Relationship between connexin43-derived gap junction proteins in the bladder and age-related detrusor underactivity in rats

Changes in urethral smooth muscle and external urethral sphincter function with age in rats

To confirm changes in urethral activity with age, both intravesical pressure and urethral perfusion pressure (UPP) were recorded and external urethral sphincter electromyography (EUS-EMG) was performed. A total of 33 female Sprague Dawley rats aged 3 months (young rats), 12 months (middle-aged rats), and 24 months (aged rats) were used. Bladder activity was evaluated using continuous cystometry. Urethral activity was evaluated by simultaneously recording intravesical pressure and UPP in isovolumetric conditions under urethane anesthesia in each group. Additionally, EUS-EMG activity was monitored under the same conditions. In continuous cystometry, the amplitude of bladder contractions was not different among the three groups; nevertheless, residual urine volume was significantly increased in middle-aged and aged rats, as compared in young rats. With respect to UPP, the change in UPP was significantly smaller in aged rats (60%) and middle-aged rats (64%) than in young rats. Furthermore, the mean amplitude of high-frequency oscillations of the EUS was significantly lower in aged (61%) and middle-aged rats (70%) than in young rats. EUS-EMG revealed EUS bursting activity during voiding with clear active and silent phases in young rats but unclear active and silent phases in aged rats. Masson's trichrome staining of the urethra showed EUS atrophy in aged rats compared to young and middle-aged rats. The results indicate that aging induces two urethral dysfunctions in the urethral smooth muscle and EUS, which may lead to dyscoordination between the urinary bladder and urethra.

TGF-β1 and connexin-43 expression in neurogenic bladder from rats with sacral spinal cord injury

AIMS

Sacral spinal cord injury (SCI) could induce underactive bladder (UAB). Malfunction of connexin 43 (CX43) regulated by TGF-β1 might involve in urinary bladder dysfunction. We studied the changes of CX43 and TGF-β1/Smad3 signaling in detrusor of neurogenic bladder (NB) in sacral SCI rats.

METHODS

Sacral SCI was produced by hemisection (SSCH) or transection (SSCT) of spinal cord between L4 and L5 in female Wistar rats. BBB scores, residual urine volume and bladder weight as well as characteristic cystometric parameters at 6th week were used to confirm the successful establishment of NB. Western blotting and qRT-PCR were used to exam the protein and mRNA expression levels of CX43, CX45, TGF-β1, and Smad3 in detrusor.

RESULTS

BBB scores were significantly decreased, with the lowest in SSCT rats (P < 0.01). The residual urine volume, mean bladder weight, and cystometric parameters were increased, with the highest in SSCT rats. CX43 and phospho-CX43 protein levels were significantly decreased, but those of TGF-β1, Smad3, and phospho-Smad3 were significantly increased. It was the protein and mRNA levels of CX43 but not those of CX45 which were decreased in negative accordance with those of TGF-β1 and Smad3. Those changes were more significant in SSCT than in SSCH rats.

CONCLUSIONS

This study indicates that voiding dysfunction is related to the decreased CX43 function in detrusor from NB. TGF-β1/Smad3 signaling might be involved in the down-regulation of CX43 in SCI rats. Early regulation of CX43 might be beneficial to patients with voiding dysfunction.

Pathophysiology of the underactive bladder

Underactive bladder (UAB), which has been described as a symptom complex suggestive of detrusor underactivity, is usually characterized by prolonged urination time with or without a sensation of incomplete bladder emptying, usually with hesitancy, reduced sensation on filling, and slow stream often with storage symptoms. Several causes such as aging, bladder outlet obstruction, diabetes mellitus, neurologic disorders, and nervous injury to the spinal cord, cauda equine, and peripheral pelvic nerve have been assumed to be responsible for the development of UAB. Several contributing factors have been suggested in the pathophysiology of UAB, including myogenic failure, efferent and/or afferent dysfunctions, and central nervous system dysfunction. In this review article, we have described relationships between individual contributing factors and the pathophysiology of UAB based on previous reports. However, many pathophysiological uncertainties still remain, which require more investigations using appropriate animal models.

