cGMP-hydrolyzing Phosphodiesterases Research Articles

Pros and Cons of Pharmacological Manipulation of cGMP-PDEs in the Prevention and Treatment of Breast Cancer.

The cyclic nucleotides, cAMP and cGMP, are ubiquitous second messengers responsible for translating extracellular signals to intracellular biological responses in both normal and tumor cells. When these signals are aberrant or missing, cells may undergo neoplastic transformation or become resistant to chemotherapy. cGMP-hydrolyzing phosphodiesterases (PDEs) are attracting tremendous interest as drug targets for many diseases, including cancer, where they regulate cell growth, apoptosis and sensitization to radio- and chemotherapy. In breast cancer, PDE5 inhibition is associated with increased intracellular cGMP levels, which is responsible for the phosphorylation of PKG and other downstream molecules involved in cell proliferation or apoptosis. In this review, we provide an overview of the most relevant studies regarding the controversial role of PDE inhibitors as off-label adjuvants in cancer therapy.

Dual roles of PDE9a in meiotic maturation of zebrafish oocytes

The essential role of cyclic guanosine monophosphate (cGMP) signaling in regulating the oocyte meiotic cell cycle has been established. However, control of the level of cGMP in ovarian follicles is unclear. The cGMP-hydrolyzing phosphodiesterases (PDEs) are important in regulating the cellular cGMP level. We used zebrafish as a model to study the role of a cGMP-hydrolyzing phosphodiesterase-9a (PDE9a) in meiotic maturation of oocytes. Three PDE9a coding genes (PDE9aa, PDE9ab, and PDE9ac) were identified in zebrafish. Both pde9aa and pde9ac are expressed in most adult tissues including the ovary, but pde9ab is only expressed in the ovary, kidney, pituitary, and brain. All three pde9as mRNA exhibited different expression profiles during folliculogenesis. All of them are highly expressed in the oocyte but not in the follicular cell. The expression of both pde9aa and pde9ab, but not pde9ac, in ovarian follicles increases during oocyte maturation either in natural ovulatory cycle or induced by administration of hCG in vivo. We overexpressed pde9aa by injection of capped pde9aa mRNA into the oocytes. The cGMP level was decreased, and oocyte maturation was stimulated. When the activity of PDE9a was blocked by a specific inhibitor, Bay736691, the oocyte maturation was also stimulated. The stimulatory effect could be blocked by a gap junction blocker. However, the spontaneous oocyte maturation of denuded oocytes was not largely affected after treatment with Bay736691. All of the mature oocytes obtained by either treatment of Bay736691 or injection of pde9aa mRNA, could be fertilized in vitro. These results demonstrate the dual roles of PDE9a in oocyte maturation. The basal level of PDE9a is responsible for maintaining the meiotic arrest, and the increased level of PDE9a induced by LH signaling is helpful for stimulating meiotic maturation by hydrolyzing cGMP in oocytes.

Cardiac Cyclic Nucleotide Phosphodiesterases: Function, Regulation, and Therapeutic Prospects

The second messengers cAMP and cGMP exist in multiple discrete compartments and regulate a variety of biological processes in the heart. The cyclic nucleotide phosphodiesterases, by catalyzing the hydrolysis of cAMP and cGMP, play crucial roles in controlling the amplitude, duration, and compartmentalization of cyclic nucleotide signaling. Over 60 phosphodiesterase isoforms, grouped into 11 families, have been discovered to date. In the heart, both cAMP- and cGMP-hydrolyzing phosphodiesterases play important roles in physiology and pathology. At least 7 of the 11 phosphodiesterase family members appear to be expressed in the myocardium, and evidence supports phosphodiesterase involvement in regulation of many processes important for normal cardiac function including pacemaking and contractility, as well as many pathological processes including remodeling and myocyte apoptosis. Pharmacological inhibitors for a number of phosphodiesterase families have also been used clinically or preclinically to treat several types of cardiovascular disease. In addition, phosphodiesterase inhibitors are also being considered for treatment of many forms of disease outside the cardiovascular system, raising the possibility of cardiovascular side effects of such agents. This review will discuss the roles of phosphodiesterases in the heart, in terms of expression patterns, regulation, and involvement in physiological and pathological functions. Additionally, the cardiac effects of various phosphodiesterase inhibitors, both potentially beneficial and detrimental, will be discussed.

