Impaired Relaxation of Airway Smooth Muscle in Mice Lacking the Actin-Binding Protein Gelsolin

Conditional deficiency of Rho-associated kinases disrupts endothelial cell junctions and impairs respiratory function in adult mice

The Ras homology (Rho) family of GTPases serves various functions, including promotion of cell migration, adhesion, and transcription, through activation of effector molecule targets. One such pair of effectors, the Rho-associated coiled-coil kinases (ROCK1 and ROCK2), induce reorganization of actin cytoskeleton and focal adhesion through substrate phosphorylation. Studies on ROCK knockout mice have confirmed that ROCK proteins are essential for embryonic development, but their physiological functions in adult mice remain unknown. In this study, we aimed to examine the roles of ROCK1 and ROCK2 proteins in normal adult mice. Tamoxifen (TAM)-inducible ROCK1 and ROCK2 single and double knockout mice (ROCK1flox/flox and/or ROCK2flox/flox;Ubc-CreERT2) were generated and administered a 5-day course of TAM. No deaths occurred in either of the single knockout strains, whereas all of the ROCK1/ROCK2 double conditional knockout mice (DcKO) had died by Day 11 following the TAM course. DcKO mice exhibited increased lung tissue vascular permeability, thickening of alveolar walls, and a decrease in percutaneous oxygen saturation compared with noninducible ROCK1/ROCK2 double-floxed control mice. On Day 3 post-TAM, there was a decrease in phalloidin staining in the lungs in DcKO mice. On Day 5 post-TAM, immunohistochemical analysis also revealed reduced staining for vascular endothelial (VE)-cadherin, β-catenin, and p120-catenin at cell-cell contact sites in vascular endothelial cells in DcKO mice. Additionally, VE-cadherin/β-catenin complexes were decreased in DcKO mice, indicating that ROCK proteins play a crucial role in maintaining lung function by regulating cell-cell adhesion.

How do cells stiffen?

Cell stiffness is an important characteristic of cells and their response to external stimuli. In this review, we survey methods used to measure cell stiffness, summarize stimuli that alter cell stiffness, and discuss signaling pathways and mechanisms that control cell stiffness. Several pathological states are characterized by changes in cell stiffness, suggesting this property can serve as a potential diagnostic marker or therapeutic target. Therefore, we consider the effect of cell stiffness on signaling and growth processes required for homeostasis and dysfunction in healthy and pathological states. Specifically, the composition and structure of the cell membrane and cytoskeleton are major determinants of cell stiffness, and studies have identified signaling pathways that affect cytoskeletal dynamics both directly and by altered gene expression. We present the results of studies interrogating the effects of biophysical and biochemical stimuli on the cytoskeleton and other cellular components and how these factors determine the stiffness of both individual cells and multicellular structures. Overall, these studies represent an intersection of the fields of polymer physics, protein biochemistry, and mechanics, and identify specific mechanisms involved in mediating cell stiffness that can serve as therapeutic targets.

Basal Vascular Smooth Muscle Cell Tone in eNOS Knockout Mice Can Be Reversed by Cyclic Stretch and Is Independent of Age

Introduction and Aims: Endothelial nitric oxide synthase (eNOS) knockout mice develop pronounced cardiovascular disease. In the present study, we describe the alterations in aortic physiology and biomechanics of eNOS knockout and C57Bl/6 control mice at 2–12 months of age, including a thorough physiological investigation of age and cyclic stretch-dependent VSMC contractility and aortic stiffness.

Methods and Results: Peripheral blood pressure and aortic pulse wave velocity were measured in vivo, and aortic biomechanical studies and isometric contractions were investigated ex vivo. Age-dependent progression of aortic stiffness, peripheral hypertension, and aortic contractility in eNOS knockout mice was absent, attenuated, or similar to C57Bl/6 control mice. Voltage-gated calcium channel (VGCC)-dependent calcium influx inversely affected isometric contraction and aortic stiffening by α₁-adrenergic stimulation in eNOS knockout mice. Baseline aortic stiffness was selectively reduced in eNOS knockout mice after ex vivo cyclic stretch exposure in an amplitude-dependent manner, which prompted us to investigate cyclic stretch dependent regulation of aortic contractility and stiffness. Aortic stiffness, both in baseline conditions and after activation of vascular smooth muscle cell (VSMC) contraction, was reduced with increasing cyclic stretch amplitude. This cyclic stretch dependency was attenuated with age, although aged eNOS knockout mice displayed better preservation of cyclic stretch-dependency compared to C57Bl/6 control mice. Store operated calcium entry-medicated aortic stiffening as induced by inhibiting sarcoplasmic reticulum calcium ATPase pumps with 10 µM CPA was most pronounced in the aorta of aged mice and at low cyclic stretch amplitude, but independent of eNOS. Basal aortic tonus and VSMC depolarization were highly dependent on eNOS, and were most pronounced at low cyclic stretch, with attenuation at increasing cyclic stretch amplitude.

