Genomic organization, chromosomal localization, and alternative splicing of the human phosphodiesterase 8B gene

Phosphodiesterase 8 (PDE8): Distribution and Cellular Expression and Association with Alzheimer's Disease

Phosphodiesterase 8 (PDE8), as a member of PDE superfamily, specifically promotes the hydrolysis and degradation of intracellular cyclic adenosine monophosphate (cAMP), which may be associated with pathogenesis of Alzheimer's disease (AD). However, little is currently known about potential role in the central nervous system (CNS). Here we investigated the distribution and expression of PDE8 in brain of mouse, which we believe can provide evidence for studying the role of PDE8 in CNS and the relationship between PDE8 and AD. Here, C57BL/6J mice were used to observe the distribution patterns of two subtypes of PDE8, PDE8A and PDE8B, in different sexes in vivo by western blot (WB). Meanwhile, C57BL/6J mice were also used to demonstrate the distribution pattern of PDE8 in selected brain regions and localization in neural cells by WB and multiplex immunofluorescence staining. Furthermore, the triple transgenic (3×Tg-AD) mice and wild type (WT) mice of different ages were used to investigate the changes of PDE8 expression in the hippocampus and cerebral cortex during the progression of AD. PDE8 was found to be widely expressed in multiple tissues and organs including heart, kidney, stomach, brain, and liver, spleen, intestines, and uterus, with differences in expression levels between the two subtypes of PDE8A and PDE8B, as well as two sexes. Meanwhile, PDE8 was widely distributed in the brain, especially in areas closely related to cognitive function such as cerebellum, striatum, amygdala, cerebral cortex, and hippocampus, without differences between sexes. Furthermore, PDE8A was found to be expressed in neuronal cells, microglia and astrocytes, while PDE8B is only expressed in neuronal cells and microglia. PDE8A expression in the hippocampus of both female and male 3×Tg-AD mice was gradually increased with ages and PDE8B expression was upregulated only in cerebral cortex of female 3×Tg-AD mice with ages. However, the expression of PDE8A and PDE8B was apparently increased in both cerebral cortex and hippocampus in both female and male 10-month-old 3×Tg-AD mice compared WT mice. These results suggest that PDE8 may be associated with the progression of AD and is a potential target for its prevention and treatment in the future.

Functional characteristics and research trends of PDE11A in human diseases (Review)

cAMP and cGMP are important secondary messengers involved in cell regulation and metabolism driven by the G protein-coupled receptor. cAMP is converted via adenylyl cyclase (AC) and activates protein kinase A to phosphorylate intracellular proteins that mediate specific responses. cAMP signaling serves a role at multiple steps in tumorigenesis. The level of cAMP is increased in association with cancer cell formation through activation of AC-stimulatory G protein by mutation. Phosphodiesterases (PDEs) hydrolyze cAMP and cGMP to AMP and GMP. PDEs are composed of 11 families, and each can hydrolyze cAMP and cGMP or both cAMP and cGMP. PDEs perform various roles depending on their location and expression site, and are involved in several diseases, including male erectile dysfunction, pulmonary hypertension, Alzheimer's disease and schizophrenia. PDE11A is the 11th member of the PDE family and is characterized by four splice variants with varying tissue expression and N-terminal regulatory regions. Among tissues, the expression of PDE11A was highest in the prostate, and it was also expressed in hepatic skeletal muscle, pituitary, pancreas and kidney. PDE11A is the first PDE associated with an adrenocortical tumor associated genetic condition. In several studies, three PDE11A mutations have been reported in patients with Cushing syndrome with primary pigmented nodular adrenocortical disease or isolated micronodular adrenocortical disease without other genetic defects. It has been reported that an increase in PDE11A expression affects the proliferation of glioblastoma and worsens patient prognosis. The present mini-review summarizes the location of PDE11A expression, the impact of structural differences and disease relevance.

Cyclic nucleotide phosphodiesterase inhibition as a potential therapeutic target in renal ischemia reperfusion injury

AIMS

Ischemia/reperfusion (I/R) occurs in renal artery stenosis, partial nephrectomy and most commonly during kidney transplantation. It brings serious consequences such as DGF (Delayed Graft Function) or organ dysfunction leading to renal failure and ultimate death. There is no effective therapy to handle the consequences of Renal Ischemia/Reperfusion (I/R) injury. Cyclic nucleotides, cAMP and cGMP are the important second messengers that stimulate intracellular signal transduction for cell survival in response to growth factors and peptide hormones in normal tissues and in kidneys plays significant role that involves vascular tone regulation, inflammation and proliferation of parenchymal cells. Renal ischemia and subsequent reperfusion injury stimulate signal transduction pathways involved in oxidative stress, inflammation, alteration in renal blood flow leading to necrosis and apoptosis of renal cell.

MATERIALS AND METHODS

An extensive literature review of various search engines like PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out. To understand the functioning of Phosphodiesterases (PDEs) and its pharmacological modulation in Renal Ischemia-Reperfusion Injury.

KEY FINDINGS

Current therapeutic options may not be enough to treat renal I/R injury in group of patients and therefore, the current review has discussed the general characteristics and physiology of PDEs and preclinical-studies defining the relationship between PDEs expression in renal injury due to I/R and its outcome on renal function.

