Airway hyperresponsiveness (AHR) and inflammation are key pathophysiological features of asthma. Enhanced contraction of bronchial smooth muscle (BSM) is one of the causes of the AHR. It is thus important for development of asthma therapy to understand the change in the contractile signaling of airway smooth muscle cells associated with the AHR. In addition to the Ca2+-mediated phosphorylation of myosin light chain (MLC), contractile agonists also enhance MLC phosphorylation level, Ca2+-independently, by inactivating MLC phosphatase (MLCP), called Ca2+ sensitization of contraction, in smooth muscle cells including airways. To date, involvements of RhoA/ROCKs and PKC/Ppp1r14a (also called as CPI-17) pathways in the Ca2+ sensitization have been identified. Our previous studies revealed that the agonist-induced Ca2+ sensitization of contraction is markedly augmented in BSMs of animal models of allergen-induced AHR. In BSMs of these animal models, the expression of RhoA and CPI-17 proteins were significantly increased, indicating that both the Ca2+ sensitizing pathways are augmented. Interestingly, incubation of BSM cells with asthma-associated cytokines, such as interleukin-13 (IL-13), IL-17, and tumor necrosis factor-α (TNF-α), caused up-regulations of RhoA and CPI-17 in BSM cells of naive animals and cultured human BSM cells. In addition to the transcription factors such as STAT6 and NF-κB activated by these inflammatory cytokines, an involvement of down-regulation of miR-133a, a microRNA that negatively regulates RhoA translation, has also been suggested in the IL-13- and IL-17-induced up-regulation of RhoA. Thus, the Ca2+ sensitizing pathways and the cytokine-mediated signaling including microRNAs in BSMs might be potential targets for treatment of allergic asthma, especially the AHR.

These findings indicate that IL-17 directly acts on BSM cells and up-regulates RhoA protein probably via a down-regulation of miR-133a-3p, resulting in an induction of the BSM hyperresponsiveness.

Progranulin (PGRN) is a growth factor with multiple biological functions and has been suggested as an endogenous inhibitor of Tumor necrosis factor-α (TNF-α)-mediated signaling. TNF-α is believed to be one of the important mediators of the pathogenesis of asthma, including airway hyperresponsiveness (AHR). In the present study, effects of recombinant PGRN on TNF-α-mediated signaling and antigen-induced hypercontractility were examined in bronchial smooth muscles (BSMs) both in vitro and in vivo. Cultured human BSM cells (hBSMCs) and male BALB/c mice were used. The mice were sensitized and repeatedly challenged with ovalbumin antigen. Animals also received intranasal administrations of recombinant PGRN into the airways 1 h before each antigen inhalation. In hBSMCs, PGRN inhibited both the degradation of IκB-α (an index of NF-κB activation) and the upregulation of RhoA (a contractile machinery-associated protein that contributes to the BSM hyperresponsiveness) induced by TNF-α, indicating that PGRN has an ability to inhibit TNF-α-mediated signaling also in the BSM cells. In BSMs of the repeatedly antigen-challenged mice, an augmented contractile responsiveness to acetylcholine with an upregulation of RhoA was observed: both the events were ameliorated by pretreatments with PGRN intranasally. Interestingly, a significant decrease in PGRN expression was found in the airways of the repeatedly antigen-challenged mice rather than those of control animals. In conclusion, exogenously applied PGRN into the airways ameliorated the antigen-induced BSM hyperresponsiveness, probably by blocking TNF-α-mediated response. Increasing PGRN levels might be a promising therapeutic for AHR in allergic asthma.

RationaleAugmented smooth muscle contractility of the airways is one of the causes of airway hyperresponsiveness in asthmatics. However, the mechanism of the altered properties of airway smooth muscle cells is not well understood.ObjectivesTo identify differentially expressed genes (DEGs) related to the bronchial smooth muscle (BSM) hyper-contractility in a murine asthma model.MethodsThe ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Transcriptomic profiles were generated by microarray analysis of BSM tissues from the OA-challenged and control animals, and KEGG (Kyoto Encyclopedia of Genes and Genomes) Pathway Analysis was applied.Measurements and main resultsTension study showed a BSM hyperresponsiveness to acetylcholine (ACh) in the OA-challenged mice. A total of 770 genes were differentially expressed between the OA-challenged and control animals. Pathway analysis showed a significant change in arachidonic acid (AA) metabolism pathway in BSM tissues of the OA-challenged mice. Validation of DEGs by quantitative RT-PCR showed a significant increase in PLA2 group 4c (Pla2g4c)/COX-2 (Ptgs2)/PGD2 synthase 2 (Hpgds) axis. PGD2 level in bronchoalveolar fluids of the OA-challenged mice was significantly increased. A 24-h incubation of BSM tissues with PGD2 caused a hyperresponsiveness to ACh in naive control mice.ConclusionsAA metabolism is shifted towards PGD2 production in BSM tissues of asthma. Increased PGD2 level in the airways might be a cause of the BSM hyperresponsiveness in asthma.

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