Epithelial-Mesenchymal Interactions in the Bladder

Fibrosis and the bladder, implications for function ICI-RS 2017

AIMS

Most benign bladder pathologies are associated with an increase of extracellular matrix (ECM-fibrosis) and may progress from formation of stiffer matrix to a more compliant structure. The aims were to summarize current knowledge of the origins of bladder fibrosis and consequences in bladder function.

METHODS

A meeting at the International Consultation on Incontinence Research Society 2017 congress discussed the above aims and considered paradigms to reduce the extent of fibrosis. Discussants based their arguments on the basis of their own expertise, supplemented by review of the literature through PubMed. Proposals for future work were derived from the discussion.

RESULTS

Altered urodynamic compliance when ECM deposition is increased is mirrored by changes in the elastic modulus of isolated tissue, whether compliance is decreased or increased. No changes to compliance or fibrosis have been reported after botulinum toxin injections. Several paracrine and autocrine agents increase ECM deposition, the role of TGF-β was particularly emphasized. None of these agents has a net long-term effect on detrusor contractility and the reduction of contractile performance with increased ECM is due solely to a loss of detrusor mass. Several strategies to reduce fibrosis were described, ranging from potential therapeutic roles for vitamin-D or endostatin, manipulation of intracellular pathways that mediate myofibroblast differentiation and the potential role of the anti-fibrotic hormone relaxin. An understanding of epigenetic regulation of ECM deposition was also considered.

CONCLUSIONS

The conclusion that reduced bladder contractile function with increased fibrosis is due largely to the replacement of detrusor with ECM offers a way forward for future research to consider approaches that will restore bladder function by reducing ECM deposition.

Co-culturing porcine normal urothelial cells, urinary bladder fibroblasts and smooth muscle cells for tissue engineering research

New strategies for culturing and co-culturing of the main types of urinary bladder cells are essential for successful establishment of biomimetic in vitro models, which could be applied for research into, and management of, diverse urological disorders. Porcine normal urothelial cells are available in nearly unlimited amounts and have many properties equivalent to human urothelial cells. In the present study, we established normal differentiated porcine urothelial cells in co-cultures with porcine urinary bladder normal fibroblasts and/or smooth muscle cells. The optimal culture medium for establishment of differentiated urothelial cells, demonstrated by positive immunofluorescence of uroplakins, cytokeratins (CK 7, CK 20), zonula occludens 1 (ZO-1), claudin 4, claudin 8, and E-cadherin, was the medium composed of equal parts of Advanced Dulbecco's modified Eagle's medium (A-DMEM) and MCDB 153 medium with physiological calcium concentration of 2.5 mM and without fetal bovine serum, named UroM (+Ca²⁺  - S). This medium was also proven to be suitable for culturing of bladder fibroblasts and smooth muscle cells and co-culturing of urothelial cells with these mesenchymal cells. Urothelial cell differentiation was optimal in UroM (+Ca²⁺  - S) medium in all co-culture conditions and when compared to all conditioned-media combinations. To summarize, these strategies for culturing and co-culturing of urinary bladder urothelial cells with mesenchymal cells could be used as new in vitro models for future basic and applicable research of the urinary bladder and thus potentially also for translational tissue engineering studies.

Sodium Tanshinone IIA Sulfonate Ameliorates Bladder Fibrosis in a Rat Model of Partial Bladder Outlet Obstruction by Inhibiting the TGF-β/Smad Pathway Activation

