Subcellular Organization of the cAMP Signaling Pathway

Decreased adenosine 3',5'-cyclic monophosphate is a driving factor of P300/SIRT1-mediated histone hyperacetylation in obesity-related hypertension

BACKGROUND

Obesity is the most significant risk factor associated with primary hypertension. A high-fat diet may lead to obesity-related hypertension, with evidence indicating that individuals with this condition exhibit a diminished adenosine 3',5'-cyclic monophosphate (cAMP) signaling pathway, although the exact mechanisms remain unclear. This study aimed to investigate the regulatory role of the cAMP signaling pathway in obesity-related hypertension.

METHODS

A rat model of obesity-related hypertension was established by feeding with a high-fat diet for 16 weeks. Changes in the cAMP signaling pathway and SIRT1 in rat renal tissues were explored using immunohistochemistry, immunofluorescence, and RT-qPCR. The effects and mechanisms of the cAMP signaling pathway on histone 3 lysine 27 acetylation and ACE1 were investigated by intervening in human renal tubular epithelial cells with P300, cAMP activators, SIRT1, cAMP inhibitors, and oleic acid.

RESULTS

The cAMP signaling pathway was found to be suppressed in rat renal tissue after feeding a high-fat diet, and a simultaneous decrease in histone deacetylase was observed. Furthermore, we identified that the inhibition of cAMP leads to the reduction of SIRT1 and the induction of P300. In addition, vitro experiments suggested that oleic acid suppressed the cAMP signaling pathway, which subsequently upregulated histone 3 lysine 27 acetylation and angiotensin converting enzyme 1 (ACE1) by increasing the expression of P300 and decreasing the expression of SIRT1.

CONCLUSION

The reduced cAMP signaling pathway in obesity could promote histone 3 lysine 27 acetylation modification and upregulate ACE1 expression by regulating P300 and SIRT1 levels, which may have important implications in the management of obesity-related hypertension.

LncRNA MRF targeting FSHR inhibits the osteogenic differentiation of BMSCs and bone defect repair through the regulation of the cAMP-PKA-CREB signaling pathway

BACKGROUND

Mesenchymal stem cells (MSCs), known for their ability to differentiate into osteoblasts, play a pivotal role in bone metabolism. In our previous investigations, we identified a novel long non-coding RNA (lncRNA) named MCP1 Regulatory Factor (MRF), which exhibits significant involvement in immune regulation of BMSCs. Moreover, we observed noticeable expression changes of MRF during the osteogenic differentiation of BMSCs. However, the exact role and underlying mechanism of MRF in the osteogenic differentiation of BMSCs remain elusive.

METHODS

QRT-PCR analysis was employed to assess the expression levels of MRF. RNA interference and overexpression plasmids were utilized to modulate MRF expression, allowing for the observation of changes in the osteogenic differentiation capacity of BMSCs. Downstream pathways involved in the MRF-mediated regulation of BMSCs' osteogenic differentiation were predicted using transcriptome sequencing. The functionality of MRF in vivo was validated through a mouse tibial drilling defect model.

RESULTS

In patients with osteoporosis, there is a notable increase in the expression of MRF within BMSCs. During the osteogenic differentiation of BMSCs, the MRF expression progressively decreases. The knockdown of MRF significantly enhances the osteogenic differentiation of BMSCs, promoting an increased expression of bone-related proteins such as RUNX2, ALP, and COL1A1. Transcriptome sequencing and western blot indicated that cAMP/PKA/CREB signaling pathway was significantly activated after lncRNA-MRF knockdown. Moreover, in the mouse tibial drilling defect model, MRF knockdown significantly promotes ossification in vivo.

CONCLUSIONS

MRF modulates the cAMP/PKA/CREB signaling pathway via the follicle stimulating hormone receptor (FSHR), thereby influencing the ossification differentiation of BMSCs. Our research suggests that MRF may serve as a potential target for bone-related disorders.

Wuling San regulates AVPR2-cAMP-PKA-CREB pathway to delay cellular senescence and ameliorate acute kidney injury

ETHNOPHARMACOLOGICAL RELEVANCE

Cellular senescence in renal resident cells plays a pivotal role in the progression of acute kidney injury (AKI), necessitating the expansion of effective drug targets. Traditional Chinese medicine (TCM) formulations, characterized by their multi-target effects, offer a promising perspective for advancing research on AKI. Wuling San (WLS), a well-established compound used in treating urological disorders, has yet to elucidate its potential pharmacological targets and mechanisms in ameliorating AKI and delaying cellular senescence.

AIM OF THE STUDY

This study sought to elucidate the mechanisms by which WLS modulates the AVPR2-cAMP-PKA-CREB pathway to mitigate cellular senescence and promote recovery from AKI.

METHODS

We first prepared WLS-containing serum and performed RT-qPCR experiments to screen for GPCRs that were differentially expressed in response to WLS. Next, we established an in vitro AKI mouse model to assess the renal protective effects of the WLS by measuring renal function, renal pathology, and oxidative stress levels. After this, we performed RNA sequencing (RNA-Seq) profiling to identify differentially expressed genes (DEGs) affected by WLS treatment. We also conducted Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to identify potential signaling pathways involved. We then utilized the Gene Expression Omnibus (GEO) data to screen for cellular senescence related differentially expressed genes (CSRDEGs) in AKI patients and performed enrichment analysis, as well as a joint analysis of specific genes in relation to the RNA-Seq profiling results. We also examined how WLS affects the expression of proteins linked to cellular senescence in the AKI mouse model by targeting the AVPR2-cAMP-PKA-CREB pathway.

RESULTS

WLS markedly enhanced the expression of Arginine Vasopressin Receptor 2 (AVPR2) and ameliorated renal function indicators, as well as pathological changes and oxidative stress levels in the mouse model of AKI. RNA-Seq profiling revealed significant enrichment of the cAMP signaling pathway following WLS intervention. Bioinformatics analysis indicated that genes associated with cellular senescence in AKI patients were notably enriched in the p53 signaling pathway. Data mining from the GEO database, in conjunction with RNA-Seq profiling, demonstrated a substantial reduction in key genes after WLS treatment. Additionally, WLS elevated both the expression and phosphorylation of pivotal proteins within the AVPR2-cAMP-PKA-CREB pathway, while concurrently decreasing proteins associated with cellular senescence.

CONCLUSION

The results demonstrated that WLS significantly elevated the expression of AVPR2, which may underlie its nephroprotective effects and facilitate the mitigation of AKI by modulating the AVPR2-cAMP-PKA-CREB pathway, ultimately contributing to a delay in cellular senescence.

Intersection of GPCR trafficking and cAMP signaling at endomembranes

GPCRs comprise the largest family of signaling receptors and control essentially every physiological process. Many biochemical reactions underlying GPCR signaling are now elucidated to atomic resolution in cell-free preparations, but how elemental signaling reactions are organized in intact cells remains less clear. Significant progress has been made toward bridging this knowledge gap by leveraging new tools and methodologies enabling the experimental detection, localization, and manipulation of defined signaling reactions in living cells. Here, we chronicle advances at this rapidly moving frontier of molecular and cell biology, focusing on GPCR-initiated signaling through the classical cAMP pathway as an example. We begin with a brief review of established concepts. We then discuss the still-evolving understanding that ligand-induced GPCR signaling occurs from endomembranes as well as the plasmalemma, and that this enables cells to flexibly sculpt downstream signaling responses in both space and time. Finally, we note some key limitations of the present understanding and propose some promising directions for future investigation.

Promoting proteostasis by cAMP/PKA and cGMP/PKG

Proteasome functional insufficiency (PFI) is implicated in neurodegeneration and heart failure, where aberrant protein aggregation is common and impairs the ubiquitin (Ub)-proteasome system (UPS), exacerbating increased proteotoxic stress (IPTS) and creating a vicious circle. Breaking this circle represents a key to treating these diseases. Protein kinase (PK)-A and PKG can activate the proteasome and promote proteasomal degradation of misfolded proteins. PKA does so by phosphorylating Ser14-RPN6/PSMD11, but how PKG activates the proteasome remains unknown. Emerging evidence supports a strategy to treat diseases with IPTS by augmenting cAMP/PKA and cGMP/PKG. Conceivably, targeted activation of PKA and PKG at proteasome nanodomains would minimize the undesired effects from their actions on other targets. In this review, we discuss PKA and PKG regulation of proteostasis via the UPS.

