The sphingosine-1-phosphate pathway is upregulated in response to partial urethral obstruction in male rats and activates RhoA/Rho-kinase signalling

Urinary Sphingosine-1-Phosphate as a Biomarker for Bladder Pain Syndrome

IMPORTANCE

Sphingosine-1-phosphate (S1P) is a signaling molecule involved in inflammation and bladder contraction.

OBJECTIVES

The aims of this case-control pilot study were to compare urinary S1P concentrations in bladder pain syndrome (BPS) participants to controls and determine whether these concentrations correlate with disease severity and duration.

STUDY DESIGN

Adult females with BPS and controls were enrolled. Bladder pain syndrome participants completed an O'Leary-Sant questionnaire. Information on duration of symptoms and treatment history was obtained. Urinary S1P and creatinine concentrations were determined. Mann-Whitney U tests were used to compare groups, and Spearman correlation was used to test for associations between concentrations and duration and severity of symptoms.

RESULTS

Twenty-five participants were in each group. Median S1P concentration was 1,225 ng/dL in the BPS group and 2,183 ng/dL in the control group, which was significantly different (P < 0.0001). This difference did not persist when normalized to urinary creatinine (P = 0.58). No differences were noted in urinary S1P concentrations between treated and untreated participants (P = 0.53) or with symptom scores of 13 or greater and less than 13 (P = 0.69). Sphingosine-1-phosphate levels did not correlate with O'Leary-Sant scores (P = 0.08) or duration of symptoms (P = 0.67). Results did not change when using S1P concentrations normalized to creatinine.

CONCLUSIONS

This study demonstrated successful quantification of human urinary S1P concentrations. A difference in urinary S1P was found between BPS participants and controls but not when normalized to creatinine. While this is the first study to investigate urinary S1P as a biomarker for BPS, results suggest that it may have a potential role as a biomarker requiring further research.

Determination of the roles of cADPR and NAADP as intracellular calcium mobilizing messengers in S1P-induced contractions in rat bladders having IC/PBS

AIMS

Interstitial cystitis/painful bladder syndrome (IC/PBS) is characterized by lower abdominal pain and increased frequency and urgency of urine. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that plays role in calcium homeostasis in smooth muscle. The intracellular calcium mobilizing secondary messengers are also involved in smooth muscle contraction. The role of intracellular calcium storing depots in S1P-induced contraction was investigated in permeabilized detrusor smooth muscle having cystitis.

MAIN METHODS

IC/PBS was induced by cyclophosphamide injection. The detrusor smooth muscle strips isolated from rats were permeabilized with β-escin.

KEY FINDINGS

S1P-induced contraction was increased in cystitis. S1P-induced enhanced contraction was inhibited by cyclopiazonic acid, ryanodine and heparin showing involvement of sarcoplasmic reticulum (SR) calcium stores. Inhibition of S1P-induced contraction by bafilomycin and NAADP suggested the participation of lysosome-related organelles.

SIGNIFICANCE

IC/PBS triggers S1P-induced increase in intracellular calcium from SR and lysosome-related organelles in permeabilized detrusor smooth muscle.

Fingolimod (FTY720) prevents chronic rejection of rodent cardiac allografts through inhibition of the RhoA pathway

The Fingolimod (FTY720, Gilenya) is clinically approved for the treatment of multiple sclerosis (MS). Its therapeutic effect on MS is based on the ability to bind sphingosine 1-phosphate (S1P) receptors and block the exit of immune cells from the lymphoid organs, thus preventing immune cell-dependent injury to the central nervous system (CNS). We showed recently that, besides the S1P-related activity, the FTY720 also down-regulates RhoA, which is a master regulator of the actin cytoskeleton. Our previous studies showed that FTY720 also down-regulates Rictor, which is a signature molecule of mTORC2 complex, which regulates RhoA and dictates actin cytoskeleton specificity. Because, our previous studies showed that chronic rejection correlates with the upregulation of RhoA and mTORC2 components and that the inhibition of RhoA pathway prevents chronic rejection, here we studied the effect of FTY720 on the chronic rejection of rat and mouse cardiac allografts. We show that FTY720 in conjunction with the inhibitors of early T cell response, (CTA4-Ig in mice and Everolimus in rats) blocks macrophage infiltration into the grafts and prevents chronic rejection of rat and mouse cardiac transplants. This indicates that FTY720 may be repurposed from the MS application to the clinical transplantation as an anti-chronic rejection drug.

