Spontaneous voiding by mice reveals strain-specific lower urinary tract function to be a quantitative genetic trait.

Lower urinary tract (LUT) symptoms become prevalent with aging and affect millions; however, therapy is often ineffective because the etiology is unknown. Existing assays of LUT function in animal models are often invasive; however, a noninvasive assay is required to study symptom progression and determine genetic correlates. Here, we present a spontaneous voiding assay that is simple, reproducible, quantitative, and noninvasive. Young female mice from eight inbred mouse strains (129S1/SvImJ, A/J, C57BL/6J, NOD/ShiLtJ, NZO/H1LtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ) were tested for urination patterns on filter paper. Repeat testing at different times of the day showed minimal within-individual and within-strain variations, but all parameters (spot number, total volume, percent area in primary void, corner voiding, and center voiding) exhibited significant variations between strains. Calculation of the intraclass correlation coefficient, an estimate of broad-sense heritability, for each time of day and for each voiding parameter revealed highly significant heritability [spot number: 61%, percent urine in primary void: 90%, and total volume: 94% (afternoon data)]. Cystometrograms confirmed strong strain-specific urodynamic characteristics. Behavior-voiding correlation analysis showed no correlation with anxiety phenotypes. Diagnostically, the assay revealed LUT symptoms in several systems, including a demonstration of voiding abnormalities in older C57BL/6J mice (18-24 mo), in a model of protamine sulfate-induced urothelial damage and in a model of sucrose-induced diuresis. This assay may be used to derive pathophysiological LUT readouts from mouse models. Voiding characteristics are heritable traits, opening the way for genetic studies of LUT symptoms using outbred mouse populations.

Loss of ß1-integrin from urothelium results in overactive bladder and incontinence in mice: a mechanosensory rather than structural phenotype.

Bladder urothelium senses and communicates information about bladder fullness. However, the mechanoreceptors that respond to tissue stretch are poorly defined. Integrins are mechanotransducers in other tissues. Therefore, we eliminated ß1-integrin selectively in urothelium of mice using Cre-LoxP targeted gene deletion. ß1-Integrin localized to basal/intermediate urothelial cells by confocal microscopy. ß1-Integrin conditional-knockout (ß1-cKO) mice lacking urothelial ß1-integrin exhibited down-regulation and mislocalization of α3- and α5-integrins by immunohistochemistry but, surprisingly, had normal morphology, permeability, and transepithelial resistance when compared with Cre-negative littermate controls. ß1-cKO mice were incontinent, as judged by random urine leakage on filter paper (4-fold higher spotting, P<0.01; 2.5-fold higher urine area percentage, P<0.05). Urodynamic function assessed by cystometry revealed bladder overfilling with 80% longer intercontractile intervals (P<0.05) and detrusor hyperactivity (3-fold more prevoid contractions, P<0.05), but smooth muscle contractility remained intact. ATP secretion into the lumen was elevated (49 vs. 22 nM, P<0.05), indicating abnormal filling-induced purinergic signaling, and short-circuit currents (measured in Ussing chambers) revealed 2-fold higher stretch-activated ion channel conductances in response to hydrostatic pressure of 1 cmH2O (P<0.05). We conclude that loss of integrin signaling from urothelium results in incontinence and overactive bladder due to abnormal mechanotransduction; more broadly, our findings indicate that urothelium itself directly modulates voiding.