Disruption of type 5 adenylyl cyclase gene preserves cardiac function against pressure overload

Adenylyl cyclase isoforms 5 and 6 in the cardiovascular system: complex regulation and divergent roles

Adenylyl cyclases (ACs) are crucial effector enzymes that transduce divergent signals from upstream receptor pathways and are responsible for catalyzing the conversion of ATP to cAMP. The ten AC isoforms are categorized into four main groups; the class III or calcium-inhibited family of ACs comprises AC5 and AC6. These enzymes are very closely related in structure and have a paucity of selective activators or inhibitors, making it difficult to distinguish them experimentally. AC5 and AC6 are highly expressed in the heart and vasculature, as well as the spinal cord and brain; AC6 is also abundant in the lungs, kidney, and liver. However, while AC5 and AC6 have similar expression patterns with some redundant functions, they have distinct physiological roles due to differing regulation and cAMP signaling compartmentation. AC5 is critical in cardiac and vascular function; AC6 is a key effector of vasodilatory pathways in vascular myocytes and is enriched in fetal/neonatal tissues. Expression of both AC5 and AC6 decreases in heart failure; however, AC5 disruption is cardio-protective, while overexpression of AC6 rescues cardiac function in cardiac injury. This is a comprehensive review of the complex regulation of AC5 and AC6 in the cardiovascular system, highlighting overexpression and knockout studies as well as transgenic models illuminating each enzyme and focusing on post-translational modifications that regulate their cellular localization and biological functions. We also describe pharmacological challenges in the design of isoform-selective activators or inhibitors for AC5 and AC6, which may be relevant to developing new therapeutic approaches for several cardiovascular diseases.

Dysfunctional mitochondria elicit bioenergetic decline in the aged heart

Aging represents a complex biological progression affecting the entire body, marked by a gradual decline in tissue function, rendering organs more susceptible to stress and diseases. The human heart holds significant importance in this context, as its aging process poses life-threatening risks. It entails macroscopic morphological shifts and biochemical changes that collectively contribute to diminished cardiac function. Among the numerous pivotal factors in aging, mitochondria play a critical role, intersecting with various molecular pathways and housing several aging-related agents. In this comprehensive review, we provide an updated overview of the functional role of mitochondria in cardiac aging.

Oral angiotensin-converting enzyme inhibitor captopril protects the heart from Porphyromonas gingivalis LPS-induced cardiac dysfunction in mice

Although angiotensin converting enzyme (ACE) inhibitors are considered useful for the treatment of human heart failure, some experimental failing-heart models have shown little beneficial effect of ACE inhibitors in animals with poor oral health, particularly periodontitis. In this study, we examined the effects of the ACE inhibitor captopril (Cap; 0.1 mg/mL in drinking water) on cardiac dysfunction in mice treated with Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose (0.8 mg/kg/day) equivalent to the circulating level in patients with periodontal disease. Mice were divided into four groups: 1) Control, 2) PG-LPS, 3) Cap, and 4) PG-LPS + Cap. After1 week, we evaluated cardiac function by echocardiography. The left ventricular ejection fraction was significantly decreased in PG-LPS-treated mice compared to the control (from 66 ± 1.8 to 59 ± 2.5%), while Cap ameliorated the dysfunction (63 ± 1.1%). The area of cardiac fibrosis was significantly increased (approximately 2.9-fold) and the number of apoptotic myocytes was significantly increased (approximately 5.6-fold) in the heart of PG-LPS-treated group versus the control, and these changes were suppressed by Cap. The impairment of cardiac function in PG-LPS-treated mice was associated with protein kinase C δ phosphorylation (Tyr-311), leading to upregulation of NADPH oxidase 4 and xanthine oxidase, and calmodulin kinase II phosphorylation (Thr-286) with increased phospholamban phosphorylation (Thr-17). These changes were also suppressed by Cap. Our results suggest that the renin-angiotensin system might play an important role in the development of cardiac diseases induced by PG-LPS.

Effects of the angiotensin-converting enzyme inhibitor captopril on occlusal-disharmony-induced cardiac dysfunction in mice

Occlusal disharmony is known to affect not only the oral cavity environment, but also the autonomic nervous system in the heart. Since the renin-angiotensin system (RAS) inhibitor captopril (Cap) is one of the first-line drugs for preventing cardiac remodeling in patients with heart failure, we hypothesized that Cap might prevent cardiac dysfunction induced by occlusal disharmony. Here, to test this idea, we used our bite-opening (BO) mouse model, which was developed by cementing a suitable appliance onto the mandibular incisor. Mice were divided into four groups: (1) Control, (2) BO, (3) Cap, and (4) BO + Cap. After 2 weeks, we evaluated cardiac function by echocardiography and confirmed that cardiac function was significantly decreased in the BO group compared to the control, while Cap ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and oxidative stress-induced myocardial damage in the BO group were significantly increased versus the control, and these increases were suppressed by Cap. Cardiac dysfunction induced by BO was associated with dual phosphorylation on PKCδ (Tyr-311/Thr-505), leading to activation of CaMKII with increased phosphorylation of RyR2 and phospholamban. Our results suggest that the RAS might play an important role in the development of cardiac diseases induced by occlusal anomalies.

Modulation of cardiac cAMP signaling by AMPK and its adjustments in pressure overload-induced myocardial dysfunction in rat and mouse

The beta-adrenergic system is a potent stimulus for enhancing cardiac output that may become deleterious when energy metabolism is compromised as in heart failure. We thus examined whether the AMP-activated protein kinase (AMPK) that is activated in response to energy depletion may control the beta-adrenergic pathway. We studied the cardiac response to beta-adrenergic stimulation of AMPKα2-/- mice or to pharmacological AMPK activation on contractile function, calcium current, cAMP content and expression of adenylyl cyclase 5 (AC5), a rate limiting step of the beta-adrenergic pathway. In AMPKα2-/- mice the expression of AC5 (+50%), the dose response curve of left ventricular developed pressure to isoprenaline (p<0.001) or the response to forskolin, an activator of AC (+25%), were significantly increased compared to WT heart. Similarly, the response of L-type calcium current to 3-isobutyl-l-methylxanthine (IBMX), a phosphodiesterase inhibitor was significantly higher in KO (+98%, p<0.01) than WT (+57%) isolated cardiomyocytes. Conversely, pharmacological activation of AMPK by 5-aminoimidazole-4-carboxamide riboside (AICAR) induced a 45% decrease in AC5 expression (p<0.001) and a 40% decrease of cAMP content (P<0.001) as measured by fluorescence resonance energy transfer (FRET) compared to unstimulated rat cardiomyocytes. Finally, in experimental pressure overload-induced cardiac dysfunction, AMPK activation was associated with a decreased expression of AC5 that was blunted in AMPKα2-/- mice. The results show that AMPK activation down-regulates AC5 expression and blunts the beta-adrenergic cascade. This crosstalk between AMPK and beta-adrenergic pathways may participate in a compensatory energy sparing mechanism in dysfunctional myocardium.

