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Plexin-A1 is required for Toll-like receptor-mediated microglial activation in the development of lipopolysaccharide-induced encephalopathy.

Ito T, Yoshida K, Negishi T, Miyajima M, Takamatsu H, Kikutani H, Kumanogoh A, Yukawa K - Int. J. Mol. Med. (2014)

Bottom Line: Plexin-A1-/- mice administered LPS did not show significant increases in ventricle size or infiltration of leukocytes into the brain, as compared with the saline-treated group.In WT, but not in the Plexin-A1-/- primary microglia treated with LPS, Sema3A induced significantly more nitric oxide production than in the immunoglobulin G control.These results revealed the crucial role of the Sema3A-Plexin-A1 interaction in the Toll-like receptor 4-mediated signaling of the LPS-induced activation of microglia.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Faculty of Pharmacy, Meijo University, Nagoya 468-8503, Japan.

ABSTRACT
Recent investigations have suggested that semaphorins, which are known repulsive axon guidance molecules, may play a crucial role in maintaining brain homeostasis by regulating microglial activity. Sema3A, secreted in higher amounts from injured neurons, is considered to suppress excessive inflammatory responses by inducing microglial apoptosis through its binding to Plexin-A1 receptors on activated microglia. To clarify the in vivo role of Plexin-A1-mediated signaling in lipopolysaccharide (LPS)-induced injury in mouse brain, we examined the neuroinflammatory changes initiated by LPS administration to the cerebral ventricles of wild-type (WT) and Plexin-A1-deficient (-/-) mice. WT mice administered LPS exhibited a significantly higher expression of COX-2, iNOS, IL-1β and TNF-α in the hippocampus, and a significantly greater ventricular enlargement and intracerebral infiltration of leukocytes, as compared with the saline-treated group. By contrast, Plexin-A1-/- mice administered LPS did not exhibit a significantly increased expression of COX-2, iNOS, IL-1β or TNF-α in the hippocampus as compared with the saline-treated group. Plexin-A1-/- mice administered LPS did not show significant increases in ventricle size or infiltration of leukocytes into the brain, as compared with the saline-treated group. In WT, but not in the Plexin-A1-/- primary microglia treated with LPS, Sema3A induced significantly more nitric oxide production than in the immunoglobulin G control. These results revealed the crucial role of the Sema3A-Plexin-A1 interaction in the Toll-like receptor 4-mediated signaling of the LPS-induced activation of microglia. Thus, results of the present study revealed the essential role of Plexin-A1 in the development of LPS-induced neuroinflammation in mice, suggesting the possible application of microglial control of the semaphorin-plexin signaling system to the treatment of LPS-induced encephalopathy and other psychiatric diseases associated with neuroinflammation.

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Sema3A increases NO production through Plexin-A1 receptor on microglia in response to LPS. (A) In culture, NO production level is significantly lower in LPS-stimulated Plexin-A1−/− microglia as compared with LPS-treated WT microglia. (B) MTT assay reveals no significant differences in cell viability between each experimental group. (C) Addition of Sema3A and LPS in culture to WT microglia significantly increases NO production as compared with microglia treated with LPS and control IgG. Treatment of Plexin-A1−/− microglia with Sema3A and LPS shows no significant increase of NO production as compared with Plexin-A1−/− microglia treated with LPS and control IgG. (D) MTT assay shows no significant differences between each experimental group. VEH, vehicle; LPS, lipopolysaccharide; WT, wild-type; A1−/−, Plexin-A1−/− microglia.
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f8-ijmm-33-05-1122: Sema3A increases NO production through Plexin-A1 receptor on microglia in response to LPS. (A) In culture, NO production level is significantly lower in LPS-stimulated Plexin-A1−/− microglia as compared with LPS-treated WT microglia. (B) MTT assay reveals no significant differences in cell viability between each experimental group. (C) Addition of Sema3A and LPS in culture to WT microglia significantly increases NO production as compared with microglia treated with LPS and control IgG. Treatment of Plexin-A1−/− microglia with Sema3A and LPS shows no significant increase of NO production as compared with Plexin-A1−/− microglia treated with LPS and control IgG. (D) MTT assay shows no significant differences between each experimental group. VEH, vehicle; LPS, lipopolysaccharide; WT, wild-type; A1−/−, Plexin-A1−/− microglia.

Mentions: To directly demonstrate the role of microglial Plexin-A1 in the response to LPS, NO production was measured by the Griess reaction in cultures of WT or Plexin-A1−/− primary microglia stimulated with LPS. The Griess reaction revealed a significant reduction of NO production in Plexin-A1−/− microglia stimulated with LPS as compared with LPS-treated WT microglia (Fig. 8A). There were no significant differences in cell viability among WT and Plexin-A1−/− primary microglia with or without LPS stimulation (Fig. 8B). To examine whether Sema3A enhances the cell response to LPS, NO production was quantified in WT and Plexin-A1−/− primary microglia stimulated with LPS and Sema3A (Fig. 8C). Under stimulation with LPS, the addition of Sema3A to WT microglia exhibited a significant increase of NO production as compared with the addition of control IgG. By contrast, Plexin-A1−/− microglia stimulated with LPS and Sema3A did not exhibit any significant increase in NO production as compared with Plexin-A1−/− microglia stimulated by LPS and control IgG (Fig. 8C). There were no significant differences in cell viability as determined by MTT assay among any of the experimental groups of WT and Plexin-A1−/− microglia (Fig. 8D). Thus, these data suggest a synergistic action of Plexin-A1 activation and TLR4-mediated signaling in microglia.


