Shinji Omura

Genetic ablation of the transcription repressor Bach1 leads to myocardial protection against ischemia/reperfusion in mice

Bach1 is a transcriptional repressor of heme oxygenase‐1 gene (Hmox‐1) and β‐globin gene. Heme oxygenase (HO)‐1 is an inducible cytoprotective enzyme that degrades pro‐oxidant heme to carbon monoxide (CO) and biliverdin/bilirubin, which are thought to mediate anti‐inflammatory and anti‐oxidant actions of HO‐1. In the present study, we investigated the role of Bach1 in tissue protection against myocardial ischemia/reperfusion (I/R) injury in vivo using mice lacking the Bach1 gene (Bach1−/−) and wild‐type (Bach1+/+) mice. In Bach1−/− mice, myocardial expression of HO‐1 protein was constitutively up‐regulated by 3.4‐fold compared to that in Bach1+/+ mice. While myocardial I/R induced HO‐1 protein in ischemic myocytes in both strains of mice, the extent of induction was significantly greater in Bach1−/− mice than in Bach1+/+ mice. Myocardial infarction was markedly reduced in size by 48.4% in Bach1−/− mice. Pretreatment of Bach1−/− mice with zinc‐protoporphyrin, an inhibitor of HO activity, abolished the infarction‐reducing effect of Bach1 disruption, indicating that reduction in the infarct size was mediated, at least in part, by HO‐1 activity. Thus, Bach1 plays a pivotal role in setting the levels of both constitutive and inducible expression of HO‐1 in the myocardium. Bach1 inactivation during I/R appears to be a key mechanism controlling the activation level of cytoprotective program involving HO‐1.

Effects of genetic ablation of bach1 upon smooth muscle cell proliferation and atherosclerosis after cuff injury

Bach1 is a transcriptional repressor of the cytoprotective enzyme heme oxygenase‐1 (HO‐1). Although HO‐1 protects against atherosclerosis, the function of Bach1 in this process is poorly understood. We isolated peritoneal macrophages and aortic smooth muscle cells (SMC) from wild‐type and bach1‐deficient mice. bach1‐deficient macrophages expressed increased levels of HO‐1 and showed elevated phagocytic activity when incubated with 0.75 µm microspheres. In SMC, bach1‐ablation resulted in increased expression of HO‐1 and decreased proliferation in bromodeoxyuridine incorporation assay as compared with wild‐type cells. The up‐regulated phagocytic activity and reduced SMC proliferation of bach1‐deficient cells were not restored by Zinc (II) protoporphyrin IX, an inhibitor of HO, suggesting that HO‐independent mechanisms are also involved in the regulation of phagocytosis of macrophages and proliferation of SMC by Bach1. In wild‐type mice, cuff placement around femoral artery caused pronounced intimal proliferation without affecting the media, thus resulting in intimal to medial (I/M) volume ratio of 65.6%. bach1‐deficient mice had less degree of intimal growth (I/M ratio of 45.6%). These results indicate that Bach1 plays a critical role in the regulation of HO‐1 expression, macrophage function, SMC proliferation and neointimal formation. Bach1 may regulate gene expression in these cells during inflammation and atherogenesis.

841-4 Bach1 is a key-repressor of heme oxygenase-1 and regulates cell proliferation

Va sc ul ar D is ea se , H yp er te ns io n, a nd P re ve nt io n Material & Methods Ten histologic sections of human coronary plaque rupture were contrasted with ten cases of stable fibrocalcific plaques for the presence of peri-adventitial fat macrophages (Kp-1 positive cells). Quantitative morphometry was performed. Results. The ten plaque rupture cases had a markedly greater macrophage infiltration as evidenced by number/mm2 peri-adventitial fat. Moreover, the highest density in fibrocalcific cases (56/mm2) was lower than the lowest density in cases of plaque rupture (171/mm2). As expected, plaque rupture sections showed typical features of thin cap fibroatheroma with large lipid cores and high density of plaque macrophages that were accompanied by a significant macrophage infiltrate in the adventitia and peri-adventitial fat. S100 and Toluidine blue staining ruled out the possibility that these cells might represent dendritic cells or mast cells, respectively. Conclusion. This study shows the presence of active macrophages in the peri-adventitial fat of human coronary arteries. These cells were present in much greater quantity in the setting of plaque rupture as opposed to burnt-out fibrocalcific plaques. There appeared to be no significant difference in macrophage density between adventitia and peri-adventitial fat. Peri-adventitial fat inflammation might play a significant pathogenic role in atherosclerosis progression and complications.