Status of β1-Adrenoceptor Signal Transduction System in Cardiac Hypertrophy and Heart Failure

Although β 1-adrenoceptor ( β 1-AR) signal transduction, which maintains cardiac function, is downregulated in failing hearts, the mechanisms for such a defect in heart failure are not fully understood. Since cardiac hypertrophy is invariably associated with heart failure, it is possible that the loss of β 1-AR mechanisms in failing heart occurs due to hypertrophic process. In this regard, we have reviewed the information from a rat model of adaptive cardiac hypertrophy and maladaptive hypertrophy at 4 and 24 weeks after inducing pressure overload as well as adaptive cardiac hypertrophy and heart failure at 4 and 24 weeks after inducing volume overload, respectively. Varying degrees of alterations in β 1-AR density as well as isoproterenol-induced increases in cardiac function, intracellular Ca 2 + -concentration in cardiomyocytes and adenylyl cyclase activity in crude membranes have been reported under these hypertrophic conditions. Adaptive hypertrophy at 4 weeks of pressure or volume overload showed unaltered or augmented increases in the activities of different components of β 1-AR signaling. On the other hand, maladaptive hypertrophy due to pressure overload and heart failure due to volume overload at 24 weeks revealed depressions in the activities of β 1-AR signal transduction pathway. These observations provide evidence that β 1-AR signal system is either unaltered or upregulated in adaptive cardiac hypertrophy and downregulated in maladaptive cardiac hypertrophy or heart failure. Furthermore, the information presented in this article supports the concept that downregulation of β 1-AR mechanisms in heart failure or maladaptive cardiac hypertrophy is not due to hypertrophic process per se. It is suggested that a complex mechanism involving the autonomic imbalance may be of a critical importance in determining differential alterations in non-failing and failing hearts.

Vidarabine, an anti-herpes agent, improves Porphyromonas gingivalis lipopolysaccharide-induced cardiac dysfunction in mice

In this work, we examined the involvement of type 5 adenylyl cyclase (AC5) in cardiac dysfunction induced in mice given Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose equivalent to the circulating levels in periodontitis (PD) patients. Cardiac function was significantly decreased in mice given PG-LPS compared to the control, but treatment for 1 week with the AC5 inhibitor vidarabine ameliorated the dysfunction. Cardiac fibrosis and myocyte apoptosis were significantly increased in the PG-LPS group, but vidarabine blocked these changes. The PG-LPS-induced cardiac dysfunction was associated with activation of cyclic AMP/Ca2+-calmodulin-dependent protein kinase II signaling and increased phospholamban phosphorylation at threonine 17. These results suggest that pharmacological AC5 inhibition may be a promising approach to treat PD-associated cardiovascular disease.

Characterization of Adenylyl Cyclase Isoform 6 Residues Interacting with Forskolin

BACKGROUND

The adenylyl cyclase (AC) pathway, crucial for pulmonary vasodilation, is inhibited by hypoxia. Forskolin (FSK) binds allosterically to AC, stimulating ATP catalysis. As AC6 is the primary AC isoform in the pulmonary artery, selective reactivation of AC6 could provide targeted reinstatement of hypoxic AC activity. This requires elucidation of the FSK binding site in AC6.

METHODS

HEK293T cells stably overexpressing AC 5, 6, or 7 were incubated in normoxia (21% O₂) or hypoxia (10% O₂) or exposed to s-nitrosocysteine (CSNO). AC activity was measured using terbium norfloxacin assay; AC6 structure built by homology modeling; ligand docking to examine FSK-interacting amino acids; roles of selected residues determined by site-directed mutagenesis; FSK-dependent cAMP generation measured in wild-type and FSK-site mutants by biosensor-based live cell assay.

RESULTS

Only AC6 is inhibited by hypoxia and nitrosylation. Homology modeling and docking revealed residues T500, N503, and S1035 interacting with FSK. Mutation of T500, N503, or S1035 decreased FSK-stimulated AC activity. FSK site mutants were not further inhibited by hypoxia or CSNO; however, mutation of any of these residues prevented AC6 activation by FSK following hypoxia or CSNO treatment.

CONCLUSIONS

FSK-interacting amino acids are not involved in the hypoxic inhibition mechanism. This study provides direction to design FSK derivatives for selective activation of hypoxic AC6.

Inflammageing and Cardiovascular System: Focus on Cardiokines and Cardiac-Specific Biomarkers

The term "inflammageing" was introduced in 2000, with the aim of describing the chronic inflammatory state typical of elderly individuals, which is characterized by a combination of elevated levels of inflammatory biomarkers, a high burden of comorbidities, an elevated risk of disability, frailty, and premature death. Inflammageing is a hallmark of various cardiovascular diseases, including atherosclerosis, hypertension, and rapid progression to heart failure. The great experimental and clinical evidence accumulated in recent years has clearly demonstrated that early detection and counteraction of inflammageing is a promising strategy not only to prevent cardiovascular disease, but also to slow down the progressive decline of health that occurs with ageing. It is conceivable that beneficial effects of counteracting inflammageing should be most effective if implemented in the early stages, when the compensatory capacity of the organism is not completely exhausted. Early interventions and treatments require early diagnosis using reliable and cost-effective biomarkers. Indeed, recent clinical studies have demonstrated that cardiac-specific biomarkers (i.e., cardiac natriuretic peptides and cardiac troponins) are able to identify, even in the general population, the individuals at highest risk of progression to heart failure. However, further clinical studies are needed to better understand the usefulness and cost/benefit ratio of cardiac-specific biomarkers as potential targets in preventive and therapeutic strategies for early detection and counteraction of inflammageing mechanisms and in this way slowing the progressive decline of health that occurs with ageing.

Gαs, adenylyl cyclase, and their relationship to the diagnosis and treatment of depression

The relationship between depression, its etiology and therapy, and the cAMP signaling system have been studies for decades. This review will focus on cAMP, G proteins and adenylyl cyclase and depression or antidepressant action. Both human and animal studies are compared and contrasted. It is concluded that there is some synteny in the findings that cAMP signaling is attenuated in depression and that this is reversed by successful antidepressant therapy. The G protein that activates adenylyl cyclase, Gα_s, appears to have diminished access to adenylyl cyclase in depression, and this is rectified by successful antidepressant treatment. Unfortunately, attempts to link specific isoforms of adenylyl cyclase to depression or antidepressant action suffer from discontinuity between human and animal studies.

Discovery of levodopa-induced dyskinesia-associated genes using genomic studies in patients and Drosophila behavioral analyses

Although levodopa is the most effective medication for Parkinson’s disease, long-term levodopa treatment is largely compromised due to late motor complications, including levodopa-induced dyskinesia (LID). However, the genetic basis of LID pathogenesis has not been fully understood. Here, we discover genes pathogenic for LID using Drosophila genetics and behavioral analyses combined with genome-wide association studies on 578 patients clinically diagnosed with LID. Similar to the therapeutic effect of levodopa in patients, acute levodopa treatments restore the motor defect of Parkinson’s disease model flies, while prolonged treatments cause LID-related symptoms, such as increased yawing, freezing and abrupt acceleration of locomotion. These symptoms require dopamine 1-like receptor 1 and are induced by neuronal overexpression of the receptor. Among genes selected from our analyses in the patient genome, neuronal knockdown of adenylyl cyclase 2 suppresses the levodopa-induced phenotypes and the receptor overexpression-induced symptoms in Drosophila. Together, our study provides genetic insights for LID pathogenesis through the D1-like receptor-adenylyl cyclase 2 signaling axis.

