Motor neuron (MN) diseases such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) lead to progressive degeneration of MNs, presenting first with muscle weakness, followed by locomotor defects and frequently death due to respiratory failure. While progress has been made in identifying genes associated with MN degeneration, the molecular and cellular processes underlying disease onset and progression remain unclear, and no effective therapies are available. Our project seeks to identify the underlying causes of MN degeneration, focusing first on SMA, using stem cell-derived motor neurons harboring genetic mutations associated with SMA as a model system. In the first year of our project, we have developed an innovative assay platform for stimulating and recording the activity of stem cell derived motor neurons using optical methods rather than more traditional electrical activity measurements. This modification greatly improves the speed and ease with which motor neuron activity measurements can be made, allowing us to evaluate activity differences at a population level rather than individual cells. This difference is important for discerning subtle disease phenotypes and may serve as the basis for drug screening in the future. With this system, we have identified differences in the manner by which normal and SMA-diseased motor neurons communicate with muscle cells that occur before signs of motor neuron degeneration have occurred. These findings suggest that further insights into SMA pathology may be gained from examining this aspect of motor neuron function in greater detail. Through this approach, we seek to identify novel means for correcting these communication defects to improve motor neuron survival and ultimately patient health.
Reporting Period:
Year 2
Motor neuron (MN) diseases such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) lead to progressive degeneration of MNs, presenting first with muscle weakness, followed by locomotor defects and frequently death due to respiratory failure. While progress has been made in identifying genes associated with MN degeneration, the molecular and cellular processes underlying disease onset and progression remain unclear, and no effective therapies are available. Our project aims to identify the underlying causes of MN degeneration, focusing first on SMA, using stem cell-derived MNs harboring genetic mutations associated with SMA as a model system. Thus far, we have developed an innovative assay platform for stimulating and recording the activity of stem cell derived MNs using optical methods rather than more traditional electrical activity measurements. This modification improves the speed and ease with which MN function can evaluated, allowing us to evaluate activity differences at a population level rather than individual cells. In the past year, we have used this platform to characterize defects in the manner by which SMA MNs communicate with muscle cells. Two major defects can be seen: some SMA MNs fail to respond to stimulation, while others show activity independent of stimulation, leading to inappropriate spontaneous muscular contractions reminiscent of fasciculations seen in MN disease patients. We have further discovered that these MN activity differences are most likely related to changes in the inherent electrical properties of the SMA MNs, resulting in hyperexcitability in most cases. We have also observed differences in the size and morphological features of the SMA MNs over time, and are actively investigating how these changes relate to alterations in MN excitability and degeneration. Our ongoing studies seek to discover the root causes of these differences in MN morphology and activity, and means for correcting. Through this approach, we hope to identify therapeutic agents that could improve MN function and combat MN disease progression.
Reporting Period:
Year 3
Motor neuron (MN) diseases such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) lead to progressive degeneration of MNs, presenting first with muscle weakness, followed by locomotor deficits and frequently death due to respiratory failure. While progress has been made in identifying genes associated with MN degeneration, the molecular and cellular processes underlying disease onset and progression remain unclear, and no effective therapies are available. Our project aims to identify the underlying causes of MN degeneration, using stem cell-derived MNs harboring genetic mutations associated with SMA as a model system. We first developed an innovative assay platform for stimulating and recording the activity of stem cell derived MNs using optical methods rather than more traditional electrical activity measurements. This modification improves the speed with which MN function can evaluated, allowing us to measure activity differences at a population level rather than individual cells. We used this platform to characterize defects in how SMA MNs communicate with muscle cells. Two major defects were seen: some SMA MNs fail to respond to stimulation, while others show activity independent of stimulation, leading to inappropriate spontaneous muscular contractions reminiscent of fasciculations seen in MN disease patients. We have further discovered that these MN activity differences are most likely related to changes in the inherent electrical properties of the SMA MNs, resulting in hyperexcitability in most cases. We have also observed differences in the size and molecular features of the SMA MNs, and are actively investigating how these changes affect MN excitability and degeneration. Our ongoing studies seek to discover the root causes of these differences in MN morphology and activity, and means for correcting. Through this approach, we hope to identify therapeutic agents that could improve MN function and combat MN disease progression.
Reporting Period:
Year 4 (NCE)
Motor neuron (MN) diseases such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS) lead to progressive degeneration of MNs, presenting first with muscle weakness, followed by locomotor deficits and frequently death due to respiratory failure. While progress has been made in identifying genes associated with MN degeneration, the molecular and cellular processes underlying disease onset and progression remain unclear, and no effective therapies are available. Our project aims to identify the underlying causes of MN degeneration, using stem cell-derived MNs harboring genetic mutations associated with SMA as a model system. We first developed an innovative assay platform for stimulating and recording the activity of stem cell derived MNs using optical methods rather than more traditional electrical activity measurements. This modification improves the speed with which MN function can evaluated, allowing us to measure activity differences at a population level rather than individual cells. We used this platform to characterize defects in how SMA MNs communicate with muscle cells. Two major defects were seen: some SMA MNs fail to respond to stimulation, while others show activity independent of stimulation, leading to inappropriate spontaneous muscular contractions reminiscent of fasciculations seen in MN disease patients. We have further discovered that these MN activity differences are most likely related to changes in the inherent electrical properties of the SMA MNs, resulting in hyperexcitability in most cases. Our ongoing and future studies will seek to discover the root causes of these differences in MN activity, and means for correcting. Through this approach, we hope to identify therapeutic agents that could improve MN function and combat MN disease progression.
Grant Application Details
Application Title:
In vitro modeling of human motor neuron disease
Public Abstract:
Motor neuron (MN) diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis lead to progressive degeneration of MNs, presenting first with muscle weakness, followed by locomotor defects and frequently death due to respiratory failure. While progress has been made in identifying genes associated with MN degeneration, the molecular and cellular processes underlying disease onset and progression remain unclear, and no effective therapies are available. Methods to direct the development of normal and diseased motor neurons from human embryonic and induced pluripotent stem cells have recently been developed, raising hope that these cells could offer a means for investigating the root causes of MN disease and devising screens for neuroprotective agents. Most stem cell-based disease modeling efforts have thus far focused on the issue of MN survival at the end stages of disease progression. However, studies in animal models and human patients indicate that MN function declines well before MN death is prevalent. We have developed a simple, yet physiologically relevant platform for measuring the activity of normal and diseased human MNs and muscle cells in a manner that has not previously been possible. Here we propose to explore how MN function declines; eventually we hope to test new therapeutics. These studies provide a crucial bridge between studies of motor circuit function in animal models and the molecular and cellular tools available to study cells in culture.
Statement of Benefit to California:
Neurological diseases are among the most debilitating medical conditions that affect millions of Californians each year, and many more worldwide. Few effective treatments for these diseases currently exist, in part because we know very little about the mechanisms underlying these conditions. Through the use of human embryonic stem cell and induced pluripotent stem cell technologies, it is now possible to create neurons from patients suffering from a variety of neurological disorders that can serve as the basis for cell culture-based models to study disease pathologies. Our proposed research specifically seeks to develop an innovative system for investigating the early stages of neuromuscular disease onset and progression in an experimentally accessible cell culture setting. The generation of this model will constitute an important step towards understanding the root cause of neurological dysfunction and developing a platform for the discovery of drugs that can alter disease outcomes and improve the productivity and quality of life for many Californians. Moreover, progress in this field will help solidify the leadership role of California in bringing stem cell research to the clinic, and stimulate the future growth of the biotechnology and pharmaceutical industries within the state.
