An Alpha-1A Adrenergic Receptor Agonist Prevents Acute Doxorubicin Cardiomyopathy in Male Mice

Right ventricular dysfunction following surgical repair of tetralogy of Fallot: Molecular pathways and therapeutic prospects

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease (CHD). Although surgical correction of TOF is possible, patients often face challenges related to right ventricle dysfunction (RVD) post-surgery, which can significantly impact their long-term survival. The causes of RVD in TOF patients are complex, involving both the unique structural characteristics of the TOF heart and damage resulting from surgical interventions. Residual anatomical issues following TOF repair are often unavoidable, placing the RV under stress and leading to the activation of multiple molecular pathways. This review comprehensively outlines the causes of RVD in patients after TOF surgery, particularly focusing the molecular pathways that contribute to RVD, including established signaling pathways as well as emerging pathways identified through transcriptomic analysis of RV myocardium in TOF patients. We also highlight the features of these molecular pathways concerning RVD, as well as the influence of gender disparities on these molecular pathways. By interpreting the causes and molecular mechanisms underlying RVD after TOF surgery, this review provides new insights for managing RVD in repaired TOF, potentially paving the way for targeted therapies aimed at improving long-term outcomes for those affected by RVD.

Agomelatine ameliorates doxorubicin-induced cortical and hippocampal brain injury via inhibition of TNF-alpha/NF-kB pathway

Side effects of doxorubicin (DOX) are mainly due to oxidative stress, with the involvement of inflammatory and apoptotic mechanisms. Agomelatine (AGO) is a melatonin receptor agonist with antioxidant, anti-inflammatory, and anti-apoptotic features. This study aimed to evaluate the effects of AGO with different doses on DOX-induced neurotoxicity. Rats were divided into four groups as control, DOX (40 mg/kg, intraperitoneal single dose), DOX + AGO20 (20 mg/kg AGO oral gavage for 14 days), and DOX + AGO40 (40 mg/kg AGO oral gavage for 14 days). On day 14, brain tissues were collected for biochemical, histopathological, and genetic examinations. DOX significantly increased malondialdehyde and decreased superoxide dismutase and catalase (CAT) levels. CAT levels were significantly increased only in the DOX + AGO40 group compared to the DOX group (p = 0.040) while other changes in oxidant and antioxidant indicators were insignificant. DOX-induced significant increases in TNF-alpha and NF-κB were reversed following both low and high-dose AGO administration in a dose-dependent manner (p < 0.001 for both doses). Cellular shrinkage, pycnotic change, and vacuolization in apoptotic bodies were apparent in the cortical and hippocampal areas of DOX-treated samples. Both doses of AGO alleviated these histopathological changes (p = 0.01 for AGO20 and p = 0.05 for AGO40). Significantly increased apoptosis shown with caspase-3 immunostaining in the DOX group was alleviated following AGO administration, with additional improvement after high-dose treatment (p < 0.01 for DOX compared to both AGO groups and p < 0.05 for AGO40 compared to AGO20). AGO can be protective against DOX-induced neurotoxicity by antioxidant, anti-inflammatory, and anti-apoptotic mechanisms in a dose-dependent manner.

The alpha-1A adrenergic receptor regulates mitochondrial oxidative metabolism in the mouse heart

AIMS

The sympathetic nervous system regulates numerous critical aspects of mitochondrial function in the heart through activation of adrenergic receptors (ARs) on cardiomyocytes. Mounting evidence suggests that α1-ARs, particularly the α1A subtype, are cardioprotective and may mitigate the deleterious effects of chronic β-AR activation by shared ligands. The mechanisms underlying these adaptive effects remain unclear. Here, we tested the hypothesis that α1A-ARs adaptively regulate cardiomyocyte oxidative metabolism in both the uninjured and infarcted heart.

METHODS

We used high resolution respirometry, fatty acid oxidation (FAO) enzyme assays, substrate-specific electron transport chain (ETC) enzyme assays, transmission electron microscopy (TEM) and proteomics to characterize mitochondrial function comprehensively in the uninjured hearts of wild type and α1A-AR knockout mice and defined the effects of chronic β-AR activation and myocardial infarction on selected mitochondrial functions.

RESULTS

We found that isolated cardiac mitochondria from α1A-KO mice had deficits in fatty acid-dependent respiration, FAO, and ETC enzyme activity. TEM revealed abnormalities of mitochondrial morphology characteristic of these functional deficits. The selective α1A-AR agonist A61603 enhanced fatty-acid dependent respiration, fatty acid oxidation, and ETC enzyme activity in isolated cardiac mitochondria. The β-AR agonist isoproterenol enhanced oxidative stress in vitro and this adverse effect was mitigated by A61603. A61603 enhanced ETC Complex I activity and protected contractile function following myocardial infarction.

