Background/Objectives: Metabolic dysfunction-associated steatotic liver disease (MASLD) is highly prevalent worldwide and represents a growing healthcare challenge due to its risk of progression and association with metabolic comorbidities. Extracellular vesicles (EVs), nanosized membrane-bound particles mediating intercellular communication, have emerged as candidate biomarkers in multiple diseases. This study aimed to characterize serum EV profiles in MASLD patients, stratified into obese and lean groups using a body mass index cutoff of 23 for Asians. Methods: We enrolled 170 MASLD patients, 83 obese (median age 50, range 20–80) and 87 lean (median age 50, range 20–87), along with 57 non-MASLD controls (median age 44, range 21–86). Serum EV concentrations and particle sizes were quantified using nanoparticle tracking analysis and correlated with clinical and laboratory parameters. EV cargo proteins, including tetraspanins (CD9, CD63) and lipid droplet-associated perilipins (PLIN2, PLIN3), were assessed by Western blotting. Results: Obese MASLD patients displayed marked biochemical abnormalities, whereas lean MASLD patients showed levels comparable to non-MASLD controls. Nevertheless, serum EV concentrations were elevated in both the obese and lean MASLD groups. Importantly, in lean MASLD, EV levels correlated strongly with disruptions in lipid and glycemic homeostasis. Furthermore, a reduction in the PLIN3/CD63 ratio was observed in EVs isolated from lean MASLD patients. Conclusions: Circulating EVs are elevated in both obese and lean MASLD, but lean patients demonstrate a distinctive decrease in the EV PLIN3/CD63 ratio. These findings highlight the potential of EV profiling to uncover disease heterogeneity and to inform risk stratification in MASLD.

Background/Objectives: Type 2 diabetes mellitus (T2DM) is a major metabolic disorder and is frequently accompanied by liver steatosis. Apolipoprotein J (ApoJ) is a glucose-regulated molecular chaperone that has been implicated in hepatic lipid deposition under nutrient overload. This study aimed to investigate the role of hepatocyte-specific ApoJ deletion in hepatic metabolism under diabetic conditions. Methods: A T2DM mouse model with hepatocyte-specific ApoJ knockout (HKO) was established through a high-fat diet combined with streptozotocin injection. Hepatic metabolic profiles were analyzed using untargeted metabolomics with UHPLC–MS/MS. Differential metabolites were subjected to KEGG pathway and Sankey diagram analyses to identify biologically relevant pathways. Results: In total, 140 metabolites showed significant differential abundance in HKO mouse liver, primarily encompassing organic acids and derivatives as well as lipids and lipid-like molecules. KEGG analysis revealed that ApoJ deletion enhanced pathways related to vitamin digestion and absorption, thiamine metabolism, amino acid biosynthesis, lysine degradation, and 2-oxocarboxylic acid metabolism. In contrast, pathways associated with galactose metabolism, cysteine and methionine metabolism, purine metabolism, and the pentose phosphate pathway were suppressed. Sankey diagram analysis further demonstrated that ApoJ deletion markedly reshapes hepatic metabolic networks in T2DM. Conclusions: Given the central role of hepatic dysmetabolism in the pathogenesis of diabetes and its complications, targeting ApoJ may represent a promising therapeutic approach for restoring hepatic metabolic homeostasis and preventing diabetes-associated steatosis.