G protein-dependent and G protein-independent signaling pathways and their impact on cardiac function

Effect of Cannabistilbene I in Attenuating Angiotensin II-Induced Cardiac Hypertrophy: Insights into Cytochrome P450s and Arachidonic Acid Metabolites Modulation

Introduction: This research investigated the impact of Cannabistilbene I on Angiotensin II (Ang II)-induced cardiac hypertrophy and its potential role in cytochrome P450 (CYP) enzymes and arachidonic acid (AA) metabolic pathways. Cardiac hypertrophy, a response to increased stress on the heart, can lead to severe cardiovascular diseases if not managed effectively. CYP enzymes and AA metabolites play critical roles in cardiac function and hypertrophy, making them important targets for therapeutic intervention. Methods: Adult human ventricular cardiomyocyte cell line (AC16) was cultured and treated with Cannabistilbene I in the presence and absence of Ang II. The effects on mRNA expression related to cardiac hypertrophic markers and CYP were analyzed using real-time polymerase chain reaction, while CYP protein levels were measured by Western blot analysis. AA metabolites were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: Results showed that Ang II triggered hypertrophy, as evidenced by the increase in hypertrophic marker expression, and enlarged the cell surface area, effects that were alleviated by Cannabistilbene I. Gene expression analysis indicated that Cannabistilbene I upregulated CYP1A1, leading to increased enzymatic activity, as evidenced by 7-ethoxyresorufin-O-deethylase assay. Furthermore, LC-MS/MS analysis of AA metabolites revealed that Ang II elevated midchain (R/S)-hydroxyeicosatetraenoic acid (HETE) concentrations, which were reduced by Cannabistilbene I. Notably, Cannabistilbene I selectively increased 19(S)-HETE concentration and reversed the Ang II-induced decline in 19(S)-HETE, suggesting a unique protective role. Conclusion: This study provides new insights into the potential of Cannabistilbene I in modulating AA metabolites and reducing Ang II-induced cardiac hypertrophy, revealing a new candidate as a therapeutic agent for cardiac hypertrophy.

Game-changing breakthroughs to redefine the landscape of the renin-angiotensin-aldosterone system in health and disease

Novel perspectives on the role of the renin-angiotensin-aldosterone system (RAAS) offer a groundbreaking understanding of the system's role in health and illness. Our understanding of the role of the RAAS in several diseases, such as heart failure, hypertension, metabolic disorders, and chronic renal disease, has been broadened by recent studies. Specific variations in RAAS pathways can affect the course of disease and response to treatment, as shown by genetic and molecular research. The dynamic and fast-evolving nature of RAAS research described in this special issue might transform our approach to managing renal, neurological, and cardiovascular health, among other disease conditions, including cancer.

Adrenergic orchestration of immune cell dynamics in response to cardiac stress

Immune cells contribute approximately 5-10 % of the heart's total cell population, including several myeloid cell and lymphocyte cell subsets, which, despite their relatively small percentages, play important roles in cardiac homeostasis and remodeling responses to various forms of injury and long-term stress. Pathological cardiac stress activates the sympathetic nervous system (SNS), resulting in the release of the catecholamines epinephrine and norepinephrine either systemically or from sympathetic nerve terminals within various lymphoid organs. Acting at α- or β-adrenergic receptors (αAR, βAR), catecholamines regulate immune cell hematopoiesis, egress and migration in response to stress. Classically, αAR stimulation tends to promote inflammatory responses while βAR stimulation has typically been shown to be immunosuppressive, though the effects can be nuanced depending on the immune cells subtype, the site of regulation and pathophysiological context. Herein, we will discuss several facets of SNS-mediated regulation of immune cells and their response to cardiac stress, including: catecholamine response to cardiovascular stress and action at their receptors, adrenergic regulation of hematopoiesis, immune cell retention and release from the bone marrow, adrenergic regulation of splenic immune cells and their retention, as well as adrenergic regulation of immune cell recruitment to the injured heart, including neutrophils, monocytes and macrophages. A particular focus will be given to βAR-mediated effects on myeloid cells in response to acute or chronic cardiac stress.

Loss of cardiomyocyte-specific adhesion G-protein-coupled receptor G1 (ADGRG1/GPR56) promotes pressure overload-induced heart failure

Adhesion G-protein-coupled receptors (AGPCRs), containing large N-terminal ligand-binding domains for environmental mechano-sensing, have been increasingly recognized to play important roles in numerous physiologic and pathologic processes. However, their impact on the heart, which undergoes dynamic mechanical alterations in healthy and failing states, remains understudied. ADGRG1 (formerly known as GPR56) is widely expressed, including in skeletal muscle where it was previously shown to mediate mechanical overload-induced muscle hypertrophy; thus, we hypothesized that it could impact the development of cardiac dysfunction and remodeling in response to pressure overload. In this study, we generated a cardiomyocyte (CM)-specific ADGRG1 knockout mouse model, which, although not initially displaying features of cardiac dysfunction, does develop increased systolic and diastolic LV volumes and internal diameters over time. Notably, when challenged with chronic pressure overload, CM-specific ADGRG1 deletion accelerates cardiac dysfunction, concurrent with blunted CM hypertrophy, enhanced cardiac inflammation and increased mortality, suggesting that ADGRG1 plays an important role in the early adaptation to chronic cardiac stress. Altogether, the present study provides an important proof-of-concept that targeting CM-expressed AGPCRs may offer a new avenue for regulating the development of heart failure.

A molecular mechanism for angiotensin II receptor blocker-mediated slit membrane protection: Angiotensin II increases nephrin endocytosis via AT1-receptor-dependent ERK 1/2 activation

Albuminuria is characterized by a disruption of the glomerular filtration barrier, which is composed of the fenestrated endothelium, the glomerular basement membrane, and the slit diaphragm. Nephrin is a major component of the slit diaphragm. Apart from hemodynamic effects, Ang II enhances albuminuria by β-Arrestin2-mediated nephrin endocytosis. Blocking the AT1 receptor with candesartan and irbesartan reduces the Ang II-mediated nephrin-β-Arrestin2 interaction. The inhibition of MAPK ERK 1/2 blocks Ang II-enhanced nephrin-β-Arrestin2 binding. ERK 1/2 signaling, which follows AT1 receptor activation, is mediated by G-protein signaling, EGFR transactivation, and β-Arrestin2 recruitment. A mutant AT1 receptor defective in EGFR transactivation and β-Arrestin2 recruitment reduces the Ang II-mediated increase in nephrin β-Arrestin2 binding. The mutation of β-Arrestin2K11,K12, critical for AT1 receptor binding, completely abrogates the interaction with nephrin, independent of Ang II stimulation. β-Arrestin2K11R,K12R does not influence nephrin cell surface expression. The data presented here deepen our molecular understanding of a blood-pressure-independent molecular mechanism of AT-1 receptor blockers (ARBs) in reducing albuminuria.

Chronic modulation of cAMP signaling elicits synaptic scaling irrespective of activity

Homeostatic plasticity mechanisms act in a negative feedback manner to stabilize neuronal firing around a set point. Classically, homeostatic synaptic plasticity is elicited via rather drastic manipulation of activity in a neuronal population. Here, we employed a chemogenetic approach to regulate activity via eliciting G protein-coupled receptor (GPCR) signaling in hippocampal neurons to trigger homeostatic synaptic plasticity. We demonstrate that chronic activation of hM4D(Gi) signaling induces mild and transient activity suppression, yet still triggers synaptic upscaling akin to tetrodotoxin (TTX)-induced complete activity suppression. Therefore, this homeostatic regulation was irrespective of Gi-signaling regulation of activity, but it was mimicked or occluded by direct manipulation of cyclic AMP (cAMP) signaling in a manner that intersected with the retinoic acid receptor alpha (RARα) signaling pathway. Our data suggest chemogenetic tools can uniquely be used to probe cell-autonomous mechanisms of synaptic scaling and operate via direct modulation of second messenger signaling bypassing activity regulation.