CONCLUSIONS

Collectively, these novel findings position α1A-ARs as critical regulators of cardiomyocyte metabolism in the basal state and suggest that metabolic mechanisms may underlie the protective effects of α1A-AR activation in the failing heart.

A PAM of the α1A-Adrenergic receptor rescues biomarker, long-term potentiation, and cognitive deficits in Alzheimer's disease mouse models without effects on blood pressure

α1-Adrenergic Receptors (ARs) regulate the sympathetic nervous system by the binding of norepinephrine (NE) and epinephrine (Epi) through different subtypes (α1A, α1B, α1D). α1A-AR activation is hypothesized to be memory forming and cognitive enhancing but drug development has been stagnant due to unwanted side effects on blood pressure. We recently reported the pharmacological characterization of the first positive allosteric modulator (PAM) for the α1A-AR with predictive pro-cognitive and memory properties. In this report, we now demonstrate the in vivo characteristics of Compound 3 (Cmpd-3) in two genetically-different Alzheimer's Disease (AD) mouse models. Drug metabolism and pharmacokinetic studies indicate sufficient brain penetrance and rapid uptake into the brain with low to moderate clearance, and a favorable inhibition profile against the major cytochrome p450 enzymes. Oral administration of Cmpd-3 (3-9 mg/kg QD) can fully rescue long-term potentiation defects and AD biomarker profile (amyloid β-40, 42) within 3 months of dosing to levels that were non-significant from WT controls and which outperformed donepezil (1 mg/kg QD). There were also significant effects on paired pulse facilitation and cognitive behavior. Long-term and high-dose in vivo studies with Cmpd-3 revealed no effects on blood pressure. Our results suggest that Cmpd-3 can maintain lasting therapeutic levels and efficacy with disease modifying effects with a once per day dosing regimen in AD mouse models with no observed side effects.

Increased length-dependent activation of human engineered heart tissue after chronic α1A-adrenergic agonist treatment: testing a novel heart failure therapy

Chronic stimulation of cardiac α1A-adrenergic receptors (α1A-ARs) improves symptoms in multiple preclinical models of heart failure. However, the translational significance remains unclear. Human engineered heart tissues (EHTs) provide a means of quantifying the effects of chronic α1A-AR stimulation on human cardiomyocyte physiology. EHTs were created from thin slices of decellularized pig myocardium seeded with human induced pluripotent stem cell (iPSC)-derived cardiomyocytes and fibroblasts. With a paired experimental design, EHTs were cultured for 3 wk, mechanically tested, cultured again for 2 wk with α1A-AR agonist A61603 (10 nM) or vehicle control, and retested after drug washout for 24 h. Separate control experiments determined the effects of EHT age (3-5 wk) or repeat mechanical testing. We found that chronic A61603 treatment caused a 25% increase of length-dependent activation (LDA) of contraction compared with vehicle treatment (n = 7/group, P = 0.035). EHT force was not increased after chronic A61603 treatment. However, after vehicle treatment, EHT force was increased by 35% relative to baseline testing (n = 7/group, P = 0.022), suggesting EHT maturation. Control experiments suggested that increased EHT force resulted from repeat mechanical testing, not from EHT aging. RNA-seq analysis confirmed that the α1A-AR is expressed in human EHTs and found chronic A61603 treatment affected gene expression in biological pathways known to be activated by α1A-ARs, including the MAP kinase signaling pathway. In conclusion, increased LDA in human EHT after chronic A61603 treatment raises the possibility that chronic stimulation of the α1A-AR might be beneficial for increasing LDA in human myocardium and might be beneficial for treating human heart failure by restoring LDA.NEW & NOTEWORTHY Chronic stimulation of α1A-adrenergic receptors (α1A-ARs) is known to mediate therapeutic effects in animal heart failure models. To investigate the effects of chronic α1A-AR stimulation in human cardiomyocytes, we tested engineered heart tissue (EHT) created with iPSC-derived cardiomyocytes. RNA-seq analysis confirmed human EHT expressed α1A-ARs. Chronic (2 wk) α1A-AR stimulation with A61603 (10 nM) increased length-dependent activation (LDA) of contraction. Chronic α1A-AR stimulation might be beneficial for treating human heart failure by restoring LDA.