CGMP-Prkg1 signaling and Pde5 inhibition shelter cochlear hair cells and hearing function

Noise-induced hearing loss (NIHL) is a global health hazard with considerable pathophysiological and social consequences that has no effective treatment. In the heart, lung and other organs, cyclic guanosine monophosphate (cGMP) facilitates protective processes in response to traumatic events. We therefore analyzed NIHL in mice with a genetic deletion of the gene encoding cGMP-dependent protein kinase type I (Prkg1) and found a greater vulnerability to and markedly less recovery from NIHL in these mice as compared to mice without the deletion. Prkg1 was expressed in the sensory cells and neurons of the inner ear of wild-type mice, and its expression partly overlapped with the expression profile of cGMP-hydrolyzing phosphodiesterase 5 (Pde5). Treatment of rats and wild-type mice with the Pde5 inhibitor vardenafil almost completely prevented NIHL and caused a Prkg1-dependent upregulation of poly (ADP-ribose) in hair cells and the spiral ganglion, suggesting an endogenous protective cGMP-Prkg1 signaling pathway that culminates in the activation of poly (ADP-ribose) polymerase. These data suggest vardenafil or related drugs as possible candidates for the treatment of NIHL.

Calcium/Calpain mediated regulation of cyclic nucleotide phosphodiesterases, PDE3A and PDE5, in human platelets

Background Calpain, intracellular non-lysosomal calcium-dependent proteinase, is activated by a number of signaling pathways that lead to the elevation of intraplatelet calcium concentrations. Physiological roles of calpain, highly expressed in platelets, include regulation of platelet aggregation and adhesion, while excessive activation of calpain in such pathological disorders as diabetes could cause changes in platelet functions, resulting in platelet hyperactivation. Platelets from diabetic patients are also characterized by resistance to nitric oxide inhibition. Here we examined if calpain could regulate major cAMP and cGMP hydrolyzing phosphodiesterases (PDEs), PDE3A and PDE5, in human platelets.

Exquisite sensitivity to subsecond, picomolar nitric oxide transients conferred on cells by guanylyl cyclase-coupled receptors

Nitric oxide (NO) functions as a diffusible transmitter in most tissues of the body and exerts its effects by binding to receptors harboring a guanylyl cyclase transduction domain, resulting in cGMP accumulation in target cells. Despite its widespread importance, very little is known about how this signaling pathway operates at physiological NO concentrations and in real time. To address these deficiencies, we have exploited the properties of a novel cGMP biosensor, named δ-FlincG, expressed in cells containing varying mixtures of NO-activated guanylyl cyclase and cGMP-hydrolyzing phosphodiesterase activity. Responsiveness to NO, signifying a physiologically relevant rise in cGMP to 30 nM or more, was seen at concentrations as low as 1 pM, making cells by far the most sensitive NO detectors yet encountered. Even cells coexpressing phosphodiesterase-5, a cGMP-activated isoform found in many NO target cells, responded to NO in concentrations as low as 10 pM. The dynamics of NO capture and signal transduction was revealed by administering timed puffs of NO from a local pipette. A puff lasting only 100 ms, giving a calculated peak intracellular NO concentration of 23 pM, was detectable. The results could be encapsulated in a quantitative model of cellular NO-cGMP signaling, which recapitulates the NO responsiveness reported previously from crude cGMP measurements on native cells, and which explains how NO is able to exert physiological effects at extremely low concentrations, when only a tiny proportion of its receptors would be occupied.

Cardiac hypertrophy is not amplified by deletion of cGMP-dependent protein kinase I in cardiomyocytes.

