Deficiency of M2 muscarinic acetylcholine receptors increases susceptibility of ventricular function to chronic adrenergic stress

Remodeling of the Intracardiac Ganglia During the Development of Cardiovascular Autonomic Dysfunction in Type 2 Diabetes: Molecular Mechanisms and Therapeutics

Type 2 diabetes mellitus (T2DM) is one of the most significant health issues worldwide, with associated healthcare costs estimated to surpass USD 1054 billion by 2045. The leading cause of death in T2DM patients is the development of cardiovascular disease (CVD). In the early stages of T2DM, patients develop cardiovascular autonomic dysfunction due to the withdrawal of cardiac parasympathetic activity. Diminished cardiac parasympathetic tone can lead to cardiac arrhythmia-related sudden cardiac death, which accounts for 50% of CVD-related deaths in T2DM patients. Regulation of cardiovascular parasympathetic activity is integrated by neural circuitry at multiple levels including afferent, central, and efferent components. Efferent control of cardiac parasympathetic autonomic tone is mediated through the activity of preganglionic parasympathetic neurons located in the cardiac extensions of the vagus nerve that signals to postganglionic parasympathetic neurons located in the intracardiac ganglia (ICG) on the heart. Postganglionic parasympathetic neurons exert local control on the heart, independent of higher brain centers, through the release of neurotransmitters, such as acetylcholine. Structural and functional alterations in cardiac parasympathetic postganglionic neurons contribute to the withdrawal of cardiac parasympathetic tone, resulting in arrhythmogenesis and sudden cardiac death. This review provides an overview of the remodeling of parasympathetic postganglionic neurons in the ICG, and potential mechanisms contributing to the withdrawal of cardiac parasympathetic tone, ventricular arrhythmogenesis, and sudden cardiac death in T2DM. Improving cardiac parasympathetic tone could be a therapeutic avenue to reduce malignant ventricular arrhythmia and sudden cardiac death, increasing both the lifespan and improving quality of life of T2DM patients.

Protective role of acetylcholine and the cholinergic system in the injured heart

This review explores the roles of the cholinergic system in the heart, comprising the neuronal and non-neuronal cholinergic systems. Both systems are essential for maintaining cardiac homeostasis by regulating the release of acetylcholine (ACh). A reduction in ACh release is associated with the early onset of cardiovascular diseases (CVDs), and increasing evidence supports the protective roles of ACh against CVD. We address the challenges and limitations of current strategies to elevate ACh levels, including vagus nerve stimulation and pharmacological interventions such as cholinesterase inhibitors. Additionally, we introduce alternative strategies to increase ACh in the heart, such as stem cell therapy, gene therapy, microRNAs, and nanoparticle drug delivery methods. These findings offer new insights into advanced treatments for regenerating the injured human heart.

Acetylcholine receptor agonists effectively attenuated multiple program cell death pathways and improved left ventricular function in trastuzumab-induced cardiotoxicity in rats

AIMS

Cardiotoxicity is a seriously debilitating complication of trastuzumab (TRZ) therapy in patients with cancer as a consequence of overexpression of the human epidermal growth factor receptor 2. Although most TRZ-induced cardiotoxicity (TIC) cases are reversible, some patients experience chronic cardiac dysfunction, and these irreversible concepts may be associated with cardiomyocyte death. Acetylcholine receptor (AChR) activation has been shown to exert cardioprotection in several heart diseases, but the effects of AChR agonists against TIC have not been investigated.

MAIN METHOD

Forty adult male Wistar rats were randomized into 5 groups: (i) CON (0.9 % normal saline), (ii) TRZ (4 mg/kg/day), (iii) TRZ + α7nAChR agonist (PNU-282987: 3 mg/kg/day), (iv) TRZ + mAChR agonists (bethanechol: 12 mg/kg/day), and (v) TRZ + combined treatment (Combined PNU-282987 and bethanechol).

KEY FINDINGS

The progression of TIC was driven by mitochondrial dysfunction, autophagic deficiency, and excessive myocyte death including by pyroptosis, ferroptosis, and apoptosis, which were significantly alleviated by α7nAChR and mAChR agonists. Interestingly, necroptosis was not associated with development of TIC. More importantly, the in vitro study validated the cytoprotective effects of AChR activation in TRZ-treated H9c2 cells, while not interfering with the anticancer properties of TRZ. All of these findings indicated that TRZ induced mitochondrial dysfunction, autophagic deficiency, and excessive myocyte death including pyroptosis, ferroptosis, and apoptosis, leading to impaired cardiac function. These pathological alterations were attenuated by α7nAChR and mAChR agonists.

SIGNIFICANCE

α7nAChR and mAChR agonists might be used as a future therapeutic target in the mitigation of TIC.

Immunoreactivity of Kir3.1, muscarinic receptors 2 and 3 on the brainstem, vagus nerve and heart tissue under experimental demyelination

AIMS

Demyelination affects the propogation of neuronal action potential by slowing down the progression. This process results in a neuro-impairment like Multiple Sclerosis (MS). Evidence show that MS also contributes to involvement of the autonomic system. In the molecular approach to this involvement, we aimed to observe muscarinic ACh receptor 2-3 (mAChR2-3), and inwardly rectifying potassium channel 3.1 (Kir3.1) immunoreactivities on the brainstem, vagus nerve, and heart under cuprizone model.

MAIN METHODS

Wistar albino rats were randomly divided into 8 groups; duplicating 4 groups as male and female: control groups (n = 3 +3), Cuprizone groups (n = 12 +12), sham groups (n = 4 +4), and carboxy-methyl-cellulose groups (n = 3 +3). Cuprizone-fed rats underwent demyelination via Luxol fast blue (LFB) staining of the hippocampus (Gyrus dentatus and Cornu Ammonis) and cortex. Immunohistochemistry analysis followed to the pathologic measurement of the brainstem, vagus nerve, and heart for mAChR2, mAChR3 and Kir3.1 proteins KEY FINDINGS: A significant demyelination was observed in the hippocampus and cortex tissues of rats in the female and male cuprizone groups. Myelin basic protein immunoreactivity demonstrated that cuprizone groups, in both males and females, had down-regulation in the hippocampus and cortex areas. The weights of the cuprizone-fed rats significantly decreased over six weeks. Dilated blood vessels and neuronal degeneration were severe in the hippocampus and cortex of the cuprizone groups. In the female cuprizone group, expression of mAChR2 and mAChR2 was significantly increased in the brainstem, atrium/ventricle of heart, and left/right sections of vagus nerve. Kir3.1 channels were also up-regulated in the left vagus nerve and heart sections of the female cuprizone group SIGNIFICANCE: Especially in our data where female-based significant results were obtained reveal that demyelination may lead to significant mAChR2, mAChR3 and Kir3.1 changes in brainstem, vagus nerve, and heart. A high immunoreactive response to demyelination at cholinergic centers may be a new target.

Characterization of immune checkpoint inhibitor-induced cardiotoxicity reveals interleukin-17A as a driver of cardiac dysfunction after anti-PD-1 treatment

BACKGROUND AND PURPOSE

Immune checkpoint inhibitors (ICI), such as anti-PD-1 monoclonal antibodies, have revolutionized cancer therapy by enhancing the cytotoxic effects of T-cells against tumours. However, enhanced T-cell activity also may cause myocarditis and cardiotoxicity. Our understanding of the mechanisms of ICI-induced cardiotoxicity is limited. Here, we aimed to investigate the effect of PD-1 inhibition on cardiac function and explore the molecular mechanisms of ICI-induced cardiotoxicity.

