Enzyme-induced hypoxia leads to inflammation in urothelial cells in vitro

PURPOSE

To determine the contributions of different durations of hypoxia to NLRP3 inflammasome activation in urothelial cells and how ischemic changes in bladder tissues is an important chemical que that leads to pathological changes seen in BOO.

METHODS

A rat urothelial cell line (MYP3) was exposed to either a short duration (2 h) or long duration (6 h) of enzyme-induced hypoxia. Following exposure to a short duration of hypoxia, NO and ATP concentrations were measured from supernatant media and caspase-1 levels were measured from cell lysates. In a separate experiment, cells were fixed following hypoxia exposure and immunostained for HIF-1α stabilization.

RESULTS

Although short exposure of low oxygen conditions resulted in a hypoxic response in MYP3 cells, as indicated by HIF-1α stabilization and increased NO activity, NLRP3 inflammasome activation was not observed as caspase-1 activity remained unchanged. However, exposure of MYP3 cells to a longer duration of hypoxia resulted in an increase in intracellular caspase-1 activity. Furthermore, treatment with antioxidant (GSH) or TXNIP inhibitor (verapamil) attenuated the hypoxia-induced increase in caspase-1 levels indicating that hypoxia primarily drives inflammation through a ROS-mediated TXNIP/NLRP3 pathway.

CONCLUSION

We conclude that hypoxia induced bladder damage requires a duration that is more likely related to elevated storage pressures/hypoxia, seen in later stages of BOO, as compared to shorter duration pressure elevation/hypoxia that is encountered in normal micturition cycles or early in the BOO pathology where storage pressures are still normal.

Recurrent infections drive persistent bladder dysfunction and pain via sensory nerve sprouting and mast cell activity

Urinary tract infections (UTIs) account for almost 25% of infections in women. Many are recurrent (rUTI), with patients frequently experiencing chronic pelvic pain and urinary frequency despite clearance of bacteriuria after antibiotics. To elucidate the basis for these bacteria-independent bladder symptoms, we examined the bladders of patients with rUTI. We noticed a notable increase in neuropeptide content in the lamina propria and indications of enhanced nociceptive activity. In mice subjected to rUTI, we observed sensory nerve sprouting that was associated with nerve growth factor (NGF) produced by recruited monocytes and tissue-resident mast cells. Treatment of rUTI mice with an NGF-neutralizing antibody prevented sprouting and alleviated pelvic sensitivity, whereas instillation of native NGF into naïve mice bladders mimicked nerve sprouting and pain behavior. Nerve activation, pain, and urinary frequency were each linked to the presence of proximal mast cells, because mast cell deficiency or treatment with antagonists against receptors of several direct or indirect mast cell products was each effective therapeutically. Thus, our findings suggest that NGF-driven sensory sprouting in the bladder coupled with chronic mast cell activation represents an underlying mechanism driving bacteria-independent pain and voiding defects experienced by patients with rUTI.

Male Akita mice develop signs of bladder underactivity independent of NLRP3 as a result of a decrease in neurotransmitter release from efferent neurons

Diabetic Bladder Dysfunction (DBD) is a prevalent diabetic complication that is recalcitrant to glucose control. Using the Akita mouse model (type 1) bred to be NLRP3^+/+ or NLRP3^-/-, we previously found that females (mild hyperglycemia) progress from an overactive to an underactive bladder phenotype and this progression was dependent on NLRP3-induced inflammation. Here we examined DBD in the male Akita (severe hyperglycemia) and found by urodynamics only a compensated underactive-like phenotype (increased void volume and decreased frequency but unchanged efficiency). Surprisingly, this phenotype was still present in the NLRP3^-/- strain and so was not dependent on NLRP3 inflammasome-induced inflammation. Examining the cause of the compensated underactive-like phenotype, we assessed overall nerve density and afferent nerves (Aδ-fibers). Both were decreased in density during diabetes but denervation was absent in the diabetic NLRP3^-/- strain so it was deemed unlikely to cause the underactive-like symptoms. Changes in bladder smooth muscle (BSM) contractility to cell depolarization and receptor activation were also not responsible as KCl (depolarizing agent), carbachol (muscarinic agonist) and α, β-methylene-ATP (purinergic agonist) elicited equivalent contractions in denuded bladder strips in all groups. However, electrical field stimulation revealed a diabetes-induced decrease in contractility that was not blocked in the NLRP3^-/- strains suggesting that bladder compensated underactive-like phenotype in the male Akita is likely through a decrease in efferent neurotransmitter release.

Why Are Some People with Lower Urinary Tract Symptoms (LUTS) Depressed? New Evidence That Peripheral Inflammation in the Bladder Causes Central Inflammation and Mood Disorders

Anecdotal evidence has long suggested that patients with lower urinary tract symptoms (LUTS) develop mood disorders, such as depression and anxiety, at a higher rate than the general population and recent prospective studies have confirmed this link. Breakthroughs in our understanding of the diseases underlying LUTS have shown that many have a substantial inflammatory component and great strides have been made recently in our understanding of how this inflammation is triggered. Meanwhile, studies on mood disorders have found that many are associated with central neuroinflammation, most notably in the hippocampus. Excitingly, work on other diseases characterized by peripheral inflammation has shown that they can trigger central neuroinflammation and mood disorders. In this review, we discuss the current evidence tying LUTS to mood disorders, its possible bidirectionally, and inflammation as a common mechanism. We also review modern theories of inflammation and depression. Finally, we discuss exciting new animal studies that directly tie two bladder conditions characterized by extensive bladder inflammation (cyclophosphamide-induced hemorrhagic cystitis and bladder outlet obstruction) to neuroinflammation and depression. We conclude with a discussion of possible mechanisms by which peripheral inflammation is translated into central neuroinflammation with the resulting psychiatric concerns.

Diabetes causes NLRP3-dependent barrier dysfunction in mice with detrusor overactivity but not underactivity

Approximately half of the patients with diabetes develop diabetic bladder dysfunction (DBD). The initiation and progression of DBD is largely attributed to inflammation due to dysregulated glucose and the production of toxic metabolites that activate the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome. NLRP3 activation leads to the production and release of proinflammatory cytokines and causes urothelial pyroptosis, a form of programmed cell necrosis, which we hypothesize compromises urothelial barrier integrity. Here, we investigated how NLRP3-dependent inflammation impacts barrier function during the progression of diabetes using a type 1 diabetic female Akita mouse model that progresses from an early overactive to a late underactive detrusor phenotype at 15 and 30 wk, respectively. To determine the specific role of NLRP3, Akita mice were crossbred with mice lacking the NLRP3 gene. To determine barrier function, permeability to small molecules was assessed, ex vivo using Evans blue dye and in vivo using sulfo-NHS-biotin. Both ex vivo and in vivo permeabilities were increased in diabetic mice at 15 wk. Expression of uroplakin and tight junction components was also significantly downregulated at 15 wk. Interestingly, diabetic mice lacking the NLRP3 gene showed no evidence of barrier damage or downregulation of barrier genes and proteins. At the 30-wk time point, ex vivo and in vivo barrier damage as well as barrier component downregulation was no longer evident in diabetic mice, suggesting urothelial repair or remodeling occurs between the overactive and underactive stages of DBD. Collectively, these findings demonstrate the role of NLRP3-mediated inflammation in urothelial barrier damage associated with detrusor overactivity but not underactivity.NEW & NOTEWORTHY This is the first study to demonstrate that NLRP3-mediated inflammation is responsible for urothelial barrier damage in type 1 diabetic female Akita mice with an overactive bladder. Eliminating the NLRP3 gene in these diabetic mice prevented barrier damage as a result of diabetes. By the time female Akita mice develop an underactive phenotype, the urothelial barrier has been restored, suggesting that inflammation is a critical causative factor early in the development of diabetic bladder dysfunction.

Inflammation triggered by the NLRP3 inflammasome is a critical driver of diabetic bladder dysfunction

Diabetes is a rapidly expanding epidemic projected to affect as many as 1 in 3 Americans by 2050. This disease is characterized by devastating complications brought about high glucose and metabolic derangement. The most common of these complications is diabetic bladder dysfunction (DBD) and estimates suggest that 50-80% of patients experience this disorder. Unfortunately, the Epidemiology of Diabetes Interventions and Complications Study suggests that strict glucose control does not decrease ones risk for incontinence, although it does decrease the risk of other complications such as retinopathy, nephropathy and neuropathy. Thus, there is a significant unmet need to better understand DBD in order to develop targeted therapies to alleviate patient suffering. Recently, the research community has come to understand that diabetes produces a systemic state of low-level inflammation known as meta-inflammation and attention has focused on a role for the sterile inflammation-inducing structure known as the NLRP3 inflammasome. In this review, we will examine the evidence that NLRP3 plays a central role in inducing DBD and driving its progression towards an underactive phenotype.

