Study On The Mitochondrial Gene Mutation Of Sperm And Male Infertility

At present,Infertility occurs in 10-15% of all reproductive age couples.Approximately half of the cases are due to male factors. There are many factorsresulted in male infertility. Majority is associated with sperm count,morphology and motility. Men with oligospermia, asthenospermia,teratozoospermia and azoospermia account for 20-25% of the cases.Mitochondrion is the main organ that produces cellular energy currency, whichparticipates in spermatogenesis, capacitation, swimming and fertilization etc.,but mitochondrion itself is a cell vehicle sensitive to the outside world damageand has limited proof reading and DNA repair mechanism. Most mtDNA pointmutations once occurred would accumulate within the protection by histoneproteins. It is reported that some diseases is associated with mitochondrialmutations, such as Leber hereditary disease, and muscle clonic epilepsy,diabetes-deafness syndrome, MELAS syndrome. Thus mitochondrial geneticstructure caused universal concern. In recent years, researches onmitochondrion become hot.With the development of Molecular Biology and Genetics and theconstruction of mtDNA physical map, the researches on male infertility's etiology isup to molecular level. Ruiz-Pesini et al. (2001) have shown thatasthenozoospermia (low sperm motility), but not oligozoospermia (low spermnumbers), is associated with certain mtDNA haplogroups. Mitochondrialhaplogroup H is more abundant in non-asthenozoo-spermia;haplogroup T ismore abundant in asthenozoospermia. The two groups showed significantdifferences in their spermatozoal OXPHOS performance. Unlike the situationwith oocytes, sperm mitochondria before fertilization commonly harbormultiple DNA deletions (Reynier et al., 1998). In a man with the mtDNAA3243G mutation, separating sperm with Percoll into five fractions withdecreasing motility correlated with an increase in mutant mtDNA from 42 to64% (Spiropoulos et al., 2002). A polymorphism affecting pol-gamma (DNApolymerase γ) and resulting in multiple deletions is relatively commonlyassociated with male infertility analysis of POLG genotypes in differentpopulations identified an association between absence of the common,ten-repeat allele and male infertility typified by a range of sperm quality defectsbut excluding azoospermia (Rovio et al., 2001) . More generally, semensamples with high numbers of multiple mtDNA deletions appear to beassociated with male infertility (St John et al., 2001). In a reported case ofKearnes-Sayre syndrome (KSS) due to Del mtDNA 4977, oligoasthenospermiawas associated with multiple mtDNA deletions in sperm (Kao et al., 1995),implying that mitochondrial defects accentuate the degree of mtDNA damagethat is commonly acquired during spermatogenesis and epididymal transit.The article aimed to investigate the association between male infertilityand the mutation in the ATPase6 gene of mitochondrial DNA. The researchersanalyzed mitochondrial tRNA-leu, ATPase 6 and ND4 genes. (1) It is knownthat the A-to-G at np3243 in t RNA leu is the most frequently encounteredmtDNA point mutation. PCR-RFLP analysis was applied to detect the mutationthe A-to-G at np3243 of mtDNA for male infertility patients. PCR productionsare digested by restriction enzyme Apa I. The individual PCR productionsexisted A3243G mutation display two bands in agarose electrophoresis. (2)PCR-RFLP-SSCP analysis was applied to detect the mutation in the ATPase6,ND4 genes of mtDNA for male infertility patients. PCR-RFLP was applied toanalyze the mutation detected and confirm genotype. (3) PCR amplify gene thatis 3450 bp in length. PCR production is digested by restriction enzyme Fok Iand obtain eight short fragments. SSCP was applied to screen mutations. Resultnine percent of the men with poor semen parameters had A8784G and C8829Tmutations that were in a homoplasmic state and healthy subjects were notdetected with any mutations. Conclusion we propose that for mutations thatoccurred in the third codon and did not change the amino acid. It is likely toaffect sperm's energy production through decrease translation level ofmtATPase6 gene of male infertility and compromise the semen quality of thesemen, which further research is needed.