Dietary GABA Remodels Hepatic Protein Networks and Lipid Droplet Architecture in Mice with Diet-Induced Hepatic Steatosis

Background/Objectives: Dietary γ-aminobutyric acid (GABA) is a food-derived bioactive compound with potential metabolic benefits. However, its effects on hepatic protein networks and lipid droplet (LD) organization under high-fat diet (HFD)-induced steatosis remain incompletely understood. This study investigated the hepatic responses to dietary GABA supplementation in mice with HFD-induced hepatic steatosis. Methods: Male C57BL/6J mice with HFD-induced hepatic steatosis supplemented GABA orally at 180 mg/kg/day for 5 weeks. Hepatic responses were evaluated using label-free quantitative proteomics and scanning electron microscopy (SEM)-based analysis of LD morphology and spatial organization. Differentially expressed proteins (DEPs; adjusted p < 0.1, |log2FC| > 1) and protein–protein interaction networks were analyzed to characterize functional pathways and protein modules associated with GABA supplementation. Results: Proteomic profiling identified 108 DEPs (38 upregulated, 70 downregulated), indicating changes in protein networks related to proteostasis, lipid metabolism, and immune- and stress-responsive processes. Protein–protein interaction analysis identified a hub module enriched in ubiquitin-dependent protein quality control components, including ubiquilin-1 (UBQLN1) and ubiquitin carboxyl-terminal hydrolase L3 (UCHL3), which showed reduced abundance following GABA supplementation. GABA also increased the abundance of LD-associated proteins, including perilipin-5 (PLIN5) and glycerol-3-phosphate acyltransferase 4 (GPAT4), while changes were also observed in immune- and stress-responsive proteins, including poly(ADP-ribose) polymerase family member 9 (PARP9). SEM revealed remodeling of hepatic LD architecture in HFD with GABA-supplemented mice compared with HFD mice, with reduced mean LD area (593.30 vs. 1267.24 μm2, p = 0.012), decreased nearest-neighbor distance (32.69 vs. 46.95 μm, p = 0.015), and increased perimeter-to-area ratio (0.17 vs. 0.12, p < 0.001). Total hepatic lipid content and body weight were not significantly altered. Conclusions: Dietary GABA supplementation was associated with remodeling of hepatic LD architecture and changes in protein networks related to proteostasis, lipid metabolism, and immune- and stress-responsive pathways, without reducing total hepatic lipid burden.