Subcellular Organization of the cAMP Signaling Pathway

CRHR1 endocytosis: Spatiotemporal regulation of receptor signaling

Corticotropin releasing hormone (CRH) is crucial for basal and stress-initiated reactions in the hypothalamic-pituitary-adrenal axis (HPA) and extrahypothalamic brain circuits, where it acts as a neuromodulator to organize behavioral and humoral responses to stress. We review and describe cellular components and molecular mechanisms involved in CRH system signaling through G protein-coupled receptors (GPCRs) CRHR1 and CRHR2, under the current view of GPCR signaling from the plasma membrane but also from intracellular compartments, which establish the bases of signal resolution in space and time. Focus is placed on latest studies of CRHR1 signaling in physiologically significant contexts of the neurohormone function that disclosed new mechanistic features of cAMP production and ERK1/2 activation. We also introduce in a brief overview the pathophysiological function of the CRH system, underlining the need for a complete characterization of CRHRs signaling to design new and specific therapies for stress-related disorders.

Chemical signaling in the developing avian retina: Focus on cyclic AMP and AKT-dependent pathways

Communication between developing progenitor cells as well as differentiated neurons and glial cells in the nervous system is made through direct cell contacts and chemical signaling mediated by different molecules. Several of these substances are synthesized and released by developing cells and play roles since early stages of Central Nervous System development. The chicken retina is a very suitable model for neurochemical studies, including the study of regulation of signaling pathways during development. Among advantages of the model are its very well-known histogenesis, the presence of most neurotransmitter systems found in the brain and the possibility to make cultures of neurons and/or glial cells where many neurochemical functions develop in a similar way than in the intact embryonic tissue. In the chicken retina, some neurotransmitters or neuromodulators as dopamine, adenosine, and others are coupled to cyclic AMP production or adenylyl cyclase inhibition since early stages of development. Other substances as vitamin C and nitric oxide are linked to the major neurotransmitter glutamate and AKT metabolism. All these different systems regulate signaling pathways, including PKA, PKG, SRC, AKT and ERK, and the activation of the transcription factor CREB. Dopamine and adenosine stimulate cAMP accumulation in the chick embryo retina through activation of D1 and A2a receptors, respectively, but the onset of dopamine stimulation is much earlier than that of adenosine. However, adenosine can inhibit adenylyl cyclase and modulate dopamine-dependent cAMP increase since early developmental stages through A1 receptors. Dopamine stimulates different PKA as well as EPAC downstream pathways both in intact tissue and in culture as the CSK-SRC pathway modulating glutamate NMDA receptors as well as vitamin C release and CREB phosphorylation. By the other hand, glutamate modulates nitric oxide production and AKT activation in cultured retinal cells and this pathway controls neuronal survival in retina. Glutamate and adenosine stimulate the release of vitamin C and this vitamin regulates the transport of glutamate, activation of NMDA receptors and AKT phosphorylation in cultured retinal cells. In the present review we will focus on these reciprocal interactions between neurotransmitters or neuromodulators and different signaling pathways during retinal development.

Cyclic Adenosine Monophosphate: A Central Player in Gamete Development and Fertilization, and Possible Target for Infertility Therapies

Human infertility, of both male and female origin, is often caused by the deficient response of the testis and the ovary to hormonal stimuli that govern sperm and oocyte development and fertilization. The effects of hormones and other extracellular ligands involved in these events are often mediated by G-protein-coupled receptors that employ cyclic adenosine monophosphate (cAMP) as the principal second messenger transducing the receptor-generated signal to downstream elements. This opinion article summarizes the actions of cAMP in sperm and oocyte development and fertilization, leading to therapeutic actions targeting cAMP metabolism to alleviate human male and female infertility.

cAMP-Dependent Signaling and Ovarian Cancer

cAMP-dependent pathway is one of the most significant signaling cascades in healthy and neoplastic ovarian cells. Working through its major effector proteins-PKA and EPAC-it regulates gene expression and many cellular functions. PKA promotes the phosphorylation of cAMP response element-binding protein (CREB) which mediates gene transcription, cell migration, mitochondrial homeostasis, cell proliferation, and death. EPAC, on the other hand, is involved in cell adhesion, binding, differentiation, and interaction between cell junctions. Ovarian cancer growth and metabolism largely depend on changes in the signal processing of the cAMP-PKA-CREB axis, often associated with neoplastic transformation, metastasis, proliferation, and inhibition of apoptosis. In addition, the intracellular level of cAMP also determines the course of other pathways including AKT, ERK, MAPK, and mTOR, that are hypo- or hyperactivated among patients with ovarian neoplasm. With this review, we summarize the current findings on cAMP signaling in the ovary and its association with carcinogenesis, multiplication, metastasis, and survival of cancer cells. Additionally, we indicate that targeting particular stages of cAMP-dependent processes might provide promising therapeutic opportunities for the effective management of patients with ovarian cancer.

Similarities and Differences between the Orai1 Variants: Orai1α and Orai1β

Orai1, the first identified member of the Orai protein family, is ubiquitously expressed in the animal kingdom. Orai1 was initially characterized as the channel responsible for the store-operated calcium entry (SOCE), a major mechanism that allows cytosolic calcium concentration increments upon receptor-mediated IP₃ generation, which results in intracellular Ca²⁺ store depletion. Furthermore, current evidence supports that abnormal Orai1 expression or function underlies several disorders. Orai1 is, together with STIM1, the key element of SOCE, conducting the Ca²⁺ release-activated Ca²⁺ (CRAC) current and, in association with TRPC1, the store-operated Ca²⁺ (SOC) current. Additionally, Orai1 is involved in non-capacitative pathways, as the arachidonate-regulated or LTC4-regulated Ca²⁺ channel (ARC/LRC), store-independent Ca²⁺ influx activated by the secretory pathway Ca²⁺-ATPase (SPCA2) and the small conductance Ca²⁺-activated K⁺ channel 3 (SK3). Furthermore, Orai1 possesses two variants, Orai1α and Orai1β, the latter lacking 63 amino acids in the N-terminus as compared to the full-length Orai1α form, which confers distinct features to each variant. Here, we review the current knowledge about the differences between Orai1α and Orai1β, the implications of the Ca²⁺ signals triggered by each variant, and their downstream modulatory effect within the cell.

Integrated analysis of mRNA and microRNA transcriptome related to immunity and autophagy in shrimp hemocytes infected with Spiroplasma eriocheiris

In recent years, the industry in charge of the cultivation of Macrobrachium nipponense (M.nipponense) has suffered significant economic losses due to an infectious pathogen called Spiroplasma eriocheiris (S.eriocheiris). There has therefore been a need to identify the key immune and autophagy genes that respond to M.nipponense's infection with S. eriocheiris to analyze its immune response mechanism and the regulation of related microRNAs (miRNAs). In this study, the mRNA and miRNA transcriptome of M.nipponense's hemocytes were analyzed at different stages of infection. This analysis employed the second and third-generation sequencing technologies. In the mRNA transcriptome, 1656 genes were expressed in healthy and susceptible M.nipponense. 892 of these were significantly up-regulated, while 764 were down-regulated. 118 genes with significant differences in autophagy, endocytosis, lysosome, Toll, IMD, and VEGF pathways were obtained from the transcriptome. In the miRNA transcriptome, 312 miRNAs (Conserved: 112, PN-type: 18, PC-type: 182) were sequenced. 74 were significantly up-regulated, and 57 were down-regulated. There were 25 miRNAs involved in regulating the Toll and IMD pathways, 41 in endocytosis, 30 in lysosome, and 12 in the VEGF pathway. An integrated analysis of immune-related miRNAs and mRNAs showed that miRNAs with significant differences (P < 0.05) such as ame-miR-29b-3p, dpu-miR-1and PC-3p-945_4074, had corresponding regulatory relationships with 118 important immune genes such as Relish, Dorsal, Caspase-3, and NF-κB. This study obtained the key immune and autophagy-related genes and corresponding regulatory miRNAs in M. nipponense's hemocytes in response to an infection by S.eriocheiris. The results can provide vital data that further reveals the defense mechanism of M.nipponense's immune system against S.eriocheiris. It can also help further comprehension and interpretation of M.nipponense's resistance mechanism to the invading S.eriocheiris, and provide molecular research information for the realization of host-directed therapies (HDT) for M.nipponense.