EXPERIMENTAL APPROACH

C57BL6/J and BALB/c mice were treated with isotype control or anti-PD-1 antibody. Echocardiography was used to assess cardiac function. Cardiac transcriptomic changes were investigated by bulk RNA sequencing. Inflammatory changes were assessed by qRT-PCR and immunohistochemistry in heart, thymus, and spleen of the animals. In follow-up experiments, anti-CD4 and anti-IL-17A antibodies were used along with PD-1 blockade in C57BL/6J mice.

KEY RESULTS

Anti-PD-1 treatment led to cardiac dysfunction and left ventricular dilation in C57BL/6J mice, with increased nitrosative stress. Only mild inflammation was observed in the heart. However, PD-1 inhibition resulted in enhanced thymic inflammatory signalling, where Il17a increased most prominently. In BALB/c mice, cardiac dysfunction was not evident, and thymic inflammatory activation was more balanced. Inhibition of IL-17A prevented anti-PD-1-induced cardiac dysfunction in C57BL6/J mice. Comparing myocardial transcriptomic changes in C57BL/6J and BALB/c mice, differentially regulated genes (Dmd, Ass1, Chrm2, Nfkbia, Stat3, Gsk3b, Cxcl9, Fxyd2, and Ldb3) were revealed, related to cardiac structure, signalling, and inflammation.

CONCLUSIONS

PD-1 blockade induces cardiac dysfunction in mice with increased IL-17 signalling in the thymus. Pharmacological inhibition of IL-17A treatment prevents ICI-induced cardiac dysfunction.

Neuronal cholinergic signaling constrains norepinephrine activity in the heart

It is well known that cholinergic hypofunction contributes to cardiac pathology; yet, the mechanisms involved remain unclear. Our previous publication has shown that genetically engineered model of cholinergic deficit, the vesicular acetylcholine transporter knockdown homozygous (VAChT KDHOM) mice exhibit pathological cardiac remodeling and a gradual increase in cardiac mass with aging. Given that an increase in cardiac mass is often caused by adrenergic hyperactivity, we hypothesized that VAChT KDHOM mice might have an increase in cardiac norepinephrine (NE) levels. We thus investigated the temporal changes in NE content in the heart from 3, 6 and 12 month-old VAChT mutants. Interestingly, mice with cholinergic hypofunction showed a gradual elevation in cardiac NE content, which was already increased at 6 months of age. Consistent with this finding, 6 month-old VAChT KDHOM mice showed enhanced sympathetic activity and a greater abundance of tyrosine hydroxylase positive sympathetic nerves in the heart. VAChT mutants exhibited an increase in peak calcium transient, and mitochondrial oxidative stress in cardiomyocytes along with enhanced GRK5 and NFAT staining in the heart. These are known targets of adrenergic signaling in the cell. Moreover, vagotomized-mice displayed an increase in cardiac NE content confirming the data obtained in VAChT KDHOM mice. Establishing a causal relationship between acetylcholine and NE, VAChT KDHOM mice treated with pyridostigmine, a cholinesterase inhibitor, showed reduced cardiac NE content, rescuing the phenotype. Our findings unveil a yet unrecognized role of cholinergic signaling as a modulator of cardiac NE, providing novel insights into the mechanisms that drive autonomic imbalance.

RGS3L allows for an M2 muscarinic receptor-mediated RhoA-dependent inotropy in cardiomyocytes

The role and outcome of the muscarinic M₂ acetylcholine receptor (M₂R) signaling in healthy and diseased cardiomyocytes is still a matter of debate. Here, we report that the long isoform of the regulator of G protein signaling 3 (RGS3L) functions as a switch in the muscarinic signaling, most likely of the M₂R, in primary cardiomyocytes. High levels of RGS3L, as found in heart failure, redirect the G_i-mediated Rac1 activation into a G_i-mediated RhoA/ROCK activation. Functionally, this switch resulted in a reduced production of reactive oxygen species (- 50%) in cardiomyocytes and an inotropic response (+ 18%) in transduced engineered heart tissues. Importantly, we could show that an adeno-associated virus 9-mediated overexpression of RGS3L in rats in vivo, increased the contractility of ventricular strips by maximally about twofold. Mechanistically, we demonstrate that this switch is mediated by a complex formation of RGS3L with the GTPase-activating protein p190RhoGAP, which balances the activity of RhoA and Rac1 by altering its substrate preference in cardiomyocytes. Enhancement of this complex formation could open new possibilities in the regulation of the contractility of the diseased heart.

Aerobic exercise ameliorates cardiac hypertrophy by regulating mitochondrial quality control and endoplasmic reticulum stress through M2 AChR

Aerobic exercise increases M2 AChR, which thus improves cardiac function in cardiovascular disease (CVD) rats. This study aimed to determine whether aerobic exercise could ameliorate pressure overload-induced heart hypertrophy through M2 AChR, and to elucidate the underlying mechanisms of action. Mice were used to establish the myocardial hypertrophy model by transverse aortic constriction (TAC), and subjected to 2, 4, and 8 weeks of moderate-intensity aerobic exercise and choline intervention (14 mg/kg/day). Our results showed that 4 and 8 weeks of exercise and choline intervention reduced excessive mitochondrial fission and autophagy of myocardial mitochondria, thereby improving the ultrastructure and function of mitochondria after TAC. Moreover, 8-week exercise and choline intervention have enhanced parasympathetic function and promoted the expression of M2 AChR. In addition, 8-week exercise and choline intervention also inhibited the protein expression of myocardial MFN2, PERK/eIF2α/ATF4, and NLRP3/caspase-1/IL-1β signaling pathways, thereby effectively reducing mitochondrial fusion, endoplasmic reticulum stress, and inflammation. Taken together, these data suggest that pressure overload led to cardiac hypertrophy, cardiac dysfunction, and decreased parasympathetic function in cardiac tissues. Aerobic exercise attenuated cardiac dysfunction by modulating the expression of proteins involved in mitochondrial quality control, and induced endoplasmic reticulum stress and inflammation, thereby reducing cardiac hypertrophy and improving cardiac function in impaired heart tissues following TAC, which was likely mediated by M2 AChR activation.

Altered Cardiovascular Reactivity to and Recovery from Cold Face Test-Induced Parasympathetic Stimulation in Essential Hypertension

Essential hypertension is associated with increased sympathetic and diminished parasympathetic activity as well as impaired reactivity to sympathetic stimulation. However, reactivity and recovery from parasympathetic stimulation in hypertension are unknown. We investigated reactivity and recovery to primarily parasympathetic stimulation by Cold Face Test (CFT) in essential hypertension. Moreover, we tested whether chronic stress modulates CFT-reactivity dependent on hypertension status. The CFT was conducted by applying a cold face-mask for 2 min in 24 unmedicated, otherwise healthy hypertensive men and in 24 normotensive controls. Systolic and diastolic blood pressure (BP) and heart rate (HR) were measured repeatedly. Chronic stress was assessed with the Trier-Inventory-for-Chronic-Stress-Screening-Scale. Hypertensives did not exhibit diastolic BP decreases after CFT-cessation (p = 0.59) as did normotensives (p = 0.002) and failed to show HR decreases in immediate response to CFT (p = 0.62) when compared to normotensives (p < 0.001). Systolic BP reactivity and recovery patterns did not differ between hypertensives and normotensives (p = 0.44). Chronic stress moderated HR (p = 0.045) but not BP CFT-reactivity (p's > 0.64) with chronically stressed normotensives showing similar HR reactivity as hypertensives. Our findings indicate impaired diastolic BP and HR reactivity to and recovery from CFT in hypertensives and a moderating effect of chronic stress on HR reactivity potentially reflecting reduced relaxation ability of the cardiovascular system.

