The phosphodiesterase 8B gene rs4704397 is associated with thyroid function, risk of myocardial infarction, and body height: the Tromsø study

OBJECTIVE

High serum thyrotropin (TSH) levels predict cardiovascular disease (CVD). Recently several single nucleotide polymorphisms (SNPs) associated with TSH levels have been identified, one of them being the rs4704397 SNP in the phosphodiesterase 8B (PDE8B) gene. If the relation between thyroid function and CVD is causal, one could also expect rs4704397 genotypes to predict CVD and possibly health in general.

METHODS

DNA was prepared and genotyping performed for rs4704397 in subjects who participated in the fourth survey of the Tromsø Study in 1994-1995 and who were registered with the endpoints myocardial infarction (MI), type 2 diabetes (T2DM), cancer, or death, as well as a randomly selected control group. Similarly, genotyping was performed in subjects who had participated in clinical trials where serum TSH, free T4 (fT4), and free T3 (fT3) were measured.

RESULTS

From the Tromsø Study, 8938 subjects without thyroid disease or thyroid medication were successfully genotyped for rs4704397. Among these, 2098 were registered with MI, 1025 with T2DM, 2748 with cancer, and 3592 had died. The minor homozygote genotype (A:A) had a median serum TSH level that was 0.29 mIU/L higher than in the major homozygote genotype (G:G). The A:A genotype had a significantly increased risk of MI as compared to the G:G genotype (1.14 [1.00-1.29], hazard ratio [confidence interval], Cox regression with adjustment for age, sex, and body mass index). No significant associations were seen with the other endpoints or CVD risk factors. Furthermore, subjects with the G:G genotype were significantly taller than subjects with the A:A genotype (mean difference 1.5 cm). In 584 subjects with serum TSH, fT4, and fT3 measurements, the subjects with the A:A genotype had significantly higher serum TSH and nonsignificantly lower serum fT3 (mean difference 0.15 pmol/L) levels than subjects with the G:G genotype.

CONCLUSION

rs4704397 is associated with thyroid function, risk of MI, and body height. However, confirmation in other cohorts is needed before firm conclusions can be drawn.

Frequency and effect on serum TSH of phosphodiesterase 8B (PDE8B) gene polymorphisms in patients with sporadic nonautoimmune subclinical hypothyroidism

BACKGROUND

Nonautoimmune subclinical hypothyroidism (NSH) is characterized by elevated serum TSH in presence of normal thyroid hormone levels and absence of anti-thyroid antibodies. As result of a genomic-wide study, a strong association between three polymorphic variants in intron 1 of human PDE8B gene (rs4704397, rs6885099, rs2046045) and serum TSH has been reported in euthyroid subjects.

AIM

The aim of this study was to evaluate frequency and effects on serum TSH of PDE8B gene polymorphisms in patients with sporadic NSH and verify if differences in serum TSH levels are associated to these polymorphic variants.

SUBJECTS AND METHODS

A total of 58 Italian selected patients affected by NSH, with elevated serum TSH, normal FT3 and FT4 and without TSHr gene mutations, were subjected to genotyping for specific single nucleotide polymorphism of PDE8B gene.

RESULTS

In all patients, the integrity of TSH receptor gene was attested. The ancestral allele associated with increased serum TSH was present in 42/58 patients (72.4 %) for rs4704397, in 42/58 patients (72.4 %) for rs6885099 and in 44/58 patients (75.9 %) for rs2046045. However, similar values of serum TSH were detected in patients with minor or major allele for each polymorphism.

CONCLUSIONS

A prevalence of the minor allele of PDE8B gene polymorphism associated with elevated serum levels of TSH was demonstrated in patients affected by sporadic NSH; however, significant differences in circulating TSH in patients with minor or major alleles for each polymorphism were not identified demonstrating the lack of association between the polymorphisms and serum TSH levels in these patients.