The role of the type 7 adenylyl cyclase isoform in alcohol use disorder and depression

The translation of extracellular signals to intracellular responses involves a number of signal transduction molecules. A major component of this signal transducing function is adenylyl cyclase, which produces the intracellular "second messenger," cyclic AMP. What was initially considered as a single enzyme for cyclic AMP generation is now known to be a family of nine membrane-bound enzymes, and one cytosolic enzyme. Each member of the adenylyl cyclase family is distinguished by factors that modulate its catalytic activity, by the cell, tissue, and organ distribution of the family members, and by the physiological/behavioral functions that are subserved by particular family members. This review focuses on the Type 7 adenylyl cyclase (AC7) in terms of its catalytic characteristics and its relationship to alcohol use disorder (AUD, alcoholism), and major depressive disorder (MDD). AC7 may be part of the inherited system predisposing an individual to AUD and/or MDD in a sex-specific manner, or this enzyme may change in its expression or activity in response to the progression of disease or in response to treatment. The areas of brain expressing AC7 are related to responses to stress and evidence is available that CRF1 receptors are coupled to AC7 in the amygdala and pituitary. Interestingly, AC7 is the major form of the cyclase contained in bone marrow-derived cells of the immune system and platelets, and in microglia. AC7 is thus, poised to play an integral role in both peripheral and brain immune function thought to be etiologically involved in both AUD and MDD. Both platelet and lymphocyte adenylyl cyclase activity have been proposed as markers for AUD and MDD, as well as prognostic markers of positive response to medication for MDD. We finish with consideration of paths to medication development that may selectively modulate AC7 activity as treatments for MDD and AUD.

Therapeutic strategy targeting host lipolysis limits infection by SARS-CoV-2 and influenza A virus

The biosynthesis of host lipids and/or lipid droplets (LDs) has been studied extensively as a putative therapeutic target in diverse viral infections. However, directly targeting the LD lipolytic catabolism in virus-infected cells has not been widely investigated. Here, we show the linkage of the LD-associated lipase activation to the breakdown of LDs for the generation of free fatty acids (FFAs) at the late stage of diverse RNA viral infections, which represents a broad-spectrum antiviral target. Dysfunction of membrane transporter systems due to virus-induced cell injury results in intracellular malnutrition at the late stage of infection, thereby making the virus more dependent on the FFAs generated from LD storage for viral morphogenesis and as a source of energy. The replication of SARS-CoV-2 and influenza A virus (IAV), which is suppressed by the treatment with LD-associated lipases inhibitors, is rescued by supplementation with FFAs. The administration of lipase inhibitors, either individually or in a combination with virus-targeting drugs, protects mice from lethal IAV infection and mitigates severe lung lesions in SARS-CoV-2-infected hamsters. Moreover, the lipase inhibitors significantly reduce proinflammatory cytokine levels in the lungs of SARS-CoV-2- and IAV-challenged animals, a cause of a cytokine storm important for the critical infection or mortality of COVID-19 and IAV patients. In conclusion, the results reveal that lipase-mediated intracellular LD lipolysis is commonly exploited to facilitate RNA virus replication and furthermore suggest that pharmacological inhibitors of LD-associated lipases could be used to curb current COVID-19- and future pandemic outbreaks of potentially troublesome RNA virus infection in humans.

Role of the cAMP signaling pathway in the dissemination and development on pepper fruit anthracnose disease caused by Colletotrichum scovillei

The ascomycete fungus Colletotrichum scovillei causes severe anthracnose disease on the fruit of sweet pepper and chili pepper (Capsicum annuum L.) worldwide. Understanding the biology of C. scovillei would improve the management of fruit anthracnose diseases. The cyclic adenosine monophosphate (cAMP) signaling pathway regulates diverse cellular and physiological processes in several foliar fungal pathogens. We investigated the roles of the cAMP signaling pathway in C. scovillei using pharmaceutical and genetic approaches. Exogenous cAMP was found to increase conidiation, appressorium formation, and anthracnose disease development in C. scovillei. CsAc1, CsCap1, and CsPdeH, which regulate the intracellular cAMP level, were deleted by homology-dependent gene replacement. Expectedly, the intracellular cAMP level was significantly decreased in ΔCsac1 and ΔCscap1 but increased in ΔCspdeh. All three deletion mutants exhibited serious defects in multiple fungal developments and pathogenicity, suggesting regulation of the intracellular cAMP level is important for C. scovillei. Notably, exogenous cAMP recovered the defect of ΔCsac1 in appressorium development, but not penetration, which was further recovered by adding CaCl2. This result suggests that CsAc1 is associated with both the cAMP and Ca2+ signaling pathways in C. scovillei. ΔCscap1 produced morphologically abnormal conidia with reduced tolerance to thermal stress. ΔCspdeh was completely defective in conidiation in C. scovillei, unlike other foliar pathogens. Taken together, these results demonstrate the importance of cAMP signaling in anthracnose disease caused by C. scovillei.

A multi-adenylate cyclase regulator at the flagellar tip controls African trypanosome transmission

Signaling from ciliary microdomains controls developmental processes in metazoans. Trypanosome transmission requires development and migration in the tsetse vector alimentary tract. Flagellar cAMP signaling has been linked to parasite social motility (SoMo) in vitro, yet uncovering control of directed migration in fly organs is challenging. Here we show that the composition of an adenylate cyclase (AC) complex in the flagellar tip microdomain is essential for tsetse salivary gland (SG) colonization and SoMo. Cyclic AMP response protein 3 (CARP3) binds and regulates multiple AC isoforms. CARP3 tip localization depends on the cytoskeletal protein FLAM8. Re-localization of CARP3 away from the tip microdomain is sufficient to abolish SoMo and fly SG colonization. Since intrinsic development is normal in carp3 and flam8 knock-out parasites, AC complex-mediated tip signaling specifically controls parasite migration and thereby transmission. Participation of several developmentally regulated receptor-type AC isoforms may indicate the complexity of the in vivo signals perceived.

Trypanosomes can sense signal molecules and coordinate their movement in response to such signals, a phenomenon termed social motility (SoMo). Here, Bachmaier et al show that cyclic AMP response protein 3 (CARP3) localization to the flagellar tip and its interaction with a number of different adenylate cyclases is essential for migration to tsetse fly salivary glands and for SoMo, therewith linking SoMo and cAMP signaling to trypanosome transmission.

Probing spatiotemporal PKA activity at the ryanodine receptor and SERCA2a nanodomains in cardomyocytes

Spatiotemporal regulation of subcellular protein kinase A (PKA) activity for precise substrate phosphorylation is essential for cellular responses to hormonal stimulation. Ryanodine receptor 2 (RyR2) and (sarco)endoplasmic reticulum calcium ATPase 2a (SERCA2a) represent two critical targets of β adrenoceptor (βAR) signaling on the sarcoplasmic reticulum membrane for cardiac excitation and contraction coupling. Using novel biosensors, we show that cardiac β1AR signals to both RyR2 and SERCA2a nanodomains in cardiomyocytes from mice, rats, and rabbits, whereas the β2AR signaling is restricted from these nanodomains. Phosphodiesterase 4 (PDE4) and PDE3 control the baseline PKA activity and prevent β2AR signaling from reaching the RyR2 and SERCA2a nanodomains. Moreover, blocking inhibitory G protein allows β2AR signaling to the RyR2 but not the SERCA2a nanodomains. This study provides evidence for the differential roles of inhibitory G protein and PDEs in controlling the adrenergic subtype signaling at the RyR2 and SERCA2a nanodomains in cardiomyocytes.

