Acetylcholine-induced translocation of RhoA in freshly isolated single smooth muscle cells of rat bronchi

Targeting of G-protein coupled receptor 40 alleviates airway hyperresponsiveness through RhoA/ROCK1 signaling pathway in obese asthmatic mice

Obesity increases the severity of airway hyperresponsiveness (AHR) in individuals with asthma, but the mechanism is not well elucidated. G-protein coupled receptor 40 (GPR40) has been found to induce airway smooth muscle contraction after activated by long-chain fatty acids (LC-FFAs), suggesting a close correlation between GPR40 and AHR in obese. In this study, C57BL/6 mice were fed a high-fat diet (HFD) to induce obesity with or without ovalbumin (OVA) sensitization, the regulatory effects of GPR40 on AHR, inflammatory cells infiltration, and the expression of Th1/Th2 cytokines were evaluated by using a small-molecule antagonist of GPR40, DC260126. We found that the free fatty acids (FFAs) level and GPR40 expression were greatly elevated in the pulmonary tissues of obese asthmatic mice. DC260126 greatly reduced methacholine-induced AHR, ameliorated pulmonary pathological changes and decreased inflammatory cell infiltration in the airways in obese asthma. In addition, DC260126 could down-regulate the levels of Th2 cytokines (IL-4, IL-5, and IL-13) and pro-inflammatory cytokines (IL-1β, TNF-α), but elevated Th1 cytokine (IFN-γ) expression. In vitro, DC260126 could remarkedly reduce oleic acid (OA)-induced cell proliferation and migration in HASM cells. Mechanistically, the effects that DC260126 alleviated obese asthma was correlated with the down-regulation of GTP-RhoA and Rho-associated coiled-coil-forming protein kinase 1 (ROCK1). Herein, we proved that targeting of GPR40 with its antagonist helped to mitigate multiple parameters of obese asthma effectively.

Transforming growth factor-β enhances Rho-kinase activity and contraction in airway smooth muscle via the nucleotide exchange factor ARHGEF1

Key points

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

Abstract

Transforming growth factor‐β (TGF‐β), RhoA/Rho‐kinase and Src‐family kinases (SrcFK) have independently been implicated in airway hyper‐responsiveness, but how they interact to regulate airway smooth muscle contractility is not fully understood. We found that TGF‐β pre‐treatment enhanced acute contractile responses to bradykinin (BK) in isolated rat bronchioles, and inhibitors of RhoGEFs (Y16) and Rho‐kinase (Y27632), but not the SrcFK inhibitor PP2, prevented this enhancement. In cultured human airway smooth muscle cells (hASMCs), TGF‐β pre‐treatment enhanced the protein expression of the Rho guanine nucleotide exchange factor ARHGEF1, MLC₂₀, MYPT‐1 and the actin‐severing protein cofilin, but not of RhoA, ROCK2 or c‐Src. In hASMCs, acute treatment with BK triggered subcellular translocation of ARHGEF1 and RhoA and enhanced auto‐phosphorylation of SrcFK and phosphorylation of MYPT1 and MLC₂₀, but induced de‐phosphorylation of cofilin. TGF‐β pre‐treatment amplified the effects of BK on RhoA translocation and MYPT1/MLC₂₀ phosphorylation, but suppressed the effects of BK on RhoA‐GTP content, SrcFK auto‐phosphorylation and cofilin de‐phosphorylation. In hASMCs, an ARHGEF1 small interfering RNA suppressed the effects of BK and TGF‐β on RhoA‐GTP content, RhoA translocation and MYPT1 and MLC₂₀ phosphorylation, but minimally influenced the effects of TGF‐β on cofilin expression and phosphorylation. ARHGEF1 expression was also enhanced in ASMCs of asthmatic patients and in lungs of ovalbumin‐sensitized mice. Our data indicate that TGF‐β enhances BK‐induced contraction, RhoA translocation and Rho‐kinase activity in airway smooth muscle largely via ARHGEF1, but independently of SrcFK and total RhoA‐GTP content. A role for smooth muscle ARHGEF1 in asthmatic airway hyper‐responsiveness is worthy of further investigation.

