Molecular diversity of cyclic AMP signalling

Selectivity mechanism of phosphodiesterase isoform inhibitor through in silico investigations

Understanding the selectivity mechanism of inhibitors towards homology proteins helps to design selective candidates. Phosphodiesterase (PDE) family members act in the degradation of cAMP and cGMP, among which some isoforms such as PDE9A are attracting interest for Alzheimer's disease treatment, while PDE10A is used as target for treating schizophrenia. In this study, computational methods were used to investigate the major features of PDE9A/10A, with the purpose to provide deep understanding of the molecular mechanism of selective inhibition towards these two isoforms. Our result revealed that two conserved residues Gln453 and Phe456 were proven to be crucial for the binding affinity and inhibitory selectivity of PDE9A inhibitors. In addition, the high-affinity PDE9A inhibitors always interact with the conservative hydrophobic pocket as well as Tyr424 and Ala452 of PDE9A, while PDE10A selective inhibitors need to have two hydrophobic groups and two hydrogen bond donors to interact with the conservative Tyr693, Gln726, and Phe729 of PDE10A. This study provides valuable insights into the underlying mechanism of selective inhibition targeting PDE9A and PDE10A, for further search for potent and highly selective PDE9A/10A inhibitors.

Carvone Decreases Melanin Content by Inhibiting Melanoma Cell Proliferation via the Cyclic Adenosine Monophosphate (cAMP) Pathway

Melanin, which determines the color of the skin and hair, is initially synthesized to protect the skin from ultraviolet light; however, excessive melanin pigmentation caused by abnormal cell proliferation can result in various melanocytic lesions. Cyclic adenosine monophosphate (cAMP) is known to regulate cell cycle progression and consequently to inhibit the division of abnormally proliferating cells. In this work, we aimed to test whether carvone, a scent compound from plants, inhibits proliferation and subsequently reduces melanin content of melanoma cells and to determine whether its beneficial effects are mediated by the cAMP pathway. We found that carvone decreases melanin content and inhibits melanoma cell proliferation in a concentration-dependent manner. Meanwhile, it inhibited the activation of cell cycle-associated proteins such as cyclin-dependent kinase 1 (CDK1). Of note, the beneficial effects of carvone were abrogated by cAMP inhibition. Our findings indicate potential benefits of carvone for the treatment of melanomas and presumably other hyperpigmentation-related dermatological disorders such as melasmas, lentigines, and excessive freckles.

The chilling of adenylyl cyclase 9 and its translational potential

A recent break-through paper has revealed for the first time the high-resolution, three-dimensional structure of a mammalian trans-membrane adenylyl cyclase (tmAC) obtained by cryo-electronmicroscopy (cryo-EM). Reporting the structure of adenylyl cyclase 9 (AC9) in complex with activated Gsα, the cryo-EM study revealed that AC9 has three functionally interlinked, yet structurally distinct domains. The array of the twelve transmembrane helices is connected to the cytosolic catalytic core by two helical segments that are stabilized through the formation of a parallel coiled-coil. Surprisingly, in the presence of Gsα, the isoform-specific carboxyl-terminal tail of AC9 occludes the forskolin- as well as the active substrate-sites, resulting in marked autoinhibition of the enzyme. As AC9 has the lowest primary sequence homology with the eight further mammalian tmAC paralogues, it appears to be the best candidate for selective pharmacologic targeting. This is now closer to reality as the structural insight provided by the cryo-EM study indicates that all of the three structural domains are potential targets for bioactive agents. The present paper summarizes for molecular physiologists and pharmacologists what is known about the biological role of AC9, considers the potential modes of physiologic regulation, as well as pharmacologic targeting on the basis of the high-resolution cryo-EM structure. The translational potential of AC9 is considered upon highlighting the current state of genome-wide association screens, and the corresponding experimental evidence. Overall, whilst the high- resolution structure presents unique opportunities for the full understanding of the control of AC9, the data on the biological role of the enzyme and its translational potential are far from complete, and require extensive further study.

Direct stimulation of adenylyl cyclase 9 by the fungicide imidazole miconazole

In mammals, nine genes encode trans-membrane adenylyl cyclase (tmAC) isoforms that synthesize the intracellular messenger compound cAMP from ATP. As cAMP is produced in virtually all types of cell, isoform-selective modulators of tmAC would have major research and therapeutic potential. This study investigated the effects of fungicide imidazoles previously shown to suppress cAMP production in various tissues on the activities of tmAC isoforms AC1, 2, or 9 stably expressed in human embryonic kidney 293 cells. Intact cells, as well as crude membranes, were exposed to various imidazoles or known stimulators of tmAC and the ensuing changes in the production of cAMP analyzed. In crude membranes, the activity of AC9 in the presence of GDP-β-S was enhanced by miconazole with an EC₅₀ of ~ 8 μM, while AC1 and AC2 were inhibited with an IC₅₀ of ~ 20 μM. Clotrimazole (10-100 μM) was an inhibitor of all the ACs tested. Substrate saturation analysis indicated that miconazole increased the V_max of AC9 by 3-fold while having no effect on the K_m. In intact cells, the effect of miconazole on cAMP production through AC9 was additive with that of isoproterenol. The stimulation of cAMP production by miconazole was inhibited by Ca²⁺, and this could be prevented by the calcineurin blocker FK506. In sum, activation of AC9 by miconazole is through a mechanism distinct from that of forskolin, activated G proteins, or the COOH-terminal mediated autoinhibition. However, it is subject to the AC9 isoform-specific inhibition by Ca²⁺/calcineurin. Differential modulation of mammalian tmAC paralogs appears to be achievable by an imidazole with phenylated side chains. Optimization of the lead compound and exploration of the underlying mechanism(s) of action in more detail could exploit this further.

Magnocellular Vasopressin and the Mechanism of "Glucocorticoid Escape"

It is now widely accepted that magnocellular vasopressinergic neurons in the supraoptic and paraventricular nuclei participate in the control of adrenocorticotropin secretion by the anterior pituitary gland. However, it remains to be explored in further detail, when and how these multifunctional neurons are involved in the control of anterior pituitary function. This paper highlights the role of magnocellular vasopressin in the hypothalamic pituitary adrenocortical axis with special reference to escape from glucocorticoid feedback inhibition. The signaling mechanisms underlying glucocorticoid escape by pituitary corticotrope cells, as well as the wider physiologic and pathologic contexts in which escape is known to occur-namely strenuous exercise, and autoimmune inflammation will be considered. It is proposed that by inducing escape from glucocorticoid feedback inhibition at the pituitary level, magnocellular vasopressin is critically important for the anti-inflammatory, and immunosuppressant actions of endogenous corticosteroids.

