BRIDGING the GAP: a Theoretical Model of Mechanotransduction THROUGH Erksignalling

BRIDGING THE GAP: a theoretical model of mechanotransduction THROUGH ERKsignalling

Johan Kerkhofs (1,2,3), Liesbet Geris (1,3), Bart Bosmans (2), Hans Van Oosterwyck (2,3)

1. Biomechanics Research Unit, U.Liège, Belgium; 2. Biomechanics section, K.U.Leuven, Belgium; 3. Prometheus Leuven R&D division of skeletal tissue engineering, K.U.Leuven, Belgium

Introduction

Integrins play a crucial role in the mechanotransduction of anchorage-dependent cells. They transmit the mechanical signalsand initiate signalling pathways which ultimately alters transcription in the cell nucleus. The dynamics of this process is poorly understood. We present a theoretical model that bridges the gap between mechanical signals and their regulation of intracellular signalling pathways. Specifically, we model the effect of integrin activation on the extracellular-signal regulated kinase (ERK) pathway and their interplay.

Methods

The model comprises an Ordinary Differential Equations (ODE) model of the ERK signalling pathway (adapted from [Faratian, 2009]), coupled to a 1D rheological model of cell-matrix mechanics (adapted from [Moreo, 2007])that considers extracellular matrix (ECM), integrin, cytoskeletal and nuclear (visco)elasticity and acto-myosin contractility. The ERK pathway is activated by stretching of integrin molecules. Integrin activationwas made proportional to its deformation. Several feedback mechanisms between the intracellular and the mechanical model were implemented (Fig.1).

Results

The model predicted markedly different ERK activation for static versus dynamical loading (fig. 1).

Figure 1: Coupling of cell mechanics to intracellular ERK model:

A different response to static versus dynamic load arises from the interplay between the cell mechanical model and the intracellular ERK model.

Furthermore, a sensitivity analysis among others demonstrated the importance of substrate stiffness for ERK signalling.Low substrate stiffness led to larger integrin deformation, thereby increasing the stimulation of the ERK pathway.

Discussion

The predicted ERK response to static versus dynamic loading qualitatively correspondedto the experimental results of [Fitzgerald, 2006]. In the model the differential response is the result of the interplay between repeated activation of the ERK phosphorylation pathway and the deactivation and recovery of the dephosphorylation pathway in synchrony with the force. At higher frequencies the dephosphorylation does not have enough time to recover. These results show the model’s potential in elucidating mechanotransduction phenomena.

The sensitivity to an alteration in the ECM stiffnessillustrates how the ECM stiffness influences intracellularsignalling, which may give rise to different cell fates. The mechanical environment may have to be tailored to a specific cell fate, a finding which is e.g. important to tissue engineering and in fracture healing where the extracellular matrix becomes progressively stiffer.

Acknowledgements

Johan Kerkhofs is a PhD Fellow of the Research Foundation Flanders (FWO – Vlaanderen).

References

Faratianet al, Cancer res, 69:6713-6720, 2009.

Fitzgerald et al, J Biol Chem, 34:24095-103, 2006.

Moreoet al, Acta biomater, 4:613-621, 2007.