Abstract 12446: Lipocalin10 Deficiency Exacerbates Myocardial Ischemia/Reperfusion Injury via Impairing Macrophage Efferocytosis

Introduction: Efficient clearance of dead cells by macrophages (termed as efferocytosis) is critical for timely repairing the injured heart after ischemia/reperfusion (I/R), as defective removal of dying cells could cause secondary necrosis and infarct expansion. Recent studies have shown that lipocalin 10 (Lcn10) is significantly downregulated in cardiac tissue from patients with heart failure. However, the role of Lcn10 is virtually unknown during cardiac I/R, and its function in macrophage efferocytosis has never been explored. Hypothesis: Our initial data showed that Lcn10 expression was upregulated in bone marrow-derived macrophages (BMDMs) during efferocytosis. Thus, we hypothesize that knockout (KO) of Lcn10 would diminish macrophage efferocytosis, leading to exacerbated cardiac I/R injury. Methods/Results: Since Lcn10 is a secreted protein, we generated a global Lcn10-KO mouse model. After co-culturing BMDMs with GFP-labeled dead myocytes for 2h, we observed a 25% reduction on efferocytosis by KO-BMDMs, compared to wild-type (WT) controls. Using Lcn10-KO mCherry mouse model (cardiac-specific overexpression of mCherry in Lcn10-KO mice), we detected that KO cardiac macrophages ingested fewer dead myocytes at 3 days post-I/R, compared to WT-mCherry controls. Accordingly, cardiac contractile function, measured by echocardiography at the same time, was significantly declined in KO-mice, together with increased accumulation of apoptotic cells and higher serum levels of troponin I, a marker of cardiac damage, compared with WTs (n=7-10, p <0.05). In addition, pre-treatment of KO-BMDMs with recombinant Lcn10 protein could rescue the impaired efferocytosis. Mechanistically, RNA-seq analysis showed that many downregulated genes (i.e., ItgaV, Itga6, Cx3cr1, and Msr) in KO-macrophages are associated with efferocytosis. Interestingly, we identified that Lcn10 contains a potential phosphatidylserine (PS)-binding motif (RxKRK), located at a helix-turn-helix structure, which is the primary “find-me” signal for efferocytosis. Conclusions: Our data indicate that Lcn10 is pivotal for macrophage efferocytosis to remove cardiac dead cells during I/R. Thus, Lcn10 could be used as a new mediator for the treatment of cardiac I/R injury.