There have been no studies that specifically investigate whether microgravity results in the degeneration of articular cartilage. Articular cartilage breakdown could be a major consequence of long-term space travel because, unlike bone, once cartilage degradation begins it cannot be reversed, typically leading to osteoarthritis. The mobility of an individual affected by even mid-stage osteoarthritis would be compromised leading to a failure to complete the full range of mission duties.
Specifically, knees and elbows were dissected from 6 flight mice and a cohort of vivarium controls. The right elbows and knees from each mouse were placed in formalin in preparation for histological and immunohistochemical analyses. The left elbows and knees were placed in RNALater for RNA preservation for gene expression analysis. Ground control dissections were also planned.
Effects on cartilage of 30 days exposure to microgravity. There was significant proteoglycan loss, as shown by reduced toluidine staining in the knee cartilage of flight animals compared to the non-flight animals (p=0.008, students t-test). Interestingly, many of the chondrocytes within the middle zone remain blue. Despite this proteoglycan degradation, no clear structural changes to the articular cartilage surface of the flight mice were present suggesting that, with 30 days of unloading, the collagen II network remains intact.
Extensive literature exists in humans and in animals suggesting that a normal range of biomechanical forces is required for cartilage homeostasis. Consistent with this is our finding that the reduced biomechanical environment of microgravity induces cartilage breakdown. Although there is clear evidence of proteoglycan loss after 15 days of microgravity on STS-131, there is clear evidence of proteoglycan loss after 30 days on BION. In addition, the mRNA changes in BION are consistent with reduced cartilage matrix synthesis and further support the finding that cartilage atrophy occurs in spaceflight.
Based on these data we speculate that the maintenance of biomechanical loading during Spaceflight will reduce cartilage destruction. Exercise is the countermeasure.
No data submitted. Summarized and analyzed data may be available through publications.
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