AKAP12 Upregulation Associates With PDE8A to Accelerate Cardiac Dysfunction

BACKGROUND

In heart failure, signaling downstream the β2-adrenergic receptor is critical. Sympathetic stimulation of β2-adrenergic receptor alters cAMP (cyclic adenosine 3',5'-monophosphate) and triggers PKA (protein kinase A)-dependent phosphorylation of proteins that regulate cardiac function. cAMP levels are regulated in part by PDEs (phosphodiesterases). Several AKAPs (A kinase anchoring proteins) regulate cardiac function and are proposed as targets for precise pharmacology. AKAP12 is expressed in the heart and has been reported to directly bind β2-adrenergic receptor, PKA, and PDE4D. However, its roles in cardiac function are unclear.

METHODS

cAMP accumulation in real time downstream of the β2-adrenergic receptor was detected for 60 minutes in live cells using the luciferase-based biosensor (GloSensor) in AC16 human-derived cardiomyocyte cell lines overexpressing AKAP12 versus controls. Cardiomyocyte intracellular calcium and contractility were studied in adult primary cardiomyocytes from male and female mice overexpressing cardiac AKAP12 (AKAP12OX) and wild-type littermates post acute treatment with 100-nM isoproterenol (ISO). Systolic cardiac function was assessed in mice after 14 days of subcutaneous ISO administration (60 mg/kg per day). AKAP12 gene and protein expression levels were evaluated in left ventricular samples from patients with end-stage heart failure.

RESULTS

AKAP12 upregulation significantly reduced total intracellular cAMP levels in AC16 cells through PDE8. Adult primary cardiomyocytes from AKAP12OX mice had significantly reduced contractility and impaired calcium handling in response to ISO, which was reversed in the presence of the selective PDE8 inhibitor (PF-04957325). AKAP12OX mice had deteriorated systolic cardiac function and enlarged left ventricles. Patients with end-stage heart failure had upregulated gene and protein levels of AKAP12.

CONCLUSIONS

AKAP12 upregulation in cardiac tissue is associated with accelerated cardiac dysfunction through the AKAP12-PDE8 axis.

Adaptor molecules mediate negative regulation of macrophage inflammatory pathways: a closer look

Macrophages play a central role in initiating, maintaining, and terminating inflammation. For that, macrophages respond to various external stimuli in changing environments through signaling pathways that are tightly regulated and interconnected. This process involves, among others, autoregulatory loops that activate and deactivate macrophages through various cytokines, stimulants, and other chemical mediators. Adaptor proteins play an indispensable role in facilitating various inflammatory signals. These proteins are dynamic and flexible modulators of immune cell signaling and act as molecular bridges between cell surface receptors and intracellular effector molecules. They are involved in regulating physiological inflammation and also contribute significantly to the development of chronic inflammatory processes. This is at least partly due to their involvement in the activation and deactivation of macrophages, leading to changes in the macrophages' activation/phenotype. This review provides a comprehensive overview of the 20 adaptor molecules and proteins that act as negative regulators of inflammation in macrophages and effectively suppress inflammatory signaling pathways. We emphasize the functional role of adaptors in signal transduction in macrophages and their influence on the phenotypic transition of macrophages from pro-inflammatory M1-like states to anti-inflammatory M2-like phenotypes. This endeavor mainly aims at highlighting and orchestrating the intricate dynamics of adaptor molecules by elucidating the associated key roles along with respective domains and opening avenues for therapeutic and investigative purposes in clinical practice.

Insights Into the Role of Angiotensin-II AT1 Receptor-Dependent β-Arrestin Signaling in Cardiovascular Disease

β-arrestins are a family of intracellular signaling proteins that play a key role in regulating the activity of G protein-coupled receptors. The angiotensin-II type 1 receptor is an important G protein-coupled receptor involved in the regulation of cardiovascular function and has been implicated in the progression of cardiovascular diseases. In addition to canonical G protein signaling, G protein-coupled receptors including the angiotensin-II type 1 receptor can signal via β-arrestin. Dysregulation of β-arrestin signaling has been linked to several cardiovascular diseases including hypertension, atherosclerosis, and heart failure. Understanding the role of β-arrestins in these conditions is critical to provide new therapeutic targets for the treatment of cardiovascular disease. In this review, we will discuss the beneficial and maladaptive physiological outcomes of angiotensin-II type 1 receptor-dependent β-arrestin activation in different cardiovascular diseases.

Interactions between AT1R and GRKs: the determinants for activation of signaling pathways involved in blood pressure regulation

The success of Angiotensin II receptor blockers, specifically Angiotensin II type 1 receptor (AT1R) antagonists as antihypertensive drug emphasizes the involvement of AT1R in Essential hypertension. The structural insights and mutational studies of Ang II-AT1R have brought about the vision to design Ang II analogs that selectively activate the pathways with beneficial and cardioprotective effects such as cell survival and hinder the deleterious effects such as hypertrophy and cell death. AT1R belongs to G-protein coupled receptors and is regulated by G-protein coupled receptor kinases (GRKs) that either uncouples Gq protein for receptor desensitization or phosphorylate C-terminus to recruit β-arrestin for internalization of the receptor. The interaction of GRKs with ligand activated AT1R induces conformational changes and signal either Gq dependent or Gq independent pathways. These interactions might explain the complex regulatory mechanisms and offer promising ideas for hypertension therapeutics. This article reviews the functional role of AT1R, organization of GRK genes and regulation of AT1R by GRKs that play significant role in desensitization and internalization of the receptors.

Urotensin II Receptor Modulation with 1,3,4-Benzotriazepin-2-one Tetrapeptide Mimics

Urotensin II receptor (UT) modulators that differentiate the effects of the endogenous cyclic peptide ligands urotensin II (UII) and urotensin II-related peptide (URP) offer potential for dissecting their respective biological roles in disease etiology. Selective modulators of hUII and URP activities were obtained using 1,3,4-benzotriazepin-2-one mimics of a purported bioactive γ-turn conformation about the Bip-Lys-Tyr tripeptide sequence of urocontrin ([Bip4]URP). Considering an active β-turn conformer about the shared Phe-Trp-Lys-Tyr sequence of UII and URP, 8-substituted 1,3,4-benzotriazepin-2-ones were designed to mimic the Phe-Bip-Lys-Tyr tetrapeptide sequence of urocontrin, synthesized, and examined for biological activity. Subtle 5- and 8-position modifications resulted in biased signaling and selective modulation of hUII- or URP-induced vasoconstriction. For example, p-hydroxyphenethyl analogs 17b-d were strong Gα13 and βarr1 activators devoid of Gαq-mediated signaling. Tertiary amides 15d and 17d negatively modulated hUII-induced vasoconstriction without affecting URP-mediated responses. Benzotriazepinone carboxamides proved to be exceptional tools for elucidating the pharmacological complexity of UT.

Paternal methamphetamine exposure induces higher sensitivity to methamphetamine in male offspring through driving ADRB1 on CaMKII-positive neurons in mPFC

Paternal abuse of drugs, such as methamphetamine (METH), elevates the risk of developing addiction in subsequent generations, however, its underlying molecular mechanism remains poorly understood. Male adult mice (F0) were exposed to METH for 30 days, followed by mating with naïve female mice to create the first-generation mice (F1). When growing to adulthood, F1 were subjected to conditioned place preference (CPP) test. Subthreshold dose of METH (sd-METH), insufficient to induce CPP normally, were used in F1. Selective antagonist (betaxolol) for β1-adrenergic receptor (ADRB1) or its knocking-down virus were administrated into mPFC to regulate ADRB1 function and expression on CaMKII-positive neurons. METH-sired male F1 acquired sd-METH-induced CPP, indicating that paternal METH exposure induce higher sensitivity to METH in male F1. Compared with saline (SAL)-sired male F1, CaMKII-positive neuronal activity was normal without sd-METH, but strongly evoked after sd-METH treatment in METH-sired male F1 during adulthood. METH-sired male F1 had higher ADRB1 levels without sd-METH, which was kept at higher levels after sd-METH treatment in mPFC. Either inhibiting ADRB1 function with betaxolol, or knocking-down ADRB1 level on CaMKII-positive neurons (ADRB1CaMKII) with virus transfection efficiently suppressed sd-METH -evoked mPFC activation, and ultimately blocked sd-METH-induced CPP in METH-sired male F1. In the process, the p-ERK1/2 and ΔFosB may be potential subsequent signals of mPFC ADRB1CaMKII. The mPFC ADRB1CaMKII mediates paternal METH exposure-induced higher sensitivity to drug addiction in male offspring, raising a promising pharmacological target for predicting or treating transgenerational addiction.

