Ca2+-calmodulin-dependent phosphodiesterase (PDE1): Current perspectives

Ca2+-dependent phosphodiesterase 1 regulates the plasticity of striatal spiny projection neuron glutamatergic synapses

Long-term synaptic plasticity at glutamatergic synapses on striatal spiny projection neurons (SPNs) is central to learning goal-directed behaviors and habits. Our studies reveal that SPNs manifest a heterosynaptic, nitric oxide (NO)-dependent form of long-term postsynaptic depression of glutamatergic SPN synapses (NO-LTD) that is preferentially engaged at quiescent synapses. Plasticity is gated by Ca2+ entry through CaV1.3 Ca2+ channels and phosphodiesterase 1 (PDE1) activation, which blunts intracellular cyclic guanosine monophosphate (cGMP) and NO signaling. Both experimental and simulation studies suggest that this Ca2+-dependent regulation of PDE1 activity allows for local regulation of dendritic cGMP signaling. In a mouse model of Parkinson disease (PD), NO-LTD is absent because of impaired interneuronal NO release; re-balancing intrastriatal neuromodulatory signaling restores NO release and NO-LTD. Taken together, these studies provide important insights into the mechanisms governing NO-LTD in SPNs and its role in psychomotor disorders such as PD.

Ca 2+ -dependent phosphodiesterase 1 regulates the plasticity of striatal spiny projection neuron glutamatergic synapses

Long-term synaptic plasticity at glutamatergic synapses on striatal spiny projection neurons (SPNs) is central to learning goal-directed behaviors and habits. Although considerable attention has been paid to the mechanisms underlying synaptic strengthening and new learning, little scrutiny has been given to those involved in the attenuation of synaptic strength that attends suppression of a previously learned association. Our studies revealed a novel, non-Hebbian, long-term, postsynaptic depression of glutamatergic SPN synapses induced by interneuronal nitric oxide (NO) signaling (NO-LTD) that was preferentially engaged at quiescent synapses. This form of plasticity was gated by local Ca 2+ influx through CaV1.3 Ca 2+ channels and stimulation of phosphodiesterase 1 (PDE1), which degraded cyclic guanosine monophosphate (cGMP) and blunted NO signaling. Consistent with this model, mice harboring a gain-of-function mutation in the gene coding for the pore-forming subunit of CaV1.3 channels had elevated depolarization-induced dendritic Ca 2+ entry and impaired NO-LTD. Extracellular uncaging of glutamate and intracellular uncaging of cGMP suggested that this Ca 2+ -dependent regulation of PDE1 activity allowed for local regulation of dendritic NO signaling. This inference was supported by simulation of SPN dendritic integration, which revealed that dendritic spikes engaged PDE1 in a branch-specific manner. In a mouse model of Parkinson's disease (PD), NO-LTD was absent not because of a postsynaptic deficit in NO signaling machinery, but rather due to impaired interneuronal NO release. Re-balancing intrastriatal neuromodulatory signaling in the PD model restored NO release and NO-LTD. Taken together, these studies provide novel insights into the mechanisms governing NO-LTD in SPN and its role in psychomotor disorders, like PD.

Hesperetin Relaxes Depolarizing Contraction in Human Umbilical Vein by Inhibiting L-Type Ca2+ Channel

OBJECTIVE

To study hesperetin-induced vasorelaxation after depolarizing contraction in human umbilical veins (HUVs) to elucidate the role of L-type Ca2+ channel (LTCC) and related signaling pathway.

METHODS

Isometric tension recording was performed in HUV rings pre-contracted with K+. Hesperetin relaxing mechanism was investigated using a LTCC opener (BayK8644) and blockers of cyclic nucleotides and phosphodiesterases (PDEs). Whole-cell patch-clamping in A7r5 cells, a rat vascular smooth muscle cell line, was performed to study the effect of hesperetin on LTCC current.

RESULTS

After depolarizing precontraction, hesperetin induced HUV relaxation concentration-dependently and endothelium-independently; 1 mmol/L hesperetin reduced denuded HUV ring tension by 68.7% ± 4.3% compared to matching vehicle, osmolality, and time controls (P<0.0001). Importantly, hesperetin competitively inhibited BayK8644-induced contraction, shifting the half maximal effective concentration of BayK8644 response from 1.08 nmol/L [95% confidence interval (CI) 0.49-2.40] in vehicle control to 11.30 nmol/L (95% CI 5.45-23.41) in hesperetin (P=0.0001). Moreover, hesperetin elicited further vasorelaxation in denuded HUV rings pretreated with inhibitors of soluble guanylyl cyclase, adenylyl cyclase, PDE3, PDE4, and PDE5 (P<0.01), while rings pretreated with PDE1 inhibitors could not be relaxed by hesperetin (P>0.05). However, simultaneously applying inhibitors of soluble guanylyl cyclase and adenylyl cyclase could not inhibit hesperetin's effect (P>0.05). In whole-cell patch-clamping, hesperetin rapidly decreased LTCC current in A7r5 cells to 66.7% ± 5.8% (P=0.0104).

CONCLUSIONS

Hesperetin diminishes depolarizing contraction of human vascular smooth muscle through inhibition of LTCC, and not cyclic nucleotides nor PDEs. Our evidence supports direct LTCC interaction and provides additional basis for the use of hesperetin and its precursor hesperidin as vasodilators and may lead to future vasodilator drug development as a treatment alternative for cardiovascular diseases.

Advances in targeting Phosphodiesterase 1: From mechanisms to potential therapeutics

Phosphodiesterase 1 (PDE1) is an enzyme entrusted with the hydrolysis of the second messengers cAMP and cGMP, thereby governing a plethora of metabolic processes, encompassing ion channel modulation and cellular apoptosis. Recent advancements in the realm of small molecule structural variations have greatly facilitated the exploration of innovative applications for PDE1. Remarkably, a recent series of PDE1 inhibitors (PDE1i) have been meticulously formulated and devised, showcasing enhanced selectivity and potency. Among them, ITI-214 has entered Phase II clinical trials, holding promise for the treatment of Parkinson's disease and heart failure. Nevertheless, the majority of current PDE1 inhibitors have encountered substantial side effects in clinical trials attributable to their limited selectivity, this predicament presents a formidable obstacle in the development of specific small molecule inhibitors targeting PDE1. This Perspective endeavors to illuminate the potential design approaches, structure-activity relationships, and biological activities of current PDE1i, aiming to offer support and insights for clinical practice and the development of novel PDE1i.

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

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

Once upon a Testis: The Tale of Cyclic Nucleotide Phosphodiesterase in Testicular Cancers

Phosphodiesterases are key regulators that fine tune the intracellular levels of cyclic nucleotides, given their ability to hydrolyze cAMP and cGMP. They are critical regulators of cAMP/cGMP-mediated signaling pathways, modulating their downstream biological effects such as gene expression, cell proliferation, cell-cycle regulation but also inflammation and metabolic function. Recently, mutations in PDE genes have been identified and linked to human genetic diseases and PDEs have been demonstrated to play a potential role in predisposition to several tumors, especially in cAMP-sensitive tissues. This review summarizes the current knowledge and most relevant findings regarding the expression and regulation of PDE families in the testis focusing on PDEs role in testicular cancer development.

Ca 2+ /Calmodulin Dependent Protein Kinase Kinase-2 (CaMKK2) promotes Protein Kinase G (PKG)-dependent actin cytoskeletal assembly to increase tumor metastasis

Triple-negative breast cancers (TNBCs) tend to become highly invasive early during cancer development. Despite some successes in the initial treatment of patients diagnosed with early-stage localized TNBC, the rate of metastatic recurrence remains high with poor long-term survival outcomes. Here we show that elevated expression of the serine/threonine-kinase, Calcium/Calmodulin (CaM)-dependent protein kinase kinase-2 (CaMKK2), is highly correlated with tumor invasiveness. We determined that genetic disruption of CaMKK2 expression, or inhibition of its activity, disrupted spontaneous metastatic outgrowth from primary tumors in murine xenograft models of TNBC. High-grade serous ovarian cancer (HGSOC), a high-risk, poor-prognosis ovarian cancer subtype, shares many genetic features with TNBC, and importantly, CaMKK2 inhibition effectively blocked metastatic progression in a validated xenograft model of this disease. Probing the mechanistic links between CaMKK2 and metastasis we defined the elements of a new signaling pathway that impacts actin cytoskeletal dynamics in a manner which increases cell migration/invasion and metastasis. Notably, CaMKK2 increases the expression of the phosphodiesterase PDE1A which decreases the cGMP-dependent activity of protein kinase G1 (PKG1). This inhibition of PKG1 results in decreased phosphorylation of Vasodilator-Stimulated Phosphoprotein (VASP), which in its hypophosphorylated state binds to and regulates F-actin assembly to facilitate contraction/cell movement. Together, these data establish a targetable CaMKK2-PDE1A-PKG1-VASP signaling pathway that controls cancer cell motility and metastasis. Further, it credentials CaMKK2 as a therapeutic target that can be exploited in the discovery of agents for use in the neoadjuvant/adjuvant setting to restrict tumor invasiveness in patients diagnosed with early-stage TNBC or localized HGSOC.

