Urinary Retention, Incontinence, and Dysregulation of Muscarinic Receptors in Male Mice Lacking Mras

Here we show that male, but not female mice lacking expression of the GTPase M-Ras developed urinary retention with distention of the bladder that exacerbated with age but occurred in the absence of obvious anatomical outlet obstruction. There were changes in detrusor morphology in Mras (-/-) males: Smooth muscle tissue, which exhibited a compact organization in WT mice, appeared disorganized and became increasingly ‘layered’ with age in Mras (-/-) males, but was not fibrotic. Bladder tissue near the apex of bladders of Mras (-/-) males exhibited hypercontractility in response to the cholinergic agonist carbachol in in vitro, while responses in Mras (-/-) females were normal. In addition, spontaneous phasic contractions of detrusors from Mras (-/-) males were increased, and Mras (-/-) males exhibited urinary incontinence. We found that expression of the muscarinic M2 and M3 receptors that mediate the cholinergic contractile stimuli of the detrusor muscle was dysregulated in both Mras (-/-) males and females, although only males exhibited a urinary phenotype. Elevated expression of M2R in young males lacking M-Ras and failure to upregulate M3R with age resulted in significantly lower ratios of M3R/M2R expression that correlated with the bladder abnormalities. Our data suggests that M-Ras and M3R are functionally linked and that M-Ras is an important regulator of male bladder control in mice. Our observations also support the notion that bladder control is sexually dimorphic and is regulated through mechanisms that are largely independent of acetylcholine signaling in female mice.