We have recently determined that ATP can be released from the urinary bladder epithelium (urothelium) in response to stretch and chemical stimulation through pannexin channels. As purinergic signaling is thought to play a critical role i the development of bladder pathology, pannexin channels may be an important target in the treatment of disorders of the urinary bladder such as interstitial cystitis/painful bladder syndrom (IC/PBS). Therefore our proposed research aims to further examine the role of pannexin channels in purinergic signaling in the urothelium. In our first aim, we propose to examine the pathways responsible for the activation or inactivation of the pannexin channel itself, such as nitrosylation or phosphorylation. While previous studies have elucidated a wide variety of stimuli responsible for causing ATP release, no studies to date have examined the pathways that connect urothelial cell stimulation to pannexin channel opening. Therefore we will attempt to determine the pathways involved in activating/deactivating pannexin channels in the urothelium. As we have previously demonstrated that simulation of urothelial cells with a3 or a7 nicotinic receptor agonists can activate or inhibit ATP release respectively, we will use these compounds in cultured rat urothelial cells as our experimental stimuli. It is our hope that these experiments will greatly increase our understanding of the mechanisms linking urothelial stimulation to ATP release. As ATP has been strongly implicated in a number of pathological bladder disorders, such as overactive bladder, we believe that this research has the potential to elucidate new targets for the treatment of bladder pathology. Because pannexin channels have been found to be important for the activation of the inflammasome in a wide variety of tissues, and inflammation is an important part of bladder pathology, the second half of our proposed study will examine how pannexin channels are important to the induction or maintenance of inflammation in the urinary bladder. To examine this question, we propose to induce bladder inflammation by injection of either bacterial lipopolysaccharides or cyclophosphamide and study the signaling pathways that connect pannexin-mediated ATP release to the increased frequency of urination observed in bladder pathology. These signaling pathways include activation of purinergic receptors on the surface of urothelial cells, the oligomerization of NLRP3/NLRC4 inflammasomes, and the activation of events downstream of IL-1 receptor stimulation, such as increased paracellular permeability. It is our hope that the experiments in this aim will elucidate a new target for pharmacological or genetic treatment of pathological bladder disorders involving inflammation, such as interstitial cystitis.
Patients that suffer from the pathological bladder disorder known as Interstitial Cystitis/Painful Bladder Syndrome (IC/PBS) pay, on average, $3000 per year more in health care costs. This represents a significant economic burden for the 13 million Americans that are thought to suffer from the disease. Altered ATP signaling in the bladder epithelium is thought to play a major role in IC/PBS. As our research aims to further elucidate the mechanism of ATP release from bladder epithelial cells, our proposal has the potential to result in significant advances in the treatment of bladder pathology and help stem the rising costs of this serious public health issue.
