Differential distribution of cathepsin B in human umbilical cord tissues.

The extracellular matrix components are differentially distributed among various structures of the umbilical cord. Wharton's jelly is especially rich in collagens and growth factors. Cathepsin B is a major cysteine protease involved in collagen degradation, as well as in the activation of precursor forms of other collagenolytic enzymes and growth factors. We assessed the activity and expression of cathepsin B in the umbilical cord arteries, veins and Wharton's jelly. Extracts of separated umbilical cord components were subjected to an activity assay with the use of specific fluorogenic substrate. The expression of cathepsin B protein was qualitatively evaluated by Western immunoblotting and quantitatively determined with an immunoenzymatic method. The total cathepsin B activity and content calculated per gram of DNA were higher in Wharton's jelly than in the umbilical cord vessels, and the latter parameter was the lowest in the umbilical cord arteries. Moreover, the expression and the activity of latent cathepsin B (following activation by pepsin digestion) calculated per gram of DNA were the highest in Wharton's jelly and the lowest in the umbilical cord arteries. High expression and activity of latent, pepsin-activatable cathepsin B related to DNA content in Wharton's jelly seem to reflect the stimulation of its cells by high amounts of collagen I and growth factors.