α1- and β-adrenoceptor stimulation differentially activate p38-MAPK and atrial natriuretic peptide production in the perfused amphibian heart

Clinically Advanced p38 Inhibitors Suppress DUX4 Expression in Cellular and Animal Models of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by misexpression of the double homeobox 4 (DUX4) developmental transcription factor in mature skeletal muscle, where it is responsible for muscle degeneration. Preventing expression of DUX4 mRNA is a disease-modifying therapeutic strategy with the potential to halt or reverse the course of disease. We previously reported that agonists of the β-2 adrenergic receptor suppress DUX4 expression by activating adenylate cyclase to increase cAMP levels. Efforts to further explore this signaling pathway led to the identification of p38 mitogen-activated protein kinase as a major regulator of DUX4 expression. In vitro experiments demonstrate that clinically advanced p38 inhibitors suppress DUX4 expression in FSHD type 1 and 2 myoblasts and differentiating myocytes in vitro with exquisite potency. Individual small interfering RNA-mediated knockdown of either p38α or p38β suppresses DUX4 expression, demonstrating that each kinase isoform plays a distinct requisite role in activating DUX4 Finally, p38 inhibitors effectively suppress DUX4 expression in a mouse xenograft model of human FSHD gene regulation. These data support the repurposing of existing clinical p38 inhibitors as potential therapeutics for FSHD. The surprise finding that p38α and p38β isoforms each independently contribute to DUX4 expression offers a unique opportunity to explore the utility of p38 isoform-selective inhibitors to balance efficacy and safety in skeletal muscle. We propose p38 inhibition as a disease-modifying therapeutic strategy for FSHD. SIGNIFICANCE STATEMENT: Facioscapulohumeral muscular dystrophy (FSHD) currently has no treatment options. This work provides evidence that repurposing a clinically advanced p38 inhibitor may provide the first disease-modifying drug for FSHD by suppressing toxic DUX4 expression, the root cause of muscle degeneration in this disease.

Small molecule-mediated refolding and activation of myosin motor function

The small molecule EMD 57033 has been shown to stimulate the actomyosin ATPase activity and contractility of myofilaments. Here, we show that EMD 57033 binds to an allosteric pocket in the myosin motor domain. EMD 57033-binding protects myosin against heat stress and thermal denaturation. In the presence of EMD 57033, ATP hydrolysis, coupling between actin and nucleotide binding sites, and actin affinity in the presence of ATP are increased more than 10-fold. Addition of EMD 57033 to heat-inactivated β-cardiac myosin is followed by refolding and reactivation of ATPase and motile activities. In heat-stressed cardiomyocytes expression of the stress-marker atrial natriuretic peptide is suppressed by EMD 57033. Thus, EMD 57033 displays a much wider spectrum of activities than those previously associated with small, drug-like compounds. Allosteric effectors that mediate refolding and enhance enzymatic function have the potential to improve the treatment of heart failure, myopathies, and protein misfolding diseases.

DOI:http://dx.doi.org/10.7554/eLife.01603.001

Our muscles contain large numbers of ‘motor proteins’ called myosins. To contract a muscle, many myosin molecules expend energy to ‘walk’ along a filament made from another molecule, called actin, and generate a pulling force. Like other proteins, myosins must fold into the correct shape to work, but high temperatures or other types of stress can disrupt their ability to adopt or maintain the correct shape. Misfolding of myosins, for example, can result in muscular diseases, including those that affect the heart; so there is an ongoing effort to find compounds that can stabilize protein folding and treat these diseases.

The small molecule EMD 57033 was discovered over 20 years ago, and its ability to increase the strength of muscle contractions suggested that it could be used to treat chronic heart failure, but the risk of side effects limited its clinical use. The effectiveness of other compounds that improve cardiac muscle function is still routinely compared to EMD 57033, however the exact mechanism responsible for its effect on muscle tissue remained unknown.

Now Radke, Taft et al. have identified the part of the myosin protein that EMD 57033 binds to, and shown how this activates muscle contraction. The experiments also, unexpectedly, revealed that EMD 57033 is able to convert misfolded myosin back into the fully functional form. By revealing this refolding effect, the findings of Radtke, Taft et al. suggest that similar small molecules could be used as drugs for the treatment of protein misfolding diseases, muscular diseases, and heart failure.