LT-IIc, A Bacterial Type II Heat-Labile Enterotoxin, Induces Specific Lethality in Triple Negative Breast Cancer Cells by Modulation of Autophagy and Induction of Apoptosis and Necroptosis

Triple negative breast cancer (TNBC) remains a serious health problem with poor prognosis and limited therapeutic options. To discover novel approaches to treat TNBC, we screened cholera toxin (CT) and the members of the bacterial type II heat-labile enterotoxin family (LT-IIa, LT-IIb, and LT-IIc) for cytotoxicity in TNBC cells. Only LT-IIc significantly reduced viability of the TNBC cell lines BT549 and MDA-MB-231 (IC₅₀ = 82.32 nM). LT-IIc had no significant cytotoxic effect on MCF10A (IC₅₀ = 2600 nM), a non-tumorigenic breast epithelial cell line, and minimal effects on MCF7 and T47D, ER⁺ cells, or SKBR-3 cells, HER2⁺ cells. LT-IIc stimulated autophagy through inhibition of the mTOR pathway, while simultaneously inhibiting autophagic progression, as seen by accumulation of LC3B-II and p62. Morphologically, LT-IIc induced the formation of enlarged LAMP2+ autolysosomes, which was blocked by co-treatment with bafilomycin A1. LT-IIc induced apoptosis as demonstrated by the increase in caspase 3/7 activity and Annexin V staining. Co-treatment with necrostatin-1, however, demonstrated that the lethal response of LT-IIc is elicited, in part, by concomitant induction of necroptosis. Knockdown of ATG-5 failed to rescue LT-IIc-induced cytotoxicity, suggesting LT-IIc can exert its cytotoxic effects downstream or independently of autophagophore initiation. Collectively, these experiments demonstrate that LT-IIc acts bifunctionally, inducing autophagy, while simultaneously blocking autolysosomal progression in TNBC cells, inducing a specific cytotoxicity in this breast cancer subtype.

Auto-inhibition of adenylyl cyclase 9 (AC9) by an isoform-specific motif in the carboxyl-terminal region

Trans-membrane adenylyl cyclase (tmAC) isoforms show markedly distinct regulatory properties that have not been fully explored. AC9 is highly expressed in vital organs such as the heart and the brain. Here, we report that the isoform-specific carboxyl-terminal domain (C2b) of AC9 inhibits the activation of the enzyme by Gs-coupled receptors (GsCR). In human embryonic kidney cells (HEK293) stably overexpressing AC9, cAMP production by AC9 induced upon the activation of endogenous β-adrenergic and prostanoid GsCRs was barely discernible. Cells expressing AC9 lacking the C2b domain showed a markedly enhanced cAMP response to GsCR. Subsequent studies of the response of AC9 mutants to the activation of GsCR revealed that residues 1268-1276 in the C2b domain were critical for auto-inhibition. Two main species of AC9 of 130 K and ≥ 170 K apparent molecular weight were observed on immunoblots of rodent and human myocardial membranes with NH₂-terminally directed anti-AC9 antibodies. The lower molecular weight AC9 band did not react with antibodies directed against the C2b domain. It was the predominant species of AC9 in rodent heart tissue and some of the human samples. There is a single gene for AC9 in vertebrates, moreover, amino acids 957-1353 of the COOH-terminus are encoded by a single exon with no apparent signs of mRNA splicing or editing making it highly unlikely that COOH-terminally truncated AC9 could arise through the processing or editing of mRNA. Thus, deductive reasoning leads to the suggestion that proteolytic cleavage of the C2b auto-inhibitory domain may govern the activation of AC9 by GsCR.

Comparative transcriptomic and proteomic analysis of Arthrobacter sp. CGMCC 3584 responding to dissolved oxygen for cAMP production

Arthrobacter sp. CGMCC 3584 is able to produce high yields of extracellular cyclic adenosine monophosphate (cAMP), which plays a vital role in the field of treatment of disease and animal food, during aerobic fermentation. However, the molecular basis of cAMP production in Arthrobacter species is rarely explored. Here, for the first time, we report the comparative transcriptomic and proteomic study of Arthrobacter cells to elucidate the higher productivity of cAMP under high oxygen supply. We finally obtained 14.1% and 19.3% of the Arthrobacter genome genes which were up-regulated and down-regulated notably, respectively, with high oxygen supply, and identified 54 differently expressed proteins. Our results revealed that high oxygen supply had two major effects on metabolism: inhibition of glycolysis, pyruvate metabolism, nitrogen metabolism, and amino acid metabolism (histidine, branched-chain amino acids and glutamate metabolism); enhancement of the tricarboxylic acid cycle and purine metabolism. We also found that regulation of adenylate cyclase and phosphodiesterase was not significant under high oxygen supply, suggesting efficient cAMP export might be important in cAMP production. These findings may contribute to further understanding of capacities of Arthrobacter species and would be highly useful in genetic regulation for desirable production.

Assessing protein-ligand binding modes with computational tools: the case of PDE4B

In a first step in the discovery of novel potent inhibitor structures for the PDE4B family with limited side effects, we present a protocol to rank newly designed molecules through the estimation of their IC[Formula: see text] values. Our protocol is based on reproducing the linear relationship between the logarithm of experimental IC[Formula: see text] values [[Formula: see text](IC[Formula: see text])] and their calculated binding free energies ([Formula: see text]). From 13 known PDE4B inhibitors, we show here that (1) binding free energies obtained after a docking process by AutoDock are not accurate enough to reproduce this linear relationship; (2) MM-GB/SA post-processing of molecular dynamics (MD) trajectories of the top ranked AutoDock pose improves the linear relationship; (3) by taking into account all representative structures obtained by AutoDock and by averaging MM-GB/SA computations on a series of 40 independent MD trajectories, a linear relationship between [Formula: see text](IC[Formula: see text]) and the lowest [Formula: see text] is achieved with [Formula: see text].

A universal stress protein (USP) in mycobacteria binds cAMP

Mycobacteria are endowed with rich and diverse machinery for the synthesis, utilization, and degradation of cAMP. The actions of cyclic nucleotides are generally mediated by binding of cAMP to conserved and well characterized cyclic nucleotide binding domains or structurally distinct cGMP-specific and -regulated cyclic nucleotide phosphodiesterase, adenylyl cyclase, and E. coli transcription factor FhlA (GAF) domain-containing proteins. Proteins with cyclic nucleotide binding and GAF domains can be identified in the genome of mycobacterial species, and some of them have been characterized. Here, we show that a significant fraction of intracellular cAMP is bound to protein in mycobacterial species, and by using affinity chromatography techniques, we identify specific universal stress proteins (USP) as abundantly expressed cAMP-binding proteins in slow growing as well as fast growing mycobacteria. We have characterized the biochemical and thermodynamic parameters for binding of cAMP, and we show that these USPs bind cAMP with a higher affinity than ATP, an established ligand for other USPs. We determined the structure of the USP MSMEG_3811 bound to cAMP, and we confirmed through structure-guided mutagenesis, the residues important for cAMP binding. This family of USPs is conserved in all mycobacteria, and we suggest that they serve as "sinks" for cAMP, making this second messenger available for downstream effectors as and when ATP levels are altered in the cell.

