Evidence for increased proteolytic activity in ageing human fibroblasts

We have shown that ultrastructural changes accompany ageing in the human fetal lung fibroblast strain MRC-5. In order to further characterise these changes a method has been devised to prepare subcellular fractions from MRC-5 fibroblasts using a discontinous gradient of metrizamide preceded by a low-speed centrifugation. An investigation was carried out to compare subcellular fractions prepared from early-passage and senescent cells. Proteolytic activity associated with lysosomes and soluble proteolytic activity were found to be increased in senescent cells.