Wallerian Degeneration Involves Rho/Rho-kinase Signaling

Yamagishi, Satoru; Fujitani, Masashi; Hata, Katsuhiko; Kitajo, Keiko; Mimura, Fumiaki; Abe, Hideki; Yamashita, Toshio

doi:10.1074/jbc.m501945200

Cited by 38 publications

(19 citation statements)

References 16 publications

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“…Then, the medium was gently poured into the dishes and recollected. For cortical explant cultures, the cortex was removed from E14-E16 (C57BL/6J mouse) or E18-E20 (Wistar rat) according to previously reported methods, with a slight modification (10). The cortex was chopped into 300 -600-m-sized pieces using tungsten needles.…”

Section: Methodsmentioning

confidence: 99%

Engulfment of Axon Debris by Microglia Requires p38 MAPK Activity

Tanaka¹,

Ueno

Yamashita

2009

Journal of Biological Chemistry

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The clearance of debris after injuries to the nervous system is a critical step for restoration of the injured neural network. Microglia are thought to be involved in elimination of degenerating neurons and axons in the central nervous system (CNS), presumably restoring a favorable environment after CNS injuries. However, the mechanism underlying debris clearance remains elusive. Here, we establish an in vitro assay system to estimate phagocytosis of axon debris. We employed a Wallerian degeneration model by cutting axons of the cortical explants. The cortical explants were co-cultured with primary microglia or the MG5 microglial cell line. The cortical neurites were then transected. MG5 cells efficiently phagocytosed the debris, whereas primary microglia showed phagocytic activity only when they were activated by lipopolysaccharide or interferon-␤. When MG5 cells or primary microglia were co-cultured with degenerated axons, p38 mitogen-activated protein kinase (MAPK) was activated in these cells. Engulfment of axon debris was blocked by the p38 MAPK inhibitor SB203580, indicating that p38 MAPK is required for phagocytic activity. Receptors that recognize dying cells appeared not to be involved in the process of phagocytosis of the axon debris. In addition, the axons undergoing Wallerian degeneration did not release lactate dehydrogenase, suggesting that degeneration of the severed axons and apoptosis may represent two distinct self-destruction programs. We observed regrowth of the severed neurites after axon debris was removed. This finding suggests that axon debris, in addition to myelin debris, is an inhibitory factor for axon regeneration.

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Section: Methodsmentioning

confidence: 99%

Engulfment of Axon Debris by Microglia Requires p38 MAPK Activity

Tanaka¹,

Ueno

Yamashita

2009

Journal of Biological Chemistry

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“…We examined the Rho activity in the axons after the spinal cord injury to assess whether RhoA plays a spatial role in the injured axons. We assessed the activity of RhoA during the early period (2h) after the spinal cord injury, since axon degeneration does not occur at this stage (29). To examine the Rho activity in situ, the in situ pull-down method was employed (17).…”

Section: Crmp-2 Abolishes the Effect Of Mag-fc-mentioning

confidence: 99%

Myelin-associated Glycoprotein Inhibits Microtubule Assembly by a Rho-kinase-dependent Mechanism

