Spinal neuron growth cones
Fluorescent spinal neurons in the developing Xenopus embryo
Hippocampal neuron immunostained to reveal green microtubule cytoskeleton
Nerve muscle co-culture
Contact adhesions in the nerve growth cone (paxillin in red, microtubules in green)
Substrate adhesions in the growth cone induced by brain derived neurotrophic factor
The complex, delicate structures that make up the nervous system — the brain, spinal cord and peripheral nerves — are susceptible to various types of injury ranging from trauma to neurodegenerative diseases that cause progressive deterioration: Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease), multiple sclerosis and multiple system atrophy.
Unfortunately, because of the complexity of the brain and spinal cord, little spontaneous regeneration, repair or healing occurs. Therefore, brain damage, paralysis from spinal cord injury and peripheral nerve damage are often permanent and incapacitating.
Patients with serious nervous system injuries or strokes often require lifelong assistance, which puts a tremendous burden on patients, their families and society. Innovative, paradigm-shifting strategies are required to advance treatment of neurological injury. The neuroregeneration research at Mayo Clinic is at the forefront of healing the nervous system.
Mayo Clinic clinicians, scientists, engineers and other specialists in the Center for Regenerative Medicine are taking a multidisciplinary integrative approach to neuroregeneration for a number of devastating neurological conditions. The research is multifaceted, ranging from basic science discovery to clinical applications.
Alzheimer's disease. Alzheimer's disease is the major cause of dementia in the elderly with progressive loss of neurons in areas of the brain responsible for learning and memory. Efforts in Alzheimer's disease research focus on understanding why neurons degenerate in brains with Alzheimer's disease and how we can either slow down the process or replace lost neurons.
Mayo researchers are investigating the effects of restoring cerebrovascular function, through transplantation of induced pluripotent stem (iPS) cell-derived vascular progenitor cells, on amyloid pathology and cognitive function in amyloid Alzheimer's disease model mice. The iPS cells converted from skin fibroblasts by transducing four transcription factors (Oct3/4, SOX2, Klf4, c-Myc) have the potential to generate all tissues in the body, including vascular cells.
This innovative approach will likely allow for rational designs of vascular regenerative therapy against Alzheimer's disease.
- Amyotrophic lateral sclerosis (ALS). Our team is testing a cell-based therapy for ALS. Still in its early stages, this research uses adipose-derived mesenchymal stem cells from the patient's own body. These cells are modified in the laboratory and delivered back into the patient's nervous system to promote neuron regeneration.
Multiple sclerosis (MS). While we understand much about the damage that happens to nerves and myelin (insulating sheath) during MS and how the immune system causes this damage, the exact reasons for the immune system attack are very poorly understood. The lack of understanding of the exact cause of MS is a challenge for the development of effective therapies, and Mayo Clinic laboratories are working to better understand this disease.
Protecting nerves and myelin from damage, or repairing myelin after it's been damaged, also holds potential for the treatment of MS. Injury to nerves and myelin can be severe in MS and is the major cause of functional impairments. However, spontaneous repair of this damage is sometimes observed in MS patients. We are actively engaged in developing therapies designed to stimulate this repair and thereby promote recovery of lost function.
Antibodies that bind to myelin and nerve cells have been identified that protect nerves from damage and stimulate myelin regeneration. A recent study also has found that regeneration of the myelin sheath can be stimulated by small folded DNA molecules called aptamers.
- Parkinson's disease. Researchers are studying the genetic contribution to susceptibility to Parkinson's disease through the establishment of a bank of skin and iPS cell lines from Parkinson's patients. Having a cell line like this provides the ability to generate the cells that die in neurodegenerative disease, allowing researchers to better understand the genetic cause of this condition and perhaps new treatments for these disorders in the future.
- Multiple system atrophy (MSA). MSA is a progressive, fatal neurodegenerative disorder. The hallmark of the disease is glial cytoplasmic inclusions. The main component of glial cytoplasmic inclusions is alpha-synuclein. Aggregation of alpha-synuclein microfibrils leads to a chain of events, including microglial activation, inflammation, and glial and neuronal degeneration. The likely mechanisms involved include growth factor (BDNF, GDNF) deficiency, toxic cytokines and oxidative injury.
