Downregulation of PIEZO2 in the Detrusor of Men With Bladder Outlet Obstruction and Its Association With Urinary Retention and Decreased Bladder Compliance

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Int Neurourol J. 2024;28(3):225-231

Publication date (electronic) : 2024 September 30

doi : https://doi.org/10.5213/inj.2448298.149

Carlos Henrique Suzuki Bellucci^,1, Thiago Souto Hemerly¹, Luisa Resende Tenório de Albuquerque¹, Ruan Pimenta², Vanessa Guimaraes Schreiter², Sabrina Thalita dos Reis², Jose de Bessa Jr³, Katia Ramos Moreira Leite², Alberto Antunes¹, Ettickan Boopathi⁴, William C. Nahas¹, Cristiano Mendes Gomes¹

¹Division of Urology, University of Sao Paulo School of Medicine, Sao Paulo, Brazil

²Laboratory of Medical Investigation (LIM55), University of Sao Paulo School of Medicine, Sao Paulo, Brazil

³Division of Urology, State University of Feira de Santana, Feira de Santana, Brazil

⁴Department of Medicine, Center for Translational Medicine, Thomas Jefferson University, Philadelphia, PA, USA

Corresponding author: Carlos Henrique Suzuki Bellucci Division of Urology, University of Sao Paulo School of Medicine, Av. Dr. Arnaldo, 455 - Cerqueira César, Sao Paulo, Brazil Email: carloshenriquesb@yahoo.com.br

Received 2024 July 18; Accepted 2024 August 26.

Abstract

INTRODUCTION

Benign prostatic hyperplasia (BPH) is a common source of lower urinary tract symptoms (LUTS) and the primary cause of bladder outlet obstruction (BOO) in adult men [1,2]. BOO can lead to deterioration of bladder function and changes in bladder morphology, with consequences including smooth muscle hypertrophy, bladder wall fibrosis, and eventual urinary retention [3-5]. Initially, smooth muscle cells undergo hypertrophy as an adaptive response to pathological stimuli. However, prolonged stimulation may cause the detrusor muscle to develop irreversible decompensation and contractile dysfunction [6,7]. Therefore, elucidating the molecular mechanisms underlying pathological detrusor hypertrophy could benefit patients experiencing BOO and impaired detrusor contraction.

Mechanical features, including stretching, shear stress, bending, and compression, are essential for maintaining organ structure and function [7-10]. The importance of mechanical forces is well-recognized in the regulation of electrical coupling, metabolic reprogramming, extracellular matrix remodeling, and the structural properties of the bladder and other contractile organs [7-9,11-13]. High mechanical stress is a primary factor contributing to bladder hypertrophy [10,14-17]. Smooth muscle cells detect these diverse mechanical stimuli and translate them into biochemical signals, potentially leading to organ dysfunction [7,14-16].

The mechanisms by which mechanical sensors coordinate the activity of detrusor smooth muscle cells and their mechanical environment remain elusive. Mechanically activated cation channels are a specialized type of mechanotransducer that respond rapidly to changes in mechanical force, either by exciting cell membranes or by triggering calcium signaling [9]. Recent discoveries have revealed that genes in the PIEZO family, specifically PIEZO1 and PIEZO2, encode critical components of mammalian mechanically activated cation channels. These findings characterize a family of mammalian genes whose expression is both necessary and sufficient for the generation of mechanically activated cationic currents [18].

Both PIEZO1 and PIEZO2 are expressed in the bladder and urethra, predominantly in the urothelium but also in the interstitial cells of Cajal and smooth muscle cells [19-22]. The exact function of these proteins in the micturition cycle is not fully understood; however, their role as mechanosensitive ion channels, essential for low-threshold bladder stretch sensing and urethral micturition reflexes, is supported by various studies [19,21-23].

A recent study identified PIEZO2 as an essential mediator of urinary tract function [22]. PIEZO2-deficient individuals were clinically examined, with many exhibiting LUTS, such as diminished bladder sensation, infrequent voiding, urge incontinence, and difficulty voiding. Animal experiments also demonstrated that mechanosensory stimuli activate PIEZO2 in urothelial cells, which in turn prompts bladder relaxation during the filling phase. Furthermore, PIEZO2 deficiency was linked to reduced bladder compliance (BC). The research also revealed that PIEZO2-deficient mice (Cre lines with PIEZO2 gene knockout in control sacral level S1 dorsal root ganglion neurons) exhibited bladder wall thickening and experienced higher bladder pressure during voiding compared to their wild-type counterparts [22].

