Alteration in cytoskeletal organization appears to underlie mechanisms of gravity sensitivity in space-flown cells. Human T lymphoblastoid cells (Jurkat) were flown on the Space Shuttle to test the hypothesis that growth responsiveness is associated with microtubule anomalies and mediated by apoptosis. Cell growth was stimulated in microgravity by increasing serum concentration. After 4 and 48 h, cells filtered from medium were fixed with formalin. Post-flight, confocal microscopy revealed diffuse, shortened microtubules extending from poorly defined microtubule organizing centers (MTOCs). In comparable ground controls, discrete microtubule filaments radiated from organized MTOCs and branched toward the cell membrane. At 4 h, 30% of flown, compared to 17% of ground, cells showed DNA condensation characteristic of apoptosis. Time-dependent increase of the apoptosis-associated Fas/ APO-1 protein in static flown, but not the in-flight 1 g centrifuged or ground controls, confirmed microgravity-associated apoptosis. By 48 h, ground cultures had increased by 40%. Flown populations did not increase, though some cells were cycling and actively metabolizing glucose. We conclude that cytoskeletal alteration, growth retardation, and metabolic changes in space-flown lymphocytes are concomitant with increased apoptosis and time-dependent elevation of Fas/APO-1 protein. We suggest that reduced growth response in lymphocytes during spaceflight is linked to apoptosis.

No abstract

No abstract

Cytoskeletal disruption and growth arrest consistently occur in space‐flown human acute leukemic T cells (Jurkat). Although the microtubules appear to reorganize during spaceflight, cells remain nonproliferative. To test the hypothesis that spaceflight alters cytoskeletal gene expression and may thus affect cytoskeletal function, we flew Jurkat cells on Space Transportation System (STS) 95 and compared RNA message by cDNA microarray in space‐flown vs. ground controls at 24 h (4,324 genes) and 48 h (>20,000 genes). Messages for 11 cytoskeleton‐related genes, including calponin, dynactin, tropomodulin, keratin 8, two myosins, an ankyrin EST, an actinlike protein, the cytoskeletal linker (plectin), and a centriole‐associated protein (C‐NAP1), were up‐regulated in space‐flown compared with ground control cells; gelsolin precursor was down‐regulated. Up‐regulation of plectin and C‐NAP1 message in both space‐flown cells and vibrated controls is a novel finding and implies their role in vibration damage repair. This first report of cDNA microarray screening of gene expression in space‐flown leukemic T cells also identifies differential expression of genes that regulate growth, metabolism, signal transduction, adhesion, transcription, apoptosis, and tumor suppression. Based on differential expression of cytoskeletal genes, we conclude that centriole‐centriole, membrane‐cytoskeletal, and cytoskeletal filament associations are altered in the orbital phase of spaceflight.

Protein kinase C (PKC) is a family of serine/threonine kinases that play an important role in mediating intracellular signal transduction in eukaryotes. U937 cells were exposed to microgravity during a space shuttle flight and stimulated with a radiolabeled phorbol ester ([3H]PDBu) to both specifically label and activate translocation of PKC from the cytosol to the particulate fraction of the cell. Although significant translocation of PKC occurred at all g levels, the kinetics of translocation in flight were significantly different from those on the ground. In addition, the total quantity of [3H]PDBu binding PKC was increased in flight compared to cells at 1 g on the ground, whereas the quantity in hypergravity (1.4 g) was decreased with respect to 1 g. Similarly, in purified human peripheral blood T cells the quantity of PKCdelta varied in inverse proportion to the g level for some experimental treatments. In addition to these novel findings, the results confirm earlier studies which showed that PKC is sensitive to changes in gravitational acceleration. The mechanisms of cellular gravisensitivity are poorly understood but the demonstrated sensitivity of PKC to this stimulus provides us with a useful means of measuring the effect of altered gravity levels on early cell activation events.

No abstract

Cultured, bone marrow-derived macrophages, murine spleen and lymph node cells, and human lymphocytes were tested for their ability to secrete cytokines in space. Lipopolysaccharide-activated bone marrow macrophages were found to secrete significantly more interleukin-1 and tumor necrosis factor when stimulated in space than when stimulated on earth. Murine spleen cells stimulated with poly I:C in space released significantly more interferon-alpha at 1 and 14 hours after stimulation than cells stimulated on earth. Similarly, murine lymph node T cells and human peripheral blood lymphocytes, stimulated with concanavalin A in space, secreted significantly more interferon-gamma than ground controls. These data suggest that space flight has a significant enhancing effect on immune cell release of cytokines in vitro.

No abstract