Hu Aihua, Nino Gustavo, Grunstein Judith S, Fatma Sumbul, Grunstein Michael M
The Joseph Stokes Jr. Research Institute, Division of Pulmonary Medicine, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Am J Physiol Lung Cell Mol Physiol. 2008 Jun;294(6):L1055-67. doi: 10.1152/ajplung.00021.2008. Epub 2008 Mar 21.
Beta2-adrenergic receptor (beta2AR) agonists acutely relieve bronchoconstriction via cAMP-mediated relaxation of airway smooth muscle (ASM). Airway constrictor responsiveness may be significantly heightened, however, following protracted exposure to these agents, presumably reflecting the effects of beta2AR desensitization in ASM accompanying prolonged cAMP signaling. Because cAMP phosphodiesterase (PDE) activity can significantly modulate ASM contractility, we investigated the mechanism regulating PDE expression and its potential role in mediating changes in agonist-induced constrictor and relaxation responsiveness in ASM following its heterologous beta2AR desensitization by prolonged exposure to cAMP-elevating agents. Isolated rabbit ASM tissues and cultured human ASM cells treated for 24 h with the receptor- or nonreceptor-coupled cAMP-stimulating agent, prostaglandin E(2) (PGE(2)) or forskolin, respectively, exhibited constrictor hyperresponsiveness to acetylcholine and impaired beta2AR-mediated relaxation and cAMP accumulation. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity, reflective of increased transcription of the PDE4D5 isoform, and were prevented by pretreatment of the ASM with a PDE4 inhibitor. Extended studies using gene silencing and pharmacological approaches to inhibit specific intracellular signaling molecules demonstrated that the mechanism underlying PGE(2)-induced transcriptional upregulation of PDE4D5 involves PKA-dependent activation of G(i) protein signaling via the betagamma-subunits, the latter eliciting downstream activation of ERK1/2 and its consequent induction of PDE4D5 transcription. Collectively, these findings identify that beta2AR desensitization in ASM following prolonged exposure to cAMP-elevating agents is associated with proasthmatic-like changes in ASM responsiveness that are mediated by upregulated PDE4 expression induced by activated cross talk between the PKA and ERK1/2 signaling pathways.
β2-肾上腺素能受体（β2AR）激动剂可通过环磷酸腺苷（cAMP）介导的气道平滑肌（ASM）舒张来急性缓解支气管收缩。然而，在长期接触这些药物后，气道收缩反应性可能会显著增强，这可能反映了ASM中β2AR脱敏伴随cAMP信号延长的影响。由于cAMP磷酸二酯酶（PDE）活性可显著调节ASM收缩性，我们研究了调节PDE表达的机制及其在介导ASM因长期暴露于升高cAMP的药物而发生异源β2AR脱敏后激动剂诱导的收缩和舒张反应性变化中的潜在作用。分别用受体或非受体偶联的cAMP刺激剂前列腺素E2（PGE2）或福斯可林处理24小时的离体兔ASM组织和培养的人ASM细胞，对乙酰胆碱表现出收缩反应性增强，β2AR介导的舒张和cAMP积累受损。ASM功能的这些类似哮喘的变化与PDE4活性上调有关，这反映了PDE4D5亚型转录增加，并且通过用PDE4抑制剂预处理ASM来预防。使用基因沉默和药理学方法抑制特定细胞内信号分子的扩展研究表明，PGE2诱导的PDE4D5转录上调的机制涉及PKA通过βγ亚基依赖性激活G（i）蛋白信号，后者引发ERK1/2的下游激活及其随后对PDE4D5转录的诱导。总体而言，这些发现表明，长期暴露于升高cAMP的药物后ASM中的β2AR脱敏与ASM反应性的类似哮喘的变化有关，这些变化由PKA和ERK1/2信号通路之间的激活串扰诱导的PDE4表达上调介导。
