Adenylyl cyclase type VI gene transfer reduces phospholamban expression in cardiac myocytes via activating transcription factor 3

Multiplexed, image-based pooled screens in primary cells and tissues with PerturbView

Optical pooled screening (OPS) is a scalable method for linking image-based phenotypes with cellular perturbations. However, it has thus far been restricted to relatively low-plex phenotypic readouts in cancer cell lines in culture due to limitations associated with in situ sequencing of perturbation barcodes. Here, we develop PerturbView, an OPS technology that leverages in vitro transcription to amplify barcodes before in situ sequencing, enabling screens with highly multiplexed phenotypic readouts across diverse systems, including primary cells and tissues. We demonstrate PerturbView in induced pluripotent stem cell-derived neurons, primary immune cells and tumor tissue sections from animal models. In a screen of immune signaling pathways in primary bone marrow-derived macrophages, PerturbView uncovered both known and novel regulators of NF-κB signaling. Furthermore, we combine PerturbView with spatial transcriptomics in tissue sections from a mouse xenograft model, paving the way to in situ screens with rich optical and transcriptomic phenotypes. PerturbView broadens the scope of OPS to a wide range of models and applications.

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.

Research progress on activation transcription factor 3: A promising cardioprotective molecule

Activation transcription factor 3 (ATF3), a member of the ATF/cyclic adenosine monophosphate response element binding family, can be induced by a variety of stresses. Numerous studies have indicated that ATF3 plays multiple roles in the development and progression of cardiovascular diseases, including atherosclerosis, hypertrophy, fibrosis, myocardial ischemia-reperfusion, cardiomyopathy, and other cardiac dysfunctions. In past decades, ATF3 has been demonstrated to be detrimental to some cardiac diseases. Current studies have indicated that ATF3 can function as a cardioprotective molecule in antioxidative stress, lipid metabolic metabolism, energy metabolic regulation, and cell death modulation. To unveil the potential therapeutic role of ATF3 in cardiovascular diseases, we organized this review to explore the protective effects and mechanisms of ATF3 on cardiac dysfunction, which might provide rational evidence for the prevention and cure of cardiovascular diseases.

The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

Signaling cascades in the failing heart and emerging therapeutic strategies

Chronic heart failure is the end stage of cardiac diseases. With a high prevalence and a high mortality rate worldwide, chronic heart failure is one of the heaviest health-related burdens. In addition to the standard neurohormonal blockade therapy, several medications have been developed for chronic heart failure treatment, but the population-wide improvement in chronic heart failure prognosis over time has been modest, and novel therapies are still needed. Mechanistic discovery and technical innovation are powerful driving forces for therapeutic development. On the one hand, the past decades have witnessed great progress in understanding the mechanism of chronic heart failure. It is now known that chronic heart failure is not only a matter involving cardiomyocytes. Instead, chronic heart failure involves numerous signaling pathways in noncardiomyocytes, including fibroblasts, immune cells, vascular cells, and lymphatic endothelial cells, and crosstalk among these cells. The complex regulatory network includes protein-protein, protein-RNA, and RNA-RNA interactions. These achievements in mechanistic studies provide novel insights for future therapeutic targets. On the other hand, with the development of modern biological techniques, targeting a protein pharmacologically is no longer the sole option for treating chronic heart failure. Gene therapy can directly manipulate the expression level of genes; gene editing techniques provide hope for curing hereditary cardiomyopathy; cell therapy aims to replace dysfunctional cardiomyocytes; and xenotransplantation may solve the problem of donor heart shortages. In this paper, we reviewed these two aspects in the field of failing heart signaling cascades and emerging therapeutic strategies based on modern biological techniques.

Adeno-associated viral (AAV) vector-mediated therapeutics for diabetic cardiomyopathy - current and future perspectives

Diabetes increases the prevalence of heart failure by 6-8-fold, independent of other comorbidities such as hypertension and coronary artery disease, a phenomenon termed diabetic cardiomyopathy. Several key signalling pathways have been identified that drive the pathological changes associated with diabetes-induced heart failure. This has led to the development of multiple pharmacological agents that are currently available for clinical use. While fairly effective at delaying disease progression, these treatments do not reverse the cardiac damage associated with diabetes. One potential alternative avenue for targeting diabetes-induced heart failure is the use of adeno-associated viral vector (AAV) gene therapy, which has shown great versatility in a multitude of disease settings. AAV gene therapy has the potential to target specific cells or tissues, has a low host immune response and has the possibility to represent a lifelong cure, not possible with current conventional pharmacotherapies. In this review, we will assess the therapeutic potential of AAV gene therapy as a treatment for diabetic cardiomyopathy.

Targeting Ca2 + Handling Proteins for the Treatment of Heart Failure and Arrhythmias

Diseases of the heart, such as heart failure and cardiac arrhythmias, are a growing socio-economic burden. Calcium (Ca²⁺) dysregulation is key hallmark of the failing myocardium and has long been touted as a potential therapeutic target in the treatment of a variety of cardiovascular diseases (CVD). In the heart, Ca²⁺ is essential for maintaining normal cardiac function through the generation of the cardiac action potential and its involvement in excitation contraction coupling. As such, the proteins which regulate Ca²⁺ cycling and signaling play a vital role in maintaining Ca²⁺ homeostasis. Changes to the expression levels and function of Ca²⁺-channels, pumps and associated intracellular handling proteins contribute to altered Ca²⁺ homeostasis in CVD. The remodeling of Ca²⁺-handling proteins therefore results in impaired Ca²⁺ cycling, Ca²⁺ leak from the sarcoplasmic reticulum and reduced Ca²⁺ clearance, all of which contributes to increased intracellular Ca²⁺. Currently, approved treatments for targeting Ca²⁺ handling dysfunction in CVD are focused on Ca²⁺ channel blockers. However, whilst Ca²⁺ channel blockers have been successful in the treatment of some arrhythmic disorders, they are not universally prescribed to heart failure patients owing to their ability to depress cardiac function. Despite the progress in CVD treatments, there remains a clear need for novel therapeutic approaches which are able to reverse pathophysiology associated with heart failure and arrhythmias. Given that heart failure and cardiac arrhythmias are closely associated with altered Ca²⁺ homeostasis, this review will address the molecular changes to proteins associated with both Ca²⁺-handling and -signaling; their potential as novel therapeutic targets will be discussed in the context of pre-clinical and, where available, clinical data.

