Combined Mek inhibition and Pparg activation Eradicates Muscle Invasive Bladder cancer in a Mouse Model of BBN-induced Carcinogenesis.

Bladder cancers (BCs) can be divided into 2 major subgroups displaying distinct clinical behaviors and mutational profiles: basal/squamous (BASQ) tumors that tend to be muscle invasive, and luminal/papillary (LP) tumors that are exophytic and tend to be non-invasive. Pparg is a likely driver of LP BC and has been suggested to act as a tumor suppressor in BASQ tumors, where it is likely suppressed by MEK-dependent phosphorylation. Here we tested the effects of rosiglitazone, a Pparg agonist, in a mouse model of BBN-induced muscle invasive BC. Rosiglitazone activated Pparg signaling in suprabasal epithelial layers of tumors but not in basal-most layers containing highly proliferative invasive cells, reducing proliferation but not affecting tumor survival. Addition of trametinib, a MEK inhibitor, induced Pparg signaling throughout all tumor layers, and eradicated 91% of tumors within 7-days of treatment. The 2-drug combination also activated a luminal differentiation program, reversing squamous metaplasia in the urothelium of tumor-bearing mice. Paired ATAC-RNA-seq analysis revealed that tumor apoptosis was most likely linked to down-regulation of Bcl-2 and other pro-survival genes, while the shift from BASQ to luminal differentiation was associated with activation of the retinoic acid pathway and upregulation of Kdm6a, a lysine demethylase that facilitates retinoid-signaling. Our data suggest that rosiglitazone, trametinib, and retinoids, which are all FDA approved, may be clinically active in BASQ tumors in patients. That muscle invasive tumors are populated by basal and suprabasal cell types with different responsiveness to PPARG agonists will be an important consideration when designing new treatments.

Gardnerella Exposures Alter Bladder Gene Expression and Augment Uropathogenic Escherichia coli Urinary Tract Infection in Mice.

The anaerobic actinobacterium Gardnerella was first isolated from the bladder by suprapubic aspiration more than 50 years ago. Since then, Gardnerella has been increasingly recognized as a common and often abundant member of the female urinary microbiome (urobiome). Some studies even suggest that the presence of Gardnerella is associated with urological disorders in women. We recently reported that inoculation of Gardnerella into the bladders of mice results in urothelial exfoliation. Here, we performed whole bladder RNA-seq in our mouse model to identify additional host pathways involved in the response to Gardnerella bladder exposure. The transcriptional response to Gardnerella reflected the urothelial turnover that is a consequence of exfoliation while also illustrating the activation of pathways involved in inflammation and immunity. Additional timed exposure experiments in mice provided further evidence of a potentially clinically relevant consequence of bladder exposure to Gardnerella-increased susceptibility to subsequent UTI caused by uropathogenic Escherichia coli. Together, these data provide a broader picture of the bladder's response to Gardnerella and lay the groundwork for future studies examining the impact of Gardnerella on bladder health.

Pparg signaling controls bladder cancer subtype and immune exclusion.

Pparg, a nuclear receptor, is downregulated in basal subtype bladder cancers that tend to be muscle invasive and amplified in luminal subtype bladder cancers that tend to be non-muscle invasive. Bladder cancers derive from the urothelium, one of the most quiescent epithelia in the body, which is composed of basal, intermediate, and superficial cells. We find that expression of an activated form of Pparg (VP16;Pparg) in basal progenitors induces formation of superficial cells in situ, that exit the cell cycle, and do not form tumors. Expression in basal progenitors that have been activated by mild injury however, results in luminal tumor formation. We find that these tumors are immune deserted, which may be linked to down-regulation of Nf-kb, a Pparg target. Interestingly, some luminal tumors begin to shift to basal subtype tumors with time, down-regulating Pparg and other luminal markers. Our findings have important implications for treatment and diagnosis of bladder cancer.

Pparg promotes differentiation and regulates mitochondrial gene expression in bladder epithelial cells.

