Abstract
We examined whether cardiolipin (CL) synthesis was required to support cholesterol (CH) production from palmitate in Hela cells. Knockdown of human cardiolipin synthase-1 (hCLS1) in Hela cells has been shown to reduce CL synthesis. Therefore Hela cells stably expressing shRNA for hCLS1 and mock control cells were incubated for 16 h with [14C(U)]palmitate bound to albumin (1:1 molar ratio) in the absence or presence of serum. Knockdown of hCLS1 in Hela cells resulted in a reduction in [14C(U)]palmitate incorporation into CL and CH. This reduction in [14C(U)]palmitate incorporation into CH was most pronounced during incubation under serum-free conditions. The reduction in [14C(U)]palmitate incorporation into CH was not due to alterations in total uptake of [14C(U)]palmitate into cells or altered palmitate metabolism, since [14C(U)]palmitate incorporation into phosphatidylcholine, the major [14C(U)]palmitate-containing lipid, and its immediate precursor, 1,2-diacyl-sn-glycerol, were unaffected by hCLS1 knockdown. In addition, knockdown of hCLS1 did not affect CH pool size, indicating that CH catabolism was unaltered. Hydroxymethylglutaryl coenzyme A reductase enzyme activity and its mRNA expression were reduced by knockdown of hCLS1 and this was most pronounced in Hela cells cultured under serum-free conditions. These data indicate that CL synthesis is required to support human de novo CH biosynthesis under conditions of increased demand for CH.