i. Identification of novel factors critical to oligodendrocyte developmental myelination, and a questioning of their recapitulation in remyelination.
Oligodendrocytes are the myelinating cells of the CNS that enable formation of myelin and saltatory nerve conduction. In Multiple Sclerosis (MS), the most common cause of neurological disability in young adults, myelin sheaths are lost through injury or death of mature oligodendrocytes (OL) as a result of autoimmune damage. White matter disorders are also associated with human newborn neurological injuries leading to Cerebral palsy (CP). CP complicates over 3.3/1000 live births in the United States and the incidence of this devastating condition is on the rise due to the increasing rates of survival of very low birth weight premature infants. In these conditions, myelin sheaths can be regenerated by oligodendrocyte progenitors (OLP) that are recruited to lesions and differentiate in a process called remyelination. In order to understand the regulatory factors relevant in human myelin disorders, it is first critical to understand the cellular mechanisms regulating developmental myelination and the remyelination repair process following injury. The developmental process of myelination and the adult regenerative process of remyelination share the common objective of investing nerve axons with myelin sheaths. A central question in myelin biology is the extent to which the mechanisms of these two processes are conserved, a concept encapsulated in the recapitulation hypothesis of remyelination. This question also has relevance for translating myelin biology into a better understanding of and eventual treatments for human myelin disorders. The lab has a focus in identifying factors involved in oligodendrocyte development, and a questioning of their recapitulation in remyelination.
ii. The human white matter lesion as a dysregulated repair environment. Why does myelin repair fail in MS and cerebral palsy?
Evidence suggests that myelin repair often fails in MS and cerebral palsy and this inhibition of remyelination contributes significantly to ongoing neurological dysfunction, axonal loss and disease progression. The human demyelinated lesion is a dysregulated environment where a fine balance exists between successful or failed repair. Indeed, in MS patients, successfully repaired lesions can be seen alongside those that have chronically failed, suggesting environmental dysregulation within particular lesions. The lab is interested in identifying mechanisms responsible for this failed myelin repair in human white matter injury. We have identified the Wnt pathway as a potent inhibitor of OPC differentiation, and provided evidence that this pathway is pathologically dysregulated in the context of human white matter injury suggesting it as a major candidate for the failed remyelination seen in these diseases.
iii. Identification and testing of therapeutics to promote repair in human white matter injury.
A significant contributor to progression in Multiple Sclerosis is the failure of the remyelination repair process. Patients taking immunosuppressive therapy or with quiescent disease continue to decline because of this failure of the myelin regenerative response. There are currently no therapies targeting remyelination in MS, and this is one of the major unmet needs for patients with this debilitating disease. Similarly, there are no treatments to promote myelin repair in neonatal hypoxic injury of premature infants. We have identified a number of potential candidates as therapeutic targets for promoting remyelination. Pharmacological inhibition of the Wnt pathway (either at the level of the beta-catenin degradation complex, or via the cell surface receptor complex for Wnt) accelerates myelin repair in vivo. Additionally, a novel high throughput in vitro screening platform has identified a number of new candidate therapeutics to promote OPC differentiation, one of which (an FDA approved drug called clemastine) we have shown to be effective in rescuing myelination defects in hypoxic injury. We remain dedicated to identifying new therapeutics for human white matter injury repair.
iv. Oligodendroglial-vascular interactions in development and disease.
During development of the central nervous system (CNS), OPCs arise from the ventricular zone in embryonic brain and spinal cord, in specific domains defined through pattern formation. From these domains, OPCs migrate widely through the CNS to achieve uniform distribution before halting migration and differentiating into oligodendrocytes that myelinate their target axons. Despite decades of work on OPC migration, it has remained unclear how this highly migratory cell type distributes so rapidly around the developing CNS. My lab has provided insight into this developmental migration recently by demonstrating that OPCs use and require vasculature as a physical scaffold for their motility. OPCs of embryonic mouse brain and spinal cord, as well as human cortex, emerge from progenitor domains and associate with the abluminal endothelial surface of nearby blood vessels. Migrating OPCs crawl along and jump between vessels. OPC migration in vivo is disrupted in mice with defective vascular architecture but normal in mice lacking pericytes, suggesting that physical interactions with the vascular endothelium are required. We remain fascinated by questions surrounding how these precursor cells migrate into remyelinating lesions in the adult, and the nature of oligodendroglial-vascular interactions throughout CNS development and repair.