Miyaso Hidenobu, Ogawa Yuki, Itoh Masahiro
Department of Anatomy, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo, 160-8402, Japan.
Department of Anatomy, School of Medicine, International University of Health and Welfare, 4-3 Kozunomori, Narita, Chiba, 286-8686, Japan.
Histochem Cell Biol. 2022 Mar;157(3):273-285. doi: 10.1007/s00418-021-02071-z. Epub 2022 Mar 5.
The male reproductive system consists of testes, a series of ducts connecting the testes to the external urethral orifice, accessory sex glands, and the penis. Spermatogonial stem cells differentiate and mature in testes and epididymides, and spermatozoa are ejaculated with exocrine fluids secreted by accessory sex glands. Many studies have clarified the detailed structure and function of the male reproductive system, and have shown that various biologic controls, including genomics, epigenetics, and the neuroendocrine-immune system regulate proliferation, differentiation, and maturation of germ cells. In other words (1) genetic deletion or abnormalities, (2) aberration of DNA methylation and histone modifications, as well as small RNA dysfunction, and (3) neuroendocrine-immune disorders are involved in functional failure of the male reproductive system. In this article, we review these three factors for germ cell microcircumstance, especially focused on the immunoendocrine environment. In particular, the relation between factors protecting germ cells with strong auto-immunogenicity and opposite factors compromising this protection are discussed. Reductions in sperm count, concentration, and semen quality are serious problems in developed countries, although the causes are complex and remain unclear. The accumulation of basic knowledge regarding the structure, function, and regulation of the male reproductive system under various experimental conditions will be important to resolve these problems.
男性生殖系统由睾丸、一系列将睾丸与尿道外口相连的管道、附属性腺和阴茎组成。精原干细胞在睾丸和附睾中分化并成熟，精子与附属性腺分泌的外分泌液一起射出。许多研究已经阐明了男性生殖系统的详细结构和功能，并表明包括基因组学、表观遗传学和神经内分泌免疫系统在内的各种生物控制机制调节生殖细胞的增殖、分化和成熟。换句话说，（1）基因缺失或异常、（2）DNA甲基化和组蛋白修饰的异常以及小RNA功能障碍，以及（3）神经内分泌免疫紊乱都与男性生殖系统的功能衰竭有关。在本文中，我们综述了影响生殖细胞微环境的这三个因素，尤其关注免疫内分泌环境。特别讨论了具有强自身免疫原性的保护生殖细胞的因素与破坏这种保护的相反因素之间的关系。精子数量、浓度和精液质量的下降在发达国家是严重问题，尽管其原因复杂且尚不清楚。积累关于各种实验条件下男性生殖系统的结构、功能和调节的基础知识对于解决这些问题将很重要。
