Spermatogonial Stem Cells for In Vitro Spermatogenesis and In Vivo Restoration of Fertility

Abstract

Spermatogonial stem cells (SSCs) are the only adult stem cells capable of passing genes onto the next generation. SSCs also have the potential to provide important knowledge about stem cells in general and to offer critical in vitro and in vivo applications in assisted reproductive technologies. After century-long research, proof-of-principle culture systems have been introduced to support the in vitro differentiation of SSCs from rodent models into haploid male germ cells. Despite recent progress in organotypic testicular tissue culture and two-dimensional or three-dimensional cell culture systems, to achieve complete in vitro spermatogenesis (IVS) using non-rodent species remains challenging. Successful in vitro production of human haploid male germ cells will foster hopes of preserving the fertility potential of prepubertal cancer patients who frequently face infertility due to the gonadotoxic side-effects of cancer treatment. Moreover, the development of optimal systems for IVS would allow designing experiments that are otherwise difficult or impossible to be performed directly in vivo, such as genetic manipulation of germ cells or correction of genetic disorders. This review outlines the recent progress in the use of SSCs for IVS and potential in vivo applications for the restoration of fertility.Cells 2020, 9, 745 2 of 31 manipulation. Moreover, optimal conditions for the in vitro culture and propagation of SSCs are also needed to help boost the potential therapeutic application of SSCs in fertility preservation or restoration. Long-term culture of rodent SSCs is well demonstrated; however, relatively few in vitro culture conditions have been examined for primate SSCs [2]. Any potential in vivo application of cultured human SSCs, such as in restoration of fertility, requires extensive studies to ensure their safety and efficacy. The establishment of efficient culture conditions for human SSCs also necessitates the availability of proper animal models, for instance, xenotransplantation techniques to assess the quality and quantity of such cultured SSCs; these assays have so far been used sporadically for testing primate SSCs [4].Spermatogenesis is a complex process of germ cell proliferation and differentiation that requires extensive interactions among different cell types, hormones, growth factors, and various other signals, making it difficult to be replicated in vitro. There are several objectives for establishing an optimal and efficient culture system to recapitulate the process of germ cell development in vitro. This includes the study of basic requirements of male germ cell development, proliferation, differentiation, and production of haploid germ cells in a controlled in vitro environment. Additionally, such culture systems could be potentially used to produce haploid male germ cells from undifferentiated germ cells isolated from the testis of infertile adult patients and/or testicular biopsies collected from prepubertal cancer patients before undergoing gonadotoxic treatment. The establishment of ...

Melatonin Protects Goat Spermatogonial Stem Cells against Oxidative Damage during Cryopreservation by Improving Antioxidant Capacity and Inhibiting Mitochondrial Apoptosis Pathway

“…SSCs are the only adult stem cells that pass genes to offspring and have been used in the treatment of male reproductive system diseases and animal genome editing [ 5 ]. This study investigated for the first time the effect of melatonin on goat SSCs during cryopreservation and explored its protective mechanisms in terms of oxidation, apoptosis, and autophagy.…”

“…SSCs both self-renew to keep the stability of the stem cell pool and differentiate to contribute to spermatogenesis, thereby maintaining the homeostasis of testicular cells [ 3 ]. As adult stem cells that produce spermatocytes, SSCs transmit genetic information to the next generation [ 4 , 5 ]. Studies have shown that SSCs can be cultured and passaged in vitro, and differentiate into sperm after transplantation [ 6 ].…”

Contributions of Flow Cytometry to the Molecular Study of Spermatogenesis in Mammals

“…The purification of SSCs will be specifically discussed later on. Importantly, for detailed lists on some of the most commonly used markers for the effective FACS sorting of SSCs from the testes of different mammals, recent review articles specifically addressing this topic, and tables therein, can be consulted [ 116 , 117 ]). Together, single-cell analyses have identified new subsets of spermatogonia and unveiled the dynamic nature of spermatogenic initiation.…”

Stem Cell-Based Disease Modeling and Cell Therapy

“…Ibtisham et al summarize the progress made in offering efficient methods for SSC isolation, characterization, in vitro 2D and 3D suspension culture systems, and in vitro differentiation, particularly using primate models. The authors also review some of the salient proposed approaches for the preservation and restoration of fertility in prepubertal and pubertal patients using currently-available and potential future SSC-driven biotechnological strategies [ 36 ].…”

“…This Special Issue includes both research [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ] and reviews articles [ 10 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ] which cover wide ranges of stem cell research: adult stem cells, cancer stem cells, pluripotent stem cells, and complex 3D organoid/cell aggregate models [ 26 , 27 , 33 ], with the focuses on stem cell biology/technology [ 10 , 23 , 24 , 25 , 26 , 31 , 32 , 34 ], and stem cell-based disease modeling [ 10 , 27 , 29 , 31 , 33 , 38 , 43 ] and cell therapy [ 24 , 28 , 30 , 32 , 35 , 36 , 37 , 39 , 40 , 41 ].…”