The role of Phosphodiesterase-1 and its natural product inhibitors in Alzheimer's disease: A review

Phosphodiesterase-1 (PDE1) is a versatile enzyme that has surprisingly received considerable attention as a possible therapeutic target in Alzheimer's disease (AD) because it maintains the homeostasis of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in the brain. 3',5'-cyclic adenosine monophosphate and 3',5'-cyclic guanosine monophosphate are the two key second messengers that regulate a broad range of intracellular processes and neurocognitive functions, specifically memory and cognition, associated with Alzheimer's disease. However, the lack of available selective drugs on the market poses challenges to identifying the beneficial effects of natural products. The present review focuses on Phosphodiesterase-1 and its isoforms, splicing variants, location, distribution, and function; the role of Phosphodiesterase-1 inhibitors in Alzheimer's disease; and the use of vinpocetine and natural products as specific Phosphodiesterase-1 inhibitors. Moreover, it aims to provide ongoing updates, identify research gaps, and present future perspectives. This review indicates the potential role of Phosphodiesterase-1 inhibitors in the treatment of neurodegenerative disorders, such as Alzheimer's disease. Certain clinical trials on the alleviation of Alzheimer's disease in patients are still in progress. Among de novo outcomes, the employment of Phosphodiesterase-1 inhibitors to treat Alzheimer's disease is an important advancement given the absence of particular therapies in the pipeline for this highly prevalent disease. To sum up, Phosphodiesterase-1 inhibition has been specifically proposed as a critical therapeutic approach for Alzheimer's disease. This study provides a comprehensive review on the biological and pharmacological aspects of Phosphodiesterase-1, its role on the Alzheimer's diseases and its significance as Alzheimer's disease therapeutic target in drug discovery from natural products. This review will help clinical trials and scientific research exploring new entities for the treatment and prevention of Alzheimer's disease.

Spatial and temporal crosstalk between the cAMP and Ca2+ signaling systems

The ubiquitous secondary messengers, Ca²⁺ and cAMP, play a vital role in shaping a diverse array of physiological processes. More significantly, accumulating evidence over the past several decades underpin extensive crosstalk between these two canonical messengers in discrete sub-cellular nanodomains across various cell types. Within such specialized nanodomains, each messenger fine-tunes signaling to maintain homeostasis by manipulating the activities of cellular machinery accountable for the metabolism or activity of the complementary pathway. Interaction between these messengers is ensured by scaffolding proteins which tether components of the signaling machinery in close proximity. Disruption of dynamic communications between Ca²⁺ and cAMP at these loci consequently is linked to several pathological conditions. This review summarizes recent novel mechanisms underlying effective crosstalk between Ca²⁺ and cAMP in such nanodomains.

Structural Modifications of Nimodipine Lead to Novel PDE1 Inhibitors with Anti-pulmonary Fibrosis Effects

Our previous research demonstrated that phosphodiesterase-1 (PDE1) could work as a potential target against idiopathic pulmonary fibrosis. Nimodipine, a calcium antagonist commonly used to improve hypertension, was reported to have inhibition against PDE1. Herein, a series of nimodipine analogues were discovered as novel selective and potent PDE1 inhibitors after structural modifications. Compound 2g exhibited excellent inhibitory activity against PDE1C (IC₅₀ = 10 nM), high selectivity over other PDEs except for PDE4, and weak calcium channel antagonistic activity. Administration of compound 2g exhibited remarkable therapeutic effects in a rat model of pulmonary fibrosis induced by bleomycin and prevented myofibroblast differentiation induced by TGF-β1. The expressions of PDE1B and PDE1C were found to be increased and concentrated in the focus of fibrosis. Compound 2g increased the levels of 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in the lungs of rats with pulmonary fibrosis, supporting the fact that the anti-fibrosis effects of 2g were through the regulation of cAMP and cGMP.

PDE1 inhibitors: a review of the recent patent literature (2008-present)

INTRODUCTION

: PDE1 has been demonstrated to be a potential drug target for a variety of diseases, such as Alzheimer's disease and cardiovascular disease. In the past decades, numerous PDE1 inhibitors with structural diversities have been developed and patented by pharmaceutical companies, providing drug candidates for exploring novel disease indications of PDE1.

AREA COVERED

: This review aims to provide an overview of PDE1 inhibitors reported in patents from 2008 to present.

EXPERT OPINION

: Among current PDE1 inhibitors, only a few of them showed high selectivity over other PDEs, which might cause severe side effects in clinic. The development of highly selective PDE1 inhibitors is still the "top priority" in the following research. The selective recognition mechanism of PDE1 with inhibitors should be further elucidated by X-ray crystallography in order to provide evidences for the rational design of selective PDE1 inhibitors. In addition, PDE1 inhibitors should be applied in the different clinical indications beyond CNS diseases.

Presynaptic AMPA Receptors in Health and Disease

AMPA receptors (AMPARs) are ionotropic glutamate receptors that play a major role in excitatory neurotransmission. AMPARs are located at both presynaptic and postsynaptic plasma membranes. A huge number of studies investigated the role of postsynaptic AMPARs in the normal and abnormal functioning of the mammalian central nervous system (CNS). These studies highlighted that changes in the functional properties or abundance of postsynaptic AMPARs are major mechanisms underlying synaptic plasticity phenomena, providing molecular explanations for the processes of learning and memory. Conversely, the role of AMPARs at presynaptic terminals is as yet poorly clarified. Accruing evidence demonstrates that presynaptic AMPARs can modulate the release of various neurotransmitters. Recent studies also suggest that presynaptic AMPARs may possess double ionotropic-metabotropic features and that they are involved in the local regulation of actin dynamics in both dendritic and axonal compartments. In addition, evidence suggests a key role of presynaptic AMPARs in axonal pathology, in regulation of pain transmission and in the physiology of the auditory system. Thus, it appears that presynaptic AMPARs play an important modulatory role in nerve terminal activity, making them attractive as novel pharmacological targets for a variety of pathological conditions.

Characterization of a functional V1B vasopressin receptor in the male rat kidney: evidence for cross talk between V1B and V2 receptor signaling pathways

Although vasopressin V_1B receptor (V_1BR) mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using the selective V_1B agonist d[Leu⁴, Lys⁸]VP, either fluorescent or radioactive, we showed that V_1BR is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V_1BR were very low compared with the V₂ receptor (V₂R). On the microdissected IMCD, d[Leu⁴, Lys⁸]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca²⁺ concentration increase mobilization with an EC₅₀ value in the nanomolar range. This effect involved both intracellular Ca²⁺ mobilization and extracellular Ca²⁺ influx. The selective V_1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca²⁺ concentration but also cAMP, suggesting a cooperation between V_1BR and V₂R in IMCD cells expressing both receptors. This cooperation arises from a cross talk between second messenger cascade involving PKC rather than receptor heterodimerization, as supported by potentiation of arginine vasopressin-stimulated cAMP production in human embryonic kidney-293 cells coexpressing the two receptor isoforms and negative results obtained by bioluminescence resonance energy transfer experiments. In vivo, only acute administration of high doses of V_1B agonist triggered significant diuretic effects, in contrast with injection of selective V₂ agonist. This study brings new data on the localization and signaling pathways of V_1BR in the kidney, highlights a cross talk between V_1BR and V₂R in the IMCD, and suggests that V_1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V₂R activation.NEW & NOTEWORTHY Although V_1BR mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using original pharmaceutical tools, this study brings new data on the localization and signaling pathways of V_1BR, highlights a cross talk between V_1BR and V₂ receptor (V₂R) in the inner medullary collecting duct, and suggests that V_1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V₂R activation.