Transforming growth factor (TGF)-β1 is known to play a pivotal role in a diverse range of biological systems including modulation of fibrosis in several organs. The precise role of TGF-β/Smad signaling in the progression of bladder fibrosis secondary to partial bladder outlet obstruction (PBOO) is yet to be conclusively. Using a rat PBOO model, we investigated TGF-β1 expression and exaimined whether sodium tanshinone IIA sulfonate (STS) could inhibit TGF-β/Smad signaling pathway activation and ameliorate bladder fibrosis. Forty-eight female Sprague-Dawley rats were randomly divided into three groups: sham operation group (n = 16), PBOO operation without STS treatment group (n = 16) and PBOO operation with STS treatment group (n = 16). Thirty-two rats underwent the operative procedure to create PBOO and subsequently received intraperitoneal injections of STS (10 mg/kg/d; n = 16) or vehicle (n = 16) two days after the surgery. Sham surgery was conducted on 16 rats, which received intraperitoneal vehicle injection two days later. In each of the three groups, an equal number of rats were sacrificed at weeks 4 and 8 after the PBOO or sham operation. The TGF-β/Smad signaling pathway was analyzed using western blotting, immunohistochemical staining and reverse transcriptase polymerase chain reaction (RT-PCR). One-way analysis of variance was conducted to draw statistical inferences. At 4 and 8 weeks, the expression of TGF-β1 and phosphorylated Smad2 and Smad3 in STS-treated PBOO rats was significantly lower than in the PBOO rats not treated with STS. Alpha smooth muscle actin (α-SMA), collagen I and collagen III expression at 4 and 8 weeks post PBOO was lower in STS-treated PBOO rats when compared to that in PBOO rats not treated with STS. Our findings indicate that STS ameliorates bladder fibrosis by inhibiting TGF-β/Smad signaling pathway activation, and may prove to be a potential therapeutic measure for preventing bladder fibrosis secondary to PBOO operation.

Development and differentiation of the ureteric bud into the ureter in the absence of a kidney collecting system

Six1-/- mice were found to have apparently normal ureters in the absence of a kidney, suggesting that the growth and development of the unbranched ureter is largely independent of the more proximal portions of the UB which differentiates into the highly branched renal collecting system. Culture of isolated urinary tracts (from normal and mutant mice) on Transwell filters was employed to study the morphogenesis of this portion of the urogenital system. Examination of the ureters revealed the presence of a multi-cell layered tubule with a lumen lined by cells expressing uroplakin (a protein exclusively expressed in the epithelium of the lower urinary tract). Cultured ureters of both the wild-type and Six1 mutant become contractile and undergo peristalsis, an activity preceded by the expression of alpha-smooth muscle actin (alphaSMA). Treatment with a number of inhibitors of signaling molecules revealed that inhibition of PI3 kinase dissociates the developmental expression of alphaSMA from ureter growth and elongation. Epidermal growth factor also perturbed smooth muscle differentiation in culture. Moreover, the peristalsis of the ureter in the absence of the kidney in the Six1-/- mouse indicates that the development of this clinically important function of ureter (peristaltic movement of urine) is not dependent on fluid flow through the ureter. In keeping with this, isolated ureters cultured in the absence of surrounding tissues elongate, differentiate and undergo peristalsis when cultured on a filter and undergo branching morphogenesis when cultured in 3-dimensional extracellular matrix gels in the presence of a conditioned medium derived from a metanephric mesenchyme (MM) cell line. In addition, ureters of Six1-/- urinary tracts (i.e., lacking a kidney) displayed budding structures from their proximal ends when cultured in the presence of GDNF and FGFs reminiscent of UB budding from the wolffian duct. Taken together with the above data, this indicates that, although the distal ureter (at least early in its development) retains some of the characteristics of the more proximal UB, the growth and differentiation (i.e., development of smooth muscle actin, peristalsis and uroplakin expression) of the distal non-branching ureter are inherent properties of this portion of the UB, occurring independently of detectable influences of either the undifferentiated MM (unlike the upper portion of the ureteric bud) or more differentiated metanephric kidney. Thus, the developing distal ureter appears to be a unique anatomical structure which should no longer be considered as simply the non-branching portion of the ureteric bud. In future studies, the ability to independently analyze and study the portion of the UB that becomes the renal collecting system and that which becomes the ureter should facilitate distinguishing the developmental nephrome (renal ontogenome) from the ureterome.

