MAL facilitates the incorporation of exocytic uroplakin-delivering vesicles into the apical membrane of urothelial umbrella cells

Cotton plants overexpressing the Bacillus thuringiensis Cry23Aa and Cry37Aa binary-like toxins exhibit high resistance to the cotton boll weevil (Anthonomus grandis)

The cotton boll weevil (CBW, Anthonomus grandis) stands as one of the most significant threats to cotton crops (Gossypium hirsutum). Despite substantial efforts, the development of a commercially viable transgenic cotton event for effective open-field control of CBW has remained elusive. This study describes a detailed characterization of the insecticidal toxins Cry23Aa and Cry37Aa against CBW. Our findings reveal that CBW larvae fed on artificial diets supplemented exclusively with Cry23Aa decreased larval survival by roughly by 69%, while supplementation with Cry37Aa alone displayed no statistical difference compared to the control. However, the combined provision of both toxins in the artificial diet led to mortality rates approaching 100% among CBW larvae (LC50 equal to 0.26 PPM). Additionally, we engineered transgenic cotton plants by introducing cry23Aa and cry37Aa genes under control of the flower bud-specific pGhFS4 and pGhFS1 promoters, respectively. Seven transgenic cotton events expressing high levels of Cry23Aa and Cry37Aa toxins in flower buds were selected for greenhouse bioassays, and the mortality rate of CBW larvae feeding on their T0 and T1 generations ranged from 75% to 100%. Our in silico analyses unveiled that Cry23Aa displays all the hallmark characteristics of β-pore-forming toxins (β-PFTs) that bind to sugar moieties in glycoproteins. Intriguingly, we also discovered a distinctive zinc-binding site within Cry23Aa, which appears to be involved in protein-protein interactions. Finally, we discuss the major structural features of Cry23Aa that likely play a role in the toxin's mechanism of action. In view of the low LC50 for CBW larvae and the significant accumulation of these toxins in the flower buds of both T0 and T1 plants, we anticipate that through successive generations of these transgenic lines, cotton plants engineered to overexpress cry23Aa and cry37Aa hold promise for effectively managing CBW infestations in cotton crops.

Deficiency of Pdcd10 causes urothelium hypertrophy and vesicle trafficking defects in ureter

The scaffolding protein programmed cell death protein 10 (Pdcd10) has been demonstrated to play a critical role in renal epithelial cell homeostasis and function by maintaining appropriate water reabsorption in collecting ducts. Both ureter and kidney collecting duct systems are derived from the ureter bud during development. Here, we report that cadherin-16 (Cdh16)-cre drives gene recombination with high specificity in the ureter, but not the bladder, urothelium. The consequences of Pdcd10 deletion on the stratified ureter urothelium were investigated using an integrated approach including messenger RNA (mRNA) expression analysis, immunocytochemistry, and high-resolution confocal and electron microscopy. Loss of Pdcd10 in the ureter urothelium resulted in increased expression of uroplakins (Upks) and keratins (Krts), as well as hypertrophy of the ureter urothelium with an associated increase in the number of proliferation marker protein Ki-67 (Ki67)-expressing cells specifically within the basal urothelium layer. Ultrastructural analysis documented significant modification of the intracellular membrane system, including intracellular vesicle genesis and transport along the basal- to umbrella-cell-layer axis. Additionally, Pdcd10 loss resulted in swelling of Golgi compartments, disruption of mitochondrial cristae structure, and increased lysosomal fusion. Lack of Pdcd10 also resulted in decreased fusiform vesicle formation in umbrella cells, increased secretion of exosome vesicles, and alteration in microvillar structure on apical membranes. Our findings indicate that Pdcd10 expression and its influence on homeostasis is associated with modulation of endomembrane trafficking and organelle biogenesis in the ureter urothelium.

