Development of a Novel DTI-MRI Tool to Monitor Remyelination in Multiple Sclerosis following Stem Cell Injection
Tools and Technologies I
Multiple Sclerosis (MS) is a widespread disease that can cause severe physical and mental disability. Relapses in MS are typically characterized by development of new lesions in white matter of the brain including the spinal cord. This includes varying degree of inflammation, destruction of myelin (a fatty sheath that surrounds the axis of nerve cells) and ultimate damage to the axis or axons of neural cells. Though mechanisms are not well-understood, histological and magnetic resonance imaging (MRI) studies have revealed that remyelination (i.e., repair of the myelin sheath) can occur spontaneously in some lesions by endogeneous progenitor cells (i.e., stem cells that are naturally present in the brain) evolving into myelin producing cells known as oligodendrocytes. It has been suggested that transplanted stem cells evolving into oligodendrocytes could facilitate the remyelination process and hence help patients in their recovery. Indeed studies in animals have shown that certain stem cells are able to achieve remyelination. However, there are currently no non-invasive tools to tell which specific brain pathways are damaged or likely to be damaged by demyelination, to quantify the damage, or to assess the degree of remyelination and repair of axons following a specific therapy inside a living person. This proposal will apply recent MRI techniques such as Diffusion Tensor Imaging (DTI) and DTI-tractography to develop a tool that will be able to quantify non-invasively the degree of demyelination and axonal damage prior to therapy, and then quantify the remyelination and axonal repair achieved by transplanted stem cells intended to facilitate the remyelination process. The proposed two-year phase will focus on developmental studies using a rat MS model but the tool developed will be translatable to humans.
Statement of Benefit to California:
Multiple Sclerosis (MS) is a significant health problem in California with a multitude of clinical trials underway to test new drugs and treatment strategies. Persistent myelin damage is a hallmark of MS. The risk is that demyelination over time may damage certain axons, leading to impairment of specific cognitive function. Though the mechanisms are not well-understood, it is known that spontaneous remyelination, attributed to endogeneous progenitor cells, occurs in some cases but also fails in others. It has been suggested that transplanted stem cells evolving into oligodendrocytes would facilitate the remyelination process and thus transplanted stem-cell therapy represents a treatment for MS with great potential and hope for the future. California is one of the few states in the US where such treatments could be designed and tested in humans and thus stands to benefit from strategies and tools designed to facilitate the development of stem cell therapy in MS. Currently there are no non-invasive tools to quantify the damage to axons by demyelination or to assess the degree of remyelination and repair of axons in-vivo following stem cell therapy. This proposal will apply recently developed MRI techniques such as Diffusion Tensor Imaging (DTI) and DTI-tractography to develop a tool that will be able to detect the location of demyelinated regions non-invasively and in-vivo. It will also be able to quantify the degree of demyelination, identify specific brain pathways and axonal tracts affected by the lesions, and quantify damage to these pathways before and after stem-cell treatment. The proposed two-year phase will focus on developmental studies using a rat MS model but the tool developed will be translatable to humans. Thus the proposed development of the DTI tool should be of great use to the State of California as it spearheads the move toward monitoring the viability and efficacy of stem-cell therapy in MS.
This proposal focuses on the development of a technology to assess remyelination and axonal repair in a rat model of multiple sclerosis (MS). Specifically, the applicants propose to use two recently developed methods, diffusion tensor imaging (DTI) and DTI-tractography, to monitor the efficacy of stem cell therapy in MS. After performing baseline anatomical and DTI studies in rats, the applicants plan to induce experimental autoimmune encephalomyelitis (EAE) and monitor the efficacy of introducing rodent neural stem cells (NSCs) and human embryonic stem cells (hESCs) into this animal model of MS. Finally they propose to use histopathology to validate their DTI-based measures of remyelination and axonal repair. Reviewers agreed that the application of these new technologies to animal models of MS has a potentially important impact, as it will provide the tools we need to detect repair by endogenous cells or transplants in MS patients. Moreover, from a clinical standpoint one reviewer found that the potential results derived from this project would be vital, as the need to be able to predict outcome in this variable disease and to identify those patients in whom repair is occurring is impossible at present. However, one reviewer found this proposal somewhat premature as s/he noted that the two methods suggested have not yet been validated techniques in small animal models and the necessary comparison of MRI (basis of the two methods) and axon tract histology has not been performed yet. In terms of feasibility, reviewers praised the quality of the preliminary data but questioned whether the EAE disease model was the best choice in which to perform the present study. They noted that this model has high variability in demyelination and the proposal’s power analysis is based on data from genetic models of MS with much less variability. In addition, remyelination by stem cell transplantation has only been demonstrated in genetic models, not the EAE model. These were considered major flaws by the reviewers. One reviewer was confused by the power analysis in general, wondering why, after stating that the number of animals per group is expected to be 16 after treating 20, the applicants use an n of 20 for power analysis. One reviewer noted that the studies presented as preliminary data dealt with the problem of averaging across different brains while this proposal presents a different problem of measuring longitudinal differences in the same brains. Yet there is no measure of reproducibility of the metrics. Reviewers felt it would be important to analyze how variable the metrics are from day to day. Reviewers also noted a number of technical issues with the experimental design. For example, the applicants outline the collection of T1 and T2 weighted MRI data but don’t present a clear plan for its analysis. A reviewer also noted that the proposed DTI setup differs from that cited and it is not clear that the applicants’ magnet can acquire the appropriate DTI. Also, since the work referenced in the proposal was done at a higher resolution and with different parameters, the reviewer felt that there should be some effort devoted to developing the ideal DTI sequence before the project gets underway. Reviewers also expressed concern that the number of animals proposed for the study might not be enough to generate the number of images required to determine if the cells actually migrated to the injury site. Finally, the section discussing validation of imaging data by histological sectioning describes remyelination of the spinal cord while the entire grant is focused on brain imaging. Reviewers felt that the assembled research team is strong, with significant expertise in the areas of stem cell biology and image processing. However they noted a lack of expertise in image creation and the EAE disease model that they felt was reflected in the research plan. The budget seems appropriate. Overall, while this proposal uses innovative technology to address an important problem in stem cell research, reviewers questioned the choice of animal model and the project’s feasibility.