Phosphodiesterase types 3 and 4 regulate the phasic contraction of neonatal rat bladder smooth myocytes via distinct mechanisms

Combination phosphodiesterase type 4 inhibitor and phosphodiesterase type 5 inhibitor treatment reduces non-voiding contraction in a rat model of overactive bladder

Introduction

Current treatments for overactive bladder (OAB) are often discontinued due to side effects or lack of efficacy. The goal of this study was to determine if combining a phosphodiesterase type 4 inhibitor (PDE4i); with a type 5 inhibitor (PDE5i); would have a beneficial effect on OAB symptoms and if a reduced dose of PDE4i in combination with PDE5i could also provide a beneficial effect in OAB. We hypothesized that PDE5i and PDE4i combination treatment could be utilized to reduce non-voiding contractions and smooth muscle disruption in a rat model of OAB.

Methods

Fifty-eight age-matched Sprague-Dawley rats underwent PBOO and daily gavage with PDE4i alone (roflumilast; 1mg/kg), PDE5i alone (tadalafil;10mg/kg), high dose combination (PDE4i 1mg/kg, PDE5i 10mg/kg), low dose combination (PDE4i 0.2mg/kg, PDE5i 10mg/kg), or vehicle for 28 days. Fourteen animals underwent sham PBOO with vehicle. Rats underwent conscious and anesthetized cystometry 28 days after PBOO and were euthanized for qualitative bladder histology. One-way ANOVA on ranks with a Dunn’s post hoc test was used to indicate statistically significant differences between groups (p<0.05).

Results

Bladder & urethral weight was significantly increased after PBOO with vehicle, PDE4i alone, and PDE5i alone, but not with either combination treatment. Frequency of non-voiding contractions during both conscious and anesthetized cystometry increased significantly after PBOO with vehicle, but not after PDE4i or high dose combination treatments compared to sham PBOO. Threshold pressure for voiding was significantly decreased with high dose combination compared to vehicle. PBOO treated with PDE4i alone or high dose combination showed less bladder smooth muscle fibrosis than vehicle, PDE5i alone, or low dose combination treatments.

Conclusion

A PDE4i and PDE5i combination treatment has potential benefit in reducing OAB symptoms, but future research is needed.

Contribution of BKCa channels to vascular tone regulation by PDE3 and PDE4 is lost in heart failure

Aims

Regulation of vascular tone by 3′,5′-cyclic adenosine monophosphate (cAMP) involves many effectors including the large conductance, Ca2+-activated, K+ (BKCa) channels. In arteries, cAMP is mainly hydrolyzed by type 3 and 4 phosphodiesterases (PDE3, PDE4). Here, we examined the specific contribution of BKCa channels to tone regulation by these PDEs in rat coronary arteries, and how this is altered in heart failure (HF).

Methods and results

Concomitant application of PDE3 (cilostamide) and PDE4 (Ro-20-1724) inhibitors increased BKCa unitary channel activity in isolated myocytes from rat coronary arteries. Myography was conducted in isolated, U46619-contracted coronary arteries. Cilostamide (Cil) or Ro-20-1724 induced a vasorelaxation that was greatly reduced by iberiotoxin (IBTX), a BKCa channel blocker. Ro-20-1724 and Cil potentiated the relaxation induced by the β-adrenergic agonist isoprenaline (ISO) or the adenylyl cyclase activator L-858051 (L85). IBTX abolished the effect of PDE inhibitors on ISO but did not on L85. In coronary arteries from rats with HF induced by aortic stenosis, contractility and response to acetylcholine were dramatically reduced compared with arteries from sham rats, but relaxation to PDE inhibitors was retained. Interestingly, however, IBTX had no effect on Ro-20-1724- and Cil-induced vasorelaxations in HF. Expression of the BKCa channel α-subunit, of a 98 kDa PDE3A and of a 80 kDa PDE4D were lower in HF compared with sham coronary arteries, while that of a 70 kDa PDE4B was increased. Proximity ligation assays demonstrated that PDE3 and PDE4 were localized in the vicinity of the channel.

