Upregulated FASN-mediated lipogenesis in senescent macrophages contributes to liver fibrosis progression

Liver fibrosis represents a common advanced pathological stage of various chronic liver diseases. Macrophages serve as key regulators of innate immunity and play important roles in the development of liver fibrosis. Cellular senescence is an irreversible cell cycle arrest state. However, the mechanisms underlying the role of senescent macrophages in liver fibrosis remain incompletely understood.

Liver fibrosis was induced in young (8-week) and middle-aged (12-month) mice by intraperitoneal injection of 25% carbon tetrachloride (CCl₄). Hepatic function and the immune microenvironment were evaluated using histopathology, serum biochemistry, Western blotting, RT-qPCR, immunohistochemistry, and immunofluorescence. A senescent macrophage model was established in RAW264.7 cells by exposure to H₂O₂. Conditioned medium from senescent macrophages was transferred to LX-2 cells to assess hepatic stellate cell (HSC) activation. Transcriptome sequencing of senescent RAW264.7 cells was performed to identify underlying mechanisms. FASN protein stability was examined using cycloheximide (CHX) chase assays, and degradation pathways were preliminarily explored by combined treatment with MG132 and chloroquine (CQ).

In vivo, middle-aged mice treated with CCl₄ exhibited more severe hepatic collagen deposition, fibrosis, and senescence than young mice. In vitro, senescent macrophages showed upregulated expression of SASP components, including pro-inflammatory cytokines and chemokines, and DNA damage markers, and their conditioned medium promoted LX-2 cell activation. Transcriptome sequencing of senescent RAW264.7 cells revealed a bidirectional fatty acid metabolic reprogramming characterized by downregulation of genes involved in fatty acid β-oxidation and upregulation of genes involved in fatty acid synthesis. Furthermore, FASN protein was found to undergo dual degradation via both the ubiquitin-proteasome and autophagy pathways. Moreover, pharmacological inhibition of FASN attenuated the DNA damage response in senescent macrophages.

Macrophages in middle-aged fibrotic livers exhibit cellular senescence. FASN-mediated enhancement of fatty acid synthesis leads to lipid metabolic disorder and accumulation in senescent macrophages. These senescent macrophages promote HSC activation and drive the progression of liver fibrosis.