Nongenomic modulation of the large conductance voltage- and Ca2+-activated K+ channels by estrogen: A novel regulatory mechanism in human detrusor smooth muscle

Nocturia in Menopausal Women: The Link Between Two Common Problems of the Middle Age

INTRODUCTION AND HYPOTHESIS

The aim of this review is to discuss the link between menopause and nocturia and to give an overview of the increasing prevalence, risk factors, causative factors, treatment needs and options for nocturia in peri-menopausal women.

METHODS

This opinion article is a narrative review based on the expertise and consensus of a variety of key opinion leaders, in combination with an extensive literature review. This literature search included a thorough analysis of potential publications on both the PubMed Database and the Web of Science and was conducted between November 2022 and December 2022. The following key words were used "nocturia" and "menopause" or "nocturnal frequency and menopause." Moreover, key words including "incidence," "prevalence," "insomnia," "estrogen therapy," "metabolic syndrome," and "hot flushes" were used in combination with the aforementioned key words. Last, the reference lists of articles obtained were screened for other relevant literature.

RESULTS

The perimenopause can be a trigger for inducing nocturia. Typically, obesity, body mass index (BMI), and waist circumference are risk factors for developing peri-menopausal nocturia. Presumably the development of peri-menopausal nocturia is multifactorial, with interplay among bladder, sleep, and kidney problems due to estrogen depletion after the menopause. First, impaired stimulation of estrogen receptors in the urogenital region leads to vaginal atrophy and reduced bladder capacity. Moreover, menopause is associated with an increased incidence of overactive bladder syndrome. Second, estrogen deficiency can induce salt and water diuresis through blunted circadian rhythms for the secretion of antidiuretic hormone and the activation of the renin-angiotensin-aldosterone system. Additionally, an increased incidence of sleep disorders, including vasomotor symptoms and obstructive sleep apnea signs, is observed. Oral dryness and a consequent higher fluid intake are common peri-menopausal symptoms. Higher insulin resistance and a higher risk of cardiovascular diseases may provoke nocturia. Given the impact of nocturia on general health and quality of life, bothersome nocturia should be treated. Initially, behavioral therapy should be advised. If these modifications are inadequate, specific treatment should be proposed. Systemic hormone replacement is found to have a beneficial effect on nocturia, without influencing sodium and water clearance in patients with nocturnal polyuria. It is presumed that the improvement in nocturia from hormonal treatment is due to an improvement in sleep disorders.

Hormone therapy as a possible solution for postmenopausal women with nocturia: results of a pilot trial

OBJECTIVE

To observe the impact of different hormonal treatment options on nocturia, its causative factors and bother in postmenopausal women.

METHODS

This prospective study recruited 245 postmenopausal women and divided them into four treatment groups based on patient's choice: Estrogen + Progesterone (E+P), Estrogen-only in patients with a prior hysterectomy, tissue-selective estrogen complex (TSEC) and no treatment. Nocturia and its causative factors were observed using two standardized questionnaires before and after treatment: the International Consultation on Incontinence Questionnaire Nocturia Module and the Targeting the individual's Aetiology of Nocturia to Guide Outcomes (TANGO). The results of the Targeting the individual's Aetiology of Nocturia to Guide Outcomes were divided in four influencing topics of which the sum score was calculated.

RESULTS

A significant reduction in prevalence of nocturia ≥ twice per night was seen after treatment, as the prevalence decreased from 27.7% (59/213) to 16.4% (35/213). Specified per therapy, a significant reduction in nocturnal voiding frequency was observed in patients treated with E+P and TSEC (P = 0.018 and P = 0.018, respectively). This improvement could be explained by a significant reduction in SLEEP sum score in patients treated with E+P and TSEC (P < 0.001, P = 0.013, respectively). Estrogen-only led to a significant change in URINARY TRACT sum score, which is the result of a reduction in urgency prevalence (P = 0.039).

CONCLUSIONS

E+P and TSEC treatment led to a significant reduction in nocturia prevalence and bother in women with ≥ 2 nocturnal voids. This effect is mainly the result of improvement in sleep disorders, however an improvement in bladder disorders can be suggested as well. More research is necessary to confirm these findings.

