The role of Epac proteins, novel cAMP mediators, in the regulation of immune, lung and neuronal function

Regulatory pathways and therapeutic potential of PDE4 in liver pathophysiology

Phosphodiesterase 4 (PDE4), crucial in regulating the cyclic adenosine monophosphate (cAMP) signaling pathway, significantly impacts liver pathophysiology. This article highlights the comprehensive effects of PDE4 on liver health and disease, and its potential as a therapeutic agent. PDE4's role in degrading cAMP disrupts intracellular signaling, increasing pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). This contributes to liver inflammation in conditions such as hepatitis and non-alcoholic steatohepatitis (NASH). Additionally, PDE4 is a key factor in liver fibrosis, characterized by excessive extracellular matrix deposition. Inhibiting PDE4 shows promise in reducing liver fibrosis by decreasing the activation of hepatic stellate cells, which is pivotal in fibrogenesis. PDE4 also influences hepatocyte apoptosis a common feature of liver diseases. PDE4 inhibitors protect against hepatocyte apoptosis by raising intracellular cAMP levels, thus activating anti-apoptotic pathways. This suggests potential in targeting PDE4 to prevent hepatocyte loss. Moreover, PDE4 regulates hepatic glucose production and lipid metabolism, essential for liver function. Altering cAMP levels through PDE4 affects enzymes in these metabolic pathways, making PDE4 a target for metabolic disorders like type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). Since PDE4 plays a multifaceted role in liver pathophysiology, influencing PDE4's mechanisms in liver diseases could lead to novel therapeutic strategies. Still, extensive research is required to explore the molecular mechanisms and clinical potential of targeting PDE4 in liver pathologies.

Role of EPAC1 in chronic pain

Chronic pain usually lasts over three months and commonly occurs in chronic diseases (cancer, arthritis, and diabetes), injuries (herniated discs, torn ligaments), and many major pain disorders (neuropathic pain, fibromyalgia, chronic headaches). Unfortunately, there is currently a lack of effective treatments to help people with chronic pain to achieve complete relief. Therefore,it is particularly important to understand the mechanism of chronic pain and find new therapeutic targets. The exchange protein directly activated by cyclic adenosine monophosphate(cAMP) (EPAC) has been recognized for its functions in nerve regeneration, stimulating insulin release, controlling vascular pressure, and controlling other metabolic activities. In recent years, many studies have found that the subtype of EPAC, EPAC1 is involved in the regulation of neuroinflammation and plays a crucial role in the regulation of pain, which is expected to become a new therapeutic target for chronic pain. This article reviews the major contributions of EPAC1 in chronic pain.

Development of green fluorescent protein-based cAMP indicators for covering a wide range of cAMP concentrations

There is a wide range in the concentration of intracellular cyclic adenosine 3',5'-monophosphate (cAMP), which mediates specific effects as a second messenger in pathways affecting many physiological processes. Here, we developed green fluorescent cAMP indicators, named Green Falcan (Green fluorescent protein-based indicator visualizing cAMP dynamics) with various EC₅₀ values (0.3, 1, 3, 10 μM) for covering the wide range of intracellular cAMP concentrations. The fluorescence intensity of Green Falcans increased in a cAMP dose-dependent manner, with a dynamic range of over 3-fold. Green Falcans showed a high specificity for cAMP over its structural analogues. When we expressed Green Falcans in HeLa cells, these indicators were applicable for visualization of cAMP dynamics in the low concentration range compared to the previously developed cAMP indicators, and visualized distinct kinetics of cAMP in various pathways with high spatiotemporal resolution in living cells. Furthermore, we demonstrated that Green Falcans are applicable to dual-color imaging with R-GECO, a red fluorescent Ca²⁺ indicator, in the cytoplasm and the nucleus. This study shows that Green Falcans open up a new avenue for understanding hierarchal and cooperative interactions with other molecules in various cAMP signaling pathways by multi-color imaging.

A novel type of serum‑free medium for culturing human airway epithelium cells

The present study aimed to evaluate the ability of a novel serum-free medium (SFM) to culture human airway epithelium cells (hAECs). hAECs were cultured in the novel SFM as the experimental group in the PneumaCult-Ex medium and Dulbecco's modified eagle medium (DMEM) and fetal bovine serum (FBS) as the control groups. Cell morphology, proliferative capacity, differentiation capacity and expression levels of basal cell markers were assessed accordingly in both culture systems. Optical microscope photos of hAECs were collected for cell morphology assessment. Cell Counting Kit-8 assay was conducted to assess the proliferation ability, and an air-liquid interface (ALI) assay was conducted to assess the differentiation capacity. Markers for proliferating basal and differentiated cells were relatively identified by immunohistochemical and immunofluorescent analysis. The results show that whether grown in the novel SFM or Ex medium, hAECs exhibited similar morphology at every passage, whereas cells could hardly form colonies in the DMEM + FBS group. Cells typically exhibited cobblestone shape, while a proportion of them in the novel SFM at late passage exhibited a larger shape. White vesicles appeared in the cytoplasm of some control cells at the later stage of culture. Basal cell markers (P63⁺KRT5⁺KI67⁺CC10^-) for proliferating ability were found in the hAECs cultured by the novel SFM and Ex medium. hAECs at passage 3 cultured in the novel SFM and Ex medium both had the capacity to differentiate into ciliated cells (acetylated tubulin⁺), goblet cells (MUC5AC⁺) and club cells (CC10⁺) in the ALI culture assay. In conclusion, the novel SFM was capable of culturing hAECs. The hAECs cultured by the novel SFM could proliferate and differentiate in vitro. The novel SFM does not change the morphological characteristics or biomarkers of hAECs. The novel SFM has the potential for the amplification of hAECs for scientific research and clinical application.

Epac: A Promising Therapeutic Target for Vascular Diseases: A Review

Vascular diseases affect the circulatory system and comprise most human diseases. They cause severe symptoms and affect the quality of life of patients. Recently, since their identification, exchange proteins directly activated by cAMP (Epac) have attracted increasing scientific interest, because of their role in cyclic adenosine monophosphate (cAMP) signaling, a well-known signal transduction pathway. The role of Epac in cardiovascular disease and cancer is extensively studied, whereas their role in kidney disease has not been comprehensively explored yet. In this study, we aimed to review recent studies on the regulatory effects of Epac on various vascular diseases, such as cardiovascular disease, cerebrovascular disease, and cancer. Accumulating evidence has shown that both Epac1 and Epac2 play important roles in vascular diseases under both physiological and pathological conditions. Additionally, there has been an increasing focus on Epac pharmacological modulators. Therefore, we speculated that Epac could serve as a novel therapeutic target for the treatment of vascular diseases.

Ligustrazine Inhibits Lung Phosphodiesterase Activity in a Rat Model of Allergic Asthma

Objectives

This study sought to examine whether ligustrazine was capable of inhibiting phosphodiesterase (PDE) activity and improving lung function in a rat model of asthma.

Methods

Rats were initially sensitized using ovalbumin (OVA) and then were challenged daily with aerosolized OVA beginning 14 days later (30 min/day) to generate a rat model of asthma. Changes in airway function following methacholine (MCh) injection were evaluated by monitoring lung resistance (R_L) and dynamic lung compliance (C_dyn) values using an AniRes2005 analytic system. In addition, serum IgE was measured via ELISA, while PDE expression was evaluated via qPCR and western blotting. Key Findings. Ligustrazine significantly impaired allergen-induced lung hyperresponsivity and inflammation in this asthma model system. Ligustrazine treatment was also associated with reduced expression of PDEs including PDE4 in the lungs of these rats.

Conclusions

Ligustrazine suppresses airway inflammation and bronchial hyperresponsivity in this rat model system, and these changes are associated with decreased PDE expression at the protein and mRNA levels.

