Caragana jubata ethanol extract ameliorates the symptoms of STZ-HFD-induced T2DM mice by PKC/GLUT4 pathway

Caragana jubata (Pall.) Poir., a traditional Tibetan medicinal plant in China, is renowned in Tibetan medicine for its hypoglycemic properties and long-standing use in treating diabetes. Despite its extensive clinical use, the mechanisms underlying its blood sugar-lowering effects still need to be explored. Our investigation contributes a new understanding of the hypoglycemic mechanism of C. jubata, validating its traditional medicinal application by demonstrating its ability to increase GLUT4 expression and glucose uptake, crucial elements in treating type 2 diabetes mellitus (T2DM). This study investigated the potential anti-diabetic effects of C. jubata ethanol extract (CJEE) by upregulating GLUT4 expression and promoting its integration into the plasma membrane in L6 skeletal muscle cells and diabetic mice. Additionally, the research aimed to uncover the mechanisms involved, particularly focusing on the involvement of the PKC signaling pathway and Ca2⁺ release. The chemical composition of CJEE was evaluated using UPLC-Q-TOF/MS. Glucose uptake, GLUT4 expression, and plasma membrane fusion in L6 cells were assessed through a glucose oxidase kit, Western blotting, and laser confocal microscopy, respectively. The modulation of GLUT4 by Akt, AMPK, and PKC signaling pathways was investigated utilizing specific inhibitors. The impact of CJEE on intracellular Ca2⁺ concentration was determined with Fluo-4 dye. Additionally, an in vivo study was conducted on high-fat diet (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice to evaluate the effects of CJEE on blood glucose levels, insulin resistance, lipid metabolism, and pancreatic function. Chemical analysis of CJEE revealed 18 major constituents, primarily flavonoids. In L6 cells, CJEE was found to significantly enhance glucose uptake, increase GLUT4 expression, and facilitate its fusion with the plasma membrane. The study illustrated that CJEE predominantly activates the PKC pathway, with minimal involvement of the Akt pathway, emphasizing the critical role of Ca2⁺ release in GLUT4 regulation. Diabetic mice treated with CJEE exhibited decreased fasting blood glucose levels, enhanced oral glucose tolerance, reduced insulin resistance, and ameliorated lipid metabolism disorders. Additionally, CJEE elevated GLUT4 expression in insulin-sensitive tissues and alleviated pancreatic and hepatic lesions. Our results demonstrated that the activation of the PKC pathway and release of Ca2⁺ by CJEE induce GLUT4 exp