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

Immunocytochemical evidence for PDBu-induced activation of RhoA/ROCK in human internal anal sphincter smooth muscle cells

Studies were performed to determine the unknown status of PKC and RhoA/ROCK in the phorbol 12,13-dibutyrate (PDBu)-stimulated state in the human internal anal sphincter (IAS) smooth muscle cells (SMCs). We determined the effects of PDBu (10(-7) M), the PKC activator, on PKCα and RhoA and ROCK II translocation in the human IAS SMCs. We used immunocytochemistry and fluorescence microcopy in the basal state, following PDBu, and before and after PKC inhibitor calphostin C (10(-6) M), cell-permeable RhoA inhibitor C3 exoenzyme (2.5 μg/ml), and ROCK inhibitor Y 27632 (10(-6) M). We also determined changes in the SMC lengths via computerized digital micrometry. In the basal state PKCα was distributed almost uniformly throughout the cell, whereas RhoA and ROCK II were located in the higher intensities toward the periphery. PDBu caused significant translocation of PKCα, RhoA, and ROCK II. PDBu-induced translocation of PKCα was attenuated by calphostin C and not by C3 exoenzyme and Y 27632. However, PDBu-induced translocation of RhoA was blocked by C3 exoenzyme, and that of ROCK II was attenuated by both C3 exoenzyme and Y 27632. Contraction of the human IAS SMCs caused by PDBu in parallel with RhoA/ROCK II translocation was attenuated by C3 exoenzyme and Y 27632 but not by calphostin C. In human IAS SMCs RhoA/ROCK compared with PKC are constitutively active, and contractility by PDBu is associated with RhoA/ROCK activation rather than PKC. The relative contribution of RhoA/ROCK vs. PKC in the pathophysiology and potential therapy for the IAS dysfunction remains to be determined.

MicroRNAs and their therapeutic potential for human diseases: MiR-133a and bronchial smooth muscle hyperresponsiveness in asthma

MicroRNAs (miRNAs) play important roles in normal and diseased cell functions. The small-GTPase RhoA is one of the key proteins of bronchial smooth muscle (BSM) contraction, and an upregulation of RhoA has been demonstrated in BSMs of experimental asthma. Although the mechanism of RhoA upregulation in the diseased BSMs is not fully understood, recent observations suggest that RhoA translation is controlled by a miRNA, miR-133a, in cardiomyocytes. Similarly, in human BSM cells (hBSMCs), our recent studies revealed that an upregulation of RhoA was induced when the function of endogenous miR-133a was inhibited by its antagomir. Treatment of hBSMCs with interleukin-13 (IL-13) caused an upregulation of RhoA and a downregulation of miR-133a. In a mouse model of allergic bronchial asthma, increased expression of IL-13 and RhoA and the BSM hyperresponsiveness were observed. The level of miR-133a was significantly decreased in BSMs of the diseased animals. These findings suggest that RhoA expression is negatively regulated by miR-133a in BSMs and that the miR-133a downregulation causes an upregulation of RhoA, resulting in an augmentation of the contraction. MiR-133a might be a key regulator of BSM hyperresponsiveness and provide us with new insight into the treatment of airway hyperresponsiveness in asthmatics.

RhoA, a possible target for treatment of airway hyperresponsiveness in bronchial asthma

Airway hyperresponsiveness to nonspecific stimuli is one of the characteristic features of allergic bronchial asthma. An elevated contractility of bronchial smooth muscle has been considered as one of the causes of the airway hyperresponsiveness. The contraction of smooth muscles including airway smooth muscles is mediated by both Ca²+-dependent and Ca²+-independent pathways. The latter Ca²+-independent pathway, termed Ca²+ sensitization, is mainly regulated by a monomeric GTP-binding protein, RhoA, and its downstream target Rho-kinase. In animal models of allergic bronchial asthma, an augmented agonist-induced, RhoA-mediated contraction of bronchial smooth muscle has been suggested. The RhoA/Rho-kinase signaling is now proposed as a novel target for the treatment of airway hyperresponsiveness in asthma. Herein, we will discuss the mechanism of development of bronchial smooth muscle hyperresponsiveness, one of the causes of the airway hyperresponsiveness, based on the recent studies using animal models of allergic bronchial asthma and/or cultured airway smooth muscle cells. The possibility of RhoA as a therapeutic target in asthma, especially airway hyperresponsiveness, will also be described.

Galpha13 regulates methacholine-induced contraction of bronchial smooth muscle via phosphorylation of MLC20

Reversible airway constriction is induced by an increase in airway smooth muscle contractility in response to methacholine likely as a bronchospastic stimulus. Despite the finding of Galpha12 and Galpha13 up-regulation in airway hyperresponsive animals, their functional role of contraction in airway smooth muscle has not been directly explored. This study investigated the differential regulatory role of Galpha12/Galpha13 in methacholine-induced contraction of trachea and bronchus in Galpha12 or Galpha13 gene knockout mice after ovalbumin sensitization and challenges. Organ bath assays and videomicroscopy revealed that Galpha13 deficiency delayed methacholine-induced contractile response of bronchiolar smooth muscle, but not that of tracheal smooth muscle. In primary bronchial smooth muscle cells, knockdown of Galpha13 blocked methacholine-induced phosphorylation of 20 kDa regulatory light chain of myosin II (MLC20), a prerequisite step for the contractile initiation of actin and myosin. Galpha13-dependent MLC20 phosphorylation was confirmed in murine embryonic fibroblasts. After ovalbumin sensitization and challenges, wild type mice exhibited methacholine-induced bronchial contraction of lung tissue. Heterozygous absence of the Galpha13 gene abrogated methacholine-induced contractions, whereas homozygous absence of the Galpha12 gene failed to do so. Our findings indicate that Galpha13, but not Galpha12, specifically regulates cholinergic bronchial contraction in airway responsiveness via controlling phosphorylation of MLC20 by methacholine.

