The effects of Ins2(Akita) diabetes and chronic angiotensin II infusion on cystometric properties in mice

Insights into the associative role of hypertension and angiotensin II receptor in lower urinary tract dysfunction

In men, the lower urinary tract comprises the urinary bladder, urethra, and prostate, and its primary functions include urine storage and voiding. Hypertension is a condition that causes multi-organ damage and an age-dependent condition. Hypertension and the renin-angiotensin system activation are associated with the development of lower urinary tract dysfunction. Hypertensive animal models show bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. In the renin-angiotensin system, angiotensin II and the angiotensin II type 1 receptor, which are expressed in the lower urinary tract, have been implicated in the pathogenesis of lower urinary tract dysfunction. Moreover, among the several antihypertensives, renin-angiotensin system inhibitors have proven effective in human and animal models of lower urinary tract dysfunction. This review aimed to elucidate the hitherto known mechanisms underlying the development of lower urinary tract dysfunction in relation to hypertension and the angiotensin II/angiotensin II type 1 receptor axis and the effect of renin-angiotensin system inhibitors on lower urinary tract dysfunction. Possible mechanisms through which hypertension or activation of Ang II/AT1 receptor axis causes LUTD such as bladder dysfunction, urethral dysfunction, and prostatic hyperplasia. LUT: lower urinary tract, LUTD: lower urinary tract dysfunction, AT1: angiotensin II type 1, ACE: angiotensin-converting enzyme.

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 NLR family pyrin domain containing 3 (NLRP3)+/+ or NLRP3-/-, we have previously found that females (mild hyperglycemia) progress from an overactive to underactive bladder phenotype and that this progression was dependent on NLRP3-induced inflammation. Here, we examined DBD in the male Akita mouse (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. To examine the cause of the compensated underactive-like phenotype, we assessed overall nerve bundle density and afferent nerve bundles (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 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-/- strain, suggesting that the bladder compensated underactive-like phenotype in the male Akita mouse is likely through a decrease in efferent neurotransmitter release.NEW & NOTEWORTHY In this study, we show that diabetic bladder dysfunction (the most common diabetic complication) manifests through different mechanisms that may be related to severity of hyperglycemia and/or sex. Male Akita mice, which have severe hyperglycemia, develop bladder underactivity as a result of a decrease in efferent neurotransmitter release that is independent of inflammation. This contrasts with females, who have milder hyperglycemia, where diabetic bladder dysfunction progresses from overactivity to underactivity in an inflammation-dependent manner.

A Spectrum of Age- and Gender-Dependent Lower Urinary Tract Phenotypes in Three Mouse Models of Type 2 Diabetes

Lower urinary tract symptoms are extremely common in people with diabetes and obesity, but the causes are unclear. Furthermore, it has proven difficult to reliably demonstrate bladder dysfunction in diabetic mouse models, thus limiting the ability to gain mechanistic insights. Therefore, the main objective of this experimental study was to characterize diabetic bladder dysfunction in three promising polygenic mouse models of type 2 diabetes. We performed periodic assessments of glucose tolerance and micturition (void spot assay) for eight to twelve months. Males and females and high-fat diets were tested. NONcNZO10/LtJ mice did not develop bladder dysfunction over twelve months. TALLYHO/JngJ males were severely hyperglycemic from two months of age (fasted blood glucose ~550 mg/dL), while females were moderately so. Although males exhibited polyuria, neither they nor the females exhibited bladder dysfunction over nine months. KK.Cg-A^y/J males and females were extremely glucose intolerant. Males exhibited polyuria, a significant increase in voiding frequency at four months (compensation), followed by a rapid drop in voiding frequency by six months (decompensation) which was accompanied by a dramatic increase in urine leakage, indicating loss of outlet control. At eight months, male bladders were dilated. Females also developed polyuria but compensated with larger voids. We conclude KK.Cg-A^y/J male mice recapitulate key symptoms noted in patients and are the best model of the three to study 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.

Best practices for cystometric evaluation of lower urinary tract function in muriform rodents

AIMS

Rodent cystometry has provided valuable insights into the impact of the disease, injury, and aging on the cellular and molecular pathways, neurologic processes, and biomechanics of lower urinary tract function. The purpose of this white paper is to highlight the benefits and shortcomings of different experimental methods and strategies and to provide guidance on the proper interpretation of results.

METHODS

Literature search, selection of articles, and conclusions based on discussions among a panel of workers in the field.

RESULTS

A range of cystometric tests and techniques used to explore biological phenomena relevant to the lower urinary tract are described, the advantages and disadvantages of various experimental conditions are discussed, and guidance on the practical aspects of experimental execution and proper interpretation of results are provided.

