Research ArticleNeuroscience

The transcription factor C/EBPβ in the dorsal root ganglion contributes to peripheral nerve trauma–induced nociceptive hypersensitivity

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Science Signaling  11 Jul 2017:
Vol. 10, Issue 487, eaam5345
DOI: 10.1126/scisignal.aam5345
  • Fig. 1 Peripheral nerve injury–induced increases in Cebpb mRNA and C/EBPβ protein in the ipsilateral DRG.

    (A) Cebpb mRNA abundance in the ipsilateral (Ipsi) and contralateral (Contral) L3/4 DRGs (top) and C/EBPβ protein expression in the ipsilateral L3/4 DRGs (bottom) after CCI. Unilateral L3/4 DRGs from two mice were pooled together to obtain enough RNA and protein. n = 3 biological replicates (six mice) per time point. One-way analysis of variance (ANOVA) followed by Tukey post hoc test, F3,11 = 26.87 for Cebpb mRNA and F3,11 = 14.04 for C/EBPβ protein. *P < 0.05 or **P < 0.01 compared to the corresponding control group (0 day). H3, histone 3. (B) C/EBPβ protein abundance in the contralateral L3/4 DRGs after CCI. Representative Western blots and a summary of densitometric analysis are shown. n = 3 biological replicates (six mice) per time point. One-way ANOVA followed by Tukey post hoc test, F3,11 = 0.49. (C) C/EBPβ protein abundance in the ipsilateral L3/4 spinal cord after CCI. n = 3 biological replicates (three mice) per time point. One-way ANOVA followed by Tukey post hoc test, F3,11 = 1.99. (D) In situ hybridization histochemistry (ISHH) for Cebpb mRNA and immunohistochemistry of different DRG cell markers: β III tubulin, glutamine synthetase (GS), NF200, IB4, or CGRP in the DRG. n = 3 mice. Scale bar, 25 μm. (E) Distribution of Cebpb mRNA–labeled neuronal somata. Large, 31%; medium, 43%; small, 26%. (F) Neurons labeled by Cebpb mRNA in the ipsilateral L4 DRG on day 7 after CCI or sham surgery. n = 3 mice per group. **P < 0.01 compared to the corresponding sham group by two-tailed paired Student’s t test. Scale bar, 25 μm.

  • Fig. 2 Effect of DRG pre-microinjection of Cebpb siRNA on CCI-induced development of pain hypersensitivity and dorsal horn central sensitization.

    (A) The abundance of C/EBPβ, OCT1, and mTOR after transfection of Cebpb or negative control siRNA (NC) into cultured DRG neurons. Representative Western blots and a summary of densitometric analysis are shown. n = 3 biological replicates per treatment. One-way ANOVA followed by Tukey post hoc test, F2,8 = 9.647 for C/EBPβ, F2,8 = 0.497 for OCT1, and F2,8 = 0.037 for mTOR. *P < 0.05 compared to naïve group. GAPDH, glyceraldhyde-3-phosphate dehydrogenase. (B and C) Effect of pre-microinjection of Cebpb siRNA (Si) into the ipsilateral L3/4 DRGs on basal or CCI-induced increases in Cebpb mRNA expression (B) and C/EBPβ protein abundance (C) on day 7 after CCI or post-sham surgery in the ipsilateral L3/4 DRGs. Unilateral L3/4 DRGs from two mice were pooled together. n = 6 to 8 mice per group. One-way ANOVA followed by Tukey post hoc test, F4,16 = 17.041 in (B) and F4,19 = 9.614 in (C). **P < 0.01 compared to the vehicle (V) plus sham group. #P < 0.05 or ##P < 0.01 compared to the vehicle plus CCI group. (D to J) Effect of pre-microinjection of Cebpb siRNA, vehicle, or negative control siRNA into the ipsilateral L3/4 DRGs on paw withdrawal frequencies to mechanical stimuli (D and E), paw withdrawal latency to thermal stimulation (F), and paw jumping latency to cold stimulation (G) on the ipsilateral side and on basal paw withdrawal responses to mechanical (H and I) and thermal (J) stimuli on the contralateral side at different days after CCI or sham surgery. n = 10 mice per group. Two-way ANOVA followed by Tukey post hoc test, F4,199 = 37.159 in (D), F4,199 = 27.312 in (E), F4,199 = 37.336 in (F), F4,199 = 56.651 in (G), F4,199 = 2.071 in (H), F4,199 = 0.472 in (I), and F4,199 = 0.681 in (J). **P < 0.01 compared to the corresponding baseline (day −4). (K and L) Effect of pre-microinjection of Cebpb siRNA into the ipsilateral L3/4 DRGs on CCI-induced increases in the phosphorylation of ERK1/2 (p-ERK1/2) and abundance of GFAP in the ipsilateral L3/4 dorsal horn on day 5 post–spinal nerve ligation (SNL). Representative Western blots (K) and a summary of densitometric analysis (L) are shown. n = 6 to 8 mice per group. One-way ANOVA followed by Tukey post hoc test, F2,9 = 9.003 for p-ERK1, F2,9 = 8.899 for p-ERK2, F2,11 = 0.156 for ERK1, F2,11 = 0.192 for ERK2, and F2,11 = 8.163 for GFAP. *P < 0.05 compared to the corresponding vehicle plus sham group. #P < 0.05 compared to the corresponding vehicle plus CCI group.