A signal transduction blind spot: the function of adenylyl cyclase transmembrane domains

Signal transduction of external primary signals into intracellular elevations of the second messenger cyclic AMP is an ancient and universal regulatory mechanism in biology. In mammals, 9 of the 10 adenylyl cyclases (ACs) share a common topology that includes a large transmembrane (TM) domain assembled from two clusters of six helices. This domain accounts for ~ 35% of the coding sequence but, remarkably, its function is still an open question. In this viewpoint, we consider how the first primary AC sequences spurred ideas for the purpose of AC TM domains, including voltage-sensing and transporter functions. In the original conceptions of second messenger signalling, ACs were put forward as potential receptors, and we discuss emerging evidence in support of this function. We also consider growing evidence that cyclase TM helical bundles help to organise multiprotein signalling complexes by engaging in interactions with other membrane-embedded proteins. Cyclase TM regions are more diverse between isoforms than the catalytic domain-we conclude by considering how this might be exploited in therapeutic strategies targeting specific cyclase isoforms.

5-hydroxymethylcytosine features of portal venous blood predict metachronous liver metastases of colorectal cancer and reveal phosphodiesterase 4 as a therapeutic target

Metachronous liver metastases (MLM) are characterised by high incidence and high mortality in clinical colorectal cancer treatment. Currently traditional clinical methods cannot effectively predict and prevent the occurrence of metachronous liver metastasis in colorectal cancer. Based on 5hmC-Seal analysis of blood and tissue samples, this study found that portal venous blood was more relevant to tumour gDNA than peripheral blood. We performed a novel epigenetic liquid biopsy strategy using the 10 5hmC epigenetic alterations, to accurately distinguish MLM patients from patients without metastases. Among these epigenetic alterations, phosphodiesterase 4 (PDE4D) was highly increased in MLM patients and correlated with poor survival. Moreover, our studies demonstrated that PDE4D was a key metastasis-driven target for drug development. Interfering with the function of PDE4D significantly repressed liver metastases. Similarly, roflumilast, a PDE4 inhibitor for chronic obstructive pulmonary disease (COPD) therapy, also inhibits liver metastases. Further studies indicate that blocking the function of PDE4D can affect CRC invasion through the HIF-1α-CCN2 pathway. To develop a more efficient PDE4 inhibitor and reduce the occurrence of adverse events, we also designed several new compounds based on 2-arylbenzofurans and discovered lead L11 with potent affinity for PDE4D and significant suppression of liver metastases. In this work, our study provides a promising strategy for predicting metachronous liver metastasis and discovers L11 as a potential repurposed drug for inhibiting liver metastasis, which have the potential to benefit patients with CRC in the future. KEY POINTS: 5hmC epigenetic markers derived from portal venous blood could accurately predict metachronous metastasis of colorectal cancer. PDE4D was a key metastasis-driven target that promoted metachronous metastasis via the HIF-1α-CCN2 pathway. The newly synthesised compound L11 could specifically inhibit PDE4D and abolish metachronous metastasis of colorectal cancer without obvious toxic side effects.

Malnutrition exacerbating neuropsychiatric symptoms on the Alzheimer's continuum is relevant to the cAMP signaling pathway: Human and mouse studies

INTRODUCTION

Malnutrition correlates with neuropsychiatric symptoms (NPSs) in Alzheimer's disease (AD); however, the potential mechanism underlying this association remains unclear.

METHODS

Baseline and longitudinal associations of nutritional status with NPSs were analyzed in 374 patients on the AD continuum and 61 healthy controls. Serum biomarkers, behavioral tests, cerebral neurotransmitters, and differentially gene expression were evaluated in standard and malnourished diet-fed transgenic APPswe/PSEN1dE9 (APP/PS1) mice.

RESULTS

Poor nutritional status and increased cerebral blood flow in the midbrain and striatum were associated with severe general NPSs and subtypes, especially depression, anxiety, and apathy. APP/PS1 mice fed a malnourished diet showed poor nutritional status, depression- and anxiety-like behaviors, altered neurotransmitter levels, and downregulated c-Fos expression in the midbrain and striatum; these were associated with suppressed cyclic adenosine monophosphate (cAMP) signaling pathway.

DISCUSSION

Malnutrition exacerbating NPSs is relevant to suppressed cAMP pathway in the midbrain and striatum, suggesting the potential for targeted nutritional interventions to mitigate NPSs in the AD continuum.

HIGHLIGHTS

Poor nutritional status linked to general and specific neuropsychiatric symptom (NPS) deterioration. Malnutrition affects NPSs, usually involving the midbrain and striatum. Malnourished diet induces depression- and anxiety-like behaviors in APP/PS1 mice. Malnutrition exacerbates NPSs associated with cAMP signaling pathway in the midbrain and striatum.

Intracellular cAMP signaling-induced Ca2+ influx mediated by calcium homeostasis modulator 1 (CALHM1) in human odontoblasts

In odontoblasts, intracellular Ca2+ signaling plays key roles in reactionary dentin formation and generation of dentinal pain. Odontoblasts also express several Gs protein-coupled receptors that promote production of cyclic AMP (cAMP). However, the crosstalk between intracellular cAMP and Ca2+ signaling, as well as the role of cAMP in the cellular functions of odontoblasts, remains unclear. In this study, we measured intracellular cAMP levels and intracellular free Ca2+ concentration ([Ca2+]i). We also investigated the effect of intracellular cAMP on mineralization by the odontoblasts. In the presence of extracellular Ca2+, the application of forskolin (adenylyl cyclase activator) or isoproterenol (Gs protein-coupled beta-2 adrenergic receptor agonist) increased intracellular cAMP levels and [Ca2+]i in odontoblasts. The [Ca2+]i increases could not be observed by removing extracellular Ca2+, indicating that cAMP is capable to activate Ca2+ entry. Forskolin-induced [Ca2+]i increase was inhibited by a protein kinase A inhibitor in odontoblasts. The [Ca2+]i increase was sensitive to Gd3+, 2APB, or Zn2+ but not verapamil, ML218, or La3+. In immunofluorescence analyses, odontoblasts were immunopositive for calcium homeostasis modulator 1 (CALHM1), which was found close to ionotropic ATP receptor subtype, P2X3 receptors. When CALHM1 was knocked down, forskolin-induced [Ca2+]i increase was suppressed. Alizarin red and von Kossa staining showed that forskolin decreased mineralization. These findings suggest that activation of adenylyl cyclase elicited increases in the intracellular cAMP level and Ca2+ influx via protein kinase A activation in odontoblasts. Subsequent cAMP-dependent Ca2+ influx was mediated by CALHM1 in odontoblasts. In addition, the intracellular cAMP signaling pathway in odontoblasts negatively mediated dentinogenesis.

Cyclic nucleotide phosphodiesterases as drug targets

Cyclic nucleotides are synthesized by adenylyl and/or guanylyl cyclase, and downstream of this synthesis, the cyclic nucleotide phosphodiesterase families (PDEs) specifically hydrolyze cyclic nucleotides. PDEs control cyclic adenosine-3',5'monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) intracellular levels by mediating their quick return to the basal steady state levels. This often takes place in subcellular nanodomains. Thus, PDEs govern short-term protein phosphorylation, long-term protein expression, and even epigenetic mechanisms by modulating cyclic nucleotide levels. Consequently, their involvement in both health and disease is extensively investigated. PDE inhibition has emerged as a promising clinical intervention method, with ongoing developments aiming to enhance its efficacy and applicability. In this comprehensive review, we extensively look into the intricate landscape of PDEs biochemistry, exploring their diverse roles in various tissues. Furthermore, we outline the underlying mechanisms of PDEs in different pathophysiological conditions. Additionally, we review the application of PDE inhibition in related diseases, shedding light on current advancements and future prospects for clinical intervention. SIGNIFICANCE STATEMENT: Regulating PDEs is a critical checkpoint for numerous (patho)physiological conditions. However, despite the development of several PDE inhibitors aimed at controlling overactivated PDEs, their applicability in clinical settings poses challenges. In this context, our focus is on pharmacodynamics and the structure activity of PDEs, aiming to illustrate how selectivity and efficacy can be optimized. Additionally, this review points to current preclinical and clinical evidence that depicts various optimization efforts and indications.

Phosphodiesterases: Evolving Concepts and Implications for Human Therapeutics

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides. While the 11 PDE subfamilies share common features, key differences confer signaling specificity. The differences include substrate selectivity, enzymatic activity regulation, tissue expression, and subcellular localization. Selective inhibitors of each subfamily have elucidated the protean role of PDEs in normal cell function. PDEs are also linked to diseases, some of which affect the immune, cardiac, and vascular systems. Selective PDE inhibitors are clinically used to treat these specific disorders. Ongoing preclinical studies and clinical trials are likely to lead to the approval of additional PDE-targeting drugs for therapy in human disease. In this review, we discuss the structure and function of PDEs and examine current and evolving therapeutic uses of PDE inhibitors, highlighting their mechanisms and innovative applications that could further leverage this crucial family of enzymes in clinical settings.