It has been suggested that cGMP kinase I (cGKI) dampens cardiac hypertrophy. We have compared the effect of isoproterenol (ISO) and transverse aortic constriction (TAC) on hypertrophy in WT [control (CTR)] mice, total cGKI-KO mice, and cGKIbeta rescue mice (betaRM) lacking cGKI specifically in cardiomyocytes (CMs). Infusion of ISO did not change the expression of cGKI in the hearts of CTR mice or betaRM but raised the heart weight by approximately 20% in both. An identical hypertrophic growth response was measured in CMs from CTR mice and betaRM and in isolated adult CMs cultured with or without 1 muM ISO. In both genotypes, ISO infusion induced similar changes in the expression of hypertrophy-associated cardiac genes and significant elevation of serum atrial natriuretic peptide and total cardiac cGMP. No differences in cardiac hypertrophy were obtained by 7-day ISO infusion in 4- to 6-week-old conventional cGKI-KO and CTR mice. Furthermore, TAC-induced hypertrophy of CTR mice and betaRM was not different and did not result in changes of the cGMP-hydrolyzing phosphodiesterase activities in hypertropic hearts or CMs. These results strongly suggest that cardiac myocyte cGKI does not affect the development of heart hypertrophy induced by pressure overload or chronic ISO infusion.

New insight into the functioning of nitric oxide-receptive guanylyl cyclase: physiological and pharmacological implications

The cellular counterpart of the "soluble" guanylyl cyclase found in tissue homogenates over 30 years ago is now recognized as the physiological receptor for nitric oxide (NO). The ligand-binding site is a prosthetic haem group that, when occupied by NO, induces a conformational change in the protein that propagates to the catalytic site, triggering conversion of GTP into cGMP. This review focuses on recent research that takes this basic information forward to the beginnings of a quantitative depiction of NO signal transduction, analogous to that achieved for other major transmitters. At its foundation is an explicit enzyme-linked receptor mechanism for NO-activated guanylyl cyclase that replicates all its main properties. In cells, NO signal transduction is subject to additional, activity-dependent modifications, notably through receptor desensitization and changes in the activity of cGMP-hydrolyzing phosphodiesterases. The measurement of these parameters under varying conditions in rat platelets has made it possible to formulate a cellular model of NO-cGMP signaling. The model helps explain cellular responses to NO and their modification by therapeutic agents acting on the guanylyl cyclase or phosphodiesterase limbs of the pathway.

Cyclic GMP Signaling Is Involved in the Luteinizing Hormone-Dependent Meiotic Maturation of Mouse Oocytes1

It is well established that cAMP signaling is an important regulator of the oocyte meiotic cell cycle. Conversely, the function of cGMP during oocyte maturation is less clear. Herein, we evaluated the expression of cGMP-hydrolyzing phosphodiesterases (PDEs) in the somatic and germ cell compartments of the mouse ovarian follicle and demonstrate that PDE5 is preferentially expressed in somatic cells. Cyclic GMP is a potent inhibitor of cAMP hydrolysis from oocyte extracts, with a 50% inhibitory concentration of 97 nM. Luteinizing hormone (LH) stimulation of cultured preovulatory follicles results in a marked decrease in cGMP content, and a nadir is reached in 1.5 h; similarly, oocyte cGMP levels decrease after gonadotropin stimulation in vivo. The LH-dependent decrease in cGMP requires activation of the epidermal growth factor network. Treatment of follicles with a PDE5 inhibitor increases cGMP in the follicle well above unstimulated levels. Although LH causes a decrease in cGMP in follicles preincubated with PDE5 inhibitors, the levels of this nucleotide remain above unstimulated levels. Under these conditions of elevated cGMP, LH stimulation does not cause oocyte maturation after 5 h of incubation. Microinjection of a cGMP-specific PDE into oocytes causes meiotic maturation of wild-type oocytes, suggesting that an intraoocyte pool of cGMP is involved in the maintenance of meiotic arrest. This effect is absent in PDE3A-deficient oocytes. Taken together, these findings provide evidence that cGMP and cAMP signaling cooperate in maintaining meiotic arrest via regulation of PDE3A and that a decrease in cGMP in the somatic compartment is one of the signals contributing to meiotic maturation.

