Platelet-derived growth factor receptor-α cells in mouse urinary bladder: a new class of interstitial cells

Molecular characterization of suburothelial fibrosis in murine acute recurrent bladder inflammation

Chronic fibrosis replaces functional organ tissue with scar tissue by overproduction of a thick and stiff extracellular matrix. Bladder fibrosis decreases bladder compliance, ultimately resulting in overactive bladder. The phenoconversion of fibroblasts into myofibroblasts is the defining feature of fibrosis. Recently, regionally distinct populations of bladder platelet-derived growth factor receptor alpha positive (PDGFRα+) cells were identified as fibroblasts. Because of this heterogeneity, the identity of the bladder fibroblast cells that undergo phenotypic conversion into myofibroblasts is not clear. The current study utilized cyclophosphamide (CYP)-induced bladder inflammation to identify and characterize bladder PDGFRα+ cells that become myofibroblasts. We found that suburothelial PDGFRα+ cells and detrusor PDGFRα+ cells display different gene expression profiles. Suburothelial PDGFRα+ cells are more abundant than detrusor PDGFRα+ cells and express higher levels of fibrosis-related genes. CYP-treatment increased the number of suburothelial PDGFRα+ cells, increased Pdgfra, Col1a1, and Fn1 transcription in suburothelial PDGFRα+ cells, and increased α-smooth muscle actin, collagen, and fibronectin protein expression. CYP-treatment likely activated TNF-α and TGF-ß pathways, as indicated by nuclear translocation of SMAD2, SMAD3, and NFκB. In conclusion, we identify suburothelial PDGFRα+ cells as the fibroblast population which convert into myofibroblasts via activation of TNF-α and TGF-ß signaling pathways, due to bladder inflammation.

Cells and ionic conductances contributing to spontaneous activity in bladder and urethral smooth muscle

Smooth muscle organs of the lower urinary tract comprise the bladder detrusor and urethral wall, which have a reciprocal contractile relationship during urine storage and micturition. As the bladder fills with urine, detrusor smooth muscle cells (DSMCs) remain relaxed to accommodate increases in intravesical pressure while urethral smooth muscle cells (USMCs) sustain tone to occlude the urethral orifice, preventing leakage. While neither organ displays coordinated regular contractions as occurs in small intestine, lymphatics or renal pelvis, they do exhibit patterns of rhythmicity at cellular and tissue levels. In rabbit and guinea-pig urethra, electrical slow waves are recorded from USMCs. This activity is linked to cells expressing vimentin, c-kit and Ca2+-activated Cl- channels, like interstitial cells of Cajal in the gastrointestinal tract. In mouse, USMCs are rhythmically active (firing propagating Ca2+ waves linked to contraction), and this cellular rhythmicity is asynchronous across tissues and summates to form tone. Experiments in mice have failed to demonstrate a voltage-dependent mechanism for regulating this rhythmicity or contractions in vitro, suggesting that urethral tone results from an intrinsic ability of USMCs to 'pace' their own Ca2+ mobilization pathways required for contraction. DSMCs exhibit spontaneous transient contractions, increases in intracellular Ca2+ and action potentials. Consistent across numerous species, including humans, this activity relies on voltage-dependent Ca2+ influx in DSMCs. While interstitial cells are present in the bladder, they do not 'pace' the organ in an excitatory manner. Instead, specialized cells (PDGFRα+ interstitial cells) may 'negatively pace' DSMCs to prevent bladder overexcitability.

Involvement of ANO1 currents in pacemaking of PDGFRα-positive specialised smooth muscle cells in rat caudal epididymis

The epididymal duct exhibits spontaneous phasic contractions (SPCs) to store and transport sperm. Here, we explored molecular identification of pacemaker cells driving SPCs in the caudal epididymal duct and also investigated properties of pacemaker currents underlying SPCs focusing on ANO1 Ca2+-activated Cl- channels (CaCCs). Immunohistochemistry was performed to visualise the distribution of platelet-derived growth factor receptor α (PDGFRα)- or ANO1-positive cells in the rat caudal epididymal duct. Perforated whole-cell patch clamp technique was applied to enzymatically isolated epididymal cells, while SPCs were recorded with video edge-tracking technique. Immunohistochemistry revealed the distribution of α-smooth muscle actin (α-SMA)-positive cells co-expressing both PDGFRα and ANO1 in the innermost smooth muscle layer. Approximately one-third of isolated epididymis cells exhibited spontaneous transient inward currents (STICs) at the holding potential -60 mV. The reversal potential for STICs was close to the calculated chloride equivalent potential depending on intracellular Cl- concentrations. Ani9 (3 µM), the ANO1 specific inhibitor, decreased both amplitude and frequency of STICs, while cyclopiazonic acid (CPA, 30 µM), a sarco-/endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor, abolished STICs. Ani9 (3 or 10 µM) reduced the frequency of SPCs without changing their amplitude. Thus, PDGFRα+, ANO1+ specialised smooth muscle cells (SMCs) appear to function as pacemaker cells to electrically drive epididymal SPCs by generating ANO1-dependnet STICs. STICs arising from spontaneous Ca2+ release from intracellular Ca2+ store and subsequent opening of ANO1 result in depolarisations that spread into adjacent SMCs where L-type voltage-dependent Ca2+ channels are activated to develop SPCs.

Computational modeling of inhibitory signal transduction in urinary bladder PDGFRα+ cells

A crucial aspect of bladder function is the maintenance of a normo-active detrusor during bladder filling. The physiological mechanisms and pathways underlying this function are yet to be fully elucidated. Premature detrusor contractions are a key phenotype in detrusor overactivity, a common pathophysiological condition of the urinary bladder. Recent literature has identified PDFGRα+ cells as mediators in transducing inhibitory signals to detrusor smooth muscle cells via gap junctions. We employ computational modeling to study transduction pathways via which inhibitory signals are generated in PDFGRα+ cells in response to purinergic, nitrergic and mechanical stimuli. The key focus of our study here is to explore the effect of ATP, stretch and NO on the membrane potential of PDFGRα+ cells, which is driven to hyperpolarized potentials via the activation of SK3 channels. Our results indicate that purinergic, mechanical and nitrergic inputs can induce significant membrane hyperpolarizations of 20-35 mV relative to the resting membrane potential. Given the interconnections between PDFGRα+ cells and detrusor SMCs through gap junctions, these hyperpolarizations can have significant functional implications in the maintenance of a normo-active detrusor as also in departures from this state as seen in detrusor overactivity.

