Cartilage Unloading Project Summary

While several studies have investigated the influence of long-duration space flight on muscle and bone tissue, it remains unclear how unloading influences cartilage health. It has been shown in animals that decreased loading results in cartilage deterioration with compositional changes similar to those of osteoarthritis (OA). However, it is unclear if these same changes are experienced in astronauts during space flight. If long-duration unloading results in biochemical changes within the cartilage, it may be a medical risk-factor for the development of OA later in life. OA is a progressive degenerative disease that is characterized by changes in proteoglycan and water content. Recent advancement in MR technology allow for an increased ability to monitor these biochemical levels in vivo. Furthermore, the reversibility reported in animal work with remobilization has yet to be observed in humans. The proposed study will utilize state-of-the-art MR techniques to monitor knee cartilage composition with non-weight-bearing (simulated zero-gravity) and return to full-weight-bearing (relative increased loading). The primary objective of this proposal is to quantify changes in cartilage composition with loading deprivation using advanced MR techniques (including T2 and T1ρ relaxation time mapping). A secondary objective is to demonstrate reversibility of compositional changes of articular cartilage associated with OA in vivo. The results of this study are necessary to determine if biochemical changes associated with early OA occurs in humans after a period of non-weight-bearing and to determine how these changes respond when returning to full weight bearing. Future studies will use this information to design cartilage-protecting protocols of in-space exercise programs as well as post-flight reintegration
into full-gravity conditions.

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