Dynamic Tensile Loading and Altered Cell Contractility Modulate Nuclear Deformation and Cytoskeletal Connectivity

Effective use of progenitor cells in orthopaedic tissue engineering will require a thorough understanding of the mechanisms by which forces are transmitted and sensed, and how these change with differentiation. Nesprins are a family of structural proteins that partially localize to the nuclear envelope where they interact with both cytoskeletal and nucleoskeletal proteins [1]. At their C-terminus, nesprins interact through a KASH domain with proteins of the nuclear membrane, including SUN and Lamin A/C [1]. Multiple isoforms of the 4 nesprin genes are produced by alternative transcriptional initiation, translation and splicing. Specifically, nesprin 1 and nesprin 2 giant contain an N-terminal calponin homology domain (CH) that binds to and co-localizes with F-actin [2]. These nesprins are necessary for transmission of stress to the nucleus and are also differentially regulated with myogenesis, neurogenesis and adipogenesis [3,4]. We previously demonstrated that addition of TGF-3 induced nuclear Lamin A/C reorganization and nuclear stiffening in mesenchymal stem cells (MSCs), along with increased cell contractility and altered accumulation of smaller nesprin isoforms [5,6]. This study sought to determine the importance of contractility in transmission of force to the nucleus and the effect of dynamic loading on the expression of the giant nesprin isoforms.