Induction of urothelial cell proliferation by fibroblast growth factor-7 in RAG1-deficient mice

Chronic hyperglycemia aggravates lung function in a Scnn1b-Tg murine model

Cystic fibrosis-related diabetes (CFRD), the most common comorbidity in cystic fibrosis (CF), leads to increased mortality by accelerating the decline in lung function. Scnn1b-Tg transgenic mice overexpressing the epithelial sodium channel β subunit exhibit spontaneous CF-like lung disease, including airway mucus obstruction and chronic inflammation. Here, we established a chronic CFRD-like model using Scnn1b-Tg mice made diabetic by injection of streptozotocin (STZ). In Ussing chamber recordings of the trachea, Scnn1b-Tg mice exhibited larger amiloride-sensitive currents and forskolin-activated currents, without a difference in adenosine triphosphate (ATP)-activated currents compared with wild-type (WT) littermates. Both diabetic WT (WT-D) and diabetic Scnn1b-Tg (Scnn1b-Tg-D) mice on the same genetic background exhibited substantially elevated blood glucose at 8 wk; glucose levels also were elevated in bronchoalveolar lavage fluid (BALF). Bulk lung RNA-seq data showed significant differences between WT-D and Scnn1b-Tg-D mice. Neutrophil counts in BALF were substantially increased in Scnn1b-Tg-D lungs compared with controls (Scnn1b-Tg-con) and compared with WT-D lungs. Lung histology data showed enhanced parenchymal destruction, alveolar wall thickening, and neutrophilic infiltration in Scnn1b-Tg-D mice compared with WT-D mice, consistent with the development of a spontaneous lung infection. We intranasally administered Pseudomonas aeruginosa to induce lung infection in these mice for 24 h, which led to severe lung leukocytic infiltration and an increase in pro-inflammatory cytokine levels in the BALF. In summary, we established a chronic CFRD-like lung mouse model using the Scnn1b-Tg mice. The model can be used for future studies toward understanding the mechanisms underlying the lung pathophysiology associated with CFRD and developing novel therapeutics.NEW & NOTEWORTHY We established a chronic CFRD-like mouse model using the Scnn1b-Tg transgenic mice overexpressing the epithelial sodium channel β subunit made diabetic by injection of streptozotocin. The results underscore the urgent need to develop novel therapeutics for CF lung disease.

Implications for bidirectional signaling between afferent nerves and urothelial cells-ICI-RS 2014

AIMS

To present a synopsis of the presentations and discussions from Think Tank I, "Implications for afferent-urothelial bidirectional communication" of the 2014 International Consultation on Incontinence-Research Society (ICI-RS) meeting in Bristol, UK.

METHODS

The participants presented what is new, currently understood or still unknown on afferent-urothelial signaling mechanisms. New avenues of research and experimental methodologies that are or could be employed were presented and discussed.

RESULTS

It is clear that afferent-urothelial interactions are integral to the regulation of normal bladder function and that its disruption can have detrimental consequences. The urothelium is capable of releasing numerous signaling factors that can affect sensory neurons innervating the suburothelium. However, the understanding of how factors released from urothelial cells and afferent nerve terminals regulate one another is incomplete. Utilization of techniques such as viruses that genetically encode Ca(2+) sensors, based on calmodulin and green fluorescent protein, has helped to address the cellular mechanisms involved. Additionally, the epithelial-neuronal interactions in the urethra may also play a significant role in lower urinary tract regulation and merit further investigation.

CONCLUSION

The signaling capabilities of the urothelium and afferent nerves are well documented, yet how these signals are integrated to regulate bladder function is unclear. There is unquestionably a need for expanded methodologies to further our understanding of lower urinary tract sensory mechanisms and their contribution to various pathologies.