Conclusion: eNOS knockout mice display attenuated progression of arterial disease as compared to C57Bl/6 control mice. Basal VSMC tone in eNOS knockout mice could be reduced by ex vivo exposure to cyclic stretch through stretch-dependent regulation of cytosolic calcium. Both baseline and active aortic stiffness were highly dependent on cyclic stretch regulation, which was more pronounced in young versus aged mice. Other mediators of VSMC contraction and calcium handling were dependent on cyclic stretch mechanotransduction, but independent of eNOS.

Bitter Taste Receptors in the Airway Cells Functions

G protein-coupled receptors (GPCRs) play a central role in regulating the functions of a diverse range of cell types in the airway. Taste 2 receptor (T2R) family of GPCRs is responsible for the transduction of bitter taste; however, recent studies have demonstrated that different subtypes of T2Rs and key components of T2R signaling are expressed in several extra-oral tissues including airways with many physiological roles. In the lung, expression of T2Rs has been confirmed in multiple airway cell types including airway smooth muscle (ASM) cells, various epithelial cell subtypes, and on both resident and migratory immune cells. Most importantly, activation of T2Rs with a variety of putative agonists elicits unique signaling in ASM and specialized airway epithelial cells resulting in the inhibition of ASM contraction and proliferation, promotion of ciliary motility, and innate immune response in chemosensory airway epithelial cells. Here we discuss the expression of T2Rs and the mechanistic basis of their function in the structural cells of the airways with some useful insights on immune cells in the context of allergic asthma and other upper airway inflammatory disorders. Emphasis on T2R biology and pharmacology in airway cells has an ulterior goal of exploiting T2Rs for therapeutic benefit in obstructive airway diseases.

Extracellular Matrix Rigidity Modulates Human Cervical Smooth Muscle Contractility-New Insights into Premature Cervical Failure and Spontaneous Preterm Birth

Spontaneous preterm birth (sPTB), a major cause of infant morbidity and mortality, must involve premature cervical softening/dilation for a preterm vaginal delivery to occur. Yet, the mechanism behind premature cervical softening/dilation in humans remains unclear. We previously reported the non-pregnant human cervix contains considerably more cervical smooth muscle cells (CSMC) than historically appreciated and the CSMC organization resembles a sphincter. We hypothesize that premature cervical dilation leading to sPTB may be due to (1) an inherent CSMC contractility defect resulting in sphincter failure and/or (2) altered cervical extracellular matrix (ECM) rigidity which influences CSMC contractility. To test these hypotheses, we utilized immunohistochemistry to confirm this CSMC phenotype persists in the human pregnant cervix and then assessed in vitro arrays of contractility (F:G actin ratios, PDMS pillar arrays) using primary CSMC from pregnant women with and without premature cervical failure (PCF). We show that CSMC from pregnant women with PCF do not have an inherent CSMC contractility defect but that CSMC exhibit decreased contractility when exposed to soft ECM. Given this finding, we used UPLC-ESI-MS/MS to evaluate collagen cross-link profiles in the cervical tissue from non-pregnant women with and without PCF and found that women with PCF have decreased collagen cross-link maturity ratios, which correlates to softer cervical tissue. These findings suggest having soft cervical ECM may lead to decreased CSMC contractile tone and a predisposition to sphincter laxity that contributes to sPTB. Further studies are needed to explore the interaction between cervical ECM properties and CSMC cellular behavior when investigating the pathophysiology of sPTB.

