Computational modelling of plasma membrane electrophysiology and calcium dynamics in microglia

Microglia, a type of glial cell, perform many tasks while interacting with neurons, astrocytes, and oligodendrocytes. Despite moderate advances in the characterisation of microglia in laboratory rodents, very little information is known about the physiology of microglia in the human brain. This is a challenging task and consequently this thesis attempts to advance knowledge of microglia function through mathematical modelling. Microglia restructure their intracellular actin cytoskeleton to enable motility; this requires a complex molecular cascade involving a set of ionic channels, membrane-coupled receptors, and cytosolic components. In this research, we develop a theoretical foundation for studying P2-mediated calcium and PI3K/Akt signalling in human microglial cells. Firstly, a detailed mathematical model is built for the dynamics of human P2XRs in microglia. Subsequently, experimental whole-cell currents are used to derive the P2X-mediated electrophysiology of human microglia (sodium and calcium dynamics, and membrane potential). Secondly, microglial-directed motility involves a complex family of intracellular signalling pathways that are mainly controlled by P2Y-mediated cytosolic calcium (Ca2+) signalling and activation of the PI3K/Akt pathway. This thesis addresses the development of mathematical models for these two complex aspects of microglial functions and investigates the interconnecting role of PI3K pathway to Ca2+. Our predictions reveal new quantitative insights into how P2Rs regulate ionic concentrations in terms of physiological interactions and transient responses. Simulation results show that kink-like, intricate Ca2+ responses mediated by P2XRs arise from a complex cooperative activation of both P2XRs, and ionic extruders and pumps. More importantly, the proposed model supports our hypothesis that calcium influx via P2YR and P2XR can explain the experimentally observed twin peaks in the phosphorylated Akt. To the best of our knowledge, this is the first biophysical model that aims to predict complicated Akt and P2-mediated Ca2+ responses in microglia. The biophysical models provide direction for new fundamental experimental research.