PDE2 Inhibits PKA-Mediated Phosphorylation of TFAM to Promote Mitochondrial Ca2+-Induced Colorectal Cancer Growth

Growing evidence indicates that the dysregulation of mitochondrial calcium (Ca²⁺) plays a critical role in the growth of tumor cells, including colorectal cancer (CRC). However, the underling mechanism is not fully elucidated. In this study, the regulatory effects of mitochondrial Ca²⁺ on phosphodiesterase 2 (PDE2)/cAMP/PKA axis and the phosphorylation of mitochondrial transcription factor A (TFAM) as well as the growth of CRC cells were systematically investigated both in vitro and in vivo. Our findings demonstrated that MCU-induced mitochondrial Ca²⁺ uptake activated mitochondrial PDE2 in CRC cells. Moreover, overexpression MCU in CRC led to a 1.9-fold increase in Ca²⁺ uptake compared to control cells. However, knockdown of MCU resulted in 1.5-fould decrease in Ca²⁺ uptake in mitochondria compared to the controls. Activation of mitochondrial PDE2 significantly inhibited the activity of mitochondrial protein kinase A (PKA), which subsequently leads to decreased phosphorylation of TFAM. Our data further revealed that PKA regulates the phosphorylation of TFAM and promotes the degradation of phosphorylated TFAM. Thus, TFAM protein levels accumulated in mitochondria when the activity of PKA was inhibited. Overall, this study showed that the overexpression of MCU enhanced CRC growth through promoting the accumulation of TFAM proteins in mitochondria. Conversely, knockdown of MCU in CRC cells resulted in decreased CRC growth. Collectively, these data suggest that the mitochondrial Ca²⁺-activated PDE2/cAMP/PKA axis plays a key role in regulating TFAM stability and the growth of CRC cells.

The Role of PDE8 in T Cell Recruitment and Function in Inflammation

Inhibitors targeting cyclic nucleotide phosphodiesterases (PDEs) expressed in leukocytes have entered clinical practice to treat inflammatory disorders, with three PDE4 inhibitors currently in clinical use as therapeutics for psoriasis, psoriatic arthritis, atopic dermatitis and chronic obstructive pulmonary disease. In contrast, the PDE8 family that is upregulated in pro-inflammatory T cells is a largely unexplored therapeutic target. It was shown that PDE8A plays a major role in controlling T cell and breast cancer cell motility, including adhesion to endothelial cells under physiological shear stress and chemotaxis. This is a unique function of PDE8 not shared by PDE4, another cAMP specific PDE, employed, as noted, as an anti-inflammatory therapeutic. Additionally, a regulatory role was shown for the PDE8A-rapidly accelerated fibrosarcoma (Raf)-1 kinase signaling complex in myelin antigen reactive CD4⁺ effector T cell adhesion and locomotion by a mechanism differing from that of PDE4. The PDE8A-Raf-1 kinase signaling complex affects T cell motility, at least in part, via regulating the LFA-1 integrin mediated adhesion to ICAM-1. The findings that PDE8A and its isoforms are expressed at higher levels in naive and myelin oligodendrocyte glycoprotein (MOG)_35–55 activated effector T (Teff) cells compared to regulatory T (Treg) cells and that PDE8 inhibition specifically affects MOG_35–55 activated Teff cell adhesion, indicates that PDE8A could represent a new beneficial target expressed in pathogenic Teff cells in CNS inflammation. The implications of this work for targeting PDE8 in inflammation will be discussed in this review.

Phosphodiesterase 1 Bridges Glutamate Inputs with NO- and Dopamine-Induced Cyclic Nucleotide Signals in the Striatum

The calcium-regulated phosphodiesterase 1 (PDE1) family is highly expressed in the brain, but its functional role in neurones is poorly understood. Using the selective PDE1 inhibitor Lu AF64196 and biosensors for cyclic nucleotides including a novel biosensor for cGMP, we analyzed the effect of PDE1 on cAMP and cGMP in individual neurones in brain slices from male newborn mice. Release of caged NMDA triggered a transient increase of intracellular calcium, which was associated with a decrease in cAMP and cGMP in medium spiny neurones in the striatum. Lu AF64196 alone did not increase neuronal cyclic nucleotide levels, but blocked the NMDA-induced reduction in cyclic nucleotides indicating that this was mediated by calcium-activated PDE1. Similar effects were observed in the prefrontal cortex and the hippocampus. Upon corelease of dopamine and NMDA, PDE1 was shown to down-regulate the D1-receptor mediated increase in cAMP. PDE1 inhibition increased long-term potentiation in rat ventral striatum, showing that PDE1 is implicated in the regulation of synaptic plasticity. Overall, our results show that PDE1 reduces cyclic nucleotide signaling in the context of glutamate and dopamine coincidence. This effect could have a therapeutic value for treating brain disorders related to dysfunctions in dopamine neuromodulation.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

Modulation of polycystic kidney disease by G-protein coupled receptors and cyclic AMP signaling

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a systemic disorder associated with polycystic liver disease (PLD) and other extrarenal manifestations, the most common monogenic cause of end-stage kidney disease, and a major burden for public health. Many studies have shown that alterations in G-protein and cAMP signaling play a central role in its pathogenesis. As for many other diseases (35% of all approved drugs target G-protein coupled receptors (GPCRs) or proteins functioning upstream or downstream from GPCRs), treatments targeting GPCR have shown effectiveness in slowing the rate of progression of ADPKD. Tolvaptan, a vasopressin V2 receptor antagonist is the first drug approved by regulatory agencies to treat rapidly progressive ADPKD. Long-acting somatostatin analogs have also been effective in slowing the rates of growth of polycystic kidneys and liver. Although no treatment has so far been able to prevent the development or stop the progression of the disease, these encouraging advances point to G-protein and cAMP signaling as a promising avenue of investigation that may lead to more effective and safe treatments. This will require a better understanding of the relevant GPCRs, G-proteins, cAMP effectors, and of the enzymes and A-kinase anchoring proteins controlling the compartmentalization of cAMP signaling. The purpose of this review is to provide an overview of general GPCR signaling; the function of polycystin-1 (PC1) as a putative atypical adhesion GPCR (aGPCR); the roles of PC1, polycystin-2 (PC2) and the PC1-PC2 complex in the regulation of calcium and cAMP signaling; the cross-talk of calcium and cAMP signaling in PKD; and GPCRs, adenylyl cyclases, cyclic nucleotide phosphodiesterases, and protein kinase A as therapeutic targets in ADPKD.

Recombinant outer membrane protein C of Aeromonas salmonicida subsp. masoucida, a potential vaccine candidate for rainbow trout (Oncorhynchus mykiss)

Aeromonas salmonicida subsp. masoucida (ASM) is an important bacterial pathogen of salmonid fish, which can cause huge economic losses to the fish farming industry. In order to screen effective vaccine candidate proteins, four outer membrane proteins of ASM, including OmpA, OmpC, OmpK and OmpW, were selected and recombinantly expressed in Escherichia coli. The result of western blotting showed that these four recombinant proteins could be recognized by rainbow trout anti-ASM antibodies. The immune protective effects of the four rOMPs were also investigated, and the relative percentage survival (RPS) of rOmpA, rOmpC, rOmpK and rOmpW were 71.1%, 81.6%, 55.3% and 42.1%, respectively. The RPS of rOmpC was significantly higher than the other three rOMPs, so the immune responses of rainbow trout induced by rOmpC were further investigated. The results showed that vaccination with rOmpC could significantly induced the production of specific serum antibodies and proliferation of sIg + lymphocytes in peripheral blood. Meanwhile, RT-qPCR analysis showed that rOmpC could significantly enhance the expression of the MHC-II, TCR, CD4, CD8, IL-8 and IgM genes compared with the BSA immunized group. These results demonstrated that rOmpC could induce strong humoral immune response in rainbow trout and provided effective immune protection against ASM challenge, which indicated that OmpC is a promising vaccine candidate against Aeromonas salmonicida infection.

