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Regulation of Wnt signaling by nociceptive input in animal models.

Shi Y, Yuan S, Li B, Wang J, Carlton SM, Chung K, Chung JM, Tang SJ - Mol Pain (2012)

Bottom Line: In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers.Furthermore, Wnt5a, a prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models.Our results suggest that Wnt signaling pathways are regulated by nociceptive input.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX 77555, USA.

ABSTRACT

Background: Central sensitization-associated synaptic plasticity in the spinal cord dorsal horn (SCDH) critically contributes to the development of chronic pain, but understanding of the underlying molecular pathways is still incomplete. Emerging evidence suggests that Wnt signaling plays a crucial role in regulation of synaptic plasticity. Little is known about the potential function of the Wnt signaling cascades in chronic pain development.

Results: Fluorescent immunostaining results indicate that β-catenin, an essential protein in the canonical Wnt signaling pathway, is expressed in the superficial layers of the mouse SCDH with enrichment at synapses in lamina II. In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers. Immunoblotting analysis indicates that both Wnt3a a β-catenin are up-regulated in the SCDH of various mouse pain models created by hind-paw injection of capsaicin, intrathecal (i.t.) injection of HIV-gp120 protein or spinal nerve ligation (SNL). Furthermore, Wnt5a, a prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models.

Conclusion: Our results suggest that Wnt signaling pathways are regulated by nociceptive input. The activation of Wnt signaling may regulate the expression of spinal central sensitization during the development of acute and chronic pain.

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Up-regulation of Wnt signaling proteins in the capsaicin pain model.A. Time course of mechanical allodynia induced by intradermal (i.d.) capsaicin injection in mouse hind paws. Mice with saline injection were used as controls (vehicle). Following capsaicin administration, mechanical hypersensitivity peaked at 3 h post-injection and gradually returned to baseline (*, p < 0.05; n = 6). B-D. Protein levels of Wnt3a (B), active β-catenin (ABC, C), and total β-catenin (TBC, D) at different time points after capsaicin injection. Proteins levels gradually increased and peaked around 3 h after injection. E-F. Temporal expression profiles of Wnt5a (E) and Ror2 C (F) following capsaicin injection. The levels of both proteins transiently increased after the injection. β-actin was included as a loading control. In the summary graphs (right panels), protein levels from at least three independent experiments are presented as relative units to the vehicle controls (mean ± SEM; *, p < 0.05; one-way ANOVA).
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Figure 6: Up-regulation of Wnt signaling proteins in the capsaicin pain model.A. Time course of mechanical allodynia induced by intradermal (i.d.) capsaicin injection in mouse hind paws. Mice with saline injection were used as controls (vehicle). Following capsaicin administration, mechanical hypersensitivity peaked at 3 h post-injection and gradually returned to baseline (*, p < 0.05; n = 6). B-D. Protein levels of Wnt3a (B), active β-catenin (ABC, C), and total β-catenin (TBC, D) at different time points after capsaicin injection. Proteins levels gradually increased and peaked around 3 h after injection. E-F. Temporal expression profiles of Wnt5a (E) and Ror2 C (F) following capsaicin injection. The levels of both proteins transiently increased after the injection. β-actin was included as a loading control. In the summary graphs (right panels), protein levels from at least three independent experiments are presented as relative units to the vehicle controls (mean ± SEM; *, p < 0.05; one-way ANOVA).

Mentions: The expression of Wnt3a and β-catenin in SCDH superficial layers suggests a potential role of Wnt signaling in nociceptive processing. Thus, we sought to determine whether peripheral painful stimulation affected the expression of the Wnt signaling proteins in SCDH. We first employed the capsaicin pain model, created by intradermal (i.d.) injection of capsaicin in hind paw [52]. It is well established that this pain model develops central sensitization [50,53,54]. Following capsaicin administration, mice developed mechanical hypersensitivity demonstrated by a decrease in paw withdrawal threshold (PWT) (Figure 6 A). The mechanical allodynia was observed at 1 h after capsaicin injection, and it peaked at 3 h. After 7 h post-injection, the mechanical sensitivity gradually decreased and PWT returned to normal. Results of immunoblotting showed that Wnt3a, active β-catenin (ABC) and total β-catenin (TBC) increased in the SCDH during the period of increased mechanical sensitivity (Figure 6 B-D). Consistent with the assumption that Wnt3a and β-catenin are in the same (canonical) pathway, Wnt3a, ABC and TBC proteins followed similar temporal profiles of up-regulation. The protein levels started to increase at 1 h after capsaicin injection and peaked at 3–5 h. Furthermore, significantly higher levels of these proteins were still observed at 9 h (Figure 6 B-D). The magnitude of increase differed for each protein: Wnt3a peaked at ~2.5 fold increase whereas ABC or TBC peaked at ~1.8 fold increase. Although cautions were taken to avoid potential contamination of the dorsal horn tissues from DRGs and dorsal root fibers, we anticipate that there were still peripheral fibers intermingling in the dissected dorsal horn. Thus, although it is likely that the observed up-regulation of Wnt signaling proteins was mainly contributed by the dorsal horn cells, we cannot exclude the possibility that the up-regulation also occurred in peripheral sensory neurons.


Regulation of Wnt signaling by nociceptive input in animal models.