Considering recent findings implicating PIEZO2 as an essential mediator of lower urinary tract function that is associated with BC, bladder wall thickening, and increased bladder pressure, we explored the hypothesis that PIEZO2 expression is associated with lower urinary tract dysfunction in men with BOO due to BPH.

MATERIALS AND METHODS

RESULTS

The study included 19 men, with a median age of 70.0 years (IQR, 66.0–76.0 years). The indication for surgery was urinary retention in 12 patients (63.2%) and LUTS refractory to medical therapy in the remaining 7 (36.8%). All patients with urinary retention had failed at least 2 attempts at catheter removal, despite receiving alpha-blocker treatment for a minimum of 4 weeks. The median prostatic specific antigen level was 5.6 ng/mL (IQR, 2.9–12.1 ng/mL), and the median prostate volume was 114.0 cm³ (IQR, 98.0–180.0 cm³). For patients not experiencing urinary retention, the median IPSS was 28.0 (IQR, 18.0– 33.0). The urodynamic parameters are detailed in Table 1.

Table 1.

Urodynamic parameters in men with BPH

The expression profile of the PIEZO2 gene in the detrusor of BPH specimens (0.0006±0.0003) was found to be downregulated compared to that of the control group (0.0020±0.0020, P=0.01) (Fig. 1).

Fig. 1.

PIEZO2 messenger RNA (mRNA) expression in men with benign prostatic hyperplasia (BPH) compared to controls.

Among patients with BPH, those experiencing urinary retention with an indwelling catheter showed significantly lower PIEZO2 mRNA expression levels than patients who could void spontaneously (0.0005±0.0003 vs. 0.0008±0.0002, respectively; P=0.04) (Fig. 2A). No significant difference in PIEZO2 mRNA expression was found between men with and without DO (0.0005±0.0003 vs. 0.0008±0.0004, respectively; P=0.128) (Fig. 2B).

Fig. 2.

(A) PIEZO2 messenger RNA (mRNA) expression in patients with urinary retention compared to patients with spontaneous voiding. (B) PIEZO2 mRNA expression in patients with DO versus those without DO. (C) Correlation between PIEZO2 mRNA expression and bladder compliance in 19 men with BPH. BPH, benign prostatic hyperplasia; DO, detrusor overactivity; WDO, without detrusor overactivity.

A positive correlation was observed between PIEZO2 mRNA expression levels and BC (r=0.53, P=0.018) (Fig. 2C). The expression of PIEZO2 mRNA was not influenced by factors including age, prostate volume, MCC, Qmax, PdetQmax, PVR urine volume, BOOI, or BCI (data not shown).

DISCUSSION

PIEZO channels are crucial for transducing mechanical stimuli into biological responses, and they play key roles in a variety of physiological processes [27]. These structures fulfill diverse biological functions across human systems. Increasing evidence points to the involvement of PIEZO channels in the function of the lower urinary tract, yet their role in human pathologies is not fully understood. This study represented an exploratory investigation of the association between PIEZO2 expression in the detrusor smooth muscle and lower urinary tract dysfunction in men with BOO due to BPH. We found that men with BOO resulting from BPH exhibit downregulation of PIEZO2 expression. Furthermore, our results suggest a positive correlation between PIEZO2 expression and BC.

Currently, limited evidence is available regarding the role of PIEZO-mediated mechanotransduction in bladder contraction and relaxation, particularly under pathological conditions. We opted to investigate PIEZO2 expression in men with BPH following recent findings by Marshall et al. [22], which identified PIEZO2 as a key mechanotransducer in lower urinary tract function and suggested that deficiency could be linked to LUTS in humans. Clinical examinations of individuals with PIEZO2 deficiency revealed that a meaningful number reported LUTS, aligning with our data indicating that men with BPH-associated BOO exhibit reduced PIEZO2 expression. Furthermore, Marshall et al. [22] conducted experiments in PIEZO2 knockout mice, showing that mechanosensory inputs activate PIEZO2 in urothelial cells, facilitating bladder relaxation during the filling phase, and that the absence of PIEZO2 is associated with decreased BC. This aligns with our findings, which demonstrate a positive correlation between PIEZO2 expression and BC, suggesting that bladder smooth muscle relaxation may be compromised in PIEZO2 knockout mice and in the detrusor muscle of patients with BOO due to reduced PIEZO2 expression.

