Role of cyclic nucleotide-dependent actin cytoskeletal dynamics:Ca(2+)](i) and force suppression in forskolin-pretreated porcine coronary arteries

PDE3 Inhibition Reduces Epithelial Mast Cell Numbers in Allergic Airway Inflammation and Attenuates Degranulation of Basophils and Mast Cells

Epithelial mast cells are generally present in the airways of patients with allergic asthma that are inadequately controlled. Airway mast cells (MCs) are critically involved in allergic airway inflammation and contribute directly to the main symptoms of allergic patients. Phosphodiesterase 3 (PDE3) tailors signaling of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), which are critical intracellular second messenger molecules in various signaling pathways. This paper investigates the pathophysiological role and disease-modifying effects of PDE3 in mouse bone marrow-derived MCs (bmMCs), human LAD2- and HMC1 mast cell lines, human blood basophils, and peripheral blood-derived primary human MCs (HuMCs). In a chronic house dust mite (HDM)-driven allergic airway inflammation mouse model, we observed that PDE3 deficiency or PDE3 inhibition (PDE3i) therapy reduced the numbers of epithelial MCs, when compared to control mice. Mouse bone marrow-derived MCs (bmMCs) and the human HMC1 and LAD2 cell lines predominantly expressed PDE3B and PDE4A. BmMCs from Pde3^−/− mice showed reduced loss of the degranulation marker CD107b compared with wild-type BmMCs, when stimulated in an immunoglobulin E (IgE)-dependent manner. Following both IgE-mediated and substance P-mediated activation, PDE3i-pretreated basophils, LAD2 cells, and HuMCs, showed less degranulation than diluent controls, as measured by surface CD63 expression. MCs lacking PDE3 or treated with the PDE3i enoximone exhibited a lower calcium flux upon stimulation with ionomycine. In conclusion PDE3 plays a critical role in basophil and mast cell degranulation and therefore its inhibition may be a treatment option in allergic disease.

Nanotechnology Enabled Modulation of Signaling Pathways Affects Physiologic Responses in Intact Vascular Tissue

IMPACT STATEMENT

Subarachnoid hemorrhage (SAH) is associated with vasospasm that is refractory to traditional vasodilators, and inhibition of vasospasm after SAH remains a large unmet clinical need. SAH causes changes in the phosphorylation state of the small heat shock proteins (HSPs), HSP20 and HSP27, in the vasospastic vessels. In this study, the levels of HSP27 and HSP20 were manipulated using nanotechnology to mimic the intracellular phenotype of SAH-induced vasospasm, and the effect of this manipulation was tested on vasomotor responses in intact tissues. This work provides insight into potential therapeutic targets for the development of more effective treatments for SAH induced vasospasm.

The AMP-Related Kinase (AMPK) Induces Ca 2+ -Independent Dilation of Resistance Arteries by Interfering With Actin Filament Formation

Rationale:

Decreasing Ca 2+ sensitivity of vascular smooth muscle (VSM) allows for vasodilation without lowering of cytosolic Ca 2+ . This may be particularly important in states requiring maintained dilation, such as hypoxia. AMP-related kinase (AMPK) is an important cellular energy sensor in VSM. Regulation of Ca 2+ sensitivity usually is attributed to myosin light chain phosphatase activity, but findings in non-VSM identified changes in the actin cytoskeleton. The potential role of AMPK in this setting is widely unknown.

Objective:

To assess the influence of AMPK on the actin cytoskeleton in VSM of resistance arteries with regard to potential Ca 2+ desensitization of VSM contractile apparatus.

Methods and Results:

AMPK induced a slowly developing dilation at unchanged cytosolic Ca 2+ levels in potassium chloride–constricted intact arteries isolated from mouse mesenteric tissue. This dilation was not associated with changes in phosphorylation of myosin light chain or of myosin light chain phosphatase regulatory subunit. Using ultracentrifugation and confocal microscopy, we found that AMPK induced depolymerization of F-actin (filamentous actin). Imaging of arteries from LifeAct mice showed F-actin rarefaction in the midcellular portion of VSM. Immunoblotting revealed that this was associated with activation of the actin severing factor cofilin. Coimmunoprecipitation experiments indicated that AMPK leads to the liberation of cofilin from 14-3-3 protein.

Conclusions:

AMPK induces actin depolymerization, which reduces vascular tone and the response to vasoconstrictors. Our findings demonstrate a new role of AMPK in the control of actin cytoskeletal dynamics, potentially allowing for long-term dilation of microvessels without substantial changes in cytosolic Ca 2+ .