Mimura

Yamagishi²,

Arimura

et al. 2006

Journal of Biological Chemistry

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Myelin-associated glycoprotein (MAG) and Nogo are potent inhibitors of neurite outgrowth from a variety of neurons, and they have been identified as possible components of the central nervous system myelin that prevents axonal regeneration in the adult vertebrate central nervous system. The activation of RhoA and Rhokinase is reported to be an essential part of the signaling mechanism of these proteins. Here, we report that the collapsing response mediator protein-2 (CRMP-2) is phosphorylated by a Rho-kinasedependent mechanism downstream of MAG or Nogo-66. The overexpression of the nonphosphorylated form of CRMP-2 at threonine 555, which is the phosphorylation site for Rho-kinase, counteracts the inhibitory effect of MAG on the postnatal cerebellar neurons. Additionally, the expression of the dominant negative form of CRMP-2 or knockdown of the gene using small interference RNA (siRNA) mimics the effect of MAG in vitro. Consistent with the function of CRMP-2, which promotes microtubule assembly, microtubule levels are down-regulated in the cerebellar neurons that are stimulated with MAG in vitro. Reduction in the density of microtubules is also observed in the injured axons following the spinal cord injury, and this effect depends on the Rho-kinase activity. Our data suggest the important roles of CRMP-2 and microtubules in the inhibition of the axon regeneration by the myelin-derived inhibitors.Several myelin-derived proteins have been identified as components of the central nervous system myelin that prevents axonal regeneration in the adult vertebrate central nervous system. To date, three major inhibitors that are expressed by oligodendrocytes and myelinated fiber tracts have been identified (1). These are Nogo, myelin-associated glycoprotein (MAG), 2 and oligodendrocyte-myelin glycoprotein. All these proteins act on neurons through the p75 receptor (p75) (2-4) in complex with the Nogo receptor. One potential clue to understanding the signal transduction mechanism downstream of p75 and the Nogo receptor is found through observations that demonstrate the small GTPase RhoA as a key intracellular effector for growth inhibitory signaling by myelin. In its active GTP-bound form, RhoA rigidifies the actin cytoskeleton, thereby inhibiting axon elongation and mediating growth cone collapse. RhoA is activated by MAG, Nogo-66, and oligodendrocyte-myelin glycoprotein through a p75-dependent mechanism; thus, inhibiting neurite outgrowth from postnatal sensory neurons and cerebellar neurons (2-5). The regulation of RhoA activity by MAG and Nogo through p75 is mediated by the release of RhoA from Rho GDI, which suppresses the RhoA activity (6, 7).Although RhoA and one of its effectors, Rho-kinase, appear to play a key role in regulating axon growth, the mechanism by which the myelinderived proteins regulate axon outgrowth remains to be elucidated. The outgrowth of axons is based on the dynamic rearrangement of the cytoskeleton (8). Cues that influence the axon outgrowth are sensed by the growth cone, which is a highly mot...

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“…JOURNAL OF NEUROTRAUMA 26:81-95 ( January 2009) Harper et al, 2004;Mukhopadhyay et al, 1994;Ramer et al, 2004;Schwab et al, 2004;Tanaka et al, 2004;Yamagishi et al, 2005). It remains possible that more complete in vivo inhibition of Rho activation might provide a valuable and effective approach to treat SCI (Baptiste and Fehlings, 2006;McKerracher and Higuchi, 2006;Mueller et al, 2005).…”

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confidence: 99%

Ibuprofen Enhances Recovery from Spinal Cord Injury by Limiting Tissue Loss and Stimulating Axonal Growth

Wang

Budel

Baughman

et al. 2009

Journal of Neurotrauma

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The GTP-binding protein RhoA regulates microfilament dynamics in many cell types and mediates the inhibition of axonal regeneration by myelin and chondroitin sulfate proteoglycans. Unlike most other nonsteroidal anti-inflammatory drugs, ibuprofen suppresses basal RhoA activity (Zhou et al., 2003). A recent report suggested that ibuprofen promotes corticospinal axon regeneration after spinal cord injury (Fu et al., 2007). Here, we confirm that ibuprofen reduces ligand-induced Rho signaling and myelin-induced inhibition of neurite outgrowth in vitro. Following 4 weeks of subcutaneous administration of ibuprofen, beginning 3 days after spinal cord contusion, animals recovered walking function to a greater degree, with twice as many rats achieving a hind limb weight-bearing status. We examined the relative role of tissue sparing, axonal sprouting, and axonal regeneration in the action of ibuprofen. Histologically, ibuprofen-treated animals display an increase in spared tissue without an alteration in astrocytic or microglial reaction. Ibuprofen increases axonal sprouting from serotonergic raphespinal axons, and from rostral corticospinal fibers in the injured spinal cord, but does not permit caudal corticospinal regeneration after spinal contusion. Treatment of mice with complete spinal cord transection demonstrates long-distance raphespinal axon regeneration in the presence of ibuprofen. Thus, administration of ibuprofen improves the recovery of rats from a clinically relevant spinal cord trauma by protecting tissue, stimulating axonal sprouting, and allowing a minor degree of raphespinal regeneration.

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Wallerian Degeneration Involves Rho/Rho-kinase Signaling

Cited by 38 publications

References 16 publications

Engulfment of Axon Debris by Microglia Requires p38 MAPK Activity

Engulfment of Axon Debris by Microglia Requires p38 MAPK Activity

Myelin-associated Glycoprotein Inhibits Microtubule Assembly by a Rho-kinase-dependent Mechanism

Ibuprofen Enhances Recovery from Spinal Cord Injury by Limiting Tissue Loss and Stimulating Axonal Growth

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