Phosphodiesterase-4 Inhibitors for Non-COPD Respiratory Diseases

Selective phosphodiesterase (PDE) inhibitors are a class of nonsteroid anti-inflammatory drugs for treating chronic inflammatory diseases. Modulation of systemic and airway inflammation is their pivotal mechanism of action. Furthermore, PDE inhibitors modulate cough reflex and inhibit airway mucus secretion. Roflumilast, a selective PDE4 inhibitor, has been extensively studied for the efficacy and safety in chronic obstructive pulmonary disease (COPD) patients. According to the mechanisms of action, the potential roles of PDE inhibitors in treating chronic respiratory diseases including severe asthma, asthma-COPD overlap (ACO), noncystic fibrosis bronchiectasis, and chronic cough are discussed. Since roflumilast inhibits airway eosinophilia and neutrophilia in COPD patients, it reduces COPD exacerbations in the presence of chronic bronchitis in addition to baseline therapies. The clinical studies in asthma patients have shown the comparable efficacy of roflumilast to inhaled corticosteroids for improving lung function. However, the clinical trials of roflumilast in severe asthma have been limited. Although ACO is common and is also associated with poor outcomes, there is no clinical trial regarding its efficacy in patients with ACO despite a promising role in reducing COPD exacerbation. Since mucus hypersecretion is a result of neutrophil secretagogue in patients with chronic bronchitis, experimental studies have shown that PDE4s are regulators of the cystic fibrosis transmembrane conductance regulator (CFTR) in human airway epithelial cells. Besides, goblet cell hyperplasia is associated with an increased expression of PDE. Bronchiectasis and chronic bronchitis are considered neutrophilic airway diseases presenting with mucus hypersecretion. They commonly coexist and thus lead to severe disease. The role of roflumilast in noncystic fibrosis bronchiectasis is under investigation in clinical trials. Lastly, PDE inhibitors have been shown modulating cough from bronchodilation, suppressing transient receptors potential (TRP), and anti-inflammatory properties. Hence, there is the potential role of the drug in the management of unexplained cough. However, clinical trials for examining its antitussive efficacy are pivotal. In conclusion, selective PDE4 inhibitors may be potential treatment options for chronic respiratory diseases apart from COPD due to their promising mechanisms of action.

Overexpression of miR-338-5p in exosomes derived from mesenchymal stromal cells provides neuroprotective effects by the Cnr1/Rap1/Akt pathway after spinal cord injury in rats

Growing evidence has shown that microRNAs (miRNAs) play crucial roles in the physiopathology of spinal cord injury (SCI). Recent studies have confirmed that miR-338-5p regulates myelination, suggesting a potential role in the treatment of SCI. However, the molecular mechanism of miR-338-5p on SCI is still unknown. Recently, exosomes have emerged as an ideal vector to deliver therapeutic molecules such as miRNAs. Here, we explored the effects of miR-338-5p-overexpressing exosomes derived from bone marrow-derived mesenchymal stromal cells (BMSCs) on SCI. In vivo, a model of contusion SCI in rats was established, and we observed that overexpression of miR-338-5p in exosomes profoundly increased the expression levels of neurofilament protein-M and growth-associated protein-43 and decreased those of myelin-associated glycoprotein and glial fibrillary acidic protein, which provided neuroprotective effects after acute SCI. In an in vitro study, we found that overexpression of miR-338-5p in exosomes repressed cell apoptosis following H₂O₂-induced oxidative stress injury in PC12 cells. Additionally, we confirmed that cannabinoid receptor 1 (Cnr1) was the target gene of miR-338-5p by dual-luciferase reporter assays and that Rap1 was the downstream gene by the KEGG pathway analysis. We found that miR-338-5p increased cAMP accumulation as a consequence of downregulated expression of the target gene Cnr1, and then, Rap1 was activated by cAMP. Eventually, the activation of the PI3K/Akt pathway attenuated cell apoptosis and promoted neuronal survival by cAMP-mediated Rap1 activation. In brief, these findings showed that exosomes overexpressing miR-338-5p were a promising treatment strategy for SCI.

A central role for cAMP/EPAC/RAP/PI3K/AKT/CREB signaling in LH-induced follicular Pgr expression at medaka ovulation†

Nuclear progestin receptor (PGR) is a ligand-activated transcription factor that has been identified as a pivotal mediator of many processes associated with ovarian and uterine function, and aberrant control of PGR activity causes infertility and disease including cancer. The essential role of PGR in vertebrate ovulation is well recognized, but the mechanisms by which PGR is rapidly and transiently induced in preovulatory follicles after the ovulatory LH surge are not known in lower vertebrates. To address this issue, we utilized the small freshwater teleost medaka Oryzias latipes, which serves as a good model system for studying vertebrate ovulation. In the in vitro ovulation system using preovulatory follicles dissected from the fish ovaries, we found that inhibitors of EPAC (brefeldin A), RAP (GGTI298), PI3K (Wortmannin), AKT (AKT inhibitor IV), and CREB (KG-501) inhibited LH-induced follicle ovulation, while the PKA inhibitor H-89 had no effect on follicle ovulation. The inhibitors capable of inhibiting follicle ovulation also inhibited follicular expression of Pgr and matrix metalloproteinase-15 (Mmp15), the latter of which was previously shown to not only be a downstream effector of Pgr but also a proteolytic enzyme indispensable for follicle rupture in medaka ovulation. Further detailed analysis revealed for the first time that the cAMP/EPAC/RAP/PI3K/AKT/CREB signaling pathway mediates the LH signal to induce Pgr expression in preovulatory follicles. Our data also showed that phosphorylated Creb1 is a transcription factor essential for pgr expression and that Creb1 phosphorylated by Akt1, rather than PKA, may be preferably used to induce pgr expression.

Transcription factors regulated by cAMP in smooth muscle of the myometrium at human parturition

Cyclic adenosine monophosphate (cAMP) contributes to maintenance of a quiescent (relaxed) state in the myometrium (i.e. uterine smooth muscle) during pregnancy, which most commonly has been attributed to activation of protein kinase A (PKA). PKA-mediated phosphorylation of cytosolic contractile apparatus components in myometrial smooth muscle cells (mSMCs) are known to promote relaxation. Additionally, PKA also regulates nuclear transcription factor (TF) activity to control expression of genes important to the labour process; these are mostly involved in actin-myosin interactions, cell-to-cell connectivity and inflammation, all of which influence mSMC transition from a quiescent to a contractile (pro-labour) phenotype. This review focuses on the evidence that cAMP modulates the activity of TFs linked to pro-labour gene expression, predominantly cAMP response element (CRE) binding TFs, nuclear factor κB (NF-κB), activator protein 1 (AP-1) family and progesterone receptors (PRs). This review also considers the more recently described exchange protein directly activated by cAMP (EPAC) that may oppose the pro-quiescent effects of PKA, as well as explores findings from other cell types that have the potential to be of novel relevance to cAMP action on TF function in the myometrium.

Epac1 Signaling Pathway Mediates the Damage and Apoptosis of Inner Ear Hair Cells after Noise Exposure in a Rat Model

To investigate the role of the exchange protein directly activated by cAMP (Epac) signaling pathway in inner ear hair cell damage and apoptosis after noise exposure, we analyzed the expression level of Epac1 in a rat model of noise-induced hearing loss (NIHL), based on rat exposure to a 4-kHz and 106-dB sound pressure level (SPL) for 8 h. Loss of outer hair cells (OHCs), mitochondrial lesions, and hearing loss were examined after treatment with the Epac agonist, 8-CPT, or the Epac inhibitor, ESI-09. The effects of 8-CPT and ESI-09 on cell proliferation and apoptosis were examined by CCK-8 assays, holographic microscopy imaging, and Annexin-V FITC/PI staining in HEI-OC1 cells. The effects of 8-CPT and ESI-09 on Ca²⁺ entry were evaluated by confocal Ca²⁺ fluorescence measurement. We found that the expression level of Epac1 was significantly increased in the cochlear tissue after noise exposure. In NIHL rats, 8-CPT increased the loss of OHCs, mitochondrial lesions, and hearing loss compared to control rats, while ESI-09 produced the opposite effects. Oligomycin was used to induce HEI-OC1 cell damage in vitro. In HEI-OC1 cells treated with oligomycin, 8-CPT and ESI-09 increased and reduced cell apoptosis, respectively. Moreover, 8-CPT promoted Ca²⁺ uptake in HEI-OC1 cells, while ESI-09 inhibited this process. In conclusion, our data provide strong evidence that the Epac1 signaling pathway mediates early pathological damage in NIHL, and that Epac1 inhibition protects from NIHL, identifying Epac1 as a new potential therapeutic target for NIHL.

The ADCY9 genetic variants are associated with glioma susceptibility and patient prognosis

PURPOSE

Genetic factor is a risk factor in glioma occurrence. This study was designed to detect the effect of ADCY9 polymorphisms on glioma risk and prognosis.

