Spinal Muscular Atrophy (SMA) is one of the most common lethal genetic diseases in children. One in thirty five people carry a mutation in a gene called survival of motor neurons 1 (SMN1) which is responsible for this disease. If two carriers have children together they have a one in four chance of having a child with SMA. Children with Type I SMA seem fine until around 6 months of age, at which time they begin to show lack of muscular development and slowly develop a "floppy" syndrome over the next 6 months. Following this period, SMA children become less able to move and are eventually paralyzed by the disease by 3 years of age or earlier. We know that this mutation causes the death of motor neurons - which are important for making muscle cells work. Interestingly, there is a second gene which can lessen the severity of the disease process (SMN2). Children with more copies of this modifying gene have less severe symptoms and can live for longer periods of time (designated Type II, III and IV and living longer periods respectively).
There is no therapy for SMA at the current time. One of the roadblocks is that there are no human models for this disorder as it is very difficult to make the motor neurons that die in the disease in the laboratory. The researchers in the current proposal have recently created pluripotent stem cells from a patient with Type I SMA (the most severe) and shown that motor neurons grown out from the pluripotent stem cells also die in the culture dish just like they do in children. This is an important model for SMA.
The proposed research takes this model of SMA and extends it to Type II and Type III children in order to have a wider range of disease severity in the culture dish (Type IV is very rare and difficult to get samples from). It then develops new technologies to produce very large numbers of motor neurons and perform large scale analysis of their survival profiles. Finally, it will explore whether novel compounds can slow down the degeneration of motor neurons in this model which should lead to the discovery of dew drugs that then may be used to treat the disease.
The aim of this research is to develop novel drugs to treat a lethal childhood disease - SMA. There would be three immediate benefits to the state of California and its citizens.
1. Children in California would have access to novel drugs to slow or prevent their disease.
2. SMA is a world wide disease. The institutions involved with the research would be able to generate income from any new drugs developed and the profit from this would come back to California.
3. The project will employ a number of research staff in Californian institutions
This is a proposal to develop patient-specific induced pluripotent stem cell (iPSC) lines for use in the development of high content screening (HCS) assays to identify novel compounds for the treatment of Spinal Muscular Atrophy (SMA). SMA is a childhood disease in which motor neuron death in the spinal cord leads to paralysis and death: currently there are no cures or treatments for SMA. Although this disease results from mutations in a single gene, SMN1, there are four levels of disease severity depending on the gene copy number and resulting expression level of a disease-modifying gene, SMN2. In this proposal, the principal investigator (PI) proposes three Specific Aims. Aim 1 involves the use non-integrating viral vectors to generate patient specific iPSC lines for Types I, II, and III SMA. The applicant will then derive motor neuron lines from the IPSCs and characterize their cellular phenotypes. In Aim 2, the PI will develop HCS assays with motor neuron reporter lines derived from SMA iPSCs. In Aim 3, the PI will use the cell lines and assays from Aims 1 and 2 to perform HCS with the goal of identifying novel therapeutic compounds for the treatment of SMA.
The reviewers agreed that the potential impact of identifying a therapeutic compound for SMA is great and that the lack of a treatment or cure for SMA is a significant bottleneck. Although the development of patient-specific iPSC lines for drug screening use was not considered particularly novel, reviewers noted that the generation of multipotent neural stem cells lines and the avoidance of integrating vectors in the production of iPSCs is both innovative and useful. Further, reviewers recognized the innovative and elegant approach proposed for generation and use of the motor neuron reporter lines.
Reviewers believed the likelihood for the success of Aim 1 to be high. The preliminary data supporting the investigator’s ability to establish in vitro disease phenotypes was strong and alternative plans were presented. Reviewers appreciated the elegant molecular biology described in the proposal as well as the carefully designed scientific approach. Reviewers did suggest that this portion of the proposal would have been stronger had the PI considered the reintroduction of the SMN1 protein to demonstrate reversal of phenotype or the correction of the SMN1 mutation, which would allow generation of a perfectly matched control cell line for further studies. Enthusiasm for Aims 2 and 3 was not as strong as that for Aim 1. Reviewers noted that the figures in the preliminary data section were difficult to see and interpret. Reviewers were not confident that the PI would be able to generate cell lines with reproducible phenotypes that meet the needed assay sensitivity levels. Preliminary data demonstrating disease phenotypes displayed by cell lines derived from patients with less severe forms of SMA (Type II and III) would have strengthened the proposal. Additionally, reviewers were uncertain that the applicant would be able to scale up the production of the cells lines for use in HCS assays and commented that the proposed activities are ambitious for the proposed timeline.
Reviewers agreed that the PI has assembled an outstanding group of collaborators. The PI is one of the world’s experts in the use of human pluripotent stem cells for understanding neurodegeneration, and the PI’s track record in stem cell research supports the likely success of the project. However, reviewers expressed some concern that the team lacks strong expertise in HCS.
Overall, reviewers were generally enthusiastic about this proposal from an excellent investigator and agreed that the successful generation of the proposed tool and technology would be of high impact. However, concerns regarding the feasibility of the HCS portion of the application tempered the reviewers’ enthusiasm for the proposed research.
- A motion was made to move this application into Tier 1, Recommended for Funding. Reviewers noted that this disease-in-a-dish proposal would eventually be used for drug screening, could generate a useful tool and could have strong impact in a disease that has no current treatment options. The motion carried.