Diabetic bladder dysfunction progresses from an overactive to an underactive phenotype in a type-1 diabetic mouse model (Akita female mouse) and is dependent on NLRP3

AIMS

Diabetic bladder dysfunction (DBD) is a prevalent diabetic complication thought to progress from overactive (OAB) to underactive (UAB) bladder. Previously we found OAB at 15 weeks in the Akita mouse, a genetic model of Type 1 diabetes. The first aim of this study assesses bladder function at 30 weeks to assess progression. In addition, inflammation triggered by the NLRP3 inflammasome is implicated in DBD. In a second aim we assessed a role for NLRP3 by crossing Akita mice with NLRP3^-/- mice.

MAIN METHODS

Akita mice were bred with NLRP3^-/- mice. The effect of diabetes was assessed by comparing nondiabetic to diabetic mice (all NLRP3^+/+). The effect of diabetes in the absence of the NLRP3 inflammasome was assessed by comparing nondiabetic/NLRP3^-/- to diabetic/NLRP3^-/- mice. Mice were assessed at 30 weeks for blood glucose (glucometer), inflammation (Evans blue), bladder morphology (histology) and bladder function (urodynamics).

KEY FINDINGS

At 30 weeks blood glucose of nondiabetics and diabetics was not affected by the presence of absence of NLRP3. Diabetic/NLRP3^+/+ mice showed bladder inflammation and detrusor hypertrophy which was blocked in the diabetic/NLRP3^-/- mice, clearly showing a role for NLRP3. When bladder function was examined, diabetic/NLRP3^+/+ showed an increase in voiding volume and a decrease in frequency, two signs of underactive bladder. However, in the NLRP3^-/- mice, diabetes was unable to effectuate these changes, demonstrating that NLRP3-induced inflammation is responsible for UAB symptoms in these mice.

SIGNIFICANCE

Akita diabetic mice progress from OAB to UAB. NLRP3 is a possible target to treat DBD.

Specialized pro-resolution mediators in the bladder: Receptor expression and recovery of bladder function from cystitis

Inflammation is a central process in most benign bladder disorders, and its control is a delicate balance between initiating factors and resolving factors. While recent discoveries have shown a central role for the NLRP3 inflammasome in initiation, the resolving pathways remain unexplored. Resolution is controlled by specialized pro-resolution mediators (SPMs) functioning through seven receptors (six in rodents). Here we demonstrate expression of all seven in humans (six in mice) through immunocytochemistry. Expression was universal in urothelia with most also expressed in smooth muscle. We next explored the therapeutic potential of three SPMs; Resolvin E1 (RvE1), Maresin 1 (MaR1), and Protectin D1 (PD1). SPMs promote epithelial wound/barrier repair and RvE1 triggered dose-dependent wound closure in urothelia in vitro (scratch assay) (EC90 = 12.5 nM). MaR1 and PD1 were equally effective at this concentration. In vivo analyses employed a cyclophosphamide (CP) model of bladder inflammation (Day 0-CP [150 mg/kg], Day 1 to 3 SPM [25 µg/kg/day], Day 4 - analysis). All three SPMs reduced bladder inflammation (Evans blue) and bladder weights to control levels. Effects of RvE1 were also examined by urodynamics. CP decreased void volume, increased frequency and decreased bladder capacity while RvE1 restored values to control levels. Finally, SPMs reduce fibrosis and RvE1 reduced urothelial expression of TGF-β and collagen I to control values. Together these results expand the known SPMs active in the bladder tissue and provide promising therapeutic targets for controlling inflammation in a wide variety of inflammation-associated benign bladder diseases.

Specialized Pro-resolution Mediators in the bladder; Annexin-A1 normalizes inflammation and bladder dysfunction during bladder outlet obstruction

Bladder Outlet Obstruction (BOO) is ultimately experienced by ≈90% of men, most commonly secondary to benign prostatic hyperplasia. Inflammation is a critical driver of BOO pathology in the bladder and can be divided into two critical steps; initiation and resolution. While great strides have been made toward understanding initiation of inflammation in the bladder (through the NLRP3 inflammasome), no studies have examined resolution. Resolution is controlled by 5 classes of compounds known as Specialized Pro-resolving Mediators (SPMs), all of which bind to one or more of 7 different receptors. Using immunocytochemistry, we show the presence of 6 of the known SPM receptors in the bladder of control and BOO rats; the 7^th has no rodent homolog. The expression was predominantly localized to the urothelia, often with some expression in the smooth muscle, but little to none in the interstitial cells. We next examined the therapeutic potential of the Annexin-A1 resolution system, also present in control and BOO bladders. Using the peptide mimetic Ac2-26, we blocked inflammation-initiating pathways (NLRP3 activation), diminished BOO-induced inflammation (Evans blue dye extravasation), and normalized bladder dysfunction (urodynamics). Excitingly, Ac2-26 also promoted faster and more complete functional recovery after surgical de-obstruction. Together, the results demonstrate that the bladder expresses a wide variety of potential pro-resolving pathways and that modulation of just one of these pathways can alleviate many detrimental aspects of BOO and speed recovery after de-obstruction. This work establishes a precedent for future studies evaluating SPM effectiveness in resolving the many conditions associated with bladder inflammation.

A possible mechanism underlying mood disorders associated with LUTS: Chronic bladder outlet obstruction causes NLRP3-dependent inflammation in the hippocampus and depressive behavior in rats

AIMS

Reports link urinary dysfunction and mood disorders, such as depression, but a causative mechanism has never been postulated. Contemporary discoveries demonstrate a local inflammatory response in peripheral organs can trigger inflammation in the brain, particularly the hippocampus, mediated through the NLRP3 inflammasome. Critically, central inflammation causes depressive behavior. Since bladder outlet obstruction (BOO) evokes a local inflammatory response in the bladder, we hypothesize it will induce NLRP3-dependent inflammation in the hippocampus and depressive behavior.

METHODS

There were four groups of rats: control, sham, BOO, or BOO + glyburide (an NLRP3 inhibitor). BOO was created by urethral ligation over a 1 mm catheter. Sham was tied loosely. Glyburide was provided by slow-release pellet (subcutaneous 50 mg, 21 day, replaced as needed). Rats were analyzed 12 weeks post-op for: hippocampal inflammation, microglial density, neurogenesis, and depression symptoms (open field and sucrose preference).

RESULTS

BOO elicited hippocampal inflammation, accompanied by an increase in activated microglia (22%) and a decrease in neurogenesis (35%), which was blocked by glyburide. In addition, BOO rats displayed anxiety (57% decrease in exploratory behavior in the open field assay) and anhedonia (21% decrease in sucrose preference), two symptoms of depression. Like inflammation, these symptoms were diminished by glyburide to levels not statistically significantly different from controls.

CONCLUSIONS

BOO, a bladder-localized event, stimulates NLRP3-dependent inflammation in the rat hippocampus after 12 weeks and this inflammation causes depressive behavior. This is the first mechanistic explanation of the link between BOO and depression and provides evidence for a distinct bladder-brain axis.

A highly polarized TH2 bladder response to infection promotes epithelial repair at the expense of preventing new infections

Urinary tract infections (UTIs) typically evoke prompt and vigorous innate bladder immune responses, including extensive exfoliation of the epithelium. To explain the basis for the extraordinarily high recurrence rates of UTIs, we examined adaptive immune responses in mouse bladders. We found that, following each bladder infection, a highly T helper type 2 (TH2)-skewed immune response directed at bladder re-epithelialization is observed, with limited capacity to clear infection. This response is initiated by a distinct subset of CD301b+OX40L+ dendritic cells, which migrate into the bladder epithelium after infection before trafficking to lymph nodes to preferentially activate TH2 cells. The bladder epithelial repair response is cumulative and aberrant as, after multiple infections, the epithelium was markedly thickened and bladder capacity was reduced relative to controls. Thus, recurrence of UTIs and associated bladder dysfunction are the outcome of the preferential focus of the adaptive immune response on epithelial repair at the expense of bacterial clearance.