Gene deletion in urothelium by specific expression of Cre recombinase

Urothelium that lines almost the entire urinary tract acts as a permeability barrier and is involved in the pathogenesis of major urinary diseases, including urothelial carcinoma, urinary tract infection, and interstitial cystitis. However, investigation of urothelial biology and diseases has been hampered by the lack of tissue-specific approaches. To address this deficiency, we sought to develop a urothelium-specific knockout system using the Cre/loxP strategy. Transgenic mouse lines were generated in which a 3.6-kb mouse uroplakin II (UPII) promoter was used to drive the expression of Cre recombinase (Cre). Among the multiple tissues analyzed, Cre was found to be expressed exclusively in the urothelia of the transgenic mice. Crossing a UPII-Cre transgenic line with a ROSA26-LacZ reporter line, in which LacZ expression depends on Cre-mediated deletion of a floxed "stop" sequence, led to LacZ expression only in the urothelium. Gene recombination was also observed when the UPII-Cre line was crossed to an independent line in which a part of the p53 gene was flanked by the loxP sequences (floxed p53). Truncation of the p53 gene and mRNA was observed exclusively in the urothelia of double transgenic mice harboring both the UPII-Cre transgene and the floxed p53 allele. These results demonstrate for the first time the feasibility and potentially wide applicability of the UPII-Cre transgenic mice to inactivate any genes of interest in the urothelium.

Induction of smooth muscle cell-like phenotype in marrow-derived cells among regenerating urinary bladder smooth muscle cells

Tissue regeneration on acellular matrix grafts has great potential for therapeutic organ reconstruction. However, hollow organs such as the bladder require smooth muscle cell regeneration, the mechanisms of which are not well defined. We investigated the mechanisms by which bone marrow cells participate in smooth muscle formation during urinary bladder regeneration, using in vivo and in vitro model systems. In vivo bone marrow cells expressing green fluorescent protein were transplanted into lethally irradiated rats. Eight weeks following transplantation, bladder domes of the rats were replaced with bladder acellular matrix grafts. Two weeks after operation transplanted marrow cells repopulated the graft, as evidenced by detection of fluorescent staining. By 12 weeks they reconstituted the smooth muscle layer, with native smooth muscle cells (SMC) infiltrating the graft. In vitro, the differential effects of distinct growth factor environments created by either bladder urothelial cells or bladder SMC on phenotypic changes of marrow cells were examined. First, supernatants of cultured bladder cells were used as conditioned media for marrow cells. Second, these conditions were reconstituted with exogenous growth factors. In each case, a growth factor milieu characteristic of SMC induced an SMC-like phenotype in marrow cells, whereas that of urothelial cells failed. These findings suggest that marrow cells differentiate into smooth muscle on acellular matrix grafts in response to the environment created by SMC.

Creation of luminal tissue covered with urothelium by implantation of cultured urothelial cells into the peritoneal cavity

PURPOSE

We established the culture condition of seeding urothelial cells onto a scaffold for implantation into the peritoneal cavity and evaluated the histology of implanted urothelial cells.

MATERIALS AND METHODS

In part 1 of the study cultured porcine bladder urothelial cells were seeded onto 3 types of collagen gel made on microporous membrane, including collagen gel with or without cultured porcine bladder fibroblasts, or a feeder layer. The macroscopic and microscopic appearance of the gel with urothelial cells were examined in vitro. As an in vivo study, cultured porcine bladder urothelial cells were seeded onto a collagen gel/sponge matrix with or without cultured fibroblasts, or a feeder layer. Urothelial cell survival on each matrix was evaluated 28 days after implantation onto the omentum or mesentery of nude rats. In part 2 of the study rat urothelial cells were cultured and seeded onto fibrin gel/atelocollagen sponge matrix as an autologous implantation model. After 7 days of cultivation the matrix was folded with urothelial cells inside, implanted onto the mesentery and serially evaluated.

RESULTS

Gel containing cultured fibroblasts was shrunken and basement membrane formation was observed on the gel with cultured fibroblasts or the feeder layer in vitro. Urothelial cells cultured with the feeder layer better survived on the collagen based matrix and formed a hollow-like lumen when implanted into the peritoneal cavity. The regenerated urothelium in an autologous implantation showed the same histological features as normal bladder urothelium.

CONCLUSIONS

Selection of less degradable matrix and formation of basement membrane are critical for survival of implanted urothelial cells. The regenerated urothelium in an autologous implantation model seems to have the similar properties to the normal urothelium.