Expression of Transgenes in Native Bladder Urothelium Using Adenovirus-Mediated Transduction

In addition to forming a high-resistance barrier, the urothelium lining the renal pelvis, ureters, bladder, and proximal urethra is hypothesized to sense ...

University of Pittsburgh School of Medicine

The basal, intermediate, and superficial cell layers of the urothelium undergo rapid and complete recovery following acute injury; however, the effects of chronic injury on urothelial regeneration have not been well defined. To address this discrepancy, we employed a mouse model to explore urothelial changes in response to spinal cord injury (SCI), a condition characterized by life-long bladder dysfunction. One day post SCI there was a focal loss of umbrella cells, which are large cells that populate the superficial cell layer and normally express uroplakins (UPKs) and KRT20, but not KRT5, KRT14, or TP63. In response to SCI, regions of urothelium devoid of umbrella cells were replaced with small superficial cells that lacked KRT20 expression and appeared to be derived in part from the underlying intermediate cell layer, including cells positive for KRT5 and TP63. We also observed KRT14-positive basal cells that extended thin cytoplasmic extensions, which terminated in the bladder lumen. Both KRT14-positive and KRT14-negative urothelial cells proliferated 1 day post SCI, and by 7 days, cells in the underlying lamina propria, detrusor, and adventitia were also dividing. At 28 days post SCI, the urothelium appeared morphologically patent, and the number of proliferative cells decreased to baseline levels; however, patches of small superficial cells were detected that coexpressed UPKs, KRT5, KRT14, and TP63, but failed to express KRT20. Thus, unlike the rapid and complete restoration of the urothelium that occurs in response to acute injuries, regions of incompletely differentiated urothelium were observed even 28 days post SCI.

Urothelial proliferation and regeneration after spinal cord injury.

Lysosomal dysfunction is associated with a number of age-related pathologies that affect all organ systems. While much research has focused on neurodegenerative diseases and aging-induced changes in neurons, much less is known about the impact that aging has on lower urinary tract function. Our studies explored age-dependent changes in the content of endo-lysosomal organelles (i.e., multivesicular bodies, lysosomes, and the product of their fusion, endolysosomes) and age-induced effects on lysosomal degradation in the urothelium, the epithelial tissue that lines the inner surface of the bladder, ureters, and renal pelvis. When examined by transmission electron microscopy, the urothelium from young adult rats (~3 months), mature adult rats (~12 months), and aged rats (~26 months old) demonstrated a progressive age-related accumulation of aberrantly large endolysosomes (up to 7μm in diameter) that contained undigested content, likely indicating impaired degradation. Stereological analysis confirmed that aged endolysosomes occupied approximately 300% more volume than their younger counterparts while no age-related change was observed in multivesicular bodies or lysosomes. Consistent with diminished endolysosomal degradation, we observed that cathepsin B activity was significantly decreased in aged versus young urothelial cell lysates as well as in live cells. Further, the endolysosomal pH of aged urothelium was higher than that of young adult (pH 6.0 vs pH 4.6). Our results indicate that there is a progressive decline in urothelial endolysosomal function during aging. How this contributes to bladder dysfunction in the elderly is discussed.

Age-related endolysosome dysfunction in the rat urothelium.

The proper function of the organs that make up the urinary tract (kidneys, ureters, bladder, and urethra) depends on their ability to sense and respond to mechanical forces, including shear stress and wall tension. However, we have limited understanding of the mechanosensors that function in these organs and the tissue sites in which these molecules are expressed. Possible candidates include stretch-activated PIEZO channels (PIEZO1 and PIEZO2), which have been implicated in mechanically regulated body functions including touch sensation, proprioception, lung inflation, and blood pressure regulation. Using reporter mice expressing a COOH-terminal fusion of  with the sequence for the tandem-dimer  gene, we found that PIEZO1 is expressed in the kidneys, ureters, bladder, and urethra as well as organs in close proximity, including the prostate, seminal vesicles and ducts, ejaculatory ducts, and the vagina. We further found that PIEZO1 expression is not limited to one cell type; it is observed in the endothelial and parietal cells of the renal corpuscle, the basolateral surfaces of many of the epithelial cells that line the urinary tract, the interstitial cells of the bladder and ureters, and populations of smooth and striated muscle cells. We propose that in the urinary tract, PIEZO1 likely functions as a mechanosensor that triggers responses to wall tension.

