Selective up-regulation of phosphodiesterase-4 cyclic adenosine 3',5'-monophosphate (cAMP)-specific phosphodiesterase variants by elevated cAMP content in human myometrial cells in culture

Evaluating aminophylline and progesterone combination treatment to modulate contractility and labor-related proteins in pregnant human myometrial tissues

Progesterone (P4) and cyclic adenosine monophosphate (cAMP) are regarded as pro-quiescent factors that suppress uterine contractions during pregnancy. We previously used human primary cells in vitro and mice in vivo to demonstrate that simultaneously enhancing myometrial P4 and cAMP levels may reduce inflammation-associated preterm labor. Here, we assessed whether aminophylline (Ami; phosphodiesterase inhibitor) and P4 can reduce myometrial contractility and contraction-associated proteins (CAPs) better together than individually; both agents are clinically used drugs. Myometrial tissues from pregnant non-laboring women were treated ex vivo with Ami acutely (while spontaneous contracting) or throughout 24-h tissue culture (±P4); isometric tension measurements, PKA assays, and Western blotting were used to assess tissue contractility, cAMP action, and inflammation. Acute (1 h) treatment with 250 and 750 μM Ami reduced contractions by 50% and 84%, respectively, which was not associated with a directly proportional increase in whole tissue PKA activity. Sustained myometrial relaxation was observed during 24-h tissue culture with 750 μM Ami, which did not require P4 nor reduce CAPs. COX-2 protein can be reduced by 300 nM P4 but this did not equate to myometrial relaxation. Ami (250 μM) and P4 (100 and 300 nM) co-treatment did not prevent oxytocin-augmented contractions nor reduce CAPs during interleukin-1β stimulation. Overall, Ami and P4 co-treatment did not suppress myometrial contractions more than either agent alone, which may be attributed to low specificity and efficacy of Ami; cAMP and P4 action at in utero neighboring reproductive tissues during pregnancy should also be considered.

Effects of PDE4 gene polymorphisms on efficacy and adverse drug events of ritodrine therapy in preterm labor patients: a prospective observational study

PURPOSE

Phosphodiesterase (PDE) terminates the signaling pathway of myometrial relaxation by degradating cAMP to the inactive 5'-AMP. The PDE4 family is one of the most predominant PDE families that display high affinity to cAMP. The objective of this study was to evaluate the effects of PDE4 gene polymorphisms on tocolytic effects and adverse drug events (ADEs) of ritodrine therapy in patients with preterm labor.

METHODS

A total of 170 preterm labor patients were included in this study. To elucidate the effects of genetic polymorphisms on the inter-individual variability of ritodrine efficacy and ADEs, 8 single nucleotide polymorphisms (SNPs) were genotyped: PDE4D (rs1544791, rs983280, rs1504982, rs10940648, rs829259) and PDE4B2 (rs598961, rs2180335, and rs17128809). Additionally, rs1042719 of the ADRB2 gene was included for multivariate analysis. The primary endpoint of this prospective study was the time to delivery (hr). The secondary endpoint was ritodrine-induced ADEs.

RESULTS

The mutant-type homozygote carriers of PDE4B2 rs598961 polymorphism showed shorter median time to delivery than those with other genotypes (adjusted hazard ratio 1.6, 95% confidence interval 1.0 to 2.4, P = 0.035). On the other hand, patients with wild-type homozygotes of PDE4B2 rs17128809 showed 2.6~2.9 times higher ADEs compared to those with other genotypes. Among demographic characteristics, gestational age at start of drug therapy and modified Bishop score were significant factors for time to delivery, whereas height, weight, and BSA were significant factors for ritodrine-induced ADEs after adjusting other factors.

CONCLUSIONS

This pharmacogenomic study suggested that PDE4 genetic polymorphisms impact individual susceptibility to β2-adrenergic receptor targeted therapy in patients with preterm labor.

Dexamethasone Inhibits Synergistic Induction of PDE4B Expression by Roflumilast and Bacterium NTHi

Phosphodiesterase 4B (PDE4B) plays an important role in inflammation. Recently we have reported that roflumilast as a PDE4-selective inhibitor, synergizes with nontypeable Haemophilus influenzae (NTHi) to up-regulate PDE4B expression in vitro and in vivo. Clinical evidence and our previous results suggest that synergistic induction of PDE4B could be counterproductive for suppressing inflammation or may contribute to tolerance to roflumilast. We thus investigated if dexamethasone inhibits the synergistic induction of PDE4B by roflumilast and NTHi as well as inflammation. Here, dexamethasone markedly suppressed the synergistic induction of PDE4B in human lung epithelial cells and in vivo. We also found that dexamethasone further suppressed NTHi-induced inflammatory response in vitro and in vivo. Moreover, Compound A, as a dissociating non-steroidal glucocorticoid receptor (GR) ligand, inhibited the synergistic induction of PDE4B, thereby suggesting the requirement of dexamethasone-mediated GR activation in the suppression of PDE4B expression. Taken together, our data suggest that dexamethasone may help attenuate inflammation and tolerance through suppressing the PDE4B expression in chronic obstructive pulmonary disease (COPD) patients using roflumilast.

Relaxant and anti-inflammatory effect of two thalidomide analogs as PDE-4 inhibitors in pregnant rat uterus

The aim of this study was to evaluate the relaxant and anti-inflammatory effects of two thalidomide analogs as phosphodiesterase-4 (PDE-4) inhibitors in pregnant rat uterus. Uteri from Wistar female rats were isolated at 19 day of pregnancy. Uterine samples were used in functional studies to evaluate the inhibitory effects of the thalidomide analogs, methyl 3-(4-nitrophthalimido)-3-(3,4-dimethoxyphenyl)-propanoate (4NO2PDPMe) and methyl 3-(4-aminophthalimido)-3-(3,4-dimethoxyphenyl)-propanoate (4APDPMe), on prostaglandin-F2α (PGF2α)-induced phasic, K⁺-induced tonic, and Ca²⁺-induced contractions. Accumulation of cAMP was quantified in uterine homogenates by ELISA. Anti-inflammatory effect was assessed by using ELISA for determination of the pro-inflammatory cytokines tumor necrosis factor-α (TNFα) and interleukin (IL)-1β, and anti-inflammatory IL-10, from uterine explants stimulated with lipopolysaccharide (LPS). Nifedipine, forskolin and rolipram were used as positive controls where required. Both thalidomide analogs induced a significant inhibition of the uterine contractions induced by the pharmaco- and electro-mechanic stimuli. Nifedipine and forskolin were more potent than the analogs to inhibit the uterine contractility, but these were more potent than rolipram, and 4APDPMe was equieffective to nifedipine. Thalidomide analogs increased uterine cAMP-levels in a concentration-dependent manner. The LPS-induced TNFα and IL-1β uterine secretion was diminished in a concentration-dependent fashion by both analogs, whereas IL-10 secretion was increased significantly. The thalidomide analogs induced utero-relaxant and anti-inflammatory effects, which were associated with the increased cAMP levels as PDE-4 inhibitors in the pregnant rat uterus. Such properties place these thalidomide analogs as potentially safe and effective tocolytic agents in a field that urgently needs improved pharmacological treatments, as in cases of preterm labor.

