Forskolin: a specific stimulator of adenylyl cyclase or a diterpene with multiple sites of action?

Activation of Piezo1 Inhibits Kidney Cystogenesis

The disruption of calcium signaling associated with polycystin deficiency has been proposed as the primary event underlying the increased abnormally patterned epithelial cell growth characteristic of Polycystic Kidney Disease. Calcium can be regulated through mechanotransduction, and the mechanosensitive cation channel Piezo1 has been implicated in sensing of intrarenal pressure and in urinary osmoregulation. However, a possible role for PIEZO1 in kidney cystogenesis remains undefined. We hypothesized that cystogenesis in ADPKD reflects altered mechanotransduction, suggesting activation of mechanosensitive cation channels as a therapeutic strategy for ADPKD. Here, we show that Yoda-1 activation of PIEZO1 increases intracellular Ca 2+ and reduces forskolin-induced cAMP levels in mIMCD3 cells. Yoda-1 reduced forskolin-induced IMCD cyst surface area in vitro and in mouse metanephros ex vivo in a dose-dependent manner. Knockout of polycystin-2 dampened the efficacy of PIEZO1 activation in reducing both cAMP levels and cyst surface area in IMCD3 cells. However, collecting duct-specific Piezo1 knockout neither induced cystogenesis in wild-type mice nor affected cystogenesis in the Pkd1 RC/RC model of ADPKD. Our study suggests that polycystin-2 and PIEZO1 play a role in mechanotransduction during cystogenesis in vitro , and ex vivo , but that in vivo cyst expansion may require inactivation or repression of additional suppressors of cystogenesis and/or growth. Our study provides a preliminary proof of concept for PIEZO1 activation as a possible component of combination chemotherapy to retard or halt cystogenesis and/or cyst growth.

The Adenylyl Cyclase Activator Forskolin Increases Influenza Virus Propagation in MDCK Cells by Regulating ERK1/2 Activity

Vaccination is the most effective method for preventing the spread of the influenza virus. Cell-based influenza vaccines have been developed to overcome the disadvantages of egg-based vaccines and their production efficiency has been previously discussed. In this study, we investigated whether treatment with forskolin (FSK), an adenylyl cyclase activator, affected the output of a cell-based influenza vaccine. We found that FSK increased the propagation of three influenza virus subtypes (A/H1N1/California/4/09, A/H3N2/Mississippi/1/85, and B/Shandong/7/97) in Madin-Darby canine kidney (MDCK) cells. Interestingly, FSK suppressed the growth of MDCK cells. This effect could be a result of protein kinase A (PKA)-Src axis activation, which downregulates extracellular signal-regulated kinase (ERK)1/2 activity and delays cell cycle progression from G1 to S. This delay in cell growth might benefit the binding and entry of the influenza virus in the early stages of viral replication. In contrast, FSK dramatically upregulated ERK1/2 activity via the cAMP-PKA-Raf-1 axis at a late stage of viral replication. Thus, increased ERK1/2 activity might contribute to increased viral ribonucleoprotein export and influenza virus propagation. The increase in viral titer induced by FSK could be explained by the action of cAMP in assisting the entry and binding of the influenza virus. Therefore, FSK addition to cell culture systems could help increase the production efficiency of cell-based vaccines against the influenza virus.

Forskolin versus cAMP-Induced Decidualization and Survival of Endometrial Stromal Cells of Endometriosis Patients

Impairment of decidualization of eutopic human endometrial stromal cells (hESCs) may cause an increase in cell survival of endometrial tissue in the peritoneal cavity constituting a precondition for endometriosis development. Decidualization is a physiological process involving progesterone action and cAMP signaling. We here evaluated the effect of 8-Br-cAMP, the adenylate cyclase activator forskolin and of the progestin progesterone and medroxyprogesterone acetate (MPA) alone and in combination on decidualization induction using prolactin ELISA, and on cell size, cell granularity, and cell survival via flow cytometry in hESCs of patients with and without endometriosis. While progestins alone did not induce functional decidualization in hESCs, 8-Br-cAMP and forskolin induced decidualization in hESCs from both cohorts, whereas the induction of FOXO1 transcription and prolactin secretion by forskolin was significantly lower than by 8-Br-cAMP. 8-Br-cAMP- and forskolin-induced prolactin secretion was significantly enhanced by MPA, but not by progesterone. Decidualization entailed a decrease in cell size and in cell granularity. In general, hESCs from women with mild (ASRM I/II) as well as severe (ASRM III/IV) endometriosis in trend displayed a higher granularity, whereas mainly hESCs from severe endometriosis showed a stronger resistance to the induction of cell death after decidualization induction. In both cohorts, the amount of the decidual marker protein prolactin rather exhibited an anti-proportional correlation to cell death induction during six day treatment. This study contributes to widen our understanding of the connection of decidualization and cell death in endometriosis.

Effects of Perfluorooctane Sulfonate on Cerebellar Cells via Inhibition of Type 2 Iodothyronine Deiodinase Activity

Perfluorooctane sulfonate (PFOS) has been used in a wide variety of industrial and commercial products. The adverse effects of PFOS on the developing brain are becoming of a great concern. However, the molecular mechanisms of PFOS on brain development have not yet been clarified. We investigated the effect of early-life exposure to PFOS on brain development and the mechanism involved. We investigated the change in thyroid hormone (TH)-induced dendrite arborization of Purkinje cells in the primary culture of newborn rat cerebellum. We further examined the mechanism of PFOS on TH signaling by reporter gene assay, quantitative RT-PCR, and type 2 iodothyronine deiodinase (D2) assay. As low as 10-7 M PFOS suppressed thyroxine (T4)-, but not triiodothyronine (T3)-induced dendrite arborization of Purkinje cells. Reporter gene assay showed that PFOS did not affect TRα1- and TRβ1-mediated transcription in CV-1 cells. RT-PCR showed that PFOS suppressed D2 mRNA expression in the absence of T4 in primary cerebellar cells. D2 activity was also suppressed by PFOS in C6 glioma-derived cells. These results indicate that early-life exposure of PFOS disrupts TH-mediated cerebellar development possibly through the disruption of D2 activity and/or mRNA expression, which may cause cerebellar dysfunction.

Hypoxia sensing requires H2S-dependent persulfidation of olfactory receptor 78

Oxygen (O2) sensing by the carotid body is critical for maintaining cardiorespiratory homeostasis during hypoxia. Hydrogen sulfide (H2S) signaling is implicated in carotid body activation by low O2. Here, we show that persulfidation of olfactory receptor 78 (Olfr78) by H2S is an integral component of carotid body activation by hypoxia. Hypoxia and H2S increased persulfidation in carotid body glomus cells and persulfidated cysteine240 in Olfr78 protein in heterologous system. Olfr78 mutants manifest impaired carotid body sensory nerve, glomus cell, and breathing responses to H2S and hypoxia. Glomus cells are positive for GOlf, adenylate cyclase 3 (Adcy3) and cyclic nucleotide-gated channel alpha 2 (Cnga2), key molecules of odorant receptor signaling. Adcy3 or Cnga2 mutants exhibited impaired carotid body and glomus cell responses to H2S and breathing responses to hypoxia. These results suggest that H2S through redox modification of Olfr78 participates in carotid body activation by hypoxia to regulate breathing.

Characterization of Adenylyl Cyclase Isoform 6 Residues Interacting with Forskolin

BACKGROUND

The adenylyl cyclase (AC) pathway, crucial for pulmonary vasodilation, is inhibited by hypoxia. Forskolin (FSK) binds allosterically to AC, stimulating ATP catalysis. As AC6 is the primary AC isoform in the pulmonary artery, selective reactivation of AC6 could provide targeted reinstatement of hypoxic AC activity. This requires elucidation of the FSK binding site in AC6.

METHODS

HEK293T cells stably overexpressing AC 5, 6, or 7 were incubated in normoxia (21% O₂) or hypoxia (10% O₂) or exposed to s-nitrosocysteine (CSNO). AC activity was measured using terbium norfloxacin assay; AC6 structure built by homology modeling; ligand docking to examine FSK-interacting amino acids; roles of selected residues determined by site-directed mutagenesis; FSK-dependent cAMP generation measured in wild-type and FSK-site mutants by biosensor-based live cell assay.

