Stromal and Hematopoietic Progenitors from C57/BI/6N Murine Bone Marrow After 30-Day “BION-M1” Spaceflight

Heterotypic Cell Culture from Mouse Bone Marrow under Simulated Microgravity: Lessons for Stromal Lineage Functions

Muscle and skeleton structures are considered most susceptible to negative factors of spaceflights, namely microgravity. Three-dimensional clinorotation is a ground-based simulation of microgravity. It provides an opportunity to elucidate the effects of microgravity at the cellular level. The extracellular matrix (ECM) content, transcriptional profiles of genes encoding ECM and remodelling molecules, and secretory profiles were investigated in a heterotypic primary culture of bone marrow cells after 14 days of 3D clinorotation. Simulated microgravity negatively affected stromal lineage cells, responsible for bone tissue formation. This was evidenced by the reduced ECM volume and stromal cell numbers, including multipotent mesenchymal stromal cells (MSCs). ECM genes encoding proteins responsible for matrix stiffness and cell-ECM contacts were downregulated. In a heterotypic population of bone marrow cells, the upregulation of genes encoding ECM degrading molecules and the formation of a paracrine profile that can stimulate ECM degradation, may be mechanisms of osteodegenerative events that develop in real spaceflight.

Stromal Lineage Precursors from Rodent Femur and Tibia Bone Marrows after Hindlimb Unloading: Functional Ex Vivo Analysis

Rodent hindlimb unloading (HU) model was developed to elucidate responses/mechanisms of adverse consequences of space weightlessness. Multipotent mesenchymal stromal cells (MMSCs) were isolated from rat femur and tibia bone marrows and examined ex vivo after 2 weeks of HU and subsequent 2 weeks of restoration of load (HU + RL). In both bones, decrease of fibroblast colony forming units (CFU-f) after HU with restoration after HU + RL detected. In CFU-f and MMSCs, levels of spontaneous/induced osteocommitment were similar. MMSCs from tibia initially had greater spontaneous mineralization of extracellular matrix but were less sensitive to osteoinduction. There was no recovery of initial levels of mineralization in MMSCs from both bones during HU + RL. After HU, most bone-related genes were downregulated in tibia or femur MMSCs. After HU + RL, the initial level of transcription was restored in femur, while downregulation persisted in tibia MMSCs. Therefore, HU provoked a decrease of osteogenic activity of BM stromal precursors at transcriptomic and functional levels. Despite unidirectionality of changes, the negative effects of HU were more pronounced in stromal precursors from distal limb-tibia. These observations appear to be on demand for elucidation of mechanisms of skeletal disorders in astronauts in prospect of long-term space missions.

Spaceflight-Associated Vascular Remodeling and Gene Expression in Mouse Calvaria

Astronauts suffer from a loss of bone mass at a rate of 1.5% per month from lower regions of the body during the course of long-duration (>30 days) spaceflight, a phenomenon that poses important risks for returning crew. Conversely, a gain in bone mass may occur in non-load bearing regions of the body as related to microgravity-induced cephalad fluid shift. Representing non-load bearing regions with mouse calvaria and leveraging the STS-131 (15-day) and BION-M1 (30-day) flights, we examined spatial and temporal calvarial vascular remodeling and gene expression related to microgravity exposure compared between spaceflight (SF) and ground control (GC) cohorts. We examined parasagittal capillary numbers and structures in calvaria from 16 to 23 week-old C57BL/6 female mice (GC, n = 4; SF, n = 5) from STS-131 and 19–20 week-old C57BL/6 male mice (GC, n = 6; SF, n = 6) from BION-M1 using a robust isolectin-IB4 vessel marker. We found that the vessel diameter reduces significantly in mice exposed to 15 days of spaceflight relative to control. Capillarization increases by 30% (SF vs. GC, p = 0.054) in SF mice compared to GC mice. The vessel numbers and diameter remain unchanged in BION-M1 mice calvarial section. We next analyzed the parietal pro-angiogenic (VEGFA) and pro-osteogenic gene (BMP-2, DMP1, RUNX2 and OCN) expression in BION-M1 mice using quantitative RT-PCR. VEGFA gene expression increased 15-fold while BMP-2 gene expression increased 11-fold in flight mice compared to GC. The linkage between vascular morphology and gene expression in the SF conditions suggests that angiogenesis may be important in the regulation of pathological bone growth in non-weight bearing regions of the body. Short-duration microgravity-mediated bone restructuring has implications in planning effective countermeasures for long-duration flights and extraterrestrial human habitation.