Endomembrane GPCR signaling: 15 years on, the quest continues

G-protein-coupled receptors (GPCRs) are the largest family of cell receptors. They mediate the effects of a multitude of endogenous and exogenous cues, are deeply involved in human physiology and disease, and are major pharmacological targets. Whereas GPCRs were long thought to signal exclusively at the plasma membrane, research over the past 15 years has revealed that they also signal via classical G-protein-mediated pathways on membranes of intracellular organelles such as endosomes and the Golgi complex. This review provides an overview of recent advances and emerging concepts related to endomembrane GPCR signaling, as well as ongoing research aimed at a better understanding of its mechanisms, physiological relevance, and potential therapeutic applications.

Stochastic neuropeptide signals compete to calibrate the rate of satiation

Neuropeptides have important roles in neural plasticity, spiking and behaviour1. Yet, many fundamental questions remain regarding their spatiotemporal transmission, integration and functions in the awake brain. Here we examined how MC4R-expressing neurons in the paraventricular nucleus of the hypothalamus (PVHMC4R) integrate neuropeptide signals to modulate feeding-related fast synaptic transmission and titrate the transition to satiety2-6. We show that hunger-promoting AgRP axons release the neuropeptide NPY to decrease the second messenger cAMP in PVHMC4R neurons, while satiety-promoting POMC axons release the neuropeptide αMSH to increase cAMP. Each release event is all-or-none, stochastic and can impact multiple neurons within an approximately 100-µm-diameter region. After release, NPY and αMSH peptides compete to control cAMP-the amplitude and persistence of NPY signalling is blunted by high αMSH in the fed state, while αMSH signalling is blunted by high NPY in the fasted state. Feeding resolves this competition by simultaneously elevating αMSH release and suppressing NPY release7,8, thereby sustaining elevated cAMP in PVHMC4R neurons throughout a meal. In turn, elevated cAMP facilitates potentiation of feeding-related excitatory inputs with each bite to gradually promote satiation across many minutes. Our findings highlight biochemical modes of peptide signal integration and information accumulation to guide behavioural state transitions.

The role of compartmentalized β-AR/cAMP signaling in the regulation of lipolysis in white and brown adipocytes

White and brown adipocytes are central mediators of lipid metabolism and thermogenesis, respectively. Their function is tightly regulated by all three β-adrenergic receptor (β-AR) subtypes which are coupled to the production of the second messenger 3',5'-cyclic adenosine monophosphate (cAMP). While known for decades in other cell types, compartmentation of adipocyte β-AR/cAMP signaling by spatial organization of the pathway and by cAMP degrading phosphodiesterases (PDEs) as well as its role in the regulation of lipolysis is only beginning to emerge. Here, we provide a short overview of recent findings which shed light on compartmentalized signaling using live cell imaging of cAMP in adipocytes and discuss possible future directions of research which could open up new avenues for the treatment of metabolic disorders.

G Protein-Coupled Receptor 17 Inhibits Glucagon-like Peptide-1 Secretion via a Gi/o-Dependent Mechanism in Enteroendocrine Cells

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered. Here, we expressed the human GPR17 long isoform (hGPR17L) in GLUTag cells, a murine EEC line, and we used the GPR17 synthetic agonist MDL29,951 together with pharmacological probes and genetic approaches to quantitatively assess the contribution of GPR17 signaling to GLP-1 secretion. Constitutive hGPR17L activity inhibited GLP-1 secretion, and MDL29,951 treatment further inhibited this secretion, which was attenuated by treatment with the GPR17 antagonist HAMI3379. MDL29,951 promoted both Gi/o and Gq protein coupling to mediate cyclic AMP (cAMP) and calcium signaling. hGPR17L regulation of GLP-1 secretion appeared to be Gq-independent and dependent upon Gi/o signaling, but was not correlated with MDL29,951-induced whole-cell cAMP signaling. Our studies revealed key signaling mechanisms underlying the role of GPR17 in regulating GLP-1 secretion and suggest future opportunities for pharmacologically targeting GPR17 with inverse agonists to maximize GLP-1 secretion.

SPTLC3 regulates plasma membrane sphingolipid composition to facilitate hepatic gluconeogenesis

SPTLC3, an inducible subunit of the serine palmitoyltransferase (SPT) complex, causes production of alternative sphingoid bases, including a 16-carbon dihydrosphingosine, whose biological function is only beginning to emerge. High-fat feeding induced SPTLC3 in the liver, prompting us to produce a liver-specific knockout mouse line. Following high-fat feeding, knockout mice showed decreased fasting blood glucose, and knockout primary hepatocytes showed suppressed glucose production, a core function of hepatocytes. Stable isotope tracing revealed suppression of the gluconeogenic pathway, finding that SPTLC3 was required to maintain expression of key gluconeogenic genes via adenylate cyclase/cyclic AMP (cAMP)/cAMP response element binding protein (CREB) signaling. Additionally, by employing a combination of a recently developed lipidomics methodology, exogenous C14/C16 fatty acid treatment, and in situ adenylate cyclase activity, we implicated a functional interaction between sphingomyelin with a d16 backbone and adenylate cyclase at the plasma membrane. This work pinpoints a specific sphingolipid-protein functional interaction with broad implications for understanding sphingolipid signaling and metabolic disease.

Differential effects of Phosphodiesterase 4A5 on cAMP-dependent forms of long-term potentiation

cAMP signalling is critical for memory consolidation and certain forms of long-term potentiation (LTP). Phosphodiesterases (PDEs), enzymes that degrade the second messengers cAMP and cGMP, are highly conserved during evolution and represent a unique set of drug targets, given the involvement of these enzymes in several pathophysiological states including brain disorders. The PDE4 family of cAMP-selective PDEs exert regulatory roles in memory and synaptic plasticity, but the specific roles of distinct PDE4 isoforms in these processes are poorly understood. Building on our previous work demonstrating that spatial and contextual memory deficits were caused by expressing selectively the long isoform of the PDE4A subfamily, PDE4A5, in hippocampal excitatory neurons, we now investigate the effects of PDE4A isoforms on different cAMP-dependent forms of LTP. We found that PDE4A5 impairs long-lasting LTP induced by theta burst stimulation (TBS) while sparing long-lasting LTP induced by spaced four-train stimulation (4 × 100 Hz). This effect requires the unique N-terminus of PDE4A5 and is specific to this long isoform. Targeted overexpression of PDE4A5 in area CA1 is sufficient to impair TBS-LTP, suggesting that cAMP levels in the postsynaptic neuron are critical for TBS-LTP. Our results shed light on the inherent differences among the PDE4A subfamily isoforms, emphasizing the importance of the long isoforms, which have a unique N-terminal region. Advancing our understanding of the function of specific PDE isoforms will pave the way for developing isoform-selective approaches to treat the cognitive deficits that are debilitating aspects of psychiatric, neurodevelopmental and neurodegenerative disorders. KEY POINTS: Hippocampal overexpression of PDE4A5, but not PDE4A1 or the N-terminus-truncated PDE4A5 (PDE4A5Δ4), selectively impairs long-term potentiation (LTP) induced by theta burst stimulation (TBS-LTP). Expression of PDE4A5 in area CA1 is sufficient to cause deficits in TBS-LTP. Hippocampal overexpression of the PDE4A isoforms PDE4A1 and PDE4A5 does not impair LTP induced by repeated tetanic stimulation at the CA3-CA1 synapses. These results suggest that PDE4A5, through its N-terminus, regulates cAMP pools that are critical for memory consolidation and expression of specific forms of long-lasting synaptic plasticity at CA3-CA1 synapses.

Quercetin: A Flavonoid with Potential for Treating Acute Lung Injury

In intensive care units, acute lung injury (ALI) is a syndrome that is frequently encountered. It is associated with a high rate of morbidity and mortality. Despite the extensive research conducted by the medical community on its treatment, no specific effective drugs have been identified. Quercetin is a natural flavonoid with many biological activities and pharmacological effects. Research indicates that Quercetin can modulate various targets and signaling pathways, inhibiting oxidative stress, inflammatory responses, ferroptosis, apoptosis, fibrosis, and bacterial and viral infections in ALI. This regulation suggests its potential therapeutic application for the condition. Currently, there is no comprehensive review addressing the application of Quercetin in the treatment of ALI. This paper begins with a classification of ALI, followed by a detailed summary of the mechanisms through which Quercetin may treat ALI to evaluate its potential as a novel therapeutic option.