Heat Shock-Related Protein 20 Peptide Decreases Human Airway Constriction Downstream of β2-Adrenergic Receptor

Severe bronchospasm refractory to β-agonists is a challenging aspect of asthma therapy, and novel therapeutics are needed. β-agonist-induced airway smooth muscle (ASM) relaxation is associated with increases in the phosphorylation of the small heat shock-related protein (HSP) 20. We hypothesized that a transducible phosphopeptide mimetic of HSP20 (P20 peptide) causes relaxation of human ASM (HASM) by interacting with target(s) downstream of the β2-adrenergic receptor (β2AR) pathway. The effect of the P20 peptide on ASM contractility was determined in human and porcine ASM using a muscle bath. The effect of the P20 peptide on filamentous actin dynamics and migration was examined in intact porcine ASM and cultured primary HASM cells. The efficacy of the P20 peptide in vivo on airway hyperresponsiveness (AHR) was determined in an ovalbumin (OVA) sensitization and challenge murine model of allergic airway inflammation. P20 peptide caused dose-dependent relaxation of carbachol-precontracted ASM and blocked carbachol-induced contraction. The β2AR inhibitor, (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI 118,551), abrogated isoproterenol but not P20 peptide-mediated relaxation. The P20 peptide decreased filamentous actin levels in intact ASM, disrupted stress fibers, and inhibited platelet-derived growth factor-induced migration of HASM cells. The P20 peptide treatment reduced methacholine-induced AHR in OVA mice without affecting the inflammatory response. These results suggest that the P20 peptide decreased airway constriction and disrupted stress fibers through regulation of the actin cytoskeleton downstream of β2AR. Thus, the P20 peptide may be a potential therapeutic for asthma refractory to β-agonists.

Differential impact of acute and prolonged cAMP agonist exposure on protein kinase A activation and human myometrium contractile activity

KEY POINTS

Over 15 million babies are born prematurely each year with approximately 1 million of these babies dying as a direct result of preterm delivery. β₂ -Adrenoreceptor agonists that act via cAMP can reduce uterine contractions to delay preterm labour, but their ability to repress uterine contractions lasts ≤ 48 h and their use does not improve neonatal outcomes. Previous research has suggested that cAMP inhibits myometrial contractions via protein kinase A (PKA) activation, but this has yet to be demonstrated with PKA-specific agonists. We investigated the role of PKA in mediating cAMP-induced human myometrial relaxation, and the impact of prolonged cAMP elevation on myometrial contractility. Our findings suggest that PKA is not the sole mediator of cAMP-induced myometrial relaxation and that prolonged prophylactic elevation of cAMP alone is unlikely to prevent preterm labour (PTL).

ABSTRACT

Acute cAMP elevation inhibits myometrial contractility, but the mechanisms responsible are not fully elucidated and the long-term effects are uncertain. Both need to be defined in pregnant human myometrium before the therapeutic potential of cAMP-elevating agents in the prevention of preterm labour can be realised. In the present study, we tested the hypotheses that PKA activity is necessary for cAMP-induced myometrial relaxation, and that prolonged cAMP elevation can prevent myometrial contractions. Myometrial tissues obtained from term, pre-labour elective Caesarean sections were exposed to receptor-independent cAMP agonists to determine the relationship between myometrial contractility (spontaneous and oxytocin-induced), PKA activity, HSP20 phosphorylation and expression of contraction-associated and cAMP signalling proteins. Acute (1 h) application of cAMP agonists promoted myometrial relaxation, but this was weakly related to PKA activation. A PKA-specific activator, 6-Bnz-cAMP, increased PKA activity (6.8 ± 2.0 mean fold versus vehicle; P = 0.0313) without inducing myometrial relaxation. Spontaneous myometrial contractility declined after 24 h but was less marked when tissues were constantly exposed to cAMP agonists, especially for 8-bromo-cAMP (4.3 ± 1.2 mean fold versus vehicle; P = 0.0043); this was associated with changes to calponin, cofilin and HSP20 phosphorylated/total protein levels. Oxytocin-induced contractions were unaffected by pre-incubation with cAMP agonists despite treatments being able to enhance PKA activity and HSP20 phosphorylation. These data suggest that cAMP-induced myometrial relaxation is not solely dependent on PKA activity and the ability of cAMP agonists to repress myometrial contractility is lost with prolonged exposure. We conclude that cAMP agonist treatment alone may not prevent preterm labour.