α1-Adrenergic Receptors: Insights into Potential Therapeutic Opportunities for COVID-19, Heart Failure, and Alzheimer's Disease

α1-Adrenergic receptors (ARs) are members of the G-Protein Coupled Receptor superfamily and with other related receptors (β and α2), they are involved in regulating the sympathetic nervous system through binding and activation by norepinephrine and epinephrine. Traditionally, α1-AR antagonists were first used as anti-hypertensives, as α1-AR activation increases vasoconstriction, but they are not a first-line use at present. The current usage of α1-AR antagonists increases urinary flow in benign prostatic hyperplasia. α1-AR agonists are used in septic shock, but the increased blood pressure response limits use for other conditions. However, with the advent of genetic-based animal models of the subtypes, drug design of highly selective ligands, scientists have discovered potentially newer uses for both agonists and antagonists of the α1-AR. In this review, we highlight newer treatment potential for α1A-AR agonists (heart failure, ischemia, and Alzheimer's disease) and non-selective α1-AR antagonists (COVID-19/SARS, Parkinson's disease, and posttraumatic stress disorder). While the studies reviewed here are still preclinical in cell lines and rodent disease models or have undergone initial clinical trials, potential therapeutics discussed here should not be used for non-approved conditions.

Midodrine to optimize heart failure therapy in patients with concurrent hypotension

According to the Centers for Disease Control and Prevention statistics, about 6.2 million adults in the United States have heart failure. Guideline-Directed Medical Therapy (GDMT) involving the use of renin-angiotensin-aldosterone system inhibitors with or without a neprilysin inhibitor, β-blockers, mineralocorticoid-receptor-antagonists, and sodium-glucose cotransporter-2 inhibitors serve as the backbone for heart failure with reduced ejection fraction (HFrEF) therapy. However, in patients with refractory hypotension, the initiation of GDMT may not be possible. We present four cases where the use of midodrine, an alpha adrenergic agonist, serves as bridge therapy for the initiation or continuation of GDMT with marked clinical improvement. These cases illustrate how exacerbations of HFrEF may be ameliorated with outpatient midodrine titration among patients with baseline, persistent hypotension such that GDMT may be better tolerated.

Sympatho-adrenergic mechanisms in heart failure: new insights into pathophysiology

The sympathetic nervous system is activated in the setting of heart failure (HF) to compensate for hemodynamic instability. However, acute sympathetic surge or sustained high neuronal firing rates activates β-adrenergic receptor (βAR) signaling contributing to myocardial remodeling, dysfunction and electrical instability. Thus, sympatho-βAR activation is regarded as a hallmark of HF and forms pathophysiological basis for β-blocking therapy. Building upon earlier research findings, studies conducted in the recent decades have significantly advanced our understanding on the sympatho-adrenergic mechanism in HF, which forms the focus of this article. This review notes recent research progress regarding the roles of cardiac β2AR or α1AR in the failing heart, significance of β1AR-autoantibodies, and βAR signaling through G-protein independent signaling pathways. Sympatho-βAR regulation of immune cells or fibroblasts is specifically discussed. On the neuronal aspects, knowledge is assembled on the remodeling of sympathetic nerves of the failing heart, regulation by presynaptic α2AR of NE release, and findings on device-based neuromodulation of the sympathetic nervous system. The review ends with highlighting areas where significant knowledge gaps exist but hold promise for new breakthroughs.

Impact of Aldosterone on the Failing Myocardium: Insights from Mitochondria and Adrenergic Receptors Signaling and Function

The mineralocorticoid aldosterone regulates electrolyte and blood volume homeostasis, but it also adversely modulates the structure and function of the chronically failing heart, through its elevated production in chronic human post-myocardial infarction (MI) heart failure (HF). By activating the mineralocorticoid receptor (MR), a ligand-regulated transcription factor, aldosterone promotes inflammation and fibrosis of the heart, while increasing oxidative stress, ultimately induding mitochondrial dysfunction in the failing myocardium. To reduce morbidity and mortality in advanced stage HF, MR antagonist drugs, such as spironolactone and eplerenone, are used. In addition to the MR, aldosterone can bind and stimulate other receptors, such as the plasma membrane-residing G protein-coupled estrogen receptor (GPER), further complicating it signaling properties in the myocardium. Given the salient role that adrenergic receptor (ARs)-particularly βARs-play in cardiac physiology and pathology, unsurprisingly, that part of the impact of aldosterone on the failing heart is mediated by its effects on the signaling and function of these receptors. Aldosterone can significantly precipitate the well-documented derangement of cardiac AR signaling and impairment of AR function, critically underlying chronic human HF. One of the main consequences of HF in mammalian models at the cellular level is the presence of mitochondrial dysfunction. As such, preventing mitochondrial dysfunction could be a valid pharmacological target in this condition. This review summarizes the current experimental evidence for this aldosterone/AR crosstalk in both the healthy and failing heart, and the impact of mitochondrial dysfunction in HF. Recent findings from signaling studies focusing on MR and AR crosstalk via non-conventional signaling of molecules that normally terminate the signaling of ARs in the heart, i.e., the G protein-coupled receptor-kinases (GRKs), are also highlighted.