A new role for IFRD1 in regulation of ER stress in bladder epithelial homeostasis

A healthy bladder requires the homeostatic maintenance of and rapid regeneration of urothelium upon stress/injury/infection. Several factors have been identified to play important roles in urothelial development, injury and disease response, however, little is known about urothelial regulation at homeostasis. Here, we identify a new role for IFRD1, a stress-induced gene that has recently been demonstrated to play a critical role in adult tissue proliferation and regeneration, in maintenance of urothelial function/ homeostasis in a mouse model. We show that the mouse bladder expresses IFRD1 at homeostasis and its loss alters the global transcriptome of the bladder with significant accumulation of cellular organelles including multivesicular bodies with undigested cargo, lysosomes and mitochondria. We demonstrate that IFRD1 interacts with several mRNA-translation-regulating factors in human urothelial cells and that the urothelium of Ifrd1 -/- mice reveal decreased global translation and enhanced endoplasmic reticulum (ER) stress response. Ifrd1 -/- bladders have activation of the unfolded protein response (UPR) pathway, specifically the PERK arm, with a concomitant increase in oxidative stress and spontaneous exfoliation of urothelial cells. Further, we show that such increase in cell shedding is associated with a compensatory proliferation of the basal cells but impaired regeneration of superficial cells. Finally, we show that upon loss of IFRD1, mice display aberrant voiding behavior. Thus, we propose that IFRD1 is at the center of many crucial cellular pathways that work together to maintain urothelial homeostasis, highlighting its importance as a target for diagnosis and/or therapy in bladder conditions.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

Short histological kaleidoscope - recent findings in histology. Part I

This article is a review of new advances in histology, concerning either classification or structure of different tissular elements (basement membrane, hemidesmosomes, urothelium, glandular epithelia, adipose tissue, astrocytes), and various organs' constituents (blood-brain barrier, human dental cementum, tubarial salivary glands, hepatic stellate cells, pineal gland, fibroblasts of renal interstitium, Leydig testicular cells, ovarian hilar cells), as well as novel biotechnological techniques (tissue engineering in angiogenesis), recently introduced.

The MAL Protein, an Integral Component of Specialized Membranes, in Normal Cells and Cancer

The MAL gene encodes a 17-kDa protein containing four putative transmembrane segments whose expression is restricted to human T cells, polarized epithelial cells and myelin-forming cells. The MAL protein has two unusual biochemical features. First, it has lipid-like properties that qualify it as a member of the group of proteolipid proteins. Second, it partitions selectively into detergent-insoluble membranes, which are known to be enriched in condensed cell membranes, consistent with MAL being distributed in highly ordered membranes in the cell. Since its original description more than thirty years ago, a large body of evidence has accumulated supporting a role of MAL in specialized membranes in all the cell types in which it is expressed. Here, we review the structure, expression and biochemical characteristics of MAL, and discuss the association of MAL with raft membranes and the function of MAL in polarized epithelial cells, T lymphocytes, and myelin-forming cells. The evidence that MAL is a putative receptor of the epsilon toxin of Clostridium perfringens, the expression of MAL in lymphomas, the hypermethylation of the MAL gene and subsequent loss of MAL expression in carcinomas are also presented. We propose a model of MAL as the organizer of specialized condensed membranes to make them functional, discuss the role of MAL as a tumor suppressor in carcinomas, consider its potential use as a cancer biomarker, and summarize the directions for future research.

Immunohistochemistry as a paramount tool in research of normal urothelium, bladder cancer and bladder pain syndrome

The urothelium, an epithelium of the urinary bladder, primarily functions as blood-urine permeability barrier. The urothelium has a very slow turnover under normal conditions but is capable of extremely fast response to injury. During regeneration urothelium either restores normal function or undergoes altered differentiation pathways, the latter being the cause of several bladder diseases. In this review, we describe the structure of the apical plasma membrane that enables barrier function, the role of urothelium specific proteins uroplakins and the machinery for polarized membrane transports in terminally differentiated superficial umbrella cells. We address key markers, such as keratins, cancer stem cell markers, retinoic acid signalling pathway proteins and transient receptor potential channels and purinergic receptors that drive normal and altered differentiation in bladder cancer and bladder pain syndrome. Finally, we discuss uncertainties regarding research, diagnosis and treatment of bladder pain syndrome. Throughout the review, we emphasise the contribution of immunohistochemistry in advancing our understanding of processes in normal and diseased bladder as well as the most promising possibilities for improved bladder cancer and bladder pain syndrome management.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Mitochondrial lipid droplet formation as a detoxification mechanism to sequester and degrade excessive urothelial membranes

