Mapping the neurite outgrowth inhibitory domain of myelin -associated glycoprotein (MAG) and blocking the inhibitory effect of MAG by interleukin -6.
Item
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Title
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Mapping the neurite outgrowth inhibitory domain of myelin -associated glycoprotein (MAG) and blocking the inhibitory effect of MAG by interleukin -6.
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Identifier
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AAI3103093
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identifier
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3103093
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Creator
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Cao, Zixuan.
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Contributor
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Adviser: Marie T. Filbin
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Date
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2003
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience
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Abstract
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Myelin-associated glycoprotein (MAG) is one of the potent CNS myelin-associated inhibitors of axonal growth after injury. MAG is a member of the Siglec protein family, a subgroup of the immunoglobulin superfamily that binds sialic acid residues. It has been established that sialic acid-dependent binding of MAG to neurons is not sufficient to inhibit axonal growth. Here, we demonstrate that the neurite outgrowth inhibition site is located on the fifth extracellular Ig-like domain of MAG, and that this region is distinct from the sialic-acid-binding site. First, we show that a truncated form of MAG, MAG(d3--5), is unable to perform sialic-acid-specific binding, yet retains the ability to inhibit neurite outgrowth. On the contrary, MAG(d1--3) can still bind to sialic acid residues, but has no effect on neurite extension. Furthermore, we constructed three chimeric proteins: Sn(d1--3)MAG(d4--5), Sn(d1--3)MAG(d4)Sn(d5) and Sn(d1--4)MAG(d5). Each of these chimeric proteins consists of only MAG Ig domain 4, 5 or both, the remaining Ig domains were replaced by the corresponding parts from the sialoadhesin protein. We found that Sn(d1--3)MAG(d4--5) and Sn(d1--4)MAG(d5) still inhibit axonal regeneration, whereas Sn(d1--3)MAG(d4)Sn(d5) can bind to sialic acid residues but is unable to inhibit neurite outgrowth. These results indicated that the inhibition site on MAG is primarily located within extracellular domain 5. Based on these findings, a series of peptides derived from MAG Ig domain 5 have been tested in our neurite outgrowth assays. Preliminary investigations indicate that these peptides can function as antagonists to block MAG or CNS myelin-mediated neurite outgrowth inhibition in vitro.;The lack of axonal regeneration observed following injury to the adult mammalian CNS is attributable to several factors, including the myelin-associated inhibitors. It has been shown that increasing intracellular cAMP levels can abrogate the inhibitory effects of these molecules in a transcription-dependent manner. One of the genes whose expression is elevated by cAMP is the cytokine Interleukin-6, (IL-6). Here, we show that there is a robust increase in expression of IL-6 by cultured primary neurons after treatment with the cAMP analog, dbcAMP. When added to primary neurons in culture, IL-6 can overcome the inhibition of axonal growth by both MAG and myelin in a dose-dependent and transcription-dependent manner. In addition, following in vivo delivery of IL-6 via mini-osmotic pumps, DRG neurons are able to extend long neurites when subsequently grown on a monolayer of MAG-expressing CHO cells. Furthermore, blocking of the IL-6-associated signaling elements gp130 or JAKs, abrogate the IL-6-induced reversal of the MAG and myelin-mediated inhibition of neurite outgrowth. Taken together, this data suggests that IL-6 may be one of the regeneration-associated genes that play a role in the cAMP-induced enhancement of neurite outgrowth in the presence of MAG or myelin and it may also provide a potential therapeutic approach to encourage axonal regeneration following CNS injury.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