Chemical, Biochemical, and Structural Similarities and Differences of Dermatological cAMP Phosphodiesterase-IV Inhibitors

Roflumilast, the third phosphodiesterase-IV (PDE4) inhibitor approved for use in dermatology, is indicated for topical treatment of psoriasis, seborrheic dermatitis, and atopic dermatitis, whereas its 2 predecessors, apremilast and crisaborole, are indicated for oral treatment of psoriasis and topical treatment of atopic dermatitis, respectively. All 3 are rationally designed PDE4 inhibitors, but roflumilast is the most potent and effective among the 3, with in vitro inhibitory constant half-maximal inhibitory concentration value of 0.7 nM (roflumilast), 0.14 μM (apremilast), and 0.24 μM (crisaborole), representing differences of over 3 orders of magnitude. PDE4 is a cAMP (an intracellular secondary messenger) hydrolase consisting of at least 4 subtypes of exon-spliced isoforms, which are primarily expressed in immune cells for inflammatory response. PDE4 inhibition lengthens the duration of cAMP signals and increases cellular cAMP concentrations, generating anti-inflammatory effects. We examined the physicochemical principles that make PDE4 inhibitors effective and propose chemical modifications to improve them. Sequence alignment of the catalytic domains of all phosphodiesterases identified many previously unreported invariant residues. These residues bind 1 Zn and 1 Mg ion plus 5 structural water molecules for orienting an attacking μ-hydroxyl/μ-oxo anion and for stabilizing 2 nonbridging phosphate oxygen atoms. The arrangement of the 2 divalent metal ions in phosphodiesterases is not related to that of the classic mechanism for general phosphoryl transfer.

Exploring Framework Nucleic Acids: A Perspective on Their Cellular Applications

Cells are fundamental units of life. The coordination of cellular functions and behaviors relies on a cascade of molecular networks. Technologies that enable exploration and manipulation of specific molecular events in living cells with high spatiotemporal precision would be critical for pathological study, disease diagnosis, and treatment. Framework nucleic acids (FNAs) represent a novel class of nucleic acid materials characterized by their monodisperse and rigid nanostructure. Leveraging their exceptional programmability, convenient modification property, and predictable atomic-level architecture, FNAs have attracted significant attention in diverse cellular applications such as cell recognition, imaging, manipulation, and therapeutic interventions. In this perspective, we will discuss the utilization of FNAs in living cell systems while critically assessing the opportunities and challenges presented in this burgeoning field.

Characterizing metabolomic and transcriptomic changes, and investigating the therapeutic mechanism of Psoralea corylifolia linn. In the treatment of kidney-yang deficiency syndrome in rats

Kidney-yang deficiency syndrome (KYDS) is characterized by a metabolic disorder stemming from neuroendocrine dysregulation, often associated with hepatic dysfunction. In traditional Chinese medicine, Psoralea corylifolia Linn. (BGZ) is commonly utilized for treating KYDS. However, the specific therapeutic effects of BGZ on liver function regulation remain unclear. To evaluate the protective effects of BGZ against KYDS in rats, organ index, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and other biochemical indices were analyzed. Hematoxylin and eosin (HE) staining was utilized to assess liver histopathology. Additionally, transcriptomic and metabolomic analyses were conducted to identify potential biomarkers. BGZ treatment led to a significant reduction in ALT and AST levels, accompanied by improvements in liver histopathology in rats with KYDS. Moreover, BGZ induced significant alterations in 92 differentially expressed genes (DEGs) and 20 metabolites in the KYDS rat model. The comprehensive examination of metabolites and DEGs identified potential mechanisms underlying the therapeutic effects of BGZ, highlighting the neuroactive ligand-receptor interaction, cAMP signaling pathway, calcium signaling pathway, and cytokine-cytokine receptor interaction as key mechanisms. Validation of key targets within the cAMP pathway was substantiated through enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction. The cAMP pathway emerges as a plausible mechanism through which BGZ exerts protective effects against KYDS. The findings of this study contribute to an improved understanding of the therapeutic actions of BGZ and establish a groundwork for further research into the complex pathways involved, as well as the potential for drug-targeted therapies for KYDS.

Spatial-temporal regulation of the prostanoid receptor EP2 co-ordinates PGE2-mediated cAMP signaling in decidualizing human endometrium

Decidualization denotes the differentiation of endometrial stromal cells into specialized decidual cells, essential for embryo implantation and pregnancy. The process requires coordination of progesterone and cAMP signaling, which converge on downstream transcription factors. PGE2 and relaxin, acting, respectively, through Gαs-coupled GPCRs EP2 and RXFP1, are putative candidates for generating cAMP in differentiating stromal cells. Here, we show that PGE2 is less efficacious than relaxin in elevating intracellular cAMP levels in primary stromal cells but more effective at driving the expression of decidual genes. PGE2-and relaxin-induced cAMP generation involves receptor internalization, but EP2 is endocytosed into very early endosomes (VEEs). Perturbation of VEE machinery through depletion of key trafficking proteins; APPL1 and GIPC, dysregulates PGE2-dependent cAMP profiles and disrupts key decidual signaling pathways, resulting in a disordered differentiation response. We demonstrate that regulation of EP2 via internalization is essential for coordinated activation of the downstream signaling cascades that govern decidualization.

G protein-coupled receptor 17 inhibits glucagon-like peptide-1 secretion via a Gi/o-dependent mechanism in enteroendocrine cells

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered. Here, we expressed the human GPR17 long isoform (hGPR17L) in GLUTag cells, a murine EEC line, and we used the GPR17 synthetic agonist MDL29,951 together with pharmacological probes and genetic approaches to quantitatively assess the contribution of GPR17 signaling to GLP-1 secretion. Constitutive hGPR17L activity inhibited GLP-1 secretion, and MDL29,951 treatment further inhibited this secretion, which was attenuated by treatment with the GPR17 antagonist HAMI3379. MDL29,951 promoted both Gi/o and Gq protein coupling to mediate cyclic AMP (cAMP) and calcium signaling. hGPR17L regulation of GLP-1 secretion was Gq-independent and dependent upon Gi/o signaling, but was not correlated with MDL29,951-induced whole-cell cAMP signaling. Our studies revealed key signaling mechanisms underlying the role of GPR17 in regulating GLP-1 secretion and suggest future opportunities for pharmacologically targeting GPR17 with inverse agonists to maximize GLP-1 secretion.

A mutation in the PRKAR1B gene drives pathological mechanisms of neurodegeneration across species

Protein kinase A (PKA) neuronal function is controlled by the interaction of a regulatory (R) subunit dimer with two catalytic subunits. Recently, the L50R variant in the gene encoding the RIβ subunit was identified in individuals with a novel neurodegenerative disease. However, the mechanisms driving the disease phenotype remained unknown. In this study, we generated a mouse model carrying the RIβ-L50R mutation to replicate the human disease phenotype and study its progression with age. We examined post-mortem brains of affected individuals as well as live cell cultures. Employing biochemical assays, immunohistochemistry and behavioural assessments, we investigated the impact of the mutation on PKA complex assembly, protein aggregation and neuronal degeneration. We reveal that RIβ is an aggregation-prone protein that progressively accumulates in wildtype and Alzheimer's mouse models with age, while aggregation is accelerated in the RIβ-L50R mouse model. We define RIβ-L50R as a causal mutation driving an age-dependent behavioural and disease phenotype in human and mouse models. Mechanistically, this mutation disrupts RIβ dimerization, leading to aggregation of its monomers. Intriguingly, interaction with the catalytic subunit protects the RIβ-L50R from self-aggregating, in a dose-dependent manner. Furthermore, cAMP signaling induces RIβ-L50R aggregation. The pathophysiological mechanism elucidated here for a newly recognized neurodegenerative disease, in which protein aggregation is the result of disrupted homodimerization, sheds light on a remarkably under-appreciated but potentially common mechanism across several neurodegenerative diseases.

