PSMB4/MHC-I Signaling in the Cerebrospinal Fluid-Contacting Nucleus Mediates Neuroinflammatory Depression in Mice

Neuroinflammation is increasingly implicated in depression pathogenesis, yet the underlying mechanisms are still unclear. This study explores whether PSMB4/MHC-I signaling in the cerebrospinal fluid (CSF)-contacting nucleus mediates neuroinflammatory depression. A persistent neuroinflammation-associated depression model was established in mice by repeated intracerebroventricular lipopolysaccharide (LPS) administration. Depressive-like behaviors were evaluated using established assays. Neuroinflammatory responses and target protein expression were assessed by immunofluorescence, Western blotting, RT-qPCR, and laser capture microdissection. Neuronal activity was mapped by c-Fos staining and manipulated using chemogenetics, alongside pharmacological and genetic interventions. Repeated LPS administration induced significant depressive-like behaviors and obvious neuroinflammation in the CSF-contacting nucleus. Under these conditions, neuronal activity in this nucleus was selectively enhanced. Crucially, chemogenetic activation of these neurons alleviated depressive phenotypes, whereas their inhibition induced depression. Molecularly, LPS significantly upregulated PSMB4 and MHC-I expression. Pharmacological suppression of upstream neuroinflammation reversed this PSMB4 upregulation, and targeted PSMB4 knockdown reduced MHC-I expression, ultimately ameliorating depressive-like behaviors. These findings identify the CSF-contacting nucleus as a critical node in neuroinflammation-induced depression and reveal a novel PSMB4/MHC-I signaling axis linking central inflammatory responses to behavioral deficits.