SIGNIFICANCE

The role of PDE inhibitors in renal I/R injury and the clinical status of drugs for various renal diseases have been summarized in this review.

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

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

An update of cyclic nucleotide phosphodiesterase as a target for cardiac diseases

INTRODUCTION

Cyclic nucleotides, cAMP, and cGMP, are important second messengers of intracellular signaling and play crucial roles in cardiovascular biology and diseases. Cyclic nucleotide phosphodiesterases (PDEs) control the duration, magnitude, and compartmentalization of cyclic nucleotide signaling by catalyzing the hydrolysis of cyclic nucleotides. Individual PDEs modulate distinct signaling pathways and biological functions in the cell, making it a potential therapeutic target for the treatment of different cardiovascular disorders. The clinical success of several PDE inhibitors has ignited continued interest in PDE inhibitors and in PDE-target therapeutic strategies.

AREAS COVERED

This review concentrates on recent research advances of different PDE isoforms with regard to their expression patterns and biological functions in the heart. The limitations of current research and future directions are then discussed. The current and future development of PDE inhibitors is also covered.

EXPERT OPINION

Despite the therapeutic success of several marketed PDE inhibitors, the use of PDE inhibitors can be limited by their side effects, lack of efficacy, and lack of isoform selectivity. Advances in our understanding of the mechanisms by which cellular functions are changed through PDEs may enable the development of new approaches to achieve effective and specific PDE inhibition for various cardiac therapies.

Phosphodiesterase inhibitors say NO to Alzheimer's disease

Phosphodiesterases (PDEs) consisted of 11 subtypes (PDE1 to PDE11) and over 40 isoforms that regulate levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the second messengers in cell functions. PDE inhibitors (PDEIs) have been attractive therapeutic targets due to their involvement in diverse medical conditions, e.g. cardiovascular diseases, autoimmune diseases, Alzheimer's disease (AD), etc. Among them; AD with a complex pathology is a progressive neurodegenerative disorder which affect mostly senile people in the world and only symptomatic treatment particularly using cholinesterase inhibitors in clinic is available at the moment for AD. Consequently, novel treatment strategies towards AD are still searched extensively. Since PDEs are broadly expressed in the brain, PDEIs are considered to modulate neurodegenerative conditions through regulating cAMP and cGMP in the brain. In this sense, several synthetic or natural molecules inhibiting various PDE subtypes such as rolipram and roflumilast (PDE4 inhibitors), vinpocetine (PDE1 inhibitor), cilostazol and milrinone (PDE3 inhibitors), sildenafil and tadalafil (PDE5 inhibitors), etc have been reported showing encouraging results for the treatment of AD. In this review, PDE superfamily will be scrutinized from the view point of structural features, isoforms, functions and pharmacology particularly attributed to PDEs as target for AD therapy.

Methylxanthines: Potential Therapeutic Agents for Glioblastoma

Glioblastoma (GBM) is the most common and aggressive primary brain tumor. Currently, treatment is ineffective and the median overall survival is 20.9 months. The poor prognosis of GBM is a consequence of several altered signaling pathways that favor the proliferation and survival of neoplastic cells. One of these pathways is the deregulation of phosphodiesterases (PDEs). These enzymes participate in the development of GBM and may have value as therapeutic targets to treat GBM. Methylxanthines (MXTs) such as caffeine, theophylline, and theobromine are PDE inhibitors and constitute a promising therapeutic anti-cancer agent against GBM. MTXs also regulate various cell processes such as proliferation, migration, cell death, and differentiation; these processes are related to cancer progression, making MXTs potential therapeutic agents in GBM.

A Polygenic Risk Score of Lipolysis-Increasing Alleles Determines Visceral Fat Mass and Proinsulin Conversion

CONTEXT

Primary dysregulation of adipose tissue lipolysis caused by genetic variation and independent of insulin resistance could explain unhealthy body fat distribution and its metabolic consequences.

OBJECTIVE

To analyze common single nucleotide polymorphisms (SNPs) in 48 lipolysis-, but not insulin-signaling-related genes, to form polygenic risk scores of lipolysis-associated SNPs, and to investigate their effects on body fat distribution, glycemia, insulin sensitivity, insulin secretion, and proinsulin conversion.

STUDY DESIGN, PARTICIPANTS, AND METHODS

SNP array, anthropometric, and metabolic data were available from up to 2789 participants without diabetes of the Tübingen Family study of type 2 diabetes characterized by oral glucose tolerance tests. In a subgroup (n = 942), magnetic resonance measurements of body fat stores were available.

RESULTS

We identified insulin-sensitivity-independent nominal associations (P < 0.05) of SNPs in 10 genes with plasma free fatty acids (FFAs), in 7 genes with plasma glycerol and in 6 genes with both, plasma FFAs and glycerol. A score formed of the latter SNPs (in ADCY4, CIDEA, GNAS, PDE8B, PRKAA1, PRKAG2) was associated with plasma FFA and glycerol measurements (1.4*10-9 ≤ P ≤ 1.2*10-5), visceral adipose tissue mass (P = 0.0326), and proinsulin conversion (P ≤ 0.0272). The more lipolysis-increasing alleles a subject had, the lower was the visceral fat mass and the lower the proinsulin conversion.