The effect of selective inhibition of cyclic GMP hydrolyzing phosphodiesterases 2 and 5 on learning and memory processes and nitric oxide synthase activity in brain during aging

Our previous studies have shown that there is a lower cGMP concentration in the aged brain as well as an alteration in the activity of cGMP-hydrolyzing phosphodiesterases (PDEs) and nitric oxide synthase (NOS). The aim of this study was to investigate the effect of specific inhibitors of selected PDEs on object recognition memory and locomotor activity during aging, and to correlate their action with NOS activity in the following brain regions: hippocampus, striatum, and cerebral cortex. The study was carried out using 3, 12, and 24 month-old rats. Inhibitors of PDE2 and PDE5 (Bayer 60-7550 and zaprinast, respectively) were used. Evaluation of memory and locomotor activity was carried out using an object recognition task and the open field test. NOS activity was determined using a radiochemical method after behavioral analysis in the cytosolic fraction from all brain areas investigated. We have found that the inhibitor of PDE2, Bay60-7550, improves object recognition memory in all age groups investigated and increases basal constitutive NOS activity in the hippocampus and striatum. Moreover, in 3 month-old rats, additional inhibition of PDE5 by zaprinast improves object memory and elevates NOS activity in all brain regions studied. Specific inhibition of nNOS eliminates the effect of Bay60-7550 on memory function and on NOS activity in 24 month-old rats. In summary, our results indicate that inhibition of PDE2 is able to improve cognition and memory function in 3, 12, and 24 month-old rats through the enhancement of nNOS activity in the brain, whereas inhibition of PDE5 is effective only in 3 month-old animals.

Pharmacologic Modulators of Soluble Guanylate Cyclase/Cyclic Guanosine Monophosphate in the Vascular System - From Bench Top to Bedside

Guanosine-dependent cyclic nucleotide second messenger signaling has been implicated as a pivotal mediator of vascular function under both homeostatic eutrophic conditions as well as in the inimical environs of injury and/or disease. This biological system is highly regulated through reciprocal, complimentary, and often redundant upstream and downstream molecular and cellular elements and feedback controls. Key endogenous factors of the guanosine-dependent cyclic nucleotide cascade include upstream gaseous activating ligands (nitric oxide, carbon monoxide), downstream substrates (cGMP-gated ion channels, cGMP-dependent protein kinases), and cGMP hydrolyzing phosphodiesterases. This intricate system also has capacity to "cross-talk" with parallel adenosine-dependent cyclic nucleotide machinery. Numerous complexes of ligands, enzymes, cofactors, and substrates present significant targets for pharmacologic modulation at the cellular, genetic, and/or molecular level eventuating therapeutically as constructive functional responses observed in vascular physiology and/or pathophysiology. Interestingly, emerging evidence based largely on transgenic mouse models challenges the historically accepted concept that this signaling system functions principally as a therapeutic modality in cardiac and vascular tissues. The general purpose of this update is to provide current information on recently described neoteric agents that impact multifaceted and critical cGMP-dependent signaling in the vascular system. Emphasis will be placed on novel agents that exert significant and often multiple actions on upstream and downstream sites and are capable of eliciting robust effects on guanosine-dependent cellular actions. Individual sections will be devoted to agents that rely on an intact and functional cyclase heme and those that operate independently of the sGC heme. Attention will be placed on the physiologic and pathophysiologic clinical manifestations of these pharmacologic regimens. This review will conclude with some thoughts for future directions for study and continued discovery of novel sGC/cGMP controllers in the vascular system at the basic science and clinical levels.

Pharmacologic Modulators of Soluble Guanylate Cyclase/Cyclic Guanosine Monophosphate in the Vascular System - From Bench Top to Bedside