Chronic stimulation of group II metabotropic glutamate receptors in the medulla oblongata attenuates hypertension development in spontaneously hypertensive rats

Baroreflex dysfunction is partly implicated in hypertension and one responsible region is the dorsal medulla oblongata including the nucleus tractus solitarius (NTS). NTS neurons receive and project glutamatergic inputs to subsequently regulate blood pressure, while G-protein-coupled metabotropic glutamate receptors (mGluRs) play a modulatory role for glutamatergic transmission in baroreflex pathways. Stimulating group II mGluR subtype 2 and 3 (mGluR2/3) in the brainstem can decrease blood pressure and sympathetic nervous activity. Here, we hypothesized that the chronic stimulation of mGluR2/3 in the dorsal medulla oblongata can alleviate hypertensive development via the modulation of autonomic nervous activity in young, spontaneously hypertensive rats (SHRs). Compared with that in the sham control group, chronic LY379268 application (mGluR2/3 agonist; 0.40 μg/day) to the dorsal medulla oblongata for 6 weeks reduced the progression of hypertension in 6-week-old SHRs as indicated by the 40 mmHg reduction in systolic blood pressure and promoted their parasympathetic nervous activity as evidenced by the heart rate variability. No differences in blood catecholamine levels or any echocardiographic indices were found between the two groups. The improvement of reflex bradycardia, a baroreflex function, appeared after chronic LY379268 application. The mRNA expression level of mGluR2, but not mGluR3, in the dorsal medulla oblongata was substantially reduced in SHRs compared to that of the control strain. In conclusion, mGluR2/3 signaling might be responsible for hypertension development in SHRs, and modulating mGluR2/3 expression/stimulation in the dorsal brainstem could be a novel therapeutic strategy for hypertension via increasing the parasympathetic activity.

Immunomodulatory role of non-neuronal cholinergic signaling in myocardial injury

Whereas prior studies have demonstrated an important immunomodulatory role for the neuronal cholinergic system in the heart, the role of the non-neuronal cholinergic system is not well understood. To address the immunomodulatory role of the non-neuronal cholinergic system in the heart we used a previously validated diphtheria toxin (DT)-induced cardiomyocyte ablation model (Rosa26-DTMlc2v-Cre mice). DT-injected Rosa26-DTMlc2v-Cre mice were treated with diluent or Pyridostigmine Bromide (PYR), a reversible cholinesterase inhibitor. PYR treatment resulted in increased survival and decreased numbers of MHC-IIlowCCR2+ macrophages in DT-injected Rosa26-DTMlc2v-Cre mice compared to diluent treated Rosa26-DTMlc2v-Cre mice. Importantly, the expression of CCL2/7 mRNA and protein was reduced in the hearts of PYR-treated mice. Backcrossing Rosa26-DTMlc2v-Cre mice with a transgenic mouse line (Chat-ChR2) that constitutively overexpresses the vesicular acetylcholine transporter (VAChT) resulted in decreased expression of Ccl2/7 mRNA and decreased numbers of CD68+ cells in DT-injured Rosa26-DTMlc2v-Cre/Chat-ChR2 mouse hearts, consistent with the pharmacologic studies with PYR. In vitro studies with cultures of LPS-stimulated peritoneal macrophages revealed a concentration-dependent reduction in CCL2 secretion following stimulation with ACh, nicotine and muscarine. Viewed together, these findings reveal a previously unappreciated immunomodulatory role for the non-neuronal cholinergic system in regulating homeostatic responses in the heart following tissue injury.

Acute restraint stress modifies the heart rate biorhythm in the poststress period

We studied the changes in the heart and the activity biorhythms in mice exposed to acute (one 120-minute session) and repeated (7 two-hour sessions) restraint stress in 129J1/CF1 mice (WT) and in mice without M₂ muscarinic receptors (M₂KO) during the prestress period, during stress (STR) and for five days after the last stress session (POST). There were changes in the mesor (a midline based on the distribution of values across the circadian cycles; decreased in M₂KO by 6% over all POST), day means (inactive period of diurnal rhythm in mice; higher in M₂KO and further increased on STR and on the second to the fifth POST) and night means (active period; lower by 13% in M₂KO and remained decreased in STR and in POST). The total area under the curve was decreased both in the WT and M₂KO on STR and in all POST. Repeated stress caused changes over all days of STR, but the initial values were restored in POST. The average night values were decreased, and the day means were increased by 16% over all STR in M₂KO. The day means decreased by 14% in the 4 POST in WT. The activity biorhythm parameters were almost unchanged. We show here that stress can specifically affect heart biorhythm in M₂KO mice, especially when the stress is acute. This implies the role of M₂ muscarinic receptor in stress response.

Muscarinic M2 receptor promotes vasopressin synthesis in mice supraoptic nuclei

Muscarinic acetylcholine receptors have been suggested to be implicated in arginine-vasopressin secretion because intracerebroventricular muscarinic agonist administration induces arginine-vasopressin release into the circulation. Although which subtype is involved in the regulation of arginine-vasopressin secretion is unclear, M₂ receptors have been reported to be highly expressed in the hypothalamus. In the present study, M₂ receptor-knockout mice were used to elucidate whether M₂ receptor regulates arginine-vasopressin synthesis in the paraventricular nuclei and supraoptic nuclei of the hypothalamus. The number of arginine-vasopressin-immunoreactive neurons in M₂ receptor-knockout mice was significantly decreased in the supraoptic nuclei, but not in the paraventricular nuclei compared with wild-type mice. Plasma arginine-vasopressin level in M₂ receptor-knockout mice was also significantly lower than in the wild-type mice. Urinary volume and frequency as well as water intake in M₂ receptor-knockout mice were significantly higher than those in wild-type mice. The V₂ vasopressin receptor expression in kidneys of M₂ receptor-knockout mice was comparable with that of wild-type mice, and increased urination in M₂ receptor-knockout mice was significantly decreased by administration of desmopressin, a specific V₂ receptor agonist, suggesting that V₂ receptors in the kidneys of M₂ receptor-knockout mice are intact. These results suggest that M₂ receptors promote arginine-vasopressin synthesis in the supraoptic nuclei and play a role in the regulation and maintenance of body fluid.

Expression and relevance of the G protein-gated K+ channel in the mouse ventricle

The atrial G protein-gated inwardly rectifying K⁺ (GIRK) channel is a critical mediator of parasympathetic influence on cardiac physiology. Here, we probed the details and relevance of the GIRK channel in mouse ventricle. mRNAs for the atrial GIRK channel subunits (GIRK1, GIRK4), M2 muscarinic receptor (M₂R), and RGS6, a negative regulator of atrial GIRK-dependent signaling, were detected in mouse ventricle at relatively low levels. The cholinergic agonist carbachol (CCh) activated small GIRK currents in adult wild-type ventricular myocytes that exhibited relatively slow kinetics and low CCh sensitivity; these currents were absent in ventricular myocytes from Girk1^-/- or Girk4^-/- mice. While loss of GIRK channels attenuated the CCh-induced shortening of action potential duration and suppression of ventricular myocyte excitability, selective ablation of GIRK channels in ventricle had no effect on heart rate, heart rate variability, or electrocardiogram parameters at baseline or after CCh injection. Additionally, loss of ventricular GIRK channels did not impact susceptibility to ventricular arrhythmias. These data suggest that the mouse ventricular GIRK channel is a GIRK1/GIRK4 heteromer, and show that while it contributes to the cholinergic suppression of ventricular myocyte excitability, this influence does not substantially impact cardiac physiology or ventricular arrhythmogenesis in the mouse.