CONCLUSIONS

We found evidence for a genetic basis of adipose tissue lipolysis resulting from common SNPs in CIDEA, AMP-activated protein kinase subunits, and cAMP signaling components. A genetic score of lipolysis-increasing alleles determined lower visceral fat mass and lower proinsulin conversion.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Genetic Understanding of Stroke Treatment: Potential Role for Phosphodiesterase Inhibitors

Phosphodiesterase (PDE) gene family is a large family having at least 21 genes and multiple versions (isoforms) of the phosphodiesterase enzymes. These enzymes catalyze the inactivation of intracellular mediators of signal transduction such as cAMP and cGMP and therefore, play a pivotal role in various cellular functions. PDE inhibitors (PDEI) are drugs that block one or more of the five subtypes of the PDE family and thereby prevent inactivation of the intracellular cAMP and cGMP by the respective PDE-subtypes. The first clinical use of PDEI was reported almost three decades ago. Studies later found the ability of these compounds to increase the levels of ubiquitous secondary messenger molecules that can cause changes in vascular tone, cardiac function and other cellular events and thus these findings paved the way for their use in various medical emergencies. PDEs are found to be distributed in many tissues including brain. Therefore, new therapeutic agents in the form of PDEI are being explored in neurodegenerative diseases including stroke. Although studies have revealed their use in cerebral infarction prevention, their full-fledged application in times of neurological emergency or stroke in specific has been very limited so far. Nevertheless, recent investigations suggest PDE4 and PDE5 inhibitors to play a vital role in mitigating stroke symptoms by modulating signaling mechanisms in PDE pathway. Further, extensive research in terms of their pharmacological properties like dosing, drug specific activities, use of simultaneous medications, ancillary properties of these compounds and studies on adverse drug reactions needs to be carried out to set them as standard drugs of use in stroke.

Alterations of Phosphodiesterases in Adrenocortical Tumors

Alterations in the cyclic (c)AMP-dependent signaling pathway have been implicated in the majority of benign adrenocortical tumors (ACTs) causing Cushing syndrome (CS). Phosphodiesterases (PDEs) are enzymes that regulate cyclic nucleotide levels, including cyclic adenosine monophosphate (cAMP). Inactivating mutations and other functional variants in PDE11A and PDE8B, two cAMP-binding PDEs, predispose to ACTs. The involvement of these two genes in ACTs was initially revealed by a genome-wide association study in patients with micronodular bilateral adrenocortical hyperplasia. Thereafter, PDE11A or PDE8B genetic variants have been found in other ACTs, including macronodular adrenocortical hyperplasias and cortisol-producing adenomas. In addition, downregulation of PDE11A expression and inactivating variants of the gene have been found in hereditary and sporadic testicular germ cell tumors, as well as in prostatic cancer. PDEs confer an increased risk of ACT formation probably through, primarily, their action on cAMP levels, but other actions might be possible. In this report, we review what is known to date about PDE11A and PDE8B and their involvement in the predisposition to ACTs.

Distribution and function of 3',5'-Cyclic-AMP phosphodiesterases in the human ovary

The concentration of the important second messenger cAMP is regulated by phosphodiesterases (PDEs) and hence an attractive drug target. However, limited human data are available about the PDEs in the ovary. The aim of the present study was to describe and characterise the PDEs in the human ovary. Results were obtained by analysis of mRNA microarray data from follicles and granulosa cells (GCs), combined RT-PCR and enzymatic activity analysis in GCs, immunohistochemical analysis of ovarian sections and by studying the effect of PDE inhibitors on progesterone production from cultured GCs. We found that PDE3, PDE4, PDE7 and PDE8 are the major families present while PDE11A was not detected. PDE8B was differentially expressed during folliculogenesis. In cultured GCs, inhibition of PDE7 and PDE8 increased basal progesterone secretion while PDE4 inhibition increased forskolin-stimulated progesterone secretion. In conclusion, we identified PDE3, PDE4, PDE7 and PDE8 as the major PDEs in the human ovary.

cAMP-specific phosphodiesterase inhibitors: promising drugs for inflammatory and neurological diseases

INTRODUCTION

PDEs are key enzymes in the adenosine and guanosine cyclic nucleotides (cAMP and cGMP) signaling cascade. Their inhibition increases cyclic nucleotide levels inside the cell. Thus, pharmacological modulation of PDE activity can have profound effects on the function of cells and organ systems throughout the body.

AREAS COVERED

Among the large PDE families, only PDE4, PDE7 and PDE8 are cAMP-specific hydrolyzing enzymes. cAMP is an important second messenger not only by its involvement in a vast number of physiological processes but also by activation of protein kinase A, exchange protein activated by cAMP (Epac) and cAMP response element-binding (CREB) or cyclic nucleotide-gated channels. Clearly, such enzymes represent ideal drug targets for the pharmacological treatment of many pathologies. The discovery and development of small molecules targeting cAMP-specific PDEs reported in the last 5 years is the focus of the present review.

EXPERT OPINION

The first PDE4 inhibitors recently reached the market, having avoided, by different strategies, their dose-limiting side effects (after more than two decades of drug development). Meanwhile, new cAMP-specific PDE7 and PDE8 inhibitors emerged as effective and safe drugs for severe unmet diseases. The therapeutic potential of these inhibitors will be tested in the near future, as many of these drug candidates are ready to start clinical trials.

