Aquaporin-2 plays an important role in water transportation through the bladder wall in rats

Effect of Arsenate and p-Phenylenediamine on the Expression of Aquaporins in Cultured Human Urothelial Cells

BACKGROUND

Exposure to arsenic (As) or p‑phenylenediamine (PPD) can lead to dysfunction, or even cancer, in various types of organs, including the urinary bladder, yet the underlying mechanisms remain unclear. Aquaporins (AQPs) are widely expressed small water channel proteins that provide the major route for the transport of water and other small molecules across plasma membranes in diverse cell types. Altered expression of AQPs has been associated with pathologies in all major organs, including the urinary bladder.

OBJECTIVE

The present in vitro study was performed as a first step towards exploring the possible involvement of AQPs in As- and PPD‑induced bladder diseases.

METHODS

An immortalized normal human urothelial cell line was employed. Cells were exposed to different concentrations of sodium arsenate (0‑20 μM) or PPD (0‑200 μM) for 48 h. Cell viability was subsequently assessed. The mRNA and protein expression levels of AQPs (specifically, AQP3, 4, 7, 9, and 11) were analyzed using reverse transcription‑quantitative polymerase chain reaction and Western blot analyses, respectively.

RESULTS

The viability of the cells was decreased in a concentration-dependent manner upon exposure to arsenate. The mRNA and protein expression levels of AQP3, 4, 7, and 9 were substantially reduced, whereas the expression of AQP11 was largely unchanged. As for the experiments with PPD, treatment with increasing concentrations of PPD induced a gradual decrease in cell viability. The mRNA and protein expression levels of AQP3, 4, and 11 were generally unaltered; however, a marked reduction in the expression levels of AQP7 was observed, contrasting with a gradual concentration-dependent decrease in the expression of AQP9.

CONCLUSION

The importance of the differential expression profiles of the AQPs induced by arsenate and PPD requires further investigation; nevertheless, the findings of the present study suggest that AQPs have a role in As‑ and PPD‑induced bladder diseases.

Effective Treatments of UTI—Is Intravesical Therapy the Future?

Urinary tract infection (UTI) afflicts millions of patients globally each year. While the majority of UTIs are successfully treated with orally administered antibiotics, the impact of oral antibiotics on the host microbiota is under close research scrutiny and the potential for dysbiosis is a cause for concern. Optimal treatment of UTI relies upon the selection of an agent which displays appropriate pharmacokinetic-pharmacodynamic (PK-PD) properties that will deliver appropriately high concentrations in the urinary tract after oral administration. Alternatively, high local concentrations of antibiotic at the urothelial surface can be achieved by direct instillation into the urinary tract. For antibiotics with the appropriate physicochemical properties, this can be of critical importance in cases for which an intracellular urothelial bacterial reservoir is suspected. In this review, we summarise the underpinning biopharmaceutical barriers to effective treatment of UTI and provide an overview of the evidence for the deployment of the intravesical administration route for antibiotics.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

The Role of PIEZO1 in Urinary Bladder Function and Dysfunction in a Rodent Model of Cyclophosphamide-Induced Cystitis

In the urinary bladder, mechanosensitive ion channels (MSCs) underlie the transduction of bladder stretch into sensory signals that are relayed to the PNS and CNS. PIEZO1 is a recently identified MSC that is Ca²⁺ permeable and is widely expressed throughout the lower urinary tract. Recent research indicates that PIEZO1 is activated by mechanical stretch or by pharmacological agonism via Yoda1. Aberrant activation of PIEZO1 has been suggested to play a role in clinical bladder pathologies like partial bladder outlet obstruction and interstitial cystitis/bladder pain syndrome (IC/BPS). In the present study, we show that intravesical instillation of Yoda1 in female Wistar rats leads to increased voiding frequency for up to 16 hours after administration compared to vehicle treatment. In a cyclophosphamide (CYP) model of cystitis, we found that the gene expression of several candidate MSCs (Trpv1, Trpv4, Piezo1, and Piezo2) were all upregulated in the urothelium and detrusor following chronic CYP-induced cystitis, but not acute CYP-induced cystitis. Functionally with this model, we show that Ca²⁺ activity is increased in urothelial cells following PIEZO1 activation via Yoda1 in acute and intermediate CYP treatment, but not in naïve (no CYP) nor chronic CYP treatment. Lastly, we show that activation of PIEZO1 may contribute to pathological bladder dysfunction through the downregulation of several tight junction genes in the urothelium including claudin-1, claudin-8, and zona occludens-1. Together, these data suggest that PIEZO1 activation plays a role in dysfunctional voiding behavior and may be a future, clinical target for the treatment of pathologies like IC/BPS.

Urinary reabsorption in the rat kidney by anticholinergics

Anticholinergics, therapeutic agents for overactive bladder, are clinically suggested to reduce urine output. We investigated whether this effect is due to bladder or kidney urine reabsorption. Various solutions were injected into the bladder of urethane-anesthetized SD rats. The absorption rate for 2 h was examined following the intravenous administration of the anticholinergics imidafenacin (IM), atropine (AT), and tolterodine (TO). The bilateral ureter was then canulated and saline was administered to obtain a diuretic state. Anticholinergics or 1-deamino-[8-D-arginine]-vasopressin (dDAVP) were intravenously administered. After the IM and dDAVP administrations, the rat kidneys were immunostained with AQP2 antibody, and intracellular cAMP was measured. The absorption rate was ~ 10% of the saline injected into the bladder and constant even when anticholinergics were administered. The renal urine among peaked 2 h after the saline administration. Each of the anticholinergics significantly suppressed the urine production in a dose-dependent manner, as did dDAVP. IM and dDAVP increased the intracellular cAMP levels and caused the AQP2 molecule to localize to the collecting duct cells' luminal side. The urinary reabsorption mechanism through the bladder epithelium was not activated by anticholinergic administration. Thus, anticholinergics suppress urine production via an increase in urine reabsorption in the kidneys' collecting duct cells via AQP2.