Targeting Adrenergic Receptors in Metabolic Therapies for Heart Failure

The heart has a reduced capacity to generate sufficient energy when failing, resulting in an energy-starved condition with diminished functions. Studies have identified numerous changes in metabolic pathways in the failing heart that result in reduced oxidation of both glucose and fatty acid substrates, defects in mitochondrial functions and oxidative phosphorylation, and inefficient substrate utilization for the ATP that is produced. Recent early-phase clinical studies indicate that inhibitors of fatty acid oxidation and antioxidants that target the mitochondria may improve heart function during failure by increasing compensatory glucose oxidation. Adrenergic receptors (α1 and β) are a key sympathetic nervous system regulator that controls cardiac function. β-AR blockers are an established treatment for heart failure and α1A-AR agonists have potential therapeutic benefit. Besides regulating inotropy and chronotropy, α1- and β-adrenergic receptors also regulate metabolic functions in the heart that underlie many cardiac benefits. This review will highlight recent studies that describe how adrenergic receptor-mediated metabolic pathways may be able to restore cardiac energetics to non-failing levels that may offer promising therapeutic strategies.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

Premedication with pioglitazone prevents doxorubicin-induced left ventricular dysfunction in mice

BACKGROUND

Doxorubicin (DOX) is widely used as an effective chemotherapeutic agent for cancers; however, DOX induces cardiac toxicity, called DOX-induced cardiomyopathy. Although DOX-induced cardiomyopathy is known to be associated with a high cumulative dose of DOX, the mechanisms of its long-term effects have not been completely elucidated. Pioglitazone (Pio) is presently contraindicated in patients with symptomatic heart failure owing to the side effects. The concept of drug repositioning led us to hypothesize the potential effects of Pio as a premedication before DOX treatment, and to analyze this hypothesis in mice.

METHODS

First, for the hyperacute (day 1) and acute (day 7) DOX-induced dysfunction models, mice were fed a standard diet with or without 0.02% (wt/wt) Pio for 5 days before DOX treatment (15 mg/kg body weight [BW] via intraperitoneal [i.p.] administration). The following 3 treatment groups were analyzed: standard diet + vehicle (Vehicle), standard diet + DOX (DOX), and Pio + DOX. Next, for the chronic model (day 35), the mice were administrated DOX once a week for 5 weeks (5 mg/kg BW/week, i.p.).

RESULTS

In the acute phase after DOX treatment, the percent fractional shortening of the left ventricle (LV) was significantly decreased in DOX mice. This cardiac malfunction was improved in Pio + DOX mice. In the chronic phase, we observed that LV function was preserved in Pio + DOX mice.

CONCLUSIONS

Our findings may provide a new pathophysiological explanation by which Pio plays a role in the treatment of DOX-induced cardiomyopathy, but the molecular links between Pio and DOX-induced LV dysfunction remain largely elusive.

The mRNA expression of Il6 and Pdcd1 are predictive and protective factors for doxorubicin‑induced cardiotoxicity

Anthracyclines, such as doxorubicin (DOX), have been widely used in the treatment of a number of different solid and hematological malignancies. However, these drugs can inflict cumulative dose-dependent and irreversible damage to the heart, and can occasionally lead to heart failure. The cardiotoxic susceptibility varies among patients treated with anthracycline, and delays in the recognition of cardiotoxicity can result in poor prognoses. Accordingly, if the risk of cardiotoxicity could be predicted prior to drug administration, it would aid in safer and more effective chemotherapy treatment. The present study was carried out to identify genes that can predict DOX-induced cardiotoxicity (DICT). In an in vivo study, mice cumulatively treated with DOX demonstrated increases in serum levels of cardiac enzymes (aspartate aminotransferase, lactate dehydrogenase, creatine kinase MB isoenzyme and troponin T), in addition to decreases in body and heart weights. These changes were indicative of DICT, but the severity of these effects varied among individual mice. In the current study, the correlation in these mice between the extent of DICT and circulating blood concentrations of relevant transcripts before DOX administration was analyzed. Among various candidate genes, the plasma mRNA levels of the genes encoding interleukin 6 (Il6) and programmed cell death 1 (Pdcd1) in blood exhibited significant and positive correlations with the severity of DICT. In an in vitro study using cardiomyocyte H9c2 cells, knockdown of Il6 or Pdcd1 by small interfering RNA was revealed to enhance DOX-induced apoptosis, as determined by luminescent assays. These results suggested that the levels of transcription of Il6 and Pdcd1 in cardiomyocytes serve a protective role against DICT, and that the accumulation of these gene transcripts in blood is a predictive marker for DICT. To the best of our knowledge, this is the first report to demonstrate a role for Il6 and Pdcd1 mRNA expression in DICT.

