Additionally, microgravity and hindlimb unloading also dramatically suppress immune function and endocrine function, specifically the reduction of growth hormone secretion in rodents, non-human primates and humans. In essence, spaceflight has been shown to induce musculoskeletal weakness and reduce the release of various anabolic hormones responsible for growth promoting processes. Normal dense fibrous connective tissue regeneration is significantly impacted by tissue load histories and responds to growth promoting hormones and various cytokines. The rodent model for knee ligament injury and repair has been well characterized and has been used to study wound healing mechanisms by serving as a testing physiological system for implementing countermeasures. The primary objective of our proposal is to use the rodent knee ligament injury repair model to study the impact hindlimb unloading has on the wound healing processes.
Growth hormone is a potent modulator of protein synthesis.
We will use recombinant growth hormone as a active countermeasure to promote wound healing during hindlimb unloading in the second half of the study. The study will focus on the critical regenerative responses of the injured knee ligaments after three weeks and seven weeks post-surgery. Collagen metabolism, tissue cytokine gene expression, collagen fibril organization and tissue material properties in surgically oblated and non-surgical sham ligaments will be thoroughly examined. Similar studies can eventually be proposed during a short term or long term spaceflight mission.