INCREASED FERRITIN GENE-EXPRESSION IN ATHEROSCLEROTIC LESIONS

To identify genes potentially implicated in atherogenesis, a cDNA libr ary was constructed from human atherosclerotic aorta and differentiall y screened with P-32-labeled-cDNAs prepared from human normal and athe rosclerotic aortas. Two cDNA clones exhibiting higher hybridization to the P-32-labeled cDNAs from atherosclerotic vessels were isolated and identified to be genes encoding L-ferritin and H-ferritin, respective ly, Northern blot analysis confirmed that the expression of both ferri tin genes was notably higher in human and rabbit atherosclerotic aorta s than in their normal counterparts. A time-course study illustrated t hat both L- and H-ferritin mRNAs were markedly increased in aortas of rabbits after feeding with a high cholesterol diet for 6 wk, which was also the time period after which the formation of lesions became evid ent. In situ hybridization revealed that both L- and H-ferritin mRNAs were induced in endothelial cells and macrophages of human early lesio ns. The signals were also detected in the smooth muscle cells of advan ced lesions, Immunostaining further identified the presence of ferriti n protein in atherosclerotic lesions. On the other hand, Prussian blue stain revealed the presence of iron deposits in advanced lesions but not in early human or rabbit lesions. Further experiments with culture d human monocytic THP-1 cells and aortic smooth muscle cells demonstra ted that ferritin mRNAs were subjected to up-regulation by treatment w ith IL-1 or TNF, while TGF, PDGF, and oxidized LDL did not affect the expression of either ferritin gene in both cell lines. Collectively, t hese results clearly demonstrate that ferritin genes are susceptible t o induction in the course of plaque formation.