title: Haptotaxis is cell type specific and limited by substrate adhesiveness.
abstract: Motile cells navigate through tissue by relying on tactile cues from gradients provided by extracellular matrix (ECM) such as ligand density or stiffness. Mesenchymal stem cells (MSCs) and fibroblasts encounter adhesive or 'haptotactic' gradients at the interface between healthy and fibrotic tissue as they migrate towards an injury site. Mimicking this phenomenon, we developed tunable RGD and collagen gradients in polyacrylamide hydrogels of physiologically relevant stiffness using density gradient multilayer polymerization (DGMP) to better understand how such ligand gradients regulate migratory behaviors. Independent of ligand composition and fiber deformation, haptotaxis was observed in mouse 3T3 fibroblasts. Human MSCs however, haptotaxed only when cell-substrate adhesion was indirectly reduced via addition of free soluble matrix ligand mimetic peptides. Under basal conditions, MSCs were more contractile than fibroblasts. However, the presence of soluble adhesive peptides reduced MSC-induced substrate deformations; increased contractility may contribute to limited migration, but modulating cytoskeletal assembly was ineffective at promoting MSC haptotaxis. When introduced to gradients of increased absolute ligand concentrations, 3T3s displayed increased contractility and no longer haptotaxed. These data suggest that haptotactic behaviors are limited by adhesion and that although both cell types may home to tissue to aid in repair, fibroblasts may be more responsive to ligand gradients than MSCs.
authors.affiliation: Department of Bioengineering, UC San Diego; La Jolla, CA, 92093, USA.
authors.forename: Jessica H
authors.initials: JH
authors.lastname: Wen
authors.affiliation: Department of Biomedical Engineering, National Yang-Ming University; Beitou District, Taipei City, 112 Taiwan.
authors.forename: Onkiu
authors.initials: O
authors.lastname: Choi
authors.affiliation: Department of Bioengineering, UC San Diego; La Jolla, CA, 92093, USA.
authors.forename: Hermes
authors.initials: H
authors.lastname: Taylor-Weiner
authors.affiliation: Department of Bioengineering, UC San Diego; La Jolla, CA, 92093, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Fuhrmann
authors.affiliation: Department of Biomedical Sciences, UC San Diego, La Jolla, CA, 92093, USA.
authors.forename: Jerome V
authors.initials: JV
authors.lastname: Karpiak
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
authors.forename: Adah
authors.initials: A
authors.lastname: Almutairi
authors.affiliation: Department of Bioengineering, UC San Diego; La Jolla, CA, 92093, USA ; Sanford Consortium for Regenerative Medicine, La Jolla, CA 92037, USA.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Engler
keywords: elasticity; fibroblast; ligand gradient; mesenchymal stem cell; migration; surface modification