Investigating the Role of Phospholipid Regulation in Glial Pruning

Abstract

In both the peripheral and central nervous systems, glia remove unnecessary neuron endings to sculpt neural circuitry. This process, here termed glial pruning, is critical for nervous system development and function, and implicated in neurodegenerative disease. Glial pruning is thought to depend on neuronal exposure of the “eat me” signal phosphatidylserine (PS), which is carefully regulated by the activity of enzymes known as flippases and scramblases. While loss of many of these enzymes causes neurological disease, few have been identified as regulators of pruning. Further, their potential role in glia, or the involvement of other phospholipid substrates, remains unknown. Phospholipid distribution must also be maintained at intracellular membranes. Notably, endolysosomal compartment dysfunction is a known contributor to neurodegenerative disease, but potential links to glial pruning are unexplored. In this thesis, I review the current knowledge on glial pruning and phospholipid regulation across species and highlight my work using C. elegans to interrogate the role of various phospholipid regulators during glial pruning of a single associated sensory neuron ending. First, I verify the involvement of PS flippases and scramblases in directing glial pruning. Additionally, I uncover a novel role for the phosphatidylethanolamine (PE) flippase TAT-5 in regulating glial trafficking and lysosome biology to promote pruning, with concomitant impacts on neuron shape and function. Further, knockdown of mammalian orthologs ATP9A/B in cultured rat astrocytes causes similar defects in pruning and lysosome biology. Together, this dissertation provides a conserved and disease-relevant new framework for understanding the complex relationship between phospholipid regulation, endolysosomal function, and glial pruning.