Abstract
The effects of spaceflight on cartilaginous structure are largely unknown. To address this deficiency, articular cartilage (AC) and sternal cartilage (SC) from mice exposed to 30 days of microgravity on the BION-M1 craft were investigated for pathological changes. The flight AC showed some evidence of degradation at the tissue level with loss of proteoglycan staining and a reduction in mRNA expression of mechano-responsive and structural cartilage matrix proteins compared to non-flight controls. These data suggest that degradative changes are underway in the AC extracellular matrix exposed to microgravity. In contrast, there was no evidence of cartilage breakdown in SC flight samples and the gene expression profile was distinct from that of AC with a reduction in metalloproteinase gene transcription. Since the two cartilages respond differently to microgravity we propose that each is tuned to the biomechanical environments in which they are normally maintained. That is, the differences between magnitude of normal terrestrial loading and the unloading of microgravity dictates the tissue response. Weight-bearing articular cartilage, but not minimally loaded sternal fibrocartilage, is negatively affected by the unloading of microgravity. We speculate that the maintenance of physiological loading on AC during spaceflight will minimize AC damage.
Highlights
The major load-bearing tissue within the joint is articular cartilage (AC)
Gene expression analysis showed several sustained changes in gene activation in SF compared to ground controls (GC) samples
Articular cartilage Spaceflight (SF) AC samples demonstrated less proteoglycan compared to AC ground controls (GC) (Fig. 1a)
Summary
The major load-bearing tissue within the joint is articular cartilage (AC). AC is exquisitely sensitive to changes in biomechanical loading (reviewed by Sanchez-Adams et al.[1]). Deviation from the normal range of biomechanical forces,[2,3,4,5] including complete unloading,[6,7,8] tips the balance from maintenance to pathology typically leading to cartilage erosion and later osteoarthritis. While the effects of the biomechanical unloading environment of spaceflight on bone and skeletal muscle are well-studied,[9,10] the effects on AC are largely unknown. The responses of AC to microgravity are important to define because it is clear from clinical studies that load-bearing AC is different from bone and skeletal tissue in that has a very poor capacity to restore damaged tissue.[11] microgravityinduced joint pathology could compromise flight crew mobility, interfere with mission activities, and accelerate short- and longterm joint degradation in flight personnel
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