Low-Intensity Extracorporeal Shock Wave Therapy Ameliorates Detrusor Hyperactivity with Impaired Contractility via Transient Potential Vanilloid Channels: A Rat Model for Ovarian Hormone Deficiency

This study explores low-intensity extracorporeal shock wave therapy (LiESWT)'s efficacy in alleviating detrusor hyperactivity with impaired contractility (DHIC) induced by ovarian hormone deficiency (OHD) in ovariectomized rats. The rats were categorized into the following four groups: sham group; OVX group, subjected to bilateral ovariectomy (OVX) for 12 months to induce OHD; OVX + SW4 group, underwent OHD for 12 months followed by 4 weeks of weekly LiESWT; and OVX + SW8 group, underwent OHD for 12 months followed by 8 weeks of weekly LiESWT. Cystometrogram studies and voiding behavior tracing were used to identify the symptoms of DHIC. Muscle strip contractility was evaluated through electrical-field, carbachol, ATP, and KCl stimulations. Western blot and immunofluorescence analyses were performed to assess the expressions of various markers related to bladder dysfunction. The OVX rats exhibited significant bladder deterioration and overactivity, alleviated by LiESWT. LiESWT modified transient receptor potential vanilloid (TRPV) channel expression, regulating calcium concentration and enhancing bladder capacity. It also elevated endoplasmic reticulum (ER) stress proteins, influencing ER-related Ca2+ channels and receptors to modulate detrusor muscle contractility. OHD after 12 months led to neuronal degeneration and reduced TRPV1 and TRPV4 channel activation. LiESWT demonstrated potential in enhancing angiogenic remodeling, neurogenesis, and receptor response, ameliorating DHIC via TRPV channels and cellular signaling in the OHD-induced DHIC rat model.

Insights on Platelet-Derived Growth Factor Receptor α-Positive Interstitial Cells in the Male Reproductive Tract

Male infertility is a significant factor in approximately half of all infertility cases and is marked by a decreased sperm count and motility. A decreased sperm count is caused by not only a decreased production of sperm but also decreased numbers successfully passing through the male reproductive tract. Smooth muscle movement may play an important role in sperm transport in the male reproductive tract; thus, understanding the mechanism of this movement is necessary to elucidate the cause of sperm transport disorder. Recent studies have highlighted the presence of platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells (PICs) in various smooth muscle organs. Although research is ongoing, PICs in the male reproductive tract may be involved in the regulation of smooth muscle movement, as they are in other smooth muscle organs. This review summarizes the findings to date on PICs in male reproductive organs. Further exploration of the structural, functional, and molecular characteristics of PICs could provide valuable insights into the pathogenesis of male infertility and potentially lead to new therapeutic approaches.

Pacemaking in the lymphatic system

Lymphatic collecting vessels exhibit spontaneous phasic contractions that are critical for lymph propulsion and tissue fluid homeostasis. This rhythmic activity is driven by action potentials conducted across the lymphatic muscle cell (LMC) layer to produce entrained contractions. The contraction frequency of a lymphatic collecting vessel displays exquisite mechanosensitivity, with a dynamic range from <1 to >20 contractions per minute. A myogenic pacemaker mechanism intrinsic to the LMCs was initially postulated to account for pressure-dependent chronotropy. Further interrogation into the cellular constituents of the lymphatic vessel wall identified non-muscle cell populations that shared some characteristics with interstitial cells of Cajal, which have pacemaker functions in the gastrointestinal and lower urinary tracts, thus raising the possibility of a non-muscle cell pacemaker. However, recent genetic knockout studies in mice support LMCs and a myogenic origin of the pacemaker activity. LMCs exhibit stochastic, but pressure-sensitive, sarcoplasmic reticulum calcium release (puffs and waves) from IP3R1 receptors, which couple to the calcium-activated chloride channel Anoctamin 1, causing depolarisation. The resulting electrical activity integrates across the highly coupled lymphatic muscle electrical syncytia through connexin 45 to modulate diastolic depolarisation. However, multiple other cation channels may also contribute to the ionic pacemaking cycle. Upon reaching threshold, a voltage-gated calcium channel-dependent action potential fires, resulting in a nearly synchronous calcium global calcium flash within the LMC layer to drive an entrained contraction. This review summarizes the key ion channels potentially responsible for the pressure-dependent chronotropy of lymphatic collecting vessels and various mechanisms of IP3R1 regulation that could contribute to frequency tuning.

Identifying peristaltic pacemaker cells in the upper urinary tract

Urine expulsion from the upper urinary tract is a necessary process that eliminates waste, promotes renal filtration and prevents nephron damage. To facilitate the movement of urine boluses throughout the upper urinary tract, smooth muscle cells that line the renal pelvis contract in a coordinated effort to form peristaltic waves. Resident pacemaker cells in the renal pelvis are critical to this process and spontaneously evoke transient depolarizations that initiate each peristaltic wave and establish rhythmic contractions. Renal pacemakers have been termed atypical smooth muscle cells due to their low expression of smooth muscle myosin and poor organization of myofilaments compared to typical (or contractile) smooth muscle cells that perform peristalsis. Recent findings discovered that pacemaker cells also express the tyrosine kinase receptor PDGFRα, enabling their identification and purification amongst other renal pelvis cell types. Improved identification methods have determined that the calcium-activated chloride channel, ANO1, is expressed by pacemaker cells and may contribute to spontaneous depolarization. A greater understanding of pacemaker and peristaltic mechanisms is warranted since aberrant contractile function may underlie diseases such as hydronephrosis, a deleterious condition that can cause significant and irreversible nephron injury.