New mouse model of underactive bladder developed by placement of a metal ring around the bladder neck

OBJECTIVE

To develop a new mouse model of underactive bladder (UAB) caused by chronic bladder outlet obstruction (BOO).

METHODS

BOO was created in 6-week-old male C57BL/6 mice using surgery to loosely place a silver jump ring around the bladder neck of each mouse. Micturition behavior (assessed with a metabolic cage) and cystometry were used to evaluate bladder function at 8 and 16 weeks after BOO. Following completion of the functional studies, the bladders of the mice were excised, weighed, and subjected to histological analysis.

RESULTS

Micturition behavior analysis showed that mice subjected to BOO for 16 weeks had a lower frequency of micturition (7.3 ± 1.1 vs 12.5 ± 3.0 times/d, P < .05) and volume per void (106.0 ± 0.1 vs 133.9 ± 3.2 μL, P < .05) than mice subjected to BOO for 8 weeks. Cystometry revealed that mice subjected to BOO for 16 weeks had lower baseline pressure (8.4 ± 0.6 vs 14.0 ± 0.7 cmH₂ O, P < .01) and micturition pressure (13.9 ± 1.1 vs 42.8 ± 1.7 cmH₂ O, P < .05) than mice subjected to BOO for 8 weeks. BOO caused progressive increases in bladder mass and collagen deposition over time.

CONCLUSIONS

We successfully established a novel mouse model of UAB using surgery to place a silver jump ring loosely on the bladder neck. BOO initially induced bladder overactivity but subsequently resulted in UAB due to deterioration of detrusor smooth muscle contractility and progressive deposition of collagen in the bladder wall.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

ICI-RS 2019 nocturia think tank: How can experimental science guide us in understanding the pathophysiology of nocturia?

INTRODUCTION

The following is a report on the proceedings of the 2019 International Consultation on Incontinence-Research Society nocturia think tank (NTT).

OBJECTIVES

The objectives of the 2019 NTT were as follows: (a) to evaluate the role of urothelium in the pathophysiology of nocturia; (b) to determine whether nocturia is a circadian disorder; (c) to discuss the role of melatonin in nocturia; (d) to consider ambulatory urodynamic monitoring in evaluating patients with nocturia; (e) to explore studies of water handling in human compartments utilizing heavy water; and (f) to explore whether basic science is the key to understanding the treatment options for diminished bladder capacity in patients with nocturia.

METHODS

A compendium of discussions of the role of experimental science in understanding the pathophysiology of nocturia is described herein.

RESULTS AND CONCLUSIONS

Translational science will play an increasing role in understanding the pathophysiology of nocturia, which may result in improved treatment strategies.

Sodium plays an important role in the absorption of intravesical fluid

OBJECTIVES

To investigate the role of sodium in intravesical absorption of water in the bladder and the sodium pathway in the urothelium.

METHODS

Adult female Sprague-Dawley rats received either saline or a 5% glucose solution injection into their bladders. The changes in intravesical fluid volume; concentrations of sodium and chlorine and osmolality; and expression of aquaporin-2, epithelial sodium channel, and claudins were compared after 3 hours.

RESULTS

Intravesical volume decreased significantly in the saline group compared to that in the 5% glucose solution group. The expression of claudin-3 and -6 was higher in the saline group than in the glucose group. There was a significant correlation between changes in the intravesical saline volume and the concentration of sodium and chlorine. Intravesical administration of amiloride did not affect changes in the fluid volume and concentration of sodium.

CONCLUSIONS

The presence of sodium is important for the absorption of intravesical fluid through aquaporin-2 in the urinary bladders of rats. Claudin-3 and -6 may be associated with the transport of sodium through the bladder urothelium.

Aging increases the expression of vasopressin receptors in both the kidney and urinary bladder

AIMS

The goal of this study was to determine whether aging effects the expression of V_1a and V₂ vasopressin receptors in the urinary bladder mucosa (UBM) and kidney.

METHODS

UBM and kidneys were obtained from young (3 months-of-age) and old (25-30 months-of-age) female Fisher 344 rats. Tissue samples were analyzed by western blotting for V_1a and V₂ receptor expression, and rat plasma levels of vasopressin levels were measured by ELISA.

RESULTS

V_1a and V₂ receptors were detected in both the UBM and kidneys. Aging significantly (P < 0.05) increased the expression of V₂ receptors by 2.80 ± 0.52 and 6.52 ± 1.24-fold in the UBM and kidneys, respectively. Aging also increased V_1a receptor expression in the kidneys (5.52 ± 1.05 fold; P < 0.05), but not in the UBM. To the best of our knowledge, because this is the first detection of V₂ receptors in the mammalian bladder mucosa, we also probed human UBM for V₂ receptors and observed high expression in human UBM. Unlike V_1a and V₂ receptors, aging had only a minor effect on plasma vasopressin levels (8% increase).

CONCLUSIONS

V₂ receptors are substantially increased in the aging UBM. The role of these receptors in UBM is as yet undefined, but given their presence and action in the kidneys, the possible effect of these receptors in free water regulation should be considered. The large age-related increase in the expression of V₂ receptors in both the UBM and kidney may contribute to the effectiveness of desmopressin in age-related nocturia.