A PDE3A Promoter Polymorphism Regulates cAMP-Induced Transcriptional Activity in Failing Human Myocardium

BACKGROUND

The phosphodiesterase 3A (PDE3A) gene encodes a PDE that regulates cardiac myocyte cyclic adenosine monophosphate (cAMP) levels and myocardial contractile function. PDE3 inhibitors (PDE3i) are used for short-term treatment of refractory heart failure (HF), but do not produce uniform long-term benefit.

OBJECTIVES

The authors tested the hypothesis that drug target genetic variation could explain clinical response heterogeneity to PDE3i in HF.

METHODS

PDE3A promoter studies were performed in a cloned luciferase construct. In human left ventricular (LV) preparations, mRNA expression was measured by reverse transcription polymerase chain reaction, and PDE3 enzyme activity by cAMP-hydrolysis.

RESULTS

The authors identified a 29-nucleotide (nt) insertion (INS)/deletion (DEL) polymorphism in the human PDE3A gene promoter beginning 2,214 nt upstream from the PDE3A1 translation start site. Transcription factor ATF3 binds to the INS and represses cAMP-dependent promoter activity. In explanted failing LVs that were homozygous for PDE3A DEL and had been treated with PDE3i pre-cardiac transplantation, PDE3A1 mRNA abundance and microsomal PDE3 enzyme activity were increased by 1.7-fold to 1.8-fold (p < 0.05) compared with DEL homozygotes not receiving PDE3i. The basis for the selective up-regulation in PDE3A gene expression in DEL homozygotes treated with PDE3i was a cAMP response element enhancer 61 nt downstream from the INS, which was repressed by INS. The DEL homozygous genotype frequency was also enriched in patients with HF.

CONCLUSIONS

A 29-nt INS/DEL polymorphism in the PDE3A promoter regulates cAMP-induced PDE3A gene expression in patients treated with PDE3i. This molecular mechanism may explain response heterogeneity to this drug class, and may inform a pharmacogenetic strategy for a more effective use of PDE3i in HF.

Cardiac-Directed Expression of Adenylyl Cyclase Catalytic Domain (C1C2) Attenuates Deleterious Effects of Pressure Overload

A fusion protein (C1C2) constructed by fusing the intracellular C1 and C2 segments of adenylyl cyclase type 6 (AC6) retains beneficial effects of AC6 expression, without increasing cyclic adenosine monophosphate generation. The effects of cardiac-directed C1C2 expression in pressure overload is unknown. Left ventricular (LV) pressure overload was induced by transverse aortic constriction (TAC) in C1C2 mice and in transgene negative (TG-) mice. Four weeks after TAC, LV systolic function and diastolic function were measured, and Ca2+ handling was assessed. Four weeks after TAC, TG- animals showed reduced LV peak +dP/dt. LV peak +dP/dt in C1C2 mice was statistically indistinguishable from that of normal mice and was higher than that seen in TG- mice 4 weeks after TAC (p = 0.02), despite similar and substantial cardiac hypertrophy. In addition to higher LV peak +dP/dt in vivo, cardiac myocytes from C1C2 mice showed shorter time-to-peak Ca2+ transient amplitude (p = 0.002) and a reduced time constant of cytosolic Ca2+ decline (Tau; p = 0.003). Sarcomere shortening fraction (p < 0.03) and the rate of sarcomere shortening (p < 0.02) increased in C1C2 cardiac myocytes. Myofilament sensitivity to Ca2+ was increased in systole (p = 0.02) and diastole (p = 0.04) in C1C2 myocytes. These findings indicate enhanced Ca2+ handling associated with C1C2 expression. Favorable effects on Ca2+ handling and LV function were associated with increased LV SERCA2a protein content (p = 0.015) and reduced LV fibrosis (p = 0.008). Cardiac-directed C1C2 expression improves Ca2+ handling and increases LV contractile function in pressure overload. These data provide a rationale for further exploration of C1C2 gene transfer as a potential treatment for heart failure.

Design of a Phase 3 trial of intracoronary administration of human adenovirus 5 encoding human adenylyl cyclase type 6 (RT-100) gene transfer in patients with heart failure with reduced left ventricular ejection fraction: The FLOURISH Clinical Trial