A combined research approach using GWAS on Parkinson's disease patients and a Drosophila model of L-DOPA-induced dyskinesia (LID) reveals that LID is linked to ADCY2 signaling.

cAMP Signalling Pathway in Biocontrol Fungi

Biocontrol is a complex process, in which a variety of physiological and biochemical characteristics are altered. The cAMP signalling pathway is an important signal transduction pathway in biocontrol fungi and consists of several key components. The G-protein system contains G-protein coupled receptors (GPCRs), heterotrimeric G-proteins, adenylate cyclase (AC), cAMP-dependent protein kinase (PKA), and downstream transcription factors (TFs). The cAMP signalling pathway can regulate fungal growth, development, differentiation, sporulation, morphology, secondary metabolite production, environmental stress tolerance, and the biocontrol of pathogens. However, few reviews of the cAMP signalling pathway in comprehensive biocontrol processes have been reported. This work reviews and discusses the functions and applications of genes encoding each component in the cAMP signalling pathway from biocontrol fungi, including the G-protein system components, AC, PKA, and TFs, in biocontrol behaviour. Finally, future suggestions are provided for constructing a complete cAMP signalling pathway in biocontrol fungi containing all the components and downstream effectors involved in biocontrol behavior. This review provides useful information for the understanding the biocontrol mechanism of biocontrol fungi by utilising the cAMP signalling pathway.

Role of TLR4 signaling on Porphyromonas gingivalis LPS-induced cardiac dysfunction in mice

Oral infections, particularly periodontitis, are a well-established risk factor for cardiovascular diseases, although the molecular mechanisms involved remain elusive. The aims of the present study were to investigate the effects of lipopolysaccharide derived from Porphyromonas gingivalis (PG-LPS) on cardiac function in mice, and to elucidate the underlying mechanisms. Mice (C57BL/6) were injected with PG-LPS (0.8 mg/kg/day) with or without an inhibitor of Toll-like receptor 4 (TLR4) signaling (TAK-242, 0.8 mg/kg/day) for 4 weeks. Left ventricular ejection function was significantly decreased at 1 week (from 67 ± 0.5 to 58 ± 1.2%) and remained low at 4 weeks (57 ± 1.0%). The number of apoptotic myocytes was increased (approximately 7.4-fold), the area of fibrosis was increased (approximately 3.3-fold) and the number of 8-hydroxydeoxyguanosine-positive myocytes, a sensitive indicator of oxidative DNA damage, was increased (approximately 7.6-fold) at 4 weeks in the heart of PG-LPS treated mice. However, levels of various serum pro-inflammatory cytokines in PG-LPS-treated mice were similar to those in control mice. The impairment of cardiac function in PG-LPS-treated mice appears to involve activation of TLR4-NADPH oxidase (NOX) 4 signaling, leading to abundant production of reactive oxygen species and Ca²⁺ leakage from sarcoplastic reticulumn induced by calmodulin kinase II (CaMKII)-mediated phosphorylation of phospholamban (at Thr-17) and ryanodine receptor 2 (at Ser-2448). Pharmacological inhibition of TLR4 with TAK-242 attenuated the changes in cardiac function in PG-LPS-treated mice. Our results indicate that TLR4-NOX4 signaling may be a new therapeutic target for treatment of cardiovascular diseases in patients with periodontitis.

Physiological roles of mammalian transmembrane adenylyl cyclase isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors (GPCRs). The transmembrane ACs display varying expression patterns across tissues, giving the potential for them to have a wide array of physiological roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs, so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform-specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Targeting adipocytic discoidin domain receptor 2 impedes fat gain while increasing bone mass

Obesity is closely associated with low-bone-mass disorder. Discoidin domain receptor 2 (DDR2) plays essential roles in skeletal metabolism, and is probably involved in fat metabolism. To test the potential role of DDR2 in fat and fat-bone crosstalk, Ddr2 conditional knockout mice (Ddr2^Adipo) were generated in which Ddr2 gene is exclusively deleted in adipocytes by Adipoq Cre. We found that Ddr2^Adipo mice are protected from fat gain on high-fat diet, with significantly decreased adipocyte size. Ddr2^Adipo mice exhibit significantly increased bone mass and mechanical properties, with enhanced osteoblastogenesis and osteoclastogenesis. Marrow adipocyte is diminished in the bone marrow of Ddr2^Adipo mice, due to activation of lipolysis. Fatty acid in the bone marrow was reduced in Ddr2^Adipo mice. RNA-Seq analysis identified adenylate cyclase 5 (Adcy5) as downstream molecule of Ddr2. Mechanically, adipocytic Ddr2 modulates Adcy5-cAMP-PKA signaling, and Ddr2 deficiency stimulates lipolysis and supplies fatty acid for oxidation in osteoblasts, leading to the enhanced osteoblast differentiation and bone mass. Treatment of Adcy5 specific inhibitor abolishes the increased bone mass gain in Ddr2^Adipo mice. These observations establish, for the first time, that Ddr2 plays an essential role in the crosstalk between fat and bone. Targeting adipocytic Ddr2 may be a potential strategy for treating obesity and pathological bone loss simultaneously.

Vidarabine, an anti-herpes agent, prevents occlusal-disharmony-induced cardiac dysfunction in mice

We recently reported a positive relationship between occlusal disharmony and cardiovascular disease via activation of β-adrenergic signaling in mice. Furthermore, inhibition of type 5 adenylyl cyclase (AC5), a major cardiac subtype in adults, protects the heart against oxidative stress. Here, we examined the role of AC5 in the development of occlusal-disharmony-induced cardiovascular disease in bite-opening (BO) mice, prepared by cementing a suitable appliance onto the mandibular incisor. We first examined the effects of BO treatment on cardiac function in mice treated or not treated for 2 weeks with vidarabine, which we previously identified as an inhibitor of cardiac AC. Cardiac function was significantly decreased in the BO group compared to the control group, but vidarabine ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but vidarabine blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as increased activation of the Ca2+-calmodulin-dependent protein kinase II/receptor-interacting protein 3 signaling pathway. These data suggest that AC5 inhibition with vidarabine might be a new therapeutic approach for the treatment of cardiovascular disease associated with occlusal disharmony.

Effects of chronic Porphylomonas gingivalis lipopolysaccharide infusion on cardiac dysfunction in mice

OBJECTIVE

Periodontitis (PD) is a chronic inflammatory disease of tooth-supportive tissue. An association between PD and cardiovascular disease (CVD) has been established. Although PD is generally accepted as a risk factor for CVD, the existence of a relationship remains debatable. Possible mechanisms include the release of inflammatory mediators such as lipopolysaccharide (LPS), which may spread systemically and promote CVD.