Defining the molecular fingerprint of bladder and kidney fibroblasts

Fibroblasts are integral to the organization and function of all organs and play critical roles in pathologies such as fibrosis; however, we have limited understanding of the fibroblasts that populate the bladder and kidney. In this review, I describe how transcriptomics is leading to a revolution in our understanding of fibroblast biology by defining the molecular fingerprint (i.e., transcriptome) of universal and specialized fibroblast types, revealing gene signatures that allows one to resolve fibroblasts from other mesenchymal cell types, and providing a new comprehension of the fibroblast lineage. In the kidney, transcriptomics is giving us new insights into the molecular fingerprint of kidney fibroblasts, including those for cortical fibroblasts, medullary fibroblasts, and erythropoietin (EPO)-producing Norn fibroblasts, as well as new information about the gene signatures of kidney myofibroblasts and the transition of kidney fibroblasts into myofibroblasts. Transcriptomics has also revealed that the major cell type in the bladder interstitium is the fibroblast, and that multiple fibroblast types, each with their own molecular fingerprint, are found in the bladder wall. Interleaved throughout is a discussion of how transcriptomics can drive our future understanding of fibroblast identification, diversity, function, and their roles in bladder and kidney biology and physiology in health and in disease states.

Studies of ultrastructure, gene expression, and marker analysis reveal that mouse bladder PDGFRA+ interstitial cells are fibroblasts

Fibroblasts are crucial to normal and abnormal organ and tissue biology, yet we lack basic insights into the fibroblasts that populate the bladder wall. Candidates may include bladder interstitial cells (also referred to as myofibroblasts, telocytes, and interstitial cells of Cajal-like cells), which express the fibroblast-associated marker PDGFRA along with VIM and CD34 but whose form and function remain enigmatic. By applying the latest insights in fibroblast transcriptomics, coupled with studies of gene expression, ultrastructure, and marker analysis, we observe the following: 1) that mouse bladder PDGFRA+ cells exhibit all of the ultrastructural hallmarks of fibroblasts including spindle shape, lack of basement membrane, abundant endoplasmic reticulum and Golgi, and formation of homotypic cell-cell contacts (but not heterotypic ones); 2) that they express multiple canonical fibroblast markers (including Col1a2, CD34, LY6A, and PDGFRA) along with the universal fibroblast genes Col15a1 and Pi16 but they do not express Kit; and 3) that PDGFRA+ fibroblasts include suburothelial ones (which express ACTA2, CAR3, LY6A, MYH10, TNC, VIM, Col1a2, and Col15a1), outer lamina propria ones (which express CD34, LY6A, PI16, VIM, Col1a2, Col15a1, and Pi16), intermuscular ones (which express CD34, VIM, Col1a2, Col15a1, and Pi16), and serosal ones (which express CD34, PI16, VIM, Col1a2, Col15a1, and Pi16). Collectively, our study revealed that the ultrastructure of PDFRA+ interstitial cells combined with their expression of multiple canonical and universal fibroblast-associated gene products indicates that they are fibroblasts. We further propose that there are four regionally distinct populations of fibroblasts in the bladder wall, which likely contribute to bladder function and dysfunction.NEW & NOTEWORTHY We currently lack basic insights into the fibroblasts that populate the bladder wall. By exploring the ultrastructure of mouse bladder connective tissue cells, combined with analyses of their gene and protein expression, our study revealed that PDGRA+ interstitial cells (also referred to as myofibroblasts, telocytes, and interstitial cells of Cajal-like cells) are fibroblasts and that the bladder wall contains multiple, regionally distinct populations of these cells.

Transient receptor potential vanilloid type 4 (TRPV4) in urinary bladder structure and function

Bladder pain syndrome (BPS)/interstitial cystitis (IC) is a urologic, chronic pelvic pain syndrome characterized by pelvic pain, pressure, or discomfort with urinary symptoms. Symptom exacerbation (flare) is common with multiple, perceived triggers including stress. Multiple transient receptor potential (TRP) channels (TRPA1, TRPV1, TRPV4) expressed in the bladder have specific tissue distributions in the lower urinary tract (LUT) and are implicated in bladder disorders including overactive bladder (OAB) and BPS/IC. TRPV4 channels are strong candidates for mechanosensors in the urinary bladder and TRPV4 antagonists are promising therapeutic agents for OAB. In this perspective piece, we address the current knowledge of TRPV4 distribution and function in the LUT and its plasticity with injury or disease with an emphasis on BPS/IC. We review our studies that extend the knowledge of TRPV4 in urinary bladder function by focusing on (i) TRPV4 involvement in voiding dysfunction, pelvic pain, and non-voiding bladder contractions in NGF-OE mice; (ii) distention-induced luminal ATP release mechanisms and (iii) involvement of TRPV4 and vesicular release mechanisms. Finally, we review our lamina propria studies in postnatal rat studies that demonstrate: (i) the predominance of the TRPV4+ and PDGFRα+ lamina propria cellular network in early postnatal rats; (ii) the ability of exogenous mediators (i.e., ATP, TRPV4 agonist) to activate and increase the number of lamina propria cells exhibiting active Ca2+ events; and (iii) the ability of ATP and TRPV4 agonist to increase the rate of integrated Ca2+ activity corresponding to coupled lamina propria network events and the formation of propagating wavefronts.

The hyperpolarization-activated, cyclic nucleotide-gated channel resides on myocytes in mouse bladders and contributes to adrenergic-induced detrusor relaxation

Control of urinary continence is predicated on sensory signaling about bladder volume. Bladder sensory nerve activity is dependent on tension, implicating autonomic control over detrusor myocyte activity during bladder filling. Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels are known contributors to bladder control, but their mechanism of action is not well understood. The lack of a definitive identification of cell type(s) expressing HCN in the bladder presents a significant knowledge gap. We recently reported a complete transcriptomic atlas of the C57BL/6 mouse bladder showing the dominant HCN paralog in mouse bladder, Hcn1, is limited to a subpopulation of detrusor smooth myocytes (DSMs). Here, we report details of these findings, along with results of patch-clamp experiments, immunohistochemistry, and functional myobath/tension experiments in bladder strips. With the use of a transgenic mouse expressing fluorescence-tagged α-smooth muscle actin, our data confirmed location and function of DSM HCN channels. Despite previous associations of HCN with postulated bladder interstitial cells, neither evidence of specific interstitial cell types nor an association of nonmyocytes with HCN was discovered. We confirm that HCN activation participates in reducing sustained (tonic) detrusor tension via cAMP, with no effect on intermittent (phasic) detrusor activity. In contrast, blockade of HCN increases phasic activity induced by a protein kinase A (PKA) blocker or a large-conductance Ca²⁺-activated K⁺ (BK) channel opener. Our findings, therefore, suggest a central role for detrusor myocyte HCN in regulating and constraining detrusor myocyte activity during bladder filling.