  • Fig. 3 Effect of DRG post-microinjection of Cebpb siRNA into the ipsilateral L3/4 DRGs on CCI-induced maintenance of pain hypersensitivity.

    (A to G) Effect of DRG microinjection of Cebpb siRNA, vehicle, or negative control siRNA starting on day 5 after CCI on paw withdrawal frequencies to mechanical stimuli (A and B), paw withdrawal latency to thermal stimulation (C), and paw jumping latency to cold stimulation (D) on the ipsilateral side and on basal paw withdrawal responses to mechanical (E and F) and thermal (G) stimuli on the contralateral side on days 12 and 14 after CCI. n = 10 mice per group. Two-way ANOVA followed by Tukey post hoc test, F2,119 = 26.777 in (A), F2,119 = 31.439 in (B), F2,119 = 15.275 in (C), F2,119 = 18.089 in (D), F2,119 = 0.093 in (E), F2,119 < 0.001 in (F), and F2,119 = 0.157 in (G). **P < 0.01 compared to the vehicle plus CCI group at the corresponding time points.

  • Fig. 4 Effect of DRG C/EBPβ overexpression on nociceptive thresholds in naïve mice.

    (A and B) Cebpb mRNA expression (A) and C/EBPβ protein abundance (B) in the ipsilateral L3/4 DRGs 8 weeks after microinjection of AAV5-C/EBPβ or control AAV5-EGFP. n = 6 mice per group. Two-tailed, independent Student’s t test, *P < 0.05 compared to the AAV5-EGFP group. (C to F) Effect of microinjection of AAV5-C/EBPβ or AAV5-EGFP into the unilateral L3/4 DRGs on paw withdrawal frequencies to mechanical stimuli (C and D), paw withdrawal latency to thermal stimulation (E), and paw jumping latency to cold stimulation (F) on the ipsilateral and contralateral sides at the different weeks after microinjection. n = 10 mice per group. Two-way ANOVA followed by Tukey post hoc test, F3,239 = 42.76 in (C), F3,239 = 39.60 in (D), F3,239 = 59.08 in (E), and F1,119 = 49.879 in (F). **P < 0.01 compared to the control AAV5-EGFP group on the ipsilateral side at the corresponding time points. (G and H) Effect of microinjection of AAV5-C/EBPβ or AAV5-EGFP into the unilateral L3/4 DRGs on spontaneous ongoing pain as assessed by CPP paradigm. n = 16 mice per group. **P < 0.01 compared to the corresponding preconditioning (G) or the AAV5-EGFP group (H) by two-tailed, independent Student’s t test.

  • Fig. 5 C/EBPβ-triggered transcriptional activation of Ehmt2 in the ipsilateral DRG after CCI.