Inhibition of Uterine Contractility by Thalidomide Analogs via Phosphodiesterase-4 Inhibition and Calcium Entry Blockade

Uterine relaxation is crucial during preterm labor. Phosphodiesterase-4 (PDE-4) inhibitors have been proposed as tocolytics. Some thalidomide analogs are PDE-4 inhibitors. The aim of this study was to assess the uterus-relaxant properties of two thalidomide analogs, methyl 3-(4-nitrophthalimido)-3-(3,4-dimethoxyphenyl)-propanoate (4NO2PDPMe) and methyl 3-(4-aminophthalimido)-3-(3,4-dimethoxyphenyl)-propanoate (4APDPMe) and were compared to rolipram in functional studies of spontaneous phasic, K⁺-induced tonic, and Ca²⁺-induced contractions in isolated pregnant human myometrial tissues. The accumulation of cAMP was quantified in HeLa cells. The presence of PDE-4B2 and phosphorylated myosin light-chain (pMLC), in addition to the effect of thalidomide analogs on oxytocin-induced pMLC, were assessed in human uterine myometrial cells (UtSMCs). Thalidomide analogs had concentration-dependent inhibitory effects on spontaneous and tonic contractions and inhibited Ca²⁺-induced responses. Tonic contraction was equipotently inhibited by 4APDPMe and rolipram (IC₅₀ = 125 ± 13.72 and 98.45 ± 8.86 µM, respectively). Rolipram and the thalidomide analogs inhibited spontaneous and tonic contractions equieffectively. Both analogs increased cAMP accumulation in a concentration-dependent manner (p < 0.05) and induced changes in the subcellular localization of oxytocin-induced pMLC in UtSMCs. The inhibitory effects of thalidomide analogs on the contractions of pregnant human myometrium tissue may be due to their PDE-4 inhibitory effect and novel mechanism as calcium-channel blockers.

Differential impact of acute and prolonged cAMP agonist exposure on protein kinase A activation and human myometrium contractile activity

KEY POINTS

Over 15 million babies are born prematurely each year with approximately 1 million of these babies dying as a direct result of preterm delivery. β₂ -Adrenoreceptor agonists that act via cAMP can reduce uterine contractions to delay preterm labour, but their ability to repress uterine contractions lasts ≤ 48 h and their use does not improve neonatal outcomes. Previous research has suggested that cAMP inhibits myometrial contractions via protein kinase A (PKA) activation, but this has yet to be demonstrated with PKA-specific agonists. We investigated the role of PKA in mediating cAMP-induced human myometrial relaxation, and the impact of prolonged cAMP elevation on myometrial contractility. Our findings suggest that PKA is not the sole mediator of cAMP-induced myometrial relaxation and that prolonged prophylactic elevation of cAMP alone is unlikely to prevent preterm labour (PTL).

ABSTRACT

Acute cAMP elevation inhibits myometrial contractility, but the mechanisms responsible are not fully elucidated and the long-term effects are uncertain. Both need to be defined in pregnant human myometrium before the therapeutic potential of cAMP-elevating agents in the prevention of preterm labour can be realised. In the present study, we tested the hypotheses that PKA activity is necessary for cAMP-induced myometrial relaxation, and that prolonged cAMP elevation can prevent myometrial contractions. Myometrial tissues obtained from term, pre-labour elective Caesarean sections were exposed to receptor-independent cAMP agonists to determine the relationship between myometrial contractility (spontaneous and oxytocin-induced), PKA activity, HSP20 phosphorylation and expression of contraction-associated and cAMP signalling proteins. Acute (1 h) application of cAMP agonists promoted myometrial relaxation, but this was weakly related to PKA activation. A PKA-specific activator, 6-Bnz-cAMP, increased PKA activity (6.8 ± 2.0 mean fold versus vehicle; P = 0.0313) without inducing myometrial relaxation. Spontaneous myometrial contractility declined after 24 h but was less marked when tissues were constantly exposed to cAMP agonists, especially for 8-bromo-cAMP (4.3 ± 1.2 mean fold versus vehicle; P = 0.0043); this was associated with changes to calponin, cofilin and HSP20 phosphorylated/total protein levels. Oxytocin-induced contractions were unaffected by pre-incubation with cAMP agonists despite treatments being able to enhance PKA activity and HSP20 phosphorylation. These data suggest that cAMP-induced myometrial relaxation is not solely dependent on PKA activity and the ability of cAMP agonists to repress myometrial contractility is lost with prolonged exposure. We conclude that cAMP agonist treatment alone may not prevent preterm labour.

Cross-talk between PKA-Cβ and p65 mediates synergistic induction of PDE4B by roflumilast and NTHi

Phosphodiesterase 4B (PDE4B) plays a key role in regulating inflammation. Roflumilast, a phosphodiesterase (PDE)4-selective inhibitor, has recently been approved for treating severe chronic obstructive pulmonary disease (COPD) patients with exacerbation. However, there is also clinical evidence suggesting the development of tachyphylaxis or tolerance on repeated dosing of roflumilast and the possible contribution of PDE4B up-regulation, which could be counterproductive for suppressing inflammation. Thus, understanding how PDE4B is up-regulated in the context of the complex pathogenesis and medications of COPD may help improve the efficacy and possibly ameliorate the tolerance of roflumilast. Here we show that roflumilast synergizes with nontypeable Haemophilus influenzae (NTHi), a major bacterial cause of COPD exacerbation, to up-regulate PDE4B2 expression in human airway epithelial cells in vitro and in vivo. Up-regulated PDE4B2 contributes to the induction of certain important chemokines in both enzymatic activity-dependent and activity-independent manners. We also found that protein kinase A catalytic subunit β (PKA-Cβ) and nuclear factor-κB (NF-κB) p65 subunit were required for the synergistic induction of PDE4B2. PKA-Cβ phosphorylates p65 in a cAMP-dependent manner. Moreover, Ser276 of p65 is critical for mediating the PKA-Cβ-induced p65 phosphorylation and the synergistic induction of PDE4B2. Collectively, our data unveil a previously unidentified mechanism underlying synergistic up-regulation of PDE4B2 via a cross-talk between PKA-Cβ and p65 and may help develop new therapeutic strategies to improve the efficacy of PDE4 inhibitor.

