An A beta 42 uptake and degradation via Rg3 requires an activation of caveolin, clathrin and A beta-degrading enzymes in microglia

Abstract

We demonstrated previously that ginsenoside Rg3 enhances the expression of macrophage scavenger receptor class A (SRA) and amyloid beta peptide 1-42 (A beta 42) uptake in BV2 cells. In this study, we investigated the biochemical and mechanistic roles of Rg3 in human microglia and animal models to identify the determinants that participate in restoring memory and learning in brains disrupted by the A beta 42 peptide. SRA was expressed highly in Rg3-treated rats, and learning and memory functions were maintained at a normal level after the infusion of A beta 42. SRA-transfected HMO6 human microglial cells (HMO6.hSRA) overexpressed SRA and took up a remarkable amount of A beta 42. Rg3-treated HMO6 cells showed highly enhanced SRA expression and dramatically promoted A beta 42 uptake. Moreover, high levels of clathrin and caveolin 1 supported the roles of Rg3 in endocytic biogenesis by activating p38 and extracellular signal-regulated protein kinase signaling. Notably, both neprilysin (NEP) and insulin-degrading enzyme (IDE) were significantly expressed by Rg3, suggesting independent and compensatory hydrolytic activity for the A beta peptide. In conclusion, Rg3 successfully triggered A beta 42 uptake via SRA and clathrin-/caveolae-mediated endocytic mechanisms and further contributed to accelerate the degradation of A beta peptide via the increase of intracellular NEP and IDE, which may be a promising Alzheimer's disease therapy. (C) 2015 Elsevier B.V. All rights reserved.