METHODS

We performed a case-control study of 1080 participants (584 cases and 496 controls) to assess the relationship of ADCY9 polymorphisms with the risk and prognosis of glioma among the Chinses Han population. Odds ratios (ORs) and 95% confidence intervals (CIs) were computed to evaluate the relationship between ADCY9 variants and glioma risk. The correlation of SNPs with survival was analyzed by the Cox regression model.

RESULTS

Our study showed that rs2230742 and rs2531992 polymorphisms played protective roles in glioma susceptibility (OR 0.65, p = 0.001; OR 0.73, p = 0.038, respectively). While rs2230742 significantly increased the susceptibility of III-V grade glioma patients (OR 1.50, p = 0.036). Haplotype analysis revealed that C_rs879620A_rs2230742A_rs2230741 haplotype was related to a significantly decreased glioma risk (OR 0.65, p = 0.002). Notably, rs2531995 and rs879620 polymorphisms significantly enhanced death risk in high-grade glioma patients (hazard ratio [HR] 1.36, p = 0.041; HR 1.37, p = 0.042; respectively). For rs2230742 and rs2531992 SNPs, glioma patients had a worse prognosis (HR 2.30, p = 0.021; HR 2.30, p = 0.021; respectively). We further observed that age, chemotherapy, and surgical scope can affect the glioma prognosis.

CONCLUSION

We firstly studied the association of ADCY9 variants with glioma risk and prognosis, which might give scientific evidence for exploring the molecular mechanism of glioma.

The effects of polydeoxyribonucleotide on wound healing and tissue regeneration: a systematic review of the literature

Aim: The present study evaluated the effects of polydeoxyribonucleotide (PDRN) on tissue regeneration, paying special attention to the molecular mechanisms that underlie its tissue remodeling actions to better identify its effective therapeutic potential in wound healing. Materials & methods: Strategic searches were conducted through MEDLINE/PubMed, Google Scholar, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials, from their earliest available dates to March 2020. The studies were included with the following eligibility criteria: studies evaluating tissue regeneration, and being an in vitro, in vivo and clinical study. Results: Out of more than 90 articles, 34 fulfilled the eligibility criteria. All data obtained proved the ability of PDRN in promoting a physiological tissue repair through salvage pathway and adenosine A2A receptor activation. Conclusion: Up to date PDRN has proved promising results in term of wound regeneration, healing time and absence of side effects.

Role of cyclic nucleotides and their downstream signaling cascades in memory function: Being at the right time at the right spot

A plethora of studies indicate the important role of cAMP and cGMP cascades in neuronal plasticity and memory function. As a result, altered cyclic nucleotide signaling has been implicated in the pathophysiology of mnemonic dysfunction encountered in several diseases. In the present review we provide a wide overview of studies regarding the involvement of cyclic nucleotides, as well as their upstream and downstream molecules, in physiological and pathological mnemonic processes. Next, we discuss the regulation of the intracellular concentration of cyclic nucleotides via phosphodiesterases, the enzymes that degrade cAMP and/or cGMP, and via A-kinase-anchoring proteins that refine signal compartmentalization of cAMP signaling. We also provide an overview of the available data pointing to the existence of specific time windows in cyclic nucleotide signaling during neuroplasticity and memory formation and the significance to target these specific time phases for improving memory formation. Finally, we highlight the importance of emerging imaging tools like Förster resonance energy transfer imaging and optogenetics in detecting, measuring and manipulating the action of cyclic nucleotide signaling cascades.

Exchange protein activated by cyclic-adenosine monophosphate (Epac) regulates atrial fibroblast function and controls cardiac remodelling

Aims

Heart failure (HF) produces left atrial (LA)-selective fibrosis and promotes atrial fibrillation. HF also causes adrenergic activation, which contributes to remodelling via a variety of signalling molecules, including the exchange protein activated by cAMP (Epac). Here, we evaluate the effects of Epac1-signalling on LA fibroblast (FB) function and its potential role in HF-related atrial remodelling.

Methods and results

HF was induced in adult male mongrel dogs by ventricular tachypacing (VTP). Epac1-expression decreased in LA-FBs within 12 h (-3.9-fold) of VTP onset. The selective Epac activator, 8-pCPT (50 µM) reduced, whereas the Epac blocker ESI-09 (1 µM) enhanced, collagen expression in LA-FBs. Norepinephrine (1 µM) decreased Epac1-expression, an effect blocked by prazosin, and increased FB collagen production. The β-adrenoceptor (AR) agonist isoproterenol increased Epac1 expression, an effect antagonized by ICI (β2-AR-blocker), but not by CGP (β1-AR-blocker). β-AR-activation with isoproterenol decreased collagen expression, an effect mimicked by the β2-AR-agonist salbutamol and blocked by the Epac1-antagonist ESI-09. Transforming growth factor-β1, known to be activated in HF, suppressed Epac1 expression, an effect blocked by the Smad3-inhibitor SIS3. To evaluate effects on atrial fibrosis in vivo, mice subjected to myocardial infarction (MI) received the Epac-activator Sp-8-pCPT or vehicle for 2 weeks post-MI; Sp-8-pCPT diminished LA fibrosis and attenuated cardiac dysfunction.

Conclusions

HF reduces LA-FB Epac1 expression. Adrenergic activation has complex effects on FBs, with α-AR-activation suppressing Epac1-expression and increasing collagen expression, and β2-AR-activation having opposite effects. Epac1-activation reduces cardiac dysfunction and LA fibrosis post-MI. Thus, Epac1 signalling may be a novel target for the prevention of profibrillatory cardiac remodelling.

Pro-cognitive effect of upregulating cyclic guanosine monophosphate signalling during memory acquisition or early consolidation is mediated by increased AMPA receptor trafficking

BACKGROUND

Episodic memory consists of different mnemonic phases, including acquisition and early and late consolidation. Each of these phases is characterised by distinct molecular processes. Although both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are implicated in the acquisition phase, early consolidation only depends on cGMP, whereas late consolidation is mediated by cAMP. Accordingly, the cGMP-selective phosphodiesterase 5 (PDE5) inhibitor vardenafil or the cAMP-selective PDE4 inhibitor rolipram can improve memory acquisition or consolidation when applied during their respective time windows.

AIMS

Considering the important role of glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) during normal memory function, we aimed to investigate whether the differential actions of these PDE inhibitors are mediated through AMPAR dynamics.

METHODS

For biochemical analysis, mice were treated with either vardenafil or rolipram and sacrificed shortly after injection. For the behavioural studies, mice received either of the inhibitors during the different mnemonic phases, while their spatial memory was tested using the object location task, and they were sacrificed 24 hours later.

RESULTS

Administration of either vardenafil or rolipram causes rapid changes in AMPARs. Moreover, treatment with vardenafil during the acquisition or early consolidation of spatial memory resulted in increased surface levels of AMPARs which were still augmented 24 hours after learning. Membrane levels of AMPARs were not affected anymore 24 hours after learning when rolipram was administrated at either the acquisition or late consolidation phase.

CONCLUSIONS

These results suggest that dissociative molecular mechanisms could mediate the pro-cognitive function of different classes of PDE inhibitors, and in the case of vardenafil, this phenomenon could be explained by changes in AMPAR dynamics.

Exchange protein directly activated by cAMP (Epac) protects against airway inflammation and airway remodeling in asthmatic mice

Background

β₂ receptor agonists induce airway smooth muscle relaxation by increasing intracellular cAMP production. PKA is the traditional downstream signaling pathway of cAMP. Exchange protein directly activated by cAMP (Epac) was identified as another important signaling molecule of cAMP recently. The role of Epac in asthmatic airway inflammation and airway remodeling is unclear.

Methods

We established OVA-sensitized and -challenged acute and chronic asthma mice models to explore the expression of Epac at first. Then, airway inflammation and airway hyperresponsiveness in acute asthma mice model and airway remodeling in chronic asthma mice model were observed respectively after treatment with Epac-selective cAMP analogue 8-pCPT-2′-O-Me-cAMP (8pCPT) and Epac inhibitor ESI-09. Next, the effects of 8pCPT and ESI-09 on the proliferation and apoptosis of in vitro cultured mouse airway smooth muscle cells (ASMCs) were detected with CCK-8 assays and Annexin-V staining. Lastly, the effects of 8pCPT and ESI-09 on store-operated Ca²⁺ entry (SOCE) of ASMCs were examined by confocal Ca²⁺ fluorescence measurement.