Reduced allergic lung inflammation and airway responsiveness in mice lacking the cytoskeletal protein gelsolin

Airway smooth muscle hyperresponsiveness associated with chronic airway inflammation leads to the typical symptoms of asthma including bronchoconstriction and wheezing. Asthma severity is associated with airway inflammation; therefore reducing airway inflammation is an important therapeutic target. Gelsolin is an actin capping and severing protein that has been reported to be involved in modulation of the inflammatory response. Using mice genetically lacking gelsolin, we evaluated the role of gelsolin in the establishment of house dust mite (HDM) antigen-induced allergic lung inflammation. The genetic absence of gelsolin was found to be protective against HDM sensitization, resulting in reduced lung inflammation, inflammatory cytokines and Muc5AC protein in bronchoalveolar lavage (BAL) fluid. The number of eosinophils, lymphocytes and interstitial macrophages in the BAL were increased after HDM sensitization in wild type mice, but were attenuated in gelsolin null mice. The observed attenuation of inflammation may be partly due to delayed migration of immune cells, because the reduced eosinophils in the BALs from gelsolin null mice compared to controls occurred despite similar amounts of the chemoattractant eotaxin. Splenic T cells demonstrated similar proliferation rates, but ex vivo alveolar macrophage migration was delayed in gelsolin null mice. In vivo, the reduced lung inflammation after HDM sensitization in gelsolin null mice was associated with significantly diminished airway resistance to inhaled methacholine compared with HDM-treated wild type mice. Our results suggest that modulation of gelsolin expression or function in selective inflammatory cell types that modulate allergic lung inflammation could be a therapeutic approach for asthma.

Detection of Six β-Agonists by Three Multiresidue Immunosensors Based on an Anti-bovine Serum Albumin-Ractopamine-Clenbuterol-Salbutamol Antibody

According to an indirect competitive immunoassay, six β-agonists (clenbuterol (CL), salbutamol (SAL), ractopamine (RAC), terbutaline (TER), mabuterol (MAB), and tulobuterol (TUL)) were detected by three novel multiresidue immunosensors on the basis of the successful preparation of bovine serum albumin (BSA)-RAC-CL-SAL multideterminant antigen and anti-BSA-RAC-CL-SAL antibody. A new strategy was reported to detect six β-agonists by combining nanotechnology, electrochemical detection, and specific immune technology. At the same concentration, the amperometric response for detection of six β-agonists was in a sequence of GCE/GNP/SAL > GCE/GNP/RAC > GCE/GNP/CL. Detection limits of six β-agonists show that the multiresidue detection performance of the GCE/GNP/RAC immunosensor is better than those of GCE/GNP/SAL and GCE/GNP/CL immunosensors. Three immunosensors manifest superior properties with a wide linear range, low detection limit, excellent reproducibility, and stability. The proposed GCE/GNP/RAC immunosensor displays high accuracy and can be effectively used for real sample detection.

Generation of functional lungs via conditional blastocyst complementation using pluripotent stem cells

Millions of people worldwide with incurable end-stage lung disease die because of inadequate treatment options and limited availability of donor organs for lung transplantation1. Current bioengineering strategies to regenerate the lung have not been able to replicate its extraordinary cellular diversity and complex three-dimensional arrangement, which are indispensable for life-sustaining gas exchange2,3. Here we report the successful generation of functional lungs in mice through a conditional blastocyst complementation (CBC) approach that vacates a specific niche in chimeric hosts and allows for initiation of organogenesis by donor mouse pluripotent stem cells (PSCs). We show that wild-type donor PSCs rescued lung formation in genetically defective recipient mouse embryos unable to specify (due to Ctnnb1cnull mutation) or expand (due to Fgfr2cnull mutation) early respiratory endodermal progenitors. Rescued neonates survived into adulthood and had lungs functionally indistinguishable from those of wild-type littermates. Efficient chimera formation and lung complementation required newly developed culture conditions that maintained the developmental potential of the donor PSCs and were associated with global DNA hypomethylation and increased H4 histone acetylation. These results pave the way for the development of new strategies for generating lungs in large animals to enable modeling of human lung disease as well as cell-based therapeutic interventions4-6.

Transgelin-2 as a therapeutic target for asthmatic pulmonary resistance

There is a clinical need for new bronchodilator drugs in asthma, because more than half of asthmatic patients do not receive adequate control with current available treatments. We report that inhibition of metallothionein-2 protein expression in lung tissues causes the increase of pulmonary resistance. Conversely, metallothionein-2 protein is more effective than β₂-agonists in reducing pulmonary resistance in rodent asthma models, alleviating tension in tracheal spirals, and relaxing airway smooth muscle cells (ASMCs). Metallothionein-2 relaxes ASMCs via transgelin-2 (TG2) and induces dephosphorylation of myosin phosphatase target subunit 1 (MYPT1). We identify TSG12 as a nontoxic, specific TG2-agonist that relaxes ASMCs and reduces asthmatic pulmonary resistance. In vivo, TSG12 reduces pulmonary resistance in both ovalbumin- and house dust mite-induced asthma in mice. TSG12 induces RhoA phosphorylation, thereby inactivating the RhoA-ROCK-MYPT1-MLC pathway and causing ASMCs relaxation. TSG12 is more effective than β₂-agonists in relaxing human ASMCs and pulmonary resistance with potential clinical advantages. These results suggest that TSG12 could be a promising therapeutic approach for treating asthma.