Cardiac α1A-adrenergic receptors: emerging protective roles in cardiovascular diseases

α1-Adrenergic receptors (ARs) are catecholamine-activated G protein-coupled receptors (GPCRs) that are expressed in mouse and human myocardium and vasculature, and play essential roles in the regulation of cardiovascular physiology. Though α1-ARs are less abundant in the heart than β1-ARs, activation of cardiac α1-ARs results in important biologic processes such as hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Data from the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) indicate that nonselectively blocking α1-ARs is associated with a twofold increase in adverse cardiac events, including heart failure and angina, suggesting that α1-AR activation might also be cardioprotective in humans. Mounting evidence implicates the α1A-AR subtype in these adaptive effects, including prevention and reversal of heart failure in animal models by α1A agonists. In this review, we summarize recent advances in our understanding of cardiac α1A-ARs.

Stimulation of Alpha1-Adrenergic Receptor Ameliorates Cellular Functions of Multiorgans beyond Vasomotion through PPARδ

Cells can shift their metabolism between glycolysis and oxidative phosphorylation to enact their cell fate program in response to external signals. Widely distributed α₁-adrenergic receptors (ARs) are physiologically stimulated during exercise, were reported to associate with the activating energetic AMPK pathway, and are expected to have biological effects beyond their hemodynamic effects. To investigate the effects and mechanism of AR stimulation on the physiology of the whole body, various in vitro and in vivo experiments were conducted using the AR agonist midodrine, 2-amino-N-[2-(2,5-dimethoxyphenyl)-2-hydroxy-ethyl]-acetamide. The expression of various biomarkers involved in ATP production was estimated through Western blotting, reverse transcription polymerase chain reaction, oxygen consumption rate, enzyme-linked immunosorbent assay (ELISA), fluorescence staining, and Oil red O staining in several cell lines (skeletal muscle, cardiac muscle, liver, macrophage, vascular endothelial, and adipose cells). In spontaneously hypertensive rats, blood pressure, blood analysis, organ-specific biomarkers, and general biomolecules related to ATP production were measured with Western blot analysis, immunohistochemistry, ELISA, and echocardiography. Pharmacological activation of α₁-adrenergic receptors in C2C12 skeletal muscle cells promoted mitochondrial oxidative phosphorylation and ATP production by increasing the expression of catabolic molecules, including PPARδ, AMPK, and PGC-1α, through cytosolic calcium signaling and increased GLUT4 expression, as seen in exercise. It also activated those energetic molecules and mitochondrial oxidative phosphorylation with cardiomyocytes, endothelial cells, adipocytes, macrophages, and hepatic cells and affected their relevant cell-specific biological functions. All of those effects occurred around 3 h (and peaked 6 h) after midodrine treatment. In spontaneously hypertensive rats, α₁-adrenergic receptor stimulation affected mitochondrial oxidative phosphorylation and ATP production by activating PPARδ, AMPK, and PGC-1α and the relevant biologic functions of multiple organs, suggesting organ crosstalk. The treatment lowered blood pressure, fat and body weight, cholesterol levels, and inflammatory activity; increased ATP content and insulin sensitivity in skeletal muscles; and increased cardiac contractile function without exercise training. These results suggest that the activation of α₁-adrenergic receptor stimulates energetic reprogramming via PPARδ that increases mitochondrial oxidative phosphorylation and has healthy and organ-specific biological effects in multiple organs, including skeletal muscle, beyond its vasomotion effect. In addition, the action mechanism of α₁-adrenergic receptor may be mainly exerted via PPARδ.

Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist

RATIONALE

Gq signaling in cardiac myocytes is classically considered toxic. Targeting Gq directly to test this is problematic, because cardiac myocytes have many Gq-coupled receptors.

OBJECTIVE

Test whether Gq coupling is required for the cardioprotective effects of an alpha-1A-AR (adrenergic receptor) agonist.

METHODS AND RESULTS

In recombinant cells, a mouse alpha-1A-AR with a 6-residue substitution in the third intracellular loop does not couple to Gq signaling. Here we studied a knockin mouse with this alpha-1A-AR mutation. Heart alpha-1A receptor levels and antagonist affinity in the knockin were identical to wild-type. In wild-type cardiac myocytes, the selective alpha-1A agonist A61603-stimulated phosphoinositide-phospholipase C and myocyte contraction. In myocytes with the alpha-1A knockin, both A61603 effects were absent, indicating that Gq coupling was absent. Surprisingly, A61603 activation of cardioprotective ERK (extracellular signal-regulated kinase) was markedly impaired in the KI mutant myocytes, and A61603 did not protect mutant myocytes from doxorubicin toxicity in vitro. Similarly, mice with the α1A KI mutation had increased mortality after transverse aortic constriction, and A61603 did not rescue cardiac function in mice with the Gq coupling-defective alpha-1A receptor.

CONCLUSIONS

Gq coupling is required for cardioprotection by an alpha-1A-AR agonist. Gq signaling can be adaptive.

