Detection Of The Activity Of Human Lactate Dehydrogenase C4 And Its Relationship With Male Infertility

In recent years, semen quality of males in their reproductive ages was in a declining trend all over the world, and male infertility has become a common worldwide health problem. However, only few infertile cases have clear causes, whereas 60%~75% of the infertile patients present with unknown etiology, which makes lots of troubles for its diagnosis and treatment.Lactate dehydrogenase C4(LDH-C4) is one of the lactate dehydrogenase isoenzymes identified by Goldberg and another team in 1960 s. LDH-C4 catalyzes the reversible reaction between pyruvate and lactate. Expression of LDH-C4 reveals high tissue-specificity, which only presents in mature mammalian testis and spermatozoa. LDH-C4 is a key enzyme in sperm energy production and relevant to spermatogenesis, metabolism and capacitation. We speculate that decreased LDH-C4 activity is likely to be caused by down-regulated LDH-C4 expression in part of all infertile cases; the lowered LDH-C4 protein compromised the enzyme activity, which further affected sperm motility and function, and finally resulted in male infertility.The proportion of infertile cases with abnormal LDH-C4 activity remains largely unknown thus far. The current study measured the enzyme activity in 1000 infertile males with unexplained reasons and revealed that patients with reduced LDH-C4 activity in spermatozoa account for 11.5% of all infertile cases. Moreover, the present study evaluated the correlation between LDH-C4 activity and other clinical parameters, with a result that LDH-C4 activity was positively correlated with sperm motility, but had no correction with seminal plasma elastase, acrosomal enzyme activity, hepatitis B virus DNA and ROS. In order to further investigate the causes of reduced LDH-C4 expression, the study evaluated the m RNA and protein level of LDH-C4 using Real-time PCR, immunofluorescence and Western blot analyses. The result showed that LDH-C4 m RNA and protein levels were both decreased in low LDH-C4 activity patients. The study imitated the status of enzyme abnormality in spermatozoa by blocking LDH-C4 activity with sodium oxamate(a specific LDH-C4 inhibitor), and further evaluated the effects of LDH-C4 activity on sperm motility and function, utilizing a series of analyses as CASA and capacitation tests. We finally found that sperms from reduced LDH-C4 activity subjects all yielded impaired capacitation.The current study may provide evidence that abnormal LDH-C4 activity is a cause of male infertility, and also provide a new etiological explanation for male infertility. Our data also help to enhance the experimental bases for the diagnosis as well as the treatment of male infertility.