Ubiquitin C-Terminal Hydrolase L1 regulates myoblast proliferation and differentiation

Skeletal muscles are dynamic tissues that possess regenerative abilities, which require multiple processes and regulatory factors. Ubiquitin C-Terminal Hydrolase L1 (UCHL1), which is primarily expressed in neuronal tissues, was upregulated in skeletal muscles in disease conditions but its functional role in skeletal muscles is unknown. Using mouse myoblast cells C2C12 as an in vitro model, this study reported that UCHL1 elicits different regulation in myoblast cell proliferation and differentiation. We first observed that UCHL1 protein level was continuously declined during cell differentiation. Gene knockdown of UCHL1 by siRNA resulted in a significant decrease in cell proliferation but marked acceleration of cell differentiation and myotube formation. Meanwhile, UCHL1 gene knockdown upregulated myogenic factors myoD and Myogenin (MyoG). In mice, UCHL1 was significantly upregulated in denervated skeletal muscle. Overall, these novel data suggest that UCHL1 may play a role in myogenesis by promoting myoblast proliferation and inhibiting differentiation.

Nicotinic acetylcholine receptor-mediated protection of the rat heart exposed to ischemia reperfusion

Reperfusion injury following acute myocardial infarction is associated with significant morbidity. Activation of neuronal or non-neuronal cholinergic pathways in the heart has been shown to reduce ischemic injury and this effect has been attributed primarily to muscarinic acetylcholine receptors. In contrast, the role of nicotinic receptors, specifically alpha-7 subtype (α7nAChR) in the myocardium remains unknown which offers an opportunity to potentially repurpose several agonists/modulators that are currently under development for neurologic indications. Treatment of ex vivo and in vivo rat models of cardiac ischemia/reperfusion (I/R) with a selective α7nAChR agonist (GTS21) showed significant increases in left ventricular developing pressure, and rates of pressure development without effects on heart rate. These positive functional effects were blocked by co-administration with methyllycaconatine (MLA), a selective antagonist of α7nAChRs. In vivo, delivery of GTS21 at the initiation of reperfusion, reduced infarct size by 42% (p<0.01) and decreased tissue reactive oxygen species (ROS) by 62% (p<0.01). Flow cytometry of MitoTracker Red stained mitochondria showed that mitochondrial membrane potential was normalized in mitochondria isolated from GTS21 treated compared to untreated I/R hearts. Intracellular ATP concentration in cultured cardiomyocytes exposed to hypoxia/reoxygenation was reduced (p<0.001), but significantly increased to normoxic levels with GTS21 treatment, and this was abrogated by MLA pretreatment. Activation of stress-activated kinases, JNK and p38MAPK, were significantly reduced by GTS21 in I/R. We conclude that targeting myocardial 17nAChRs in I/R may provide therapeutic benefit by improving cardiac contractile function through a mechanism that preserves mitochondrial membrane potential, maintains intracellular ATP and reduces ROS generation, thus limiting infarct size.

Chemerin Elicits Potent Constrictor Actions via Chemokine-Like Receptor 1 (CMKLR1), not G-Protein-Coupled Receptor 1 (GPR1), in Human and Rat Vasculature

BACKGROUND

Circulating levels of chemerin are significantly higher in hypertensive patients and positively correlate with blood pressure. Chemerin activates chemokine-like receptor 1 (CMKLR1 or ChemR23) and is proposed to activate the "orphan" G-protein-coupled receptor 1 (GPR1), which has been linked with hypertension. Our aim was to localize chemerin, CMKLR1, and GPR1 in the human vasculature and determine whether 1 or both of these receptors mediate vasoconstriction.

METHODS AND RESULTS

Using immunohistochemistry and molecular biology in conduit arteries and veins and resistance vessels, we localized chemerin to endothelium, smooth muscle, and adventitia and found that CMKLR1 and GPR1 were widely expressed in smooth muscle. C9 (chemerin149-157) contracted human saphenous vein (pD2=7.30±0.31) and resistance arteries (pD2=7.05±0.54) and increased blood pressure in rats by 9.1±1.0 mm Hg at 200 nmol. Crucially, these in vitro and in vivo vascular actions were blocked by CCX832, which we confirmed to be highly selective for CMKLR1 over GPR1. C9 inhibited cAMP accumulation in human aortic smooth muscle cells and preconstricted rat aorta, consistent with the observed vasoconstrictor action. Downstream signaling was explored further and, compared to chemerin, C9 showed a bias factor=≈5000 for the Gi protein pathway, suggesting that CMKLR1 exhibits biased agonism.

CONCLUSIONS

Our data suggest that chemerin acts at CMKLR1, but not GPR1, to increase blood pressure. Chemerin has an established detrimental role in metabolic syndrome, and these direct vascular actions may contribute to hypertension, an additional risk factor for cardiovascular disease. This study provides proof of principle for the therapeutic potential of selective CMKLR1 antagonists.

Molecular and cellular neurocardiology: development, and cellular and molecular adaptations to heart disease

The nervous system and cardiovascular system develop in concert and are functionally interconnected in both health and disease. This white paper focuses on the cellular and molecular mechanisms that underlie neural-cardiac interactions during development, during normal physiological function in the mature system, and during pathological remodelling in cardiovascular disease. The content on each subject was contributed by experts, and we hope that this will provide a useful resource for newcomers to neurocardiology as well as aficionados.

Priming the proteasome by protein kinase G: a novel cardioprotective mechanism of sildenafil

The proteasome mediates the degradation of most cellular proteins including misfolded proteins, pivotal to intracellular protein hemostasis. Proteasome functional insufficiency is implicated in a large subset of human failing hearts. Experimental studies have established proteasome functional insufficiency as a major pathogenic factor, rationalizing proteasome enhancement as a potentially new therapeutic strategy for congestive heart failure. Protein kinase G activation known to be cardioprotective was recently found to facilitate proteasomal degradation of misfolded proteins in cardiomyocytes; sildenafil was shown to activate myocardial protein kinase G, improve cardiac protein quality control and slow down the progression of cardiac proteinopathy in mice. This identifies the first clinically used drug that is capable of benign proteasome enhancement and unveils a potentially novel cardioprotective mechanism for sildenafil.

Reduced vagal control of the heart in high-fat diet mice: a potential role of increased butyrylcholinesterase

Suppressed parasympathetic function is commonly present in cardiovascular diseases, aging, obesity, and various other health conditions. Impaired parasympathetic action is known as a detrimental factor and contributes to the adverse outcomes in these conditions. However, the underlying mechanisms remain to be fully addressed. In this study, using high-fat diet (HFD)-induced obese mice as a model, the potential peripheral mechanisms underlying the impaired parasympathetic vagal control of the heart was examined. The HFD induced obesity and metabolic disorder in mice. These obese mice exhibited an attenuated response in heart rate to vagal stimulation, indicating impairment of peripheral parasympathetic activity in the heart. In cholinergic function-related proteins in the atria, protein levels of choline transporter and vesicular acetylcholine transporter were not decreased but increased, and type 2 muscarinic receptors showed a trend toward a reduction in HFD mice atria as compared with regular diet (RD) mice controls. While the protein level of acetylcholinesterase was not different, butyrylcholinesterase (BChE) protein level showed a twofold increase in HFD mice atria as compared with RD mice. Functionally, inhibition of BChE activity partially and significantly improved the attenuated response in heart rate to vagal stimulation in HFD mice. Collectively, these data suggest that increased BChE activity in the atria may contribute to the decreased parasympathetic function in HFD-induced obese mice.