The prognosis of patients with HFrEF remains poor despite the use of current medical and device therapies. Preclinical studies of HFrEF using IC delivery of RT-100, a replication deficient, E1/E3-deleted human adenovirus 5 encoding human AC6 was associated with favorable effects on LV function and remodeling. A recent multicenter, double-blind, placebo-controlled, phase 2 study demonstrated the safety of IC delivery of RT-100 in HFrEF patients and potential efficacy at the higher doses. This phase 2 dose finding study, which included doses not expected to be effective, identified a potential reduction in congestive heart failure admissions in the AC6-treated group one year after randomization. The FLOURISH study is designed to investigate the prospect of reduction of heart failure hospitalization and other clinical adverse events and improvement in EF. The FLOURISH study is a double-blind, placebo-controlled, multicenter Phase 3 clinical trial that will randomize 536 patients to a one-time IC administration of RT-100 (10¹² vp) or placebo in a 1:1 ratio. Subjects will be 18-80 years of age, on optimal standard of care HF therapy with LVEF ≥10% and ≤35% by echocardiogram, and will undergo IC administration of RT-100 vs. placebo on Day 1. Follow-up study visits will be performed at Weeks 1 and 4, and Months 3, 6, and 12. Patients will be followed for an additional 36 months for safety assessments with telephone contact at Months 24, 36, and 48. The primary objective is to determine the efficacy of IC RT-100 vs. placebo in reducing the event rate of all (first and repeat) HF hospitalizations occurring from baseline to 12 months. The secondary objectives are to determine the efficacy of IC RT-100 on CV death, all cause death, and all HF events and in improving NYHA functional classification. Exploratory endpoints will include echocardiographic parameters of left ventricular systolic and diastolic function, HF symptoms and physical limitations, 6-minute walking distance, Borg dyspnea score, and NT-proBNP levels. The FLOURISH study, which received fast track designation from the Food and Drug Administration in December 2017, will further investigate the role of a one-time intracoronary injection of RT-100 in reducing HF hospitalizations and will serve as a registration trial (potentially pivotal investigation) for RT-100 as a treatment for HFrEF.

Cardiac-directed expression of a catalytically inactive adenylyl cyclase 6 protects the heart from sustained β-adrenergic stimulation

Objectives

Increased expression of adenylyl cyclase type 6 (AC6) has beneficial effects on the heart through cyclic adenosine monophosphate (cAMP)-dependent and cAMP-independent pathways. We previously generated a catalytically inactive mutant of AC6 (AC6mut) that has an attenuated response to β-adrenergic receptor stimulation, and, consequently, exhibits reduced myocardial cAMP generation. In the current study we test the hypothesis that cardiac-directed expression of AC6mut would protect the heart from sustained β-adrenergic receptor stimulation, a condition frequently encountered in patients with heart failure.

Methods and results

AC6mut mice and transgene negative siblings received osmotic mini-pumps to provide continuous isoproterenol infusion for seven days. Isoproterenol infusion caused deleterious effects that were attenuated by cardiac-directed AC6mut expression. Both groups showed reduced left ventricular (LV) ejection fraction, but the reduction was less in AC6mut mice (p = 0.047). In addition, AC6mut mice showed superior left ventricular function, manifested by higher values for LV peak +dP/dt (p = 0.03), LV peak -dP/dt (p = 0.008), end-systolic pressure-volume relationship (p = 0.003) and cardiac output (p<0.03). LV samples of AC6mut mice had more sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a) protein (p<0.01), which likely contributed to better LV function. AC6mut mice had lower rates of cardiac myocyte apoptosis (p = 0.016), reduced caspase 3/7 activity (p = 0.012) and increased B-cell lymphoma 2 (Bcl2) expression (p = 0.0001).

Conclusion

Mice with cardiac-directed AC6mut expression weathered the deleterious effects of continuous isoproterenol infusion better than control mice, indicating cardiac protection.

Randomized Clinical Trials of Gene Transfer for Heart Failure with Reduced Ejection Fraction

Despite improvements in drug and device therapy for heart failure, hospitalization rates and mortality have changed little in the past decade. Randomized clinical trials using gene transfer to improve function of the failing heart are the focus of this review. Four randomized clinical trials of gene transfer in heart failure with reduced ejection fraction (HFrEF) have been published. Each enrolled patients with stable symptomatic HFrEF and used either intracoronary delivery of a virus vector or endocardial injection of a plasmid. The initial CUPID trial randomized 14 subjects to placebo and 25 subjects to escalating doses of adeno-associated virus type 1 encoding sarcoplasmic reticulum calcium ATPase (AAV1.SERCA2a). AAV1.SERCA2a was well tolerated, and the high-dose group met a 6 month composite endpoint. In the subsequent CUPID-2 study, 243 subjects received either placebo or the high dose of AAV1.SERCA2a. AAV1.SERCA2a administration, while safe, failed to meet the primary or any secondary endpoints. STOP-HF used plasmid endocardial injection of stromal cell-derived factor-1 to promote stem-cell recruitment. In a 93-subject trial of patients with ischemic etiology heart failure, the primary endpoint (symptoms and 6 min walk distance) failed, but subgroup analyses showed improvements in subjects with the lowest ejection fractions. A fourth trial randomized 14 subjects to placebo and 42 subjects to escalating doses of adenovirus-5 encoding adenylyl cyclase 6 (Ad5.hAC6). There were no safety concerns, and patients in the two highest dose groups (combined) showed improvements in left ventricular function (left ventricular ejection fraction and -dP/dt). The safety data from four randomized clinical trials of gene transfer in patients with symptomatic HFrEF suggest that this approach can be conducted with acceptable risk, despite invasive delivery techniques in a high-risk population. Additional trials are necessary before the approach can be endorsed for clinical practice.

Cardiac-Directed Expression of Adenylyl Cyclase Catalytic Domain Reverses Cardiac Dysfunction Caused by Sustained Beta-Adrenergic Receptor Stimulation

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Cardiac-targeted expression of C1C2 reduces cAMP production yet mice maintain normal cardiac function through increased Ca²⁺ handling.

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Sustained isoproterenol infusion reduces heart function in normal mice, but improves heart function in mice with increased cardiac C1C2 expression.

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Reduced cardiac cAMP generation and resistance to catecholamine cardiomyopathy are attractive features of this potential heart failure therapeutic.