Conclusion

BKCa channels mediate the relaxation of coronary artery induced by PDE3 and PDE4 inhibition. This is achieved by co-localization of both PDEs with BKCa channels, enabling tight control of cAMP available for channel opening. Contribution of the channel is prominent at rest and on β-adrenergic stimulation. This coupling is lost in HF.

Activation of bitter taste receptors (tas2rs) relaxes detrusor smooth muscle and suppresses overactive bladder symptoms

Bitter taste receptors (TAS2Rs) are traditionally thought to be expressed exclusively on the taste buds of the tongue. However, accumulating evidence has indicated that this receptor family performs non-gustatory functions outside the mouth in addition to taste. Here, we examined the role of TAS2Rs in human and mouse detrusor smooth muscle (DSM). We showed that mRNA for various TAS2R subtypes was expressed in both human and mouse detrusor smooth muscle (DSM) at distinct levels. Chloroquine (CLQ), an agonist for TAS2Rs, concentration-dependently relaxed carbachol- and KCl-induced contractions of human DSM strips. Moreover, 100 μM of CLQ significantly inhibited spontaneous and electrical field stimulation (EFS)-induced contractions of human DSM strips. After a slight contraction, CLQ (1 mM) entirely relaxed carbachol-induced contraction of mouse DSM strips. Furthermore, denatonium and quinine concentration-dependently decreased carbachol-induced contractions of mouse DSM strips. Finally, we demonstrated that CLQ treatment significantly suppressed the overactive bladder (OAB) symptoms of mice with partial bladder outlet obstruction (PBOO). In conclusion, we for the first time provide evidence of the existence of TAS2Rs in the urinary DSM and demonstrate that TAS2Rs may represent a potential target for OAB. These findings open a new approach to develop drugs for OAB in the future.

Expression and function of phosphodiesterases (PDEs) in the rat urinary bladder

Background

It has been shown that hosphodiesterases (PDEs) play an important role in mediating the smooth muscle tone of rat urinary bladder. However, the gene expression profiles of them were still unknown.

Methods

Urinary bladder Strips were obtained from both neonatal and adult Sprague-Dawley rats. RT-PCR/western blot and organ bath were used to measure the expression and function of PDEs.

Results

Adult rat urinary bladder expressed various PDE mRNA with the following rank order: PDE5A ≈ PDE9A ≈ PDE10A > PDE2A ≈ PDE4A ≈ PDE4D > PDE4B ≈ PDE3B ≈ PDE8B ≈ PDE7A ≈ PDE7B > PDE1A. PDE1B, PDE1C, PDE3A, PDE4C, PDE8A, and PDE11A were not detected. Of interest, the mRNA and protein of PDE3A were significantly decreased in adult rat urinary bladder compared to neonatal rat urinary bladder. Cilostamide, a specific inhibitor for PDE3, significantly inhibited the amplitude and frequency of carbachol-enhanced phasic contractions of neonatal rat bladder strips by 38.8% and 12.1%, respectively. Compared to the neonatal rat bladder, the effect of cilostamide was significantly blunted in adult rat urinary bladder: the amplitude and frequency of carbachol-enhanced phasic contractions were decreased by 13.4% (P < 0.01 vs neonatal rat bladder) and 4.4%, respectively. However, the mRNA and the protein levels of PDE3B were similar between neonatal and adult rat bladder.

Conclusion

We found that several PDE isoforms were expressed in the rat urinary bladder with distinct levels. Moreover, we showed that the function of PDE3 was blunted in adult rat bladder likely due to the decreased expression of PDE3A.