Shi Y, Yuan S, Li B, Wang J, Carlton SM, Chung K, Chung JM, Tang SJ - Mol Pain (2012)

Up-regulation of Wnt signaling proteins in the capsaicin pain model.A. Time course of mechanical allodynia induced by intradermal (i.d.) capsaicin injection in mouse hind paws. Mice with saline injection were used as controls (vehicle). Following capsaicin administration, mechanical hypersensitivity peaked at 3 h post-injection and gradually returned to baseline (*, p < 0.05; n = 6). B-D. Protein levels of Wnt3a (B), active β-catenin (ABC, C), and total β-catenin (TBC, D) at different time points after capsaicin injection. Proteins levels gradually increased and peaked around 3 h after injection. E-F. Temporal expression profiles of Wnt5a (E) and Ror2 C (F) following capsaicin injection. The levels of both proteins transiently increased after the injection. β-actin was included as a loading control. In the summary graphs (right panels), protein levels from at least three independent experiments are presented as relative units to the vehicle controls (mean ± SEM; *, p < 0.05; one-way ANOVA).
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Related In: Results  -  Collection

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Figure 6: Up-regulation of Wnt signaling proteins in the capsaicin pain model.A. Time course of mechanical allodynia induced by intradermal (i.d.) capsaicin injection in mouse hind paws. Mice with saline injection were used as controls (vehicle). Following capsaicin administration, mechanical hypersensitivity peaked at 3 h post-injection and gradually returned to baseline (*, p < 0.05; n = 6). B-D. Protein levels of Wnt3a (B), active β-catenin (ABC, C), and total β-catenin (TBC, D) at different time points after capsaicin injection. Proteins levels gradually increased and peaked around 3 h after injection. E-F. Temporal expression profiles of Wnt5a (E) and Ror2 C (F) following capsaicin injection. The levels of both proteins transiently increased after the injection. β-actin was included as a loading control. In the summary graphs (right panels), protein levels from at least three independent experiments are presented as relative units to the vehicle controls (mean ± SEM; *, p < 0.05; one-way ANOVA).
Mentions: The expression of Wnt3a and β-catenin in SCDH superficial layers suggests a potential role of Wnt signaling in nociceptive processing. Thus, we sought to determine whether peripheral painful stimulation affected the expression of the Wnt signaling proteins in SCDH. We first employed the capsaicin pain model, created by intradermal (i.d.) injection of capsaicin in hind paw [52]. It is well established that this pain model develops central sensitization [50,53,54]. Following capsaicin administration, mice developed mechanical hypersensitivity demonstrated by a decrease in paw withdrawal threshold (PWT) (Figure 6 A). The mechanical allodynia was observed at 1 h after capsaicin injection, and it peaked at 3 h. After 7 h post-injection, the mechanical sensitivity gradually decreased and PWT returned to normal. Results of immunoblotting showed that Wnt3a, active β-catenin (ABC) and total β-catenin (TBC) increased in the SCDH during the period of increased mechanical sensitivity (Figure 6 B-D). Consistent with the assumption that Wnt3a and β-catenin are in the same (canonical) pathway, Wnt3a, ABC and TBC proteins followed similar temporal profiles of up-regulation. The protein levels started to increase at 1 h after capsaicin injection and peaked at 3–5 h. Furthermore, significantly higher levels of these proteins were still observed at 9 h (Figure 6 B-D). The magnitude of increase differed for each protein: Wnt3a peaked at ~2.5 fold increase whereas ABC or TBC peaked at ~1.8 fold increase. Although cautions were taken to avoid potential contamination of the dorsal horn tissues from DRGs and dorsal root fibers, we anticipate that there were still peripheral fibers intermingling in the dissected dorsal horn. Thus, although it is likely that the observed up-regulation of Wnt signaling proteins was mainly contributed by the dorsal horn cells, we cannot exclude the possibility that the up-regulation also occurred in peripheral sensory neurons.

Bottom Line: In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers.Furthermore, Wnt5a, a prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models.Our results suggest that Wnt signaling pathways are regulated by nociceptive input.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX 77555, USA.

ABSTRACT

Background: Central sensitization-associated synaptic plasticity in the spinal cord dorsal horn (SCDH) critically contributes to the development of chronic pain, but understanding of the underlying molecular pathways is still incomplete. Emerging evidence suggests that Wnt signaling plays a crucial role in regulation of synaptic plasticity. Little is known about the potential function of the Wnt signaling cascades in chronic pain development.

Results: Fluorescent immunostaining results indicate that β-catenin, an essential protein in the canonical Wnt signaling pathway, is expressed in the superficial layers of the mouse SCDH with enrichment at synapses in lamina II. In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers. Immunoblotting analysis indicates that both Wnt3a a β-catenin are up-regulated in the SCDH of various mouse pain models created by hind-paw injection of capsaicin, intrathecal (i.t.) injection of HIV-gp120 protein or spinal nerve ligation (SNL). Furthermore, Wnt5a, a prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models.

Conclusion: Our results suggest that Wnt signaling pathways are regulated by nociceptive input. The activation of Wnt signaling may regulate the expression of spinal central sensitization during the development of acute and chronic pain.

Show MeSH
Related in: MedlinePlus