Distribution of cathepsin L in human umbilical cord tissues
The extracellular matrix components show specific distribution patterns within various structures of the umbilical cord, among which Wharton's jelly is especially collagen- and growth factor- rich tissue. Cathepsin L is a potent cysteine protease engaged in degradation of extracellular matrix proteins, including collagens. We evaluated the activity and expression of cathepsin L, and the inhibitory effect of cysteine protease inhibitors in the umbilical cord arteries, vein and Wharton’s jelly. Extracts of separated umbilical cord tissues were quantitated for cathepsin L activity and for anti-papain inhibitory effect of cysteine protease inhibitors using fluorogenic substrates. The results were calculated per DNA content. The enzyme expression was assessed by Western immunoblotting. The active cathepsin L activity (without activation by pepsin digestion), its percentage in the total activity, and the expression of the mature single-chain enzyme were the lowest in the umbilical cord arteries and the highest in Wharton’s jelly. The effect of cysteine protease inhibitors showed similar distribution as in the case of the active enzyme, being the highest in Wharton’s jelly. Distribution of the activity and expression of mature cathepsin L within the umbilical cord probably results from distinctions in the proenzyme activation process. Differences in the action of cysteine protease inhibitors can partly restrict those in the enzyme activity that could be estimated from its expression alone. Differential enzyme action seems to contribute to tissue-specific collagen turnover within the umbilical cord, especially in Wharton’s jelly.
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