Oxidative-modified and acetylated low-density lipoproteins differ in their effects on cholesterol synthesis and stimulate synthesis of apolipoprotein E in rat peritoneal macrophages by different mechanisms.
Apolipoprotein (apo) E plays an important role in the recognition of lipoproteins by cellular lipoprotein receptors. Unlike other apolipoproteins, apo E is expressed by many extrahepatic tissues including macrophages (M phi). Resident M phi express low levels of apo E. However, their synthesis of apo E is substantially increased after M phi have been incubated with acetylated low-density lipoprotein (LDL). But acetylation of LDL is not known to occur in vivo. On the other hand, modification of LDL by oxidation and by enzymatic action is believed to happen physiologically. In this report, we compared the effects of various modified LDLs on the synthesis of apo E by M phi. Freshly isolated human LDL was modified by (1) repeated addition of acetic anhydride (Ac-LDL); (2) incubation with 20 mumol/L CuSO4 at 37 degrees C for 24 hours (Ox-LDL); and (3) incubation with phospholipase C at 37 degrees C for 1 hour (PI-LDL). Resident peritoneal M phi were collected by lavage from rats and allowed to attach to plastic culture dishes. Although native LDL had no effect, treatment with Ac-, Ox-, and PI-LDL (50 micrograms/mL each) was found to increase medium apo E by (-fold) 4.19 +/- 0.26, 4.20 +/- 0.34, and 2.02 +/- 0.20 (mean +/- SEM, n = 5), respectively, as compared with untreated cells. Northern blot analysis revealed that cellular apo E mRNA was increased in parallel to apo E protein by Ac-LDL and PI-LDL. However, increases of apo E protein and mRNA by Ox-LDL were not equal.(ABSTRACT TRUNCATED AT 250 WORDS)
Zhang
M Y
MY
Department of Medicine, Indiana University School of Medicine, Indianapolis.
Lin
R C
RC
D000704:Analysis of Variance; D000818:Animals; D001057:Apolipoproteins E / Q000096:biosynthesis*; D015152:Blotting, Northern; D002478:Cells, Cultured; D002784:Cholesterol / Q000096:biosynthesis*; D008077:Lipoproteins, LDL / Q000494:pharmacology / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar
D001057:Apolipoproteins E; D008077:Lipoproteins, LDL; C032629:acetyl-LDL; D002784:Cholesterol