Bladder pain syndrome (BPS)/interstitial cystitis (IC) is a chronic pain disorder characterized by at least six weeks of lower urinary tract symptoms and unpleasant sensations (pain, pressure and discomfort) thought to be related to the urinary bladder and not meeting exclusion criteria. While the etiology is not known, BPS/IC may involve a "vicious circle" of uroepithelial dysfunction, inflammation and peripheral and central sensitization. We propose that the urinary bladder inflammatory insult partly mediates voiding dysfunction and visceral neurogenic pain characteristic of BPS/IC. Several studies from our laboratory have already demonstrated the role(s) of cytokines and their downstream targets in the functional alterations in micturition reflex pathways following chemically (cyclophosphamide, CYP)-induced cystitis. More recently, the pleiotropic protein, TGF-β, has been implicated in the pathogenesis of CYP-induced cystitis.
TGF-β is activated locally at the initial site of injury by protease-dependent or protease-independent mechanisms to initiate a proinflammatory milieu. Depending on its contextual cues, TGF-β may then aid in resolving the primary immune response and support tissue repair. Though TGF-β is necessary to maintain normal immunological function, its aberrant expression and activation may have detrimental effects on responding tissues and cell types. A sustained increase in peripheral TGF-β reactivity, such as what may be observed in chronic inflammatory bladder conditions, may influence bladder afferent excitability to amplify nociceptive transmission and CNS input. The subsequent sensitization of peripheral afferent nociceptors at the level of the DRG or urothelium may promote spinal cord "wind-up" and cascade into visceral hyperalgesia and allodynia.
In the first aim of this dissertation we investigated the functional profile of TGF-β isoforms and receptor (TβR) variants in the normal and inflamed (CYP-induced cystitis) urinary bladder with qRT-PCR, ELISA, IHC and in vivo cystometry. Our studies determined (i) the involvement of TGF-β in lower urinary tract neuroplasticity following urinary bladder inflammation, (ii) a functional role for TGF-β signaling in the afferent limb of the micturition reflex and (iii) urinary bladder TβR-1 as a viable target to reduce voiding frequency with cystitis. In the second aim of this dissertation we investigated the sensory components of the urinary bladder that may underlie the pathophysiology of aberrant TGF-β activation with bladder-pelvic nerve electrophysiology and luciferin-luciferase assays for ATP measurement. Our studies determined that TGF-β1 increased bladder afferent nerve excitability by stimulating ATP release from the urothelium via vesicular exocytosis mechanisms with minimal contribution from pannexin-1 channels. Furthermore, blocking aberrant TGF-β signaling in CYP-induced cystitis with TβR-1 inhibition decreased afferent nerve excitability with an equivalent decrease in ATP release.
Taken together, these results establish a causal link between an inflammatory mediator, TGF-β, and intrinsic signaling mechanisms of the urothelium that may contribute to the altered sensory processing of bladder filling to facilitate increased voiding frequency. The distinct interactions of multiple mediators underscore the challenges for single target therapies and support the development of combinatory therapeutics for bladder dysfunction. Ultimately, these studies have increased our understanding of functional disorders and visceral pain and have the potential to improve the health of those suffering from inflammation-associated bladder syndromes.
| Identifer | oai:union.ndltd.org:uvm.edu/oai:scholarworks.uvm.edu:graddis-1552 |
| Date | 01 January 2016 |
| Creators | Gonzalez, Eric James |
| Publisher | ScholarWorks @ UVM |
| Source Sets | University of Vermont |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate College Dissertations and Theses |
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