Temporal and spatial regulation of cAMP signaling in disease: role of cyclic nucleotide phosphodiesterases

Since its discovery, cAMP has been proposed as one of the most versatile second messengers. The remarkable feature of cAMP to tightly control highly diverse physiological processes, including metabolism, homeostasis, secretion, muscle contraction, cell proliferation and migration, immune response, and gene transcription, is reflected by millions of different articles worldwide. Compartmentalization of cAMP in space and time, maintained by mainly phosphodiesterases, contributes to the maintenance of equilibrium inside the cell where one signal can trigger many different events. Novel cAMP sensors seem to carry out certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Measuring space and time events with biosensors will increase our current knowledge on the pathophysiology of diseases, such as chronic obstructive pulmonary disease, asthma, cognitive impairment, cancer, and renal and heart failure. Further insights into the cAMP dynamics will help to optimize the pharmacological treatment for these diseases.

Clinical and molecular genetics of the phosphodiesterases (PDEs)

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that have the unique function of terminating cyclic nucleotide signaling by catalyzing the hydrolysis of cAMP and GMP. They are critical regulators of the intracellular concentrations of cAMP and cGMP as well as of their signaling pathways and downstream biological effects. PDEs have been exploited pharmacologically for more than half a century, and some of the most successful drugs worldwide today affect PDE function. Recently, mutations in PDE genes have been identified as causative of certain human genetic diseases; even more recently, functional variants of PDE genes have been suggested to play a potential role in predisposition to tumors and/or cancer, especially in cAMP-sensitive tissues. Mouse models have been developed that point to wide developmental effects of PDEs from heart function to reproduction, to tumors, and beyond. This review brings together knowledge from a variety of disciplines (biochemistry and pharmacology, oncology, endocrinology, and reproductive sciences) with emphasis on recent research on PDEs, how PDEs affect cAMP and cGMP signaling in health and disease, and what pharmacological exploitations of PDEs may be useful in modulating cyclic nucleotide signaling in a way that prevents or treats certain human diseases.

Phosphodiesterase 8B gene polymorphism in women with recurrent miscarriage: a retrospective case control study

Background

Recurrent miscarriage affects approximately 1% of all couples. There is a known relation between hypothyroidism and recurrent miscarriage. Phosphodiesterase 8B (PDE8B) is a regulator of cyclic adenosine monophosphate (cAMP) with important influence on human thyroid metabolism. Single nucleotide polymorphism (SNP) rs 4704397 in the PDE8B gene has been shown to be associated with variations in serum Thyroid Stimulating Hormone (TSH) and thyroxine (T4) levels. The aim of this study was to investigate whether there is an association between the SNP rs 4704397 in the PDE8B gene and recurrent miscarriage.

Methods

The study was designed as a retrospective case control study. 188 cases with recurrent miscarriage were included and compared with 391 controls who had delivered at least once and with no history of miscarriage or assisted reproduction.

Results

No difference between cases and controls concerning age was found. Bivariate associations between homozygous A/A (OR 1.57, 95% CI 0.98-2.52) as well as G/G carriers (OR 1.52, 95% CI 1.02-2.25) of SNP rs 4704397 in PDE8B and recurrent miscarriage were verified (test for trend across all 3 genotypes, p = 0.059). After adjustment for known confounders such as age, BMI and smoking the association between homozygous A/A (AOR 1.63, 95% CI 1.01 - 2.64, p = 0.045) and G/G (AOR 1.52, 95% CI 1.02 - 2.27, p = 0.039) carriers of SNP rs 4704397 in PDE8B and recurrent miscarriage remained.

Conclusions

Our findings suggest that there is an association between homozygous A/A as well as homozygous G/G carriers of SNP rs 4704397 in PDE8B and recurrent miscarriage.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

Impact of phosphodiesterase 8B gene rs4704397 variation on thyroid homeostasis in childhood obesity

CONTEXT

Several studies demonstrated that obese children have higher TSH than normal-weight children. The polymorphism rs4704397 in the phosphodiesterase 8B (PDE8B) gene showed an association with TSH.

OBJECTIVES

i) To assess the effect of PDE8B on TSH in obese children; ii) to dissect the role of obesity degree in modulating this association; and iii) to stratify the individual risk to show hyperthyrotropinaemia according to PDE8B genotype.

METHODS

Eight hundred and sixty-seven Italian obese children were investigated. Clinical data and thyroid hormones were evaluated and the PDE8B rs4704397 was genotyped.

RESULTS

PDE8B A/A homozygous subjects showed higher TSH (P=0.0005) compared with A/G or G/G. No differences were found for peripheral thyroid hormones. Among A/A children, 22% had hyperthyrotropinaemia, compared with 11.6% of heterozygotes and 10.8% of G/G (P=0.0008). Consistently, A/A had an odds ratio (OR) to show abnormal TSH level of 2.25 (P=0.0004). Body mass index (BMI) appeared correlated with TSH (P=0.0001), but the strength of the effect of PDE8B on TSH was independent of BMI (P=0.1). Children were subdivided into six groups according to obesity degree and genotypes. PDE8B A/A with BMI SDS above 3 had the highest OR (OR 2.6, P=0.0015) to have hyperthyrotropinaemia, whereas G/G with BMI SDS below 3 showed the lowest possibilities (OR 0.3, P=0.005).

