The interplay between active and passive mechanics in the aging bladder

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The prevalence of lower urinary tract symptoms (LUTS), such as contractile dysfunction and urinary retention, increases significantly with age and an estimated 2.6 billion people worldwide suffered from at least one LUTS in 2008. The aging human bladder has altered mechanical properties and increased residual urine volume. The detrusor is the smooth muscle that responsible for bladder contraction and is embedded in and surrounded by a wavy, collagen-rich extracellular matrix (ECM). The etiologies of many age-related LUTS in humans are tied to alterations in smooth muscle cell (SMC) contractility and signaling pathways, which has also been shown in mouse models of the aging bladder. However, the physical interactions that occur between SMCs and ECM are unknown and are likely a key factor in understanding the active and passive mechanics of bladder dysfunction with aging. The work described in this proposal will use optogenetics, multiphoton microscopy, and a custom testing system to develop an ex vivo methodology that incorporates concentric contraction into bladder mechanical testing. The proposed studies will be conducted by a team with complementary expertise in proteomics, ECM biology and soft tissue biomechanics (PI Calve), urinary bladder mechanics and mechanical testing (co-I Tuttle), and constitutive model development and finite element (FE) analysis (co-I Roccabianca). In Aim 1, the ability of detrusor contraction to restore the bladder ECM to the native empty organization will be tested. Two methods for inducing SMC contraction will be compared (i.e. optogenetic and cholinergic) to determine how effective light-mediated stimulation is in replicating cholinergic detrusor contraction using SM22- Cretg;ChR2(H134R)-EYFP mice. The morphological and mechanical data will be implemented in an FE model, that will be used to evaluate the importance of ECM organization on the mechanical response. Validation of our approach will increase agreement between in vivo and ex vivo testing conditions and uncover the effect of detrusor contraction on ECM organization. In Aim 2 we will test the hypothesis that remodeling of the ECM in the aging bladder inhibits the ability of the detrusor to adequately contract the tissue to the healthy resting configuration. Bladders from aged SM22-Cretg;ChR2(H134R)-EYFP mice will be tested ex vivo to study how aging affects ECM and SMC organization. Proteomics will be used to quantify how the ECM and muscarinic receptor abundance changes with aging. This data will be used to inform FE modeling to help resolve the effect of aging on tissue composition, ECM organization, and mechanics. Successful completion of this project will increase the fundamental understanding of bladder function gain insight into how this contraction-reorganization behavior is diminished in the aging bladder, which we hypothesize contributes to LUTS development and progression. The experimental methodology developed will be useful in evaluating bladder dysfunction in various diseases and open doors to new research into the functional effects of pharmacological treatments for LUTS.