Lupin Peptide T9 (GQEQSHQDEGVIVR) Modulates the Mutant PCSK9(D374Y) Pathway: in vitro Characterization of its Dual Hypocholesterolemic Behavior

GQEQSHQDEGVIVR (T9) is a peptide originated by the tryptic digestion of lupin β-conglutin that is absorbed in human intestinal Caco-2 cells. A previous study has shown that T9 impairs the protein–protein interaction between mutant D374Y Proprotein Convertase Subtilisin/Kexin 9 (PCSK9(D374Y)) and the low-density lipoprotein receptor (LDLR), thus exerting a hypocholesterolemic effect. Moreover, a bioinformatic study predicting that T9 may potentially act as an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCoAR), has suggested a complementary cholesterol-lowering activity. The present study demonstrates that T9 inhibits in vitro the HMGCoAR functionality with an IC(50) value of 99.5 ± 0.56 µM. Through the inhibition of either HMGCoAR or PCSK9(D374Y) activities, T9 enhances the LDLR protein levels leading to an improved ability of HepG2 cells transfected with the mutant PCSK9(D374Y)-FLAG plasmid to uptake extracellular LDL with a final cholesterol-lowering effect. In addition, T9 modulates the PCSK9(D374Y) signaling pathway in transfected HepG2 cells leading to a decrease of PCSK9(D374Y) and HNF-1α protein levels. All these results indicate that the hypocholesterolemic effects of T9 are due to a dual mechanism of action involving either the modulation of the PCSK9(D374Y) or LDLR pathways. This may represent an added value from a therapeutic point of view.