title: Substrate Stiffness Controls Osteoblastic and Chondrocytic Differentiation of Mesenchymal Stem Cells without Exogenous Stimuli.
abstract: Stem cell fate has been linked to the mechanical properties of their underlying substrate, affecting mechanoreceptors and ultimately leading to downstream biological response. Studies have used polymers to mimic the stiffness of extracellular matrix as well as of individual tissues and shown mesenchymal stem cells (MSCs) could be directed along specific lineages. In this study, we examined the role of stiffness in MSC differentiation to two closely related cell phenotypes: osteoblast and chondrocyte. We prepared four methyl acrylate/methyl methacrylate (MA/MMA) polymer surfaces with elastic moduli ranging from 0.1 MPa to 310 MPa by altering monomer concentration. MSCs were cultured in media without exogenous growth factors and their biological responses were compared to committed chondrocytes and osteoblasts. Both chondrogenic and osteogenic markers were elevated when MSCs were grown on substrates with stiffness <10 MPa. Like chondrocytes, MSCs on lower stiffness substrates showed elevated expression of ACAN, SOX9, and COL2 and proteoglycan content; COMP was elevated in MSCs but reduced in chondrocytes. Substrate stiffness altered levels of RUNX2 mRNA, alkaline phosphatase specific activity, osteocalcin, and osteoprotegerin in osteoblasts, decreasing levels on the least stiff substrate. Expression of integrin subunits α1, α2, α5, αv, β1, and β3 changed in a stiffness- and cell type-dependent manner. Silencing of integrin subunit beta 1 (ITGB1) in MSCs abolished both osteoblastic and chondrogenic differentiation in response to substrate stiffness. Our results suggest that substrate stiffness is an important mediator of osteoblastic and chondrogenic differentiation, and integrin β1 plays a pivotal role in this process.
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States of America.
authors.forename: Rene
authors.initials: R
authors.lastname: Olivares-Navarrete
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Lee
authors.affiliation: Medshape, Inc., Atlanta, Georgia, United States of America.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Smith
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States of America.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Hyzy
authors.affiliation: School of Biology, Georgia Institute of Technology, Atlanta, Georgia, United States of America.
authors.forename: Maryam
authors.initials: M
authors.lastname: Doroudi
authors.affiliation: Children's Healthcare of Atlanta, Atlanta, Georgia, United States of America.
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Williams
authors.affiliation: Medshape, Inc., Atlanta, Georgia, United States of America.|Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States of America.
authors.forename: Ken
authors.initials: K
authors.lastname: Gall
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America.
authors.forename: Barbara D
authors.initials: BD
authors.lastname: Boyan
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States of America.|Department of Periodontics, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Schwartz
mesh_terms: D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism; D020219:Chondrogenesis / Q000502:physiology*; D005109:Extracellular Matrix / Q000737:chemistry*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D010012:Osteogenesis / Q000502:physiology*