Three-dimensional analysis of interstitial cells in the lamina propria of the murine vas deferens by confocal laser scanning microscopy and FIB/SEM

The present study aimed to explore the three-dimensional (3D) ultrastructure of interstitial cells (ICs) within the lamina propria of the murine vas deferens and the spatial relationships between epithelial cells and surrounding cells. Focused ion beam scanning electron microscopy and confocal laser scanning microscopy were performed. ICs within the lamina propria had a flat, sheet-like structure of cytoplasm with multiple cellular processes. In addition, two types of 3D structures that comprised cell processes of flat, sheet-like ICs were observed: one was an accordion fold-like structure and the other was a rod-shaped structure. ICs were located parallel to the epithelium and were connected to each other via gap junctions or adherens junctions. Moreover, multiple sphere-shaped extracellular vesicle-like structures were frequently observed around the ICs. The ICs formed a complex 3D network comprising sheet-like cytoplasm and multiple cell processes with different 3D structures. From this morphological study, we noted that ICs within the lamina propria of murine vas deferens may be involved in signal transmission between the epithelium and smooth muscle cells by physical interaction and by exchanging extracellular vesicles.

Imatinib Mesylate Reduces Voiding Frequency in Female Mice With Acute Cyclophosphamide-Induced Cystitis

Lamina propria interstitial cells that express the tyrosine kinase receptor, platelet-derived growth factor receptor alpha (PDGFRα) may play a role in urinary sensory signaling. Imatinib mesylate, also referred to as imatinib, is a tyrosine kinase inhibitor that can inhibit PDGFRα and has been widely used in urological research. We evaluated the functional effects of imatinib administration (via oral gavage or intravesical infusion) with two different experimental designs (prevention and treatment), in a cyclophosphamide (CYP)-induced cystitis (acute, intermediate, and chronic), male and female rodent model using conscious cystometry and somatic sensitivity testing. Imatinib significantly (0.0001 ≤ p ≤ 0.05) decreased voiding frequency and increased bladder capacity in acute CYP-induced cystitis, by the prevention (females) and treatment (females and males) designs. Imatinib was not effective in preventing or treating intermediate or chronic CYP-induced cystitis in either sex. Interestingly, in the prevention experiments, imatinib administration increased (0.0001 ≤ p ≤ 0.01) voiding frequency and decreased bladder capacity in control mice. However, in the treatment experiments, imatinib administration decreased (0.01 ≤ p ≤ 0.05) voiding frequency and increased bladder capacity in control mice. Bladder function improvements observed with imatinib treatment in acute CYP-induced cystitis mice remained and additionally improved with a second dose of imatinib 24 hours after CYP treatment. Imatinib administration did not affect pelvic somatic sensitivity in female mice with acute CYP-induced cystitis. Our studies suggest that (1) imatinib improves bladder function in mice with acute CYP-induced cystitis with a prevention and treatment design and (2) interstitial cells may be a useful target to improve bladder function in cystitis.

Imatinib Mesylate Reduces Neurotrophic Factors and pERK and pAKT Expression in Urinary Bladder of Female Mice With Cyclophosphamide-Induced Cystitis

Imatinib mesylate is a tyrosine kinase inhibitor that inhibits platelet-derived growth factor receptor (PDGFR)-α, -β, stem cell factor receptor (c-KIT), and BCR-ABL. PDGFRα is expressed in a subset of interstitial cells in the lamina propria (LP) and detrusor muscle of the urinary bladder. PDGFRα + interstitial cells may contribute to bladder dysfunction conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) or overactive bladder (OAB). We have previously demonstrated that imatinib prevention via oral gavage or treatment via intravesical infusion improves urinary bladder function in mice with acute (4 hour, h) cyclophosphamide (CYP)-induced cystitis. Here, we investigate potential underlying mechanisms mediating the bladder functional improvement by imatinib using a prevention or treatment experimental design. Using qRT-PCR and ELISAs, we examined inflammatory mediators (NGF, VEGF, BDNF, CCL2, IL-6) previously shown to affect bladder function in CYP-induced cystitis. We also examined the distribution of phosphorylated (p) ERK and pAKT expression in the LP with immunohistochemistry. Imatinib prevention significantly (0.0001 ≤ p ≤ 0.05) reduced expression for all mediators examined except NGF, whereas imatinib treatment was without effect. Imatinib prevention and treatment significantly (0.0001 ≤ p ≤ 0.05) reduced pERK and pAKT expression in the upper LP (U. LP) and deeper LP (D. LP) in female mice with 4 h CYP-induced cystitis. Although we have previously demonstrated that imatinib prevention or treatment improves bladder function in mice with cystitis, the current studies suggest that reductions in inflammatory mediators contribute to prevention benefits of imatinib but not the treatment benefits of imatinib. Differential effects of imatinib prevention or treatment on inflammatory mediators may be influenced by the route and frequency of imatinib administration and may also suggest other mechanisms (e.g., changes in transepithelial resistance of the urothelium) through which imatinib may affect urinary bladder function following CYP-induced cystitis.

Role of detrusor PDGFRα+ cells in mouse model of cyclophosphamide-induced detrusor overactivity

Cyclophosphamide (CYP)-induced cystitis is a rodent model that shares many features common to the cystitis occurring in patients, including detrusor overactivity (DO). Platelet-derived growth factor receptor alpha positive (PDGFRα⁺) cells have been proposed to regulate muscle excitability in murine bladders during filling. PDGFRα⁺ cells express small conductance Ca²⁺-activated K⁺ channels (predominantly SK3) that provide stabilization of membrane potential during filling. We hypothesized that down-regulation of the regulatory functions of PDGFRα⁺ cells and/or loss of PDGFRα⁺ cells generates the DO in CYP-treated mice. After CYP treatment, transcripts of Pdgfrα and Kcnn3 and PDGFRα and SK3 protein were reduced in detrusor muscle extracts. The distribution of PDGFRα⁺ cells was also reduced. Inflammatory markers were increased in CYP-treated detrusor muscles. An SK channel agonist, CyPPA, increased outward current and hyperpolarization in PDGFRα⁺ cells. This response was significantly depressed in PDGFRα⁺ cells from CYP-treated bladders. Contractile experiments and ex vivo cystometry showed increased spontaneous contractions and transient contractions, respectively in CYP-treated bladders with a reduction of apamin sensitivity, that could be attributable to the reduction in the SK conductance expressed by PDGFRα⁺ cells. In summary, PDGFRα⁺ cells were reduced and the SK3 conductance was downregulated in CYP-treated bladders. These changes are consistent with the development of DO after CYP treatment.

