A Nicotinic Acetylcholine Receptor Is Involved in the Acrosome Reaction of Human Sperm Initiated by Recombinant Human ZP31

Abstract

One of the essential steps in mammalian fertilization is the acrosome reaction (AR), a modified exocytotic event in the sperm head that occurs upon contact with the glycoprotein matrix of the zona pellucida (ZP) surrounding the oocyte. Acetylcholine (ACh) at concentrations of 10-250 micro M and nicotine at 10-250 nM significantly initiate the AR of capacitated human sperm. Preincubation with three antagonists of the nicotinic acetylcholine receptor (nAChR), alpha-bungarotoxin (alpha-BTX, 100 nM), alpha-conotoxin IMI (alpha-CTX IMI, 250 nM and 25 nM), and methyllycaconitine (MLA, 100 nM and 10 nM), significantly blocked AR initiation by ACh. alpha-BTX is an anatagonist of several nAChRs, including the alpha7 nAChR, and alpha-CTX IMI and MLA are highly specific antagonists of alpha7 subunit-containing AChRs. The sperm nAChR plays a role in the AR initiated in vitro by a purified recombinant human ZP protein (rhZP3). Previously, rhZP3 was able to stimulate the AR by mechanisms similar to those seen with native ZP. Preincubation of human sperm with alpha-BTX (from 10 micro M to 100 nM), alpha-CTX IMI (250 and 100 nM), or MLA (100 nM and 10 nM) caused a significant inhibition in the rhZP3-initated AR. The inhibition of the ACh-initiated and rhZP3-initiated AR by these nAChR antagonists strongly suggests the involvement of an alpha7 subunit-containing nAChR in the AR initiated by both ligands. AR initiation by progesterone was not inhibited by MLA or alpha-BTX, suggesting that this particularnAChR is not involved in the AR initiated by that ligand. In vitro results show for the first time that ACh can initiate the human sperm AR and strongly suggest that a human sperm alpha7 subunit-containing nAChR plays a role in the rhZP3-initiated AR. This nAChR ligand-gated ion channel may be important to the signal transduction events of ZP-initiated AR in vivo.

PATE Gene Clusters Code for Multiple, Secreted TFP/Ly-6/uPAR Proteins That Are Expressed in Reproductive and Neuron-rich Tissues and Possess Neuromodulatory Activity

“…Furthermore, the human acrosome reaction initiated by acetylcholine or recombinant egg zona pellucida protein ZP3 involves the ␣7 nAChR (31,32), and it has been proposed that the sperm nAChRs may be key regulators of signaling pathways important to the acrosome reaction and sperm motility (29,33). This nAChR commonality in both sperm and neurons has even led to the classification of a sperm cell as "a neuron with a tail" (34).…”

Expression and subcellular localization of the μ-opioid receptor in equine spermatozoa: evidence for its functional role

“…These modifications of the sperm surface are consequent to intimate endosalpingeal -sperm head interactions, due to the local influence of ovarian endocrine programming in specific regions of the fallopian tube epithelium (Roser 2001, Yanagimachi 2002. Despite investigations on processes occurring at the sperm plasma membrane (Flesch and Gadella 2000) and their derived signal transduction reactions, carried out in recent years (Flesch andGadella 2000, Baldi et al 2002), the exact nature of the primary receptors and channels sequentially activated on the sperm plasma membrane remains elusive (Bray et al 2002). Although a number of intracellular messenger systems were implicated in the complex biochemistry of capacitation and acrosome reaction, it appears that gating of Ca 2þ channels and consequent Ca 2þ influx play a central role in the cascade of events leading to sperm activation and oocyte fertilization (Ren et al 2001, Jagannathan et al 2002.…”

Sperm Epidermal Growth Factor Receptor (EGFR) Mediates α7 Acetylcholine Receptor (AChR) Activation to Promote Fertilization

“…It is also known that AChRs exist in sperm and that its ligand, ACh, increases sperm motility and intracellular calcium levels (31,32,34,36). Moreover, it has been shown that ␣7nAChR participates in the acrosome reaction (33,34,64). In the present study, we examined the mechanism by which ␣7nAChR activates the AR and its importance in initiating the process.…”

“…Moreover, a cholinergic receptor has been identified in ram sperm (32). It has been shown that ␣7nAChR is involved in the zona pellucida-induced acrosome reaction (33,34) and that ␣7-null sperm have impaired motility (35). It also has been found that acetylcholine (ACh) increases intracellular calcium levels (36).…”