Myelin at the crossroads of Development and Disease

The oligodendrocyte, the largest cell in mammalian biology, greatly enables central nervous system (CNS) function through production of a single substance: myelin. Oligodendrocytes undergo a dramatic 1-2 day metamorphosis during myelination, increasing their cell surface area ~6500-fold with proteolipid extensions to nerve axons in the CNS white matter. How is this synthetic feat accomplished? We lack a comprehensive understanding of machinery that precisely coordinates transcription, translation, lipid synthesis and energy production. Moreover, how do these mechanisms become so intensively upregulated during myelination? Does this extraordinary transient state put the myelinating oligodendrocyte at risk of death in diseases of white matter? These questions underlie the Aims of the proposal “Myel-IN-crisis.” I propose (Aim 1) testing whether an “Integrated Synthetic Programme (ISP)” controls oligodendrocyte differentiation, metabolic and synthetic requirements of developmental myelination. In Aim 2, I will investigate roles for “smart sensor” oxygen (HIF) and nutrient (mTOR) pathways in regulating initiation and termination of the ISP. During development, extrinsic white matter injury in preterm infants leads to cerebral palsy, while intrinsic defects in myelin protein PLP1 cause the fatal human leukodystrophy, Pelizaeus-Merzbacher disease (PMD). Preliminary studies indicate transcriptional and translational dysregulation in human PLP1-mutant oligodendrocytes, which become iron overloaded leading to apoptotic cell death. In Aim 3, I propose that either extrinsic (e.g., hypoxia) or intrinsic (e.g., PLP1 mutation) factors promote a “Universal Stress Response (USR)” in the pre-myelinating oligodendrocyte that leads to toxic dysregulation of the ISP. Finally, in Aim 4 we will identify the key pathways of the USR to generate strategies for rescue of myelination with potential translational impact in cerebral palsy and leukodystrophy, multiple sclerosis and stroke.