Senescence and cell density of human diploid fibroblasts influence metabolism of insulin-like growth factor binding proteins.

Abstract

In order to analyze changes in metabolism of insulin-like growth factor binding proteins (IGFBPs) related to cell senescence and cell density, we compared human diploid fibroblasts (HDF) in the proliferatively vigorous first half (young cells) and senescent HDF in the last 10% (old cells) of the replicative lifespan after seeding cells over an eightfold range and proliferation to high density. Increasing the seeding cell density of both young and old HDF led to elevated rates of IGFBP-3 secretion, an increasing ratio of the 42/38 kDa species of IGFBP-3, and degradation of all species of IGFBPs derived from both the fetal bovine serum component of the culture medium and from HDF. At a given seeding density old HDF produced more IGFBP-3 and degraded more IGFBPs than young HDF. IGFBP-4 was degraded by a protease that appeared to be different from the protease(s) involved in degradation of the other IGFBPs. Young HDF at all seeding densities contained a cell-associated 29 kDa IGFBP, whereas this protein could not be detected in old cells. Thus, although certain changes in IGFBP metabolism are similar in young HDF seeded at high densities and in old HDF, young and old phenotypes can be distinguished by characteristic qualitative and quantitative changes in IGFBPs derived from fetal bovine serum and from HDF.