Remyelination involves reinvesting demyelinated axons with new myelin sheaths. In stark contrast to the situation that follows loss of neurons or axonal damage, remyelination in the CNS can be a highly effective regenerative process. It is mediated by a population of precursor cells called oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, despite its efficiency in experimental models and in some clinical diseases, remyelination is often inadequate in demyelinating diseases such as multiple sclerosis (MS), the most common demyelinating disease and a cause of neurological disability in young adults. The failure of remyelination has profound consequences for the health of axons, the progressive and irreversible loss of which accounts for the progressive nature of these diseases. The mechanisms of remyelination therefore provide critical clues for regeneration biologists that help them to determine why remyelination fails in MS and in other demyelinating diseases and how it might be enhanced therapeutically.
"The loss of oligodendrocytes may be replaced by proliferating nerve/glial antigen 2 (NG2) cells, also known as oligodendrocyte precursor cells (Tripathi and McTigue, 2007). These OPCs are able to migrate to the damaged site and differentiate into mature myelinating oligodendrocytes if the environment is permissive (Franklin and Ffrench-Constant, 2008). For instance, degenerated myelin contains inhibitory molecules such as NogoA, Oligodendrocyte-myelin glycoprotein (OMgp) and myelin-associated glycoprotein (MAG). "
[Show abstract][Hide abstract] ABSTRACT: Besides myelination of neuronal axons by oligodendrocytes to facilitate propagation of action potentials, oligodendrocytes also support axon survival and function. A key transcription factor involved in these processes is nuclear factor-κB (NF-κB), a hetero or homodimer of the Rel family of proteins, including p65, c-Rel, RelB, p50, and p52. Under unstimulated, NF-κB remains inactive in the cytoplasm through interaction with NF-κB inhibitors (IκBs). Upon activation of NF-κB the cytoplasmic IκBs gets degradated, allowing the translocation of NF-κB into the nucleus where the dimer binds to the κB consensus DNA sequence and regulates gene transcription. In this review we describe how oligodendrocytes are, directly or indirectly via neighboring cells, regulated by NF-κB signaling with consequences for innate and adaptive immunity and for regulation of cell apoptosis and survival.
"Since both Olig2 and Nogo-A are expressed in the oligodendrocyte lineage cells, it suggests a possibility that inhibition of NgR1 activation could induce differentiation of NSPs into oligodendrocytes, but the cells could not survive in the in vitro conditions. Since oligodendrocytes can promote survival of neuronal cells3334, the transient increase in oligodendrocyte population could contribute to the augmented proportion of neuronal cells observed in the differentiation Day 10. Our results indicated that inhibition of NgR1 in adult NSCs can promote neuronal cell production. "
[Show abstract][Hide abstract] ABSTRACT: Inhibition of Nogo-66 receptor (NgR) can promote recovery following spinal cord injury. The ecto-domain of NgR can be phosphorylated by protein kinase A (PKA), which blocks activation of the receptor. Here, we found that infusion of PKA plus ATP into the damaged spinal cord can promote recovery of locomotor function. While significant elongation of cortical-spinal axons was not detectable even in the rats showing enhanced recovery, neuronal precursor cells were observed in the region where PKA plus ATP were directly applied. NgR1 was expressed in neural stem/progenitor cells (NSPs) derived from the adult spinal cord. Both an NgR1 antagonist NEP1-40 and ecto-domain phosphorylation of NgR1 promote neuronal cell production of the NSPs, in vitro. Thus, inhibition of NgR1 in NSPs can promote neuronal cell production, which could contribute to the enhanced recovery of locomotor function following infusion of PKA and ATP.
"Demyelination is associated with many central nervous system (CNS) disorders, including multiple sclerosis, stroke, spinal cord injury, brain trauma, abuse of drugs such as alcohol and cocaine, Alzheimer's disease, and aging (Bartzokis 2004). As demyelination is mainly caused by defects in OLs, the replacement of lost or damaged OLs by cell transplantation may represent an effective therapeutic approach (Franklin and Ffrench-Constant 2008; McTigue and Tripathi 2008; Sheret al. 2008). However, successful implementation of such transplantation therapies in human cases has been difficult to achieve. "
[Show abstract][Hide abstract] ABSTRACT: Cell transplantation therapy with oligodendrocyte precursor cells (OPCs) is a promising and effective treatment for diseases involving demyelination in the central nervous system (CNS). In previous studies, we succeeded in producing O4(+) oligodendrocytes (OLs) from mouse- and human-induced pluripotent stem cells (iPSCs) in vitro; however, the efficiency of differentiation into OLs was lower for iPSCs than that for embryonic stem cells (ESCs). To clarify the cause of this difference, we compared the expression of proteins that contribute to OL differentiation in mouse iPSC-derived cells and in mouse ESC-derived cells. The results showed that the expression levels of cyclin dependent kinase inhibitor P27/Kip1, mitogen-activated protein kinase (MAPK) JNK3, and transcription factor Mash1 were lower in iPSC-derived cells. In contrast, the expression levels of MAPK P38α, P38γ, and thyroid hormone receptor β1 were higher in iPSC-derived cells. We attempted to compensate for the expression changes in P27/Kip1 protein and Mash1 protein in iPSC-derived cells through retrovirus vector-mediated gene expression. Although the overexpression of Mash1 had no effect, the overexpression of P27/Kip1 increased the differentiation efficiency of iPSC-derived cells into O4(+) OLs.
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