[Soluble forms of adenylyl cyclases of spermatozoa]

Soluble (cytosolic) forms of adenylyl cyclases (sAC), the enzymes catalyzing the conversion of ATP to the second messenger cAMP, play a key role in the regulation of spermatogenesis, control maturation of spermatozoa in the epididymis and their capacitation in the female genital tract, which determines their ability to fertilize. In the last years the significant progress was made in the study of the structural and functional organization and regulatory properties of sAC, their localization in the spermatozoa as well as in the investigation of intracellular cascades functionally coupled with sAC, including protein kinase A, cAMP-dependent phosphodiesterase, non-receptor tyrosine kinases, tyrosine phosphatases, transcription factors of CREB/CREM-family. The molecular mechanisms involved in the regulation of the intracellular concentration of bicarbonate anions, the main endogenous activators of sAC, were deciphered. Many evidences were obtained that the decrease of functional activity of sAC and signaling cascades and effector proteins coupled to it, as well as bicarbonate anion transporters lead to disturbances of spermatogenesis. As a consequence, the development of approaches for controlling the activity of sAC in spermatozoa is one of the priority ways to treat dysfunctions of the male reproductive system. Present review is devoted to advances in the study of soluble forms of AC and functionally coupled to them signaling cascades and effector proteins in the spermatozoa, as well as to the unresolved issues in this area.

Loss of the histidine kinase DhkD results in mobile mounds during development of Dictyostelium discoideum

Background

Histidine kinases are receptors for sensing cellular and environmental signals, and in response to the appropriate cue they initiate phosphorelays that regulate the activity of response regulators. The Dictyostelium discoideum genome encodes 15 histidine kinases that function to regulate several processes during the multicellular developmental program, including the slug to culmination transition, osmoregulation, and spore differentiation. While there are many histidine kinases, there is only a single response regulator, RegA. Not surprisingly given the ubiquitous involvement of cAMP in numerous processes of development in Dictyostelium, RegA is a cAMP phosphodiesterase that is activated upon receiving phosphates through a phosphorelay. Hence, all of the histidine kinases characterized to date regulate developmental processes through modulating cAMP production. Here we investigate the function of the histidine kinase DhkD.

Principal Findings

The dhkD gene was disrupted, and the resulting cells when developed gave a novel phenotype. Upon aggregation, which occurred without streaming, the mounds were motile, a phenotype termed the pollywog stage. The pollywog phenotype was dependent on a functional RegA. After a period of random migration, the pollywogs attempted to form fingers but mostly generated aberrant structures with no tips. While prestalk and prespore cell differentiation occurred with normal timing, proper patterning did not occur. In contrast, wild type mounds are not motile, and the cAMP chemotactic movement of cells within the mound facilitates proper prestalk and prespore patterning, tip formation, and the vertical elongation of the mound into a finger.

Conclusions

We postulate that DhkD functions to ensure the proper cAMP distribution within mounds that in turn results in patterning, tip formation and the transition of mounds to fingers. In the absence of DhkD, aberrant cell movements in response to an altered cAMP distribution result in mound migration, a lack of proper patterning, and an inability to generate normal finger morphology.

Identification of gene expression profiles associated with cortisol secretion in adrenocortical adenomas

CONTEXT

The cortisol secretion of adrenocortical adenomas can be either subtle or overt. The mechanisms leading to the autonomous hypersecretion of cortisol are unknown.

OBJECTIVE

The objective of the study was to identify the gene expression profile associated with the autonomous and excessive cortisol secretion of adrenocortical adenomas.

PATIENTS AND METHODS

The transcriptome of 22 unilateral adrenocortical adenomas (5 nonsecreting, 6 subclinical cortisol producing, 11 cortisol producing) was studied and correlated with cortisol secretion. Phosphodiesterase 8B (PDE8B) expression was measured by Western blot.

RESULTS

Unsupervised clustering identified 2 groups of adenomas with a difference in secretion level (P = .008). Cluster 1 included only cortisol-producing adenomas (8 of 11), whereas cluster 2 was an admixture of the nonsecreting, the subclinical cortisol-secreting, and 3 of the 11 cortisol-secreting adenomas (Fisher exact, P = .002). This cluster was driven by genes related to cortisol secretion and to extracellular matrix. More than 3000 genes correlated with cortisol secretion. Among the positively correlated were the steroidogenic enzymes, genes involved in cholesterol metabolism, and glutathione S-transferases. Among the negatively correlated genes were genes related to transcripts translation and the transcription factor GATA-6. The PDE8B, which inactivates the protein kinase A pathway, unexpectedly showed the strongest positive correlation with cortisol secretion, confirmed by Western blot. The protein kinase A-activity to cAMP ratio was increased in adenomas with high PDE8B levels, suggesting counterregulation to limit downstream activation of the pathway.