Inhibition of adenylyl cyclase 1 by ST034307 inhibits IP3-evoked changes in sino-atrial node beat rate

Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial-specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. We investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sino-atrial node (SAN) cells to the α-adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.5% to 8.2% (p = 0.005) in the presence of 1 μM ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.2%, ST034307 = 16.3%; p > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transients (CaT) generated by 10 μM PE in the presence and absence of 1 μM ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; p = 0.003) but did not inhibit changes in CaT amplitude in response to PE in atrial cells. The results presented here demonstrate pharmacologically the involvement of AC1 in the downstream response of atrial pacemaker activity to α-adrenoreceptor stimulation and IP3R calcium release.

Eugenol, A Major Component of Clove Oil, Attenuates Adiposity and Modulates Gut Microbiota in High-Fat Diet-fed Mice

SCOPE

Eugenol (EU), the major aromatic compound derived from clove oil, is being focused recently due to its potential in preventing several chronic conditions. Herein, we aimed to evaluate the potential of EU in obesity prevention and to delineate the mechanisms involved.

METHODS AND RESULTS

Five-week-old male C57BL/6J mice were fed with high-fat diet (HFD) or HFD supplemented with EU (0.2%, w/w) for 13 weeks. EU significantly reduced obesity-related indexes including final body weight, body weight gain, adipocyte size, visceral fat-pad weight, and fasting blood glucose. EU prevented HFD-induced gut dysbiosis, as indicated by the increase of Firmicutes and decrease of Desulfobacterota at phylum level, and the increase of Dubosiella, Blautia, unclassified_f_Oscillospiraceae, and unclassified_f_Ruminococcaceae, and the decrease of Alistipes, Alloprevotella, and Bilophila at genus level. Notably, the obesity-related indexes were positively correlated with the relative abundances of Bacteroides, unclassified_f_Lachnospiraceae, Colidextribacter, and Bilophila, and negatively correlated with the relative abundances of norank_f_Muribaculaceae and Lachnospiraceae_NK4A136_group. Moreover, the preventive effects of EU on obesity were accompanied by the transcriptomic reprogramming of white adipose tissue.

CONCLUSION

These findings demonstrated that EU prevents the HFD-induced adiposity and modulates gut dysbiosis, and highlighted the potential of EU in obesity intervention as a functional dietary supplement. This article is protected by copyright. All rights reserved.

Strategies to safely target widely expressed soluble adenylyl cyclase for contraception

In humans, the prototypical second messenger cyclic AMP is produced by 10 adenylyl cyclase isoforms, which are divided into two classes. Nine isoforms are G protein coupled transmembrane adenylyl cyclases (tmACs; ADCY1-9) and the 10th is the bicarbonate regulated soluble adenylyl cyclase (sAC; ADCY10). This review details why sAC is uniquely druggable and outlines ways to target sAC for novel forms of male and female contraception.

A cAMP Sensor Based on Ligand-Dependent Protein Stabilization

cAMP is a ubiquitous second messenger with many functions in diverse organisms. Current cAMP sensors, including Föster resonance energy transfer (FRET)-based and single-wavelength-based sensors, allow for real time visualization of this small molecule in cultured cells and in some cases in vivo. Nonetheless the observation of cAMP in living animals is still difficult, typically requiring specialized microscopes and ex vivo tissue processing. Here we used ligand-dependent protein stabilization to create a new cAMP sensor. This sensor allows specific and sensitive detection of cAMP in living zebrafish embryos, which may enable new understanding of the functions of cAMP in living vertebrates.

Negative Feedback of the cAMP/PKA Pathway Regulates the Effects of Endoplasmic Reticulum Stress-Induced NLRP3 Inflammasome Activation on Type II Alveolar Epithelial Cell Pyroptosis as a Novel Mechanism of BLM-Induced Pulmonary Fibrosis

Endoplasmic reticulum stress (ER stress) contributes to the development of pulmonary fibrosis, especially in type II alveolar epithelial cells (AECs) apoptosis. ER stress also promotes NLRP3 inflammasome activation which is inhibited by upregulation of cAMP/PKA pathway. However, it is confused whether ER stress-induced NLRP3 inflammasome activation and pyroptosis in type II alveolar epithelial cells which exacerbates pulmonary fibrosis via a mechanism that is suppressed by cAMP/PKA pathway. In our research, we explored that potential links among NLRP3 inflammasome, ER stress, and cAMP/PKA pathway in type II AECs to explain the new mechanisms of pulmonary fibrosis. We found that in vivo, ER stress, NLRP3 inflammasome, and PKA upregulated in the alveolar epithelial area in animal models of pulmonary fibrosis. In addition, immunofluorescence staining further confirmed that ER stress, NLRP3 inflammasome, and cAMP/PKA had potential links on type II AECs in BLM group. In vitro, ER stress stimulated NLRP3 inflammasome activation, promoted pyroptosis, and also upregulated cAMP/PKA pathway. Upregulation of cAMP/PKA pathway inhibited ER stress-induced pyroptosis of A549 cells and vice versa. These results initially supported conclusion that ER stress may stimulate NLRP3 inflammasome activation and pyroptosis in type II AECs, which exacerbated pulmonary fibrosis, and cAMP/PKA pathway may act as a feedback regulator.

Mice Lacking the cAMP Effector Protein POPDC1 Show Enhanced Hippocampal Synaptic Plasticity

Extensive research has uncovered diverse forms of synaptic plasticity and an array of molecular signaling mechanisms that act as positive or negative regulators. Specifically, cyclic 3',5'-cyclic adenosine monophosphate (cAMP)-dependent signaling pathways are crucially implicated in long-lasting synaptic plasticity. In this study, we examine the role of Popeye domain-containing protein 1 (POPDC1) (or blood vessel epicardial substance (BVES)), a cAMP effector protein, in modulating hippocampal synaptic plasticity. Unlike other cAMP effectors, such as protein kinase A (PKA) and exchange factor directly activated by cAMP, POPDC1 is membrane-bound and the sequence of the cAMP-binding cassette differs from canonical cAMP-binding domains, suggesting that POPDC1 may have an unique role in cAMP-mediated signaling. Our results show that Popdc1 is widely expressed in various brain regions including the hippocampus. Acute hippocampal slices from Popdc1 knockout (KO) mice exhibit PKA-dependent enhancement in CA1 long-term potentiation (LTP) in response to weaker stimulation paradigms, which in slices from wild-type mice induce only transient LTP. Loss of POPDC1, while not affecting basal transmission or input-specificity of LTP, results in altered response during high-frequency stimulation. Popdc1 KO mice also show enhanced forskolin-induced potentiation. Overall, these findings reveal POPDC1 as a novel negative regulator of hippocampal synaptic plasticity and, together with recent evidence for its interaction with phosphodiesterases (PDEs), suggest that POPDC1 is involved in modulating activity-dependent local cAMP-PKA-PDE signaling.

