Shen Shanwei, Al-Thumairy Hamad W, Hashmi Fiza, Qiao Li-Ya
Departments of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University, Richmond, VA, USA.
Departments of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University, Richmond, VA, USA.
Exp Neurol. 2017 Sep;295:104-115. doi: 10.1016/j.expneurol.2017.06.007. Epub 2017 Jun 3.
The transient receptor potential cation channel subfamily V member 1 (TRPV1), also known as the capsaicin receptor or vanilloid receptor 1 (VR1), is expressed in nociceptive neurons in the dorsal root ganglia (DRG) and participates in the transmission of pain. The present study investigated the underlying molecular mechanisms by which TRPV1 was regulated by nerve growth factor (NGF) signaling pathways in colonic hypersensitivity in response to colitis. We found that during colitis TRPV1 protein levels were significantly increased in specifically labeled colonic afferent neurons in both L1 and S1 DRGs. TRPV1 protein up-regulation in DRG was also enhanced by NGF treatment. We then found that TRPV1 protein up-regulation in DRG was regulated by activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway both in vivo and in vitro. Suppression of endogenous PI3K/Akt activity during colitis or NGF treatment with a specific PI3K inhibitor LY294002 reduced TRPV1 protein production in DRG neurons, and also reduced colitis-evoked TRPV1-mediated visceral hypersensitivity tested by hyper-responsiveness to colorectal distention (CRD) and von Frey filament stimulation of abdomen. Further studies showed that TRPV1 mRNA levels in the DRG were not regulated by either colitis or NGF. We then found that an up-regulation of the protein synthesis pathway was involved by which both colitis and NGF caused a PI3K-dependent increase in the phosphorylation level of eukaryotic translation initiation factor 4E-binding protein (4E-BP)1. These results suggest a novel mechanism in colonic hypersensitivity which involves PI3K/Akt-mediated TRPV1 protein, not mRNA, up-regulation in primary afferent neurons, likely through activation of the protein synthesis pathways.
瞬时受体电位阳离子通道亚家族V成员1（TRPV1），也被称为辣椒素受体或香草酸受体1（VR1），在背根神经节（DRG）的伤害性神经元中表达，并参与疼痛的传递。本研究调查了在结肠炎引起的结肠超敏反应中，TRPV1受神经生长因子（NGF）信号通路调控的潜在分子机制。我们发现，在结肠炎期间，L1和S1 DRG中特异性标记的结肠传入神经元中TRPV1蛋白水平显著增加。NGF处理也增强了DRG中TRPV1蛋白的上调。然后我们发现，DRG中TRPV1蛋白的上调在体内和体外均受磷酸肌醇3激酶（PI3K）/Akt通路激活的调控。在用特异性PI3K抑制剂LY294002进行结肠炎或NGF处理期间，抑制内源性PI3K/Akt活性可降低DRG神经元中TRPV1蛋白的产生，也可降低通过对结直肠扩张（CRD）的高反应性和腹部的von Frey细丝刺激测试的结肠炎诱发的TRPV1介导的内脏超敏反应。进一步研究表明，DRG中的TRPV1 mRNA水平不受结肠炎或NGF的调控。然后我们发现，蛋白质合成途径的上调参与其中，结肠炎和NGF均可通过该途径导致真核翻译起始因子4E结合蛋白（4E-BP）1的磷酸化水平呈PI3K依赖性增加。这些结果提示了结肠超敏反应中的一种新机制，该机制涉及PI3K/Akt介导的初级传入神经元中TRPV1蛋白而非mRNA的上调，可能是通过激活蛋白质合成途径实现的。
