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Epigenetic transcriptional activation of monocyte chemotactic protein 3 contributes to long-lasting neuropathic pain

Satoshi Imai, Daigo Ikegami, Akira Yamashita, Toshikazu Shimizu, Michiko Narita, Keiichi Niikura, Masaharu Furuya, Yasuhisa Kobayashi, Kazuhiko Miyashita, Daiki Okutsu, Akira Kato, Atsushi Nakamura, Akiko Araki, Kazuo Omi, Masaya Nakamura, Hirotaka James Okano, Hideyuki Okano, Takayuki Ando, Hideyuki Takeshima, Toshikazu Ushijima, Naoko Kuzumaki, Tsutomu Suzuki, Minoru Narita
DOI: http://dx.doi.org/10.1093/brain/aws330 828-843 First published online: 30 January 2013

Summary

A multiplex analysis for profiling the expression of candidate genes along with epigenetic modification may lead to a better understanding of the complex machinery of neuropathic pain. In the present study, we found that partial sciatic nerve ligation most remarkably increased the expression of monocyte chemotactic protein 3 (MCP-3, known as CCL7) a total of 33 541 genes in the spinal cord, which lasted for 4 weeks. This increase in MCP-3 gene transcription was accompanied by the decreased trimethylation of histone H3 at Lys27 at the MCP-3 promoter. The increased MCP-3 expression associated with its epigenetic modification observed in the spinal cord was almost abolished in interleukin 6 knockout mice with partial sciatic nerve ligation. Consistent with these findings, a single intrathecal injection of recombinant proteins of interleukin 6 significantly increased MCP-3 messenger RNA with a decrease in the level of Lys27 trimethylation of histone H3 at the MCP-3 promoter in the spinal cord of mice. Furthermore, deletion of the C–C chemokine receptor type 2 (CCR2) gene, which encodes a receptor for MCP-3, failed to affect the acceleration of MCP-3 expression in the spinal cord after partial sciatic nerve ligation. A robust increase in MCP-3 protein, which lasted for up to 2 weeks after surgery, in the dorsal horn of the spinal cord of mice with partial sciatic nerve ligation was seen mostly in astrocytes, but not microglia or neurons. On the other hand, the increases in both microglia and astrocytes in the spinal cord by partial sciatic nerve ligation were mostly abolished in interleukin 6 knockout mice. Moreover, this increase in microglia was almost abolished by CCR2 gene deletion, whereas the increase in astrocytes was not affected in nerve-ligated mice that lacked the CCR2 gene. We also found that either in vivo or in vitro treatment with MCP-3 caused robust microglia activation. Under these conditions, intrathecal administration of MCP-3 antibody suppressed the increase in microglia within the mouse spinal cord and neuropathic pain-like behaviours after nerve injury. With the use of a functional magnetic resonance imaging analysis, we demonstrated that a single intrathecal injection of MCP-3 induced dramatic increases in signal intensity in pain-related brain regions. These findings suggest that increased MCP-3 expression associated with interleukin 6 dependent epigenetic modification at the MCP-3 promoter after nerve injury, mostly in spinal astrocytes, may serve to facilitate astrocyte–microglia interaction in the spinal cord and could play a critical role in the neuropathic pain-like state.

  • microglia
  • neuropathic pain
  • chemokines
  • spinal cord plasticity
  • nerve injury
  • Abbreviations
    CCL
    C-C Chemokine ligand
    CCR2
    C-C chemokine receptor type 2
    FEAT
    FMRI expert analysis tool
    IL6
    interleukin 6
    JAK
    Janus kinase signal
    MCP-3
    monocyte chemotactic protein 3
    PBS
    phosphate buffered saline
    RANTES
    regulated upon activation normal T expressed and presumably secreted
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