Selective Uptake from LDL Is Stimulated by Unsaturated Fatty Acids and Modulated by Cholesterol Content in the Plasma Membrane:  Role of Plasma Membrane Composition in Regulating Non-SR-BI-Mediated Selective Lipid Transfer

Abstract

We previously reported that unsaturated fatty acids stimulated low-density lipoprotein (LDL) particle uptake in J774 macrophages by increasing LDL receptor activity. Since free fatty acids (FFA) also change plasma membrane properties, a putative cholesteryl ester (CE) acceptor for selective uptake (SU), we questioned the ability of FFA to modulate SU from LDL. Using [(3)H]cholesteryl ether/(125)I-LDL to trace CE core and whole particle uptake, we found that oleic acid and eicosapentaenoic acid, but not saturated stearic acid, increased SU by 30% over control levels. An ACAT inhibitor, Dup128, abolished FFA effects on SU, indicating that increased SU by FFA was secondary to changes in cell-free cholesterol (FC). Consistent with these observations, ACAT inhibition increased cell FC and reduced LDL SU by half. The important role of plasma membrane composition was further demonstrated in that beta-cyclodextrin- (beta-CD-) mediated FC removal from the plasma membrane increased SU from LDL and was further stimulated by U18666A, a compound that inhibits FC transport between lysosomes and the plasma membrane. In contrast, cholesterol-saturated beta-CD markedly reduced LDL SU. In contrast to LDL SU, oleic acid, ACAT inhibition, U18666A, or beta-CD had no effects on HDL SU. Moreover, HDL SU was inhibited by antimouse SR-BI antibody by more than 50% but had little effect on LDL SU. In C57BL/6 mice fed a high fat diet, plasma FFA levels increased, and SU accounted for an almost 4-fold increased proportion of total cholesterol delivery to the arterial wall. Taken together, these data suggest that LDL SU is mediated by pathways independent of SR-BI and is influenced by plasma membrane FC content. Moreover, in conditions where elevated plasma FFA occur, SU from LDL can be an important mechanism for cholesterol delivery in vivo.

Saturated fat–rich diet enhances selective uptake of LDL cholesteryl esters in the arterial wall

“…Of total injected LDL, 45-72% was recovered in the liver. Consistent with results of previous studies (13), SU contributed to LDL-CE delivery to some tissues (i.e., liver, spleen, muscle). In the liver, SU contributed 16.2% and 14.2% to total LDL-CE uptake in chow-and SAT-fed mice, respectively.…”

“…We previously demonstrated that non-SR-BI-mediated SU in cultured macrophages was markedly enhanced by FFAs (13). Thus, it is possible that alterations in plasma FFA levels and/or composition, induced by diet or by disease (e.g., diabetes), lead to increased cholesterol delivery via SU to the arterial wall.…”

Dynamic and Regulated Association of Caveolin with Lipid Bodies: Modulation of Lipid Body Motility and Function by a Dominant Negative Mutant

“…In adipocytes, removal of surface cholesterol with cyclodextrin caused mobilization of cholesterol from cholesterol ester stores in the LBs and redistribution of free cholesterol to efflux sites at the PM, suggesting an efflux pathway from LBs to the PM (Prattes et al, 2000). Both pharmacological inhibition of cholesterol esterification and treatment of cells with free fatty acids has been shown to cause changes in surface free cholesterol levels (Seo et al, 2002). Taken together with the results presented here, these studies suggest that LBs play a hitherto unexplored role in maintenance of surface cholesterol levels.…”

Oleic Acid Modulates the Post-translational Glycosylation of Macrophage ApoE to Increase Its Secretion

“…It has been previously reported that fatty acids modulate membrane sterol balance in cells (12,30). We have previously shown that sterols increase apoE secretion from macrophages via a post-translational mechanism (28).…”