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Removing the large transmembrane domains of AC6 and fusing the two intracellular domains provides a small molecule, C1C2, that replicates many of the beneficial effects of AC6, but is sufficiently small to be expressed in an AAV vector for gene transfer.

Transgenic mice with cardiac-directed C1C2, a fusion protein of the intracellular C1 and C2 segments of adenylyl cyclase type 6, had normal left ventricular (LV) function, but diminished cAMP generation. Cardiac myocytes from C1C2 mice showed increased Ca²⁺ release. Mice underwent continuous isoproterenol infusion to stress the heart. In C1C2 mice, sustained isoproterenol infusion increased rather than decreased LV function. LV SERCA2a and Ca²⁺ release were increased. Reduced cAMP generation and resistance to catecholamine cardiomyopathy are attractive features of this potential heart failure therapeutic.

Intracoronary Gene Transfer of Adenylyl Cyclase 6 in Patients With Heart Failure: A Randomized Clinical Trial

IMPORTANCE

Gene transfer has rarely been tested in randomized clinical trials.

OBJECTIVE

To evaluate the safety and efficacy of intracoronary delivery of adenovirus 5 encoding adenylyl cyclase 6 (Ad5.hAC6) in heart failure.

DESIGN, SETTING, AND PARTICIPANTS

A randomized, double-blind, placebo-controlled, phase 2 clinical trial was conducted in US medical centers (randomization occurred from July 19, 2010, to October 30, 2014). Participants 18 to 80 years with symptomatic heart failure (ischemic and nonischemic) and an ejection fraction (EF) of 40% or less were screened; 86 individuals were enrolled, and 56 were randomized. Data analysis was of the intention-to-treat population. Participants underwent exercise testing and measurement of left ventricular EF (echocardiography) and then cardiac catheterization, where left ventricular pressure development (+dP/dt) and decline (-dP/dt) were recorded. Participants were randomized (3:1 ratio) to receive 1 of 5 doses of intracoronary Ad5.hAC6 or placebo. Participants underwent a second catheterization 4 weeks later for measurement of dP/dt. Exercise testing and EF were assessed 4 and 12 weeks after randomization.

INTERVENTIONS

Intracoronary administration of Ad5.hAC6 (3.2 × 109 to 1012 virus particles) or placebo.

MAIN OUTCOMES AND MEASURES

Primary end points included exercise duration and EF before and 4 and 12 weeks after randomization and peak rates of +dP/dt and -dP/dt before and 4 weeks after randomization. Fourteen placebo participants were compared (intention to treat) with 24 Ad5.hAC6 participants receiving the highest 2 doses (D4 + 5).

RESULTS

Fifty-six individuals were randomized and monitored for up to 1 year. Forty-two participants (75%) received Ad5.hAC6 (mean [SE] age, 63 [1] years; EF, 30% [1%]), and 14 individuals (25%) received placebo (age, 62 [1] years; EF, 30% [2%]). Exercise duration showed no significant group differences (4 weeks, P = .27; 12 weeks, P = .47, respectively). The D4 + 5 participants had increased EF at 4 weeks (+6.0 [1.7] EF units; n = 21; P < .004), but not 12 weeks (+3.0 [2.4] EF units; n = 21; P = .16). Placebo participants showed no increase in EF at 4 weeks or 12 weeks. Exercise duration showed no between-group differences (4-week change from baseline: placebo, 27 [36] seconds; D4 + 5, 44 [25] seconds; P = .27; 12-week change from baseline: placebo, 44 [28] seconds; D4 + 5, 58 [29 seconds, P = .47). AC6 gene transfer increased basal left ventricular peak -dP/dt (4-week change from baseline: placebo, +93 [51] mm Hg/s; D4 + 5, -39 [33] mm Hg/s; placebo [n = 21]; P < .03); AC6 did not increase arrhythmias. The admission rate for patients with heart failure was 9.5% (4 of 42) in the AC6 group and 28.6% (4 of 14) in the placebo group (relative risk, 0.33 [95% CI, 0.08-1.36]; P = .10).

CONCLUSIONS AND RELEVANCE

AC6 gene transfer safely increased LV function beyond standard heart failure therapy, attainable with one-time administration. Larger trials are warranted.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00787059.

Role of LRP1 and ERK and cAMP Signaling Pathways in Lactoferrin-Induced Lipolysis in Mature Rat Adipocytes

Lactoferrin (LF) is a multifunctional glycoprotein present in milk. A clinical study showed that enteric-coated bovine LF tablets decrease visceral fat accumulation. Furthermore, animal studies revealed that ingested LF is partially delivered to mesenteric fat, and in vitro studies showed that LF promotes lipolysis in mature adipocytes. The aim of the present study was to determine the mechanism underlying the induction of lipolysis in mature adipocytes that is induced by LF. To address this question, we used proteomics techniques to analyze protein expression profiles. Mature adipocytes from primary cultures of rat mesenteric fat were collected at various times after exposure to LF. Proteomic analysis revealed that the expression levels of hormone-sensitive lipase (HSL), which catalyzes the rate-limiting step of lipolysis, were upregulated and that HSL was activated by protein kinase A within 15 min after the cells were treated with LF. We previously reported that LF increases the intracellular concentration of cyclic adenosine monophosphate (cAMP), suggesting that LF activates the cAMP signaling pathway. In this study, we show that the expression level and the activity of the components of the extracellular signal-regulated kinase (ERK) signaling pathway were upregulated. Moreover, LF increased the activity of the transcription factor cAMP response element binding protein (CREB), which acts downstream in the cAMP and ERK signaling pathways and regulates the expression levels of adenylyl cyclase and HSL. Moreover, silencing of the putative LF receptor low-density lipoprotein receptor-related protein 1 (LRP1) attenuated lipolysis in LF-treated adipocytes. These results suggest that LF promoted lipolysis in mature adipocytes by regulating the expression levels of proteins involved in lipolysis through controlling the activity of cAMP/ERK signaling pathways via LRP1.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