Visualization of cyclic nucleotide dynamics in neurons

The second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) transduce many neuromodulatory signals from hormones and neurotransmitters into specific functional outputs. Their production, degradation and signaling are spatiotemporally regulated to achieve high specificity in signal transduction. The development of genetically encodable fluorescent biosensors has provided researchers with useful tools to study these versatile second messengers and their downstream effectors with unparalleled spatial and temporal resolution in cultured cells and living animals. In this review, we introduce the general design of these fluorescent biosensors and describe several of them in more detail. Then we discuss a few examples of using cyclic nucleotide fluorescent biosensors to study regulation of neuronal function and finish with a discussion of advances in the field. Although there has been significant progress made in understanding how the specific signaling of cyclic nucleotide second messengers is achieved, the mechanistic details in complex cell types like neurons are only just beginning to surface. Current and future fluorescent protein reporters will be essential to elucidate the role of cyclic nucleotide signaling dynamics in the functions of individual neurons and their networks.

Molecular dynamics-based discovery of novel phosphodiesterase-9A inhibitors with non-pyrazolopyrimidinone scaffolds

Phosphodiesterase-9A (PDE9A) is a promising therapeutic target for the treatment of diabetes and Alzheimer's disease (AD). The Pfizer PDE9A inhibitor PF-04447943 has completed Phase II clinical trials in subjects with mild to moderate AD in 2013. However, most of the reported PDE9A inhibitors share the same scaffold as pyrazolopyrimidinone, which lacks structural diversity and is unfavorable for the development of novel PDE9A inhibitors. In the present study, a combinatorial method including pharmacophores, molecular docking, molecular dynamics simulations, binding free energy calculations, and bioassay was used to discover novel PDE9A inhibitors with new scaffolds rather than pyrazolopyrimidinones from the SPECS database containing about 200,000 compounds. As a result, 15 hits out of 29 molecules (a hit rate of 52%) with five novel scaffolds were identified to be PDE9A inhibitors with inhibitory affinities no more than 50 μM to enrich the structural diversity, different from the pyrazolopyrimidinone-derived family. The high hit ratio of 52% for this virtual screening method indicated that the combinatorial method is a good compromise between computational cost and accuracy. Binding pattern analyses indicate that those hits with non-pyrazolopyrimidinone scaffolds can bind the same active site pocket of PDE9A as classical PDE9A inhibitors. In addition, structural modification of compound AG-690/40135604 (IC50=8.0 μM) led to a new one, 16, with an improved inhibitory affinity of 2.1 μM as expected. The five novel scaffolds discovered in the present study can be used for the rational design of PDE9A inhibitors with higher affinities.

Crosstalk between Mycobacterium tuberculosis and the host cell

The successful establishment and maintenance of a bacterial infection depend on the pathogen's ability to subvert the host cell's defense response and successfully survive, proliferate, or persist within the infected cell. To circumvent host defense systems, bacterial pathogens produce a variety of virulence factors that potentiate bacterial adherence and invasion and usurp host cell signaling cascades that regulate intracellular microbial survival and trafficking. Mycobacterium tuberculosis, probably one of the most successful pathogens on earth, has coexisted with humanity for centuries, and this intimate and persistent connection between these two organisms suggests that the pathogen has evolved extensive mechanisms to evade the human immune system at multiple levels. While some of these mechanisms are mediated by factors released by M. tuberculosis, others rely on host components that are hijacked to prevent the generation of an effective immune response thus benefiting the survival of M. tuberculosis within the host cell. Here, we describe several of these mechanisms, with an emphasis on the cyclic nucleotide signaling and subversion of host responses that occur at the intracellular level when tubercle bacilli encounter macrophages, a cell that becomes a safe-house for M. tuberculosis although it is specialized to kill most microbes.

Rationale for the use of prostaglandins and phosphodiesterase inhibitors in the treatment of functional bladder disorders

In this paper a general discussion of the available data on the role of prostaglandin (PG) and phosphodiesterase is discussed. Functional studies would be a next step to understand the functional meaning of the data described in this paper. The data presented are a basis for further research on selective modulation of the EP1 and EP2 receptor which could be a therapeutic target in functional bladder disorders such as OAB. PDE inhibitors are closer to clinical use, as these drugs have been studied and registered for other indications such as erectile dysfunction in men. Therefore, in vivo studies in human subjects can be conducted on short term. However, from a scientific point of view, it is very important to unravel the exact site of action and role of PDE inhibition with in vitro and in vivo studies as is the case with PG. In this way, a combination of drugs targeting different mechanisms involved in bladder physiology such as PG, cGMP, cAMP, and muscarinic receptors, could reduce side effects and improve efficacy.

Localization of angiotensin-II type 1(AT1) receptors on buffalo spermatozoa: AT1 receptor activation during capacitation triggers rise in cyclic AMP and calcium

The purpose of this study was to determine the role of Ang-II in buffalo spermatozoa; localize angiotensin type 1 (AT1) receptors on the sperm surface and understand the signaling mechanisms involved therein. Immunoblotting and immunocytochemistry using polyclonal Rabbit anti-AT1 (N-10) IgG were performed to confirm the presence of AT1 receptors. Intracellular levels of cyclic adenosine monophosphate (cAMP) were determined by non-radioactive enzyme immunoassay, while that of Calcium [Ca(2+)] were estimated by fluorimetry using Fura2AM dye. The results obtained showed that AT1 receptors were found on the post-acrosomal region, neck and tail regions. Immunoblotting revealed a single protein band with molecular weight of 40 kDa. Ang-II treated cells produced significantly higher level of cAMP compared to untreated cells (22.66 ± 2.4 vs. 10.8 ± 0.98 pmol/10(8) cells, p < 0.01). The mean levels of Ca(2+) were also higher in Ang-II treated cells compared to control (117.4 ± 6.1 vs. 61.15 ± 4.2 nmol/10(8) cells; p < 0.01). The stimulatory effect of Ang-II in both the cases was significantly inhibited in the presence of Losartan (AT1 antagonist; p < 0.05) indicating the involvement of AT1 receptors. Further, presence of neomycin (protein kinase C inhibitor) inhibited significantly the Ang-II mediated rise in Ca(2+) indicating the involvement of PKC pathway. These findings confirm the presence of AT1 receptors in buffalo spermatozoa and that Ang-II mediates its actions via the activation of these receptors. Ang-II stimulates the rise in intracellular levels of cAMP and Ca(2+) during capacitation.