Adrenoceptor regulation of the mechanistic target of rapamycin in muscle and adipose tissue

A vital role of adrenoceptors in metabolism and energy balance has been well documented in the heart, skeletal muscle, and adipose tissue. It has been only recently demonstrated, however, that activation of the mechanistic target of rapamycin (mTOR) makes a significant contribution to various metabolic and physiological responses to adrenoceptor agonists. mTOR exists as two distinct complexes named mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) and has been shown to play a critical role in protein synthesis, cell proliferation, hypertrophy, mitochondrial function, and glucose uptake. This review will describe the physiological significance of mTORC1 and 2 as a novel paradigm of adrenoceptor signalling in the heart, skeletal muscle, and adipose tissue. Understanding the detailed signalling cascades of adrenoceptors and how they regulate physiological responses is important for identifying new therapeutic targets and identifying novel therapeutic interventions. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Alpha-1 Adrenergic Receptor Agonist Phenylephrine Inhibits Sepsis-Induced Cardiomyocyte Apoptosis and Cardiac Dysfunction via Activating ERK1/2 Signal Pathway

It was demonstrated that α1 adrenergic receptor (α1-AR) activation by phenylephrine (PE) attenuated cardiac dysfunction in lipopolysaccharide (LPS)-challenged mice. However, it is unclear whether PE suppresses sepsis-induced cardiomyocyte apoptosis. Here, we investigated the effects of PE on cardiomyocyte apoptosis in LPS-treated adult rat ventricular myocytes (ARVMs) and septic rats induced by cecal ligation and puncture. Cardiomyocyte apoptosis and caspase activity were detected by TUNEL and spectrophotometrical assay, respectively. Bax, Bcl-2 and cytochrome c (Cyt c) levels as well as IκBα, ERK1/2, p38 MAPK, JNK and cardiac troponin I (cTnI) phosphorylation were analyzed by Western blotting, and TNF-α concentration was analyzed by ELISA. PE inhibited LPS-induced caspase-3 activation in ARVMs, which was reversed by prazosin (a membrane permeable α1-AR antagonist), but not by CGP12177A (a membrane impermeable α1-AR antagonist). PE upregulated phosphorylated ERK1/2 and Bcl-2 contents, decreased TNF-α and Bax levels, Cyt c release, caspase-8/-9 activities as well as IκBα, p38MAPK and JNK phosphorylation in LPS-treated ARVMs, all of which were abolished by prazosin. Treatment with U0126 (a specific ERK1/2 inhibitor) reversed the effects of PE on IκBα, p38MAPK and JNK phosphorylation as well as caspase-3/-8/-9 activation in LPS-treated ARVMs. In septic rats, PE not only inhibited myocardial apoptosis as well as IκBα, p38MAPK, and JNK phosphorylation, but also upregulated myocardial phosphorylated ERK1/2. Furthermore, PE inhibited myocardial cTnI phosphorylation and improved cardiac function in septic rats. Taken together, our data suggest that α1-AR activation by PE inhibits sepsis-induced cardiomyocyte apoptosis and cardiac dysfunction via activating ERK1/2 signal pathway.

Reversal of right ventricular failure by chronic α1A-subtype adrenergic agonist therapy

Right ventricular (RV) failure (RVF) is a serious disease with no effective treatment available. We recently reported a disease prevention study showing that chronic stimulation of α1A-adrenergic receptors (α1A-ARs), started at the time of RV injury, prevented the development of RVF. The present study used a clinically relevant disease reversal design to test if chronic α1A-AR stimulation, started after RVF was established, could reverse RVF. RVF was induced surgically by pulmonary artery constriction in mice. Two weeks after pulmonary artery constriction, in vivo RV fractional shortening as assessed by MRI was reduced by half relative to sham-operated controls (25 ± 2%, n = 27, vs. 52 ± 2%, n = 13, P < 10-11). Subsequent chronic treatment with the α1A-AR agonist A61603 for a further 2 wk resulted in a substantial recovery of RV fractional shortening (to 41 ± 2%, n = 17, P < 10-7 by a paired t-test) along with recovery of voluntary exercise capacity. Mechanistically, chronic A61603 treatment resulted in increased activation of the prosurvival kinase ERK, increased abundance of the antiapoptosis factor Bcl-2, and decreased myocyte necrosis evidenced by a decreased serum level of cardiac troponin. Moreover, A61603 treatment caused increased abundance of the antioxidant glutathione peroxidase-1, decreased level of reactive oxygen species, and decreased oxidative modification (carbonylation) of myofilament proteins. Consistent with these effects, A61603 treatment resulted in increased force development by cardiac myofilaments, which might have contributed to increased RV function. These findings suggest that the α1A-AR is a therapeutic target to reverse established RVF. NEW & NOTEWORTHY Currently, there are no effective therapies for right ventricular (RV) failure (RVF). This project evaluated a novel therapy for RVF. In a mouse model of RVF, chronic stimulation of α1A-adrenergic receptors with the agonist A61603 resulted in recovery of in vivo RV function, improved exercise capacity, reduced oxidative stress-related carbonylation of contractile proteins, and increased myofilament force generation. These results suggest that the α1A-adrenergic receptor is a therapeutic target to treat RVF.

