Deletion of Mechanosensory β1-integrin From Bladder Smooth Muscle Results in Voiding Dysfunction and Tissue Remodeling

Abstract

The bladder undergoes large shape changes as it fills and empties and experiences complex mechanical forces. These forces become abnormal in diseases of the lower urinary tract such as overactive bladder, neurogenic bladder and urinary retention. As the primary mechanosensors linking the actin cytoskeleton to the extracellular matrix (ECM), integrins are likely to play vital roles in maintaining bladder smooth muscle (BSM) homeostasis. In a tamoxifen-inducible smooth muscle conditional knockout of β1-integrin there was concomitant loss of α1- and α3-integrins from BSM and upregulation of αV- and β3-integrins. Masson's staining showed a reduction in smooth muscle with an increase in collagenous ECM. Functionally mice exhibited a changing pattern of urination by voiding spot assay up to eight weeks after tamoxifen. By eight weeks there was increased frequency with reductions in voided volume, consistent with overactivity. Cystometrograms confirmed there was a significant reduction in intercontractile interval with reduced maximal bladder pressure. Muscle strip myography revealed a loss of contraction force in response to electrical field stimulation, that was entirely due to loss of muscarinic contractility. Quantitative western blotting showed a loss of M3 receptor and no change in P2X1. qPCR on extracellular matrix and interstitial genes revealed loss of Ntpd2, a marker of an interstitial cell subpopulation; and an upregulation of S100A4 which is often associated with fibroblasts. Collectively, the data show that loss of appropriate mechanosensation through integrins results in cellular and extracellular remodeling, and concomitant bladder dysfunction that resembles lower urinary tract symptoms seen in older people.

A Spectrum of Age- and Gender-Dependent Lower Urinary Tract Phenotypes in Three Mouse Models of Type 2 Diabetes

“…Void spot areas were quantitated using an in-house-developed machine learning object recognition algorithm. The results were compared with our formerly published UrineQuant software [29], and the results for all parameters demonstrated correlation coefficients of R 2 > 0.98, thus validating its accuracy and consistency with previously published data from our group [29,32,33,35]. [34] and observations from this study.…”

“…We have found, over a number of years of characterizing VSA in mice of different strains and in different models, that several key parameters can be used to describe voiding phenotypes [ 29 , 31 , 32 ]. Total urine volume is useful for assessing polyuria.…”

“…VSAs were performed in the afternoon, as described previously [ 29 , 32 ]. Mice were moved individually to empty mouse cages with precut filter paper (Blicks Cosmos blotting paper #10422–1005) covering the bottom.…”