PDE4 inhibitor, roflumilast protects cardiomyocytes against NO-induced apoptosis via activation of PKA and Epac dual pathways

Ras, RhoA, and vascular pharmacology in neurodevelopment and aging

Small GTPases Ras, Rac, and RhoA are crucial regulators of cellular functions. They also act in dysregulated cell proliferation and transformation. Multiple publications have focused on illuminating their roles and mechanisms, including in immune system pathologies. Their functions in neurology-related diseases, neurodegeneration and neurodevelopment, are also emerging, as well as their potential as pharmacological targets in both pathologies. Observations increasingly suggest that these pathologies may relate to activation (or suppression) of signaling by members of the Ras superfamily, especially Ras, Rho, and Rac isoforms, and components of their signaling pathways. Germline (or embryonic) mutations that they harbor are responsible for neurodevelopmental disorders, such as RASopathies, autism spectrum disorder, and dilated cardiomyopathy. In aging, they promote neurodegenerative diseases, with Rho GTPase featuring in their pharmacology, as in the case of Alzheimer's disease (AD). Significantly, drugs with observed anti-AD activity, particularly those involved in cardiovascular systems, are associated with the RhoA signaling, as well as cerebral vasculature in brain development and aging. This leads us to suggest that anti-AD drugs could inform neurodevelopmental disorders, including pediatric low-grade gliomas pharmacology. Neurodevelopmental disorders associated with RhoA, like autism, are also connected with vascular systems, thus could be targets of vascular system-connected drugs.

Neutrophil and endothelial cell membranes coassembled roflumilast nanoparticles attenuate myocardial ischemia/reperfusion injury

Aim: This study aimed to develop biomimetic nanoparticles (NPs) of roflumilast (ROF) for attenuating myocardial ischemia/reperfusion (MI/R) injury. Materials & methods: We synthesized biomimetic ROF NPs and assembled ROF NPs in neutrophil and endothelial cell membranes (NE/ROF NPs). The physical properties of NE/ROF NPs were characterized and biological functions of NE/ROF NPs were tested in vitro. Targeting characteristics, therapeutic efficacy and safety of NE/ROF NPs were examined in mice model of MI/R. Results: NE/ROF NPs exhibited significant anti-inflammatory and antiadhesion effects. Meanwhile, they was effective in reducing MI/R injury in mice. Furthermore, NE/ROF NPs exhibited stronger targeting capabilities and demonstrated good safety. Conclusion: NE/ROF NPs may be a versatile biomimetic drug-delivery system for attenuating MI/R injury.

Roflumilast reduces myocardial ischemia reperfusion injury in vivo and in vitro by activating the AMPK signaling pathway

Myocardial tissue cell damage induced by myocardial ischemia/reperfusion (MI/R) notably elevates the mortality rate, increases the complications of patients with myocardial infarction and decreases reperfusion benefit in patients suffering from acute myocardial infarction. Roflumilast protect against cardiotoxicity. Therefore, the present study aimed to investigate the effect of roflumilast on MI/R injury and the underlying mechanisms. To simulate MI/R in vivo and in vitro, the rat model of MI/R was established and H9C2 cells were subjected to hypoxia/reoxygenation (H/R) induction, respectively. The myocardial infarction areas were observed by 2,3,5-triphenyltetrazolium chloride staining. The myocardial enzyme levels in serum and levels of inflammatory cytokines and oxidative stress markers in cardiac tissue were assessed by corresponding assay kits. The cardiac damage was observed by hematoxylin and eosin staining. The mitochondrial membrane potential in cardiac tissue and H9C2 cells was detected using the JC-1 staining kit. The viability and apoptosis of H9C2 cells were detected by Cell Counting Kit-8 and TUNEL assay, respectively. The levels of inflammatory cytokines, oxidative stress markers and ATP in H/R-induced H9C2 cells were analyzed by corresponding assay kits. Western blotting was used for the estimation of AMP-activated protein kinase (AMPK) signaling pathway-, apoptosis- and mitochondrial regulation-associated protein levels. The mPTP opening was detected using a calcein-loading/cobalt chloride-quenching system. The results indicated that roflumilast decreased MI/R-induced myocardial infarction by alleviating myocardial injury and mitochondrial damage through the activation of the AMPK signaling pathway. In addition, roflumilast mitigated viability damage, alleviated oxidative stress, attenuated the inflammatory response and decreased mitochondrial damage in H/R-induced H9C2 cells by activating the AMPK signaling pathway. However, compound C, an inhibitor of the AMPK signaling pathway, reversed the effect of roflumilast on H/R-induced H9C2 cells. In conclusion, roflumilast alleviated myocardial infarction in MI/R rats and attenuated H/R-induced oxidative stress, inflammatory response and mitochondrial damage in H9C2 cells by activating the AMPK signaling pathway.

Phosphodiesterase-4 Inhibition in Parkinson's Disease: Molecular Insights and Therapeutic Potential

Clinicians and researchers are exploring safer and novel treatment strategies for treating the ever-prevalent Parkinson's disease (PD) across the globe. Several therapeutic strategies are used clinically for PD, including dopamine replacement therapy, DA agonists, MAO-B blockers, COMT blockers, and anticholinergics. Surgical interventions such as pallidotomy, particularly deep brain stimulation (DBS), are also employed. However, they only provide temporal and symptomatic relief. Cyclic adenosine monophosphate (cAMP) is one of the secondary messengers involved in dopaminergic neurotransmission. Phosphodiesterase (PDE) regulates cAMP and cGMP intracellular levels. PDE enzymes are subdivided into families and subtypes which are expressed throughout the human body. PDE4 isoenzyme- PDE4B subtype is overexpressed in the substantia nigra of the brain. Various studies have implicated multiple cAMP-mediated signaling cascades in PD, and PDE4 is a common link that can emerge as a neuroprotective and/or disease-modifying target. Furthermore, a mechanistic understanding of the PDE4 subtypes has provided perceptivity into the molecular mechanisms underlying the adverse effects of phosphodiesterase-4 inhibitors (PDE4Is). The repositioning and development of efficacious PDE4Is for PD have gained much attention. This review critically assesses the existing literature on PDE4 and its expression. Specifically, this review provides insights into the interrelated neurological cAMP-mediated signaling cascades involving PDE4s and the potential role of PDE4Is in PD. In addition, we discuss existing challenges and possible strategies for overcoming them.

Recent advances of Phosphodiesterase 4B in cancer

INTRODUCTION

Phosphodiesterase 4B (PDE4B) is a crucial enzyme in the phosphodiesterases (PDEs), acting as a regulator of cyclic adenosine monophosphate (cAMP). It is involved in cancer process through PDE4B/cAMP signaling pathway. Cancer occurs and develops with the regulation of PDE4B in the body, suggesting that PDE4B is a promising therapeutic target.

AREAS COVERED

This review covereed the function and mechanism of PDE4B in cancer. We summarized the possible clinical applications of PDE4B, and highlighted the possible ways to develop clinical applications of PDE4B inhibitors. We also discussed some common PDEs inhibitors, and expected the development of combined targeting PDE4B and other PDEs drugs in the future.

EXPERT OPINION

The existing research and clinical data can strongly prove the role of PDE4B in cancer. PDE4B inhibition can effectively increase cell apoptosis, inhibit cell proliferation, transformation, migration, etc., indicating that PDE4B inhibition can effectively inhibit the development of cancer. Other PDEs may antagonize or coordinate this effect. As for the further study on the relationship between PDE4B and other PDEs in cancer, it is still a challenge to develop multi-targeted PDEs inhibitors.