A cAMP signalosome in primary cilia drives gene expression and kidney cyst formation

The primary cilium constitutes an organelle that orchestrates signal transduction independently from the cell body. Dysregulation of this intricate molecular architecture leads to severe human diseases, commonly referred to as ciliopathies. However, the molecular underpinnings how ciliary signaling orchestrates a specific cellular output remain elusive. By combining spatially resolved optogenetics with RNA sequencing and imaging, we reveal a novel cAMP signalosome that is functionally distinct from the cytoplasm. We identify the genes and pathways targeted by the ciliary cAMP signalosome and shed light on the underlying mechanisms and downstream signaling. We reveal that chronic stimulation of the ciliary cAMP signalosome transforms kidney epithelia from tubules into cysts. Counteracting this chronic cAMP elevation in the cilium by small molecules targeting activation of phosphodiesterase-4 long isoforms inhibits cyst growth. Thereby, we identify a novel concept of how the primary cilium controls cellular functions and maintains tissue integrity in a specific and spatially distinct manner and reveal novel molecular components that might be involved in the development of one of the most common genetic diseases, polycystic kidney disease.

Absence of EPAC1 Signaling to Stabilize CFTR in Intestinal Organoids

The plasma membrane (PM) stability of the cystic fibrosis transmembrane conductance regulator (CFTR), the protein which when mutated causes Cystic Fibrosis (CF), relies on multiple interaction partners that connect CFTR to signaling pathways, including cAMP signaling. It was previously shown that activation of exchange protein directly activated by cAMP 1 (EPAC1) by cAMP promotes an increase in CFTR PM levels in airway epithelial cells. However, the relevance of this pathway in other tissues, particularly the intestinal tissue, remains uncharacterized. Here, we used Western blot and forskolin-induced swelling assay to demonstrate that the EPAC1 protein is not expressed in the intestinal organoid model, and consequently the EPAC1 stabilization pathway is not in place. On the other hand, using cell surface biotinylation, EPAC1-mediated stabilization of PM CFTR is observed in intestinal cell lines. These results indicate that the EPAC1 stabilization pathway also occurs in intestinal cells and is a potential target for the development of novel combinatorial therapies for treatment of CF.

Monoamine oxidase A and organic cation transporter 3 coordinate intracellular β1AR signaling to calibrate cardiac contractile function

We have recently identified a pool of intracellular β1 adrenergic receptors (β1ARs) at the sarcoplasmic reticulum (SR) crucial for cardiac function. Here, we aim to characterize the integrative control of intracellular catecholamine for subcellular β1AR signaling and cardiac function. Using anchored Förster resonance energy transfer (FRET) biosensors and transgenic mice, we determined the regulation of compartmentalized β1AR-PKA signaling at the SR and plasma membrane (PM) microdomains by organic cation transporter 3 (OCT3) and monoamine oxidase A (MAO-A), two critical modulators of catecholamine uptake and homeostasis. Additionally, we examined local PKA substrate phosphorylation and excitation-contraction coupling in cardiomyocyte. Cardiac-specific deletion of MAO-A (MAO-A-CKO) elevates catecholamines and cAMP levels in the myocardium, baseline cardiac function, and adrenergic responses. Both MAO-A deletion and inhibitor (MAOi) selectively enhance the local β1AR-PKA activity at the SR but not PM, and augment phosphorylation of phospholamban, Ca2+ cycling, and myocyte contractile response. Overexpression of MAO-A suppresses the SR-β1AR-PKA activity and PKA phosphorylation. However, deletion or inhibition of OCT3 by corticosterone prevents the effects induced by MAOi and MAO-A deletion in cardiomyocytes. Deletion or inhibition of OCT3 also negates the effects of MAOi and MAO-A deficiency in cardiac function and adrenergic responses in vivo. Our data show that MAO-A and OCT3 act in concert to fine-tune the intracellular SR-β1AR-PKA signaling and cardiac fight-or-flight response. We reveal a drug contraindication between anti-inflammatory corticosterone and anti-depressant MAOi in modulating adrenergic regulation in the heart, providing novel perspectives of these drugs with cardiac implications.

Green fluorescent cAMP indicator of high speed and specificity suitable for neuronal live-cell imaging

Cyclic adenosine monophosphate (cAMP) is a canonical intracellular messenger playing diverse roles in cell functions. In neurons, cAMP promotes axonal growth during early development, and mediates sensory transduction and synaptic plasticity after maturation. The molecular cascades of cAMP are well documented, but its spatiotemporal profiles associated with neuronal functions remain hidden. Hence, we developed a genetically encoded cAMP indicator based on a bacterial cAMP-binding protein. This indicator "gCarvi" monitors [cAMP]i at 0.2 to 20 µM with a subsecond time resolution and a high specificity over cyclic guanosine monophosphate (cGMP). gCarvi can be converted to a ratiometric probe for [cAMP]i quantification and its expression can be specifically targeted to various subcellular compartments. Monomeric gCarvi also enables simultaneous multisignal monitoring in combination with other indicators. As a proof of concept, simultaneous cAMP/Ca2+ imaging in hippocampal neurons revealed a tight linkage of cAMP to Ca2+ signals. In cerebellar presynaptic boutons, forskolin induced nonuniform cAMP elevations among boutons, which positively correlated with subsequent increases in the size of the recycling pool of synaptic vesicles assayed using FM dye. Thus, the cAMP domain in presynaptic boutons is an important determinant of the synaptic strength.

cAMP Signaling in Cancer: A PKA-CREB and EPAC-Centric Approach

Cancer is one of the most common causes of death globally. Despite extensive research and considerable advances in cancer therapy, the fundamentals of the disease remain unclear. Understanding the key signaling mechanisms that cause cancer cell malignancy may help to uncover new pharmaco-targets. Cyclic adenosine monophosphate (cAMP) regulates various biological functions, including those in malignant cells. Understanding intracellular second messenger pathways is crucial for identifying downstream proteins involved in cancer growth and development. cAMP regulates cell signaling and a variety of physiological and pathological activities. There may be an impact on gene transcription from protein kinase A (PKA) as well as its downstream effectors, such as cAMP response element-binding protein (CREB). The position of CREB downstream of numerous growth signaling pathways implies its oncogenic potential in tumor cells. Tumor growth is associated with increased CREB expression and activation. PKA can be used as both an onco-drug target and a biomarker to find, identify, and stage tumors. Exploring cAMP effectors and their downstream pathways in cancer has become easier using exchange protein directly activated by cAMP (EPAC) modulators. This signaling system may inhibit or accelerate tumor growth depending on the tumor and its environment. As cAMP and its effectors are critical for cancer development, targeting them may be a useful cancer treatment strategy. Moreover, by reviewing the material from a distinct viewpoint, this review aims to give a knowledge of the impact of the cAMP signaling pathway and the related effectors on cancer incidence and development. These innovative insights seek to encourage the development of novel treatment techniques and new approaches.

An Improved Genetically Encoded Fluorescent cAMP Indicator for Sensitive cAMP Imaging and Fast Drug Screening

Cyclic adenosine 3',5'-monophosphate (cAMP) is an important intracellular second messenger molecule downstream of many G protein-coupled receptors (GPCRs). Fluorescence imaging with bright and sensitive cAMP indicators allows not only dissecting the spatiotemporal dynamics of intracellular cAMP, but also high-content screening of compounds against GPCRs. We previously reported the high-performance circularly permuted GFP (cpGFP)-based cAMP indicator G-Flamp1. Here, we developed improved G-Flamp1 variants G-Flamp2 and G-Flamp2b. Compared to G-Flamp1, G-Flamp2 exhibited increased baseline fluorescence (1.6-fold) and larger fluorescence change (ΔF/F0) (1,300% vs. 1,100%) in HEK293T cells, while G-Flamp2b showed increased baseline fluorescence (3.1-fold) and smaller ΔF/F0 (400% vs. 1,100%). Furthermore, live cell imaging of mitochondrial matrix-targeted G-Flamp2 confirmed cytosolic cAMP was able to enter the mitochondrial matrix. G-Flamp2 imaging also showed that adipose tissue extract activated the Gi protein-coupled orphan GPCR GPR50 in HEK293T cells. Taken together, our results showed that the high-performance of G-Flamp2 would facilitate sensitive intracellular cAMP imaging and activity measurement of compounds targeting GPCR-cAMP signaling pathway during early drug development.