Guanosine-dependent cyclic nucleotide second messenger signaling has been implicated as a pivotal mediator of vascular function under both homeostatic eutrophic conditions as well as in the inimical environs of injury and/or disease. This biological system is highly regulated through reciprocal, complimentary, and often redundant upstream and downstream molecular and cellular elements and feedback controls. Key endogenous factors of the guanosine-dependent cyclic nucleotide cascade include upstream gaseous activating ligands (nitric oxide, carbon monoxide), downstream substrates (cGMP-gated ion channels, cGMP-dependent protein kinases), and cGMP hydrolyzing phosphodiesterases. This intricate system also has capacity to “cross-talk” with parallel adenosine-dependent cyclic nucleotide machinery. Numerous complexes of ligands, enzymes, cofactors, and substrates present significant targets for pharmacologic modulation at the cellular, genetic, and/or molecular level eventuating therapeutically as constructive functional responses observed in vascular physiology and/or pathophysiology. Interestingly, emerging evidence based largely on transgenic mouse models challenges the historically accepted concept that this signaling system functions principally as a therapeutic modality in cardiac and vascular tissues. The general purpose of this update is to provide current information on recently described neoteric agents that impact multifaceted and critical cGMP-dependent signaling in the vascular system. Emphasis will be placed on novel agents that exert significant and often multiple actions on upstream and downstream sites and are capable of eliciting robust effects on guanosine-dependent cellular actions. Individual sections will be devoted to agents that rely on an intact and functional cyclase heme and those that operate independently of the sGC heme. Attention will be placed on the physiologic and pathophysiologic clinical manifestations of these pharmacologic regimens. This review will conclude with some thoughts for future directions for study and continued discovery of novel sGC/cGMP controllers in the vascular system at the basic science and clinical levels.

MRNA expression patterns of the cGMP‐hydrolyzing phosphodiesterases types 2, 5, and 9 during development of the rat brain

Recent evidence indicates that cGMP plays an important role in neural development and neurotransmission. Since cGMP levels depend critically on the activities of phosphodiesterase (PDE) enzymes, mRNA expression patterns were examined for several key cGMP-hydrolyzing PDEs (type 2 [PDE2], 5 [PDE5], and 9 [PDE9]) in rat brain at defined developmental stages. Riboprobes were used for nonradioactive in situ hybridization on sections derived from embryonic animals at 15 days gestation (E15) and several postnatal stages (P0, P5, P10, P21) until adulthood (3 months). At all stages PDE9 mRNA was present throughout the whole central nervous system, with highest levels observed in cerebellar Purkinje cells, whereas PDE2 and PDE5 mRNA expression was more restricted. Like PDE9, PDE5 mRNA was abundant in cerebellar Purkinje cells, although it was observed only on and after postnatal day 10 in these cells. In other brain regions, PDE5 mRNA expression was minimal, detected in olfactory bulb, cortical layers, and in hippocampus. PDE2 mRNA was distributed more widely, with highest levels in medial habenula, and abundant expression in olfactory bulb, olfactory tubercle, cortex, amygdala, striatum, and hippocampus. Double immunostaining of PDE2, PDE5, or PDE9 mRNAs with the neuronal marker NeuN and the glial cell marker glial fibrillary acidic protein revealed that these mRNAs were predominantly expressed in neuronal cell bodies. Our data indicate that three cGMP-hydrolyzing PDE families have distinct expression patterns, although specific cell types coexpress mRNAs for all three enzymes. Thus, it appears that differential expression of PDE isoforms may provide a mechanism to match cGMP hydrolysis to the functional demands of individual brain regions.