Brilliant blue FCF is a nontoxic dye for saphenous vein graft marking that abrogates response to injury

BACKGROUND

Injury to saphenous vein grafts during surgical preparation may contribute to the subsequent development of intimal hyperplasia, the primary cause of graft failure. Surgical skin markers currently used for vascular marking contain gentian violet and isopropanol, which damage tissue and impair physiologic functions. Brilliant blue FCF (FCF) is a nontoxic dye alternative that may also ameliorate preparation-induced injury.

METHODS

Porcine saphenous vein (PSV) was used to evaluate the effect of FCF on physiologic responses in a muscle bath. Cytotoxicity of FCF was measured using human umbilical venous smooth muscle cells. Effect of FCF on the development of intimal hyperplasia was evaluated in organ culture using PSV. Intracellular calcium fluxes and contractile responses were measured in response to agonists and inhibitors in rat aorta and human saphenous vein.

RESULTS

Marking with FCF did not impair smooth muscle contractile responses and restored stretch injury-induced loss in smooth muscle contractility of PSV. Gentian violet has cytotoxic effects on human umbilical venous smooth muscle cells, whereas FCF is nontoxic. FCF inhibited intimal thickening in PSV in organ culture. Contraction induced by 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate and intracellular calcium flux were inhibited by FCF, oxidized adenosine triphosphate, KN-62, and brilliant blue G, suggesting that FCF may inhibit the purinergic receptor P2X7.

CONCLUSIONS

Our studies indicated that FCF is a nontoxic marking dye for vein grafts that ameliorates vein graft injury and prevents intimal thickening, possibly due to P2X7 receptor inhibition. FCF represents a nontoxic alternative for vein graft marking and a potentially therapeutic approach to enhance outcome in autologous transplantation of human saphenous vein into the coronary and peripheral arterial circulation.

Papaverine Prevents Vasospasm by Regulation of Myosin Light Chain Phosphorylation and Actin Polymerization in Human Saphenous Vein

Objective

Papaverine is used to prevent vasospasm in human saphenous veins (HSV) during vein graft preparation prior to implantation as a bypass conduit. Papaverine is a nonspecific inhibitor of phosphodiesterases, leading to increases in both intracellular cGMP and cAMP. We hypothesized that papaverine reduces force by decreasing intracellular calcium concentrations ([Ca²⁺]_i) and myosin light chain phosphorylation, and increasing actin depolymerization via regulation of actin regulatory protein phosphorylation.

Approach and Results

HSV was equilibrated in a muscle bath, pre-treated with 1 mM papaverine followed by 5 μM norepinephrine, and force along with [Ca²⁺]_i levels were concurrently measured. Filamentous actin (F-actin) level was measured by an in vitro actin assay. Tissue was snap frozen to measure myosin light chain and actin regulatory protein phosphorylation. Pre-treatment with papaverine completely inhibited norepinephrine-induced force generation, blocked increases in [Ca²⁺]_i and led to a decrease in the phosphorylation of myosin light chain. Papaverine pre-treatment also led to increased phosphorylation of the heat shock-related protein 20 (HSPB6) and the vasodilator stimulated phosphoprotein (VASP), as well as decreased filamentous actin (F-actin) levels suggesting depolymerization of actin.

Conclusions

These results suggest that papaverine-induced force inhibition of HSV involves [Ca²⁺]_i-mediated inhibition of myosin light chain phosphorylation and actin regulatory protein phosphorylation-mediated actin depolymerization. Thus, papaverine induces sustained inhibition of contraction of HSV by the modulation of both myosin cross-bridge formation and actin cytoskeletal dynamics and is a pharmacological alternative to high pressure distention to prevent vasospasm.

A role for actin polymerization in persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is defined as the failure of normal pulmonary vascular relaxation at birth. Hypoxia is known to impede postnatal disassembly of the actin cytoskeleton in pulmonary arterial myocytes, resulting in elevation of smooth muscle α-actin and γ-actin content in elastic and resistance pulmonary arteries in PPHN compared with age-matched controls. This review examines the original histological characterization of PPHN with attention to cytoskeletal structural remodeling and actin isoform abundance, reviews the existing evidence for understanding the biophysical and biochemical forces at play during neonatal circulatory transition, and specifically addresses the role of the cortical actin architecture, primarily identified as γ-actin, in the transduction of mechanical force in the hypoxic PPHN pulmonary circuit.