Takafumi Suzuki

During spaceflight, astronauts are exposed to extreme conditions such as microgravity, cosmic radiation, and confinement, which can cause a wide range of health problems. To elucidate the molecular mechanisms underlying these issues and to develop intervention strategies for maintaining physiological homeostasis during space missions, space life science research using mouse models is actively conducted on the International Space Station (ISS). However, because of the high cost and technical complexity of spaceflight experiments, it is essential to maximize the scientific value of each mission by ensuring broad accessibility to both data and biospecimens. To this end, we present the integrated biobank for Space Life Science (ibSLS; https://ibsls.megabank.tohoku.ac.jp), a data-visualization and sample-sharing platform that provides access to transcriptomic and metabolomic datasets generated from Mouse Habitat Unit (MHU) missions conducted by the Japan Aerospace Exploration Agency (JAXA). The platform features a user-friendly interface, tools for cross-mission analysis, and links to human multi-omics databases to support cross-species interpretation. In addition, ibSLS facilitates biospecimen requests to support downstream research. By promoting open access to spaceflight-derived data and biological resources, ibSLS encourages the participation of researchers from diverse fields in space life science.

Kelch-like ECH-associated protein 1 (Keap1) acts as a repressor of nuclear factor-erythroid 2-related factor 2 (Nrf2), a major transcription factor regulating cellular antioxidant response. Keap1 is the substrate adaptor subunit of the cullin 3-RING E3 ubiquitin ligase complex that specifically facilitates Nrf2 ubiquitination and its proteasomal degradation. Keap1 is rich in cysteine residues, and several of them undergo various modifications, such as sulphydration, nitrosylation and glutathionylation under cellular stress conditions. Some of these modifications alter the conformation of Keap1, preventing Nrf2 from ubiquitination and subsequent proteasome-mediated degradation. As a result, newly synthesised Nrf2 translocates to the nucleus to induce the expression of diverse genes involved in protecting cells against oxidative stress. Protein CoAlation is a reversible redox-dependent post-translational modification (PTM) in which coenzyme A (CoA) forms disulphide bonds with oxidised cysteine residues under oxidative or metabolic stress. In this study, we demonstrate for the first time that disulphide Keap1 dimer undergoes CoAlation in cellular response to oxidative stress induced by various oxidising compounds. Furthermore, glucose deprivation also induces CoAlation of the disulphide Keap1 dimer in HEK293/Pank1β cells. We also demonstrate that the Keap1^{11 Cys-less} mutant is not CoAlated in response to diamide treatment or glucose deprivation. In summary, this study uncovers a novel PTM of Keap1 by the key metabolic integrator CoA, which provides new insights into the regulation of the Keap1-Nrf2 antioxidant pathway under oxidative and metabolic stress.

Kelch-like ECH-associated protein 1 (Keap1) acts as a repressor of nuclear factor-erythroid 2-related factor 2 (Nrf2), a major transcription factor regulating cellular antioxidant response. Keap1 is the substrate adaptor subunit of the cullin 3-RING E3 ubiquitin ligase complex that specifically facilitates Nrf2 ubiquitination and its proteasomal degradation. Keap1 is rich in cysteine residues and several of them undergo various modifications, such as sulfhydration, nitrosylation and glutathionylation under cellular stress conditions. Some of these modifications alter the conformation of Keap1, preventing Nrf2 from ubiquitination and subsequent proteasome-mediated degradation. As a result, newly synthesised Nrf2 translocates to the nucleus to induce the expression of diverse genes involved in protecting cells against oxidative stress. Protein CoAlation is a reversible redox-dependent post-translational modification (PTM) in which coenzyme A (CoA) forms disulphide bonds with oxidised cysteine residues under oxidative or metabolic stress. In this study, we demonstrate for the first time that disulphide Keap1 dimer undergoes CoAlation in cellular response to oxidative stress induced by various oxidising compounds. Furthermore, glucose deprivation also induces CoAlation of disulphide Keap1 dimer in HEK293/Pank1β cells. We also demonstrate that Keap1^{11 Cys-less} mutant is not CoAlated in response to diamide treatment or glucose deprivation. In summary, this study uncovers a novel PTM of Keap1 by the key metabolic integrator CoA, which provides new insights into the regulation of the Keap1-Nrf2 antioxidant pathway under oxidative and metabolic stress.

Keap1-Kelch-targeting protein–protein interaction inhibitors (left) increase the thermostability of Keap1-mCherry, whereas double Michael acceptors (right) decrease the thermostability of Keap1-mCherry in the cellular environment.

As human space exploration advances, understanding how different gravity levels affect skeletal muscle is critical for long-term health. Among the major organ systems, skeletal muscle is particularly sensitive to gravitational unloading, yet the gravity threshold required to maintain homeostasis remains unclear. Using the Multiple Artificial-gravity Research System aboard the International Space Station, mice were exposed to graded gravity levels, microgravity, 0.33 g , 0.67 g , and 1 g , and their muscles were analyzed postflight. In the gravity-sensitive soleus, the cross-sectional area was preserved at 0.33 g , while the slow-to-fast myofiber transition was partially suppressed at 0.33 g and fully prevented at 0.67 g . Functional measures, including forelimb grip strength and electrical impedance myography, indicated that 0.67 g was sufficient to maintain muscle performance. Plasma metabolomics identified 11 metabolites with gravity-dependent changes, suggesting potential biomarkers for monitoring physiological adaptation. Collectively, these results identify 0.67 g as a critical threshold for mitigating spaceflight-induced muscle atrophy and myofiber type transitions.

The maintenance of cellular redox balance is crucial for cell survival and homeostasis and is disrupted with aging. Selenoproteins, comprising essential antioxidant enzymes, raise intriguing questions about their involvement in hematopoietic aging and potential reversibility. Motivated by our observation of messenger RNA downregulation of key antioxidant selenoproteins in aged human hematopoietic stem cells (HSCs) and previous findings of increased lipid peroxidation in aged hematopoiesis, we used selenocysteine transfer RNA (tRNASec) gene (Trsp) knockout (KO) mouse model to simulate disrupted selenoprotein synthesis. This revealed insights into the protective roles of selenoproteins in preserving HSC stemness and B-lineage maturation, despite negligible effects on myeloid cells. Notably, Trsp KO exhibited B lymphocytopenia and reduced HSCs’ self-renewal capacity, recapitulating certain aspects of aged phenotypes, along with the upregulation of aging-related genes in both HSCs and pre-B cells. Although Trsp KO activated an antioxidant response transcription factor NRF2, we delineated a lineage-dependent phenotype driven by lipid peroxidation, which was exacerbated with aging yet ameliorated by ferroptosis inhibitors such as vitamin E. Interestingly, the myeloid genes were ectopically expressed in pre-B cells of Trsp KO mice, and KO pro-B/pre-B cells displayed differentiation potential toward functional CD11b+ fraction in the transplant model, suggesting that disrupted selenoprotein synthesis induces the potential of B-to-myeloid switch. Given the similarities between the KO model and aged wild-type mice, including ferroptosis vulnerability, impaired HSC self-renewal and B-lineage maturation, and characteristic lineage switch, our findings underscore the critical role of selenoprotein-mediated redox regulation in maintaining balanced hematopoiesis and suggest the preventive potential of selenoproteins against aging-related alterations.