Siponimod (Mayzent) Downregulates RhoA and Cell Surface Expression of the S1P1 and CX3CR1 Receptors in Mouse RAW 264.7 Macrophages

The Siponimod (Mayzent) is a newly developed drug, similar to Fingolimod (FTY720) but with fewer side effects, approved by the Food and Drug Administration for the treatment of multiple sclerosis (MS). The therapeutic effect of siponimod and FTY720 in MS relies on their inhibitory effect on the sphingosine 1-phosphate (S1P) signaling. These drugs bind to the S1P receptors and block the CCL2 chemokine pathway that is responsible for the exit of the immune cells from the lymphoid organs, and circulation, thus preventing immune cell-dependent injury to the nervous system. We recently found that FTY720 beside its effect on the S1P pathway also blocks the RhoA pathway, which is involved in the actin cytoskeleton-related function of macrophages, such as expression/recycling of fractalkine (CX3CL1) receptors (CX3CR1), which direct macrophages to the transplanted organs during the development of the long-term (chronic) rejection. Here we tested the effects of siponimod on the RhoA pathway and the expression of the S1P1 and CX3CR1 receptors in mouse RAW 264.7 macrophages. We found that siponimod downregulates the expression of RhoA protein and decreases the cell surface expression of S1P1 and CX3CR1 receptors. This newly discovered crosstalk between S1P and RhoA/CX3CR1 pathways may help in the development of novel anti-chronic rejection therapies in clinical transplantation.

The sphingosine-1-phosphate/RhoA/Rho associated kinases/myosin light chain pathway in detrusor of female rats is down-regulated in response to ovariectomy

BACKGROUND

Dysuria is one of the main symptoms of genitourinary syndrome of menopause, which causes serious disruption to the normal life of peri-menopausal women. Studies have shown that it is related to decrease of detrusor contractile function, but the exact mechanism is still poorly understood. Previous results have suggested that the sphingosine-1-phosphate (S1P) pathway can regulate detrusor contraction, and this pathway is affected by estrogen in various tissues. However, how estrogen affects this pathway in the detrusor has not been investigated. In this study, we detected changes of the S1P/RhoA/Rho associated kinases (ROCK)/myosin light chain (MLC) pathway in the detrusor of ovariectomized rats in order to explore the underlying mechanism of dysuria during peri-menopause.

METHODS

Thirty-six female Sprague-Dawley rats were randomly divided into SHAM (sham operation), OVX (ovariectomy), and E groups (ovariectomy + estrogen), with 12 rats in each group. We obtained bladder detrusor tissues from each group and examined the mRNA and protein levels of the major components of the S1P/RhoA/ROCK/MLC pathway using quantitative real-time polymerase chain reaction and Western blotting, respectively. We also quantified the content of S1P in the detrusor using an enzyme linked immunosorbent assay. Finally, we compared results between the groups with one-way analysis of variance.