Cyclophosphamide-induced cystitis results in NLRP3-mediated inflammation in the hippocampus and symptoms of depression in rats

Recent breakthroughs demonstrate that peripheral diseases can trigger inflammation in the brain, causing psychosocial maladies, including depression. While few direct studies have been made, anecdotal reports associate urological disorders with mental dysfunction. Thus, we investigated if insults targeted at the bladder might elicit behavioral alterations. Moreover, the mechanism of neuroinflammation elicited by other peripheral diseases involves the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, which is present in microglia in the brain and cleaves and activates proinflammatory cytokines such as IL-1β. Thus, we further explored the importance of NLRP3 in behavioral and neuroinflammatory changes. Here, we used the well-studied cyclophosphamide (CP)-treated rat model. Importantly, CP and its metabolites do not cross the blood-brain barrier or trigger inflammation in the gut, so that any neuroinflammation is likely secondary to bladder injury. We found that CP triggered an increase in inflammasome activity (caspase-1 activity) in the hippocampus but not in the pons. Evans blue extravasation demonstrated breakdown of the blood-brain barrier in the hippocampal region and activated microglia were present in the fascia dentata. Both changes were dependent on NLRP3 activation and prevented with 2-mercaptoethane sulfonate sodium (Mesna), which masks the effects of the CP metabolite acrolein in the urine. Finally, CP-treated rats displayed depressive symptoms that were prevented by NLRP3 inhibition or treatment with Mesna or an antidepressant. Thus, we conclude that CP-induced cystitis causes NLRP3-dependent hippocampal inflammation leading to depression symptoms in rats. This study proposes the first-ever causative explanation of the previously anecdotal link between benign bladder disorders and mood disorders.

Calcium Pyrophosphate And Monosodium Urate Activate The NLRP3 Inflammasome Within Bladder Urothelium Via Reactive Oxygen Species And TXNIP

Objective

To investigate the in vitro activation of the NLRP3 inflammasome within bladder urothelium by stone-forming components. Further, to describe the contributions of reactive oxygen species (ROS) and thioredoxin-interacting protein (TXNIP), an important structural component of the inflammasome, to this activation.

Methods

Urothelial cells were harvested and incubated overnight. For agonist studies, cells were treated with varying concentrations of calcium pyrophosphate (CPPD) and monosodium urate (MSU). For inhibitor studies, cells were treated with either N-acetylcysteine (NAC) (1 hr) or Verapamil (4 hrs) prior to incubation with either CPPD (62.5 ug/mL) or MSU (1.25 ug/mL) for 24 hrs. Untreated controls were incubated with ATP (1.25 mM) for 1 hr to maximally stimulate NLRP3 inflammasome activity (measured as caspase-1 cleavage of the fluorogenic substrate Ac-YVAD-AFC). Results are reported as a percentage of maximum ATP response.

Results

CPPD and MSU activate caspase-1 in urothelial cells in a dose-dependent manner, reaching ~50% and ~25% of the ATP response, respectively. Pre-treatment with the general ROS scavenger NAC reduces this activation in a dose-dependent manner. Additionally, activation was suppressed through treatment with Verapamil, a known downregulator of TXNIP expression.

Conclusion

The stone components CPPD and MSU activate NLRP3 in an ROS and TXNIP-dependent manner in bladder urothelium. These findings demonstrate the importance of ROS and TXNIP, and suggest that targeting either may be a way to decrease stone-dependent NLRP3 inflammation within the bladder.

NLRP3 Promotes Diabetic Bladder Dysfunction and Changes in Symptom-Specific Bladder Innervation

The NLRP3 inflammasome senses diabetic metabolites and initiates inflammation implicated in diabetic complications and neurodegeneration. No studies have investigated NLRP3 in diabetic bladder dysfunction (DBD), despite a high clinical prevalence. In vitro, we found that numerous diabetic metabolites activate NLRP3 in primary urothelial cells. In vivo, we demonstrate NLRP3 is activated in urothelia from a genetic type 1 diabetic mouse (Akita) by week 15. We then bred an NLRP3^-/- genotype into these mice and found this blocked bladder inflammation and cystometric markers of DBD. Analysis of bladder innervation established an NLRP3-dependent decrease in overall nerve density and Aδ-fibers in the bladder wall along with an increase in C-fiber populations in the urothelia, which potentially explains the decreased sense of bladder fullness reported by patients and overactivity detected early in DBD. Together, the results demonstrate the role of NLRP3 in the genesis of DBD and suggest specific NLRP3-mediated neuronal changes can produce specific DBD symptoms.

Evaluation of Poly (Carbonate-Urethane) Urea (PCUU) Scaffolds for Urinary Bladder Tissue Engineering

Although the previous success of bladder tissue engineering demonstrated the feasibility of this technology, most polyester based scaffolds used in previous studies possess inadequate mechanical properties for organs that exhibit large deformation. The present study explored the use of various biodegradable elastomers as scaffolds for bladder tissue engineering and poly (carbonate-urethane) urea (PCUU) scaffolds mimicked urinary bladder mechanics more closely than polyglycerol sebacate-polycaprolactone (PGS-PCL) and poly (ether-urethane) urea (PEUU). The PCUU scaffolds also showed cyto-compatibility as well as increased porosity with increasing stretch indicating its ability to aid in infiltration of smooth muscle cells. Moreover, a bladder outlet obstruction (BOO) rat model was used to test the safety and efficacy of the PCUU scaffolds in treating a voiding dysfunction. Bladder augmentation with PCUU scaffolds led to enhanced survival of the rats and an increase in the bladder capacity and voiding volume over a 3 week period, indicating that the high-pressure bladder symptom common to BOO was alleviated. The histological analysis of the explanted scaffold demonstrated smooth muscle cell and connective tissue infiltration. The knowledge gained in the present study should contribute towards future improvement of bladder tissue engineering technology to ultimately aide in the treatment of bladder disorders.

Diabetic bladder dysfunction is associated with bladder inflammation triggered through hyperglycemia, not polyuria

Purpose

Diabetes is a grave and progressive condition characterized by debilitating complications. Diabetic bladder dysfunction (DBD) is a very common complication with no specific treatments currently available. Unlike other tissues affected by this disease, the bladder is subjected to two independent insults; 1) polyuria, created by the osmotic effects of glucose in the urine, and 2) hyperglycemia itself. Based on our understanding of inflammation as a major contributor to the underlying organ damage in several other diabetic complications, its presence in the bladder during DBD and the contribution of polyuria and hyperglycemia to its development were assessed.

Methods

Awake, restrained cystometry was performed on wild type C57BL/6 mice and diabetic (Akita) mice on a C57BL/6 background at 15 weeks of age. A subgroup of the Akita mice were treated with phlorizin, an inhibitor of sodium-glucose linked transporter types 1 and 2 that prevents glucose reabsorption in the kidney. All groups were assessed for serum glucose, 4-hour voiding totals, and inflammation in the bladder (Evans blue assay).

Results

Akita mice develop cystometrically-defined DBD by 15 weeks of age, as evidenced by an increase in urinary frequency, a decrease in voiding volume, and an increase in post-voiding residual volume. Phlorizin effectively normalized serum glucose in these animals while increasing the urine output. Inflammation in the bladder was present in the diabetic animals at this time point, but not detectable in animals receiving phlorizin.

Conclusion

Inflammation in the bladder of diabetic mice correlates with the development of DBD and is triggered by hyperglycemia, not polyuria.

Bladder decompensation and reduction in nerve density in a rat model of chronic bladder outlet obstruction are attenuated with the NLRP3 inhibitor glyburide

Bladder outlet obstruction (BOO) leads to progressive voiding dysfunction. Acutely, obstruction triggers inflammation that drives bladder dysfunction. Over time, inflammation leads to decreased bladder nerve density and increased fibrosis, responsible for eventual decompensation and irreversibility. We have previously shown that BOO triggers inflammation, reduced bladder nerve density and increased fibrosis via activation of the NLRP3 inflammasome in an acutely obstructed (12-day) rat model. However, as BOO progresses, the bladder may become decompensated with an increase in postvoid residual volume and decreased voiding efficiency. Currently, we have examined rat bladder function and nerve densities after chronic BOO to determine whether NLRP3 plays a role in the decompensation at this stage. Four groups were examined: control, sham-operated, BOO, or BOO+gly (glyburide; an NLRP3 inhibitor). After 42 days, bladder weight, inflammation (Evans blue), urodynamics, and nerve density were measured. BOO greatly enhanced bladder weights and inflammation, while inflammation was prevented by glyburide. Voiding pressures were increased, and flow rates decreased in BOO and BOO+gly groups, demonstrating physical obstruction. No difference in frequency or voided volume was detected. However, postvoid residual volumes were greatly increased in BOO rats while BOO+gly rats were not different than controls. Moreover, there was a dramatic decrease in voiding efficiency in the chronic BOO rats, which was prevented with glyburide treatment. Finally, a reduction in nerve density was apparent with BOO and attenuated with glyburide. Together the results suggest a critical role for NLRP3 in mediating bladder decompensation and nerve density during chronic BOO.

