Background

We have demonstrated that accumulated macrophages in human coronary arteries strongly express angiotensin converting enzyme in accordance with the development of atheromatous plaques. However, there are few reports on the regulation of the renin-angiotensin system in macrophages and in monocytes as their source.

Objective

To examine whether the renin-angiotensin system is upregulated during the differentiation of monocytes to macrophages, and whether it is further regulated by angiotensin II and cytokines.

Materials and methods

We used a human leukemia cell line, THP-1, for monocytes. Differentiated THP-1, induced by adding phorbol 12-myristate 13-acetate for 24 h, were used as macrophages. Expression of messenger RNA of the renin-angiotensin system components was measured by quantitative reverse-transcriptase polymerase chain reaction. Angiotensin converting enzyme activity and subtype-specific angiotensin-binding sites of cultured cells, and angiotensin II production in the culture medium were measured.

Results

Macrophages expressed all components of the renin-angiotensin system except chymase. Cellular angiotensin converting enzyme activity and angiotensin II in the medium were increased 3.2 and 4.5-fold during differentiation, respectively. Expression of angiotensin II type 1 (AT 1) and type 2 (AT 2) receptors was increased 6.2 and 6.4-fold during differentiation, and was sustained for 7 days. Incubation with angiotensin II for 24 h caused downregulation of both AT 1 and AT 2 receptor messenger RNA, but the expression levels were still more than threefold higher compared with monocytes. The density of binding sites of AT 1 and AT 2 receptors in macrophages was 0.26±0.02 and 0.15±0.01 fmol/106 cells, respectively.

Conclusion

The renin-angiotensin system is markedly activated during monocyte/macrophage differentiation, and may participate in the development of atherosclerosis.