DOI:http://dx.doi.org/10.7554/eLife.01603.002

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

p38 MAP kinase inhibitor reverses stress-induced myocardial dysfunction in vivo

Recent clinical reports strongly support the intriguing possibility that emotional stress alone is sufficient to cause reversible myocardial dysfunction in patients. We previously reported that a combination of prenatal stress followed by restraint stress (PS+R) results in echocardiographic evidence of myocardial dysfunction in anesthetized rats compared with control rats subjected to the same restraint stress (Control+R). We now report results of our catheter-based hemodynamic studies in both anesthetized and freely ambulatory awake rats, comparing PS+R vs. Control+R. Systolic function [positive rate of change in left ventricular pressure over time (+dP/dt)] was significantly depressed (P < 0.01) in PS+R vs. Control+R both under anesthesia (6,287 +/- 252 vs. 7,837 +/- 453 mmHg/s) and awake (10,438 +/- 741 vs. 12,111 +/- 652 mmHg/s). Diastolic function (-dP/dt) was also significantly depressed (P < 0.05) in PS+R vs. Control+R both under anesthesia (-5,686 +/- 340 vs. -7,058 +/- 458 mmHg/s) and awake (-8,287 +/- 444 vs. 10,440 +/- 364 mmHg/s). PS+R also demonstrated a significantly attenuated (P < 0.05) hemodynamic response to increasing doses of the beta-adrenergic agonist isoproterenol. Intraperitoneal injection of the p38 MAP kinase inhibitor SB-203580 reversed the baseline reduction in +dP/dt and -dP/dt as well as the blunted isoproterenol response. Intraperitoneal injection of SB-203580 also reversed p38 MAP kinase and troponin I phosphorylation in cardiac myocytes isolated from PS+R. Thus the combination of prenatal stress followed by restraint stress results in reversible depression in both systolic and diastolic function as well as defective beta-adrenergic receptor signaling. Future studies in this animal model may provide insights into the basic mechanisms contributing to reversible myocardial dysfunction in patients with ischemic and nonischemic cardiomyopathies.

The gp130/STAT3 signaling pathway mediates beta-adrenergic receptor-induced atrial natriuretic factor expression in cardiomyocytes

beta-Adrenergic receptor (beta-AR)-induced cardiac remodeling is closely linked with the re-expression of the atrial natriuretic factor (ANF) gene. However, the exact molecular mechanism of this response remains elusive. Here, we demonstrate that the beta-AR agonist isoproterenol potently evokes the tyrosine phosphorylation of STAT3 and increases its transcriptional activity in an extracellularly regulated kinase 1/2 and glycoprotein (gp)130 signaling-dependent manner in rat cardiomyocytes. Interestingly, both specific silencing of signal transducers and activators of transcription 3 (STAT3) expression by lentivirus-mediated RNA interference and antagonism of gp130 signaling lead to significant inhibition of isoproterenol-stimulated ANF expression. Together, these results indicate that gp130/STAT3 signaling has an essential role in ANF expression by beta-AR stimulation.

Catestatin (chromogranin A344-364) is a novel cardiosuppressive agent: inhibition of isoproterenol and endothelin signaling in the frog heart

The catecholamine release-inhibitory catestatin [Cts; human chromogranin (Cg) A(352-372), bovine CgA(344-364)] is a vasoreactive and anti-hypertensive peptide derived from CgA. Using the isolated avascular frog heart as a bioassay, in which the interactions between the endocardial endothelium and the subjacent myocardium can be studied without the confounding effects of the vascular endothelium, we tested the direct cardiotropic effects of bovine Cts and its interaction with beta-adrenergic (isoproterenol, ISO) and endothelin-1 (ET-1) signaling. Cts dose-dependently decreased stroke volume and stroke work, with a threshold concentration of 11 nM, approaching the in vivo level of the peptide. Cts reduced contractility by inhibiting phosphorylation of phospholamban (PLN). Furthermore, the Cts effect was abolished by pretreatment with either nitric oxide synthase (N(G)-monomethyl-l-arginine) or guanylate cyclase (ODQ) inhibitors, or an ET(B) receptor (ET(BR)) antagonist (BQ-788). Cts also noncompetitively inhibited the positive inotropic action of ISO. In addition, Cts inhibited the positive inotropic effect of ET-1, mediated by ET(A) receptors, and did not alter the negative inotropic ET-1 influence mediated by ET(BR). Cts action through ET(BR) was further suggested when, in the presence of BQ-788, Cts failed to inhibit the positive inotropism of both ISO and ET-1 stimulation and PLN phosphorylation. We concluded that the cardiotropic actions of Cts, including the beta-adrenergic and ET-1 antagonistic effects, support a novel role of this peptide as an autocrine-paracrine modulator of cardiac function, particularly when the stressed heart becomes a preferential target of both adrenergic and ET-1 stimuli.

