Identification of novel collagen breakdown products by human osteoclasts in vitro and in vivo
Bibliographic record
Abstract
Abstract Bone resorption involves dissolution of minerals and enzymatic degradation of bone matrix. The primary enzyme is cathepsin K but other proteases including matrix metalloproteinases are involved. Some cathepsin K cleavage products have been partially identified, including cross-linked telopeptides of type I collagen. Here, we aimed to characterize the entire complement of bone breakdown products resulting from osteoclast action under controlled conditions in vitro. We analyzed extracellular media from human osteoclasts cultured on dentin substrates, using untargeted liquid chromatography mass spectrometry. We discovered 22 breakdown products resulting from osteoclastic action. These products were peptide fragment sequences that mapped to various collagen proteins present in bone and dentin. Nine peptide fragments mapped exclusively to collagen I alpha-1 chain (COL1A1), the most abundant protein in bone. We subsequently detected 21 of the fragment products, initially observed in vitro, in human serum and/or urine. Consistent positive correlations were observed between the COL1A1-specific peptide fragments and established bone biochemical markers in serum and urine. Ten urine fragments and two serum fragments markedly increased (p < .05) following total hip arthroplasty, capturing the transient local peri-prosthetic osteolysis observed in these patients (serum, n = 86 patients; urine, n = 83 patients). Among these candidate osteolytic markers, four (two COL1A1-specific products) showed decreases from baseline (p < .05) in patients on denosumab (n = 10 patients). Additionally, two fragment peptides were higher (p < .05, fold change >2) in urine from patients with bone metastasis (24 out of 112) among a lung cancer cohort. The range of collagen peptide fragments we discovered as a direct result of osteoclast activity indicates a complexity of bone resorption pathways not previously known, extending beyond the known proteolytic cleavage events in bone collagen proteins. Monitoring biofluid concentrations of these novel bone markers has the potential to capture multiple pathways of bone resorption activity beyond the existing assays based on cathepsin K.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".