Ageing-related bladder dysfunctions and their gender differences in mice: in vitro and in vivo functional and gene expression changes

Objective To investigate aging-related changes and their sex differences in in vivo and in vitro functions and gene expression in the bladder of mice. Materials and Methods Mature (12-month old) and aged (27–30-month old) mice of both sexes were studied. In in vivo experiments, frequency, volume, and conscious free-moving cystometry measurements were investigated. In in vitro experiments, organ bath studies using detrusor strips were performed to observe functional changes, and serum sex hormone levels and mRNA expression of muscarinic, purinergic, and β-adrenergic receptors in the bladder using a cDNA microarray were evaluated. Results Although few differences were detected in the frequency/volume measurements between the two groups in either sex, aged mice showed a lower mean flow rate and higher number of non-voiding contractions in both sexes and lower maximum pressure and smaller voided volume and bladder capacity was observed in males according to cystometry measurements. Detrusor strips from aged mice showed weaker contractile responses to carbachol and electrical field stimulation, particularly in the cholinergic component, and relaxant responses to isoproterenol, which were accompanied by a decreased mRNA expression of M3 muscarinic receptors in aged males and β2-adrenoceptors in aged females. This aging-related bladder dysfunction was more severe in males, and the serum testosterone level in aged males was significantly decreased. Gene expression changes in the bladder with aging were different between sexes: 469 and 544 genes in males, 392 and 75 in females, and 8 and 37 in both sexes were significantly upregulated and downregulated, respectively, with aging. Conclusions Aged mice of both sexes demonstrated both voiding and storage dysfunctions, which were more pronounced in males. Sex hormone and genomic changes associated with aging may contribute to this functional deterioration in mice. C57BL/6 male and female mice were divided into two groups: matured mice (12 months-old; male: N = 4, female: N = 4, respectively) and aged mice (27-30 months-old; male: N = 4, female: N = 4, respectively). Mice were maintained under standard laboratory conditions with a 12:12 h light (9:00 a.m. to 9:00 p.m.) and dark (9:00 p.m. to 9:00 a.m.) cycles, and free access to food pellets and tap water. Experimental protocols were approved by the Animal Ethics Committee, The University of Tokyo Graduate School of Medicine, Tokyo, Japan, and were in line with NIH guidelines for the care and use of experimental animals. Mice were obtained from the Tokyo Metropolitan Institute of Gerontology, and after 1-week adaptation period, they were used for measurements.