Proteomics as a Complementary Technique to Characterize Bladder Cancer

Simple Summary

Although immunohistochemistry is a routine technique in clinics, and genomics has been rapidly incorporated, proteomics is a step behind. This general situation is also the norm in bladder cancer research. This review shows the contributions of proteomics to the molecular classification of bladder cancer, and to the study of histopathology due to tissue insults caused by tumors. Furthermore, the importance of proteomics for understanding the cellular and molecular changes as a consequence of the therapy of bladder cancer cannot be neglected.

Abstract

Bladder cancer (BC) is the most common tumor of the urinary tract and is conventionally classified as either non-muscle invasive or muscle invasive. In addition, histological variants exist, as organized by the WHO-2016 classification. However, innovations in next-generation sequencing have led to molecular classifications of BC. These innovations have also allowed for the tracing of major tumorigenic pathways and, therefore, are positioned as strong supporters of precision medicine. In parallel, immunohistochemistry is still the clinical reference to discriminate histological layers and to stage BC. Key contributions have been made to enlarge the panel of protein immunomarkers. Moreover, the analysis of proteins in liquid biopsy has also provided potential markers. Notwithstanding, their clinical adoption is still low, with very few approved tests. In this context, mass spectrometry-based proteomics has remained a step behind; hence, we aimed to develop them in the community. Herein, the authors introduce the epidemiology and the conventional classifications to review the molecular classification of BC, highlighting the contributions of proteomics. Then, the advances in mass spectrometry techniques focusing on maintaining the integrity of the biological structures are presented, a milestone for the emergence of histoproteomics. Within this field, the review then discusses selected proteins for the comprehension of the pathophysiological mechanisms of BC. Finally, because there is still insufficient knowledge, this review considers proteomics as an important source for the development of BC therapies.

Morphological analysis of interstitial cells in murine epididymis using light microscopy and transmission electron microscopy

Smooth muscle contraction of the epididymis plays an important role in sperm transport. Although PDGFRα-positive interstitial cells (PDGFRα (+) ICs) are thought to be involved in controlling smooth muscle movement via intercellular signaling, they have not yet been reported to date in the epididymis. Therefore, we aimed to investigate the morphological characteristics of PDGFRα (+) ICs in the interstitial space of the murine epididymis. Immunohistochemistry showed that PDGFRα (+) ICs co-labeled with CD34 (PDGFRα (+) CD34 (+) ICs were distributed in the interstitial space of the murine epididymis from the initial segment (IS) to the cauda of the epididymis. PDGFRα (+) ICs that were not co-labeled with CD34 (PDGFRα (+) CD34 (-) ICs) were observed just beneath the epithelium from the corpus to the cauda but not in the IS. Both types of PDGFRα (+) ICs were in close proximity to each other as well as the surrounding nerves and macrophages. In addition, PDGFRα (+) CD34 (-) ICs beneath the epithelium were also in close proximity to the basal cells. Using transmission electron microscopy, we identified ICs that possessed elongated and woven cellular processes and were in close proximity to each other, surrounding the cells in the interstitial space. In the murine epididymis, it is suggested that there are two subtypes of ICs that show different distribution patterns depending on the segment, which may reflect segmental differences in mechanisms of sperm transport, forming a cellular network by physical interactions in the murine epididymis.

Molecular and functional characterization of detrusor PDGFRα positive cells in spinal cord injury-induced detrusor overactivity

Volume accommodation occurs via a novel mechanism involving interstitial cells in detrusor muscles. The interstitial cells in the bladder are PDGFRα+, and they restrain the excitability of smooth muscle at low levels and prevents the development of transient contractions (TCs). A common clinical manifestation of spinal cord injury (SCI)-induced bladder dysfunction is detrusor overactivity (DO). Although a myogenic origin of DO after SCI has been suggested, a mechanism for development of SCI-induced DO has not been determined. In this study we hypothesized that SCI-induced DO is related to loss of function in the regulatory mechanism provided by PDGFRα+ cells. Our results showed that transcriptional expression of Pdgfra and Kcnn3 was decreased after SCI. Proteins encoded by these genes also decreased after SCI, and a reduction in PDGFRα+ cell density was also documented. Loss of PDGFRα+ cells was due to apoptosis. TCs in ex vivo bladders during filling increased dramatically after SCI, and this was related to the loss of regulation provided by SK channels, as we observed decreased sensitivity to apamin. These findings show that damage to the mechanism restraining muscle contraction during bladder filling that is provided by PDGFRα+ cells is causative in the development of DO after SCI.

Identification of PDGFRα-positive interstitial cells in the distal segment of the murine vas deferens

Platelet-derived growth factor receptor-α (PDGFRα)-positive interstitial cells (ICs) are widely distributed in various organs and may be involved in the motility of various tubular organs. We, for the first time, aimed to investigate the distribution, immunohistochemical characteristics, and ultrastructure of PDGFRα-positive ICs in murine vas deferens, using confocal laser scanning microscopy, transmission electron microscopy (TEM), and immuno-electron microscopy (immuno-EM). For immunofluorescence, we used antibodies against PDGFRα and other markers of ICs. PDGFRα-positive ICs were distributed widely in the lamina propria, smooth muscles, and serosal layers. Although most PDGFRα-positive ICs labeled CD34, they did not label CD34 in the subepithelial layers. Additionally, PDGFRα-positive ICs were in close proximity to each other, as also to the surrounding cells. TEM and immuno-EM findings revealed that PDGFRα-positive ICs established close physical interactions with adjacent ICs. Extracellular vesicles were also detected around the PDGFRα-positive ICs. Our morphological findings suggest that PDGFRα-positive ICs may have several subpopulations, which can play an important role in intercellular signaling via direct contact with the IC network and the extracellular vesicles in the murine vas deferens. Further investigation on PDGFRα-positive ICs in the vas deferens may lead to understanding the vas deferens mortility.