Results

We found that in lung tissues of acute and chronic asthma mice models, both mRNA and protein expression of Epac1 and Epac2, two isoforms of Epac, were lower than that of control mice. In acute asthma mice model, the airway inflammatory cell infiltration, Th2 cytokines secretion and airway hyperresponsiveness were significantly attenuated by 8pCPT and aggravated by ESI-09. In chronic asthma mice model, 8pCPT decreased airway inflammatory cell infiltration and airway remodeling indexes such as collagen deposition and airway smooth muscle cell proliferation, while ESI-09 increased airway inflammation and airway remodeling. In vitro cultured mice ASMCs, 8pCPT dose-dependently inhibited, whereas ESI-09 promoted ASMCs proliferation. Interestingly, 8pCPT promoted the apoptosis of ASMCs, whereas ESI-09 had no effect on ASMCs apoptosis. Lastly, confocal Ca²⁺ fluorescence examination found that 8pCPT could inhibit SOCE in ASMCs at 100 μM, and ESI-09 promoted SOCE of ASMCs at 10 μM and 100 μM. In addition, the promoting effect of ESI-09 on ASMCs proliferation was inhibited by store-operated Ca²⁺ channel blocker, SKF-96365.

Conclusions

Our results suggest that Epac has a protecting effect on asthmatic airway inflammation and airway remodeling, and Epac reduces ASMCs proliferation by inhibiting SOCE in part.

Behavior and Hippocampal Epac Signaling to Nicotine CPP in Mice

Tobacco use is a major challenge to public health in the United States and across the world. Many studies have demonstrated that adult men and women differ in their responses to tobacco smoking, however neurobiological studies about the effect of smoking on males and females were limited. Exchange protein directly activated by cAMP (Epac) signaling participates in drug addictive behaviors. In this study, we examined the hippocampal Epac signaling in nicotine-induced place conditioning mice. Nicotine at 0.2 mg/kg and 0.4 mg/kg induced a conditioned place preference (CPP) in male and female mice, respectively. After CPP, male mice presented less anxiety-like behavior as demonstrated by an open-field test. The hippocampal Epac2 protein was elevated in both male and female nicotine place conditioning mice. However, Rap1 protein was elevated and CREB phosphorylation was reduced in female nicotine place conditioning mice. Our data provide direct evidence that hippocampal Epac signaling is altered in nicotine-induced CPP mice. Pharmacology manipulation Epac signaling may open a new avenue for the treatment of nicotine abuse and dependence.

Overexpression of EPAC2 reduces the invasion of glioma cells via MMP-2

Exchange proteins directly activated by cAMP (EPACs) are crucial cyclic adenosine 3′,5′-monophosphate- determined signaling pathway intercessors, which are associated with the pathogenesis of neurological disorders and numerous human diseases. To the best of our knowledge, the role of EPAC2 signaling via matrix metalloproteinase 2 (MMP-2) in the pathogenesis of glioma has not been studied. Therefore, the present study focused on the role of EPAC2 in glioma, and assessed the invasiveness of human glioma cell lines following EPAC2 overexpression. Expression levels of EPAC2 in normal brain tissues and clinical glioma specimens were detected by western blotting. An EPAC2 overexpression vector was transfected into U251 and U87 cell lines to increase the expression levels of EPAC2. Expression levels of MMP-2 were detected by western blotting, and the invasive abilities of glioma cells were detected by a Transwell assay. EPAC2 was relatively highly expressed in normal brain tissue, while EPAC2 expression was significantly decreased in clinical glioma specimens (P<0.01). In vitro transfection of EPAC2 overexpression vector significantly reduced the MMP-2 protein levels of glioma cells, and, at the same time, the invasive cell number was significantly decreased in a Transwell assay. The present study demonstrated that MMP-2 regulation via EPAC2 overexpression is a novel promising therapeutic route in malignant types of glioma.

Orally active Epac inhibitor reverses mechanical allodynia and loss of intraepidermal nerve fibers in a mouse model of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect of cancer treatment that significantly compromises quality of life of cancer patients and survivors. Identification of targets for pharmacological intervention to prevent or reverse CIPN is needed. We investigated exchange protein regulated by cAMP (Epac) as a potential target. Epacs are cAMP-binding proteins known to play a pivotal role in mechanical allodynia induced by nerve injury and inflammation. We demonstrate that global Epac1-knockout (Epac1-/-) male and female mice are protected against paclitaxel-induced mechanical allodynia. In addition, spinal cord astrocyte activation and intraepidermal nerve fiber (IENF) loss are significantly reduced in Epac1-/- mice as compared to wild-type mice. Moreover, Epac1-/- mice do not develop the paclitaxel-induced deficits in mitochondrial bioenergetics in the sciatic nerve that are a hallmark of CIPN. Notably, mice with cell-specific deletion of Epac1 in Nav1.8-positive neurons (N-Epac1-/-) also show reduced paclitaxel-induced mechanical allodynia, astrocyte activation, and IENF loss, indicating that CIPN develops downstream of Epac1 activation in nociceptors. The Epac-inhibitor ESI-09 reversed established paclitaxel-induced mechanical allodynia in wild-type mice even when dosing started 10 days after completion of paclitaxel treatment. In addition, oral administration of ESI-09 suppressed spinal cord astrocyte activation in the spinal cord and protected against IENF loss. Ex vivo, ESI-09 blocked paclitaxel-induced abnormal spontaneous discharges in dorsal root ganglion neurons. Collectively, these findings implicate Epac1 in nociceptors as a novel target for treatment of CIPN. This is clinically relevant because ESI-09 has the potential to reverse a debilitating and long-lasting side effect of cancer treatment.

cAMP guided his way: a life for G protein-mediated signal transduction and molecular pharmacology-tribute to Karl H. Jakobs

Karl H. Jakobs, former editor-in-chief of Naunyn-Schmiedeberg's Archives of Pharmacology and renowned molecular pharmacologist, passed away in April 2018. In this article, his scientific achievements regarding G protein-mediated signal transduction and regulation of canonical pathways are summarized. Particularly, the discovery of inhibitory G proteins for adenylyl cyclase, methods for the analysis of receptor-G protein interactions, GTP supply by nucleoside diphosphate kinases, mechanisms in phospholipase C and phospholipase D activity regulation, as well as the development of the concept of sphingosine-1-phosphate as extra- and intracellular messenger will presented. His seminal scientific and methodological contributions are put in a general and timely perspective to display and honor his outstanding input to the current knowledge in molecular pharmacology.

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

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

Function of cAMP scaffolds in obstructive lung disease: Focus on epithelial-to-mesenchymal transition and oxidative stress

Over the past decades, research has defined cAMP as one of the central cellular nodes in sensing and integrating multiple pathways and as a pivotal role player in lung pathophysiology. Obstructive lung disorders, such as chronic obstructive pulmonary disease (COPD), are characterized by a persistent and progressive airflow limitation and by oxidative stress from endogenous and exogenous insults. The extent of airflow obstruction depends on the relative deposition of different constituents of the extracellular matrix, a process related to epithelial-to-mesenchymal transition, and which subsequently results in airway fibrosis. Oxidative stress from endogenous and also from exogenous sources causes a profound worsening of COPD. Here we describe how cAMP scaffolds and their different signalosomes in different subcellular compartments may contribute to COPD. Future research will require translational studies to alleviate disease symptoms by pharmacologically targeting the cAMP scaffolds. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Cilostazol protects rats against alcohol-induced hepatic fibrosis via suppression of TGF-β1/CTGF activation and the cAMP/Epac1 pathway

Alcohol abuse and chronic alcohol consumption are major causes of alcoholic liver disease worldwide, particularly alcohol-induced hepatic fibrosis (AHF). Liver fibrosis is an important public health concern because of its high morbidity and mortality. The present study examined the mechanisms and effects of the phosphodiesterase III inhibitor cilostazol on AHF. Rats received alcohol infusions via gavage to induce liver fibrosis and were treated with colchicine (positive control) or cilostazol. The serum alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities and the albumin/globulin (A/G), enzymes and hyaluronic acid (HA), type III precollagen (PC III), laminin (LA), and type IV collagen (IV-C) levels were measured using commercially available kits. α-smooth muscle actin (α-SMA), collagen I and III, transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), adenosine 3',5'-cyclic monophosphate (cAMP) and exchange protein directly activated by cAMP (Epac) 1/2 expression in liver tissue were measured using western blotting. The results demonstrated that cilostazol significantly increased the serum ADH and ALDH activities and decreased the liver hydroxyproline levels. Cilostazol increased the serum A/G ratio and inhibited the total serum protein, enzymes, HA, PCIII, LA and IV-C levels. Western blotting revealed that cilostazol effectively decreased liver α-SMA, collagen I and III, TGF-β1 and CTGF expression. Cilostazol significantly increased the cAMP and Epac1 levels in hepatic tissue. The present study suggests that cilostazol protects rats against AHF via suppression of TGF-β1/CTGF activation and the cAMP/Epac1 pathway.

