Region-Dependent Aggrecan Degradation Patterns in the Rat Intervertebral Disc Are Affected by Mechanical Loading In Vivo
Bibliographic record
Abstract
In Brief Study Design. Immunoblotting study to evaluate aggrecan degradation patterns in rat intervertebral discs (IVDs) subjected to mechanical overload. Objective. To evaluate the effects of in vivo dynamic compression overloading on aggrecan degradation products associated with matrix metalloproteinase (MMP) and aggrecanase activity in different regions of the IVD. Summary of Background Data. Aggrecan cleavage at the MMP and aggrecanase sites is an important event in human IVD aging, with distinct cleavage patterns in the anulus and nucleus regions. No such information is available on regional variations in rat IVDs, nor on how such cleavage is affected by mechanical loading. Methods. Sprague-Dawley rats were instrumented with an Ilizarov-type device and subjected to dynamic compression (1 MPa and 1 Hz for 8 hours per day for 8 weeks). Control, sham, and overloaded IVDs were separated by disc region and analyzed for aggrecan degradation products using immunoblotting techniques, with antibodies specific for the aggrecanase and MMP cleavage sites in the interglobular domain of aggrecan. Results. Control IVDs exhibited strong regional variation in aggrecan degradation patterns with minimal degradation products being present in the nucleus pulposus, degradation products associated with aggrecanase cleavage predominating in the inner anulus fibrosus (AF), and degradation products associated with MMP cleavage predominating in the outer AF. Dynamic compression overloading increased the amount of aggrecan degradation products associated with MMP cleavage not only in the AF but also in the nucleus pulposus. Degradation profiles of sham IVDs were similar to control. Conclusion. Aggrecan G1 regions resulting from proteolysis were found to have a strong regionally specific pattern in the rat IVD, which was altered under excessive loading. The shift from aggrecanase to MMP-induced degradation products with dynamic compression overloading suggests that protein degradation and loss can precede major structural disruption in the IVD, and that MMP-induced aggrecan degradation may be a marker of mechanically induced disc degeneration. Aggrecan degradation as indicated by accumulation of its G1 domain was assessed by immunoblotting in rat caudal intervertebral discs subjected to dynamic compression overload. Control discs exhibited strong regional differences in accumulation of degradation products from aggrecanase and matrix metalloproteinase activity. Chronic cyclic compression overloading increased accumulation of matrix metalloproteinase-associated degradation products.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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 | 0.000 | 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".