Elevated hydrostatic pressure stimulates ATP release which mediates activation of the NLRP3 inflammasome via P2X4 in rat urothelial cells

Partial bladder outlet obstruction (pBOO) is a prevalent urological condition commonly accompanied by increased intravesical pressure, inflammation, and fibrosis. Studies have demonstrated that pBOO results in increased NLRP3 inflammasome and caspase-1 activation and that ATP is released from urothelial cells in response to elevated pressure. In the present study, we investigated the role of elevated pressure in triggering caspase-1 activation via purinergic receptors activation in urothelial cells. Rat urothelial cell line, MYP3 cells, was subjected to hydrostatic pressures of 15 cmH₂O for 60 min, or 40 cmH₂O for 1 min to simulate elevated storage and voiding pressure conditions, respectively. ATP concentration in the supernatant media and intracellular caspase-1 activity in cell lysates were measured. Pressure experiments were repeated in the presence of antagonists for purinergic receptors to determine the mechanism for pressure-induced caspase-1 activation. Exposure of MYP3 cells to both pressure conditions resulted in an increase in extracellular ATP levels and intracellular caspase-1 activity. Treatment with P2X₇ antagonist led to a decrease in pressure-induced ATP release by MYP3 cells, while P2X₄ antagonist had no effect but both antagonists inhibited pressure-induced caspase-1 activation. Moreover, when MYP3 cells were treated with extracellular ATP (500 µM), P2X₄ antagonist inhibited ATP-induced caspase-1 activation, but not P2X₇ antagonist. We concluded that pressure-induced extracellular ATP in urothelial cells is amplified by P2X₇ receptor activation and ATP-induced-ATP release. The amplified ATP signal then activates P2X₄ receptors, which mediate activation of the caspase-1 inflammatory response.

The Emerging Role of Inflammasomes as Central Mediators in Inflammatory Bladder Pathology

Irritative voiding symptoms (e.g. increased frequency and urgency) occur in many common pathologic conditions such as urinary tract infections and bladder outlet obstruction, and these conditions are well-established to have underlying inflammation that directly triggers these symptoms. However, it remains unclear as to how such diverse stimuli individually generate a common inflammatory process. Jürg Tschopp provided substantial insight into this conundrum when, working with extracts from THP-1 cells, he reported the existence of the inflammasome. He described it as a structure that senses multiple diverse signals from intracellular/extracellular sources and pathogens and triggers inflammation by the maturation and release of the pro-inflammatory cytokines interleukin-1β and interleukin-18. Recently, many of these sensors were found in the bladder and the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3, has been shown to be a central mediator of inflammation in several urological diseases. In this review, we introduce the nucleotide-binding domain, leucine-rich-containing family, pyrin domaincontaining-3 inflammasome, highlight its emerging role in several common urologic conditions, and speculate on the potential involvement of other inflammasomes in bladder pathology.

NLRP3/IL-1β mediates denervation during bladder outlet obstruction in rats

AIMS

Denervation of the bladder is a detrimental consequence of bladder outlet obstruction (BOO). We have previously shown that, during BOO, inflammation triggered by the NLRP3 inflammasome in the urothelia mediates physiological bladder dysfunction and downstream fibrosis in rats. The aim of this study was to assess the effect of NLRP3-mediated inflammation on bladder denervation during BOO.

METHODS

There were five groups of rats: (i) Control (no surgery); (ii) Sham-operated; (iii) BOO rats given vehicle; (iv) BOO rats given the NLRP3 inhibitor glyburide; and (v) BOO rats given the IL-1 receptor antagonist anakinra. BOO was constructed by ligating the urethra over a 1 mm catheter and removing the catheter. Medications were given prior to surgery and once daily for 12 days. Bladder sections were stained for PGP9.5, a pan-neuronal marker. Whole transverse sections were used to identify and count nerves while assessing cross-sectional area. For in vitro studies, pelvic ganglion neurons were isolated and treated with IL-1β. After a 48 h incubation apoptosis, neurite length and branching were assessed.

RESULTS

In obstructed bladders, the number of nerves decreased while total area increased, indicating a loss of cell number and/or branching. The decrease in nerve density was blocked by glyburide or anakinra, clearly implicating the NLRP3 pathway in denervation. In vitro analysis demonstrated that IL-1β, a product of the inflammasome, induced apoptosis in pelvic ganglion neurons, suggesting one mechanism of BOO-induced denervation is NLRP3/IL-1β triggered apoptosis.

CONCLUSIONS

The NLRP3/IL-1β-mediated inflammation pathway plays a significant role in denervation during BOO.

Bladder fibrosis during outlet obstruction is triggered through the NLRP3 inflammasome and the production of IL-1β

Bladder outlet obstruction (BOO) triggers inflammation in the bladder through the NLRP3 inflammasome. BOO also activates fibrosis, which is largely responsible for the decompensation of the bladder in the chronic state. Because fibrosis can be driven by inflammation, we have explored a role for NLRP3 (and IL-1β produced by NLRP3) in the activation and progression of BOO-induced fibrosis. Female rats were divided into five groups: 1) control, 2) sham, 3) BOO + vehicle, 4) BOO + the NLRP3 inhibitor glyburide, or 5) BOO + the IL-1β receptor antagonist anakinra. Fibrosis was assessed by Masson's trichrome stain, collagen secretion via Sirius Red, and protein localization by immunofluorescence. BOO increased collagen production in the bladder, which was blocked by glyburide and anakinra, clearly implicating the NLRP3/IL-1β pathway in fibrosis. The collagen was primarily found in the lamina propria and the smooth muscle, while IL-1 receptor 1 and prolyl 4-hydroylase (an enzyme involved in the intracellular modification of collagen) both localized to the urothelium and the smooth muscle. Lysyl oxidase, the enzyme involved in the final extracellular assembly of mature collagen fibrils, was found to some extent in the lamina propria where its expression was greatly enhanced during BOO. In vitro studies demonstrated isolated urothelial cells from BOO rats secreted substantially more collagen than controls, and collagen expression in control cultures could be directly stimulated by IL-1β. In summary, NLRP3-derived-IL-1β triggers fibrosis during BOO, most likely through an autocrine loop in which IL-1β acts on urothelia to drive collagen production.

The NACHT, LRR and PYD Domains-Containing Protein 3 (NLRP3) Inflammasome Mediates Inflammation and Voiding Dysfunction in a Lipopolysaccharide-Induced Rat Model of Cystitis

OBJECTIVE

NOD-like receptors (NLRs) sense sterile and non-sterile signals and form inflammasomes which trigger an inflammatory response through the activation of caspase-1 and release of IL-1β. Recently we have shown the presence of several NLRs in the bladder urothelia and demonstrated the importance of NLRP3 in bladder outlet obstruction and cyclophosphamide-induced cystitis, both models of sterile inflammation. In this study we explore a role for NLRP3 in mediating the response to LPS, a key antigen of uropathogenic bacteria.

METHOD

In order to bypass the protective glycosaminoglycan layer lining the urothelium, LPS was directly injected into the bladder wall of Sprague-Dawley rats. Glyburide (a NLRP3 inhibitor) or vehicle was administered orally prior to and after injection. Rats were analyzed 24 h later. Inflammasome activity (caspase-1 activity, IL-1β release) and inflammation (Evan's Blue extravasation, bladder weight) were assessed, as was physiological bladder function (urodynamics).

RESULTS

Injection of LPS stimulated inflammasome activation (caspase-1 activity) and the release of IL-1β into the urine which was prevented by glyburide. Likewise, LPS increased inflammation, (bladder weight and the extravasation of Evan's blue dye), and this was reversed by glyburide. Functionally, animals injected with saline alone demonstrated decreased voiding volume as measured by urodynamics. In the presence of LPS, additional urinary dysfunction was evident with decreased voiding pressures and threshold pressures. The decrease in voiding pressure was blocked by glyburide but the decrease in threshold pressure was not, suggesting that LPS has significant effects mediated by inflammasome-dependent and -independent mechanisms.

CONCLUSION

Overall, the results demonstrate the potential importance of inflammasomes in bacterial cystitis as well as the ability of the bladder wall injection technique to isolate the in vivo effects of specific inflammasome ligands to the physiological changes associated with cystitis.

The potential repertoire of the innate immune system in the bladder: expression of pattern recognition receptors in the rat bladder and a rat urothelial cell line (MYP3 cells)

PURPOSE

The urothelium is a frontline sensor of the lower urinary tract, sampling the bladder lumen and stimulating an immune response to infectious and noxious agents. Pattern recognition receptors (PRRs) recognize such agents and coordinate the innate response, often by forming inflammasomes that activate caspase-1 and the release of interleukin-1. We have shown the presence of one PRR (NLRP3) in the urothelia and its central role in the inflammatory response to cyclophosphamide. The purpose of this study was to (1) assess the likely range of the PPR response by assessing the repertoire present in the rat bladder and (2) determine the utility of the MYP3 rat urothelia cell line for in vitro studies by assessing its PPR repertoire and functional responsiveness.

METHODS

Immunohistochemistry was performed for seven PPRs (NLRP1, NLRP3, NLRP6, NLRP7, NLRP12, NLRC4 and AIM2) on bladder sections and MYP3 cells. For functionality, MYP3 cells were challenged with the quintessential NLRP3 activator ATP and assessed for caspase-1 activation.