Bupleurum chinense DC improves CUMS-induced depressive symptoms in rats through upregulation of the cAMP/PKA/CREB signalling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Bupleurum chinense DC. (B. chinense) is the dried root of B. chinense, belonging to the Umbelliferae family. B. chinense has been reported since ancient times for its effect of soothing the liver and relieving depression. Additionally, its important role in treating depression, depressed mood disorders and anti-inflammation has been proven in previous studies. However, its specific mechanism of action remains unknown.

AIM OF THE STUDY

The key targets and metabolites of the antidepressant effect of B. chinense were investigated based on the cAMP signalling pathway. The study examined the mechanism for the antidepressant effect of B. chinense by target prediction, analysis of related metabolites and potential metabolic pathways.

MATERIALS AND METHODS

A network pharmacology approach was used to predict the antidepressant targets and pathways of B. chinense. A depression rat model was established through the CUMS (chronic unpredictable mild stress) procedure. The depression model was assessed by body weight, sugar-water preference, water maze and enzyme-linked immunosorbent assay (ELISA) indicators (5hydroxytryptamine, etc.). The key metabolic pathways were screened by correlations between metabolites and key targets. Finally, a quantitative analysis of key targets and metabolites was experimentally validated.

RESULTS

B. chinense significantly ameliorated the reduction in body weight, sugar-water preference rate and cognitive performance in the water maze experiment in rats with depression induced by CUMS. ELISA, Western blotting (WB) and reverse transcription-polymerase chain reaction (RT-PCR) assays showed that B. chinense significantly improves the expression of protein kinase cyclic adenylic acid (cAMP)-activated catalytic subunit alpha (PRKACA), cAMP-response element-binding protein (CREB) and cAMP activation in the rat brain induced by CUMS. According to metabolic pathway analysis, B. chinense shows an antidepressant effect primarily by regulating the cAMP metabolic pathway.

CONCLUSION

B. chinense upregulated PRKACA and CREB expression and the level of the key metabolite cAMP in the cAMP/PKA/CREB pathway while reducing the inflammatory response to depression treatment. These new findings support future research on the antidepressant effects of B. chinense.

A multiscale model of the regulation of aquaporin 2 recycling

The response of cells to their environment is driven by a variety of proteins and messenger molecules. In eukaryotes, their distribution and location in the cell are regulated by the vesicular transport system. The transport of aquaporin 2 between membrane and storage region is a crucial part of the water reabsorption in renal principal cells, and its malfunction can lead to Diabetes insipidus. To understand the regulation of this system, we aggregated pathways and mechanisms from literature and derived three models in a hypothesis-driven approach. Furthermore, we combined the models to a single system to gain insight into key regulatory mechanisms of Aquaporin 2 recycling. To achieve this, we developed a multiscale computational framework for the modeling and simulation of cellular systems. The analysis of the system rationalizes that the compartmentalization of cAMP in renal principal cells is a result of the protein kinase A signalosome and can only occur if specific cellular components are observed in conjunction. Endocytotic and exocytotic processes are inherently connected and can be regulated by the same protein kinase A signal.

Neuronal ER-Signalosome Proteins as Early Biomarkers in Prodromal Alzheimer's Disease Independent of Amyloid-β Production and Tau Phosphorylation

There exists considerable interest to unveil preclinical period and prodromal stages of Alzheimer's disease (AD). The mild cognitive impairment (MCI) is characterized by significant memory and/or other cognitive domains impairments, and is often considered the prodromal phase of AD. The cerebrospinal fluid (CSF) levels of β-amyloid (βA), total tau (t-tau), and phosphorylated tau (p-tau) have been used as biomarkers of AD albeit their significance as indicators during early stages of AD remains far from accurate. The new biomarkers are being intensively sought as to allow identification of pathological processes underlying early stages of AD. Fifty-three participants (75.4 ± 8.3 years) were classified in three groups as cognitively normal healthy controls (HC), MCI, and subjective memory complaints (SMC). The subjects were subjected to a battery of neurocognitive tests and underwent lumbar puncture for CSF extraction. The CSF levels of estrogen-receptor (ER)-signalosome proteins, βA, t-tau and p-tau, were submitted to univariate, bivariate, and multivariate statistical analyses. We have found that the components of the ER-signalosome, namely, caveolin-1, flotilin-1, and estrogen receptor alpha (ERα), insulin growth factor-1 receptor β (IGF1Rβ), prion protein (PrP), and plasmalemmal voltage dependent anion channel 1 (VDAC) could be detected in the CSF from all subjects of the HC, MCI, and SMC groups. The six proteins appeared elevated in MCI and slightly increased in SMC subjects compared to HC, suggesting that signalosome proteins undergo very early modifications in nerve cells. Using a multivariate approach, we have found that the combination of ERα, IGF-1Rβ, and VDAC are the main determinants of group segregation with resolution enough to predict the MCI stage. The analyses of bivariate relationships indicated that collinearity of ER-signalosome proteins vary depending on the stage, with some pairs displaying opposed relationships between HC and MCI groups, and the SMC stage showing either no relationships or behaviors similar to either HC or MCI stages. The multinomial logistic regression models of changes in ER-signalosome proteins provide reliable predictive criteria, particularly for the MCI. Notably, most of the statistical analyses revealed no significant relationships or interactions with classical AD biomarkers at either disease stage. Finally, the multivariate functions were highly correlated with outcomes from neurocognitive tests for episodic memory. These results demonstrate that alterations in ER-signalosome might provide useful diagnostic information on preclinical stages of AD, independently from classical biomarkers.

The organic cation Transporter 2 regulates dopamine D1 receptor signaling at the Golgi apparatus

Dopamine is a key catecholamine in the brain and kidney, where it is involved in a number of physiological functions such as locomotion, cognition, emotion, endocrine regulation, and renal function. As a membrane-impermeant hormone and neurotransmitter, dopamine is thought to signal by binding and activating dopamine receptors, members of the G protein coupled receptor (GPCR) family, only on the plasma membrane. Here, using novel nanobody-based biosensors, we demonstrate for the first time that the dopamine D1 receptor (D1DR), the primary mediator of dopaminergic signaling in the brain and kidney, not only functions on the plasma membrane but becomes activated at the Golgi apparatus in the presence of its ligand. We present evidence that activation of the Golgi pool of D1DR is dependent on organic cation transporter 2 (OCT2), a dopamine transporter, providing an explanation for how the membrane-impermeant dopamine accesses subcellular pools of D1DR. We further demonstrate that dopamine activates Golgi-D1DR in murine striatal medium spiny neurons, and this activity depends on OCT2 function. We also introduce a new approach to selectively interrogate compartmentalized D1DR signaling by inhibiting Gαs coupling using a nanobody-based chemical recruitment system. Using this strategy, we show that Golgi-localized D1DRs regulate cAMP production and mediate local protein kinase A activation. Together, our data suggest that spatially compartmentalized signaling hubs are previously unappreciated regulatory aspects of D1DR signaling. Our data provide further evidence for the role of transporters in regulating subcellular GPCR activity.