Expression and distribution of PIEZO1 in the mouse urinary tract.

The epithelial junctional complex, composed of tight junctions, adherens junctions, desmosomes, and an associated actomyosin cytoskeleton, forms the apical junctional ring (AJR), which must maintain its continuity in the face of external mechanical forces that accompany normal physiological functions. The AJR of umbrella cells, which line the luminal surface of the bladder, expands during bladder filling and contracts upon voiding; however, the mechanisms that drive these events are unknown. Using native umbrella cells as a model, we observed that the umbrella cell's AJR assumed a nonsarcomeric organization in which filamentous actin and ACTN4 formed unbroken continuous rings, while nonmuscle myosin II (NMMII) formed linear tracts along the actin ring. Expansion of the umbrella cell AJR required formin-dependent actin assembly, but was independent of NMMII ATPase function. AJR expansion also required membrane traffic, RAB13-dependent exocytosis, specifically, but not trafficking events regulated by RAB8A or RAB11A. In contrast, the voiding-induced contraction of the AJR depended on NMMII and actin dynamics, RHOA, and dynamin-dependent endocytosis. Taken together, our studies indicate that a mechanism by which the umbrella cells retain continuity during cyclical changes in volume is the expansion and contraction of their AJR, processes regulated by the actomyosin cytoskeleton and membrane trafficking events.

Expansion and contraction of the umbrella cell apical junctional ring in response to bladder filling and voiding.

The mechanisms that link visceral mechanosensation to the perception of internal organ status (i.e., interoception) remain elusive. In response to bladder filling, the urothelium releases ATP, which is hypothesized to stimulate voiding function by communicating the degree of bladder fullness to subjacent tissues, including afferent nerve fibers. To determine if PIEZO channels function as mechanosensors in these events, we generated conditional urothelial Piezo1-, Piezo2-, and dual Piezo1/2-knockout (KO) mice. While functional PIEZO1 channels were expressed in all urothelial cell layers, Piezo1-KO mice had a limited phenotype. Piezo2 expression was limited to a small subset of superficial umbrella cells, yet male Piezo2-KO mice exhibited incontinence (i.e., leakage) when their voiding behavior was monitored during their active dark phase. Dual Piezo1/2-KO mice had the most affected phenotype, characterized by decreased urothelial responses to mechanical stimulation, diminished ATP release, bladder hypoactivity in anesthetized Piezo1/2-KO females but not males, and urinary incontinence in both male and female Piezo1/2-KO mice during their dark phase but not inactive light one. Our studies reveal that the urothelium functions in a sex- and circadian rhythm-dependent manner to link urothelial PIEZO1/2 channel-driven mechanotransduction to normal voiding function and behavior, and in the absence of these signals, bladder dysfunction ensues.

Dennis R. Clayton

Renal-Electrolyte Division,
Department of Medicine,
Renal-Electrolyte Division, Department of Medicine

University of Pittsburgh School of Medicine

Expression of Transgenes in Native Bladder Urothelium Using Adenovirus-Mediated Transduction

Dennis R. Clayton

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Renal-Electrolyte Division,Department of Medicine,Renal-Electrolyte Division, Department of Medicine

University of Pittsburgh School of Medicine

Expression of Transgenes in Native Bladder Urothelium Using Adenovirus-Mediated Transduction

Renal-Electrolyte Division,
Department of Medicine,
Renal-Electrolyte Division, Department of Medicine