Clinical Guidelines for Female Lower Urinary Tract Symptoms (second edition)

The present article is an abridged English translation of the Japanese Clinical Guidelines for Female Lower Urinary Tract Symptoms (second edition), published in September 2019. These guidelines consist of a total of 212 pages and are unique worldwide in that they cover female lower urinary tract symptoms other than urinary incontinence. They contain two algorithms for "primary treatment" and "specialized treatment," respectively. These guidelines, consisting of six chapters, address a total of 26 clinical questions including: (i) treatment algorithms; (ii) what are female lower urinary tract symptoms?; (iii) epidemiology and quality of life; (iv) pathology and illness; (v) diagnosis; and (vi) treatment. When the patient's symptoms mainly involve voiding and post-micturition symptoms, specialized treatment should be considered. In the event of voiding symptoms concurrent with storage symptoms, residual urine should be measured; if the residual urine volume is <100 mL, then diagnosis and treatment for storage symptoms is prioritized, and if the volume is ≥100 mL, then specialized treatment should be considered. When storage symptoms are the primary condition, then the patient is subject to the primary treatment algorithm. Specialized treatment for refractory overactive bladder includes botulinum toxin injection and sacral nerve stimulation. For stress urinary incontinence, surgical treatment is indicated, such as urethral slings. The two causes of voiding symptoms and post-micturition symptoms are lower urinary tract obstruction and detrusor underactivity (underactive bladder). Mechanical lower urinary tract obstruction, such as pelvic organ prolapse, is expected to improve with surgery.

Nocturia through the menopausal transition and beyond: a narrative review

INTRODUCTION AND HYPOTHESIS

Nocturia, defined as the act of waking to pass urine during sleeping, is a common problem in older women and is associated with significant morbidity and impairments in health-related quality of life. The aim of this review was to synthesize the current evidence regarding the incidence, impact, pathophysiology, and specific diagnostic approach of nocturia in the postmenopausal population.

METHODS

We searched PubMed and Web of Science databases to identify relevant studies published through June 2020. Reference lists of the reviews obtained were screened for other articles deemed pertinent by the authors.

RESULTS

Genitourinary symptoms attributed to the menopause have been reported to occur in nearly 90% of postmenopausal women, and nocturia is one of the most common. The relative deficiency in endogenous estrogen production after the menopause is thought to exacerbate all major pathophysiological mechanisms that may underlie nocturia, including reduced bladder capacity, nocturnal polyuria, global polyuria, and sleep disorders. Diminished estrogen may induce anatomical and physiological bladder changes, contributing to a reduction in functional bladder capacity. Excess nocturnal urine production can also be provoked by estrogen depletion, either via free water-predominant diuresis by an impaired secretion of antidiuretic hormone, or a salt-predominant diuresis owing to diminished activation of the renin-angiotensin-aldosterone axis. Additionally, a relationship between the transition to menopause and impaired sleep has been described, mediated by increased incidence in vasomotor symptoms and obstructive sleep apnea signs during the menopause.

CONCLUSION

Further research is necessary to better characterize and manage nocturia in postmenopausal women.

Pharmacologic management of nocturnal polyuria: a contemporary assessment of efficacy, safety, and progress toward individualized treatment

This narrative review synthesizes current evidence on the medical management of nocturnal polyuria, including antidiuretic replacement therapy as well as other emerging modalities, with particular emphasis on areas of active investigation and future research directions. Relative to earlier formulations, the pharmacological profiles of novel desmopressin acetate nasal spray and orally disintegrating tablet formulations appear favorable in optimizing the balance between efficacy and safety. Additionally, several highly selective small-molecule arginine vasopressin 2 receptor agonists are under active development, while appropriately timed short-acting diuretics, pharmacotherapy for hypertension, nonsteroidal anti-inflammatory drugs, and sex hormone replacement therapy are also a focal point of extensive ongoing nocturnal polyuria research. Emerging laboratory technologies now make feasible a sub-stratification of nocturnal polyuria patients into substrate-based phenotypes for individualized treatment. An increasingly refined understanding of the pathogenesis of nocturnal polyuria, and arginine vasopressin dysregulation in particular, has also introduced new opportunities for point-of-care testing in patients with nocturnal polyuria.

Detrusor Smooth Muscle KV7 Channels: Emerging New Regulators of Urinary Bladder Function

Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.

Characterizing nocturia among Belgian healthy postmenopausal women: Prevalence, degree of bother, etiology and risk factors for nocturia

INTRODUCTION

Limited literature concerning nocturia in early postmenopausal women is available. However, due to the lack of endogenous estrogen in these women, an increased prevalence of nocturia is expected.

MATERIAL AND METHODS

This prospective observational trial recruited 210 'early' postmenopausal women consulting the Ghent University menopause clinic. Postmenopausal status was biochemically confirmed. Women completed 3 questionnaires: the ICI questionnaire on nocturia (ICIQ-N); 'Targeting the individual's Aetiology of Nocturia to Guide Outcomes' (TANGO) and the Perceived Stress Scale (PSS). Moreover, information concerning women's age, anthropometrics and lifestyle was collected. Nocturia was defined as two or more nocturnal voids.