Profiling of basal and ligand-dependent GPCR activities by means of a polyvalent cell-based high-throughput platform

Representing the most attractive and successful druggable receptors of the proteome, GPCRs regulate a myriad of physiological and pathophysiological functions. Although over half of present pharmaceuticals target GPCRs, the advancement of drug discovery is hampered by a lack of adequate screening tools, the majority of which are limited to probing agonist-induced G-protein and β-arrestin-2-mediated events as a measure of receptor activation. Here, we develop Tango-Trio, a comprehensive cell-based high-throughput platform comprising cumate-inducible expression of transducers, capable of the parallelized profiling of both basal and agonist-dependent GPCR activities. We capture the functional diversity of GPCRs, reporting β-arrestin-1/2 couplings, selectivities, and receptor internalization signatures across the GPCRome. Moreover, we present the construction of cumate-induced basal activation curves at approximately 200 receptors, including over 50 orphans. Overall, Tango-Trio's robustness is well-suited for the functional characterization and screening of GPCRs, especially for parallel interrogation, and is a valuable addition to the pharmacological toolbox.

Pepducin-mediated G Protein-Coupled Receptor Signaling in the Cardiovascular System

ABSTRACT

Pepducins are small-lipidated peptides designed from the intracellular loops of G protein-coupled receptors (GPCRs) that act in an allosteric manner to modulate the activity of GPCRs. Over the past 2 decades, pepducins have progressed initially from pharmacologic tools used to manipulate GPCR activity in an orthosteric site-independent manner to compounds with therapeutic potential that have even been used safely in phase 1 and 2 clinical trials in human subjects. The effect of pepducins at their cognate receptors has been shown to vary between antagonist, partial agonist, and biased agonist outcomes in various primary and clonal cell systems, with even small changes in amino acid sequence altering these properties and their receptor selectivity. To date, pepducins designed from numerous GPCRs have been studied for their impact on pathologic conditions, including cardiovascular diseases such as thrombosis, myocardial infarction, and atherosclerosis. This review will focus in particular on pepducins designed from protease-activated receptors, C-X-C motif chemokine receptors, formyl peptide receptors, and the β2-adrenergic receptor. We will discuss the historic context of pepducin development for each receptor, as well as the structural, signaling, pathophysiologic consequences, and therapeutic potential for each pepducin class.

Identification of key genes for hypertrophic cardiomyopathy using integrated network analysis of differential lncRNA and gene expression

Objective

Hypertrophic cardiomyopathy (HCM) is a complex heterogeneous heart disease. Recent reports found that long non-coding RNAs (lncRNAs) play an important role in the progression of cardiovascular diseases. The present study aimed to identify the novel lncRNAs and messenger RNAs (mRNAs) and determine the key pathways involved in HCM.

Methods

The lncRNA and mRNA sequencing datasets of GSE68316 and GSE130036 were downloaded from the Gene Expression Omnibus (GEO) database. An integrated co-expression network analysis was conducted to identify differentially expressed lncRNAs and differentially expressed mRNAs in patients with HCM. Then, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were explored to identify the biological functions and signaling pathways of the co-expression network. Protein–protein interaction (PPI) and hub gene networks were constructed by using Cytoscape software. Plasma samples of patients with HCM and the GSE89714 dataset were used to validate the bioinformatics results.

Results

A total of 1,426 differentially expressed long non-coding RNAs (lncRNAs) and 1,715 differentially expressed mRNAs were obtained from GSE68316, of which 965 lncRNAs and 896 mRNAs were upregulated and 461 lncRNAs and 819 mRNAs were downregulated. A total of 469 differentially expressed lncRNAs and 2,407 differentially expressed mRNAs were screened from GSE130036, of which 183 lncRNAs and 1,283 mRNAs were upregulated and 286 lncRNAs and 1,124 mRNAs were downregulated. A co-expression network was constructed and contained 30 differentially expressed lncRNAs and 63 differentially expressed mRNAs, which were primarily involved in ‘G-protein beta/gamma-subunit complex binding,' ‘polyubiquitin modification-dependent protein binding,' ‘Apelin signaling pathway,' and ‘Wnt signaling pathway.' The 10 hub genes in the upregulated network [G Protein Subunit Alpha I2 (GNAI2), G Protein Subunit Alpha I1 (GNAI1), G Protein Subunit Alpha I3 (GNAI3), G Protein Subunit Gamma 2 (GNG2), G Protein Subunit Beta 1 (GNB1), G Protein Subunit Gamma 13 (GNG13), G Protein Subunit Gamma Transducin 1 (GNGT1), G Protein Subunit Gamma 12 (GNG12), AKT Serine/Threonine Kinase 1 (AKT1) and GNAS Complex Locus (GNAS)] and the 10 hub genes in the downregulated network [Nucleotide-Binding Oligomerization Domain Containing Protein 2 (NOD2), Receptor-Interacting Serine/Threonine Kinase 2 (RIPK2), Nucleotide-Binding Oligomerization Domain Containing Protein 1 (NOD1), Mitochondrial Antiviral Signaling Protein (MAVS), Autophagy Related 16-Like 1 (ATG16L1), Interferon Induced With Helicase C Domain 1 (IFIH1), Autophagy Related 5 (ATG5), TANK-Binding Kinase 1 (TBK1), Caspase Recruitment Domain Family Member 9 (CARD9), and von Willebrand factor (VWF)] were screened using cytoHubba. The expression of LA16c-312E8.2 and RP5-1160K1.3 in the plasma of patients with HCM was elevated, and the expression of the MIR22 host gene (MIR22HG) was decreased, which was consistent with our analysis, while the expression of LINC00324 and Small Nucleolar RNA Host Gene 12 (SNHG12) was not significantly different between the two groups. Verification analyses performed on GSE89714 showed the upregulated mRNAs of Chloride Voltage-Gated Channel 7 (CLCN7), N-Acetylglucosamine-1-Phosphate Transferase Subunit Gamma (GNPTG), Unk Like Zinc Finger (UNKL), Adenosine Monophosphate Deaminase 2 (AMPD2), GNAI3, WD Repeat Domain 81 (WDR81), and Serpin Family F Member 1 (SERPINF1) and downregulated mRNAs of TATA-Box Binding Protein Associated Factor 12 (TAF12) co-expressed with five crucial lncRNAs. Moreover, GNAI2, GNAI3, GNG12, and vWF were upregulated and GNAS was downregulated in the top 10 hub genes of upregulated and downregulated PPI networks.

Conclusion

These findings from integrative biological analysis of lncRNA-mRNA co-expression networks explored the key genes and pathways and provide new insights into the understanding of the mechanism and discovering new therapeutic targets for HCM. Three differentially expressed pivotal lncRNAs (LA16c-312E8.2, RP5-1160K1.3, and MIR22HG) in the co-expression network may serve as biomarkers and intervention targets for the diagnosis and treatment of HCM.