CONCLUSION

The transcriptome of adrenocortical adenomas reveals a major association with cortisol secretion and identifies specific groups of genes implicated in steroid secretion, suggesting that cAMP signaling alterations might be frequent in cortisol-secreting adenomas.

Identification of novel genetic variants in phosphodiesterase 8B (PDE8B), a cAMP-specific phosphodiesterase highly expressed in the adrenal cortex, in a cohort of patients with adrenal tumours

BACKGROUND

Genetic aberrations in various components of cAMP signalling pathway predispose to endocrine tumours. Mutations in the phosphodiesterases (PDEs) are involved in the predisposition to adrenocortical neoplastic conditions.

OBJECTIVE

To screen for genetic variations in PDE8B among patients with different types of adrenocortical tumours.

DESIGN AND SUBJECTS

This is a case-control study followed by functional analyses. Two hundred and sixteen unrelated patients with different types of adrenocortical tumours and 192 healthy control individuals participated in the study.

METHODS

Bidirectional Sanger sequencing, in vitro cell line transfection and in silico modelling are used in this study.

RESULTS

Nine different PDE8B sequence changes, six novel and three previously reported, were identified in our patients and controls. Two of the variations, seen only in the patient group, showed significant potential to impair protein function, both in vitro and in silico.

CONCLUSION

PDE8B is another PDE gene in which variations may contribute to predisposition of adrenocortical tumours.

Methylomic analysis identifies frequent DNA methylation of zinc finger protein 582 (ZNF582) in cervical neoplasms

Background

Despite of the trend that the application of DNA methylation as a biomarker for cancer detection is promising, clinically applicable genes are few. Therefore, we looked for novel hypermethylated genes for cervical cancer screening.

Methods and Findings

At the discovery phase, we analyzed the methylation profiles of human cervical carcinomas and normal cervixes by methylated DNA immunoprecipitation coupled to promoter tiling arrays (MeDIP-on-chip). Methylation-specific PCR (MSP), quantitative MSP and bisulfite sequencing were used to verify the methylation status in cancer tissues and cervical scrapings from patients with different severities. Immunohistochemical staining of a cervical tissue microarray was used to confirm protein expression. We narrowed to three candidate genes: DBC1, PDE8B, and ZNF582; their methylation frequencies in tumors were 93%, 29%, and 100%, respectively. At the pre-validation phase, the methylation frequency of DBC1 and ZNF582 in cervical scraping correlated significantly with disease severity in an independent cohort (n = 330, both P<0.001). For the detection of cervical intraepithelial neoplasia 3 (CIN3) and worse, the area under the receiver operating characteristic curve (AUC) of ZNF582 was 0.82 (95% confidence interval  = 0.76–0.87).

Conclusions

Our study shows ZNF582 is frequently methylated in CIN3 and worse lesions, and it is demonstrated as a potential biomarker for the molecular screening of cervical cancer.

Repeated immobilization stress disturbed steroidogenic machinery and stimulated the expression of cAMP signaling elements and adrenergic receptors in Leydig cells

