Jeffrey C. Petruska - US grants

DESCRIPTION (provided by applicant): This proposal is an innovative effort to develop a novel tool that could revolutionize the execution and application of in vivo sharp electrode intracellular electrophysiology, the fundamental approach for examining cellular and synaptic mechanisms of systems-level functions. This tool is a reporter gene that will be detectible by electrophysiological methods in real-time by sharp electrodes in vivo, without the need for secondary factors (i.e., light stimulus or exogenous ligands). This could provide a necessary link to enable a more thorough incorporation of classic-type systems physiology with the reduced preparations and lower species that make up the majority of current experimental approaches used to understand genetic manipulations. An ideal electrophysiological reporter is one that is genetically-encoded, is "visible" to electrophysiological methods, has a signal that is easily recognized and distinguished from native processes in real time, and does not interfere with normal physiological function. We have identified a lab-generated mutant ion channel that fits these criteria, and appears to be an excellent candidate. We will make use of new viral vector technology to deliver candidate gene to adult rats. Aim 1 will use both in vivo and in vitro single-cell electrophysiological approaches to determine if the signal from the reporter gene can be detected against the well characterized background of the model systems (dorsal root ganglion sensory neurons and spinal motoneurons). Aim 2 is hypothesis driven and will determine if constitutive signaling by trkC, the receptor for neurotrophin-3, plays a necessary role in maintenance of the cellular and synaptic properties of adult motoneurons. The issue of maintenance of cellular properties by target-derived factors is in a question of fundamental importance in terms of the principles of neuroscience/neurobiology, and also in terms of biomedical issues in the adult nervous system such as aging, neurodegeneration, traumatic injury, and learning and memory. PUBLIC HEALTH RELEVANCE: This project is aimed at developing a new tool for research - a gene that will report the status of genetic manipulations to electrophysiological probes. If successful, it will greatly facilitate the execution of, and interpretation of data from, systems-level in vivo neurophysiology, an experimental approach that is particularly relevant to functional studies of the role of specific genes/cell-types in systems-level processes such as aging, locomotion, sensori-motor integration, models of psychiatric disorders and addiction/substance abuse, and nervous system disease/injury/insult and the responses to treatments. This project also Aims to determine the effect of altering the expression of trkC (the receptor for neurotrophin-3) on the cellular and synaptic electrophysiological properties of a subpopulation of neurons, which is relevant to conditions or disease states that may include reduced neurotrophin-receptor signaling in the pathophysiology, such as aging, diabetic neuropathy, traumatic nervous system injury, and neurodegeneration.

DESCRIPTION (provided by applicant): Numerous neurological diseases and pathologies include, or are hypothesized to include, cellular injury and/or stress as part of the mechanism. Experimental approaches to examine these mechanisms, or even determine if they are indeed at play in certain conditions, are generally limited. They include post-mortem analyses of known stress-response genes/molecules, in vivo pharmacological manipulations which are often systemic, or functional assessments/manipulations which often cannot separate stressed from non-stressed neurons. Ideally, it would be possible to determine, a priori on a cell-by-cell basis, which neurons in a mixed population were exhibiting a cell-stress response. Further, since some stress responses, or at least some components of the stress response, are only transiently expressed even though the overall stress responses may have a cumulative effect on the cell, it would be highly useful to have an a priori indication of which neurons had exhibited a stress response at some point in the past. It would also be highly useful to be able to selectively assess the cellular and inter-cellular functionality of the stressed neurons. To these ends we propose to generate new functional-reporter transgenic mouse lines which will incorporate these characteristics. The reporters will be driven by the promoter region of Activating Transcription Factor 3 (ATF3), a hub protein involved in a variety of cellular stress responses. Generation of the mice will be via BAC-transgenes in order to preserve function of the native ATF3 alleles, which are necessary for certain cellular processes. The BAC transgene with the ATF3 locus will drive production of the light-gated ion channel channelrhodopsin-2 (ChR2) fused to a fluorescent protein. One model will have the reporters produced in an analogue fashion (i.e., to reflect native ATF3 expression). A second model will use an inducible Cre-recombinase system to permanently switch-on reporter production, thus allowing, at any later time, identification of neurons that previously expressed a stress response. These functional-reporter models will allow offline anatomical assessments, FACS or laser-capture separations, fate-tracing of previously-stressed neurons, and in vivo or in vitro functional assessments specifically of stressed neurons (i.e., those expressing ChR2). PUBLIC HEALTH RELEVANCE: This project is intended to generate research tools, specifically 2 new lines of transgenic mice that will produce functional and anatomical reporters in response to cellular stress. These lines would significantly enhance basic science approaches to understand neurological processes and conditions that have a cellular injury and/or stress component. They would provide capabilities that are currently either highly limited or entirely lacking.