Research focuses on the prevention of alpha-synuclein aggregation by drugs such as rifampicin or paroxetine; the use of mesenchymal stem cells to provide and deliver growth factors; and attacking microglial activation and the inflammatory response by agents such as intravenous immunoglobulin.
Immune response and neuroregeneration. Our team is developing numerous approaches to attenuate specific immune cell types in central nervous system (CNS) inflammation and applying strategies to a variety of diseases, including inflammation developing in the course of stem cell transplant, gene therapy or factor-driven regeneration of CNS tissues.
We have demonstrated a therapeutic effect in reducing motor dysfunction and blood-brain barrier disruption in model systems of multiple sclerosis through the removal of antigen-specific CD8 T cell responses. By optimizing the imaging of neuroinflammation with high-resolution confocal microscopy, small animal MRI and the profiling of CNS-infiltrating immune cells using flow cytometry, we can isolate and phenotype CNS-infiltrating immune cells in vivo and visualize in real time the events leading to inflammatory destruction of nervous tissue.
Spinal cord repair. Regrowth of axons (nerve fibers) is essential to repair and functional recovery of the spinal cord. Tissue destruction with cysts and gliosis at the site of injury forms a barrier to regeneration.
Ongoing research is using tissue engineering with biodegradable polymer scaffolds (PLGA, PCLF, OPF) loaded with different growth-promoting cells (Schwann cells, neural progenitor cells, mesenchymal stem cells) and different growth factors (GDNF, NT3, BDNF) to bridge the gap, and to promote axonal regeneration and functional restoration in the spinal cords of rats and mice, eventually for future use in patients.
Further, we are investigating the effects of exercise training and local delivery of steroids on axon regeneration and functional recovery.
Peripheral nerve regeneration and repair. Our team is developing strategies to expand the time window of opportunity and improve the functional recovery following peripheral nerve injury and repair.
One strategy is to apply polymer microspheres to deliver vascular endothelial growth factor (VEGF) to the nerve repair site in a controlled sustainable release manner. VEGF promotes angiogenesis and neurogenesis, and thus leads to a better functional outcome and larger window of opportunity for the nerve to be permissive to prolonged regeneration.
The other strategy is to counteract the lack of healthy Schwann cells at the nerve repair site by supplementing functioning Schwann cells derived from nerves prepared in an in vitro system or Schwann cells induced from stem cells of the adipose tissue.
Novel animal models are being developed to delineate the nature and time course of denervation muscle changes; identify the key indicators of muscle receptivity, including electromyographic changes, muscle fiber type changes and changes of myogenic genes; and evaluate the impact of these changes on nerve regeneration and the potential success of a nerve repair.
- Nerve cell regrowth: Axogenesis. Mayo researchers are using zebrafish as an animal model system to investigate how special cues in the brain and spinal cord can entice or block nerve cell growth — experiments that help scientists understand why conditions at the site of nerve injury retard regeneration. This work is providing new understanding into how nerve cells grow during development of the nervous system and how nerve regeneration might be improved after injury.
Stroke neuroregeneration. Following stroke, neurons near the penumbra are vulnerable to delayed but progressive damage as a result of ischemia. There is no effective treatment to rescue such dying neurons. We hypothesized that mesenchymal stem cells (MSC) can rescue damaged neurons following exposure to oxygen-glucose deprivation (OGD) stress.
We have demonstrated that the MSC can differentiate into bone, cartilage and fat tissues. Experiments in animal models of hemorrhagic stroke showed MSC therapy improves limb function. Taken together, our data will form the basis for using MSC to treat patients with recent hemorrhagic stroke.
Neuro-oncology and neuroregenerative research. Our work currently focuses on gliomas, an invasive brain tumor for which patients receive a very poor prognosis. However, there are other brain tumors — oligodendroglioma, astrocytoma — that have a much better prognosis. We are interested in the mutations that are involved in the development of each of these different tumor types and why the tumors behave differently.
A target locus in a gene-poor region initially discovered by genome scanning has been identified. Our research efforts are focused on studying the function of this alteration. Using mouse models, murine and human neural stem cells, and human induced pluripotent stem cells, we are investigating how the alteration modifies glial cell development.
