Crocetin, the Key Hypoglycemic Agent in Gardenia jasminoides Identified by Spectrum-Effect Relationship, Targets GRK5 to Phosphorylate AKT2 and Improve Glucose Homeostasis

Natural remedies are often used as standalone treatments or as complementary approaches to modern medicine for controlling type 2 diabetes. Gardenia jasminoides, a substance used in both food and medicine, has been clinically employed in traditional Chinese medicine to treat hyperglycemia. Here, we first identified crocetin as the compound responsible for the primary hypoglycemic activity of G. jasminoides and revealed that G protein-coupled receptor kinase 5 (GRK5) is the key target through which crocetin improves glucose homeostasis and insulin resistance. To identify the bioactive components in G. jasminoides, we conducted high-resolution mass spectrometry analysis and bioactivity-guided fractionation, confirming that crocetin is the primary bioactive constituent. We demonstrated the direct binding of crocetin to GRK5 via cellular thermal shift (CETSA) and surface plasmon resonance (SPR) assays. Further knockdown experiments confirmed the essential role of GRK5 in enhancing crocetin-mediated improvements in glucose metabolism. Additionally, we explored direct downstream targets of GRK5 and demonstrated for the first time that AKT2 is a novel GRK5-interacting protein. Collectively, these findings reveal that crocetin is a promising glucose-regulating phytochemical that targets GRK5 to phosphorylate AKT2, thereby improving glucose homeostasis.