Transfer of cholesterol between high density lipoproteins and cultured rat Sertoli cells

Abstract

In the testes, the Sertoli cells are separated from the blood capillaries by the basement membrane, thereby excluding the passage of low density lipoproteins (LDLs) but allowing the passage of high density lipoproteins (HDLs). The present study examines first the capacity of Sertoli cells to uptake cholesterol from HDL and secondly the role of apolipoproteins (apo) A-I and E in cholesterol flux between HDL and cultured rat Sertoli cells. In the presence of HDL in cultured medium, rat Sertoli cells accumulated few amounts of esterified cholesterol. Incubation of [14C]cholesterol–labelled Sertoli cells with [3H]cholesterol–labelled HDL showed that the amount of cholesterol influx slightly exceeded its efflux, thus resulting in a net uptake of cholesterol from HDL to rat Sertoli cells. The amount of HDL–cholesterol converted to steroids by Sertoli cells was about 32% of influx. Uptake of cholesterol by Sertoli cells was three times higher with phospholipid – apo A-I vesicles and seven times higher with phospholipid – apo E vesicles than that with phospholipid vesicles without apolipoprotein. Phospholipid – apo A-I vesicles promoted cholesterol efflux at the same rate as native HDL and twice as efficiently as phospholipid – apo E vesicles. Thus, this study shows that rat Sertoli cells have the capacity to take up HDL–cholesterol for membrane renewal and steroid production mainly by apo E dependent pathways.Key words: apolipoproteins, cholesterol flux, phospholipid vesicle, steroid, testis.