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Down-Regulation of miR-133a Contributes to Up-Regulation of RhoA in Bronchial Smooth Muscle Cells

¹ Department of Pharmacology, School of Pharmacy, Hoshi University, Tokyo, Japan

Correspondence and requests for reprints should be addressed to Yoshihiko Chiba, Ph.D., Department of Pharmacology, School of Pharmacy, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan. E-mail: chiba{at}hoshi.ac.jp

Rationale: Augmented bronchial smooth muscle (BSM) contraction is one of the causes of bronchial hyperresponsiveness. The protein RhoA and its downstream pathways have now been proposed as a new target for asthma therapy. MicroRNAs (miRNAs) play important roles in normal and diseased cell functions, and a contribution of miR-133 to RhoA expression has been suggested in cardiomyocytes.

Objectives: To make clear the mechanism(s) of up-regulation of RhoA observed in the BSMs of experimental asthma, the role of miR-133a in RhoA expression was tested.

Methods: Total proteins and RNAs (containing miRNAs) were extracted from cultured human BSM cells (hBSMCs) that were treated with antagomirs and/or IL-13, and bronchial tissues of BALB/c mice that were sensitized and repeatedly challenged with ovalbumin. RhoA protein and miR-133a were detected by immunoblotting and quantified real-time reverse transcriptase–polymerase chain reaction, respectively.

Measurements and Main Results: In hBSMCs, an up-regulation of RhoA was observed when the function of endogenous miR-133a was inhibited by its antagomir. Treatment of hBSMCs with IL-13 caused an up-regulation of RhoA and a down-regulation of miR-133a. In bronchial tissues of the repeatedly ovalbumin-challenged mice, a significant increase in RhoA was observed. Interestingly, the level of miR-133a was significantly decreased in BSMs of the challenged mice.

Conclusions: These findings suggest that RhoA expression is negatively regulated by miR-133a in BSMs. IL-13 might, at least in part, contribute to the reduction of miR-133a.

Key Words: microRNA (miRNA) • miR-133a • RhoA • asthma • bronchial smooth muscle hyperresponsiveness

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject RhoA is one of the key proteins of bronchial smooth muscle (BSM) contraction and up-regulation of RhoA has been demonstrated in rodent BSMs of experimental asthma models. The mechanism(s) of up-regulation of RhoA is unclear, although the contribution of a microRNA, miR-133, to RhoA expression has been suggested in cardiomyocytes. What This Study Adds to the Field Our data show that miR-133a is a key regulator of BSM RhoA expression and provide new insights into the treatment of airway hyperresponsiveness in asthma.