CONCLUSIONS

Cystometric evaluation of rodents comprises an extensive collection of functional tests that can be performed under a variety of experimental conditions. Decisions regarding which approaches to choose should be determined by the specific questions to be addressed and implementation of the test should follow standardized procedures.

Urological complications of obesity and diabetes in males and females of three mouse models: temporal manifestations

Diabetic bladder dysfunction is a frequent complication of diabetes. Although many mouse models of diabetes now exist, there has been little systematic effort to characterize them for the timing of onset and severity of bladder dysfunction. We monitored metabolic status and tested bladder function by void spot assay and limited anesthetized cystometry in both male and female mice of three models of obesity and diabetes: a type 1 diabetes model (the Akita mouse) and two type 2 diabetes models [the diet-induced obese (DIO) model and the ob/ob mouse]. Akita mice had insulin pellets implanted subcutaneously every 3 mo to mimic poorly controlled type 1 diabetes in humans. Mice were hyperglycemic by 48 days after implants. Female mice exhibited no bladder dysfunction at any age up to 20 mo and gained weight normally. In contrast, by 7 mo, male Akita mice developed a profound polyuria and failed to show normal weight gain. There were no observable signs of bladder dysfunction in either sex. DIO mice on high/low-fat diets for 16 mo exhibited mild hyperglycemia in female mice (not in male mice), mild weight gain, and no evidence of bladder dysfunction. Ob/ob mice were followed for 8 mo and became extremely obese. Male and female mice were glucose intolerant, insulin intolerant, and hyperinsulinemic at 4 mo. By 8 mo, their metabolic status had improved but was still abnormal. Urine volume increased in male mice but not in female mice. Bladder dysfunction was observed in the spotting patterns of female mice at 4 and 6 mo of age, resolving by 8 mo. We conclude there are dramatic sex-related differences in lower urinary tract function in these models. Male Akita mice may be a good model for polyuria-related bladder remodeling, whereas female ob/ob mice may better mimic storage problems related to loss of outlet control in a setting of type 2 diabetes complicated by obesity.

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.

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.

Effect of filling rate on cystometric parameters in young and middle aged mice

OBJECTIVES

To investigate the effect of changing the bladder filling rate during cystometry in younger (2-3 months) and older (13-14 months) C57BL/6J male mice.

METHODS

Cystometry was performed on mice under anesthesia. Voiding cycles were established in each mouse at a pump delivery rate of 17 μl/min. After 30 min, the rate was increased sequentially to 25, 33, 41 and 49 μl/min. Each rate was maintained for 30 min. The following cystometric parameters were quantified: peak pressure amplitude, intercontractile interval (ICI), compliance, micturition pressure threshold and voiding efficiency.

RESULTS

Bladder weights were significantly greater in older mice (42 mg vs. 27 mg, P < 0.01), but functional capacities were not different. The pressure amplitudes did not change as filling rate increased, nor did they differ between the 4-month and 13-month-old males. ICIs were not significantly different between young and mature mice. However, both groups exhibited a non-linear reduction in ICI with increasing filling rate, best described by a power curve (R² > 0.93). Compliance was higher in the older mice at low filling rates (17 and 25 μl/min) but this difference diminished at higher rates. Compliance decreased with increasing flow rate in a non-linear manner, again with greater effects at low filling rates. Micturition pressure thresholds increased with increasing flow rate in a linear manner and older mice began voiding at higher pressures than younger. Both young and old mice exhibited voiding efficiencies of ~70%.

CONCLUSIONS

The rate of volume delivery has complex effects on the timing of voiding and compliance. These findings argue for greater standardization of cystometry protocols and further investigation into afferent signaling to higher centers at different filling rates.

Evaluation of voiding assays in mice: impact of genetic strains and sex

Void spot assays (VSA) and cystometry are two of the most common tests performed in mice to assess lower urinary tract function. Assay protocols and methodology vary greatly among laboratories, and little is known about reproducibility of results generated by different laboratories. We performed VSA in four mouse strains, comparing males with females and comparing results between two independent laboratories. Unique aspects of the current study include direct comparison of results of VSA performed in a similar manner in two locations and comparison of cystometry performed using two different rates of infusion in these two laboratories. Both assays were performed in male and female 129S1/SvImJ, C57BL/6J, NOD/ShiLtJ, and CAST/EiJ mice, and cystometry was performed under urethane anesthesia (10/group). Assays were performed and results analyzed as previously described. Results obtained in female mice were compared with previously reported values. Results of lower urinary tract function testing in mice vary in a consistent manner with strain and sex. Variables in husbandry, testing techniques, and analysis of results can significantly affect conclusions, particularly those obtained by cystometry. Although VSA results were remarkably similar between the two laboratories, consistent methods for performing lower urinary tract function testing in mice are required to compare results among studies with confidence.