Calcium in Vascular Smooth Muscle Cell Elasticity and Adhesion: Novel Insights Into the Mechanism of Action

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the arterial wall. These cells play a critical role in maintaining vascular homeostasis including vasoconstriction and vasodilatation through active contraction and relaxation. Dysregulation of VSMC function alters the response of blood vessels to mechanical stress, contributing to the pathogenesis of vascular diseases, particularly atherosclerosis and hypertension. The stiffness of VSMCs is a major regulator of vascular function. Previous studies suggest that intracellular Ca2+ controls the stiffness of VSMCs by a mechanism involving myosin contractile apparatus. More recent studies highlight important functions of cytoskeletal α-smooth muscle actin (α-SMA), α5β1 integrin, and integrin-mediated cell-extracellular matrix (ECM) interactions in Ca2+-dependent regulation of VSMC stiffness and adhesion to the ECM, providing novel insights into the mechanism of calcium action.

Toward the Identification of Extra-Oral TAS2R Agonists as Drug Agents for Muscle Relaxation Therapies via Bioinformatics-Aided Screening of Bitter Compounds in Traditional Chinese Medicine

Significant advances have been made in the past decade in mapping the distributions and the physiological functions of extra-oral bitter taste receptors (TAS2Rs) in non-gustatory tissues. In particular, it has been found that TAS2Rs are expressed in various muscle tissues and activation of TAS2Rs can lead to muscle cell relaxation, which suggests that TAS2Rs may be important new targets in muscle relaxation therapy for various muscle-related diseases. So far, however, there is a lack of potent extra-oral TAS2R agonists that can be used as novel drug agents in muscle relaxation therapies. Interestingly, traditional Chinese medicine (TCM) often characterizes a drug’s property in terms of five distinct flavors (bitter, sweet, sour, salty, and pungent) according to its taste and function, and commonly regards “bitterness” as an intrinsic property of “good medicine.” In addition, many bitter flavored TCM are known in practice to cause muscle relaxation after long term use, and in lab experiments the compounds identified from some bitter flavored TCM do activate TAS2Rs and thus relax muscle cells. Therefore, it is highly possible to discover very useful extra-oral TAS2R agonists for muscle relaxation therapies among the abundant bitter compounds used in bitter flavored TCM. With this perspective, we reviewed in literature the distribution of TAS2Rs in different muscle systems with a focus on the map of bitter flavored TCM which can regulate muscle contractility and related functional chemical components. We also reviewed the recently established databases of TCM chemical components and the bioinformatics software which can be used for high-throughput screening and data mining of the chemical components associated with bitter flavored TCM. All together, we aim to present a knowledge-based approach and technological platform for identification or discovery of extra-oral TAS2R agonists that can be used as novel drug agents for muscle relaxation therapies through screening and evaluation of chemical compounds used in bitter flavored TCM.

Airway smooth muscle photorelaxation via opsin receptor activation

Nonvisual opsin (OPN) receptors have recently been implicated in blue light-mediated photorelaxation of smooth muscle in various organs. Since photorelaxation has not yet been demonstrated in airway smooth muscle (ASM) or in human tissues, we questioned whether functional OPN receptors are expressed in mouse and human ASM. mRNA, encoding the OPN 3 receptor, was detected in both human and mouse ASM. To demonstrate the functionality of the OPN receptors, we performed wire myography of ex vivo ASM from mouse and human upper airways. Blue light-mediated relaxation of ACh-preconstricted airways was intensity and wavelength dependent (maximum relaxation at 430-nm blue light) and was inhibited by blockade of the large-conductance calcium-activated potassium channels with iberiotoxin. We further implicated OPN receptors as key mediators in functional photorelaxation by demonstrating increased relaxation in the presence of a G protein receptor kinase 2 inhibitor or an OPN chromophore (9- cis retinal). We corroborated these responses in peripheral airways of murine precision-cut lung slices. This is the first demonstration of photorelaxation in ASM via an OPN receptor-mediated pathway.