Virulence regulation in plant-pathogenic bacteria by host-secreted signals

Bacterial pathogens manipulate host signaling pathways and evade host defenses using effector molecules, coordinating their deployment to ensure successful infection. However, host-derived metabolites as signals, and their critical role in regulating bacterial virulence requires further insights. Effective regulation of virulence, which is essential for pathogenic bacteria, involves controlling factors that enable colonization, defense evasion, and tissue damage. This regulation is dynamic, influenced by environmental cues including signals from host plants like exudates. Plant exudates, comprising of diverse compounds released by roots and tissues, serve as rich chemical signals affecting the behavior and virulence of associated bacteria. Plant nutrients act as signaling molecules that are sensed through membrane-localized receptors and intracellular response mechanisms in bacteria. This review explains how different bacteria detect and answer to secreted chemical signals, regulating virulence gene expression. Our main emphasis is exploring the recognition process of host-originated signaling molecules through molecular sensors on cellular membranes and intracellular signaling pathways. This review encompasses insights into how bacterial strains individually coordinate their virulence in response to various distinct host-derived signals that can positively or negatively regulate their virulence. Furthermore, we explained the interruption of plant defense with the perception of host metabolites to dampen pathogen virulence. The intricate interplay between pathogens and plant signals, particularly in how pathogens recognize host metabolic signals to regulate virulence genes, portrays a crucial initial interaction leading to profound influences on infection outcomes. This work will greatly aid researchers in developing new strategies for preventing and treating infections.

Red blood cell signaling is functionally conserved in Plasmodium invasion

It is widely recognized that Plasmodium merozoites secrete ligands that interact with RBC receptors. Meanwhile the question on whether these interactions trigger RBC signals essential for invasion remains unresolved. There is evidence that Plasmodium falciparum parasites manipulate native RBC Ca2+ signaling to facilitate invasion. Here, we demonstrate a key role of RBC Ca2+ influx that is conserved across different Plasmodium species during invasion. RH5-basigin interaction triggers RBC cAMP increase to promote Ca2+ influx. The RBC signaling pathways can be blocked by a range of inhibitors during Plasmodium invasion, providing the evidence of a functionally conserved host cAMP-Ca2+ signaling that drives invasion and junction formation. Furthermore, RH5-basigin binding induces a pre-existing multimeric RBC membrane complex to undergo increased protein association containing the cAMP-inducing β-adrenergic receptor. Our work presents evidence of a conserved host cell signaling cascade necessary for Plasmodium invasion and will create opportunities to therapeutically target merozoite invasion.

A nonnatural peptide targeting the A-kinase anchoring function of PI3Kγ for therapeutic cAMP modulation in pulmonary cells

A-kinase anchoring proteins (AKAPs) are key orchestrators of cAMP signaling that act by recruiting protein kinase A (PKA) in proximity of its substrates and regulators to specific subcellular compartments. Modulation of AKAPs function offers the opportunity to achieve compartment-restricted modulation of the cAMP/PKA axis, paving the way to new targeted treatments. For instance, blocking the AKAP activity of phosphoinositide 3-kinase γ (PI3Kγ) improves lung function by inducing cAMP-mediated bronchorelaxation, ion transport, and antiinflammatory responses. Here, we report the generation of a nonnatural peptide, D-retroinverso (DRI)-Pep #20, optimized to disrupt the AKAP function of PI3Kγ. DRI-Pep #20 mimicked the native interaction between the N-terminal domain of PI3Kγ and PKA, demonstrating nanomolar affinity for PKA, high resistance to protease degradation and high permeability to the pulmonary mucus barrier. DRI-Pep #20 triggered cAMP elevation both in vivo in the airway tract of mice upon intratracheal administration, and in vitro in bronchial epithelial cells of cystic fibrosis (CF) patients. In CF cells, DRI-Pep #20 rescued the defective function of the cAMP-operated channel cystic fibrosis transmembrane conductance regulator, by boosting the efficacy of approved cystic fibrosis transmembrane conductance regulator modulators. Overall, this study unveils DRI-Pep #20 as a potent PI3Kγ/PKA disruptor for achieving therapeutic cAMP elevation in chronic respiratory disorders.

GZMA suppressed GPX4-mediated ferroptosis to improve intestinal mucosal barrier function in inflammatory bowel disease

BACKGROUND

Our previous study has demonstrated a decreased colonic CD8+CD39+ T cells, enrichment of granzyme A (GZMA), was found in pediatric-onset colitis and inflammatory bowel disease (IBD) characterized by impaired intestinal barrier function. However, the influence of GZMA on intestinal barrier function remains unknown.

METHODS

Western blotting(WB), real-time PCR (qPCR), immunofluorescence (IF) and in vitro permeability assay combined with intestinal organoid culture were used to detect the effect of GZMA on intestinal epithelial barrier function in vivo and in vitro. Luciferase, immunoprecipitation (IP) and subcellular fractionation isolation were performed to identify the mechanism through which GZMA modulated intestinal epithelial barrier function.

RESULTS

Herein, we, for the first time, demonstrated that CD8+CD39+ T cells promoted intestinal epithelial barrier function through GZMA, leading to induce Occludin(OCLN) and Zonula Occludens-1(ZO-1) expression, which was attributed to enhanced CDX2-mediated cell differentiation caused by increased glutathione peroxidase 4(GPX4)-induced ferroptosis inhibition in vivo and in vitro. Mechanically, GZMA inhibited intestinal epithelial cellular PDE4B activation to trigger cAMP/PKA/CREB cascade signaling to increase CREB nuclear translocation, initiating GPX4 transactivity. In addition, endogenous PKA interacted with CREB, and this interaction was enhanced in response to GZMA. Most importantly, administration of GZMA could alleviate DSS-induced colitis in vivo.

CONCLUSION

These findings extended the novel insight of GZMA contributed to intestinal epithelial cell differentiation to improve barrier function, and enhacement of GZMA could be a promising strategy to patients with IBD.

Spatiotemporal orchestration of calcium-cAMP oscillations on AKAP/AC nanodomains is governed by an incoherent feedforward loop

The nanoscale organization of enzymes associated with the dynamics of second messengers is critical for ensuring compartmentation and localization of signaling molecules in cells. Specifically, the spatiotemporal orchestration of cAMP and Ca2+ oscillations is critical for many cellular functions. Previous experimental studies have shown that the formation of nanodomains of A-kinase anchoring protein 79/150 (AKAP150) and adenylyl cyclase 8 (AC8) on the surface of pancreatic MIN6 β cells modulates the phase of Ca2+-cAMP oscillations from out-of-phase to in-phase. In this work, we develop computational models of the Ca2+/cAMP pathway and AKAP/AC nanodomain formation that give rise to the two important predictions: instead of an arbitrary phase difference, the out-of-phase Ca2+/cAMP oscillation reaches Ca2+ trough and cAMP peak simultaneously, which is defined as inversely out-of-phase; the in-phase and inversely out-of-phase oscillations associated with Ca2+-cAMP dynamics on and away from the nanodomains can be explained by an incoherent feedforward loop. Factors such as cellular surface-to-volume ratio, compartment size, and distance between nanodomains do not affect the existence of in-phase or inversely out-of-phase Ca2+/cAMP oscillation, but cellular surface-to-volume ratio and compartment size can affect the time delay for the inversely out-of-phase Ca2+/cAMP oscillation while the distance between two nanodomains does not. Finally, we predict that both the Turing pattern-generated nanodomains and experimentally measured nanodomains demonstrate the existence of in-phase and inversely out-of-phase Ca2+/cAMP oscillation when the AC8 is at a low level, consistent with the behavior of an incoherent feedforward loop. These findings unveil the key circuit motif that governs cAMP and Ca2+ oscillations and advance our understanding of how nanodomains can lead to spatial compartmentation of second messengers.

TXNIP Regulates NLRP3 Inflammasome-Induced Pyroptosis Related to Aging via cAMP/PKA and PI3K/Akt Signaling Pathways

Aging is an inevitable natural process with time-dependent dysfunction and the occurrence of various diseases, which impose heavy burdens on individuals, families, and society. It has been reported that NLRP3 inflammasome-induced pyroptosis contributes significantly to age-related diseases and aging, while TXNIP is suggested to be involved in regulating pyroptosis mediated by NLRP3. However, the mechanism between TXNIP and NLRP3 inflammasome is still unclear. In this study, we used HT-22 cells to explore the effect of TXNIP on pyroptosis and its potential association with the aging. Also, we delved into the underlying mechanisms. Our findings revealed that TXNIP significantly augmented pyroptosis in HT-22 cells, primarily by enhancing the activation of the NLRP3 inflammasome and promoting the release of proinflammatory cytokines. Remarkably, as TXNIP levels increased, we observed a corresponding rise in the number of p16-positive cells, which is indicative of aging. Furthermore, we conducted experiments to modulate the improvement of TXNIP on NLRP3 inflammasome-induced pyroptosis, that is, the PI3K activator 740 Y-P and the PKA activator DC2797 inhibited the effect, while the PI3K inhibitor LY294002 and the PKA inhibitor H89 enhanced the effect. In conclusion, our study demonstrated that TXNIP regulates NLRP3 inflammasome-induced pyroptosis in HT-22 cells related to aging via the PI3K/Akt and cAMP/PKA pathways.