Autonomic cardiocirculatory control in mice with reduced expression of the vesicular acetylcholine transporter

In cardiovascular diseases, sympathetic tone has been comprehensively studied, whereas parasympathetic tone has received minor attention. The vesicular ACh transporter (VAChT) knockdown homozygous (VAChT KD(HOM)) mouse is a useful model for examining the cardiocirculatory sympathovagal balance. Therefore, we investigated whether cholinergic dysfunction caused by reduced VAChT expression could adversely impact hemodynamic parameter [arterial pressure (AP) and heart rate (HR)] daily oscillation, baroreflex sensitivity, hemodynamic variability, sympathovagal balance, and cardiovascular reactivity to restraint stress. Wild-type and VAChT KD(HOM) mice were anesthetized for telemetry transmitter implantation, and APs and HRs were recorded 10 days after surgical recovery. Changes in HR elicited by methylatropine and propranolol provided the indexes of sympathovagal tone. Cardiovascular reactivity in response to a restraint test was examined 24 h after continuous recordings of AP and HR. VAChT KD(HOM) mice exhibited reduced parasympathetic and elevated sympathetic tone. Daily oscillations of AP and HR as well as AP variability were similar between groups. Nevertheless, HR variability, patterns with two dissimilar variations from symbolic analysis, and baroreflex sensitivity were reduced in VAChT KD(HOM) mice. The change in mean AP due to restraint stress was greater in VAChT KD(HOM) mice, whereas the tachycardic response was not. These findings demonstrate that the cholinergic dysfunction present in the VAChT KD(HOM) mouse did not adversely impact basal hemodynamic parameters but promoted autonomic imbalance, an attenuation of baroreflex sensitivity, and a greater pressure response to restraint stress. These results provide a framework for understanding how autonomic imbalance impacts cardiovascular function.

A systematic review concerning the relation between the sympathetic nervous system and heart failure with preserved left ventricular ejection fraction

BACKGROUND

Heart failure with preserved left ventricular ejection fraction (HFPEF) affects about half of all patients diagnosed with heart failure. The pathophysiological aspect of this complex disease state has been extensively explored, yet it is still not fully understood. Since the sympathetic nervous system is related to the development of systolic HF, we hypothesized that an increased sympathetic nerve activation (SNA) is also related to the development of HFPEF. This review summarizes the available literature regarding the relation between HFPEF and SNA.

METHODS AND RESULTS

Electronic databases and reference lists through April 2014 were searched resulting in 7722 unique articles. Three authors independently evaluated citation titles and abstracts, resulting in 77 articles reporting about the role of the sympathetic nervous system and HFPEF. Of these 77 articles, 15 were included for critical appraisal: 6 animal and 9 human studies. Based on the critical appraisal, we selected 9 articles (3 animal, 6 human) for further analysis. In all the animal studies, isoproterenol was administered to mimic an increased sympathetic activity. In human studies, different modalities for assessment of sympathetic activity were used. The studies selected for further evaluation reported a clear relation between HFPEF and SNA.

CONCLUSION

Current literature confirms a relation between increased SNA and HFPEF. However, current literature is not able to distinguish whether enhanced SNA results in HFPEF, or HFPEF results in enhanced SNA. The most likely setting is a vicious circle in which HFPEF and SNA sustain each other.

Cholinergic activity as a new target in diseases of the heart

The autonomic nervous system is an important modulator of cardiac signaling in both health and disease. In fact, the significance of altered parasympathetic tone in cardiac disease has recently come to the forefront. Both neuronal and nonneuronal cholinergic signaling likely play a physiological role, since modulating acetylcholine (ACh) signaling from neurons or cardiomyocytes appears to have significant consequences in both health and disease. Notably, many of these effects are solely due to changes in cholinergic signaling, without altered sympathetic drive, which is known to have significant adverse effects in disease states. As such, it is likely that enhanced ACh-mediated signaling not only has direct positive effects on cardiomyocytes, but it also offsets the negative effects of hyperadrenergic tone. In this review, we discuss recent studies that implicate ACh as a major regulator of cardiac remodeling and provide support for the notion that enhancing cholinergic signaling in human patients with cardiac disease can reduce morbidity and mortality. These recent results support the idea of developing large clinical trials of strategies to increase cholinergic tone, either by stimulating the vagus or by increased availability of Ach, in heart failure.

The M2 muscarinic receptors are essential for signaling in the heart left ventricle during restraint stress in mice

We hypothesized that muscarinic receptors (MRs) in the heart have a role in stress responses and thus investigated changes in MR signaling (gene expression, number of receptors, adenylyl cyclase (AC), phospholipase C (PLC), protein kinase A and C (PKA and PKC) and nitric oxide synthase [NOS]) in the left ventricle, together with telemetric measurement of heart rate (HR) in mice (wild type [WT] and M2 knockout [KO]) during and after one (1R) or seven sessions (7R) of restraint stress (seven mice per group). Stress decreased M2 MR mRNA and cell surface MR in the left ventricle in WT mice. In KO mice, 1R, but not 7R, decreased surface MR. Similarly, AC activity was decreased in WT mice after 1R and 7R, whereas in KO mice, there was no change. PLC activity was also decreased after 1R in WT and KO mice. This is in accord with the concept that cAMP is a key player in HR regulation. No change was found with stress in NOS activity. Amount of AC and PKA protein was not changed, but was altered for PKC isoenzymes (PKCα, β, γ, η and ϵ (increased) in KO mice, and PKCι (increased) in WT mice). KO mice were more susceptible to stress as shown by inability to compensate HR during 120 min following repeated stress. The results imply that not only M2 but also M3 are involved in stress signaling and in allostasis. We conclude that for a normal stress response, the expression of M2 MR to mediate vagal responses is essential.

Pyridostigmine restores cardiac autonomic balance after small myocardial infarction in mice

The effect of pyridostigmine (PYR) - an acetylcholinesterase inhibitor - on hemodynamics and cardiac autonomic control, was never studied in conscious myocardial infarcted mice. Telemetry transmitters were implanted into the carotid artery under isoflurane anesthesia. Seven to ten days after recovery from the surgery, basal arterial pressure and heart rate were recorded, while parasympathetic and sympathetic tone (ΔHR) was evaluated by means of methyl atropine and propranolol. After the basal hemodynamic recording the mice were subjected to left coronary artery ligation for producing myocardial infarction (MI), or sham operation, and implantation of minipumps filled with PYR or saline. Separate groups of anesthetized (isoflurane) mice previously (4 weeks) subjected to MI, or sham coronary artery ligation, were submitted to cardiac function examination. The mice exhibited an infarct length of approximately 12%, no change in arterial pressure and increased heart rate only in the 1st week after MI. Vagal tone decreased in the 1^st week, while the sympathetic tone was increased in the 1^st and 4^th week after MI. PYR prevented the increase in heart rate but did not affect the arterial pressure. Moreover, PYR prevented the increase in sympathetic tone throughout the 4 weeks. Concerning the parasympathetic tone, PYR not only impaired its attenuation in the 1^st week, but enhanced it in the 4^th week. MI decreased ejection fraction and increased diastolic and systolic volume. Therefore, the pharmacological increase of peripheral acetylcholine availability by means of PYR prevented tachycardia, increased parasympathetic and decreased sympathetic tone after MI in mice.

