Piya Ghose, Ph.D. - US grants

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) and ischemic stroke are leading causes of morbidity and disability, excitotoxically killing neurons via a combination of hypoxia and oxidative stress, glutamate receptor overactivation, and deregulated calcium homeostasis. In particular, the hypoxia resulting from trauma or stroke results in membrane depolarization and hence release of the neurotransmitter glutamate from affected neurons. High levels of acute glutamate overactivate receptors on neighboring neurons, thereby resulting in calcium influx and excitotoxicity. Agents that directly interfere with receptor activation have had limited clinical applicability because of their dramatic effect on receptor physiological function. Thus, it is important to identify new therapeutic targets in order to mitigate excitotoxicity after TBI or stroke. The discovery that regulated trafficking of glutamate receptors can modify synaptic efficacy has changed the thinking about mechanisms by which receptors contribute to excitotoxicity after neuronal trauma. In particular, the movement of receptors into and out of synaptic membranes after post-trauma hypoxia in some cultured neuronal systems can modulate excitotoxicity. Do changes in glutamate receptor trafficking contribute to neuronal death in the intact animal, or are they part of a neuroprotective response to hypoxia? What factors regulate glutamate receptor trafficking in response to hypoxia? This proposal takes a genetic approach in C. elegans to understand how hypoxia impacts neuron cell biology. In Aim 1, it examines how hypoxia and the known hypoxia response pathway alters the membrane trafficking of receptors. In Aim 2, it characterizes how EGL-9, a PHD protein that senses oxygen levels, regulates LIN-10, a PTB/PDZ-domain protein known to regulate glutamate receptor trafficking, in response to hypoxia. The proposed experiments advance the field in several ways. First, they identify a novel hypoxia response pathway. Second, they demonstrate a new response pathway by which neurons protect themselves from hypoxia. Third, they show that regulated receptor trafficking is the underlying mechanism. Finally, they provide potential new therapeutic targets for minimizing brain damage following TBI and ischemic stroke. PUBLIC HEALTH RELEVANCE: Traumatic brain injury and stroke create conditions of hypoxia (low oxygen) in the brain, triggering the excessive release of the neurotransmitter glutamate. High levels of glutamate in turn kill neurons by over- activating their glutamate receptors. It is critical to understand how glutamate receptors are regulated in response to hypoxia in order to develop novel applications for the treatment and prevention of brain damage resulting after traumatic injury or stroke.

Project Summary/Abstract Programmed cell death (PCD) has vital roles in organismal health and is an essential part of normal development. Inappropriate cell survival is a hallmark of tumor progression. Apoptosis is genetically programmed and mutations in regulatory genes contribute greatly to cancer therapy resistance. Timely clearance of cellular debris following cell death is also critical as defects lead to inflammation and are linked to autoimmune disease. Most cells in the body are highly differentiated and have intricate morphologies. This presents challenges in the execution of cell death and clearance, as the subcellular architecture and microenvironment of different regions of the same cell may differ vastly. Complex cells can die as a whole or in part. In the case of region-specific degeneration, cellular extensions, such as axons, are exclusively dismantled leaving the rest of the cell intact. For neurons, such pruning is important in establishing appropriate connectivity and thus for proper brain function. While distinct programs are thought to control the degeneration of different cell regions, the precise cell biological and molecular mechanisms governing compartment-specific destruction are not well understood. Are degenerative mechanisms in each part of the cell inter-related or do they influence one another? What role do caspases, essential executers of apoptosis, play in the different cell compartments? Is the clearance of structurally diverse cell compartments mechanistically similar and mediated by the same canonical engulfment programs? This proposal takes a genetic approach in C. elegans to address these questions in the tail-spike cell, a morphologically complex cell that undergoes PCD during development. Preliminary data demonstrates that the tail-spike cell is an informative model for complex cell degeneration, given its compartment-specific degeneration kinetics and differential genetic regulation at the levels of both killing and clearance. Aim 1 of the project characterizes novel, compartment-specific, functions of CED- 3/caspase. Aim 2 examines how the cell fusion receptor EFF-1 mediates a novel process-specific clearance program. The proposed experiments advance the field in several ways. They demonstrate a new mode of degeneration in complex cells; they identify novel regulators of programmed cell death and clearance; they hold the potential to help devise targeted therapies against cell-death-related disease; and they may broaden our understanding of neurite degeneration and pruning, which are prevalent in development, plasticity, injury and disease of the nervous system.

Project Summary/Abstract Programmed cell death (PCD) and has vital roles in organismal health and is essential to normal development. Apoptosis is genetically programmed and mutations in regulatory genes contribute greatly to cancer therapy resistance. Timely clearance of cellular debris following cell death is also critical as defects lead to inflammation and are linked to autoimmune disease. Most cells in the body are highly differentiated and have intricate morphologies. This presents challenges in the execution of cell death and clearance, as the subcellular architecture and microenvironment of different compartments of the same cell may differ vastly. Complex cells can die as a whole or in part. In the case of region-specific degeneration, cellular extensions are exclusively dismantled leaving the rest of the cell intact. For neurons, such pruning is important in establishing appropriate connectivity and thus for proper brain function. The central question addressed here is how morphologically complex cells are eliminated. The C. elegans tail-spike cell is a valuable model to study complex cell degeneration, dying through an elaborate, likely universal, compartment-specific program of cell death during embryonic development. We have termed this remarkable program Compartmentalized Cell Elimination (CCE), which also occurs in a set of sex-specific neurons, suggesting this may be a universal program of death. The tail-spike cell also shows differential genetic regulation at the levels of both compartmental killing and clearance. As such, a study of this single cell can provide insights on many facets of cell elimination. This proposal leverages the fact that the tail-spike cell can be studied in its native context in the living animal as well as the facile genetics of C. elegans to tackle three broadly related overarching questions: How does mitochondrial trafficking influence cell process elimination? What novel genes govern CCE and hence cell death and removal broadly? What novel genes regulate CCE in other complex cells, such as neurons? We will perform advanced cell biological and genetic studies to address these questions. The proposed experiments, by illuminating fundamental principles of basic cell biology, will advance the field of cell death in several ways. They will identify novel regulators of PCD and clearance; they hold the potential to help devise targeted therapies against cell-death-related disease, including cancer, neurodegeneration, immune and developmental disorders.