Functionally distinct PI 3-kinase pathways regulate myelination in the peripheral nervous system

Functionally and spatially distinct PI 3-K pathways act either early to promote myelination downstream of axonal Neuregulin1 or late to inhibit myelination downstream of α6β4 integrin and Sgk1

Epitope-Tagged P0Glycoprotein Causes Charcot-Marie-Tooth–Like Neuropathy in Transgenic Mice

In peripheral nerve myelin, the intraperiod line results from compaction of the extracellular space due to homophilic adhesion between extracellular domains (ECD) of the protein zero (P0) glycoprotein. Point mutations in this region of P0 cause human hereditary demyelinating neuropathies such as Charcot-Marie-Tooth. We describe transgenic mice expressing a full-length P0 modified in the ECD with a myc epitope tag. The presence of the myc sequence caused a dysmyelinating peripheral neuropathy similar to two distinct subtypes of Charcot-Marie-Tooth, with hypomyelination, altered intraperiod lines, and tomacula (thickened myelin). The tagged protein was incorporated into myelin and was associated with the morphological abnormalities. In vivo and in vitro experiments showed that P0myc retained partial adhesive function, and suggested that the transgene inhibits P0-mediated adhesion in a dominant-negative fashion. These mice suggest new mechanisms underlying both the pathogenesis of P0 ECD mutants and the normal interactions of P0 in the myelin sheath

Kif13b Regulates PNS and CNS Myelination Through the Dlg1 Scaffold

Microtubule-based kinesin motors have many cellular functions, including the transport of a variety of cargos. However, unconventional roles have recently emerged, and kinesins have also been reported to act as scaffolding proteins and signaling molecules. In this work, we further extend the notion of unconventional functions for kinesin motor proteins, and we propose that Kif13b kinesin acts as a signaling molecule regulating peripheral nervous system (PNS) and central nervous system (CNS) myelination. In this process, positive and negative signals must be tightly coordinated in time and space to orchestrate myelin biogenesis. Here, we report that in Schwann cells Kif13b positively regulates myelination by promoting p38γ mitogen-activated protein kinase (MAPK)-mediated phosphorylation and ubiquitination of Discs large 1 (Dlg1), a known brake on myelination, which downregulates the phosphatidylinositol 3-kinase (PI3K)/v-AKT murine thymoma viral oncogene homolog (AKT) pathway. Interestingly, Kif13b also negatively regulates Dlg1 stability in oligodendrocytes, in which Dlg1, in contrast to Schwann cells, enhances AKT activation and promotes myelination. Thus, our data indicate that Kif13b is a negative regulator of CNS myelination. In summary, we propose a novel function for the Kif13b kinesin in glial cells as a key component of the PI3K/AKT signaling pathway, which controls myelination in both PNS and CNS

Notch controls embryonic Schwann cell differentiation, postnatal myelination and adult plasticity

Notch signaling is central to vertebrate development, and analysis of Notch has provided important insights into pathogenetic mechanisms in the CNS and many other tissues. However, surprisingly little is known about the role of Notch in the development and pathology of Schwann cells and peripheral nerves. Using transgenic mice and cell cultures, we found that Notch has complex and extensive regulatory functions in Schwann cells. Notch promoted the generation of Schwann cells from Schwann cell precursors and regulated the size of the Schwann cell pool by controlling proliferation. Notch inhibited myelination, establishing that myelination is subject to negative transcriptional regulation that opposes forward drives such as Krox20. Notably, in the adult, Notch dysregulation resulted in demyelination; this finding identifies a signaling pathway that induces myelin breakdown in vivo. These findings are relevant for understanding the molecular mechanisms that control Schwann cell plasticity and underlie nerve pathology, including demyelinating neuropathies and tumorigenesi

Human diseases reveal novel roles for neural laminins

Extracellular matrix molecules such as laminins have a central role in regulating cell behaviour. However, our understanding of their functions in the mammalian nervous system is incomplete. It is important to establish these functions, both for an understanding of normal development and to devise strategies to enhance repair. Here, we review how insights gained from human diseases caused by genetic mutations in laminins or their receptors have revealed significant and sometimes unexpected roles for laminins in neural stem cells, migrating neurons and myelinating glia, in both the PNS and CNS

Ablation of the UPR-Mediator CHOP Restores Motor Function and Reduces Demyelination in Charcot-Marie-Tooth 1B Mice

SummaryDeletion of serine 63 from P0 glycoprotein (P0S63del) causes Charcot-Marie-Tooth 1B neuropathy in humans, and P0S63del produces a similar demyelinating neuropathy in transgenic mice. P0S63del is retained in the endoplasmic reticulum and fails to be incorporated into myelin. Here we report that P0S63del is misfolded and Schwann cells mount a consequential canonical unfolded protein response (UPR), including expression of the transcription factor CHOP, previously associated with apoptosis in ER-stressed cells. UPR activation and CHOP expression respond dynamically to P0S63del levels and are reversible but are associated with only limited apoptosis of Schwann cells. Nonetheless, Chop ablation in S63del mice completely rescues their motor deficit and reduces active demyelination 2-fold. This indicates that signaling through the CHOP arm of the UPR provokes demyelination in inherited neuropathy. S63del mice also provide an opportunity to explore how cells can dysfunction yet survive in prolonged ER stress—important for neurodegeneration related to misfolded proteins