Mandatory role of proteinase-activated receptor 1 in experimental bladder inflammation

Abstract

BackgroundIn general, inflammation plays a role in most bladder pathologies and represents a defense reaction to injury that often times is two edged. In particular, bladder neurogenic inflammation involves the participation of mast cells and sensory nerves. Increased mast cell numbers and tryptase release represent one of the prevalent etiologic theories for interstitial cystitis and other urinary bladder inflammatory conditions. The activity of mast cell-derived tryptase as well as thrombin is significantly increased during inflammation. Those enzymes activate specific G-protein coupled proteinase-activated receptors (PAR)s.Four PARs have been cloned so far, and not only are all four receptors highly expressed in different cell types of the mouse urinary bladder, but their expression is altered during experimental bladder inflammation. We hypothesize that PARs may link mast cell-derived proteases to bladder inflammation and, therefore, play a fundamental role in the pathogenesis of cystitis.ResultsHere, we demonstrate that in addition to the mouse urinary bladder, all four PA receptors are also expressed in the J82 human urothelial cell line. Intravesical administration of PAR-activating peptides in mice leads to an inflammatory reaction characterized by edema and granulocyte infiltration. Moreover, the inflammatory response to intravesical instillation of known pro-inflammatory stimuli such as E. coli lipopolysaccharide (LPS), substance P, and antigen was strongly attenuated by PAR1-, and to a lesser extent, by PAR2-deficiency.ConclusionOur results reveal an overriding participation of PAR1 in bladder inflammation, provide a working model for the involvement of downstream signaling, and evoke testable hypotheses regarding the role of PARs in bladder inflammation. It remains to be determined whether or not mechanisms targeting PAR1 gene silencing or PAR1 blockade will ameliorate the clinical manifestations of cystitis.

Thrombin Induces Macrophage Migration Inhibitory Factor Release and Upregulation in Urothelium: A Possible Contribution to Bladder Inflammation

“…Expression of PAR1-4 receptors has also been reported for an additional human urothelial cancer cell line (J82) however, receptor functionality was not investigated [21]. In the current study we document (using RT-PCR) expression of PAR receptors 1 through 4 in normal transformed human urothelial cells (UROtsa) [29], [30].…”

“…Treatment with intravesical PAR1, PAR2 and PAR4 agonists induced inflammation in the mouse bladder [21]. Moreover, PAR1 receptors appear to mediate inflammation caused by a variety of inflammatory stimuli thus emphasizing their central role in the development of cystitis [21].…”

“…Moreover, PAR1 receptors appear to mediate inflammation caused by a variety of inflammatory stimuli thus emphasizing their central role in the development of cystitis [21]. In addition, activation of PAR1 receptors with specific agonists administered systemically results in plasma extravasation in the rat bladder due to release of SP from terminal afferents [38].…”

Regulatory network of inflammation downstream of proteinase-activated receptors

“…Comparison of inflammatory responses in wild type, PAR1- and PAR2-deficient mice, revealed a mandatory role of PAR1 and, to a lesser extent, PAR2 in mediating bladder responses to a variety of pro-inflammatory stimuli [23]. …”

VEGF receptors and neuropilins are expressed in the urothelial and neuronal cells in normal mouse urinary bladder and are upregulated in inflammation

“…Although the "usual suspects" vascular and lymphatic endothelial cells are the target of VEGF signaling in many normal and diseased tissues, expression of VEGF receptors by bladder cancer cells (15,33) suggested that the situation might be different or, at least, more complex in this organ. To answer this question experimentally, we chose to use two different stimuli that have been proven to induce significant and reproducible bladder inflammation and alter VEGF signaling upon intravesical instillation, namely protease-activated receptors activating peptides (PAR-APs) (39,41) and BCG (37).…”