Philip John Horner, Ph.D. - US grants

Spinal cord injury (SCl) is a devastating condition currently affecting approximately 200,000 people in the United States, with approximately 10,000 new cases diagnosed each year 4'5. Following injury to the spinal cord, endogenous progenitor cells are activated and participate in a partial restoration of the injury zone 6'7'8. The anatomical source of dividing progenitor cells following spinal cord lesion is now a major focus of study. Here we propose that new spinal cord gila are generated from separate astrocyte and oligodendrocyte producing aNPC lineages. We hypothesize that epidermal growth factor (EGF) specifically directs the formation of the oligodendrocyte lineage from activated progenitor cells following traumatic spinal cord injury. This hypothesis is based on the following observations. First, acute mitotic labeling in the adult spinal cord reveals only two significant populations of dividing cells: astrocyte and oligodendrocyte progenitor cells. Second, EGF infused intraventricularly selectively increases the proliferation of oligodendrocyte progenitor cells but not astrocyte progenitor cells. Thirdly, fate determination of EGF expanded progenitor cells shows an increase in new oligodendrocytes but no change in the number of new astrocytes. We propose to use a combination of molecular and histological tools to determine if EGF can selectively amplify glial progenitor cells in a model of SCI. Aim I will determine the effect of EGF on proliferation of progenitor cells and net survival of differentiated gila in a model of spinal cord trauma. Aim II will characterize the fate of a distinct population of glial progenitor cells that respond to EGF. Aim III will characterize the formation of myelin by EGF expanded progenitor cells following injury. These studies will lead to a better understanding of the molecular controls that govern stem cell fate following injury and potentially reveal a novel mechanism for inducing cellular regeneration.

[unreadable] DESCRIPTION (provided by applicant): Our knowledge of glial cells in the central nervous system has expanded, helping researchers understand that glia are much more than support cells for neurons. Glia provide structure to CNS tissue, guide migrating cells, regulate neurotransmitters in the extracellular milieu, produce signaling molecules, maintain synaptic connections, form the blood-brain barrier, monitor the environment and respond in myriad ways to injury and disease. Glial response to injury is called gliosis, and involves upregulation of intermediate filaments within the cell, changes in the complement of ion channels, secretion of signaling molecules and can also include proliferation. Gliosis occurs early in the chronic mouse model of glaucoma, and the magnitude of the response in all glial populations (M[unreadable]ller glia, astrocytes and microglia) is significant. As of yet, the positive or negative impact of gliosis on RGC health and the progression of glaucoma has not been studied. It is likely that gliosis works to signal commencement of injury, perhaps to initiate compensatory mechanisms that will allow maintainenance of function in injured tissue but also to limit tissue compromise. We propose to learn what role gliosis plays in glaucoma by tempering the glial response in the DBA/2 mouse. The DBA/2 has mutations in two genes that cause pigment dispersion and iris atrophy which in turn, lead to angle closure and secondary glaucoma. Intraocular pressure increases with pigment dispersion in these mice. There are numerous signaling pathways involved in gliosis development. The NF-?B [unreadable] pathway has been implicated in gliosis by its transcriptional control of cell adhesion molecules, iNOS, BDNF,1 COX-2 and by virtue of its role in promoting glia cells' transition to a nonpermissive substrate for neurite outgrowth.2 NF-?B is a heterodimeric transcription factor kept in the cytoplasm through binding to I?B. Phosphorylation of I?B by the I?B -kinase complex causes I?B to become ubiquitinated then degraded in the proteasome, thereby releasing NF-?B for it translocation to the nucleus where it binds specific regions in the DNA. We will target the NF-?B pathway to decrease gliosis in glaucoma by breeding a mouse overexpressing a dominant negative form of I?B (inhibitor of NF-?B) with our mouse model of glaucoma, the DBA/2J. NF-?B has such diverse function in the CNS that it is necessary to target the pathway in specific cell types. Public Health Relevance Statement Loss of function in progressive diseases of the central nervous system, including Parkinson's, Alzheimer's, Huntington's, and ALS, accompanies severe axonopathy that often precedes neuronal cell death. These diseases are an increasingly costly and psychologically onerous consequence of general senescence of the brain and are rendered more severe by the rapid aging of our population. Like these diseases, glaucoma is an axonapathy, blinding through the progressive degeneration of the optic nerve. And like diseases of the brain, glaucoma is becoming increasingly prevalent and already represents the third leading cause of blindness worldwide, affecting some 70-80 million individuals. Indeed age is a greater indicator for glaucoma than ocular pressure itself. Loss of vision in glaucoma contributes to a dramatic decrease in quality of life that is a primary fear associated with aging, hand-in-hand with loss of cognitive ability. Therefore, attempts to study and understand the underlying mechanisms of axonal degeneration in glaucoma are useful not only from an ophthalmological standpoint, but also from the perspective of understanding the cellular pathologies associated with general neuronal senescence. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): The goal of this research is to develop and test a method to guide repair and regeneration of the central nervous system following injury or degeneration. We propose that by creating both a regenerative environment as well as directing intrinsic plasticity among neurons, we can achieve a new milestone in neural repair. If successful, this approach could be used to treat patients suffering from central nervous system damage such as traumatic brain injury, stroke, or spinal cord injury in order to reduce the burden of neurological disease on individuals and society. Our studies employ a novel combination of targeted electrical microstimulation and stem cell therapies to guide the formation of appropriate and functional connections bypassing an injury. We will test our approach in a rodent model of incomplete cervical spinal cord injury that is representative of insults throughout the central nervous system. It is known that during development of the nervous system, stem cells produce immature astrocytes that create an environment to support axon guidance and synaptic plasticity. Here, we hypothesize that neural plasticity and the repair of damaged neurons can be facilitated by re-creating the developmental phenotype of astrocytes surrounding an injury site. In a first of its kind approach, we will derive immature astrocytes from autologous adult stem cells and transplant them near a spinal cord lesion to create a supportive environment for plasticity and neural repair. We propose that providing environmental support alone has had limited success because it does not address the intrinsic drive of neurons to grow. Synchronous and appropriate neural activity is also needed to direct the formation of functional synaptic connections in the intact and injured nervous system. Here we will use a neuroprosthetic device to deliver microstimulation to targeted sites within the spinal cord below the injury that is synchronized with functionally related activity in the motor cortex. Targeted microstimulation will strengthen appropriate and functional connections via mechanisms of Hebbian plasticity. Rather than attempt long-tract regeneration in the spinal cord, our approach aims to promote the formation of indirect connections via spared pathways bypassing the lesion. The extent of recovery will be measured using behavioral tasks, and electrophysiological and histological methods. This will determine the ability of synchronous, targeted microstimulation to guide implanted stem cells in the formation of appropriate and functional connections following damage to the central nervous system. We contend that microstimulation will collaborate with the transplant environment to produce a multiplicative effect on local plasticity. PUBLIC HEALTH RELEVANCE: This research aims to develop a treatment for damage to the brain or spinal cord as occurs, for example, following traumatic brain injury, stroke, or spinal cord injury. Targeted electrical microstimulation will be applied across the injury in order to guide implanted stem cells to make appropriate connections and restore function following injury.

