Approaching the convergent point: Downstream effectors of cyclic AMP and MAG on cytoskeleton reorganization in rat primary neurons.
Item
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Title
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Approaching the convergent point: Downstream effectors of cyclic AMP and MAG on cytoskeleton reorganization in rat primary neurons.
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Identifier
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AAI3169901
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identifier
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3169901
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Creator
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Deng, Kangwen.
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Contributor
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Adviser: Marie T. Filbin
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Date
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2005
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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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Chemistry, Biochemistry | Biology, Molecular | Biology, Cell
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Abstract
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Inhibitors in myelin such as myelin-associated glycoprotein (MAG) are major impediments to axonal regeneration after injury. Elevation of cyclic AMP (cAMP) induces up-regulation of Arginase I (ArgI) and polyamines (putrescine, spermidine and spermine), which are each sufficient to overcome the inhibition by MAG. We demonstrate here that both ArgI and polyamines levels increase after a conditioning lesion. If synthesis of polyamines is blocked along with a sciatic nerve lesion, the inhibition by MAG remained. Intrathecal delivery of putrescine, without a peripheral lesion, is sufficient to switch the neurons' response to MAG.;Inhibition of spermidine synthase activity by its inhibitor---BCHS resulted in accumulation of putrescine. However, when putrescine is elevated by BCHS even in the presence of dbcAMP or putrescine, inhibition by MAG remained. This suggests that putrescine alone is insufficient to overcome the inhibition by MAG, and its conversion to spermidine is required. Moreover, priming neurons with spermidine is sufficient to block the inhibition by MAG and myelin. In addition, intrathecal deliver of spermidine overcomes inhibition by MAG.;Cytoskeleton rearrangement must be the ultimate convergent point of these extracellular signals. We suggested that simultaneously strengthening tubulin polymerization with taxol and destabilizing microfilaments with cytochalasin D resulted in improved neurite outgrowth on MAG and myelin. Tubulin is known to undergo several post-translational modifications. Newly synthesized tubulin is tyrosinated while more stable tubulin is detyrosinated or acetylated. Taxol treatment resulted in a loss of tyrosinated-tubulin (Tyr-T) and increased of acetylated-tubulin (Acet-T). Both Tyr-T and Acet-T content are increased by dbcAMP. However, the presence of MAG results in less Tyr-T. More importantly, the effect of myelin on tubulin modification is reversed by dbcAMP.;Activity of cyclin-dependent kianse 5 (CDK5) has been shown to be critical for neurite elongation and cytoskeleton stability. The present study demonstrates that neurotrophins through activation of the Erk pathway induce expression of p35, the neuronal specific activator for CDK5. This in turn induces the kinase activity of CDK5. We show that elevated activity of CDK5 is required for neurotrophins, dbcAMP or polyamines to overcome inhibition by MAG and myelin.
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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.