A recent study by Dalghi et al. [21] demonstrated that the urothelium functions as a mechanotransducer, with its activity partially dependent on the expression of PIEZO1 or PIEZO2, and that ATP release from the urothelium is contingent upon PIEZO1/2. They further showed that the urothelium acts as a nonneuronal interoceptor, linking PIEZO1/2 mechanotransduction with ATP release and normal voiding function and behavior. Notably, mice lacking PIEZO1/2 exhibited overactive bladder and urinary incontinence [21]. In our study, we observed no significant differences in detrusor PIEZO2 expression between patients with and without DO. Therefore, the evidence regarding the role of PIEZO channels in detrusor contraction is conflicting. While some studies have shown that activation of PIEZO1/2 stimulates detrusor contraction [22,28], research by Dalghi et al. [21] indicated that PIEZO1/2 knockout mice develop overactive bladder. Consequently, current evidence does not support the hypothesis that overexpression of urothelial PIEZO1/2 leads to DO. Research has suggested that the biophysical properties of PIEZO channels, such as their inactivation characteristics, may be altered in certain pathological states [19]. Notably, we acknowledge the limitations of the present study, including the small sample size and the inclusion of patients with urinary retention who were using a Foley catheter. The catheter keeps the bladder in an empty state, thereby reducing the occurrence of DO, which typically depends on bladder filling. The observation that patients with BPH in retention exhibited lower PIEZO2 expression compared to men with BPH who void spontaneously supports the hypothesis that PIEZO2 expression is influenced by mechanical stretching. The use of an indwelling catheter keeps the bladder empty, thus preventing the mechanical stretch stress that results from DO or highpressure detrusor voiding contractions, as seen in men with BPH who void spontaneously.

Recent research has highlighted that activation of PIEZO1, whether through specific agonists or mechanical stretching, plays a key role in the development of pathological cardiac hypertrophy [13]. This study identified PIEZO1 as a novel mechanosensor in hypertrophy induced by pressure overload. Michishita et al. found that PIEZO1 expression in the suburothelium and detrusor increased shortly after the establishment of BOO in rats, suggesting that PIEZO1 may mediate bladder hypertrophy triggered by pressure overload [29]. One might expect PIEZO2 to play a similar role in bladder smooth muscle hypertrophy. However, our research offers a new perspective, demonstrating that men with high bladder pressures due to BPH exhibit a decrease in PIEZO2 expression in the detrusor relative to the control group. This novel finding warrants further investigation in future studies, along with an evaluation of PIEZO1 expression and an exploration of both PIEZO1 and PIEZO2 expression in the urothelium and detrusor.

The present study contributes valuable insights into PIEZO2 expression in men with lower urinary tract dysfunction associated with BPH. To our knowledge, this is the first study to evaluate PIEZO2 expression in this patient population. Nevertheless, several limitations must be recognized and addressed in subsequent research. First, our study was exploratory in nature, and we assessed only transcriptional regulation, even though translational regulation and activity levels are also crucial for complete analysis. In another limitation, we did not evaluate PIEZO1. As previously mentioned, our focus on PIEZO2 was influenced by the study by Marshall et al. [22], which provided evidence linking PIEZO2 deficiency to LUTS in humans. Additionally, we were unable to examine the relationship between PIEZO2 expression and the severity and characteristics of LUTS. The predominance of urinary retention in our patient cohort precluded subgroup analyses, such as comparing patients with and without DO. Furthermore, given our small sample size and the presence of large prostates and severe BOO in our patients, we could not investigate the association between the severity of obstruction and PIEZO2 expression. In contrast to studies utilizing animal models of obstruction, translational research in men with BPH faces limitations in selecting an appropriate control group. Our controls were cadaveric organ donors, typically healthy young individuals, who were unlikely to have experienced lower urinary tract dysfunction. We recognize the age disparity between the BPH group and the control group as a potential confounding factor. However, obtaining bladder biopsies from agematched men poses ethical challenges. Moreover, the high prevalence of LUTS and BPH in the older male population would require urodynamic assessments, further complicating the acquisition of control samples.

In conclusion, men with BOO resulting from BPH exhibit downregulation of PIEZO2, which correlates with poor BC. These findings suggest that PIEZO2 may be involved in the pathophysiology of obstruction-induced lower urinary tract dysfunction. Further research is necessary to elucidate the mechanisms and therapeutic potential of PIEZO2. However, targeting PIEZO2 could offer new strategies for managing lower urinary tract dysfunction.

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