Abstract
We previously reported that apolipoprotein (Apo) E-deficient, ApoB48-containing (E–/B48) lipoproteins inhibited expression of lysosomal hydrolase and transformed mouse peritoneal macrophages (MPMs) into foam cells. The present study examined the effect of 2-aminopurine (2-AP), an inhibitor of eukaryotic initiation factor (eIF)-2α phosphorylation, on E–/B48 lipoprotein-induced changes in gene expression and foam cell formation. Our data demonstrated that E–/B48 lipoproteins enhanced phosphorylation of eIF-2α in macrophages. Incubation of MPMs with E–/B48 lipoproteins inhibited the translation efficiency of mRNAs encoding lysosomal acid lipase, cathepsin B, and cation-dependent mannose 6 phosphate receptor, with a parallel reduction in the level of these proteins. Addition of 2-AP to the culture media alleviated the suppressive effect of E–/B48 lipoproteins on lysosomal hydrolase mRNA translation, increased macrophage degradation of E–/B48 lipoproteins, and inhibited foam cell formation. Transfection of MPMs with a nonphosphorylatable eIF-2α mutant also attenuated the suppressive effect of E–/B48 lipoproteins on expression of lysosomal acid lipase, associated with a reduced accumulation of cellular cholesterol esters. This is the first demonstration that ApoE-deficient lipoproteins inhibit lysosomal hydrolase synthesis and transform macrophages into foam cells through induction of eIF-2α phosphorylation.
Footnotes
-
This study was supported by National Institutes of Health Grants K01HL076623 and G12RR003032 (to H.Y.), U54NS041071 (to J.S.G.), and R01ES014471 (to Z.G.).
-
D.W. and H.Y. contributed equally to this work.
-
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
-
doi:10.1124/jpet.107.134833.
-
ABBREVIATIONS: Apo, apolipoprotein; MPM, mouse peritoneal macrophage; E–/B48, apolipoprotein E-deficient, ApoB48-containing; MPR46, cation-dependent mannose 6 phosphate receptor; eIF, eukaryotic initiation factor; ER, endoplasmic reticulum; PERK, RNA-dependent protein kinase-like endoplasmic reticulum kinase; UPR, unfolded protein response; GRP, glucose-regulated protein; ATF, activating transcription factor; 2-AP, 2-aminopurine; SR, scavenger receptor; LAL, lysosomal acid lipase; PBS, phosphate-buffered saline; RT, reverse transcription; PCR, polymerase chain reaction; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; MAPK, mitogen-activated protein kinase; WT, wild type.
- Received November 29, 2007.
- Accepted May 6, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|