Mechanical forces accelerate collagen digestion by bacterial collagenase in lung tissue strips
Yi, Eunice Sunyoung
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Most tissues in the body are under mechanical tension, and while enzymes mediate many cellular and extracellular processes, the effects of mechanical forces on enzyme reactions in native extracellular matrix (ECM) are not well known. Previous studies have shown that elastin remodeling in the lung occurs during the progression of emphysema, a disease that involves enzymatic cleavage of various ECM proteins of the parenchyma. Here we hypothesize that physiological levels of mechanical forces are also capable of modifying the activity of collagenase, a key remodeling enzyme of the ECM, leading to increased collagen deterioration, which results in decreased ECM stiffness. To test this, we measured the changes in mechanical properties of lung tissue strips under various conditions of stretch and digestion. Specifically, we analyzed the stiffness and nonlinearity index of tissue strips tested under uniaxial static stretch (amplitudes of 0, 20, 40, and 80% strain), as well as cyclic mechanical loading (amplitudes of ±10% and ±20% superimposed on 40% static stretch, and frequencies of 0.1 and 1Hz). We also used confocal and electron microscopy to determine and quantify changes in ECM structure. In particular, we observed qualitatively the effect of mechanical loading on enzyme activity through the increased destruction seen in our confocal and electron images. We also analyzed the changes in equivalent diameter and distortion index measurements of the alveolar structures through analysis of the confocal images. The decline in stiffness during digestion positively correlated with the increase in equivalent diameters and negatively correlated with the distortion index. These results suggest that the decline in stiffness results from collagen rupture within and of the alveolar wall, and changes in shape of the airspaces subsequent to local tissue failure. In general, from these studies, we found that mechanical forces accelerated collagen digestion and lead to increased destruction of ECM structure of the alveoli. This research may provide new understanding of the role of collagen degradation in general tissue remodeling and disease progression.
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