Phosphodiesterase type 5 (PDE5) is co-localized with key proteins of the nitric oxide/cyclic GMP signaling in the human prostate

PURPOSE

Experimental studies have provided the basis for the evaluation of inhibitors of the phosphodiesterase type 5 (PDE5) in the treatment of lower urinary tract symptomatology (LUTS) secondary to benign prostatic hyperplasia (BPH). It has been speculated that the clinical efficacy of PDE5 inhibitors in patients with LUTS/BPH can be explained by their effects on the urinary bladder rather than on the prostate. Hence, the significance of the nitric oxide (NO)/cyclic GMP signaling in the control of the human prostate requires further clarification.

METHODS

The present study aimed to investigate by means of immunohistochemistry in the human prostate the expression and distribution of key mediators of the NO pathway, namely cyclic GMP, the neuronal nitric oxide synthase (nNOS), and cyclic GMP-binding protein kinases type I (cGKIα, cGKIß), in relation to PDE5, protein kinase A (cAK), and the vasoactive intestinal polypeptide (VIP).

RESULTS

In the smooth muscle portion of the transition zone, immunosignals specific for the PDE5 were found co-localized with cyclic GMP, cGKIα, and cGKIß, as well as with the cyclic cAMP-binding protein kinase A. Smooth muscle bundles were seen innervated by slender varicose nerves characterized by the expression of nNOS. Some of these nerves also presented staining related to the neuropeptide VIP.

CONCLUSIONS

The findings give hints that the cyclic GMP- and cyclic AMP-dependent signal transduction may synergistically work together in regulating muscle tension in the transition zone. This might be of significance for the identification of new pharmacological avenues to treat patients with symptomatic BPH.

Synaptic effects induced by alcohol

Ethanol (EtOH) has effects on numerous cellular molecular targets, and alterations in synaptic function are prominent among these effects. Acute exposure to EtOH activates or inhibits the function of proteins involved in synaptic transmission, while chronic exposure often produces opposing and/or compensatory/homeostatic effects on the expression, localization, and function of these proteins. Interactions between different neurotransmitters (e.g., neuropeptide effects on release of small molecule transmitters) can also influence both acute and chronic EtOH actions. Studies in intact animals indicate that the proteins affected by EtOH also play roles in the neural actions of the drug, including acute intoxication, tolerance, dependence, and the seeking and drinking of EtOH. This chapter reviews the literature describing these acute and chronic synaptic effects of EtOH and their relevance for synaptic transmission, plasticity, and behavior.

Early mechanisms of pathobiology are revealed by transcriptional temporal dynamics in hippocampal CA1 neurons of prion infected mice

Prion diseases typically have long pre-clinical incubation periods during which time the infectious prion particle and infectivity steadily propagate in the brain. Abnormal neuritic sprouting and synaptic deficits are apparent during pre-clinical disease, however, gross neuronal loss is not detected until the onset of the clinical phase. The molecular events that accompany early neuronal damage and ultimately conclude with neuronal death remain obscure. In this study, we used laser capture microdissection to isolate hippocampal CA1 neurons and determined their pre-clinical transcriptional response during infection. We found that gene expression within these neurons is dynamic and characterized by distinct phases of activity. We found that a major cluster of genes is altered during pre-clinical disease after which expression either returns to basal levels, or alternatively undergoes a direct reversal during clinical disease. Strikingly, we show that this cluster contains a signature highly reminiscent of synaptic N-methyl-D-aspartic acid (NMDA) receptor signaling and the activation of neuroprotective pathways. Additionally, genes involved in neuronal projection and dendrite development were also altered throughout the disease, culminating in a general decline of gene expression for synaptic proteins. Similarly, deregulated miRNAs such as miR-132-3p, miR-124a-3p, miR-16-5p, miR-26a-5p, miR-29a-3p and miR-140-5p follow concomitant patterns of expression. This is the first in depth genomic study describing the pre-clinical response of hippocampal neurons to early prion replication. Our findings suggest that prion replication results in the persistent stimulation of a programmed response that is mediated, at least in part, by synaptic NMDA receptor activity that initially promotes cell survival and neurite remodelling. However, this response is terminated prior to the onset of clinical symptoms in the infected hippocampus, seemingly pointing to a critical juncture in the disease. Manipulation of these early neuroprotective pathways may redress the balance between degeneration and survival, providing a potential inroad for treatment.

Neurodegenerative diseases affect an ever-increasing proportion of the population; therefore, there is an urgent need to develop treatments. Prion disorders belong to this group of diseases and although rare and uniquely transmissible, share many features on a sub-cellular level. Central to disease is progressive synaptic impairment that invariably leads to the irreversible loss of neurons. Understanding this process is undoubtedly essential for rational drug discovery. In this study we looked at neurons very early in disease, when prions are barely detectable and there are no clinical symptoms observed. Specifically, we performed a comprehensive analysis of transcriptional changes within a particularly dense area of neurons, the CA1 hippocampus region, from prion-infected and control mice. In this way we were able to enrich our data for molecular changes unique to neurons and minimize those changes characteristic of support cells such as astrocytes and microglia. We detected the activation of a transcriptional program indicative of a protective mechanism within these neurons early in disease. This mechanism diminished as disease progressed and was lost altogether, concurrently with the onset of clinical symptoms. These findings demonstrate the ability of neurons to mount an initial neuroprotective response to prions that could be exploited for therapy development.

Structure-based discovery of highly selective phosphodiesterase-9A inhibitors and implications for inhibitor design

A new series of phosphodiesterase-9 (PDE9) inhibitors that contain a scaffold of 6-amino-pyrazolopyrimidinone have been discovered by a combination of structure-based design and computational docking. This procedure significantly saved the load of chemical synthesis and is an effective method for the discovery of inhibitors. The best compound 28 has an IC(50) of 21 nM and 3.3 μM, respectively, for PDE9 and PDE5 and about 3 orders of magnitude of selectivity against other PDE families. The crystal structure of the PDE9 catalytic domain in complex with 28 has been determined and shows a hydrogen bond between 28 and Tyr424. This hydrogen bond may account for the 860-fold selectivity of 28 against PDE1B, in comparison with about 30-fold selectivity of BAY73-6691. Thus, our studies suggest that Tyr424, a unique residue of PDE8 and PDE9, is a potential target for improvement of selectivity of PDE9 inhibitors.