RESULTS

The components of the S1P pathway and the RhoA/ROCK/MLC pathway of the OVX group were significantly decreased, as compared with SHAM group. The percent decreases of the components in the S1P pathway were as follows: sphingosine kinase 1 (mRNA: 39%, protein: 45%) (both P < 0.05), S1P (21.73 ± 1.09 nmol/g vs. 18.86 ± 0.69 nmol/g) (P < 0.05), and S1P receptor 2/3 (S1PR2/3) (mRNA: 25%, 27%, respectively) (P < 0.05). However, the protein expression levels of S1PR2/3 and the protein and mRNA levels of SphK2 and S1PR1 did not show significant differences between groups (P > 0.05). The percent decreases of the components in the RhoA/ROCK/MLC pathway were as follows: ROCK2 (protein: 41%, mRNA: 36%) (both P < 0.05), p-MYPT1 (protein: 54%) (P < 0.05), and p-MLC20 (protein: 47%) (P < 0.05), but there were no significant differences in the mRNA and protein levels of RhoA, ROCK1, MYPT1, and MLC20 (all P > 0.05). In addition, all of the above-mentioned decreases could be reversed after estrogen supplementation (E group vs. SHAM group) (all P > 0.05).

CONCLUSION

In this study, we confirmed that ovariectomy is closely associated with the down-regulation of the S1P/RhoA/ROCK/MLC pathway in the rat detrusor, which may be one mechanism of dysuria caused by decreased contractile function of the female detrusor during peri-menopause.

Upregulation of sphingosine kinase 1 contributes to ventilator-associated lung injury in a two-hit model

Ventilator‑associated lung injury (VALI) remains a significant medical problem in intensive care units. The present study aimed to investigate the role of sphingosine kinase 1 (SPHK1) in VALI using a two‑hit model and explore the potential underlying molecular mechanism. Mice were divided into five groups: i) Non‑ventilated group; ii) non‑ventilated + lipopolysaccharide (LPS) group; iii) ventilated group; iv) ventilated + LPS group; and v) ventilated + LPS + SPHK1 inhibitor group. Mice were administered LPS (1 mg/kg) via an intraperitoneal injection. After 12 h, the mice were anesthetized and connected to a ventilator (10 ml/kg at 150 breaths/min) for 4 h. SPHK1 inhibitor (50 mg/kg) was injected intraperitoneally 1 h prior to ventilation. Mouse lung vascular endothelial cells were treated with LPS and SPHK1 inhibitor, and then subjected to cyclic stretch for 4 h. The present results suggested that the expression of SPHK1 and sphingosine 1 phosphate was upregulated in the two‑hit model of VALI; SPHK1 inhibitor could attenuate VALI in the two‑hit model as observed by hematoxylin and eosin staining, and affected the cell count and the protein content levels in the bronchoalveolar lavage fluid. In addition, treatment with SPHK1 inhibitor reduced the wet‑to‑dry ratio of the lungs and suppressed Evans blue dye leakage into the lung tissue. Furthermore, SPHK1 inhibitor exhibited protective effects on the two‑hit model of VALI by inhibiting the Ras homolog family member a‑mediated phosphorylation of myosin phosphatase target subunit 1 (MYPT‑1) and endothelial hyperpermeability. Additionally, mice were divided into five additional groups: i) Non‑ventilated group; ii) non‑ventilated + LPS group; iii) ventilated group; iv) ventilated + LPS group; and v) ventilated + LPS + Rho‑associated coiled‑coil forming protein kinase (ROCK)1 inhibitor group. ROCK1 inhibitor (10 mg/kg) was injected intraperitoneally 1 h prior to ventilation. The present results suggested that ROCK1 inhibitor could attenuate mechanical stretch‑induced lung endothelial injury and the phosphorylation of MYPT‑1 in vivo and in vitro. Collectively, the present findings indicated that upregulation of SPHK1 may contribute to VALI in a two‑hit model.

