Pelizaeus-Merzbacher Disease (PMD) is a severe pediatric neurodegenerative myelin disorder and archetype for the class of myelin disorders known as leukodystrophies. Though a monogenic, X-linked disease, the diversity of genetic mutations found in proteolipid protein 1 (PLP1) and the wide spectrum of clinical phenotypes associated with these mutations have confounded prior attempts to study PMD in animal models. Direct studies in human cells have been similarly limited due to the inaccessibility of primary oligodendrocytes and poor preservation of structures in post mortem tissues. With the advent of induced pluripotent stem cell (iPSC) technologies and cell fate reengineering, we now have methods for oligodendrocyte generation in vitro, providing unprecedented access to PMD patient-specific cells. I have developed a panel of unique PMD patient samples that recapitulates the genotypic and phenotypic heterogeneity found across the greater patient population. I have reprogrammed each line into iPSCs and validated their pluripotent identity and PLP1 mutations. Building off my lab's work in rodents and other labs' recent human protocols, I have used developmental cues to quickly and robustly generate PMD patient-specific and control oligodendrocytes. Preliminary in vitro results reveal PMD patient-specific defects in PLP1 trafficking, endoplasmic reticulum stress, and oligodendrocyte morphology. When injected into mice, oligodendrocytes derived from both control human embryonic stem cells and PMD point mutation iPSCs were capable of engrafting, migrating extensively, and wrapping myelin around endogenous axons, but the PMD line failed to fully mature, suggesting a etiology of disease in this patient. The studies proposed here aim to perform comprehensive molecular and cellular analyses, in vitro and in vivo, across this large panel of PMD-derived oligodendrocytes in order to identify patient-specific deficits in ER stress, protein trafficking, nd myelin ultrastructure. Identification of these deficits will direct the search for patient-relevant molecular and genetic therapeutics. Ultimately, we hope that the breadth of the panel will grant us the first opportunity to classify PLP1 mutations by disease-relevant metrics, making our results generalizable across the wider PMD patient population.
Myelin deficits in the brain and spinal cord cause severe neurodegenerative diseases in millions of people in the U.S. However, therapies for these diseases are severely lacking, and only palliative when they do exist. The advent of induced pluripotent stem cell and cell fate reengineering technologies provides us with the first robust method to model myelin diseases in patient-derived cells. This study aims to discover the etiology of a severe leukodystrophy, Pelizaeus-Merzbacher Disease, and create a platform for developing molecular and genetic therapeutics for this and other myelin diseases.
| Nevin, Zachary S; Factor, Daniel C; Karl, Robert T et al. (2017) Modeling the Mutational and Phenotypic Landscapes of Pelizaeus-Merzbacher Disease with Human iPSC-Derived Oligodendrocytes. Am J Hum Genet 100:617-634 |