Neuroprotective Effect of Piclamilast-Induced Post-Ischemia Pharmacological Treatment in Mice

Various studies have evidenced the neuroprotective role of PDE4 inhibitors. However, whether PDE4 inhibitor, Piclamilast pharmacological post-treatment is protective during cerebral ischemia reperfusion-induced injury remains unknown. Therefore, this study design included testing the hypothesis that Piclamilast administered at the beginning of a reperfusion phase (Piclamilast pPost-trt) shows protective effects and explores & probes underlying downstream mechanisms. Swiss albino male mice were subjected to global ischemic and reperfusion injury for 17 min. The animals examined cerebral infarct size, biochemical parameters, inflammatory mediators, and motor coordination. For memory, assessment mice were subjected to morris water maze (MWM) and elevated plus maze (EPM) test. Histological changes were assessed using HE staining. Piclamilast pPost-trt significantly reduced I/R injury-induced deleterious effects on biochemical parameters of oxidative stress, inflammatory parameters, infarct size, and histopathological changes, according to the findings. These neuroprotective effects of pPost-trt are significantly abolished by pre-treatment with selective CREB inhibitor, 666-15. Current study concluded that induced neuroprotective benefits of Piclamilast Post-trt, in all probability, maybe mediated through CREB activation. Hence, its neuroprotective effects can be further explored in clinical settings.

Catecholamine-induced cardiotoxicity: A critical element in the pathophysiology of stroke-induced heart injury

Cerebrovascular diseases such as ischemic stroke, brain hemorrhage, and subarachnoid hemorrhage provoke cardiac complications such as heart failure, neurogenic stress-related cardiomyopathy and Takotsubo cardiomyopathy. With regards to the pathophysiology of stroke-induced heart injury, several mechanisms have been postulated to contribute to this complex interaction between brain and heart, including damage from gut dysbiosis, immune and systematic inflammatory responses, microvesicle- and microRNA-mediated vascular injury and damage from a surge of catecholamines. All these cerebrovascular diseases may trigger pronounced catecholamine surges through diverse ways, including stimulation of hypothalamic-pituitary adrenal axis, dysregulation of autonomic system, and secretion of adrenocorticotropic hormone. Primary catecholamines involved in this pathophysiological response include norepinephrine (NE) and epinephrine. Both are important neurotransmitters that connect the nervous system with the heart, leading to cardiac damage via myocardial ischemia, calcium (Ca²⁺) overload, oxidative stress, and mitochondrial dysfunction. In this review, we will aim to summarize the molecular mechanisms behind catecholamine-induced cardiotoxicity including Ca²⁺ overload, oxidative stress, apoptosis, cardiac hypertrophy, interstitial fibrosis, and inflammation. In addition, we will focus on how synchronization among these pathways evokes cardiotoxicity.

Epac: new emerging cAMP-binding protein

The well-known second messenger cyclic adenosine monophosphate (cAMP) regulates the morphology and physiology of neurons and thus higher cognitive brain functions. The discovery of exchange protein activated by cAMP (Epac) as a guanine nucleotide exchange factor for Rap GTPases has shed light on protein kinase A (PKA)-independent functions of cAMP signaling in neural tissues. Studies of cAMP-Epac-mediated signaling in neurons under normal and disease conditions also revealed its diverse contributions to neurodevelopment, synaptic remodeling, and neurotransmitter release, as well as learning, memory, and emotion. In this mini-review, the various roles of Epac isoforms, including Epac1 and Epac2, highly expressed in neural tissues are summarized, and controversies or issues are highlighted that need to be resolved to uncover the critical functions of Epac in neural tissues and the potential for a new therapeutic target of mental disorders.

Roflumilast Attenuates Doxorubicin-Induced Cardiotoxicity by Targeting Inflammation and Cellular Senescence in Cardiomyocytes Mediated by SIRT1

Background and Purpose

Cardiotoxicity is an important side effect of the treatment of a malignant tumor with Doxorubicin. Currently, decreasing the dosage of Doxorubicin to alleviate the side effects on cardiac function is the common method to deal with the cardiotoxicity induced by Doxorubicin. The present study aims to investigate the therapeutic effects of Roflumilast on Doxorubicin-induced inflammation and cellular senescence, as well as the potential mechanism in H9c2 myocardial cells.

Methods

The injured cardiac cell model was established by incubation with 5 μmol/L Doxorubicin. MTT was used to evaluate the cell viability of treated H9c2 cardiac cells. The expression of 4-HNE was determined using an immunofluorescence assay. The gene expression levels of IL-17, IL-6, TNF-α, IL-4, PAI-1, p21, and SIRT1 were evaluated using qRT-PCR and the protein levels of Gpx4, PAI-1, p21, and SIRT1 were determined using Western blot analysis. Secretions of IL-17, IL-6, TNF-α, IL-4, CK-MB, and cTnI were measured using ELISA. Cellular senescence was assessed using SA-β-Gal staining. Si-RNA technology was used to knockdown the expression of SIRT1 in H9c2 cardiac cells.

Results

Cell viability of H9c2 cardiac cells was significantly inhibited by Doxorubicin but rescued by Roflumilast. The upregulated 4-HNE and downregulated Gpx4 were reversed by Roflumilast. The secretions of IL-6 and IL-17 were promoted by Doxorubicin and suppressed by Roflumilast. The increased SA-β-Gal staining induced by Doxorubicin was inhibited by Roflumilast. P21 and PAI-1 were significantly upregulated and SIRT1 was greatly downregulated by Doxorubicin, all of which were reversed by Roflumilast. The anti-senescent effect of Roflumilast was abolished by knocking down SIRT1.

Conclusion

Roflumilast might attenuate Doxorubicin-induced inflammation and cellular senescence in cardiomyocytes by upregulating SIRT1.

Cardiomyocyte Induction and Regeneration for Myocardial Infarction Treatment: Cell Sources and Administration Strategies

Occlusion of coronary artery and subsequent damage or death of myocardium can lead to myocardial infarction (MI) and even heart failure-one of the leading causes of deaths world wide. Notably, myocardium has extremely limited regeneration potential due to the loss or death of cardiomyocytes (i.e., the cells of which the myocardium is comprised) upon MI. A variety of stem cells and stem cell-derived cardiovascular cells, in situ cardiac fibroblasts and endogenous proliferative epicardium, have been exploited to provide renewable cellular sources to treat injured myocardium. Also, different strategies, including direct injection of cell suspensions, bioactive molecules, or cell-incorporated biomaterials, and implantation of artificial cardiac scaffolds (e.g., cell sheets and cardiac patches), have been developed to deliver renewable cells and/or bioactive molecules to the MI site for the myocardium regeneration. This article briefly surveys cell sources and delivery strategies, along with biomaterials and their processing techniques, developed for MI treatment. Key issues and challenges, as well as recommendations for future research, are also discussed.

Levosimendan prevents doxorubicin-induced cardiotoxicity in time- and dose-dependent manner: implications for inotropy

AIMS

Levosimendan (LEVO) a clinically-used inodilator, exerts multifaceted cardioprotective effects. Case-studies indicate protection against doxorubicin (DXR)-induced cardiotoxicity, but this effect remains obscure. We investigated the effect and mechanism of different regimens of levosimendan on sub-chronic and chronic doxorubicin cardiotoxicity.

