Uropathic Observations in Mice Expressing a Constitutively Active Point Mutation in the 5-HT_3AReceptor Subunit

Abstract

Mutant mice with a hypersensitive serotonin (5-HT) 3A receptor were generated through targeted exon replacement. A valine to serine mutation (V13ЈS) in the channel-lining M2 domain of the 5-HT 3A receptor subunit rendered the 5-HT 3 receptor ϳ70-fold more sensitive to serotonin and produced constitutive activity when combined with the 5-HT 3B subunit. Mice homozygous for the mutant allele (5-HT 3A vs/vs ) had decreased levels of 5-HT 3A mRNA. Measurements on sympathetic ganglion cells in these mice showed that whole-cell serotonin responses were reduced, and that the remaining 5-HT 3 receptors were hypersensitive. Male 5-HT 3A vs/vs mice died at 2-3 months of age, and heterozygous (5-HT 3A vs/ϩ ) males and homozygous mutant females died at 4 -6 months of age from an obstructive uropathy. Both male and female 5-HT 3A mutant mice had urinary bladder mucosal and smooth muscle hyperplasia and hypertrophy, whereas male mutant mice had additional prostatic smooth muscle and urethral hyperplasia. 5-HT 3A mutant mice had marked voiding dysfunction characterized by a loss of micturition contractions with overflow incontinence. Detrusor strips from 5-HT 3A vs/vs mice failed to contract to neurogenic stimulation, despite overall normal responses to a cholinergic agonist, suggestive of altered neuronal signaling in mutant mouse bladders. Consistent with this hypothesis, decreased nerve fiber immunoreactivity was observed in the urinary bladders of 5-HT 3A vs/vs compared with 5-HT 3A wild-type (5-HT 3A ϩ/ϩ ) mice. These data suggest that persistent activation of the hypersensitive and constitutively active 5-HT 3A receptor in vivo may lead to excitotoxic neuronal cell death and functional changes in the urinary bladder, resulting in bladder hyperdistension, urinary retention, and overflow incontinence.

5-HT3 Receptors

“…As might be expected due to their role in emesis, 5-HT 3 receptors are involved in information transfer in the gastrointestinal tract, and in the enteric nervous system they regulate gut motility and peristalsis [23]. They also play an important role in the urinary tract, and indeed expression of hypersensitive and constitutively active 5-HT 3 receptors in mice lead to excitotoxic neuronal cell death, resulting in early death due to uropathy [24]. 5-HT 3 receptors in the CNS may play roles in a variety of functions including emesis, cognition and anxiety.…”

The L293 residue in transmembrane domain 2 of the 5-HT3A receptor is a molecular determinant of allosteric modulation by 5-hydroxyindole

“…Both 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) and the 5-HT 3 receptor competitive antagonist MDL 72222 have been used to detect spontaneous channel activity in the 5-HT 3A mutant receptors (Zhang et al, 2002;Bhattacharya et al, 2004). The application of 100 μM TMB-8 or 300 nM MDL 72222 failed to alter the holding current in cells expressing the L293S receptor (Fig.…”

Dynamic Expression of Serotonin Receptor 5-HT3A in Developing Sensory Innervation of the Lower Urinary Tract

“…Specifically, antagonizing 5-HT3A alleviates pain associated with intestinal inflammation and irritable bowel syndrome (Chen et al, 2009; Walstab et al, 2010; Machu, 2011). Additionally, normal 5-HT3A receptor activity is required for adult LUT innervation and bladder function (Bhattacharya et al, 2004). However, it remains unclear what sensory subtypes normally express the 5-HT3A receptor and the extent to which 5-HT3A+ neurons contribute to normal bladder innervation.…”

“…Differentiation of DRG neurons and acquisition of sensory subtype-specific markers has been reported around 14.5 dpc (Marmigerè and Ernfors, 2007; Bachy et al, 2011; Zou et al, 2012). Despite evidence that points to an effect of 5-HT3A on bladder function (Espey et al, 1998; Bhattacharya et al, 2004; Hall et al, 2015), no prior studies have assessed the expression of this receptor in DRG during the developmental stages when the LUT is being innervated. To date, Htr3a gene expression in DRG has only been characterized via in situ hybridization at a single developmental time point (Tecott et al, 1993; Diez-Roux et al, 2011).…”