The apical surface of the terminally differentiated mammalian urothelial umbrella cell is mechanically stable and highly impermeable, in part due to its coverage by urothelial plaques consisting of 2D crystals of uroplakin particles. The mechanism for regulating the uroplakin/plaque level is unclear. We found that genetic ablation of the highly tissue-specific sorting nexin Snx31, which localizes to plaques lining the multivesicular bodies (MVBs) in urothelial umbrella cells, abolishes MVBs suggesting that Snx31 plays a role in stabilizing the MVB-associated plaques by allowing them to achieve a greater curvature. Strikingly, Snx31 ablation also induces a massive accumulation of uroplakin-containing mitochondria-derived lipid droplets (LDs), which mediate uroplakin degradation via autophagy/lipophagy, leading to the loss of apical and fusiform vesicle plaques. These results suggest that MVBs play an active role in suppressing the excessive/wasteful endocytic degradation of uroplakins. Failure of this suppression mechanism triggers the formation of mitochondrial LDs so that excessive uroplakin membranes can be sequestered and degraded. Because mitochondrial LD formation, which occurs at a low level in normal urothelium, can also be induced by disturbance in uroplakin polymerization due to individual uroplakin knockout and by arsenite, a bladder carcinogen, this pathway may represent an inducible, versatile urothelial detoxification mechanism.

Clostridium perfringens Epsilon Toxin Compromises the Blood-Brain Barrier in a Humanized Zebrafish Model

Clostridium perfringens epsilon toxin (ETX) is hypothesized to mediate blood-brain barrier (BBB) permeability by binding to the myelin and lymphocyte protein (MAL) on the luminal surface of endothelial cells (ECs). However, the kinetics of this interaction and a general understanding of ETX's behavior in a live organism have yet to be appreciated. Here we investigate ETX binding and BBB breakdown in living Danio rerio (zebrafish). Wild-type zebrafish ECs do not bind ETX. When zebrafish ECs are engineered to express human MAL (hMAL), proETX binding occurs in a time-dependent manner. Injection of activated toxin in hMAL zebrafish initiates BBB leakage, hMAL downregulation, blood vessel stenosis, perivascular edema, and blood stasis. We propose a kinetic model of MAL-dependent ETX binding and neurovascular pathology. By generating a humanized zebrafish BBB model, this study contributes to our understanding of ETX-induced BBB permeability and strengthens the proposal that MAL is the ETX receptor.

Epsilon toxin from Clostridium perfringens induces cytotoxicity in FRT thyroid epithelial cells

Epsilon toxin (Etx) is produced by Clostridium perfringens and induces enterotoxemia in ruminants. Etx crosses the blood-brain barrier, binds to myelin structures, and kills oligodendrocytes, inducing central nervous system demyelination. In addition, Etx has a cytotoxic effect on distal and collecting kidney tubules. There are few cell lines sensitive to Etx. At present, the most sensitive in vitro model for Etx is the Madin-Darby canine kidney (MDCK) cell line, where Etx oligomerizes and forms a pore with consequent ion efflux and cell death. Although the Etx receptor has not yet been fully clarified, it is known that caveolin 1 and 2 potentiate Etx cytotoxicity and oligomerization, and more recently, the myelin and lymphocyte (MAL) protein has been implicated in Etx binding and activity. Here, we studied the effect of Etx on Fischer rat thyroid cells (FRT) and observed similar effects as those seen in MDCK cells. Etx incubated with FRT cells showed binding to the plasma membrane, and western blotting assays revealed oligomeric complex formation. Moreover, cytotoxic assays on FRT cells after Etx incubation indicated cell death at a similar level as in MDCK cells. In addition, a luminescent ATP detection assay revealed ATP depletion in FRT cells after Etx exposure. Previous studies have reported that FRT cells do not express caveolins and do not form caveolae but express MAL protein in glycolipid-enriched membrane microdomains. Our results indicate that caveolins are not directly implicated in Etx cytotoxicity, supporting the notion that the MAL protein is involved in Etx action. In addition, a cell line of thyroid origin is described for the first time as a good model to study Etx action.