METHODS AND RESULTS

Based on preliminary in vivo experiments, rats serving as a sub-chronic model of doxorubicin-cardiotoxicity and were divided into: Control (N/S-0.9%), DXR (18 mg/kg-cumulative), DXR+LEVO (LEVO, 24 μg/kg-cumulative), and DXR+LEVO (acute) (LEVO, 24 μg/kg-bolus) for 14 days. Protein kinase-B (Akt), endothelial nitric oxide synthase (eNOS), and protein kinase-A and G (PKA/PKG) pathways emerged as contributors to the cardioprotection, converging onto phospholamban (PLN). To verify the contribution of PLN, phospholamban knockout (PLN-/-) mice were assigned to PLN-/-/Control (N/S-0.9%), PLN-/-/DXR (18 mg/kg), and PLN-/-/DXR+LEVO (ac) for 14 days. Furthermore, female breast cancer-bearing (BC) mice were divided into: Control (normal saline 0.9%, N/S 0.9%), DXR (18 mg/kg), LEVO, and DXR+LEVO (LEVO, 24 μg/kg-bolus) for 28 days. Echocardiography was performed in all protocols. To elucidate levosimendan's cardioprotective mechanism, primary cardiomyocytes were treated with doxorubicin or/and levosimendan and with N omega-nitro-L-arginine methyl ester (L-NAME), DT-2, and H-89 (eNOS, PKG, and PKA inhibitors, respectively); cardiomyocyte-toxicity was assessed. Single bolus administration of levosimendan abrogated DXR-induced cardiotoxicity and activated Akt/eNOS and cAMP-PKA/cGMP-PKG/PLN pathways but failed to exert cardioprotection in PLN-/- mice. Levosimendan's cardioprotection was also evident in the BC model. Finally, in vitro PKA inhibition abrogated levosimendan-mediated cardioprotection, indicating that its cardioprotection is cAMP-PKA dependent, while levosimendan preponderated over milrinone and dobutamine, by ameliorating calcium overload.

CONCLUSION

Single dose levosimendan prevented doxorubicin cardiotoxicity through a cAMP-PKA-PLN pathway, highlighting the role of inotropy in doxorubicin cardiotoxicity.

Stimulation of GLP-1 Receptor Inhibits Methylglyoxal-Induced Mitochondrial Dysfunctions in H9c2 Cardiomyoblasts: Potential Role of Epac/PI3K/Akt Pathway

Accumulation of methylglyoxal (MG) contributes to oxidative stress, apoptosis, and mitochondrial dysfunction, leading to the development of type 2 diabetes and cardiovascular diseases. Inhibition of mitochondrial abnormalities induced by MG in the heart may improve and delay the progression of heart failure. Although glucagon-like peptide-1 receptor (GLP-1R) agonists have been used as anti-diabetic drugs and GLP-1R has been detected in the heart, the cardioprotective effects of GLP-1R agonists on the inhibition of MG-induced oxidative stress and mitochondrial abnormalities have not been elucidated. Stimulation of GLP-1Rs leads to cAMP elevation and subsequently activates PKA- and/or Epac-dependent signaling pathway. However, the signaling pathway involved in the prevention of MG-induced mitochondrial dysfunctions in the heart has not been clarified so far. In the present study, we demonstrated that stimulation of GLP-1Rs with exendin-4 inhibited MG-induced intracellular and mitochondrial reactive oxygen species (ROS) production and apoptosis in H9c2 cardiomyoblasts. GLP-1R stimulation also improved the alterations of mitochondrial membrane potential (MMP) and expressions of genes related to mitochondrial functions and dynamics induced by MG. In addition, stimulation of GLP-1R exhibits antioxidant and antiapoptotic effects as well as the improvement of mitochondrial functions through cAMP/Epac/PI3K/Akt signaling pathway in H9c2 cells. Our study is the first work demonstrating a novel signaling pathway for cardioprotective effects of GLP-1R agonist on inhibition of oxidative stress and prevention of mitochondrial dysfunction. Thus, GLP-1R agonist represents a potential therapeutic target for inhibition of oxidative stress and modulation of mitochondrial functions in the heart.

miR-134-5p inhibition reduces infarct-induced cardiomyocyte apoptosis via Creb1 upregulation

BACKGROUND

Following the recent discovery that microRNA-134-5p (miR-134-5p) is elevated in the early stages of acute myocardial infarction (AMI), we examined the specific role of miR-134-5p in cardiomyocytes during AMI.

METHODS

To study miR-134-5p's role in the context of AMI, we used a combination of in vitro experiments in H₂O₂-treated or hypoxic cardiomyocyte cell cultures as well as in vivo experiments in a murine model of AMI.

RESULTS

H₂O₂- and hypoxia-induced cardiomyocyte injury upregulated miR-134-5p expression. miR-134-5p overexpression increased cardiomyocyte apoptosis, whereas miR-134-5p inhibition reduced cardiomyocyte apoptosis. We discovered that the transcription factor cAMP-responsive element binding protein 1 (Creb1) is a functional target of miR-134-5p responsible for regulating cardiomyocyte apoptosis. In vivo AMI resulted in the upregulation and downregulation of miR-134-5p and Creb1 in the infarct area, respectively. Circulating miR-134-5p levels were also increased at days 1 and 2 post-AMI. Modulation of myocardial miR-124-5p expression by intramyocardial injection of antagomiR-134-5p or agomiR-134-5p significantly affected cardiomyocyte apoptosis, infarct size, and cardiac function in vivo.

CONCLUSIONS

miR-134-5p/Creb1 axis dysregulation plays a role in hypoxia- or oxidative stress-induced cardiomyocyte apoptosis as well as AMI. Circulating miR-134-5p may show promise as a biomarker for AMI or post-AMI cardiac dysfunction. Manipulating the miR-134-5p/Creb1 axis through either inhibition of miR-134-5p or overexpression of Creb1 may show promise as a novel therapeutic strategy to attenuate cardiac dysfunction following AMI.

Inhibition of PDE4 protects neurons against oxygen-glucose deprivation-induced endoplasmic reticulum stress through activation of the Nrf-2/HO-1 pathway

Inhibition of phosphodiesterase 4 (PDE4) produces neuroprotective effects against cerebral ischemia. However, the involved mechanism remains unclear. Augmentation of endoplasmic reticulum (ER) stress promotes neuronal apoptosis, and excessive oxidative stress is an inducer of ER stress. The present study aimed to determine whether suppression of ER stress is involved in the protective effects of PDE4 inhibition against cerebral ischemia. We found that exposing HT-22 cells to oxygen-glucose deprivation (OGD) significantly activated ER stress, as evidenced by increased expression of the 78-kDa glucose-regulated protein (GRP78), phosphorylated eukaryotic translation-initiation factor 2α (eIF2α), and C/EBP-homologous protein (CHOP). Overexpression of PDE4B increased ER stress, while knocking down PDE4B or treatment with the PDE4 inhibitor, FCPR03, prevented OGD-induced ER stress in HT-22 cells. Furthermore, FCPR03 promoted the translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) from the cytoplasm to the nucleus. Importantly, the Nrf-2 inhibitor, ML385, blocked the inhibitory role of FCPR03 on OGD-induced ER stress. ML385 also abolished the protective role of FCPR03 in HT-22 cells subjected to OGD. Knocking down heme oxygenase-1 (HO-1), which is a target of Nrf-2, also blocked the protective role of FCPR03, enhanced the level of reactive oxygen species (ROS), and increased ER stress and cell death. We then found that FCPR03 or the antioxidant, N-Acetyl-l-cysteine, reduced oxidative stress in cells exposed to OGD. This effect was accompanied by increased cell viability and decreased ER stress. In primary cultured neurons, we found that FCPR03 reduced OGD-induced production of ROS and phosphorylation of eIF2α. The neuroprotective effect of FCPR03 against OGD in neurons was blocked by ML385. These results demonstrate that inhibition of PDE4 activates Nrf-2/HO-1, attenuates the production of ROS, and thereby attenuates ER stress in neurons exposed to OGD. Additionally, we conclude that FCPR03 may represent a promising therapeutic agent for the treatment of ER stress-related disorders.

