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Phagocytic liver protection
Chronic liver injury is characterized by sustained inflammation that can lead to organ failure. Reprogramming the immune response toward an anti-inflammatory phenotype could help limit the inflammation during liver injury. Now, Wan et al. showed that a noncanonical form of autophagy called LC3-associated phagocytosis (LAP) is a protective mechanism activated in monocytes during liver injury that inhibit proinflammatory and profibrogenic pathways in human samples and in a mouse model of liver injury. LAP blockade in monocytes increased liver damage, whereas increasing LAP reduced inflammation and fibrosis in a mouse model of liver injury. The results suggest that LAP might be targeted for treating liver injury.
Abstract
Sustained hepatic and systemic inflammation, particularly originating from monocytes/macrophages, is a driving force for fibrosis progression to end-stage cirrhosis and underlies the development of multiorgan failure. Reprogramming monocyte/macrophage phenotype has emerged as a strategy to limit inflammation during chronic liver injury. Here, we report that LC3-associated phagocytosis (LAP), a noncanonical form of autophagy, protects against hepatic and systemic inflammation during chronic liver injury in rodents, with beneficial antifibrogenic effects. LAP is enhanced in blood and liver monocytes from patients with fibrosis and cirrhosis. Pharmacological inhibition of LAP components in human monocytes from patients with cirrhosis or genetic disruption of LAP in mice with chronic liver injury exacerbates both the inflammatory signature in isolated human monocytes and the hepatic inflammatory profile in mice, resulting in enhanced liver fibrosis. Mechanistically, patients with cirrhosis showed increased monocyte expression of Fc fragment of IgG receptor IIA (FcγRIIA) and enhanced engulfment of immunoglobulin G in LC3+ phagosomes that triggers an FcγRIIA/Src homology region 2 domain–containing phosphatase-1 (SHP-1) inhibitory immunoreceptor tyrosine-based activation motif (ITAMi) anti-inflammatory pathway. Mice overexpressing human FcγRIIA in myeloid cells show enhanced LAP in response to chronic liver injury and resistance to inflammation and liver fibrosis. Activation of LAP is lost in monocytes from patients with multiorgan failure and restored by specifically targeting ITAMi signaling with anti-FcγRIIA F(ab′)2 fragments, or with intravenous immunoglobulin (IVIg). These data suggest the existence of an ITAMi-mediated mechanism by which LAP might protect against inflammation. Sustaining LAP may open therapeutic perspectives for patients with chronic liver disease.
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