OS was defined several years ago as the disequilibrium betweenpro-oxidative and anti-oxidative molecules in a complex biological system,where the oxidants override defensive systems. Oxidative mole-cules, namelyreactive oxygen species (ROS), are produced primarily by the physiologicalmetabolism of O2 in cells in aerobic conditions. These molecules are highlyreactive to some cellular structures, undermining or eliminating their biologicalfunctions and properties. The presence of various antioxidant systems, togetherwith that of oxidant products of normal metabolism, has been described inspermatozoa and seminal plasma. An equilibrium between these is necessary forthe preservation of sperm DNA integrity, an adequate acrosome reaction andsperm-oocyte fusion, among other functions . The presence of variousantioxidant systems, together with that of oxidant products of normalmetabolism, has been described in spermatozoa and seminal plasma. Anequilibrium between these is necessary for the preservation of sperm DNAintegrity, an adequate acrosome reaction and sperm-oocyte fusion, among otherfunctions.In conclusion, this study has demonstrated that mtDNA 4977 bp deletion wasassociated with male infertility. In these patients who are candidates forintracytoplasmic sperm injection (ICSI), their spermatozoa may harbour geneticdefects.