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Overexpression of PDE4 increased ER stress under both basal and OGD conditions.

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Inhibition of PDE4 reduced ER stress and neuronal apoptosis in neurons exposed to OGD.

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PDE4 inhibition activated Nrf-2, and increased the level of antioxidant enzyme HO-1.

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Inhibition of Nrf-2 attenuated the role of FCPR03 on ER stress and cell viability.

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HO-1 knockdown abolished the effects of FCPR03 on ER stress and ROS production.

Zileuton, a 5-Lipoxygenase Inhibitor, Exerts Anti-Angiogenic Effect by Inducing Apoptosis of HUVEC via BK Channel Activation

The arachidonic acid metabolism through 5-lipoxygenase (5-LO) pathways is involved in modulating both tumorigenesis and angiogenesis. Although anti-carcinogenic activities of certain 5-LO inhibitors have been reported, the role of zileuton, a well known 5-LO inhibitor, on the endothelial cell proliferation and angiogenesis has not been fully elucidated. Here, we report that zileuton has an anti-angiogenic effect, and the underlying mechanisms involved activation of the large-conductance Ca²⁺-activated K⁺ (BK) channel. Our results show that zileuton significantly prevented vascular endothelial growth factor (VEGF)-induced proliferation of human umbilical vein endothelial cells (HUVECs) in vitro, as well as in vivo. However, such anti-angiogenic effect of zileuton was abolished by iberiotoxin (IBTX), a BK channel blocker, suggesting zileuton-induced activation of BK channel was critical for the observed anti-angiogenic effect of zileuton. Furthermore, the anti-angiogenic effect of zileuton was, at least, due to the activation of pro-apoptotic signaling cascades which was also abolished by IBTX. Additionally, zileuton suppressed the expression of VCAM-1, ICAM-1, ETS related gene (Erg) and the production of nitric oxide (NO). Taken together, our results show that zileuton prevents angiogenesis by activating the BK channel dependent-apoptotic pathway, thus highlighting its therapeutic capacity in angiogenesis-related diseases, such as cancer.

Protein Kinase A as a Promising Target for Heart Failure Drug Development

Heart failure (HF) is a clinical syndrome characterized by impaired ability of the heart to fill or eject blood. HF is rather prevalent and it represents the foremost reason of hospitalization in the United States. The costs linked to HF overrun those of all other causes of disabilities, and death in the United States and all over the developed as well as the developing countries which amplify the supreme significance of its prevention. Protein kinase (PK) A plays multiple roles in heart functions including, contraction, metabolism, ion fluxes, and gene transcription. Altered PKA activity is likely to cause the progression to cardiomyopathy and HF. Thus, this review is intended to focus on the roles of PKA and PKA-mediated signal transduction in the healthy heart as well as during the development of HF. Furthermore, the impact of cardiac PKA inhibition/activation will be highlighted to identify PKA as a potential target for the HF drug development.

Targeting phosphodiesterase 4 as a potential therapeutic strategy for enhancing neuroplasticity following ischemic stroke

Sensorimotor recovery following ischemic stroke is highly related with structural modification and functional reorganization of residual brain tissues. Manipulations, such as treatment with small molecules, have been shown to enhance the synaptic plasticity and contribute to the recovery. Activation of the cAMP/CREB pathway is one of the pivotal approaches stimulating neuroplasticity. Phosphodiesterase 4 (PDE4) is a major enzyme controlling the hydrolysis of cAMP in the brain. Accumulating evidences have shown that inhibition of PDE4 is beneficial for the functional recovery after cerebral ischemia; i. subtype D of PDE4 (PDE4D) is viewed as a risk factor for ischemic stroke; ii. inhibition of PDE4 enhances neurological behaviors, such as learning and memory, after stroke in rodents; iii.PDE4 inhibition increases dendritic density, synaptic plasticity and neurogenesis; iv. activation of cAMP/CREB signaling by PDE4 inhibition causes an endogenous increase of BDNF, which is a potent modulator of neuroplasticity; v. PDE4 inhibition is believed to restrict neuroinflammation during ischemic stroke. Cumulatively, these findings provide a link between PDE4 inhibition and neuroplasticity after cerebral ischemia. Here, we summarized the possible roles of PDE4 inhibition in the recovery of cerebral stroke with an emphasis on neuroplasticity. We also made some recommendations for future research.

Analysis of the microRNA transcriptome of Daphnia pulex during aging

Daphnia pulex is an important food organism that exhibits a particular mode of reproduction known as cyclical parthenogenesis (asexual) and sexual reproduction. Regulation of the aging process by microRNAs (miRNAs) is a research hotspot in miRNA studies. To investigate a possible role of miRNAs in regulating aging and senescence, we used Illumina HiSeq to sequence two miRNA libraries from 1-day-old (1d) and 25-day-old (25d) D. pulex specimens. In total, we obtained 11,218,097 clean reads and 28,569 unique miRNAs from 1d specimens and 11,819,106 clean reads and 44,709 unique miRNAs from 25d specimens. Bioinformatic analyses was used to identify 1335 differentially expressed miRNAs from known miRNAs, including 127 miRNAs that exhibited statistically significant differences (P < 0.01); 92 miRNAs were upregulated and 35 were downregulated. Quantitative real-time (qRT)-PCR experiments were performed for nine miRNAs from five samples (1d, 5d, 10d, 15d, 20d and 25d) during the aging process, and the sequencing and qRT-PCR data were found to be consistent. Ninety-four miRNAs were predicted to correspond to 2014 target genes in known miRNAs with 4032 target gene sites. Sixteen pathways changed significantly (P < 0.05) at different developmental stages, revealing many important principles of the miRNA regulatory aging network of D. pulex. Overall, the difference in miRNA expression profile during aging of D. pulex forms a basis for further studies aimed at understanding the role of miRNAs in regulating aging, reproductive transformation, senescence, and longevity.

Ginseng Compatibility Environment Attenuates Toxicity and Keeps Efficacy in Cor Pulmonale Treated by Fuzi Beimu Incompatibility Through the Coordinated Crosstalk of PKA and Epac Signaling Pathways

Cor pulmonale is characterized by severe right ventricular dysfunction caused by lung disease, particularly chronic obstructive pulmonary disease, which can lead to pulmonary hypertension. Our previous study has demonstrated that Fuzi and Beimu compatibility (FBC), a traditional TCM compatibility taboo, improves lung function in early-stage of pulmonary hypertension through the synergistic action of β-ARs signals. However, FBC increases cardiotoxicity with prolonged treatment and disease progression. Considering that the compatibility environment influences the exertion of the medicine, we selected ginseng for coordinating the compatibility environment to improve the security and extend the therapeutic time window of FBC. Monocrotaline-induced cor pulmonale rats were treated with FBC, ginseng, or ginseng combined with FBC (G/FBC). Then, the pulmonary and cardiac functions of the rats were examined to evaluate the toxicity and efficacy of the treatments. The crosstalk between PKA and Epac pathways was also studied. Results showed that G/FBC ameliorated lung function similar to or even better than FBC treatment did. Furthermore, G/FBC treatment attenuated FBC-induced cardiotoxicity, which significantly restored cardiac dysfunction and clearly decreased myocardial enzymes and apoptosis. The βAR-Gs-PKA/CaMKII pathway was inhibited and the Epac1/ERK1/2 axis was activated in G/FBC group. These findings indicate that ginseng compatibility environment could improve pulmonary function and attenuate cardiotoxicity in cor pulmonale via the coordinated crosstalk of PKA and Epac pathways, implying that ginseng could be used to prevent detrimental cardiotoxicity in cor pulmonale treatment.

