Ethan G. Hughes, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): The assembly of CMS synapses is a complex and dynamic process, requiring the coordinated exchange of signals between pre- and postsynaptic neurons and surrounding glia. Astrocytes, one type of glia, have been shown to increase the formation and function of excitatory synapses, in part by releasing soluble factors as well as by contact. However/the role that astrocytes play in inhibitory synapse formation and function has not been well studied. It is the goal of this proposal to examine the role of astrocytes in inhibitory synaptogenesis in the developing nervous system. Previous work from the Balice-Gordon lab and my preliminary studies in hippocampal neurons in vitro suggest that astrocytes release soluble signals into the media (astrocyte conditioned media, ACM) that increase inhibitory neuron axon elongation, branching as well as synaptogenesis, by the criteria of increasing the number of GABAergic presynaptic terminals co-localized with postsynaptic GABAAR clusters (Elmariah et a I.", 2005; Hughes et al., 2005). My preliminary studies also suggest that neuronal contact with astrocytes, but not ACM, increase the number of functional GABAergic synapses. This leads to the hypothesis that secreted and contact signals from astrocytes differentially mediate the formation and function of inhibitory synapses during neural development. To test this hypothesis, I will: (1) Determine how astrocyte soluble signals affect inhibitory axon outgrowth, branching and synaptogenesis in a series of experiments. (2) Examine the role of neuron- astrocyte contact in the development of inhibitory synapse function. (3) Identify soluble signals released by astrocytes that increase inhibitory axon outgrowth, branching and synaptogenesis. Taken together, these experiments will extend our understanding of how inhibitory synapses are formed during neural development. The results of these studies will extend our understanding of how neuron-glia signaling modulates synapse formation and function, and set the stage for defining the underlying cellular and molecular mechanisms. Understanding these mechanisms will provide a foundation of knowledge that may, in the future, suggest avenues for therapeutic intervention for disorders of development such as epilepsy, autism and mental retardation, in which synapse formation and/or function are aberrant or reduced. [unreadable] [unreadable]

Project Summary Multiple sclerosis (MS) is an inflammatory disease of the central nervous system that affects more than 2.5 million people worldwide with an unknown etiology. People with MS can experience relapsing-remitting or progressive forms of disease, with the latter associated with cortical atrophy and cognitive decline. While MS is classically regarded as a disease of the white matter, recent evidence suggests that there is significant myelin loss in the gray matter of patients with MS. Cortical lesions are common in early MS and their increasing abundance during late stages of MS suggests that they may be an important therapeutic target. B cells are directly implicated in MS pathology, with recent evidence implicating IgG-mediated demyelination in pathology and the effectiveness of anti-B cell therapies in treatment of MS. However, mechanisms regulating myelin injury and repair in cortical lesions are incompletely understood. Progress in the understanding of MS has been constrained by the paucity of animal models that recapitulate hallmarks of the disease and inability to detect the dynamics of cortical demyelination in living patients. To overcome these limitations, we have developed both a novel mouse model of MS antibody-dependent demyelination and approaches to visualize myelin, oligodendrocytes, and their precursors in the living mouse brain. Here we propose to capitalize on these innovative approaches to discern the dynamics of demyelination and repair myelin in cortical lesions. The objectives of this proposal are: 1) Develop and evaluate a new model of antibody-mediated MS cortical demyelination and 2) Elucidate the mechanisms underlying remyelination in cortical lesions. This proposal breaks new ground by developing novel approaches to understand the mechanisms underlying cortical lesions that characterize MS and provide an in vivo mouse model platform that will allow for the evaluation of new therapeutic candidates for MS.

Nearly 1 million people in the United States alone are affected by Multiple Sclerosis (MS). MS is an inflammatory, demyelinating disease of the central nervous system (CNS). While MS is classically regarded as a disease of the white matter, the number of white matter lesions does not correlate with physical disability or cognitive impairment. Recent evidence indicates that gray matter areas have significant myelin loss and increased cortical lesion load is associated with increased cortical atrophy and cognitive decline. Functional imaging of patients with MS reveals increased hyperexcitability within primary motor cortex and throughout the motor network. Moreover, functional recovery in MS patients is associated with normalization of aberrant cortical activity, suggesting a relationship between motor network hyperexcitability and impaired motor behavior. However, our understanding of how myelin loss influences the activity of single neurons, or neural circuits, within grey matter is extremely limited. Outstanding questions such as, what are the consequences of demyelination on neural physiology in the intact CNS, how demyelinating injuries affect the acquisition of new skills, and can therapies that can enhance remyelination can restore neural and behavioral function remain unknown. Recently, we have developed new approaches to visualize myelin, oligodendrocytes, and their precursors in the intact mouse brain, as well as longitudinal approaches to record and monitor neural activity in behaving animals. We have also identified novel behavioral interventions that enhance myelin repair. In this application, we propose to capitalize on the dynamics revealed by these techniques to discern the effects of myelin loss and repair on local circuit activity and motor behavior. The objectives of this proposal are: 1) evaluate how myelin loss affects neuronal circuit function and 2) to elucidate the effectiveness of remyelination therapies on restoring neural function and behavior. This proposal will demonstrate the effects of demyelination on cortical neuronal and circuit function in vivo. These studies will validate an in vivo mouse model platform to test efficacy of new therapeutic candidates for MS, and provide clinically relevant data regarding the efficacy of therapies that stimulate endogenous remyelination in MS on restoring neural and behavioral function.