Preserved cardiac function despite marked impairment of cAMP generation

Objectives

So many clinical trials of positive inotropes have failed, that it is now axiomatic that agents that increase cAMP are deleterious to the failing heart. An alternative strategy is to alter myocardial Ca²⁺ handling or myofilament response to Ca²⁺ using agents that do not affect cAMP. Although left ventricular (LV) function is tightly linked to adenylyl cyclase (AC) activity, the beneficial effects of AC may be independent of cAMP and instead stem from effects on Ca²⁺ handling. Here we ask whether an AC mutant molecule that reduces LV cAMP production would have favorable effects on LV function through its effects on Ca²⁺ handling alone.

Methods and Results

We generated transgenic mice with cardiac-directed expression of an AC6 mutant (AC6mut). Cardiac myocytes showed impaired cAMP production in response to isoproterenol (74% reduction; p<0.001), but LV size and function were normal. Isolated hearts showed preserved LV function in response to isoproterenol stimulation. AC6mut expression was associated with increased sarcoplasmic reticulum Ca²⁺ uptake and the EC₅₀ for SERCA2a activation was reduced. Cardiac myocytes isolated from AC6mut mice showed increased amplitude of Ca²⁺ transients in response to isoproterenol (p = 0.0001). AC6mut expression also was associated with increased expression of LV S100A1 (p = 0.03) and reduced expression of phospholamban protein (p = 0.01).

Conclusion

LV AC mutant expression is associated with normal cardiac function despite impaired cAMP generation. The mechanism appears to be through effects on Ca²⁺ handling — effects that occur despite diminished cAMP.

Prospects for gene transfer for clinical heart failure

Congestive heart failure is an inexorable disease associated with unacceptably high morbidity and mortality. Preclinical results indicate that gene transfer using various proteins is a safe and effective approach for increasing function of the failing heart. In the current review, we provide a summary of cardiac gene transfer in general and summarize findings using adenylyl cyclase 6 as therapeutic gene in the failing heart. We also discuss the potential usefulness of a new treatment for congestive heart failure, paracrine-based gene transfer.

Unanticipated signaling events associated with cardiac adenylyl cyclase gene transfer

The published papers on the effects of increased cardiac expression of adenylyl cyclase type 6 (AC6) are reviewed. These include the effects of AC on normal and failing left ventricle in several pathophysiological models in mice and pigs. In addition, the effects of increased expression of AC6 in cultured neonatal and adult rat cardiac myocytes are discussed in the context of attempting to establish mechanisms for the unanticipated beneficial effects of AC6 on the failing heart. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Angiotensin II signaling up-regulates the immediate early transcription factor ATF3 in the left but not the right atrium

The atria respond to various pathological stimuli including pressure and volume overload with remodeling and dilatation. Dilatation of the left atrium is associated with atrial fibrillation. The mechanisms involved in chamber-specific hypertrophy are largely unknown. Angiotensin II is hypothesized to take part in mediating this response. ATF3 is an immediate early gene found at the receiving end of multiple stress and growth stimuli. Here we characterize ATF3 as a direct target gene for angiotensin II. ATF3 expression is regulated by angiotensin receptor-mediated signaling in vivo and in vitro at the transcriptional level. ATF3 induction is mediated by cooperation between both the AT(1A) and AT₂ receptor subtypes. While AT₂R blocker (PD123319) efficiently blocks ATF3 induction in response to angiotensin II injection, it results in an increase in blood pressure indicating that the effect of angiotensin II on ATF3 is independent of its effect on blood pressure. In contrast to adrenergic stimulation that induces ATF3 in all heart chambers, ATF3 induction in response to angiotensin II occurs primarily in the left chambers. We hypothesize that the activation of differential signaling pathways accounts for the chamber-specific induction of ATF3 expression in response to angiotensin II stimulation. Angiotensin II injection rapidly activates the EGFR-dependent pathways including ERK and PI3K-AKT in the left but not the right atrium. EGF receptor inhibitor (Gefitinib/Iressa) as well as the AKT inhibitor (Triciribine) significantly abrogates ATF3 induction by angiotensin II in the left chambers. Collectively, our data strongly place ATF3 as a unique nuclear protein target in response to angiotensin II stimulation in the atria. The spatial expression of ATF3 may add to the understanding of the signaling pathways involved in cardiac response to neuro-hormonal stimulation, and in particular to the understanding of left atrial-generated pathology such as atrial fibrillation.

Activated expression of cardiac adenylyl cyclase 6 reduces dilation and dysfunction of the pressure-overloaded heart

BACKGROUND AND OBJECTIVE

Cardiac-directed adenylyl cyclase 6 (AC6) expression attenuates left ventricular (LV) hypertrophy and dysfunction in cardiomyopathy, but its effects in the pressure-overloaded heart are unknown.

METHODS

Mice with cardiac-directed and regulated expression of AC6 underwent transaortic constriction (TAC) to induce LV pressure overload. Ten days prior to TAC, and for the duration of the 4 week study, cardiac myocyte AC6 expression was activated in one group (AC-On) but not the other (AC-Off). Multiple measures of LV systolic and diastolic function were obtained 4 weeks after TAC, and LV samples assessed for alterations in Ca2+ signaling.