RESULTS

All PPRs examined were expressed in the bladder and localized to the urothelial layer with several also in the detrusor (none in the interstitia). MYP3 cells also expressed all PRRs with a variable intracellular location. ATP-stimulated caspase-1 activity in MYP3 cells in a dose-dependent manner was reduced by knockdown of NLRP3 expression.

CONCLUSION

The results suggest that the bladder possesses the capacity to initiate an innate immune response to a wide array of uropathological agents and the MYP3 cells will provide an excellent investigational tool for this field.

A novel urodynamic model for lower urinary tract assessment in awake rats

OBJECTIVES

To develop a urodynamic model incorporating external urethral sphincter (EUS) electromyography (EMG) in awake rats.

MATERIALS AND METHODS

Bladder catheters and EUS EMG electrodes were implanted in female Sprague Dawley rats. Assessments were performed in awake, lightly restrained rats on postoperative day 12-14. Measurements were repeated in the same rat on day 16 under urethane anaesthesia. Urodynamics and EUS EMG were performed simultaneously. In addition, serum creatinine and bladder histology was assessed.

RESULTS

No significant differences in urodynamic parameters were found between bladder catheter only vs bladder catheter and EUS EMG electrode groups. Urethane anaesthesia evoked prominent changes in both urodynamic parameters and EUS EMG. Serum creatinine was within the normal limits in all rats. Bladder weight and bladder wall thickness were significantly increased in both the bladder catheter only and the bladder catheter and EUS EMG group compared with controls.

CONCLUSIONS

Our novel urodynamic model allows repetitive measurements of both bladder and EUS function at different time points in the same rat under fully awake conditions and opens promising avenues to investigate lower urinary tract dysfunction in a translational approach.

S-Nitrosoglutathione protects the spinal bladder: novel therapeutic approach to post-spinal cord injury bladder remodeling

AIMS

Bladder and renal dysfunction are secondary events of the inflammatory processes induced by spinal cord injury (SCI). S-Nitrosoglutathione (GSNO), an endogenous nitrosylating agent is pleiotropic and has anti-inflammatory property. Hence, GSNO ameliorates inflammatory sequelae observed in bladder and renal tissues after SCI. Thus, we postulate that GSNO will improve the recovery of micturition dysfunction by quenching the bladder tissue inflammation associated with SCI.

METHODS

Contusion-based mild SCI was induced in female Sprague-Dawley rats. Sham operated rats served as the controls. SCI rats were gavaged daily with GSNO (50 µg/kg) or vehicle. Bladder function was assessed by urodynamics at 2 and 14 days following SCI. Urine protein concentration and osmolality were measured. Bladder and kidney tissues were analyzed by histology and immunofluorescence for a variety of endpoints related to inflammation.

RESULTS

Two days after SCI, urodynamics demonstrated a hyperreflexive bladder with overflow and no clear micturition events. By Day 14, vehicle animals regained a semblance of a voiding cycle but with no definite intercontraction intervals. GSNO-treated SCI-rats showed nearly normal cystometrograms. Vehicle-treated SCI rats had increased bladder wet weight, proteinuria, and urine osmolality at Day 14, which was reversed by GSNO treatment. In addition, the SCI-induced increase in immune cell infiltration, collagen deposition, iNOS, and ICAM-1 expression and apoptosis were attenuated by GSNO.

CONCLUSIONS

These results indicate that oral administration of GSNO hastens the recovery of bladder function after mild contusion-induced SCI through dampening the inflammation sequelae. These findings also suggest that GSNO-mediated redox modulation may be a novel therapeutic target for the treatment of mild SCI-induced renal and bladder dysfunction.

Inflammasomes are important mediators of cyclophosphamide-induced bladder inflammation

Bladder inflammation (cystitis) underlies numerous bladder pathologies and is elicited by a plethora of agents such as urinary tract infections, bladder outlet obstruction, chemotherapies, and catheters. Pattern recognition receptors [Toll-like receptors (TLRs) and Nod-like receptors (NLRs)] that recognize pathogen- and/or damage-associated molecular patterns (PAMPs and/or DAMPs, respectively) are key components of the innate immune system that coordinates the production (TLRs) and maturation (NLRs) of proinflammatory IL-1β. Despite multiple studies of TLRs in the bladder, none have investigated NLRs beyond one small survey. We now demonstrate that NLRP3 and NLRC4, and their binding partners apoptosis-associated speck-like protein containing a COOH-terminal caspase recruitment domain (ASC) and NLR family apoptosis inhibitory protein (NAIP), are expressed in the bladder and localized predominantly to the urothelia. Activated NLRs form inflammasomes that activate caspase-1. Placement of a NLRP3- or NLRC4-activating PAMP or NLRP3-activating DAMPs into the lumen of the bladder stimulated caspase-1 activity. To investigate inflammasomes in vivo, we induced cystitis with cyclophosphamide (CP, 150 mg/kg ip) in the presence or absence of the inflammasome inhibitor glyburide. Glyburide completely blocked CP-induced activation of caspase-1 and the production of IL-1β at 4 h. At 24 h, glyburide reduced two markers of inflammation by 30-50% and reversed much of the inflammatory morphology. Furthermore, glyburide reversed changes in bladder physiology (cystometry) induced by CP. In conclusion, NLRs/inflammasomes are present in the bladder urothelia and respond to DAMPs and PAMPs, whereas NLRP3 inhibition blocks bladder dysfunction in the CP model. The coordinated response of NLRs and TLRs in the urothelia represents a first-line innate defense that may provide an important target for pharmacological intervention.

Development of a Peptide-derived orally-active kappa-opioid receptor agonist targeting peripheral pain

Kappa-opioid agonists are particularly efficacious in the treatment of peripheral pain but suffer from central nervous system (CNS)-mediated effects that limit their development. One promising kappa-agonist is the peptidic compound CR665. Although not orally available, CR665 given i.v. exhibits high peripheral to CNS selectivity and benefits patients with visceral and neuropathic pain. In this study we have generated a series of derivatives of CR665 and screened them for oral activity in the acetic acid-induced rat writhing assay for peripheral pain. Five compounds were further screened for specificity of activation of kappa receptors as well as agonism and antagonism at mu and delta receptors, which can lead to off-target effects. All active derivatives engaged the kappa receptor with EC50s in the low nM range while agonist selectivity for kappa over mu or delta was >11,000-200,000-fold. No antagonist activity was detected. One compound was chosen for further analysis (Compound 9). An oral dose response of 9 in rats yielded an EC50 of 4.7 mg/kg, approaching a druggable level for an oral analgesic. To assess the peripheral selectivity of this compound an i.v. dose response in rats was assessed in the writhing assay and hotplate assay (an assay of CNS-mediated pain). The EC50 in the writhing assay was 0.032 mg/kg while no activity was detectable in the hotplate assay at doses as high as 30 mg/kg, indicating a peripheral selectivity of >900-fold. We propose that compound 9 is a candidate for development as an orally-available peripherally-restricted kappa agonist.

Cyclophosphamide Induces an Early Wave of Acrolein-Independent Apoptosis in the Urothelium

PURPOSE

Hemorrhagic cystitis (HC or bladder inflammation) affects a significant number of patients undergoing cyclophosphamide (CP) chemotherapy despite treatment with 2-mercaptoethane sulfonate (Mesna) to inactivate the metabolite acrolein. While the mechanism is unknown, there is clearly acrolein-independent damage to the urothelium. In this study we have explored the induction of apoptosis in the urothelium as a marker of damage and the mechanism underlying the acrolein-independent apoptosis.

MATERIALS AND METHODS

Apoptosis in urothelium (caspase-3/7 activity and Poly (ADP-ribosyl) polymerase (PARP) cleavage) was measured following CP administration (80 mg/kg). Sodium 2-mercaptoethane sulfonate (Mesna) was used to mask acrolein's effect. An IL-1β receptor antagonist and a cell-permeable caspase-1 inhibitor were used to assess the involvement of IL-1β and caspase-1, respectively.

RESULTS

Two waves of apoptosis were detected following CP administration, one peaking at 2 h and a second at 48 h. The first wave was independent of acrolein. Caspase-1 was also active at 2 h and activation of caspase-3/7 was blocked by a caspase-1 inhibitor but not an IL-1β receptor antagonist suggesting the direct activation of caspase-3/7 by caspase-1 without the need for IL-1β as an intermediate.

CONCLUSIONS

Our results indicate that CP initiates an early, acrolein-independent wave of apoptosis that results from direct cleavage of caspase-3/7 by caspase-1.

Simvastatin suppresses cyclophosphamide-induced changes in urodynamics and bladder inflammation

OBJECTIVE

To assess the ability of daily oral simvastatin administration to reduce the negative urodynamic changes associated with cyclophosphamide (CP)-induced cystitis and to prevent bladder inflammation. Patients undergoing CP chemotherapy frequently develop cystitis, leading to urinary dysfunction and hemorrhage. Recent studies have suggested statins possess anti-inflammatory properties and might be uroprotective.