Computational Modeling Reveals Frequency Modulation of Calcium-cAMP/PKA Pathway in Dendritic Spines

Dendritic spines are the primary excitatory postsynaptic sites that act as subcompartments of signaling. Ca²⁺ is often the first and most rapid signal in spines. Downstream of calcium, the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway plays a critical role in the regulation of spine formation, morphological modifications, and ultimately, learning and memory. Although the dynamics of calcium are reasonably well-studied, calcium-induced cAMP/PKA dynamics, particularly with respect to frequency modulation, are not fully explored. In this study, we present a well-mixed model for the dynamics of calcium-induced cAMP/PKA dynamics in dendritic spines. The model is constrained using experimental observations in the literature. Further, we measured the calcium oscillation frequency in dendritic spines of cultured hippocampal CA1 neurons and used these dynamics as model inputs. Our model predicts that the various steps in this pathway act as frequency modulators for calcium, and the high frequency of calcium input is filtered by adenylyl cyclase 1 and phosphodiesterases in this pathway such that cAMP/PKA only responds to lower frequencies. This prediction has important implications for noise filtering and long-timescale signal transduction in dendritic spines. A companion manuscript presents a three-dimensional spatial model for the same pathway.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Regulation of cAMP accumulation and activity by distinct phosphodiesterase subtypes in INS-1 cells and human pancreatic β-cells

Pancreatic β-cells express multiple phosphodiesterase (PDE) subtypes, but the specific roles for each in β-cell function, particularly in humans, is not clear. We evaluated the cellular role of PDE1, PDE3, and PDE4 activity in the rat insulinoma cell line INS-1 and in primary human β-cells using subtype-selective PDE inhibitors. Using a genetically encoded, FRET-based cAMP sensor, we found that the PDE1 inhibitor 8MM-IBMX, elevated cAMP levels in the absence of glucose to a greater extent than either the PDE3 inhibitor cilostamide or the PDE4 inhibitor rolipram. In 18 mM glucose, PDE1 inhibition elevated cAMP levels to a greater extent than PDE3 inhibition in INS-1 cells, while PDE4 inhibition was without effect. Inhibition of PDE1 or PDE4, but not PDE3, potentiated glucose-stimulated insulin secretion in INS-1 cells. PDE1 inhibition, but not PDE3 or PDE4 inhibition, reduced palmitate-induced caspase-3/7 activation, and enhanced CREB phosphorylation in INS-1 cells. In human β-cells, only PDE3 or PDE4 inhibition increased cAMP levels in 1.7 mM glucose, but PDE1, PDE3, or PDE4 inhibition potentiated cAMP levels in 16.7 mM glucose. Inhibition of PDE1 or PDE4 increased cAMP levels to a greater extent in 16.7 mM glucose than in 1.7 mM glucose in human β-cells. In contrast, elevation of cAMP levels by PDE3 inhibition was not different at these glucose concentrations. PDE1 inhibition also potentiated insulin secretion from human islets, suggesting that the role of PDE1 may be conserved between INS-1 cells and human pancreatic β-cells. Our results suggest that inhibition of PDE1 may be a useful strategy to potentiate glucose-stimulated insulin secretion, and to protect β-cells from the toxic effects of excess fatty acids.

Protein-Protein Interactions of Phosphodiesterases

BACKGROUND

Phosphodiesterases (PDEs) are enzymes that play a key role in terminating cyclic nucleotides signalling by catalysing the hydrolysis of 3', 5'- cyclic adenosine monophosphate (cAMP) and/or 3', 5' cyclic guanosine monophosphate (cGMP), the second messengers within the cell that transport the signals produced by extracellular signalling molecules which are unable to get into the cells. However, PDEs are proteins which do not operate alone but in complexes that made up of a many proteins.

OBJECTIVE

This review highlights some of the general characteristics of PDEs and focuses mainly on the Protein-Protein Interactions (PPIs) of selected PDE enzymes. The objective is to review the role of PPIs in the specific mechanism for activation and thereby regulation of certain biological functions of PDEs.

METHODS

The article discusses some of the PPIs of selected PDEs as reported in recent scientific literature. These interactions are critical for understanding the biological role of the target PDE.

RESULTS

The PPIs have shown that each PDE has a specific mechanism for activation and thereby regulation a certain biological function.

CONCLUSION

Targeting of PDEs to specific regions of the cell is based on the interaction with other proteins where each PDE enzyme binds with specific protein(s) via PPIs.

Arginase II activity regulates cytosolic Ca2+ level in a p32-dependent manner that contributes to Ca2+-dependent vasoconstriction in native low-density lipoprotein-stimulated vascular smooth muscle cells

Although arginase II (ArgII) is abundant in mitochondria, Ca²⁺-accumulating organelles, the relationship between ArgII activity and Ca²⁺ translocation into mitochondria and the regulation of cytosolic Ca²⁺ signaling are completely unknown. We investigated the effects of ArgII activity on mitochondrial Ca²⁺ uptake through mitochondrial p32 protein (p32m) and on CaMKII-dependent vascular smooth muscle cell (VSMC) contraction. Native low-density lipoprotein stimulation induced an increase in [Ca²⁺]m as measured by CoCl₂-quenched calcein-AM fluorescence, which was prevented by Arg inhibition in hAoSMCs and reduced in mAoSMCs from ArgII^−/− mice. Conversely, [Ca²⁺]c analyzed with Fluo-4 AM was increased by Arg inhibition and ArgII gene knockout. The increased [Ca²⁺]c resulted in CaMKII and MLC 20 phosphorylation, which was associated with enhanced vasoconstriction activity to phenylephrine (PE) in the vascular tension assay. Cy5-tagged siRNA against mitochondrial p32 mRNA (sip32m) abolished mitochondrial Ca²⁺ uptake and induced activation of CaMKII. Spermine, a polyamine, induced mitochondrial Ca²⁺ uptake and dephosphorylation of CaMKII and was completely inhibited by sip32m incubation. In mAoSMCs from ApoE-null mice fed a high-cholesterol diet (ApoE^−/− +HCD), Arg activity was increased, and spermine concentration was higher than that of wild-type mice. Furthermore, [Ca²⁺]m and p32m levels were elevated, and CaMKII phosphorylation was reduced in mAoSMCs from ApoE^−/− +HCD. In vascular tension experiments, an attenuated response to vasoconstrictors in de-endothelialized aorta from ApoE^−/− +HCD was recovered by incubation of sip32m. ArgII activity-dependent production of spermine augments Ca²⁺ transition from the cytosol to the mitochondria in a p32m-dependent manner and regulates CaMKII-dependent constriction in VSMCs.

Researchers have illuminated how a protein, arginase II (ArgII), is involved in development of vascular diseases such as atherosclerosis, or narrowing of the arteries by plaque deposits. Blood vessel diameter is regulated by layers of muscle; the balance between constriction and relaxation is critical for blood flow and vascular health. Increased ArgII is known to be a factor in arterial disease; however, the details of regulation, and how they relate to plaque deposition, remain poorly understood. Sungwoo Ryoo at Kangwon National University, Chuncheon, South Korea and co-workers investigated how ArgII levels affect arterial constriction and relaxation in mice. Decreasing ArgII restored the muscle cells’ contraction response by preventing excessive calcium accumulation in the cellular powerhouse, mitochondria. These results may aid in developing treatments for one of the leading causes of death worldwide.

A simple, robust, universal assay for real-time enzyme monitoring by signalling changes in nucleoside phosphate anion concentration using a europium(iii)-based anion receptor

Enzymes that consume and produce nucleoside polyphosphate (NPP) anions represent major targets in drug discovery. For example, protein kinases are one of the largest classes of drug targets in the fight against cancer. The accurate determination of enzyme kinetics and mechanisms is a critical aspect of drug discovery research. To increase confidence in the selection of lead drug compounds it is crucial that pharmaceutical researchers have robust, affordable assays to measure enzyme activity accurately. We present a simple, sensitive microplate assay for real-time monitoring of a range of pharmaceutically important enzyme reactions that generate NPP anions, including kinases and glycosyltransferases. Our assay utilises a single, stable europium(iii) complex that binds reversibly to NPP anions, signalling the dynamic changes in NPP product/substrate ratio during an enzyme reaction using time-resolved luminescence. This supramolecular approach to enzyme monitoring overcomes significant limitations in existing assays, obviating the need for expensive antibodies or equipment, chemically labelled substrates or products and isolation or purification steps. Our label and antibody-free method enables rapid and quantitative analysis of enzyme activities and inhibition, offering a potentially powerful tool for use in drug discovery, suitable for high-throughput screening of inhibitors and accurate measurements of enzyme kinetic parameters.