Spatial organization of adenylyl cyclase and its impact on dopamine signaling in neurons

The cAMP cascade is increasingly recognized to transduce physiological effects locally through spatially limited cAMP gradients. However, little is known about how adenylyl cyclase enzymes that initiate cAMP gradients are localized. Here we address this question in physiologically relevant striatal neurons and investigate how AC localization impacts downstream signaling function. We show that the major striatal AC isoforms are differentially sorted between ciliary and extraciliary domains of the plasma membrane, and that one isoform, AC9, is uniquely concentrated in endosomes. We identify key sorting determinants in the N-terminal cytoplasmic domain responsible for isoform-specific localization. We further show that AC9-containing endosomes accumulate activated dopamine receptors and form an elaborately intertwined network with juxtanuclear PKA stores bound to Golgi membranes. Finally, we provide evidence that endosomal localization enables AC9 to selectively elevate PKA activity in the nucleus relative to the cytoplasm. Together, these results reveal a precise spatial landscape of the cAMP cascade in neurons and a key role of AC localization in directing downstream PKA signaling to the nucleus.

Mesenchymal stem cells in tumor microenvironment: drivers of bladder cancer progression through mitochondrial dynamics and energy production

Mesenchymal stem cells (MSCs) in tumor microenvironment (TME) are crucial for the initiation, development, and metastasis of cancer. The impact and mechanism of MSCs on bladder cancer are uncertain. Here we analyzed 205 patient samples to explore the relationships between tumor-stroma ratio and clinicopathological features. A co-culture model and nude mouse transplantation were used to explore the biological roles and molecular mechanisms of MSCs on bladder cancer cells. We found that a high tumor-stroma ratio was significantly associated with a larger tumor size and higher T stage, pathological grade, number of vascular invasions, and poor overall survival. MSCs in TME promoted the ability of bladder cancer cells to proliferate, migrate, and invade in vitro and in vivo. Next, we demonstrated that MSCs enhance mitochondrial autophagy and mitochondrial biogenesis of bladder cancer cells, and increase energy production, thereby promoting bladder cancer cell progression. Kynurenine (Kyn) produced by MSCs could enhance mitochondrial function by activating the AMPK pathway. IDO1 inhibitor could reverse the tumor‑promoting effects of MSCs in vitro and in vivo. Our results demonstrated that tryptophan metabolites Kyn of MSCs in TME could enhance mitochondrial function by activating the AMPK pathway, thereby promoting bladder cancer cell progression.

Comparison of the Genomic Activity of an EP4-Receptor and β2-Adrenoceptor Agonist in BEAS-2B Human Bronchial Epithelial Cells: In Search of Compartmentalized, cAMP-Dependent Gene Expression

It has been proposed that inhaled E-prostanoid 4 (EP4)-receptor agonists could represent a new class of bronchodilators for the treatment of asthma that are as effective as β 2-adrenoceptor agonists. However, the genomic impact of such drugs is unknown despite being potentially deleterious to respiratory health. Herein, we used mRNA-seq to compare the transcriptomic responses produced by 2-[3-[(1R,2S,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxo-cyclopentyl]sulphanylpropylsulphanyl] acetic acid (ONO-AE1-329; an EP4-receptor agonist) and vilanterol (a β 2-adrenoceptor agonist) in BEAS-2B human airway epithelial cells. We also determined if an increase in cAMP mediated by different G protein-coupled receptors (GPCRs) promoted distinct transcriptional signatures by expanding this inquiry to include the adenosine A2B- and I-prostanoid receptor agonists, 2-[[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]-2-pyridinyl]thio]-acetamide (Bay60-6583) and taprostene, respectively. Maximally-effective concentrations of ONO-AE1-329 and vilanterol significantly regulated (q ≤ 0.05; ≥1.5-/≤0.67-fold) 232 and 320 genes, respectively of which 217 were shared. Spearman analysis showed these gene expression changes to be highly rank order correlated, indicating that the functional overlap between the two interventions should be considerable. Unexpectedly, the genomic effects of ONO-AE1-329, vilanterol, Bay 60-6583, and taprostene were also highly rank order correlated. This finding suggests that cAMP generated by any GPCR would initiate the same transcriptional program. Nevertheless, relative to vilanterol, ONO-AE1-329 typically behaved as a partial agonist that varied across transcripts. These data indicate that each ONO-AE1-329-regulated gene differs in sensitivity to cAMP and is defined by a unique receptor occupancy-response relationship. Moreover, if this relatively modest genomic response in BEAS-2B cells is retained in vivo, then inhaled EP4-receptor agonists could represent an alternative, and possibly safer, class of bronchodilators. SIGNIFICANCE STATEMENT: The genomic consequences of β 2-adrenoceptor agonists in asthma are often overlooked despite being potentially harmful to lung health. We determined that ONO-AE1-329, an EP4-receptor agonist and effective bronchodilator, produced gene expression changes in BEAS-2B cells that were typically modest relative to the β 2-adrenoceptor agonist vilanterol. Furthermore, ONO-AE1-329 behaved as a partial agonist that varied across transcripts. If this genomic activity is reproduced in vivo, then EP4-receptor agonists could represent an alternative, and possibly safer, class of bronchodilators.

Cyclic adenosine 3', 5'-monophosphate (cAMP) signaling is a crucial therapeutic target for ulcerative colitis

The pathogenesis of ulcerative colitis (UC), a chronic intestine inflammatory disease primarily affecting adolescents, remains uncertain. Contemporary studies suggest that a confluence of elements, including genetic predispositions, environmental catalysts, dysregulated immune responses, and disturbances in the gut microbiome, are instrumental in the initiation and advancement of UC. Among them, inflammatory activation and mucosal barrier damage caused by abnormal immune regulation are essential links in the development of UC. The impairment of the mucosal barrier is intricately linked to the interplay of various cellular mechanisms, including oxidative stress, autophagy, and programmed cell death. An extensive corpus of research has elucidated that level of cyclic adenosine 3',5'-monophosphate (cAMP) undergo modifications in the midst of inflammation and participate in a diverse array of cellular operations that mitigate inflammation and the impairment of the mucosal barrier. Consequently, a plethora of pharmacological agents are currently under development, with some advancing through clinical trials, and are anticipated to garner approval as novel therapeutics. In summary, cAMP exerts a crucial influence on the onset and progression of UC, with fluctuations in its activity being intimately associated with the severity of the disease's manifestation. Significantly, this review unveils the paramount role of cAMP in the advancement of UC, offering a tactical approach for the clinical management of individuals afflicted with UC.

Investigating the potential role of the pituitary adenylate cyclase-activating polypeptide (PACAP) in regulating the ubiquitin signaling pathway in poultry

The physiological processes in animal production are regulated through biologically active molecules like peptides, proteins, and hormones identified through the development of the fundamental sciences and their application. One of the main polypeptides that plays an essential role in regulating physiological responses is the pituitary adenylate cyclase-activating polypeptide (PACAP). PACAP belongs to the glucagon/growth hormone-releasing hormone (GHRH)/vasoactive intestinal proteins (VIP) family and regulates feed intake, stress, and immune response in birds. Most of these regulations occur after PACAP stimulates the cAMP signaling pathway, which can regulate the expression of genes like MuRF1, FOXO1, Atrogin 1, and other ligases that are essential members of the ubiquitin system. On the other hand, PACAP stimulates the secretion of CRH in response to stress, activating the ubiquitin signaling pathway that plays a vital role in protein degradation and regulates oxidative stress and immune responses. Many studies conducted on rodents, mammals, and other models confirm the regulatory effects of PACAP, cAMP, and the ubiquitin pathway; however, there are no studies testing whether PACAP-induced cAMP signaling in poultry regulates the ubiquitin pathway. Besides, it would be interesting to investigate if PACAP can regulate ubiquitin signaling during stress response via CRH altered by HPA axis stimulation. Therefore, this review highlights a summary of research studies that indicate the potential interaction of the PACAP and ubiquitin signaling pathways on different molecular and physiological parameters in poultry species through the cAMP and stress signaling pathways.