Transient receptor potential channels in sensory mechanisms of the lower urinary tract

Disruptions to sensory pathways in the lower urinary tract commonly occur and can give rise to lower urinary tract symptoms (LUTS). The unmet clinical need for treatment of LUTS has stimulated research into the molecular mechanisms that underlie neuronal control of the bladder and transient receptor potential (TRP) channels have emerged as key regulators of the sensory processes that regulate bladder function. TRP channels function as molecular sensors in urothelial cells and afferent nerve fibres and can be considered the origin of bladder sensations. TRP channels in the lower urinary tract contribute to the generation of normal and abnormal bladder sensations through a variety of mechanisms, and have demonstrated potential as targets for the treatment of LUTS in functional disorders of the lower urinary tract.

Role of Ano1 Ca2+-activated Cl- channels in generating urethral tone

Urinary continence is maintained in the lower urinary tract by the contracture of urethral sphincters, including smooth muscle of the internal urethral sphincter. These contractions occlude the urethral lumen, preventing urine leakage from the bladder to the exterior. Over the past 20 years, research on the ionic conductances that contribute to urethral smooth muscle contractility has greatly accelerated. A debate has emerged over the role of interstitial cell of Cajal (ICC)-like cells in the urethra and their expression of Ca²⁺-activated Cl^- channels encoded by anoctamin-1 [Ano1; transmembrane member 16 A (Tmem16a) gene]. It has been proposed that Ano1 channels expressed in urethral ICC serve as a source of depolarization for smooth muscle cells, increasing their excitability and contributing to tone. Although a clear role for Ano1 channels expressed in ICC is evident in other smooth muscle organs, such as the gastrointestinal tract, the role of these channels in the urethra is unclear, owing to differences in the species (rabbit, rat, guinea pig, sheep, and mouse) examined and experimental approaches by different groups. The importance of clarifying this situation is evident as effective targeting of Ano1 channels may lead to new treatments for urinary incontinence. In this review, we summarize the key findings from different species on the role of ICC and Ano1 channels in urethral contractility. Finally, we outline proposals for clarifying this controversial and important topic by addressing how cell-specific optogenetic and inducible cell-specific genetic deletion strategies coupled with advances in Ano1 channel pharmacology may clarify this area in future studies.NEW & NOTEWORTHY Studies from the rabbit have shown that anoctamin-1 (Ano1) channels expressed in urethral interstitial cells of Cajal (ICC) serve as a source of depolarization for smooth muscle cells, increasing excitability and tone. However, the role of urethral Ano1 channels is unclear, owing to differences in the species examined and experimental approaches. We summarize findings from different species on the role of urethral ICC and Ano1 channels in urethral contractility and outline proposals for clarifying this topic using cell-specific optogenetic approaches.

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.

Identification and classification of interstitial cells in the mouse renal pelvis

KEY POINTS

Platelet-derived growth factor receptor-α (PDGFRα) is a novel biomarker along with smooth myosin heavy chain for the pacemaker cells (previously termed 'atypical' smooth muscle cells) in the murine and cynomolgus monkey pelvis-kidney junction. PDGFRα⁺ cells present in adventitial and urothelial layers of murine renal pelvis do not express smooth muscle myosin heavy chain (smMHC) but are in close apposition to nerve fibres. Most c-Kit⁺ cells in the renal pelvis are mast cells. Mast cells (CD117⁺ /CD45⁺ ) are more abundant in the proximal renal pelvis and pelvis-kidney junction regions whereas c-Kit⁺ interstitial cells (CD117⁺ /CD45^- ) are found predominantly in the distal renal pelvis and ureteropelvic junction. PDGFRα⁺ cells are distinct from c-Kit⁺ interstitial cells. A subset of PDGFRα⁺ cells express the Ca²⁺ -activated Cl^- channel, anoctamin-1, across the entire renal pelvis. Spontaneous Ca²⁺ transients were observed in c-Kit⁺ interstitial cells, smMHC⁺ PDGFRα cells and smMHC^- PDGFRα cells using mice expressing genetically encoded Ca²⁺ sensors.

ABSTRACT

Rhythmic contractions of the renal pelvis transport urine from the kidneys into the ureter. Specialized pacemaker cells, termed atypical smooth muscle cells (ASMCs), are thought to drive the peristaltic contractions of typical smooth muscle cells (TSMCs) in the renal pelvis. Interstitial cells (ICs) in close proximity to ASMCs and TSMCs have been described, but the role of these cells is poorly understood. The presence and distributions of platelet-derived growth factor receptor-α⁺ (PDGFRα⁺ ) ICs in the pelvis-kidney junction (PKJ) and distal renal pelvis were evaluated. We found PDGFRα⁺ ICs in the adventitial layers of the pelvis, the muscle layer of the PKJ and the adventitia of the distal pelvis. PDGFRα⁺ ICs were distinct from c-Kit⁺ ICs in the renal pelvis. c-Kit⁺ ICs are a minor population of ICs in murine renal pelvis. The majority of c-Kit⁺ cells were mast cells. PDGFRα⁺ cells in the PKJ co-expressed smooth muscle myosin heavy chain (smMHC) and several other smooth muscle gene transcripts, indicating these cells are ASMCs, and PDGFRα is a novel biomarker for ASMCs. PDGFRα⁺ cells also express Ano1, which encodes a Ca²⁺ -activated Cl^- conductance that serves as a primary pacemaker conductance in ICs of the GI tract. Spontaneous Ca²⁺ transients were observed in c-Kit⁺ ICs, smMHC⁺ PDGFRα cells and smMHC^- PDGFRα cells using genetically encoded Ca²⁺ sensors. A reporter strain of mice with enhanced green fluorescent protein driven by the endogenous promotor for Pdgfra was shown to be a powerful new tool for isolating and characterizing the phenotype and functions of these cells in the renal pelvis.