Integrated Analysis of miRNA and mRNA Expression Profiles in Spleen of Specific Pathogen-Free Chicken Infected with Avian Reticuloendotheliosis Virus Strain SNV

The Reticuloendotheliosis virus (REV) primarily causes avian severe immunosuppression, in addition to other symptoms, which include avian dwarfing syndrome and chronic tumors in lymphoid and other tissue. To date, REV’s molecular mechanisms leading to immunosuppression have not been fully elucidated. In the current study, we aimed to elucidate the role of microRNAs (miRNA) in regulating gene expression during REV infections. Therefore, we used a high-dose spleen necrosis virus (SNV) model of REV to inoculate one-day-old specific pathogen-free (SPF) chickens, thereby inducing congenital infections. We analyzed miRNA and mRNA expression profiles using Next Generation Sequencing (NGS) in a total of 19 spleen samples that were collected at 7, 14, and 21 days post infection (dpi). The results showed that 63 differentially expressed miRNAs (DEmiRNAs) (30 known miRNAs and 33 novel miRNAs) and 482 differentially expressed target genes (DETGs) were identified. Integration analysis identified 886 known miRNA–mRNA and 580 novel miRNA–mRNA interaction pairs, which involved miRNAs that were inversely correlated with the above DETGs. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that the DETGs were considerably enriched in the immune-relevant pathways category, such as immune system, cell growth and death, signaling molecules and interaction, signal transduction, etc. We further verified selected immune-relevant miRNA and their DETGs while using quantitative RT-PCR (qRT-PCR). Overall, our data revealed valuable immune-related miRNA–mRNA interaction information that occurred during REV infections, thereby broadening our understanding of the REV-induced immunosuppression.

The cAMP effectors, Rap2b and EPAC, are involved in the regulation of the development of the Coxiella burnetii containing vacuole by altering the fusogenic capacity of the vacuole

Cyclic Adenosine 3′,5′-monophosphate (cAMP) is a key second messenger known to directly regulate not only the protein kinase A (PKA) activity but also other important molecules such as the exchange protein activated by cAMP (EPAC), which is as a guanine nucleotide exchange factor (GEF) of the low molecular weight GTPase, Rap2. Coxiella burnetii is a Gram negative bacterium that survives and grows in a large Coxiella replicative vacuole (CRV), which displays lysosomal and autophagic features. In this report, we present evidence that both, EPAC and its downstream effector Rap2b, were recruited to the CRV. The transient over-expression of the Rap2b wt protein, but not its inactive mutant Rap2b ΔAAX, markedly inhibited the development of the large CRV. Additionally, Rap2b wtinhibited the fusion of early Coxiella phagosomes with the fully developed CRV, indicating that homotypic fusion events are altered in the presence of high levels of Rap2b wt. Likewise, the fusion of endosome/lysosomal compartments (heterotypic fusions) with the large CRV was also affected by the over-expression of this GTPase. Interestingly, cell overexpression of Rap2b wt markedly decreased the levels of the v-SNARE, Vamp7, suggesting that this down-regulation impairs the homotypic and heterotypic fusions events of the Coxiella vacuole.

Experimental and investigational phosphodiesterase inhibitors in development for asthma

INTRODUCTION

Severe, inadequately-controlled asthma remains a clinical challenge. For this reason, clinical trials and preclinical experimental studies on novel agents as an add-on therapies continue emerge. Phosphodiesterases (PDEs) are enzymes that regulate the function of immune cells by hydrolyzing cyclic guanosine monophosphate/cGMP and cyclic adenosine monophosphate/cAMP. PDEs are divided into subfamilies [PDE3, PDE4, PDE5 and PDE7] which are mainly found in the respiratory tract. Inhibitors of PDEs have already been approved for COPD and pulmonary hypertension.

AREAS COVERED

The role of PDE inhibitors in asthma treatment and the possible mechanism of action via their anti-inflammatory and/or bronchodilating effect are discussed.

EXPERT OPINION

Novel PDE inhibitors exhibiting fewer adverse events may have a role as add-on therapies in asthma treatment in the future. More clinical trials are necessary to prove their efficacy and evaluate their safety profile before approval by regulatory bodies is granted.

PDE4 and Epac1 Synergistically Promote Rectal Carcinoma via the cAMP Pathway

Objective

To assess the expression levels of exchange protein 1 directly activated by cAMP (Epac1) and phosphodiesterase 4 (PDE4) in rectal carcinoma, and their associations with clinicopathological indexes. In addition, the associations of PDE4 and Epac1 with A-kinase anchor protein 95, connexin 43, cyclin D1, and cyclin E1 were evaluated.

Methods

The PV-9000 two-step immunohistochemistry method was used to determine protein expression in 44 rectal carcinoma tissue samples and 16 paracarcinoma tissue specimens.

Results

The positive rate of PDE4 protein expression in rectal carcinoma tissues was higher than that of paracarcinoma tissues (59.09% vs. 12.5%, P < 0.05). Similar findings were obtained for Epac1 (55% vs. 6.25%, P < 0.05). No significant associations of PDE4 and Epac1 with degree of differentiation, histological type, and lymph node metastasis were found in rectal carcinoma (P > 0.05). Correlations between PDE4 and Epac1, PDE4 and Cx43, PDE4 and cyclin E1, and Epac1 and Cx43 were observed (all P < 0.05). There was no correlation between the other protein pairs examined (P > 0.05).

Conclusion

PDE4 and Epac1 expression levels are increased in rectal carcinoma tissues, suggesting that the two proteins may be involved in the development of this malignancy. Meanwhile, correlations between PDE4 and Epac1, PDE4 and Cx43, PDE4 and cyclin E1, and Epac1 and Cx43 suggested synergistic effects of these proteins in promoting rectal carcinoma.

Glucagon-like peptide-2 reduces the obesity-associated inflammation in the brain

Growing evidence suggests a link between obesity and neurodegeneration. The purpose of the present study was to explore the neuroprotective potential of glucagon-like peptide-2 (GLP-2) in the brain of high fat diet (HFD)-fed mice. Markers of inflammation and oxidative stress were analysed in the brains of obese mice chronically treated with [Gly²]-GLP-2 (teduglutide), the stable analogue of the GLP-2, and they were compared to age-matched untreated obese and lean animals. Neurodegeneration was examined by TUNEL assay. HFD feeding increased the expression of pro-inflammatory mediators (NF-kB, IL-8, TNF-α, IL-1β and IL-6), glial fibrillary acidic protein (GFAP), index of gliosis and neurodegeneration, stress marker proteins (p-ERK, Hsp60 and i-NOS), amyloid-β precursor protein (APP). [Gly²]-GLP-2 treatment significantly attenuated the HFD-induced increased expression of the various markers, as well as the higher levels of reactive oxygen species found in brains of untreated-HFD mice. Immunofluorescence confirmed that the increase of GFAP or APP in the brain cortex of HFD mice were less prominent in the [Gly²]-GLP-2 treated group. TUNEL-positive cell number in brain sections of [Gly²]-GLP-2-treated HFD-fed mice was significantly lesser in comparison with untreated-HFD animals and similar to STD fed mice. In conclusion, the results of the present study suggest that GLP-2 stable analogue improves the obesity-associated neuroinflammation and the central stress conditions, it reduces the neuronal apoptotic death, providing evidence for a neuroprotective role of the peptide.

Class II MHC cytoplasmic domain-mediated signaling in B cells: A tail of two signals

In addition to their role in antigen presentation, class II MHC molecules also transmit signals to B lymphocytes. Class II MHC-mediated signals initiate a range of events in B cells, including induction of cell surface proteins, initiation of cell-cycle progression/proliferation, activation of or protection from apoptosis, and antigen-dependent plasma cell differentiation. Although various transmembrane signaling proteins associate with class II MHC molecules, the class II MHC cytoplasmic domains are essential for signals leading to increased intracellular cAMP and activation of protein kinase C (PKC). Although truncation and mutagenesis studies have provided considerable information about the cytoplasmic domain sequences required, how class II MHC molecules elicit cAMP and PKC activation is not known. Further, appropriate T-dependent B cell responses require intact cAMP and PKC signaling, but the extent to which class II MHC signals are involved is also unknown. This review details our current knowledge of class II MHC cytoplasmic domain signaling in B cells with an emphasis on the likely importance of class II MHC signals for T-dependent antibody responses.