The Involvement of Ca(2+) Signal Pathways in Distal Colonic Myocytes in a Rat Model of Dextran Sulfate Sodium-induced Colitis

Background:

Disrupted Ca²⁺ homeostasis contributes to the development of colonic dysmotility in ulcerative colitis (UC), but the underlying mechanisms are unknown. This study aimed to examine the alteration of colonic smooth muscle (SM) Ca²⁺ signaling and Ca²⁺ handling proteins in a rat model of dextran sulfate sodium (DSS)-induced UC.

Methods:

Male Sprague-Dawley rats were randomly divided into control (n = 18) and DSS (n = 17) groups. Acute colitis was induced by 5% DSS in the drinking water for 7 days. Contractility of colonic SM strips (controls, n = 8 and DSS, n = 7) was measured in an organ bath. Cytosolic resting Ca²⁺ levels (n = 3 in each group) and Ca²⁺ transients (n = 3 in each group) were measured in single colonic SM cells. Ca²⁺ handling protein expression was determined by Western blotting (n = 4 in each group). Differences between control and DSS groups were analyzed by a two-sample independent t-test.

Results:

Average tension and amplitude of spontaneous contractions of colonic muscle strips were significantly enhanced in DSS-treated rats compared with controls (1.25 ± 0.08 g vs. 0.96 ± 0.05 g, P = 0.007; and 2.67 ± 0.62 g vs. 0.52 ± 0.10 g, P = 0.013). Average tensions of carbachol-evoked contractions were much weaker in the DSS group (1.08 ± 0.10 g vs. 1.80 ± 0.19 g, P = 0.006). Spontaneous Ca²⁺ transients were observed in more SM cells from DSS-treated rats (15/30 cells) than from controls (5/36 cells). Peak caffeine-induced intracellular Ca²⁺ release was lower in SM cells of DSS-treated rats than controls (0.413 ± 0.046 vs. 0.548 ± 0.041, P = 0.033). Finally, several Ca²⁺ handling proteins in colonic SM were altered by DSS treatment, including sarcoplasmic reticulum calcium-transporting ATPase 2a downregulation and phospholamban and inositol 1,4,5-trisphosphate receptor 1 upregulation.

Conclusions:

Impaired intracellular Ca²⁺ signaling of colonic SM, caused by alteration of Ca²⁺ handing proteins, contribute to colonic dysmotility in DSS-induced UC.

Efficient Differentiation of TBX18+/WT1+ Epicardial-Like Cells from Human Pluripotent Stem Cells Using Small Molecular Compounds

The epicardium promotes neovascularization and cardiomyocyte regeneration by generating vascular smooth muscle cells (SMCs) and producing regenerative factors after adult heart infarction. It is therefore a potential cell resource for repair of the injured heart. However, the epicardium also participates in fibrosis and scarring of the injured heart, complicating its use in regenerative medicine. In this study, we report coexpression of TBX18 and WT1 in the majority of epicardial cells during mouse embryonic epicardial development. Furthermore, we describe a convenient chemically defined, immunogen-free, small molecule-based method for generating TBX18⁺/WT1⁺ epicardial-like cell populations with 80% homogeneity from human pluripotent stem cells by modulation of the WNT and retinoic acid signaling pathways. These epicardial-like cells exhibited characteristic epicardial cell morphology following passaging and differentiation into functional SMCs or cardiac fibroblast-like cells. Our findings add to existing understanding of human epicardial development and provide an efficient and stable method for generating both human epicardial-like cells and SMCs.

RNA-binding protein CUGBP1 regulates insulin secretion via activation of phosphodiesterase 3B in mice

AIMS/HYPOTHESIS

CUG-binding protein 1 (CUGBP1) is a multifunctional RNA-binding protein that regulates RNA processing at several stages including translation, deadenylation and alternative splicing, as well as RNA stability. Recent studies indicate that CUGBP1 may play a role in metabolic disorders. Our objective was to examine its role in endocrine pancreas function through gain- and loss-of-function experiments and to further decipher the underlying molecular mechanisms.