PGE 2 desensitizes β -agonist effect on human lung fibroblast-mediated collagen gel contraction through upregulating PDE4

In the current study, we investigated the effect of a long-acting β-agonist (salmeterol) and a phosphodiesterase 4 (PDE4) inhibitor (cilomilast) on human lung fibroblast-mediated collagen gel contraction. Higher concentrations of salmeterol (10⁻⁷ and 10⁻⁶ M) inhibited fibroblast-mediated collagen gel contraction. No effect was observed with cilomilast alone (up to 10⁻⁵ M). In the presence of 10⁻⁸ M salmeterol, however, cilomilast could significantly inhibit fibroblast-mediated collagen gel contraction in a concentration-dependent manner (10⁻⁷~10⁻⁵ M). Blockade of endogenous PGE₂ by indomethacin further potentiated the inhibitory effect of salmeterol on fibroblast-mediated collagen gel contraction, but it did not affect cilomilast's effect. Pretreatment with PGE₂ abolished the inhibitory effect of salmeterol, but it potentiated the inhibitory effect of cilomilast on fibroblast-mediated collagen gel contraction. Finally, indomethacin slightly inhibited PDE4C expression, while PGE₂ stimulated the expression of PDE4A and -4C in human lung fibroblasts. These findings suggest that long-acting β-agonist and PDE4 inhibitor have a synergistic effect in regulating fibroblast tissue repair functions and that PGE₂ can modulate the effect of β-agonist and PDE4 inhibitor at least in part through the mechanism of regulating PDE4 expression.

Bresol inhibits phosphodiesterase 4 gene expression and modulates the levels of select mediators of inflammation in human monocytic cells

Bresol-a poly-herbal formulation, has been reported to be effective against bronchial asthma and allergic rhinitis in children. In vivo studies have supported the anti-histaminic and anti-anaphylactic action of bresol. However, the mechanism of action of bresol in modulation of inflammation has not been studied at the cellular and molecular level. The present study was aimed to elucidate the mechanism(s) of action of bresol at the cellular and molecular levels, using human monocyte leukemia cells. The effects of bresol on phosphodiesterase 4B (PDE4B) gene expression were analyzed using human monocytic U937 leukemia cells. The ability of bresol to stimulate cAMP formation in these cells, as well as its effects on mediators of inflammation like tumor necrosis factor-α (TNFα), nitric oxide (NO), and cycloxygenase-2 (COX-2) in lipopolysaccharide (LPS)-stimulated U937 cells, were also studied. The results here indicated that bresol exhibited potential anti-inflammatory properties by inhibiting LPS-induced PDE4B gene expression in the cells. Bresol also dose dependently activated cAMP formation, and inhibited TNFα, NO, as well as COX-2 formation in the LPS-stimulated cells. Based upon the results, we concluded that the reported anti-inflammatory activity of bresol might be attributed to its abilities to inhibit PDE4B and thus elevate cAMP levels in human monocytes. The anti-inflammatory effects of bresol might also be a result of the capacity of bresol to modulate the formation of TNFα, NO, and COX-2 in monocytes.

Evidence that corticotropin-releasing hormone modulates myometrial contractility during human pregnancy

As human pregnancy advances, CRH increases exponentially and is hypothesized to trigger the transition from myometrial quiescence to active contractions at labor. Paradoxically, CRH stimulates cAMP production, suggesting it should cause relaxation. To evaluate CRH as a mediator of quiescence, the effect of CRH on contractions in preterm and term myometria with concurrent progesterone (P4) was determined. In late gestation, we hypothesized that high concentrations of CRH down-regulate agonist-activated-cAMP relaxatory pathways and that increased phosphodiesterase (PDE) activity induces heterologous down-regulation of agonist-activated-cAMP pathways. CRH caused dose-dependent relaxation of spontaneously contracting myometrial strips of 31 +/- 8% (mean +/- sem; n = 12) and 35 +/- 20% (n = 3) in term and preterm samples, respectively. CRH with P4 pretreatment caused a 40 +/- 13% (n = 4) reduction in contractility, whereas in matched samples, CRH alone exerted a 26 +/- 6% (n = 4) reduction, with a shift of CRH dose-response curves (P < 0.01, ANOVA). Pretreatment of strips with 10(-7) m CRH did not attenuate relaxation induced by subsequent CRH (n = 3) or salbutamol (beta(2)-agonist) treatment (n = 9). PDE inhibition by rolipram showed a 2.2- and 1.5-fold increase in maximal relaxation induced by CRH and salbutamol, respectively, with a shift of both dose-response curves (P < 0.05 and P < 0.01, ANOVA). In conclusion, CRH at physiological concentrations acts synergistically with P4 contributing to myometrial quiescence. P4 withdrawal may reduce CRH-mediated relaxation. Our functional model does not support homologous or heterologous down-regulation of agonist-stimulated-cAMP pathways by high CRH concentrations. PDE inhibition potentiates CRH and salbutamol-induced relaxation. Up-regulation of PDEs, through chronic cAMP elevation by CRH, could provide a mechanism for down-regulation of agonist-stimulated-cAMP pathways at term.