RESULTS

LV contractility, as reflected in the end-systolic pressure-volume relationship (Emax), was increased (p=0.01) by activation of AC6 expression. In addition, diastolic function was improved (p<0.05) and LV dilation was reduced (p<0.05). LV samples from AC-On mice showed reduced protein expression of sodium/calcium exchanger (NCX1) (p<0.05), protein phosphatase 1 (PP1) (p<0.01), and increased phosphorylation of phospholamban (PLN) at Ser16 (p<0.05). Finally, sarcoplasmic reticulum (SR) Ca2+ content was increased in cardiac myocytes isolated from AC-On mice (p<0.05).

CONCLUSIONS

Activation of cardiac AC6 expression improves function of the pressure-overloaded and failing heart. The predominant mechanism for this favorable adaptation is improved Ca2+ handling, a consequence of increased PLN phosphorylation, reduced NCX1, reduced PP1 expression, and increased SR Ca2+ content.

Beneficial effects of adenylyl cyclase type 6 (AC6) expression persist using a catalytically inactive AC6 mutant

Cardiac-directed expression of AC6 has pronounced favorable effects on cardiac function possibly not linked with cAMP production. To determine rigorously whether cAMP generation is required for the beneficial effects of increased AC6 expression, we generated a catalytically inactive AC6 mutant (AC6mut) that has markedly diminished cAMP generating capacity by replacing aspartic acid with alanine at position 426 in the C1 domain (catalytic region) of AC6. Gene transfer of AC6 or AC6mut (adenovirus-mediated) in adult rat cardiac myocytes resulted in similar expression levels and intracellular distribution, but AC6mut expression was associated with marked reduction in cAMP production. Despite marked reduction in cAMP generation, AC6mut influenced intracellular signaling events similarly to that observed after expression of catalytically intact AC6. For example, both AC6 and AC6mut reduced phenylephrine-induced cardiac myocyte hypertrophy and apoptosis (p < 0.001), expression of cardiac ankyrin repeat protein (p < 0.01), and phospholamban (p < 0.05). AC6mut expression, similar to its catalytically intact cohort, was associated with increased Ca2+ transients in cardiac myocytes after isoproterenol stimulation. Many of the biological effects of AC6 expression are replicated by a catalytically inactive AC6 mutant, indicating that the mechanisms for these effects do not require increased cAMP generation.

Bitransgenesis with beta(2)-adrenergic receptors or adenylyl cyclase fails to improve beta(1)-adrenergic receptor cardiomyopathy

Cardiomyopathic effects of beta-adrenergic receptor (betaAR) signaling are primarily due to the beta(1)AR subtype. beta(1)/beta(2)AR and beta(1)/adenylyl cyclase type 5 (AC5) bitransgenic mice were created to test the hypothesis that beta(2)AR or AC5 co-overexpression has beneficial effects in beta(1)AR-mediated cardiomyopathy. In young mice, beta(1)/beta(2) hearts had a greater increase in basal and isoproterenol-stimulated contractility compared to beta(1)/AC5 and beta(1)AR hearts. By 6 months, beta(1)AR and beta(1)/beta(2) hearts retained elevated basal contractility but were unresponsive to agonist. In contrast, beta(1)/AC5 hearts maintained a small degree of agonist responsiveness, which may be due to a lack of beta(1)AR downregulation that was noted in beta(1)- and beta(1)/beta(2) hearts. However, by 9 -months, beta(1), beta(1)/beta(2), and beta(1)/AC5 mice had all developed severely depressed fractional shortening in vivo and little response to agonist. p38 mitogen activated protein kinase (MAPK) was minimally activated by beta(1)AR, but was markedly enhanced in the bitransgenics. Akt activation was only found with the bitransgenics. The small increase in cystosolic second mitochondria-derived activator of caspase (Smac), indicative of apoptosis in 9-month beta(1)AR hearts, was suppressed in beta(1)/AC5, but not in beta(1)/beta(2), hearts. Taken together, the unique signaling effects of enhanced beta(2)AR and AC5, which have the potential to afford benefit in heart failure, failed to salvage ventricular function in beta(1)AR-mediated cardiomyopathy.

Repression of cardiac phospholamban gene expression is mediated by thyroid hormone receptor-{alpha}1 and involves targeted covalent histone modifications

Phospholamban (PLB) is a critical regulator of Ca(2+) cycling in heart muscle cells, and its gene expression is markedly down-regulated by T(3). Nonetheless, little is known about the molecular mechanisms of T(3)-dependent gene silencing in cardiac muscle, and it remains unclear whether thyroid hormone receptors (TRs) directly bind at the PLB gene in vivo and facilitate transcriptional repression. To investigate the regulatory role of TRs in PLB transcription, we used a physiological murine heart muscle cell line (HL-1) that retains cardiac electrophysiological properties, expresses both TRalpha1 and TRbeta1 subtypes, and exhibits T(3)-dependent silencing of PLB expression. By performing RNA interference assays with HL-1 cells, we found that TRalpha1, but not TRbeta1, is essential for T(3)-dependent PLB gene repression. Interestingly, a PLB reporter gene containing only the core promoter sequences -156 to +64 displayed robust T(3)-dependent silencing in HL-1 cells, thus suggesting that transcriptional repression is facilitated by TRalpha1 via the PLB core promoter, a regulatory region highly conserved in mammals. Consistent with this notion, chromatin immunoprecipitation and in vitro binding assays show that TRalpha1 directly binds at the PLB core promoter region. Furthermore, addition of T(3) triggered alterations in covalent histone modifications at the PLB promoter that are associated with gene silencing, namely a pronounced decrease in both histone H3 acetylation and histone H3 lysine 4 methylation. Taken together, our data reveal that T(3)-dependent repression of PLB in cardiac myocytes is directly facilitated by TRalpha1 and involves the hormone-dependent recruitment of histone-modifying enzymes associated with transcriptional silencing.

