Department of Experimental Genome Research, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Laboratory of Reproductive Systems Biology, Center for Experimental Medicine and Systems Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Exp Anim. 2024 Feb 14;73(1):1-10. doi: 10.1538/expanim.23-0055. Epub 2023 Jul 10.
Mammalian sperm flagellum contains the midpiece characterized by a mitochondrial sheath that packs tightly around the axoneme and outer dense fibers. Mitochondria are known as the "powerhouse" of the cell, and produce ATP through the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS). However, the contribution of the TCA cycle and OXPHOS to sperm motility and male fertility is less clear. Cytochrome c oxidase (COX) is an oligomeric complex localized within the mitochondrial inner membrane, and the terminal enzyme of the mitochondrial electron transport chain in eukaryotes. Both COX6B2 and COX8C are testis-enriched COX subunits whose functions in vivo are poorly studied. Here, we generated Cox6b2 and Cox8c knockout (KO) mice using the CRISPR/Cas9 system. We examined their fertility and sperm mitochondrial function to determine the significance of testis-enriched COX subunits in male fertility. The mating test revealed that disrupting COX6B2 induces male subfertility, while disrupting COX8C does not affect male fertility. Cox6b2 KO spermatozoa showed low sperm motility, but mitochondrial function was normal according to oxygen consumption rates. Therefore, low sperm motility seems to cause subfertility in Cox6b2 KO male mice. These results also indicate that testis-enriched COX, COX6B2 and COX8C, are not essential for OXPHOS in mouse spermatozoa.
哺乳动物精子的鞭毛包含中段，其特征是线粒体鞘紧密地包裹着轴丝和外致密纤维。线粒体被称为细胞的“动力工厂”，通过三羧酸（TCA）循环和氧化磷酸化（OXPHOS）产生 ATP。然而，TCA 循环和 OXPHOS 对精子运动和男性生育力的贡献尚不清楚。细胞色素 c 氧化酶（COX）是一种定位于线粒体内膜的寡聚复合物，是真核生物线粒体电子传递链的末端酶。COX6B2 和 COX8C 都是富含睾丸的 COX 亚基，其在体内的功能研究甚少。在这里，我们使用 CRISPR/Cas9 系统生成了 Cox6b2 和 Cox8c 敲除（KO）小鼠。我们检查了它们的生育能力和精子线粒体功能，以确定富含睾丸的 COX 亚基在男性生育力中的意义。交配试验表明，破坏 COX6B2 会导致雄性生育力下降，而破坏 COX8C 则不会影响雄性生育力。Cox6b2 KO 精子显示出低精子运动能力，但根据耗氧量，线粒体功能正常。因此，低精子运动能力似乎导致 Cox6b2 KO 雄性小鼠的生育力下降。这些结果还表明，富含睾丸的 COX、COX6B2 和 COX8C 对于小鼠精子的 OXPHOS 并非必不可少。