METHODS

To compare the effects of lipopolysaccharide derived from Porphylomonas gingivalis (PG-LPS) on cardiac muscle in mice, mice were treated for 1 week with/without PG-LPS at a dose equivalent to the circulating level in PD patients (0.8 mg/kg/day).

RESULTS

Cardiac function in terms of left ventricular ejection function was significantly decreased at 1 week compared to that in the control (from 66 ± 0.5% to 57 ± 1.1%). Compared to the controls, the number of apoptotic myocytes and the area of fibrosis were significantly increased by approximately 2.7-fold and 14-fold, respectively. The impairment of cardiac function appeared to involve the activation of cAMP/PKA signaling and cAMP/calmodulin kinase II signaling (CaMKII), leading to cardiac fibrosis, myocyte apoptosis and heart failure.

CONCLUSIONS

Our results indicate that cAMP/PKA and cAMP/CaMKII signaling may be a new therapeutic target for the treatment of cardiovascular diseases in patients with periodontitis.

Cardiovascular Aging and Longevity: JACC State-of-the-Art Review

Cardiovascular aging and longevity are interrelated through many pathophysiological mechanisms. Many factors that promote atherosclerotic cardiovascular disease are also implicated in the aging process and vice versa. Indeed, cardiometabolic disorders such as hyperglycemia, insulin resistance, dyslipidemia, and arterial hypertension share common pathophysiological mechanisms with aging and longevity. Moreover, genetic modulators of longevity have a significant impact on cardiovascular aging. The current knowledge of genetic, molecular, and biochemical pathways of aging may serve as a substrate to introduce interventions that might delay cardiovascular aging, thus approaching the goal of longevity. In the present review, the authors describe pathophysiological links between cardiovascular aging and longevity and translate these mechanisms into clinical data by reporting genetic, dietary, and environmental characteristics from long-living populations.

Effects of Whole-Body Adenylyl Cyclase 5 (Adcy5) Deficiency on Systemic Insulin Sensitivity and Adipose Tissue

Genome-wide association studies have identified adenylyl cyclase type 5 (ADCY5) as candidate gene for diabetes-related quantitative traits and an increased risk of type 2 diabetes. Mice with a whole-body deletion of Adcy5 (Adcy5-/-) do not develop obesity, glucose intolerance and insulin resistance, have improved cardiac function and increased longevity. Here, we investigated Adcy5 knockout mice (Adcy5-/-) to test the hypothesis that changes in adipose tissue (AT) may contribute to the reported healthier phenotype. In contrast to previous reports, we found that deletion of Adcy5 did not confer any physiological or biochemical benefits. However, this unexpected finding allowed us to investigate the effects of Adcy5 depletion on AT independently of lower body weight and a metabolically healthier phenotype. Adcy5-/- mice exhibited an increased number of smaller adipocytes, lower mean adipocyte size and a distinct AT gene expression pattern with midline 1 (Mid1) as the most significantly downregulated gene compared to control mice. Our Adcy5-/- model challenges previously described beneficial effects of Adcy5 deficiency and suggests that targeting Adcy5 does not improve insulin sensitivity and may therefore limit the relevance of ADCY5 as potential drug target.

Cardiac cAMP-PKA Signaling Compartmentalization in Myocardial Infarction

Under physiological conditions, cAMP signaling plays a key role in the regulation of cardiac function. Activation of this intracellular signaling pathway mirrors cardiomyocyte adaptation to various extracellular stimuli. Extracellular ligand binding to seven-transmembrane receptors (also known as GPCRs) with G proteins and adenylyl cyclases (ACs) modulate the intracellular cAMP content. Subsequently, this second messenger triggers activation of specific intracellular downstream effectors that ensure a proper cellular response. Therefore, it is essential for the cell to keep the cAMP signaling highly regulated in space and time. The temporal regulation depends on the activity of ACs and phosphodiesterases. By scaffolding key components of the cAMP signaling machinery, A-kinase anchoring proteins (AKAPs) coordinate both the spatial and temporal regulation. Myocardial infarction is one of the major causes of death in industrialized countries and is characterized by a prolonged cardiac ischemia. This leads to irreversible cardiomyocyte death and impairs cardiac function. Regardless of its causes, a chronic activation of cardiac cAMP signaling is established to compensate this loss. While this adaptation is primarily beneficial for contractile function, it turns out, in the long run, to be deleterious. This review compiles current knowledge about cardiac cAMP compartmentalization under physiological conditions and post-myocardial infarction when it appears to be profoundly impaired.

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

Secreted frizzled protein 3 is a novel cardioprotective mechanism unique to the clinically relevant fourth window of ischemic preconditioning

Most studies on ischemic preconditioning (IPC) use one or two ischemic stimuli before examining cardioprotection. To better simulate the clinical situation, we examined, in pigs, the effects of six episodes of 10 min coronary artery occlusion (CAO) 12 h apart, followed by 60 min CAO. We named this model the fourth window of IPC. To determine the novel mechanisms mediating cardioprotection in the fourth window, gene analysis was examined in fourth window IPC cardiac tissue 60 min after the last episode of 10 min CAO. Secreted frizzled-related protein 3 (sFRP3) was the most significantly upregulated gene that was unique to the fourth window, that is, not found in the first, second, or third window IPC. To study the effects of sFRP3 on cardioprotection, sFRP3 was injected in the hearts of wild-type (WT) mice. In the [CAO/coronary artery reperfusion (CAR)] model (30 min CAO followed by 24 h CAR), infarct size was less, P < 0.01, after sFRP3 injection (14% ± 1.7%) compared with vehicle injection (48% ± 1.6%). sFRP3 injection also protected the development of heart failure following permanent CAO for 2 wk. Left ventricular ejection fraction was significantly improved, P < 0.05, at 2 wk after CAO with sFRP3 (53% ± 5%) compared with vehicle (36% ± 2%) and was accompanied by significant, P < 0.01, reductions in myocardial fibrosis (53% ± 4%), myocyte size (17% ± 3%), apoptosis (100%), and mortality (56%). Thus, sFRP3, unique to the clinically relevant fourth window IPC model, is a novel mechanism mediating ischemic cardioprotection.NEW & NOTEWORTHY1) This investigation identifies the novel fourth window of ischemic preconditioning. 2) sFRP3 was identified as the most significantly upregulated gene in the fourth window and was shown to induce cardioprotection when administered to the hearts of wild-type mice.

An update of cyclic nucleotide phosphodiesterase as a target for cardiac diseases

INTRODUCTION

Cyclic nucleotides, cAMP, and cGMP, are important second messengers of intracellular signaling and play crucial roles in cardiovascular biology and diseases. Cyclic nucleotide phosphodiesterases (PDEs) control the duration, magnitude, and compartmentalization of cyclic nucleotide signaling by catalyzing the hydrolysis of cyclic nucleotides. Individual PDEs modulate distinct signaling pathways and biological functions in the cell, making it a potential therapeutic target for the treatment of different cardiovascular disorders. The clinical success of several PDE inhibitors has ignited continued interest in PDE inhibitors and in PDE-target therapeutic strategies.