Lysyl oxidase promotes renal fibrosis via accelerating collagen cross-link driving by β-arrestin/ERK/STAT3 pathway

Lysyl oxidase (LOX) is a copper‐dependent monoamine oxidase whose primary function is the covalent cross‐linking of collagen in the extracellular matrix (ECM). Evidence has shown that LOX is associated with cancer and some fibrotic conditions. We recently found that serum LOX is a potential diagnostic biomarker for renal fibrosis, but the mechanism by which LOX is regulated and contributes to renal fibrosis remains unknown. The current study demonstrates the following: (1) LOX expression was increased in fibrotic kidneys including ischemia‐reperfusion injury‐(IRI‐), unilateral ureteral obstruction‐(UUO‐), and folic acid‐ (FA‐) induced fibrotic kidneys as well as in the paraffin‐embedded sections of human kidneys from the patients with renal fibrosis. (2) The increasing deposition and cross‐linking of collagen induced by LOX was observed in IRI‐, UUO‐ and FA‐kidneys. (3) LOX was regulated by the β‐arrestin‐ERK‐STAT3 pathway in renal fibrosis. STAT3 was the downstream of AT1R‐β‐arrestin‐ERK, ERK entered the nucleus and activated STAT3‐pY705 but not STAT3‐pS727. (4) STAT3 nuclear subtranslocation and binding to the LOX promoter may be responsible for the upregulation of LOX expression. (5) Pharmacologic inhibition of LOX with BAPN in vivo inhibited the upregulation of LOX, decreased collagen over cross‐linking and ameliorated renal fibrosis after ischemic injury. Collectively, these observations suggest that LOX plays an essential role in the development of renal fibrosis by catalyzing collagen over cross‐linking. Thus, strategies targeting LOX could be a new avenue in developing therapeutics against renal fibrosis.

GPCR-mediated EGFR transactivation ameliorates skin toxicities induced by afatinib

Many G-protein-coupled receptor (GPCR) agonists have been studied for transactivating epidermal growth factor receptor (EGFR) signaling through extracellular or intracellular pathways. Accumulated evidence has confirmed that GPCR transactivation participates in various diseases. However, the clinical application of GPCR transactivation has not been explored, and more translational studies are needed to develop therapies to target GPCR-mediated EGFR transactivation. In cancer patients treated with EGFR inhibitors (EGFRi), especially afatinib, a unique acneiform rash is frequently developed. In this study, we first established the connection between GPCR transactivation and EGFRi-induced skin disease. We examined the ability of three different GPCR agonists to reverse signaling inhibition and ameliorate rash induced by EGFRi. The activation of different agonists follows unique time and kinase patterns. Rats treated with EGFRi show a similar skin phenotype, with rash occurring in the clinic; correspondingly, treatment with GPCR agonists reduced keratinocyte apoptosis, growth retardation and infiltration of inflammatory cytokines by transactivation. This phenomenon demonstrates that EGFR inhibition in keratinocytes regulates key factors associated with rash. Our findings indicate that maintaining EGFR signaling by GPCR agonists might provide a possible therapy for EGFR inhibitor-induced skin toxicities. Our study provides the first example of the translational application of GPCR transactivation in treating diseases.

Contribution of adrenergic mechanisms for the stress-induced breast cancer carcinogenesis

Breast cancer is the most common and deadliest type of cancer in women. Stress exposure has been associated with carcinogenesis and the stress released neurotransmitters, noradrenaline and adrenaline, and their cognate receptors, can participate in the carcinogenesis process, either by regulating tumor microenvironment or by promoting systemic changes. This work intends to provide an overview of the research done in this area and try to unravel the role of adrenergic ligands in the context of breast carcinogenesis. In the initiation phase, adrenergic signaling may favor neoplastic transformation of breast epithelial cells whereas, during cancer progression, may favor the metastatic potential of breast cancer cells. Additionally, adrenergic signaling can alter the function and activity of other cells present in the tumor microenvironment towards a protumor phenotype, namely macrophages, fibroblasts, and by altering adipocyte's function. Adrenergic signaling also promotes angiogenesis and lymphangiogenesis and, systemically, may induce the formation of preneoplastic niches, cancer-associated cachexia and alterations in the immune system which contribute for the loss of quality of life of breast cancer patients and their capacity to fight cancer. Most studies points to a major contribution of β₂ -adrenoceptor activated pathways on these effects. The current knowledge of the mechanistic pathways activated by β₂ -adrenoceptors in physiology and pathophysiology, the availability of selective drugs approved for clinical use and a deeper knowledge of the basic cellular and molecular pathways by which adrenergic stimulation may influence cancer initiation and progression, opens the possibility to use new therapeutic alternatives to improve efficacy of breast cancer treatments.

AT1 Receptors: Their Actions from Hypertension to Cognitive Impairment

Hypertension is one of the most prevalent cardiovascular disorders worldwide, affecting 1.13 billion people, or 14% of the global population. Hypertension is the single biggest risk factor for cerebrovascular dysfunction. According to the American Heart Association, high blood pressure (BP), especially in middle-aged individuals (~ 40 to 60 years old), is associated with an increased risk of dementia, later in life. Alzheimer’s disease and cerebrovascular disease are the two leading causes of dementia, accounting for around 80% of the total cases and usually combining mixed pathologies from both. Little is known regarding how hypertension affects cognitive function, so the impact of its treatment on cognitive impairment has been difficult to assess. The brain renin-angiotensin system (RAS) is essential for BP regulation and overactivity of this system has been established to precede the development and maintenance of hypertension. Angiotensin II (Ang-II), the main peptide within this system, induces vasoconstriction and impairs neuro-vascular coupling by acting on brain Ang-II type 1 receptors (AT₁R). In this review, we systemically analyzed the association between RAS and biological mechanisms of cognitive impairment, from the perspective of AT₁R located in the central nervous system. Additionally, the possible contribution of brain AT₁R to global cognition decline in COVID-19 cases will be discussed as well.

OUP accepted manuscript

Discovering cell–surface markers based on a comprehensive understanding of development is utilized to isolate a particular cell type with high purity for therapeutic purposes. Given that latrophilin-2 (Lphn2) substantially contributes to cardiac differentiation, we examined whether Lphn2 regulates functional significance in heart development and repair. We performed whole-mount immunostaining followed by clearing technique of embryo, RNA sequencing related to Lphn2-knockout (KO) embryo, and in vivo functional analyses of Lphn2+ cells using echocardiography. After immunostaining the cleared embryo sample, Lphn2 was exclusively observed in cardiac cells expressing α-sarcomeric actinin at embryonic days E9.5 and E10.5. Homozygous Lphn2-KO mice were embryonically lethal and showed underdevelopment of the ventricular myocardium. However, Lphn2 was not required to develop vessels, including endothelial cells and smooth muscle cells. For the purpose of cardiac regeneration, we transplanted pluripotent stem cell (PSC)–derived Lphn2+ cells into the infarcted heart. PSC–derived Lphn2+ cells differentiated into cardiomyocytes and regenerated the myocardium when transplanted into the infarcted heart, unlike Lphn2− cells. Transplanted Lphn2+ cells improved left-ventricle systolic function and reduced infarct size. We demonstrated that Lphn2 exhibits potential as a cardiomyogenic marker to facilitate targeted stem cell therapy for heart repair in clinical practice.

Inhibition of β1-AR/Gαs signaling promotes cardiomyocyte proliferation in juvenile mice through activation of RhoA-YAP axis

The regeneration potential of the mammalian heart is incredibly limited, as cardiomyocyte proliferation ceases shortly after birth. β-adrenergic receptor (β-AR) blockade has been shown to improve heart functions in response to injury; however, the underlying mechanisms remain poorly understood. Here, we inhibited β-AR signaling in the heart using metoprolol, a cardio-selective β blocker for β1-adrenergic receptor (β1-AR) to examine its role in heart maturation and regeneration in postnatal mice. We found that metoprolol enhanced cardiomyocyte proliferation and promoted cardiac regeneration post myocardial infarction, resulting in reduced scar formation and improved cardiac function. Moreover, the increased cardiomyocyte proliferation was also induced by the genetic deletion of Gnas, the gene encoding G protein alpha subunit (Gαs), a downstream effector of β-AR. Genome wide transcriptome analysis revealed that the Hippo-effector YAP, which is associated with immature cardiomyocyte proliferation, was upregulated in the cardiomyocytes of β-blocker treated and Gnas cKO hearts. Moreover, the increased YAP activity is modulated by RhoA signaling. Our pharmacological and genetic studies reveal that β1-AR-Gαs-YAP signaling axis is involved in regulating postnatal cardiomyocyte proliferation. These results suggest that inhibiting β-AR-Gαs signaling promotes the regenerative capacity and extends the cardiac regenerative window in juvenile mice by activating YAP-mediated transcriptional programs.