Hierarchical transcriptional profile of urothelial cells development and differentiation

The urothelial lining of the lower urinary tract is the most efficient permeability barrier in animals, exhibiting a highly differentiated phenotype and a remarkable regenerative capacity upon wounding. During development and possibly during repair, cells undergo a sequence of hierarchical transcriptional events that mark the transition of these cells from the least differentiated urothelial phenotype characteristic of the basal cell layer, to the most differentiated cellular phenotype characteristic of the superficial cell layer. Unraveling normal urothelial differentiation program is essential to uncover the underlying causes of many congenital abnormalities and for the development of an appropriate differentiation niche for stem cells, for future use in urinary tract tissue engineering and organ reconstruction. Kruppel like factor-5 appears to be at the top of the hierarchy activating several downstream transcription factors, the most prominent of which is peroxisome proliferator activator receptor-γ. Eventually those lead to the activation of transcription factors that directly regulate the expression of uroplakin proteins along with other proteins that mediate the permeability function of the urothelium. In this review, we discuss the most recent findings in the area of urothelial cellular differentiation and transcriptional regulation, aiming for a comprehensive overview that aids in a refined understanding of this process.

Brucella TIR-like protein TcpB/Btp1 specifically targets the host adaptor protein MAL/TIRAP to promote infection

Brucella spp. are known to avoid host immune recognition and weaken the immune response to infection. Brucella like accomplish this by employing two clever strategies, called the stealth strategy and hijacking strategy. The TIR domain-containing protein (TcpB/Btp1) of Brucella melitensis is thought to be involved in inhibiting host NF-κB activation by binding to adaptors downstream of Toll-like receptors. However, of the five TIR domain-containing adaptors conserved in mammals, whether MyD88 or MAL, even other three adaptors, are specifically targeted by TcpB has not been identified. Here, we confirmed the effect of TcpB on B.melitensis virulence in mice and found that TcpB selectively targets MAL. By using siRNA against MAL, we found that TcpB from B.melitensis is involved in intracellular survival and that MAL affects intracellular replication of B.melitensis. Our results confirm that TcpB specifically targets MAL/TIRAP to disrupt downstream signaling pathways and promote intra-host survival of Brucella spp.

Sequential and compartmentalized action of Rabs, SNAREs, and MAL in the apical delivery of fusiform vesicles in urothelial umbrella cells

As major urothelial differentiation products, uroplakins are targeted to the apical surface of umbrella cells. Via the sequential actions of Rabs 11, 8, and 27b and their effectors, uroplakin vesicles are transported to a subapical zone above a K20 network and fuse, via a SNARE-mediated and MAL-facilitated step, with the urothelial apical membrane.

Uroplakins (UPs) are major differentiation products of urothelial umbrella cells and play important roles in forming the permeability barrier and in the expansion/stabilization of the apical membrane. Further, UPIa serves as a uropathogenic Escherichia coli receptor. Although it is understood that UPs are delivered to the apical membrane via fusiform vesicles (FVs), the mechanisms that regulate this exocytic pathway remain poorly understood. Immunomicroscopy of normal and mutant mouse urothelia show that the UP-delivering FVs contained Rab8/11 and Rab27b/Slac2-a, which mediate apical transport along actin filaments. Subsequently a Rab27b/Slp2-a complex mediated FV–membrane anchorage before SNARE-mediated and MAL-facilitated apical fusion. We also show that keratin 20 (K20), which forms a chicken-wire network ∼200 nm below the apical membrane and has hole sizes allowing FV passage, defines a subapical compartment containing FVs primed and strategically located for fusion. Finally, we show that Rab8/11 and Rab27b function in the same pathway, Rab27b knockout leads to uroplakin and Slp2-a destabilization, and Rab27b works upstream from MAL. These data support a unifying model in which UP cargoes are targeted for apical insertion via sequential interactions with Rabs and their effectors, SNAREs and MAL, and in which K20 plays a key role in regulating vesicular trafficking.