Short-Term Reloading After Prolonged Unloading Ensures Restoration of Stromal but Not Hematopoietic Precursor Activity in Tibia Bone Marrow of C57Bl/6N Mice

Bone and muscle tissues are mostly susceptible to different kinds of hypodynamia, including real and simulated microgravity (sμg). To evaluate the effect of sμg on bone marrow (BM), male C57Bl/6N mice were divided into three groups: vivarium control (VC), 30-day hindlimb suspension (HS), and subsequent 12-h short-term support reloading (RL). The effects on BM total mononucleated cells (MNCs) as well as stromal and hematopoietic progenitors from murine tibia were studied. The number of BM MNCs, immunophenotype, proliferation, colony-forming units (CFUs), differentiation and secretory activity of hematopoietic and stromal BM cells were determined. HS led to a twofold decrease in MNCs, alteration of surface molecule expression profiles, suppression of proliferative activity of BM cells, and change of soluble mediators' levels. The stromal compartment was characterized by a decrease of CFU of fibroblasts and suppression of spontaneous osteo-commitment after HS. Among the hematopoietic precursors, a decrease in the total number of CFUs was found mainly at the expense of suppression of CFU-GM and CFU-GEMM. After RL, restoration of the stromal precursor's functional activity to control levels and overabundance of paracrine mediator's production were detected, whereas the complete recovery of hematopoietic precursor's activity did not occur. These data demonstrate the fast functional reaction of the stromal compartment on restoration of loading support.

The individual and combined effects of spaceflight radiation and microgravity on biologic systems and functional outcomes

Both microgravity and radiation exposure in the spaceflight environment have been identified as hazards to astronaut health and performance. Substantial study has been focused on understanding the biology and risks associated with prolonged exposure to microgravity, and the hazards presented by radiation from galactic cosmic rays (GCR) and solar particle events (SPEs) outside of low earth orbit (LEO). To date, the majority of the ground-based analogues (e.g., rodent or cell culture studies) that investigate the biology of and risks associated with spaceflight hazards will focus on an individual hazard in isolation. However, astronauts will face these challenges simultaneously Combined hazard studies are necessary for understanding the risks astronauts face as they travel outside of LEO, and are also critical for countermeasure development. The focus of this review is to describe biologic and functional outcomes from ground-based analogue models for microgravity and radiation, specifically highlighting the combined effects of radiation and reduced weight-bearing from rodent ground-based tail suspension via hind limb unloading (HLU) and partial weight-bearing (PWB) models, although in vitro and spaceflight results are discussed as appropriate. The review focuses on the skeletal, ocular, central nervous system (CNS), cardiovascular, and stem cells responses.

Effect of simulated microgravity conditions of hindlimb unloading on mice hematopoietic and mesenchymal stromal cells

Conditions in space, such as microgravity, may affect the hematopoietic and bone marrow‐derived mesenchymal stromal cells (BM‐MSCs) of astronauts. However, to date, few detailed phenotype change data about the different type of hematopoietic cells have reported. In this study, C57BL/6 mice were randomly divided into two groups: a control group (control) and a hindlimb suspension group (treated). After four weeks of hindlimb suspension, we found that this simulated microgravity (sµg) condition could increase the percentage of monocytes and macrophages and decrease the percentage of B lymphocytes and mature red cells in bone marrow. The percentage of B lymphocytes in the spleen and the red blood cell count in peripheral blood also decreased, consistent with the response of bone marrow. The cytoskeleton in the BM‐MSCs was disrupted. The expression levels of hematopoietic‐related genes, such as fms‐like tyrosine kinase‐3 ligand, granulocyte‐macrophage colony stimulating factor, interleukin‐3, and adipogenic differentiation associated genes, leptin and proliferator‐activated receptor γ type 2, were upregulated under sµg conditions. These results indicated that simulating microgravity can affect the phenotype of certain types of hematopoietic cells and the morphology and gene expression pattern of BM‐MSCs.