Critical role of transcription factor cyclic AMP response element modulator in beta1-adrenoceptor-mediated cardiac dysfunction

BACKGROUND

Chronic stimulation of the beta(1)-adrenoceptor (beta(1)AR) plays a crucial role in the pathogenesis of heart failure; however, underlying mechanisms remain to be elucidated. The regulation by transcription factors cAMP response element-binding protein (CREB) and cyclic AMP response element modulator (CREM) represents a fundamental mechanism of cyclic AMP-dependent gene control possibly implicated in beta(1)AR-mediated cardiac deterioration.

METHODS AND RESULTS

We studied the role of CREM in beta(1)AR-mediated cardiac effects, comparing transgenic mice with heart-directed expression of beta(1)AR in the absence and presence of functional CREM. CREM inactivation protected from cardiomyocyte hypertrophy, fibrosis, and left ventricular dysfunction in beta(1)AR-overexpressing mice. Transcriptome and proteome analysis revealed a set of predicted CREB/CREM target genes including the cardiac ryanodine receptor, tropomyosin 1alpha, and cardiac alpha-actin as altered on the mRNA or protein level along with the improved phenotype in CREM-deficient beta(1)AR-transgenic hearts.

CONCLUSIONS

The results imply the regulation of genes by CREM as an important mechanism of beta(1)AR-induced cardiac damage in mice.

Adenylyl cyclase type VI increases Akt activity and phospholamban phosphorylation in cardiac myocytes

Increased expression of adenylyl cyclase VI has beneficial effects on the heart, but strategies that increase cAMP production in cardiac myocytes usually are harmful. Might adenylyl cyclase VI have beneficial effects unrelated to increased beta-adrenergic receptor-mediated signaling? We previously reported that adenylyl cyclase VI reduces cardiac phospholamban expression. Our focus in the current studies is how adenylyl cyclase VI influences phospholamban phosphorylation. In cultured cardiac myocytes, increased expression of adenylyl cyclase VI activates Akt by phosphorylation at serine 473 and threonine 308 and is associated with increased nuclear phospho-Akt. Activated Akt phosphorylates phospholamban, a process that does not require beta-adrenergic receptor stimulation or protein kinase A activation. These previously unrecognized signaling events would be predicted to promote calcium handling and increase contractile function of the intact heart independently of beta-adrenergic receptor activation. We speculate that phospholamban phosphorylation, through activation of Akt, may be an important mechanism by which adenylyl cyclase VI increases the function of the failing heart.

The repression of IRS2 gene by ATF3, a stress-inducible gene, contributes to pancreatic beta-cell apoptosis

OBJECTIVE

beta-Cell failure is an essential component of all types of diabetes, and the insulin receptor substrate 2 (IRS2) branch of signaling plays a key role in beta-cell survival and function. We tested the hypothesis that activating transcription factor 3 (ATF3), a stress-inducible proapoptotic gene, downregulates the expression of IRS2 in beta-cells.

RESEARCH DESIGN AND METHODS

We used both the gain- and loss-of-function approaches to test the effects of ATF3 on IRS2 gene expression. We also analyzed the binding of ATF3 to the IRS2 promoter by chromatin immunoprecipitation assay and the transcription of the IRS2 gene by polymerase II occupancy assay. Furthermore, we tested the ability of IRS2 to alleviate the proapoptotic effects of ATF3 in cultured beta-cells and in transgenic mice using the rat insulin promoter to drive the transgenes.

RESULTS

Expression of ATF3 is sufficient to reduce IRS2 gene expression; in contrast, knockdown or knockout of ATF3 reduces the ability of stress signals to downregulate IRS2 expression. ATF3 binds to the IRS2 promoter in vivo, and the binding of ATF3 correlates with decreased IRS2 gene transcription. Functionally, expression of IRS2 protects beta-cells from ATF3-induced apoptosis.

CONCLUSIONS

IRS2 is a target gene of ATF3, and its repression by ATF3 contributes, at least partly, to the apoptosis induced by ATF3. Because ATF3 is a stress-inducible gene, our work provides a direct link to explain how environmental stress factors can modulate IRS2 gene transcription.

New signaling pathways associated with increased cardiac adenylyl cyclase 6 expression: implications for possible congestive heart failure therapy

Congestive heart failure (CHF) affects more than five million people in the United States and results in considerable morbidity, mortality, and economic costs. Patients with class III and IV CHF have a 40% to 50% probability of dying 5 years after symptom onset despite optimal therapy, a prognosis worse than many cancers. A variety of drugs and devices have improved survival-the 50% survival time in 1980 was just 18 months-but the outlook for patients remains dismal and the prevalence of CHF continues to increase. This unmet medical need underscores the importance of developing new approaches for the treatment of CHF. This brief review focuses on data from preclinical experiments regarding the effects of increased adenylyl cyclase type 6 (AC6) expression on cellular and cardiac function, and possible mechanisms for the unexpected favorable effects of increased AC6 content on the failing heart.

Adenylyl cyclase gene transfer in heart failure

The rationale for gene transfer of adenylyl cyclase type VI (AC(VI)) for clinical congestive heart failure (CHF) is based on recent experimental studies that have extended from cultured cardiac myocytes to preclinical studies in animal models of CHF. Over the past several years substantial data have indicated an unexpected and pronounced favorable effect of AC(VI) expression in cardiovascular disease. Preclinical studies have shown that increased cardiac AC content improves left ventricular function and attenuates deleterious remodeling in the failing heart, and reduces mortality in heart failure and in acute myocardial infarction. A brief review of the preclinical studies that have examined changes associated with increased AC expression in the heart is presented here.