This study was designed to evaluate the effect of acute (2 h daily) and repeated (2 h daily for 2 or 10 consecutive days) immobilization stress (IMO) on: 1) the steroidogenic machinery homeostasis; 2) cAMP signaling; and the expression of receptors for main markers of 3) adrenergic and 4) glucocorticoid signaling in Leydig cells of adult rats. The results showed that acute IMO inhibited steroidogenic machinery in Leydig cells by downregulation of Scarb1 (scavenger receptor class B), Cyp11a1 (cholesterol side-chain cleavage enzyme), Cyp17a1 (17α-hydroxylase/17,20 lyase), and Hsd17b3 (17β-hydroxysteroid dehydrogenase) expression. In addition to acute IMO effects, repeated IMO increased transcription of Star (steroidogenic acute regulatory protein) and Arr19 (androgen receptor corepressor 19 kDa) in Leydig cells. In the same cells, the transcription of adenylyl cyclases (Adcy7, Adcy9, Adcy10) and cAMP-specific phosphodiesterases (Pde4a, Pde4b, Pde4d, Pde7a, Pde8a) was stimulated, whereas the expression of the genes encoding protein kinase A subunits were unaffected. Ten times repeated IMO increased the levels of all adrenergic receptors and β-adrenergic receptor kinase (Adrbk1) in Leydig cells. The transcription analysis was supported by cAMP/testosterone production. In this signaling scenario, partial recovery of testosterone production in medium/content was detected. The physiological significance of the present results was proven by ex vivo application of epinephrine, which increased cAMP/testosterone production by Leydig cells from control rats in greater fashion than from stressed. IMO did not affect the expression of transcripts for Crhr1/Crhr2 (corticotropin releasing hormone receptors), Acthr (adrenocorticotropin releasing hormone receptor), Gr (glucocorticoid receptor), and Hsd11b1 [hydroxysteroid (11-β) dehydrogenase 1], while all types of IMO stimulated the expression of Hsd11b2, the unidirectional oxidase with high affinity to inactivate glucocorticoids. Thus, presented data provide new molecular/transcriptional base for "fight/adaptation" of Leydig cells and new insights into the role of cAMP, epinephrine, and glucocorticoid signaling in recovery of stress-impaired Leydig cell steroidogenesis.

Evolution of self-organisation in Dictyostelia by adaptation of a non-selective phosphodiesterase and a matrix component for regulated cAMP degradation

Dictyostelium discoideum amoebas coordinate aggregation and morphogenesis by secreting cyclic adenosine monophosphate (cAMP) pulses that propagate as waves through fields of cells and multicellular structures. To retrace how this mechanism for self-organisation evolved, we studied the origin of the cAMP phosphodiesterase PdsA and its inhibitor PdiA, which are essential for cAMP wave propagation. D. discoideum and other species that use cAMP to aggregate reside in group 4 of the four major groups of Dictyostelia. We found that groups 1-3 express a non-specific, low affinity orthologue of PdsA, which gained cAMP selectivity and increased 200-fold in affinity in group 4. A low affinity group 3 PdsA only partially restored aggregation of a D. discoideum pdsA-null mutant, but was more effective at restoring fruiting body morphogenesis. Deletion of a group 2 PdsA gene resulted in disruption of fruiting body morphogenesis, but left aggregation unaffected. Together, these results show that groups 1-3 use a low affinity PdsA for morphogenesis that is neither suited nor required for aggregation. PdiA belongs to a family of matrix proteins that are present in all Dictyostelia and consist mainly of cysteine-rich repeats. However, in its current form with several extensively modified repeats, PdiA is only present in group 4. PdiA is essential for initiating spiral cAMP waves, which, by organising large territories, generate the large fruiting structures that characterise group 4. We conclude that efficient cAMP-mediated aggregation in group 4 evolved by recruitment and adaptation of a non-selective phosphodiesterase and a matrix component into a system for regulated cAMP degradation.

[Association analysis of PDE8B gene polymorphisms with the susceptibility to Hyperthyroxinemia in Chinese Han population]

OBJECTIVE

To explore the correlations of the polymorphisms of phosphodiesterase 8B (PDE8B) gene with Hyperthyroxinemia in Chinese Han population.

METHODS

A case-control study of genotype 657366 SNPs was performed by Illumina Human660-Quad BeadChips in 98 Hyperthyroxinemia patients and 1300 controls. And 25 SNPs within PDE8B gene intron 1 were used for association analyses.