RESULTS

Nocturia was reported in 24.8% (52/210) of the postmenopausal women. Bother increased with every nocturnal void. Women with two or more nighttime voids were found to have significantly increased prevalence of urgency compared with women with only one (p < 0.001; 38.5% versus 22.7%). Trouble initiating sleep at the start of the night and insomnia during the night were significantly different in women with a different nocturnal frequency (initiating sleep p = 0.09, no voids 34.4 %, 1 void 39.2 %, ≥ 2 voids 53.8 %; insomnia p < 0.001; no voids 1.6%, 1 void 22.7 %, ≥ 2 voids 53.8 %). In addition to bladder and sleep dysfunctions, waist circumference was a risk factor for nocturia (OR 1.04; 95 % CI: 1.01-1.08).

CONCLUSION

Nocturia is an important problem in early postmenopausal women, affecting a quarter of the questioned women. Etiology of nocturia in this population is multifactorial as estrogen withdrawal is accompanied by bladder and sleep dysfunctions.

Subunits of BK channels promote breast cancer development and modulate responses to endocrine treatment in preclinical models

BACKGROUND AND PURPOSE

Pore-forming α subunits of the voltage- and Ca²⁺ -activated K⁺ channel with large conductance (BKα) promote malignant phenotypes of breast tumour cells. Auxiliary subunits such as the leucine-rich repeat containing 26 (LRRC26) protein, also termed BKγ1, may be required to permit activation of BK currents at a depolarized resting membrane potential that frequently occur in non-excitable tumour cells.

EXPERIMENTAL APPROACH

Anti-tumour effects of BKα loss were investigated in breast tumour-bearing MMTV-PyMT transgenic BKα knockout (KO) mice, primary MMTV-PyMT cell cultures, and in a syngeneic transplantation model of breast cancer derived from these cells. The therapeutic relevance of BK channels in the context of endocrine treatment was assessed in human breast cancer cell lines expressing either low (MCF-7) or high (MDA-MB-453) levels of BKα and BKγ1, as well as in BKα-negative MDA-MB-157.

KEY RESULTS

BKα promoted breast cancer onset and overall survival in preclinical models. Conversely, lack of BKα and/or knockdown of BKγ1 attenuated proliferation of murine and human breast cancer cells in vitro. At low concentrations, tamoxifen and its major active metabolites stimulated proliferation of BKα/γ1-positive breast cancer cells, independent of the genomic signalling controlled by the oestrogen receptor. Finally, tamoxifen increased the relative survival time of BKα KO but not of wild-type tumour cell recipient mice.

CONCLUSION AND IMPLICATIONS

Breast cancer initiation, progression, and tamoxifen sensitivity depend on functional BK channels thereby providing a rationale for the future exploration of the oncogenic actions of BK channels in clinical outcomes with anti-oestrogen therapy.

Managing overactive bladder

Overactive bladder (OAB) is a common and distressing condition which is known to increase with age and has a significant effect on quality of life. Whilst OAB is a symptomatic diagnosis, many patients will require basic investigations prior to initiating the appropriate management. This article will review the initial clinical assessment and management of women complaining of OAB including conservative measures and drug therapy, and will also focus on the role of estrogen. In addition, the management of refractory OAB will also be discussed including more invasive strategies such as neuromodulation, Botulinum Toxin, and reconstructive surgery.

The mysteries of menopause and urogynecologic health: clinical and scientific gaps

OBJECTIVES

A significant body of knowledge implicates menopausal estrogen levels in the pathogenesis of the common pelvic floor disorders (PFDs). These health conditions substantially decrease quality of life, increase depression, social isolation, caregiver burden, and economic costs to the individuals and society.

METHODS

This review summarizes the epidemiology of the individual PFDs with particular attention to the understanding of the relationship between each PFD and menopausal estrogen levels, and the gaps in science and clinical care that affect menopausal women. In addition, we review the epidemiology of recurrent urinary tract infection (rUTI)-a condition experienced frequently and disproportionately by menopausal women and hypothesized to be potentiated by menopausal estrogen levels.

RESULTS

The abundance of estrogen receptors in the urogenital tract explains why the natural reduction of endogenous estrogen, the hallmark of menopause, can cause or potentiate PFDs and rUTIs. A substantial body of epidemiological literature suggests an association between menopause, and PFDs and rUTIs; however, the ability to separate this association from age and other comorbid conditions makes it difficult to draw definitive conclusions on the role of menopause alone in the development and/or progression of PFDs. Similarly, the causative link between the decline in endogenous estrogen levels and the pathogenesis of PFDs and rUTIs has not been well-established.

