title: Chondrocyte dedifferentiation increases cell stiffness by strengthening membrane-actin adhesion.
abstract: OBJECTIVE
  Chondrocyte dedifferentiation is known to influence cell mechanics leading to alterations in cell function. This study examined the influence of chondrocyte dedifferentiation in monolayer on cell viscoelastic properties and associated changes in actin organisation, bleb formation and membrane-actin cortex interaction.
  
  
  METHODS
  Micropipette aspiration was used to estimate the viscoelastic properties of freshly isolated articular chondrocytes and the same cells after passage in monolayer. Studies quantified the cell membrane-actin cortex adhesion by measuring the critical pressure required for membrane detachment and bleb formation. We then examined the expression of ezrin, radixin and moesin (ERM) proteins which are involved in linking the membrane and actin cortex and combined this with theoretical modelling of bleb dynamics.
  
  
  RESULTS
  Dedifferentiated chondrocytes at passage 1 (P1) were found to be stiffer compared to freshly isolated chondrocytes (P0), with equilibrium modulus values of 0.40 and 0.16 kPa respectively. The critical pressure increased from 0.59 kPa at P0 to 0.74 kPa at P1. Dedifferentiated cells at P1 exhibited increased cortical F-actin organisation and increased expression of total and phosphorylated ERM proteins compared to cells at P0. Theoretical modelling confirmed the importance of membrane-actin cortex adhesion in regulating bleb formation and effective cellular elastic modulus.
  
  
  CONCLUSIONS
  This study demonstrates that chondrocyte dedifferentiation in monolayer strengthens membrane-actin cortex adhesion associated with increased F-actin organisation and up-regulation of ERM protein expression. Thus dedifferentiated cells have reduced susceptibility to bleb formation which increases cell modulus and may also regulate other fundamental aspects of cell function such as mechanotransduction and migration.
authors.affiliation: Institute of Bioengineering and School of Engineering and Materials Science, Queen Mary University of London, Mile End Rd, London, E1 4NS, United Kingdom; Laboratoire Physico-chimie Curie-UMR 168, Institut Curie, Centre de Recherche, Paris, F-75248, France.
authors.forename: K
authors.initials: K
authors.lastname: Sliogeryte
authors.affiliation: Institute of Bioengineering and School of Engineering and Materials Science, Queen Mary University of London, Mile End Rd, London, E1 4NS, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Botto
authors.affiliation: Institute of Bioengineering and School of Engineering and Materials Science, Queen Mary University of London, Mile End Rd, London, E1 4NS, United Kingdom.
authors.forename: D A
authors.initials: DA
authors.lastname: Lee
authors.affiliation: Institute of Bioengineering and School of Engineering and Materials Science, Queen Mary University of London, Mile End Rd, London, E1 4NS, United Kingdom. Electronic address: m.m.knight@qmul.ac.uk.
authors.forename: M M
authors.initials: MM
authors.lastname: Knight
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism; D002417:Cattle; D002448:Cell Adhesion / Q000502:physiology; D054337:Cell Dedifferentiation / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004548:Elasticity; D008297:Male; D040542:Mechanotransduction, Cellular / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology; D014783:Viscosity; D000099149:Ezrin
chemical_list: D000199:Actins; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D000099149:Ezrin; C071058:moesin; C071776:radixin
keywords: Cell mechanics; Chondrocyte dedifferentiation; ERM proteins; Membrane-actin interaction; Micropipette aspiration