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.

P17 induces chemotaxis and differentiation of monocytes via MRGPRX2-mediated mast cell-line activation

BACKGROUND

P17, a peptide isolated from Tetramorium bicarinatum ant venom, is known to induce an alternative phenotype of human monocyte-derived macrophages via activation of an unknown G protein-coupled receptor (GPCR).

OBJECTIVE

We sought to investigate the mechanism of action and the immunomodulatory effects of P17 mediated through MRGPRX2 (Mas-related G protein-coupled receptor X2).

METHODS

To identify the GPCR for P17, we screened 314 GPCRs. Upon identification of MRGPRX2, a battery of in silico, in vitro, ex vivo, and in vivo assays along with the receptor mutation studies were performed. In particular, to investigate the immunomodulatory actions, we used β-hexosaminidase release assay, cytokine releases, quantification of mRNA expression, cell migration and differentiation assays, immunohistochemical labeling, hematoxylin and eosin, and immunofluorescence staining.

RESULTS

P17 activated MRGPRX2 in a dose-dependent manner in β-arrestin recruitment assay. In LAD2 cells, P17 induced calcium and β-hexosaminidase release. Quercetin- and short hairpin RNA-mediated knockdown of MRGPRX2 reduced P17-evoked β-hexosaminidase release. In silico and in vitro mutagenesis studies showed that residue Lys8 of P17 formed a cation-π interaction with the Phe172 of MRGPRX2 and [Ala8]P17 lost its activity partially. P17 activated LAD2 cells to recruit THP-1 and human monocytes in Transwell migration assay, whereas MRGPRX2-impaired LAD2 cells cannot. In addition, P17-treated LAD2 cells stimulated differentiation of THP-1 and human monocytes, as indicated by the enhanced expression of macrophage markers cluster of differentiation 11b and TNF-α by quantitative RT-PCR. Immunohistochemical and immunofluorescent staining suggested monocyte recruitment in mice ears injected with P17.

CONCLUSIONS

Our data provide novel structural information regarding the interaction of P17 with MRGPRX2 and intracellular pathways for its immunomodulatory action.

Intravitreal brimonidine inhibits form-deprivation myopia in guinea pigs

Background

The use of ocular hypotensive drugs has been reported to attenuate myopia progression. This study explores whether brimonidine can slow myopia progression in the guinea pig form-deprivation (FD) model.

Methods

Three-week-old pigmented male guinea pigs (Cavia porcellus) underwent monocular FD and were treated with 3 different methods of brimonidine administration (eye drops, subconjunctival or intravitreal injections). Four different concentrations of brimonidine were tested for intravitreal injection (2 μg/μL, 4 μg/μL, 20 μg/μL, 40 μg/μL). All treatments continued for a period of 21 days. Tonometry, retinoscopy, and A-scan ultrasonography were used to monitor intraocular pressure (IOP), refractive error and axial length (AL), respectively. On day 21, guinea pigs were sacrificed for RNA sequencing (RNA-seq) to screen for associated transcriptomic changes.

Results

The myopia model was successfully established in FD animals (control eye vs. FD eye, respectively: refraction at day 20, 0.97 ± 0.18 D vs. − 0.13 ± 0.38 D, F = 6.921, P = 0.02; AL difference between day 0 and day 21, 0.29 ± 0.04 mm vs. 0.45 ± 0.03 mm, F = 11.655, P = 0.004). Among the 3 different brimonidine administration methods, intravitreal injection was the most effective in slowing myopia progression, and 4 μg/μL was the most effective among the four different concentrations of brimonidine intravitreal injection tested. The AL and the refraction of the brimonidine intravitreal injection group was significantly shorter or more hyperopic than those of other 2 groups. Four μg/μL produced the smallest difference in AL and spherical equivalent difference values. FD treatment significantly increased the IOP. IOP was significantly lower at 1 day after intravitreal injections which was the lowest in FD eye of intravitreal injection of brimonidine. At day 21, gene expression analyses using RNA-seq showed upregulation of Col1a1 and Mmp2 expression levels by intravitreal brimonidine.

Conclusions

Among the 3 different administration methods, intravitreal injection of brimonidine was the most effective in slowing myopia progression in the FD guinea pig model. Intravitreal brimonidine at 4 μg/μL significantly reduced the development of FD myopia in guinea pigs. Expression levels of the Col1a1 and Mmp2 genes were significantly increased in the retinal tissues of the FD-Inj-Br group.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40662-021-00248-0.

Predominance of Heart Failure With Preserved Ejection Fraction in Postmenopausal Women: Intra- and Extra-Cardiomyocyte Maladaptive Alterations Scaffolded by Estrogen Deficiency

Heart failure (HF) remains a public health concern as it is associated with high morbidity and death rates. In particular, heart failure with preserved ejection fraction (HFpEF) represents the dominant (>50%) form of HF and mostly occurring among postmenopausal women. Hence, the initiation and progression of the left ventricular diastolic dysfunctions (LVDD) (a typically clinical manifestation of HFpEF) in postmenopausal women have been attributed to estrogen deficiency and the loss of its residue cardioprotective effects. In this review, from a pathophysiological and immunological standpoint, we discuss the probable multiple pathomechanisms resulting in HFpEF, which are facilitated by estrogen deficiency. The initial discussions recap estrogen and estrogen receptors (ERs) and β-adrenergic receptors (βARs) signaling under physiological/pathological states to facilitate cardiac function/dysfunction, respectively. By reconciling these prior discussions, attempts were made to explain how the loss of estrogen facilitates the disruptions both ERs and βARs-mediated signaling responsible for; the modulation of intra-cardiomyocyte calcium homeostasis, maintenance of cardiomyocyte cytoskeletal and extracellular matrix, the adaptive regulation of coronary microvascular endothelial functions and myocardial inflammatory responses. By scaffolding the disruption of these crucial intra- and extra-cardiomyocyte physiological functions, estrogen deficiency has been demonstrated to cause LVDD and increase the incidence of HFpEF in postmenopausal women. Finally, updates on the advancements in treatment interventions for the prevention of HFpEF were highlighted.

Salt-Inducible Kinase 3 Promotes Vascular Smooth Muscle Cell Proliferation and Arterial Restenosis by Regulating AKT and PKA-CREB Signaling

Objective

Arterial restenosis is the pathological narrowing of arteries after endovascular procedures, and it is an adverse event that causes patients to experience recurrent occlusive symptoms. Following angioplasty, vascular smooth muscle cells (SMCs) change their phenotype, migrate, and proliferate, resulting in neointima formation, a hallmark of arterial restenosis. SIKs (salt-inducible kinases) are a subfamily of the AMP-activated protein kinase family that play a critical role in metabolic diseases including hepatic lipogenesis and glucose metabolism. Their role in vascular pathological remodeling, however, has not been explored. In this study, we aimed to understand the role and regulation of SIK3 in vascular SMC migration, proliferation, and neointima formation.

Approach and Results

We observed that SIK3 expression was low in contractile aortic SMCs but high in proliferating SMCs. It was also highly induced by growth medium in vitro and in neointimal lesions in vivo. Inactivation of SIKs significantly attenuated vascular SMC proliferation and up-regulated p21CIP1 and p27KIP1. SIK inhibition also suppressed SMC migration and modulated actin polymerization. Importantly, we found that inhibition of SIKs reduced neointima formation and vascular inflammation in a femoral artery wire injury model. In mechanistic studies, we demonstrated that inactivation of SIKs mainly suppressed SMC proliferation by down-regulating AKT (protein kinase B) and PKA (protein kinase A)-CREB (cAMP response element-binding protein) signaling. CRTC3 (CREB-regulated transcriptional coactivator 3) signaling likely contributed to SIK inactivation-mediated antiproliferative effects.

Conclusions

These findings suggest that SIK3 may play a critical role in regulating SMC proliferation, migration, and arterial restenosis. This study provides insights into SIK inhibition as a potential therapeutic strategy for treating restenosis in patients with peripheral arterial disease.

