Purine metabolism in bone marrow microenvironment inhibits hematopoietic stem cell differentiation under microgravity

Abstract

Background Spaceflight and microgravity environments have been shown to cause significant health impairments, including bone loss, immune dysfunction, and hematopoietic disorders. Hematopoietic stem cells (HSCs), as progenitors of the hematopoietic system, are critical for the continuous renewal and regulation of immune cells. Therefore, elucidating the regulatory mechanisms governing HSC fate and differentiation in microgravity environments is of paramount importance. Methods In this study, hindlimb unloading (HU) was employed in mice to simulate microgravity conditions. After 28 days of HU, cells were isolated for analysis. Flow cytometry and colony-forming assays were utilized to assess changes in HSC proliferation and differentiation. Additionally, transcriptomic and untargeted metabolomic sequencing were performed to elucidate alterations in the metabolic pathways of the bone marrow microenvironment and their molecular regulatory effects on HSCs fate. Results Our findings revealed that 28 days of HU impaired hematopoietic function, leading to multi-organ damage and hematological disorders. The simulated microgravity environment significantly increased the HSCs population in the bone marrow, particularly within the long-term and short-term subtypes, while severely compromising the differentiation capacity of hematopoietic stem/progenitor cells. Transcriptomic analysis of HSCs, combined with metabolomic profiling of bone marrow supernatants, identified 1,631 differentially expressed genes and 58 metabolites with altered abundance. Gene set enrichment analysis indicated that HU suppressed key pathways, including hematopoietic cell lineage and MAPK signaling. Furthermore, integrated analyses revealed that metabolites affected by HU, particularly hypoxanthine enriched in the purine metabolism pathway, were closely associated with hematopoietic cell lineage and MAPK signaling pathways. Molecular docking simulations and in vitro experiments confirmed that hypoxanthine interacts directly with core molecules within these pathways, influencing their expression. Conclusions These findings demonstrate that hypoxanthine in the bone marrow supernatant acts as a signaling mediator under microgravity, influencing HSCs fate by modulating hematopoietic cell lineage and MAPK signaling pathways. This study offers novel insights into the impact of microgravity on HSC fate and gene expression, underscoring the pivotal role of bone marrow microenvironmental metabolic changes in regulating key signaling pathways that determine hematopoietic destiny.

1. Introduction

With the advent of long-duration space missions, the complexity of the space environment and its impact on human physiology have garnered increasing attention [1]. The space environment is characterized by extreme conditions, including high radiation, microgravity, and high vacuum [2]. Among these, microgravity exerts particularly profound effects on biological systems [3]. Research has demonstrated that microgravity can lead to immune dysfunction [4], disrupted hematopoiesis [5], and bone marrow (BM) impairment [6], thereby increasing the risk of hematological disorders. These adverse effects are especially pronounced during extended space missions.

Under microgravity, the human hematopoietic system undergoes a series of physiological changes, including impaired platelet (PLT) function, reduced lymphocyte (LYM) counts, and suppressed LYM activity. For instance, a study reported a marked decrease in the absolute number of T and B LYMs in astronauts during spaceflight [7]. However, due to limited sample sizes and significant inter-individual variability, these findings remain inconclusive.