AREAS COVERED

This review concentrates on recent research advances of different PDE isoforms with regard to their expression patterns and biological functions in the heart. The limitations of current research and future directions are then discussed. The current and future development of PDE inhibitors is also covered.

EXPERT OPINION

Despite the therapeutic success of several marketed PDE inhibitors, the use of PDE inhibitors can be limited by their side effects, lack of efficacy, and lack of isoform selectivity. Advances in our understanding of the mechanisms by which cellular functions are changed through PDEs may enable the development of new approaches to achieve effective and specific PDE inhibition for various cardiac therapies.

Physiological And Pathological Roles Of Protein Kinase A In The Heart

Protein kinase A (PKA) is a central regulator of cardiac performance and morphology. Myocardial PKA activation is induced by a variety of hormones, neurotransmitters and stress signals, most notably catecholamines secreted by the sympathetic nervous system. Catecholamines bind β-adrenergic receptors to stimulate cAMP-dependent PKA activation in cardiomyocytes. Elevated PKA activity enhances Ca2+ cycling and increases cardiac muscle contractility. Dynamic control of PKA is essential for cardiac homeostasis, as dysregulation of PKA signaling is associated with a broad range of heart diseases. Specifically, abnormal PKA activation or inactivation contributes to the pathogenesis of myocardial ischemia, hypertrophy, heart failure, as well as diabetic, takotsubo, or anthracycline cardiomyopathies. PKA may also determine sex-dependent differences in contractile function and heart disease predisposition. Here, we describe the recent advances regarding the roles of PKA in cardiac physiology and pathology, highlighting previous study limitations and future research directions. Moreover, we discuss the therapeutic strategies and molecular mechanisms associated with cardiac PKA biology. In summary, PKA could serve as a promising drug target for cardioprotection. Depending on disease types and mechanisms, therapeutic intervention may require either inhibition or activation of PKA. Therefore, specific PKA inhibitors or activators may represent valuable drug candidates for the treatment of heart diseases.

Healthful aging mediated by inhibition of oxidative stress

The progressive increase in lifespan over the past century carries with it some adversity related to the accompanying burden of debilitating diseases prevalent in the older population. This review focuses on oxidative stress as a major mechanism limiting longevity in general, and healthful aging, in particular. Accordingly, the first goal of this review is to discuss the role of oxidative stress in limiting longevity, and compare healthful aging and its mechanisms in different longevity models. Secondly, we discuss common signaling pathways involved in protection against oxidative stress in aging and in the associated diseases of aging, e.g., neurological, cardiovascular and metabolic diseases, and cancer. Much of the literature has focused on murine models of longevity, which will be discussed first, followed by a comparison with human models of longevity and their relationship to oxidative stress protection. Finally, we discuss the extent to which the different longevity models exhibit the healthful aging features through physiological protective mechanisms related to exercise tolerance and increased β-adrenergic signaling and also protection against diabetes and other metabolic diseases, obesity, cancer, neurological diseases, aging-induced cardiomyopathy, cardiac stress and osteoporosis.

Effects of occlusal disharmony on susceptibility to atrial fibrillation in mice

Tooth loss or incorrect positioning causes occlusal disharmony. Furthermore, tooth loss and atrial fibrillation (AF) are both risk factors for ischemic stroke and coronary heart disease. Therefore, we hypothesized that occlusal disharmony-induced stress increases susceptibility to AF, and we designed the present study to test this idea in mice. Bite-opening (BO) was done by cementing a suitable appliance onto the mandibular incisor to cause occlusal disharmony by increasing the vertical height of occlusion by 0.7 mm for a period of 2 weeks. AF susceptibility, evaluated in terms of the duration of AF induced by transesophageal burst pacing, was significantly increased concomitantly with atrial remodeling, including fibrosis, myocyte apoptosis and oxidative DNA damage, in BO mice. The BO-induced atrial remodeling was associated with increased calmodulin kinase II-mediated ryanodine receptor 2 phosphorylation on serine 2814, as well as inhibition of Akt phosphorylation. However, co-treatment with propranolol, a non-selective β-blocker, ameliorated these changes in BO mice. These data suggest that improvement of occlusal disharmony by means of orthodontic treatment might be helpful in the treatment or prevention of AF.

Effects of occlusal disharmony on cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage in mice

Occlusal disharmony leads to morphological changes in the hippocampus and osteopenia of the lumbar vertebra and long bones in mice, and causes stress. Various types of stress are associated with increased incidence of cardiovascular disease, but the relationship between occlusal disharmony and cardiovascular disease remain poorly understood. Therefore, in this work, we examined the effects of occlusal disharmony on cardiac homeostasis in bite-opening (BO) mice, in which a 0.7 mm space was introduced by cementing a suitable applicance onto the mandibular incisior. We first examined the effects of BO on the level of serum corticosterone, a key biomarker for stress, and on heart rate variability at 14 days after BO treatment, compared with baseline. BO treatment increased serum corticosterone levels by approximately 3.6-fold and the low frequency/high frequency ratio, an index of sympathetic nervous activity, was significantly increased by approximately 4-fold by the BO treatment. We then examined the effects of BO treatment on cardiac homeostasis in mice treated or not treated with the non-selective β-blocker propranolol for 2 weeks. Cardiac function was significantly decreased in the BO group compared to the control group, but propranolol ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but propranolol blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as inhibition of Akt/mTOR signaling and autophagic flux. These data suggest that occlusal disharmony might affect cardiac homeostasis via alteration of the autonomic nervous system.

Annexin A4 N-terminal peptide inhibits adenylyl cyclase 5 and limits β-adrenoceptor-mediated prolongation of cardiac action potential

Adenylyl cyclases (AC) are essential for the normal and pathophysiological response of many cells. In cardiomyocytes, the predominant AC isoforms are AC5 and AC6. Specific AC5 inhibition was suggested as an option for the treatment of heart failure potentially advantageous over β-blockers. We previously reported an interaction between the calcium-binding protein annexin A4 (ANXA4) and AC5 in human embryonic kidney 293 (HEK293) cells and an inhibition of cyclic adenosine monophosphate (cAMP) production in cardiomyocytes. Here, we investigated whether ANXA4 is able to differentiate between AC5 and AC6. In transfected HEK293 cells, ANXA4 specifically co-immunoprecipitated with AC5 and not with AC6, via its N-terminal domain. Both ANXA4 and a peptide comprising the ANXA4 N-terminal sequence (A4N_1-22 ) decreased the cAMP production in AC5 and not in AC6 expressing cells. In line with ACs inhibition, in myocytes from ANXA4-deficient mice, β-adrenoceptor (βAR) stimulation led to a higher increase of the L-type calcium current (I_CaL ) and to an excessive action potential duration (APD) prolongation as compared to wild-type cardiomyocytes. This enhanced response was reversed in the presence of A4N_1-22 peptide likely via specific AC5 inhibition. We conclude that via the N-terminal domain ANXA4 inhibits AC5 not AC6, and that A4N_1-22 as a specific AC5 inhibitor could serve as a novel therapeutic tool for the treatment of AC5-linked diseases.

