title: Extracellular matrix protein adsorption to phosphate-functionalized gels from serum promotes osteogenic differentiation of human mesenchymal stem cells.
abstract: One of the primary goals for tissue engineering is to induce new tissue formation by stimulating specific cell function. Human mesenchymal stem cells (hMSCs) are a particularly important cell type that has been widely studied for differentiation down the osteogenic (bone) lineage, and we recently found that simple phosphate functional groups incorporated into poly(ethylene glycol) (PEG) hydrogels could induce osteogenesis without using differentiation medium by unknown mechanisms. Here, we aimed to determine whether direct or indirect cell/materials interactions were responsible for directing hMSCs down the osteogenic lineage on phosphate (PO(4))-functionalized PEG hydrogels. Our results indicated that serum components adsorbed onto PO(4)-PEG hydrogels from medium in a presoaking step were sufficient for attachment and spreading of hMSCs, even when seeded in serum-free conditions. Blocking antibodies for collagen and fibronectin (targeted to the hydrogel), as well as β1 and β3 integrin blocking antibodies (targeted to the cells), each reduced attachment of hMSCs to PO(4)-PEG hydrogels, suggesting that integrin-mediated interactions between cells and adsorbed matrix components facilitate attachment and spreading. Outside-in signaling, and not merely shape change, was found to be required for osteogenesis, as alkaline phosphatase activity and expression of CBFA1, osteopontin and collagen-1 were each significantly down regulated upon inhibition of focal adhesion kinase phosphorylation even though the focal adhesion structure or cell shape was unchanged. Our results demonstrate that complex function (i.e. osteogenic differentiation) can be controlled using simple functionalization strategies, such as incorporation of PO(4), but that the role of these materials may be due to more complex influences than has previously been appreciated.
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA.
authors.forename: Navakanth R
authors.initials: NR
authors.lastname: Gandavarapu
authors.forename: Peter D
authors.initials: PD
authors.lastname: Mariner
authors.forename: Michael P
authors.initials: MP
authors.lastname: Schwartz
authors.forename: Kristi S
authors.initials: KS
authors.lastname: Anseth
mesh_terms: D000327:Adsorption; D001483:Base Sequence; D001842:Bone and Bones / Q000166:cytology*; D002448:Cell Adhesion; D002454:Cell Differentiation; D002478:Cells, Cultured; D017931:DNA Primers; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D006801:Humans; D020100:Hydrogels; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D044967:Serum
chemical_list: D017931:DNA Primers; D016326:Extracellular Matrix Proteins; D020100:Hydrogels; D010710:Phosphates