Intact urothelial barrier function in a mouse model of ketamine-induced voiding dysfunction

Ketamine is a popular choice for young drug abusers. Ketamine abuse causes lower urinary tract symptoms, with the underlying pathophysiology poorly understood. Disruption of urothelial barrier function has been hypothesized to be a major mechanism for ketamine cystitis, yet the direct evidence of impaired urothelial barrier function is still lacking. To address this question, 8-wk-old female C57BL/6J mice were injected intraperitoneally with 30 mg·kg(-1)·day(-1) ketamine for 12 wk to induce ketamine cystitis. A spontaneous voiding spot assay showed that ketamine-treated mice had increased primary voiding spot numbers and smaller primary voiding spot sizes than control mice (P < 0.05), indicating a contracted bladder and bladder overactivity. Consistently, significantly increased voiding frequency was observed in ketamine-treated mice on cystometrograms. These functional experiments indicate that ketamine induces voiding dysfunction in mice. Surprisingly, urothelial permeability in ketamine-treated mice was not changed when measured using an Ussing chamber system with isotopic urea and water. Mouse urothelial structure was also not altered, and intact umbrella cell structure was observed by both transmission and scanning electron microscopy. Furthermore, immunostaining and confocal microscopy confirmed the presence of a well-defined distribution of zonula occuldens-1 in tight junctions and uroplakin in umbrella cells. In conclusion, these data indicate that ketamine injection induces voiding dysfunction in mice but does not necessarily disrupt mouse bladder barrier function. Disruption of urothelial barrier function may not be the major mechanism in ketamine cystitis.

Anatomy and Physiology of the Urinary Tract: Relation to Host Defense and Microbial Infection

The urinary tract exits to a body surface area that is densely populated by a wide range of microbes. Yet, under most normal circumstances, it is typically considered sterile, i.e., devoid of microbes, a stark contrast to the gastrointestinal and upper respiratory tracts where many commensal and pathogenic microbes call home. Not surprisingly, infection of the urinary tract over a healthy person's lifetime is relatively infrequent, occurring once or twice or not at all for most people. For those who do experience an initial infection, the great majority (70% to 80%) thankfully do not go on to suffer from multiple episodes. This is a far cry from the upper respiratory tract infections, which can afflict an otherwise healthy individual countless times. The fact that urinary tract infections are hard to elicit in experimental animals except with inoculum 3-5 orders of magnitude greater than the colony counts that define an acute urinary infection in humans (105 cfu/ml), also speaks to the robustness of the urinary tract defense. How can the urinary tract be so effective in fending off harmful microbes despite its orifice in a close vicinity to that of the microbe-laden gastrointestinal tract? While a complete picture is still evolving, the general consensus is that the anatomical and physiological integrity of the urinary tract is of paramount importance in maintaining a healthy urinary tract. When this integrity is breached, however, the urinary tract can be at a heightened risk or even recurrent episodes of microbial infections. In fact, recurrent urinary tract infections are a significant cause of morbidity and time lost from work and a major challenge to manage clinically. Additionally, infections of the upper urinary tract often require hospitalization and prolonged antibiotic therapy. In this chapter, we provide an overview of the basic anatomy and physiology of the urinary tract with an emphasis on their specific roles in host defense. We also highlight the important structural and functional abnormalities that predispose the urinary tract to microbial infections.

The Myelin and Lymphocyte Protein MAL Is Required for Binding and Activity of Clostridium perfringens ε-Toxin

Clostridium perfringens ε-toxin (ETX) is a potent pore-forming toxin responsible for a central nervous system (CNS) disease in ruminant animals with characteristics of blood-brain barrier (BBB) dysfunction and white matter injury. ETX has been proposed as a potential causative agent for Multiple Sclerosis (MS), a human disease that begins with BBB breakdown and injury to myelin forming cells of the CNS. The receptor for ETX is unknown. Here we show that both binding of ETX to mammalian cells and cytotoxicity requires the tetraspan proteolipid Myelin and Lymphocyte protein (MAL). While native Chinese Hamster Ovary (CHO) cells are resistant to ETX, exogenous expression of MAL in CHO cells confers both ETX binding and susceptibility to ETX-mediated cell death. Cells expressing rat MAL are ~100 times more sensitive to ETX than cells expressing similar levels of human MAL. Insertion of the FLAG sequence into the second extracellular loop of MAL abolishes ETX binding and cytotoxicity. ETX is known to bind specifically and with high affinity to intestinal epithelium, renal tubules, brain endothelial cells and myelin. We identify specific binding of ETX to these structures and additionally show binding to retinal microvasculature and the squamous epithelial cells of the sclera in wild-type mice. In contrast, there is a complete absence of ETX binding to tissues from MAL knockout (MAL-/-) mice. Furthermore, MAL-/- mice exhibit complete resistance to ETX at doses in excess of 1000 times the symptomatic dose for wild-type mice. We conclude that MAL is required for both ETX binding and cytotoxicity.