A predictive computational model reveals that GIV/girdin serves as a tunable valve for EGFR-stimulated cyclic AMP signals

Cellular levels of the versatile second messenger cyclic (c)AMP are regulated by the antagonistic actions of the canonical G protein → adenylyl cyclase pathway that is initiated by G-protein–coupled receptors (GPCRs) and attenuated by phosphodiesterases (PDEs). Dysregulated cAMP signaling drives many diseases; for example, its low levels facilitate numerous sinister properties of cancer cells. Recently, an alternative paradigm for cAMP signaling has emerged in which growth factor–receptor tyrosine kinases (RTKs; e.g., EGFR) access and modulate G proteins via a cytosolic guanine-nucleotide exchange modulator (GEM), GIV/girdin; dysregulation of this pathway is frequently encountered in cancers. In this study, we present a network-based compartmental model for the paradigm of GEM-facilitated cross-talk between RTKs and G proteins and how that impacts cellular cAMP. Our model predicts that cross-talk between GIV, Gα_s, and Gα_i proteins dampens ligand-stimulated cAMP dynamics. This prediction was experimentally verified by measuring cAMP levels in cells under different conditions. We further predict that the direct proportionality of cAMP concentration as a function of receptor number and the inverse proportionality of cAMP concentration as a function of PDE concentration are both altered by GIV levels. Taking these results together, our model reveals that GIV acts as a tunable control valve that regulates cAMP flux after growth factor stimulation. For a given stimulus, when GIV levels are high, cAMP levels are low, and vice versa. In doing so, GIV modulates cAMP via mechanisms distinct from the two most often targeted classes of cAMP modulators, GPCRs and PDEs.

Nutritional recovery from a low-protein diet during pregnancy does not restore the kinetics of insulin secretion and Ca2+ or alterations in the cAMP/PKA and PLC/PKC pathways in islets from adult rats

We investigated the insulin release induced by glucose, the Ca²⁺ oscillatory pattern, and the cyclic AMP (cAMP)/protein kinase A (PKA) and phospholipase C (PLC)/protein kinase C (PKC) pathways in islets from adult rats that were reared under diets with 17% protein (C) or 6% protein (LP) during gestation, suckling, and after weaning and in rats receiving diets with 6% protein during gestation and 17% protein after birth (R). First-phase glucose-induced insulin secretion was reduced in LP and R islets, and the second phase was partially restored in the R group. Glucose stimulation did not modify intracellular Ca²⁺ concentration, but it reduced the Ca²⁺ oscillatory frequency in the R group compared with the C group. Intracellular cAMP concentration was higher and PKA-Cα expression was lower in the R and LP groups compared with the C group. The PKCα content in islets from R rats was lower than that in C and LP rats. Thus, nutritional recovery from a low-protein diet during fetal life did not repair the kinetics of insulin release, impaired Ca²⁺ handling, and altered the cAMP/PKA and PLC/PKC pathways.

Phosphodiesterase 1b (PDE1B) Regulates Spatial and Contextual Memory in Hippocampus

Augmentation of cyclic nucleotide signaling through inhibition of phosphodiesterase (PDE) activity has long been understood to enhance memory. Efforts in this domain have focused predominantly on PDE4, a cAMP-specific phosphodiesterase implicated in consolidation. But less is known about the function of other PDEs expressed in neuroanatomical regions critical to memory. The PDE1 isoforms are the only PDEs to regulate neuronal cAMP and cGMP levels in a Ca²⁺/Calmodulin (CaM) dependent manner. Here, we show that knock-down of PDE1B in hippocampus of adult mice enhances contextual and spatial memory without effect on non-cognitive behaviors. Pharmacological augmentation of memory in rats was observed with a selective inhibitor of PDE1 dosed before and immediately after training, but not with drug dosed either 1 h after training or before recall. Our data clearly demonstrate a role for the PDE1B isoforms as negative regulators of memory, and they implicate PDE1 in an early phase of consolidation, but not retrieval. Inhibition of PDE1B is a promising therapeutic mechanism for treating memory impairment.

Mouse Cardiac Pde1C Is a Direct Transcriptional Target of Pparα

Phosphodiesterase 1C (PDE1C) is expressed in mammalian heart and regulates cardiac functions by controlling levels of second messenger cyclic AMP and cyclic GMP (cAMP and cGMP, respectively). However, molecular mechanisms of cardiac Pde1c regulation are currently unknown. In this study, we demonstrate that treatment of wild type mice and H9c2 myoblasts with Wy-14,643, a potent ligand of nuclear receptor peroxisome-proliferator activated receptor alpha (PPARα), leads to elevated cardiac Pde1C mRNA and cardiac PDE1C protein, which correlate with reduced levels of cAMP. Furthermore, using mice lacking either Pparα or cardiomyocyte-specific Med1, the major subunit of Mediator complex, we show that Wy-14,643-mediated Pde1C induction fails to occur in the absence of Pparα and Med1 in the heart. Finally, using chromatin immunoprecipitation assays we demonstrate that PPARα binds to the upstream Pde1C promoter sequence on two sites, one of which is a palindrome sequence (agcTAGGttatcttaacctagc) that shows a robust binding. Based on these observations, we conclude that cardiac Pde1C is a direct transcriptional target of PPARα and that Med1 may be required for the PPARα mediated transcriptional activation of cardiac Pde1C.

Inhibitors of phosphodiesterase as cancer therapeutics

Phosphodiesterases (PDEs) are a class of enzymes that hydrolyze cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which is involved in many physiological processes including visual transduction, cell proliferation and differentiation, cell-cycle regulation, gene expression, inflammation, apoptosis, and metabolic function. PDEs are composed of 11 different families and each family contains different subtypes. The distribution, expression, regulation mode and sensitivity to inhibitors of each subtype are different, and they are involved in cancer, inflammation, asthma, depression, erectile dysfunction and other pathological processes of development. A large number of studies have shown that PDEs play an important role in the development of tumors by affecting the intracellular level of cAMP and/or cGMP and PDEs could become diagnostic markers or therapeutic targets. This review will give a brief overview of the expression and regulation of PDE families in the process of tumorigenesis and their anti-tumor inhibitors, which may guide the design of novel therapeutic drugs targeting PDEs for anticancer agent.

Inhibition of phosphodiesterases as a strategy to achieve neuroprotection in Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative condition, due to a mutation in the IT15 gene encoding for huntingtin. Currently, disease-modifying therapy is not available for HD, and only symptomatic drugs are administered for the management of symptoms. In the last few years, preclinical and clinical studies have indicated that pharmacological strategies aimed at inhibiting cyclic nucleotide phosphodiesterase (PDEs) may develop into a novel therapeutic approach in neurodegenerative disorders. PDEs are a family of enzymes that hydrolyze cyclic nucleotides into monophosphate isoforms. Cyclic nucleotides are second messengers that transduce the signal of hormones and neurotransmitters in many physiological processes, such as protein kinase cascades and synaptic transmission. An alteration in their balance results in the dysregulation of different biological mechanisms (transcriptional dysregulation, immune cell activation, inflammatory mechanisms, and regeneration) that are involved in neurological diseases. In this review, we discuss the action of phosphodiesterase inhibitors and their role as therapeutic agents in HD.

Roles of A-Kinase Anchoring Proteins and Phosphodiesterases in the Cardiovascular System

A-kinase anchoring proteins (AKAPs) and cyclic nucleotide phosphodiesterases (PDEs) are essential enzymes in the cyclic adenosine 3′-5′ monophosphate (cAMP) signaling cascade. They establish local cAMP pools by controlling the intensity, duration and compartmentalization of cyclic nucleotide-dependent signaling. Various members of the AKAP and PDE families are expressed in the cardiovascular system and direct important processes maintaining homeostatic functioning of the heart and vasculature, e.g., the endothelial barrier function and excitation-contraction coupling. Dysregulation of AKAP and PDE function is associated with pathophysiological conditions in the cardiovascular system including heart failure, hypertension and atherosclerosis. A number of diseases, including autosomal dominant hypertension with brachydactyly (HTNB) and type I long-QT syndrome (LQT1), result from mutations in genes encoding for distinct members of the two classes of enzymes. This review provides an overview over the AKAPs and PDEs relevant for cAMP compartmentalization in the heart and vasculature and discusses their pathophysiological role as well as highlights the potential benefits of targeting these proteins and their protein-protein interactions for the treatment of cardiovascular diseases.

