Identification of novel collagen breakdown products by human osteoclasts in vitro and in vivo
Bibliographic record
Abstract
Abstract Bone resorption involves dissolution of mineral and enzymatic degradation of bone matrix. The primary enzyme is cathepsin K but other proteases including matrix metalloproteinases are involved. Some cleavage products of cathepsin K have been partially identified, including crossed-linked telopeptides of type I collagen. However, the pathway of type I bone collagen degradation has not been fully elucidated. The aim of this study was to comprehensively characterise the entire complement of bone breakdown products resulting from osteoclast action under controlled conditions in vitro . Complete characterisation of these breakdown products will advance understanding of osteoclast biology and has the potential to reveal new biomarkers of bone resorption. We analysed extracellular media from osteoclasts cultured on dentine 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 dentine matrix. Nine peptide fragments mapped exclusively to collagen I alpha-1 chain (COL1A1), the most abundant protein in bone. Analysis of the reported cleavage sites in the COL1A1 protein sequence indicated 7/9 COL1A1-specific fragments not explained by known proteolytic events. We subsequently showed that 14 of the fragment products were present in human serum and/or urine from metabolomic datasets obtained from patients with the inherited metabolic disease alkaptonuria (serum) and lung cancer (urine). Two products were at higher concentration (P <0.05, fold change >2) in urine from patients with bone metastasis (29/112) from the 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. Monitoring the concentrations of these novel bone markers in biofluids has the potential to capture multiple pathways of bone resorption activity beyond the existing assays based on Cathepsin K. Lay summary Breakdown of bone tissue is performed by specialised bone cells called osteoclasts in a process known as bone resorption. Knowledge of specific molecules produced from osteoclasts acting on bone is important for a) understanding bone resorption in health and disease, and b) clinical tests of bone resorption from measurement of these breakdown products. Here we aimed to characterise the entire complement of bone breakdown products resulting from osteoclast action under controlled conditions in the laboratory. We found a total of 22 breakdown products produced from osteoclasts cultured on wafers of dentine, a tissue with almost identical composition to bone. Analysis of the structures of these products revealed fragments of varying size produced from digestion of specific proteins present in bone. We then showed that 14/22 bone protein fragments observed in our cell culture experiments were also present in human blood and/or urine. In our analysis of urine from patients with lung cancer, we found that two of the protein fragments we identified were higher in a subset (29/112) of patients with bone metastasis. Our findings provide new insights into the mechanisms of bone resorption and show the potential for monitoring the range of urine bone protein fragments in bone disorders.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".