Mechanical Suppression of Microgravity-Induced Chondrocyte Hypertrophy in Engineered Human Cartilage
Bibliographic record
Abstract
Articular cartilage (AC) of the knee exists under a low oxygen and mechanically active environment. Mechanical unloading conditions of spaceflight microgravity pose a risk for astronauts to develop knee osteoarthritis-like pathology, which culminates in AC atrophy and breakdown, joint space narrowing, subchondral bone thickening, and the formation of bone spurs. Mesenchymal stem cells (MSC) are a promising cell source for AC replacement given their potential to form AC precursor cells – chondrocytes, but current protocols can lead to undesirable hypertrophic differentiation that progresses to bone through the process of endochondral ossification when implanted in vivo. We have previously found that combining low oxygen and mechanical loading (mechano-hypoxia conditioning) during cartilage development from human bone marrow (hBM) derived-MSC under gravity loading conditions can reduce OA-like molecular characteristics. This research explored the treatment of mechano-hypoxia conditioning during chondrogenic stimulation of MSC under simulated microgravity (SMG) as a methodology to produce stable chondrocytes without the propensity to form bone. This was explored through the following objectives: 1. Determine the effect of mechano-hypoxia conditioning on chondrogenically stimulated MSC under SMG. 2. Determine if mechano-hypoxia-conditioned tissue-engineered cartilage from MSC resists bone formation after implantation in vivo. To achieve these objectives, hBM MSC sourced from four male (ages 25-51) and four female (ages 19-41) donors were isolated, expanded, and chondrogenically induced to form engineered cartilage models. The engineered cartilage models were subjected to static (gravity) conditions, SMG for 3 weeks, SMG for 6 weeks, and SMG for 3 weeks + dynamic compression (DC) respectively. SMG was applied to the constructs by culturing in a rotatory wall vessel bioreactor for the specified time. At the experimental endpoint, tissue constructs were randomly distributed for downstream analyses including gene expression, mechanical tests, biochemical assays for extracellular matrix, histology, and subcutaneous implantation in mice following University of Alberta animal use protocols. After 5 weeks, the implanted tissue was retrieved and imaged via micro-CT, micro-X-ray fluorescent imaging for biomineralization and scanning electron microscope (SEM) imaging for the structure and composition of calcification. Data from this study shows that Mechano-hypoxia conditioning significantly reduced the heightened expression of collagen X induced by SMG, validating this conditioning method as a countermeasure to microgravity-induced chondrocyte hypertrophy. Additionally, Matrix gla protein (MGP), a potent inhibitor of bone formation, was significantly upregulated by mechano-hypoxia conditioning. This increase was found to be correlated with a significant resistance to bone formation in vivo, measured through micro-CT analysis. This data suggests that mechano-hypoxia conditioning has the potential to counteract osteoarthritic characteristics induced in cartilage from SMG and lends insight into the mechanisms involved in the process of mechanosignalling for osteoarthritis and new areas of drug discovery research. The outcome of this experiment will advance our understanding of the molecular processes of cartilage breakdown in microgravity and avenues for prevention.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".