PDE5 Inhibitors as Potential Tools in the Treatment of Cystic Fibrosis

Despite great advances in the understanding of the genetics and pathophysiology of cystic fibrosis (CF), there is still no cure for the disease. Using phosphodiesterase type 5 (PDE5) inhibitors, we and others have provided evidence of rescued F508del-CFTR trafficking and corrected deficient chloride transport activity. Studies using PDE5 inhibitors in mice homozygous for the clinically relevant F508del mutation have been conducted with the aim of restoring F508del-CFTR protein function. We demonstrated, by measuring transepithelial nasal potential difference in F508del mice following intraperitoneal injection of sildenafil, vardenafil, or taladafil at clinical doses are able to restore the decreased CFTR-dependent chloride transport across the nasal mucosa. Moreover, vardenafil, but not sildenafil, stimulates chloride transport through the normal CFTR protein. We developed a specific nebulizer setup for mice, with which we demonstrated, through a single inhalation of PDE5 inhibitors, local activation of CFTR protein in CF. Significant potential advantages of inhalation drug therapy over oral or intravenous routes include rapid onset of pharmacological action, reduced systemic secondary effects, and reduced effective drug doses compared to the drug delivered orally; this underlines the relevance and impact of our work for translational science. More recently, we analyzed the bronchoalveolar lavage of CF and wild-type mice for cell infiltrates and expression of pro-inflammatory cytokines and chemokines; we found that the CFTR activating effect of vardenafil, selected as a representative long-lasting PDE5 inhibitor, breaks the vicious circle of lung inflammation which plays a major role in morbi-mortality in CF. Our data highlight the potential use of PDE5 inhibitors in CF. Therapeutic approaches using clinically approved PDE5 inhibitors to address F508del-CFTR defects could speed up the development of new therapies for CF.

New paradigms in cAMP signalling

Signalling through adenosine 3'5' monophosphate (cAMP) is known to be important in virtually every cell. The mapping of the human genome over the past two decades has revealed an unexpected complexity of cAMP signalling, which is shared from insects to mammals. A more recent technical advance is the ability to monitor intracellular cAMP levels at subcellular spatial resolution within the time-domains of fast biochemical reactions. Thus, new light has been shed on old paradigms, some of which turn out to be multiple new ones. The novel aspects of cAMP signalling are highlighted here: (1) agonist induced plasticity - showing how the repertory of cAMP signalling genes supports homeostatic adaptation; (2) sustained cAMP signalling after endocytosis; (3) pre-assembled receptor-Gs-adenylyl cyclase complexes. Finally, a hypothetical model of propagating neuronal cAMP signals travelling form dendrites to the cell body is presented.

Interactions between intracellular free Ca2+ and cyclic AMP in neuroendocrine cells

Calcium ions and cyclic adenosine monophosphate (cAMP) are virtually ubiquitous intracellular signaling molecules in mammalian cells. This paper will focus on the cross-talk between Ca(2+) and cAMP mobilizing signaling pathways and summarize the underlying molecular mechanisms. Subsequently, workings of adenohypophyseal corticotrope cells will be reviewed to highlight the physiological relevance of a Ca(2+) cAMP interactions in neuroendocrinology.

Bi-stage control of dissolved oxygen to enhance cyclic adenosine monophosphate production by Arthrobacter A302

Experiments confirmed dissolved oxygen (DO) definitely affects cyclic adenosine monophosphate (cAMP) production by Arthrobacter A302. Production of cAMP by batch fermentation was investigated under various DO conditions. A two-stage DO control strategy was proposed to achieve optimal production of cAMP based on the kinetic analysis: the DO level was controlled at 40% during the first 18 h and then switched to 30%. Relatively high cAMP production (9.9 g L(-1)) was achieved by applying this strategy. The cAMP productivity (0.14 g L(-1) h(-1)) was also successfully improved by 85.1, 59.3, 15.1 and 28.0%, compared to cases in which DO was uncontrolled or DO levels were held at 20, 30 and 40%, respectively. This is the first report of the use of a two-stage DO control strategy in cAMP production, and it was verified to be an effective method for enhancing the cAMP yield via this strain.

Activation of protein kinase A and C prevents recovery from persistent depolarization produced by oxygen and glucose deprivation in rat hippocampal neurons

Intracellular recordings were made from rat hippocampal CA1 neurons in rat brain slice preparations to investigate whether cAMP-dependent protein kinase (PKA) and calcium/phospholipid-dependent protein kinase C (PKC) contribute to the membrane dysfunction induced by oxygen and glucose deprivation (OGD). Superfusion of oxygen- and glucose-deprived medium produced a rapid depolarization ∼5 min after the onset of the superfusion. When oxygen and glucose were reintroduced immediately after the rapid depolarization, the membrane depolarized further (persistent depolarization) and reached 0 mV after 5 min from the reintroduction. The pretreatment of the slice preparation with PKA inhibitors, H-89 and Rp-cAMPS, and an adenylate cyclase inhibitor, SQ 22, 536, significantly restored the membrane toward the preexposure potential level after the reintroduction of oxygen and glucose in a concentration-dependent manner. On the other hand, a phospholipase C inhibitor, U73122, a PKC inhibitor, GF109203X, and a nonselective protein kinase inhibitor, staurosporine, also significantly restored the membrane after the reintroduction. Moreover, an inositol-1,4,5-triphosphate receptor antagonist, 2-aminoethyl diphenylborinate, and calmodulin inhibitors, trifluoperazine and W-7, significantly restored the membrane after the reintroduction, while neither an α-subunit-selective antagonist for stimulatory G protein, NF449, a Ca(2+)/calmodulin-dependent kinase II inhibitor, KN-62, nor a myosin light chain kinase inhibitor, ML-7, significantly restored the membrane after the reintroduction. These results suggest that the activation of PKA and/or PKC prevents the recovery from the persistent depolarization produced by OGD. The Ca(2+)/calmodulin-stimulated adenylate cyclase may contribute to the activation of PKA.

Theory of the origin, evolution, and nature of life

Life is an inordinately complex unsolved puzzle. Despite significant theoretical progress, experimental anomalies, paradoxes, and enigmas have revealed paradigmatic limitations. Thus, the advancement of scientific understanding requires new models that resolve fundamental problems. Here, I present a theoretical framework that economically fits evidence accumulated from examinations of life. This theory is based upon a straightforward and non-mathematical core model and proposes unique yet empirically consistent explanations for major phenomena including, but not limited to, quantum gravity, phase transitions of water, why living systems are predominantly CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur), homochirality of sugars and amino acids, homeoviscous adaptation, triplet code, and DNA mutations. The theoretical framework unifies the macrocosmic and microcosmic realms, validates predicted laws of nature, and solves the puzzle of the origin and evolution of cellular life in the universe.

Subcellular signaling in the endothelium: cyclic nucleotides take their place

When lecturing on the topic of cellular signaling I have had occasion to ask the class for examples of cellular processes NOT impacted by cyclic AMP (cAMP) and am struck by how few examples exist. Indeed, studies spanning the past 60 years have detailed how this ubiquitous second messenger impacts virtually all cellular processes, including intermediary metabolism, contractility, motility, proliferation, and gene expression in most mammalian cells. Since the hydrophobic cAMP could in principle diffuse rapidly throughout the cell once formed, the remarkable spatial and temporal specificity of its numerous actions in cells is truly impressive. Herein I introduce the main players involved in coordinating actions of cAMP in vascular endothelial cells (VECs), and focus on the increasing awareness of the dominant role that cyclic nucleotide phosphodiesterases (PDEs), the sole cellular enzymes capable of hydrolytically inactivating cAMP, play in fostering this specificity.