The urothelium is an epithelial barrier lining the bladder that protects against infection, fluid exchange and damage from toxins. The nuclear receptor Pparg promotes urothelial differentiation in vitro, and Pparg mutations are associated with bladder cancer. However, the function of Pparg in the healthy urothelium is unknown. Here we show that Pparg is critical in urothelial cells for mitochondrial biogenesis, cellular differentiation and regulation of inflammation in response to urinary tract infection (UTI). Superficial cells, which are critical for maintaining the urothelial barrier, fail to mature in Pparg mutants and basal cells undergo squamous-like differentiation. Pparg mutants display persistent inflammation after UTI, and Nf-KB, which is transiently activated in response to infection in the wild type urothelium, persists for months. Our observations suggest that in addition to its known roles in adipogegnesis and macrophage differentiation, that Pparg-dependent transcription plays a role in the urothelium controlling mitochondrial function development and regeneration.

Polyploid Superficial Cells that Maintain the Urothelial Barrier Are Produced via Incomplete Cytokinesis and Endoreplication.

The urothelium is an epithelia barrier lined by a luminal layer of binucleated, octoploid, superficial cells. Superficial cells are critical for production and transport of uroplakins, a family of proteins that assemble into a waterproof crystalline plaque that helps protect against infection and toxic substances. Adult urothelium is nearly quiescent, but rapidly regenerates in response to injury. Yet the mechanism by which binucleated, polyploid, superficial cells are produced remains unclear. Here, we show that superficial cells are likely to be derived from a population of binucleated intermediate cells, which are produced from mononucleated intermediate cells via incomplete cytokinesis. We show that binucleated intermediate and superficial cells increase DNA content via endoreplication, passing through S phase without entering mitosis. The urothelium can be permanently damaged by repetitive or chronic injury or disease. Identification of the mechanism by which superficial cells are produced may be important for developing strategies for urothelial repair.

An illustrated anatomical ontology of the developing mouse lower urogenital tract.

Malformation of the urogenital tract represents a considerable paediatric burden, with many defects affecting the lower urinary tract (LUT), genital tubercle and associated structures. Understanding the molecular basis of such defects frequently draws on murine models. However, human anatomical terms do not always superimpose on the mouse, and the lack of accurate and standardised nomenclature is hampering the utility of such animal models. We previously developed an anatomical ontology for the murine urogenital system. Here, we present a comprehensive update of this ontology pertaining to mouse LUT, genital tubercle and associated reproductive structures (E10.5 to adult). Ontology changes were based on recently published insights into the cellular and gross anatomy of these structures, and on new analyses of epithelial cell types present in the pelvic urethra and regions of the bladder. Ontology changes include new structures, tissue layers and cell types within the LUT, external genitalia and lower reproductive structures. Representative illustrations, detailed text descriptions and molecular markers that selectively label muscle, nerves/ganglia and epithelia of the lower urogenital system are also presented. The revised ontology will be an important tool for researchers studying urogenital development/malformation in mouse models and will improve our capacity to appropriately interpret these with respect to the human situation.

Retinoid signaling in progenitors controls specification and regeneration of the urothelium.

The urothelium is a multilayered epithelium that serves as a barrier between the urinary tract and blood, preventing the exchange of water and toxic substances. It consists of superficial cells specialized for synthesis and transport of uroplakins that assemble into a tough apical plaque, one or more layers of intermediate cells, and keratin 5-expressing basal cells (K5-BCs), which are considered to be progenitors in the urothelium and other specialized epithelia. Fate mapping, however, reveals that intermediate cells rather than K5-BCs are progenitors in the adult regenerating urothelium, that P cells, a transient population, are progenitors in the embryo, and that retinoids are critical in P cells and intermediate cells, respectively, for their specification during development and regeneration. These observations have important implications for tissue engineering and repair and, ultimately, may lead to treatments that prevent loss of the urothelial barrier, a major cause of voiding dysfunction and bladder pain syndrome.

Stromal protein Ecm1 regulates ureteric bud patterning and branching.