Beta-arrestin 2 mediates cardiac hypertrophy induced by thyroid hormones via AT1R

We have previously reported that angiotensin II receptor type 1 (AT1R) contributes to the hypertrophic effects of thyroid hormones (TH) in cardiac cells. Even though evidence indicates crosstalks between TH and AT1R, the underlying mechanisms are poorly understood. Beta-arrestin (ARRB) signaling has been described as noncanonical signal transduction pathway that exerts important effects in the cardiovascular system through G-protein-coupled receptors, as AT1R. Herein, we investigated the contribution of ARRB signaling in TH-induced cardiomyocyte hypertrophy. Primary cardiomyocyte cultures were treated with Triiodothyronine (T3) to induce cell hypertrophy. T3 rapidly activates extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, which was partially inhibited by AT1R blockade. Also, ERK1/2 inhibition attenuated the hypertrophic effects of T3. ARRB2 was upregulated by T3, and small interfering RNA assays revealed the role of ARRB2-but not ARRB1-on ERK1/2 activation and cardiomyocyte hypertrophy. Corroborating these findings, the ARRB2-overexpressed cells showed increased expression of hypertrophic markers, which were attenuated by ERK1/2 inhibition. Immunocytochemistry and immunoprecipitation assays revealed the increased expression of nuclear AT1R after T3 stimulation and the increased interaction of AT1R/ARRB2. The inhibition of endocytosis also attenuated the T3 effects on cardiac cells. Our results evidence the contribution of ARRB2 on ERK1/2 activation and cardiomyocyte hypertrophy induced by T3 via AT1R.

Epidermal growth factor receptor-dependent maintenance of cardiac contractility

AIMS

Epidermal growth factor receptor (EGFR) is essential to the development of multiple tissues and organs and is a target of cancer therapeutics. Due to the embryonic lethality of global EGFR deletion and conflicting reports of cardiac-overexpressed EGFR mutants, its specific impact on the adult heart, normally or in response to chronic stress, has not been established. Using complimentary genetic strategies to modulate cardiomyocyte-specific EGFR expression, we aim to define its role in the regulation of cardiac function and remodeling.

METHODS AND RESULTS

A floxed EGFR mouse model with α-myosin heavy chain-Cre-mediated cardiomyocyte-specific EGFR downregulation (CM-EGFR-KD mice) developed contractile dysfunction by 9 weeks of age, marked by impaired diastolic relaxation, as monitored via echocardiographic, hemodynamic and isolated cardiomyocyte contractility analyses. This contractile defect was maintained over time without overt cardiac remodeling until 10 months of age, after which the mice ultimately developed severe heart failure and reduced lifespan. Acute downregulation of EGFR in adult floxed EGFR mice with adeno-associated virus 9 (AAV9)-encoded Cre with a cardiac troponin T promoter (AAV9-cTnT-Cre) recapitulated the CM-EGFR-KD phenotype, while AAV9-cTnT-EGFR treatment of adult CM-EGFR-KD mice rescued the phenotype. Notably, chronic administration of the β-adrenergic receptor (βAR) agonist isoproterenol effectively and reversibly compensated for the contractile dysfunction in the absence of cardiomyocyte hypertrophy in CM-EGFR-KD mice. Mechanistically, EGFR downregulation reduced the expression of protein phosphatase 2 A (PP2A) regulatory subunit Ppp2r3a/PR72, which was associated with decreased phosphorylation of phospholamban (PLB) and Ca2+ clearance, and whose re-expression via AAV9-cTnT-PR72 rescued the CM-EGFR-KD phenotype.

CONCLUSIONS

Altogether our study highlights a previously unrecognized role for EGFR in maintaining contractile homeostasis under physiologic conditions in the adult heart via regulation of PR72 expression.

TRANSLATIONAL PERSPECTIVE

Our study highlights a previously unrecognized role for EGFR in maintaining contractile homeostasis under physiologic conditions in the adult heart via regulation of PR72, a PP2A regulatory subunit with an unknown impact on cardiac function. Further, we have shown that cardiomyocyte-expressed EGFR is required for the promotion of cardiac hypertrophy under conditions of chronic catecholamine stress. Altogether, our study provides new insight into the dynamic nature of cardiomyocyte-specific EGFR.

Role of pregnancy on insulin-induced vasorelaxation: the influence of angiotensin II receptors

Insulin resistance is a feature of pregnancy and is associated with increased levels of angiotensin II (Ang II) and insulin. Therefore, pregnancy may change insulin-induced vasodilation through changes in Ang II receptors. Insulin-induced vasorelaxation was evaluated in phenylephrine-precontracted aortic rings of pregnant and non-pregnant rats, using a conventional isolated organ preparation. Experiments were performed in thoracic or abdominal aorta rings with or without endothelium in the presence and absence of N^G-nitro-L-arginine methyl ester (L-NAME) (10^-5 M), losartan (10^-7 M), or PD123319 (10^-7 M). AT1 and AT2 receptor expressions were detected by immunohistochemistry. Insulin-induced vasodilation was endothelium- and nitric oxide-dependent and decreased in the thoracic aorta but increased in the abdominal segment of pregnant rats. The insulin's vasorelaxant effect was increased by losartan mainly on the thoracic aorta. PD123319 decreased insulin-induced vasorelaxation mainly in the pregnant rat abdominal aorta. AT1 receptor expression was decreased while AT2 receptor expression was increased by pregnancy. In conclusion, pregnancy changes insulin-induced vasorelaxation. Moreover, insulin vasodilation is tonically inhibited by AT1 receptors, while AT2 receptors appear to have an insulin-sensitizing effect. The role of pregnancy and Ang II receptors differ depending on the aorta segment. These results shed light on the role of pregnancy and Ang II receptors on the regulation of insulin-mediated vasodilation.

Lysophosphatidic Acid Receptor 4 Is Transiently Expressed during Cardiac Differentiation and Critical for Repair of the Damaged Heart

Efficient differentiation of pluripotent stem cells (PSCs) into cardiac cells is essential for the development of new therapeutic modalities to repair damaged heart tissue. We identified a novel cell surface marker, the G protein-coupled receptor lysophosphatidic acid receptor 4 (LPAR4), specific to cardiac progenitor cells (CPCs) and determined its functional significance and therapeutic potential. During in vitro differentiation of mouse and human PSCs toward cardiac lineage, LPAR4 expression peaked after 3−7 days of differentiation in cardiac progenitors and then declined. In vivo, LPAR4 was specifically expressed in the early stage of embryonal heart development, and as development progressed, LPAR4 expression decreased and was non-specifically distributed. We identified the effective agonist octadecenyl phosphate and a p38 MAPK blocker as the downstream signal blocker. Sequential stimulation and inhibition of LPAR4 using these agents enhanced the in vitro efficiency of cardiac differentiation from mouse and human PSCs. Importantly, in vivo, this sequential stimulation and inhibition of LPAR4 reduced the infarct size and rescued heart dysfunction in mice. In conclusion, LPAR4 is a novel CPC marker transiently expressed only in heart during embryo development. Modulation of LPAR4-positive cells may be a promising strategy for repairing myocardium after myocardial infarction.

Epidermal growth factor receptor association with β1-adrenergic receptor is mediated via its juxtamembrane domain

β1-adrenergic receptor (β1AR)-mediated transactivation of epidermal growth factor receptor (EGFR) engages downstream signaling events that impact numerous cellular processes including growth and survival. While association of these receptors has been shown to occur basally and be important for relaying transactivation-specific intracellular events, the mechanism by which they do so is unclear and elucidation of which would aid in understanding the consequence of disrupting their interaction. Using fluorescence resonance energy transfer (FRET) and immunoprecipitation (IP) analyses, we evaluated the impact of C-terminal truncations of EGFR on its ability to associate with β1AR. While loss of the last 230 amino acid C-terminal phosphotyrosine-rich domain did not disrupt the ability of EGFR to associate with β1AR, truncation of the entire intracellular domain of EGFR resulted in almost complete loss of its interaction with β1AR, suggesting that either the kinase domain or juxtamembrane domain (JMD) may be required for this association. Treatment with the EGFR antagonist gefitinib did not prevent β1AR-EGFR association, however, treatment with a palmitoylated peptide encoding the first 20 amino acids of the JMD domain (JMD-A) disrupted β1AR-EGFR association over time and prevented β1AR-mediated ERK1/2 phosphorylation, both in general and specifically in association with EGFR. Conversely, neither a mutated JMD-A peptide nor a palmitoylated peptide fragment consisting of the subsequent 18 amino acids of the JMD domain (JMD-B) were capable of doing so. Altogether, the proximal region of the JMD of EGFR is responsible for its association with β1AR, and its disruption prevents β1AR-mediated transactivation, thus providing a new tool to study the functional consequences of disrupting β1AR-EGFR downstream signaling.