CONCLUSIONS

Innovative human studies, focused on the independent effects of menopausal estrogen levels, uncoupled from tissue and cellular senescence, are needed.

Preparation and Utilization of Freshly Isolated Human Detrusor Smooth Muscle Cells for Characterization of 9-Phenanthrol-Sensitive Cation Currents

Detrusor smooth muscle (DSM) cells present within the urinary bladder wall ultimately facilitate urine storage and voiding. Preparation of the viable, fresh, and isolated DSM cells presents an important technical challenge whose achievement provides optimal cells for subsequent functional and molecular studies. The method developed and elaborated herein, successfully used by our group for over a decade, describes dissection of human urinary bladder specimens obtained from open bladder surgeries followed by an enzymatic two-step treatment of DSM pieces and mechanical trituration to obtain freshly isolated DSM cells. The initial step involves dissection to separate the DSM layer (also known as muscularis propria) from mucosa (urothelium, lamina propria, and muscularis mucosa) and the adjacent connective, vascular, and adipose tissues present. The DSM is then cut into pieces (2-3 mm x 4-6 mm) in nominal Ca2+-containing dissection/digestion solution (DS). DSM pieces are next transferred to and sequentially treated separately with DS containing papain and collagenase at ~37 °C for 30-45 min per step. Following washes with DS containing enzyme-free bovine serum and trituration with a fire-polished pipette, the pieces release single DSM cells. Freshly isolated DSM cells are ideally suited for patch-clamp electrophysiological and pharmacological characterizations of ion channels. Specifically, we show that the TRPM4 channel blocker 9-phenanthrol reduces voltage-step evoked cation currents recorded with the amphotericin-B perforated patch-clamp approach. DSM cells can also be studied by other techniques such as single cell RT-PCR, microarray analysis, immunocytochemistry, in situ proximity ligation assay, and Ca2+ imaging. The main advantage of utilizing single DSM cells is that the observations made relate directly to single cell characteristics revealed. Studies of freshly isolated human DSM cells have provided important insights characterizing the properties of various ion channels including cation-permeable in the urinary bladder and will continue as a gold standard in elucidating DSM cellular properties and regulatory mechanisms.

BK ablation attenuates osteoblast bone formation via integrin pathway

Impaired bone formation is one of the major causes of low bone mass and skeletal fragility that occurs in osteoporosis. However, the mechanisms underlying the defects in bone formation are not well understood. Here, we report that big conductance calcium-activated potassium channels (BKs) are required for bone formation and osteoblast function both in vivo and in vitro. By 15 weeks of age, BK knockout (BKO) mice exhibited a decline in bone mineral density and trabecular bone volume of the tibiae and lumbar vertebrae, which were associated with impaired bone formation and osteoblast activity. Mechanistically, BK ablation in bone and bone marrow mesenchymal stem cells (BMSCs) of BKO mice inhibited integrin signaling. Furthermore, the binding of α subunit of BK with integrin β1 protein in osteoblasts was confirmed, and FAK-ERK1/2 signaling was proved to be involved by genetic modification of KCNMA1 (which encodes the α subunit of BK) in ROS17/2.8 osteoblast cells. These findings indicated that BK regulates bone formation by promoting osteoblast differentiation via integrin pathway, which provided novel insight into ion transporter crosstalk with the extracellular matrix in osteoblast regulation and revealed a new potential strategy for intervention in correcting bone formation defects.

The molecular nature of the 17β-Estradiol binding site in the voltage- and Ca2+-activated K+ (BK) channel β1 subunit

The accessory β1 subunit modulates the Ca²⁺- and voltage-activated K⁺ (BK) channel gating properties mainly by increasing its apparent Ca²⁺ sensitivity. β1 plays an important role in the modulation of arterial tone and blood pressure by vascular smooth muscle cells (SMCs). 17β-estradiol (E2) increases the BK channel open probability (P_o) in SMCs, through a β1 subunit-dependent modulatory effect. Here, using molecular modeling, bioinformatics, mutagenesis, and electrophysiology, we identify a cluster of hydrophobic residues in the second transmembrane domain of the β1 subunit, including the residues W163 and F166, as the binding site for E2. We further show that the increase in P_o induced by E2 is associated with a stabilization of the voltage sensor in its active configuration and an increase in the coupling between the voltage sensor activation and pore opening. Since β1 is a key molecular player in vasoregulation, the findings reported here are of importance in the design of novel drugs able to modulate BK channels.