Human cyclic nucleotide phosphodiesterases possess a much broader substrate-specificity than previously appreciated

Phosphodiesterases (PDEs) capable of degrading cAMP and cGMP are indispensable for the regulation of cyclic nucleotide-mediated signals. The existence of other cyclic nucleotides such as cCMP and cUMP has been discussed controversially in the literature. Despite publications on PDEs hydrolyzing cCMP or cUMP, the molecular identity of such enzymes remained elusive. Recently, we have provided evidence for a role of cCMP as second messenger in vascular relaxation and inhibition of platelet aggregation. Using an HPLC-MS based assay, here, we show that human PDEs belonging to various families hydrolyze not only cAMP and cGMP but also other cyclic nucleotides.

Therapeutic potential of boron-containing compounds

Relative to carbon, hydrogen, nitrogen and oxygen, very little is currently known about boron in therapeutics. In addition, there are very few boron-containing natural products identified to date to serve as leads for medicinal chemists. Perceived risks of using boron and lack of synthetic methods to handle boron-containing compounds have caused the medicinal chemistry community to shy away from using the atom. However, physical, chemical and biological properties of boron offer medicinal chemists a rare opportunity to explore and pioneer new areas of drug discovery. Boron therapeutics are emerging that show different modes of inhibition against a variety of biological targets. With one boron-containing therapeutic agent on the market and several more in various stages of clinical trials, the occurrence of this class of compound is likely to grow over the next decade and boron could become widely accepted as a useful element in future drug discovery.

Structural and functional analysis of the Lmo2642 cyclic nucleotide phosphodiesterase from Listeria monocytogenes

Listeria monocytogenes is a facultative intracellular pathogen invading humans and animals with the highest fatality rate among the food-borne pathogens. The Listeria pathogenic processes, such as cell entry and escape from phagosomes, depend on the actions of diverse bacterial factors, including lipoproteins. Here, we report the crystal structure of Lmo2642, a conserved putative lipoprotein containing a Ser/Thr phosphatase domain. The protein consists of two distinct domains: a catalytic domain that belongs to the metallophosphoesterase superfamily and an auxiliary α-helical bundle domain. The active site in the catalytic domain of Lmo2642 contains a dinuclear metal center in which Mn²(+) and Fe³(+) are preferentially positioned at the site1 and site2, respectively. On the basis of the structural analysis and enzymatic assays, we identified the biochemical activity of the protein as a cyclic nucleotide phosphodiesterase toward 2',3'- and 3',5'-cyclic nucleotides. Considering the cNMP phosphodiesterase activity and the putative surface localization of Lmo2642, we speculate that Lmo2642 has some potential roles in the host-pathogen interactions by changing the cAMP concentration of host cells during L. monocytogenes infection.

Type 7 Adenylyl Cyclase is Involved in the Ethanol and CRF Sensitivity of GABAergic Synapses in Mouse Central Amygdala

The GABAergic system in the central amygdala (CeA) plays a major role in ethanol dependence and in the anxiogenic response to ethanol withdrawal. Previously, we found that both ethanol and corticotropin releasing factor (CRF) increase GABAergic transmission in mouse and rat CeA neurons, in part by enhancing the release of GABA via activation of presynaptic CRF1 receptors. CRF1 receptors are coupled to the enzyme adenylyl cyclase (AC), which produces the second messenger cyclic AMP. There are nine isoforms of AC, but we recently found that CRF1 receptors in the pituitary were coupled to the Type 7 AC (AC7). Therefore, using an in vitro electrophysiological approach in brain slices, here we have investigated a possible role of the AC7 signaling pathway in ethanol and CRF effects on CeA GABAergic synapses of genetically modified mice with diminished brain Adcy7 activity (HET) compared to their littermate male wild-type (WT) mice. We found no significant differences in basal membrane properties, mean baseline amplitude of evoked GABA(A) receptor-mediated inhibitory postsynaptic potentials (IPSPs), or paired-pulse facilitation (PPF) of GABA(A)-IPSPs between HET and WT mice. In CeA neurons of WT mice, ethanol superfusion significantly augmented (by 39%) GABAA-IPSPs and decreased PPF (by 25%), suggesting increased presynaptic GABA release. However, these effects were absent in HET mice. CRF superfusion also significantly augmented IPSPs (by 38%) and decreased PPF (by 23%) in WT CeA neurons, and still elicited a significant but smaller (by 13%) increase of IPSP amplitude, but no effect on PPF, in HET mice. These electrophysiological data suggest that AC7 plays an important role in ethanol and CRF modulation of presynaptic GABA release in CeA and thus may underlie ethanol-related behaviors such as anxiety and dependence.

Cyclic nucleotide metabolism including nitric oxide and phosphodiesterase-related targets in the lower urinary tract

The clinical data on the use of the orally active phosphodiesterase (PDE) type 5 inhibitors sildenafil (VIAGRA™), vardenafil (LEVITRA™), and tadalafil (CIALIS™) for the treatment of male erectile dysfunction have boosted research activities on the physiology and pharmacology of the organs of the lower urinary tract (LUT). This includes both intracellular signal transduction in the prostate, urinary bladder (detrusor), and urethra, as well as central brain and spinal cord pathways controlling the function of the LUT. Such efforts provided the basis for the development of new therapeutic modalities into the management of dysfunctions/ syndromes of the LUT, some of which are already offered to the patients. The pharmacological treatment of the overactive bladder and the so-called benign prostatic syndrome, including LUT symptomatology and bladder outlet obstruction secondary to benign prostatic enlargement, has primarily focused on selective, orally available drugs acting by influencing intracellular regulatory mechanisms. These agents are regarded efficacious, have a fast onset of drug action in the target tissue and an improved effect-to-side-effect ratio. Better understanding of the functional significance of proteins related to cyclic nucleotide-dependent pathways, such as nitric oxide synthase, cytosolic and membrane-bound guanylyl cyclases, PDE isoenzymes and cyclic AMP- and cyclic GMP-binding protein kinases, the relative distribution in tissues of the LUT, and the consequences for urogenital function, seems to be of particular interest in order to identify new or more selective pharmacological approaches to manage disorders of the LUT. The present review focuses on cyclic nucleotide-related targets involved in the control of the function of the bladder, prostate, and urethra and the significance of those proteins in the process of evolving new pharmacological options for the treatment of LUT symptoms secondary to benign prostatic hyperplasia as well as dysfunctions of the storage and voiding capability of the urinary bladder.

