Effect of lipoproteins on cholesterol synthesis in rat Sertoli cells.

Lipoprotein metabolism has been investigated in cultured rat Sertoli cells. Cells incubated with low-density lipoproteins (LDLs) or high-density lipoproteins (HDLs) showed a concentration-dependent decrease of sterol synthesis, indicating a net cholesterol delivery to the Sertoli cells. At 50 micrograms/mL, lipoproteins inhibited the incorporation of [14C]acetate into free cholesterol by 83% for the LDL and 47% for the HDL. Electron microscopic examinations of the Sertoli cells provide evidence of the internalization of gold-labelled HDL into coated pits and coated vesicles. Competitive studies between human LDL and rat HDL indicate that Sertoli cells take up cholesterol from LDL and HDL containing apolipoprotein (apo) E by common pathways. These results suggest that Sertoli cells possess apo B and E receptors for the uptake and degradation of LDL and HDL, although the basement membrane excludes the passage of LDL from blood capillaries to the Sertoli cells. At 50 micrograms/mL, apo-E-depleted HDL inhibited the incorporation of [14C]acetate into free cholesterol by 34%. Thus, this study shows that Sertoli cells are capable of taking up apo-E-depleted HDL cholesterol for cell metabolism.