DESCRIPTION (provided by applicant): Although neural stem cells give rise to new neurons in several regions of the adult mammalian brain, rates of neurogenesis do not remain constant. Aging leads to decreased neuron production, while voluntary exercise and high-fat diet have been shown to increase rates of adult neurogenesis. We propose changes in availability of metabolic fuels as a common mechanism underlying these phenomena. Using a flow culture chamber fitted to measure multiple real-time respiratory endpoints, we have shown that both young and aged neural stem cells have extraordinarily high rates of oxidative metabolism and do not require glucose to sustain oxygen consumption. These results suggest that neural stem cells are dependent upon some novel endogenous fuel to maintain high levels of aerobic respiration necessary for cellular division. We hypothesize that adult neural stem cells are dependent upon metabolism of fatty acids or ketone bodies for metabolic and mitotic activity. During development, the brain is dependent upon polyunsaturated fatty acids and ketone bodies derived from mothers'milk;metabolic dependence upon these fuels may be a conserved energetic profile in neural stem cells across the lifespan, by which B-oxidation provides large quantities of ATP necessary for cellular division. We also hypothesize that high metabolic demand met by fewer mitochondria in aged neural stem cells leads to increased levels of reactive oxygen species and a higher occurrence of mitochondrial mutations. We propose identifying the fuel resources of neural stem cells, determining the metabolic costs of cellular division, and investigating whether fuel availability affects rates of neurogenesis in vivo. Manipulating the fuels available to neural stem cells in vitro and in vivo may uncover a novel mechanism by which organismal behavior, energy consumption, and cellular activity are coupled in the adult mammalian brain. We hope to impact public health by identifying mechanisms underlying behavior-induced changes in cellular activity, especially in cells capable of regeneration within the adult and aging brain. PUBLIC HEALTH RELEVANCE: A characterization of normal aging on a molecular, cellular and organismal level will be necessary before we can fully understand the pathological aspects of age-related diseases, such as cancer or neurodegeneration. We hope to impact public health by identifying mechanisms underlying behavior-induced changes in cellular activity, especially in cells capable of regeneration within the adult and aging brain. Studying the links between metabolism and neural stem cell activity will be useful both in characterizing the cellular mechanisms of aging and in potentially treating age-related cell loss in the central nervous system in a safe manner.

DESCRIPTION: Traumatic brain injury (TBI), commonly caused by motor vehicle injury and falls in the young and elderly, afflicts nearly 1.7 million people in the United States each year. n addition to being a leading cause of death in children and young adults, TBI is also a major cause of permanent disability in the United States. There are currently no curative treatments for TBI, and the main course of action is to minimize secondary damage that results from changes in blood pressure, brain swelling, or intracranial pressure that is triggered by the initia injury. The overall goal of this project is to first develop a well-tolerated means of transferring genes to neural progenitor cells in the brain and then to use this technology to direct cortical neurogenesis after injury. We propose to use focused ultrasound to enhance non-viral gene transfer to neural progenitor cells in the brain mediated by a targeted polymer delivery vector, thus enabling the delivery of genes encoding fibroblast growth factor-2 and neurogenin2, proteins shown to enhance neurogenesis and direct neuron differentiation, respectively. We will evaluate in an animal model of TBI whether induced migration and increased neuronal integration can lead to functional improvement through a combination of histology, cognitive evaluations, and motor assessments. .