    (A and B) Ehmt2 mRNA expression (A), the abundance of G9a’s two protein isoforms (B), and the amount of H3K9me2-marked protein (B) in the ipsilateral L3/4 DRGs 7 days after CCI or sham surgery in the mice pre-microinjected with vehicle, negative control siRNA, or Cebpb siRNA into the ipsilateral L3/4 DRGs. Unilateral L3/4 DRGs from two mice were pooled together. n = 6 to 8 mice per group. One-way ANOVA followed by Tukey post hoc test, F4,16 = 33.704 for Ehmt2 mRNA, F4,19 = 16.879 for G9a-L, F4,19 = 28.072 for G9a-S, and F4,14 = 19.035 for H3K9me2. **P < 0.01 compared to the corresponding vehicle plus sham group; #P < 0.05 or ##P < 0.01 compared to the corresponding vehicle plus CCI group. L, long isoform; S, short isoform. (C and D) The amounts of Ehmt2 mRNA (C), G9a’s two protein isoforms (D), and H3K9me2 protein (D) in the injected L3/4 DRGs 8 weeks after microinjection of AAV5-C/EBPβ or control AAV5-EGFP. n = 6 to 8 mice per group. Two-tailed, independent Student’s t test, *P < 0.05 compared to the corresponding AAV5-EGFP group. (E) Coexpression of Cebpb mRNA with Ehmt2 mRNA in small, medium, and large DRG neurons. Gapdh mRNA was used a positive control. n = 3 biological replicates. M, ladder marker. (F) ChIP analysis of C/EBPβ binding to a fragment of the Ehmt2 gene distal promoter in the ipsilateral L3/4 DRGs on day 7 after CCI or sham surgery. Input, total purified fragments. Ipsilateral L3/4 DRGs from 3 mice were pooled together. n = 9 mice per group. (G to I) The abundance of C/EBPβ, G9a’s two protein isoforms, and H3K9me2 in mouse cultured DRG neurons transduced as indicated. Representative Western blots (G) and a summary of densitometric analysis [C/EBPβ (H) and G9a-L, G9a-S, and H3K9me2 (I)] are shown. n = 5 biological replicates per treatment. One-way ANOVA followed by Tukey post hoc test, F5,29 = 51.42 for C/EBPβ, F5,29 = 19.66 for G9a-L, F5,29 = 27.95 for G9a-S, and F5,29 = 10.16 for H3K9me2. **P < 0.01 compared to the corresponding naïve group; ##P < 0.01 compared to the corresponding C/EBPβ-treated group.

  • Fig. 6 G9a is required for the effect of C/EBPβ in CCI-induced suppression of MOR and Kv1.2 in the ipsilateral DRGs.

    (A and B) Oprm1 and Kcan2 mRNA expression (A) and protein abundance (B) in the ipsilateral L3/4 DRGs 7 days after sham surgery or CCI in the mice pre-microinjected with vehicle, negative control siRNA, or Cebpb siRNA into the ipsilateral L3/4 DRGs. Unilateral L3/4 DRGs were pooled together. n = 6 to 8 mice per group. One-way ANOVA followed by Tukey post hoc test, F4,16 = 13.249 for Oprm1 mRNA, F4,16 = 14.464 for Kcna2 mRNA, F4,19 = 12.658 for MOR protein, and F4,19 = 11.820 for Kv1.2 protein. *P < 0.05 or **P < 0.01 compared to the corresponding vehicle plus sham group; #P < 0.05 compared to the corresponding vehicle plus CCI group. (C and D) Oprm1 and Kcna2 mRNA expression (C) and MOR and Kv1.2 protein abundance (D) in the injected L3/4 DRGs 8 weeks after microinjection of AAV5-C/EBPβ or control AAV5-EGFP. n = 6 to 8 mice per group. Two-tailed, independent Student’s t test, *P < 0.05 compared to the corresponding AAV5-EGFP group. (E and F) Coexpression of Cebpb mRNA with Oprm1 mRNA (E) or Kcna2 mRNA (F) in small, medium, and large DRG neurons. Gapdh mRNA was used as a positive control. n = 3 biological replicates per gene. (G and H) The abundance of C/EBPβ protein, G9a’s two protein isoforms, and H3K9me2 protein (G) and MOR and Kv1.2 protein (H) in cultured DRG neurons from adult wild-type (WT) (G9afl/fl mice) or G9a conditional knockout (KO) mice. The cultured neurons were collected 2 days after they were transduced with AAV5-EGFP or AAV5-C/EBPβ. n = 3 biological replicates per group. One-way ANOVA with Tukey post hoc test, F3,11 = 10.206 for C/EBPβ, F3,11 = 51.332 for G9a-L, F3,11 = 38.517 for G9a-S, F3,11 = 52.955 for H3K9me2, F3,11 = 27.503 for MOR, and F3,11 = 30.199 for Kv1.2. *P < 0.05 or **P < 0.01 compared to the corresponding AAV5-EGFP–treated WT mice; ##P < 0.01 compared to the corresponding the AAV5-C/EBPβ–treated WT mice. (I) Venn diagram of genes from microarray analysis of the DRG in the mice that overexpressed Ehmt2 (11) and from RNA sequencing data of the injured DRG in a neuropathic pain mouse model treated with a G9a inhibitor (21). About 254 genes overlapped between these two databases.