G-Protein Coupled Receptor Signaling and Mammalian Target of Rapamycin Complex 1 Regulation

The mammalian target of rapamycin (mTOR) senses upstream stimuli to regulate numerous cellular functions such as metabolism, growth, and autophagy. Increased activation of mTOR complex 1 (mTORC1) is typically observed in human disease and continues to be an important therapeutic target. Understanding the upstream regulators of mTORC1 will provide a crucial link in targeting hyperactivated mTORC1 in human disease. In this mini-review, we will discuss the regulation of mTORC1 by upstream stimuli, with a specific focus on G-protein coupled receptor signaling to mTORC1. SIGNIFICANCE STATEMENT: mTORC1 is a master regulator of many cellular processes and is often hyperactivated in human disease. Therefore, understanding the molecular underpinnings of G-protein coupled receptor signaling to mTORC1 will undoubtedly be beneficial for human disease.

Receptor-associated independent cAMP nanodomains mediate spatiotemporal specificity of GPCR signaling

G protein-coupled receptors (GPCRs) relay extracellular stimuli into specific cellular functions. Cells express many different GPCRs, but all these GPCRs signal to only a few second messengers such as cAMP. It is largely unknown how cells distinguish between signals triggered by different GPCRs to orchestrate their complex functions. Here, we demonstrate that individual GPCRs signal via receptor-associated independent cAMP nanodomains (RAINs) that constitute self-sufficient, independent cell signaling units. Low concentrations of glucagon-like peptide 1 (GLP-1) and isoproterenol exclusively generate highly localized cAMP pools around GLP-1- and β₂-adrenergic receptors, respectively, which are protected from cAMP originating from other receptors and cell compartments. Mapping local cAMP concentrations with engineered GPCR nanorulers reveals gradients over only tens of nanometers that define the size of individual RAINs. The coexistence of many such RAINs allows a single cell to operate thousands of independent cellular signals simultaneously, rather than function as a simple "on/off" switch.

Tuning the Consonance of Microscopic Neuro-Cardiac Interactions Allows the Heart Beats to Play Countless Genres

Different from skeletal muscle, the heart autonomously generates rhythmic contraction independently from neuronal inputs. However, speed and strength of the heartbeats are continuously modulated by environmental, physical or emotional inputs, delivered by cardiac innervating sympathetic neurons, which tune cardiomyocyte (CM) function, through activation of β-adrenoceptors (β-ARs). Given the centrality of such mechanism in heart regulation, β-AR signaling has been subject of intense research, which has reconciled the molecular details of the transduction pathway and the fine architecture of cAMP signaling in subcellular nanodomains, with its final effects on CM function. The importance of mechanisms keeping the elements of β-AR/cAMP signaling in good order emerges in pathology, when the loss of proper organization of the transduction pathway leads to detuned β-AR/cAMP signaling, with detrimental consequences on CM function. Despite the compelling advancements in decoding cardiac β-AR/cAMP signaling, most discoveries on the subject were obtained in isolated cells, somehow neglecting that complexity may encompass the means in which receptors are activated in the intact heart. Here, we outline a set of data indicating that, in the context of the whole myocardium, the heart orchestra (CMs) is directed by a closely interacting and continuously attentive conductor, represented by SNs. After a roundup of literature on CM cAMP regulation, we focus on the unexpected complexity and roles of cardiac sympathetic innervation, and present the recently discovered Neuro-Cardiac Junction, as the election site of "SN-CM" interaction. We further discuss how neuro-cardiac communication is based on the combination of extra- and intra-cellular signaling micro/nano-domains, implicating neuronal neurotransmitter exocytosis, β-ARs and elements of cAMP homeostasis in CMs, and speculate on how their dysregulation may reflect on dysfunctional neurogenic control of the heart in pathology.

Multifaceted Roles of cAMP Signaling in the Repair Process of Spinal Cord Injury and Related Combination Treatments

Spinal cord injury (SCI) results in multiple pathophysiological processes, including blood–spinal cord barrier disruption, hemorrhage/ischemia, oxidative stress, neuroinflammation, scar formation, and demyelination. These responses eventually lead to severe tissue destruction and an inhibitory environment for neural regeneration.cAMP signaling is vital for neurite outgrowth and axonal guidance. Stimulating intracellular cAMP activity significantly promotes neuronal survival and axonal regrowth after SCI.However, neuronal cAMP levels in adult CNS are relatively low and will further decrease after injury. Targeting cAMP signaling has become a promising strategy for neural regeneration over the past two decades. Furthermore, studies have revealed that cAMP signaling is involved in the regulation of glial cell function in the microenvironment of SCI, including macrophages/microglia, reactive astrocytes, and oligodendrocytes. cAMP-elevating agents in the post-injury milieu increase the cAMP levels in both neurons and glial cells and facilitate injury repair through the interplay between neurons and glial cells and ultimately contribute to better morphological and functional outcomes. In recent years, combination treatments associated with cAMP signaling have been shown to exert synergistic effects on the recovery of SCI. Agents carried by nanoparticles exhibit increased water solubility and capacity to cross the blood–spinal cord barrier. Implanted bioscaffolds and injected hydrogels are potential carriers to release agents locally to avoid systemic side effects. Cell transplantation may provide permissive matrices to synergize with the cAMP-enhanced growth capacity of neurons. cAMP can also induce the oriented differentiation of transplanted neural stem/progenitor cells into neurons and increase the survival rate of cell grafts. Emerging progress focused on cAMP compartmentation provides researchers with new perspectives to understand the complexity of downstream signaling, which may facilitate the clinical translation of strategies targeting cAMP signaling for SCI repair.

Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts

Cardiac contractility is regulated by several neural, hormonal, paracrine, and autocrine factors. Amongst these, signaling through β-adrenergic and serotonin receptors generates the second messenger cyclic AMP (cAMP), whereas activation of natriuretic peptide receptors and soluble guanylyl cyclases generates cyclic GMP (cGMP). Both cyclic nucleotides regulate cardiac contractility through several mechanisms. Phosphodiesterases (PDEs) are enzymes that degrade cAMP and cGMP and therefore determine the dynamics of their downstream effects. In addition, the intracellular localization of the different PDEs may contribute to regulation of compartmented signaling of cAMP and cGMP. In this review, we will focus on the role of PDEs in regulating contractility and evaluate changes in heart failure.

Cardiac Transverse Tubules in Physiology and Heart Failure

In mammalian cardiac myocytes, the plasma membrane includes the surface sarcolemma but also a network of membrane invaginations called transverse (t-) tubules. These structures carry the action potential deep into the cell interior, allowing efficient triggering of Ca2+ release and initiation of contraction. Once thought to serve as rather static enablers of excitation-contraction coupling, recent work has provided a newfound appreciation of the plasticity of the t-tubule network's structure and function. Indeed, t-tubules are now understood to support dynamic regulation of the heartbeat across a range of timescales, during all stages of life, in both health and disease. This review article aims to summarize these concepts, with consideration given to emerging t-tubule regulators and their targeting in future therapies.

Engineered synaptic tools reveal localized cAMP signaling in synapse assembly

The physiological mechanisms driving synapse formation are elusive. Although numerous signals are known to regulate synapses, it remains unclear which signaling mechanisms organize initial synapse assembly. Here, we describe new tools, referred to as "SynTAMs" for synaptic targeting molecules, that enable localized perturbations of cAMP signaling in developing postsynaptic specializations. We show that locally restricted suppression of postsynaptic cAMP levels or of cAMP-dependent protein-kinase activity severely impairs excitatory synapse formation without affecting neuronal maturation, dendritic arborization, or inhibitory synapse formation. In vivo, suppression of postsynaptic cAMP signaling in CA1 neurons prevented formation of both Schaffer-collateral and entorhinal-CA1/temporoammonic-path synapses, suggesting a general principle. Retrograde trans-synaptic rabies virus tracing revealed that postsynaptic cAMP signaling is required for continuous replacement of synapses throughout life. Given that postsynaptic latrophilin adhesion-GPCRs drive synapse formation and produce cAMP, we suggest that spatially restricted postsynaptic cAMP signals organize assembly of postsynaptic specializations during synapse formation.