ERK mediated survival signaling is dependent on the Gq-G-protein coupled receptor type and subcellular localization in adult cardiac myocytes

G protein-coupled receptors that signal through Gαq (GqPCRs), like α1-adrenergic and angiotensin receptors (α1-AR, AT-R), are traditionally thought to mediate pathologic remodeling in heart failure, including cardiac myocyte death. However, we previously demonstrated that α1- ARs are cardioprotective and identified an α1A-subtype-ERK survival-signaling pathway in adult cardiac myocytes. Recently, we demonstrated that α1-ARs localize to and signal from the nucleus, whereas AT-R localize to and signal from the sarcolemma in adult cardiac myocytes. Thus, we proposed a novel paradigm, predicated on compartmentalization of GqPCR signaling, to explain the phenotypic diversity of GqPCRs. Here, we tested the hypothesis that differential subcellular compartmentalization of α1-AR and AT-R mediated activation of ERK might explain the differential effects of these receptors on cardiac myocyte survival. Using a fluorescent ERK activity FRET-based biosensor, EKAR, to measure subcellular localization and extent of receptor-mediated ERK activation in single adult cardiac myocytes, we found that α1-ARs induced ERK activity at the nucleus and in the cytosol in 60% of cardiac myocytes, whereas AT-Rs showed no consistent ERK activation. The cell-specific α1-mediated activation of ERK in 60% of adult cardiac myocytes showed concordance with previous studies indicating that the α1A-subtype is expressed in only 60% of cardiac myocytes. Consistent with the ability to activate ERK, we found that only α1-ARs induced phosphorylation of Bcl-2 family member Bad, improved mitochondrial membrane stability, and promoted cardiac myocyte survival. In summary, our results suggest that compartmentalization of GqPCRs dictate activation of ERK and cardiac myocyte survival in adult cardiac myocytes.

Updates in Anthracycline-Mediated Cardiotoxicity

Cardiotoxicity is one of the main adverse effects of chemotheraphy, affecting the completion of cancer therapies and the short- and long-term quality of life. Anthracyclines are currently used to treat many cancers, including the various forms of leukemia, lymphoma, melanoma, uterine, breast, and gastric cancers. World Health Organization registered anthracyclines in the list of essential medicines. However, anthracyclines display a major cardiotoxicity that can ultimately culminate in congestive heart failure. Taking into account the growing rate of cancer survivorship, the clinical significance of anthracycline cardiotoxicity is an emerging medical issue. In this review, we focus on the key progenitor cells and cardiac cells (cardiomyocytes, fibroblasts, and vascular cells), focusing on the signaling pathways involved in cellular damage, and the clinical biomarkers in anthracycline-mediated cardiotoxicity.

Human Myocardium Has a Robust α1A-Subtype Adrenergic Receptor Inotropic Response

Recent studies report that a single subtype of α1-adrenergic receptor (α1-AR), the α1A-subtype, mediates robust cardioprotective effects in multiple experimental models of heart failure, suggesting that the α1A-subtype is a potential therapeutic target for an agonist to treat heart failure. Moreover, we recently found that the α1A-subtype is present in human heart. The goal of this study was to assess the inotropic response mediated by the α1A-subtype in human myocardium, and to determine whether the response is downregulated in myocardium from failing human heart. We measured in vitro contractile responses of cardiac muscle preparations (trabeculae) isolated from the right ventricle from nonfailing and failing human hearts. Addition of the α1A-subtype agonist A61603 (100 nM) resulted in a large positive inotropic response (force increased ≈ 2-fold). This response represented ≈70% of the response mediated by the β-adrenergic receptor agonist isoproterenol (1 μM). Moreover, in myocardium from failing hearts, α1A-subtype responses remained robust, and only slightly reduced relative to nonfailing hearts. We conclude that α1A-subtype-mediated inotropy could represent a significant source of inotropic support in the human heart. Furthermore, the α1A-subtype remains functional in myocardium from failing human hearts and thus, might be a therapeutic target to support cardioprotective effects in patients with heart failure.

Shift toward greater pathologic post-myocardial infarction remodeling with loss of the adaptive hypertrophic signaling of alpha1 adrenergic receptors in mice

Rationale

We have hypothesized that post-infarction cardiac remodeling can be influenced by shifts in the balance between intracellular mediators of “pathologic” and “physiologic” hypertrophy. Although alpha1 adrenergic receptors (alpha1-ARs) mediate pro-adaptive hypertrophy during pressure overload, little is known about their role or downstream mediators after myocardial infarction.