Addressing challenges in underactive bladder: recommendations and insights from the Congress on Underactive Bladder (CURE-UAB)

Underactive bladder (UAB) is an expanding troublesome health issue, exerting a major influence on the health and independence of older people with a disproportionally low level of attention received. The 2nd International Congress on Underactive Bladder (CURE-UAB 2) convened in Denver, CO on December 3 and 4, 2015, and comprised of top clinicians, scientists, and other stakeholders to address the challenges in UAB. A series of workshops aimed to define UAB and its phenotype, define detrusor underactivity (DU) and create a subtyping of DU, evaluate existing animal models for DU, and lastly to establish research priorities for UAB.

Efficacy and Safety of Intravesical OnabotulinumtoxinA Injection in Patients with Detrusor Hyperactivity and Impaired Contractility

We investigated the efficacy and safety of intravesical onabotulinumtoxinA injection in patients with detrusor hyperactivity and impaired contractility (DHIC). Twenty-one patients with urodynamically proven DHIC and 21 age-matched patients with overactive bladder (OAB) with urodynamic detrusor overactivity were treated with intravesical injections of 100 U of onabotulinumtoxinA. The overactive bladder symptom score, urgency severity score, patient perception of bladder condition, global response assessment, voiding diary, and procedure-related adverse events (AE) at baseline, two weeks, one, three, and six months after treatment were assessed. The results showed that the subjective symptom scores improved significantly in both groups, and the scores did not differ between the groups. The decrease in urgency episodes and urgency urinary incontinence were noted in OAB patients but not in DHIC patients. Although the incidence of AEs was comparable between the groups, the therapeutic efficacy lasted for a mean of 4.9 ± 4.8 months in DHIC patients and 7.2 ± 3.3 months in OAB patients (p = 0.03). We concluded that the efficacy of intravesical onabotulinumtoxinA injection for DHIC patients was limited and short-term. Nevertheless, AEs did not increase in DHIC. Intravesical onabotulinumtoxinA might not be a good indication in patients with DHIC and high post-voiding residual urine. Physicians should inform patients of the potential benefits and risks of onabotulinumtoxinA injection for treatment of DHIC.

Changes of muscarinic receptors and connexin-43 expression as a mechanism of overactive bladder in ovariectomized rats

PURPOSE

After menopause, the bladder is known to become overactive. To investigate the mechanisms involved in these changes, we examined the muscarinic receptors M2, M3 and gap junction protein connexin-43 in an ovariectomized rat bladder.

METHODS

Twenty 10-week-old female SD rats were used. Ten rats were ovariectomized, (Ovx group) and 10 rats received a sham operation (Con group). Four weeks after the operation, urodynamic tests were performed to verify overactive bladder, and the animals were killed. The body, bladder and uterus weights were measured. The bladder specimens were prepared for immunohistochemical staining for muscarinic receptors M2, M3 and connexin-43. Western blotting was also used for the same protein measurement (M2, M3 and connexin-43). A t test with a p value of 0.05 was considered significant, and SPSS 12.0 for Windows was used to analyze the data.

RESULTS

The mean body weight of the Ovx group (315.8 ± 18.1 g) was heavier than the Con group (270.0 ± 23.6 g) (p = 0.009). The mean uterus weight of the Ovx group (260.4 ± 186.8 g) was lighter than the Con group, (600.6 ± 175.9 g) (p = 0.028) and the mean bladder weight of the Ovx group (80.2 ± 15.9 g) was lighter than the Con group (97.4 ± 10.6 g) (p = 0.041). The mean bladder contraction of the Ovx group (5.5 ± 2.3/10 min) was more frequent than that of the Con group (3.2 ± 2.8) (p < 0.05). The expressions of M2 and M3 were not different between the Ovx and the Con group, but the expression of connexin-43 in the Ovx group was more intense than in the Con group in immunohistochemical staining. These findings were also confirmed by Western blotting results.

CONCLUSIONS

Ovariectomized rats showed frequent bladder contraction and increased connexin-43 expression without changes in M2 and M3 receptor expression. These results imply that ovariectomy-induced overactive bladder may be due to an altered gap junction protein function rather than muscarinic receptor modification.