Inhibition of protein kinase A and GIRK channel reverses fentanyl-induced respiratory depression

Opioid-induced respiratory depression is a major obstacle to improving the clinical management of moderate to severe chronic pain. Opioids inhibit neuronal activity via various pathways, including calcium channels, adenylyl cyclase, and potassium channels. Currently, the underlying molecular pathway of opioid-induced respiratory depression is only partially understood. This study aimed to investigate the mechanisms of opioid-induced respiratory depression in vivo by examining the effects of different pharmacological agents on fentanyl-induced respiratory depression. Respiratory parameters were detected using whole body plethysmography in conscious rats. We show that pre-treatment with the protein kinase A (PKA) inhibitor H89 reversed the fentanyl-related effects on respiratory rate, inspiratory time, and expiratory time. Pre-treatment with the G protein-gated inwardly rectifying potassium (GIRK) channel blocker Tertiapin-Q dose-dependently reversed the fentanyl-related effects on respiratory rate and inspiratory time. A phosphodiesterase 4 (PDE4) inhibitor and cyclic adenosine monophosphate (cAMP) analogs did not affect fentanyl-induced respiratory depression. These findings suggest that PKA and GIRK may be involved in fentanyl-induced respiratory depression and could represent useful therapeutic targets for the treatment of fentanyl-induced ventilatory depression.

Extracellular adenosine-induced Rac1 activation in pulmonary endothelium: Molecular mechanisms and barrier-protective role

We have previously shown that Gs-coupled adenosine receptors (A2a) are primarily involved in adenosine-induced human pulmonary artery endothelial cell (HPAEC) barrier enhancement. However, the downstream events that mediate the strengthening of the endothelial cell (EC) barrier via adenosine signaling are largely unknown. In the current study, we tested the overall hypothesis that adenosine-induced Rac1 activation and EC barrier enhancement is mediated by Gs-dependent stimulation of cAMP-dependent Epac1-mediated signaling cascades. Adenoviral transduction of HPAEC with constitutively-active (C/A) Rac1 (V12Rac1) significantly increases transendothelial electrical resistance (TER) reflecting an enhancement of the EC barrier. Conversely, expression of an inactive Rac1 mutant (N17Rac1) decreases TER reflecting a compromised EC barrier. The adenosine-induced increase in TER was accompanied by activation of Rac1, decrease in contractility (MLC dephosphorylation), but not Rho inhibition. Conversely, inhibition of Rac1 activity attenuates adenosine-induced increase in TER. We next examined the role of cAMP-activated Epac1 and its putative downstream targets Rac1, Vav2, Rap1, and Tiam1. Depletion of Epac1 attenuated the adenosine-induced Rac1 activation and the increase in TER. Furthermore, silencing of Rac1 specific guanine nucleotide exchange factors (GEFs), Vav2 and Rap1a expression significantly attenuated adenosine-induced increases in TER and activation of Rac1. Depletion of Rap1b only modestly impacted adenosine-induced increases in TER and Tiam1 depletion had no effect on adenosine-induced Rac1 activation and TER. Together these data strongly suggest that Rac1 activity is required for adenosine-induced EC barrier enhancement and that the activation of Rac1 and ability to strengthen the EC barrier depends, at least in part, on cAMP-dependent Epac1/Vav2/Rap1-mediated signaling.

Epac Function and cAMP Scaffolds in the Heart and Lung

Evidence collected over the last ten years indicates that Epac and cAMP scaffold proteins play a critical role in integrating and transducing multiple signaling pathways at the basis of cardiac and lung physiopathology. Some of the deleterious effects of Epac, such as cardiomyocyte hypertrophy and arrhythmia, initially described in vitro, have been confirmed in genetically modified mice for Epac1 and Epac2. Similar recent findings have been collected in the lung. The following sections will describe how Epac and cAMP signalosomes in different subcellular compartments may contribute to cardiac and lung diseases.

Effect of the asthma-chronic obstructive pulmonary disease syndrome on the stroke, Parkinson's disease, and dementia: a national cohort study

Background

To evaluate the association of asthma–chronic obstructive pulmonary disease syndrome (ACOS) with neurodegenerative diseases (stroke, Parkinson's disease and dementia) and the role of the steroids in the neurodegenerative diseases among the ACOS cohort.

Materials and Methods

Comparison of the ACOS cohort (N = 10,260) with the non-ACOS cohort (n = 20,513) based on the patients aged ≧40 years in the National Health Insurance Research Database from January 1, 2000 to December 31, 2010. These patients follow up to diagnosis of neurodegenerative diseases or the December 31, 2011; using multivariable Cox proportional hazards models.

Results

After adjustment for potential confounders, the [adjusted hazard ratio (aHR), 95% confidence interval (CI)] in the ACOS cohort were [1.39, 1.28–1.50] [1.56, 1.34–1.81] and [1.43, 1.29–1.59] for stroke, Parkinson's disease, dementia; respectively. The [aHR, 95% CI] for ACOS cohort with (inhaler corticosteroids ≧0.13 gram/ oral steroids ≧0.08gram) were with less risk (all aHR<1, p values <0.05) for these 3 neurodegenerative diseases except Parkinson's disease with inhaler corticosteroids >0.43 gram. The risk of stroke and dementia were the lower in patients with < 250 μg/d of a fluticasone equivalent inhaler corticosteroids (aHR = 0.53, 95% CI = 0.35–0.79; aHR = 0.53, 95% CI = 0.31–0.90, respectively).

Conclusions

The ACOS cohort had a higher risk of the neurodegenerative diseases. The lower dose of the inhaler corticosteroids with cumulative dose ≧0.13 gram have the less risk of stroke and dementia.

Structure-Activity Relationship Studies with Tetrahydroquinoline Analogs as EPAC Inhibitors

EPAC proteins are therapeutic targets for the potential treatment of cardiac hypertrophy and cancer metastasis. Several laboratories use a tetrahydroquinoline analog, CE3F4, to dissect the role of EPAC1 in various disease states. Here, we report SAR studies with tetrahydroquinoline analogs that explore various functional groups. The most potent EPAC inhibitor 12a exists as a mixture of inseparable E (major) and Z (minor) rotamers. The rotation about the N-formyl group indeed impacts the activity against EPAC.

Two independent but synchronized Gβγ subunit-controlled pathways are essential for trailing-edge retraction during macrophage migration

Chemokine-induced directional cell migration is a universal cellular mechanism and plays crucial roles in numerous biological processes, including embryonic development, immune system function, and tissue remodeling and regeneration. During the migration of a stationary cell, the cell polarizes, forms lamellipodia at the leading edge (LE), and triggers the concurrent retraction of the trailing edge (TE). During cell migration governed by inhibitory G protein (G_i)-coupled receptors (GPCRs), G protein βγ (Gβγ) subunits control the LE signaling. Interestingly, TE retraction has been linked to the activation of the small GTPase Ras homolog family member A (RhoA) by the Gα_12/13 pathway. However, it is not clear how the activation of G_i-coupled GPCRs at the LE orchestrates the TE retraction in RAW264.7 macrophages. Here, using an optogenetic approach involving an opsin to activate the G_i pathway in defined subcellular regions of RAW cells, we show that in addition to their LE activities, free Gβγ subunits also govern TE retraction by operating two independent, yet synchronized, pathways. The first pathway involves RhoA activation, which prevents dephosphorylation of the myosin light chain, allowing actomyosin contractility to proceed. The second pathway activates phospholipase Cβ and induces myosin light chain phosphorylation to enhance actomyosin contractility through increasing cytosolic calcium. We further show that both of these pathways are essential, and inhibition of either one is sufficient to abolish the G_i-coupled GPCR-governed TE retraction and subsequent migration of RAW cells.

