Rita M. Cowell, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Nitric Oxide (NO) mediates many processes in the nervous system, including neurotransmission, synaptic plasticity, and excitotoxic neuronal injury. The long-term goal of this research is to delineate the mechanisms by which NO influences normal cellular homeostasis and survival so as to develop strategies to prevent neuronal cell death in neurological disorders. Preliminary experiments indicate that low concentrations of NO can increase mitochondrial number in primary rat dorsal root ganglia (DRG) neurons; the mechanisms of mitochondrial biogenesis in neurons are unknown but may involve NO and peroxisome proliferator-activated receptor y coactivator-1 (PGC-1) signaling pathways. In addition, it is possible that NO mediates its neuroprotective effects, in part, through the activation of PGC-1 in neurons and the execution of the mitochondrial biogenesis program. Therefore, the specific aims of this proposal are 1) to determine the effects of NO and the cGMP/protein kinase G pathway on mitochondrial number, 2) to investigate the regulation of mitochondrial biogenesis by PGC-1 and its downstream gene products, and 3) to determine if NO-mediated neuroprotection involves PGC-1 signaling in primary rat DRG neurons and differentiated PC12 cells. Experiments will involve the quantitation of mitochondria after exposure to NO donors or pharmacological inhibitors/activators of the cGMP pathway, evaluation of NO-induced changes in the expression of key mitochondrial biogenesis proteins, and inhibition or overexpression of PGC-1 to determine its role in mitochondrial biogenesis and neuroprotection. These experiments will address fundamental questions in neurobiology while revealing mechanisms of neuronal survival that could lead to new treatments for patients with neurological disorders. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): For much of her scientific research career, Dr. Cowell has studied the cellular mechanisms underlying neuronal cell death and injury. However, she has recently made a significant change in long-term research interests and is in the process of entering the field of mental health research. This proposal outlines a strategy for didactic and technical training and exposure to emerging concepts in translational schizophrenia research, with the goal of promoting Dr. Cowell's success as an independent, extramurally funded, academic investigator in mental health. Dr. Cowell's development plan involves the completion of coursework and attendance at research conferences, workshops in career development and ethical conduct in research, and a program of research that will contribute technically and intellectually to her progress towards independence. Based on preliminary data suggesting that peroxisome proliferator activated receptor g (PPARg) coactivator 1a (PGC-1a) is involved in metabolic homeostasis in inhibitory neurons, experiments are designed to test the hypotheses that 1) PGC-1a regulates metabolism and synaptic plasticity in GABAergic neurons in vitro and in vivo, 2) adverse perinatal events (hypoxia) have a long-term effect on the maturation of GABAergic circuits by disrupting normal PGC-1a expression and histone acetylation in development, and 3) the expression levels of PGC-1a and related metabolic genes are altered in inhibitory interneurons in the cortex of schizophrenic patients. To test these hypotheses, Dr. Cowell has chosen a panel of consultants with extensive experience in cell culture, rodent models of perinatal hypoxia, assessment of chromatin acetylation/methylation status, and laser capture microdissection from human postmortem brain tissue. This plan will equip the applicant with the knowledge and technical expertise to address key issues in mental health research, while elucidating the mechanisms by which disturbances in brain development contribute to the pathogenesis of schizophrenia. Schizophrenia is a significant health concern; it has been estimated that 1% of the general population and 14% of the homeless population has schizophrenia. In 1990 alone, schizophrenia accounted for $32.5 billion in medical costs. New treatments are needed to improve the lives of those with schizophrenia and to prevent the emergence of schizophrenia in high-risk populations. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Huntington's Disease (HD) is a debilitating genetic disorder involving progressive deterioration of psychiatric and motor function over a period of years, leading to death. Studies indicate that the expression of the transcriptional co-activator peroxisome proliferator activated receptor co-activator 1 (PGC-1) is decreased in striatum and muscle tissue from patients with HD and that mutant huntingtin (mHtt) interferes with normal expression and activity of PGC-1. Furthermore, polymorphisms in the PGC-1 gene influence the age of onset of motor symptoms. In light of the proposed role for PGC-1 in metabolic regulation, scientists have hypothesized that deficiencies in PGC-1 contribute to neuronal vulnerability and mitochondrial defects in HD. The roles of PGC-1 in the brain are not well-defined. PGC-1 is concentrated specifically in neurons that express the enzyme glutamic acid decarboxylase 67 (GAD67), and new data from the Cowell lab indicate that PGC-1 is required for the appropriate expression of the calcium buffer parvalbumin. Furthermore, PGC-1 null animals show abnormalities in GABAergic signaling, long-term potentiation, and motor function. Preliminary studies show that PGC-1 is consistently downregulated in cell culture models of HD, and the expression of PGC-1 and its targets parvalbumin and glucose transporter 4 are decreased in the striatum, hippocampus, and cortex in a mouse model. These data are interesting, considering that parvalbumin-positive (PV+) interneuron function is compromised in the cortex prior to the onset of motor symptoms in mouse models of HD. In addition, because of the strong feed-forward inhibitory effect PV+ neurons exert on medium spiny neurons and cortical pyramidal neurons, even slight disturbances in PV+ neuron function could profoundly influence striatal/cortical output and motor function. We propose that a deficiency in PGC-1 predisposes PV+ neurons to vulnerability in HD and compromises their ability to properly inhibit local projection neurons and coordinate motor output. The experiments proposed in this application will test this hypothesis by determining 1) the requirement for PGC-1 in striatal PV+ interneuron survival, morphology, signaling, calcium homeostasis, and motor function, 2) the effects of PGC-1 ablation on other vulnerable neuronal populations in the striatum, 3) the regional and cellular specificity of changes in PGC-1 and PGC-1-target gene expression in mouse models of HD, and 4) the impact of PGC-1 overexpression on cellular survival and motor function in a mouse model of HD. The proposed experiments are necessary to determine the cell autonomous and non-cell autonomous effects of PGC-1 dysfunction on neuronal viability and function with the goal of determining whether PGC-1 is an appropriate target for the treatment of HD. PUBLIC HEALTH RELEVANCE: Huntington Disease (HD) is a devastating neurological disorder that occurs in as many as 7 in every 100,000 people. While the genetic basis for HD is known, there are no effective therapies available. These studies will test whether transcriptional pathways that control mitochondrial function and calcium homeostasis in interneurons have potential as targets for treatment of patients with HD.

Dopaminergic neurons of the substantia nigra are particularly susceptible to dysfunction and loss with aging and disease. A potential contributor to this vulnerability is the requirement for the maintenance of intrinsic pacemaking activity. However, little is known about how this pacemaking activity is regulated in physiological and pathological states. Understanding how nigral neurons maintain their firing rate and adapt to cellular stressors has the potential to reveal novel pathways for prevention of cellular damage and death. In this application, we are proposing to test the novel hypotheses that the molecular clock is a key regulator of pacemaking activity and other processes required for normal function of dopaminergic neurons and that disruption of this clock contributes to cell dysfunction and death in models of Parkinson Disease (PD). In support of these hypotheses, we have found that dopaminergic neuron firing rate varies with time of day and that this variation is abolished in mice with midbrain-specific deletion of the obligate transcriptional regulator of circadian function, Bmal1. Furthermore, we have found day/night differences in the expression of genes involved in pacemaking activity in the substantia nigra, suggesting that pathways important for nigral function may be regulated at the transcriptional level by the molecular clock. Interestingly, we have discovered alpha synuclein mouse models of PD display disrupted day/night differences in pacemaking activity, leading to the hypothesis that the impairment of circadian-regulated processes could contribute to neuronal dysfunction and death in disease. In Aim 1, experiments are designed to determine the mechanisms by which the molecular clock regulates dopaminergic neuron function at the transcriptional, electrophysiological, and behavioral levels, using recently developed tools to evaluate molecular clock rhythmicity and transcription in a cell-specific way. In Aim 2, experiments will utilize approaches to reset the molecular clock in a time-of-day-dependent manner in mice with ?-synuclein- induced pathology to determine the role for circadian dysregulation in the progression of ?-synuclein-mediated neurotoxicity and behavioral impairment. Altogether, these experiments have the potential to reveal a novel regulatory mechanism of nigral function and vulnerability and could give critical insight into disease progression and pathogenesis.