CC chemokine ligand 2 upregulates the current density and expression of TRPV1 channels and Nav1.8 sodium channels in dorsal root ganglion neurons.
CC chemokine ligand 2 upregulates the current density and expression of TRPV1 channels and Nav1.8 sodium channels in dorsal root ganglion neurons.
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DOI：
10.1186/1742-2094-9-189
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发表时间：
2012-08-08
影响因子：
9.3
通讯作者：
Wang HL
中科院分区：
文献类型：
--
作者：
Kao DJ;Li AH;Chen JC;Luo RS;Chen YL;Lu JC;Wang HL
炎症或神经损伤诱导的趋化因子CC趋化因子配体2 （CCL2）在背根神经节（DRG）内的上调和释放被认为可增强DRG伤害性神经元的活性并引起痛觉过敏。瞬时受体电位香草素受体1 （TRPV1）和抗河豚毒素（TTX）的Nav1.8钠通道在调节DRG伤害性神经元的兴奋性和疼痛传递中起重要作用。因此，我们验证了CCL2通过上调TRPV1和Nav1.8通道的功能和表达导致伤害性DRG神经元外周敏化的假设。取3周龄的Sprague-Dawley大鼠制备DRG神经元培养物，用不同浓度的CCL2孵育24 ~ 36小时。全细胞电压钳记录TRPV1激动剂辣椒素引起的内向电流或ttx不敏感的Na+电流来自对照或ccl2处理的小DRG感觉神经元。实时定量RT-PCR检测CCL2对TRPV1或Nav1.8 mRNA表达的影响。CCL2预处理24 ~ 36小时（EC50值= 0.6±0.05 nM），辣椒素诱导的小DRG伤害性神经元电流密度呈剂量依赖性增加。在5 nM CCL2预孵育的DRG神经元中，TRPV1 mRNA的表达显著上调。CCL2预处理小DRG感觉神经元后，ttx耐钠电流密度呈浓度依赖性增加（EC50值= 0.7±0.06 nM）。CCL2预处理后DRG神经元中Nav1.8 mRNA水平显著升高。相比之下，CCL2预孵育未能影响耐ttx的Nav1.9的mRNA水平。在特异性磷脂酰肌醇-3激酶（PI3K）抑制剂LY294002或Akt抑制剂IV存在的情况下，CCL2预处理不能增加辣椒素诱导的内向电流或ttx不敏感Na+电流的电流密度以及TRPV1或Nav1.8的mRNA水平。结果表明，CCL2通过激活PI3K/Akt信号通路，提高DRG小感觉神经元TRPV1通道和Nav1.8钠通道的功能和mRNA水平。这些结果提示，在组织炎症或周围神经损伤后，DRG内CCL2的上调和释放可促进DRG痛觉神经元介导的疼痛传递，并可通过上调DRG痛觉神经元中TRPV1和Nav1.8通道的表达和功能诱导痛觉过敏。
Inflammation or nerve injury-induced upregulation and release of chemokine CC chemokine ligand 2 (CCL2) within the dorsal root ganglion (DRG) is believed to enhance the activity of DRG nociceptive neurons and cause hyperalgesia. Transient receptor potential vanilloid receptor 1 (TRPV1) and tetrodotoxin (TTX)-resistant Nav1.8 sodium channels play an essential role in regulating the excitability and pain transmission of DRG nociceptive neurons. We therefore tested the hypothesis that CCL2 causes peripheral sensitization of nociceptive DRG neurons by upregulating the function and expression of TRPV1 and Nav1.8 channels. DRG neuronal culture was prepared from 3-week-old Sprague–Dawley rats and incubated with various concentrations of CCL2 for 24 to 36 hours. Whole-cell voltage-clamp recordings were performed to record TRPV1 agonist capsaicin-evoked inward currents or TTX-insensitive Na+ currents from control or CCL2-treated small DRG sensory neurons. The CCL2 effect on the mRNA expression of TRPV1 or Nav1.8 was measured by real-time quantitative RT-PCR assay. Pretreatment of CCL2 for 24 to 36 hours dose-dependently (EC50 value = 0.6 ± 0.05 nM) increased the density of capsaicin-induced currents in small putative DRG nociceptive neurons. TRPV1 mRNA expression was greatly upregulated in DRG neurons preincubated with 5 nM CCL2. Pretreating small DRG sensory neurons with CCL2 also increased the density of TTX-resistant Na+ currents with a concentration-dependent manner (EC50 value = 0.7 ± 0.06 nM). The Nav1.8 mRNA level was significantly increased in DRG neurons pretreated with CCL2. In contrast, CCL2 preincubation failed to affect the mRNA level of TTX-resistant Nav1.9. In the presence of the specific phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002 or Akt inhibitor IV, CCL2 pretreatment failed to increase the current density of capsaicin-evoked inward currents or TTX-insensitive Na+ currents and the mRNA level of TRPV1 or Nav1.8. Our results showed that CCL2 increased the function and mRNA level of TRPV1 channels and Nav1.8 sodium channels in small DRG sensory neurons via activating the PI3K/Akt signaling pathway. These findings suggest that following tissue inflammation or peripheral nerve injury, upregulation and release of CCL2 within the DRG could facilitate pain transmission mediated by nociceptive DRG neurons and could induce hyperalgesia by upregulating the expression and function of TRPV1 and Nav1.8 channels in DRG nociceptive neurons.
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