? DESCRIPTION (provided by applicant): Affecting axonal growth as a means to enhance recovery and alleviate pathology in conditions of nervous system injury, insult, or disease is a major goal for the healthcare and biomedical research endeavors. Significant effort is directed at inducing neural plasticity to enhance axonal growth to establish functionally- adaptive connections. However, these efforts must also prevent, and not induce, maladaptive plasticity, a balance which requires a clear understanding of the processes regulating axon growth. A major factor confounding efforts to understand neural plasticity is that the traumatically-injured nervou system contains both directly-injured axons and the NON-injured axons. This project examines the long-standing question and controversy regarding the mechanisms of the two major forms of axon growth in the adult nervous system - growth of injured axons (Regeneration) and that of non-injured axons (Collateral Sprouting - CS). We aim to objectively determine the degree to which the intrinsic molecular mechanisms controlling these processes are similar or different. Doing so will enable identification of sets of genes which control a specific mode and may thus be targeted to affect just that one mode, or may be shared between modes and thus targeted to affect both, and could identify an entire new set of genes capable of regulating adult axonal plasticity. Axonal Regeneration and CS are both relatively robust in the PNS, and the injured and non-injured neurons can be clearly separated. Nerve crush provides a model of successful axon regeneration. Using the spared dermatome model (where intact non-injured neurons of a single dorsal root ganglion are induced to grow by denervating the skin bordering their dermatome) we have generated a transcriptomic profile of genes regulated during CS. Bioinformatic analyses indicate that the genes involved in regeneration and CS are highly distinct. Preliminary data using mice with genetic deletion of transcription factors (TFs) that appear to be specific for each axon growth mode supports the concept that the growth modes involve separate genetic programs. Aim 1 will use mice with mode-specific-TF knockout to thoroughly examine the impact of the gene- deletions on the different modes of axon growth using behavioral and histological assessments of axon growth. This will determine if the flagship mode-specific-TFs are indeed responsible for controlling that single mode. We have data demonstrating 1) a mutually-exclusive expression of the mode-specific TFs and 2) that conditioning with one mode of growth appears to influence the functional execution of the other mode. This is rational considering that there must be a large change in which genes are expressed, and proper orchestration of such a significant change could be delayed or prevented. Aim 2 will test the hypothesis that the modes negatively-influence each other and involve mutually-exclusive genetic programs by alternately applying the different models to the same neurons (i.e., regeneration-then-sprouting or sprouting-then-regeneration). This will determine how execution of one mode influences the other. For both Aims, experimental outcomes in accord with preliminary data would strongly support the concept that there are indeed two different growth modes, each with distinct genetic control. Outcomes contrary to preliminary data could include 1) effects on some neural populations but not others, which would suggest that there may still be distinct modes with distinct genetic control, but that these modes may be based not on injury- status, but on cell-type, and/or 2) that the apparent mode-specific genetic control systems act as facilitators but are not necessary (i.e., in their absence the processes occur anyway, but much more slowly), which would suggest that there are not necessarily two fully-distinct modes. All outcomes will serve to address both the conceptual framework and the specific molecular control regarding axon growth in the adult nervous system.

Affecting axonal growth as a means to enhance recovery and alleviate pathology in conditions of nervous system injury, insult, or disease is a major goal for the healthcare and biomedical research endeavors. Significant effort is directed at inducing neural plasticity to enhance axonal growth to establish functionally- adaptive connections. However, these efforts must also prevent, and not induce, maladaptive plasticity, a balance which requires a clear understanding of the processes regulating axon growth. We have recently determined that the mechanisms of the two major forms of axon growth in the adult nervous system ? growth of injured axons (Regeneration) and that of non-injured axons (Collateral Sprouting - CS) ? differ significantly and involve distinct transcriptional profiles. We have identified Camk4 as a gene necessary for Collateral Sprouting but not involved in Regeneration. We have further determined that during CS, Camk4 expression is regulated not at the coding sequence, but at the 3? UTR. Camk4, and particularly Camk4 with this novel sprouting-related 3? UTR, is expressed in neurons known to have a high degree of constitutive plasticity capacity such as sensory nociceptors, hippocampus, cerebellum, and cortex. These findings point to additional potential mechanisms by which CamK4 may be acting, and also opens additional potential therapeutic targets. However, tools to examine those mechanisms are lacking. We aim to determine the range and character of transcript isoforms expressed by neurons at basal state and during plasticity (regeneration and sprouting). These data will have significant value on their own, but will be used here to direct the design of a novel mouse with conditional-deletion of the novel long-isoform of the 3? UTR without disrupting the protein coding sequence. This will allow us to determine the role of this important transcript segment in protein expression and localization, and examine other protein-independent functions which may exist. Although vital for mechanistic studies of axonal plasticity, these data and the new mice will also be useful for any cells which express Camk4 and use the novel long 3? UTR (e.g., testicular cells, kidney podocytes, adipocytes, T cells, etc.) and we have established collaborative arrangements with a range of labs that would like to use these new mice in their research.