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Function of the cytoskeleton in gravisensing during spaceflight
1Laboratory of Cell Growth, Northern California Institute for Research and Education, University of California San Francisco, San Francisco, California 94121, USA. millehf@aol.com
Advances in Space Research : the Official Journal of the Committee on Space Research (COSPAR)
|March 9, 2004
Summary
Spaceflight causes significant bone loss due to cellular changes. Microgravity alters osteoblast growth and cytoskeleton, impacting cell cycle regulation and potentially leading to G1 or G2/M phase arrest.
Area of Science:
- Space Biology
- Cell Biology
- Biophysics
Background:
- Astronauts experience significant bone loss in microgravity.
- Previous studies show cellular and extracellular matrix changes in bone cells under microgravity.
- Osteoblast cell shape changes occur even with brief microgravity exposure.
Purpose of the Study:
- To investigate physiological changes in cellular bone growth and cytoskeleton in the absence of gravity.
- To understand the impact of microgravity on osteoblast function and cell cycle.
- To identify potential mechanisms for microgravity-induced bone loss.
Main Methods:
- Culturing various bone cells (e.g., Ros 17/2.8, Mc3T3-E1, MG-63, hFOB) in microgravity conditions.
- Analyzing changes in cell shape, actin cytoskeleton, and focal adhesions.
- Measuring osteoblast growth and prostaglandin E2 (PGE2) release.
- Investigating fibronectin gene and protein expression.
- Assessing cell cycle progression (G1 and G2/M phases).
Main Results:
- Microgravity significantly reduced osteoblast growth by 60% and paradoxically increased PGE2 release twofold.
- Observed collapse of the actin cytoskeleton and loss of focal adhesions in osteoblasts after 4 days in microgravity.
- Flown cells under 1g conditions maintained normal cytoskeleton and fibronectin matrix, indicating microgravity's specific effect.
- No differences in fibronectin message or protein synthesis were noted.
- Evidence suggests impaired anabolic signal transduction and potential cell cycle arrest (G1 or G2/M) in microgravity.
Conclusions:
- Microgravity induces significant alterations in osteoblast cytoskeleton and growth.
- Impaired signal transduction pathways, likely involving growth factor receptors and kinases, contribute to these changes.
- Cytoskeletal disruptions in microgravity may inhibit cell cycle progression, contributing to bone loss.
- Further research is needed to fully elucidate the mechanisms of microgravity-induced bone loss.