Isolation of macrophage-like cell mutants resistant to the cytotoxic effect of oxidized low density lipoprotein

A high concentration of oxidized low density lipo- protein (Ox-LDL) showed a cytotoxic effect on mouse mac- rophage-derived J774 cells. Mutant cells were selected from these cells that were resistant to the cytotoxic effect of Ox- LDL. One mutant form, named JO21b cells, was character- ized in the present study. In spite of a marked resistance to the cytotoxic effect of Ox-LDL, JO21b cells were apparently as sensitive as the parent cells not only to toxic moieties of Ox- LDL, such as 7-ketocholesterol and lysophosphatidylcholine, but also to t -butyl hydroperoxide, an artificial lipid hydroper- oxide analog. However, the cellular association of 125 I-labeled Ox-LDL with, and subsequent endocytic degradation by JO21b cells was reduced by 70-80% compared with J774 cells. Similarly, accumulation of cholesteryl esters in JO21b cell by Ox-LDL was also reduced by 70%. Northern blot analyses of type I and type II macrophage scavenger receptors (type I and type II MSR) demonstrated that the mRNA levels of JO21b cells were lower than those of J774 cells. Moreover, peritoneal macrophages obtained from MSR-knockout mice showed a higher resistance to the cytotoxic effect of Ox-LDL than those from their wild-type littermates. Our results suggest, there- fore, that macrophage scavenger receptor-mediated en- docytic uptake of oxidized low density lipoproteins (Ox-LDL) may play an enhancing role in Ox-LDL cytotoxicity to mac- rophages or macrophage-derived cells.— Hakamata, H., A. Miyazaki, M. Sakai, H. Matsuda, H. Suzuki, T. Kodama, and S. Horiuchi. Isolation of macrophage-like cell mutants resistant to the cytotoxic effect of oxidized low density lipoproteins. J. Lipid Res. 1998. 39: 482-494.