A molecular mechanism to diversify Ca2+ signaling downstream of Gs protein-coupled receptors

A long-held tenet in inositol-lipid signaling is that cleavage of membrane phosphoinositides by phospholipase Cβ (PLCβ) isozymes to increase cytosolic Ca2+ in living cells is exclusive to Gq- and Gi-sensitive G protein-coupled receptors (GPCRs). Here we extend this central tenet and show that Gs-GPCRs also partake in inositol-lipid signaling and thereby increase cytosolic Ca2+. By combining CRISPR/Cas9 genome editing to delete Gαs, the adenylyl cyclase isoforms 3 and 6, or the PLCβ1-4 isozymes, with pharmacological and genetic inhibition of Gq and G11, we pin down Gs-derived Gβγ as driver of a PLCβ2/3-mediated cytosolic Ca2+ release module. This module does not require but crosstalks with Gαs-dependent cAMP, demands Gαq to release PLCβ3 autoinhibition, but becomes Gq-independent with mutational disruption of the PLCβ3 autoinhibited state. Our findings uncover the key steps of a previously unappreciated mechanism utilized by mammalian cells to finetune their calcium signaling regulation through Gs-GPCRs.

Role of autonomic nervous system in BDE-209 maternal exposure induced immunotoxicity in female offspring

Decabrominated diphenyl ether (BDE-209) is a typical persistent organic pollutant that can cross the placental barrier, increasing the exposure risk for offspring. Norepinephrine (NE) from nerve terminals and acetylcholine (Ach) can bind to specific receptors on immune cells, inhibit the immune function of the body then cause immunotoxicity. However, whether maternal exposure to BDE-209 could lead to immunotoxicity in the offspring by acting on the sympathetic and parasympathetic nervous systems remains unclear. In view of this, the pregnancy and lactation rat BDE-209 exposure model was established and the results demonstrated that pregnancy and lactation BDE-209 exposure could induce immunotoxicity to female offspring via affecting immunopathology (hematological and biochemical parameters, organ indices, and spleen histopathological), decreasing humoral immunity (serum hemolysin, immunoglobulins, and cytokine productions), damaging cellular immunity (splenic lymphocytes and spleen cytokine productions), and restraining nonspecific immunity. Moreover, a dramatically significant correlation was observed between spleen nerve indices and immunity indices. Additionally, the mechanism revealed that maternal BDE-209 exposure caused offspring immunotoxicity through (1) activating MHC/PKCθ/NF-κB pathway; (2) promoting sympathetic nervous pathway, by upregulating the expression of β2AR protein, which in turn elevating cAMP, following activate PKA and phosphorylate CREB, ultimately leading to immunotoxicity;(3) activating parasympathetic nerve pathway by reducing the binding with Ach and α7nAchR, upregulating the expression of JAK2 and phosphorylating STAT3, induced immunotoxicity of female offspring.

Cyclic Adenosine Monophosphate Signaling in Chronic Kidney Disease: Molecular Targets and Therapeutic Potentials

Chronic kidney disease (CKD) is characterized by a steady decline in kidney function and affects roughly 10% of the world's population. This review focuses on the critical function of cyclic adenosine monophosphate (cAMP) signaling in CKD, specifically how it influences both protective and pathogenic processes in the kidney. cAMP, a critical secondary messenger, controls a variety of cellular functions, including transcription, metabolism, mitochondrial homeostasis, cell proliferation, and apoptosis. Its compartmentalization inside cellular microdomains ensures accurate signaling. In kidney physiology, cAMP is required for hormone-regulated activities, particularly in the collecting duct, where it promotes water reabsorption through vasopressin signaling. Several illnesses, including Fabry disease, renal cell carcinoma, nephrogenic diabetes insipidus, Bartter syndrome, Liddle syndrome, diabetic nephropathy, autosomal dominant polycystic kidney disease, and renal tubular acidosis, have been linked to dysfunction in the cAMP system. Both cAMP analogs and phosphodiesterase inhibitors have the potential to improve kidney function and reduce kidney damage. Future research should focus on developing targeted PDE inhibitors for the treatment of CKD.

Live Cell Monitoring of Phosphodiesterase Inhibition by Sulfonylurea Drugs

Sulfonylureas (SUs) are a class of antidiabetic drugs widely used in the management of diabetes mellitus type 2. They promote insulin secretion by inhibiting the ATP-sensitive potassium channel in pancreatic β-cells. Recently, the exchange protein directly activated by cAMP (Epac) was identified as a new class of target proteins of SUs that might contribute to their antidiabetic effect, through the activation of the Ras-like guanosine triphosphatase Rap1, which has been controversially discussed. We used human embryonic kidney (HEK) 293 cells expressing genetic constructs of various Förster resonance energy transfer (FRET)-based biosensors containing different versions of Epac1 and Epac2 isoforms, alone or fused to different phosphodiesterases (PDEs), to monitor SU-induced conformational changes in Epac or direct PDE inhibition in real time. We show that SUs can both induce conformational changes in the Epac2 protein but not in Epac1, and directly inhibit the PDE3 and PDE4 families, thereby increasing cAMP levels in the direct vicinity of these PDEs. Furthermore, we demonstrate that the binding site of SUs in Epac2 is distinct from that of cAMP and is located between the amino acids E443 and E460. Using biochemical assays, we could also show that tolbutamide can inhibit PDE activity through an allosteric mechanism. Therefore, the cAMP-elevating capacity due to allosteric PDE inhibition in addition to direct Epac activation may contribute to the therapeutic effects of SU drugs.

Beyond PDE4 inhibition: A comprehensive review on downstream cAMP signaling in the central nervous system

Cyclic adenosine monophosphate (cAMP) is a key second messenger that regulates signal transduction pathways pivotal for numerous biological functions. Intracellular cAMP levels are spatiotemporally regulated by their hydrolyzing enzymes called phosphodiesterases (PDEs). It has been shown that increased cAMP levels in the central nervous system (CNS) promote neuroplasticity, neurotransmission, neuronal survival, and myelination while suppressing neuroinflammation. Thus, elevating cAMP levels through PDE inhibition provides a therapeutic approach for multiple CNS disorders, including multiple sclerosis, stroke, spinal cord injury, amyotrophic lateral sclerosis, traumatic brain injury, and Alzheimer's disease. In particular, inhibition of the cAMP-specific PDE4 subfamily is widely studied because of its high expression in the CNS. So far, the clinical translation of full PDE4 inhibitors has been hampered because of dose-limiting side effects. Hence, focusing on signaling cascades downstream activated upon PDE4 inhibition presents a promising strategy, offering novel and pharmacologically safe targets for treating CNS disorders. Yet, the underlying downstream signaling pathways activated upon PDE(4) inhibition remain partially elusive. This review provides a comprehensive overview of the existing knowledge regarding downstream mediators of cAMP signaling induced by PDE4 inhibition or cAMP stimulators. Furthermore, we highlight existing gaps and future perspectives that may incentivize additional downstream research concerning PDE(4) inhibition, thereby providing novel therapeutic approaches for CNS disorders.

"Radical" differences between two FLIM microscopes affect interpretation of cell signaling dynamics

The outcome of cell signaling depends not only on signal strength but also on temporal progression. We use Fluorescence Lifetime Imaging of Resonance Energy Transfer (FLIM/FRET) biosensors to investigate intracellular signaling dynamics. We examined the β1 receptor-Gαs-cAMP signaling axis using both widefield frequency domain FLIM (fdFLIM) and fast confocal time-correlated single photon counting (TCSPC) setups. Unexpectedly, we observed that fdFLIM revealed transient cAMP responses in HeLa and Cos7 cells, contrasting with sustained responses as detected with TCSPC. Investigation revealed no light-induced effects on cAMP generation or breakdown. Rather, folic acid present in the imaging medium appeared to be the culprit, as its excitation with blue light sensitized degradation of β1 agonists. Our findings highlight the impact of subtle phototoxicity on experimental outcomes, advocating confocal TCSPC for reliable analysis of response kinetics and stressing the need for full disclosure of chemical formulations by scientific vendors.

Role of the V2R-βarrestin-Gβγ complex in promoting G protein translocation to endosomes

Classically, G protein-coupled receptors (GPCRs) promote signaling at the plasma membrane through activation of heterotrimeric Gαβγ proteins, followed by the recruitment of GPCR kinases and βarrestin (βarr) to initiate receptor desensitization and internalization. However, studies demonstrated that some GPCRs continue to signal from internalized compartments, with distinct cellular responses. Both βarr and Gβγ contribute to such non-canonical endosomal G protein signaling, but their specific roles and contributions remain poorly understood. Here, we demonstrate that the vasopressin V2 receptor (V2R)-βarr complex scaffolds Gβγ at the plasma membrane through a direct interaction with βarr, enabling its transport to endosomes. Gβγ subsequently potentiates Gαs endosomal translocation, presumably to regenerate an endosomal pool of heterotrimeric Gs. This work shines light on the mechanism underlying G protein subunits translocation from the plasma membrane to the endosomes and provides a basis for understanding the role of βarr in mediating sustained G protein signaling.