Testosterone regulates the expression and functional activity of sphingosine-1-phosphate receptors in the rat corpus cavernosum

The bioactive lipid sphingosine‐1‐phosphate (S1P) regulates smooth muscle (SM) contractility predominantly via three G protein‐coupled receptors. The S1P1 receptor is associated with nitric oxide (NO)‐mediated SM relaxation, while S1P2 & S1P3 receptors are linked to SM contraction via activation of the Rho‐kinase pathway. This study is to determine testosterone (T) modulating the expression and functional activity of S1P receptors in corpus cavernosum (CC). Adult male Sprague‐Dawley rats were randomly divided into three groups: sham‐operated controls, surgical castration and T supplemented group. Serum S1P levels were detected by high‐performance liquid chromatography. The expression of S1P1‐3 receptors and sphingosine kinases was detected by real‐time RT‐PCR. In vitro organ bath contractility and in vivo intracavernous pressure (ICP) measurement were also performed. T deprivation significantly decreased ICP rise. Meanwhile, surgical castration induced a significant increase in serum S1P level and the expression of S1P2‐3 receptors by twofold (P < 0.05) but a decrease in the expression of S1P1 receptor. Castration also augmented exogenous phenylephrine (PE), S1P, S1P1,3 receptor agonist FTY720‐P contractility and S1P2‐specific antagonist JTE013 relaxation effect. T supplemented could restore the aforementioned changes. We provide novel data that castration increased serum S1P concentration and up‐regulated the expression of S1P2‐3 receptors in CC. Consistently, agonizing S1P receptors induced CCSM contraction and antagonizing mediated relaxation were augmented. This provides the first clear evidence that S1P system dysregulation may contribute to hypogonadism‐related erectile dysfunction (ED), and S1P receptors may be expected as a potential target for treating ED.

The effect of sphingosine-1-phosphate on colonic smooth muscle contractility: Modulation by TNBS-induced colitis

Aim

Increased levels of circulating sphingosine-1-phosphate (S1P) have been reported in ulcerative colitis. The objective of this study was to examine the effect of S1P on colonic smooth muscle contractility and how is it affected by colitis.

Methods

Colonic inflammation was induced by intrarectal administration of trinitrobenzene sulfonic acid. Five days later colon segments were isolated and used for contractility experiments and immunoblotting.

Results

S1P contracted control and inflamed colon segments and the contraction was significantly greater in inflamed colon segments. S1P-induced contraction was mediated by S1PR1 and S1PR2 in control and S1PR2 in inflamed colon segments. S1PR3 did not play a significant role in S1P-induced contractions in control or inflamed colon. S1PR1, S1PR2 and S1PR3 proteins were expressed in colon segments from both groups. The expression of S1PR1 and S1PR2 was significantly enhanced in control and inflamed colon segments, respectively. S1PR3 levels however were not significantly different between the two groups. Nifedipine significantly reduced S1P-induced contraction in control but not inflamed colon segments. Thapsigargin significantly reduced S1P-induced contraction of the inflamed colon. GF 109203X and Y-27632, alone abolished S1P-induced contraction of the control but not inflamed colon segments. Combination of GF 109203X, Y-27632 and thapsigargin abolished S1P-induced contraction of inflamed colon segments.

Conclusion

S1P contracted control colon via S1PR1 and S1PR2 and inflamed colon exclusively via S1PR2. Calcium influx (control) or release (inflamed) and calcium sensitization are involved in S1P-induced contraction. Exacerbated response to S1P in colitic colon segments may explain altered colonic motility reported in patients and experimental models of inflammatory bowel disease.

Sphingosine Kinase 1 urothelial expression is increased in patients with neurogenic detrusor overactivity

Objectives:

To evaluate the expression of sphingosine kinase 1 (SPK1) in the bladder wall in patients with neurogenic lower urinary tract dysfunction and its association with clinical, urodynamic and pathological features.

Materials and Methods:

The expression of SPK1 was studied in bladder wall specimens obtained from cystectomy using immunohistochemistry in ten patients with spinal cord injury (n=8) or multiple sclerosis (n=2) with urodynamically proven neuropathic bladder dysfunction, and in controls (n=5). Inflammation and fibrosis were analysed with histological criteria and SPK1 expression was determined by individual immunohistochemical staining.