RESULTS

Only AC6 is inhibited by hypoxia and nitrosylation. Homology modeling and docking revealed residues T500, N503, and S1035 interacting with FSK. Mutation of T500, N503, or S1035 decreased FSK-stimulated AC activity. FSK site mutants were not further inhibited by hypoxia or CSNO; however, mutation of any of these residues prevented AC6 activation by FSK following hypoxia or CSNO treatment.

CONCLUSIONS

FSK-interacting amino acids are not involved in the hypoxic inhibition mechanism. This study provides direction to design FSK derivatives for selective activation of hypoxic AC6.

Rapid emergence from dexmedetomidine sedation in Sprague Dawley rats by repurposing an α2-adrenergic receptor competitive antagonist in combination with caffeine

BACKGROUND

The α2 adrenergic receptor agonist dexmedetomidine is an important intravenous sedative with analgesic properties. Currently available dexmedetomidine reversal agents, like the α2-receptor antagonist atipamezole, cause serious adverse effects at the large dosages required for effective reversal; they are not used clinically. Without reversal agents, emergence times from dexmedetomidine sedation are slow. In this study we tested the ability of low-dose atipamezole, in combination with caffeine, to reverse dexmedetomidine sedation. The low dose of atipamezole employed should not be associated with unwanted effects.

METHODS

Two different sedation protocols were employed. In the first protocol, a bolus of dexmedetomidine was rapidly applied and the drug was allowed to equilibrate for 10 min before rats received either saline (as control) or low-dose atipamezole with caffeine. Following this procedure, rats were placed on their backs. Emergence from sedation was the time for rats to recover their righting reflex and stand with 4 paws on the floor. A second sedation protocol simulated a pediatric magnetic resonance imaging (MRI) scan. Adult rats were sedated with dexmedetomidine for one hour followed by 30 min with both dexmedetomidine and propofol. At the end of 90 min, rats received either saline (control) or a combination of low-dose atipamezole, and caffeine. Recovery of the righting reflex was used as a proxy for emergence from sedation.

RESULTS

Emergence from sedation, the time for rats to recover their righting reflex, decreased by ~ 90% when using an atipamezole dose ~ 20 fold lower than manufacturer's recommendation, supplemented with caffeine. Using an atipamezole dose ~ tenfold lower than recommended, with caffeine, emergence times decreased by ~ 97%. A different stimulant, forskolin, when tested, was as effective as caffeine. For the MRI simulation, emergence times were decreased by ~ 93% by low-dose atipamezole with caffeine.

CONCLUSIONS

Low dose atipamezole with caffeine was effective at reversing dexmedetomidine sedation. Emergence was rapid and the rats regained not only their righting reflex but also their balance and their ability to carry out complex behaviors. These findings suggest that the combination of low dose atipamezole with caffeine may permit rapid clinical reversal of dexmedetomidine without unwanted effects.

Biologically Active Diterpenoids in the Clerodendrum Genus—A Review

One of the key areas of interest in pharmacognosy is that of the diterpenoids; many studies have been performed to identify new sources, their optimal isolation and biological properties. An important source of abietane-, pimarane-, clerodane-type diterpenoids and their derivatives are the members of the genus Clerodendrum, of the Lamiaceae. Due to their diverse chemical nature, and the type of plant material, a range of extraction techniques are needed with various temperatures, solvent types and extraction times, as well as the use of an ultrasound bath. The diterpenoids isolated from Clerodendrum demonstrate a range of cytotoxic, anti-proliferative, antibacterial, anti-parasitic and anti-inflammatory activities. This review describes the various biological activities of the diterpenoids isolated so far from species of Clerodendrum with the indication of the most active ones, as well as those from other plant sources, taking into account their structure in terms of their activity, and summarises the methods for their extraction.

Regulation of cellular communication network factor 1 by Ras homolog family member A in bovine steroidogenic luteal cells

Development of the corpus luteum (CL) requires the growth of a new capillary network from preexisting vasculature, a process known as angiogenesis. Successful building of this capillary network occurs through a sequence of cellular events-differentiation, proliferation, migration, and adhesion-which are regulated by a suite of angiogenic proteins that includes cellular communication network factor 1 (CCN1). We previously reported that the expression of CCN1 was highest in luteal tissue obtained from the early-cycle, 4-d-old bovine CL (i.e., corpus hemorrhagicum) compared to the mid- and late-cycle CL. In the present study, we treated steroidogenic bovine luteal cells from early-cycle CL with luteinizing hormone (LH), but it had no effect on CCN1 expression. Direct stimulation of the canonical LH pathway with forskolin and dibutyryl-cyclic adenosine monophosphate (cAMP), however, inhibited CCN1 mRNA expression. In endothelial cells, stimulation of Ras homolog family member A (RhoA) induces CCN1 expression, whereas RhoA inactivation inhibits it. Yet, it is unknown if regulation of CCN1 in steroidogenic luteal cells works likewise. We hypothesized that a similar mechanism of CCN1 regulation exists in bovine luteal cells and that thrombin, a known RhoA activator, may be a physiologic trigger for this mechanism in the early-cycle CL. To test this hypothesis, ovaries were collected from lactating dairy cows on days 3 or 4 of the estrous cycle, and corpora lutea were dissected and dissociated. Steroidogenic luteal cells were suspended in defined Ham's F12 medium, supplemented with insulin/transferrin/selenium and gentamicin, and seeded into 6-well plates. After 24 h, spent medium was replaced with fresh Ham's F12, and the cells were cultured for 24 to 48 h. Cells were treated for 2 h with defined medium, 10% fetal bovine serum (FBS), thrombin (1, 5, 10 U/mL), or Rho Activator II (0.25, 1, 2 μg/mL). Cells were then lysed for RNA extraction, followed by cDNA generation, and quantitative polymerase chain reaction (qPCR). Thrombin (1, 5, 10 U/mL; n = 3) and Rho Activator II (0.25, 1, 2 μg/mL; n = 6) increased (P < 0.05) CCN1 mRNA expression. In summary, CCN1 in bovine steroidogenic luteal cells was induced by thrombin and appeared to be regulated in a Rho-dependent manner. Future work will elucidate the signaling partners downstream of Rho which leads to CCN1 gene expression.

Characterization of Proteins Regulated by Androgen and Protein Kinase a Signaling in VCaP Prostate Cancer Cells

Androgen signaling via the androgen receptor (AR) is involved in normal prostate development and prostate cancer progression. In addition to androgen binding, a variety of protein kinases, including cyclic AMP-dependent protein kinase A (PKA), can activate the AR. Although hormone deprivation, especially that of androgen, continues to be an important strategy for treating prostate cancer patients, the disease ultimately progresses to castration-resistant prostate cancer (CRPC), despite a continuous hormone-deprived environment. To date, it remains unclear which pathways in this progression are active and targetable. Here, we performed a proteomic analysis of VCaP cells stimulated with androgen or forskolin to identify proteins specific for androgen-induced and androgen-bypassing signaling, respectively. Patterns of differentially expressed proteins were quantified, and eight proteins showing significant changes in expression were identified. Functional information, including a Gene Ontology analysis, revealed that most of these proteins are involved in metabolic processes and are associated with cancer. The mRNA and protein expression of selected proteins was validated, and functional correlations of identified proteins with signaling in VCaP cells were assessed by measuring metabolites related to each enzyme. These analyses offered new clues regarding effector molecules involved in prostate cancer development, insights that are supported by the demonstration of increased expression levels of the eight identified proteins in prostate cancer patients and assessments of the progression-free interval. Taken together, our findings show that aberrant levels of eight proteins reflect molecular changes that are significantly regulated by androgen and/or PKA signaling pathways, suggesting possible molecular mechanisms of CRPC.