Inhibition of phosphodiesterase 4 by FCPR16 protects SH-SY5Y cells against MPP+-induced decline of mitochondrial membrane potential and oxidative stress

Phosphodiesterase 4 (PDE4) is a promising target for the treatment of Parkinson's disease (PD). However, the underlying mechanism has not yet been well elucidated. Additionally, most of current PDE4 inhibitors produce severe nausea and vomiting response in patients, which limit their clinical application. FCPR16 is a novel PDE4 inhibitor with little emetic potential. In the present study, the neuroprotective effect and underlying mechanism of FCPR16 against cellular apoptosis induced by 1-methyl-4-phenylpyridinium (MPP⁺) were examined in SH-SY5Y cells. FCPR16 (12.5–50 μM) dose-dependently reduced MPP⁺-induced loss of cell viability, accompanied by reductions in nuclear condensation and lactate dehydrogenase release. The level of cleaved caspase 3 and the ratio of Bax/Bcl-2 were also decreased after treatment with FCPR16 in MPP⁺-treated cells. Furthermore, FCPR16 (25 μM) significantly suppressed the accumulation of reactive oxygen species (ROS), prevented the decline of mitochondrial membrane potential (Δψm) and attenuated the expression of malonaldehyde level. Further studies disclosed that FCPR16 enhanced the levels of cAMP and the exchange protein directly activated by cAMP (Epac) in SH-SY5Y cells. Western blotting analysis revealed that FCPR16 increased the phosphorylation of cAMP response element-binding protein (CREB) and protein kinase B (Akt) down-regulated by MPP⁺ in SH-SY5Y cells. Moreover, the inhibitory effects of FCPR16 on the production of ROS and Δψm loss could be blocked by PKA inhibitor H-89 and Akt inhibitor KRX-0401. Collectively, these results suggest that FCPR16 attenuates MPP⁺-induced dopaminergic degeneration via lowering ROS and preventing the loss of Δψm in SH-SY5Y cells. Mechanistically, cAMP/PKA/CREB and Epac/Akt signaling pathways are involved in these processes. Our findings indicate that FCPR16 is a promising pre-clinical candidate for the treatment of PD and possibly other oxidative stress-related neuronal diseases.

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FCPR16 protected SH-SY5Y cells against MPP⁺-induced apoptosis.

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FCPR16 attenuated Δψm loss and ROS generation in SH-SY5Y cells treated with MPP⁺.

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FCPR16 activated cAMP/PKA/CREB and Epac/Akt signaling pathways in SH-SY5Y cells.

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Blocking cAMP/PKA/CREB or Epac/Akt pathways canceled the protective role of FCPR16.

The Phosphodiesterase 4 Inhibitor Roflumilast Protects against Cigarette Smoke Extract-Induced Mitophagy-Dependent Cell Death in Epithelial Cells

Background

Recent studies show that mitophagy, the autophagy-dependent turnover of mitochondria, mediates pulmonary epithelial cell death in response to cigarette smoke extract (CSE) exposure and contributes to the development of emphysema in vivo during chronic cigarette smoke (CS) exposure, although the underlying mechanisms remain unclear.

Methods

In this study, we investigated the role of mitophagy in the regulation of CSE-exposed lung bronchial epithelial cell (Beas-2B) death. We also investigated the role of a phosphodiesterase 4 inhibitor, roflumilast, in CSE-induced mitophagy-dependent cell death.

Results

Our results demonstrated that CSE induces mitophagy in Beas-2B cells through mitochondrial dysfunction and increased the expression levels of the mitophagy regulator protein, PTEN-induced putative kinase-1 (PINK1), and the mitochondrial fission protein, dynamin-1-like protein (DRP1). CSE-induced epithelial cell death was significantly increased in Beas-2B cells exposed to CSE but was decreased by small interfering RNA-dependent knockdown of DRP1. Treatment with roflumilast in Beas-2B cells inhibited CSE-induced mitochondrial dysfunction and mitophagy by inhibiting the expression of phospho-DRP1 and -PINK1. Roflumilast protected against cell death and increased cell viability, as determined by the lactate dehydrogenase release test and the MTT assay, respectively, in Beas-2B cells exposed to CSE.

Conclusion

These findings suggest that roflumilast plays a protective role in CS-induced mitophagy-dependent cell death.

Roflumilast Ameliorates Airway Hyperresponsiveness Caused by Diet-Induced Obesity in a Murine Model

Obese patients with asthma respond poorly to conventional asthma medications, resulting in severe symptoms and poor prognosis. Roflumilast, a phosphodiesterase-4 inhibitor that lowers the levels of various substances that are implicated in obese subjects with asthma, may be effective in the treatment of those subjects. We evaluated the potential of roflumilast as a novel therapeutic agent for obese subjects with asthma. We designed three models: diet-induced obesity (DIO); DIO with ovalbumin (OVA); and OVA. We fed C57BL/6J mice a high-fat diet for 3 months with or without OVA sensitization and challenge. Roflumilast or dexamethasone was administered orally three times at 2-day intervals in the last experimental week. Airway hyperresponsiveness resulting from DIO significantly improved in the roflumilast-treated group compared with the dexamethasone-treated groups. Although DIO did not affect the cell proliferation in bronchoalveolar lavage fluid, increased fibrosis was seen in the DIO group, which significantly improved from treatment with roflumilast. DIO-induced changes in adiponectin and leptin levels were improved by roflumilast, whereas dexamethasone aggravated them. mRNA levels and proteins of TNF-α, transforming growth factor-β, IL-1β, and IFN-γ increased in the DIO group and decreased with roflumilast. The reactive oxygen species levels were also increased in the DIO group and decreased by roflumilast. In the DIO plus OVA and OVA models, roflumilast improved Th1 and Th2 cell activation to a greater extent than dexamethasone. Roflumilast is significantly more effective than dexamethasone against airway hyperresponsiveness caused by DIO in the murine model. Roflumilast may represent a promising therapeutic agent for the treatment of obese patients with asthma.

The role of Epac in the heart

As one of the most important second messengers, 3',5'-cyclic adenosine monophosphate (cAMP) mediates various extracellular signals including hormones and neurotransmitters, and induces appropriate responses in diverse types of cells. Since cAMP was formerly believed to transmit signals through only two direct target molecules, protein kinase A and the cyclic nucleotide-gated channel, the sensational discovery in 1998 of another novel direct effecter of cAMP [exchange proteins directly activated by cAMP (Epac)] attracted a great deal of scientific interest in cAMP signaling. Numerous studies on Epac have since disclosed its important functions in various tissues in the body. Recently, observations of genetically manipulated mice in various pathogenic models have begun to reveal the in vivo significance of previous in vitro or cellular-level findings. Here, we focused on the function of Epac in the heart. Accumulating evidence has revealed that both Epac1 and Epac2 play important roles in the structure and function of the heart under physiological and pathological conditions. Accordingly, developing the ability to regulate cAMP-mediated signaling through Epac may lead to remarkable new therapies for the treatment of cardiac diseases.