Structural insight into the substrate specificity of phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) share a highly conserved catalytic domain that hydrolyzes cAMP, cGMP, or both nucleotides. However, the mechanism that allows the PDE catalytic sites to specifically recognize these nucleotides and distinguish between their subtle differences is still unclear. An early model, called the "glutamine switch", proposed that the side chain of an invariant glutamine adopts two different conformations to allow for formation of two hydrogen bonds with cAMP and cGMP, thereby differentiating these nucleotides. However, the structure of PDE4D2 in complex with cAMP shows that Gln369 forms only one hydrogen bond with the substrate. In addition, the structures of PDE10A in complex with cAMP and cGMP reveal that cAMP and cGMP bind to the active site in different orientations and have different interactions with PDE10A residues. These structures suggest that the invariant glutamine does not appear to be a key residue to differentiate between cAMP and cGMP, although it is important for substrate binding. The structure-based sequence alignment shows that most of the active site residues change across PDE families. These residues may not only contribute differently to the substrate specificity, but also generate slightly different shapes and sizes of the active sites in different PDE families. Therefore, the substrate specificity of PDEs is likely to be determined jointly by multiple elements at the active site, yet the detailed mechanism needs further study.

Treatment of erectile dysfunction and lower urinary tract symptoms by phosphodiesterase inhibitors

To date, it is widely accepted that several disorders of the male and female urogenital tract, such as erectile dysfunction, bladder overactivity, urinary stone disease, the benign prostatic syndrome, as well as symptoms of female sexual arousal and orgasmic dysfunctions, can be therapeutically approached by influencing the function of the smooth musculature of the respective organs. To achieve a pronounced drug effect without significant adverse events, a certain degree of tissue selectivity is mandatory. Selective intervention in intracellular pathways regulating smooth muscle tone has become the most promising strategy to modulate tissue and organ function. Since the concept of taking a pill to relieve symptoms of lower urinary tract dysfunction is now widely accepted following the successes of phosphodiesterase 5 (PDE5) inhibitor treatment of erectile dysfunction, the treatment of urological diseases has focused on orally available drugs acting via influencing intracellular signaling pathways, thereby combining a high response rate with the advantage of an on-demand intake. Specifically, the use of isoenzyme-selective PDE inhibitors offers great opportunities in the medical treatment of various genitourinary diseases. These agents are regarded to be safe and to be efficacious, i.e., having a fast onset of drug action and an improved effect-to-side-effect ratio. As experience with this class of compounds and their use in urology is rapidly growing, basic and clinical research in this field will most likely expand the pharmacological armamentarium of innovative treatment options in the next few years. The purpose of this review is to summarize current, as well as potential, upcoming indications for the use of PDE inhibitors in the pharmacotherapy of male erectile dysfunction and lower urinary tract symptoms.

Increase of cytosolic calcium induced by trichosanthin suppresses cAMP/PKC levels through the inhibition of adenylyl cyclase activity in HeLa cells

Increase of cytosolic free calcium played a pivotal role in apoptotic cells induced by trichosanthin. However, little is known about the influence of cytosolic calcium increase on adenylyl cyclase activity and intracellular cAMP signaling pathway in HeLa cells. The present study showed that an influx of extracellular Ca2+ initiated by trichosanthin was required for the suppression of adenylyl cyclase activity and decrease of intracellular cAMP level. Furthermore, this inhibition was abolished by activation of PKC rather than PKA. Therefore, our results suggested that increase of cytosolic calcium induced by trichosanthin inhibits cAMP levels via suppression of adenylyl cyclase activity.

Adenosine neuromodulation and traumatic brain injury

Adenosine is a ubiquitous signaling molecule, with widespread activity across all organ systems. There is evidence that adenosine regulation is a significant factor in traumatic brain injury (TBI) onset, recovery, and outcome, and a growing body of experimental work examining the therapeutic potential of adenosine neuromodulation in the treatment of TBI. In the central nervous system (CNS), adenosine (dys)regulation has been demonstrated following TBI, and correlated to several TBI pathologies, including impaired cerebral hemodynamics, anaerobic metabolism, and inflammation. In addition to acute pathologies, adenosine function has been implicated in TBI comorbidities, such as cognitive deficits, psychiatric function, and post-traumatic epilepsy. This review presents studies in TBI as well as adenosine-related mechanisms in co-morbidities of and unfavorable outcomes resulting from TBI. While the exact role of the adenosine system following TBI remains unclear, there is increasing evidence that a thorough understanding of adenosine signaling will be critical to the development of diagnostic and therapeutic tools for the treatment of TBI.

Apremilast, a novel PDE4 inhibitor, inhibits spontaneous production of tumour necrosis factor-alpha from human rheumatoid synovial cells and ameliorates experimental arthritis

Introduction

Type 4 phosphodiesterases (PDE4) play an important role in immune cells through the hydrolysis of the second messenger, cAMP. Inhibition of PDE4 has previously been shown to suppress immune and inflammatory responses, demonstrating PDE4 to be a valid therapeutic target for immune-mediated pathologies. We assessed the anti-inflammatory effects of a novel PDE4 inhibitor, apremilast, in human synovial cells from rheumatoid arthritis (RA) patients, as well as two murine models of arthritis.

Methods

Cells liberated from tissue excised from arthritic joints of RA patients were cultured in the presence of increasing concentrations of apremilast for 48 hours and spontaneous tumour necrosis factor-alpha (TNFα) production was analysed in culture supernatants by ELISA. In addition, arthritis was induced in BALB/c and DBA/1 mice by passive transfer of anti-type II collagen mAb and immunisation with type II collagen, respectively. Mice with established arthritis received 5 or 25 mg/kg apremilast and disease severity was monitored relative to mice receiving vehicle alone. At the end of the study, paws were removed and processed for histopathological assessment. Behavioural effects of apremilast, relative to rolipram, were assessed in naïve DBA/1 mice using an automated activity monitor (LABORAS).

Results

Apremilast dose dependently inhibited spontaneous release of TNFα from human rheumatoid synovial membrane cultures. Furthermore, apremilast significantly reduced clinical score in both murine models of arthritis over a ten day treatment period and maintained a healthy joint architecture in a dose-dependent manner. Importantly, unlike rolipram, apremilast demonstrated no adverse behavioural effects in naïve mice.

Conclusions

Apremilast is an orally available PDE4 inhibitor that reduces TNFα production from human synovial cells and significantly suppresses experimental arthritis. Apremilast appears to be a potential new agent for the treatment of rheumatoid arthritis.