Potential depression and antidepressant-response biomarkers in human lymphoblast cell lines from treatment-responsive and treatment-resistant subjects: roles of SSRIs and omega-3 polyunsaturated fatty acids

While several therapeutic strategies exist for depression, most antidepressant drugs require several weeks before reaching full biochemical efficacy and remission is not achieved in many patients. Therefore, biomarkers for depression and drug-response would help tailor treatment strategies. This study made use of banked human lymphoblast cell lines (LCLs) from normal and depressed subjects; the latter divided into remitters and non-remitters. Due to the fact that previous studies have shown effects on growth factors, cytokines, and elements of the cAMP-generating system as potential biomarkers for depression and antidepressant action, these were examined in LCLs. Initial gene and protein expression profiles for signaling cascades related to neuroendocrine and inflammatory functions differ among the three groups. Growth factor genes, including VEGFA and BDNF were significantly down-regulated in cells from depressed subjects. In addition, omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to act as both antidepressants and anti-inflammatories, but the mechanisms for these effects are not established. Here we showed that n-3 PUFAs and escitalopram (selective serotonin reuptake inhibitors, SSRIs) treatment increased adenylyl cyclase (AC) and BDNF gene expression in LCLs. These data are consistent with clinical observations showing that n-3 PUFA and SSRI have antidepressant affects, which may be additive. Contrary to observations made in neuronal and glial cells, n-3 PUFA treatment attenuated cAMP accumulation in LCLs. However, while lymphoblasts show paradoxical responses to neurons and glia, patient-derived lymphoblasts appear to carry potential depression biomarkers making them an important tool for studying precision medicine in depressive patients. Furthermore, these data validate usefulness of n-3 PUFAs in treatment for depression.

Identification and validation of the phosphorylation sites on Aristaless-related homeobox protein

The Aristaless-related homeobox protein (ARX) is a transcription factor expressed in the developing forebrain, skeletal muscle, pancreas, testis, and a variety of other tissues. It is known to have context-dependent transcriptional activator and repressor activity, although how it can achieve these opposing functions remains poorly understood. We hypothesized phosphorylation status might play a role in pivoting ARX between functioning as an activator or repressor. To gain further mechanistic insight as to how ARX functions, we identified multiple phosphorylation sites on ARX. We further established PKA as the kinase that phosphorylates ARX at least at Ser²⁶⁶ in mice. Two other kinases, CK2α and CDK4/cyclin D1, were also identified as kinases that phosphorylate ARX in vitro. Unexpectedly, phosphorylation status did not change either the nuclear localization or transcriptional function of ARX.

seco-Labdanes: A Study of Terpenoid Structural Diversity Resulting from Biosynthetic C-C Bond Cleavage

The cleavage of a C-C bond is a complexity generating process, which complements oxidation and cyclisation events in the biosynthesis of terpenoids. This process leads to increased structural diversity in a cluster of related secondary metabolites by modification of the parent carbocyclic core. In this review, we highlight the diversifying effect of C-C bond cleavage by examining the literature related to seco-labdanes-a class of diterpenoids arising from such C-C bond cleavage events.

Fungal Endophytes as Efficient Sources of Plant-Derived Bioactive Compounds and Their Prospective Applications in Natural Product Drug Discovery: Insights, Avenues, and Challenges

Fungal endophytes are well-established sources of biologically active natural compounds with many producing pharmacologically valuable specific plant-derived products. This review details typical plant-derived medicinal compounds of several classes, including alkaloids, coumarins, flavonoids, glycosides, lignans, phenylpropanoids, quinones, saponins, terpenoids, and xanthones that are produced by endophytic fungi. This review covers the studies carried out since the first report of taxol biosynthesis by endophytic Taxomyces andreanae in 1993 up to mid-2020. The article also highlights the prospects of endophyte-dependent biosynthesis of such plant-derived pharmacologically active compounds and the bottlenecks in the commercialization of this novel approach in the area of drug discovery. After recent updates in the field of 'omics' and 'one strain many compounds' (OSMAC) approach, fungal endophytes have emerged as strong unconventional source of such prized products.

In vitro and in silico studies of 8(17),12E,14-labdatrien-18-oic acid in airways smooth muscle relaxation: new molecular insights about its mechanism of action

In the field of experimental pharmacology, researchers continuously investigate new relaxant agents of the airway smooth muscle cells (ASMCs), since the pathophysiology of respiratory illnesses, such as asthma, involves hyperresponsiveness and changes in ASMC homeostasis. In this scenario, labdane-type diterpenes, like forskolin (FSK), are a class of compounds known for their relaxing action on smooth muscle cells (SMCs), being this phenomenon related to the direct activation of AC-cAMP-PKA pathway. Considering the continuous effort of our group to study the mechanism of action and prospecting for compounds isolated from natural sources, in this paper, we presented how the diterpene 8(17),12E,14-labdatrien-18-oic acid (LBD) promotes relaxant effect on ASMC, performing in vitro experiments using isolated guinea pig trachea and in silico molecular docking/dynamics simulations. In vitro experiments showed that in the presence of aminophylline, FSK and LBD had their relaxant effect potentiated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 1.5 ± 0.3 × 10^-6 M for LBD and from 2.0 ± 0.2 × 10^-7 M to 6.4 ± 0.4 × 10^-8 M for FSK) while in the presence of Rp-cAMPS this effect was attenuated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 3 × 10^-4 M for LBD and from 2.0 ± 0.2 × 10^-7 to 3.1 ± 1.0 × 10^-6 M for FSK). Additionally, in silico simulations evidenced that the lipophilic character of LBD is probably responsible for its stability on AC binding site. LBD presented two preferential orientations, where the double bonds of the isoprene moiety as well as the unique polar group (carboxylic acid) in this compound form important anchoring points. In this sense, we consider that the LBD can interact stabilizing the catalytic dimmer of AC as the FSK, although less efficiently.

Caffeine reverses the unconsciousness produced by light anesthesia in the continued presence of isoflurane in rats

Currently no drugs are employed clinically to reverse the unconsciousness induced by general anesthetics. Our previous studies showed that caffeine, when given near the end of an anesthesia session, accelerated emergence from isoflurane anesthesia, likely caused by caffeine’s ability to elevate intracellular cAMP levels and to block adenosine receptors. These earlier studies showed that caffeine did not rouse either rats or humans from deep anesthesia (≥ 1 minimum alveolar concentration, MAC). In this current crossover study, we examined whether caffeine reversed the unconsciousness produced by light anesthesia (< 1 MAC) in the continued presence of isoflurane. The primary endpoint of this study was to measure isoflurane levels at the time of recovery of righting reflex, which was a proxy for consciousness. Rats were deeply anesthetized with 2% isoflurane (~1.5 MAC) for 20 minutes. Subsequently, isoflurane was reduced to 1.2% for 10 minutes, then by 0.2% every 10 min; animals were monitored until the recovery of righting reflex occurred, in the continued presence of isoflurane. Respiration rate, heart rate and electroencephalogram (EEG) were monitored. Our results show that caffeine-treated rats recovered their righting reflex at a significantly higher inspired isoflurane concentration, corresponding to light anesthesia, than the same rats treated with saline (control). Respiration rate and heart rate increased initially after caffeine injection but were then unchanged for the rest of the anesthesia session. Deep anesthesia is correlated with burst suppression in EEG recordings. Our data showed that caffeine transiently reduced the burst suppression time produced by deep anesthesia, suggesting that caffeine altered neuronal circuit function but not to a point where it caused arousal. In contrast, under light anesthesia, caffeine shifted the EEG power to high frequency beta and gamma bands. These data suggest that caffeine may represent a clinically viable drug to reverse the unconsciousness produced by light anesthesia.

SynaptoPAC, an optogenetic tool for induction of presynaptic plasticity

Optogenetic manipulations have transformed neuroscience in recent years. While sophisticated tools now exist for controlling the firing patterns of neurons, it remains challenging to optogenetically define the plasticity state of individual synapses. A variety of synapses in the mammalian brain express presynaptic long-term potentiation (LTP) upon elevation of presynaptic cyclic adenosine monophosphate (cAMP), but the molecular expression mechanisms as well as the impact of presynaptic LTP on network activity and behavior are not fully understood. In order to establish optogenetic control of presynaptic cAMP levels and thereby presynaptic potentiation, we developed synaptoPAC, a presynaptically targeted version of the photoactivated adenylyl cyclase bPAC. In cultures of hippocampal granule cells of Wistar rats, activation of synaptoPAC with blue light increased action potential-evoked transmission, an effect not seen in hippocampal cultures of non-granule cells. In acute brain slices of C57BL/6N mice, synaptoPAC activation immediately triggered a strong presynaptic potentiation at mossy fiber synapses in CA3, but not at Schaffer collateral synapses in CA1. Following light-triggered potentiation, mossy fiber transmission decreased within 20 min, but remained enhanced still after 30 min. The optogenetic potentiation altered the short-term plasticity dynamics of release, reminiscent of presynaptic LTP. Our work establishes synaptoPAC as an optogenetic tool that enables acute light-controlled potentiation of transmitter release at specific synapses in the brain, facilitating studies of the role of presynaptic potentiation in network function and animal behavior in an unprecedented manner. Read the Editorial Highlight for this article on page 270.

