Hematoma Resolution In Vivo Is Directed by Activating Transcription Factor 1

Abstract

Rationale: The efficient resolution of tissue hemorrhage is an important homeostatic function. In human macrophages in vitro, heme activates an AMPK (AMP-activated protein kinase)/ATF1 (activating transcription factor-1) pathway that directs Mhem macrophages through coregulation of HO-1 (heme oxygenase-1; HMOX1 ) and lipid homeostasis genes. Objective: We asked whether this pathway had an in vivo role in mice. Methods and Results: Perifemoral hematomas were used as a model of hematoma resolution. In mouse bone marrow–derived macrophages, heme induced HO-1, lipid regulatory genes including LXR (lipid X receptor), the growth factor IGF1 (insulin-like growth factor-1), and the splenic red pulp macrophage gene Spic . This response was lost in bone marrow–derived macrophages from mice deficient in AMPK ( Prkab1 −/ − ) or ATF1 ( Atf1 −/− ). In vivo, femoral hematomas resolved completely between days 8 and 9 in littermate control mice (n=12), but were still present at day 9 in mice deficient in either AMPK ( Prkab1 −/− ) or ATF1 ( Atf1 −/− ; n=6 each). Residual hematomas were accompanied by increased macrophage infiltration, inflammatory activation and oxidative stress. We also found that fluorescent lipids and a fluorescent iron-analog were trafficked to lipid-laden and iron-laden macrophages respectively. Moreover erythrocyte iron and lipid abnormally colocalized in the same macrophages in Atf1 −/− mice. Therefore, iron-lipid separation was Atf1 -dependent. Conclusions: Taken together, these data demonstrate that both AMPK and ATF1 are required for normal hematoma resolution. Graphic Abstract: An online graphic abstract is available for this article.