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Apolipoprotein E synthesis by cultured human ovarian granulosa cells: regulation by human chorionic gonadotropin and
M W Beckmann1, L M Olson, J R Schreiber
1Department of Obstetrics and Gynecology, University of Chicago, Illinois 60637.
Objective:
Apolipoprotein E (Apo E) is a surface component of several classes of plasma lipoproteins and functions as a receptor ligand for the low-density lipoprotein (LDL) (B/E) receptor, the hepatic E receptor, and the LDL receptor related protein. In continuing studies of Apo E synthesis by extrahepatic steroidogenic tissue, we have examined Apo E production and its control in cultured human granulosa cells (GC).
Design:
Human GC obtained at the time of oocyte aspiration for in vitro fertilization were cultured, and the following parameters were measured: progesterone secretion into the medium, Apo E synthesis and secretion, and Apo E messenger ribonucleic acid (mRNA) content of the GC.
Results:
Human chorionic gonadotropin induces a decrease in Apo E protein synthesis and Apo E mRNA content. The addition of aminoglutethimide (which blocks cholesterol conversion to pregnenolone) and/or LDL (which provides the cell with cholesterol), both result in an increase in Apo E protein synthesis and Apo E mRNA content. These latter findings are in agreement with studies in nonsteroidogenic cells, which show that Apo E production is positively correlated with cell cholesterol content.