Erdem Tabdanov

Cardiac myocyte remodeling mediated by N-cadherin-dependent mechanosensing.

Cell-to-cell adhesions are crucial in maintaining the structural and functional integrity of cardiac cells. Little is known about the mechanosensitivity and mechanotransduction of cell-to-cell interactions. Most studies of cardiac mechanotransduction and myofibrillogenesis have focused on cell-extracellular matrix (ECM)-specific interactions. This study assesses the direct role of intercellular adhesion, specifically that of N-cadherin-mediated mechanotransduction, on the morphology and internal organization of neonatal ventricular cardiac myocytes. The results show that cadherin-mediated cell attachments are capable of eliciting a cytoskeletal network response similar to that of integrin-mediated force response and transmission, affecting myofibrillar organization, myocyte shape, and cortical stiffness. Traction forces mediated by N-cadherin were shown to be comparable to those sustained by ECM. The directional changes in predicted traction forces as a function of imposed loads (gel stiffness) provide the added evidence that N-cadherin is a mechanoresponsive adhesion receptor. Strikingly, the mechanical sensitivity response (gain) in terms of the measured cell-spread area as a function of imposed load (adhesive substrate rigidity) was consistently higher for N-cadherin-coated surfaces compared with ECM protein-coated surfaces. In addition, the cytoskeletal architecture of myocytes on an N-cadherin adhesive microenvironment was characteristically different from that on an ECM environment, suggesting that the two mechanotransductive cell adhesion systems may play both independent and complementary roles in myocyte cytoskeletal spatial organization. These results indicate that cell-to-cell-mediated force perception and transmission are involved in the organization and development of cardiac structure and function.

α-Actinin links extracellular matrix rigidity-sensing contractile units with periodic cell-edge retractions

During cell migration, the cell edge undergoes periodic protrusion–retraction cycles. Quantitative analyses of the forces at the cell edge that drive these cycles are provided. We show that α-actinin links local contractile units and the global actin flow forces at the cell edge and present a novel model based on these results.

Micropatterning of TCR and LFA-1 ligands reveals complementary effects on cytoskeleton mechanics in T cells.

The formation of the immunological synapse between a T cell and the antigen-presenting cell (APC) is critically dependent on actin dynamics, downstream of T cell receptor (TCR) and integrin (LFA-1) signalling. There is also accumulating evidence that mechanical forces, generated by actin polymerization and/or myosin contractility regulate T cell signalling. Because both receptor pathways are intertwined, their contributions towards the cytoskeletal organization remain elusive. Here, we identify the specific roles of TCR and LFA-1 by using a combination of micropatterning to spatially separate signalling systems and nanopillar arrays for high-precision analysis of cellular forces. We identify that Arp2/3 acts downstream of TCRs to nucleate dense actin foci but propagation of the network requires LFA-1 and the formin FHOD1. LFA-1 adhesion enhances actomyosin forces, which in turn modulate actin assembly downstream of the TCR. Together our data shows a mechanically cooperative system through which ligands presented by an APC modulate T cell activation.

T-Cell Receptor Activation Initiates Multiple Modes of Actin Polymerization within the Immune Synapse

The immune synapse is a key point of communication between T cells and antigen presenting cells. The layout of this interface is driven in large part by a complex cytoskeletal structure. This report focuses on modulation of the cytoskeleton by T Cell Receptor (TCR) signaling using micropatterned surfaces presenting OKT3 (an antibody that activates the TCR signaling component CD3) and ICAM-1 to T cells. Previous studies by our group demonstrated that micro-scale features of OKT3 (red, top row) induce lamellipodial polymerization (white arrows) of actin (green) on surrounding regions of ICAM-1. We show here a second type of polymerization, the formation of linear, consolidated F-actin structures from sites of CD3 engagement (blue arrow), resembling actin comets observed in other systems. This mode of actin polymerization occurs concurrent to lamellipodium extension. Furthermore, polymerization is initiated by sharp, external corners of angular patterns of OKT3 (bottom row). This latter result suggests mechanical forces, which are concentrated at such corners under cellular tension, initiate this modality of actin polymerization. The different contributions of these behaviors on immune synapse function remain to be determined.View Large Image | View Hi-Res Image | Download PowerPoint Slide