Results:

Significant increased SPK1 urothelial immunoreactivity was shown in patients compared to control group (p=0.03). By contrast, SPK1 immunoreactivity in patients was significantly decreased in the sub-urothelium, muscles and nerves, p=0.02; 0.01 and 0.003, respectively. Patients with neurogenic detrusor overactivity (NDO) had higher SPK1 urothelium expression than those without any DO (p=0.04).

Conclusions:

SPK1 is expressed in the human bladder wall, specifically the urothelium, in bladder specimens from patients with NDO. The role of SPK1 in the pathophysiology of NDO needs further elucidation.

Sphingosine-1-phosphate induced contraction of bladder smooth muscle

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that contracts most smooth muscles. Although S1P has been shown to contract bladder smooth muscle, the mechanism(s) by which S1P initiates contraction has not been extensively investigated. The goal of this study was to determine if S1P-induced force generation and myosin light chain (MLC) phosphorylation are dependent on calcium sensitization pathways mediated by protein kinase C (PKC) and Rho kinase (ROCK) and which S1P receptor is important in this response. Bladder smooth muscle strips from rabbit and rat were mounted for isometric force recording and contracted in response to carbachol or S1P in the presence and absence of an inhibitor of PKC (3 µM Bisindolylmaleimide-1) or ROCK (1 µM H-1172). 10 µM S1P produced approximately 40% of the force generated in response to 110 mM KCl in rabbit bladder smooth muscle. S1P, up to 100 µM, did not produce a response in rat bladder smooth muscle, any response evoked was due to solvent (NaOH). S1P-dependent force development was associated with a concomitant increase in Ser(19), but not dual Thr(18)/Ser(19) MLC phosphorylation. Inhibition of PKC decreased force development, whereas inhibition of ROCK abolished S1P-induced force. An inhibitor of the S1P2 receptor, JTE-013, relaxed a S1P-induced contraction; whereas, an agonist with low affinity to the S1P2 receptor, dihydro-S1P, did not elicit a contraction. Our results suggest that S1P contracts rabbit, but not rat, bladder smooth muscle via the S1P2 receptor and is dependent on MLC phosphorylation and myofilament calcium sensitization primarily in response to ROCK activation.

4F, apolipoprotein AI mimetic peptide, attenuates acute lung injury and improves survival in endotoxemic rats

BACKGROUND

4F, apolipoprotein AI mimetic peptide, mimics anti-inflammatory properties of high-density lipoprotein (HDL). The aim of this study was to investigate whether 4F attenuates acute lung injury and improves survival in endotoxemic rats and to determine whether the therapeutic benefits of 4F are associated with the stimulation of sphingosine-1-phosphate receptor 1 (S1P1), the activation of Akt, the down-regulation of the nuclear factor-κB (NF-κB) pathway, and the suppression of cell adhesion molecules.

METHODS

To induce endotoxemia in rats, lipopolysaccharide (LPS, 10 mg/kg) was injected into a tail vein and 10 minutes later, vehicle or 4F (10 mg/kg) was administered intraperitoneally, respectively. We observed the survival of subjects for 72 hours. At 6-hour post-LPS, we killed animals and measured S1P1 expression, phosphorylated Akt/Akt ratio, cytoplasmic phosphorylated inhibitor κB-α/inhibitor κB-α ratio, nuclear NF-κB p65 expression and DNA-binding activity, endothelial leukocyte adhesion molecule-1 (E-selectin) and intercellular adhesion molecule-1 expression, myeloperoxidase activity, and histologic damages in lung tissues. We also measured serum HDL cholesterol level.

RESULTS

4F improved survival in endotoxemic rats. 4F restored LPS-induced diminution of serum HDL cholesterol level and increased lung S1P1 expression and phosphorylated Akt/Akt ratio in LPS-treated rats. Furthermore, 4F suppressed inhibitor κB-α degradation, NF-κB activation, E-selectin and intercellular adhesion molecule-1 expression, and myeloperoxidase activity, and attenuated histologic damages in lung tissues.