Incorporation of amino moiety to alepterolic acid improve activity against cancer cell lines: Synthesis and biological evaluation

Aleuritopteris argentea (S. G. Gmél.) Fée is a medicinal fern consisting of an ent-labdane diterpene, i.e. alepterolic aicd, as the major metabolite. We recently isolated grams of alepterolic acid from A. argentea enabling subsequent structural modification. By incorporation of amino moiety to alepterolic acid, fifteen amide derivatives were synthesized, characterized, and further biological evaluated regarding their activity against four cancer cells and normal human liver cells. The potency of synthesized amides dramatically improved as compared to alepterolic aicd itself. The best hit (compound 11) inhibits HeLa cells with an IC₅₀ of 7.39 ± 0.80 μM, and is nearly nontoxic to normal cells. Compound 11 exhibits an inhibitory effect on the colony forming ability of the four cancer cells, especially of HeLa cells. Moreover, it induces apoptosis of HeLa cells by decreasing mitochondrial membrane potential and altering expression of apoptosis-associated proteins. Release of cytochrome c, activation of caspases-3, caspases-9 and alteration of Bax/Bcl-2 balance was detected in the biological assays. These results imply that compound 11 can inhibit the proliferation of cervical cancer cell line HeLa and induce apoptosis through the mitochondrial pathway. These findings encourage further rational structural modification of 15- carboxyl group of alepterolic acid.

Mitochondrial cAMP-PKA signaling: What do we really know?

Mitochondria are key organelles for cellular homeostasis. They generate the most part of ATP that is used by cells through oxidative phosphorylation. They also produce reactive oxygen species, neurotransmitters and other signaling molecules. They are important for calcium homeostasis and apoptosis. Considering the role of this organelle, it is not surprising that most mitochondrial dysfunctions are linked to the development of pathologies. Various mechanisms adjust mitochondrial activity according to physiological needs. The cAMP-PKA signaling emerged in recent years as a direct and powerful mean to regulate mitochondrial functions. Multiple evidence demonstrates that such pathway can be triggered from cytosol or directly within mitochondria. Notably, specific anchor proteins target PKA to mitochondria whereas enzymes necessary for generation and degradation of cAMP are found directly in these organelles. Mitochondrial PKA targets proteins localized in different compartments of mitochondria, and related to various functions. Alterations of mitochondrial cAMP-PKA signaling affect the development of several physiopathological conditions, including neurodegenerative diseases. It is however difficult to discriminate between the effects of cAMP-PKA signaling triggered from cytosol or directly in mitochondria. The specific roles of PKA localized in different mitochondrial compartments are also not completely understood. The aim of this work is to review the role of cAMP-PKA signaling in mitochondrial (patho)physiology.

Investigational Drug Therapies for Overactive Bladder Syndrome: The Potential Alternatives to Anticolinergics

Background

Overactive bladder is a high prevalent and quality of life affecting disease. The mainstay of the medical therapy is represented by antimuscarinic drugs, but their side effects markedly affect patient compliance and prompt studies on novel investigational drugs.

Methods

A systematic literature search of peer-reviewed papers and meeting abstracts published by December 2008 was performed. PubMed databank was searched for original English articles, by using the following search terms: “overactive bladder” or “detrusor overactivity” or “urinary incontinence” and “treatment”, alone and linked to any potential molecular target or novel drug cited in the literature.

Results

Effective alternative pharmacological treatments are currently scarce, but many new promising compounds are emerging which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include central nervous system GABAergic inhibitory pathway, dopaminergic and serotoninergic systems, b-adrenoceptors and cAMP metabolism, nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems, vanilloid receptor, bladder sensory nervous terminals, nonneuronal bladder signalling systems including urothelium and interstitial cells, prostanoids, Rho-kinase and different subtypes of potassium and calcium channels.

Conclusions

Despite the enormous amount of new biologic insight, very few novel pharmacological therapies seems to have passed the proof-of-concept clinical stage. The ultimate clinical utility of new drugs will depend on the ability to exploit tissue-specific differences and disease-related changes in molecular expression/function and to improve storage phase dysfunctions without interfering with the emptying phase. Further preclinical investigations and controlled clinical trials are urgently needed in this challenging field.

Transcriptional regulation of CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression pattern in colorectal cancer HCT116 cells

The CacyBP/SIP protein is expressed at a particularly high level in brain, spleen, and various tumors. In this work, we have studied transcriptional regulation of the CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression in colorectal cancer HCT116 cells. We have shown that E2F1, EGR1, and CREB transcription factors bind to the CacyBP/SIP gene promoter and stimulate transcription of CacyBP/SIP gene. The role of CREB was further confirmed by the observation that forskolin, a strong activator of CREB phosphorylation/activity, increased CacyBP/SIP gene promoter activity. Moreover, we have shown that CREB dominant negative mutants, CREB133 and KCREB, inhibits CacyBP/SIP promoter activity. To check the biological significance of increased CacyBP/SIP expression/level we have applied RNA microarray analysis and have found that upregulation of CacyBP/SIP entails changes in mRNA level of many genes involved, among others, in immune processes. © 2017 IUBMB Life, 70(1):50-59, 2018.

Deep Sequencing Reveals the Significant Involvement of cAMP-Related Signaling Pathways Following Sciatic Nerve Crush

Peripheral nerve injury and regeneration is a complex biological process jointly mediated by numerous factors. Cyclic adenosine monophosphate (cAMP) modifies the cellular behaviors of neurons and Schwann cells, and thus may contribute to peripheral nerve regeneration. Despite the importance of cAMP, the temporal and spatial expressions of genes involved in cAMP-related signaling pathways during peripheral nerve regeneration remain unclear. In the current study, by using rat sciatic nerve crush model, we analyzed previously obtained RNA deep sequencing data, explored the significance of cAMP-mediated signaling pathway and protein kinase A (PKA) signaling pathway after peripheral nerve injury, and examined the expression patterns of genes involved in these cAMP-related signaling pathways. Our results, from the genetic aspect, emphasized the critical involvement of cAMP-related signaling pathways, identified the dynamic changes of some key signaling cascades, and may help the discovery of potential therapeutic targets for peripheral nerve repair and regeneration.

Caffeine accelerates recovery from general anesthesia via multiple pathways

Various studies have explored different ways to speed emergence from anesthesia. Previously, we have shown that three drugs that elevate intracellular cAMP (forskolin, theophylline, and caffeine) accelerate emergence from anesthesia in rats. However, our earlier studies left two main questions unanswered. First, were cAMP-elevating drugs effective at all anesthetic concentrations? Second, given that caffeine was the most effective of the drugs tested, why was caffeine more effective than forskolin since both drugs elevate cAMP? In our current study, emergence time from anesthesia was measured in adult rats exposed to 3% isoflurane for 60 min. Caffeine dramatically accelerated emergence from anesthesia, even at the high level of anesthetic employed. Caffeine has multiple actions including blockade of adenosine receptors. We show that the selective A2a adenosine receptor antagonist preladenant or the intracellular cAMP ([cAMP]i)-elevating drug forskolin, accelerated recovery from anesthesia. When preladenant and forskolin were tested together, the effect on anesthesia recovery time was additive indicating that these drugs operate via different pathways. Furthermore, the combination of preladenant and forskolin was about as effective as caffeine suggesting that both A2A receptor blockade and [cAMP]i elevation play a role in caffeine's ability to accelerate emergence from anesthesia. Because anesthesia in rodents is thought to be similar to that in humans, these results suggest that caffeine might allow for rapid and uniform emergence from general anesthesia in humans at all anesthetic concentrations and that both the elevation of [cAMP]i and adenosine receptor blockade play a role in this response.NEW & NOTEWORTHY Currently, there is no method to accelerate emergence from anesthesia. Patients "wake" when they clear the anesthetic from their systems. Previously, we have shown that caffeine can accelerate emergence from anesthesia. In this study, we show that caffeine is effective even at high levels of anesthetic. We also show that caffeine operates by both elevating intracellular cAMP levels and by blocking adenosine receptors. This complicated pharmacology makes caffeine especially effective in accelerating emergence from anesthesia.