Effect of Angiotensin II on Gene Expression of cGMP-Specific Phosphodiesterases

Background and Objectives:Angiotensin II (Ang II)opposes the actions of nitric oxide (NO). A balance between Ang II and NO is critical for the maintenance of normal vessel tone, and is dependent on the intracellular cGMP level. We examined the effect of Ang II treatment on cGMP-hydrolyzing phosphodiesterases (PDEs), such as PDE1 and PDE5, the two major cGMP-hydrolyzing PDEs present in rat aortic vascular smooth muscle cells (VSMCs). We also investigated whether the Ang II signaling pathway affects the expression of the cGMP-hydrolyzing PDEs gene. Materials and Methods:VSMCs from SpragueDawley rats were incubated. Relative quantitative RT-PCR was performed for quantitation of PDE1A1, PDE5A1 mRNA expression a following in vitro Ang II treatment, and also done after pretreatment with inhibitors of the Ang II type1 (AT1) receptor, protein kinase C (PKC), mitogen activated protein kinase kinase (MEK) 1/2 and janus kinase 2 (JAK2) to investigate the effect of the Ang II signaling pathway on PDE1A1, PDE5A1 gene expression. Western blot analyses were performed to evaluate the changes of PDE1A1 and PDE5A1 protein level following treatment with Ang II. Results:Ang II (400 nM) increased the PDE1A1 and the PDE5A1 mRNA expression by 2.4 and 2.3-fold, respectively, 1 hour after treatment. Ang II also increased the protein level 2 hours after treatment. Inductions of PDE1A1 and PDE5A1 mRNA were blocked by the AT1 receptor inhibitors, PKC, MEK 1/2 and JAK2. Conclusion:In vitro Ang II treatment upregulates the PDE1A1, PDE5A1 gene expressions and the protein levels. The PKC, MEK1/2 and JAK2 signaling pathways were essential for the Ang II-mediated PDEs gene regulation. These findings may suggest that Ang II antagonizes NO actions through the upregulation of cGMP-hydrolyzing PDEs gene expressions. (Korean Circulation J 2003;33(2):130-138)

Characterization and Phosphorylation of PDE10A2, a Novel Alternative Splice Variant of Human Phosphodiesterase That Hydrolyzes cAMP and cGMP

We have isolated a novel alternative splice variant of human cAMP- and cGMP-hydrolyzing phosphodiesterase (PDE10A2) from human fetal lung. The N-terminal sequence of human PDE10A2 differed from that of human PDE10A1 reported previously. PDE10A1 and PDE10A2 expressed in COS-7 cells have cGMP Km values of 14 and 13 μM, low cAMP Km values of 0.28 and 0.22 μM, and high cAMP Km values of 0.96 and 1.1 μM, respectively, at high concentrations of cGMP and cAMP. PCR analysis demonstrated that both PDE10A1 and PDE10A2 transcripts are present in various human tissues and that PDE10A2 transcripts are a major form in some human tissues. The unique N-terminus of PDE10A2 has a putative phosphorylation site by cAMP-dependent protein kinase (cAK), but PDE10A1 does not. The recombinant PDE10A2 protein is preferentially phosphorylated by cAK, although the recombinant PDE10A1 protein is not phosphorylated by cAK.

YC-1 potentiates nitric oxide- and carbon monoxide-induced cyclic GMP effects in human platelets.

Nitric oxide (NO), the physiological activator of soluble guanylyl cyclase (sGC), induces inhibitory effects on platelet activation via elevation of cGMP levels and stimulation of the cGMP-dependent protein kinase. YC-1, a benzylindazole derivative, was shown to activate sGC in intact platelets, resulting in inhibition of platelet aggregation. In a previous study, we demonstrated that YC-1 not only stimulates purified sGC but also potentiates the stimulatory action of submaximally effective NO and carbon monoxide (CO) concentrations. Here, we investigated the potentiating effect of YC-1 in intact platelets. YC-1 together with NO or CO led to complete inhibition of platelet aggregation at concentrations that were ineffective by themselves. Maximally effective 2, 2-diethyl-1-nitroso-oxyhydrazine (3 microM) and YC-1 (100 microM) concentrations each elevated the cGMP levels in intact platelets approximately 13-fold, and administration of the two drugs together resulted in enormous potentiation of cGMP formation, which greatly exceeded the effect on the purified enzyme and yielded a >1300-fold increase in cGMP levels. Similar results were obtained using CO instead of NO. Furthermore, YC-1 not only stimulated sGC but also inhibited cGMP-hydrolyzing phosphodiesterases in platelets. The enormous elevation of cGMP levels led to enhanced phosphorylation of the cGMP-dependent protein kinase substrate vasodilator-stimulated phosphoprotein. Thus, by the combination of two effects (i.e., potentiation of NO-induced sGC stimulation and phosphodiesterase inhibition), YC-1-like substances are potent activators of the sGC/cGMP pathways and are therefore interesting candidates to act as modulators of cGMP-mediated effects, especially within the cardiovascular system.