Host Responses to Urinary Tract Infections and Emerging Therapeutics: Sensation and Pain within the Urinary Tract

Urinary tract infection (UTI) pathogenesis is understood increasingly at the level of the uropathogens and the cellular and molecular mediators of host inflammatory responses. However, little is known about the mediators of symptoms during UTI and what distinguishes symptomatic events from asymptomatic bacteriuria. Here, we review bladder physiology and sensory pathways in the context of an emerging literature from murine models dissecting the host and pathogen factors mediating pain responses during UTI. The bladder urothelium is considered a mediator of sensory responses and appears to play a role in UTI pain responses. Virulence factors of uropathogens induce urothelial damage that could trigger pain due to compromised bladder-barrier function. Instead, bacterial glycolipids are the major determinants of UTI pain independent of urothelial damage, and the O-antigen of lipopolysaccharide modulates pain responses. The extent of pain modulation by O-antigen can have profound effects, from abolishing pain responses to inducing chronic pain that results in central nervous system features reminiscent of neuropathic pain. Although these effects are largely dependent upon Toll-like receptors, pain is independent of inflammation. Surprisingly, some bacteria even possess analgesic properties, suggesting that bacteria exhibit a wide range of pain phenotypes in the bladder. In summary, UTI pain is a complex form of visceral pain that has significant potential to inform our understanding of bacterial pathogenesis and raises the specter of chronic pain resulting from transient infection, as well as novel approaches to treating pain.

Cytokeratin 15 marks basal epithelia in developing ureters and is upregulated in a subset of urothelial cell carcinomas

The mammalian ureter contains a water-tight epithelium surrounded by smooth muscle. Key molecules have been defined which regulate ureteric bud initiation and drive the differentiation of ureteric mesenchyme into peristaltic smooth muscle. Less is known about mechanisms underlying the developmental patterning of the multilayered epithelium characterising the mature ureter. In skin, which also contains a multilayered epithelium, cytokeratin 15 (CK15), an acidic intermediate filament protein, marks cells whose progeny contribute to epidermal regeneration following wounding. Moreover, CK15+ precursor cells in skin can give rise to basal cell carcinomas. In the current study, using transcriptome microarrays of embryonic wild type mouse ureters, Krt15, coding for CK15, was detected. Quantitative polymerase chain reaction analyses confirmed the initial finding and demonstrated that Krt15 levels increased during the fetal period when the ureteric epithelium becomes multilayered. CK15 protein was undetectable in the ureteric bud, the rudiment from which the ureter grows. Nevertheless, later in fetal development, CK15 was immunodetected in a subset of basal urothelial cells in the ureteric stalk. Superficial epithelial cells, including those positive for the differentiation marker uroplakin III, were CK15-. Transformation-related protein 63 (P63) has been implicated in epithelial differentiation in murine fetal urinary bladders. In wild type fetal ureters, CK15+ cells were positive for P63, and p63 homozygous null mutant ureters lacked CK15+ cells. In these mutant ureters, sections of the urothelium were monolayered versus the uniform multilayering found in wild type littermates. Human urothelial cell carcinomas account for considerable morbidity and mortality. CK15 was upregulated in a subset of invasive ureteric and urinary bladder cancers. Thus, in ureter development, the absence of CK15 is associated with a structurally simplified urothelium whereas, postnatally, increased CK15 levels feature in malignant urothelial overgrowth. CK15 may be a novel marker for urinary tract epithelial precursor cells.

Urothelial signaling

The urothelium, which lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, not only forms a high-resistance barrier to ion, solute and water flux, and pathogens, but also functions as an integral part of a sensory web which receives, amplifies, and transmits information about its external milieu. Urothelial cells have the ability to sense changes in their extracellular environment, and respond to chemical, mechanical and thermal stimuli by releasing various factors such as ATP, nitric oxide, and acetylcholine. They express a variety of receptors and ion channels, including P2X3 purinergic receptors, nicotinic and muscarinic receptors, and TRP channels, which all have been implicated in urothelial-neuronal interactions, and involved in signals that via components in the underlying lamina propria, such as interstitial cells, can be amplified and conveyed to nerves, detrusor muscle cells, and ultimately the central nervous system. The specialized anatomy of the urothelium and underlying structures, and the possible communication mechanisms from urothelial cells to various cell types within the bladder wall are described. Changes in the urothelium/lamina propria ("mucosa") produced by different bladder disorders are discussed, as well as the mucosa as a target for therapeutic interventions.