Highly Functionalized Ring B Labdane Synthesis as Key Intermediate in the Route to Forskolin

Sclareol has been employed as starting material for the synthesis of several advanced intermediates towards the synthesis of highly ring B oxygenated labdanes. Dinorlabdanes 6,7,8,9-tetraoxygenated with 6,7-dioxygenated functionalities with α- cis or β- cis dispositions, have been prepared and can be used for forskolin or analogues synthesis.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Lysine post-translational modification of glyceraldehyde-3-phosphate dehydrogenase regulates hepatic and systemic metabolism

Reciprocal regulation of hepatic glycolysis and gluconeogenesis contributes to systemic metabolic homeostasis. Recent evidence from lower order organisms has found that reversible post-translational modification of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), particularly acetylation, contributes to the reciprocal regulation of glycolysis/gluconeogenesis. However, whether this occurs in mammalian hepatocytes in vitro or in vivo is unknown. Several proteomics studies have identified 4 lysine residues in critical regions of mammalian GAPDH that are altered by multiple post-translational modifications. In FAO hepatoma cells, mutation of all 4 lysine residues (4K-R GAPDH) to mimic their unmodified state reduced GAPDH glycolytic activity and glycolytic flux and increased gluconeogenic GAPDH activity and glucose production. Hepatic expression of 4K-R GAPDH in mice increased GAPDH gluconeogenic activity and the contribution of gluconeogenesis to endogenous glucose production in the unfed state. Consistent with the increased reliance on the energy-consuming gluconeogenic pathway, plasma free fatty acids and ketones were elevated in mice expressing 4K-R GAPDH, suggesting enhanced lipolysis and hepatic fatty acid oxidation. In normal mice, food withholding and refeeding, as well as hormonal regulators of reciprocal glycolysis/gluconeogenesis, such as insulin, glucagon, and norepinephrine, had no effect on global GAPDH acetylation. However, GAPDH acetylation was reduced in obese and type 2 diabetic db/db mice. These findings show that post-translational modification of GAPDH lysine residues regulates hepatic and systemic metabolism, revealing an unappreciated role for hepatic GAPDH in substrate selection and utilization.-Bond, S. T., Howlett, K. F., Kowalski, G. M., Mason, S., Connor, T., Cooper, A., Streltsov, V., Bruce, C. R., Walder, K. R., McGee, S. L. Lysine post-translational modification of glyceraldehyde-3-phosphate dehydrogenase regulates hepatic and systemic metabolism.

Arachidonic acid triggers [Ca2+]i increases in rat round spermatids by a likely GPR activation, ERK signalling and ER/acidic compartments Ca2+ release

Arachidonic acid (AA), a compound secreted by Sertoli cells (SC) in a FSH-dependent manner, is able to induce the release of Ca²⁺ from internal stores in round spermatids and pachytene spermatocytes. In this study, the possible site(s) of action of AA in round spermatids, the signalling pathways associated and the intracellular Ca²⁺ stores targeted by AA-induced signalling were pharmacologically characterized by measuring intracellular Ca²⁺ using fluorescent Ca²⁺ probes. Our results suggest that AA acts by interacting with a fatty acid G protein coupled receptor, initiating a G protein signalling cascade that may involve PLA2 and ERK activation, which in turn opens intracellular ryanodine-sensitive channels as well as NAADP-sensitive channels in acidic intracellular Ca²⁺ stores. The results presented here also suggest that AMPK and PKA modulate this AA-induced Ca²⁺ release from intracellular Ca²⁺ stores in round spermatids. We propose that unsaturated free fatty acid lipid signalling in the seminiferous tubule is a novel regulatory component of rat spermatogenesis.

Adenylyl cyclase signalling complexes - Pharmacological challenges and opportunities

Signalling pathways involving the vital second messanger, cAMP, impact on most significant physiological processes. Unsurprisingly therefore, the activation and regulation of cAMP signalling is tightly controlled within the cell by processes including phosphorylation, the scaffolding of protein signalling complexes and sub-cellular compartmentalisation. This inherent complexity, along with the highly conserved structure of the catalytic sites among the nine membrane-bound adenylyl cyclases, presents significant challenges for efficient inhibition of cAMP signalling. Here, we will describe the biochemistry and cell biology of the family of membrane-bound adenylyl cyclases, their organisation within the cell, and the nature of the cAMP signals that they produce, as a prelude to considering how cAMP signalling might be perturbed. We describe the limitations associated with direct inhibition of adenylyl cyclase activity, and evaluate alternative strategies for more specific targeting of adenylyl cyclase signalling. The inherent complexity in the activation and organisation of adenylyl cyclase activity may actually provide unique opportunities for selectively targeting discrete adenylyl cyclase functions in disease.

The Natural cAMP Elevating Compound Forskolin in Cancer Therapy: Is It Time?

Cancer is a major public health problem and the second leading cause of mortality around the world. Although continuous advances in the science of oncology and cancer research are now leading to improved outcomes for many cancer patients, novel cancer treatment options are strongly demanded. Naturally occurring compounds from a variety of vegetables, fruits, and medicinal plants have been shown to exhibit various anticancer properties in a number of in vitro and in vivo studies and represent an attractive research area for the development of new therapeutic strategies to fight cancer. Forskolin is a diterpene produced by the roots of the Indian plant Coleus forskohlii. The natural compound forskolin has been used for centuries in traditional medicine and its safety has also been documented in conventional modern medicine. Forskolin directly activates the adenylate cyclase enzyme, that generates cAMP from ATP, thus, raising intracellular cAMP levels. Notably, cAMP signaling, through the PKA-dependent and/or -independent pathways, is very relevant to cancer and its targeting has shown a number of antitumor effects, including the induction of mesenchymal-to-epithelial transition, inhibition of cell growth and migration and enhancement of sensitivity to conventional antitumor drugs in cancer cells. Here, we describe some features of cAMP signaling that are relevant to cancer biology and address the state of the art concerning the natural cAMP elevating compound forskolin and its perspectives as an effective anticancer agent. J. Cell. Physiol. 232: 922-927, 2017. © 2016 Wiley Periodicals, Inc.

Gliotoxin Suppresses Macrophage Immune Function by Subverting Phosphatidylinositol 3,4,5-Trisphosphate Homeostasis

Aspergillus fumigatus, an opportunistic fungal pathogen, spreads in the environment by releasing numerous conidia that are capable of reaching the small alveolar airways of mammalian hosts. In otherwise healthy individuals, macrophages are responsible for rapidly phagocytosing and eliminating these conidia, effectively curbing their germination and consequent invasion of pulmonary tissue. However, under some circumstances, the fungus evades phagocyte-mediated immunity and persists in the respiratory tree. Here, we report that A. fumigatus escapes macrophage recognition by strategically targeting phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P₃] metabolism through gliotoxin, a potent immunosuppressive mycotoxin. Time-lapse microscopy revealed that, in response to the toxin, macrophages cease to ruffle, undergo abrupt membrane retraction, and fail to phagocytose large targets effectively. Gliotoxin was found to prevent integrin activation and interfere with actin dynamics, both of which are instrumental for phagocytosis; similar effects were noted in immortalized and primary phagocytes. Detailed studies of the underlying molecular mechanisms of toxicity revealed that inhibition of phagocytosis is attributable to impaired accumulation of PtdIns(3,4,5)P₃ and the associated dysregulation of downstream effectors, including Rac and/or Cdc42. Strikingly, in response to the diacylglycerol mimetic phorbol 12-myristate 13-acetate, gliotoxin-treated macrophages reactivate beta integrins, reestablish actin dynamics, and regain phagocytic capacity, despite the overt absence of plasmalemmal PtdIns(3,4,5)P₃. Together, our findings identify phosphoinositide metabolism as a critical upstream target of gliotoxin and also indicate that increased diacylglycerol levels can bypass the requirement for PtdIns(3,4,5)P₃ signaling during membrane ruffling and phagocytosis.

