Loss of a critical neutral protease in ageing WI-38 cells

Abstract

THE limited lifespan of normal human diploid cells in vitro seems to be related to the number of mitotic divisions the cells have undergone rather than to passage of time^1–3. In spite of considerable research^3–7 it is still unclear what biochemical events actually mediate the cell death or more accurately the absence of growth. In other systems it has been postulated that regulation of growth may be mediated by activity at the cell membrane. Specifically it has been suggested that cellular division is controlled in part by membrane mediated cell contact, and proteases and lysosomal enzymes have ben implicated in the control of mitosis and growth^8–11. Thus cell surface events may be either primary or secondary events mediating cell ageing. Acid hydrolases have been postulated as modifying the cell surface in sublethal autolysis, electrophoretic mobility of cells gives an indication of cell surface chemistry and neutral proteases have been implicated in modification of cell external surfaces^9–15. We now demonstrate that two cell surface parameters are greatly affected by in vitro ageing: activity of a pH 7.8 protease and cell surface net charge as measured by electrophoretic mobility. It should be emphasised that the small standard deviations for the electrophoretic mobility data reported herein are a function of the large n (number of independent observations) and do not preclude population heterogeneity.