Epac1-deficient mice have bleeding phenotype and thrombocytes with decreased GPIbβ expression

Epac1 (Exchange protein directly activated by cAMP 1) limits fluid loss from the circulation by tightening the endothelial barrier. We show here that Epac1-/- mice, but not Epac2-/- mice, have prolonged bleeding time, suggesting that Epac1 may limit fluid loss also by restraining bleeding. The Epac1-/- mice had deficient in vitro secondary hemostasis. Quantitative comprehensive proteomics analysis revealed that Epac1-/- mouse platelets (thrombocytes) had unbalanced expression of key components of the glycoprotein Ib-IX-V (GPIb-IX-V) complex, with decrease of GP1bβ and no change of GP1bα. This complex is critical for platelet adhesion under arterial shear conditions. Furthermore, Epac1-/- mice have reduced levels of plasma coagulation factors and fibrinogen, increased size of circulating platelets, increased megakaryocytes (the GP1bβ level was decreased also in Epac1-/- bone marrow) and higher abundance of reticulated platelets. Viscoelastic measurement of clotting function revealed Epac1-/- mice with a dysfunction in the clotting process, which corresponds to reduced plasma levels of coagulation factors like factor XIII and fibrinogen. We propose that the observed platelet phenotype is due to deficient Epac1 activity during megakaryopoiesis and thrombopoiesis, and that the defects in blood clotting for Epac1-/- is connected to secondary hemostasis.

Glucagon and glucagon-like peptide-1 as novel anti-inflammatory and immunomodulatory compounds

Glucagon and glucagon-like peptide-1 (GLP-1) are polypeptide hormones that are produced by pancreatic α-cells and the intestine, respectively, whose main function is to control glucose homeostasis. The glucagon and GLP-1 levels are imbalanced in diabetes. Furthermore, type 1 diabetic patients and animals present with a diminished inflammatory response, which is related to some morbidities of diabetes, such as a higher incidence of infectious diseases, including sepsis. The focus of this review is to briefly summarize the state of the art concerning the effects of glucagon and GLP-1 on the inflammatory response. Here, we propose that glucagon and GLP-1 have anti-inflammatory properties, making them possible prototypes for the design and synthesis of new compounds to treat inflammatory diseases. In addition, glucagon, GLP-1 or their analogues or new derivatives may not only be important for managing inflammatory diseases but may also have the therapeutic potential to prevent, cure or ameliorate diabetes in patients by counteracting the deleterious effects of pro-inflammatory cytokines on the function and viability of pancreatic β-cells. In addition, GLP-1, its analogues or drugs that inhibit GLP-1 metabolism may have a doubly beneficial effect in diabetic patients by inhibiting the inflammatory response and reducing glycaemia.

Identification of novel 2-(benzo[d]isoxazol-3-yl)-2-oxo-N-phenylacetohydrazonoyl cyanide analoguesas potent EPAC antagonists

Two series of novel EPAC antagonists are designed, synthesized and evaluated in an effort to develop diversified analogues based on the scaffold of the previously identified high-throughput (HTS) hit 1 (ESI-09). Further SAR studies reveal that the isoxazole ring A of 1 can tolerate chemical modifications with either introduction of flexible electron-donating substitutions or structurally restrictedly fusing with a phenyl ring, leading to identification of several more potent and diversified EPAC antagonists (e.g., 10 (NY0617), 14 (NY0460), 26 (NY0725), 32 (NY0561), and 33 (NY0562)) with low micromolar inhibitory activities. Molecular docking studies on compounds 10 and 33 indicate that these two series of compounds bind at a similar site with substantially different interactions with the EPAC proteins. The findings may serve as good starting points for the development of more potent EPAC antagonists as valuable pharmacological probes or potential drug candidates.

Roles of roflumilast, a selective phosphodiesterase 4 inhibitor, in airway diseases

Asthma and chronic obstructive pulmonary disease (COPD) are common chronic respiratory diseases. Both diseases have incompletely distinct pathophysiology, clinical manifestation, and treatment responsiveness. Pulmonary and systemic inflammations are the hallmarks of COPD. Most asthma responds to inhaled corticosteroid (ICS) treatment. In contrast, COPD is a corticosteroid-resistant disease. Bronchodilators are a preferred treatment method of COPD, with the aim of improving symptoms and preventing exacerbation. In addition, corticosteroid insensitivity is an underlying mechanism in severe asthma. An overlap of features between asthma and COPD, which was described as asthma-COPD overlap syndrome (ACOS) is not uncommon in practice. Novel nonsteroidal therapies focusing on inflammation in asthma and COPD have been developed. Selective phosphodiesterase 4 (PDE4) inhibitor is a promising class of drugs that has been studied for the treatment of COPD. Selective PDE4 inhibitor is different from xanthine in terms of mechanisms and pharmacokinetic profiles. This review focuses on clinical data on PDE4 inhibitors and its future roles in asthma, COPD, bronchiectasis, ACOS and other chronic non-pulmonary diseases.

Microtubule-regulating proteins and cAMP-dependent signaling in neuroblastoma differentiation

Neurons are highly differentiated cells responsible for the conduction and transmission of information in the nervous system. The proper function of a neuron relies on the compartmentalization of their intracellular domains. Differentiated neuroblastoma cells have been extensively used to study and understand the physiology and cell biology of neuronal cells. Here, we show that differentiation of N1E-115 neuroblastoma cells is more pronounced upon exposure of a chemical analog of cyclic AMP (cAMP), db-cAMP. We next analysed the expression of key microtubule-regulating proteins in differentiated cells and the expression and activation of key cAMP players such as EPAC, PKA and AKAP79/150. Most of the microtubule-promoting factors were up regulated during differentiation of N1E-115 cells, while microtubule-destabilizing proteins were down regulated. We observed an increase in tubulin post-translational modifications related to microtubule stability. As expected, db-cAMP increased PKA- and EPAC-dependent signalling. Consistently, pharmacological modulation of EPAC activity instructed cell differentiation, number of neurites, and neurite length in N1E-115 cells. Moreover, disruption of the PKA-AKAP interaction reduced these morphometric parameters. Interestingly, PKA and EPAC act synergistically to induce neuronal differentiation in N1E-115. Altogether these results show that the changes observed in the differentiation of N1E-115 cells proceed by regulating several microtubule-stabilizing factors, and the acquisition of a neuronal phenotype is a process involving concerted although independent functions of EPAC and PKA.

Prostaglandin E2 Inhibition of IL-27 Production in Murine Dendritic Cells: A Novel Mechanism That Involves IRF1

IL-27, a multifunctional cytokine produced by APCs, antagonizes inflammation by affecting conventional dendritic cells (cDC), inducing IL-10, and promoting development of regulatory Tr1 cells. Although the mechanisms involved in IL-27 induction are well studied, much less is known about the factors that negatively impact IL-27 expression. PGE₂, a major immunomodulatory prostanoid, acts as a proinflammatory agent in several models of inflammatory/autoimmune disease, promoting primarily Th17 development and function. In this study, we report on a novel mechanism that promotes the proinflammatory function of PGE₂ We showed previously that PGE₂ inhibits IL-27 production in murine bone marrow-derived DCs. In this study, we show that, in addition to bone marrow-derived DCs, PGE₂ inhibits IL-27 production in macrophages and in splenic cDC, and we identify a novel pathway consisting of signaling through EP2/EP4→induction of cAMP→downregulation of IFN regulatory factor 1 expression and binding to the p28 IFN-stimulated response element site. The inhibitory effect of PGE₂ on p28 and irf1 expression does not involve endogenous IFN-β, STAT1, or STAT2, and inhibition of IL-27 does not appear to be mediated through PKA, exchange protein activated by cAMP, PI3K, or MAPKs. We observed similar inhibition of il27p28 expression in vivo in splenic DC following administration of dimethyl PGE₂ in conjunction with LPS. Based on the anti-inflammatory role of IL-27 in cDC and through the generation of Tr1 cells, we propose that the PGE₂-induced inhibition of IL-27 in activated cDC represents an important additional mechanism for its in vivo proinflammatory functions.