Cholinergic signaling exerts protective effects in models of sympathetic hyperactivity-induced cardiac dysfunction

Cholinergic control of the heart is exerted by two distinct branches; the autonomic component represented by the parasympathetic nervous system, and the recently described non-neuronal cardiomyocyte cholinergic machinery. Previous evidence has shown that reduced cholinergic function leads to deleterious effects on the myocardium. Yet, whether conditions of increased cholinergic signaling can offset the pathological remodeling induced by sympathetic hyperactivity, and its consequences for these two cholinergic axes are unknown. Here, we investigated two models of sympathetic hyperactivity: i) the chronic beta-adrenergic receptor stimulation evoked by isoproterenol (ISO), and ii) the α_2A/α_2C-adrenergic receptor knockout (KO) mice that lack pre-synaptic adrenergic receptors. In both models, cholinergic signaling was increased by administration of the cholinesterase inhibitor, pyridostigmine. First, we observed that isoproterenol produces an autonomic imbalance characterized by increased sympathetic and reduced parasympathetic tone. Under this condition transcripts for cholinergic proteins were upregulated in ventricular myocytes, indicating that non-neuronal cholinergic machinery is activated during adrenergic overdrive. Pyridostigmine treatment prevented the effects of ISO on autonomic function and on the ventricular cholinergic machinery, and inhibited cardiac remodeling. α_2A/α_2C-KO mice presented reduced ventricular contraction when compared to wild-type mice, and this dysfunction was also reversed by cholinesterase inhibition. Thus, the cardiac parasympathetic system and non-neuronal cardiomyocyte cholinergic machinery are modulated in opposite directions under conditions of increased sympathetic drive or ACh availability. Moreover, our data support the idea that pyridostigmine by restoring ACh availability is beneficial in heart disease.

Muscarinic 2 receptors modulate cardiac proteasome function in a protein kinase G-dependent manner

Proteasome function insufficiency and inadequate protein quality control are strongly implicated in a large subset of cardiovascular disease and may play an important role in their pathogenesis. Protein degradation by the ubiquitin proteasome system can be physiologically regulated. Cardiac muscarinic 2 (M2) receptors were pharmacologically interrogated in intact mice and cultured neonatal rat ventricular myocytes (NRVMs). Proteasome-mediated proteolysis was measured with a surrogate misfolded protein, proteasome peptidase assay, and by characterizing key proteasome subunits. Successful M2 receptor manipulation in cardiomyocytes was determined by measuring an endogenous protein substrate, and in mice, the cardiovascular physiological response. M2 receptor stimulation was associated with increased proteasome-mediated proteolysis and enhanced peptidase activities, while M2 receptor inhibition yielded opposing results. Additionally, M2 receptor manipulation did not alter abundance of the key proteasome subunits, Rpt6 and β5, but significantly shifted their isoelectric points. Inhibition of protein kinase G abrogated the stimulatory effects on proteasome-mediated proteolysis from M2 receptor activation. We conclude that M2 receptor stimulation enhances, whereas M2 receptor inhibition reduces, proteasome-mediated proteolysis likely through posttranslational modifications. Protein kinase G appears to be the mediator of the M2 receptors actions.

Ubiquitin C-terminal hydrolase L1 interacts with choline transporter in cholinergic cells

Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme, which is highly expressed in neuronal cells. Previous studies have indicated that UCHL1 is involved in cognitive function, neurodegenerative diseases, and neuromuscular junction development. Acetylcholine (Ach) is a critical neurotransmitter in these functions. Yet, the effect of UCHL1 on the cholinergic system has not been reported. In this study, using a cholinergic neuronal cell line, SN56, as an invitro model, we detected the physical interaction of UCHL1 and high affinity choline transporter (CHT), which is a key protein regulating Ach re-synthesis. Reduction of UCHL1 by siRNA gene knockdown significantly increased poly-ubiquitinated CHT and decreased native CHT protein level, but did not affect CHT mRNA expression. Biotinylation assay showed that UCHL1 is localized only in the cytosol of the cells and that the gene knockdown of UCHL1 significantly reduced cytosolic CHT but had no significant effect on membrane CHT level. These data provide novel and potentially important evidence that UCHL1 may play a role in the regulation of cholinergic function by affecting CHT ubiquitination and degradation.

Regulation of cholinergic activity by the vesicular acetylcholine transporter

Acetylcholine, the first chemical to be identified as a neurotransmitter, is packed in synaptic vesicles by the activity of VAChT (vesicular acetylcholine transporter). A decrease in VAChT expression has been reported in a number of diseases, and this has consequences for the amount of acetylcholine loaded in synaptic vesicles as well as for neurotransmitter release. Several genetically modified mice targeting the VAChT gene have been generated, providing novel models to understand how changes in VAChT affect transmitter release. A surprising finding is that most cholinergic neurons in the brain also can express a second type of vesicular neurotransmitter transporter that allows these neurons to secrete two distinct neurotransmitters. Thus a given neuron can use two neurotransmitters to regulate different physiological functions. In addition, recent data indicate that non-neuronal cells can also express the machinery used to synthesize and release acetylcholine. Some of these cells rely on VAChT to secrete acetylcholine with potential physiological consequences in the periphery. Hence novel functions for the oldest neurotransmitter known are emerging with the potential to provide new targets for the treatment of several pathological conditions.

Electrophysiological and pharmacological evaluation of the nicotinic cholinergic system in chagasic rats

Background

Two theories attempt to explain the changes observed in the nicotinic acetylcholine receptors (nAChRs) in chagasic cardiomyopathy. The neurogenic theory proposes that receptor changes are due to loss of intracardiac ganglia parasympathetic neurons. The immunogenic theory proposes that the nAChRs changes are the result of autoantibodies against these receptors. Both theories agreed that nAChRs functional expression could be impaired in Chagas disease.

Methods

We evaluated nAChRs functional integrity in 54 Sprague Dawley rats, divided in two groups: healthy and chronic chagasic rats. Rats were subjected to electrocardiographic studies in the whole animal under pentobarbital anesthesia, by isolation and stimulation of vagus nerves and in isolated beating hearts (Langendorff’s preparation).

Results

Nicotine, 10 μM, induced a significant bradycardia in both groups. However, rats that had previously received reserpine did not respond to nicotine stimulation. β-adrenergic stimulation, followed by nicotine treatment, induced tachycardia in chagasic rats; while inducing bradycardia in healthy rats. Bilateral vagus nerve stimulation induced a significantly higher level of bradycardia in healthy rats, compared to chagasic rats; physostigmine potentiated the bradycardic response to vagal stimulation in both experimental groups. Electric stimulation (e.g., ≥ 2 Hz), in the presence of physostigmine, produced a comparable vagal response in both groups. In isolated beating-heart preparations 1 μM nicotine induced sustained bradycardia in healthy hearts while inducing tachycardia in chagasic hearts. Higher nicotine doses (e.g.,10 – 100 uM) promoted the characteristic biphasic response (i.e., bradycardia followed by tachycardia) in both groups. 10 nM DHβE antagonized the effect of 10 μM nicotine, unmasking the cholinergic bradycardic effect in healthy rats only. 1 nM α-BGT alone induced bradycardia in healthy hearts but antagonized the 10 μM nicotine-induced tachycardia in chagasic rats. In healthy but not in chagasic hearts, 10 μM nicotine shortened PQ and PR interval, an effect counteracted by MA, DHβE and αBGT

Conclusion

Our results suggest that cholinergic function is impaired in chronic Chagas disease in rats, a phenomena that could be related to alteration on the nAChR expression.

