title: Experimental and computational assessment of F-actin influence in regulating cellular stiffness and relaxation behaviour of fibroblasts.
abstract: In biomechanics, a complete understanding of the structures and mechanisms that regulate cellular stiffness at a molecular level remain elusive. In this paper, we have elucidated the role of filamentous actin (F-actin) in regulating elastic and viscous properties of the cytoplasm and the nucleus. Specifically, we performed colloidal-probe atomic force microscopy (AFM) on BjhTERT fibroblast cells incubated with Latrunculin B (LatB), which results in depolymerisation of F-actin, or DMSO control. We found that the treatment with LatB not only reduced cellular stiffness, but also greatly increased the relaxation rate for the cytoplasm in the peripheral region and in the vicinity of the nucleus. We thus conclude that F-actin is a major determinant in not only providing elastic stiffness to the cell, but also in regulating its viscous behaviour. To further investigate the interdependence of different cytoskeletal networks and cell shape, we provided a computational model in a finite element framework. The computational model is based on a split strain energy function of separate cellular constituents, here assumed to be cytoskeletal components, for which a composite strain energy function was defined. We found a significant influence of cell geometry on the predicted mechanical response. Importantly, the relaxation behaviour of the cell can be characterised by a material model with two time constants that have previously been found to predict mechanical behaviour of actin and intermediate filament networks. By merely tuning two effective stiffness parameters, the model predicts experimental results in cells with a partly depolymerised actin cytoskeleton as well as in untreated control. This indicates that actin and intermediate filament networks are instrumental in providing elastic stiffness in response to applied forces, as well as governing the relaxation behaviour over shorter and longer time-scales, respectively.
authors.affiliation: Department of Solid Mechanics, KTH Royal Institute of Technology, Teknikringen 8, 100 44 Stockholm, Sweden. Electronic address: bfa@kth.se.
authors.forename: Björn
authors.initials: B
authors.lastname: Fallqvist
authors.affiliation: NANOLAB, KTH Royal Institute of Technology, Roslagstullsbacken 21, 100 44 Stockholm, Sweden. Electronic address: fielden@kth.se.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Fielden
authors.affiliation: Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 56-58, 100 44 Stockholm, Sweden. Electronic address: torbj@kth.se.
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Pettersson
authors.affiliation: SP Chemistry, Materials and Surfaces, SP Technical Research Institute of Sweden, 114 86 Stockholm, Sweden. Electronic address: niklas.nordgren@sp.se.
authors.forename: Niklas
authors.initials: N
authors.lastname: Nordgren
authors.affiliation: Department of Solid Mechanics, KTH Royal Institute of Technology, Teknikringen 8, 100 44 Stockholm, Sweden. Electronic address: martinkr@kth.se.
authors.forename: Martin
authors.initials: M
authors.lastname: Kroon
authors.affiliation: Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Nobels väg 16, 171 77 Stockholm, Sweden. Electronic address: annica.gad@ki.se.
authors.forename: Annica K B
authors.initials: AKB
authors.lastname: Gad
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry*; D000199:Actins / Q000737:chemistry*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002460:Cell Line; D048430:Cell Shape; D004548:Elasticity; D005347:Fibroblasts / Q000166:cytology*; D006801:Humans; D053778:Thiazolidines / Q000494:pharmacology
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D053778:Thiazolidines; C037068:latrunculin B
keywords: Actin; Cytoskeleton; Intermediate; Mechanical; Network