NPY promotes macrophage polarization and hepatic fibrogenesis via PI3K/MAPK-dependent neuroimmune mechanisms

Neuropeptide Y (NPY) is a key regulator of neuroimmune homeostasis. However, its role in the intrahepatic immune microenvironment and hepatic fibrosis remains unclear. We aimed to elucidate whether NPY participates in hepatic fibrogenesis via neuroimmune crosstalk and to dissect the underlying molecular mechanisms. Liver tissues from cirrhotic and non-cirrhotic human subjects were collected. Hepatic fibrosis was induced in mice via intraperitoneal carbon tetrachloride (CCl₄) injection or the 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet. The distribution of NPY and its receptors was detected in human and mouse hepatic tissues. NPY-knockout mice were used to evaluate the impact of NPY deletion on hepatic fibrosis, inflammation, and macrophage polarization. Hepatic NPY receptors were silenced in vivo, and the corresponding receptors or downstream kinases were blocked in vitro, to define the underlying signaling mechanisms. NPY was elevated in fibrotic human and mouse livers and primarily secreted by intrahepatic sympathetic nerves. NPY1R and NPY2R (but not NPY4R/NPY5R) were increased and localized in hepatic macrophages. NPY deletion mitigated liver injury, collagen deposition, and inflammation, and suppressed both M1 and M2 macrophage polarization. In vivo knockdown of NPY1R or NPY2R recapitulated these protective effects. In vitro, NPY enhanced M1 polarization via NPY1R/NPY2R-coupled PI3K–PAK1–c-Jun signaling, whereas it promoted M2 polarization through the PI3K–PAK1–RSK cascade. NPY drives both M1 and M2 macrophage polarization and accelerates hepatic fibrogenesis through NPY1R/NPY2R–PI3K–MAPK-dependent neuroimmune signaling. These findings identify NPY and its receptors as potential therapeutic targets for hepatic fibrosis. Intrahepatic sympathetic nerve-derived NPY promotes M1 and M2 macrophage polarization through NPY1R/NPY2R–PI3K–PAK1 cascades (c-Jun for M1, RSK for M2), driving hepatic stellate cell activation via profibrotic cytokines (TNF-α, IL-1β, TGF-β, and PDGF-BB). Solid lines: experimentally validated pathways. Dashed lines: putative unvalidated intercellular interactions (direct NPY–hepatic stellate cell axis and macrophage–hepatic stellate cell crosstalk)