A Role for cAMP and Protein Kinase A in Experimental Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease that has been associated with Cronobacter sakazakii and typically affects premature infants. Although NEC has been actively investigated, little is known about the mechanisms underlying the pathophysiology of epithelial injury and intestinal barrier damage. Cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) are important mediators and regulators of apoptosis. To test the hypothesis that C. sakazakii increases cAMP and PKA activation in experimental NEC resulting in increased epithelial apoptosis, we investigated the effects of C. sakazakii on cAMP and PKA in vitro and in vivo. Specifically, rat intestinal epithelial cells and a human intestinal epithelial cell line were infected with C. sakazakii, and cAMP levels and phosphorylation of PKA were measured. An increase in cAMP was demonstrated after infection, as well as an increase in phosphorylated PKA. Similarly, increased intestinal cAMP and PKA phosphorylation were demonstrated in a rat pup model of NEC. These increases were correlated with increased intestinal epithelial apoptosis. The additional of a PKA inhibitor (KT5720) significantly ameliorated these effects and decreased the severity of experimental NEC. Findings were compared with results from human tissue samples. Collectively, these observations indicate that cAMP and PKA phosphorylation are associated with increased apoptosis in NEC and that inhibition of PKA activation protects against apoptosis and experimental NEC.

Inhibition of Epac1 suppresses mitochondrial fission and reduces neointima formation induced by vascular injury

Vascular smooth muscle cell (VSMC) activation in response to injury plays an important role in the development of vascular proliferative diseases, including restenosis and atherosclerosis. The aims of this study were to ascertain the physiological functions of exchange proteins directly activated by cAMP isoform 1 (Epac1) in VSMC and to evaluate the potential of Epac1 as therapeutic targets for neointima formation during vascular remodeling. In a mouse carotid artery ligation model, genetic knockdown of the Epac1 gene led to a significant reduction in neointima obstruction in response to vascular injury. Pharmacologic inhibition of Epac1 with an Epac specific inhibitor, ESI-09, phenocopied the effects of Epac1 null by suppressing neointima formation and proliferative VSMC accumulation in neointima area. Mechanistically, Epac1 deficient VSMCs exhibited lower level of PI3K/AKT signaling and dampened response to PDGF-induced mitochondrial fission and reactive oxygen species levels. Our studies indicate that Epac1 plays important roles in promoting VSMC proliferation and phenotypic switch in response to vascular injury, therefore, representing a therapeutic target for vascular proliferative diseases.

Epac1 knockdown inhibits the proliferation of ovarian cancer cells by inactivating AKT/Cyclin D1/CDK4 pathway in vitro and in vivo

Ovarian cancer is the leading cause of death among gynecological malignancies, and high grade serous ovarian carcinoma is the most common and most aggressive subtype. Recently, it was demonstrated that cAMP mediates protein kinase A-independent effects through Epac (exchange protein directly activated by cAMP) proteins. Epac proteins, including Epac1 and Epac2, are implicated in several diverse cellular responses, such as insulin secretion, exocytosis, cellular calcium handling and formation of cell-cell junctions. Several reports document that Epac1 could play vital roles in promoting proliferation, invasion and migration of some cancer cells. However, the expression levels and roles of Epac1 in ovarian cancer have not been investigated. In the present study, we detected the expression levels of Epac1 mRNA and protein in three kinds of ovarian cancer cells SKOV3, OVCAR3 and CAOV3. Furthermore, the effect of Epac1 knockdown on the proliferation and apoptosis of SKOV3 and OVCAR3 cells was evaluated in vitro and in vivo. The results showed that there was higher expression of Epac1 mRNA and protein in SKOV3 and OVCAR3 cells. Epac1 knockdown inhibited the proliferation of SKOV3 and OVCAR3 cells in vitro and in vivo. Decreased proliferation may be due to downregulation of Epac1-induced G1 phase arrest by inactivating the AKT/Cyclin D1/CDK4 pathway, but not to alterations in the MAPK pathway or to apoptosis. Taken together, our data provide new insight into the essential role of Epac1 in regulating growth of ovarian cancer cells and suggest that Epac1 might represent an attractive therapeutic target for treatment of ovarian cancer.

Cardioprotection against experimental myocardial ischemic injury using cornin

Phosphorylated-cyclic adenosine monophosphate response element-binding protein (Phospho-CREB) has an important role in the pathogenesis of myocardial ischemia. We isolated the iridoid glycoside cornin from the fruit of Verbena officinalis L, investigated its effects against myocardial ischemia and reperfusion (I/R) injury in vivo, and elucidated its potential mechanism in vitro. Effects of cornin on cell viability, as well as expression of phospho-CREB and phospho-Akt in hypoxic H9c2 cells in vitro, and myocardial I/R injury in vivo, were investigated. Cornin attenuated hypoxia-induced cytotoxicity significantly in H9c2 cells in a concentration-dependent manner. Treatment of H9c2 cells with cornin (10 µM) blocked the reduction of expression of phospho-CREB and phospho-Akt in a hypoxic condition. Treatment of rats with cornin (30 mg/kg, iv) protected them from myocardial I/R injury as indicated by a decrease in infarct volume, improvement in hemodynamics, and reduction of severity of myocardial damage. Cornin treatment also attenuated the reduction of expression of phospho-CREB and phospho-Akt in ischemic myocardial tissue. These data suggest that cornin exerts protective effects due to an increase in expression of phospho-CREB and phospho-Akt.

Urocortin-1 Mediated Cardioprotection Involves XIAP and CD40-Ligand Recovery: Role of EPAC2 and ERK1/2

Aims

Urocortin-1 (Ucn-1) is an endogenous peptide that protects heart from ischemia and reperfusion (I/R) injuries. Ucn-1 is known to prevent cardiac cell death, but its role in the transcription of specific genes related to survival signaling pathway has not been fully defined. The aim of this study was to investigate the molecular signaling implicated in the improvement of cardiac myocytes survival induced by Ucn-1.

Methods and Results

Ucn-1 administration before ischemia and at the onset of reperfusion, in rat hearts perfused in Langendorff system, fully recovered heart contractility and other hemodynamic parameters. Ucn-1 enhanced cell viability and decreased lactate dehydrogenase (LDH) release in adult cardiac myocytes subjected to simulated I/R. Annexin V-FITC/PI staining indicated that Ucn-1 promoted cell survival and decreased cell necrosis through Epac2 (exchange protein directly activated by cAMP) and ERK1/2 (extracellular signal–regulated kinases 1/2) activation. We determined that Ucn-1 shifted cell death from necrosis to apoptosis and activated caspases 9 and 3/7. Furthermore, mini-array, RT-qPCR and protein analyses of apoptotic genes showed that Ucn-1 upregulated the expression of CD40lg, Xiap and BAD in cells undergoing I/R, involving Epac2 and ERK1/2 activation.

Conclusions

Our data indicate that Ucn-1 efficiently protected hearts from I/R damage by increasing the cell survival and stimulated apoptotic genes, CD40lg, Xiap and BAD, overexpression through the activation of Epac2 and ERK1/2.

