[Sparm stem Cells]
Effect of space environment on fertility of spermatogonial stem cells

RESEARCH OVERVIEW

• Several previous studies suggest that spermatogenesis declines during spaceflight. However, it is unknown whether this is caused by damage to spermatogenic cells or somatic cells. Using a purified germ cell population, the Effect of the Space Environment on Fertility of Spermatogonial Stem Cells (Sperm Stem Cells) investigation examines the degree of damage to the cells during spaceflight.
• Sperm Stem Cells seeks to clarify the impact of spaceflight on the phenotype and functional properties of spermatogonial stem cells (SSCs). Scientists may also find out which genes are influenced by spaceflight in both SSCs, and offspring derived from SSCs. Through these analyses, it can be examined whether SSCs remain normal, even in spaceflight.
• Offspring born from SSCs preserved or cultured on the space station demonstrate the robustness of SSCs. Unlike sperm, SSCs can increase their number, have DNA repair capacity, and undergo meiosis, which creates genetic diversity. In this sense, SSCs are superior to sperm in germline preservation and production of normal offspring from SSCs can create new opportunities for future human reproduction protection and conservation in space.

DESCRIPTION

Germline preservation is often carried out by sperm or embryos. In the Effect of the Space Environment on Fertility of Spermatogonial Stem Cells (Sperm Stem Cells) investigation, the research team examines the usefulness of spermatogenic stell cells (SSCs), which can also produce offspring by transplantation into the seminiferous tubules. Because SSCs can proliferate in vitro and undergo meiosis, they have several advantages not found in traditional methods. Although spermatogenic abnormalities are often found in testes of animals during spaceflight, it is unknown whether such defects are caused by damages in germ cells or somatic cells. By freezing or culturing mouse SSCs, the robustness of SSCs in spaceflight is studied.

SPACE APPLICATIONS

Previous studies suggest that production of sperm declines during spaceflight, but whether the cause is damage to spermatogenic cells or somatic cells is still unclear. Although studies have examined sperm and embryonic stem cells, spermatogonial stem cells (SSCs) have different properties. This analysis of SSCs complements previous studies and could contribute to preserving these cells during long spaceflights.

EARTH APPLICATIONS

In cancer therapy, irradiation or chemical treatments are generally used. These treatments often induce male infertility and the reduction of differentiated spermatogenic cells, which is similar to those found in testes of several animals in space. This study is useful not only for understanding why spermatogenic defects occur during spaceflight, but also for future human life in space

OPERATIONAL REQUIREMENTS AND PROTOCOLS

This investigation consists of two experiments. One experiment (Exp#1) is to store frozen cell samples at -95°C in the on-board Minus Eighty Laboratory Freezer for ISS (MELFI) for 6, 12, 24, and 36 months. Another (Exp#2) cultures SSCs in an enclosed cell culture chamber for 7 and 21 days, followed by the fixation and the preservation of the cells.

For Exp#1, samples containing SSCs are kept frozen (-95°C) during launch and are transferred from a cargo vehicle to MELFI. The only on-board operation is to store the samples at -95°C in MELFI. After 6, 12, 24, and 36 months, the samples are returned to Earth under frozen conditions (-95°C).

For Exp#2, SSCs in enclosed cell culture chambers (Disposable Cultivation Chamber: DCC) are launched under frozen conditions (-95°C) and are stored frozen in MELFI until the start of the experiment. Cells are thawed and the liquid inside the DCCs is replaced with cell culture medium. DCCs are maintained at 37°C under microgravity or 1G conditions in the JAXA Cell Biology Experiment Facility (CBEF). Half of the cell samples are cultured for 7 days, and the other for 21 days. For the latter samples, the cell culture medium needs to be replaced occasionally (3-6 days interval). Thereafter, the cells are either fixed or preserved for return to Earth. The fixed samples are stored at 4°C in MELFI, and the preserved samples are stored at -95°C in MELFI. For return to Earth, the fixed and preserved samples should be stored under 4°C and -95°C conditions, respectively.

SHINOHARA Takashi [Kyoto University]