Primary cilia, A-kinase anchoring proteins and constitutive activity at the orphan G protein-coupled receptor GPR161: A tale about a tail

Primary cilia are non-motile antennae-like structures responsible for sensing environmental changes in most mammalian cells. Ciliary signalling is largely mediated by the Sonic Hedgehog (Shh) pathway, which acts as a master regulator of ciliary protein transit and is essential for normal embryonic development. One particularly important player in primary cilia is the orphan G protein-coupled receptor, GPR161. In this review, we introduce GPR161 in the context of Shh signalling and describe the unique features on its C-terminus such as PKA phosphorylation sites and an A-kinase anchoring protein motif, which may influence the function of the receptor, cAMP compartmentalisation and/or trafficking within primary cilia. We discuss the recent putative pairing of GPR161 and spexin-1, highlighting the additional steps needed before GPR161 could be considered 'deorphanised'. Finally, we speculate that the marked constitutive activity and unconventional regulation of GPR161 may indicate that the receptor may not require an endogenous ligand. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Differential Downregulation of β1-Adrenergic Receptor Signaling in the Heart

BACKGROUND

Chronic sympathetic stimulation drives desensitization and downregulation of β1 adrenergic receptor (β1AR) in heart failure. We aim to explore the differential downregulation subcellular pools of β1AR signaling in the heart.

METHODS AND RESULTS

We applied chronic infusion of isoproterenol to induced cardiomyopathy in male C57BL/6J mice. We applied confocal and proximity ligation assay to examine β1AR association with L-type calcium channel, ryanodine receptor 2, and SERCA2a ((Sarco)endoplasmic reticulum calcium ATPase 2a) and Förster resonance energy transfer-based biosensors to probe subcellular β1AR-PKA (protein kinase A) signaling in ventricular myocytes. Chronic infusion of isoproterenol led to reduced β1AR protein levels, receptor association with L-type calcium channel and ryanodine receptor 2 measured by proximity ligation (puncta/cell, 29.65 saline versus 14.17 isoproterenol, P<0.05), and receptor-induced PKA signaling at the plasma membrane (Förster resonance energy transfer, 28.9% saline versus 1.9% isoproterenol, P<0.05) and ryanodine receptor 2 complex (Förster resonance energy transfer, 30.2% saline versus 10.6% isoproterenol, P<0.05). However, the β1AR association with SERCA2a was enhanced (puncta/cell, 51.4 saline versus 87.5 isoproterenol, P<0.05), and the receptor signal was minimally affected. The isoproterenol-infused hearts displayed decreased PDE4D (phosphodiesterase 4D) and PDE3A and increased PDE2A, PDE4A, and PDE4B protein levels. We observed a reduced role of PDE4 and enhanced roles of PDE2 and PDE3 on the β1AR-PKA activity at the ryanodine receptor 2 complexes and myocyte shortening. Despite the enhanced β1AR association with SERCA2a, the endogenous norepinephrine-induced signaling was reduced at the SERCA2a complexes. Inhibiting monoamine oxidase A rescued the norepinephrine-induced PKA signaling at the SERCA2a and myocyte shortening.

CONCLUSIONS

This study reveals distinct mechanisms for the downregulation of subcellular β1AR signaling in the heart under chronic adrenergic stimulation.

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

Cyclic Adenosine Monophosphate in Cardiac and Sympathoadrenal GLP-1 Receptor Signaling: Focus on Anti-Inflammatory Effects

Glucagon-like peptide-1 (GLP-1) is a multifunctional incretin hormone with various physiological effects beyond its well-characterized effect of stimulating glucose-dependent insulin secretion in the pancreas. An emerging role for GLP-1 and its receptor, GLP-1R, in brain neuroprotection and in the suppression of inflammation, has been documented in recent years. GLP-1R is a G protein-coupled receptor (GPCR) that couples to Gs proteins that stimulate the production of the second messenger cyclic 3',5'-adenosine monophosphate (cAMP). cAMP, acting through its two main effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), exerts several anti-inflammatory (and some pro-inflammatory) effects in cells, depending on the cell type. The present review discusses the cAMP-dependent molecular signaling pathways elicited by the GLP-1R in cardiomyocytes, cardiac fibroblasts, central neurons, and even in adrenal chromaffin cells, with a particular focus on those that lead to anti-inflammatory effects by the GLP-1R. Fully elucidating the role cAMP plays in GLP-1R's anti-inflammatory properties can lead to new and more precise targets for drug development and/or provide the foundation for novel therapeutic combinations of the GLP-1R agonist medications currently on the market with other classes of drugs for additive anti-inflammatory effect.

Jiao-tai-wan and its effective component-berberine improve diabetes and depressive disorder through the cAMP/PKA/CREB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Jiao-tai-wan (JTW), a classic herbal formula of traditional Chinese medicine recorded in Han Shi Yi Tong, has been used to alleviate sleep disorders since ancient times. In modern pharmacological research, JTW has been adopted for treating diabetes mellitus and even exerts antidepressant effects. However, the potential mechanisms deserve further elucidation.

AIM OF THE STUDY

The prevalence of diabetes mellitus combined with depressive disorder (DD) is continuing to increase, yet it is currently under-recognized and its treatment remains inadequate. The present study aims to explore the underlying therapeutics and mechanisms of JTW on DD.

MATERIALS AND METHODS

Chronic restraint stress was used on db/db mice to construct a mouse model of DD. The therapeutic effects of JTW were assessed by glucolipid metabolic indexes, behavioral tests, and depression-related neurotransmitter levels. The inflammatory status and cell apoptosis of different mice were investigated and the changes in the cAMP/PKA/CREB pathway were detected. Combining the results of fingerprinting with molecular docking, the active components of JTW were screened. A cellular model was constructed by intervention of glucose combined with corticosterone (CORT). The levels of apoptosis and depression-related neurotransmitters in HT-22 cells were examined, and the changes in the cAMP/PKA/CREB pathway were tested. Finally, the activator and inhibitor of the PKA protein were used for reverse validation experiments.

RESULTS

JTW could improve the impaired glucose tolerance, lipid metabolism disorders, and depression-like symptoms in DD mice. Meanwhile, JTW could alleviate the inflammatory status, suppress the microglia activation, and improve hippocampal neuron apoptosis in DD mice. The dual effects of JTW might be associated with the activation of the cAMP/PKA/CREB pathway. Berberine (Ber) was identified for the in vitro experiment, it could reverse the apoptosis of HT-22 cells and up-regulate the depression-related neurotransmitter levels, and the effects of Ber were related to the activation of the cAMP/PKA/CREB pathway as well.

CONCLUSION

JTW could exert both hypoglycemic and antidepressant effects through activating the cAMP/PKA/CREB signaling pathway, its active component, Ber, could improve the damage to HT-22 cells induced by glucose combined with CORT via the activation of the cAMP/PKA/CREB pathway. Ber may be one of the effective components of the dual effects of JTW.

How enzyme-centered approaches are advancing research on cyclic oligo-nucleotides

Cyclic nucleotides are the most diversified category of second messengers and are found in all organisms modulating diverse pathways. While cAMP and cGMP have been studied over 50 years, cyclic di-nucleotide signaling in eukaryotes emerged only recently with the anti-viral molecule 2´3´cGAMP. Recent breakthrough discoveries have revealed not only the astonishing chemical diversity of cyclic nucleotides but also surprisingly deep-rooted evolutionary origins of cyclic oligo-nucleotide signaling pathways and structural conservation of the proteins involved in their synthesis and signaling. Here we discuss how enzyme-centered approaches have paved the way for the identification of several cyclic nucleotide signals, focusing on the advantages and challenges associated with deciphering the activation mechanisms of such enzymes.

Systems level analysis of time and stimuli specific signaling through PKA

It is well known that eukaryotic cells create gradients of cAMP across space and time to regulate the cAMP dependent protein kinase (PKA) and, in turn, growth and metabolism. However, it is unclear how PKA responds to different concentrations of cAMP. Here, to address this question, we examine PKA signaling in Saccharomyces cerevisiae in different conditions, timepoints, and concentrations of the chemical inhibitor 1-NM-PP1, using phosphoproteomics. These experiments show that there are numerous proteins that are only phosphorylated when cAMP and PKA activity are at/near their maximum level, while other proteins are phosphorylated even when cAMP levels and PKA activity are low. The data also show that PKA drives cells into distinct growth states by acting on proteins with different thresholds for phosphorylation in different conditions. Analysis of the sequences surrounding the 118 PKA-dependent phosphosites suggests that the phosphorylation thresholds are set, at least in part, by the affinity of PKA for each site.

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.