Abstract
Matrix metalloproteinases (MMPs) play a crucial role in enzymatically digesting cartilage extracellular matrix (ECM) components, resulting in degraded cartilage with altered mechanical loading capacity. Overexpression of MMPs is often caused by trauma, physiologic conditions and by disease. To understand the synergistic impact MMPs have on cartilage biomechanical properties, MMPs from two subfamilies: collagenase (MMP-1) and gelatinase (MMP-9) were investigated in this study. Three different ratios of MMP-1 (c) and MMP-9 (g), c1:g1, c3:g1 and c1:g3 were considered to develop a degradation model. Thirty samples, harvested from bovine femoral condyles, were treated in groups of 10 with one concentration of enzyme mixture. Each sample was tested in a healthy state prior to introducing degradative enzymes to establish a baseline. Samples were subjected to indentation loading up to 20% bulk strain. Both control and treated samples were mechanically and histologically assessed to determine the impact of degradation. Young’s modulus and peak load of the tissue under indentation were compared between the control and degraded cartilage explants. Cartilage degraded with the c3:g1 enzyme concentration resulted in maximum 33% reduction in stiffness and peak load compared to the other two concentrations. The abundance of collagenase is more responsible for cartilage degradation and reduced mechanical integrity.
Highlights
Matrix metalloproteinases (MMPs) play a crucial role in enzymatically digesting cartilage extracellular matrix (ECM) components, resulting in degraded cartilage with altered mechanical loading capacity
Low levels of MMP expression are essential in regulating collagen homeostasis by digesting the collagen network; this balance is imperative for tissue development, remodeling, and r epair[41]
All of the degradative enzymes belonging to the collagenase family (MMP-1, 8, and 13) are expressed at low levels in healthy joint tissue and experience increased expression in arthritic tissue
Summary
Matrix metalloproteinases (MMPs) play a crucial role in enzymatically digesting cartilage extracellular matrix (ECM) components, resulting in degraded cartilage with altered mechanical loading capacity. MMP-9 (gelatinase B) were primarily considered representatives of two protease classes Other collagenases, such as MMP-13 have often been s tudied[22,23,24] as the major catabolic effector in OA and have been perceived to be more active than MMP-1 on type II collagen. To understand the correlation between the biochemical changes and mechanical loading, a limited number of in vivo studies based on contact forces were conducted on OA patients’ knee joints[27,28,29] These studies failed to address the kinematic changes in degraded cartilage associated with early-stage O A30. The current in vitro study is designed to investigate the macro-mechanical properties of cartilage treated with different concentrations of MMP-1 and MMP-9 in combination to unfold the mutual effect of MMPs on cartilage biomechanics
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