PEROXISOMES AND STEROL CARRIER PROTEIN-2 IN LUTEAL CELL STEROIDOGENESIS - A POSSIBLE ROLE IN CHOLESTEROL TRANSPORT FROM LIPID DROPLETS TO MITOCHONDRIA

In the present investigation, we have studied peroxisomes and sterol c arrier protein-2 (SCP2) in control and luteinizing hormone stimulated rat luteal cells. Superovulated immature rats in mid-luteal phase (8 d ays after ovulation) were divided into two groups (n=4/group) and trea ted with vehicle (0.2 ml saline), or luteinizing hormone (LH, 20 mu g/ rat). In this animal model, LH acutely stimulates steroidogenesis. Thi rty minutes later, corpora lutea were fixed by whole body perfusion an d processed for (1) electron microscopic immunocytochemistry to locali ze SCP2 via the protein A gold immunolabeling technique, and for (2) e lectron microscopic histochemistry to stain peroxisomal catalase via t he alkaline 3,3'-diaminobenzidine tetrahydrochloride method. In the st eroidogenic, mid-phase luteal cells of vehicle treated rats (controls) , SCP2 was highly concentrated in peroxisomes and sparsely scattered o n mitochondria, but no labeling was observed in lipid droplets. In the luteal cells of rats acutely stimulated with LH, peroxisomes immunola beled for SCP2 were observed within the luteal cell lipid droplets and mitochondria, and in union with lipid droplets and mitochondria. More over, in contrast to control lutea[ cells, significant immunolabeling for SCP2 was detected within the lipid droplets and mitochondria in lu teal cells of LH-treated rats. As SCP2 binds cholesterol to 1:1 molar ratio and is known to be involved in the intracellular movement of cho lesterol, these findings suggest that peroxisomes and SCP2 may possibl y be involved in delivering cholesterol from lipid droplets to the mit ochondria when luteal cell steroidogenesis is acutely stimulated by LH .