Cyclic adenosine monophosphate (cAMP)-specific phosphodiesterase is functional in bovine mammary gland

Previous studies have shown that using nonspecific phosphodiesterase (PDE) inhibitors such as caffeine improved milk production, supporting the premise that modulation of intracellular concentration of cyclic nucleotides (cyclic AMP, cyclic guanosine 3'-5'-monophosphate) is involved. Intracellular cyclic nucleotides are degraded by the PDE enzyme family. The contribution of type IV PDE (PDE4) in the secretion of casein has been reported in rat mammary gland. The objective of this study was to demonstrate the functional presence of the PDE4 family in the bovine mammary gland. To understand the enzymatic expression pattern in the mammary gland, tissue samples were taken randomly from udders obtained from a local slaughterhouse. Reverse transcription PCR revealed that the PDE4D transcript was amplified, and the expected size fragment was obtained in a 1% agarose gel. Sequence analysis of the amplicon resulted in 99% homology to PDE4D. Moreover, Western blotting using a specific PDE4D antibody has confirmed that the protein of the isoenzyme PDE4D1 is present. A clear immunoreactive signal was also observed within the acini where epithelial cells are located. Assaying cyclic AMP PDE activity reported a total activity of 38.71 +/- 3.22 fmol/min per microg of total protein. Rolipram, a specific PDE4 inhibitor, showed a sensitive activity of 8.48 +/- 1.28 fmol/min per microg of total protein, indicating that PDE4 is responsible for one-fifth of the total enzymatic activity of PDE in the mammary gland. To further validate the presence of PDE4D in the bovine mammary epithelial cells, protein extracts from bovine mammary epithelial cells were separated on SDS-PAGE gels, and PDE4D protein was detected. The PDE assays reported a total activity of 30.16 +/- 4.82 fmol/min per microg of total protein. Rolipram showed a sensible activity of 11.91 +/- 5.93 fmol/min per microg of total protein. In conclusion, these results not only demonstrate the presence of PDE4D transcript and protein, but also show an active enzyme, suggesting a functional role of PDE4D in bovine mammary gland.

Utero-relaxant effect of PDE4-selective inhibitor alone and in simultaneous administration with beta2-mimetic on oxytocin-induced contractions in pregnant myometrium

BACKGROUND

The objective of the study was to observe the effect of rolipram, the prototype phosphodiesterase 4 selective inhibitor, on oxytocin-induced contractions of human term myometrial strips, and compare the effect with salbutamol, beta(2)-adrenergic agonist, in single and the simultaneous application.

METHODS

Human myometrium was obtained from pregnant women in term that had a term delivery by the caesarian section. Myometrial strips were excised from the lower uterine segment and placed into an organ-bath with Krebs-Henseleit buffer. The mean peak amplitude of contraction (mN) of the myometrial smooth muscle to the doses of oxytocin (10(-6) mmol/L(-1)) with subsequent single administration of rolipram (10(-4) mmol/L(-1)), salbutamol (10(-4) mmol/L(1)) and simultaneous administration of rolipram and salbutamol (both 10(-4) mmol/L(-1)), was used as a parameter of myometrial reactivity.

RESULTS

Rolipram alone decreased the oxytocin-induced contractile amplitude to 47.98%, single salbutamol application resulted in amplitudinal decrease to 56.07%, and the combination of both compounds in their simultaneous administration resulted in the decrease of oxytocin-induced contractile amplitude to 29.1%.

CONCLUSION

Our data are consistent with previous studies of the enhanced efficiency of the beta(2)-adrenergic agonist, when administered together with the phosphodiesterase 4-inhibitor. Moreover we have shown that rolipram alone has a more profound effect on oxytocin-induced contractions than salbutamol alone.

Relaxin signalling in primary cultures of human myometrial cells

In myometrium of pigs and rats, though not humans, relaxin appears to mediate an inhibition of spontaneous and oxytocin-induced contractility, presumably acting through a G-protein coupled receptor (RXFP1) to generate cAMP. In humans, circulating relaxin is highest in the first trimester, including the time of implantation, when transitory uterine quiescence could help a blastocyst to implant. We investigated whether relaxin can activate adenylate cyclase in primary human myometrial cells from non-pregnant tissue, and we show that relaxin is able to stimulate the generation of cAMP in a manner, which is dependent upon a tyrosine phosphorylation activity, as in the endometrium. We identified transcripts for the relaxin receptor RXFP1 as full-length variants, though a minor splice variant missing exon 2 was also present in low amounts. These cells also express transcripts encoding RXFP2, the receptor for the closely related hormone, INSL3. Although able to respond to relaxin at high concentrations, this receptor does not appear to function by contributing to the cAMP production in human myometrial cells, nor does INSL3 act as a functional agonist or antagonist of relaxin action. In conclusion, the inability of relaxin to inhibit contractility in human myometrial cells would appear to be due to events downstream of simple cAMP generation.

Short-term or long-term treatments with a phosphodiesterase-4 (PDE4) inhibitor result in opposing agonist-induced Ca(2+) responses in endothelial cells

BACKGROUND AND PURPOSE

We previously reported that agonist-induced rises in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) in human umbilical vein endothelial cells (HUVEC) were inhibited after a short-term (2 min) pre-treatment with cAMP-elevating agents. The aim of this work was to study the effects of longer term (8 h) pre-treatment with dibutyryl-cAMP (db-cAMP) or rolipram, a specific inhibitor of phosphodiesterase-4 (PDE4), on [Ca(2+)](i), cAMP levels and PDE activity and expression in HUVEC.

EXPERIMENTAL APPROACH

[Ca(2+)](i) changes were measured in isolated HUVEC by Fura-2 imaging. Intracellular cAMP levels and PDE4 activity were assessed by enzyme-immunoassay and radio-enzymatic assay, respectively. PDE expression was measured by northern and western blot analysis.

KEY RESULTS

Long-term pre-treatment of HUVEC with rolipram or db-cAMP significantly increased ATP-, histamine- and thrombin-induced [Ca(2+)](i) rises. Short-term pre-treatment with rolipram was associated with an increase in cAMP, whereas long-term pre-treatment was associated with a decrease in cAMP. Long-term pre-treatment with rolipram or db-cAMP induced a significant increase in PDE4 activity and the expression of 74 kDa-PDE4A and 73 kDa-PDE4B was specifically enhanced. All these effects were suppressed by cycloheximide.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that sustained inhibition of PDE4 by rolipram induced an increase in PDE4 activity, possibly as a compensatory mechanism to accelerate cAMP degradation and that PDE4A and PDE4B were implicated in the regulation of [Ca(2+)](i). Thus, isozyme-specific PDE4 inhibitors might be useful as therapeutic agents in diseases where [Ca(2+)](i) handling is altered, such as atherosclerosis, hypertension and tolerance to beta-adrenoceptor agonists.

