A Genetic Model of NMDA Receptor Function in Cell Death

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DESCRIPTION (provided by applicant): Excitatory cell death is responsible for the loss of nervous tissue in neurodegenerative disorders such as Alzheimer's or Parkinson's disease and after insults to the nervous system, for instance through stroke or alcohol abuse. This type of cell death is caused by an overstimulation of calcium uptake through glutamate receptors, in particular the N-methyl-D-aspartate receptor (NMDAR). Despite the medical importance of excitatory cell death, a coherent model of the events downstream of receptor activation has been slow to emerge. Progress has been hampered by the complexity of cell death under pathological conditions and the lack of an accessible animal model that allows a genetic dissection of the process. This project is based on the discovery that NMDAR is required for non-pathological programmed cell death in the genetic model organism Drosophila melanogaster. Death of the larval salivary glands during metamorphosis, which constitutes an important model system in cell death research, fails when NMDAR activity is reduced. This opens up the possibility to study the role of NMDAR in cell death using the powerful tools and approaches of model organism research. As a first result of this research, the protein tyrosine phosphatase Ptpmeg was identified as a putative partner of NMDAR in cell death control. Salivary glands deficient in Ptpmeg do not die and carry a lowered calcium load. Cell death control by Ptpmeg is a novel function that likely extends to its human homologs, which are dysregulated in cancers and suspected to be tumor suppressors. The broad objective of this project is to determine how NMDAR and Ptpmeg cooperate in cell death control and how the two proteins affect steps in the evolutionarily conserved cell death program. Specifically, the project will (1) use genetic approaches in transgenic animals to determine how NMDAR and Ptpmeg cooperate in regulating intracellular Ca2+ and cell death. Co- immunolocalization and pull-down assays will be used to examine physical interactions between NMDAR and Ptpmeg. Staining with a phospho-specific antibody will reveal the expression profile of the tyrosine-phosphorylated form of NMDAR and its dependence on Ptpmeg. (2) The role of Ca2+ in cell death will be examined in transgenic animals using a Ca2+-buffer protein. Downstream targets of NMDAR signaling will be identified by analyzing the effects of reduced NMDAR activity on Ca2+-dependent cell clearance pathways and markers of apoptosis and autophagy. (3) Biochemical and genetic assays will be used to identify steps in apoptotic and Ca2+-signaling pathways that are affected by a lack of Ptpmeg. Together, the results of the proposed research are likely to bring to light evolutionarily conserved, basic mechanisms of cell death control by NMDAR and Ptpmeg. Thus, the project will help understand the function of these proteins under pathological conditions and aid in the development of therapeutic measures.