Endomembrane-Based Signaling by GPCRs and G-Proteins

G-protein-coupled receptors (GPCRs) and G-proteins have a range of roles in many physiological and pathological processes and are among the most studied signaling proteins. A plethora of extracellular stimuli can activate the GPCR and can elicit distinct intracellular responses through the activation of specific transduction pathways. For many years, biologists thought that GPCR signaling occurred entirely on the plasma membrane. However, in recent decades, many lines of evidence have proved that the GPCRs and G-proteins may reside on endomembranes and can start or propagate signaling pathways through the organelles that form the secretory route. How these alternative intracellular signaling pathways of the GPCR and G-proteins influence the physiological and pathological function of the endomembranes is still under investigation. Here, we review the general role and classification of GPCRs and G-proteins with a focus on their signaling pathways in the membrane transport apparatus.

Intra-islet glucagon confers β-cell glucose competence for first-phase insulin secretion and favors GLP-1R stimulation by exogenous glucagon

We report that intra-islet glucagon secreted from α-cells signals through β-cell glucagon and GLP-1 receptors (GcgR and GLP-1R), thereby conferring to rat islets their competence to exhibit first-phase glucose-stimulated insulin secretion (GSIS). Thus, in islets not treated with exogenous glucagon or GLP-1, first-phase GSIS is abolished by a GcgR antagonist (LY2786890) or a GLP-1R antagonist (Ex[9-39]). Mechanistically, glucose competence in response to intra-islet glucagon is conditional on β-cell cAMP signaling because it is blocked by the cAMP antagonist prodrug Rp-8-Br-cAMPS-pAB. In its role as a paracrine hormone, intra-islet glucagon binds with high affinity to the GcgR, while also exerting a "spillover" effect to bind with low affinity to the GLP-1R. This produces a right shift of the concentration-response relationship for the potentiation of GSIS by exogenous glucagon. Thus, 0.3 nM glucagon fails to potentiate GSIS, as expected if similar concentrations of intra-islet glucagon already occupy the GcgR. However, 10 to 30 nM glucagon effectively engages the β-cell GLP-1R to potentiate GSIS, an action blocked by Ex[9-39] but not LY2786890. Finally, we report that the action of intra-islet glucagon to support insulin secretion requires a step-wise increase of glucose concentration to trigger first-phase GSIS. It is not measurable when GSIS is stimulated by a gradient of increasing glucose concentrations, as occurs during an oral glucose tolerance test in vivo. Collectively, such findings are understandable if defective intra-islet glucagon action contributes to the characteristic loss of first-phase GSIS in an intravenous glucose tolerance test that is diagnostic of type 2 diabetes in the clinical setting.

Identifying the heat resistant genes by multi-tissue transcriptome sequencing analysis in Turpan Black sheep

Heat stress not only affects the physical condition but also affects reproductive performance in sheep. A thorough understanding of the molecular and physiological mechanisms underlying heat stress would certainly improve livestock productivity and provide genetic evaluation ways for heat resistant breeds selection. In this study, 85 Turpan Black sheep, a breed exhibited excellent heat resistance from long-term artificial selection, and 85 heat sensitive Kazakh sheep in Turpan basin were tested for physiological and reproductive performance from July to August in summer. The results showed that the estrus rate was significantly higher in Turpan Black sheep (P < 0.05), while the heart rate and respiratory rate of Turpan Black sheep are significantly lower than that of Kazakh sheep (P < 0.05). Furthermore, to clarify genes participated in heat stress response, the pituitary, ovarian and hepatic tissues from three Turpan Black sheep and three Kazakh sheep were subjected to RNA-seq. The results indicated that 32, 49 and 69 genes were up-regulated, and 39, 60 and 145 genes were down-regulated in pituitary, ovarian and hepatic tissues in Turpan Black sheep compared with that of the Kazakh sheep, respectively. KEGG and gene set enrichment analysis showed that the differentially expressed genes were mainly involved in signal transduction pathways. In particular, the differentially expressed genes in hepar were enriched in the energy metabolism pathway, while the differentially expressed genes in ovarian tissue were enriched in the ovarium steroidogenesis pathway. In conclusion, our results implied that the pituitary-ovary axis might include hepar as downstream targeted organism in heat resistant regulation. Under heat stress, the signals released from pituitary would impact steroidogenesis in ovary, and further alter energy metabolism in hepar. As we know, this is the first comparative study to investigate the gene expression in multi-tissue in sheep under heat stress.

Targeting GPCRs and Their Signaling as a Therapeutic Option in Melanoma

Simple Summary

Sixteen G-protein-coupled receptors (GPCRs) have been involved in melanogenesis or melanomagenesis. Here, we review these GPCRs, their associated signaling, and therapies.

Abstract

G-protein-coupled receptors (GPCRs) serve prominent roles in melanocyte lineage physiology, with an impact at all stages of development, as well as on mature melanocyte functions. GPCR ligands are present in the skin and regulate melanocyte homeostasis, including pigmentation. The role of GPCRs in the regulation of pigmentation and, consequently, protection against external aggression, such as ultraviolet radiation, has long been established. However, evidence of new functions of GPCRs directly in melanomagenesis has been highlighted in recent years. GPCRs are coupled, through their intracellular domains, to heterotrimeric G-proteins, which induce cellular signaling through various pathways. Such signaling modulates numerous essential cellular processes that occur during melanomagenesis, including proliferation and migration. GPCR-associated signaling in melanoma can be activated by the binding of paracrine factors to their receptors or directly by activating mutations. In this review, we present melanoma-associated alterations of GPCRs and their downstream signaling and discuss the various preclinical models used to evaluate new therapeutic approaches against GPCR activity in melanoma. Recent striking advances in our understanding of the structure, function, and regulation of GPCRs will undoubtedly broaden melanoma treatment options in the future.

Deciphering cellular signals in adult mouse sinoatrial node cells

Sinoatrial node (SAN) cells are the pacemakers of the heart. This study describes a method for culturing and infection of adult mouse SAN cells with FRET-based biosensors that can be exploited to examine signaling events. SAN cells cultured in media with blebbistatin or (S)-nitro-blebbistatin retain their morphology, protein distribution, action potential (AP) waveform, and cAMP dynamics for at least 40 h. SAN cells expressing targeted cAMP sensors show distinct β-adrenergic-mediated cAMP pools. Cyclic GMP, protein kinase A, Ca2+/CaM kinase II, and protein kinase D in SAN cells also show unique dynamics to different stimuli. Heart failure SAN cells show a decrease in cAMP and cGMP levels. In summary, a reliable method for maintaining adult mouse SAN cells in culture is presented, which facilitates studies of signaling networks and regulatory mechanisms during physiological and pathological conditions.