A Novel in situ Approach to Studying Detrusor Smooth Muscle Cells in Mice

The aim of our study was to develop a novel approach to investigating mouse detrusor smooth muscle cell (SMC) physiological activity, utilizing an acute tissue dissection technique and confocal calcium imaging. The bladder of a sacrificed adult female NMRI mouse was dissected. We used light and transmission electron microscopy to assess morphology of SMCs within the tissue. Calcium imaging in individual SMCs was performed using confocal microscopy during stimulation with increasing concentrations of carbamylcholine (CCh). SMCs were identified according to their morphology and calcium activity. We determined several parameters describing the SMC responses: delays to response, recruitment, relative activity, and contraction of the tissue. CCh stimulation revealed three different SMC phenotypes: spontaneously active SMCs with and without CCh-enhanced activity and SMCs with CCh-induced activity only. SMCs were recruited into an active state in response to CCh-stimulation within a narrow range (1-25 µM); causing activation of virtually all SMCs. Maximum calcium activity of SMCs was at about 25 µM, which coincided with a visible tissue contraction. Finally, we observed shorter time lags before response onsets with higher CCh concentrations. In conclusion, our novel in situ approach proved to be a robust and reproducible method to study detrusor SMC morphology and physiology.

Single-Cell Transcriptomic Map of the Human and Mouse Bladders

BACKGROUND

Having a comprehensive map of the cellular anatomy of the normal human bladder is vital to understanding the cellular origins of benign bladder disease and bladder cancer.

METHODS

We used single-cell RNA sequencing (scRNA-seq) of 12,423 cells from healthy human bladder tissue samples taken from patients with bladder cancer and 12,884 cells from mouse bladders to classify bladder cell types and their underlying functions.

RESULTS

We created a single-cell transcriptomic map of human and mouse bladders, including 16 clusters of human bladder cells and 15 clusters of mouse bladder cells. The homology and heterogeneity of human and mouse bladder cell types were compared and both conservative and heterogeneous aspects of human and mouse bladder evolution were identified. We also discovered two novel types of human bladder cells. One type is ADRA2A ⁺ and HRH2 ⁺ interstitial cells which may be associated with nerve conduction and allergic reactions. The other type is TNNT1 ⁺ epithelial cells that may be involved with bladder emptying. We verify these TNNT1 ⁺ epithelial cells also occur in rat and mouse bladders.

CONCLUSIONS

This transcriptomic map provides a resource for studying bladder cell types, specific cell markers, signaling receptors, and genes that will help us to learn more about the relationship between bladder cell types and diseases.

Spontaneous Activity and the Urinary Bladder

The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.

Expression and distribution of PIEZO1 in the mouse urinary tract

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 Piezo1 with the sequence for the tandem-dimer Tomato 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.

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

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.

The KV 7 channel activator retigabine suppresses mouse urinary bladder afferent nerve activity without affecting detrusor smooth muscle K+ channel currents

KEY POINTS

K_V 7 channels are a family of voltage-dependent K⁺ channels expressed in many cell types, which open in response to membrane depolarization to regulate cell excitability. Drugs that target K_V 7 channels are used clinically to treat epilepsy. Interestingly, these drugs also cause urinary retention, but it was unclear how. In this study, we focused on two possible mechanisms by which retigabine could cause urinary retention: by decreasing smooth muscle excitability, or by decreasing sensory nerve outflow. Urinary bladder smooth muscle had no measurable K_V 7 channel currents. However, the K_V 7 channel agonist retigabine nearly abolished sensory nerve outflow from the urinary bladder during bladder filling. We conclude that K_V 7 channel activation likely affects urinary bladder function by blocking afferent nerve outflow to the brain, which is key to sensing bladder fullness.

ABSTRACT

K_V 7 channels are voltage-dependent K⁺ channels that open in response to membrane depolarization to regulate cell excitability. K_V 7 activators, such as retigabine, were used to treat epilepsy but caused urinary retention. Using electrophysiological recordings from freshly isolated mouse urinary bladder smooth muscle (UBSM) cells, isometric contractility of bladder strips, and ex vivo measurements of bladder afferent activity, we explored the role of K_V 7 channels as regulators of murine urinary bladder function. The K_V 7 activator retigabine (10 μM) had no effect on voltage-dependent K⁺ currents or resting membrane potential of UBSM cells, suggesting that these cells lacked retigabine-sensitive K_V 7 channels. The K_V 7 inhibitor XE-991 (10 μM) inhibited UBSM K⁺ currents; the properties of these currents, however, were typical of K_V 2 channels and not K_V 7 channels. Retigabine inhibited voltage-dependent Ca²⁺ channel (VDCC) currents and reduced steady-state contractions to 60 mM KCl in bladder strips, suggesting that reduction in VDCC current was sufficient to directly affect UBSM function. To determine if retigabine altered ex vivo bladder sensory outflow, we measured afferent activity during simulated transient contractions (TCs) of the bladder wall. Simulated TCs caused bursts of afferent activity that were nearly abolished by retigabine. The effects of retigabine were blocked by co-incubation with XE-991, suggesting specific activation of K_V 7 channels on afferent nerves. These results indicate that retigabine primarily affects urinary bladder function by inhibiting TC generation and afferent nerve activity, which are key to sensing bladder fullness. Any direct inhibition of UBSM contractility is likely to be from non-specific effects on VDCCs and K_V 2 channels.

Urothelial Senescence in the Pathophysiology of Diabetic Bladder Dysfunction-A Novel Hypothesis

Diabetic bladder dysfunction (DBD) is a well-recognized and common symptom affecting up to 50% of all diabetic patients. DBD has a broad range of clinical presentations ranging from overactive to underactive bladder symptoms that develops in middle-aged to elderly patients with long standing and poorly controlled diabetes. Low efficacy of current therapeutics and lifestyle interventions combined with high national healthcare costs highlight the need for more research into bladder dysfunction pathophysiology and novel treatment options. Cellular senescence is an age-related physiologic process in which cells undergo irreversible growth arrest induced by replicative exhaustion and damaging insults. While controlled senescence negatively regulates cell proliferation and promotes tissue regeneration, uncontrolled senescence is known to result in tissue dysfunction through enhanced secretion of inflammatory factors. This review presents previous scientific findings and current hypotheses that characterize diabetic bladder dysfunction. Further, we propose the novel hypothesis that cellular senescence within the urothelial layer of the bladder contributes to the pro-inflammatory/pro-oxidant environment and symptoms of diabetic bladder dysfunction. Our results show increased cellular senescence in the urothelial layer of the bladder; however, whether this phenomenon is the cause or effect of DBD is unknown. The urothelial layer of the bladder is made up of transitional epithelia specialized to contract and expand with demand and plays an active role in transmission by modulating afferent activity. Transition from normal functioning urothelial cells to secretory senescence cells would not only disrupt the barrier function of this layer but may result in altered signaling and sensation of bladder fullness; dysfunction of this layer is known to result in symptoms of frequency and urgency. Future DBD therapeutics may benefit from targeting and preventing early transition of urothelial cells to senescent cells.