Aspergillus fumigatus is the most frequent cause of human infections in the Aspergillus genus. In immunocompromised populations, invasive aspergillosis (IA) is associated with a mortality rate of up to 90%, and current antifungal therapies have failed to prevent or reverse the infection. Therefore, a deeper understanding of the interactions between A. fumigatus and its host is required. In healthy humans, alveolar macrophages can ingest and eliminate fungal spores, thus limiting their germination into mycotoxin-producing hyphae. Our studies reveal that gliotoxin—the most abundant Aspergillus mycotoxin—undermines the ability of phagocytes to carry out their protective functions. By targeting PtdIns(3,4,5)P₃ signaling and downregulating phagocytic immune defenses, the toxin could also exacerbate polymicrobial infections. Notably, we were able to reverse gliotoxin toxicity by addition of diacylglycerol analogues, which may provide the basis for therapeutic interventions.

Cardiac cAMP: production, hydrolysis, modulation and detection

Cyclic adenosine 3′,5′-monophosphate (cAMP) modulates a broad range of biological processes including the regulation of cardiac myocyte contractile function where it constitutes the main second messenger for β-adrenergic receptors' signaling to fulfill positive chronotropic, inotropic and lusitropic effects. A growing number of studies pinpoint the role of spatial organization of the cAMP signaling as an essential mechanism to regulate cAMP outcomes in cardiac physiology. Here, we will briefly discuss the complexity of cAMP synthesis and degradation in the cardiac context, describe the way to detect it and review the main pharmacological arsenal to modulate its availability.

The natural compound forskolin synergizes with dexamethasone to induce cell death in myeloma cells via BIM

We have previously demonstrated that activation of the cyclic adenosine monophosphate (cAMP) pathway kills multiple myeloma (MM) cells both in vitro and in vivo. In the present study we have investigated the potential of enhancing the killing of MM cell lines and primary MM cells by combining the cAMP-elevating compound forskolin with the commonly used MM therapeutic drugs melphalan, cyclophosphamide, doxorubicin, bortezomib and dexamethasone. We observed that forskolin potentiated the killing induced by all the tested agents as compared to treatment with the single agents alone. In particular, forskolin had a synergistic effect on the dexamethasone-responsive cell lines H929 and OM-2. By knocking down the proapoptotic BCL-2 family member BIM, we proved this protein to be involved in the synergistic induction of apoptosis by dexamethasone and forskolin. The ability of forskolin to maintain the killing of MM cells even at lower concentrations of the conventional agents suggests that forskolin may be used to diminish treatment-associated side effects. Our findings support a potential role of forskolin in combination with current conventional agents in the treatment of MM.

ALS associated mutant SOD1 impairs the motor neurons and astrocytes and wild type astrocyte secreted-factors reverse the impaired motor neurons

BACKGROUND

Amyotrophic Lateral Sclerosis, in which motor neurons degenerate, leading to paralysis, not only the affected motor neurons, but the surrounding non-neuronal cells also contribute significantly to the disease. However, the disease mechanism is not known.

PURPOSE

In this study we have addressed the disease mechanism by expressing the ALS associated mutant SOD1(G37R) in the motor neurons (mMN) and astrocytes (mA) cell lines.

METHODS

A series of cell culture assays, immunostaining, RT-PCR and Western blot analysis were performed.

RESULTS

We noticed impairments in both these cell types. The mMN motor neurons were insensitive to forskolin, a known activator of adenylate cyclase, which leads to motor neuron death. In addition, less number of mMN were positive for phosphorylated neurofilament-H (pNFH) unlike the normal motor neurons. Similarly, the mutant SOD1 expressing astrocytes (mA) had two impairments: The inability to activate the oxidative stress protection and the absence of secretory factor(s). Normal astrocytes and their secreted factors could restore the pNFH in the mMN but not the mA. In addition, we show that pNFH restoration is a specific function since the insensitivity of mMN to forskolin could be rescued by neither normal astrocytes nor their secreted factors.

CONCLUSION

Thus we demonstrate some of the abnormalities caused by the ALS associated mutant SOD1(G37R) and a potential way, to reverse an abnormality through cell replacement.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

Prostaglandin dependent control of an endogenous estrogen receptor agonist by osteoblasts

Estrogen receptor (ER) activation has complex effects on bone cells, and loss of circulating estradiol adversely affects skeletal status in women. Hormone replacement therapy effectively circumvents bone loss after menopause, but enhances disease risk in other tissues. Here we show that prostaglandin E2 (PGE2) augments the activity of an osteoblast-derived selective ER modulator, ObSERM. The stimulatory effect of PGE2 is replicated in part by either the PG receptor EP3 agonist 17-phenyl trinor PGE2 or by the PG receptor FP agonist PGF2α⋅ Whereas activation of the various PG receptors induces multiple downstream signals, the response to PGE2 was mimicked by activators of protein kinase C, and suppressed by inhibition of protein kinase C but not by inhibition of protein kinase A. Moreover, inhibition of nitric oxide synthesis and activation of the PTH and Wnt pathways increases ObSERM activity. Our studies therefore reveal that ObSERM activity is controlled in distinct ways and revise our understanding of ER activation within bone by agents or events associated with PG expression. They also predict ways to sustain or improve bone formation, fracture repair, and surgical healing without adding the risk of disease in other tissues where ER activation also has important biological functions.

Adenosine modulates light responses of rat retinal ganglion cell photoreceptors througha cAMP-mediated pathway

Adenosine is an established neuromodulator in the mammalian retina, with A1 adenosine receptors being especially prevalent in the innermost ganglion cell layer. Activation of A1 receptors causes inhibition of adenylate cyclase, decreases in intracellular cyclic AMP (cAMP) levels and inhibition of protein kinase A (PKA). In this work, our aim was to characterize the effects of adenosine on the light responses of intrinsically photosensitive retinal ganglion cells (ipRGCs) and to determine whether these photoreceptors are subject to neuromodulation through intracellular cAMP-related signalling pathways. Using multielectrode array recordings from postnatal and adult rat retinas, we demonstrated that adenosine significantly shortened the duration of ipRGC photoresponses and reduced the number of light-evoked spikes fired by these neurons. The effects were A1 adenosine receptor-mediated, and the expression of this receptor on melanopsin-containing ipRGCs was confirmed by calcium imaging experiments on isolated cells in purified cultures. While inhibition of the cAMP/PKA pathway by adenosine shortened ipRGC light responses, stimulation of this pathway with compounds such as forskolin had the opposite effect and lengthened the duration of ipRGC spiking. Our findings reveal that the modification of ipRGC photoresponses through a cAMP/PKA pathway is a general feature of rat ganglion cell photoreceptors, and this pathway can be inhibited through activation of A1 receptors by adenosine. As adenosine levels in the retina rise at night, adenosinergic modulation of ipRGCs may serve as an internal regulatory mechanism to limit transmission of nocturnal photic signals by ipRGCs to the brain. Targeting retinal A1 adenosine receptors for ipRGC inhibition represents a potential therapeutic target for sleep disorders and migraine-associated photophobia.

Primordial germ-cell development and epigenetic reprogramming in mammals

Primordial germ cells (PGCs) are the embryonic precursors of the gametes and represent the founder cells of the germline. Specification of PGCs is a critical divergent point during embryogenesis. Whereas the somatic lineages will ultimately perish, cells of the germline have the potential to form a new individual and hence progress to the next generation. It is therefore critical that the genome emerges intact and carrying the appropriate epigenetic information during its passage through the germline. To ensure this fidelity of transmission, PGC development encompasses extensive epigenetic reprogramming. The low cell numbers and relative inaccessibility of PGCs present a challenge to those seeking mechanistic understanding of the crucial developmental and epigenetic processes in this most fascinating of lineages. Here, we present an overview of PGC development in the mouse and compare this with the limited information available for other mammalian species. We believe that a comparative approach will be increasingly important to uncover the extent to which mechanisms are conserved and reveal the critical steps during PGC development in humans.