RESULTS

Allele frequencies of 5 SNPS in PDE8B gene intron 1 showed significant differences between the case and control groups (P < 0.05). In comparison with the control group, the genotypic distributions of rs7714529 (χ(2) = 6.430, P = 0.040), rs12514694 (χ(2) = 7.191, P = 0.027) and rs10066802 (χ(2) = 9.213, P = 0.010) in H-TSH group had significant differences. Haplotype AGTAG (rs7702192/rs7714529/rs251421/rs12514694/rs10066802) was over-represented in hyperthyrotropinemia cases versus the control group.

CONCLUSION

PDE8B gene polymorphisms may be correlated with Hyperthyroxinemia in Chinese Han population. And it may provide new concepts for the treatment of thyroid dysfunction.

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.

Non-invasive epigenetic detection of fetal trisomy 21 in first trimester maternal plasma

BACKGROUND

Down syndrome (DS) is the most common known aneuploidy, caused by an extra copy of all or part of chromosome 21. Fetal-specific epigenetic markers have been investigated for non-invasive prenatal detection of fetal DS. The phosphodiesterases gene, PDE9A, located on chromosome 21q22.3, is completely methylated in blood (M-PDE9A) and unmethylated in the placenta (U-PDE9A). Therefore, we estimated the accuracy of non-invasive fetal DS detection during the first trimester of pregnancy using this tissue-specific epigenetic characteristic of PDE9A.

METHODOLOGY/PRINCIPAL FINDINGS

A nested, case-control study was conducted using maternal plasma samples collected from 108 pregnant women carrying 18 DS and 90 normal fetuses (each case was matched with 5 controls according to gestational weeks at blood sampling). All pregnancies were singletons at or before 12 weeks of gestation between October 2008 and May 2009. The maternal plasma levels of M-PDE9A and U-PDE9A were measured by quantitative methylation-specific polymerase chain reaction. M-PDE9A and U-PDE9A levels were obtained in all samples and did not differ between male and female fetuses. M-PDE9A levels did not differ between the DS cases and controls (1854.3 vs 2004.5 copies/mL; P = 0.928). U-PDE9A levels were significantly elevated in women with DS fetuses compared with controls (356.8 vs 194.7 copies/mL, P<0.001). The sensitivities of U-PDE9A level and the unmethylation index of PDE9A for non-invasive fetal DS detection were 77.8% and 83.3%, respectively, with a 5% false-positive rate. In the risk assessment for fetal DS, the adjusted odds ratios of U-PDE9A level and UI were 46.2 [95% confidence interval: 7.8-151.6] and 63.7 [95% confidence interval: 23.2-206.7], respectively.

CONCLUSIONS

Our findings suggest that U-PDE9A level and the unmethylation index of PDE9A may be useful biomarkers for non-invasive fetal DS detection during the first trimester of pregnancy, regardless of fetal gender.

The roles of cyclic nucleotide phosphodiesterases (PDEs) in steroidogenesis

The second messenger, cAMP, is one of the most important regulatory signals for control of steroidogenesis. This review focuses on current knowledge about regulation of cyclic nucleotides by phosphodiesterases (PDEs) in steroidogenic tissues. The first PDE known to directly regulate steroidogenesis was PDE2, the cGMP-stimulated PDE. PDE2 mediates ANP/cGMP-induced decreases in aldosterone production. Recently, the PDE8 family has been shown to control steroidogenesis in two tissues. Specifically, PDE8A regulates testosterone production by itself and in concert with additional IBMX-sensitive PDEs. PDE8B modulates basal corticosterone synthesis via acute and chronic mechanisms. In addition to cAMP-dependent pathways, cGMP signaling also can promote steroidogenesis, and PDE5 modulates this process. Finally, PDE mutations may lead to several human diseases characterized by abnormal steroid 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.

