Apolipoprotein D transcription occurs specifically in nonproliferating quiescent and senescent fibroblast cultures.

We studied apolipoprotein D (apoD) mRNA in primary cultures of human diploid fibroblasts (HDF). In early-passage HDF no apoD mRNA was detected in replicating cells in sparse culture, but the gene was expressed in quiescent cells in confluent and in serum-starved cultures. In contrast, late-passage HDF expressed apoD mRNA in sparse culture, but the level increased after attainment of confluence. Thus fibroblasts, the common cell-type expressing apoD mRNA in vivo, express this characteristic following growth-arrest. The same pattern of activation was found in another fibroblast cell line deficient in apoB/E (LDL) receptors, excluding a role for cellular cholesterol delivery by the LDL-receptor pathway controlling apoD expression.