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UBC Theses and Dissertations

Characterization of elastolytic cathepsins in macrophages Nho, Boram


Atherosclerosis is characterized by a thickening of the arterial wall and loss of its elasticity. The elasticity of the arterial wall is impaired when the extracellular matrix undergoes extensive proteolytic remodeling. Cathepsins are papain-like cysteine proteases that are known to have elastolytic/fibrinolytic activities. They are highly expressed in macrophages present in plaque areas of diseased blood vessels and are thought to contribute to the tissue remodeling. Using cathepsin deficient macrophages and various protease inhibitors, the elastolytic activities of cathepsins B, K, L, and S were quantitatively determined. Up to 60% of the total elastase activity of macrophages was attributed to cathepsin activities. Deficiencies in single cathepsins appeared to be compensated by other cathepsins. The capability and potency of cathepsins B, K, L, and V to hydrolyze fibrin was also determined. The exact quantification of individual cathepsin activities with the help of inhibitors or enzyme deficiencies in biological samples is difficult due to compensatory effects. Thus, specific substrates could be a viable alternative. Commercially available cathepsin activity assay kits that exploit fluorogenic peptidyl substrates are widely used to measure individual cathepsin activities in biological samples. However, substrates marketed as cathepsin K, L and S specific were found to be only marginally specific or completely non-specific, and were hydrolyzed by various other cathepsins. Furthermore, the presence of highly potent endogenous inhibitors in biological samples and the lack of specificity of the substrates skew the measurements towards cathepsin B which is relatively resistant to endogenous inhibitors. Thus, data obtained using commercial substrate kits are to be interpreted with great caution.

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