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

Abstract
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