CONCLUSIONS

We have shown: i) in obese children, PDE8B is associated with TSH; ii) the interaction between adiposity and PDE8B on TSH is not synergistic, but follows an additive model; and iii) impact of this association in the stratification of individual risk to have hyperthyrotropinaemia.

Phosphodiesterase function and endocrine cells: links to human disease and roles in tumor development and treatment

Phosphodiesterases (PDEs) are enzymes that regulate the intracellular levels of cyclic adenosine monophosphate and cyclic guanosine monophosphate, and, consequently, exhibit a central role in multiple cellular functions. The pharmacological exploitation of the ability of PDEs to regulate specific pathways has led to the discovery of drugs with selective action against specific PDE isoforms. Considerable attention has been given to the development of selective PDE inhibitors, especially after the therapeutic success of PDE5 inhibitors in the treatment of erectile dysfunction. Several associations between PDE genes and genetic diseases have been described, and more recently PDE11A and PDE8B have been implicated in predisposition to tumor formation. This review focuses on the possible function of PDEs in a variety of tumors, primarily in endocrine glands, both in tumor predisposition and as potential therapeutic targets.

A large-scale association analysis of 68 thyroid hormone pathway genes with serum TSH and FT4 levels

OBJECTIVE

Minor variation in serum thyroid hormone (TH) levels can have important effects on various clinical endpoints. Although 45-65% of the inter-individual variation in serum TH levels is due to genetic factors, the causative genes are not well established. We therefore studied the effects of genetic variation in 68 TH pathway genes on serum TSH and free thyroxine (FT(4)) levels.

DESIGN AND METHODS

Sixty-eight genes (1512 polymorphisms) were studied in relation to serum TSH and FT(4) levels in 1121 Caucasian subjects. Promising hits (P<0.01) were studied in three independent Caucasian populations (2656 subjects) for confirmation. A meta-analysis of all four studies was performed.

RESULTS

For TSH, eight PDE8B polymorphisms (P=4×10(-17)) remained significant in the meta-analysis. For FT(4), two DIO1 (P=8×10(-12)) and one FOXE1 (P=0.0003) polymorphisms remained significant in the meta-analysis. Suggestive associations were detected for one FOXE1 (P=0.0028) and three THRB (P=0.0045) polymorphisms with TSH, and one SLC16A10 polymorphism (P=0.0110) with FT(4), but failed to reach the significant multiple-testing corrected P value (P<0.0022 and P<0.0033 respectively).

CONCLUSIONS

Using a large-scale association analysis, we replicated previously reported associations with genetic variation in PDE8B, THRB, and DIO1. We demonstrate effects of genetic variation in FOXE1 on serum FT(4) levels, and borderline significant effects on serum TSH levels. A suggestive association of genetic variation in SLC16A10 with serum FT(4) levels was found. These data provide insight into the molecular basis of inter-individual variation in TH serum levels.

A meta-analysis of the associations between common variation in the PDE8B gene and thyroid hormone parameters, including assessment of longitudinal stability of associations over time and effect of thyroid hormone replacement

OBJECTIVE

Common variants in PDE8B are associated with TSH but apparently without any effect on thyroid hormone levels that is difficult to explain. Furthermore, the stability of the association has not been examined in longitudinal studies or in patients on levothyroxine (l-T(4)).

DESIGN

Totally, four cohorts were used (n=2557): the Busselton Health Study (thyroid function measured on two occasions), DEPTH, EFSOCH (selective cohorts), and WATTS (individuals on l-T(4)).

METHODS

Meta-analysis to clarify associations between the rs4704397 single nucleotide polymorphism in PDE8B on TSH, tri-iodothyronine (T(3)), and T(4) levels.

RESULTS

Meta-analysis confirmed that genetic variation in PDE8B was associated with TSH (P=1.64 × 10(-10) 0.20 s.d./allele, 95% confidence interval (CI) 0.142, 0.267) and identified a possible new association with free T(4) (P=0.023, -0.07 s.d./allele, 95% CI -0.137, -0.01), no association was seen with free T(3) (P=0.218). The association between PDE8B and TSH was similar in 1981 (0.14 s.d./allele, 95% CI 0.04, 0.238) and 1994 (0.20 s.d./allele, 95% CI 0.102, 0.300) and even more consistent between PDE8B and free T(4) in 1981 (-0.068 s.d./allele, 95% CI -0.167, 0.031) and 1994 (-0.07 s.d./allele, 95% CI -0.170, 0.030). No associations were seen between PDE8B and thyroid hormone parameters in individuals on l-T(4).

CONCLUSION

Common genetic variation in PDE8B is associated with reciprocal changes in TSH and free T(4) levels that are consistent over time and lost in individuals on l-T(4). These findings identify a possible genetic marker reflecting variation in thyroid hormone output that will be of value in epidemiological studies and provides additional evidence that PDE8B is involved in TSH signaling in the thyroid.