G proteins: binary switches in health and disease

Cell signaling plays critical role in health and disease. The normal functioning of body depends on the homeostasis of immunity players. One of the very important cell signaling participants is G protein-coupled receptor (GPCR). GPCRs transduce extracellular signals into target cell by binding to and activating different G proteins (G αβγ, families Gi, Gs, Gq/11, G12/13) leading to range of different functions. Abnormal GPCRs signaling leads to various abnormalities, including but not limited to, cancer, pain, cardiac problems, and asthma. Mutations, which lead to activation or inactivation of GPCR pathways, permanently alter the pathways controlled by these receptors. A large number of human cancer incidence is a consequence of genetic abnormalities in signaling pathways, which influence cell division. Some bacteria and pathogens may interfere with the GPCR signaling pathways for their survival and immune evasion. Inhibition of GPCR signaling by small inhibitors is a novel way to treat various pathological conditions. There are several types of GPCRs in human genome, which due to their central role in health and disease, are the target of many commercially available drugs. Importantly, GPCRs have huge impact on drug discovery and approximately 30% of current drug targets are GPCRs. There is a need of further studies to explore more the role of G protein and the GPCRs in human health and how certain mutations can lead to disease state. Such studies may be important to adjust the signaling pathways for health improvement.

Treatments targeting inotropy

Acute heart failure (HF) and in particular, cardiogenic shock are associated with high morbidity and mortality. A therapeutic dilemma is that the use of positive inotropic agents, such as catecholamines or phosphodiesterase-inhibitors, is associated with increased mortality. Newer drugs, such as levosimendan or omecamtiv mecarbil, target sarcomeres to improve systolic function putatively without elevating intracellular Ca2+. Although meta-analyses of smaller trials suggested that levosimendan is associated with a better outcome than dobutamine, larger comparative trials failed to confirm this observation. For omecamtiv mecarbil, Phase II clinical trials suggest a favourable haemodynamic profile in patients with acute and chronic HF, and a Phase III morbidity/mortality trial in patients with chronic HF has recently begun. Here, we review the pathophysiological basis of systolic dysfunction in patients with HF and the mechanisms through which different inotropic agents improve cardiac function. Since adenosine triphosphate and reactive oxygen species production in mitochondria are intimately linked to the processes of excitation-contraction coupling, we also discuss the impact of inotropic agents on mitochondrial bioenergetics and redox regulation. Therefore, this position paper should help identify novel targets for treatments that could not only safely improve systolic and diastolic function acutely, but potentially also myocardial structure and function over a longer-term.

Therapeutic Implications for PDE2 and cGMP/cAMP Mediated Crosstalk in Cardiovascular Diseases

Phosphodiesterases (PDEs) are the principal superfamily of enzymes responsible for degrading the secondary messengers 3',5'-cyclic nucleotides cAMP and cGMP. Their refined subcellular localization and substrate specificity contribute to finely regulate cAMP/cGMP gradients in various cellular microdomains. Redistribution of multiple signal compartmentalization components is often perceived under pathological conditions. Thereby PDEs have long been pursued as therapeutic targets in diverse disease conditions including neurological, metabolic, cancer and autoimmune disorders in addition to numerous cardiovascular diseases (CVDs). PDE2 is a unique member of the broad family of PDEs. In addition to its capability to hydrolyze both cAMP and cGMP, PDE2 is the sole isoform that may be allosterically activated by cGMP increasing its cAMP hydrolyzing activity. Within the cardiovascular system, PDE2 serves as an integral regulator for the crosstalk between cAMP/cGMP pathways and thereby may couple chronically adverse augmented cAMP signaling with cardioprotective cGMP signaling. This review provides a comprehensive overview of PDE2 regulatory functions in multiple cellular components within the cardiovascular system and also within various subcellular microdomains. Implications for PDE2- mediated crosstalk mechanisms in diverse cardiovascular pathologies are discussed highlighting the prospective use of PDE2 as a potential therapeutic target in cardiovascular disorders.

Selective enhancement of cardiomyocyte efficiency results in a pernicious heart condition

Transgenic mice with selective induction of calreticulin transgene expression in cardiomyocytes (Cardiac^CRT+) were analyzed. Cardiac^CRT+ cardiomyocytes showed increased contractility and Ca²⁺ transients. Yet, in vivo assessment of cardiac performance, and ischemic tolerance of Cardiac^CRT+ mice demonstrated right ventricle dilation and reduced cardiac output, increased QT interval and decreased P amplitude. Paradoxically, ex vivo working hearts from Cardiac^CRT+ mice showed enhanced ischemic cardio-protection and cardiac efficiency. Under aerobic conditions, Cardiac^CRT+ hearts showed less efficient cardiac function than sham control hearts due to an increased ATP production from glycolysis relative to glucose oxidation. During reperfusion, this inefficiency was reversed, with Cardiac^CRT+ hearts exhibiting better functional recovery and increased cardiac efficiency compared to sham control hearts. On the other hand, mechanical stretching of isolated cardiac fibroblasts activated the IRE1α branch of the unfolded protein response pathway as well as induction of Col1A2 and TGFβ gene expression ex vivo, which were all suppressed by tauroursodeoxycholic acid.

Sequential analysis of myocardial gene expression with phenotypic change: Use of cross-platform concordance to strengthen biologic relevance

Objectives

To investigate the biologic relevance of cross-platform concordant changes in gene expression in intact human failing/hypertrophied ventricular myocardium undergoing reverse remodeling.

Background

Information is lacking on genes and networks involved in remodeled human LVs, and in the associated investigative best practices.

Methods

We measured mRNA expression in ventricular septal endomyocardial biopsies from 47 idiopathic dilated cardiomyopathy patients, at baseline and after 3–12 months of β-blocker treatment to effect left ventricular (LV) reverse remodeling as measured by ejection fraction (LVEF). Cross-platform gene expression change concordance was investigated in reverse remodeling Responders (R) and Nonresponders (NR) using 3 platforms (RT-qPCR, microarray, and RNA-Seq) and two cohorts (All 47 subjects (A-S) and a 12 patient “Super-Responder” (S-R) subset of A-S).

Results

For 50 prespecified candidate genes, in A-S mRNA expression 2 platform concordance (C_cpT), but not single platform change, was directly related to reverse remodeling, indicating C_cpT has biologic significance. Candidate genes yielded a C_cpT (PCR/microarray) of 62% for Responder vs. Nonresponder (R/NR) change from baseline analysis in A-S, and ranged from 38% to 100% in S-R for PCR/microarray/RNA-Seq 2 platform comparisons. Global gene C_cpT measured by microarray/RNA-Seq was less than for candidate genes, in S-R R/NR 17.5% vs. 38% (P = 0.036). For S-R global gene expression changes, both cross-cohort concordance (C_ccT) and C_cpT yielded markedly greater values for an R/NR vs. an R-only analysis (by 22 fold for C_ccT and 7 fold for C_cpT). Pathway analysis of concordant global changes for R/NR in S-R revealed signals for downregulation of multiple phosphoinositide canonical pathways, plus expected evidence of a β₁-adrenergic receptor gene network including enhanced Ca²⁺ signaling.

Conclusions

Two-platform concordant change in candidate gene expression is associated with LV biologic effects, and global expression concordant changes are best identified in an R/NR design that can yield novel information.