Expression of messenger ribonucleic acid encoding for phosphodiesterase isoenzymes in human female genital tissues

OBJECTIVES

The use of inhibitors of phosphodiesterase 5 (PDE5) has been suggested to treat symptoms of female sexual dysfunction (FSD). Nonetheless, there has been a relatively low success rate of PDE5 inhibitors in FSD in comparison with male erectile dysfunction. The elevated expression of PDE5 in the human penile erectile tissue is considered the reason for the high clinical efficacy of PDE5 inhibitors in the pharmacotherapy of male erectile dysfunction.

AIM

To evaluate by means of molecular biology the expression of messenger ribonucleic acid expression (mRNA) encoding for cyclic AMP and cyclic GMP PDE isoenzymes in female genital tissues.

MAIN OUTCOME MEASURES

The amount of mRNA transcripts specifically encoding for cyclic AMP- and/or cyclic GMP-degrading PDE isoenzymes was determined.

METHODS

Human clitoral, labial, and vaginal tissue was obtained from four female cadavers (age at death: 18-42 years). The expression of mRNA specifically encoding for PDE1A, 1B, 1C, 2A, 4A, 5A, 10A, and 11A was elucidated by means of real-time polymerase chain reaction (PCR) analysis (TaqMan). Human penile erectile tissue (corpus cavernosum [HCC]) was used as a reference tissue.

RESULTS

mRNA encoding for all PDE isoforms mentioned above is expressed in the female genital tissues. Different magnitudes of mRNA expression were observed: a predominant expression of mRNA encoding for PDE1A but only insignificant amounts of PDE1B, 1C, 4A, 10, and 11A mRNA were registered. With PDE1A being the only exception, the mRNA expression was always higher in the HCC than in the female genital tissues. Especially, the expression of mRNA encoding for PDE5 was several-fold higher in the HCC.

CONCLUSION

On the mRNA level, various PDE isoforms are expressed in the clitoris, labia, and vagina. It remains to be established as to whether the low expression of PDE5 in female genital tissue might be a negative predictor for the success of PDE5 inhibitors in the treatment of FSD.

PDE4 as a target in preterm labour

Cyclic nucleotide phosphodiesterases (PDE) are the enzymes catalyzing the hydrolysis and inactivation of the second messengers, cAMP and cGMP. Eleven PDE families are described to date, and selective inhibitors of some PDEs families are currently used in clinic for treating cardiovascular disorders, erectile dysfunction, and pulmonary hypertension. Isoforms of the PDE4 family are involved in smooth muscle contraction and inflammation. PDE4 selective inhibitors are currently in clinical trials for the treatment of diseases related to inflammatory disorders. Because of their myorelaxant properties, we first examined their expression in human myometrium and uncover an increased expression of one specific isoform, PDE4B2, in the near-term myometrium as compared to myometrium in the nonpregnant state. Using human myometrial cells in culture, we demonstrated that PDE4B2 can be induced by its own substrate, under the control of one of the major utero-contractile agonists, PGE2, itself upregulated by the proinflammatory cytokine IL-1beta. Functionally, augmentation of global PDE4 activity decreases the ability of beta-adrenergic agonists (the most commonly used tocolytic drugs) to inhibit myometrial contraction at the end of pregnancy and during pathophysiological situations, such as persistent intrauterine inflammation which is a major cause of very preterm delivery. Currently exploring the anti-inflammatory properties of PDE4 inhibitors in gestational tissues, we recently demonstrated the ability of these drugs to block a persistent inflammatory response of the foetal membranes in Humans and to prevent inflammation-driven preterm delivery and foetal demise in mice. These data open up a new therapeutical strategy to prevent inflammation-induced preterm delivery and its sequelae in very preterm infants.

Regulation of phosphodiesterase 5 expression and activity in human pregnant and non-pregnant myometrial cells by human chorionic gonadotropin

OBJECTIVES

This study has a twofold aim: 1) to investigate whether protein expression and enzyme activity of phosphodiesterase 5 (PDE5) can be detected in human myometrium and undergo changes in relation to the presence of pregnancy and/or labor; 2) to evaluate whether PDE5 expression and activity in myometrial cells can be influenced by human chorionic gonadotropin (HCG).

METHODS

Primary cultures of myometrial cells, obtained from non-pregnant women and from pregnant women at term, either before or during labor, were carried out in the presence of HCG or dibutyryl-cyclic AMP (db-cAMP), the non-hydrolizable analogue of cAMP. PDE5 expression in cultures of myometrial cells was detected by immunocytochemistry and western blot. PDE5 activity was detected in cell extracts by enzyme assay.

RESULTS

PDE5 is expressed and is functionally active in smooth muscle cells. Treatment of cell cultures with HCG and db-cAMP results in a reduction of PDE5 expression and activity. The effects of HCG and db-cAMP are exerted irrespective of the functional status of the myometrium (non-pregnant, pregnant not in labor, pregnant in labor).

CONCLUSIONS

PDE5 protein is expressed in human non-pregnant and pregnant myometrium. HCG reduces PDE5 expression and enzyme activity in smooth muscle cells, possibly through a pathway involving cAMP.

Hypoxia-induced remodelling of PDE4 isoform expression and cAMP handling in human pulmonary artery smooth muscle cells

Human pulmonary artery smooth muscle cells (hPASM cells) express PDE4A10, PDE4A11, PDE4B2, PDE4C and PDE4D5 isoforms. Hypoxia causes a transient up-regulation of PDE4B2 that reaches a maximum after 7 days and sustained up-regulation of PDE4A10/11 and PDE4D5 over 14 days in hypoxia. Seven days in hypoxia increases both intracellular cAMP levels, protein kinase A (PKA) activity and activated, phosphorylated extracellular signal regulated kinase (pERK) but does not alter either PKA isoform expression or total cAMP phosphodiesterase-4 (PDE4) activity or cAMP phosphodiesterase-3 (PDE3) activity. Both the cyclooxygenase inhibitor, indomethacin and the ERK inhibitors, UO126 and PD980589 reverse the hypoxia-induced increase in intracellular cAMP levels back to those seen in normoxic hPASM cells. Challenge of normoxic hPASM cells with prostaglandin E(2) (PGE(2)) elevates cAMP to levels comparable to those seen in hypoxic cells but fails to increase intracellular cAMP levels in hypoxic hPASM cells. The adenylyl cyclase activator, forskolin increases cAMP levels in both normoxic and hypoxic hPASM cells to comparable elevated levels. Challenge of hypoxic hPASM cells with indomethacin attenuates total PDE4 activity whilst challenge with UO126 increases total PDE4 activity. We propose that the hypoxia-induced activation of ERK initiates a phospholipase A(2)/COX-driven autocrine effect whereupon PGE(2) is generated, causing the activation of adenylyl cyclase and increase in intracellular cAMP. Despite the hypoxia-induced increases in the expression of PDE4A10/11, PDE4B2 and PDE4D5 and activation of certain of these long PDE4 isoforms through PKA phosphorylation, we suggest that the failure to see any overall increase in PDE4 activity is due to ERK-mediated phosphorylation and inhibition of particular PDE4 long isoforms. Such hypoxia-induced increase in expression of PDE4 isoforms known to interact with certain signalling scaffold proteins may result in alterations in compartmentalised cAMP signalling. The hypoxia-induced increase in cAMP may represent a compensatory protective mechanism against hypoxia-induced mitogens such as endothelin-1 and serotonin.