MATERIALS AND METHODS

Urodynamic properties were analyzed in 4 groups of female Sprague-Dawley rats: group 1, vehicle (300 μL, 0.5% methylcellulose, orally for 7 days); group 2, simvastatin (1 mg/rat/d); group 3, vehicle plus CP (intraperitoneally 80 mg/kg, 24 h before cystometry); and group 4, simvastatin plus CP. The inflammation in the groups was assessed using Evans blue extravasation.

RESULTS

CP stimulated significant increases in the number of nonvoiding contractions (0.83±0.26 vs 4.97±1.90; P=.03) and decreases in the peak voiding pressure (53.46±5.08 vs 33.34±4.37 cm H2O; P=.01). Simvastatin returned these parameters to the control levels of 1.62±0.73 (P=.70) and 45.98±7.78 cm H2O (P=.38). CP at this level caused a slight, but significant, increase in the voided volume (0.82±0.13 vs 1.16±0.14 mL; P=.04), which returned to control levels (0.74±0.12 mL; P=.65) with simvastatin. Other urodynamic parameters, such as the threshold pressure, were not affected by simvastatin or CP, or the combination of the 2. CP-induced inflammation in the bladder (Evans blue extravasation) was suppressed by simvastatin.

CONCLUSION

Simvastatin was effective at ameliorating the negative urodynamic changes and inflammation in the bladder after CP administration and is a potential therapy for preventing side effects in patients undergoing this chemotherapy.

The potential role of caveolin-1 in inhibition of aquaporins during the AVD

BACKGROUND INFORMATION

During apoptosis, the first morphological change is a distinct cell shrinkage known as the AVD (apoptotic volume decrease). This event is driven by a loss of intracellular K(+), which creates an osmotic gradient, drawing water out of the cell through AQPs (aquaporins). Loss of water in balance with K(+) would create a shrunken cell with an equivalent intracellular concentration of K(+) ([K(+)](i) = 140 mM). However, we have previously shown that the [K(+)](i) of the shrunken apoptotic cell is 35 mM, and this level is absolutely essential for the activation of apoptotic enzymes. We have recently found that AQPs are inactivated following the AVD, so that continued loss of K(+) will reduce the intracellular concentration to this critical level. Using thymocytes, we have investigated the expression profile and regulation of the AQP family members.

RESULTS

In the present study, we have found that AQP1, AQP8 and AQP9 are present in non-apoptotic thymocytes and localized primarily to the plasma membrane. Expression and localization did not change when these cells were induced to undergo apoptosis by growth factor withdrawal for 24 h. To explore other possible mechanisms by which these water channels are inactivated, we investigated their association with CAV-1 (caveolin-1), binding to which is known to inactivate a variety of proteins. We found that CAV-1 is present in thymocytes and that this protein co-localizes with a portion of AQP1 in normal (non-apoptotic) thymocytes. However, thymocytes induced to undergo apoptosis greatly increase their AQP1/CAV-1 association.

CONCLUSIONS

Taken together, these results indicate that AQPs are localized to the plasma membrane of shrunken apoptotic thymocytes where increased binding to CAV-1 potentially inactivates them. AQP inactivation, coupled with continued K(+) efflux, then allows the [K(+)](i) to decrease to levels conducive for the activation of downstream apoptotic enzymes and the completion of the apoptotic cascade.

Copper exposure affects hemocyte apoptosis and Perkinsus marinus infection in eastern oysters Crassostrea virginica (Gmelin)

Dermo disease in the eastern oyster (Crassostrea virginica) is caused by an intracellular protistan parasite Perkinsus marinus. The progression and outcome of this disease is determined by a complex interplay between the host's immunity and parasite's escape mechanisms, both of which can be influenced by environmental pollutants including heavy metals such as copper (Cu). The goal of the present study was to determine the effects of Cu on the levels of apoptosis (which can serve as an important host defense mechanism) in oyster immune cells (hemocytes) in vitro and in vivo as well as on the establishment of P. marinus infections in vivo. Surprisingly, Cu exerted opposing effects on apoptosis levels of hemocytes in vitro and in vivo, stimulating apoptosis in isolated hemocytes but suppressing it during Cu exposure of whole oysters. The mechanisms of this effect are presently unknown and may be related to the different bioavailability of the metal in vitro and in vivo. As expected, Cu accumulated in oyster soft tissues during in vitro exposure. Unexpectedly, this metal also strongly accumulated in hemolymph plasma which is classically considered isoionic with the surrounding seawater, likely reflecting the presence of soluble Cu-binding proteins in oyster plasma. Cu reduced growth of P. marinus in vitro and greatly reduced infection levels of hemocytes in vivo, presumably by direct toxic effects on the parasite. As a possible parasitic counterbalance, Cu accumulation in the hemocytes was reduced by P. marinus infection, although this reduction was not sufficient to prevent the parasiticidal effects of the heavy metal in vivo. This effect of Cu may be useful as a potential therapeutic against Dermo disease in aquaculture conditions. Overall, this study provides important new insights into the potential role of environmental metals in host-parasite relationships and disease dynamics in C. virginica.

Apoptosis as a host defense mechanism in Crassostrea virginica and its modulation by Perkinsus marinus

Dermo disease caused by the obligatory intracellular protozoan Perkinsus marinus causes extensive oyster mortalities leading to tremendous losses in the oyster industry and damage to estuarine ecosystems. To better understand the mechanisms of the parasite's evasion of the host immune defense system, we have investigated the molecular mechanisms of P.marinus-induced inhibition of apoptosis in oyster cells as a potential parasite's survival strategy. We found that P. marinus modulates apoptosis of oyster immune cells (hemocytes) in a way that may help the parasite to establish infection. We found an increase in apoptosis in the initial stages of infection in vitro and in vivo, consistent with a host response to this intracellular parasite. During infection with highly virulent strains of P. marinus, this was followed by suppression and a return of apoptosis to basal levels 8-24 h post-infection, strongly indicating the parasite-induced inhibition of the immune response. In contrast, during infections with intermediate or low virulence strains of P. marinus, a transient suppression of apoptosis 4-8 h post-infection was followed by sustained elevation of hemocyte apoptosis at later stages, indicating that hemocytes were able to overcome the parasite-induced suppression and successfully combat the infection. Studies of the mechanisms of P. marinus-induced apoptosis indicated that the early post-infection stimulation of apoptosis is caspase-independent. However, this process can be driven (although to a lesser degree) by the killed parasite, suggesting that oyster hemocytes respond to cell surface molecules of P. marinus. Overall, this study provides novel insights into pathogen-induced modulation of apoptosis and its role in parasite virulence and establishment of infections.

Identification and functional characterization of a stable, centrally active derivative of the neurotensin (8-13) fragment as a potential first-in-class analgesic

The neurotensin hexapapetide fragment NT(8-13) is a potent analgesic when administered directly to the central nervous system but does not cross the blood-brain barrier. A total of 43 novel derivatives of NT(8-13) were evaluated, with one, ABS212 (1), being most active in four rat models of pain when administered peripherally. Compound 1 binds to human neurotensin receptors 1 and 2 with IC(50) of 10.6 and 54.2 nM, respectively, and tolerance to the compound in a rat pain model did not develop after 12 days of daily administration. When it was administered peripherally, serum levels and neurotensin receptor binding potency of 1 peaked within 5 min and returned to baseline within 90-120 min; however, analgesic activity remained near maximum for >240 min. This could be due to its metabolism into an active fragment; however, all 4- and 5-mer hydrolysis products were inactive. This pharmacokinetic/pharmacodynamic dichotomy is discussed. Compound 1 is a candidate for development as a first-in-class analgesic.

Gamma-aminobutyric acid inhibits synergistic interleukin-6 release but not transcriptional activation in astrocytoma cells

OBJECTIVE

A decline in the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) may enhance cytokine release in Alzheimer's disease (AD) resulting in neuroinflammation. We investigated the GABA-mediated suppression of the synergistic release of interleukin (IL)-6 due to interleukin 1-beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha).

METHODS

Rat C6 astrocytoma cells were treated with IL-1 beta and TNF-alpha in the absence and presence of GABA. Activation of p38, degradation of I kappaB-alpha and total cellular IL-6 were determined by Western blot analysis. IL-6 release and gene expression were measured by ELISA and RT-PCR, respectively.

RESULTS

Although p38 and nuclear factor (NF)-kappaB are essential for the synergistic release of IL-6, GABA did not affect either p38 phosphorylation or I kappaB-alpha degradation. Additionally, GABA suppressed IL-6 release but did not alter cytokine-driven synergistic increases in IL-6 gene expression. Western blot analysis revealed that co-treatments with IL-1 beta and TNF-alpha resulted in an increase in intracellular IL-6 that was prevented by GABA.

