Chemosensory signal transduction in human sperm

输卵管中卵母细胞周围的卵丘细胞释放孕酮。在人类精子中，孕酮通过非基因组机制激活精子特异性Ca2+通道CatSper。随后的Ca2+增加控制精子的趋化性、超活化和顶体胞吐作用，从而协调受精过程。胆甾酮诱导的Ca2+信号由快速的Ca2+瞬变，随后是缓慢的持续Ca2+升高组成。Ca2+信号的瞬时和持续阶段都依赖于通过CatSper的Ca2+内流。然而，形成Ca2+反应的机制尚不清楚。特别是，通过CatSper减少Ca2+内流的机制仍然难以捉摸。我们认为这可能涉及CatSper和精子特异性Ca2+激活的K+通道Slo3之间的相互作用：通过CatSper的Ca2+内流可能激活Slo3，随后的Ca2+诱导的超极化降低了CatSper的开放概率，减少了Ca2+内流。在这项研究奋进中，我们想仔细研究这个模型。为此，我们希望通过光学方法研究甾酮诱导的人类精子的膜电压（Vm）的变化，使用快速电压敏感染料和动力学停流荧光法。为了研究CatSper和Slo3的相互作用，阐明Ca2+和Vm信号是否以及如何相互关联，并描绘事件的顺序，我们将通过荧光多路复用同时监测甾酮诱发的Ca2+和Vm响应。用这种技术获得的初步数据强烈支持这样的观点，即Vm和Ca2+信号在人类精子中紧密纠缠，并且Slo3是非基因组胆固醇信号通路的关键决定因素。

In the oviduct cumulus cells surrounding the oocyte release progesterone. In human sperm, progesterone activates the sperm-specific Ca2+ channel CatSper by a non-genomic mechanism. The ensuing Ca2+ increase controls chemotaxis, hyperactivation, and acrosomal exocytosis of sperm and, thereby, orchestrates the fertilization process. The progesterone-induced Ca2+ signal consists of a rapid Ca2+ transient followed by a slower, sustained Ca2+ elevation. Both the transient and sustained phase of the Ca2+ signal rest on Ca2+ influx via CatSper. The mechanisms shaping the Ca2+ response are, however, unknown. In particular, the mechanism that curtails Ca2+ influx via CatSper has remained elusive. We proposed that this might involve an interplay between CatSper and the sperm-specific Ca2+-activated K+ channel Slo3: Ca2+ influx via CatSper might activate Slo3 and the ensuing Ca2+-induced hyperpolarization decreases the open probability of CatSper, curtailing the Ca2+ influx. In this research endeavor, we want to scrutinize this model. To this end, we want to investigate by optical methods progesterone-induced changes of human sperm´s membrane voltage (Vm) using fast voltage-sensitive dyes and kinetic stopped-flow fluorimetry. To study the interplay of CatSper and Slo3, to elucidate whether and how Ca2+ and Vm signaling is interconnected, and to delineate the sequence of events, we will simultaneously monitor progesterone-evoked Ca2+ and Vm responses by fluorescence multiplexing. Preliminary data obtained with this technique strongly support the notion that Vm and Ca2+ signaling are intimately entangled in human sperm and that Slo3 is a critical determinant of the non-genomic progesterone-signaling pathway.