Branching actin network remodeling governs the force-velocity relationship

TL;DR

This study uses agent-based simulations to explore how branching actin networks remodel under load, revealing mechanisms that explain different force-velocity behaviors and their dependence on force history.

Contribution

The paper introduces a stochastic simulation model showing how actin network remodeling accounts for various force-velocity curves and history dependence.

Findings

Actin networks remodel by increasing filament growth against load.

The model explains both convex and concave force-velocity curves.

Force history influences actin network velocity.

Abstract

Actin networks, acting as an engine pushing against an external load, are fundamentally important to cell motility. A measure of the effectiveness of an engine is the velocity the engine is able to produce at a given force, the force-velocity curve. One type of force-velocity curve, consisting of a concave region where velocity is insensitive to increasing force followed by a decrease in velocity, is indicative of an adaptive response. In contrast, an engine whose velocity rapidly decays as a convex curve in response to increasing force would indicate a lack of adaptive response. Even taken outside of a cellular context, branching actin networks have been observed to exhibit both concave and convex force-velocity curves. The exact mechanism that can explain both force-velocity curves is not yet known. We carried out an agent-based stochastic simulation to explore such a mechanism. Our results suggest that upon loading, branching actin networks are capable of remodeling by increasing the number filaments growing against the load. Our model provides a mechanism that can account for both convex and concave force-velocity relationships observed in branching actin networks. Finally, our model gives a potential explanation to the experimentally observed force history dependence for actin network velocity.