The Transmembrane Protein 16A Ca²⁺-activated Cl⁻ Channel in Airway Smooth Muscle Contributes to Airway Hyperresponsiveness

Abstract

Rationale: Asthma is a chronic inflammatory disorder with a characteristic of airway hyperresponsiveness (AHR). Ca 21 -activated Cl 2 [Cl (Ca) ] channels are inferred to be involved in AHR, yet their molecular nature and the cell type they act within to mediate this response remain unknown. Objectives: Transmembrane protein 16A (TMEM16A) and TMEM16B are Cl (Ca) channels, and activation of Cl (Ca) channels in airway smooth muscle (ASM) contributes to agonist-induced airway contraction. We hypothesized that Tmem16a and/or Tmem16b encode Cl (Ca) channels in ASM and mediate AHR. Methods:We assessed the expression of the TMEM16 family, and the effects of niflumic acid and benzbromarone on AHR and airway contraction, in an ovalbumin-sensitized mouse model of chronic asthma. We also cloned TMEM16A from ASM and examined the Cl 2 currents it produced in HEK293 cells. We further studied the impacts of TMEM16A deletion on Ca 21 agonist-induced cell shortening, and on Cl (Ca) (Ca) currents, and weakens caffeine-and methacholineinduced cell shortening. Conclusions: Tmem16a encodes Cl (Ca) channels in ASM and contributes to Ca 21 agonist-induced contraction. In addition, up-regulation of TMEM16A and its augmented activation contribute to AHR in an ovalbumin-sensitized mouse model of chronic asthma. TMEM16A may represent a potential therapeutic target for asthma.Keywords: TMEM16A; airway smooth muscle; airway hyperresponsiveness Asthma, affecting 300 million people worldwide, is characterized by chronic inflammation, mucus overproduction, reversible airway obstruction, and airway hyperresponsiveness (AHR). AHR is a heightened tendency to airway narrowing in response to nonspecific contractile agents, and underlies much of the pathology of asthmatic symptoms. Although intensively studied, the cellular and molecular mechanisms underlying AHR remain only partially understood and controversial. A number of studies have implied that Ca 21 -activated Cl 2 [Cl (Ca) ] channels are involved in AHR. Gene expression profile studies have consistently revealed that type 3 Cl (Ca) channels (mCLCA3) are highly upregulated in mouse models of asthma (1-6), and hCLCA1, the human counterpart of mCLCA3, is significantly more abundant in the airway epithelium of patients with asthma (4, 7, 8). Moreover, suppressing the expression of mCLCA3 or hCLCA1 by antisense or its function by niflumic acid, a relatively selective inhibitor of Cl (Ca) channels, prevents allergen-or helper T-cell type 2 (Th2) cytokine (e.g., IL-13)-induced mucus overproduction and AHR (5, 9-11). Not surprisingly, mCLCA3/hCLCA1 Supported by the National Natural Science Foundation of China (grant 31272311) (to M.-S.Z.) and the Natural Science Foundation of Zhejiang Province (Y2100346) (to H.L.), and by U.S. National Heart, Lung, and Blood Institute grant HL73875 (to R.Z.G.).Author Contributions: C.-H.Z., Y.L., W.Z., and H.L. performed research; B.D.H. provided TMEM16A null mice; L.M.L. performed data analysis and edited the paper; M.-S.Z. designed and supervised the stu...

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