CONCLUSIONS

4F attenuated acute lung injury and improved survival in endotoxemic rats. The therapeutic benefits of 4F were found to be associated with the stimulation of S1P1, the activation of Akt, the down-regulation of the NF-κB pathway, and the suppression of cell adhesion molecules.

Large-conductance calcium-activated potassium channel activity, as determined by whole-cell patch clamp recording, is decreased in urinary bladder smooth muscle cells from male rats with partial urethral obstruction

OBJECTIVES

To examine the effect of partial urethral obstruction (PUO) on bladder smooth muscle outward potassium current and the contribution of the large-conductance calcium-activated potassium (Maxi-K, BKCa) channel to this activity in smooth muscle cells isolated from bladders of sham-operated and PUO male rats using whole-cell patch clamp recording techniques. To determine the effect of PUO on the expression of the Maxi-K channel α and β1 subunits and in vitro detrusor contractility.

MATERIALS AND METHODS

Twenty adult male Sprague-Dawley rats were divided equally into two groups and subjected to surgical ligation of the urethra (PUO) or sham surgery (SHAM). After 2 weeks, the detrusors from PUO and SHAM rats were used for molecular analyses (mRNA and protein quantification of Maxi-K subunits) or organ bath contractility studies, or myocytes were isolated for conventional whole-cell patch clamp analyses.

RESULTS

PUO increased bladder mass 2.5-fold and detrusor strips exhibited a more tonic-type contraction and increased contractility compared with controls (SHAM). Iberiotoxin (300 nM) sensitive Maxi-K channel current comprised about 40% of the outward whole-cell current in SHAM bladders but only about 8% in PUO bladders. Expression of the α subunit of the Maxi-K channel was significantly decreased ~40% while the expression of the β1 subunit was increased ~2-fold at the mRNA level. The increase in β1 expression was confirmed by Western blotting.

CONCLUSIONS

Our findings show that obstruction of the rat bladder is associated with decreased Maxi-K channel activity of bladder smooth muscle cells, determined via direct current measurement. Increased expression of the β1 subunit points to a compensatory reaction to decreased Maxi-K channel activity. Maxi-K channel openers or gene therapy may therefore provide therapeutic benefit for the overactive bladder.

Impact of partial urethral obstruction on bladder function: time-dependent changes and functional correlates of altered expression of Ca²⁺ signaling regulators

In animal models of partial urethral obstruction (PUO), altered smooth muscle function/contractility may be linked to changes in molecules that regulate calcium signaling/sensitization. PUO was created in male rats, and urodynamic studies were conducted 2 and 6 wk post-PUO. Cystometric recordings were analyzed for the presence or absence of nonvoiding contractions [i.e., detrusor overactivity (DO)]. RT-PCR and Western blots were performed on a subpopulation of rats to study the relationship between the expression of RhoA, L-type Ca(2+) channels, Rho kinase-1, Rho kinase-2, inositol 1,4,5-trisphosphate, ryanodine receptor, sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 and protein kinase C (PKC)-potentiated phosphatase inhibitor of 17 kDa, and urodynamic findings in the same animal. Animals displayed DO at 2 (38%) and 6 wk (43%) post-PUO, increases were seen in in vivo pressures at 2 wk, and residual volume at 6 wk. Statistical analysis of RT-PCR and Western blot data at 2 wk, during the compensatory phase of detrusor hypertrophy, documented that expression of molecules that regulate calcium signaling and sensitization was consistently lower in obstructed rats without DO than those with DO or control rats. Among rats with DO at 2 wk, linear regression analysis revealed positive correlations between in vivo pressures and protein and mRNA expression of several regulatory molecules. At 6 wk, in the presence of overt signs of bladder decompensation, no clear or consistent alterations in expression of these same targets were observed at the protein level. These data extend prior work to suggest that molecular profiling of key regulatory molecules during the progression of PUO-mediated bladder dysfunction may shed new light on potential biomarkers and/or therapeutic targets.