  • Fig. 7 Blocking CCI-induced increase in C/EBPβ in the DRG improves MOR-mediated analgesia under CCI-induced neuropathic pain conditions.

    (A) Effect of pre-microinjection of Cebpb siRNA or vehicle into the ipsilateral DRG on morphine (1 mg/kg, subcutaneously) analgesia on the ipsilateral side 3 days after CCI. n = 9 mice per group. One-way ANOVA with Tukey post hoc test, F2,26 = 7.833 on the ipsilateral side and F2,26 = 0.969 on the contralateral side. *P < 0.05 compared to the corresponding vehicle plus sham group. #P < 0.01 compared to the corresponding vehicle plus CCI group. MPAE, maximal possible analgesic effect. (B) Effect of intraperitoneal injection with methylnaltrexone (2 mg/kg) on the Cebpb siRNA–produced antinociceptive effect on day 4 after CCI on the ipsilateral side of the Cebpb siRNA–treated group. Paw withdrawal latency to thermal stimulation was measured before and 30 min after drug administration on day 4 after CCI or sham surgery. n = 9 mice per group. Two-way ANOVA with Tukey post hoc test, F2,80 = 109.908 on the ipsilateral side and F2,80 = 0.718 on the contralateral side. **P < 0.01 compared to the corresponding vehicle plus sham group −1 day after CCI or sham surgery. #P < 0.05 compared to the vehicle plus CCI group before drug administration on day 4 after CCI or sham surgery. $P < 0.05 compared to the Cebpb siRNA plus CCI group before drug administration on day 4 after CCI or sham surgery.

  • Table 1 Mean changes in locomotor function.

    SEM given in parentheses. n = 10 mice per group; five trials.

    Treatment groupsLocomotor functional test
    PlacingGraspingRighting
    Vehicle + CCI5(0)5(0)5(0)
    Cebpb siRNA + CCI5(0)5(0)5(0)
    Cebpb siRNA + sham5(0)5(0)5(0)
    Negative control siRNA + CCI5(0)5(0)5(0)
    AAV5-EGFP5(0)5(0)5(0)
    AAV5-C/EBPβ5(0)5(0)5(0)
    Saline (5 μl)5(0)5(0)5(0)
    Lidocaine (0.8%, 5 μl)5(0)5(0)5(0)

Supplementary Materials

  • www.sciencesignaling.org/cgi/content/full/10/487/eaam5345/DC1

    Fig. S1. Changes in Cebpb mRNA expression and C/EBPβ protein abundance in the DRG and spinal cord after sham surgery.

    Fig. S2. Colocalization of Cebpb mRNA with ATF3 in DRG neurons.

    Table S1. List of 254 overlapping genes from microarray and RNA sequencing databases.

    Table S2. Primer sequences.

  • Supplementary Materials for:

    The transcription factor C/EBPβ in the dorsal root ganglion contributes to peripheral nerve traumaâ€"induced nociceptive hypersensitivity

    Zhisong Li, Yuanyuan Mao, Lingli Liang, Shaogen Wu, Jingjing Yuan, Kai Mo, Weihua Cai, Qingxiang Mao, Jing Cao, Alex Bekker, Wei Zhang,* Yuan-Xiang Tao*

    *Corresponding author. Email: yuanxiang.tao{at}njms.rutgers.edu (Y.-X.T.); zhangw571012{at}126.com (W.Z.)

    This PDF file includes:

    • Fig. S1. Changes in Cebpb mRNA expression and C/EBPβ protein abundance in the DRG and spinal cord after sham surgery.
    • Fig. S2. Colocalization of Cebpb mRNA with ATF3 in DRG neurons.
    • Table S1. List of 254 overlapping genes from microarray and RNA sequencing databases.
    • Table S2. Primer sequences.

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    Citation: Z. Li, Y. Mao, L. Liang, S. Wu, J. Yuan, K. Mo, W. Cai, Q. Mao, J. Cao, A. Bekker, W. Zhang, Y.-X. Tao, The transcription factor C/EBPβ in the dorsal root ganglion contributes to peripheral nerve traumaâ€"induced nociceptive hypersensitivity. Sci. Signal. 10, eaam5345 (2017).

    © 2017 American Association for the Advancement of Science

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