Decrease in heart adrenoceptor gene expression and receptor number as compensatory tool for preserved heart function and biological rhythm in M(2) KO animals

Muscarinic receptors (MR) are main cardioinhibitory receptors. We investigated the changes in gene expression, receptor number, echocardiography, muscarinic/adrenergic agonist/antagonist changes in heart rate (HR) and HR biorhythm in M(2) KO mice (mice lacking the main cardioinhibitory receptors) in the left ventricle (LV) and right ventricle (RV). We hypothesize that the disruption of M(2) MR, key players in parasympathetic bradycardia, would change the number of receptors with antagonistic effects on the heart (β(1)- and β(2)-adrenoceptors, BAR), while the function of the heart would be changed only marginally. We have found changes in LV, but not in RV: decrease in M(3) MR, β(1)- and β(2)-adrenoceptor gene expressions that were accompanied by a decrease in MR and BAR receptor binding. No changes were found both in LV systolic and diastolic function as assessed by echocardiography (e.g., similar LV end-systolic and end-diastolic diameter, fractional shortening, mitral flow characteristics, and maximal velocity in LV outflow tract). We have found only marginal changes in specific HR biorhythm parameters. The effects of isoprenaline and propranolol on HR were similar in WT and KO (but with lesser extent). Atropine was not able to increase HR in KO animals. Carbachol decreased the HR in WT but increased HR in KO, suggesting the presence of cardiostimulatory MR. Therefore, we can conclude that although the main cardioinhibitory receptors are not present in the heart, the function is not much affected. As possible mechanisms of almost normal cardiac function, the decreases of both β(1)- and β(2)-adrenoceptor gene expression and receptor binding should be considered.

Non-neuronal cholinergic machinery present in cardiomyocytes offsets hypertrophic signals

Recent work has provided compelling evidence that increased levels of acetylcholine (ACh) can be protective in heart failure, whereas reduced levels of ACh secretion can cause heart malfunction. Previous data show that cardiomyocytes themselves can actively secrete ACh, raising the question of whether this cardiomyocyte derived ACh may contribute to the protective effects of ACh in the heart. To address the functionality of this non-neuronal ACh machinery, we used cholinesterase inhibitors and a siRNA targeted to AChE (acetylcholinesterase) as a way to increase the availability of ACh secreted by cardiac cells. By using nitric oxide (NO) formation as a biological sensor for released ACh, we showed that cholinesterase inhibition increased NO levels in freshly isolated ventricular myocytes and that this effect was prevented by atropine, a muscarinic receptor antagonist, and by inhibition of ACh synthesis or vesicular storage. Functionally, cholinesterase inhibition prevented the hypertrophic effect as well as molecular changes and calcium transient alterations induced by adrenergic overstimulation in cardiomyocytes. Moreover, inhibition of ACh storage or atropine blunted the anti-hypertrophic action of cholinesterase inhibition. Altogether, our results show that cardiomyocytes possess functional cholinergic machinery that offsets deleterious effects of hyperadrenergic stimulation. In addition, we show that adrenergic stimulation upregulates expression levels of cholinergic components. We propose that this cardiomyocyte cholinergic signaling could amplify the protective effects of the parasympathetic nervous system in the heart and may counteract or partially neutralize hypertrophic adrenergic effects.

Increase in cardiac M2-muscarinic receptor expression is regulated by GATA binding protein 4 (GATA-4) in streptozotocin-induced diabetic rats

BACKGROUND

An increase in cardiac M2-muscarinic receptor (M2-mAChR) expression in diabetic rats has been observed, but the molecular mechanism of this increase remains unclear. The transcriptional activity of GATA binding protein 4 (GATA-4) has been documented to regulate the expression of M2-mAChR genes. In this study, we were interested in identifying the role of GATA-4 in the increase in M2-mAChR in diabetic rats and a primary culture of cardiomyocytes.

METHODS

Streptozotocin-induced diabetic rats (STZ-rats) and high-glucose (D-glucose 30 mM, 24h)-treated primary cultures of cardiomyocytes from neonatal rats were used to investigate the role of GATA-4 in the change in M2-mAChR. The protein expression was determined by Western blot analysis. Phlorizin (Na(+)-glucose co-transport inhibitor), insulin, tiron (radical scavenger), PD98059 (ERK inhibitor) and SB203580 (p38 inhibitor) were used. We also silenced GATA-4 by RNAi to investigate the changes in M2-mAChR expression.

RESULTS

The cardiac output was reduced in STZ-rats with a higher expression of M2-mAChR or phosphorylated GATA-4 in the heart. These changes were reversed after correction of the blood sugar level. In cardiomyocytes, high glucose treatment also increased M2-mAChR expression and GATA-4 phosphorylation. These changes were reversed by tiron (ROS scavenger) or PD98059 (MEK/ERK inhibitor). However, an increase in M2-mAChR expression was not observed when GATA-4 was silenced by small interfering RNA (siRNA) in cardiomyocytes.

CONCLUSIONS

We suggest that hyperglycemia can cause a higher expression of M2-mAChR in cardiomyocytes mainly through ROS to enhance MEK/ERK for phosphorylation of GATA-4.

Can β2-adrenoceptor agonists, anticholinergic drugs, and theophylline contribute to the control of pulmonary inflammation and emphysema in COPD?

Chronic obstructive pulmonary disease (COPD) has become a global epidemic disease with an increased morbidity and mortality in the world. Inflammatory process progresses and contributes to irreversible airflow limitation. However, there is no available therapy to better control the inflammatory progression and therefore to reduce the exacerbations and mortality. Thus, the development of efficient anti-inflammatory therapies is a priority for patients with COPD. β(2) -Adrenoceptor agonists and anticholinergic agents are widely used as first line drugs in management of COPD because of their efficient bronchodilator properties. At present, many studies in vitro and some data obtained in laboratory animals reveal the potential anti-inflammatory effects of these bronchodilators but their protective role against chronic inflammation and the development of emphysema in patients with COPD remains to be investigated. The anti-inflammatory effects of theophylline at low doses have also been identified. Beneficial interactions between glucocorticoids and bronchodilators have been reported, and signaling pathways explaining these synergistic effects begin to be understood, especially for theophylline. Recent data demonstrating interactions between anticholinergics with β(2) -adrenoceptor agonists aiming to better control the pulmonary inflammation and the development of emphysema in animal models of COPD justify the priority to investigate the interactive effects of a tritherapy associating corticoids with the two main categories of bronchodilators.

Enhanced pressor response to acute Ang II infusion in mice lacking membrane-associated prostaglandin E2 synthase-1

AIM

To examine the contribution of vascular membrane-associated prostaglandin E2 synthase-1 (mPGES-1) to acute blood pressure homeostasis.

METHODS

Angiotensin II (AngII, 75 pmol·kg⁻¹·min⁻¹) was continuously infused via the jugular vein into wild-type and mPGES-1(-/-) mice for 30 min, and blood pressure was measured by carotid arterial catheterization. RT-PCR and immunohistochemistry were performed to detect the expression and localization of mPGES-1 in the mouse arterial vessels. Mesenteric arteries were dissected from mice of both genotypes to study vessel tension and measure vascular PGE2 levels.

