Abstract 250: Over-expression of Human Arginase (ARG1) in Macrophages Reduces Atherosclerosis in LDL-receptor Deficient Mice

Background: In previous work we have identified arginase I (ARG1) as a novel candidate gene of atherosclerosis resistance in macrophages (Teupser et al ATVB 2006). In macrophages, L-arginine can be metabolized by NO synthase and arginase to form NO and urea, respectively. Thus, high expression of ARG1 in macrophages (as observed in atherosclerosis resistant our rabbits) may be an effective mechanism of reducing macrophage NO-production and thus vascular inflammation. Methods and Results: To test the hypothesis that ARG1 exerts anti-atherogenic properties, we generated ARG1-transgenic mice, expressing human ARG1 under the control of a CMV promoter. In these animals, ARG1 was over-expressed in various tissues including bone-marrow-derived macrophages. Under basal conditions, expression of human ARG1 in macrophages of transgenic mice was significantly higher compared to endogenous murine ARG1 (27062±13652 vs. 176±81 copies ARG1/10 6 copies cyclophilin, respectively). To test the functionality of the human transgene, macrophages were incubated with lipopolysaccharide (1 μg/mL). After 6 hours of incubation, NO-release was significantly diminished in macrophages of transgenic mice, compared to non-transgenic controls (94±9 vs. 140±16 μmol/ng cell protein, respectively p = 0.03), indicating that hARG1 transgene expression influences NO synthesis by competing with iNOS for the common substrate L-arginine. To test the effect of the transgene on atherosclerosis susceptibility, bone marrow from ARG1-transgenic and non-transgenic animals were transplanted onto LDL-receptor deficient C57BL/6 recipients at 8 weeks of age. Animals were sacrified at 20 weeks of age and no significant differences in lipid and lipoprotein levels were noted. However, atherosclerosis of animals transplanted with transgenic bone marrow (n=16) was significantly reduced compared to controls (n=15) (75160±9914 vs. 121500±18410 μm 2 , p=0.03). Conclusion: Our data show for the first time that over-expression of human ARG1 in macrophages has direct anti-atherogenic properties by reducing NO-release in macrophages. We conclude that ARG1 might constitute an interesting novel target for the prevention of atherosclerosis.