Neuroregeneration and inflammation. The limited capacity for repair in the nervous system is a significant medical challenge. We are developing new tools to effectively control the process of neural injury and degeneration and to create a microenvironment that enhances the capacity for innate repair and the efficacy of other regeneration strategies, including neural cell replacement and neurorehabilitation.
Our efforts focus on how highly druggable proteases, referred to as kallikreins, can be targeted to prevent the complex cascade of tissue injury and aberrant reorganization that is a well-recognized component of CNS trauma — and which is increasingly recognized as an integral factor underlying the progression of many neurological disorders, including those classified as neurodegenerative or neuroinflammatory as well as those having an oncogenic basis.
Efforts are directed at understanding the physiological and pathophysiological consequences of a family of G protein-coupled receptors, referred to as protease-activated receptors (PARs), and determining whether PARs or the proteases that activate them can be targeted therapeutically to prevent pathogenesis and to promote CNS plasticity and repair to improve patient functional outcomes.
Deep brain stimulation for Alzheimer's disease. Anecdotal and initial trial reports concerning deep brain stimulation (DBS) to the fornix/hypothalamus have been associated with improvement in memory function and reductions in expected cognitive decline in patients with early Alzheimer's disease. The fornix constitutes the major inflow and output pathway from the hippocampus and medial temporal lobe.
Mayo researchers have started an innovative pilot study of dual hemispheric stimulation of the subthalamic nucleus and fornix/hypothalamus to determine if this approach may have positive effects in attenuating cognitive decline. If this study provides positive data, then the potential of using DBS of the fornix as a treatment for Alzheimer's disease will be considered.
Pediatric anesthesia, apoptosis and safety. Exposure to multiple anesthetics at a young age may be associated with later problems, such as learning disabilities and attention-deficit/hyperactivity disorder. We are working on a large project involving the detailed testing of 1,000 children to see if we can better define what injury (if any) may be associated with anesthetic exposure. This information will be important to see if this is really a problem in our clinical practice, and if so, how we can change our practice to minimize any problems.
We currently are performing detailed neurodevelopmental testing on a sample from a birth cohort of children, including a testing battery previously shown in primates to be affected by anesthesia exposure. The aim is to confirm (or refute) our prior findings and provide for the first time a detailed phenotype of anesthesia-associated injury (if present).
Neurogenesis. By increasing our understanding of the molecular targets involved in regulation of adult hippocampal neurogenesis (neuron generation) and related behavioral responses altered in neuropathological conditions, we can study underlying cellular and molecular mechanisms that regulate the production, maturation and integration of new neurons in the circuitry, and how aberrant neurogenesis plays a role in disease pathogenesis by employing behavioral neuroscience to quantify cognition such as learning, memory and anxiety.
We recognize the therapeutic potential of adult neurogenesis by characterizing treatment systems and clinically approved medication that can allow us to dictate neuronal development in the correct direction. Our long-term goal is to harness the regenerative capacity of adult neurogenesis toward an optimal clinical outcome and improved treatment options for brain disorders.
Neurorehabilitation. This research focuses on improving participation and quality of life of individuals after their brain functions have been altered by injury or disease. The focus is regenerative in that improved behavioral performance is possible only when adaptive anatomic and physiological change occurs within and between brain systems in response to therapeutic intervention.
By developing treatment approaches that lead to improved function and independence, our team promotes the adaptive regenerative changes in brain function that make this improved behavioral performance possible.
Transduction mechanisms mediating bidirectional nerve growth. Cues released from the breakdown of myelin after injury in the brain and spinal cord may act as chemorepellents and inhibit axon extension, which limits functional recovery. In contrast, positive cues like neurotrophins can promote axon extension and elicit chemoattraction.
This research aims to determine how chemotropic cues in the microenvironment guide nerve growth and how dysfunctional guidance mechanisms can cause disease. Understanding these mechanisms and discovering methods to manipulate them are important for developing new therapies to promote neural regeneration after degenerative disease or injury.
By determining how chemotropic cues in the microenvironment guide nerve growth and how dysfunctional guidance mechanisms can cause disease, we can define the spatiotemporal signal transduction mechanisms by which nerve growth cones detect extracellular guidance cues and dynamically regulate cellular effectors to control the direction of axon extension during normal embryonic development and neural regeneration after injury.
Longer term, we hope to define mechanisms for priming and guiding regenerating axons to appropriate synaptic targets to complete functional circuits.