ACTIVITY-DEPENDENT MITOCHONDRIAL SIGNALING DRIVES GLR-1 DYNAMICS AND BEHAVIORAL SENSITIZATION IN C. ELEGANS

Abstract

The AMPA sub-type of glutamate receptors (AMPARs) are necessary for excitatory synaptic function. Specifically, dynamic AMPAR transport and localization throughout dendrites is critical for synaptic strengthening as well as learning and memory. We are beginning to unravel the effects of neuronal activity as well as subsequent calcium influx and its downstream signaling on synaptic AMPAR localization. However, how subcellular compartments, such as mitochondria, contribute to localized signaling, and how they affect AMPAR transport and delivery dynamics are still unknown. Previous work from our lab using in vivo imaging of AMPARs in neurons of intact C. elegans animals has shown the effects of activity-dependent reactive oxygen species (ROS) signaling on AMPAR transport. For my dissertation, I show the role of mitochondria in these activity-dependent, postsynaptic changes. In Chapter 2, we first image basal and activity-driven mitochondria calcium handling changes in C. elegans AVA interneurons. We then use a mcu-1(lf) mutant to investigate the effects of reduced mitochondrial calcium influx on tagged GLR-1 transport and recruitment to synapses. ChRimson expression in AVA was used to optogenetically activate AVA to further examine activity-dependent changes. Decreased mitochondrial calcium uptake results in less GLR-1 transport from the soma as well as decreased recruitment to synapses. In Chapter 3, we expand the optogenetic activity protocols to presynaptic partners to establish a long-term reversal sensitization protocol. When combined with mitochondria and GLR-1 readouts, we found that postsynaptic, activity-dependent mitochondrial ROS production is necessary and sufficient for sensitization. This increased redox signaling results in elevated local GLR-1 membrane insertion through increased transcription. Chapter 4 examines the role of CaMKII in ROS signaling using redox resistant rescues in CaMKII mutant backgrounds. Using a catalase mutant to increase ROS, we expose a difference in regulation in the soma and neurite, dependent on relevant regulatory residues and the environment. Together, these results suggest multiple spatiotemporal signaling roles for mitochondrial function dependent on neuronal activation state and postsynaptic environment. Post-synaptic mitochondrial calcium handling regulates GLR-1 trafficking and delivery whereas ROS production increases insertion of GLR-1 at synapses after optogenetic training. These activity-dependent changes are transcriptionally regulated and lead to long-term behavior sensitization. In addition, ROS signaling through CaMKII redox shifts GLR-1 trafficking and delivery in high ROS conditions, suggesting compartmentalized regulation.