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Maintaining Muscle Mass in Space

Author(s): Kenneth M. Baldwin, PhD

The Pattern of Skeletal Myosin Heavy Chain (MHC) Isoform Transitions

Muscle fibers comprising our various muscle groups are very plastic, in that they can change their size and contractile properties depending on the chronic conditions imposed. Research involving both animals and humans suggests that if we reduce the force of gravity by sending animals and/or humans on either the space shuttle or the International Space station for several days or longer, we can change gene expression within the motor protein gene family. For example, under the conditions of spaceflight, the slow type I myosin heavy chain (MHC) gene becomes repressed and its encoded protein becomes degraded. In its place, the faster MHC genes become up-regulated (expression is increased). Thus, the muscle fibers become transformed into smaller and faster fibers. In contrast, if one is exposed to daily high levels of loading, as occurs during resistance exercise (lifting very heavy objects), the patterns of shift occur in the opposite direction: the muscle fibers get bigger and stronger, but somewhat slower.

When subjects return from space, can you predict any differences they will experience in performing tasks that are usually carried out to oppose the ongoing force of gravity?

Suggested Reading:
Baldwin, K. M. & Haddad, F. Skeletal muscle plasticity: cellular and molecular responses to altered physical activity paradigms. (2002). Am. J. Physical Med. & Rehab. 81: (Suppl) S40-S51.
Caiozzo, V. J. ,Haddad, F., Baker, M.J., Herrick, R. E., Prietto, N., & Baldwin K.M. (1996). Microgravity induced transformations of myosin isoforms and contractile properties of skeletal muscle. J. Appl. Physiol.  81: 123-132.

We know that the isoforms of myosin can be expressed in our individual fibers, and that this pattern of expression is not fixed. The various genes—and the protein products of these genes—can be manipulated. One gene can be turned on and another gene can be turned off, and now we have the ability to remodel muscle fibers, depending upon the physical conditions we are imposing onto our skeletal muscle system.

Funded by the following grant(s)

National Space Biomedical Research Institute

National Space Biomedical Research Institute

This work was supported by National Space Biomedical Research Institute through NASA cooperative agreement NCC 9-58.