Structural asymmetry of phosphodiesterase-9, potential protonation of a glutamic acid, and role of the invariant glutamine

PDE9 inhibitors show potential for treatment of diseases such as diabetes. To help with discovery of PDE9 inhibitors, we performed mutagenesis, kinetic, crystallographic, and molecular dynamics analyses on the active site residues of Gln453 and its stabilizing partner Glu406. The crystal structures of the PDE9 Q453E mutant (PDE9Q453E) in complex with inhibitors IBMX and (S)-BAY73-6691 showed asymmetric binding of the inhibitors in two subunits of the PDE9Q453E dimer and also the significant positional change of the M-loop at the active site. The kinetic analysis of the Q453E and E406A mutants suggested that the invariant glutamine is critical for binding of substrates and inhibitors, but is unlikely to play a key role in the differentiation between substrates of cGMP and cAMP. The molecular dynamics simulations suggest that residue Glu406 may be protonated and may thus explain the hydrogen bond distance between two side chain oxygens of Glu453 and Glu406 in the crystal structure of the PDE9Q453E mutant. The information from these studies may be useful for design of PDE9 inhibitors.

Expression and functional roles of guanylate cyclase isoforms in BRIN-BD11 β-cells

This study has assessed the expression and functional significance of cGMP-dependent signalling components in BRIN-BD11 cells. RT-PCR analysis revealed the expression of two subunits of soluble guanylate cyclase (sGC) suggesting the presence of an α2/β1 heterodimer. The expression of three particulate guanylate cyclases (pGC) was also detected (GC-A, GC-B and GC-C), as well as two cGMP-selective PDE isoforms (PDE5A and PDE9). Stimulation of BRIN-BD11 cells with agonists selective for sGC (NO, YC-1 and BAY 41-2272), GC-A (atrial natriuretic peptide (ANP) or GC-C (guanylin) caused an elevation in cGMP, and in the case of sGC, this was blocked by the selective inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ). The stimulatory effects of each activator on cGMP levels were further potentiated by the PDE5A inhibitor, zaprinast. Treatment of cells with sGC activators induced a loss of viability and increased insulin secretion. However these effects were not attenuated by ODQ suggesting that they were independent of a rise in cGMP. A modest increase in β-cell death and insulin secretion were also observed in guanylin and ANP treated cells, although the latter only reduced cell viability in the presence of a PDE5A inhibitor. Taken together, the data reveal that BRIN-BD11 cells express several functionally active enzymes capable of modulating cGMP levels, and they imply that signalling through these proteins may impact upon β-cell viability. The results further suggest that pGC isozymes can also regulate insulin secretion but that the pool of cGMP controlling insulin release is small relative to the global cGMP concentration in the cell.

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

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

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.

Polyphosphate kinase affects oxidative stress response by modulating cAMP receptor protein and rpoS expression in Salmonella typhimurium

Polyphosphate (polyP) plays diverse physiological functions in prokaryotes and eukaryotes, but most of their detailed mechanisms are still obscure. Here, we show that deletion of polyphosphate kinase (PPK), the principal enzyme responsible for synthesis of polyP, resulted in augmented expression of cAMP receptor protein (CRP) and rpoS and lowered H2O2 sensitivity in Salmonella Typhimurium ATCC14028. The binding of cAMP-CRP complex to rpoS promoter and further stimulation of its transcription were proved through electrophoretic mobility shift assay, lacZ fusion, and exogenous cAMP addition, respectively. The rpoS expression increased in cpdA (cAMP phosphodiesterase coding gene) mutant, further suggesting that cAMP-CRP upregulated rpoS expression. These results demonstrate that PPK affects oxidative stress response by modulating crp and rpoS expression in S. Typhimurium.

Role of a differentially expressed cAMP phosphodiesterase in regulating the induction of resistance against oxidative damage in Leishmania donovani

Differentiation-coupled induction of resistance of Leishmania parasites to macrophage oxidative damage was shown to be associated with an increased cAMP response. This study explores the significance of the cAMP response in the parasite by identifying a differentially expressed cAMP phosphodiesterase (LdPDEA) and deciphering its role in regulating antioxidant machineries in the parasite. LdPDEA, a high K(M) class I cytosolic cAMP phosphodiesterase, was expressed maximally in log-phase promastigotes, but was significantly reduced in stationary-phase promastigotes and amastigotes. Chemical inhibition or silencing of PDEA conferred enhanced resistance to pro-oxidants in these cells and this led to studies on trypanothione biosynthesis and utilization, as trypanothione is one of the major modulators of antioxidant defense in kinetoplastidae. Despite enhanced arginase and ornithine decarboxylase activity, trypanothione biosynthesis seemed to be unaffected by PDEA blockage, whereas significant elevations in the expression of tryparedoxin peroxidase, ascorbate peroxidase, and tryparedoxin were detected, suggesting a definite shift of trypanothione-pool utilization bias toward antioxidant defense. Moreover, parasites that overexpressed PDEA showed reduced resistance to oxidative damage and reduced infectivity toward activated macrophages. This study reveals the significance of a cAMP phosphodiesterase in the infectivity of Leishmania parasites.