The Orphan G Protein-coupled Receptor GPR17 Negatively Regulates Oligodendrocyte Differentiation via Gαi/o and Its Downstream Effector Molecules

Recent studies have recognized G protein-coupled receptors as important regulators of oligodendrocyte development. GPR17, in particular, is an orphan G protein-coupled receptor that has been identified as oligodendroglial maturation inhibitor because its stimulation arrests primary mouse oligodendrocytes at a less differentiated stage. However, the intracellular signaling effectors transducing its activation remain poorly understood. Here, we use Oli-neu cells, an immortalized cell line derived from primary murine oligodendrocytes, and primary rat oligodendrocyte cultures as model systems to identify molecular targets that link cell surface GPR17 to oligodendrocyte maturation blockade. We demonstrate that stimulation of GPR17 by the small molecule agonist MDL29,951 (2-carboxy-4,6-dichloro-1H-indole-3-propionic acid) decreases myelin basic protein expression levels mainly by triggering the Gαi/o signaling pathway, which in turn leads to reduced activity of the downstream cascade adenylyl cyclase-cAMP-PKA-cAMP response element-binding protein (CREB). In addition, we show that GPR17 activation also diminishes myelin basic protein abundance by lessening stimulation of the exchange protein directly activated by cAMP (EPAC), thus uncovering a previously unrecognized role for EPAC to regulate oligodendrocyte differentiation. Together, our data establish PKA and EPAC as key downstream effectors of GPR17 that inhibit oligodendrocyte maturation. We envisage that treatments augmenting PKA and/or EPAC activity represent a beneficial approach for therapeutic enhancement of remyelination in those demyelinating diseases where GPR17 is highly expressed, such as multiple sclerosis.

Phosphodiesterases in the rat ovary: effect of cAMP in primordial follicles

Phosphodiesterases (PDEs) are important regulators of the intracellular cAMP concentration, which is a central second messenger that affects a multitude of intracellular functions. In the ovaries, cAMP exerts diverse functions, including regulation of ovulation and it has been suggested that augmented cAMP levels stimulate primordial follicle growth. The present study examined the gene expression, enzyme activity and immunolocalization of the different cAMP hydrolysing PDEs families in the rat ovary. Further, the effect of PDE4 inhibition on primordial follicle activation in cultured neonatal rat ovaries was also evaluated. We found varied expression of all eight families in the ovary with Pde7b and Pde8a having the highest expression each accounting for more than 20% of the total PDE mRNA. PDE4 accounted for 15-26% of the total PDE activity. Immunoreactive PDE11A was found in the oocytes and PDE2A in the corpora lutea. Incubating neonatal rat ovaries with PDE4 inhibitors did not increase primordial follicle activation or change the expression of the developing follicle markers Gdf9, Amh, Inha, the proliferation marker Mki67 or the primordial follicle marker Tmeff2. In addition, the cAMP analogue 8-bromo-cAMP did not increase AKT1 or FOXO3A phosphorylation associated with follicle activation or increase the expression of Kitlg known to be associated with follicle differentiation but did increase the Tmeff2, Mki67 and Inha expression in a dose-dependent manner. In conclusion, this study shows that both Pde7b and Pde8a are highly expressed in the rodent ovary and that PDE4 inhibition does not cause an increase in primordial follicle activation.

Epac is required for GLP-1R-mediated inhibition of oxidative stress and apoptosis in cardiomyocytes

Although the cardioprotective effects of glucagon-like peptide-1 and its analogs have been reported, the exact mechanisms of the glucagon-like peptide-1 receptor (GLP-1R) signaling pathway in the heart are still unclear. Activation of the GLP-1R has been shown to increase cAMP levels, thus eliciting protein kinase A- and exchange protein activated by cAMP (Epac)-dependent signaling pathways in pancreatic β-cells. However, which pathway plays an important role in the antioxidant and antiapoptotic effects of GLP-1R activation in the heart is not known. In this study, we demonstrated that stimulation of GLP-1Rs with exendin-4 attenuated H2O2-induced reactive oxygen species production and increased the synthesis of antioxidant enzymes, catalase, glutathione peroxidase-1, and manganese superoxide dismutase that is dependent on Epac. Additionally, exendin-4 has an antiapoptotic effect by decreasing a number of apoptotic cells, inhibiting caspase-3 activity, and enhancing the expression of antiapoptotic protein B-cell lymphoma 2, which is mediated through both protein kinase A- and Epac-dependent pathways. These data indicate a critical role for Epac in GLP-1R-mediated cardioprotection.

Cyclic nucleotide signalling in kidney fibrosis

Kidney fibrosis is an important factor for the progression of kidney diseases, e.g., diabetes mellitus induced kidney failure, glomerulosclerosis and nephritis resulting in chronic kidney disease or end-stage renal disease. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were implicated to suppress several of the above mentioned renal diseases. In this review article, identified effects and mechanisms of cGMP and cAMP regarding renal fibrosis are summarized. These mechanisms include several signalling pathways of nitric oxide/ANP/guanylyl cyclases/cGMP-dependent protein kinase and cAMP/Epac/adenylyl cyclases/cAMP-dependent protein kinase. Furthermore, diverse possible drugs activating these pathways are discussed. From these diverse mechanisms it is expected that new pharmacological treatments will evolve for the therapy or even prevention of kidney failure.

Role of soluble adenylyl cyclase in cell death and growth

cAMP signaling is an evolutionarily conserved intracellular communication system controlling numerous cellular functions. Until recently, transmembrane adenylyl cyclase (tmAC) was considered the major source for cAMP in the cell, and the role of cAMP signaling was therefore attributed exclusively to the activity of this family of enzymes. However, increasing evidence demonstrates the role of an alternative, intracellular source of cAMP produced by type 10 soluble adenylyl cyclase (sAC). In contrast to tmAC, sAC produces cAMP in various intracellular microdomains close to specific cAMP targets, e.g., in nucleus and mitochondria. Ongoing research demonstrates involvement of sAC in diverse physiological and pathological processes. The present review is focused on the role of cAMP signaling, particularly that of sAC, in cell death and growth. Although the contributions of sAC to the regulation of these cellular functions have only recently been discovered, current data suggest that sAC plays key roles in mitochondrial bioenergetics and the mitochondrial apoptosis pathway, as well as cell proliferation and development. Furthermore, recent reports suggest the importance of sAC in several pathologies associated with apoptosis as well as in oncogenesis. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Roflumilast inhibits respiratory syncytial virus infection in human differentiated bronchial epithelial cells

Respiratory syncytial virus (RSV) causes acute exacerbations in COPD and asthma. RSV infects bronchial epithelial cells (HBE) that trigger RSV associated lung pathology. This study explores whether the phosphodiesterase 4 (PDE4) inhibitor Roflumilast N-oxide (RNO), alters RSV infection of well-differentiated HBE (WD-HBE) in vitro. WD-HBE were RSV infected in the presence or absence of RNO (0.1-100 nM). Viral infection (staining of F and G proteins, nucleoprotein RNA level), mRNA of ICAM-1, ciliated cell markers (digital high speed videomicroscopy, β-tubulin immunofluorescence, Foxj1 and Dnai2 mRNA), Goblet cells (PAS), mRNA of MUC5AC and CLCA1, mRNA and protein level of IL-13, IL-6, IL-8, TNFα, formation of H₂O₂ and the anti-oxidative armamentarium (mRNA of Nrf2, HO-1, GPx; total antioxidant capacity (TAC) were measured at day 10 or 15 post infection. RNO inhibited RSV infection of WD-HBE, prevented the loss of ciliated cells and markers, reduced the increase of MUC5AC and CLCA1 and inhibited the increase of IL-13, IL-6, IL-8, TNFα and ICAM-1. Additionally RNO reversed the reduction of Nrf2, HO-1 and GPx mRNA levels and consequently restored the TAC and reduced the H₂O₂ formation. RNO inhibits RSV infection of WD-HBE cultures and mitigates the cytopathological changes associated to this virus.

