Bioactive Silica Nanoparticles Promote Osteoblast Differentiation through Stimulation of Autophagy and Direct Association with LC3 and p62

• Type of Material: Article
• Authors: Shin-Woo Ha, Emory University; M. Neale Weitzmann, Emory University; George Beck Jr, Emory University
• Language: English
• Date: 2014-06-01
• Publisher: American Chemical Society
• Publication Version: Final Published Version
• Copyright Statement: © 2014 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
• Final Published Version (URL): http://dx.doi.org/10.1021/nn5009879
• Title of Journal or Parent Work: ACS Nano
• ISSN: 1936-0851
• Volume: 8
• Issue: 6
• Start Page: 5898
• End Page: 5910
• Grant/Funding Information: M.N. Weitzmann is also supported in part by funding from the Biomedical Laboratory Research & Development Service of the VA Office of Research and Development (5I01BX000105) and by Grants AR059364 and AR053607 from NIAMS and AG040013 from NIA.; Research reported in this publication was supported in part by the Integrated Cellular Imaging Core of the Winship Cancer Institute of Emory University and NIH/NCI under Award Number P30CA138292.; This study was supported by grants from NIAMS (AR056090), the Georgia Research Alliance (GRA.VL12.C2), and the Center for Pediatric Nanomedicine (RC159-G3) sponsored by Emory University, the Department of Biomedical Engineering at Georgia Institute of Technology, and Children’s Healthcare of Atlanta, Atlanta, GA, USA, to M.N. Weitzmann and G.R. Beck Jr., and a Biomedical Laboratory Research & Development Service Award Number I01BX002363 from the VA Office of Research and Development to G.R Beck Jr. G.R. Beck Jr. is also supported in part by a grant from the NCI (CA136716).
• Keywords: ERK1/2; LC3 beta; endocytosis; silica nanoparticles; autophagy; Technology; Nanoscience & Nanotechnology; Chemistry, Physical; Materials Science; osteoblast differentiation; p62; Physical Sciences; Chemistry
• Research Categories: Engineering, Materials Science; Chemistry, Physical; Health Sciences, General

Abstract

We recently identified an engineered bioactive silica-based nanoparticle formulation (designated herein as NP1) that stimulates in vitro differentiation and mineralization of osteoblasts, the cells responsible for bone formation, and increases bone mineral density in young mice in vivo. The results demonstrate that these nanoparticles have intrinsic biological activity; however, the intracellular fate and a complete understanding of the mechanism(s) involved remains to be elucidated. Here we investigated the cellular mechanism(s) by which NP1 stimulates differentiation and mineralization of osteoblasts. We show that NP1 enters the cells through a caveolae-mediated endocytosis followed by stimulation of the mitogen activated protein kinase ERK1/2 (p44/p42). Our findings further revealed that NP1 stimulates autophagy including the processing of LC3β-I to LC3β-II, a key protein involved in autophagosome formation, which is dependent on ERK1/2 signaling. Using a variant of NP1 with cobalt ferrite magnetic metal core (NP1-MNP) to pull down associated proteins, we found direct binding of LC3β and p62, two key proteins involved in autophagosome formation, with silica nanoparticles. Interestingly, NP1 specifically interacts with the active and autophagosome associated form of LC3β (LC3β-II). Taken together, the stimulation of autophagy and associated signaling suggests a cellular mechanism for the stimulatory effects of silica nanoparticles on osteoblast differentiation and mineralization.