Methods

We performed loss-of-function experiments via coronary ligation in alpha1A-AR knockout (AKO) mice. Post-myocardial infarction (MI) remodeling was evaluated via echocardiography, quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis of cardiac fetal gene expression, histologic analysis of myocyte size, post-MI fibrosis and apoptosis, and Western blot analysis of apoptotic regulators.

Results

Alpha1A-AR knockout paradoxically increased post-MI hypertrophy compared to wild type controls (WT), but also increased ventricular dilatation, fibrosis, apoptosis, and 4-week post-MI mortality (64% in AKO vs. 25% in WT, P = 0.02), suggesting a shift toward greater pathologic hypertrophy in the absence of pro-adaptive alpha1A effects. alpha1A-AR knockout increased phospho-p38 levels in the pre-MI myocardium compared to WT (0.55 ± 0.16 vs. 0.03 ± 0.01, P<0.05) but decreased phospho-ERK1/2 post-MI (0.49 ± 0.35 arbitrary units vs. 1.55 ± 0.43 in WT, P<0.05). Furthermore, expression of pro-apoptotic factor Bax was increased (1.19 ± 0.15 vs. 0.78 ± 0.08, P<0.05) and expression of anti-apoptotic factors Bcl2 was decreased (0.26 ± 0.01 vs. 0.55 ± 0.06, P<0.01) compared to WT.

Conclusions

Alpha1A-AR provides an important counterbalance to pathologic pathways during post-MI remodeling that may be mediated through ERK1/2 signaling; these observations provide support for further development of an alpha1A-AR/ERK-based molecular intervention for this chronic, often fatal disease.

α1A-Subtype adrenergic agonist therapy for the failing right ventricle

Failure of the right ventricle (RV) is a serious disease with a poor prognosis and limited treatment options. Signaling by α₁-adrenergic receptors (α₁-ARs), in particular the α_1A-subtype, mediate cardioprotective effects in multiple heart failure models. Recent studies have shown that chronic treatment with the α_1A-subtype agonist A61603 improves function and survival in a model of left ventricular failure. The goal of the present study was to determine if chronic A61603 treatment is beneficial in a RV failure model. We used tracheal instillation of the fibrogenic antibiotic bleomycin in mice to induce pulmonary fibrosis, pulmonary hypertension, and RV failure within 2 wk. Some mice were chronically treated with a low dose of A61603 (10 ng·kg^-1·day^-1). In the bleomycin model of RV failure, chronic A61603 treatment was associated with improved RV fractional shortening and greater in vitro force development by RV muscle preparations. Cell injury markers were reduced with A61603 treatment (serum cardiac troponin I, RV fibrosis, and expression of matrix metalloproteinase-2). RV oxidative stress was reduced (using the probes dihydroethidium and 4-hydroxynonenal). Consistent with lowered RV oxidative stress, A61603 was associated with an increased level of the cellular antioxidant superoxide dismutase 1 and a lower level of the prooxidant NAD(P)H oxidase isoform NOX4. In summary, in the bleomycin model of RV failure, chronic A61603 treatment reduced RV oxidative stress, RV myocyte necrosis, and RV fibrosis and increased both RV function and in vitro force development. These findings suggest that in the context of pulmonary fibrosis, the α_1A-subtype is a potential therapeutic target to treat the failing RV.NEW & NOTEWORTHY Right ventricular (RV) failure is a serious disease with a poor prognosis and no effective treatments. In the mouse bleomycin model of RV failure, we tested the efficacy of a treatment using the α_1A-adrenergic receptor subtype agonist A61603. Chronic A61603 treatment improved RV contraction and reduced multiple indexes of RV injury, suggesting that the α_1A-subtype is a therapeutic target to treat RV failure.

Oral administration of Ginsenoside Rg1 prevents cardiac toxicity induced by doxorubicin in mice through anti-apoptosis

Although Ginsenoside Rg1 has been reported to have protective cardiac effects, its effects on cardiac toxicity induced by doxorubicin needs to be studied. The present study investigated the effects of oral administration of Rg1 on the heart in mice treated with doxorubicin and found improved fractional shortening and ejection fraction of the heart and decreased cardiac apoptosis in mice treated with doxorubicin. The underlying mechanisms include increased phosphorylation of Akt and Erk by Rg1, increased ratio of Bcl-2 and Bax, and decreased release of cytochrome c from mitochondria, thereby protecting the heart from doxorubicin-induced apoptosis. This phenotype suggested that the oral administration of Rg1 may be a potential method preventing the cardiac toxicity caused by doxorubicin in clinical practice.