Haplotype analysis of the promoter region of phosphodiesterase type 8B (PDE8B) in correlation with inactivating PDE8B mutation and the serum thyroid-stimulating hormone levels

BACKGROUND

Human phosphodiesterase (PDE) type 8B (PDE8B) is located at 5q14.1 and is known as the PDE with the highest affinity to cAMP. We recently described a family with bilateral micronodular adrenocortical disease that was apparently caused by an inactivating PDE8B mutation (H305P). As a result of a genome-wide study, a strong association between six polymorphic variants in the PDE8B promoter and serum levels of the thyroid-stimulating hormone (TSH) has been recently reported. Despite an extended analysis of the regions surrounding 5q14.1, no other potential genetic variants that could be responsible for the associated TSH levels were found.

METHODS

In this study, we genotyped by polymerase chain reaction the described six polymorphic variants in the PDE8B promoter in the family with micronodular adrenocortical disease and inactivating PDE8B mutation and analyzed their correlation with individual TSH values in the family members.

RESULTS

We observed complete segregation between the reported association and individual TSH values in the family we studied. Haplotype analysis showed that the haplotype associated with the high TSH levels is different from the one that segregated with H305P, suggesting that the mutation most probably has arisen on an allele independent of the high TSH-associated allele.

CONCLUSIONS

The proposed mechanism by which PDE8B may influence TSH levels is through control of cAMP signaling. Our analysis revealed separate segregation of an inactivating PDE8B allele from the high-TSH-allele and showed low TSH levels in persons who carry an inactivating PDE8B allele. These data suggest that, indeed, PDE8B may be involved in regulation of TSH levels.

Autosomal-dominant striatal degeneration is caused by a mutation in the phosphodiesterase 8B gene

Autosomal-dominant striatal degeneration (ADSD) is an autosomal-dominant movement disorder affecting the striatal part of the basal ganglia. ADSD is characterized by bradykinesia, dysarthria, and muscle rigidity. These symptoms resemble idiopathic Parkinson disease, but tremor is not present. Using genetic linkage analysis, we have mapped the causative genetic defect to a 3.25 megabase candidate region on chromosome 5q13.3-q14.1. A maximum LOD score of 4.1 (Theta = 0) was obtained at marker D5S1962. Here we show that ADSD is caused by a complex frameshift mutation (c.94G>C+c.95delT) in the phosphodiesterase 8B (PDE8B) gene, which results in a loss of enzymatic phosphodiesterase activity. We found that PDE8B is highly expressed in the brain, especially in the putamen, which is affected by ADSD. PDE8B degrades cyclic AMP, a second messenger implied in dopamine signaling. Dopamine is one of the main neurotransmitters involved in movement control and is deficient in Parkinson disease. We believe that the functional analysis of PDE8B will help to further elucidate the pathomechanism of ADSD as well as contribute to a better understanding of movement disorders.

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

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

Selective phosphodiesterase inhibitors: a promising target for cognition enhancement

RATIONALE

One of the major complaints most people face during aging is an impairment in cognitive functioning. This has a negative impact on the quality of daily life and is even more prominent in patients suffering from neurodegenerative and psychiatric disorders including Alzheimer's disease, schizophrenia, and depression. So far, the majority of cognition enhancers are generally targeting one particular neurotransmitter system. However, recently phosphodiesterases (PDEs) have gained increased attention as a potential new target for cognition enhancement. Inhibition of PDEs increases the intracellular availability of the second messengers cGMP and/or cAMP.

OBJECTIVE

The aim of this review was to provide an overview of the effects of phosphodiesterase inhibitors (PDE-Is) on cognition, the possible underlying mechanisms, and the relationship to current theories about memory formation.

MATERIALS AND METHODS

Studies of the effects of inhibitors of different PDE families (2, 4, 5, 9, and 10) on cognition were reviewed. In addition, studies related to PDE-Is and blood flow, emotional arousal, and long-term potentiation (LTP) were described.

RESULTS

PDE-Is have a positive effect on several aspects of cognition, including information processing, attention, memory, and executive functioning. At present, these data are likely to be explained in terms of an LTP-related mechanism of action.

CONCLUSION

PDE-Is are a promising target for cognition enhancement; the most suitable candidates appear to be PDE2-Is or PDE9-Is. The future for PDE-Is as cognition enhancers lies in the development of isoform-specific PDE-Is that have limited aversive side effects.

Refolding and kinetic characterization of the phosphodiesterase-8A catalytic domain

Cyclic nucleotide phosphodiesterase-8 (PDE8) hydrolyzes the second messenger cAMP and is involved in many biological processes such as testosterone production. Although the bacterial and mammalian expression systems have been extensively tried, production of large quantity of soluble and active PDE8 remains to be a major hurdle for pharmacological and structural studies. Reported here is a detailed protocol of refolding and purification of large quantity of the PDE8A1 catalytic domain (residues 480-820) and kinetic characterization of the refolded protein. This protocol yielded about 8 mg of the PDE8A catalytic domain from 2l Escherichia coli culture, which has at least 40-fold higher activity than those reported in literature. The PDE8A1 catalytic domain has k(cat) of 4.0 s(-1) for Mn(2+) and 2.9s(-1) for Mg(2+), and the K(M) values of 1-1.8 microM. In addition, the PDE8A1 (205-820) fragment that contains both PAS and catalytic domains was expressed in E. coli and refolded. This PDE8A1 (205-820) fragment has k(cat) of 1.1 s(-1) and K(M) of 0.28 microM, but aggregated at high concentration. The K(M) of PDE8A1 (205-820) is 2- to 7-fold higher than the K(M) values of 40-150 nM for the full-length PDE8s in literature, but about 6-fold lower than that of the catalytic domain. Thus, the K(M) difference likely implies an allosteric regulation of the PDE8A activity by its PAS domain.

