Understanding Pathogenesis and Pathological Substrates of Inflammatory CNS Demyelinating Disorders

Mechanisms of Axonal Injury in Demyelinating Disease

Recent studies in MS indicate that axonal injury is a major cause of long-term clinical disability. Our hypothesis is that denuded axons result in the neuronal cell processes being more susceptible to immune-mediated attack. Our data indicate that the killer (CD8) T cells of the immune system account for most of the damage, and the membrane-penetrating toxic molecule perforin is the active molecule. The current goal of this project is to prove definitively that perforin is induces injury in MS. The long-term goal is to inhibit the cytotoxic T cell response or inhibit perforin release as a therapeutic approach in demyelinating disorders. Dr. Charles Howe and his group are investigating cell culture and animal models related to axonal damage resulting from viral-immune CNS demyelination (supported by NIH R01 NS32129 and NMSS RG363A2). Dr. Claudia Lucchinetti and her group are investigating immunopathological lesions in tissues from patients with CNS inflammatory demyelinating disorders and new animal models of autoimmune CNS aquaporinopathy (supported by NMSS RG-3185-A-2; RG-3185-B-3; and NIH NS049577-02). Dr. Lennon directs development of novel autoimmune models of CNS demyelination targeting the astrocytic water channel aquaporin-4 (supported by the Ralph Wilson Medical Research Foundation and Mayo Foundation). Drs. Lucchinetti, Howe and Lennon are preparing a joint research proposal for NIH. Dr. Lennon's current research activities related to IgG effectors of autoimmune neurological disorders are funded by two NIH grants: R01 DK071209 and P01 DK068055). In addition, studies are underway to study the role of CD8+ T cells in pathologic injury in experimental autoimmune encephalomyelitis (C. David, PI, NINDS R01 NS52173).

Immunobiology of Virus-induced Demyelination

In the course of investigating the mechanisms of how the Theiler's virus, a picornavirus, induces demyelination in mice, the Rodriguez laboratory has generated transgenic mice that express fragments of the Theiler's virus. The goal is to induce complete immune tolerance to portions of virus following live virus challenge. These experiments should provide important insights into how the immune system recognizes viral peptides and how that process may relate to MS-type demyelinating diseases. Collaborating scientists in this project include Drs Pease, David, Bieber, and Howe. This work is supported by grants from the National MS Society and the Peterson Foundation.

Classification of MS Lesions by Patterns of Myelin Loss and Mechanism of Damage

The Lucchinetti laboratory has identified four distinct types of active demyelinating lesions that differ among individual MS patients. The lesions vary in pattern of myelin loss and mechanism of tissue injury, but the pattern of demyelination is uniform within each patient. These findings suggest several distinct mechanisms of demyelination in early MS. Whether these patterns reflect different causes, such as autoimmune viral causes, or different host genetic factors is an area of ongoing research. This observation has major therapeutic implications because different lesion patterns may dictate the need for different treatments.

By focusing on the pattern of MS lesions to understand the mechanisms and targets of injury the Lucchinetti laboratory has established a unique tissue database of more than 700 MS patients who have undergone brain biopsy (studies done in collaboration with Drs. Parisi and Scheithauer, Department of Pathology, Rochester). This database is a vital resource for studying early stages of MS, at the onset of myelin damage. This pathological database provides a unique opportunity to investigate potential genetic factors contributing to MS lesion heterogeneity and is the focus of Dr. Lucchinetti's NIH grant (NIH NS049577).

The Lucchinetti laboratory is also investigating clinical, serological, and radiographic characteristics of these tissue donors. This project could potentially provide the physician with tools for prescribing most appropriate therapies to patients at the onset of MS. The goal is to develop radiological and genetic profiles that correlate with tissue pathology. Dr. Lucchinetti is the Principal Investigator of this international collaborative study based at Mayo Clinic and funded by the National MS Society (NMSS RG3185-B3). Dr. Brad Erickson directs the CNS imaging studies in these patients.

Role of Apoptosis in Neuronal and Axonal Injury in Models of Multiple Sclerosis

The Demyelinating Diseases laboratory, directed by Dr. Moses Rodriguez, studies the role of apoptosis in the development of demyelinating lesions. Early experiments demonstrated dying back of oligodendrocytes as a target of MS-related disorders. The most distant extension of the oligodendrocyte is in the inner glial loop where Dr. Rodriguez and colleagues detected the earliest injury in MS lesion by electron microscopy. The dying back process correlates with pattern III lesions of MS described by Dr. Lucchinetti. The primary mechanism of injury in this pattern of MS is apoptosis. The Howe and Rodriguez laboratories have been investigating anti-apoptotic drugs (Z-VAD.fNK and Ritanavir) as a therapeutic strategy for these patients. Currently approved by the FDA as anti-retroviral agents, these drugs could readily be transferred to clinical trials for MS patients. Dr. Howe and his graduate students have shown that they markedly inhibit apoptosis in the Theiler's virus mouse model of demyelination. The long-term application of this project to patient care is obvious since apoptosis is a common mechanism of injury in a number of neurologic disorders as well as clinical disorders beyond the CNS. This project is supported through the Herdrich Foundation.

The Potential Effector Functions of Kallikrein Enzymes in MS Lesions and in Animal Models of Disease

Dr. Scarisbrick, the Principal Investigator of this project, has received funding from the National MS Society, and from an NIH RO1 grant. Analyses of kallikrein expression in MS lesions and in animal models indicates potentially important effector functions for several of these novel enzymes and suggests that altering their enzymatic activity may be useful therapeutically. Several collaborators, including Dr. Scarisbrick, are engaged in ongoing studies to delineate the role of these potentially pathogenic enzymes in CNS demyelinating disease. These studies are organized under the themes of:

  1. Determining whether sera/CSF levels of kallikrein protein serve as biomarkers of disease activity/prognosis/or therapeutic outcome;
  2. Determining how the level of each kallikrein is regulated in activated immune cells to contribute to MS pathogenesis;
  3. Determining how the level of each kallikrein is regulated in resident CNS cells, including oligodendroglia, to understand its role in myelin formation/breakdown and neuronal injury;
  4. Isolating the endogenous serpin inhibitors of each kallikrein and determining their efficacy as potential therapeutic tools;
  5. Characterizing kallikrein splice variants as molecular targets for enzymatic regulation in a cell/tissue specific fashion;
  6. Studying Enzyme substrate specificity and 3-dimensional structural analysis by enzyme crystallization to understand the scope of action of each enzyme, potential regulatory mechanisms, and to facilitate the design of kallikrein-specific inhibitors.

The goal of these studies is to determine the role of kallikreins in the pathogenesis of CNS inflammatory demyelinating diseases, including MS, thereby facilitating the development of novel diagnostic and therapeutic approaches.