CONCLUSION

GABA-induced inhibition of IL-6 release appears to coincide with a reduction in cellular IL-6. The GABA-induced suppression of IL-6 release may include inhibition of IL-6 gene translation.

Decreased aquaporin expression leads to increased resistance to apoptosis in hepatocellular carcinoma

Cells undergoing apoptosis are characterized by decreased cell size due to changes in intracellular ion concentration and rapid, aquaporin (AQP)-dependent water movement out of the cell, events required for the activation of pro-apoptotic enzymes. The current study demonstrates AQP 8 and 9 expression is significantly decreased in hepatocellular carcinoma (HCC) versus normal liver. Isolation of hepatic tumor cells (H4IIE) and hepatocytes confirmed a lack of water movement across the H4IIE cell membrane via AQPs and identified an inherent resistance of H4IIE cells to apoptotic stimuli. In contrast, hepatocytes rapidly responded to osmotic challenge through AQP-dependent water movement and underwent cell death following apoptotic stimulation.

Cadmium-induced apoptosis in oyster hemocytes involves disturbance of cellular energy balance but no mitochondrial permeability transition

Exposure to environmentally prevalent heavy metals such as cadmium can have detrimental effects on a variety of commercially and ecologically important species such as oysters. Since Cd(2+) is known to induce apoptosis in immune cells of vertebrates, we have investigated the effects of this metal on isolated oyster hemocytes, the main cellular immune defense in mollusks. Enhanced apoptosis of these cells could conceivably create immunosuppressed conditions in these organisms and result in reduced disease resistance and increased opportunistic infection, resulting in decline of their populations. Cd(2+) exposure induced apoptosis in oyster hemocytes in a dose-dependent manner in the range of 10-100 micromol l(-1), as indicated by the translocation of phosphatidylserine to the outer leaflet of the plasma membrane. At higher concentrations (200-1000 micromol l(-1)), there was no further increase in apoptosis but a significant increase in the level of necrosis. In stark contrast to vertebrate immune cells, there was no decrease in the mitochondrial membrane potential or activation of caspases in response to Cd(2+) in the apoptotic range. Surprisingly, Cd(2+) exposure in this range did cause a significant decrease in intracellular ATP levels, indicating a severe disturbance of energy metabolism. Similarly, Cd(2+) exposure of isolated mitochondria resulted in partial uncoupling of mitochondria but no difference in mitochondrial membrane potential. The results demonstrate that the important environmental pollutant Cd(2+) induces apoptosis in oyster immune cells and does so through a mitochondria/caspase-independent pathway, suggesting that a novel, perhaps ancient, apoptotic pathway is active in these cells. Furthermore, it appears that the observed decrease in ATP production during apoptosis is not due to the loss of the mitochondrial proton-motive force but is more likely to be due to inhibition of the F(0)/F(1)-ATPase and/or mitochondrial ADP/ATP or substrate transport.

Plasma membrane aquaporin activity can affect the rate of apoptosis but is inhibited after apoptotic volume decrease

Apoptosis is characterized by a conserved series of morphological events beginning with the apoptotic volume decrease (AVD). This study investigated a role for aquaporins (AQPs) during the AVD. Inhibition of AQPs blocked the AVD in ovarian granulosa cells undergoing growth factor withdrawal and blocked downstream apoptotic events such as cell shrinkage, changes in the mitochondrial membrane potential, DNA degradation, and caspase-3 activation. The effects of AQP inhibition on the AVD and DNA degradation were consistent in thymocytes and with two additional apoptotic signals, thapsigargin and C6-ceramide. Overexpression of AQP-1 in Chinese hamster ovary (CHO-AQP-1) cells enhanced their rate of apoptosis. The AVD is driven by loss of K+from the cell, and we hypothesize that after the AVD, AQPs become inactive, which halts further water loss and allows K+concentrations to decrease to levels necessary for apoptotic enzyme activation. Swelling assays on granulosa cells, thymocytes, and CHO-AQP-1 cells revealed that indeed, the shrunken (apoptotic) subpopulation has very low water permeability compared with the normal-sized (nonapoptotic) subpopulation. In thymocytes, AQP-1 is present and was shown to colocalize with the plasma membrane receptor tumor necrosis factor receptor-1 (TNF-R1) both before and after the AVD, which suggests that this protein is not proteolytically cleaved and remains on the cell membrane. Overall, these data indicate that AQP-mediated water loss is important for the AVD and downstream apoptotic events, that the water permeability of the plasma membrane can control the rate of apoptosis, and that inactivation after the AVD may help create the low K+concentration that is essential in apoptotic cells. Furthermore, inactivation of AQPs after the AVD does not appear to be through degradation or removal from the cell membrane.

Estrogen regulation of aquaporins in the mouse uterus: potential roles in uterine water movement

Estrogen stimulates water imbibition in the uterine endometrium. This water then crosses the epithelial cells into the lumen, leading to a decrease in viscosity of uterine luminal fluid. To gain insight into the mechanisms underlying this estrogen-stimulated water transport, we have explored the expression profile and functionality of water channels termed aquaporins (AQPs) in the ovariectomized mouse uterus treated with ovarian steroid hormones. Using immunocytochemical analysis and immunoprecipitation techniques, we have found that AQP-1, -3, and -8 were constitutively expressed. AQP-1 expression was restricted to the myometrium and may be slightly regulated by ovarian steroid hormones. AQP-3 was expressed at low levels in the epithelial cells and myometrium, whereas AQP-8 was found in both the stromal cells and myometrium. AQP-2 was absent in vehicle controls but strongly up-regulated by estrogen in the epithelial cells and myometrium of the uterus. This localization implicates all four isotypes in movement of water during uterine imbibition and, based on their localization to the luminal epithelial cells, AQP-2 and -3 in facilitating water movement into the lumen of the uterus. The analysis of the plasma membrane permeability of luminal epithelial cells by two separate cell swelling assays confirmed a highly increased water permeability of these cells in response to estrogen treatment. This finding suggests that estrogen decreases the luminal fluid viscosity, in part, by enhancing the water permeability of the epithelial layer, most likely by increasing the expression of AQP-2 and/or the availability of AQP-3. Together these results provide novel information concerning the mechanism by which estrogen controls water imbibition and luminal fluid viscosity in the mouse uterus.

Bacterial infection of osteoblasts induces interleukin-1beta and interleukin-18 transcription but not protein synthesis

A growing body of evidence has shown that bacterially challenged bone-forming osteoblasts are a significant source of an array of cytokines and chemokines that can support immune responses during bone disease. In the present study, Staphylococcus aureus and Salmonella, two common pathogens of bone, were investigated for their ability to induce production of two related inflammatory cytokines, interleukin-1beta (IL-1beta) and IL18, in osteoblasts. Cultured mouse osteoblasts were found to respond rapidly to either bacterial challenge by upregulation in the levels of mRNA encoding both IL-1beta and IL-18. Surprisingly, this mRNA expression did not translate into intracellular accumulation of IL-1beta or IL-18 precursor proteins or secretion of mature cytokines, despite the presence of detectable caspase-1 activity in these cells. These studies demonstrate that although osteoblasts can secrete a number of key proinflammatory mediators in response to bacterial pathogens, IL-1beta and IL-18 are not among this number. We suggest that osteoblasts are an unlikely source of these cytokines during the progression of bacterial infection of bone.

Water permeability of an ovarian antral follicle is predominantly transcellular and mediated by aquaporins

Ovarian folliculogenesis is characterized, in part, by the formation and expansion of the fluid-filled antrum. Development of this cavity requires water influx, which may occur by transcellular or pericellular transport mechanisms. To assess the contribution of these mechanisms to the water permeability of an antral follicle, the rate of (3)H(2)O and (14)C-inulin (a complex sugar restricted to the extracellular compartment) uptake into isolated follicles was determined. The rate of H(2)O movement was 3.5-fold greater than that of inulin, suggesting that water enters a follicle primarily by transcellular pathways. Preincubation of the follicles with 50 microM HgCl(2) [a nonspecific aquaporin (Aqp) inhibitor] decreased H(2)O movement to levels seen with inulin, indicating that transcellular water movement is mediated through Aqp. To demonstrate the functional presence of Aqp in granulosa cells, we show that swelling in response to a hypotonic insult is attenuated by preincubation with 50 microM HgCl(2). Flow cytometry demonstrated the presence of Aqps-7, -8, and -9, thus identifying candidate Aqp potentially mediating water movement into antral follicles. These results suggest that water permeability of antral follicles occurs primarily through transcellular mechanisms, which may be mediated by Aqps -7, -8, and/or -9 in granulosa cells.