Host genotype and exercise exhibit species-level selection for members of the gut bacterial communities in the mouse digestive system

The mammalian gut microbiome can potentially impact host health and disease state. It is known that the mouse-genome, eating-behavior, and exercise-status promotes higher taxonomic rank-level alterations (e.g. family to phyla-level) of the gut microbiota. Here, host genotype or activity status was investigated to determine if selection of individual bacterial species or strains could be discerned within the murine digestive system. For this study, the fecal bacterial community of adenylyl cyclase 5 knock-out (AC5KO, n = 7) mice or their wild-type (WT, n = 10) littermates under exercise or sedentary conditions were profiled by sequencing rRNA operons. AC5KO mice were chosen since this genotype displays enhanced longevity/exercise capacity and protects against cardiovascular/metabolic disease. Profiling of rRNA operons using the Oxford MinION yielded 65,706 2-D sequences (after size selection of 3.7-5.7 kb) which were screened against an NCBI 16S rRNA gene database. These sequences were binned into 1,566 different best BLAST hits (BBHs) and counted for each mouse sample. Non-metric multidimensional scaling (NMDS) of the gut microbial community demonstrated clustering by physical activity (p = 0.001) but not by host genotype. Additionally, sequence similarity and phylogenetic analysis demonstrated that different bacterial species (closely related to Muribaculum intestinale and Parasutterella excrementihominis) inhabit AC5KO or WT mice depending on activity status. Other bacterial species of the gut microbiota did not follow such patterning (e.g. Turicibacter sanguinis and Turicimonas muris). Our results support the need of improved taxonomic resolution for better characterization of bacterial communities to deepen our understanding of the role of the gut microbiome on host health.

Structure and function of adenylyl cyclases, key enzymes in cellular signaling

The adenylyl cyclases (ACs) catalyze the production of the ubiquitous second messenger, cAMP, which in turns acts on a number of effectors and thus regulates a plethora of cellular functions. As the key enzymes in the highly evolutionarily conserved cAMP pathway, the ACs control the physiology of the cells, tissues, organs and organisms in health and disease. A comprehensive understanding of the specific role of the ACs in these processes of life requires a deep mechanistic understanding of structure and mechanisms of action of these enzymes. Here we highlight the exciting recent reports on the biochemistry and structure and higher order organization of the ACs and their signaling complexes. These studies have provided the glimpses into the principles of the AC-mediated homeostatic control of cellular physiology.

Rats are protected from the stress of chronic pressure overload compared with mice

The goal of this investigation was to compare the effects of chronic (4 wk) transverse aortic constriction (TAC) in Sprague-Dawley rats and C57BL/6J mice. TAC, after 1 day, induced similar left ventricular (LV) pressure gradients in both rats (n = 7) and mice (n = 7) (113 ± 5.4 vs. 103 ± 11.5 mmHg), and after 4 wk, the percent increase in LV hypertrophy, as reflected by LV/tibial length (51% vs 49%), was similar in rats (n = 12) and mice (n = 12). After 4 wk of TAC, LV systolic and diastolic function were preserved in TAC rats. In contrast, in TAC mice, LV ejection fraction decreased by 31% compared with sham, along with increases in LV end-diastolic pressure (153%) and LV systolic wall stress (86%). Angiogenesis, as reflected by Ki67 staining of capillaries, increased more in rats (n = 6) than in mice (n = 6; 10 ± 2 vs. 6 ± 1 Ki67-positive cells/field). Myocardial blood flow fell by 55% and coronary reserve by 28% in mice with TAC (n = 4), but they were preserved in rats (n = 4). Myogenesis, as reflected by c-kit-positive myocytes staining positively for troponin I, is another mechanism that can confer protection after TAC. However, the c-kit-positive cells in rats with TAC were all negative for troponin I, indicating the absence of myogenesis. Thus, rats showed relative tolerance to severe pressure overload compared with mice, with mechanisms involving angiogenesis but not myogenesis.

Non-coding RNAs and Cardiac Aging

Aging is an important risk factor for cardiovascular diseases. Aging increasing the morbidity and mortality in cardiovascular disease patients. With the society is aging rapidly in the world, medical burden of aging-related cardiovascular diseases increasing drastically. Hence, it is urgent to explore the underlying mechanism and treatment of cardiac aging. Noncoding RNAs (ncRNAs, including microRNAs, long noncoding RNAs and circular RNAs) have been reported to be involved in many pathological processes, including cell proliferation, cell death differentiation, hypertrophy and aging in wide variety of cells and tissues. In this chapter, we will summarize the physiology and molecular mechanisms of cardiac aging. Then, the recent research advances of ncRNAs in cardiac aging will be provided. The lessons learned from ncRNAs and cardiac aging studies would bring new insights into the regulatory mechanisms ncRNAs as well as treatment of aging-related cardiovascular diseases.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

ADCY5-Related Dyskinesia: Improving Clinical Detection of an Evolving Disorder

BACKGROUND

The phenotypic spectrum of adenylyl cyclase 5 (ADCY5)-related disease has expanded considerably since the first description of the disorder in 1978 as familial essential chorea in a multiplex family.

OBJECTIVE

To examine recent advances in the understanding of ADCY5-related dyskinesia and outline a diagnostic approach to enhance clinical detection.

METHODS

A pragmatic review of the ADCY5 literature was undertaken to examine unique genetic and pathophysiological features as well as distinguishing clinical features.

RESULTS

With over 70 cases reported to date, the phenotype is recognized to be broad, although distinctive features include prominent facial dyskinesia, motor exacerbations during drowsiness or sleep arousal, episodic painful dystonic posturing increased with stress or illness, and axial hypotonia with delayed developmental milestones. Uncommon phenotypes include childhood-onset chorea, myoclonus-dystonia, isolated nongeneralized dystonia, and alternating hemiplegia.

CONCLUSION

The ongoing expansion in clinical features suggests that ADCY5 remains underdiagnosed and may account for a proportion of "idiopathic" hyperkinetic movement disorders. Enhanced understanding of its clinical features may help clinicians improve the detection of complex or uncommon cases.

