# MMP release following cartilage injury leads to collagen loss in intact tissue: A computational study

## TL;DR

This study uses a computational model to show how cartilage injuries can lead to collagen breakdown through cell damage and enzyme release, potentially causing osteoarthritis.

## Contribution

A computational model linking mechanical injury to enzymatic collagen degradation in cartilage is developed and validated experimentally.

## Key findings

- Mechanical injury-induced cell damage triggers MMP release and collagen loss in cartilage.
- Model predictions of collagen loss matched experimental results after 12 days post-injury.
- The model explains depth-wise collagen degradation following joint trauma.

## Abstract

Collagen damage in articular cartilage plays a key role in post-traumatic osteoarthritis, but the underlying mechanobiological pathways leading to collagen fibril degeneration after injury remain incompletely understood. We hypothesized that mechanical injurious loading induces localized cellular damage in cartilage, which in turn triggers the release of collagen-degrading matrix metalloproteinases (MMPs) and depth-wise collagen loss. To investigate this, we developed a computational mechano-signaling model for injured bovine cartilage, in which injury-induced cell damage is caused by excessive localized shear strains, leading to downstream MMP release, and spatially heterogeneous collagen degradation. The model predictions were compared to ex vivo cartilage explant experiments over 12 days post-injury. By day 12, the simulated bulk and depth-wise collagen loss aligned with our experimental findings quantified via Fourier-transform infrared microspectroscopy imaging (~30% average loss in the model vs. ~ 35% in the experiment). The results suggest that injury-induced cell damage and the downstream MMP activity can partly explain the depth-wise collagen content loss observed in the early days after cartilage injury. Ultimately, combining the current mechanistic approach with joint-level computational models could enhance the prediction of the onset and progression of cartilage degeneration following joint trauma.

Joint injuries that damage articular cartilage can increase the risk of developing post-traumatic osteoarthritis, a disease that progressively impairs joint function years after injury. Cartilage is a soft, load-bearing tissue that allows the smooth articulation between bones, and its mechanical function depends strongly on collagen fibrils. After injury, collagen in cartilage can break down, but the links between mechanical injury, cell damage and collagen loss are not yet fully understood. In this study, we used a computational model to investigate how mechanical injurious loading contributes to enzymatic collagen degeneration in cartilage. The model shows that high mechanical shear strains can damage cartilage cells, which then release matrix metalloproteinases that gradually degrade collagen over time. Model results closely matched the experimental measurements of depth-dependent collagen content over a 12-day period following injurious loading. This work improves our understanding of how mechanically-driven cell damage can trigger enzymatic collagen loss in cartilage. It also supports the development of computational tools aiming to predict cartilage degeneration and osteoarthritis progression as well as evaluate potential treatments to limit protease-mediated tissue damage.