Prolactin induces regional vasoconstriction through the beta2-adrenergic and nitric oxide mechanisms

Prolactin has been associated with many effects and has been implicated in the pathogenesis of pregnancy-related hypertensive disorders, although little is known about its vascular effects. The present study was designed to determine the primary effect of prolactin on regional vascular beds and the mechanisms involved. In 37 anesthetized pigs, the infusion of 0.17 mug/kg min of prolactin at constant heart rate and arterial pressure decreased coronary, mesenteric, renal, and iliac blood flow. This response was graded in further five pigs by increasing the infused dose of the hormone between 0.017 and 1 mug/kg min. In 22 of the 37 pigs, blockade of cholinergic receptors (five pigs) and of alpha-adrenoceptors (five pigs) did not affect the prolactin-induced vascular response, which was abolished by blockade of beta(2)-adrenoceptors (five pigs) and by blockade of vascular nitric oxide (NO) synthase (seven pigs). In 15 of the 37 pigs the increases in measured blood flows caused by iv infusion of isoproterenol (five pigs) and by intraarterial administration of acetylcholine (five pigs) and of sodium nitroprusside (five pigs) were significantly reduced by infusion of prolactin. Moreover, the treatment of porcine aortic endothelial cells by prolactin caused a reduction of NO production and of the phosphorylation of ERK, Akt, and p38, which was prevented by the concomitant treatment by the beta(2)-adrenergic agonist albuterol. The present study showed that iv infusion of prolactin primarily caused coronary, mesenteric, renal, and iliac vasoconstriction. These effects were brought about by the inhibition of a vasodilatory beta(2)-adrenergic receptor-mediated effect related to the NO intracellular pathway.

Organisation of the mouse sinoatrial node: structure and expression of HCN channels

OBJECTIVE

To reveal the structural characteristics of the sinoatrial node (SAN) and the distribution of hyperpolarization-activated cyclic nucleotide-gated cation channels (HCN) in the SAN in the mouse.

METHODS

The structure of the SAN and the distribution of HCN channels in the SAN in the mouse were studied by histology and immunolabelling of ANP, Cx43 and HCN channels.

RESULTS

The mouse SAN is a comma-shaped structure with a length of approximately 1.5 mm parallel to the crista terminalis and is separated from atrial muscle by connective tissue at the border both with the crista terminalis and the atrial septum. A unique compact nodal structure with densely-packed nodal cells was identified at the head of the comma-shaped SAN. Cell size and fibre orientation vary regionally in the SAN: the cells in the compact node are small and are orientated perpendicular to the crista terminalis, whereas the cells in the more inferior part are larger and more loosely-packed and are orientated parallel to the crista terminalis. All SAN cells exhibited labelling of HCN4, but no cell exhibited detectable labelling of HCN1, HCN2, ANP and Cx43, while surrounding atrial cells exhibited labelling of ANP and Cx43, but not HCN1, HCN2 and HCN4. A specialised interface between the SAN and surrounding atrial muscle was also identified: strands of HCN4-positive nodal cells protrude into the atrial muscle and strands of Cx43-positive atrial cells protrude into the SAN; thus, there are interdigitations between the SAN and atrial muscle.

CONCLUSIONS

In the mouse, (i) the SAN is structurally complex with a densely-packed head and loosely-packed tail; (ii) HCN4 is the only HCN isoform detectable and is present throughout the SAN; and (iii) there is a specialised interface between the SAN and surrounding atrium that may be necessary for the SAN to drive the more hyperpolarized atrial muscle.

