Mechanisms underlying bladder hypersensitivity in female mice with estrogen deficiency

Takaoka E1, Suzuki T2, Mizoguchi S2, Kurobe M2, Ni J2, Kwon J2, Shimizu N2, Onozawa M3, Miyazaki J3, Nishiyama H4, Yoshimura N2

Research Type

Pure and Applied Science / Translational

Abstract Category

Female Lower Urinary Tract Symptoms (LUTS) / Voiding Dysfunction

Abstract 358
Open Discussion ePosters
Scientific Open Discussion Session 21
Thursday 30th August 2018
13:10 - 13:15 (ePoster Station 5)
Exhibition Hall
Overactive Bladder Animal Study Urgency/Frequency Pathophysiology Basic Science
1. University of Pittsburgh / International university of health and welfare, 2. University of Pittsburgh, 3. International University of health and welfare, 4. University of Tsukuba
Presenter
E

Eiichiro Takaoka

Links

Poster

Abstract

Hypothesis / aims of study
This is the first report to elucidate the detailed pathophysiological mechanisms of bladder dysfunction in a mouse model of estrogen deficiency.  It is well known clinically that the postmenopausal condition in women is often associated with bladder and urethral dysfunction.  The pathophysiology of postmenopausal urethral dysfunction in relation with stress urinary incontinence has been investigated in previous studies using a rodent model of estrogen deficiency induced by ovarienctomy (OVX).  However, the information about bladder dysfunction of OVX animal models has been limited [1].  In this study, we therefore analysed bladder function, molecular changes in bladder mucosa, and the effect of intravesical chemical irritation in OVX mice to elucidate the pathophysiological mechanisms and explore the therapeutic targets of postmenopausal bladder dysfunction.
Study design, materials and methods
In female C57BL/6N mice (8-week-old), OVX was performed via a dorsolumbar approach without touching the bladder. Sham operated animals were used as controls. Six weeks after the operation, awake cystometrograms (CMG) were recorded in sham and OVX mice. In both groups, intravesical acetic acid (AA) administration with or without intravesical administration of amiloride (an inhibitor of ASICs & ENaC) was performed, and changes in CMG parameters were evaluated.  The transcript levels of junction molecules (CDH1, Cx43), acid- and/or mechano-sensitive receptors (TRPV4, ASICs, ENaCs) in bladder mucosa were evaluated by RT-PCR.  Furthermore, intravesical AA irritation was performed in OVX mice with C-fiber afferent desensitization induced by capsaicin pretreatment [2].  A total of 90 mice (n = 39; sham group, n=51; OVX group) were used.  Among them, 62 (n = 31; sham group, n=31; OVX group) mice were used for awake CMG to evaluate the bladder dysfunction associated with OVX.  Sixteen (n = 8; sham group, n=8; OVX group) mice were used for histological and molecular studies.  Other 12 OVX mice were used for the C-fiber bladder afferent desensitization experiment with capsaicin pretreatment.
Results
Body weight was significantly increased (27±0.48 vs. 20±0.23 g, p<0.0001) and the uterus weight was significantly decreased (0.016±0.0011 vs. 0.076±0.0045 g, p<0.0001) in OVX vs. control mice. In CMG, there were no significant differences in CMG parameters between sham and OVX at baseline; i.e. intercontraction intervals (ICI) (540±35 vs. 550±37 s, p=0.85), peak amplitude during voiding (42±1.6 vs. 46±1.6 cmH2O, p=0.11), pressure at baseline (PB) (2.8±0.22 vs. 3.3±0.24 cmH2O, p=0.14), pressure threshold (PT) (6.5±0.32 vs. 6.0±0.25 cmH2O, p=0.26), a number of non-voiding contractions (0.20±0.0.027 vs. 0.14±0.025 /min, p=0.092), voided volume (94±5.8 vs. 90 ±5.8 µl, p=0.48), post-void residual (PVR) (2.4±1.3 vs. 3.1±1.0 µl, p=0.66), bladder capacity (96±5.8 vs. 91±5.9 µl, p=0.54), voiding efficiency (VE) (98±1.1 vs. 97±1.1 %, p=0.55), and compliance (0.045±0.016 vs. 0.037±0.0022 ml/H2O, p=0.61) (figure 1).  However, OVX mice showed a significant decrease in ICI (700±100 to 270±60 s, p=0.0047), voided volume (110±16 to 50±11 µl, p=0.0041), and bladder capacity (110±16 to 50±11 µl, p=0.0041) after intravesical 0.1% AA administration, whereas 0.1% AA did not affect any CMG parameters in control mice (figure 1).  Intravesical administration of 1mM amiloride blocked the effect of AA in OVX mice (figure 2).  In RT-PCR, the expression of ASIC1 was significantly increased in bladder mucosa of OVX mice (p=0.00080).  Furthermore, OVX mice with C-fiber desensitization by capsaicin pretreatment, intravesical 0.1% AA administration had no effect on bladder function; i.e. ICI (730±62 to 740±59 s, p=0.78), voided volume (120±6.9 to 120±7.0 µl, p=0.43) and bladder capacity (120±7.7 to 120±7.7 µl, p=0.99) although, in OVX mice with vehicle pretreatment, intravesical 0.1% AA irritation still significantly decreased ICI, voided volume, and bladder capacity.
Interpretation of results
OVX mice showed enhanced bladder sensitivity evident as AA-induced bladder overactivity via activation of amiloride-sensitive channels, in association with upregulation of ASIC1 in bladder mucosa.  Also, capsaicin sensitive C- fiber bladder afferent pathways contribute to bladder hypersensitivity after OVX.
Concluding message
It seems likely that the estrogen-deficient condition makes the bladder more susceptible to intravesical stimuli to induce C-fiber-dependent bladder overactivity via activation of acid-sensing receptors such as ASIC1, which might be a mechanism of storage bladder dysfunction in postmenopausal women.
Figure 1
Figure 2
References
  1. Chen HY, Chen CJ, Chen WC, Wang SJ, Chen YH. A promising protein responsible for overactive bladder in ovariectomized mice. Taiwan J Obstet Gynecol. 56: 196-203, 2017.
  2. Kadekawa K, Majima T, Shimizu T, Wada N, de Groat WC, Kanai AJ, Goto M, Yoshiyama M, Sugaya K, Yoshimura N. The role of capsaicin-sensitive C-fiber afferent pathways in the control of micturition in spinal-intact and spinal cord-injured mice. Am J Physiol Renal Physiol. 313: F796-F804, 2017.
Disclosures
Funding NIH R01-DK107450 Clinical Trial No Subjects Animal Species Mouse Ethics Committee University of Pittsburgh Institutional Animal Care and Use Committee
27/03/2024 19:54:48