INS and type 2 diabetes mellitus: Further studies have found that tryptophan, as a ligand of AHR, was metabolized by gut microbiota into 5-hydroxyindole-3-acetic acid (5-HIAA) promoting the ubiquitin–proteasome degradation of Suv39h1 by activating AhR, thereby stimulating TSC2 expression and inhibiting the activation of mTORC1 signaling, which would promote insulin signaling, improve glucose intolerance and reduce the risk of T2D (Du et al., 2024).