Plexin-A1 is required for Toll-like receptor-mediated microglial activation in the development of lipopolysaccharide-induced encephalopathy.

Ito T, Yoshida K, Negishi T, Miyajima M, Takamatsu H, Kikutani H, Kumanogoh A, Yukawa K - Int. J. Mol. Med. (2014)

Sema3A increases NO production through Plexin-A1 receptor on microglia in response to LPS. (A) In culture, NO production level is significantly lower in LPS-stimulated Plexin-A1−/− microglia as compared with LPS-treated WT microglia. (B) MTT assay reveals no significant differences in cell viability between each experimental group. (C) Addition of Sema3A and LPS in culture to WT microglia significantly increases NO production as compared with microglia treated with LPS and control IgG. Treatment of Plexin-A1−/− microglia with Sema3A and LPS shows no significant increase of NO production as compared with Plexin-A1−/− microglia treated with LPS and control IgG. (D) MTT assay shows no significant differences between each experimental group. VEH, vehicle; LPS, lipopolysaccharide; WT, wild-type; A1−/−, Plexin-A1−/− microglia.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4020473&req=5

f8-ijmm-33-05-1122: Sema3A increases NO production through Plexin-A1 receptor on microglia in response to LPS. (A) In culture, NO production level is significantly lower in LPS-stimulated Plexin-A1−/− microglia as compared with LPS-treated WT microglia. (B) MTT assay reveals no significant differences in cell viability between each experimental group. (C) Addition of Sema3A and LPS in culture to WT microglia significantly increases NO production as compared with microglia treated with LPS and control IgG. Treatment of Plexin-A1−/− microglia with Sema3A and LPS shows no significant increase of NO production as compared with Plexin-A1−/− microglia treated with LPS and control IgG. (D) MTT assay shows no significant differences between each experimental group. VEH, vehicle; LPS, lipopolysaccharide; WT, wild-type; A1−/−, Plexin-A1−/− microglia.
Mentions: To directly demonstrate the role of microglial Plexin-A1 in the response to LPS, NO production was measured by the Griess reaction in cultures of WT or Plexin-A1−/− primary microglia stimulated with LPS. The Griess reaction revealed a significant reduction of NO production in Plexin-A1−/− microglia stimulated with LPS as compared with LPS-treated WT microglia (Fig. 8A). There were no significant differences in cell viability among WT and Plexin-A1−/− primary microglia with or without LPS stimulation (Fig. 8B). To examine whether Sema3A enhances the cell response to LPS, NO production was quantified in WT and Plexin-A1−/− primary microglia stimulated with LPS and Sema3A (Fig. 8C). Under stimulation with LPS, the addition of Sema3A to WT microglia exhibited a significant increase of NO production as compared with the addition of control IgG. By contrast, Plexin-A1−/− microglia stimulated with LPS and Sema3A did not exhibit any significant increase in NO production as compared with Plexin-A1−/− microglia stimulated by LPS and control IgG (Fig. 8C). There were no significant differences in cell viability as determined by MTT assay among any of the experimental groups of WT and Plexin-A1−/− microglia (Fig. 8D). Thus, these data suggest a synergistic action of Plexin-A1 activation and TLR4-mediated signaling in microglia.

Bottom Line: Plexin-A1-/- mice administered LPS did not show significant increases in ventricle size or infiltration of leukocytes into the brain, as compared with the saline-treated group.In WT, but not in the Plexin-A1-/- primary microglia treated with LPS, Sema3A induced significantly more nitric oxide production than in the immunoglobulin G control.These results revealed the crucial role of the Sema3A-Plexin-A1 interaction in the Toll-like receptor 4-mediated signaling of the LPS-induced activation of microglia.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Faculty of Pharmacy, Meijo University, Nagoya 468-8503, Japan.

ABSTRACT
Recent investigations have suggested that semaphorins, which are known repulsive axon guidance molecules, may play a crucial role in maintaining brain homeostasis by regulating microglial activity. Sema3A, secreted in higher amounts from injured neurons, is considered to suppress excessive inflammatory responses by inducing microglial apoptosis through its binding to Plexin-A1 receptors on activated microglia. To clarify the in vivo role of Plexin-A1-mediated signaling in lipopolysaccharide (LPS)-induced injury in mouse brain, we examined the neuroinflammatory changes initiated by LPS administration to the cerebral ventricles of wild-type (WT) and Plexin-A1-deficient (-/-) mice. WT mice administered LPS exhibited a significantly higher expression of COX-2, iNOS, IL-1β and TNF-α in the hippocampus, and a significantly greater ventricular enlargement and intracerebral infiltration of leukocytes, as compared with the saline-treated group. By contrast, Plexin-A1-/- mice administered LPS did not exhibit a significantly increased expression of COX-2, iNOS, IL-1β or TNF-α in the hippocampus as compared with the saline-treated group. Plexin-A1-/- mice administered LPS did not show significant increases in ventricle size or infiltration of leukocytes into the brain, as compared with the saline-treated group. In WT, but not in the Plexin-A1-/- primary microglia treated with LPS, Sema3A induced significantly more nitric oxide production than in the immunoglobulin G control. These results revealed the crucial role of the Sema3A-Plexin-A1 interaction in the Toll-like receptor 4-mediated signaling of the LPS-induced activation of microglia. Thus, results of the present study revealed the essential role of Plexin-A1 in the development of LPS-induced neuroinflammation in mice, suggesting the possible application of microglial control of the semaphorin-plexin signaling system to the treatment of LPS-induced encephalopathy and other psychiatric diseases associated with neuroinflammation.

Show MeSH
Related in: MedlinePlus