The interactions between the nephrogenic mesenchyme and the ureteric bud during kidney development are well documented. While recent studies have shed some light on the importance of the stroma during renal development, many of the signals generated in the stroma, the genetic pathways and interaction networks involving the stroma are yet to be identified. Our previous studies demonstrate that retinoids are crucial for branching of the ureteric bud and for patterning of the cortical stroma. In the present study we demonstrate that autocrine retinoic acid (RA) signaling in stromal cells is critical for their survival and patterning, and show that Extracellular matrix 1, Ecm1, a gene that in humans causes irritable bowel syndrome and lipoid proteinosis, is a novel RA-regulated target in the developing kidney, which is secreted from the cortical stromal cells surrounding the cap mesenchyme and ureteric bud. Our studies suggest that Ecm1 is required in the ureteric bud for regulating the distribution of Ret which is normally restricted to the tips, as inhibition of Ecm1 results in an expanded domain of Ret expression and reduced numbers of branches. We propose a model in which retinoid signaling in the stroma activates expression of Ecm1, which in turn down-regulates Ret expression in the ureteric bud cleft, where bifurcation normally occurs and normal branching progresses.

Novel mechanisms of early upper and lower urinary tract patterning regulated by RetY1015 docking tyrosine in mice.

Mutations in the receptor tyrosine kinase RET are associated with congenital anomalies of kidneys or urinary tract (CAKUT). RET tyrosine Y1015 is the docking site for PLCγ, a major regulator of RET signaling. Abrogating signaling via Y1015 causes CAKUT that are markedly different than renal agenesis in Ret-null or RetY1062F mutant mice. We performed analysis of Y1015F mutant upper and lower urinary tracts in mice to delineate its molecular and developmental roles during early urinary tract formation. We found that the degeneration of the common nephric ducts (CND), the caudal-most Wolffian duct (WD) segment, depends on Y1015 signals. The CNDs in Y1015F mutants persist owing to increased proliferation and reduced apoptosis, and showed abundance of phospho-ERK-positive cells. In the upper urinary tract, the Y1015 signals are required for proper patterning of the mesonephros and metanephros. Timely regression of mesonephric mesenchyme and proper demarcation of mesonephric and metanephric mesenchyme from the WD depends on RetY1015 signaling. We show that the mechanism of de novo ectopic budding is via increased ERK activity due to abnormal mesenchymal GDNF expression. Although reduction in GDNF dosage improved CAKUT it did not affect delayed mesenchyme regression. Experiments using whole-mount immunofluorescence confocal microscopy and explants cultures of early embryos with ERK-specific inhibitors suggest an imbalance between increased proliferation, decreased apoptosis and increased ERK activity as a mechanism for WD defects in RetY1015F mice. Our work demonstrates novel inhibitory roles of RetY1015 and provides a possible mechanistic explanation for some of the confounding broad range phenotypes in individuals with CAKUT.

Non-cell-autonomous retinoid signaling is crucial for renal development.

In humans and mice, mutations in the Ret gene result in Hirschsprung's disease and renal defects. In the embryonic kidney, binding of Ret to its ligand, Gdnf, induces a program of epithelial cell remodeling that controls primary branch formation and branching morphogenesis within the kidney. Our previous studies showed that transcription factors belonging to the retinoic acid (RA) receptor family are crucial for controlling Ret expression in the ureteric bud; however, the mechanism by which retinoid-signaling acts has remained unclear. In the current study, we show that expression of a dominant-negative RA receptor in mouse ureteric bud cells abolishes Ret expression and Ret-dependent functions including ureteric bud formation and branching morphogenesis, indicating that RA-receptor signaling in ureteric bud cells is crucial for renal development. Conversely, we find that RA-receptor signaling in ureteric bud cells depends mainly on RA generated in nearby stromal cells by retinaldehyde dehydrogenase 2, an enzyme required for most fetal RA synthesis. Together, these studies suggest that renal development depends on paracrine RA signaling between stromal mesenchyme and ureteric bud cells that regulates Ret expression both during ureteric bud formation and within the developing collecting duct system.

The development of the bladder trigone, the center of the anti-reflux mechanism.

