Somatomedin-C binding to cultured human fibroblasts is dependent on donor age and culture density.

Abstract

Cultured fibroblasts have been used extensively to study age-related changes in the cellular response to serum stimulation. Since somatomedin-C (Sm-C) is an important growth factor in serum, we determined if there were age-related changes in Sm-C fibroblast receptor number or affinity and if culture density influenced these changes. Skin fibroblasts were obtained from six normal donors in three separate age groups and tested for their capacity to bind Sm-C. Sparse cultures (10-15K cells/well) derived from fetal donors had an affinity for Sm-C that was 4.7-fold greater than that of cultures derived from elderly (74-96 yr old) donors [9.4 +/- 0.2 (+/- SD) compared to 2.0 +/- 0.2 X 10(10) M-1]). When grown to high density (60-100K cells/well), the affinity of the fetal cultures was significantly reduced to 2.2 +/- 0.2 X 10(10) M-1 (P less than 0.001) and was not significantly different from the affinity of high density elderly donor cultures (2.3 +/- 0.4 X 10(10) M-1). Intermediate age donors (3-14 yr old) also had a significant reduction in receptor affinity with increasing density. Fetal donor cultures showed no density-dependent changes in receptor number. Fetal donor cells at low density had 5.2 +/- 1.0 X 10(4) receptors/cell compared to 5.9 +/- 0.6 X 10(4) receptors/cell in the high density cultures. In contrast, cells derived from donors aged 3-14 yr had 12.0 +/- 1.6 X 10(4) receptors/cell at 15K cells/well and 5.1 +/- 0.6 X 10(4) at 80K cells/well (P less than 0.05). Cultures from elderly donors had significantly greater mean receptor numbers per cell compared to fetal donor cells at four of five densities tested and had a significantly lower receptor number per cell with increasing culture density 25.2 +/- 1.2 X 10(4) (10-15K cells/well) compared to 5.2 +/- 0.2 X 10(4) (60-100K) cells/well. Thus, increasing donor age at low culture density was associated with an increase in receptor number per cell and a decrease in receptor affinity. At high culture densities, these differences were not detected. These changes in Sm-C receptor number and affinity at low density could lead to donor age-related changes in the cellular response to Sm-C.