Submitted on June 21, 2008
Revised on August 16, 2008
Accepted on September 14, 2008
The role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters
Feng Wang1, Wei Wang2, Kristiina Wähälä3, Herman Adlercreutz4, Elina Ikonen3, and Matti J. Tikkanen1*
1 Helsinki University Central Hospital, Helsinki University
2 Institute of Biomedicine/Anatomy, Helsinki University
3 University of Helsinki
4 Folkhälsan Research Center, Institute for Preventive Medicine, Nutrition and Cancer, Division of Clinical Chemistry, University of Helsinki
* To whom correspondence should be addressed. E-mail: Matti.J.Tikkanen{at}Helsinki.Fi.
Dehydroepiandrosterone-fatty acyl esters (DHEA-FAE) belong to a unique family of naturally occurring hydrophobic steroid hormone derivatives that are transported in circulating lipoproteins and may act as a source of dehydroepiendrosterone (DHEA) and other biologically active steroid hormones in cells. Here, we studied the metabolic fate of low-density lipoprotein-associated [3H]-DHEA-FAE ([3H]-DHEA-FAE-LDL) and the possible role of lysosomal acid lipase (LAL) in the hydrolysis of DHEA-FAE in cultured human cells. When HeLa cells were incubated with [3H]-DHEA-FAE-LDL, the accumulation of label in the cellular fraction increased with incubation time and could be inhibited by excess unlabeled LDL, suggesting LDL receptor or LDL receptor-related receptors dependent uptake. During 48 h of chase, decreasing amounts of [3H]-DHEA-FAE were found in the cellular fraction while in the medium, increasing amounts of unesterified [3H]-DHEA and its two metabolites, [3H]-5a-Androstanedione (5a-Adione) and [3H]-Androstenedione (4-Adione), appeared. As LDL-cholesteryl ester hydrolysis is dependent on LAL activity, we depleted LAL from HeLa cells using small interfering RNAs and compared the hydrolysis of [3H]-DHEA-FAE-LDL and [3H]-cholesteryl-FAE-LDL. The results demonstrated a more modest but significant reducing effect on the hydrolysis of [3H]-DHEA-FAE when compared to [3H]-cholesteryl-FAE. Moreover, experiments in LAL deficient human fibroblasts (Wolman disease patient cells) showed that [3H]-DHEA-FAE hydrolysis was not completely dependent on LAL activity. In summary, LDL-transported [3H]-DHEA-FAE entered cells via LDL receptor or LDL receptor-related receptors-mediated uptake, followed by intracellular hydrolysis and further metabolism into 5a-Adione and 4-Adione that were excreted from cells. Although LAL contributed to the de-esterification of DHEA-FAE, it was not solely responsible for the hydrolysis.
