Wu Hong, Guan Chaxiang, Qin Xiaoqun, Xiang Yang, Qi Mingming, Luo Ziqiang, Zhang Changqing
Department of Physiology, Xiangya School of Medicine, Central South University, Changsha, Hunan 410078, PR China.
Pulm Pharmacol Ther. 2007;20(5):513-24. doi: 10.1016/j.pupt.2006.04.002. Epub 2006 May 3.
Airway hyperresponsiveness (AHR) is present in almost all patients with symptomatic asthma, yet its mechanism is not well understood. Airway inflammation is thought to be an important underlying mechanism involved in causing AHR. Recent studies indicate release of neuropeptides from C-fiber endings plays a pivotal role in airway inflammation. Substance P (SP) is a critical neurotransmitter of sensory C-fiber and a well-known effector of inflammatory response. However, roles of other neuropeptides and interaction among these neuropeptides in airway inflammation and AHR were largely unknown. Calcitonin gene-related peptide (CGRP), another intrapulmonary neuropeptide that functions as a potent vasodilator and neutrophils activator, is released from the same C-fiber ending as SP is released. By using an ozone-stressing animal model, previously we had demonstrated that CGRP might be involved in the development of AHR in rabbits. To extend the functional roles of SP, and to explore the possible interactive roles of SP and CGRP in airway inflammation, we examined expressions of SP, SP receptor (neurokinin 1, or NK-1R) and CGRP in vivo and ex vivo. We exposed guinea pigs at intervals to inhalation of ozone to induce airway inflammation. Animals were sacrificed at different time points; SP, SP receptor and CGRP expression were determined during the onset and progression of airway inflammation by radioimmunoassay, immunohistochemistry and in situ hybridization. Our data showed that after exposure to ozone, the concentration of SP in lung homogenate and the number of SP-immunoreactive cell bodies in lung slides increased within 24h, peaked on day 2, and then decreased slowly. Interestingly, CGRP expressions exhibited a similar temporal and spatial pattern, and there was a strong correlation between SP expression and CGRP expression, indicating a possible cooperative action of these two neuropeptides. We also noted an increased expression of SP receptor NK-1R in the development of airway inflammation. In order to test the hypothesis that CGRP as a coexisting neurotransmitter with SP can regulate the expression of NK-1R in the lung, and contribute to the SP-mediated inflammatory response, we used in vitro lung tissue culture to determine the effect of CGRP on NK-1R expression. We found that NK-1R expression was induced by CGRP incubation at both mRNA and protein levels, and the induction was attenuated by additions of the inhibitors of Protein Kinase A (PKA) pathway, Calmodulin-dependent Kinase pathway, and Tyrosine Protein Kinase pathway. In conclusion, our data provide compelling evidence that SP and CGRP are involved in the development of airway inflammation. The interaction between SP and CGRP is likely to contribute to the pathogenesis of AHR and other lung inflammatory diseases.
气道高反应性（AHR）几乎在所有有症状的哮喘患者中都存在，但其机制尚未完全明确。气道炎症被认为是导致AHR的一个重要潜在机制。最近的研究表明，C纤维末梢释放的神经肽在气道炎症中起关键作用。P物质（SP）是感觉C纤维的一种关键神经递质，也是一种众所周知的炎症反应效应物。然而，其他神经肽在气道炎症和AHR中的作用以及这些神经肽之间的相互作用在很大程度上尚不清楚。降钙素基因相关肽（CGRP）是另一种肺内神经肽，具有强大的血管舒张和中性粒细胞激活功能，它与SP从同一C纤维末梢释放。通过使用臭氧应激动物模型，我们之前已经证明CGRP可能参与了兔子AHR的发生发展。为了扩展SP的功能作用，并探讨SP和CGRP在气道炎症中可能的相互作用，我们检测了SP、SP受体（神经激肽1，或NK-1R）和CGRP在体内和体外的表达。我们让豚鼠间歇性吸入臭氧以诱导气道炎症。在不同时间点处死动物；通过放射免疫分析、免疫组织化学和原位杂交在气道炎症的发生和进展过程中测定SP、SP受体和CGRP的表达。我们的数据显示，暴露于臭氧后，肺匀浆中SP的浓度和肺切片中SP免疫反应性细胞体的数量在24小时内增加，在第2天达到峰值，然后缓慢下降。有趣的是，CGRP的表达呈现出类似的时空模式，并且SP表达与CGRP表达之间存在很强的相关性，表明这两种神经肽可能存在协同作用。我们还注意到在气道炎症发展过程中SP受体NK-1R的表达增加。为了验证CGRP作为与SP共存的神经递质可以调节肺中NK-1R的表达，并促进SP介导的炎症反应这一假设，我们使用体外肺组织培养来确定CGRP对NK-1R表达的影响。我们发现，CGRP孵育在mRNA和蛋白质水平均诱导NK-1R表达，并且添加蛋白激酶A（PKA）途径、钙调蛋白依赖性激酶途径和酪氨酸蛋白激酶途径的抑制剂可减弱这种诱导作用。总之，我们的数据提供了令人信服的证据，表明SP和CGRP参与了气道炎症的发生发展。SP和CGRP之间的相互作用可能有助于AHR和其他肺部炎症性疾病的发病机制。