METHODS

A mouse model in which type 2 diabetes was induced by a high-fat diet (HFD; 60% energy from fat) and mice on a standard chow diet (10% energy from fat) were compared. Pancreas-specific CUGBP1 overexpression and knockdown mice were generated. Different lengths of the phosphodiesterase subtype 3B (PDE3B) 3' untranslated region (UTR) were cloned for luciferase reporter analysis. Purified CUGBP1 protein was used for gel shift experiments.

RESULTS

CUGBP1 is present in rodent islets and in beta cell lines; it is overexpressed in the islets of diabetic mice. Compared with control mice, the plasma insulin level after a glucose load was significantly lower and glucose clearance was greatly delayed in mice with pancreas-specific CUGBP1 overexpression; the opposite results were obtained upon pancreas-specific CUGBP1 knockdown. Glucose- and glucagon-like peptide1 (GLP-1)-stimulated insulin secretion was significantly attenuated in mouse islets upon CUGBP1 overexpression. This was associated with a strong decrease in intracellular cAMP levels, pointing to a potential role for cAMP PDEs. CUGBP1 overexpression had no effect on the mRNA levels of PDE1A, 1C, 2A, 3A, 4A, 4B, 4D, 7A and 8B subtypes, but resulted in increased PDE3B expression. CUGBP1 was found to directly bind to a specific ATTTGTT sequence residing in the 3' UTR of PDE3B and stabilised PDE3B mRNA. In the presence of the PDE3 inhibitor cilostamide, glucose- and GLP-1-stimulated insulin secretion was no longer reduced by CUGBP1 overexpression. Similar to CUGBP1, PDE3B was overexpressed in the islets of diabetic mice.

CONCLUSIONS/INTERPRETATION

We conclude that CUGBP1 is a critical regulator of insulin secretion via activating PDE3B. Repressing this protein might provide a potential strategy for treating type 2 diabetes.

Hypothalamic Phosphodiesterase 3B Pathway Mediates Anorectic and Body Weight-Reducing Effects of Insulin in Male Mice

BACKGROUND

Insulin action in the hypothalamus plays a critical role in the regulation of energy homeostasis, yet the intracellular signaling mechanisms mediating insulin action are incompletely understood. Although phosphodiesterase 3B (PDE3B) mediates insulin action in the adipose tissue and it is highly expressed in the hypothalamic areas implicated in energy homeostasis, its role, if any, in mediating insulin action in the hypothalamus is unknown. We tested the hypothesis that insulin action in the hypothalamus is mediated by PDE3B.

METHODS

Using enzymatic assay, we examined the effects of peripheral or central administration of insulin on hypothalamic PDE3B activity in adult mice. Western blotting and immunohistochemistry also examined p-Akt and p-STAT3 levels in the hypothalamus. Effects of leptin on these parameters were also compared. We injected cilostamide, a PDE3 inhibitor, prior to central injection of insulin and examined the 12- to 24-hour food intake and 24-hour body weight. Finally, we examined the effect of cilostamide on insulin-induced proopiomelanocortin (Pomc), neurotensin (Nt), neuropeptide Y (Npy) and agouti-related peptide (Agrp) gene expression in the hypothalamus by qPCR.

RESULTS

Peripheral or central injection of insulin significantly increased PDE3B activity in the hypothalamus in association with increased p-Akt levels but without any change in p-STAT3 levels. However, leptin-induced increase in PDE3B activity was associated with an increase in both p-Akt and p-STAT3 levels in the hypothalamus. Prior administration of cilostamide reversed the anorectic and body weight-reducing effects as well as stimulatory effect of insulin on hypothalamic Pomc mRNA levels. Insulin did not alter Nt, Npy and Agrp mRNA levels.

CONCLUSION

Insulin induction of hypothalamic PDE3B activity and the reversal of the anorectic and body weight-reducing effects and stimulatory effect of insulin on hypothalamic Pomc gene expression by cilostamide suggest that activation of PDE3B is a novel mechanism of insulin signaling in the hypothalamus.