Transgenic Mice Expressing MCP-1 by the Urothelium Demonstrate Bladder Hypersensitivity, Pelvic Pain and Voiding Dysfunction: A Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network Animal Model Study

Monocyte chemoattractant protein-1 (MCP-1) is one of the key chemokines that play important roles in diverse inflammatory and chronic pain conditions. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic and debilitating inflammatory condition of the urinary bladder characterized by the hallmark symptoms of pelvic pain and voiding dysfunction. To facilitate IC/BPS research, we used transgenic technology to develop a novel urothelial MCP-1 secretion mouse model (URO-MCP-1). A transgene consisting of the uroplakin II gene promoter and the mouse MCP-1 coding sequence with a secretory element was constructed and microinjected. URO-MCP-1 mice were found to express MCP-1 mRNA in the bladder epithelium and MCP-1 protein in the urine, and developed bladder inflammation 24 hours after intravesical administration of a single sub-noxious dose of lipopolysaccharide (LPS). The inflamed bladders of URO-MCP-1 mice exhibited elevated mRNAs for interleukin (IL)-1ß, IL-6, substance P precursor, and nerve growth factor as well as increased macrophage infiltration. In parallel with these phenotypic changes, URO-MCP-1 mice manifested significant functional changes at days 1 and 3 after cystitis induction. These functional changes included pelvic pain as measured by von Frey filament stimulation and voiding dysfunction (increased urinary frequency, reduced average volume voided per micturition, and reduced maximum volume voided per micturition) as measured by micturition cages. Micturition changes remained evident at day 7 after cystitis induction, although these changes were not statistically significant. Control wild-type C57BL/6 mice manifested no clear changes in histological, biochemical and behavioral features after similar cystitis induction with LPS. Taken together, our results indicate that URO-MCP-1 mice are hypersensitive to bladder irritants such as LPS and develop pelvic pain and voiding dysfunction upon cystitis induction, providing a novel model for IC/BPS research.