Attenuation of murine and human airway contraction by a peptide fragment of the cytoskeleton regulatory protein gelsolin

We have previously reported that mice genetically deficient in the actin binding protein gelsolin exhibit impaired airway smooth muscle (ASM) relaxation. Primary cultured ASM cells from these mice demonstrate enhanced inositol triphosphate (IP₃) synthesis and increased intracellular calcium in response to G_q-coupled agonists. We hypothesized that this was due to increased intracellular availability of unbound phosphatidylinositol 4,5-bisphosphate (PIP₂), based on the fact that gelsolin contains a short peptide region that binds PIP₂, presumably making it a less available substrate. We now questioned whether a peptide that corresponds to the PIP₂ binding region of gelsolin could modulate ASM signaling and contraction. The 10 amino acid sequence of the gelsolin peptide within the PIP₂-binding region was incubated with primary cultures of human ASM cells, and IP₃ synthesis was measured in response to a G_q-coupled agonist. Gelsolin peptide-treated cells generated less IP₃ under basal and bradykinin or acetylcholine (G_q-coupled) conditions. Acetylcholine-induced contractile force measured in isolated tracheal rings from mice and human tracheal muscle strips in organ baths was attenuated in the presence of the gelsolin peptide. The gelsolin peptide also attenuated methacholine-induced airway constriction in murine precision-cut lung slices. Furthermore, this peptide fragment delivered to the respiratory system of mice via nebulization attenuated subsequent methacholine-induced increases in airway resistance in vivo. The current study demonstrates that introduction of this small gelsolin peptide into the airway may be a novel therapeutic option in bronchoconstrictive diseases.

Anoctamin Channels in Human Myometrium: A Novel Target for Tocolysis

BACKGROUND

Spontaneous preterm labor leading to preterm birth is a significant obstetric problem leading to neonatal morbidity and mortality. Current tocolytics are not completely effective and novel targets may afford a therapeutic benefit.

OBJECTIVE

To determine whether the anoctamin (ANO) family, including the calcium-activated chloride channel ANO1, is present in pregnant human uterine smooth muscle (USM) and whether pharmacological and genetic modulation of ANO1 modulates USM contraction.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), quantitative RT-PCR, and immunohistochemical staining were done to determine which members of the ANO family are expressed in human USM. Uterine smooth muscle strips were studied in an organ bath to determine whether ANO1 antagonists inhibit oxytocin-induced USM contractions. Anoctamin 1 small interfering RNA (siRNA) knockdown was performed to determine its effect on filamentous-/globular (F/G)-actin ratio, a measurement of actin polymerization's role in promoting smooth muscle contraction.

RESULTS

Messenger RNA (mRNA) encoding all members of the ANO family (except ANO7) are expressed in pregnant USM tissue. Anoctamin 1 mRNA expression was decreased 15.2-fold in pregnant USM compared to nonpregnant. Anoctamin 1 protein is expressed in pregnant human USM tissue. Functional organ bath studies with pregnant human USM tissue demonstrated that the ANO1 antagonist benzbromarone attenuates the force and frequency of oxytocin-induced contractions. In human USM cells, siRNA knockdown of ANO1 decreases F-/G-actin ratios.

CONCLUSION

Multiple members of the ANO family, including the calcium-activated chloride channel ANO1, are expressed in human USM. Antagonism of ANO1 by pharmacological inhibition and genetic knockdown leads to an attenuation of contraction in pregnant human USM. Anoctamin 1 is a potentially novel target for tocolysis.

Transient stretch induces cytoskeletal fluidization through the severing action of cofilin

With every deep inspiration (DI) or sigh, the airway wall stretches, as do the airway smooth muscle cells in the airway wall. In response, the airway smooth muscle cell undergoes rapid stretch-induced cytoskeletal fluidization. As a molecular mechanism underlying the cytoskeletal fluidization response, we demonstrate a key role for the actin-severing protein cofilin. Using primary human airway smooth muscle cells, we simulated a DI by imposing a transient stretch of physiological magnitude and duration. We used traction microscopy to measure the resulting changes in contractile forces. After a transient stretch, cofilin-knockdown cells exhibited a 29 ± 5% decrease in contractile force compared with prestretch conditions. By contrast, control cells exhibited a 67 ± 6% decrease ( P < 0.05, knockdown vs. control). Consistent with these contractile force changes with transient stretch, actin filaments in cofilin-knockdown cells remained largely intact, whereas actin filaments in control cells were rapidly disrupted. Furthermore, in cofilin-knockdown cells, contractile force at baseline was higher and rate of remodeling poststretch was slower than in control cells. Additionally, the severing action of cofilin was restricted to the release phase of the transient stretch. We conclude that the actin-severing activity of cofilin is an important factor in stretch-induced cytoskeletal fluidization and may account for an appreciable part of the bronchodilatory effects of a DI.