Phosphodiesterase 8B gene polymorphism is associated with subclinical hypothyroidism in pregnancy

BACKGROUND

Maternal subclinical hypothyroidism is associated with a number of adverse outcomes in pregnancy. The Endocrine Society's recent consensus guidelines have recommended treatment with T(4) for this condition in pregnancy. The single nucleotide polymorphism rs4704397 in the phosphodiesterase 8B (PDE8B) gene has been found to be associated with altered serum TSH concentrations in the general population. We aimed to assess whether genetic variation in TSH due to the rs4704397 genotype affects the number of individuals classified as having subclinical hypothyroidism in pregnancy.

METHODS

Serum TSH, FT4, FT3, and thyroid peroxidase antibodies (TPOAbs) were measured in 970 pregnant women at 28 wk gestation. rs4704397 genotype was available on 877 subjects. Reference range calculations were based on the TPOAb-negative women.

RESULTS

TSH, but not FT4, FT3, or TPOAbs, varied with genotype and was highest in those with the AA genotype (median, 2.16, 1.84, and 1.73 mIU/liter for AA, AG, and GG genotypes, respectively; P = 0.0004). A greater proportion of women with the AA genotype had TSH concentrations above 4.21 mIU/liter, the upper limit of the reference range, compared with the AG and GG genotypes (9.6 vs. 3.5%, respectively; P = 0.004). Maternal PDE8B genotype was not associated with offspring birthweight or gestational age at delivery.

CONCLUSION

Genetic variation in TSH levels in pregnancy associated with the PDE8B rs4704397 genotype has implications for the number of women treated for subclinical hypothyroidism under current guidelines. Consideration should be made to individualization of normal ranges, potential effects on pregnancy outcome, and intention to treat for subclinical hypothyroidism in pregnancy.

Abnormalities of cAMP signaling are present in adrenocortical lesions associated with ACTH-independent Cushing syndrome despite the absence of mutations in known genes

CONTEXT

Bilateral adrenal hyperplasias (BAHs) may be caused by mutations of genes that code for molecules that participate in cAMP signaling. Little is known about cAMP signaling in adrenal lesions associated with ACTH-independent Cushing syndrome (AICS) that do not harbor mutations in known genes.

OBJECTIVE

We assessed the cAMP-signaling pathway by enzymatic and molecular studies.

DESIGN

Samples from 27 patients (ages 5-60 years) were studied and compared with normal adrenocortical tissue (n=4) and aldosterone-producing adenomas (APA, n=5). All samples were sequenced for GNAS, PRKAR1A, PDE11A, and PDE8B sequencing defects. cAMP levels and binding, protein kinase A, and phosphodiesterase (PDE) activities were assayed. Immunohistochemistry was used for certain studies and the phosphorylation status of CREB was studied.

PATIENTS

A total of 36 samples from patients were used.

RESULTS

Cortisol-producing adenomas (CPAs) and other lesions that were GNAS, PRKAR1A, PDE11A, and PDE8B gene mutation-negative were compared with PRKAR1A mutation-positive lesions, normal tissue, and APAs; abnormalities of the cAMP-signaling pathway were found in both BAHs and CPAs. Interestingly, mutation-negative CPAs had significantly decreased PDE activity.

CONCLUSION

Lesions of the adrenal associated with AICS, independently of their GNAS, PRKAR1A, PDE11A, and PDE8B mutation status, have functional abnormalities of cAMP signaling. It is probable that epigenetic events or additional defects of genes involved in this pathway are responsible for this phenomenon.