Stimulation of the ADRB3 adrenergic receptor induces relaxation of human placental arteries: influence of preeclampsia

Preeclampsia, which complicates 3-8% of pregnancies, is one of the leading causes of neonatal morbidity and mortality. Its pathophysiology remains unclear. The aim of the present study was to investigate the presence and the role of beta2- and beta2-adrenergic receptors (ADRB2 and ADRB3, respectively) in human placental arteries and to assess the influence of preeclampsia on ADRB responsiveness. SR 59119A, salbutamol, and isoproterenol (ADRB3, ADRB2, and nonselective ADRB agonists, respectively) induced a concentration-dependent relaxation of placental artery rings obtained from women with uncomplicated or preeclamptic pregnancies. SR 59119A-induced relaxation was unaffected by the blockade of ADRB1 and ADRB2 by 0.1 microM propranolol but was significantly decreased by the blockade of ADRB1, ADRB2, and ADRB3 by 10 microM propranolol. Both SR 59119A and salbutamol were associated with a significant increase in cAMP production that was significantly inhibited by pretreatment with 0.1 microM propranolol only for salbutamol. SR 59119A-induced relaxation (E(max) = 28% +/- 5% vs. 45% +/- 4%, respectively) and cAMP production (2.7 +/- 0.5 vs. 4.9 +/- 0.4 pmol/mg of protein, respectively; P < 0.01) were decreased in arteries obtained from preeclamptic compared to normotensive women. Both ADRB2 and ADRB3 transcripts were expressed at the same level between arteries from normotensive and preeclamptic women. Western blot analysis, however, revealed a decreased expression of the ADRB3 immunoreactive protein in arteries from preeclamptic compared to normotensive women. We suggest the presence of functional ADRB2 and ADRB3 in human placental arteries. Even if preeclampsia is associated with an impairment of the ADRB3 responsiveness, ADRB3 agonists may have future pharmaceutical implications in the management of pregnancy-related disorders.

Phosphodiesterase 4B (PDE4B) and cAMP-level regulation within different tissue fractions of rat hippocampal slices during long-term potentiation in vitro

Molecular events associated with mnemonic processes and neuronal plasticity are postulated to result in functional changes in synaptic structure. One possible site is the post-synaptic density, where activity-dependent changes modulate signal transduction cascades. In this report, we detail spatial-temporal changes for phosphodiesterase 4B (PDE4B) proteins and their substrate cAMP within three neuronal fractions during early and late long-term potentiation (LTP). The cAMP-dependent protein kinase A cascade--which can be regulated by distinct PDE4B activity--is required for mnemonic processes as well as mechanisms of neuronal plasticity, such as those during the maintenance or late-LTP. Fluorescence in situ hybridization studies (FISH) identified no translocation of PDE4B3 from the soma after late-LTP induction indicating a subtle, local control of PDE4B activity. Protein changes were detected within the PSD-enriched fraction. From these results, we conclude that either the changes in PDE4B are due to modulation of pre-existing mRNA, or that the protein is specifically translocated to activated synaptic structures. Furthermore, we report late changes in cAMP levels in the somato-dendritic fraction and discuss this result with the increased PDE4B1/3 doublet in the PSD-enriched fraction.

Relaxin and phosphodiesterases collaborate during decidualization

During the evolution of mammals, the endometrium has developed for one reason only: to implant an embryo in the uterus. In higher primates, should an oocyte fail to be fertilized, then the endometrial layer is sloughed off during menses and the menstrual cycle starts again with a new round of endometrial differentiation. This stromal differentiation process is called decidualization and is accompanied in vivo by sustained high levels of intracellular cAMP. The present study was conducted to determine whether manipulation of cAMP-phosphodiesterase (PDE) activities in cultured human endometrial stromal cells could positively influence the decidualization process. The combination of relaxin treatment with inhibition of PDE4 by the specific inhibitor rolipram induced a strong increase in relaxin-mediated cAMP production, both acutely, after 20 min, and after long-term treatment for 3 days, to promote a sustained intracellular cAMP concentration. Moreover, there was a dramatic synergistic effect on the decidualization phenotype, characterized both morphologically and by increased production of prolactin and insulin-like growth factor binding protein-1 gene transcripts. The observations that expression of PDE4D transcripts were selectively increased by cAMP and that inhibition of protein kinase A by H89 to potentially block negative feedback regulation enhanced the relaxin/rolipram-mediated cAMP accumulation lead to a complex picture of cAMP regulation in these cells. There appears to be a coordinated contribution by relaxin and PDE4 at different levels to promote a sustained increased cAMP concentration during decidualization, and thus to provide an adequate maternal interface for the implanting blastocyst.

