Mechanosensitivity of osteoblast cells observed via parabolic flight.
- Paper number
IAC-06-A1.P.1.09
- Author
Mr. Stephen Kearney, University College Dublin, Ireland
- Year
2006
- Abstract
Background: Mechanical stress is known to be a regulatory factor for certain biological cells. Osteoblasts, the bone forming cells, are an example of one such cell type. Within these cells, the cytoskeleton is thought to be a key element for enabling the transduction of mechanical stress from the cell’s surface to the nucleus. The cytoskeleton is a three-dimensional network composed of fibrous proteins, which contributes to cell shape, movement, internal organisation and division. Furthermore, it has been observed during spaceflight that the f-actin cytoskeleton and nuclei of osteoblasts degrade and alter morphology respectively. It is hence hypothesised that such cellular alterations are related to the phenomenon whereby astronauts may loose up to 19% of their weight bearing bone during long duration spaceflight. Methodology: To explicate these observations, we performed an experiment through the European Space Agency (ESA) Student Parabolic Flight Campaign (SPFC) 2005. Specifically, this experiment was designed to observe changes, if any, in the f-actin cytoskeleton and nuclei of osteoblast cells resulting from changes in mechanical loading caused by the varying gravitational forces encountered within parabolic flight. During the parabolic flight sequence, the cells were exposed to thirty 25-second intervals of microgravity at the top of each parabola, in addition to sixty 30-second intervals of 1.8g, each hypergravity period caused by the airplane either entering or exiting a parabola. The cells were fixed at three time-points, firstly before the first parabola begun, secondly halfway through the series of parabolas, after the 15th parabola, and thirdly after the final, 30th parabola. Additionally, control cells were fixed on the ground at time-intervals corresponding to fixation points within flight. Post-flight, the cells’ nuclei and f-actin cytoskeleton were stained with propidium iodide and phalloidin respectively, enabling subsequent imaging via confocal microscopy. Results: Changes were observed in the cytoskeleton, such that the quantity and quality of f-actin stress fibers appeared to be reduced in proportion to the number of parabolas undergone by the cells before fixation. Additionally, possible changes are apparent in nuclear envelope integrity and/or the level of cyto-nucleoplasmic transport, again relative to the mechanical stress to which the cells were exposed. Also discussed are supplementary investigations related to extra-cellular signaling and surface morphology, made possible by the preservation of cell culture medium and fixation for scanning-election microscopy respectively. Discussion/Conclusion: These results contribute to the elucidation of the mechanisms of mechanotransduction, which, besides being implicated in osteoporosis, is thought to play a role in many disease states including cancer. Finally, we conclude by outlining a proposal to progress and refine our findings, via the utilization of live cell imaging to capture in real-time cellular cytoskeletal responses to microgravity.
- Abstract document