Translocation of AT1- and AT2-Receptors by Higher Concentrations of Angiotensin II in the Smooth Muscle Cells of Rat Internal Anal Sphincter

Previous studies have reported bimodal effects by angiotensin II (Ang II) in the rat internal anal sphincter (IAS), a concentration-dependent contraction (at lower concentrations) and relaxation (at higher concentrations). The experiments suggest the above-mentioned responses are the result of Ang II subtype I receptor(s) (AT(1)-R) and subtype II receptor(s) (AT(2)-R) activation, respectively. These studies determined the role and mechanism of AT(2)-R-induced relaxation of the smooth muscle cells (SMCs) from the IAS in response to Ang II. Laser confocal microscopy showed that in the basal state, the AT(1)-Rs reside in the plasma membrane, whereas AT(2)-Rs are present in the cytosol. Higher concentrations of Ang II caused movement of AT(1)-R and AT(2)-R in opposite directions to the cytosol and the membrane, respectively. Losartan (AT(1)-R antagonist) but not S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid (PD123319; AT(2)-R antagonist) selectively inhibited these movements. These results are based on biotinylation assays, confocal images, and Western blot analyses of the densities of AT(1)-Rs and AT(2)-Rs in the plasma membrane versus cytosolic fractions of the IAS SMCs. Ang II in higher concentrations did not change the total contents of Ang II receptors. These data combined with the functional data using measurements of IAS SMC lengths suggest that internalization of AT(1)-R and externalization of AT(2)-R may be responsible for the activation of the AT(2)-R, which leads to the relaxation of the IAS with higher concentrations of Ang II.

Endothelin-1-induced translocation of RhoA is mediated by endothelin ET(A) receptors in rat bronchial smooth muscle

To clarify the receptor subtype(s) contributing to the RhoA activation by endothelin-1 in bronchial smooth muscle, the effects of BQ-123 [cycro(D-Asp-Pro-D-Val-Leu-D-Trp)], an endothelin ET(A) receptor antagonist, and/or BQ-788 [2,6-dimethylpiperidinecarbonyl-g-methyl-Leu-Nin-(Methoxycarbonyl)-D-Trp-D-Nle], an endothelin ET(B) receptor antagonist, on the endothelin-1-induced translocation of RhoA to plasma membrane were examined. Incubation of rat bronchial smooth muscle with endothelin-1 induced a distinct translocation of RhoA to plasma membrane, indicating an activation of RhoA by endothelin-1. The endothelin-1-induced translocation of RhoA was completely blocked by treatment with BQ-123, whereas BQ-788 had no effect. Thus, endothelin ET(A) but not ET(B) receptors might be involved in the endothelin-1-induced translocation of RhoA in rat bronchial smooth muscle.

The role of RhoA-mediated Ca2+ sensitization of bronchial smooth muscle contraction in airway hyperresponsiveness

Smooth muscle contraction is mediated by Ca2+-dependent and Ca2+-independent pathways. The latter Ca2+-independent pathway, termed Ca2+ sensitization, is mainly regulated by a monomeric GTP binding protein RhoA and its downstream target Rho-kinase. Recent studies suggest a possible involvement of augmented RhoA/Rho-kinase signaling in the elevated smooth muscle contraction in several human diseases. An increased bronchial smooth muscle contractility, which might be a major cause of the airway hyperresponsiveness that is a characteristic feature of asthmatics, has also been reported in bronchial asthma. Here, we will discuss the role of RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction in the pathogenesis of airway hyperresponsiveness. Agonist-induced Ca2+ sensitization is also inherent in bronchial smooth muscle. Since the Ca2+ sensitization is sensitive to a RhoA inactivator, C3 exoenzyme, and a Rho-kinase inhibitor, Y-27632, the RhoA/Rho-kinase pathway is involved in the signaling. It is of interest that the RhoA/Rho-kinase-mediated Ca2+ sensitization of bronchial smooth muscle contraction is markedly augmented in experimental asthma. Moreover, Y-27632 relaxes the bronchospasm induced by contractile agonists and antigens in vivo. Y-27632 also has an ability to inhibit airway hyperresponsiveness induced by antigen challenge. Thus, the RhoA/Rho-kinase pathway might be a potential target for the development of new treatments for asthma, especially in airway hyperresponsiveness.