Multiple sclerosis (MS) is the most common neurologic disease affecting young adults under the age of 40 with the majority of MS patients diagnosed in the second or third decade of life. MS is characterized by the gradual loss of the myelin sheath that surrounds and insulates axons that allow for the conduction of nerve impulses – a process known as demyelination. For unknown reasons, the ability to remyelinate axons is impaired in MS patients making recovery of motor skills difficult. Therefore, developing novel and effective approaches to remyelinate axons in MS patients would dramatically improve the quality of life of many MS patients. The experiments described in this research proposal utilize a well-accepted model of MS to further characterize the potential clinical applicability of human embryonic stem cells (hESCs) to remyelinate axons. Such knowledge is crucial in order to increase our understanding of stem cells with regards to treatment of numerous human diseases including MS.
California is the most populated state in the USA. As such, the costs of medical care for the treatment of patients with chronic diseases such as multiple sclerosis (MS) represents a significant and growing problem. MS is the most common neurologic disease affecting young adults under the age of 40 with the majority of MS patients diagnosed in the second or third decade of life. Given the population of California, there are many MS patients living in the state and the numbers will undoubtedly grow. It is unusual for MS patients to die from the disease and many will live normal life spans but will develop an increasing array of medical problems stemming from the progression of neurologic damage associated with MS. MS is characterized by the gradual loss of the myelin sheath that surrounds and insulates axons that allow for the conduction of nerve impulses – a process known as demyelination. For unknown reasons, the ability to remyelinate axons is impaired in MS patients making recovery of motor skills difficult. Therefore, developing novel and effective approaches to remyelinate axons in MS patients would dramatically alleviate some of the burden placed on the medical community by improving the quality of life of many MS patients. The experiments described in this research proposal utilize a well-accepted model of MS to further characterize the potential clinical applicability of human embryonic stem cells (hESCs) to remyelinate axons. Such knowledge is crucial in order to increase our understanding of stem cells with regards to treatment of human diseases with the ultimate goal of limiting patient suffering and reducing medical costs.
SYNOPSIS: The hypotheses behind this proposal are: hESC-derived oliogodendrocytes positionally migrate in response to chemotactic signals; hESCs committed to an oligodendrocyte lineage are directly responsible for remyelination in demyelinated mice. The PI provides preliminary data that shows remyelination in a viral-induced murine model of demyelination (mouse hepatitis virus, MHV) within 2 weeks of transplantation with hESC-derived oliogendrocyte precursor cells (OPCs). In aim 1, mRNA will be isolated from undifferentiated or oligodendrocyte-committed hESCs (exposed to EGF, bFGF, IFN-γ and TNFα) and then processed for a Superarray cDNA microarray that contains human chemokine and chemokines receptor genes. If a “hit” is identified, hESC or OPCs will be tested for their response to human recombinant chemokines using a Transwell plate. In aim 2, the PI will clarify the actual cell that carries out remyelination by using a mouse with a deletion in the Olig1 gene that renders the endogenous OPCs incapable of remyelination.
INNOVATION AND SIGNIFICANCE: Stem cells have the ability to differentiate into myelin-synthesizing cells, and their transplantation results in remyelination of demyelinating and dysmyelinating diseased tissue caused by viral infections and autoimmunity. Data in the literature suggest that chemokines are important in the positional migration of OPCs into the damaged CNS. The PI and co-PI have shown that murine glial-committed progenitor cells can lead to remyelination of MHV-infected mice in the face of on-going inflammation. In addition, they provide preliminary data involving extensive remyelination following transplantation of hESCs in demyelinated MHV-infected mice. These data suggest that OPCs can be used for the remyelination of human diseases, such as multiple sclerosis (MS). For this reason, successful transplantation of these cells may be fostered by a knowledge of the key molecules affecting their trafficking. As chemokines may be one of the important molecules involved cell migration in demyelinating, inflammatory lesions, most notably in MS, these are important. Therefore, knowledge derived from this study may lead to effective transplantation of these cells for therapeutic use in such diseases as MS.
The use of the Olig-/- mouse is a novel and clever approach to prove that the hESC-derived oligodendrocytes are key in the remyelination process.
STRENGTHS: The issues dealt with in this proposal are important ones with respect to the successful transplantation of OPCs. The PI and co-PI have exciting published data demonstrating that transplantation of murine glial-committed progenitor cells remyelinate mice following infection with a demyelinating virus. There are also interesting preliminary data that involve transplantation of hESC-derived OPCs into the demyelinated mice. The use of a virus-induced immune-mediated demyelinating disease model is of interest as a model of MS and provides a novel approach to test the importance of the transplanted OPCs and cell autonomy in the remyelination process.
Applicant is an expert on viral/immune aspects of the CNS including MHV-induced demyelination and the role of chemokines in inflammatory demyelination and is experienced in cell repair in this model. The co-PI is an expert on hESCs and in the differentiation and culturing hESC-derived oligodendrocytes. They are a strong team.
WEAKNESSES: The PI plans to test migration of chemokines using a Transwell system. This is an in vitro test and clearly cannot address some issues related to migration within the CNS. It might have been valuable for the PI to have also examined the effect of a particular chemokine or chemokine receptor on migration within the CNS tissue following a knock down in expression of the transplanted OPCs.
It was unclear to one reviewer whether the preliminary data provided unequivocal support for extensive remyelination following transplantation of hESCs in demyelinated MHV-infected mice. The mice receiving media + cyclosporin alone look qualitatively to have similar remyelination to those receiving cells; thus there is obviously endogenous repair stimulated by cyclosporin.
One potentially confounding part of the proposal is that chemokines induced following infection with MHV may affect migration of the OPCs. There may be value in examining another demyelinating disease model in addition to the MHV system. It remains unclear to one reviewer as to whether the MHV infected Olig-/- mice have demyelination similar to wild type mice.
The PI does not provide sufficient detail about anticipated problems and alternative plans to overcome the difficulties, for example , it is not clear how the PI will proceed if there is no remyelination in the Olig-/- mouse.
DISCUSSION: There was discssion on the suitablility of the proposed model for establishing whether the transplanted cells contribute to remyelination. Discussants noted that these mutant mice do not remyelinate well and that human cells are likely to take much longer to remylinate in the model compared to murine cells. Thus, it may be necessary to label the cells to be transplanted to unequivocally identify their remyelinating potential. There was discussion as to whether hESC make myelin in the rodent setting with point made that there are at least 3 papers that have claimed hESC differentiated to oligodendrocyte precursors can contribute to remyelination in rodents although still debate as to whether directly or indirectly..
PROGRAMMATIC REVIEW: The Working Group voted to recommend to the ICOC that this application receive special consideration for funding if additional funds become available based on: 1) proposal was scientifically well regarded and 2) the proposal has application to MS, a disease focus that is not currently included in any of the applications recommended for funding based on scientific merit.