Beyond neurons: Involvement of urothelial and glial cells in bladder function

AIM

The urothelium, or epithelial lining of the lower urinary tract (LUT), is likely to play an important role in bladder function by actively communicating with bladder nerves, smooth muscle, and cells of the immune and inflammatory systems. Recent evidence supports the importance of non-neuronal cells that may extend to both the peripheral and central processes of the neurons that transmit normal and nociceptive signals from the urinary bladder. Using cats diagnosed with a naturally occurring syndrome termed feline interstitial cystitis (FIC), we investigated whether changes in physiologic parameters occur within 3 cell types associated with sensory transduction in the urinary bladder: 1) the urothelium, 2) identified bladder dorsal root ganglion (DRG) neurons and 3) grey matter astrocytes in the lumbosacral (S1) spinal cord. As estrogen fluctuations may modulate the severity of many chronic pelvic pain syndromes, we also examined whether 17beta-estradiol (E2) alters cell signaling in rat urothelial cells.

RESULTS

We have identified an increase in nerve growth factor (NGF) and substance P (SP) in urothelium from FIC cats over that seen in urothelium from unaffected (control) bladders. The elevated NGF expression by FIC urothelium is a possible cause for the increased cell body size of DRG neurons from cats with FIC, reported in this study. At the level of the spinal cord, astrocytic GFAP immuno-intensity was significantly elevated and there was evidence for co-expression of the primitive intermediate filament, nestin (both indicative of a reactive state) in regions of the FIC S1 cord (superficial and deep dorsal horn, central canal and laminae V-VIl) that receive input from pelvic afferents. Finally, we find that E2 triggers an estrus-modifiable activation of p38 MAPK in rat urothelial cells. There were cyclic variations with E2-mediated elevation of p38 MAPK at both diestrus and estrus, and inhibition of p38 MAPK in proestrous urothelial cells.

CONCLUSION

Though urothelial cells are often viewed as bystanders in the processing of visceral sensation, these and other findings support the view that these cells function as primary transducers of some physical and chemical stimuli. In addition, the pronounced activation of spinal cord astrocytes in an animal model for bladder pain syndrome (BPS) may play an important role in the pain syndrome and open up new potential approaches for drug intervention.

Urothelial signaling

Beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and play a key role in the detection and transmission of both physiological and nociceptive stimuli. These urothelial cells exhibit the ability to sense changes in their extracellular environment including the ability to respond to chemical, mechanical and thermal stimuli that may communicate the state of the urothelial environment to the underlying nervous and muscular systems. Here, we review the specialized anatomy of the urothelium and speculate on possible communication mechanisms from urothelial cells to various cell types within the bladder wall.

Compensatory paracrine mechanisms that define the urothelial response to injury in partial bladder outlet obstruction

Diseases and conditions affecting the lower urinary tract are a leading cause of dysfunctional sexual health, incontinence, infection, and kidney failure. The growth, differentiation, and repair of the bladder's epithelial lining are regulated, in part, by fibroblast growth factor (FGF)-7 and -10 via a paracrine cascade originating in the mesenchyme (lamina propria) and targeting the receptor for FGF-7 and -10 within the transitional epithelium (urothelium). The FGF-7 gene is located at the 15q15-q21.1 locus on chromosome 15 and four exons generate a 3.852-kb mRNA. Five duplicated FGF-7 gene sequences that localized to chromosome 9 were predicted not to generate functional protein products, thus validating the use of FGF-7-null mice as an experimental model. Recombinant FGF-7 and -10 induced proliferation of human urothelial cells in vitro and transitional epithelium of wild-type and FGF-7-null mice in vivo. To determine the extent that induction of urothelial cell proliferation during the bladder response to injury is dependent on FGF-7, an animal model of partial bladder outlet obstruction was developed. Unbiased stereology was used to measure the percentage of proliferating urothelial cells between obstructed groups of wild-type and FGF-7-null mice. The stereological analysis indicated that a statistical significant difference did not exist between the two groups, suggesting that FGF-7 is not essential for urothelial cell proliferation in response to partial outlet obstruction. In contrast, a significant increase in FGF-10 expression was observed in the obstructed FGF-7-null group, indicating that the compensatory pathway that functions in this model results in urothelial repair.

Mechanisms of disease: involvement of the urothelium in bladder dysfunction

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions and solutes, a number of novel properties have been recently attributed to urothelial cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e. the ability to express a number of sensor molecules or respond to thermal, mechanical and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests that urothelial cells could be targets for neurotransmitters released from bladder nerves or that chemicals released by urothelial cells could alter afferent nerve excitability. Taken together, these and other findings highlighted in this article suggest a sensory function for the urothelium. Elucidation of mechanisms that influence urothelial function might provide insights into the pathology of bladder dysfunction.