The acrosome reaction in sperm: A special type of regulated exocytosis

精子顶体反应：一种特殊类型的调节胞吐作用

• 批准号: 170440292
• 负责人: Privatdozentin Dr. Ingrid Boekhoff, Ph.D.
• 金额: --
• 依托单位: Walther-Straub-Institut für Pharmakologie und Toxikologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/170440292?language=en
• 关键词: acrosome; reaction; sperm; special; type

One special feature of the acrosome reaction is that the lysosome-related acrosomal vesicle in the sperm head supplies Ca2+ for its own exocytosis. Investigating whether the recently described endo-lysosomal Ca2+ release channels of the two pore channel (TPC) family are expressed in mammalian spermatozoa, and whether their potential activator NAADP contributes to acrosomal secretion we found that two independent NAADP-dependent pathways cause acrosomal exocytosis, where TPC1 was found to be responsible for activating the low affinity cascade. Since our results also provide evidence for an expression of TPC2, we will now examine whether TPC2 is responsible to activate the high affinity NAADP signaling pathway, and whether a simultaneous genetic deletion of TPC1 and TPC2 affects Zona pellucida induced fusion of the acrosome and breeding successful of the animals. However, since our previous study also uncovered a possible functional cross talk between the acrosomal IP3R and TPCs, we will also investigate whether a co-stimulation of TPCs enhances an IP3 evoked Ca2+ increase in a synergistic or in an additive manner, and whether IRBIT, an inhibitor of the IP3R, which we recently identified in mammalian spermatozoa, has any impact on acrosomal secretion.During their long distant journey of ejaculated sperm to the mature egg in the oviduct, sperm are exposed to progressively changing concentrations of different chemical compounds whose recognition capacity is directly linked to the sperm`s ability to interact with the Zona pellucida surrounding the oocyte. However, our current knowledge about the molecular identity of appropriate chemosensory receptor proteins which recognize changes in pH, but also gradients of different sugars, amino acids or hormones is still rudimental. In this context, the recent discovery of an ectopic expression of taste receptors is worth mentioning, which in taste buds on the tongue are known to detect a broad spectrum of compounds with different chemical properties. Examining the expression of taste receptors in male germ cells we found that the two binding partners, which form the functional umami receptor (Tas1R1/Tas1R3, Monosodium L-Glutamat), and components of the coupled taste transduction cascade, like the G protein alpha subunit Gustducin and the cation channel TRPM5 are expressed in sperm from mice to humans. In addition, using sperm of a Tas1R1 deficient mouse strain, a significant elevation of the spontaneous acrosome reaction rate was detected. However, whether Tas1R3, Gustducin and TRPM5 also affect acrosomal secretion, is not yet clear, although it has been demonstrated that a simultaneous genetic absence of both, Tas1R3 and Gustducin renders knock-out males sterile. Therefore, we will systematically examine the functional relationship between the efficiency of acrosome reaction and Tas1Rs, Gustducin and TRPM5 in mouse as well as in human sperm.

顶体反应的一个特殊特征是精子头部的溶酶体相关顶体囊泡为其自身的胞吐提供Ca2+。研究最近描述的两孔通道（TPC）家族的内溶酶体Ca2+释放通道是否在哺乳动物精子中表达，以及它们的潜在激活剂NAADP是否有助于顶体分泌，我们发现两个独立的NAADP依赖途径引起顶体胞吐，其中TPC1被发现负责激活低亲和力级联反应。由于我们的研究结果也为TPC2的表达提供了证据，我们现在将研究TPC2是否负责激活高亲和力的NAADP信号通路，以及TPC1和TPC2的同时基因缺失是否影响透明带诱导的顶体融合和动物的繁殖成功。然而，由于我们之前的研究也发现了顶体IP3R和TPCs之间可能的功能互扰，我们还将研究TPCs的共同刺激是否以协同或加性的方式增强IP3引起的Ca2+增加，以及我们最近在哺乳动物精子中发现的IP3R抑制剂IRBIT是否对顶体分泌有任何影响。在射精到输卵管中成熟卵子的漫长旅程中，精子暴露在不同化合物浓度逐渐变化的环境中，这些化合物的识别能力与精子与卵母细胞周围的透明带相互作用的能力直接相关。然而，我们目前对识别pH值变化的合适的化学感觉受体蛋白的分子特性的认识仍然是初级的，而且还能识别不同糖、氨基酸或激素的梯度。在这种背景下，最近发现的味觉受体异位表达值得一提，它在舌头上的味蕾中可以检测到具有不同化学性质的广谱化合物。通过研究味觉受体在男性生殖细胞中的表达，我们发现形成功能性鲜味受体的两个结合伙伴（Tas1R1/Tas1R3, Monosodium L-Glutamat），以及偶联味觉转导级联的组成部分，如G蛋白α亚基Gustducin和阳离子通道TRPM5，在小鼠到人类的精子中都有表达。此外，使用Tas1R1缺陷小鼠品系的精子，检测到自发顶体反应率显著升高。然而，Tas1R3、Gustducin和TRPM5是否也影响顶体分泌尚不清楚，尽管已经证明Tas1R3和Gustducin同时基因缺失会使敲除的雄性不育。因此，我们将在小鼠和人类精子中系统地研究顶体反应效率与Tas1Rs、Gustducin和TRPM5之间的功能关系。