Effects of various oxidants and antioxidants on the p38-MAPK signalling pathway in the perfused amphibian heart

We investigated the effects of different antioxidants such as L-ascorbic acid, catalase, and superoxide dismutase (SOD), on the p38-MAPK activation induced by oxidative stress in the isolated perfused amphibian heart. Oxidative stress was exemplified by perfusing hearts with 30 microM H(2)O(2) for 5 min or with the enzymatic system of xanthine/xanthine oxidase (200 microM/10 mU/ml, respectively) for 10 min. H(2)O(2)-induced activation of p38-MAPK (7.04 +/- 0.20-fold relative to control values) was totally attenuated by L-ascorbic acid (100 microM) or catalase (150 U/ml). These results were confirmed by immunohistochemical studies in which the phosphorylated form of p38-MAPK was localised in the perinuclear region and dispersedly in the cytoplasm of the ventricular cells during H(2)O(2) treatment, a pattern that was abolished by catalase or L-ascorbic acid. p38-MAPK was also activated (2.34 +/- 0.17-fold) by perfusing amphibian hearts with the reactive oxygen species (ROS)-generating system of xanthine/xanthine oxidase and this activation sustained in the presence of 150 U/ml catalase (2.16 +/- 0.26-fold), 50 U/ml SOD (2.02 +/- 0.07) or 100 microM L-ascorbic acid (2.18 +/- 0.10), but was suppressed by the combination of 150 U/ml catalase and 50 U/ml SOD. Finally, our studies showed that xanthine/xanthine oxidase induced the phosphorylation of the potent p38-MAPK substrates MAPKAPK2 (3.14 +/- 0.27-fold) and HSP27 (5.32 +/- 0.83-fold), which are implicated in cell protection, and this activation was reduced by the simultaneous use of catalase and SOD.

Extracellular pH changes activate the p38-MAPK signalling pathway in the amphibian heart

We investigated the activation of the p38-MAPK signalling pathway during extracellular pH changes in the isolated perfused amphibian heart. Extracellular alkalosis (pH 8.5 or 9.5) maximally activated p38-MAPK within 2 min (4.17- and 3.20-fold, respectively) and this effect was reversible since the kinase phosphorylation levels decreased upon reperfusing the heart with normal Tris–Tyrode's buffer. Extracellular acidosis also activated p38-MAPK moderately, but persistently (1.65-fold, at 1 min and 1.91-fold, at 60 min). The alkalosis-induced p38-MAPK activation depended upon the Na+/H+ exchanger (NHE) and Na+/K+-ATPase, because it was abolished when the NHE inhibitors amiloride and HOE642 and the Na+/K+-ATPase inhibitor, ouabain, were used. Our studies also showed that extracellular alkalosis (pH 8.5) induced MAPKAPK2 phosphorylation (2.59-fold, 2 min) and HSP27 phosphorylation (5.33-fold, 2 min) in a p38-MAPK-dependent manner, as it was inhibited with 1 μmol l–1 SB203580. Furthermore,immunohistochemical studies of the phosphorylated forms of p38-MAPK and HSP27 revealed that these proteins were localised in the perinuclear region and dispersedly in the cytoplasm of ventricular cells during alkalosis. Finally,alkalosis induced the increase of HSP70 protein levels (1.52-fold, 5 min), but independently of p38-MAPK activation. These data indicate that the p38-MAPK signalling pathway is activated by extracellular pH changes and in the case of alkalosis this activation may have a protective role.

Inhibition of p38 mitogen-activated protein kinase attenuates interleukin-1beta-induced thermal hyperalgesia and inducible nitric oxide synthase expression in the spinal cord