? DESCRIPTION (provided by applicant): Astrocytes have been proposed to play critical roles in plasticity as well as neuronal degeneration. Despite their abundance and key homeostatic roles very little is known regarding how astrocytes are generated and the mechanisms whereby astrocytes achieve specialized functions. In contrast, there are over 130 sub-classes of neurons and the transcriptional network regarding many of these lineages have been discovered. This is in part due to the significant emphasis that has been placed on understanding neurons but also due to the number of molecular and genetic markers that have been identified for different classes of neurons. The latter has facilitated the development of lineage specific tools and animal models to decipher the various roles of neuronal subtypes in divergent behaviors such as cognition, locomotion and sensory function. Here we propose to utilize a phage display screening approach to identify unique molecular aspects of astrocytes and astrocyte subtypes in order to accelerate our understanding of astrocyte function in health and disease. Cell-based phage screening is a powerful technology that involves the selection of peptide ligands from over 2 billion unique candidate peptide sequences based on desired cell binding properties and without a priori knowledge of specific receptors. We will combine our expertise in gliogenesis and glial cell biology with that of bioengineering, drug screening and discovery to develop novel tools for subclassifying astrocytes and also for direct imaging of astrocytes in vivo. We propose: Aim 1. Identification of astrocyte-specific peptides by phage display library selection, Aim 2. Evaluation of astrocyte-specific peptides as cell-specific markers for astrocytic populations and Aim 3. Development of a molecular probe for in vivo imaging of astrocytes. This proposal takes advantage of the unique research capabilities of the two principle investigators and their long-standing collaborative history. We expect that the tools and technologies developed through this proposed project will enable rapid advances in glial biology through the identification of unique biomarkers of astrocytes in general as well as astrocyte subtypes classified by function.

This  R13  was  conceived  through  discussions  with  investigators  in  the  fields  of  neurostimulation  and  neuroplasticity  at  a  new  research  center  at  the  Houston  Methodist Research Institute. Our organizing committee and collaborators from the  University  of  Houston,  Baylor  College  of  Medicine,  Rice  University  and  UT  Health  have  formulated  a  workshop  to  spearhead  cooperation  between  neurobiologists  and  neural  engineering  experts.  Our  goal  is  to  develop  and  implement  the  first  annual  Neuroregeneration  Symposium  focused  on  the  intersection  of  electrical  activity,  brain  connectomics  and  molecular  neural  plasticity.    We  believe  this  to  be  the  first  of  its  kind  and  will  potentially  push  the  development  of  a  new  area  of  discovery  and  collaboration.  The  format  is  distinct  from  established  physiology  conferences  and  dedicated  neural  regeneration  conferences  in  several  ways  including  1)  highly  focused  on  the  gap  between  molecular  regeneration  and  electrophysiology,  2)  concept  driven  by  clinician  and  experimentalists  that  are  currently  problem  solving  in  human  therapy  and  3)  focused  on  establish  cross  training and expertise development in graduate and clinical fellows.    

Abstract Myelin structure is a critical regulator of nerve conduction and an essential factor in axon development and homeostasis. In recent years, a number of seminal observations have dispelled a long-standing dogma that myelin is a static, inflexible structure. Advances in imaging techniques as well as in the methods used to label myelin have revealed that myelin plasticity occurs at the level of wrap number and sheath length during post- natal development, aging, and regeneration after injury. Observations of myelin plasticity indicate a more profound role of myelin axon function, and thereby highlight a critical need for better tools to investigate the mechanisms of myelin formation and remodeling. Here, we propose that the limited availability of tools for myelin reporting has significantly hindered our understanding of myelin biology. Illuminating the mechanisms of myelin plasticity will dramatically impact our understanding of the function of myelin in the nervous system and how myelin contributes to aging, injury, and disease. Our lab and others have developed myelin reporter systems in the mouse, but many of the behavioral and physiological studies that could inform myelin function are better modeled in the rat. The rat nervous system is unique from the mouse in terms of critical elements of behavior, endocrine function, epigenetics, and neurogenesis. Rats are also considered superior for modeling and translating regenerative therapies. We propose to develop a versatile myelin membrane reporter system in the rat capable of discriminating between new and old myelin in the nervous system with spatial and temporal precision. To generate the first myelin reporter rat system, we propose: Aim 1: Develop a rat myelin reporter system and Aim 2: Test the specificity and efficiency of myelin promoters in the rat reporter system. Results from this research will produce a myelin tagging system that will have unique functional advantages for the study of myelin development, myelin regeneration, and myelin in aging.