Caffeine accelerates recovery from general anesthesia

General anesthetics inhibit neurotransmitter release from both neurons and secretory cells. If inhibition of neurotransmitter release is part of an anesthetic mechanism of action, then drugs that facilitate neurotransmitter release may aid in reversing general anesthesia. Drugs that elevate intracellular cAMP levels are known to facilitate neurotransmitter release. Three cAMP elevating drugs (forskolin, theophylline, and caffeine) were tested; all three drugs reversed the inhibition of neurotransmitter release produced by isoflurane in PC12 cells in vitro. The drugs were tested in isoflurane-anesthetized rats. Animals were injected with either saline or saline containing drug. All three drugs dramatically accelerated recovery from isoflurane anesthesia, but caffeine was most effective. None of the drugs, at the concentrations tested, had significant effects on breathing rates, O2 saturation, heart rate, or blood pressure in anesthetized animals. Caffeine alone was tested on propofol-anesthetized rats where it dramatically accelerated recovery from anesthesia. The ability of caffeine to accelerate recovery from anesthesia for different chemical classes of anesthetics, isoflurane and propofol, opens the possibility that it will do so for all commonly used general anesthetics, although additional studies will be required to determine whether this is in fact the case. Because anesthesia in rodents is thought to be similar to that in humans, these results suggest that caffeine might allow for rapid and uniform emergence from general anesthesia in human patients.

Cyclic AMP synergizes with butyrate in promoting β-defensin 9 expression in chickens

Host defense peptides (HDP) have both microbicidal and immunomodulatory properties. Specific induction of endogenous HDP synthesis has emerged as a novel approach to antimicrobial therapy. Cyclic adenosine monophosphate (cAMP) and butyrate have been implicated in HDP induction in humans. However, the role of cAMP signaling and the possible interactions between cAMP and butyrate in regulating HDP expression in other species remain unknown. Here we report that activation of cAMP signaling induces HDP gene expression in chickens as exemplified by β-defensin 9 (AvBD9). We further showed that, albeit being weak inducers, cAMP agonists synergize strongly with butyrate or butyrate analogs in AvBD9 induction in macrophages and primary jejunal explants. Additionally, oral supplementation of forskolin, an adenylyl cyclase agonist in the form of a Coleus forskohlii extract, was found to induce AvBD9 expression in the crop of chickens. Furthermore, feeding with both forskolin and butyrate showed an obvious synergy in triggering AvBD9 expression in the crop and jejunum of chickens. Surprisingly, inhibition of the MEK-ERK mitogen-activated protein kinase (MAPK) pathway augmented the butyrate-FSK synergy, whereas blocking JNK or p38 MAPK pathway significantly diminished AvBD9 induction in chicken macrophages and jejunal explants in response to butyrate and FSK individually or in combination. Collectively, these results suggest the potential for concomitant use of butyrate and cAMP signaling activators in enhancing HDP expression, innate immunity, and disease resistance in both animals and humans.

Transforming growth factor-β1 impairs CFTR-mediated anion secretion across cultured porcine vas deferens epithelial monolayer via the p38 MAPK pathway

The goal of this study was to determine whether transforming growth factor-β1 (TGF-β1) affects epithelial cells lining the vas deferens, an organ that is universally affected in cystic fibrosis male patients. In PVD9902 cells, which are derived from porcine vas deferens epithelium, TGF-β1 exposure significantly reduced short-circuit current (Isc) stimulated by forskolin or a cell membrane-permeant cAMP analog, 8-pCPT-cAMP, suggesting that TGF-β1 affects targets of the cAMP signaling pathway. Electrophysiological results indicated that TGF-β1 reduces the magnitude of current inhibited by cystic fibrosis transmembrane conductance regulator (CFTR) channel blockers. Real-time RT-PCR revealed that TGF-β1 downregulates the abundance of mRNA coding for CFTR, while biotinylation and Western blot showed that TGF-β1 reduces both total CFTR and apical cell surface CFTR abundance. These results suggest that TGF-β1 causes a reduction in CFTR expression, which limits CFTR-mediated anion secretion. TGF-β1-associated attenuation of anion secretion was abrogated by SB431542, a TGF-β1 receptor I inhibitor. Signaling pathway studies showed that the effect of TGF-β1 on Isc was reduced by SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). TGF-β1 exposure also increased the amount of phospho-p38 MAPK substantially. In addition, anisomycin, a p38 MAPK activator, mimicked the effect of TGF-β1, which further suggests that TGF-β1 affects PVD9902 cells through a p38 MAPK pathway. These observations suggest that TGF-β1, via TGF-β1 receptor I and p38 MAPK signaling, reduces CFTR expression to impair CFTR-mediated anion secretion, which would likely compound the effects associated with mild CFTR mutations and ultimately would compromise male fertility.

Death of multiple myeloma cells induced by cAMP-signaling involves downregulation of Mcl-1 via the JAK/STAT pathway

There is a continuous search for new therapeutic targets for treatment of multiple myeloma (MM). Here we investigated the mechanisms involved in cAMP-induced apoptosis of human MM cells. cAMP-increasing agents rapidly inhibited activation of JAK1 and its substrate STAT3. In line with STAT3 being a regulator of Mcl-1 transcription, the expression of this pro-survival factor was rapidly and selectively reduced. Notably, exogenous interleukin-6 neither prevented the inhibition of JAK1/STAT3 nor the death of MM cells induced by cAMP. Our results suggest that cAMP-mediated killing of MM cells involves inhibition of the JAK/STAT pathway, making the cAMP-pathway a promising target for treatment of MM.

5-HT(1B) receptors inhibit glutamate release from primary afferent terminals in rat medullary dorsal horn neurons

BACKGROUND AND PURPOSE

Although 5-HT(1B) receptors are expressed in trigeminal sensory neurons, it is still not known whether these receptors can modulate nociceptive transmission from primary afferents onto medullary dorsal horn neurons.

EXPERIMENTAL APPROACH

Primary afferent-evoked EPSCs were recorded from medullary dorsal horn neurons of rat horizontal brain stem slices using a conventional whole-cell patch clamp technique under a voltage-clamp condition.

KEY RESULTS

CP93129, a selective 5-HT(1B) receptor agonist, reversibly and concentration-dependently decreased the amplitude of glutamatergic EPSCs and increased the paired-pulse ratio. In addition, CP93129 reduced the frequency of spontaneous miniature EPSCs without affecting the current amplitude. The CP93129-induced inhibition of EPSCs was significantly occluded by GR55562, a 5-HT(1B/1D) receptor antagonist, but not LY310762, a 5-HT(1D) receptor antagonist. Sumatriptan, an anti-migraine drug, also decreased EPSC amplitude, and this effect was partially blocked by either GR55562 or LY310762. On the other hand, primary afferent-evoked EPSCs were mediated by the Ca(2+) influx passing through both presynaptic N-type and P/Q-type Ca(2+) channels. The CP93129-induced inhibition of EPSCs was significantly occluded by ω-conotoxin GVIA, an N-type Ca(2+) channel blocker.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that the activation of presynaptic 5-HT(1B) receptors reduces glutamate release from primary afferent terminals onto medullary dorsal horn neurons, and that 5-HT(1B) receptors could be, at the very least, a potential target for the treatment of pain from orofacial tissues.

