Monocyte-derived macrophages orchestrate multiple cell-type interactions to repair necrotic liver lesions

The liver can fully regenerate after partial resection and its underlying mechanisms have been extensively studied. The liver can also rapidly regenerate after injury with most studies focusing on hepatocyte proliferation; however, how hepatic necrotic lesions during acute or chronic liver diseases are eliminated and repaired remains obscure. Here we demonstrate that monocyte-derived macrophages (MoMFs) are rapidly recruited to and encapsulate necrotic areas during immune-mediated liver injury, and this feature is essential in repairing necrotic lesions. At the early stage of injury, infiltrating MoMFs activate the JAG1-NOTCH2 axis to induce cell death-resistant SOX9+ hepatocytes near the necrotic lesions, which acts as a barrier from further injury. Subsequently, necrotic environment (hypoxia and dead cells) induces a cluster of C1q+MoMFs that promote necrotic removal and liver repair, while Pdgfb+MoMFs activate hepatic stellate cells (HSCs) to express a-smooth muscle actin and induce a strong contraction signal (YAP, pMLC) to squeeze and finally eliminate the necrotic lesions. In conclusion, MoMFs play a key role in repairing the necrotic lesions not only by removing necrotic tissues but also by inducing cell death resistant hepatocytes to form a perinecrotic capsule and by activating a-smooth actin expressing HSCs to facilitate necrotic lesion resolution. Overall design: The liver samples were homogenized with a gentleMACS Dissociator (Miltenyi), filtered through 70-µm cell strainers, and then centrifuged through a Percoll density gradient (40% and 70%), immune cells were collected and further sorted with BD FACSMelody to isolate CD45+ CD11b+ Ccr2+ Ly6G- liver MoMFs. These Liver MoMFs were subjected to scRNA seq.