Phosphodiesterase 8B gene variants are associated with serum TSH levels and thyroid function

Thyroid-stimulating hormone (TSH) controls thyroid growth and hormone secretion through binding to its G protein-coupled receptor (TSHR) and production of cyclic AMP (cAMP). Serum TSH is a sensitive indicator of thyroid function, and overt abnormalities in thyroid function lead to common endocrine disorders affecting approximately 10% of individuals over a life span. By genotyping 362,129 SNPs in 4,300 Sardinians, we identified a strong association (p = 1.3 x 10(-11)) between alleles of rs4704397 and circulating TSH levels; each additional copy of the minor A allele was associated with an increase of 0.13 muIU/ml in TSH. The single-nucleotide polymorphism (SNP) is located in intron 1 of PDE8B, encoding a high-affinity cAMP-specific phosphodiesterase. The association was replicated in 4,158 individuals, including additional Sardinians and two genetically distant cohorts from Tuscany and the Old Order Amish (overall p value = 1.9 x 10(-20)). In addition to association of TSH levels with SNPs in PDE8B, our genome scan provided evidence for association with PDE10A and several biologically interesting candidates in a focused analysis of 24 genes. In particular, we found evidence for association of TSH levels with SNPs in the THRB (rs1505287, p = 7.3 x 10(-5)), GNAQ (rs10512065, p = 2.0 x 10(-4)), TG (rs2252696, p = 2.2 x 10(-3)), POU1F1 (rs1976324, p = 3.9 x 10(-3)), PDE4D (rs27178, p = 8.3 x 10(-3)), and TSHR (rs4903957, p = 8.6 x 10(-3)) loci. Overall, the results suggest a primary effect of PDE8B variants on cAMP levels in the thyroid. This would affect production of T4 and T3 and feedback to alter TSH release by the pituitary. PDE8B may thus provide a candidate target for the treatment of thyroid dysfunction.

A cAMP-specific phosphodiesterase (PDE8B) that is mutated in adrenal hyperplasia is expressed widely in human and mouse tissues: a novel PDE8B isoform in human adrenal cortex

Bilateral adrenocortical hyperplasia (BAH) is the second most common cause of corticotropin-independent Cushing syndrome (CS). Genetic forms of BAH have been associated with complex syndromes such as Carney Complex and McCune-Albright syndrome or may present as isolated micronodular adrenocortical disease (iMAD) usually in children and young adults with CS. A genome-wide association study identified inactivating phosphodiesterase (PDE) 11A (PDE11A)-sequencing defects as low-penetrance predisposing factors for iMAD and related abnormalities; we also described a mutation (c.914A > C/H305P) in cyclic AMP (cAMP)-specific PDE8B, in a patient with iMAD. In this study we further characterize this mutation; we also found a novel PDE8B isoform that is highly expressed in the adrenal gland. This mutation is shown to significantly affect the ability of the protein to degrade cAMP in vitro. Tumor tissues from patients with iMAD and no mutations in the coding PDE8B sequence or any other related genes (PRKAR1A, PDE11A) showed downregulated PDE8B expression (compared to normal adrenal cortex). Pde8b is detectable in the adrenal gland of newborn mice and is widely expressed in other mouse tissues. We conclude that PDE8B is another PDE gene linked to iMAD; it is a candidate causative gene for other adrenocortical lesions linked to the cAMP signaling pathway and possibly for tumors in other tissues.

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that regulate the cellular levels of the second messengers, cAMP and cGMP, by controlling their rates of degradation. There are 11 different PDE families, with each family typically having several different isoforms and splice variants. These unique PDEs differ in their three-dimensional structure, kinetic properties, modes of regulation, intracellular localization, cellular expression, and inhibitor sensitivities. Current data suggest that individual isozymes modulate distinct regulatory pathways in the cell. These properties therefore offer the opportunity for selectively targeting specific PDEs for treatment of specific disease states. The feasibility of these enzymes as drug targets is exemplified by the commercial and clinical successes of the erectile dysfunction drugs, sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). PDE inhibitors are also currently available or in development for treatment of a variety of other pathological conditions. In this review the basic biochemical properties, cellular regulation, expression patterns, and physiological functions of the different PDE isoforms will be discussed. How these properties relate to the current and future development of PDE inhibitors as pharmacological agents is especially considered. PDEs hold great promise as drug targets and recent research advances make this an exciting time for the field of PDE research.

Profiling human phosphodiesterase genes and splice isoforms

A mere 21 human phosphodiesterase (PDE) genes are responsible for modulating cellular levels of cAMP and cGMP in response to stimuli. Considering the importance of cAMP and cGMP to disparate physiological functions including visual response, smooth muscle relaxation, platelet aggregation, immune response, and cardiac contractibility, perhaps the 200 or more splice isoforms of PDE genes also play a major functional role. We profiled the human PDEs across 25 tissue samples using splice sensitive oligonucleotide microarrays containing probes for exons and exon-exon junctions. Our results suggest that PDEs exhibit tissue-specific differences in expression, as demonstrated by the high expression of PDE4B in skeletal muscle. At the splice variant level, the majority of PDE genes--notably 1A, 1C, 2A, 4C, 4D, 5A, 7A, 8A, 8B, 9A, 10A, and 11A--exhibited tissue-specific splicing with potential functional implications for PDE biology. This work validates expression of many EST transcripts, and confirms and expands on published findings based on PCR and cloning, illuminating some of the complexity of cAMP and cGMP processing.

