Insulin-mimetic action of conglutin-γ, a lupin seed protein, in mouse myoblasts

Lupin seed is referred to as an antidiabetic product in traditional medicine. Conglutin-γ, a lupin seed glycoprotein, was found to cause a significant plasma glucose reduction when orally administered to rats in glucose overload trials. Conglutin-γ was identified as being responsible for the claimed biological activity, and the aim of this work was to envisage its hypothetical insulin-mimetic cellular mechanism of action. Insulin is responsible for proteosynthesis control through IRS/AKT/P70S6k/PHAS1 pathways modulation, glucose homeostasis through PKC/Flotillin-2/caveolin-3/Cbl activation and muscle differentiation/hypertrophy via muscle-specific MHC gene transcription control.

To assess whether conglutin-γ modulates the same insulin-activated kinases, myoblastic C2C12 cells were incubated after 72 h of differentiation with 100 nM insulin or 0.5 mg/mL (∼10 μM) conglutin-γ. Metformin-stimulated cells were used as a positive control. The effect on the above mentioned pathways was evaluated after 5, 10, 20 and 30 min. In the control cells medium insulin, conglutin-γ and metformin were not added. We demonstrated that insulin or conglutin-γ cell stimulation resulted in the persistent activation of protein synthetic pathway kinases and increased glucose transport, glut4 translocation and muscle-specific gene transcription regulation.

Our results indicate that conglutin-γ may regulate muscle energy metabolism, protein synthesis and MHC gene transcription through the modulation of the same insulin signalling pathway, suggesting the potential therapeutic use of this natural legume protein in the treatment of diabetes and other insulin-resistant conditions, as well as the potential conglutin-γ influence on muscle cells differentiation and regulation of muscle growth.