Translationally controlled tumor protein (TCTP) plays a pivotal role in cardiomyocyte survival through a Bnip3-dependent mechanism

Prevention of cardiomyocyte death is an important therapeutic strategy for heart failure. In this study, we focused on translationally controlled tumor protein (TCTP), a highly conserved protein that is expressed ubiquitously in mammalian tissues, including heart. TCTP plays pivotal roles in survival of certain cell types, but its function in cardiomyocytes has not been examined. We aimed to clarify the role of TCTP in cardiomyocyte survival and the underlying mechanism. Here, we demonstrated that downregulation of TCTP with siRNA induced cell death of cardiomyocytes with apoptotic and autophagic features, accompanied with mitochondrial permeability transition pore (mPTP) opening. TCTP loss did not induce cell death of cardiac fibroblasts. Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (Bnip3) was found to mediate the TCTP-loss-induced cardiomyocyte death. In exploring the clinical significance of the TCTP expression in the heart, we found that DOX treatment markedly downregulated the protein expression of TCTP in cultured cardiomyocytes and in mouse heart tissue. Exogenous rescue of TCTP expression attenuated DOX-induced cardiomyocyte death. In mice, cardiomyocyte-specific overexpression of TCTP resulted in decreased susceptibility to DOX-induced cardiac dysfunction, accompanied with attenuated induction of Bnip3. Dihydroartemisinin, a pharmacological TCTP inhibitor, induced development of heart failure and cardiomyocyte death in control mice, but not in mice with cardiomyocyte-specific TCTP overexpression. Our findings revealed TCTP has a pivotal role in cardiomyocyte survival, at least in part through a Bnip3-dependent mechanism. TCTP could be considered as a candidate therapeutic target to prevent DOX-induced heart failure.

Pathological cardiac hypertrophy: the synergy of adenylyl cyclases inhibition in cardiac and immune cells during chronic catecholamine stress

Response to stressors in our environment and daily lives is an adaptation conserved through evolution as it is beneficial in enhancing the survival and continuity of humans. Although stressors have evolved, the drastic physiological response they elicit still remains unchanged. The chronic secretion and circulation of catecholamines to produce physical responses when they are not required may result in pathological consequences which affect cardiac function drastically. This review seeks to point out the probable implication of chronic stress in inducing an inflammation disorder in the heart. We discussed the likely synergy of a G protein-independent stimuli signaling via β₂-adrenergic receptors in both cardiomyocytes and immune cells during chronic catecholamine stress. To explain this synergy, we hypothesized the possibility of adenylyl cyclases having a regulatory effect on G protein-coupled receptor kinases. This was based on the negative correlations they exhibit during normal cardiac function and heart failures. As such, the downregulation of adenylyl cyclases in cardiomyocytes and immune cells during chronic catecholamine stress enhances the expressions of G protein-coupled receptor kinases. In addition, we explain the maladaptive roles played by G protein-coupled receptor kinase and extracellular signal-regulated kinase in the synergistic cascade that pathologically remodels the heart. Finally, we highlighted the therapeutic potentials of an adenylyl cyclases stimulator to attenuate pathological cardiac hypertrophy (PCH) and improve cardiac function in patients developing cardiac disorders due to chronic catecholamine stress.

Effects of chronic Porphyromonas gingivalis lipopolysaccharide infusion on skeletal muscles in mice

Periodontitis, which is caused by various oral organisms, predominantly affects adults, and is one of the main causes of tooth loss, as well as leading to progression of numerous systemic diseases. However, its relationship to sarcopenia (aging-associated degenerative loss of skeletal muscle mass and function) remains unclear. The aim of this study was to investigate the effects of Porphyromonas gingivalis lipopolysaccharide (PG-LPS) on skeletal muscle in mice, and to establish the underlying mechanisms. Mice (C57BL/6) were injected with PG-LPS (0.8 mg/kg/day) for 4 weeks. This treatment significantly decreased the weight of fast-twitch skeletal muscles (masseter and tibialis anterior muscles), but not that of slow-twitch skeletal muscle (soleus muscle). The area of fibrosis was significantly increased in masseter muscle, but remained unchanged in the other two muscles. The number of apoptotic myocytes was significantly increased (approximately eightfold) in masseter muscle. These data suggest that persistent subclinical exposure to PG-LPS might reduce the size of fast-twitch skeletal muscle, but not slow-twitch skeletal muscle. Masseter muscle appears to be especially susceptible to the adverse effects of PG-LPS, because muscle remodeling (muscle fibrosis and myocyte apoptosis) was induced solely in masseter muscle. Thus, periodontitis might be one of the major causes of oral sarcopenia.

Knockout of adenylyl cyclase isoform 5 or 6 differentially modifies the β1-adrenoceptor-mediated inotropic response

Although only β₂-adrenergic receptors (βAR) dually couple with stimulatory G protein (G_s) and inhibitory G protein (G_i), inactivation of G_i enhances both β₁AR and β₂AR responsiveness. We hypothesize that G_i restrains spontaneous adenylyl cyclase (AC) activity independent of receptor activation. Subcellular localization of the AC5/6 subtypes varies contributing to the compartmentation of βAR signaling. The primary objectives were to determine: (1) if β₁AR-mediated inotropic responses were dependent upon either AC5 or AC6; (2) if intrinsic G_i inhibition is AC subtype selective and (3) the role of phosphodiesterases (PDE) 3/4 to regulate β₁AR responsiveness. β₁AR-mediated increases in contractile force and cAMP accumulation in cardiomyocytes were measured from wild type, AC5 and AC6 knockout (KO) mice, with or without pertussis toxin (PTX) pretreatment to inactivate G_i and/or after selective inhibition of PDEs 3/4. Noradrenaline potency at β₁ARs was increased in AC6 KO. PDE4 inhibition increased noradrenaline potency in wild type and AC5 KO, but not AC6 KO. PTX increased noradrenaline potency only in wild type but increased the maximal β₁AR response in all mouse strains. PDE3 inhibition increased noradrenaline potency only in AC5 KO that was treated prior with PTX. β₁AR-evoked cAMP accumulation was increased more by PDE4 inhibition than PDE3 inhibition in wild type and AC5 KO that was amplified by G_i inhibition. These data indicate that β₁AR-mediated inotropic responses are not dependent upon either AC5 or AC6 alone. Inactivation of G_i enhanced β₁AR-mediated inotropic responses despite not coupling to G_i, consistent with G_i exerting a tonic receptor independent inhibition upon AC5/6. PDE4 seems the primary regulator of β₁AR signaling through AC6 in wild type. AC6 KO results in a reorganization of β₁AR compartmentation characterized by signaling through AC5 regulated by G_i, PDE3 and PDE4 that maintains normal contractile function.

Role of β-adrenergic signaling in masseter muscle

In skeletal muscle, the major isoform of β-adrenergic receptor (β-AR) is β2-AR and the minor isoform is β1-AR, which is opposite to the situation in cardiac muscle. Despite extensive studies in cardiac muscle, the physiological roles of the β-AR subtypes in skeletal muscle are not fully understood. Therefore, in this work, we compared the effects of chronic β1- or β2-AR activation with a specific β1-AR agonist, dobutamine (DOB), or a specific β2-AR agonist, clenbuterol (CB), on masseter and cardiac muscles in mice. In cardiac muscle, chronic β1-AR stimulation induced cardiac hypertrophy, fibrosis and myocyte apoptosis, whereas chronic β2-AR stimulation induced cardiac hypertrophy without histological abnormalities. In masseter muscle, however, chronic β1-AR stimulation did not induce muscle hypertrophy, but did induce fibrosis and apoptosis concomitantly with increased levels of p44/42 MAPK (ERK1/2) (Thr-202/Tyr-204), calmodulin kinase II (Thr-286) and mammalian target of rapamycin (mTOR) (Ser-2481) phosphorylation. On the other hand, chronic β2-AR stimulation in masseter muscle induced muscle hypertrophy without histological abnormalities, as in the case of cardiac muscle, concomitantly with phosphorylation of Akt (Ser-473) and mTOR (Ser-2448) and increased expression of microtubule-associated protein light chain 3-II, an autophagosome marker. These results suggest that the β1-AR pathway is deleterious and the β2-AR is protective in masseter muscle. These data should be helpful in developing pharmacological approaches for the treatment of skeletal muscle wasting and weakness.