Intracellular targeting of phosphodiesterase-4 underpins compartmentalized cAMP signaling

The phosphodiesterase-4 (PDE4) enzyme belongs to a family of cAMP-dependent phosphodiesterases that provide the major means of hydrolyzing and, thereby, inactivating the key intracellular second messenger, cAMP. As such, PDE4s are central to the regulation of many diverse signaling processes that allow cells to respond to external stimuli. Four genes (4A, 4B, 4C, and 4D) encode around 20 distinct isoform members of the PDE4 family. Each isoform is characterized by a unique N-terminal region. PDE4s are multidomain metallohydrolases with each domain serving particular roles allowing them to be targeted to varying regions and organelles of intracellular space and regulated in distinct fashions by phosphorylation and protein-protein interaction. Although identical in catalytic function, each isoform locates to distinct regions within the cell so as to create and manage spatially distinct pools of cAMP. The multiplicity of partners associating with members of the four gene PDE4 family places these enzymes in key regulatory positions, permitting them to channel complex biological signals via fundamental signaling cohorts such as G-protein-coupled receptors (GPCRs), arrestins, A-kinase-anchoring proteins (AKAPs), and tyrosyl family kinases. The cAMP cascade has long been linked to cellular growth and embryogenesis and with this comes the implication that PDE4 may play considerable roles in the regulation of progeny development in maturing cells and tissues.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

A complex pattern of mutations and abnormal splicing of Smad4 is present in thyroid tumours

Sensitivity to transforming growth factor-beta is impaired in thyroid tumours. Similar to Mad -- Mother Against Decapentaplegic-(Smad)4 is frequently altered in cancers, but its involvement in this system is unknown. We analysed 56 thyroid tumours of various histotypes for Smad4 mutations by PCR-SSCP and sequencing, linking them to Smad4 reactivity as examined by immunohistochemistry (IHC), and 29 of them also for abnormalities in RNA expression due to alternative splicing. In all, 15/56 cases (27%), both benign and malignant lesions, harbour alterations of Smad4 coding sequence. We found several novel intragenic mutations (13 missense, two silent, one frameshift and one large insertion-deletion), with high incidence in the linker region. A subset of mutated tumours failed to express Smad4 protein by IHC. We have also detected four alternatively spliced tumour-associated Smad4 isoforms, lacking portions of the linker region, and three more due to unreported internal exon-exon rearrangements. Smad4 is both frequently mutated and deregulated by aberrant splicing in thyroid tumours and these alterations may contribute as an early event to thyroid tumorigenesis.

Molecular comparison of rat cyclic nucleotide phosphodiesterase 8 family: unique expression of PDE8B in rat brain

Cyclic nucleotide phosphodiestease (PDE) type 8 is categorized into a family of 3-isobutyl-1-methylxanthine-insensitive PDE hydrolyzing cAMP with high affinity. We have isolated cDNAs encoding rat PDE8A and PDE8B from brain and testis, respectively. The sequence analysis demonstrated that rat PDE8A was a protein of 823 amino acid residues. Rat PDE8B protein was predicted as an N-terminal truncated form of 760 amino acid residues. Both of rat PDE8 proteins include REC, PAS and catalytic PDE domains. Tissue-specific expression patterns of rat PDE8A and PDE8B transcripts were demonstrated by Northern blot analysis. Rat PDE8A transcripts were rich in the liver and testis, and those of rat PDE8B were particularly abundant in the brain and were not expressed in the thyroid gland, while human thyroid gland contains PDE8B transcripts at a high level. Rat PDE8B transcripts were found in all brain regions other than cerebellum and shown to exist in the neuronal cells in in situ hybridization. Mouse PDE8B1 sequence was also identified by a database search and sequence alignment, revealing a protein of 885 amino acid residues, which is 99% and 96% identical to rat and human PDE8B1, respectively. As well as rat PDE8B, expression of mouse PDE8B transcripts was not confined to the thyroid gland. Species-dependent tissue expression pattern was quite unique features of PDE8B.

Identification and distribution of different mRNA variants produced by differential splicing in the human phosphodiesterase 9A gene

The transcript population of the human gene coding for a cGMP-dependent phosphodiesterase (PDE9A) has a complex structure. There is a high level of mRNA in intestinal and prostate tissues, a low level in blood, and intermediate in other tissues. More than 20 different variants produced by differential splicing have been observed and new exons have been identified both by PCR amplification and by the analysis of available EST sequences. In all cases the transcriptional start site is the same and no differential splicing is found in the exons coding for the catalytic domain of the protein. In some cases the protein produced by splice variants is truncated. The distribution of the splice variants is not homogeneous among the different tissues studied. The human, but not the mouse, PDE9A gene appears to have a complex regulation of expression by different isoforms.