Single-cell transcriptomic profiling maps monocyte/macrophage transitions after myocardial infarction in mice

Abstract

RationaleMonocytes and macrophages have a critical and dual role in post-ischemic cardiac repair, as they can foster both tissue healing and damage. To decipher how monocytes/macrophages acquire heterogeneous functional phenotypes in the ischemic myocardium, we profiled the gene expression dynamics at the single-cell level in circulating and cardiac monocytes/macrophages following experimental myocardial infarction (MI) in mice. Methods and resultsUsing time-series single-cell transcriptome and cell surface epitope analysis of blood and cardiac monocytes/macrophages, as well as the integration of publicly available and independently generated single-cell RNA-seq data, we tracked the transitions in circulating and cardiac monocyte/macrophage states from homeostatic conditions up to 11 days after MI in mice. We show that MI induces marked and rapid transitions in the cardiac mononuclear phagocyte population, with almost complete disappearance of tissue resident macrophages 1 day after ischemia, and rapid infiltration of monocytes that locally acquire discrete and timedependent transcriptional states within 3 to 7 days. Ischemic injury induced a shift of circulating monocytes towards granulocyte-like transcriptional features (Chil3, Lcn2, Prtn3). Trajectory inference analysis indicated that while conversion to Ly6C low monocytes appears as the default fate of Ly6C hi monocytes in the blood, infiltrated monocytes acquired diverse gene expression signatures in the injured heart, notably transitioning to two main MI-associated macrophage populations characterized by MHCII hi and Trem2 hi Igf1 hi gene expression signatures. Minor ischemia-associated macrophage populations with discrete gene expression signature suggesting specialized functions in e.g. iron handling or lipid metabolism were also observed.We further identified putative transcriptional regulators and new cell surface markers of cardiac monocyte/macrophage states. ConclusionsAltogether, our work provides a comprehensive landscape of circulating and cardiac monocyte/macrophage states and their regulators after MI, and will help to further understand their contribution to post-myocardial infarction heart repair.

Integrated scRNA-seq analysis identifies conserved transcriptomic features of mononuclear phagocytes in mouse and human atherosclerosis

“…In addition to major macrophage subsets, we observed populations consistent with a previous integrative analysis (5), including cells with a gene expression profile characteristic of small peritoneal macrophages (SPM/Cavity cluster: Itgax + Cd226 + Ccr2 + MHCII + ) (5), type I interferon response cells (IFNIC cluster: Isg15, Oasl2), and monocytes expressing genes characteristic of Ly6C hi (Ly6c2, Chil3, Ccr2) and Ly6C low (Ace, Treml4) subsets (28) (Figure 1D and F).…”

“…by employing single-cell multiplexing technologies such as cell hashing (52) or MULTI-Seq (53). Recently, we identified Trem2 hi macrophages in the ischemic mouse heart sharing gene expression similarities with the LAM/DAM/foamy signature (28), and two reports identified Trem2 enriched immunosuppressive macrophages in tumor models ( 54), (55), indicating that part of this transcriptional signature may not only be related to pathological lipid loading, but rather more generally induced in contexts of tissue damage. Our observation that macrophages with a Trem2 hi signature populate the aorta in the context of Angiotensin-II mediated inflammation corroborates this notion.…”

Consensus transcriptional states describe human mononuclear phagocyte diversity in the lung across health and disease

“…Certain programs highly associated with monocyte or macrophage likelihood did contain canonical genes associated with these cell types, such as VCAN and APOE , respectively. However, many programs showed weaker association, suggesting that many MNP populations are not well-defined by classical definitions and may represent intermediate or transitory populations (Giladi et al, 2020;Rizzo et al, 2020). Overall, we demonstrate broad utility of these gene sets to identify critical subsets, disease-associated trends, and broad population structure.…”

Post-ischemic Myocardial Inflammatory Response: A Complex and Dynamic Process Susceptible to Immunomodulatory Therapies

“…Although differentiated cardiac macrophages depend on Nr4a1 to limit inflammation, the apoptotic or proliferation processes seem unaffected ( 190 ). Second, after about 7 days, the reparative (Ly-6C lo ) monocytes, also suggested to directly correspond with F4/80 hi Ly-6C lo macrophages originated from Ly-6C hi monocytes ( 190 , 191 ), become predominant, which differentiate, in the presence of IL-4 and IL-10, toward a reparative M2 (CCR2–) phenotype, promoting the healing response, and contributing to angiogenesis and scar maturation ( 189 ). Tissue-resident CCR2+ and CCR2– macrophages differentially regulated cardiac mobilization and recruitment of peripheral monocytes where depletion of tissue-resident CCR2+ macrophages substantially reduced the recruitment of recipient monocytes and neutrophils accompanied by an improved LV systolic function following murine MI-R injury ( 185 ).…”