SECRETION OF APOLIPOPROTEIN-E BY BASAL CELLS IN CULTURES OF EPIDERMAL-KERATINOCYTES

Recently it has been shown that apolipoprotein E (apoE) secreted by ke ratinocytes in transplanted epidermal grafts reaches the systemic circ ulation In this study we ask which cells in cultures of epidermal kera tinocytes, basal or suprabasal, are the source of apoE. By fractionati ng disaggregated cultures in gradients of Ficoll400, the small nondiff erentiated cells derived from the basal compartment were shown to be t he source of apoE. The larger more differentiated cells derived from s uprabasal layers could not be shown to contain or secrete apoE, althou gh they did contain the apoE mRNA. Basal cells are the primary site fo r replication. However, analysis during growth in culture indicated th at secretion did not correlate with cell replication but appeared to b e linked to specific changes in metabolic activity of the basal cell c ompartment. Localization of apoE secretion to the basal compartment ma y provide a mechanism for lipid uptake and redistribution within the e pidermis and may be viewed within the larger context of keratinocyte d ifferentiation.