Dehydroepiandrosterone attenuates pulmonary artery and right ventricular remodeling in a rat model of pulmonary hypertension due to left heart failure

AIM

Pulmonary hypertension due to left heart failure (PH-LHF) is the most common cause of pulmonary hypertension. However, therapies for PH-LHF are lacking. Therefore, we investigated the effects and potential mechanism of dehydroepiandrosterone (DHEA) treatment in an experimental model of PH-LHF.

MAIN METHOD

PH-LHF was induced in rats via ascending aortic banding. The rats then received daily DHEA from Day 1 to Day 63 for the prevention protocol or from Day 49 to Day 63 for the reversal protocol. Other ascending aortic banding rats were left untreated to allow development of PH and right ventricular (RV) failure. Sham ascending aortic banding rats served as controls.

KEY FINDING

Significant increases in mean pulmonary arterial pressure (mPAP) and right ventricular end-diastolic diameter (RVEDD) were observed in the PH-LHF group. Therapy with DHEA prevented LHF-induced PH and RV failure by preserving mPAP and preventing RV hypertrophy and pulmonary artery remodeling. In preexisting severe PH, DHEA attenuated most lung and RV abnormalities. The beneficial effects of DHEA in PH-LHF seem to result from depression of the STAT3 signaling pathway in the lung.

SIGNIFICANT

DHEA not only prevents the development of PH-LHF and RV failure but also rescues severe preexisting PH-LHF.

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.

The Development of Compartmentation of cAMP Signaling in Cardiomyocytes: The Role of T-Tubules and Caveolae Microdomains

3′-5′-cyclic adenosine monophosphate (cAMP) is a signaling messenger produced in response to the stimulation of cellular receptors, and has a myriad of functional applications depending on the cell type. In the heart, cAMP is responsible for regulating the contraction rate and force; however, cAMP is also involved in multiple other functions. Compartmentation of cAMP production may explain the specificity of signaling following a stimulus. In particular, transverse tubules (T-tubules) and caveolae have been found to be critical structural components for the spatial confinement of cAMP in cardiomyocytes, as exemplified by beta-adrenergic receptor (β-ARs) signaling. Pathological alterations in cardiomyocyte microdomain architecture led to a disruption in compartmentation of the cAMP signal. In this review, we discuss the difference between atrial and ventricular cardiomyocytes in respect to microdomain organization, and the pathological changes of atrial and ventricular cAMP signaling in response to myocyte dedifferentiation. In addition, we review the role of localized phosphodiesterase (PDE) activity in constraining the cAMP signal. Finally, we discuss microdomain biogenesis and maturation of cAMP signaling with the help of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Understanding these mechanisms may help to overcome the detrimental effects of pathological structural remodeling.

Role of G protein-regulated inducer of neurite outgrowth 3 (GRIN3) in β-arrestin 2-Akt signaling and dopaminergic behaviors

The G protein-regulated inducer of neurite growth (GRIN) family has three isoforms (GRIN1-3), which bind to the Gαi/o subfamily of G protein that mediate signal processing via G protein-coupled receptors (GPCRs). Here, we show that GRIN3 is involved in regulation of dopamine-dependent behaviors and is essential for activation of the dopamine receptors (DAR)-β-arrestin signaling cascade. Analysis of functional regions of GRIN3 showed that a di-cysteine motif (Cys751/752) is required for plasma membrane localization. GRIN3 was co-immunoprecipitated with GPCR kinases 2/6 and β-arrestins 1/2. Among GRINs, only GRIN3, which is highly expressed in striatum, strongly interacted with β-arrestin 2. We also generated GRIN3-knockout mice (GRIN3KO). GRIN3KO exhibited reduced locomotor activity and increased anxiety-like behavior in the elevated maze test, as well as a reduced locomoter response to dopamine stimulation. We also examined the phosphorylation of Akt at threonine 308 (phospho308-Akt), which is dephosphorylated via a β-arrestin 2-mediated pathway. Dephosphorylation of phospho308-Akt via the D2R-β-arrestin 2 signaling pathway was completely abolished in striatum of GRIN3KO. Our results suggest that GRIN3 has a role in recruitment and assembly of proteins involved in β-arrestin-dependent, G protein-independent signaling.

Vidarabine, an anti-herpesvirus agent, prevents catecholamine-induced arrhythmias without adverse effect on heart function in mice

Sympathetic activation causes clinically important arrhythmias including atrial fibrillation (AF) and ventricular tachyarrhythmia. Although the usefulness of β-adrenergic receptor blockade therapy is widely accepted, its multiple critical side effects often prevent its initiation or continuation. The aim of this study is to determine the advantages of vidarabine, an adenylyl cyclase (AC)-targeted anti-sympathetic agent, as an alternative treatment for arrhythmia. We found that vidarabine, which we identified as a cardiac AC inhibitor, consistently shortens AF duration and reduces the incidence of sympathetic activation-induced ventricular arrhythmias. In atrial and ventricular myocytes, vidarabine inhibits adrenergic receptor stimulation-induced RyR2 phosphorylation, sarcoplasmic reticulum (SR) Ca²⁺ leakage, and spontaneous Ca²⁺ release from SR, the last of which has been considered as a potential arrhythmogenic trigger. Moreover, vidarabine also inhibits sympathetic activation-induced reactive oxygen species (ROS) production in cardiac myocytes. The pivotal role of vidarabine's inhibitory effect on ROS production with regard to its anti-arrhythmic property has also been implied in animal studies. In addition, as expected, vidarabine exerts an inhibitory effect on AC function, which is more potent in the heart than elsewhere. Indexes of cardiac function including ejection fraction and heart rate were not affected by a dosage of vidarabine sufficient to exert an anti-arrhythmic effect. These findings suggest that vidarabine inhibits catecholamine-induced AF or ventricular arrhythmia without deteriorating cardiac function in mice.

Function of Adenylyl Cyclase in Heart: the AKAP Connection

Cyclic adenosine monophosphate (cAMP), synthesized by adenylyl cyclase (AC), is a universal second messenger that regulates various aspects of cardiac physiology from contraction rate to the initiation of cardioprotective stress response pathways. Local pools of cAMP are maintained by macromolecular complexes formed by A-kinase anchoring proteins (AKAPs). AKAPs facilitate control by bringing together regulators of the cAMP pathway including G-protein-coupled receptors, ACs, and downstream effectors of cAMP to finely tune signaling. This review will summarize the distinct roles of AC isoforms in cardiac function and how interactions with AKAPs facilitate AC function, highlighting newly appreciated roles for lesser abundant AC isoforms.