We have reported recently that intrathecal (i.t.) injection of interleukin-1beta (IL-1beta), at a dose of 100 ng, induces inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in the spinal cord and results in thermal hyperalgesia in rats. This study further examines the role of mitogen-activated protein kinase (MAPK) in i.t. IL-1beta-mediated iNOS-NO cascade in spinal nociceptive signal transduction. All rats were implanted with an i.t. catheter either with or without an additional microdialysis probe. Paw withdrawal latency to radiant heat is used to assess thermal hyperalgesia. The iNOS and MAPK protein expression in the spinal cord dorsal horn were examined by western blot. The [NO] in CSF dialysates were also measured. Intrathecal IL-1beta leads to a time-dependent up-regulation of phosphorylated p38 (p-p38) MAPK protein expression in the spinal cord 30-240 min following IL-1beta injection (i.t.). However, neither the phosphorylated extracellular signal-regulated kinase (p-ERK) nor phosphorylated c-Jun NH2-terminal kinase (p-JNK) was affected. The total amount of p38, ERK, and JNK MAPK proteins were not affected following IL-1beta injection. Intrathecal administration of either selective p38 MAPK, or JNK, or ERK inhibitor alone did not affect the thermal nociceptive threshold or iNOS protein expression in the spinal cord. However, pretreatment with a p38 MAPK inhibitor significantly reduced the IL-1beta-induced p-p38 MAPK expression by 38-49%, and nearly completely blocked the subsequent iNOS expression (reduction by 86.6%), NO production, and thermal hyperalgesia. In contrast, both ERK and JNK inhibitor pretreatments only partially (approximately 50%) inhibited the IL-1beta-induced iNOS expression in the spinal cord. Our results suggest that p38 MAPK plays a pivotal role in i.t. IL-1beta-induced spinal sensitization and nociceptive signal transduction.

Oxidative stress stimulates multiple MAPK signalling pathways and phosphorylation of the small HSP27 in the perfused amphibian heart

We investigated the activation of three subfamilies of MAPKs (ERK, JNKs and p38-MAPK) by oxidative stress in the isolated perfused amphibian heart. Activation of p43-ERK by 100 micro mol l(-1) H(2)O(2) was maximally observed within 5 min, remained elevated for 30 min and was comparable with the effect of 1 micro mol l(-1) PMA. p43-ERK activation by H(2)O(2) was inhibited by PD98059 but not by SB203580. The p46 and p52 species of JNKs were maximally activated by 2.5- and 2.1-fold, respectively, by 100 micro mol l(-1) H(2)O(2) within 2 min. JNK activation was still detectable after 15 min, reaching control values at 30 min of treatment. p38-MAPK was maximally activated by 9.75-fold by 100 micro mol l(-1) H(2)O(2) after 2 min and this activation progressively declined thereafter, reaching control values within 45 min of treatment. The observed dose-dependent profile of p38-MAPK activation by H(2)O(2) revealed that 30 micro mol l(-1) H(2)O(2) induced maximal phosphorylation, whereas 100-300 micro mol l(-1) H(2)O(2) induced considerable activation of the kinase. Our studies also showed that the phosphorylation of MAPKAPK2 by H(2)O(2) followed a parallel time-dependent pattern and that SB203580 abolished this phosphorylation. Furthermore, our experiments clearly showed that 30 micro mol l(-1) H(2)O(2) induced a strong, specific phosphorylation of HSP27. Our immunohistochemical studies showed that immune complexes of phosphorylated forms of both p38-MAPK and HSP27 were strongly enhanced by 30 micro mol l(-1) H(2)O(2) in the perinuclear region as well as dispersedly in the cytoplasm of ventricular cells and that SB203580 abolished this phosphorylation. These data indicate that oxidative stress is a powerful activator of all three MAPK subfamilies in the amphibian heart. Stimulation of p38-MAPK and the consequent phosphorylation of HSP27 may be important in cardioprotection under such conditions.

Triazines facilitate neurotransmitter release of synaptic terminals located in hearts of frog (Rana ridibunda) and honeybee (Apis mellifera) and in the ventral nerve cord of a beetle (Tenebrio molitor)

Three triazine herbicides, atrazine, simazine and metribuzine, and some of their major metabolites (cyanuric acid and 6-azauracil) were investigated for their action on synaptic terminals using three different isolated tissue preparations from the atria of the frog, Rana ridibunda, the heart of the honeybee, Apis mellifera macedonica, and the ventral nerve cord of the beetle, Tenebrio molitor. The results indicate that triazines facilitate the release of neurotransmitters from nerve terminals, as already reported for the mammalian central nervous system. The no observed effect concentration, the maximum concentration of the herbicide diluted in the saline that has no effect on the physiological properties of the isolated tissue, was estimated for each individual preparation. According to their relative potency, the three triazines tested can be ranked as follows: atrazine (cyanuric acid), simazine>metribuzine (6-azauracil). The action of these compounds on the cholinergic (amphibians, insects), adrenergic (amphibian) and octopaminergic (insects) synaptic terminals is discussed.