The urinary tract is an outflow system that conducts urine from the kidneys to the bladder via the ureters that propel urine to the bladder via peristalsis. Once in the bladder, the ureteral valve, a mechanism that is not well understood, prevents backflow of urine to the kidney that can cause severe damage and induce end-stage renal disease. The upper and lower urinary tract compartments form independently, connecting at mid-gestation when the ureters move from their primary insertion site in the Wolffian ducts to the trigone, a muscular structure comprising the bladder floor just above the urethra. Precise connections between the ureters and the trigone are crucial for proper function of the ureteral valve mechanism; however, the developmental events underlying these connections and trigone formation are not well understood. According to established models, the trigone develops independently of the bladder, from the ureters, Wolffian ducts or a combination of both; however, these models have not been tested experimentally. Using the Cre-lox recombination system in lineage studies in mice, we find, unexpectedly, that the trigone is formed mostly from bladder smooth muscle with a more minor contribution from the ureter, and that trigone formation depends at least in part on intercalation of ureteral and bladder muscle. These studies suggest that urinary tract development occurs differently than previously thought, providing new insights into the mechanisms underlying normal and abnormal development.

Apoptosis induced by vitamin A signaling is crucial for connecting the ureters to the bladder.

Removal of toxic substances from the blood depends on patent connections between the kidney, ureters and bladder that are established when the ureter is transposed from its original insertion site in the male genital tract to the bladder. This transposition is thought to occur as the trigone forms from the common nephric duct and incorporates into the bladder. Here we re-examine this model in the context of normal and abnormal development. We show that the common nephric duct does not differentiate into the trigone but instead undergoes apoptosis, a crucial step for ureter transposition controlled by vitamin A-induced signals from the primitive bladder. Ureter abnormalities occur in 1-2% of the human population and can cause obstruction and end-stage renal disease. These studies provide an explanation for ureter defects underlying some forms of obstruction in humans and redefine the current model of ureter maturation.

Foxd1-dependent signals control cellularity in the renal capsule, a structure required for normal renal development.

Development of the metanephric kidney involves the establishment of discrete zones of induction and differentiation that are crucial to the future radial patterning of the organ. Genetic deletion of the forkhead transcription factor, Foxd1, results in striking renal abnormalities, including the loss of these discrete zones and pelvic fused kidneys. We have investigated the molecular and cellular basis of the kidney phenotypes displayed by Foxd1-null embryos and report here that they are likely to be caused by a failure in the correct formation of the renal capsule. Unlike the single layer of Foxd1-positive stroma that comprises the normal renal capsule, the mutant capsule contains heterogeneous layers of cells, including Bmp4-expressing cells, which induce ectopic phospho-Smad1 signaling in nephron progenitors. This missignaling disrupts their early patterning, which, in turn, causes mispatterning of the ureteric tree, while delaying and disorganizing nephrogenesis. In addition, the defects in capsule formation prevent the kidneys from detaching from the body wall, thus explaining their fusion and pelvic location. For the first time, functions have been ascribed to the renal capsule that include delineation of the organ and acting as a barrier to inappropriate exogenous signals, while providing a source of endogenous signals that are crucial to the establishment of the correct zones of induction and differentiation.

Distal ureter morphogenesis depends on epithelial cell remodeling mediated by vitamin A and Ret.

Almost 1% of human infants are born with urogenital abnormalities, many of which are linked to irregular connections between the distal ureters and the bladder. During development, ureters migrate by an unknown mechanism from their initial integration site in the Wolffian ducts up to the base of the bladder in a process that we call ureter maturation. Rara(-/-) Rarb2(-/-) mice display impaired vitamin A signaling and develop syndromic urogenital malformations similar to those that occur in humans, including renal hypoplasia, hydronephrosis and mega-ureter, abnormalities also seen in mice with mutations in the proto-oncogene Ret. Here we show that ureter maturation depends on formation of the 'trigonal wedge', a newly identified epithelial outgrowth from the base of the Wolffian ducts, and that the distal ureter abnormalities seen in Rara(-/-) Rarb2(-/-) and Ret(-/-) mutant mice are probably caused by a failure of this process. Our studies indicate that formation of the trigonal wedge may be essential for correct insertion of the distal ureters into the bladder, and that these events are mediated by the vitamin A and Ret signaling pathways.