Differences in cholesterol incorporation into mitochondria from hepatoma AS-30D and human term placenta

Cholesterol transport for steroidogenesis in the human placental mitochondr ia is an enigma as, contrary to other steroidogenic tissues, the human plac enta does not express steroidogenic acute regulatory protein (StAR), a prot ein known to be required for efficient utilization of cholesterol by adrena l and gonadal mitochondria. These observations suggest the possibility that cholesterol transport in human placental mitochondria involves a similar s ystem to that],resent in other non-steroidogenic tissues. We studied choles terol incorporation into mitochondria isolated from AS-30D hepatoma cells a nd the human placenta. Mitochondria from both sources incorporated choleste rol in vitro. There were no differences in cholesterol incorporation into h epatoma mitochondria treated with or without trypsin. In contrast, the huma n placental mitochondria treated with trypsin did not incorporate exogenous cholesterol. The presence of ATP increased the uptake of cholesterol by hu man placental mitochondria. This increase was inhibited by vanadate. These results suggest that cholesterol incorporation into human placental mitocho ndria is mediated by protein(s). (C) 1999 W. B. Saunders Company Ltd.