On the Role of Relay Cells in Information Propagation Speed for Dictyostelium Chemotaxis: An Agent-Based Modeling Study

Chemotactic signaling in Dictyostelium discoideums (DDs) relies on the secretion, diffusion, and enzymatic degradation of cyclic adenosine monophosphat (cAMP) molecules to coordinate collective cell responses. Understanding how information propagates through such biochemical signaling networks is important not only for explaining collective biological behavior, but also for enabling the design of bio-inspired molecular communication (MC) systems and synthetic micro-scale agent networks. To capture these spatiotemporal interactions, a scalable agent-based modelling (ABM) framework consisting of a stochastic reaction-diffusion environment and autonomous cell agents is proposed. The environment models diffusion and reaction kinetics for intercellular MC, while each cell is governed by chemical reaction networks that drive cAMP synthesis, secretion, and phosphodiesterase (PDE) production. Both molecules are released into the shared extracellular space, where they undergo diffusion and enzymatic degradation. A transmitter (TX)-receiver (RX) scenario involving multiple cells is investigated. The extracellular cAMP secreted by the TX binds to receptors on relay cells and the intended RX cell, triggering intracellular synthesis. The reaction rate parameters are tuned through a kernel approximation method to achieve stable reciprocal cAMP exchange among cells. Lagged mutual information (LMI) is used to quantify the speed of information propagation between TX and RX while varying the density of intermediate cells, which are also called relay cells and are the same type of cells as the TX and RX cell. Results reveal a sigmoidal relationship between the number of relay cells and information propagation speed. For low numbers of relays, the speed improves only marginally, indicating inefficient signal reinforcement. Beyond a critical relay density, the propagation speed increases rapidly due to cooperative amplification among cells. However, further increasing the number of relays yields diminishing returns, leading to a saturation regime. These findings highlight the existence of an effective relay density that optimizes information transfer in chemotactic signaling systems.