Molecular Mechanisms of Bladder Outlet Obstruction in Transgenic Male Mice Overexpressing Aromatase (Cyp19a1)

Abstract

We investigated the etiology and molecular mechanisms of bladder outlet obstruction (BOO). Transgenic (Tg) male mice overexpressing aromatase (Cyp19a1) under the ubiquitin C promoter in the estrogen-susceptible C57Bl/6J genetic background (AROM؉/ 6J) developed inguinal hernia by 2 months and severe BOO by 9 to 10 months, with 100% penetrance. These mice gradually developed uremia, renal failure, renal retention, and finally died. The BOO bladders were threefold larger than in age-matched wild-type (WT) males and were filled with urine on necropsy. Hypotrophic smooth muscle cells formed the thin detrusor urinae muscle, and collagen III accumulation contributed to the reduced compliance of the bladder. p-AKT and ER␣ expression were up-regulated and Pten expression was down-regulated in the BOO bladder urothelium. Expression of only ER␣ in the intradetrusor fibroblasts suggests a specific role of this estrogen receptor form in urothelial proliferation. Inactivation of Pten, which in turn activated the p-AKT pathway, was strictly related to the activation of the ER␣ pathway in the BOO bladders. Human relevance for these findings was provided by increased expression of p-AKT, PCNA, and ER␣ and decreased expression of PTEN in severe human BOO samples, compared with subnormal to mild samples. These findings clarify the involvement of estrogen excess and/or imbalance of the androgen/estrogen ratio in the molecular pathogenetic mechanisms of BOO and provide a novel lead into potential treatment strategies for BOO. A close interrelationship between lower urinary tract (bladder and urethra) symptoms, bladder outlet obstruction (BOO), and benign prostatic hyperplasia has been shown in aging men. 1-4 These symptoms, which include increased voiding frequency and urgency, nocturia, incomplete bladder emptying, hesitancy, weak stream, and straining, occur in mild to severe form in 50% to 85% of men over 50 years of age. 5-8 BOO, which reduces or prevents the flow of urine into the urethra, and urinary tract infection, bladder cancer, and incontinence comprise the major causes of lower urinary tract symptoms. 9,10 Congenital or acquired BOO can result in a stiff-walled, fibrotic bladder with low capacity, high pressure, and noncompliance, which may ultimately damage the kidneys. 10 The incidence of lower urinary tract symp-

Increased susceptibility of estrogen-induced bladder outlet obstruction in a novel mouse model

“…The pathophysiologic effect of E2, which is independent of prostate growth promotion, in BOO development has been shown in transgenic mice overexpressing aromatase. 6,27 Epidemiologic studies did not reveal a statistically significant correlation between the severity of BOO symptoms and prostate size. 4,28 Thus, the underlying causes of BOO are heterogeneous and more complex than previously appreciated and may involve 'non-prostatic' mechanisms.…”

“…The narrowing of bladder outlet and urinary obstruction in these mice could not be because of BPH, which is regarded as a primary cause of BOO in men. Given that estrogen receptors are present in the male LUT, including the bladder and urethra, 6,[24][25][26] it is plausible that extraprostatic tissues in the LUT are direct site(s) of estrogenic actions in BOO development. The pathophysiologic effect of E2, which is independent of prostate growth promotion, in BOO development has been shown in transgenic mice overexpressing aromatase.…”

“…To our knowledge, this is the first time to report bladder-neck fibrosis associated with BOO. The bladder-body detrusor fibrosis has been reported in rodents with surgical obstruction of urethra, [36][37][38] aromatase-overexpressing mice 6 and T þ E2-treated mice. 12 The abnormal deposition of collagen in the bladder neck and body, as a consequence of urinary obstruction, may further increase the stiffness and matrix rigidity of LUT leading to the decompensated stage of BOO.…”

“…6 T plus E2 (T þ E2) treatment was recently found to induce BPH-related BOO symptoms in male mice. 12 The T þ E2 regimen used to treat the mice in the present study has been reported to elevate the serum ratio of E2 to T, mimicking the hormonal milieu in aging men.…”

“…However, a number of studies have suggested that BOO is not always caused by BPH. [4][5][6] Factors or organs other than the prostate have been proposed as contributors to BOO or modifiers of the severity of its symptoms. 3,7 An imbalance between androgens and estrogens has been implicated in the development of LUTS in men, including BOO.…”