Schisandrin B Targets the PPARγ-MAPK Signaling Axis to Ameliorate High-Fat MCD Diet-Induced MASLD in Mice

Objectives: This study focuses on exploring the mechanism by which Schisandrin B (Sch B) regulates metabolic dysfunction-associated steatotic liver disease (MASLD) mice induced by a high-fat methionine–choline-deficient (MCD) diet through the activation of peroxisome proliferator-activated receptor γ (PPARγ). Methods: Male C57BL/6 mice were fed a high-fat MCD diet for 8 weeks to establish a mouse MASLD model, and the effects of Sch B on MASLD and the mechanisms were investigated. PPARγ overexpression (OE) was induced by adeno-associated virus (AAV) administration via intrahepatic portal vein injection in mice, and a negative control (NC-OE) was also established. Body weight; wet liver weight; hepatic index; serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β); and hepatic triglyceride (TG) levels were measured in the mice. The histopathology and lipid deposition were observed by hematoxylin and eosin (H&E) staining and Oil Red O staining, while the fibrosis was assessed using Masson staining. Western blot was employed to detect the expression levels of PPARγ, sterol regulatory element-binding protein 1c (SREBP-1c), carnitine palmitoyltransferase 1A (CPT1A), transforming growth factor β1 (TGF-β1), α-smooth muscle actin (α-SMA), collagen type I (collagen I), Smad family members 2/3 (Smad2/3), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38), and extracellular signal-regulated kinase 1/2 (ERK1/2), along with the phosphorylation activation status of these kinases. Results: It was confirmed that Sch B caused effects similar to those induced by PPARγ overexpression, reducing the hepatic index, AST, and ALT levels while alleviating lipid accumulation and fibrosis; and upregulating PPARγ and CPT1A while inhibiting SREBP-1c; and the phosphorylation of the TGF-β/Smad and MAPK pathways were involved in the mechanisms. Conclusions: Sch B can alleviate high-fat MCD-induced MASLD by activating PPARγ in mice.