The phosphodiesterase 4 inhibitor rolipram protects against cigarette smoke extract-induced apoptosis in human lung fibroblasts

Cigarette smoke, a major causative agent of chronic obstructive pulmonary disease (COPD), induces lung cell death by incompletely understood mechanisms. The induction of apoptosis in lung structural cells by cigarette smoke may contribute to the pathogenesis of emphysema. Phosphodiesterase-4 (PDE4) inhibitors are anti-inflammatory agents used in COPD therapy that can prevent cigarette smoke-induced emphysema in mice. We investigated the effect of rolipram, a first generation PDE4 inhibitor, on the regulation of cigarette smoke-induced apoptosis. Human lung fibroblast (MRC-5) cells were exposed to cigarette smoke extract (CSE). Cell viability and apoptosis were determined by MTT assay and Annexin-V staining, respectively. Caspase activation was determined by Western immunoblot analysis. Rolipram protected against cell death and increased viability in MRC-5 fibroblasts after CSE exposure. Furthermore, rolipram protected against apoptosis, decreased caspase-3 and -8 cleavage in MRC-5 cells exposed to CSE. Pre-treatment with rolipram enhanced Akt phosphorylation and associated cytoprotection in CSE-treated cells, which could be reversed by the PI3K inhibitor LY294002 partly. In conclusion, rolipram protects against apoptosis of MRC-5 cells through inhibition of caspase-3 and caspase-8. Rolipram may represent an effective therapeutic agent to reduce cigarette smoke-induced apoptosis of lung fibroblasts.

Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions

Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Role of Epac in brain and heart

Epacs (exchange proteins directly activated by cAMP) are guanine-nucleotide-exchange factors for the Ras-like small GTPases Rap1 and Rap2. Epacs were discovered in 1998 as new sensors for the second messenger cAMP acting in parallel to PKA (protein kinase A). As cAMP regulates many important physiological functions in brain and heart, the existence of Epacs raises many questions regarding their role in these tissues. The present review focuses on the biological roles and signalling pathways of Epacs in neurons and cardiac myocytes. We discuss the potential involvement of Epacs in the manifestation of cardiac and central diseases such as cardiac hypertrophy and memory disorders.

cAMP signalling protects proximal tubular epithelial cells from cisplatin-induced apoptosis via activation of Epac

BACKGROUND AND PURPOSE

Nephrotoxicity is the principal dose-limiting factor for cisplatin chemotherapy and is primarily associated with proximal tubular epithelial cells, including disruption of cell adhesions and induction of apoptosis. Cell adhesion and survival is regulated by, amongst other factors, the small GTPase Rap and its activator, the exchange protein directly activated by cAMP (Epac). Epac is particularly enriched in renal tubule epithelium. This study investigates the cytoprotective effects of cAMP-Epac-Rap signalling in a model of cisplatin-induced renal cell injury.

EXPERIMENTAL APPROACH

The Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP was used to activate the Epac-Rap signalling pathway in proximal tubular epithelial cells. Cells were exposed to cisplatin, in the presence or absence of 8-pCPT-2'-O-Me-cAMP, and nephrotoxicity was determined by monitoring cell-cell junctions and cell apoptosis.

KEY RESULTS

Activation of Epac-Rap signalling preserves cell-cell junctions and protects against cell apoptosis of mouse proximal tubular cells during cisplatin treatment. Activation with the Epac-selective cAMP analogue 8-pCPT-2'-O-Me-cAMP or receptor-mediated induction of cAMP both induced cytoprotection against cisplatin, whereas a PKA-selective cAMP analogue was not cytoprotective. 8-pCPT-2'-O-Me-cAMP mediated cytoprotection was blocked by RNAi-mediated silencing of Epac-Rap signalling in these cells. In contrast, 8-pCPT-2'-O-Me-cAMP did not protect against cisplatin-induced cell death of cancer cells that lacked Epac1 expression.

CONCLUSIONS AND IMPLICATIONS

Our study identifies activation of Epac-Rap signalling as a potential strategy for reducing the nephrotoxicity associated with cisplatin treatments and, as a result, broadens the therapeutic window of this chemotherapeutic agent.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

New perspectives in cAMP-signaling modulation

Cyclic adenosine 3',5'-monophosphate (cAMP) mediates the biological effects of various hormones and neurotransmitters. Stimulation of cardiac β-adrenergic receptors (β-AR) via catecholamines leads to activation of adenylyl cyclases and increases cAMP production to enhance myocardial function. Because many other receptors signaling through cAMP generation exist in cardiac myocytes, a central question is how different hormones induce distinct cellular responses through the same second messenger. A large body of evidence suggests that the localization and compartmentalization of β-AR/cAMP signaling affects the net outcome of biological functions. Spatiotemporal dynamics of cAMP action is achieved by various proteins, including protein kinase A (PKA), phosphodiesterases, and scaffolding proteins such as A-kinase-anchoring proteins. In addition, the discovery of the cAMP target Epac (exchange proteins directly activated by cAMP), which functions in a PKA-independent manner, represents a novel mechanism for governing cAMP-signaling specificity. Aberrant cAMP signaling through dysregulation of β-AR/cAMP compartmentalization may contribute to cardiac remodeling and heart failure.

Type 10 adenylyl cyclase mediates mitochondrial Bax translocation and apoptosis of adult rat cardiomyocytes under simulated ischaemia/reperfusion

AIMS

Apoptosis of cardiomyocytes significantly contributes to the development of post-ischaemic cardiomyopathy. Although mitochondria have been suggested to play a crucial role in this process, the precise mechanisms controlling the mitochondria-dependent apoptosis in cardiomyocytes under ischaemia/reperfusion are still poorly understood. Here we aimed to analyse the role of the soluble adenylyl cyclase (sAC).

METHODS AND RESULTS

Adult rat cardiomyocytes were subjected to simulated in vitro ischaemia (SI) consisting of glucose-free anoxia at pH 6.4. Apoptosis was detected by DNA laddering, chromatin condensation, and caspases cleavage. SI led to the translocation of sAC to the mitochondria and mitochondrial depolarization followed by cytochrome c release, caspase-9/-3 cleavage and apoptosis during simulated reperfusion (SR). Pharmacological inhibition of sAC during SI, but not during SR, significantly reduced the SI/SR-induced mitochondrial injury and apoptosis. Similarly, sAC knock-down mediated by an adenovirus coding for shRNA targeting sAC prevented the activation of the mitochondrial pathway of apoptosis. Analysis of the link between sAC and apoptosis revealed a sAC and protein kinase A-dependent Bax phosphorylation at Thr(167) and its translocation to mitochondria during SI, which subsequently caused mitochondrial oxygen radical formation followed by cytochrome c release and caspase-9 cleavage during SR.

CONCLUSION

These results suggest a key role of sAC in SI-induced mitochondrial Bax translocation and activation of the mitochondrial pathway of apoptosis in adult cardiomyocytes.

Phosphodiesterases and subcellular compartmentalized cAMP signaling in the cardiovascular system

Phosphodiesterases are key enzymes in the cAMP signaling cascade. They convert cAMP in its inactive form 5'-AMP and critically regulate the intensity and the duration of cAMP-mediated signals. Multiple isoforms exist that possess different intracellular distributions, different affinities for cAMP, and different catalytic and regulatory properties. This complex repertoire of enzymes provides a multiplicity of ways to modulate cAMP levels, to integrate more signaling pathways, and to respond to the specific needs of the cell within distinct subcellular domains. In this review we summarize key findings on phosphodiesterase compartmentalization in the cardiovascular system.