Rumzhum Nowshin N, Rahman M Mostafizur, Oliver Brian G, Ammit Alaina J
1 Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia.
2 Woolcock Institute of Medical Research, University of Sydney, New South Wales, Australia; and.
Am J Respir Cell Mol Biol. 2016 Jan;54(1):128-35. doi: 10.1165/rcmb.2014-0443OC.
Tachyphylaxis of the β2-adrenergic receptor limits the efficacy of bronchodilatory β2-agonists in respiratory disease. Cellular studies in airway smooth muscle (ASM) have shown that inflammatory mediators and infectious stimuli reduce β2-adrenergic responsiveness in a cyclo-oxygenase (COX)-2-mediated, prostaglandin E2 (PGE2)-dependant manner. Herein, we show that sphingosine 1-phosphate (S1P), a bioactive sphingolipid that plays an important role in pathophysiology of asthma, also induces β2-adrenergic receptor desensitization in bronchial ASM cells and exerts hyporesponsiveness to β2-agonists. We treated ASM cells with S1P (1 μM) for up to 24 hours and then examined the temporal kinetics of COX-2 mRNA expression, protein up-regulation, and PGE2 secretion. S1P significantly enhanced COX-2 expression and PGE2 secretion, and this was repressed by the selective COX-2 inhibitor celecoxib, the corticosteroid dexamethasone, or small interfering RNA (siRNA) knockdown of COX-2 expression. In combination with another proinflammatory mediator found elevated in asthmatic airways, the cytokine TNF-α, we observed that S1P-induced COX-2 mRNA expression and protein up-regulation and PGE2 secretion from ASM cells were significantly enhanced. Notably, S1P induced heterologous β2-adrenergic desensitization, as measured by inhibition of cyclic adenosine monophosphate production in response to the short-acting β2-agonist, salbutamol, and the long-acting β2-agonist, formoterol. Taken together, these data indicate that S1P represses β2-adrenergic activity in ASM cells by increasing COX-2-mediated PGE2 production, and suggest that this bioactive sphingolipid found elevated in asthma may contribute to β2-adrenergic desensitization.
β2肾上腺素能受体的快速耐受性限制了支气管扩张性β2激动剂在呼吸系统疾病中的疗效。气道平滑肌（ASM）的细胞研究表明，炎症介质和感染性刺激以环氧化酶（COX）-2介导、前列腺素E2（PGE2）依赖的方式降低β2肾上腺素能反应性。在此，我们表明，1-磷酸鞘氨醇（S1P），一种在哮喘病理生理学中起重要作用的生物活性鞘脂，也可诱导支气管ASM细胞中的β2肾上腺素能受体脱敏，并对β2激动剂产生低反应性。我们用S1P（1μM）处理ASM细胞长达24小时，然后检测COX-2 mRNA表达、蛋白上调和PGE2分泌的时间动力学。S1P显著增强了COX-2表达和PGE2分泌，而选择性COX-2抑制剂塞来昔布、皮质类固醇地塞米松或COX-2表达的小干扰RNA（siRNA）敲低可抑制这种增强。与在哮喘气道中发现升高的另一种促炎介质细胞因子肿瘤坏死因子-α联合使用时，我们观察到S1P诱导的ASM细胞COX-2 mRNA表达、蛋白上调和PGE2分泌显著增强。值得注意的是，通过抑制对短效β2激动剂沙丁胺醇和长效β2激动剂福莫特罗的反应中环磷酸腺苷的产生来测量，S1P诱导了异源性β2肾上腺素能脱敏。综上所述，这些数据表明S1P通过增加COX-2介导的PGE2产生来抑制ASM细胞中的β2肾上腺素能活性，并表明在哮喘中发现升高的这种生物活性鞘脂可能导致β2肾上腺素能脱敏。