Phosphodiesterase 1: A Unique Drug Target for Degenerative Diseases and Cognitive Dysfunction

The focus of this chapter is on the cyclic nucleotide phosphodiesterase 1 (PDE1) family. PDE1 is one member of the 11 PDE families (PDE 1-11). It is the only phosphodiesterase family that is calcium/calmodulin activated. As a result, whereas other families of PDEs 2-11 play a dominant role controlling basal levels of cyclic nucleotides, PDE1 is involved when intra-cellular calcium levels are elevated and, thus, has an "on demand" or activity-dependent involvement in the control of cyclic nucleotides in excitatory cells including neurons, cardiomyocytes and smooth muscle. As a Class 1 phosphodiesterase, PDE1 hydrolyzes the 3' bond of 3'-5'-cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Here, we review evidence for this family of enzymes as drug targets for development of therapies aimed to address disorders of the central nervous system (CNS) and of degenerative diseases. The chapter includes sections on the potential for cognitive enhancement in mental disorders, as well as a review of PDE1 enzyme structure, enzymology, tissue distribution, genomics, inhibitors, pharmacology, clinical trials, and therapeutic indications. Information is taken from public databases. A number of excellent reviews of the phosphodiesterase family have been written as well as reviews of the PDE1 family. References cited here are not comprehensive, rather pointing to major reviews and key publications.

The role of hydrogen sulfide in cyclic nucleotide signaling

Hydrogen sulfide (H₂S) is recognized as an endogenous gaseous transmitter alongside nitric oxide (NO) and carbon monoxide (CO). By integrating into multiple signaling pathways, H₂S elicits biological functions in various mammalian systems. Among these pathways, cyclic nucleotide signaling has gradually gained attention in the past decade. Based on current evidence, it seems that H₂S may differentially affect the activity of resting adenylyl cyclases (ACs) and activated ACs, therefore playing a dual role in the regulation of cyclic adenosine monophosphate (cAMP) mediated signaling. However, how H₂S achieves the differential regulation on ACs remains unknown at molecular level. In the context of cyclic guanosine monophosphate (cGMP) regulation, H₂S augments its downstream signaling at least through three different mechanisms: (1) H₂S potentiates the response of soluble guanylyl cyclases (sGCs) to NO; (2) H₂S inhibits activity of phosphodiesterases (PDEs); and (3) H₂S enhances the production of NO. By regulating cyclic nucleotide signaling, H₂S possesses therapeutic potentials particularly for hypertension and cardiac injury which have also been discussed in the current review. Nevertheless, a detailed portrayal of H₂S mediated interaction with target proteins is still required for a better understanding of the role of this important gaseous mediator in regulating cyclic nucleotide signaling.

Generation and phenotypic characterization of Pde1a mutant mice

It has been proposed that a reduction in intracellular calcium causes an increase in intracellular cAMP and PKA activity through stimulation of calcium inhibitable adenylyl cyclase 6 and inhibition of phosphodiesterase 1 (PDE1), the main enzymes generating and degrading cAMP in the distal nephron and collecting duct, thus contributing to the development and progression of autosomal dominant polycystic kidney disease (ADPKD). In zebrafish pde1a depletion aggravates and overexpression ameliorates the cystic phenotype. To study the role of PDE1A in a mammalian system, we used a TALEN pair to Pde1a exon 7, targeting the histidine-aspartic acid dipeptide involved in ligating the active site Zn⁺⁺ ion to generate two Pde1a null mouse lines. Pde1a mutants had a mild renal cystic disease and a urine concentrating defect (associated with upregulation of PDE4 activity and decreased protein kinase A dependent phosphorylation of aquaporin-2) on a wild-type genetic background and aggravated renal cystic disease on a Pkd2^WS25/- background. Pde1a mutants additionally had lower aortic blood pressure and increased left ventricular (LV) ejection fraction, without a change in LV mass index, consistent with the high aortic and low cardiac expression of Pde1a in wild-type mice. These results support an important role of PDE1A in the renal pathogenesis of ADPKD and in the regulation of blood pressure.

The regulatory 1α subunit of protein kinase A modulates renal cystogenesis

The failure of the polycystins (PCs) to function in primary cilia is thought to be responsible for autosomal dominant polycystic kidney disease (ADPKD). Primary cilia integrate multiple cellular signaling pathways, including calcium, cAMP, Wnt, and Hedgehog, which control cell proliferation and differentiation. It has been proposed that mutated PCs result in reduced intracellular calcium, which in turn upregulates cAMP, protein kinase A (PKA) signaling, and subsequently other proliferative signaling pathways. However, the role of PKA in ADPKD has not been directly ascertained in vivo, although the expression of the main regulatory subunit of PKA in cilia and other compartments (PKA-RIα, encoded by PRKAR1A) is increased in a mouse model orthologous to ADPKD. Therefore, we generated a kidney-specific knockout of Prkar1a to examine the consequences of constitutive upregulation of PKA on wild-type and Pkd1 hypomorphic (Pkd1^RC) backgrounds. Kidney-specific loss of Prkar1a induced renal cystic disease and markedly aggravated cystogenesis in the Pkd1^RC models. In both settings, it was accompanied by upregulation of Src, Ras, MAPK/ERK, mTOR, CREB, STAT3, Pax2 and Wnt signaling. On the other hand, Gli3 repressor activity was enhanced, possibly contributing to hydronephrosis and impaired glomerulogenesis in some animals. To assess the relevance of these observations in humans we looked for and found evidence for kidney and liver cystic phenotypes in the Carney complex, a tumoral syndrome caused by mutations in PRKAR1A These observations expand our understanding of the pathogenesis of ADPKD and demonstrate the importance of PRKAR1A highlighting PKA as a therapeutic target in ADPKD.

Enzymatic activity of the CaM-PDE1 system upon addition of actinyl ions

The threat of a dirty bomb which could cause internal contamination has been of major concern for the past decades. Because of their high chemical toxicity and their presence in the nuclear fuel cycle, uranium and neptunium are two actinides of high interest. Calmodulin (CaM) which is a ubiquitous protein present in all eukaryotic cells and is involved in calcium-dependent signaling pathways has a known affinity for uranyl and neptunyl ions. The impact of the complexation of these actinides on the physiological response of the protein remains, however, largely unknown. An isothermal titration calorimetry (ITC) was developed to monitor in vitro the enzymatic activity of the phosphodiesterase enzyme which is known to be activated by CaM and calcium. This approach showed that addition of actinyl ions (AnO₂ⁿ⁺), uranyl (UO₂²⁺) and neptunyl (NpO₂⁺), resulted in a decrease of the enzymatic activity, due to the formation of CaM-actinide complexes, which inhibit the enzyme and alter its interaction with the substrate by direct interaction. Results from dynamic light scattering rationalized this result by showing that the CaM-actinyl complexes adopted a specific conformation different from that of the CaM-Ca²⁺ complex. The effect of actinides could be reversed using a hydroxypyridonate actinide decorporation agent (5-LIO(Me-3,2-HOPO)) in the experimental medium demonstrating its capacity to efficiently bind the actinides and restore the calcium-dependent enzyme activation.