Activation and induction of cyclic AMP phosphodiesterase (PDE4) in rat pulmonary microvascular endothelial cells

Regulation of the rolipram-sensitive cAMP-specific phosphodiesterase 4 (PDE4) gene family was studied in rat pulmonary microvascular endothelial cells (RPMVECs). Total PDE4 hydrolysis was increased within 10 min after addition of forskolin (10 microM), reached a maximum at 20-40 min, and then gradually declined in the cells. A similar activation of PDE4 activity was observed using a protein kinase A (PKA) activator, N(6)-monobutyryl cAMP. Both the forskolin and the N(6)-monobutyryl cAMP activated PDE4 activities were blocked by the PKA-specific inhibitor, H89. This forskolin-stimulated and PKA-mediated short-term activation of PDE4 activity was further confirmed by in vitro phosphorylation of 87kDa PDE4A6 and 83kDa PDE4B3 polypeptides using exogenous PKA Calpha. Increased immunoreactivity of phosphorylated PDE4A6 in situ was detected in Western blots by a PDE4A-phospho antibody specific to the putative PKA phosphorylation sites. Following long-term treatment of RPMVECs with rolipram and forskolin medium (RFM) for more than 60 days, PDE4 activity reached ten-fold higher values than control RPMVECS with twenty-fold increases detected in intracellular cAMP content. The RFM cells showed increased immunoreactivities of the constitutive 4A6 and 4B3 isoforms plus two novel splice variants at 101kDa (4B1) and 71kDa (4B2). Treatment with H89 did not inhibit the PDE4 elevation in RFM cells. In addition to the increased levels of PDE4 in RFM cells, immunofluorescence showed a translocation of PDE4A and 4B to a nuclear region, which was normally not observed in RPMVECs. The PDE4 activity in RFM cells decayed rapidly with an even faster decline of intracellular cAMP content when forskolin/rolipram were removed from the medium. These results suggest that both the activation (short-term) and induction (long-term) of PDE4A/4B isoforms in RPMVECs are closely modulated by the intracellular cAMP content via both post-translational and synthetic mechanisms.

The human near-term myometrial beta 3-adrenoceptor but not the beta 2-adrenoceptor is resistant to desensitisation after sustained agonist stimulation

1. In order to compare the beta(2)- and beta(3)-adrenoceptor (beta-AR) desensitisation process in human near-term myometrium, we examined the influence of a pretreatment of myometrial strips with either a beta(2)- or a beta(3)-AR agonist (salbutamol or SR 59119A, respectively, both at 10 microm, for 5 and 15 h) on the relaxation and the cyclic adenosine monophosphate (cAMP) production induced by these agonists. 2. To assess some of the mechanisms potentially implicated in the beta-AR desensitisation process, we studied the influence of such treatment on the number of beta(2)- and beta(3)-AR binding sites, the beta(2)- and beta(3)-AR transcripts expression and the phosphodiesterase 4 (PDE4) activity. 3. Salbutamol, but not SR 59119A, concentration-response curve (CRC) was shifted by a 15 h salbutamol preincubation, with a significant difference in -log EC(20) values (6.31+/-0.13 vs 5.58+/-0.24, for control and 15 h salbutamol pretreatment, respectively, P<0.05). Neither salbutamol nor SR 59119A CRCs were modified after a 15 h preincubation with SR 59119A. 4. A 15 h exposure of myometrial strips to salbutamol significantly reduced the salbutamol-induced (0.60+/-0.26 vs 1.54+/-0.24 pmol mg(-1) protein, P<0.05), but not the SR 59119A-induced, cAMP production. No decrease in cAMP production was observed after a 15 h SR 59119A exposure. 5. A 15 h salbutamol exposure of myometrial strips significantly reduced the beta(2)- but not the beta(3)-AR binding site density, whereas no decrease in the number of beta(2)- and beta(3)-AR binding sites was observed after a 15 h SR 59119A treatment. 6. Neither PDE4 activity nor the beta(2)- and beta(3)-AR mRNA expression levels were affected by salbutamol or SR 59119A treatments. 7. Our results indicate that beta(3)-AR, but not beta(2)-AR, are resistant to the agonist-induced desensitisation. In our model, beta(2)-AR desensitisation is mediated by a decreased number of beta(2)-AR that was not explained by transcriptional regulation of the receptor.

Anti-inflammatory and utero-relaxant effects in human myometrium of new generation phosphodiesterase 4 inhibitors

The anti-inflammatory and utero-relaxant effects of two potent phosphodiesterase 4 (PDE4) inhibitors of the latest generation: cilomilast (one of the most advanced PDE4 inhibitors in clinical development, reportedly more selective for PDE4D) and compound A (which displays 12-fold greater selectivity toward PDE4B and/or PDE4A than toward PDE4D) were evaluated in human uterine smooth muscle. We first established that these compounds exhibit greater efficacy in inhibiting total cAMP-PDE activity in pregnant versus nonpregnant myometrium (E(max) = 78.0% +/- 3.6% and 80.3% +/- 2.2% in pregnant versus 57% +/- 4.7% and 70.5% +/- 5.9% in nonpregnant women for compound A and cilomilast, respectively; P < 0.05 for both compounds), confirming the prominent participation of PDE4 isoforms in cAMP hydrolysis in the near-term pregnant myometrium. Using pregnant myometrial explants, we have shown that both these drugs and also rolipram, the prototype PDE4 inhibitor, produce concentration-dependent inhibition of lipopolysaccharide (LPS) induced tumor necrosis factor alpha (TNFalpha) release with similar potency in each case (pD2 = 8.0 +/- 0.5, 7.9 +/- 0.2, and 7.6 +/- 0.2 for compound A, cilomilast, and rolipram, respectively). The maximum inhibition produced is 65%. Pretreatment with forskolin or 8-bromo-cAMP mimics the PDE4 inhibitor effect. Furthermore, compound A and cilomilast both produce concentration-dependent inhibition of the spontaneous contractions of myometrial strips and are more potent in pregnant than in nonpregnant myometrium (pD2 = 7.3 +/- 0.7 and 8.1 +/- 0.3 in pregnant versus 6.2 +/- 0.9 and 6.6 +/- 0.1 in nonpregnant myometrium for compound A and cilomilast, respectively; P < 0.05 for both compounds). This demonstrates that the PDE4 isoforms involved in the mechanism of contraction are different in the pregnant and nonpregnant myometrium. Our study highlights the importance of developing PDE4 inhibitors for the pharmacological management of infection-induced preterm labor.

