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Rho activation patterns after spinal cord injury and the role of activated Rho in apoptosis in the central nervous system.

Dubreuil CI, Winton MJ, McKerracher L - J. Cell Biol. (2003)

Bottom Line: After SCI, an up-regulation of p75NTR was detected by Western blot and observed in both neurons and glia.Treatment with C3-05 blocked the increase in p75NTR expression.Our results indicate that blocking overactivation of Rho after SCI protects cells from p75NTR-dependent apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Département de pathologie et biologie cellulaire, Université de Montréal, Montréal, QC H3T 1J4, Canada.

ABSTRACT
Growth inhibitory proteins in the central nervous system (CNS) block axon growth and regeneration by signaling to Rho, an intracellular GTPase. It is not known how CNS trauma affects the expression and activation of RhoA. Here we detect GTP-bound RhoA in spinal cord homogenates and report that spinal cord injury (SCI) in both rats and mice activates RhoA over 10-fold in the absence of changes in RhoA expression. In situ Rho-GTP detection revealed that both neurons and glial cells showed Rho activation at SCI lesion sites. Application of a Rho antagonist (C3-05) reversed Rho activation and reduced the number of TUNEL-labeled cells by approximately 50% in both injured mouse and rat, showing a role for activated Rho in cell death after CNS injury. Next, we examined the role of the p75 neurotrophin receptor (p75NTR) in Rho signaling. After SCI, an up-regulation of p75NTR was detected by Western blot and observed in both neurons and glia. Treatment with C3-05 blocked the increase in p75NTR expression. Experiments with p75NTR- mutant mice showed that immediate Rho activation after SCI is p75NTR dependent. Our results indicate that blocking overactivation of Rho after SCI protects cells from p75NTR-dependent apoptosis.

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Schematic diagram showing possible apoptotic cascade mediated by Rho after SCI. Both myelin-derived growth inhibitory proteins (Fig. 1) and TNF (Neumann et al., 2002) directly activate Rho. P75NTR activates Rho in the absence of neurotrophin binding (Yamashita et al., 1999). The inactivation of Rho by C3–05 after SCI blocks the increase of p75NTR protein levels (Fig. 8 C) and inhibits apoptosis (Fig. 6, B and C). Inactivation of Rho with C3–05 both prevents apoptosis, as shown in this paper, and stimulates regeneration (Lehmann et al., 1999; Dergham et al., 2002). Gray lines indicate C3–05 treatment and inactivation of Rho; black lines indicate the effects of active GTP-bound Rho.
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fig9: Schematic diagram showing possible apoptotic cascade mediated by Rho after SCI. Both myelin-derived growth inhibitory proteins (Fig. 1) and TNF (Neumann et al., 2002) directly activate Rho. P75NTR activates Rho in the absence of neurotrophin binding (Yamashita et al., 1999). The inactivation of Rho by C3–05 after SCI blocks the increase of p75NTR protein levels (Fig. 8 C) and inhibits apoptosis (Fig. 6, B and C). Inactivation of Rho with C3–05 both prevents apoptosis, as shown in this paper, and stimulates regeneration (Lehmann et al., 1999; Dergham et al., 2002). Gray lines indicate C3–05 treatment and inactivation of Rho; black lines indicate the effects of active GTP-bound Rho.

Mentions: Our results show that blocking the activation of Rho after SCI prevents an increased synthesis of p75NTR protein (Fig. 8 C), implicating Rho activation in the transcriptional changes in p75NTR expression. This result of C3–05 can be explained by a mechanism in which the change in transcriptional factor activation is Rho dependent (Fig. 9). It is known that Rho is involved in the activation of transcription factors in the nucleus that control synthesis of proapoptotic mRNAs such as c-jun and NFκβ, members of the p75NTR apoptotic cascades (Aznar and Lacal, 2001; Huang and Reichardt, 2001). Therefore, we speculate that treatment with C3–05 to block Rho activation after injury suppresses apoptosis by preventing the synthesis of proapoptotic proteins such as p75NTR.