Potassium is a critical regulator of apoptotic enzymes in vitro and in vivo

Apoptosis, or programmed cell death, is a fundamental biological process involved in many physiological and pathological phenomena. This process is predominantly catabolic in which cellular macromolecules are broken down by distinct enzymes to be later recycled in healthy cells. These enzymes are arranged in an elaborate cascade that serves to both propagate and amplify a death signal as well as process bulk macromolecules and inhibit repair systems. One of the best-characterized enzyme systems involved in apoptosis is the activation of a nuclease(s) that degrades the genome into discrete oligonucleosomal fragments, clearly committing a cell to death. Using two different in vitro models, we have shown that K+ directly inhibits this/these nuclease(s) with complete inhibition observed at cellular concentrations of K+ found in non-dying cells (150 mM). These data suggest that K+ concentrations in living cells suppress apoptotic nuclease activity. One of the nucleases involved in apoptotic DNA degradation (NUC18/Cyclophilin) has been purified in our laboratory and found to be inhibited by similar concentrations of K+. Upstream of DNA fragmentation a specific class of proteases, termed caspases, are activated which propagate an apoptotic signal and lead to downstream events such as DNA fragmentation. Using an in vitro model of caspase activation, we also observed that activation of this enzyme is also completely inhibited by normal physiological K+ levels, suggesting that K+ levels in non-dying cells suppress multiple portions of the apoptotic enzyme cascade. These results suggest that K+ concentrations may decrease in cells undergoing apoptosis and both physical and fluorescence techniques document an intracellular K+ concentration of 35 mM in apoptotic cells. This loss of K+ also accounts for changes in cell volume (cell shrinkage) that are universally associated with apoptosis. Measurements of K+ concentration in shrunken and non-shrunken cells demonstrated that only shrunken cells contain a reduced concentration of intracellular K+. Importantly, both the nuclease and caspase activity were found exclusively in this shrunken population providing an absolute correlation between the activity of these enzymes and low K+ levels within a cell. Finally, suppressing K+ efflux in whole cells prevents the activation of these enzymes whereas enhancing the efflux of this ion facilitates enzymatic activity. These results suggest a direct cause and effect relationship between the level of K+ and the activity of apoptotic enzymes. Taken together we have shown a critical and novel mechanism that regulates apoptosis by a direct effect on the apoptotic enzymes.

Staphylococcus aureus and Salmonella enterica serovar Dublin induce tumor necrosis factor-related apoptosis-inducing ligand expression by normal mouse and human osteoblasts

Staphylococcus aureus and Salmonella enterica serovar Dublin invade osteoblasts and are causative agents of human bone disease. In the present study, we examined the ability of S. aureus and Salmonella serovar Dublin to induce the production of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by normal osteoblasts. Normal mouse and human osteoblasts were cocultured with S. aureus or Salmonella serovar Dublin at different multiplicities of infection. Following initial incubation and examination of TRAIL expression, extracellular bacteria were killed by the addition of media containing the antibiotic gentamicin. Lysates and conditioned media from osteoblast cultures were then collected at various times following invasion and analyzed. The results demonstrated that S. aureus and Salmonella serovar Dublin are potent inducers of TRAIL expression by osteoblasts. Mouse and human TRAIL mRNA expression was induced by bacterial infection and demonstrated a dose-dependent response. Analysis of kinetics suggested that TRAIL mRNA was induced within 30 min after exposure to bacteria and that its level of expression remained relatively constant over the time period examined. mRNA molecules encoding TRAIL receptors were constitutively expressed by osteoblasts. Furthermore, TRAIL protein was detected as early as 45 min and up to 24 h following infection. The quantity of TRAIL protein produced also increased in a dose-dependent manner. Collectively, these findings suggest a mechanism whereby bacterial pathogens mediate bone destruction via osteoblast apoptosis.

Apoptotic nuclease assays

One of the defining biochemical characteristics of apoptosis is the degradation of chromatin into regularly sized (oligonucleosomal and approximately 30- to 50-kb) fragments. Because destruction of the genome represents a clear commitment to death, considerable interest has focused on this component of apoptosis and numerous assays have been developed to assess the relevant nucleases involved. These assays fall into two major categories: (1) those independent of chromatin structure and (2) those dependent on chromatin structure. The chromatin-independent assays (plasmid degradation assay and radioactive gel assay) examine the ability to degrade naked DNA and are advantageous because of their simplicity and speed and ability to analyze single nucleases or mixtures of nucleases. However, these assays do not mimic the conditions present in normal cells and consequently do not assess the ability of an enzyme to function in apoptosis. In contrast, chromatin structure-dependent assays (nuclear autodigestion and HeLa nuclei assay) present intact chromatin to either endogenous or exogenous enzymes and assess the ability to degrade chromatin in a manner that recapitulates the genomic destruction seen in vivo. Detailed protocols are discussed for both classes of assays. These assays have been instrumental in the identification of several apoptotic nucleases.

Identification of potassium-dependent and -independent components of the apoptotic machinery in mouse ovarian germ cells and granulosa cells

Recent studies with thymocytes have suggested a critical role for intracellular potassium in the regulation of apoptosis. In this study, we examined the pathways of K(+) regulation during ovarian cell death. In initial studies, fluorographic analysis demonstrated a significant loss of K(+) during apoptosis stimulated by doxorubicin in oocytes and trophic hormone deprivation in granulosa cells. In oocytes, suppression of potassium efflux by potassium-enriched medium prevented condensation, budding, and fragmentation, although it did not block DNA degradation, suggesting the existence of potassium-independent nucleases in oocytes. Culture of granulosa cells in potassium-enriched medium inhibited internucleosomal DNA cleavage, although high-molecular weight DNA cleavage was apparent, suggesting that the nuclease or nucleases responsible for generating 50-kilobase (kb) fragments in these cells is potassium independent. To address this directly, isolated granulosa cell nuclei were stimulated to autodigest their DNA, and internucleosomal, but not large-fragment, cleavage was completely blocked by 150 mM potassium. We next examined whether the proapoptotic caspases are targets for potassium regulation. In cell-free assays, processing of pro-interleukin-1beta and proteolysis of cellular actin by recombinant caspase-1 and caspase-3, respectively, were suppressed by the presence of 150 mM potassium. Other monovalent ions (NaCl, LiCl) exerted a similar effect in these cell-free assays. Thus, in oocytes and granulosa cells, potassium efflux appears to occur early in the cell death program and may regulate a number of apoptotic events including caspase activity and internucleosomal DNA cleavage. However, there also exist novel potassium-independent pathways in both ovarian germ cells and somatic cells that signal certain apoptotic events, such as large-fragment DNA cleavage.

Delineation of the signaling pathways involved in glucocorticoid-induced and spontaneous apoptosis of rat thymocytes

In primary rat thymocytes, both glucocorticoids and the withdrawal of in vivo survival factors elicit apoptosis. In this study we wanted to determine whether distinct pathways leading to apoptosis are engaged by these two stimuli. To address this question, we conducted a multiparametric analysis of cell viability, DNA fragmentation, activation of caspase-3-like activity, cell shrinkage, the loss of mitochondrial membrane potential, and externalization of phosphatidylserine in the absence and presence of protein and RNA synthesis. The role of caspase activity was also examined in both glucocorticoid-and survival factor withdrawal-induced cell death. We show that glucocorticoid-induced, but not spontaneous, loss of viability is dependent upon macromolecular synthesis and caspase activity. Furthermore, glucocorticoid-induced phosphatidylserine externalization and cell shrinkage are dependent upon gene regulation and caspase activity, whereas these features manifest independently of gene regulation and caspase activity in spontaneous death. In contrast, the loss of mitochondrial membrane potential was dependent upon macromolecular synthesis only in glucocorticoid-induced death and was independent of caspases in both spontaneous and dexamethasone-induced death. These results suggest that thymocytes can die by a caspase-independent mechanism and that a major difference between glucocorticoid- and survival factor deprivation-induced death is the dependence on gene expression.

A necessary role for reduced intracellular potassium during the DNA degradation phase of apoptosis

Apoptosis is a highly organized mechanism that allows specific cells to die in a controlled manner. Apoptosis can be induced by a variety of agents in a great number of cell types, but cell shrinkage and discrete chromatin cleavage remain common components of apoptosis that is manifested by constitutive enzymes. Despite intensive investigation, the actual event or events that signal this cell death process have not been completely identified. Because of their ability to effect a great number of cellular enzymes simultaneously, we have hypothesized that ions in high concentration (150 mM) in living cells may act as a repressor of apoptotic effectors. In this manuscript we review data that shows that DNA degradation only occurs in the shrunken population of lymphocytes treated with glucocorticoid, shrunken cells loose K+ and become hypotonic, and physiological concentrations on K+ inhibit nuclease activity irrespective of proteins. Together, these data suggest that the reduction in potassium levels appears necessary for the DNA degradation that occurs during apoptosis.