The hereditary motor neuronopathies (HMN) are a heterogeneous group of disorders involving the selective death of motor neurons without complete understanding of causes. We propose to study the disease mechanism of HMN by investigating the role of a novel ER membrane protein in motor neuron survival. We have found that lose of this novel protein in a mouse model resulted selective motor neuron degeneration, consistent with a childhood-onset phenotype of HMN. Importantly, we have identified an HMN family with a childhood-onset patient who inherited double mutations of the gene coded for this protein from unaffected parents. We further found that cells from the human HMN patient were particularly vulnerable to ER stress. Therefore, we hypothesize that the death of motor neurons in an early onset HMN is caused by increased ER stress. To test this hypothesis, we will generate induced pluripotent stem cells (iPSCs) from the HMN patient and test if these cells have difficult to differentiate into normal motor neurons. We will further investigate if cells from patient show elevated ER stress contributing to the vulnerability of motor neurons. We will also test if blockade of ER stress by drugs can rescue iPSC-derived motor neurons. These studies will not only elucidate the disease mechanisms of the childhood-related HMN but also identify potential drug targets for its intervention. The information is also useful to treating other neurological disorders caused by ER stress.
Statement of Benefit to California:
Thousands of Californians are suffering from motor dysfunctions due to various degree of motor neuron degeneration, especially from childhood-onset motor neuron diseases. There is no cure for these diseases and current treatments to relieve symptoms are costly and ineffective. Understanding the disease mechanism and identifying novel drug targets are critical for developing effective treatment for these diseases. Recent technical advancements in human induced pluripotent stem cell (iPSC) production have revolutionized their potential applications in studying disease mechanisms and drug targets in most relevant model system and have provided enormous hope for these patients. Based on our studies of the critical role of a novel protein in a mouse model of hereditary motor neuronopathies (HMN), we propose to elucidate the disease mechanism and test the effect of drugs directly in human iPSCs from a patient of childhood-onset HMN. These studies will not only elucidate the disease mechanism of the childhood-related HMN and identify potential drug targets for its intervention but also are useful for treating other neurological disorders caused by similar pathogenic processes. Therefore, the long-term benefit of the proposed work is to benefit California’s financial status in reducing the cost of treating these patients. It will also promote California’s leadership in the field of stem cell research in general and childhood-onset neurological disorders research in particular.
The applicant proposes to use patient-specific induced pluripotent stem cells (iPSCs) to develop an in vitro model of hereditary motor neuropathy (HMN) and explore the underlying mechanisms of disease. HMN comprises a heterogeneous group of disorders involving selective death of motor neurons. A clue to the cause of a childhood onset form of HMN comes from a murine model in which loss of a gene encoding a novel endoplasmic reticulum (ER) protein results in early motor neuron degeneration. In addition, an early onset HMN patient was found who carries different mutations in each copy of this gene. iPSCs will be derived from this patient and unaffected family members (Aim 1) and used to test the hypothesis that ER stress contributes to death of motor neurons (Aim 2). The applicant also proposes to determine whether drugs that block ER stress can rescue the disease phenotype (Aim 3).
Significance and Innovation
- The potential impact of this work is limited, as only one patient is to be studied, and the number of affected individuals carrying mutations in this gene is unclear.
- The proposed research is innovative in its focus on a gene that has not previously been linked to HMN.
- A significant but unpublished body of work from the applicant supports the rationale for these studies.
Feasibility and Experimental Design
- The preliminary data do not adequately establish the applicant’s ability to generate motor neurons from human iPSC, a key requirement for the project to be feasible. Moreover, the pitfalls associated with lack of maturity and low efficiency in producing motor neurons were neither addressed nor acknowledged.
- It is premature to begin these iPSC-based studies with only a single patient, particularly as results may be difficult to interpret and extrapolate due to the involvement of two independently mutated alleles in the affected individual.
- The research plan is significantly weakened by interdependence of the specific aims.
- The proposal should have included plans to produce isogenic control lines as a primary strategy rather than as a back up plan. Isogenic controls would likely prove less confounding than the use of controls derived from unaffected relatives.
- Reviewers appreciated the combination of molecular, biochemical and functional approaches in the experimental design as well as the detailed methodology.
Principal Investigator (PI) and Research Team
- The PI and research team appear to lack some of the critical expertise that is needed to successfully pursue this project, particularly in the differentiation and analysis of motor neurons from iPSC.
- The PI has published some solid work but has a limited record of productivity as an independent investigator.
Responsiveness to the RFA
No relevant concerns were highlighted by reviewers under this review criterion.