Gut metabolites: make orphans adopted

A commentary on “A forward chemical genetic screen reveals gut microbiota metabolites that modulate host physiology”.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Stress Coping Strategies in the Heart: An Integrated View

The heart is made up of an ordered amalgam of cardiac cell types that work together to coordinate four major processes, namely energy production, electrical conductance, mechanical work, and tissue remodeling. Over the last decade, a large body of information has been amassed regarding how different cardiac cell types respond to cellular stress that affect the functionality of their elaborate intracellular membrane networks, the cellular reticular network. In the context of the heart, the manifestations of stress coping strategies likely differ depending on the coping strategy outcomes of the different cardiac cell types, and thus may underlie the development of distinct cardiac disorders. It is not clear whether all cardiac cell types have similar sensitivity to cellular stress, how specific coping response strategies modify their unique roles, and how their metabolic status is communicated to other cells within the heart. Here we discuss our understanding of the roles of specialized cardiac cells that together make the heart function as an organ with the ability to pump blood continuously and follow a regular rhythm.

BRET-based assay to monitor EGFR transactivation by the AT1R reveals Gq/11 protein-independent activation and AT1R-EGFR complexes

The type 1 angiotensin II (AngII) receptor (AT₁R) transactivates the epidermal growth factor receptor (EGFR), which leads to pathological remodeling of heart, blood vessels and kidney. End-point assays are used as surrogates of EGFR activation, however these downstream readouts are not applicable to live cells, in real-time. Herein, we report the use of a bioluminescence resonance energy transfer (BRET)-based assay to assess recruitment of the EGFR adaptor protein, growth factor receptor-bound protein 2 (Grb2), to the EGFR. In a variety of cell lines, both epidermal growth factor (EGF) and AngII stimulated Grb2 recruitment to EGFR. The BRET assay was used to screen a panel of 9 G protein-coupled receptors (GPCRs) and further developed for other EGFR family members (HER2 and HER3); the AT₁R was able to transactivate HER2, but not HER3. Mechanistically, AT₁R-mediated ERK1/2 activation was dependent on G_q/11 and EGFR tyrosine kinase activity, whereas the recruitment of Grb2 to the EGFR was independent of G_q/11 and only partially dependent on EGFR tyrosine kinase activity. This G_q/11 independence of EGFR transactivation was confirmed using AT₁R mutants and in CRISPR cell lines lacking G_q/11. EGFR transactivation was also apparently independent of β-arrestins. Finally, we used additional BRET-based assays and confocal microscopy to provide evidence that both AngII- and EGF-stimulation promoted AT₁R-EGFR heteromerization. In summary, we report an alternative approach to monitoring AT₁R-EGFR transactivation in live cells, which provides a more direct and proximal view of this process, including the potential for complexes between the AT₁R and EGFR.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

Central administration of TRV027 improves baroreflex sensitivity and vascular reactivity in spontaneously hypertensive rats

TRV027 is a biased agonist for the Angiotensin (Ang)-II type 1 receptor (AT₁R), able to recruit β-arrestin 2 independently of G-proteins activation. β-arrestin activation in the central nervous system (CNS) was suggested to oppose the effects of Ang-II. The present study evaluates the effect of central infusion of TRV027 on arterial pressure (AP), autonomic function, baroreflex sensitivity (BRS), and peripheral vascular reactivity. Spontaneously hypertensive (SH) and Wistar Kyoto (WKY) rats were treated with TRV027 for 14 days (20 ng/h) delivered to the lateral ventricle via osmotic minipumps. Mechanistic studies were performed in HEK293T cells co-transfected with AT₁R and Ang converting enzyme type 2 (ACE2) treated with TRV027 (100 nM) or Ang-II (100 nM). TRV027 infusion in SH rats (SHR) reduced AP (~20 mmHg, P<0.05), sympathetic vasomotor activity (ΔMAP = -47.2 ± 2.8 compared with -64 ± 5.1 mmHg, P<0.05) and low-frequency (LF) oscillations of AP (1.7 ± 0.2 compared with 5.8 ± 0.4 mmHg, P<0.05) compared with the SHR control group. TRV027 also increased vagal tone, improved BRS, reduced the reactivity of mesenteric arteries to Ang-II and increased vascular sensitivity to phenylephrine (Phe), acetylcholine, (ACh), and sodium nitroprusside (SNP). In vitro, TRV027 prevented the Ang-II-induced up-regulation of ADAM17 and in contrast with Ang-II, had no effects on ACE2 activity and expression levels. Furthermore, TRV027 induced lesser interactions between AT₁R and ACE2 compared with Ang-II. Together, these data suggest that due to its biased activity for the β-arrestin pathway, TRV027 has beneficial effects within the CNS on hypertension, autonomic and vascular function, possibly through preserving ACE2 compensatory activity in neurones.

Participation of voltage-gated sodium and calcium channels in the acute cardiac effects of toluene

Inhaling solvents can lead to occurrence of cardiac arrhythmias and sudden sniffing death. Mechanisms related to this phenomenon are not fully understood. The purpose of this study was to investigate the effect of acute toluene exposure on heart reactivity to epinephrine and the participation of voltage-gated sodium and calcium channels. We found that acute toluene exposure increased perfusion pressure, left ventricular developed pressure, and heart rate. These actions were inhibited by lidocaine and nifedipine. Our results suggest that acute toluene exposure modify voltage-gated sodium and calcium channel function and expression likely due to a cardiac adrenergic mechanism and these effects could be participating, at least in part, in the presence of cardiac arrhythmias. To our best knowledge, this is the first report to establish a direct participation of voltage-gated Na⁺ and Ca²⁺ channels, toluene and epinephrine on cardiac function in rats.

Cardiac GPCR-Mediated EGFR Transactivation: Impact and Therapeutic Implications

G protein-coupled receptors (GPCRs) remain primary therapeutic targets for numerous cardiovascular disorders, including heart failure (HF), because of their influence on cardiac remodeling in response to elevated neurohormone signaling. GPCR blockers have proven to be beneficial in the treatment of HF by reducing chronic G protein activation and cardiac remodeling, thereby extending the lifespan of patients with HF. Unfortunately, this effect does not persist indefinitely, thus next-generation therapeutics aim to selectively block harmful GPCR-mediated pathways while simultaneously promoting beneficial signaling. Transactivation of epidermal growth factor receptor (EGFR) has been shown to be mediated by an expanding repertoire of GPCRs in the heart, and promotes cardiomyocyte survival, thus may offer a new avenue of HF therapeutics. However, GPCR-dependent EGFR transactivation has also been shown to regulate cardiac hypertrophy and fibrosis by different GPCRs and through distinct molecular mechanisms. Here, we discuss the mechanisms and impact of GPCR-mediated EGFR transactivation in the heart, focusing on angiotensin II, urotensin II, and β-adrenergic receptor systems, and highlight areas of research that will help us to determine whether this pathway can be engaged as future therapeutic strategy.

The Biased G-Protein-Coupled Receptor Agonism Bridges the Gap between the Insulin Receptor and the Metabolic Syndrome

Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term "metabolic syndrome". Although many of these pathologies are associated with insulin resistance, the exact mechanisms are not well understood. One area of current interest is the possibility of G-protein-coupled receptors (GPCRs) influencing or regulating IR signaling. This concept is particularly significant, because GPCRs have been shown to participate in cross-talk with the IR. More importantly, GPCR signaling has also been shown to preferentially regulate specific downstream signaling targets through GPCR agonist bias. A novel study recently demonstrated that this GPCR-biased agonism influences the activity of the IR without the presence of insulin. Although GPCR-IR cross-talk has previously been established, the notion that GPCRs can regulate the activation of the IR is particularly significant in relation to metabolic syndrome and other pathologies that develop as a result of alterations in IR signaling. As such, we aim to provide an overview of the physiological and pathophysiological roles of the IR within metabolic syndrome and its related pathologies, including cardiovascular health, gut microflora composition, gastrointestinal tract functioning, polycystic ovarian syndrome, pancreatic cancer, and neurodegenerative disorders. Furthermore, we propose that the GPCR-biased agonism may perhaps mediate some of the downstream signaling effects that further exacerbate these diseases for which the mechanisms are currently not well understood.