Wednesday, April 2, 2025
4/2/2025
Regulation and recognition of eat-me signals in the nervous system - Project Summary/Abstract The elimination of existing neuronal structures by phagocytes is essential for the development and maintenance of a functional nervous system but can also drive neurodegeneration. Although an “eat-me” signal, phosphatidylserine (PS), is known to mark neuronal structures for engulfment, how PS is detected by endogenous sensors to activate phagocytes and how the recognition of PS exposed at axon terminals affect the maintenance of synapses remains poorly understood. The goal of this proposal is to address these fundamental questions using our unique in vivo models in Drosophila. Answering these questions is an important step towards understanding how phagocytes interact with neurons to regulate the development, maintenance, and degeneration of the nervous system. Orion, a chemokine-like secreted protein in Drosophila, was recently found to be an in vivo PS sensor that bridges interactions between PS on degenerating neurons and the conserved engulfment receptor Draper on phagocytes. Although the Orion expression level correlates with phagocyte potency, how Orion enables Draper to detect PS-exposing neurons and modulates phagocyte sensitivity is unknown. In addition, preliminary studies reveal that the Drosophila neuromuscular junction displays PS exposure on synaptic boutons and synapse-derived extracellular vesicles (EVs). This proposal aims to determine the molecular mechanism by which PS sensing regulates phagocyte activation and the significance of PS recognition at the NMJ. To achieve these goals, the following three aims are proposed: 1) Determine how Draper/PS interaction is mediated by the PS sensor during engulfment of neurons. Orion sequences that interact with PS and Draper will be mapped using in vitro biochemical assays, in vivo degeneration assays, and in vivo targeted mutagenesis screens. PS-binding properties of similar human chemokines will be examined using in vivo assays in Drosophila. 2) Elucidate the molecular basis of phagocyte sensitivity to PS exposed on neurons. The effects of heparan sulfate proteoglycans (HSPGs) and phagocyte PS exposure on Orion activity and phagocyte sensitivity will be examined. 3) Reveal the role of PS exposure and sensing in the maintenance of Drosophila NMJs. The PS-exposing sites on synaptic boutons will first be precisely mapped by volume electron microscopy (vEM) and 3D reconstruction of entire NMJs. The effects of perturbing PS exposure at the NMJ and the role of Orion in the biogenesis, transmission, and disposal of axon- derived EVs will be examined. Lastly, candidate scramblases will be tested for possible involvements in NMJ PS exposure. Together, these aims will reveal mechanistic insights into PS sensing in the nervous system for understanding how PS exposure is related to the maintenance of neuronal connections and to neurodegenerative diseases.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).