Lipopolysaccharide attenuates mRNA levels of several adenylyl cyclase isoforms in vivo

Signals that elevate intracellular levels of cyclic adenosine monophosphate (cAMP) are among the factors that control lipopolysaccharide (LPS)-mediated inflammatory mediator production by macrophages. cAMP signaling is also involved in maintaining body functions that are commonly impaired in sepsis, including the endothelial cell barrier function and heart function. Several agents successfully used for sepsis intervention target cAMP signaling, and it was recently shown that liver and lung may be protected from inflammation injury by cAMP-elevating phosphodiesterase inhibitors. Here, we show that LPS attenuates adenylyl cyclase (AC) mRNA levels in liver, lung, heart, spleen and kidney in an animal model of endotoxemia, and in macrophages from liver and lung. In particular, AC5, AC6, AC7 and AC9 mRNA were reduced in most tissues examined and in tissue macrophages. In Kupffer cells, prostaglandin E2-mediated cAMP production was inhibited by LPS treatment. The reduction in AC mRNA by LPS would be expected to lead to a lowered potential for cAMP production in most organs, and in particular, changes in AC6 mRNA may affect endothelial cell barrier function and heart function. In contrast, AC4 mRNA was elevated in heart and lung. The present work indicates a possible mechanism for LPS-mediated alteration of cAMP signaling in vivo.

Increased cardiac adenylyl cyclase expression is associated with increased survival after myocardial infarction

BACKGROUND

Cardiac-directed expression of adenylyl cyclase type VI (AC(VI)) in mice results in structurally normal hearts with normal basal heart rate and function but increased responses to catecholamine stimulation. We tested the hypothesis that increased left ventricular (LV) AC(VI) content would increase mortality after acute myocardial infarction (MI).

METHODS AND RESULTS

Transgenic mice with cardiac-directed AC(VI) expression and their transgene-negative littermates (control) underwent coronary ligation, and survival, infarct size, and LV size and function were assessed 1 to 7 days after MI. Mice with increased AC(VI) expression had increased survival (control 41%, AC(VI) 74%; P = 0.004). Infarct size and myocardial apoptotic rates were similar in AC(VI) and control mice; however, AC(VI) mice had less LV dilation (P < 0.001) and increased ejection fractions (P < 0.03). Three days after MI, studies in isolated perfused hearts showed that basal LV +dP/dt was similar, but graded dobutamine infusion was associated with a more robust LV contractile response in AC(VI) mice (P < 0.05). Increased LV function was associated with increases in cAMP generation (P = 0.0002), phospholamban phosphorylation (P < 0.04), sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) affinity for calcium (P < 0.015), and reduced AV block (P = 0.04).

CONCLUSIONS

In acute MI, increased cardiac AC(VI) content attenuates adverse LV remodeling, preserves LV contractile function, and reduces mortality.

Cycloheximide treatment to identify components of the transitional transcriptome in PACAP-induced PC12 cell differentiation

Pituitary adenylate cyclase-activating polypeptide (PACAP) promotes neurite outgrowth, reduces proliferation and inhibits apoptosis of PC12 cells. We have partially characterized the transcriptome changes induced by PACAP after 6 h of treatment, when commitment to differentiation has occurred. Here, we have investigated the effects of a 6-h treatment with PACAP (10(-7) m) in the presence of cycloheximide (5 microm) to identify, via superinduction, components of the transitional transcriptome initially induced by PACAP and potentially participating in the regulation of late-response genes required for differentiation. Approximately 100 new transcripts were identified in this screen, i.e. as many individual genes as make up the 6-h PACAP differentiation transcriptome itself. Six known transcripts in this cohort were then measured at several time points between 0 and 6 h by real-time PCR to determine whether these transcripts are induced early following PACAP treatment in the absence of cycloheximide, and therefore may be of functional importance in differentiation. Five out of the six transcripts were indeed induced by PACAP alone soon (between 30 min and 3 h) after cell treatment. beta-Cell translocation gene 2, antiproliferative (Btg2), serum/glucocorticoid-regulated kinase (Sgk), nuclear factor for the kappa chain of B-cells (NFkappaB), seven in absentia homologue 2 (Siah2) and FBJ osteosarcoma related oncogene (Fos) showed a 2.5-200-fold induction by PACAP between 15 min and 3 h, and mRNA levels returned either to baseline or near baseline after 6 h. This work provides new information concerning genes whose transient regulation early after PACAP exposure may contribute to the expression of the differentiated transcriptome in PC12 cells, and should help to elucidate the molecular mechanisms involved in the control of nerve cell survival and differentiation.

Regulatory properties of adenylate cyclases type 5 and 6: A progress report

Adenylate cyclases (AC) type 5 and 6 comprise the calcium-inhibited family of adenylate cyclase isoforms. Here we review recent discoveries in the regulation of AC5 and AC6 with a focus on posttranslational modifications including glycosylation, nitrosylation, and phosphorylation by the cyclic AMP-dependent protein kinase (PKA), protein kinase C (PKC), and Raf1. We also describe novel signaling interactions such as Galpha(q)-mediated potentiation of AC6 activation. Novel regulators of AC5 and AC6, including small molecules and proteins that physically interact with AC5 and AC6 such as snapin, regulator of G protein signaling 2 (RGS2), protein associated with myc (PAM), and caveolin peptides are discussed. We also describe several recent studies that demonstrate the usefulness of transgenic or adenoviral overexpression of AC5 and AC6 in models for disease states such as cardiovascular hypertrophy. The discovery of novel regulatory mechanisms for AC5 and AC6 and their potential role in crucial physiological processes provide new avenues for research into therapeutic interventions targeting the cyclic AMP pathway.