Rho activation patterns after spinal cord injury and the role of activated Rho in apoptosis in the central nervous system.

Dubreuil CI, Winton MJ, McKerracher L - J. Cell Biol. (2003)

Schematic diagram showing possible apoptotic cascade mediated by Rho after SCI. Both myelin-derived growth inhibitory proteins (Fig. 1) and TNF (Neumann et al., 2002) directly activate Rho. P75NTR activates Rho in the absence of neurotrophin binding (Yamashita et al., 1999). The inactivation of Rho by C3–05 after SCI blocks the increase of p75NTR protein levels (Fig. 8 C) and inhibits apoptosis (Fig. 6, B and C). Inactivation of Rho with C3–05 both prevents apoptosis, as shown in this paper, and stimulates regeneration (Lehmann et al., 1999; Dergham et al., 2002). Gray lines indicate C3–05 treatment and inactivation of Rho; black lines indicate the effects of active GTP-bound Rho.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172802&req=5

fig9: Schematic diagram showing possible apoptotic cascade mediated by Rho after SCI. Both myelin-derived growth inhibitory proteins (Fig. 1) and TNF (Neumann et al., 2002) directly activate Rho. P75NTR activates Rho in the absence of neurotrophin binding (Yamashita et al., 1999). The inactivation of Rho by C3–05 after SCI blocks the increase of p75NTR protein levels (Fig. 8 C) and inhibits apoptosis (Fig. 6, B and C). Inactivation of Rho with C3–05 both prevents apoptosis, as shown in this paper, and stimulates regeneration (Lehmann et al., 1999; Dergham et al., 2002). Gray lines indicate C3–05 treatment and inactivation of Rho; black lines indicate the effects of active GTP-bound Rho.
Mentions: Our results show that blocking the activation of Rho after SCI prevents an increased synthesis of p75NTR protein (Fig. 8 C), implicating Rho activation in the transcriptional changes in p75NTR expression. This result of C3–05 can be explained by a mechanism in which the change in transcriptional factor activation is Rho dependent (Fig. 9). It is known that Rho is involved in the activation of transcription factors in the nucleus that control synthesis of proapoptotic mRNAs such as c-jun and NFκβ, members of the p75NTR apoptotic cascades (Aznar and Lacal, 2001; Huang and Reichardt, 2001). Therefore, we speculate that treatment with C3–05 to block Rho activation after injury suppresses apoptosis by preventing the synthesis of proapoptotic proteins such as p75NTR.

Bottom Line: After SCI, an up-regulation of p75NTR was detected by Western blot and observed in both neurons and glia.Treatment with C3-05 blocked the increase in p75NTR expression.Our results indicate that blocking overactivation of Rho after SCI protects cells from p75NTR-dependent apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Département de pathologie et biologie cellulaire, Université de Montréal, Montréal, QC H3T 1J4, Canada.

ABSTRACT
Growth inhibitory proteins in the central nervous system (CNS) block axon growth and regeneration by signaling to Rho, an intracellular GTPase. It is not known how CNS trauma affects the expression and activation of RhoA. Here we detect GTP-bound RhoA in spinal cord homogenates and report that spinal cord injury (SCI) in both rats and mice activates RhoA over 10-fold in the absence of changes in RhoA expression. In situ Rho-GTP detection revealed that both neurons and glial cells showed Rho activation at SCI lesion sites. Application of a Rho antagonist (C3-05) reversed Rho activation and reduced the number of TUNEL-labeled cells by approximately 50% in both injured mouse and rat, showing a role for activated Rho in cell death after CNS injury. Next, we examined the role of the p75 neurotrophin receptor (p75NTR) in Rho signaling. After SCI, an up-regulation of p75NTR was detected by Western blot and observed in both neurons and glia. Treatment with C3-05 blocked the increase in p75NTR expression. Experiments with p75NTR- mutant mice showed that immediate Rho activation after SCI is p75NTR dependent. Our results indicate that blocking overactivation of Rho after SCI protects cells from p75NTR-dependent apoptosis.

Show MeSH
Related in: MedlinePlus