| Ejaculated spermatozoa cannot immediately fertilize an egg in the female genital tract. They must undergo a series of complicated modifications in their structure and function for capacitation and acrosome reaction. This process is called spermatozoa activation, which is regulated by many biological factors. So far, the molecular mechanisms involved in spermatozoa activation are not understood completely.The level of estrogen in female genital tract is high especially in the follicular fluid and cervical mucus. Some studies indicated that potential estrogen receptors or binding sites are expressed on the membranes of humans and other mammalian spermatozoa.When traversing the female genital tract, spermatozoa probably encounter and interact with estrogen, which probably activate spermatozoa through special mechanisms. Up to now, the effects of estrogen on sperm activation have not been demonstrated in all mammalian. The role and signaling mechanisms of estrogen in human spermatozoa activation remain to be clarified.In present study, using methods of triple-stain technique, flow cytometry (FCM) and Western Blotting, the effects of estrogen on spermatozoa and thepossible mechanism were investigated.Firstly, to evaluate the role of estrogen on human spermatozoa activation and its significance for spermatozoa functions, capacitated or uncapacitated spermatozoa of fertile men and patients with unexplained infertility were treated with 17 0 -estradiol (E2) at different concentrations to detect the changes of acrosome reaction rate (AR%) and intracellular calcium concentration ([Ca2+]j).Secondly, to investigate the possible mechanism of estrogen on human spermatozoa activation, the membrane impermeable E2 conjugated to bovine serum albumin (E2-BS A) was used to stimulate spermatozoa of fertile men. And its effects on AR rate, [Ca2+]j and proteins tyrosine phosphorylation were compared with that induced by free E2. Moreover, spermatozoa were stimulated by E2 or E2-BSA in calcium-free medium and the [Ca2+]j were measure againand compared with that in calcium- medium. The results were as follows:1. In capacitated spermatozoa, 0.01/xmol/L or 0.1/imol/L E2 had no effectson AR rate (P>0.05), but lpimol/L or 10/imol/L E2 significantly increased the AR rate and [Ca2+]j (PO.05). Conversely, in uncapacitated spermatozoa, E2 with any concentrations did not increase AR rate or [Ca2+]j (P>0.05). Additionally, E2 with any concentrations did not promote AR or increase [Ca2+]j in capacitated spermatozoa of infertile men (P>0.05) .2. 10/imol/L E2-BSA significantly increased AR rate and [Ca2+]< in capacitated spermatozoa of fertile men and its effects were similar to that induced by 10^mol/L E2 (P>0.05).3. The [Ca2+]i of spermatozoa did not increase any more in calcium-free medium when they were treated with 10/imol/L E2 or lOjunol/L E2-BSA (P>0.05).4. The tyrosine phosphorylated sperm proteins with size of 86kDa~ 118kDa ware significantly enhanced by 10/imol/L E2-BSA or 10/imol/L E2 (PO.01).In conclusion, estrogens can induce spermatozoa activation and this role is related to the status of spermatozoa. Estrogens probably active spermatozoa by binding with the estrogen receptors on the membrane, which initiate signal transduction. Calcium and tyrosine phosphorylated proteins are involved in this process. Furthermore, abnormal activation of estrogen on spermatozoa is perhaps associated with the occurrence of some unexplained infertility. |
