Division of Endocrinology, CSIR-Central Drug Research Institute, Lucknow, India.
Academy of Scientific and Innovative Research, CSIR-HRDC Campus, Ghaziabad, India.
Reproduction. 2021 Oct 5;162(5):339-351. doi: 10.1530/REP-21-0202.
Sperm in most mammalian species including rat, mice and human are kept completely quiescent (motionless) and viable for up to a few weeks in the cauda epididymis before ejaculation. Vigorous motility is initiated almost instantly upon sperm release from cauda during ejaculation. The molecular mechanisms that suppress sperm motility but increase cell survival during storage in cauda epididymis are not known. Intracellular signaling via phosphorylation cascades is quick events that may regulate motility and survival of transcriptionally inactive sperm. Pathscan intracellular signaling array provided the preliminary picture of cell signaling in quiescent and motile rat sperm, indicating upregulation of cell-survival pathways in quiescent sperm, which were downregulated during motility activation. Interactome of signaling proteins involved in motility activation was constructed by Search Tool for the Retrieval of Interacting Genes (STRING) software, which identified mitogen activated protein kinase-p38 (MAPK-p38), AKT, mTOR and their downstream target p70S6K as the key kinases regulating sperm function. Further validation was achieved by western blotting and pathway activators/inhibitors. Immunofluorescence localized the kinase proteins in the sperm mid-piece region (mitochondria), a known extra-nuclear target for these signaling pathways. Activators of these kinases inhibited sperm motility but increased viability, and vice versa was true for inhibitors, in most of the cases. Activators and inhibitors also affected sperm mitochondrial membrane potential, ATP content and reactive oxygen species (ROS) levels. Data suggest that sperm motility and survival are inversely complementary and critically regulated by intracellular cell signaling. Aberrant cell signaling in caudal sperm may affect cell survival (sperm concentration) and motility of ejaculated sperm.
在射精前，包括大鼠、小鼠和人类在内的大多数哺乳动物物种的精子在附睾尾部保持完全静止（不动）和存活长达数周。在射精时，精子从尾部释放出来后，活力运动几乎立即开始。目前尚不清楚在附睾尾部储存期间抑制精子活力但增加细胞存活率的分子机制。通过磷酸化级联进行细胞内信号转导是快速事件，可能调节转录不活跃精子的运动和存活。Pathscan 细胞内信号阵列提供了静止和活跃大鼠精子细胞信号的初步图片，表明静止精子中细胞存活途径的上调，而在运动激活期间下调。通过 Search Tool for the Retrieval of Interacting Genes (STRING) 软件构建了参与运动激活的信号蛋白相互作用组，该软件确定丝裂原激活蛋白激酶-p38 (MAPK-p38)、AKT、mTOR 和它们的下游靶标 p70S6K 是调节精子功能的关键激酶。通过 Western blot 和途径激活剂/抑制剂进一步验证。免疫荧光将激酶蛋白定位于精子中段区域（线粒体），这是这些信号通路的已知核外靶标。在大多数情况下，这些激酶的激活剂抑制精子运动但增加活力，反之亦然。激活剂和抑制剂还影响精子线粒体膜电位、ATP 含量和活性氧 (ROS) 水平。数据表明，精子运动和存活是相反的互补的，并且受到细胞内细胞信号的严格调节。尾部精子中的异常细胞信号可能会影响精子浓度和射出精子的运动能力。