Glycosylation of uroplakins. Implications for bladder physiopathology

Urothelium, a specialized epithelium, covers the urinary tract and act not only as a barrier separating its light from the surrounding tissues, but fulfills an important role in maintaining the homeostasis of the urothelial tract and well-being of the whole organism. Proper function of urothelium is dependent on the precise assemble of highly specialized glycoproteins called uroplakins, the end products and differentiation markers of the urothelial cells. Glycosylation changes in uroplakins correlate with and might reflect progressive stages of pathological conditions of the urothelium such as cancer, urinary tract infections, interstitial cystitis and others. In this review we focus on sugar components of uroplakins, their emerging role in urothelial biology and disease implications. The advances in our understanding of uroplakins changes in glycan moieties composition, structure, assembly and expression of their glycovariants could potentially lead to the development of targeted therapies and discoveries of novel urine and plasma markers for the benefit of patients with urinary tract diseases.

Formation and regeneration of the urothelium

PURPOSE OF REVIEW

This review addresses significant changes in our understanding of urothelial development and regeneration. Understanding urothelial differentiation will be important in the push to find new methods of bladder reconstruction and augmentation, as well as identification of bladder cancer stem cells.

RECENT FINDINGS

This review will cover recent findings including the identification of novel progenitor cells in the embryo and adult urothelium, function of the urothelium, and regeneration of the urothelium. Using Cre-lox recombination with cell-type-specific Cre lines, lineage studies from our laboratory have revealed novel urothelial cell types and progenitors that are critical for formation and regeneration of the urothelium. Interestingly, our studies indicate that Keratin-5-expressing basal cells, which have previously been proposed to be urothelial stem cells, are a self-renewing unipotent population, whereas P-cells, a novel urothelial cell type, are progenitors in the embryo, and intermediate cells serve as a progenitor pool in the adult.

SUMMARY

These findings could have important implications for our understanding of cancer tumorigenesis and could move the fields of regeneration and reconstruction forward.

SNX31: a novel sorting nexin associated with the uroplakin-degrading multivesicular bodies in terminally differentiated urothelial cells

Uroplakins (UP), a group of integral membrane proteins, are major urothelial differentiation products that form 2D crystals of 16-nm particles (urothelial plaques) covering the apical surface of mammalian bladder urothelium. They contribute to the urothelial barrier function and, one of them, UPIa, serves as the receptor for uropathogenic Escherichia coli. It is therefore important to understand the mechanism by which these surface-associated uroplakins are degraded. While it is known that endocytosed uroplakin plaques are targeted to and line the multivesicular bodies (MVBs), it is unclear how these rigid-looking plaques can go to the highly curved membranes of intraluminal vesicles (ILVs). From a cDNA subtraction library, we identified a highly urothelium-specific sorting nexin, SNX31. SNX31 is expressed, like uroplakins, in terminally differentiated urothelial umbrella cells where it is predominantly associated with MVBs. Apical membrane proteins including uroplakins that are surface biotin-tagged are endocytosed and targeted to the SNX31-positive MVBs. EM localization demonstrated that SNX31 and uroplakins are both associated not only with the limiting membranes of MVBs containing uroplakin plaques, but also with ILVs. SNX31 can bind, on one hand, the PtdIns3P-enriched lipids via its N-terminal PX-domain, and, on the other hand, it binds uroplakins as demonstrated by co-immunoprecipitation and proximity ligation assay, and by its reduced membrane association in uroplakin II-deficient urothelium. The fact that in urothelial umbrella cells MVBs are the only major intracellular organelles enriched in both PtdIns3P and uroplakins may explain SNX31's MVB-specificity in these cells. However, in MDCK and other cultured cells transfected SNX31 can bind to early endosomes possibly via lipids. These data support a model in which SNX31 mediates the endocytic degradation of uroplakins by disassembling/collapsing the MVB-associated uroplakin plaques, thus enabling the uroplakin-containing (but ‘softened’) membranes to bud and form the ILVs for lysosomal degradation and/or exosome formation.