In silico design of novel hERG-neutral sildenafil-like PDE5 inhibitors

Cyclic nucleotide phosphodiesterase enzymes (PDEs) have functions in regulating the levels of intracellular second messengers, 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP), via hydrolysis and decomposing mechanisms in cells. They take essential roles in modulating various cellular activities such as memory and smooth muscle functions. PDE type 5 (PDE5) inhibitors enhance the vasodilatory effects of cGMP in the corpus cavernosum and they are used to treat erectile dysfunction. Patch clamp experiments showed that the IC₅₀ values of the human ether-à-go-go-related gene (hERG1) potassium (K) ion channel blocking affinity of PDE5 inhibitors sildenafil, vardenafil, and tadalafil as 33, 12, and 100 μM, respectively. hERG1 channel is responsible for the regulation of the action potential of human ventricular myocyte by contributing the rapid component of delayed rectifier K⁺ current (I_Kr) component of the cardiac action potential. In this work, interaction patterns and binding affinity predictions of selected PDE5 inhibitors against the hERG1 channel are studied. It is attempted to develop PDE5 inhibitor analogs with lower binding affinity to hERG1 ion channel while keeping their pharmacological activity against their principal target PDE5 using in silico methods. Based on detailed analyses of docking poses and predicted interaction energies, novel analogs of PDE5 inhibitors with lower predicted binding affinity to hERG1 channels without loosing their principal target activity were proposed. Moreover, molecular dynamics (MD) simulations and post-processing MD analyses (i.e. Molecular Mechanics/Generalized Born Surface Area calculations) were performed. Detailed analysis of molecular simulations helped us to better understand the PDE5 inhibitor-target binding interactions in the atomic level. Results of this study can be useful for designing of novel and safe PDE5 inhibitors with enhanced activity and other tailored properties.

Cross-regulation of Phosphodiesterase 1 and Phosphodiesterase 2 Activities Controls Dopamine-mediated Striatal α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Trafficking

Dopamine, a key striatal neuromodulator, increases synaptic strength by promoting surface insertion and/or retention of AMPA receptors (AMPARs). This process is mediated by the phosphorylation of the GluA1 subunit of AMPAR by cyclic nucleotide-dependent kinases, making cyclic nucleotide phosphodiesterases (PDEs) potential regulators of synaptic strength. In this study, we examined the role of phosphodiesterase 2 (PDE2), a medium spiny neuron-enriched and cGMP-activated PDE, in AMPAR trafficking. We found that inhibiting PDE2 resulted in enhancement of dopamine-induced surface GluA1 expression in dopamine receptor 1-expressing medium spiny neurons. Using pharmacological and genetic approaches, we found that inhibition of PDE1 resulted in a decrease in surface AMPAR levels because of the allosteric activation of PDE2. The cross-regulation of PDE1 and PDE2 activities results in counterintuitive control of surface AMPAR expression, making it possible to regulate the directionality and magnitude of AMPAR trafficking.

Deciphering and modulating G protein signalling in C. elegans using the DREADD technology

G-protein signalling is an evolutionary conserved concept highlighting its fundamental impact on developmental and functional processes. Studies on the effects of G protein signals on tissues as well as an entire organism are often conducted in Caenorhabditis elegans. To understand and control dynamics and kinetics of the processes involved, pharmacological modulation of specific G protein pathways would be advantageous, but is difficult due to a lack in accessibility and regulation. To provide this option, we designed G protein-coupled receptor-based designer receptors (DREADDs) for C. elegans. Initially described in mammalian systems, these modified muscarinic acetylcholine receptors are activated by the inert drug clozapine-N-oxide, but not by their endogenous agonists. We report a novel C. elegans-specific DREADD, functionally expressed and specifically activating G_q-protein signalling in vitro and in vivo which we used for modulating mating behaviour. Therefore, this novel designer receptor demonstrates the possibility to pharmacologically control physiological functions in C. elegans.

Modulation of Polycystic Kidney Disease Severity by Phosphodiesterase 1 and 3 Subfamilies

Aberrant intracellular calcium levels and increased cAMP signaling contribute to the development of polycystic kidney disease (PKD). cAMP can be hydrolyzed by various phosphodiesterases (PDEs). To examine the role of cAMP hydrolysis and the most relevant PDEs in the pathogenesis of PKD, we examined cyst development in Pde1- or Pde3-knockout mice on the Pkd2(-/WS25) background (WS25 is an unstable Pkd2 allele). These PDEs were selected because of their importance in cross-talk between calcium and cyclic nucleotide signaling (PDE1), control of cell proliferation and cystic fibrosis transmembrane conductance regulator (CFTR) -driven fluid secretion (PDE3), and response to vasopressin V2 receptor activation (both). In Pkd2(-/WS25) mice, knockout of Pde1a, Pde1c, or Pde3a but not of Pde1b or Pde3b aggravated the development of PKD and was associated with higher levels of protein kinase A-phosphorylated (Ser133) cAMP-responsive binding protein (P-CREB), activating transcription factor-1, and CREB-induced CRE modulator proteins in kidney nuclear preparations. Immunostaining also revealed higher expression of P-CREB in Pkd2(-/) (WS25);Pde1a(-/-), Pkd2(-) (/WS25);Pde1c(-/-), and Pkd2(-/) (WS25);Pde3a(-/-) kidneys. The cystogenic effect of desmopressin administration was markedly enhanced in Pkd2(-/WS25);Pde3a(-/-) mice, despite PDE3 accounting for only a small fraction of renal cAMP PDE activity. These observations show that calcium- and calmodulin-dependent PDEs (PDE1A and PDE1C) and PDE3A modulate the development of PKD, possibly through the regulation of compartmentalized cAMP pools that control cell proliferation and CFTR-driven fluid secretion. Treatments capable of increasing the expression or activity of these PDEs may, therefore, retard the development of PKD.

Modelling intracellular competition for calcium: kinetic and thermodynamic control of different molecular modes of signal decoding

Frequently, a common chemical entity triggers opposite cellular processes, which implies that the components of signalling networks must detect signals not only through their chemical natures, but also through their dynamic properties. To gain insights on the mechanisms of discrimination of the dynamic properties of cellular signals, we developed a computational stochastic model and investigated how three calcium ion (Ca²⁺)-dependent enzymes (adenylyl cyclase (AC), phosphodiesterase 1 (PDE1), and calcineurin (CaN)) differentially detect Ca²⁺ transients in a hippocampal dendritic spine. The balance among AC, PDE1 and CaN might determine the occurrence of opposite Ca²⁺-induced forms of synaptic plasticity, long-term potentiation (LTP) and long-term depression (LTD). CaN is essential for LTD. AC and PDE1 regulate, indirectly, protein kinase A, which counteracts CaN during LTP. Stimulations of AC, PDE1 and CaN with artificial and physiological Ca²⁺ signals demonstrated that AC and CaN have Ca²⁺ requirements modulated dynamically by different properties of the signals used to stimulate them, because their interactions with Ca²⁺ often occur under kinetic control. Contrarily, PDE1 responds to the immediate amplitude of different Ca²⁺ transients and usually with the same Ca²⁺ requirements observed under steady state. Therefore, AC, PDE1 and CaN decode different dynamic properties of Ca²⁺ signals.

BK channel regulation by phosphodiesterase type 1: a novel signaling pathway controlling human detrusor smooth muscle function

Large-conductance Ca(2+)-activated K(+) (BK) channels are critical regulators of detrusor smooth muscle (DSM) function. We aimed to investigate phosphodiesterase type 1 (PDE1) interactions with BK channels in human DSM to determine the mechanism by which PDE1 regulates human urinary bladder physiology. A combined electrophysiological, functional, and pharmacological approach was applied using human DSM specimens obtained from open bladder surgeries. The perforated whole cell patch-clamp technique was used to record transient BK currents (TBKCs) and the cell membrane potential in freshly isolated human DSM cells in combination with the selective PDE1 inhibitor, 8-methoxymethyl-3-isobutyl-1-methylxanthine (8MM-IBMX). Isometric DSM tension recordings were used to measure spontaneous phasic and electrical field stimulation-induced contractions in human DSM isolated strips. Selective pharmacological inhibition of PDE1 with 8MM-IBMX (10 μM) increased TBKC activity in human DSM cells, which was abolished by subsequent inhibition of protein kinase A (PKA) with H-89 (10 μM). The stimulatory effect of 8MM-IBMX on TBKCs was reversed upon activation of muscarinic acetylcholine receptors with carbachol (1 μM). 8MM-IBMX (10 μM) hyperpolarized the DSM cell membrane potential, an effect blocked by PKA inhibition. 8MM-IBMX significantly decreased spontaneous phasic and nerve-evoked contractions of human DSM isolated strips. The results reveal a novel mechanism that pharmacological inhibition of PDE1 attenuates human DSM excitability and contractility by activating BK channels via a PKA-dependent mechanism. The data also suggest interactions between PDE1 and muscarinic signaling pathways in human DSM. Inhibition of PDE1 can be a novel therapeutic approach for the treatment of overactive bladder associated with detrusor overactivity.

