Enhancing the biological activity of immobilized osteopontin using a type‐1 collagen affinity coating

Abstract

The covalent attachment of biomolecules onto surfaces represents a step toward the improvement of biomaterial properties by providing relevant biological signals of interest to the cell culture or tissue environment. The chemistries involved, however, often attach proteins to the surface in a random fashion, rather than the conformation or orientation most easily recognized by cells and other proteins both in vitro and in vivo. An alternative approach is to take advantage of natural interactions to both bind and orient a biomolecule "naturally," thereby enhancing its biological activity. Type 1 collagen has been shown to bind to osteopontin (OPN), a protein implicated in processes such as wound healing, endothelial cell survival, and angiogenesis. This study seeks to characterize, quantify, and exploit this interaction in order to present a more naturally recognized form of OPN to the environment surrounding a biomaterial. Binding of OPN to type 1 collagen was confirmed using Surface Plasmon Resonance (SPR). Radio-iodination of OPN showed that binding to collagen was dose-dependent and maximal in basic conditions. Principal component analysis of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) data identified differences in OPN immobilized via different techniques. Adhesion of bovine aortic endothelial cells on OPN immobilized using the affinity coating was also significantly enhanced compared to controls. Investigation into the in vivo relevance of this immobilization method is currently underway.

Angiotensin II-Induced Osteopontin Expression in Vascular Smooth Muscle Cells Involves Gq/11, Ras, ERK, Src and Ets-1

“…Importantly, OPN disruption has been shown to attenuate Ang II-accelerated atherosclerosis and aneurysm formation (10). In vitro studies have demonstrated that OPN promotes migration and proliferation of VSMC, and accumulation of extracellular matrices by directly binding to collagen and fibronectin (5,7,45,46). Ang II-induced OPN expression may be involved in the development of atherosclerosis via these biological effects.…”

Osteopontin

“…OPN contains 2 conserved N-terminal domains with heparin binding homology that are likely to regulate its binding to heparan sulfate proteoglycans. Furthermore, OPN binds directly to fibronectin 74 and collagen, 75,76 although the sequences responsible for these interactions are not yet established. Aspartic acid rich calcium binding domains as well as phosphorylated serine and threonine residues impart the mineral binding properties of OPN, which are independent of integrin binding domains.…”

Custom Design of the Cardiac Microenvironment With Biomaterials

“…Collagen I can be used to bind osteopontin to polymers in orientations that promote endothelial adhesion. 16 Thus, both spacing and orientation of adhesion sequences can regulate cellular adhesion.…”