Cystitis: from urothelial cell biology to clinical applications

Cystitis is a urinary bladder disease with many causes and symptoms. The severity of cystitis ranges from mild lower abdominal discomfort to life-threatening haemorrhagic cystitis. The course of disease is often chronic or recurrent. Although cystitis represents huge economical and medical burden throughout the world and in many cases treatments are ineffective, the mechanisms of its origin and development as well as measures for effective treatment are still poorly understood. However, many studies have demonstrated that urothelial dysfunction plays a crucial role. In the present review we first discuss fundamental issues of urothelial cell biology, which is the core for comprehension of cystitis. Then we focus on many forms of cystitis, its current treatments, and advances in its research. Additionally we review haemorrhagic cystitis with one of the leading causative agents being chemotherapeutic drug cyclophosphamide and summarise its management strategies. At the end we describe an excellent and widely used animal model of cyclophosphamide induced cystitis, which gives researches the opportunity to get a better insight into the mechanisms involved and possibility to develop new therapy approaches.

Correlation between urothelial differentiation and sensory proteins P2X3, P2X5, TRPV1, and TRPV4 in normal urothelium and papillary carcinoma of human bladder

Terminal differentiation of urothelium is a prerequisite for blood-urine barrier formation and enables normal sensory function of the urinary bladder. In this study, urothelial differentiation of normal human urothelium and of low and high grade papillary urothelial carcinomas was correlated with the expression and localization of purinergic receptors (P2X3, and P2X5) and transient receptor potential vanilloid channels (TRPV1, and TRPV4). Western blotting and immunofluorescence of uroplakins together with scanning electron microscopy of urothelial apical surface demonstrated terminal differentiation of normal urothelium, partial differentiation of low grade carcinoma, and poor differentiation of high grade carcinoma. P2X3 was expressed in normal urothelium as well as in low grade carcinoma and in both cases immunolabeling was stronger in the superficial cells. P2X3 expression decreased in high grade carcinoma. P2X5 expression was detected in normal urothelium and in high grade carcinoma, while in low grade carcinoma its expression was diminished. The expression of TRPV1 decreased in low grade and even more in high grade carcinoma when compared with normal urothelium, while TRPV4 expression was unchanged in all samples. Our results suggest that sensory proteins P2X3 and TRPV1 are in correlation with urothelial differentiation, while P2X5 and TRPV4 have unique expression patterns.

The MARVEL domain protein Nce102 regulates actin organization and invasive growth of Candida albicans

Invasive growth of the fungal pathogen Candida albicans into tissues promotes disseminated infections in humans. The plasma membrane is essential for pathogenesis because this important barrier mediates morphogenesis and invasive growth, as well as secretion of virulence factors, cell wall synthesis, nutrient import, and other processes. Previous studies showed that the Sur7 tetraspan protein that localizes to MCC (membrane compartment occupied by Can1)/eisosome subdomains of the plasma membrane regulates a broad range of key functions, including cell wall synthesis, morphogenesis, and resistance to copper. Therefore, a distinct tetraspan protein found in MCC/eisosomes, Nce102, was investigated. Nce102 belongs to the MARVEL domain protein family, which is implicated in regulating membrane structure and function. Deletion of NCE102 did not cause the broad defects seen in sur7Δ cells. Instead, the nce102Δ mutant displayed a unique phenotype in that it was defective in forming hyphae and invading low concentrations of agar but could invade well in higher agar concentrations. This phenotype was likely due to a defect in actin organization that was observed by phalloidin staining. In support of this, the invasive growth defect of a bni1Δ mutant that mislocalizes actin due to lack of the Bni1 formin was also reversed at high agar concentrations. This suggests that a denser matrix provides a signal that compensates for the actin defects. The nce102Δ mutant displayed decreased virulence and formed abnormal hyphae in mice. These studies identify novel ways that Nce102 and the physical environment surrounding C. albicans regulate morphogenesis and pathogenesis.

