Figure 3.

Mechanism of GalNAc-conjugated siRNA-mediated silencing of hepatocyte Alas1. Alas1-siRNA is conjugated to trivalent GalNAc, which is recognized and bound by asialoglycoprotein receptors that are abundantly and near-exclusively expressed on the surface of hepatocytes. This induces clathrin-mediated endocytosis and the formation of early endosomes, which mature into late endosomes that are highly acidic. The lower pH results in the release of the Alas1-siRNA from the asialoglycoprotein receptors, which are then rapidly recycled to the hepatocyte cell surface. Alas1-siRNAs then escape to the hepatocyte cytoplasm and are loaded onto RISC. The passenger (sense) strand is degraded, leaving only the guide (antisense) strand on the RISC, which binds endogenous Alas1 mRNA in a complementary manner and degrades it. Professional illustration by Patrick Lane, ScEYEnce Studios.