Estradiol-Mediated Axogenesis of Hypothalamic Neurons Requires ERK1/2 and Ryanodine Receptors-Dependent Intracellular Ca2+ Rise in Male Rats

17β-estradiol (E2) induces axonal growth through extracellular signal-regulated kinase 1 and 2 (ERK1/2)-MAPK cascade in hypothalamic neurons of male rat embryos in vitro, but the mechanism that initiates these events is poorly understood. This study reports the intracellular Ca²⁺ increase that participates in the activation of ERK1/2 and axogenesis induced by E2. Hypothalamic neuron cultures were established from 16-day-old male rat embryos and fed with astroglia-conditioned media for 48 h. E2-induced ERK phosphorylation was completely abolished by a ryanodine receptor (RyR) inhibitor (ryanodine) and partially attenuated by an L-type voltage-gated Ca²⁺ channel (L-VGCC) blocker (nifedipine), an inositol-1,4,5-trisphosphate receptor (IP₃R) inhibitor (2-APB), and a phospholipase C (PLC) inhibitor (U-73122). We also conducted Ca²⁺ imaging recording using primary cultured neurons. The results show that E2 rapidly induces an increase in cytosolic Ca²⁺, which often occurs in repetitive Ca²⁺ oscillations. This response was not observed in the absence of extracellular Ca²⁺ or with inhibitory ryanodine and was markedly reduced by nifedipine. E2-induced axonal growth was completely inhibited by ryanodine. In summary, the results suggest that Ca²⁺ mobilization from extracellular space as well as from the endoplasmic reticulum is necessary for E2-induced ERK1/2 activation and axogenesis. Understanding the mechanisms of brain estrogenic actions might contribute to develop novel estrogen-based therapies for neurodegenerative diseases.

Menopause and Ischemic Stroke: A Brief Review

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide. Females are protected against stroke before the onset of menopause. Menopause results in increased incidence of stroke when compared to men. The mechanisms of these differences remain to be elucidated. Considering that there is a postmenopausal phenomenon and females in general, are living longer sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the premenopausal protection from stroke and later to be responsible for the higher incidence and increased the severity of stroke after menopause. Animal studies suggest that administration of estrogen and progesterone is neuroprotective and decreases the incidence of stroke. However, the real-world outcomes of hormone replacement therapy have failed to decrease the stroke risk. Despite the multifactorial nature of sex differences in stroke, here, we briefly discuss the pathophysiology of sex steroid hormones, the molecular mechanisms of estrogen receptor-dependent signaling pathways in stroke, and the potential factors that determine the discrepant effects of hormone replacement therapy in stroke.

Nongenomic modulation of the large conductance voltage- and Ca2+-activated K+ channels by estrogen: A novel regulatory mechanism in human detrusor smooth muscle

Estrogens have an important role in regulating detrusor smooth muscle (DSM) function. However, the underlying molecular and cellular mechanisms by which estrogens control human DSM excitability and contractility are not well known. Here, we used human DSM specimens from open bladder surgeries on 27 patients to elucidate the mechanism by which 17β-estradiol regulates large conductance voltage- and Ca²⁺-activated K⁺ (BK) channels, the most prominent K⁺ channels in human DSM We employed single BK channel recordings on inside-out excised membrane patches, perforated whole-cell patch-clamp on freshly isolated DSM cells, and isometric tension recordings on DSM-isolated strips to investigate the mechanism by which 17β-estradiol activates BK channels. 17β-Estradiol (100 nmol/L) rapidly increased depolarization-induced whole-cell K⁺ currents in DSM cells. The 17β-estradiol stimulatory effects on whole-cell BK currents were completely abolished by the selective BK channel inhibitor paxilline (1 μmol/L), clearly indicating that 17β-estradiol specifically activates BK channels. 17β-Estradiol also increased the frequency of ryanodine receptor-mediated transient BK currents. Single BK channel recordings showed that 17β-estradiol (100 nmol/L) significantly increased the BK channel open probability of inside-out excised membrane patches, revealing that 17β-estradiol activates BK channels directly. 17β-Estradiol reduced spontaneous phasic contractions of human DSM-isolated strips in a concentration-dependent manner (100 nmol/L-1 μmol/L), and this effect was blocked by paxilline (1 μmol/L). 17β-Estradiol (100 nmol/L) also reduced nerve-evoked contractions of human DSM-isolated strips. Collectively, our results reveal that 17β-estradiol plays a critical role in regulating human DSM function through a direct nongenomic activation of BK channels.