Mediators of Neurogenic Inflammation in the Urinary Tract as Key Factors in the Painful Bladder Syndrome / Interstitial Cystitis and Bladder Dysfunction
Mediators of Neurogenic Inflammation in the Urinary Tract as Key Factors in the Painful Bladder Syndrome / Interstitial Cystitis and Bladder Dysfunction
Interstitial cystitis (IC)/chronic pelvic pain syndrome (CPPS) is a clinical syndrome of pelvic pain and/or urinary urgency/frequency in absence of a specific cause such as bacterial infection or damage to the bladder. The pathogenetic mechanisms of IC/CPPS are as yet undefined and it is largely this lack of knowledge, which precludes a systematic therapeutic approach. Experimental evidence, including results from the animal models of cystitis and the knock-out mice, indicate a participation of tachykinin receptors, especially the NK1R, in neurogenic inflammation, which is considered an important element of the IC complex. However, there is very scant information about the molecular mechanisms of IC in humans, or of the types of receptors, which participate in neurogenic inflammation. Based on our molecular biological know-how and the clinical expertise, we propose to investigate the role of the tachykinin and bradykinin receptors and their signalling partners in CPPS and bladder dysfunction in humans.
Although IC has been recognised for more than a century, its pathophysiology remains a mystery, and as a consequence the treatment of IC is largely empirical. A multitude of mechanisms of the disease have been postulated ranging from neuroinflammatory to autoimmune or possibly infectious or toxic agents. Newer studies have hinted towards a genetic basis of the disease, but in most hypotheses an inflammatory component of some kind is involved and many findings support this theory. An often-cited hypothesis is the leaky epithelium. The healthy bladder is coated with a thin mucinous substance bladder surface mucin, which is composed of numerous sulfonated glycosaminoglycans and glycoproteins. In IC patients, in contrast to controls, as well as in some animal models of IC, qualitative changes to this surface layer have been observed (Lilly et al, 1990., Moskowitz et al, 1994). An initiating event (toxin) may lead to functional changes and increased permeability. This in turn leads to nerve sensitisation and possibly up-regulation. There is increasing evidence that the progression of IC is accompanied by a significant up-regulation of sensory nerves in the bladder (Letourneau, 1996). Nerve growth factor (NGF), a neurotropin that sensitises nociceptor fibres, was reported to be increased in bladders of IC patients (Lowe, 1997), and application of NGF in Wistar rats acutely induced bladder hyperactivity (Chuang, 2001). Sensory nerves in neurogenic inflammation secrete inflammatory mediators such as Substance P (SP), a nociceptive neurotransmitter in the central and peripheral nervous system. Increased amounts of the released Substance P have been found in the urine of IC patients (Hohenfellner, et al,1992, Pang et al., 1995, Pang et al., 1996), the concentration of Substance P reflecting the patients' degree of pain (Chen et al., 1999). Substance P and related tachykinins (TKs) mediate a variety of physiological processes in the genitourinary, pulmonary and gastrointestinal tract through stimulation of NK1 and NK2 receptors. Pre-clinical evidence obtained through use of selective tachykinin receptor antagonists indicates that endogenous tachykinins are involved in regulation of smooth muscle contraction, vasodilation, water metabolism and inflammation. Recently it was shown that mRNA encoding for SP receptor NK1 is in-creased in the bladder biopsies from patients with interstitial cystitis (Marchand et al., 1998). NK1R mRNA was found in detrusor muscle, urothelium and vascular structures, and the endothelial NK1R were markedly increased. SP binding to NK1R on endothelial cells results in vasodilation, plasma extravasation, cytokine release and activation and infiltration of immune cells, all characteristic of IC. Experiments with the NK1R knockout mice allowed for the first time to demonstrate the obligatory requirement of NK1R in cystitis and participation of these receptors in the chain of events linking mast cell degranulation and inflammation (Saban et al., 2000).
Changes in the sarcolemma, and altered expression of the tachykinin and bradykinin receptors might significantly influence the downstream signalling events leading to propagation of the symptoms of chronic pelvic pain/IC. By uncovering the link between clinical symptoms and the molecular regulation of the atypical inflammatory response, we may be able to offer novel and specific options for treatment. In the current proposal, we would like to further our studies of urinary bladder pathology, in particular the symptomatic complex of PBS/interstitial cystitis, and investigate the effect of changes in human urothelium and detrusor muscle cells on the NK1R-mediated signalling.
Biopsies from controls and PBS patients will be obtained in either general or spinal anesthesia transurethrally from the bladder dome and trigone with a biopsy tong. RNA will be extracted, and the expression levels of selected genes analyzed using Taqman real-time PCR and gene expression arrays (Applied Biosystems). Calcium imaging will be used to monitor the receptor activation and protein levels analysed by SDS-PAGE and Western Blotting. Receptor tissue distribution will be analysed by immuno-cytochemistry.
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