Proteomic Profiling of Optic Nerves From SMOX-Deficient Mice Identifies Regulators of Neuroinflammation and Axonal Damage in Optic Neuritis

Purpose: Visual dysfunction due to optic neuritis (ON) is an early clinical manifestation of multiple sclerosis (MS). ON is characterized by inflammation of the optic nerve, demyelination, axonal damage, and retinal ganglion cell (RGC) loss. Previously, we showed that spermine oxidase (SMOX), a polyamine catabolizing enzyme, modulates visual function in an experimental model of ON. Using proteomic analysis, the present study aimed to identify SMOX-regulated molecular pathways involved in ON-associated visual dysfunction. Methods: Experimental autoimmune encephalomyelitis (EAE) was induced in wild-type (WT) and SMOX-deficient (Smox KO) mice. Clinical scoring of mice was recorded daily. Optic nerves from WT and Smox KO EAE mice and their controls were collected and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Pathway enrichment and comparative analyses were performed to identify key processes and pathways regulated by SMOX. Immunofluorescence was performed to detect changes in the expression of key proteins. Results: Smox KO EAE mice showed delayed and reduced clinical scores. Pathway enrichment analysis identified several key processes affected in EAE, including regulation of the actin cytoskeleton, tight junction integrity, and platelet activation/aggregation. The comparative analysis of the WT EAE and Smox KO EAE proteomes, together with false discovery rate (FDR)-corrected pathway enrichment analysis, indicated attenuation of neuroinflammatory pathways in the SMOX-deficient optic nerve. Furthermore, SMOX deficiency restored key cytoskeletal and cellular-adhesion proteins essential for neuronal integrity. Immunofluorescence studies confirmed dysregulation of receptor for activated C kinase 1 (RACK1), actinin alpha 4 (ACTN4), high mobility group box 1 (HMGB1), and S100 calcium-binding protein B (S100B), critical proteins involved in immune signaling, cytoskeletal stability, and inflammation. Conclusions: These findings indicate the impact of SMOX on inflammation and cytoskeletal stabilization in ON and its potential as a therapeutic target in preserving vision in MS.