RESULTS

Wild-type and mPGES-1(-/-) mice showed similar blood pressure levels at baseline, and the acute intravenous infusion of AngII caused a greater increase in mean arterial pressure in the mPGES-1(-/-) group, with a similar diuretic and natriuretic response in both groups. mPGES-1 was constitutively expressed in the aortic and mesenteric arteries and vascular smooth muscle cells of wild-type mice. Strong staining was detected in the smooth muscle layer of arterial vessels. Ex vivo treatment of mesenteric arteries with AngII produced more vasodilatory PGE2 in wild-type than in mPGES-1(-/-) mice. In vitro tension assays further revealed that the mesenteric arteries of mPGES-1(-/-) mice exhibited a greater vasopressor response to AngII than those arteries of wild-type mice.

CONCLUSION

Vascular mPGES-1 acts as an important tonic vasodilator, contributing to acute blood pressure regulation.

Tachycardia, reduced vagal capacity, and age-dependent ventricular dysfunction arising from diminished expression of the presynaptic choline transporter

Healthy cardiovascular function relies on a balanced and responsive integration of noradrenergic and cholinergic innervation of the heart. High-affinity choline uptake by cholinergic terminals is pivotal for efficient ACh production and release. To date, the cardiovascular impact of diminished choline transporter (CHT) expression has not been directly examined, largely due to the transporter's inaccessibility in vivo. Here, we describe findings from cardiovascular experiments using transgenic mice that bear a CHT genetic deficiency. Whereas CHT knockout (CHT(-/-)) mice exhibit early postnatal lethality, CHT heterozygous (CHT(+/-)) mice survive, grow, and reproduce normally and exhibit normal spontaneous behaviors. However, the CHT(+/-) mouse heart displays significantly reduced levels of high-affinity choline uptake accompanied by significantly reduced levels of ACh. Telemeterized recordings of cardiovascular function in these mice revealed tachycardia and hypertension at rest. After treadmill exercise, CHT(+/-) mice exhibited slower heart rate recovery, consistent with a diminished cholinergic reserve, a contention validated through direct vagal nerve stimulation. Echocardiographic and histological experiments revealed an age-dependent decrease in fractional shortening, increased left ventricular dimensions, and increased ventricular fibrosis, consistent with ventricular dysfunction. These cardiovascular phenotypes of CHT(+/-) mice encourage an evaluation of humans bearing reduced CHT expression for their resiliency in maintaining proper heart function as well as risk for cardiovascular disease.

Dysautonomia due to reduced cholinergic neurotransmission causes cardiac remodeling and heart failure

Overwhelming evidence supports the importance of the sympathetic nervous system in heart failure. In contrast, much less is known about the role of failing cholinergic neurotransmission in cardiac disease. By using a unique genetically modified mouse line with reduced expression of the vesicular acetylcholine transporter (VAChT) and consequently decreased release of acetylcholine, we investigated the consequences of altered cholinergic tone for cardiac function. M-mode echocardiography, hemodynamic experiments, analysis of isolated perfused hearts, and measurements of cardiomyocyte contraction indicated that VAChT mutant mice have decreased left ventricle function associated with altered calcium handling. Gene expression was analyzed by quantitative reverse transcriptase PCR and Western blotting, and the results indicated that VAChT mutant mice have profound cardiac remodeling and reactivation of the fetal gene program. This phenotype was attributable to reduced cholinergic tone, since administration of the cholinesterase inhibitor pyridostigmine for 2 weeks reversed the cardiac phenotype in mutant mice. Our findings provide direct evidence that decreased cholinergic neurotransmission and underlying autonomic imbalance cause plastic alterations that contribute to heart dysfunction.

Heart failure causes cholinergic transdifferentiation of cardiac sympathetic nerves via gp130-signaling cytokines in rodents

Although several cytokines and neurotrophic factors induce sympathetic neurons to transdifferentiate into cholinergic neurons in vitro, the physiological and pathophysiological roles of this remain unknown. During congestive heart failure (CHF), sympathetic neural tone is upregulated, but there is a paradoxical reduction in norepinephrine synthesis and reuptake in the cardiac sympathetic nervous system (SNS). Here we examined whether cholinergic transdifferentiation can occur in the cardiac SNS in rodent models of CHF and investigated the underlying molecular mechanism(s) using genetically modified mice. We used Dahl salt-sensitive rats to model CHF and found that, upon CHF induction, the cardiac SNS clearly acquired cholinergic characteristics. Of the various cholinergic differentiation factors, leukemia inhibitory factor (LIF) and cardiotrophin-1 were strongly upregulated in the ventricles of rats with CHF. Further, LIF and cardiotrophin-1 secreted from cultured failing rat cardiomyocytes induced cholinergic transdifferentiation in cultured sympathetic neurons, and this process was reversed by siRNAs targeting Lif and cardiotrophin-1. Consistent with the data in rats, heart-specific overexpression of LIF in mice caused cholinergic transdifferentiation in the cardiac SNS. Further, SNS-specific targeting of the gene encoding the gp130 subunit of the receptor for LIF and cardiotrophin-1 in mice prevented CHF-induced cholinergic transdifferentiation. Cholinergic transdifferentiation was also observed in the cardiac SNS of autopsied patients with CHF. Thus, CHF causes target-dependent cholinergic transdifferentiation of the cardiac SNS via gp130-signaling cytokines secreted from the failing myocardium.

Pressed for time: the circadian clock and hypertension

Hypertension is a major risk factor for cardiovascular disease and death. The "silent" rise of blood pressure that occurs over time is largely asymptomatic. However, its impact is deafening-causing and exacerbating cardiovascular disease, end-organ damage, and death. The present article addresses recent observations from human and animal studies that provide new insights into how the circadian clock regulates blood pressure, contributes to hypertension, and ultimately evolves vascular disease. Further, the molecular components of the circadian clock and their relationship with locomotor activity, metabolic control, fluid balance, and vascular resistance are discussed with an emphasis on how these novel, circadian clock-controlled mechanisms contribute to hypertension.

Loss of M2 muscarinic receptor function inhibits development of hypoxic bradycardia and alters cardiac beta-adrenergic sensitivity in larval zebrafish (Danio rerio)

Fish exposed to hypoxia develop decreased heart rate, or bradycardia, the physiological significance of which remains unknown. The general muscarinic receptor antagonist atropine abolishes the development of this hypoxic bradycardia, suggesting the involvement of muscarinic receptors. In this study, we tested the hypothesis that the hypoxic bradycardia is mediated specifically by stimulation of the M(2) muscarinic receptor, the most abundant subtype in the vertebrate heart. Zebrafish (Danio rerio) were reared at two levels of hypoxia (30 and 40 Torr PO(2)) from the point of fertilization. In hypoxic fish, the heart rate was significantly lower than in normoxic controls from 2 to 10 days postfertilization (dpf). At the more severe level of hypoxia (30 Torr PO(2)), there were significant increases in the relative mRNA expression of M(2) and the cardiac type beta-adrenergic receptors (beta1AR, beta2aAR, and beta2bAR) at 4 dpf. The hypoxic bradycardia was abolished (at 40 Torr PO(2)) or significantly attenuated (at 30 Torr PO(2)) in larvae experiencing M(2) receptor knockdown (using morpholino antisense oligonucleotides). Sham-injected larvae exhibited typical hypoxic bradycardia in both hypoxic regimens. The expression of beta1AR, beta2aAR, beta2bAR, and M(2) mRNA was altered at various stages between 1 and 4 dpf in larvae experiencing M(2) receptor knockdown. Interestingly, M(2) receptor knockdown revealed a cardioinhibitory role for the beta(2)-adrenergic receptor. This is the first study to demonstrate a specific role of the M(2) muscarinic receptor in the initiation of hypoxic bradycardia in fish.