Testosterone regulates smooth muscle contractile pathways in the rat prostate: emphasis on PDE5 signaling

Testosterone (T) plays a permissive role in the development of benign prostatic hyperplasia (BPH), and phosphodiesterase 5 inhibitors (PDE5is) have been found to be effective for BPH and lower urinary tract symptoms (LUTS) in clinical trials. This study investigated the effect of T on smooth muscle (SM) contractile and regulatory signaling pathways, including PDE5 expression and functional activity in prostate in male rats (sham-operated, surgically castrated, and castrated with T supplementation). In vitro organ bath studies, real-time RT-PCR, Western blot analysis, and immunohistochemistry were performed. Castration heavily attenuated contractility, including sensitivity to phenylephrine with SM myosin immunostaining revealing a disrupted SM cell arrangement in the stroma. PDE5 was immunolocalized exclusively in the prostate stroma, and orchiectomy signficantly reduced PDE5 immunopositivity, mRNA, and protein expression, along with nNOS and ROKβ mRNA, whereas it increased eNOS plus α(1a) and α(1b) adrenoreceptor expression in castrated animals. The PDE5i zaprinast significantly increased prostate strip relaxation to the nitric oxide donor sodium nitroprusside (SNP) in control but not castrated rats. But SNP alone was more effective on castrated rats, comparable with sham treated with SNP plus zaprinast. T supplementation prevented or restored all above changes, including SNP and zaprinast in vitro responsiveness. In conclusion, our data show that T positively regulates PDE5 expression and functional activities in prostate, and T ablation not only suppresses prostate size but also reduces prostatic SM contractility, with several potential SM contraction/relaxation pathways implicated. Zaprinast findings strongly suggest a major role for PDE5/cGMP in this signaling cascade. PDE5 inhibition may represent a novel mechanism for treatment of BPH.

Blebbistain, a myosin II inhibitor, as a novel strategy to regulate detrusor contractility in a rat model of partial bladder outlet obstruction

Partial bladder outlet obstruction (PBOO), a common urologic pathology mostly caused by benign prostatic hyperplasia, can coexist in 40–45% of patients with overactive bladder (OAB) and is associated with detrusor overactivity (DO). PBOO that induces DO results in alteration in bladder myosin II type and isoform composition. Blebbistatin (BLEB) is a myosin II inhibitor we recently demonstrated potently relaxed normal detrusor smooth muscle (SM) and reports suggest varied BLEB efficacy for different SM myosin (SMM) isoforms and/or SMM vs nonmuscle myosin (NMM). We hypothesize BLEB inhibition of myosin II as a novel contraction protein targeted strategy to regulate DO. Using a surgically-induced male rat PBOO model, organ bath contractility, competitive and Real-Time-RT-PCR were performed. It was found that obstructed-bladder weight significantly increased 2.74-fold while in vitro contractility of detrusor to various stimuli was impaired ∼50% along with decreased shortening velocity. Obstruction also altered detrusor spontaneous activities with significantly increased amplitude but depressed frequency. PBOO switched bladder from a phasic-type to a more tonic-type SM. Expression of 5’ myosin heavy chain (MHC) alternatively spliced isoform SM-A (associated with tonic-type SM) increased 3-fold while 3’ MHC SM1 and essential light chain isoform MLC_17b also exhibited increased relative expression. Total SMMHC expression was decreased by 25% while the expression of NMM IIB (SMemb) was greatly increased by 4.5-fold. BLEB was found to completely relax detrusor strips from both sham-operated and PBOO rats pre-contracted with KCl, carbachol or electrical field stimulation although sensitivity was slightly decreased (20%) only at lower doses for PBOO. Thus we provide the first thorough characterization of the response of rat bladder myosin to PBOO and demonstrate complete BLEB-induced PBOO bladder SM relaxation. Furthermore, the present study provides valuable evidence that BLEB may be a novel type of potential therapeutic agent for regulation of myogenic and nerve-evoked DO in OAB.

