Gq-mediated calcium dynamics and membrane tension modulate neurite plasticity

Abstract

The formation and disruption of synaptic connections during development is a fundamental step in neural circuit formation. Subneuronal structures such as neurites are known to be sensitive to the level of spontaneous neuronal activity but the specifics of how neurotransmitter-induced calcium activity regulates neurite homeostasis are not yet fully understood. In response to stimulation by neurotransmitters such as acetylcholine, calcium responses in cells are mediated the Gαq/phospholipase Cβ (PLCβ )/ phosphatidylinositol 4,5 bisphosphate (PI(4,5)P2) signaling pathway. Here, we show that prolonged Gαq stimulation results in the retraction of neurites in PC12 cells and rupture of neuronal synapses by modulating membrane tension. To understand the underlying cause, we dissected the behavior of individual components of the Gαq/PLCβ /PI(4,5)P2 pathway during retraction, and correlated these to the retraction of the membrane and cytoskeletal elements impacted by calcium signaling. We developed a mathematical model that combines biochemical signaling with membrane tension and cytoskeletal mechanics, to show how signaling events are coupled to retraction velocity, membrane tension and actin dynamics. The coupling between calcium and neurite retraction is shown to be operative in the C. elegans nervous system. This study uncovers a novel mechanochemical connection between the Gαq/PLCβ /PI(4,5)P2 pathway that couples calcium responses with neural plasticity. INTRODUCTION:Throughout the course of an organism's life, different neuronal connections break and reform to generate new electrical patterns that allow for optimal function during development and through adulthood. This plasticity of neuronal connections allows the rewiring of circuitry necessary for memory and learning (e.g.(1) (2) (3)). Understanding the factors that permit appropriate and efficient rewiring is essential for understanding both developmental and neurodegenerative diseases.Calcium is a key mediator of neuronal functions such as axonal growth, neurite protrusion, and spinogenesis (4, 5). Previous studies have shown that spontaneous activity in neurons can results in a frequency dependent rate of axon elongation such that the rate of axon elongation is inversely proportional to the frequency of calcium transients (6, 7). The role of calcium in neurite growth and protrusions associated with development has been studied in different contexts (e.g (8)). This outgrowth process is stimulated by neurotrophic factors that carefully regulate the spatiotemporal aspects of intracellular calcium. Neurite growth can also be triggered by stress, pharmacological agents, or starvation (9, 10). These factors may occur during disease states and contribute to inappropriate neurite growth, which can result in an increased number of smaller and non-productive neurites, as seen in autism (10).Neurodegenerative diseases are associated with the disruption of normal calcium signaling. Specifically, diseases such as autism and amyotrophic lateral sclerosis (ALS) have been link...