Cyclic AMP-dependent transcriptional up-regulation of phosphodiesterase 4D5 in human airway smooth muscle cells. Identification and characterization of a novel PDE4D5 promoter

Phosphodiesterase 4D (PDE4D), part of the complex cAMP-specific PDE4 family, plays a pivotal role in the regulation of airway smooth muscle relaxation by catalyzing the hydolysis of cAMP. Its gene on chromosome 5q12 encodes 5 splice variants, which show tissue-dependent expression and regulation. The genomic arrangement of PDE4D was determined using in silico methods, and a putative promoter of one of the protein kinase A-activated, long isoforms, PDE4D5 was identified. Promoter-luciferase constructs, transiently transfected into a beta(2) adrenoreceptor-expressing CHO-K1 cell line, were used to demonstrate that the PDE4D5 promoter up-regulated reporter gene expression in response to increased cell cAMP. Site-directed mutagenesis of the cAMP-response element (CRE) at position -201 identified this as the principal component of the mechanism underlying this cAMP responsiveness. In the second part of this study, cAMP-dependent induction of PDE4D5 transcript in primary cultured human airway smooth muscle cells (hASMs) was demonstrated using both qualitative reverse-transcriptase PCR and quantitative real-time PCR. Isolated PDE4D5 isoenzyme activity, measured after selective immunoprecipitation from hASMs, confirmed that this increase in expression led to an up-regulation of functional activity. We present evidence for cAMP-driven PDE4D5 up-regulation in hASMs and suggest a CRE-containing, isoform-specific promoter as the primary mechanism.

Phosphodiesterase isoenzyme families in human osteoarthritis chondrocytes--functional importance of phosphodiesterase 4

We studied whether selective inhibitors of cyclic nucleotide hydrolysing phosphodiesterase (PDE) isoenzymes influence IL-1beta-induced nitric oxide (NO) release from human articular chondrocytes. In addition, the pattern of PDE isoenzymes contributing to cyclic nucleotide hydrolysis in human chondrocytes was characterized. Chondrocytes were isolated from human osteoarthritic cartilage and cultured in alginate beads. IL-1beta-induced chondrocyte products (nitric oxide and prostaglandin E(2)) were measured in culture supernatants after 48 h incubation time. PDE activities were assessed in chondrocyte lysates. Inducible nitric oxide synthase (iNOS) and PDE4A-D proteins were detected by immunoblotting. The selective PDE4 inhibitors Piclamilast and Roflumilast partially attenuated IL-1beta-induced NO production whereas selective inhibitors of PDE2 (EHNA), PDE3 (Motapizone) or PDE5 (Sildenafil) were inactive. Indomethacin reversed the reduction of IL-1beta-induced NO by PDE4 inhibitors. It was shown that autocrine prostaglandin E(2) (PGE(2)) enabled PDE4 inhibitors to reduce IL-1beta-induced NO in this experimental setting. Major PDE4 and PDE1 activities were identified in chondrocyte lysates whereas only minor activities of PDE2, 3 and 5 were found. IL-1beta and cyclic AMP-mimetics upregulated PDE4 activity and this was associated with an augmentation of PDE4B2 protein. Based on the view that nitric oxide contributes to cartilage degradation in osteoarthritis our study suggests that PDE4 inhibitors may have chondroprotective effects.

Involvement of phosphodiesterase isozymes in osteoblastic differentiation

The cyclic monophosphate nucleotides (cyclic adenosine monophosphate [cAMP] and cyclic guanosine monophosphate [cGMP]) are found ubiquitously in mammalian cells and act as second messenger transducers to effect the intracellular actions of a variety of hormones, cytokines, and neurotransmitters. In turn, these nucleotides also modulate the signal transduction processes regulated by a range of cytokines and growth factors. Previously, we have reported that pentoxifylline, a nonselective phosphodiesterase (PDE) inhibitor, can promote osteoblastic differentiation by elevating intracellular cAMP levels and, consequently, enhance bone formation in vivo and in vitro. In this study, reverse-transcription polymerase chain reaction (RT-PCR) analysis of the osteoblastic cell lines, MC3T3-E1 and ST2 revealed the presence of PDE1, PDE2, PDE3, PDE4, PDE7, PDE8, and PDE9. We examined the effect of selective inhibitors for a respective PDE isozyme on the capacity of bone morphogenetic protein 4 (BMP-4)-induced alkaline phosphatase (ALP) activity, a cellular differentiation marker, in cells with osteogenetic potential. The results indicate that selective inhibitors for PDE2, PDE3, and PDE4 enhanced the BMP-4-induced ALP activity in a dose-dependent manner in ST2 cells but not in MC3T3-E1 cells. Northern blot analysis also revealed that the selective inhibitors for PDE2, PDE3, and PDE4 enhanced the levels of expression of messenger RNAs (mRNAs) of ALP, osteopontin (OP), and collagen type I in ST2 cells but not in MC3T3-E1 cells except for the treatment with PDE4 inhibitor. Given these data, we conclude that PDE isozymes are involved in the modulation of osteoblastic differentiation mainly at an early stage. Additionally, selective inhibitors for PDE2, PDE3, and PDE4 appear to promote the differentiation of osteogenic precursor cells toward an osteoblastic phenotype.

Expression of phosphodiesterase 4D (PDE4D) is regulated by both the cyclic AMP-dependent protein kinase and mitogen-activated protein kinase signaling pathways. A potential mechanism allowing for the coordinated regulation of PDE4D activity and expression in cells

Multiple families of cyclic nucleotide phosphodiesterases (PDE) have been described, and the regulated expression of these genes in cells is complex. Although cAMP is known to control the expression of certain PDE in cells, presumably reflecting a system of feedback on cAMP signaling, relatively little is known about the influence of non-cAMP signaling systems on PDE expression. In this study, we describe a novel mechanism by which activators of the protein kinase C (PKC)-Raf-MEK-ERK cascade regulate phosphodiesterase 4D (PDE4D) expression in vascular smooth muscle cells (VSMC) and assess the functional consequences of this effect. Whereas a prolonged elevation of cAMP in VSMC resulted in a protein kinase A (PKA)-dependent induction of expression of two PDE4D variants (PDE4D1 and PDE4D2), simultaneous activation of both the cAMP-PKA and PKC-Raf-MEK-ERK signaling cascades blunted this cAMP-mediated increase in PDE4D expression. By using biochemical, molecular biological, and pharmacological approaches, we demonstrate that this PDE4D-selective effect of activators of the PKC-Raf-MEK-ERK cascade was mediated through a mechanism involving altered PDE4D mRNA stability and markedly attenuated the cAMP-mediated desensitization that results from prolonged activation of the cAMP signaling system in cells. The data are presented in the context of activators of the PKC-Raf-MEK-ERK cascade having both short and long term effects on PDE4D activity and expression in cells that may influence cAMP signaling.