Emerging Role of cAMP/AMPK Signaling

The 5′-Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a natural energy sensor in mammalian cells that plays a key role in cellular and systemic energy homeostasis. At the cellular level, AMPK supports numerous processes required for energy and redox homeostasis, including mitochondrial biogenesis, autophagy, and glucose and lipid metabolism. Thus, understanding the pathways regulating AMPK activity is crucial for developing strategies to treat metabolic disorders. Mounting evidence suggests the presence of a link between cyclic AMP (cAMP) and AMPK signaling. cAMP signaling is known to be activated in circumstances of physiological and metabolic stress due to the release of stress hormones, such as adrenaline and glucagon, which is followed by activation of membrane-bound adenylyl cyclase and elevation of cellular cAMP. Because the majority of physiological stresses are associated with elevated energy consumption, it is not surprising that activation of cAMP signaling may promote AMPK activity. Aside from the physiological role of the cAMP/AMPK axis, numerous reports have suggested its role in several pathologies, including inflammation, ischemia, diabetes, obesity, and aging. Furthermore, novel reports have provided more mechanistic insight into the regulation of the cAMP/AMPK axis. In particular, the role of distinct cAMP microdomains generated by soluble adenylyl cyclase in regulating basal and induced AMPK activity has recently been demonstrated. In the present review, we discuss current advances in the understanding of the regulation of the cAMP/AMPK axis and its role in cellular homeostasis and explore some translational aspects.

Quantitative Phosphoproteomics to Study cAMP Signaling

Cyclic adenosine monophosphate (cAMP) signaling activates multiple downstream cellular targets in response to different stimuli. Specific phosphorylation of key target proteins via activation of the cAMP effector protein kinase A (PKA) is achieved via signal compartmentalization. Termination of the cAMP signal is mediated by phosphodiesterases (PDEs), a diverse group of enzymes comprising several families that localize to distinct cellular compartments. By studying the effects of inhibiting individual PDE families on the phosphorylation of specific targets it is possible to gain information on the subcellular spatial organization of this signaling pathway.We describe a phosphoproteomic approach that can detect PDE family-specific phosphorylation changes in cardiac myocytes against a high phosphorylation background. The method combines dimethyl labeling and titanium dioxide-mediated phosphopeptide enrichment, followed by tandem mass spectrometry.

Real-Time Measurements of Intracellular cAMP Gradients Using FRET-Based cAMP Nanorulers

3',5'-cyclic adenosine monophosphate (cAMP) is one of the most important and ubiquitous second messengers in cells downstream of G protein-coupled receptors (GPCRs). In a single cell, cAMP can exert innumerous specific cell functions in response to more than one hundred different GPCRs. Cells achieve this extraordinary functional specificity of cAMP signaling by limiting the spread of these signals in space and time. To do so, cells establish nanometer-size cAMP gradients by immobilizing cAMP via cAMP binding proteins and via targeted activity of cAMP-degrading phosphodiesterases (PDEs). As cAMP gradients appear to be essential for cell function, new technologies are needed to accurately measure cAMP gradients in intact cells with nanometer-resolution. Here we describe FRET-based cAMP nanorulers to measure local, nanometer-size cAMP gradients in intact cells in the direct vicinity of PDEs.

The cAMP-signaling cancers: Clinically-divergent disorders with a common central pathway

The cAMP-signaling cancers, which are defined by functionally-significant somatic mutations in one or more elements of the cAMP signaling pathway, have an unexpectedly wide range of cell origins, clinical manifestations, and potential therapeutic options. Mutations in at least 9 cAMP signaling pathway genes (TSHR, GPR101, GNAS, PDE8B, PDE11A, PRKARA1, PRKACA, PRKACB, and CREB) have been identified as driver mutations in human cancer. Although all cAMP-signaling pathway cancers are driven by mutation(s) that impinge on a single signaling pathway, the ultimate tumor phenotype reflects interactions between five critical variables: (1) the precise gene(s) that undergo mutation in each specific tumor type; (2) the effects of specific allele(s) in any given gene; (3) mutations in modifier genes (mutational "context"); (4) the tissue-specific expression of various cAMP signaling pathway elements in the tumor stem cell; and (5) and the precise biochemical regulation of the pathway components in tumor cells. These varying oncogenic mechanisms reveal novel and important targets for drug discovery. There is considerable diversity in the "druggability" of cAMP-signaling components, with some elements (GPCRs, cAMP-specific phosphodiesterases and kinases) appearing to be prime drug candidates, while other elements (transcription factors, protein-protein interactions) are currently refractory to robust drug-development efforts. Further refinement of the precise driver mutations in individual tumors will be essential for directing priorities in drug discovery efforts that target these mutations.

Nonalcoholic Fatty Liver Disease (NAFLD): Pathogenesis and Noninvasive Diagnosis

The global prevalence of nonalcoholic fatty liver disease (NAFLD) or metabolic associated fatty liver disease (MAFLD), as it is now known, has gradually increased. NAFLD is a disease with a spectrum of stages ranging from simple fatty liver (steatosis) to a severe form of steatosis, nonalcoholic steatohepatitis (NASH), which could progress to irreversible liver injury (fibrosis) and organ failure, and in some cases hepatocellular carcinoma (HCC). Although a liver biopsy remains the gold standard for accurate detection of this condition, it is unsuitable for clinical screening due to a higher risk of death. There is thus an increased need to find alternative techniques or tools for accurate diagnosis. Early detection for NASH matters for patients because NASH is the marker for severe disease progression. This review summarizes the current noninvasive tools for NAFLD diagnosis and their performance. We also discussed potential and newer alternative tools for diagnosing NAFLD.

A-Kinase Anchoring Protein 2 Promotes Protection against Myocardial Infarction

Myocardial infarction (MI) is a leading cause of maladaptive cardiac remodeling and heart failure. In the damaged heart, loss of function is mainly due to cardiomyocyte death and remodeling of the cardiac tissue. The current study shows that A-kinase anchoring protein 2 (AKAP2) orchestrates cellular processes favoring cardioprotection in infarcted hearts. Induction of AKAP2 knockout (KO) in cardiomyocytes of adult mice increases infarct size and exacerbates cardiac dysfunction after MI, as visualized by increased left ventricular dilation and reduced fractional shortening and ejection fraction. In cardiomyocytes, AKAP2 forms a signaling complex with PKA and the steroid receptor co-activator 3 (Src3). Upon activation of cAMP signaling, the AKAP2/PKA/Src3 complex favors PKA-mediated phosphorylation and activation of estrogen receptor α (ERα). This results in the upregulation of ER-dependent genes involved in protection against apoptosis and angiogenesis, including Bcl2 and the vascular endothelial growth factor a (VEGFa). In line with these findings, cardiomyocyte-specific AKAP2 KO reduces Bcl2 and VEGFa expression, increases myocardial apoptosis and impairs the formation of new blood vessels in infarcted hearts. Collectively, our findings suggest that AKAP2 organizes a transcriptional complex that mediates pro-angiogenic and anti-apoptotic responses that protect infarcted hearts.

Protein Kinase A Detection in Human Urine Samples

Actively involved in tumor maintenance, cAMP-dependent protein kinase A (PKA) has been proposed as a putative biomarker in cancer. Recently, an active PKA form has been identified in human sera and PKA autoantibodies have been detected in cancer patients. However, their serum functions, as well as diagnostic significance, remain largely unknown. Although several PKA detection assays have been developed, none refer to a laboratory diagnostic procedure. Among these, ELISA and Western blotting (WB) assays have been employed in PKA detection. Since, to the best of our knowledge, there are no data showing its presence in human urine samples, herein, we explore the possibility of PKA's existence in this biological specimen. Interestingly, among the 30 screened urines by quantitative sandwich ELISA, we recognized detectable PKA levels in 5 different samples, and of those two exhibited a considerable high concentration. To corroborate these results, we also evaluated PKA's presence in both positive and negative ELISA urines by WB. Remarkably, immunoblotting analysis confirmed PKA's existence in certain, but not in all, human urine specimens. Despite being quite preliminary, these findings firstly identify PKA in urine samples and provide evidence for its potential clinic usage as a diagnostic analyte in laboratory medicine.