Functional status and relationships of melanocortin 1 receptor signaling to the cAMP and extracellular signal-regulated protein kinases 1 and 2 pathways in human melanoma cells

Melanocortin 1 receptor (MC1R), a major determinant of skin phototype frequently mutated in melanoma, is a Gs protein-coupled receptor that regulates pigment production in melanocytes. MC1R stimulation activates cAMP synthesis and the extracellular signal-regulated (ERK) ERK1 and ERK2. In human melanocytes, ERK activation by MC1R relies on cAMP-independent transactivation of the c-KIT receptor. Thus MC1R functional coupling to the cAMP and ERK pathways may involve different structural requirements giving raise to biased effects of skin cancer-associated mutations. We evaluated the impact of MC1R mutations on ERK activation, cAMP production and agonist binding. We found that MC1R mutations impair cAMP production much more often than ERK activation, suggesting less stringent requirements for functional coupling to the ERK pathway. We examined the crosstalk of the cAMP and ERK pathways in HBL human melanoma cells (wild-type for MC1R, NRAS and BRAF). ERK activation by constitutively active upstream effectors or pharmacological inhibition had little effect on MC1R-stimulated cAMP synthesis. High cAMP levels were compatible with normal ERK activation but, surprisingly, the adenylyl cyclase activator forskolin abolished ERK activation by MC1R, most likely by a cAMP-independent mechanism. These results indicate little crosstalk of the cAMP and ERK pathways in HBL melanoma cells. Finally, we studied cAMP accumulation in a panel of 22 human melanoma cell lines stimulated with MC1R agonists or forskolin. cAMP synthesis was often inhibited, even in cells wild-type for MC1R and NRAS. Therefore, the cAMP pathway is more frequently impaired in melanoma than could be predicted by the MC1R or NRAS genotype.

Cyclic AMP relaxation of rat aortic smooth muscle is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry

Despite a large number of studies, the mechanism by which 3',5'-cyclic monophosphate (cAMP) induces vasorelaxation is not fully understood. The comparison between results obtained in different vessels or species has often been the source of conflicting reports. In order to shed more light onto this mechanism, we studied the effects of forskolin in phenylephrine-pre-contracted endothelium-denuded rat aorta and measured cAMP levels in rat aortic myocytes by enzyme-immunoassay. Nanomolar forskolin relaxed phenylephrine-induced contractions. This effect was mimicked by dibutyryl-cAMP and was potentiated by rolipram or a p38-mitogen-activated protein kinase (p38-MAPK) inhibitor (SB-203580). Nifedipine and verapamil partially relaxed phenylephrine-induced contractions, while further application of cAMP-elevating agents fully relaxed these contractions. In Ca(2+)-free extracellular solution, forskolin reduced phenylephrine-induced transient contractions and reduced the Ca(2+)-induced contraction after depletion of intracellular stores. Nanomolar concentrations of forskolin increased basal cAMP levels only in the presence of rolipram or phenylephrine, which did not modify intracellular levels of cAMP by themselves. In conclusion, relaxation by cAMP is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry. This study provides the first evidence that inhibition of PDE4 or p38-MAPK potentiates the vasodilator effect of cAMP-elevating agents in rat aortic myocytes.

Muscarinic M4 receptors regulate GABAergic transmission in rat tuberomammillary nucleus neurons

Histaminergic neurons within the tuberomammillary nucleus (TMN) play an important role in sleep-wakefulness regulation. Here, we report the muscarinic modulation of GABAergic spontaneous miniature inhibitory postsynaptic currents (mIPSCs) in mechanically dissociated rat histaminergic neurons using a conventional whole-cell patch clamp technique. Muscarine, a nonselective muscarinic acetylcholine (mACh) receptor agonist, reversibly decreased mIPSC frequency without affecting the current amplitude, indicating that muscarine acts presynaptically to decrease the probability of spontaneous GABA release. The muscarine action on GABAergic mIPSC frequency was completely blocked by atropine, a nonselective mACh receptor antagonist, and tropicamide, an M(4) receptor antagonist. The muscarine-induced decrease in mIPSC frequency was completely occluded in the presence of Cd(2+), a general voltage-dependent Ca(2+) channel blocker, or in a Ca(2+)-free external solution. However, pharmacological agents affecting adenylyl cyclase or G-protein coupled inwardly rectifying K(+) channel activity did not prevent the inhibitory action of muscarine on GABAergic mIPSCs. These results suggest that muscarine acts on M(4) receptors on GABAergic nerve terminals projecting to histaminergic neurons to inhibit spontaneous GABA release via the inhibition of Ca(2+) influx from the extracellular space. Muscarine also inhibited action potential-dependent GABA release by activating presynaptic M(4) receptors in more physiological conditions. The M(4) receptor-mediated modulation of GABAergic transmission onto TMN neurons may contribute to the regulation of sleep-wakefulness.

Labdane-type diterpenoids from hairy root cultures of Coleus forskohlii, possible intermediates in the biosynthesis of forskolin

Significant attention has been devoted to studying hairy root cultures as a promising strategy for production of various valuable secondary metabolites. These offer many advantages, such as high growth rate, genetic stability and being hormone-free. In this study, a detailed phytochemical investigation of the secondary metabolites of Coleus forskohlii hairy root cultures was undertaken and which resulted in the isolation of 22 compounds, including four forskolin derivatives and a monoterpene. Their structures were elucidated by extensive spectroscopic analyses. These compounds could be classified into four groups viz.: labdane-type diterpenes, monoterpenes, triterpenes and phenylpropanoid dimers. Apart from one compound, all labdane type diterpenes are oxygenated at C-11 as in forskolin and a scheme showing their biosynthetic relationships is proposed.

Dietary Coleus forskohlii extract generates dose-related hepatotoxicity in mice

Coleus forskohlii root extract (CFE) represented by its bioactive constituent 'forskolin' is popularly used as a natural weight-lowering product, but the association of its use with liver-related risks is very limited. In the present study, the effect of standardized CFE with 10% forskolin on liver function of mice was examined. Mice were given 0-5% CFE in an AIN93G-based diet for 3-5 weeks. Food intake, body weights, relative organ weights and liver marker enzymes [aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP)] combined with histophatological analysis were assessed. CFE (0-0.5%) only had minimal effects on food intake and body weight whereas a significant difference was observed in mice receiving the highest dose (5% CFE). The extract 0.05-5% dose-dependently decreased visceral fat weight by between 16% and 63%, and a dose-dependent several folds increase was observed in liver weights and plasma AST, ALT and ALP activities with quick onset apparent after only 1 week of 0.5% CFE intake. The hepatic effect persisted throughout the 3-weeks course but was restored towards normalization within 1 week after withdrawal of treatment. Liver histology of mice fed 0.5% CFE for 3 weeks showed hepatocyte hypertrophy and fat deposition. In contrast, none of the hepatic responses measured were altered when mice were given a diet containing pure forskolin alone at the dose corresponding to its content in 0.5% CFE. The present study clearly indicated that forskolin was not involved in the CFE-induced hepatotoxicity and was caused by other unidentified constituents in CFE which warrants further studies.

Regulation of prefrontal excitatory neurotransmission by dopamine in the nucleus accumbens core

Interactions between dopamine and glutamate signalling within the nucleus accumbens core are required for behavioural reinforcement and habit formation. Dopamine modulates excitatory glutamatergic signals from the prefrontal cortex, but the precise mechanism has not been identified. We combined optical and electrophysiology recordings in murine slice preparations from CB1 receptor-null mice and green fluorescent protein hemizygotic bacterial artificial chromosome transgenic mice to show how dopamine regulates glutamatergic synapses specific to the striatonigral and striatopallidal basal ganglia pathways. At low cortical frequencies, dopamine D1 receptors promote glutamate release to both D1 and D2 receptor-expressing medium spiny neurons while D2 receptors specifically inhibit excitatory inputs to D2 receptor-expressing cells by decreasing exocytosis from cortical terminals with a low probability of release. At higher cortical stimulation frequencies, this dopaminergic modulation of presynaptic activity is occluded by adenosine and endocannabinoids. Glutamatergic inputs to both D1 and D2 receptor-bearing medium spiny neurons are inhibited by adenosine, released upon activation of NMDA and AMPA receptors and adenylyl cyclase in D1 receptor-expressing cells. Excitatory inputs to D2 receptor-expressing cells are specifically inhibited by endocannabinoids, whose release is dependent on D2 and group 1 metabotropic glutamate receptors. The convergence of excitatory and inhibitory modulation of corticoaccumbal activity by dopamine, adenosine and endocannabinoids creates subsets of corticoaccumbal inputs, selectively and temporally reinforces strong cortical signals through the striatonigral pathway while inhibiting the weak, and may provide a mechanism whereby continued attention might be focused on behaviourally salient information.