Abstract
The observed spatiotemporal ciliary beat patterns leading to proper mucociliary clearance on multiciliated epithelia are suspected to be the result of self-organizing processes on various levels. Here, we present a simplified pluricellular epithelium model, which intends to make the self-organization of ciliary beating patterns as well as of the associated fluid transport across the airway epithelium plausible. The model is based on a two-dimensional array of locally interacting oscillating ciliated cells. Ciliated cells are represented by Boolean actuators, and abstracted hydrodynamic mucociliary interactions are formulated in terms of logical update rules (Boolean functions). In the course of a simulation, initial random conformations of an array of actuators self-organize toward metachronally coordinated states exhibiting efficient transport of mucus. Within the framework of Boolean networks ciliated cells represent the nodes of the network and as the mucus establishes the local interactions among nodes, its distribution (together with the formulated local interactions) determines the topology of the network. Consequently, we propose to consider the dynamics on multiciliated epithelia in the context of adaptive (Boolean) networks. Furthermore, we would like to present insights gained from conducted comprehensive parameter studies. In particular, the dynamical response of the network with respect to variations of the boundary conditions, updating schemes (representing intercellular signaling mechanisms) and the proportion of ciliated cells is presented.
Highlights
Motivation for the present work is to contribute to the understanding of the fascinating and omnipresent phenomenon of mucociliary transport.The epithelium of our airways constitutes a self-cleaning surface protecting our lungs from a variety of inhaled substances such as exhaust, dust, bacteria and other harmful substances of micro- and submicrometer size
We suggest that the cooperation among ciliated cells emerges from locally interacting oscillating cilia bundles belonging to different ciliated cells
As our goal was to keep our model as simple as possible, we present a virtual self-cleaning epithelium model based on symmetrically interacting two-state actuators, which we formulate in terms of an adaptive Boolean network
Summary
Motivation for the present work is to contribute to the understanding of the fascinating and omnipresent phenomenon of mucociliary transport. The mucus droplets get displaced by the action of actuators and they may block their motion in certain configurations, which is prescribed by local interaction rules This highly simplified model based on locally interacting motors selforganizes toward a virtual self-cleaning epithelium: the initially randomly distributed phases erratically displace the mucus lumps at the beginning of the simulation. As time passes the motors self-organize, which is expressed by emergent global spatiotemporal structures, resembling the metachronal wavelets, which have been observed on the ciliated tracheal epithelium (Ryser et al 2007). These metachronal wavelets efficiently transport the mucus lumps into a well-defined direction. We hypothesize about the meaning of the discovered dynamical aspects, which seem to be universal for our specific model of locally interacting cells, for the real biological system
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