Epac2 contributes to PACAP-induced astrocytic differentiation through calcium ion influx in neural precursor cells

Astrocytes play a critical role in normal brain functions and maintaining the brain microenvironment, and defects in astrocytogenesis during neurodevelopment could give rise to severe mental illness and psychiatric disorders. During neuro-embryogenesis, astrocytogenesis involves astrocytic differentiation of neural precursor cells (NPCs) induced by signals from ciliary neurotrophic factor (CNTF) or pituitary adenylate cyclase-activating peptide (PACAP). However, in contrast to the CNTF signaling pathway, the exact mechanism underlying astrocytic differentiation induced by PACAP is unknown. In the present study, we aimed to verify a signaling pathway specific to PACAP-induced astrocytogenesis, using exchange protein directly activated by cAMP2 (Epac2)-knockout mice. We found that PACAP could trigger astrocytic differentiation of NPCs via Epac2 activation and an increase in the intracellular calcium concentration via a calcium ion influx. Taken together, we concluded that astrocytogenesis stimulated by PACAP occurs through a novel signaling pathway independent from CNTF-JAK/STAT signaling, that is the well-known pathway of astrocytogenesis. [BMB Reports 2016; 49(2): 128-133]

Cannabinoid receptor-2 stimulation suppresses neuroinflammation by regulating microglial M1/M2 polarization through the cAMP/PKA pathway in an experimental GMH rat model

Excessive inflammatory responses are involved in secondary brain injury during germinal matrix hemorrhage (GMH). The process of microglial polarization to the pro-inflammatory M1 or anti-inflammatory M2 phenotypes is considered to occur in a major immunomodulatory manner during brain inflammation. We previously found that cannabinoid receptor-2 (CB2R) stimulation attenuated microglial accumulation and brain injury following experimental GMH. However, whether CB2R has effects on microglial polarization after GMH remains unclear. Herein, we investigated the effects of CB2R stimulation on neuroinflammation after experimental GMH and the potential mechanisms that mediate M1/M2 microglial phenotype regulation. The results indicated that during the GMH acute phase, microglia primarily polarized to the M1 phenotype and induced an overwhelming release of pro-inflammatory cytokines. However, JWH133, a selective CB2R agonist, significantly prevented the pro-inflammatory cytokine release while promoting an M1 to M2 phenotype transformation in microglia, resulting in an increased anti-inflammatory cytokine release. Moreover, in thrombin-induced rat primary microglial cells, JWH133 reduced the pro-inflammatory cytokine levels and M1 phenotype by enhancing the acquisition of the M2 phenotype. Additionally, JWH133 facilitated synthesis of cyclic AMP (cAMP) and its downstream effectors, phosphorylated cAMP-dependent protein kinase (p-PKA) and exchange protein activated by cyclic-AMP 1 (Epac1). The promoting effects of JWH133 on M2 polarization were attenuated with a specific PKA inhibitor but not with an Epac inhibitor, indicating that the cAMP/PKA signaling pathway was involved in the JWH133 effects. This is the first study to propose that promotion of microglial M2 polarization through the cAMP/PKA pathway participates in the CB2R-mediated anti-inflammatory effects after GMH induction. The results will help to further understand the mechanisms that underlie neuroprotection by CB2R in GMH and promote clinical translational research for CB2R agonists.

Soluble Adenylyl Cyclase Is Required for Retinal Ganglion Cell and Photoreceptor Differentiation

Purpose

We have previously demonstrated that soluble adenylyl cyclase (sAC) is necessary for retinal ganglion cell (RGC) survival and axon growth. Here, we further investigate the role of sAC in neuronal differentiation during retinal development.

Methods

Chx10 or Math5 promoter-driven Cre-Lox recombination were used to conditionally delete sAC from early and intermediate retinal progenitor cells during retinal development. We examined cell type–specific markers expressed by retinal cells to estimate their relative numbers and characterize retinal laminar morphology by immunofluorescence in adult and newborn mice.

Results

Retinal ganglion cell and amacrine cell markers were significantly lower in the retinas of adult Math5^cre/sAC^fl/fl and Chx10^cre/sAC^fl/fl mice than in those of wild-type controls. The effect on RGC development was detectable as early as postnatal day 1 and deleting sAC in either Math5- or Chx10-expressing retinal progenitor cells also reduced nerve fiber layer thickness into adulthood. The thickness of the photoreceptor layer was slightly but statistically significantly decreased in both the newborn Chx10^cre/sAC^fl/fl and Math5^cre/sAC^fl/fl mice, but this reduction and abnormal morphology persisted in the adults in only the Chx10^cre/sAC^fl/fl mice.

Conclusions

sAC plays an important role in the early retinal development of RGCs as well as in the development of amacrine cells and to a lesser degree photoreceptors.

Pharmacological analysis of epithelial chloride secretion mechanisms in adult murine airways

Defective epithelial chloride secretion occurs in humans with cystic fibrosis (CF), a genetic defect due to loss of function of CFTR, a cAMP-activated chloride channel. In the airways, absence of an active CFTR causes a severe lung disease. In mice, genetic ablation of CFTR function does not result in similar lung pathology. This may be due to the expression of an alternative chloride channel which is activated by calcium. The most probable protein performing this function is TMEM16A, a calcium-activated chloride channel (CaCC). Our aim was to assess the relative contribution of CFTR and TMEM16A to chloride secretion in adult mouse trachea. For this purpose we tested pharmacological inhibitors of chloride channels in normal and CF mice. The amplitude of the cAMP-activated current was similar in both types of animals and was not affected by a selective CFTR inhibitor. In contrast, a CaCC inhibitor (CaCCinh-A01) strongly blocked the cAMP-activated current as well as the calcium-activated chloride secretion triggered by apical UTP. Although control experiments revealed that CaCCinh-A01 also shows inhibitory activity on CFTR, our results indicate that transepithelial chloride secretion in adult mouse trachea is independent of CFTR and that another channel, possibly TMEM16A, performs both cAMP- and calcium-activated chloride transport. The prevalent function of a non-CFTR channel may explain the absence of a defect in chloride transport in CF mice.

Role of EPAC in cAMP-Mediated Actions in Adrenocortical Cells

Adrenocorticotropic hormone regulates adrenal steroidogenesis mainly via the intracellular signaling molecule cAMP. The effects of cAMP are principally relayed by activating protein kinase A (PKA) and the more recently discovered exchange proteins directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). While the intracellular roles of PKA have been extensively studied in steroidogenic tissues, those of EPACs are only emerging. EPAC1 and EPAC2 are encoded by the genes RAPGEF3 and RAPGEF4, respectively. Whereas EPAC1 is ubiquitously expressed, the expression of EPAC2 is more restricted, and typically found in endocrine tissues. Alternative promoter usage of RAPGEF4 gives rise to three different isoforms of EPAC2 that vary in their N-termini (EPAC2A, EPAC2B, and EPAC2C) and that exhibit distinct expression patterns. EPAC2A is expressed in the brain and pancreas, EPAC2B in steroidogenic cells of the adrenal gland and testis, and EPAC2C has until now only been found in the liver. In this review, we discuss current knowledge on EPAC expression and function with focus on the known roles of EPAC in adrenal gland physiology.

Epac activation sensitizes rat sensory neurons through activation of Ras

Guanine nucleotide exchange factors directly activated by cAMP (Epacs) have emerged as important signaling molecules mediating persistent hypersensitivity in animal models of inflammation, by augmenting the excitability of sensory neurons. Although Epacs activate numerous downstream signaling cascades, the intracellular signaling which mediates Epac-induced sensitization of capsaicin-sensitive sensory neurons remains unknown. Here, we demonstrate that selective activation of Epacs with 8-CPT-2'-O-Me-cAMP-AM (8CPT-AM) increases the number of action potentials (APs) generated by a ramp of depolarizing current and augments the evoked release of calcitonin gene-related peptide (CGRP) from isolated rat sensory neurons. Internal perfusion of capsaicin-sensitive sensory neurons with GDP-βS, substituted for GTP, blocks the ability of 8CPT-AM to increase AP firing, demonstrating that Epac-induced sensitization is G-protein dependent. Treatment with 8CPT-AM activates the small G-proteins Rap1 and Ras in cultures of sensory neurons. Inhibition of Rap1, by internal perfusion of a Rap1-neutralizing antibody or through a reduction in the expression of the protein using shRNA does not alter the Epac-induced enhancement of AP generation or CGRP release, despite the fact that in most other cell types, Epacs act as Rap-GEFs. In contrast, inhibition of Ras through expression of a dominant negative Ras (DN-Ras) or through internal perfusion of a Ras-neutralizing antibody blocks the increase in AP firing and attenuates the increase in the evoked release of CGRP induced by Epac activation. Thus, in this subpopulation of nociceptive sensory neurons, it is the novel interplay between Epacs and Ras, rather than the canonical Epacs and Rap1 pathway, that is critical for mediating Epac-induced sensitization.