Direct action of capsaicin in brown adipogenesis and activation of brown adipocytes

The ingestion of capsaicin, the principle pungent component of red and chili peppers, induces thermogenesis, in part, through the activation of brown adipocytes expressing genes related to mitochondrial biogenesis and uncoupling such as peroxisome proliferator-activated receptor (Ppar) γ coactivator-1α (Pgc-1α) and uncoupling protein 1 (Ucp1). Capsaicin has been suggested to induce the activation of brown adipocytes, which is mediated by the stimulation of sympathetic nerves. However, capsaicin may directly affect the differentiation of brown preadipocytes, brown adipocyte function, or both, through its significant absorption. We herein demonstrated that Trpv1, a capsaicin receptor, is expressed in brown adipose tissue, and that its expression level is increased during the differentiation of HB2 brown preadipocytes. Furthermore, capsaicin induced calcium influx in brown preadipocytes. A treatment with capsaicin in the early stage of brown adipogenesis did not affect lipid accumulation or the expression levels of Fabp4 (a gene expressed in mature adipocytes), Pparγ2 (a master regulator of adipogenesis) or brown adipocyte-selective genes. In contrast, a treatment with capsaicin in the late stage of brown adipogenesis slightly increased the expression levels of Fabp4, Pparγ2 and Pgc-1α. Although capsaicin did not affect the basal expression level of Ucp1, Ucp1 induction by forskolin was partially inhibited by capsaicin, irrespective of the dose of capsaicin. The results of the present study suggest the direct effects of capsaicin on brown adipocytes or in the late stage of brown adipogenesis.

Astemizole-Histamine induces Beclin-1-independent autophagy by targeting p53-dependent crosstalk between autophagy and apoptosis

Apoptosis and autophagy are genetically regulated, evolutionarily conserved processes that can jointly seal cancer cell fates, and numerous death stimuli are capable of activating either pathway. Although crosstalk between apoptosis and autophagy is quite complex and sometimes contradictory, it remains a key factor determining the outcomes of death-related pathologies such as cancer. In the present study, exposure of MCF-7 breast cancer cells to HIS and the H1 receptor antagonist AST both alone and together with HIS (AST-HIS) led to generation of intracellular ROS, which induced massive cellular vacuolization through dilation of the ER and mitochondria. Consequently, apoptosis by Bax translocation, cytochrome c release, and caspase activation were triggered. In addition, AST-HIS caused ER stress-induced autophagy in MCF-7 cells, as evidenced by an increased LC3-II/LC3-I ratio, with surprisingly no changes in Beclin-1 expression. Non-canonical autophagy was induced via p53 phosphorylation, which increased p53-p62 interactions to enhance Beclin-1-independent autophagy as evidenced by immunocytochemistry and immunoprecipitation. In the absence of Beclin-1, enhanced autophagy further activated apoptosis through caspase induction. In conclusion, these findings indicate that AST-HIS-induced apoptosis and autophagy can be regulated by ROS-mediated signaling pathways.

Phosphodiesterase regulation of alcohol drinking in rodents

Alcohol use disorders are chronically relapsing conditions characterized by persistent drinking despite the negative impact on one's life. The difficulty of achieving and maintaining sobriety suggests that current treatments fail to fully address the underlying causes of alcohol use disorders. Identifying additional pathways controlling alcohol consumption may uncover novel targets for medication development to improve treatment options. One family of proteins recently implicated in the regulation of alcohol consumption is the cyclic nucleotide phosphodiesterases (PDEs). As an integral component in the regulation of the second messengers cyclic AMP and cyclic GMP, and thus their cognate signaling pathways, PDEs present intriguing targets for pharmacotherapies to combat alcohol use disorders. As activation of cAMP/cGMP-dependent signaling cascades can dampen alcohol intake, PDE inhibitors may provide a novel target for reducing excessive alcohol consumption, as has been proposed for PDE4 and PDE10A. This review highlights preclinical literature demonstrating the involvement of cyclic nucleotide-dependent signaling in neuronal and behavioral responses to alcohol, as well as detailing the capacity of various PDE inhibitors to modulate alcohol intake. Together these data provide a framework for evaluating the potential utility of PDE inhibitors as novel treatments for alcohol use disorders.

Regulatory Action of Calcium Ion on Cyclic AMP-Enhanced Expression of Implantation-Related Factors in Human Endometrial Cells

Decidualization of human endometrial stroma and gland development is mediated through cyclic AMP (cAMP), but the role of intracellular calcium ion (Ca2+) on cAMP mediated-signaling in human endometrial stroma and glandular epithelia has not been well-characterized. The present study was designed to investigate the role of intracellular Ca2+ on cAMP mediated-decidualization and gland maturation events, which can be identified by the up-regulation of prolactin and IGF-binding protein (IGFBP)1 in human endometrial stromal cells (ESCs), and cyclooxygenase 2 (COX2) and prostaglandin E2 (PGE2) and glandular epithelial EM-1 cells. Increases in decidual prolactin and IGFBP-1 transcript levels, induced by cAMP-elevating agents forskolin or dibutyryl cyclic AMP, were inhibited by Ca2+ influx into ESCs with Ca2+ ionophores (alamethicin, ionomycin) in a dose-dependent manner. Conversely, inhibitors of Ca2+ influx through L-type voltage-dependent Ca2+ channel (VDCC), nifedipine and verapamil, enhanced the decidual gene expression. Furthermore, dantrolene, an inhibitor of Ca2+ release from the intracellular Ca2+ store, up-regulated prolactin and IGFBP-1 expression. Ca2+ ionophores decreased intracellular cAMP concentrations, whereas nifedipine, verapamil or dantrolene increased cAMP concentrations in ESCs. In glandular epithelial cells, similar responses in COX2 expression and PGE2 production were found when intracellular cAMP levels were up-regulated by decreases in Ca2+ concentrations. Thus, a marked decrease in cytosolic Ca2+ levels caused the elevation of cAMP concentrations, resulting in enhanced expression of implantation-related factors including decidual markers. These findings suggest that fluctuation in cytosolic Ca2+ concentrations alters intracellular cAMP levels, which then regulate differentiation of endometrial stromal and glandular epithelial cells.

Polarized axonal surface expression of neuronal KCNQ potassium channels is regulated by calmodulin interaction with KCNQ2 subunit

KCNQ potassium channels composed of KCNQ2 and KCNQ3 subunits give rise to the M-current, a slow-activating and non-inactivating voltage-dependent potassium current that limits repetitive firing of action potentials. KCNQ channels are enriched at the surface of axons and axonal initial segments, the sites for action potential generation and modulation. Their enrichment at the axonal surface is impaired by mutations in KCNQ2 carboxy-terminal tail that cause benign familial neonatal convulsion and myokymia, suggesting that their correct surface distribution and density at the axon is crucial for control of neuronal excitability. However, the molecular mechanisms responsible for regulating enrichment of KCNQ channels at the neuronal axon remain elusive. Here, we show that enrichment of KCNQ channels at the axonal surface of dissociated rat hippocampal cultured neurons is regulated by ubiquitous calcium sensor calmodulin. Using immunocytochemistry and the cluster of differentiation 4 (CD4) membrane protein as a trafficking reporter, we demonstrate that fusion of KCNQ2 carboxy-terminal tail is sufficient to target CD4 protein to the axonal surface whereas inhibition of calmodulin binding to KCNQ2 abolishes axonal surface expression of CD4 fusion proteins by retaining them in the endoplasmic reticulum. Disruption of calmodulin binding to KCNQ2 also impairs enrichment of heteromeric KCNQ2/KCNQ3 channels at the axonal surface by blocking their trafficking from the endoplasmic reticulum to the axon. Consistently, hippocampal neuronal excitability is dampened by transient expression of wild-type KCNQ2 but not mutant KCNQ2 deficient in calmodulin binding. Furthermore, coexpression of mutant calmodulin, which can interact with KCNQ2/KCNQ3 channels but not calcium, reduces but does not abolish their enrichment at the axonal surface, suggesting that apo calmodulin but not calcium-bound calmodulin is necessary for their preferential targeting to the axonal surface. These findings collectively reveal calmodulin as a critical player that modulates trafficking and enrichment of KCNQ channels at the neuronal axon.