The plasma membrane promotes virulence of the human fungal pathogen Candida albicans by acting as a protective barrier around the cell and mediating dynamic activities, such as morphogenesis, cell wall synthesis, secretion of virulence factors, and nutrient uptake. To better understand how the plasma membrane contributes to virulence, we analyzed a set of eight genes encoding MARVEL family proteins that are predicted to function in membrane organization. Interestingly, deletion of one gene, NCE102, caused a strong defect in formation of invasive hyphal growth in vitro and decreased virulence in mice. The nce102Δ mutant cells showed defects in actin organization that underlie the morphogenesis defect, since mutation of a known regulator of actin organization caused a similar defect. These studies identify a novel way in which the plasma membrane regulates the actin cytoskeleton and contributes to pathogenesis.

GAGs and GAGs diseases: when pathophysiology supports the clinic

The urinary epithelium has been the subject of considerable interest and much research in recent years. What has radically changed in the last decade is the concept of what the bladder epithelium really is. It is currently no longer considered just a simple barrier and a non-specific defence against infections, and it has been recognized as a specialized tissue regulating complex bladder functions and playing a fundamental and active role in the pathogenesis of cystitis. Researchers have been focussing on the receptors and mediators that are active in the sub-epithelial layer, with the hope that understanding the role of the urothelium defect will offer the opportunity for new therapeutic strategies. On the surface of the urothelial umbrella-cells there is a thick layer of glycoproteins and proteoglycans, which together are called Glycosaminoglycans (GAGs). They constitute a hydrophilic mucosal coating and act as a barrier against solutes found in urine. In recent years they have received special attention because injury to Gags, due to different noxae, has been identified as the first step in the genesis of chronic inflammatory bladder diseases, such as recurrent urinary tract infections, chemical or radiation cystitis, interstitial cystitis and/or Bladder Pain Syndrome. Aim of this study is to define the importance of the urothelium starting from the anatomy and physiology of the bladder wall. Furthermore, we will underline the role of glycosaminoglycans, focusing both on their pathophysiological role in the principal bladder diseases and on the therapeutic aspects from the clinical point of view.

Bladder filling and voiding affect umbrella cell tight junction organization and function

Epithelial cells are continuously exposed to mechanical forces including shear stress and stretch, although the effect these forces have on tight junction (TJ) organization and function are poorly understood. Umbrella cells form the outermost layer of the stratified uroepithelium and undergo large cell shape and surface area changes during the bladder cycle. Here we investigated the effects of bladder filling and voiding on the umbrella cell TJ. We found that bladder filling promoted a significant increase in the length of the TJ ring, which was quickly reversed within 5 min of voiding. Interestingly, when isolated uroepithelial tissue was mounted in Ussing chambers and exposed to physiological stretch, we observed a 10-fold drop in both transepithelial electrical resistance (TER) and the umbrella cell junctional resistance. The effects of stretch on TER were reversible and dependent on the applied force. Furthermore, the integrity of the umbrella cell TJ was maintained in the stretched uroepithelium, as suggested by the limited permeability of biotin, fluorescein, and ruthenium red. Finally, we found that depletion of extracellular Ca(2+) by EGTA completely disrupted the TER of unstretched, but not of stretched uroepithelium. Taken together, our studies indicate that the umbrella cell TJ undergoes major structural and functional reorganization during the bladder cycle. The impact of these changes on bladder function is discussed.

Role of membrane traffic in the generation of epithelial cell asymmetry

Epithelial cells have an apical-basolateral axis of polarity, which is required for epithelial functions including barrier formation, vectorial ion transport and sensory perception. Here we review what is known about the sorting signals, machineries and pathways that maintain this asymmetry, and how polarity proteins interface with membrane-trafficking pathways to generate membrane domains de novo. It is becoming apparent that membrane traffic does not simply reinforce polarity, but is critical for the generation of cortical epithelial cell asymmetry.