Update on corpus cavernosum smooth muscle contractile pathways in erectile function: a role for testosterone?

INTRODUCTION

Normal erectile function (EF) involves a coordinated relaxation of the arteries that supply the penis and the corpus cavernosum smooth muscle (CCSM), resulting in expansion of the sinusoids and increased intracavernous pressure. But the CCSM spends the majority of its time in the contracted state which is mediated by norepinephrine released from nerve endings and other vasoconstrictors like endothelins released from the endothelium. These agents cause smooth muscle myosin (SMM) phosphorylation by elevating intracellular calcium. When calcium returns to basal levels, the calcium sensitivity increases and prevents myosin dephosphorylation, which involves the RhoA/Rho-kinase (ROK) mechanism, thus maintaining force. Although mounting evidences demonstrate that androgens have a major influence on EF that is not just centrally mediated, this notion remains quite controversial.

AIM

To summarize the current knowledge on CCSM contractile pathways, the role they play in modulating EF, and the influence of androgens.

METHODS

The article reviews the literature and contains some previously unpublished data on CCSM contraction signaling including the role that androgens are known to play in modulating these pathways.

MAIN OUTCOME MEASURES

Data from peer-reviewed publications and previously unpublished observations.

RESULTS

In addition to downregulation of many pro-erectile molecular mechanisms, decreased testosterone (T) levels upregulate CCSM contractility, including hyperresponsiveness to α-adrenergic agonists, increased SMM phosphorylation, alteration of SMM isoform composition, activation of RhoA/ROK signaling and modulation of sphingosine-1-phosphate regulation of CCSM tone.

CONCLUSIONS

Decreased T levels upregulate CCSM contractile signaling. Meanwhile, it downregulates CCSM relaxation pathways synergizing to produce erectile dysfunction (ED). Although some urologists and researchers are still skeptical of the influence of androgens on penile erection, understanding these molecular control mechanisms as well as the influence that androgens have on these pathways should provide new evidence supporting the roles of androgens in EF and enhance the discovery of novel targets for drug development to treat ED.

Rho-kinase, a common final path of various contractile bladder and ureter stimuli

Normal urinary bladder function is based on the proper contraction and relaxation of smooth muscle (SM), which constitutes the majority of the bladder wall. The contraction and relaxation of all SM involves a phosphorylation-dephosphorylation pathway involving the enzymes smooth muscle myosin light chain kinase (SMMLCK) and smooth muscle myosin light chain phosphatase (SMMLCP), respectively. Although originally thought to function just as a passive opposition to SMMLCK-driven SM contraction, it is now clear that SMMLCP activity is under an extremely complex molecular regulation via which SMMLCP inhibition can induce "calcium sensitization." This review provides a thorough summary of the literature regarding the molecular regulation of the SMMLCP with a focus on one of its major inhibitory pathways that is RhoA/Rho-kinase (ROK) including its activation pathways, effector molecules, and its roles in various pathological conditions associated with bladder dysfunction. Newly emerging roles of ROK outside of SM contractility are also discussed. It is concluded that the RhoA/ROK pathway is critical for the maintenance of basal SM tone of the urinary bladder and serves as a common final pathway of various contractile stimuli in rabbits, rats, mice, and pigs as well as humans. In addition, this pathway is upregulated in response to a number of pathological conditions associated with bladder SM dysfunction. Similarly, RhoA/Rho-kinase signaling is essential for normal ureteral function and development and is upregulated in response to ureteral outlet obstruction. In addition to its critical role in bladder SM function, a role of ROK in the urothelium is also beginning to emerge as well as roles for ROK in bladder infection and invasion and metastasis of bladder cancer.