In vitro and in vivo characterization of the Pseudomonas aeruginosa cyclic AMP (cAMP) phosphodiesterase CpdA, required for cAMP homeostasis and virulence factor regulation

Cyclic AMP (cAMP) is an important second messenger signaling molecule that controls a wide variety of eukaryotic and prokaryotic responses to extracellular cues. For cAMP-dependent signaling pathways to be effective, the intracellular cAMP concentration is tightly controlled at the level of synthesis and degradation. In the opportunistic human pathogen Pseudomonas aeruginosa, cAMP is a key regulator of virulence gene expression. To better understand the role of cAMP homeostasis in this organism, we identified and characterized the enzyme CpdA, a putative cAMP phosphodiesterase. We demonstrate that CpdA possesses 3',5'-cAMP phosphodiesterase activity in vitro and that it utilizes an iron-dependent catalytic mechanism. Deletion of cpdA results in the accumulation of intracellular cAMP and altered regulation of P. aeruginosa virulence traits. Further, we demonstrate that the cAMP-dependent transcription factor Vfr directly regulates cpdA expression in response to intracellular cAMP accumulation, thus providing a feedback mechanism for controlling cAMP levels and fine-tuning virulence factor expression.

Insight into binding of phosphodiesterase-9A selective inhibitors by crystal structures and mutagenesis

PDE9 inhibitors have been studied as therapeutics for treatment of cardiovascular diseases, diabetes, and neurodegenerative disorders. To illustrate the inhibitor selectivity, the crystal structures of the PDE9A catalytic domain in complex with the enantiomers of PDE9 inhibitor 1-(2-chlorophenyl)-6-(3,3,3-trifluoro-2-methylpropyl)-1H-pyrazolo[3,4-d]pyrimidine-4(5H)-one ((R)-BAY73-6691 or (S)-BAY73-6691, 1r or 1s) were determined and mutagenesis was performed. The structures showed that the fluoromethyl groups of 1r and 1s had different orientations while the other parts of the inhibitors commonly interacted with PDE9A. These differences may explain the slightly different affinity of 1r (IC(50) = 22 nM) and 1s (IC(50) = 88 nM). The mutagenesis experiments revealed that contribution of the binding residues to the inhibitor sensitivity varies dramatically, from few-fold to 3 orders of magnitude. On the basis of the crystal structures, a hypothesized compound that simulates the recently published PDE9 inhibitors was modeled to provide insight into the inhibitor selectivity.

Kinetic and structural studies of phosphodiesterase-8A and implication on the inhibitor selectivity

Cyclic nucleotide phosphodiesterase-8 (PDE8) is a family of cAMP-specific enzymes and plays important roles in many biological processes, including T-cell activation, testosterone production, adrenocortical hyperplasia, and thyroid function. However, no PDE8 selective inhibitors are available for trial treatment of human diseases. Here we report kinetic properties of the highly active PDE8A1 catalytic domain prepared from refolding and its crystal structures in the unliganded and 3-isobutyl-1-methylxanthine (IBMX) bound forms at 1.9 and 2.1 A resolutions, respectively. The PDE8A1 catalytic domain has a K(M) of 1.8 microM, V(max) of 6.1 micromol/min/mg, a k(cat) of 4.0 s(-1) for cAMP, and a K(M) of 1.6 mM, V(max) of 2.5 micromol/min/mg, a k(cat) of 1.6 s(-1) for cGMP, thus indicating that the substrate specificity of PDE8 is dominated by K(M). The structure of the PDE8A1 catalytic domain has similar topology as those of other PDE families but contains two extra helices around Asn685-Thr710. Since this fragment is distant from the active site of the enzyme, its impact on the catalysis is unclear. The PDE8A1 catalytic domain is insensitive to the IBMX inhibition (IC(50) = 700 microM). The unfavorable interaction of IBMX in the PDE8A1-IBMX structure suggests an important role of Tyr748 in the inhibitor binding. Indeed, the mutation of Tyr748 to phenylalanine increases the PDE8A1 sensitivity to several nonselective or family selective PDE inhibitors. Thus, the structural and mutagenesis studies provide not only insight into the enzymatic properties but also guidelines for design of PDE8 selective inhibitors.

Design, synthesis, and structure-activity relationship, molecular modeling, and NMR studies of a series of phenyl alkyl ketones as highly potent and selective phosphodiesterase-4 inhibitors

Phosphodiesterase 4 catalyzes the hydrolysis of cyclic AMP and is a target for the development of anti-inflammatory agents. We have designed and synthesized a series of phenyl alkyl ketones as PDE4 inhibitors. Among them, 13 compounds were identified as having submicromolar IC(50) values. The most potent compounds have IC(50) values of in the mid- to low-nanomolar range. Compound 5v also showed preference for PDE4 with selectivity of >2000-fold over PDE7, PDE9, PDE2, and PDE5. Docking of 5v, 5zf, and 5za into the binding pocket of the PDE4 catalytic domain revealed a similar binding profile to PDE4 with rolipram except that the fluorine atoms of the difluoromethyl groups of 5v, 5za, and 5zf are within a reasonable range for hydrogen bond formation with the amide hydrogen of Thr 333 and the long alkyl chain bears additional van der Waals interactions with His 160, Asp 318, and Tyr 159.

Current understanding of klotho

Klotho is a new anti-aging gene. Genetic mutation of klotho causes multiple premature aging-like phenotypes and strikingly shortens lifespan. Overexpression of the klotho gene in mice suppresses aging and extends lifespan which may involve the mechanism of suppression of insulin signaling and oxidant stress. Klotho functions as a cofactor/coreceptor regulating fibroblast growth factor (FGF) 23 signaling. Klotho acts as a glucuronidase and activates ion channel TRPV5. Klotho protects against endothelial dysfunction and regulates the production of nitric oxide. Klotho also influences intracellular signaling pathways including p53/p21, cAMP, protein kinase C (PKC) and Wnt signaling pathways. The discovery of klotho has a great impact on aging research. The purpose of this review is to provide the recent progress and future directions of klotho research. Specifically, this review will cover: klotho and aging, structure and expression of the klotho gene, localization of klotho expression, source of circulating klotho, current understanding of klotho functions, and signaling pathways of klotho.

SDF-1 stimulates neurite growth on inhibitory CNS myelin

Impaired axonal regeneration is a common observation after central nervous system (CNS) injury. The stromal cell-derived factor-1, SDF-1/CXCL12, has previously been shown to promote axonal growth in the presence of potent chemorepellent molecules known to be important in nervous system development. Here, we report that treatment with SDF-1alpha is sufficient to overcome neurite outgrowth inhibition mediated by CNS myelin towards cultured postnatal dorsal root ganglion neurons. While we found both cognate SDF-1 receptors, CXCR4 and CXCR7/RDC1, to be coexpressed on myelin-sensitive dorsal root ganglion neurons, the distinct expression pattern of CXCR4 on growth cones and branching points of neurites suggests a function of this receptor in chemokine-mediated growth promotion and/or arborization. These in vitro findings were further corroborated as local intrathecal infusion of SDF-1 into spinal cord injury following thoracic dorsal hemisection resulted in enhanced sprouting of corticospinal tract axons into white and grey matter. Our findings indicate that SDF-1 receptor activation might constitute a novel therapeutic approach to promote axonal growth in the injured CNS.