An ex vivo bladder model with detrusor smooth muscle removed to analyse biologically active mediators released from the suburothelium

KEY POINTS

Studies of urothelial cells, bladder sheets or lumens of filled bladders have suggested that mediators released from urothelium into suburothelium (SubU)/lamina propria (LP) activate mechanisms controlling detrusor excitability. None of these approaches, however, has enabled direct assessment of availability of mediators at SubU/LP during filling. We developed an ex vivo mouse bladder preparation with intact urothelium and SubU/LP but no detrusor, which allows direct access to the SubU/LP surface of urothelium during filling. Pressure-volume measurements during filling demonstrated that bladder compliance is governed primarily by the urothelium. Measurements of purine mediators in this preparation demonstrated asymmetrical availability of purines in lumen and SubU/LP, suggesting that interpretations based solely on intraluminal measurements of mediators may be inaccurate. The preparations are suitable for assessments of release, degradation and transport of mediators in SubU/LP during bladder filling, and are superior to experimental approaches previously used for urothelium research.

ABSTRACT

The purpose of this study was to develop a decentralized (ex vivo) detrusor smooth muscle (DSM)-denuded mouse bladder preparation, a novel model that enables studies on availability of urothelium-derived mediators at the luminal and anti-luminal aspects of the urothelium during filling. Urinary bladders were excised from C57BL6/J mice and the DSM was removed by fine-scissor dissection without touching the mucosa. Morphology and cell composition of the preparation wall, pressure-volume relationships during filling, and fluorescent dye permeability of control, protamine sulfate- and lipopolysaccharide-treated denuded bladders were characterized. The preparation wall contained intact urothelium and suburothelium (SubU)/lamina propria (LP) and lacked the DSM and the serosa. The utility of the model for physiological research was validated by measuring release, metabolism and transport of purine mediators at SubU/LP and in bladder lumen during filling. We determined asymmetrical availability of purines (e.g. ATP, ADP, AMP and adenosine) in lumen and at SubU/LP during filling, suggesting differential mechanisms of release, degradation and bilateral transurothelial transport of purines during filling. Some observations were validated in DSM-denuded bladder of the cynomolgus monkey (Macaca fascicularis). The novel model was superior to current models utilized to study properties of the urothelium (e.g. cultured urothelial cells, bladder mucosa sheets mounted in Ussing chambers or isolated bladder strips in organ baths) in that it enabled direct access to the vicinity of SubU/LP during authentic bladder filling. The model is particularly suitable for understanding local mechanisms of urothelium-DSM connectivity and for broad understanding of the role of urothelium in regulating continence and voiding.

Ca2+ signalling in mouse urethral smooth muscle in situ: role of Ca2+ stores and Ca2+ influx mechanisms

KEY POINTS

Contraction of urethral smooth muscle cells (USMCs) contributes to urinary continence. Ca2+ signalling in USMCs was investigated in intact urethral muscles using a genetically encoded Ca2+ sensor, GCaMP3, expressed selectively in USMCs. USMCs were spontaneously active in situ, firing intracellular Ca2+ waves that were asynchronous at different sites within cells and between adjacent cells. Spontaneous Ca2+ waves in USMCs were myogenic but enhanced by adrenergic or purinergic agonists and decreased by nitric oxide. Ca2+ waves arose from inositol trisphosphate type 1 receptors and ryanodine receptors, and Ca2+ influx by store-operated calcium entry was required to maintain Ca2+ release events. Ca2+ release and development of Ca2+ waves appear to be the primary source of Ca2+ for excitation-contraction coupling in the mouse urethra, and no evidence was found that voltage-dependent Ca2+ entry via L-type or T-type channels was required for responses to α adrenergic responses.

ABSTRACT

Urethral smooth muscle cells (USMCs) generate myogenic tone and contribute to urinary continence. Currently, little is known about Ca2+ signalling in USMCs in situ, and therefore little is known about the source(s) of Ca2+ required for excitation-contraction coupling. We characterized Ca2+ signalling in USMCs within intact urethral muscles using a genetically encoded Ca2+ sensor, GCaMP3, expressed selectively in USMCs. USMCs fired spontaneous intracellular Ca2+ waves that did not propagate cell-to-cell across muscle bundles. Ca2+ waves increased dramatically in response to the α1 adrenoceptor agonist phenylephrine (10 μm) and to ATP (10 μm). Ca2+ waves were inhibited by the nitric oxide donor DEA NONOate (10 μm). Ca2+ influx and release from sarcoplasmic reticulum stores contributed to Ca2+ waves, as Ca2+ free bathing solution and blocking the sarcoplasmic Ca2+ -ATPase abolished activity. Intracellular Ca2+ release involved cooperation between ryanadine receptors and inositol trisphosphate receptors, as tetracaine and ryanodine (100 μm) and xestospongin C (1 μm) reduced Ca2+ waves. Ca2+ waves were insensitive to L-type Ca2+ channel modulators nifedipine (1 μm), nicardipine (1 μm), isradipine (1 μm) and FPL 64176 (1 μm), and were unaffected by the T-type Ca2+ channel antagonists NNC-550396 (1 μm) and TTA-A2 (1 μm). Ca2+ waves were reduced by the store operated Ca2+ entry blocker SKF 96365 (10 μm) and by an Orai antagonist, GSK-7975A (1 μm). The latter also reduced urethral contractions induced by phenylephrine, suggesting that Orai can function effectively as a receptor-operated channel. In conclusion, Ca2+ waves in mouse USMCs are a source of Ca2+ for excitation-contraction coupling in urethral muscles.

Rhythmic Calcium Events in the Lamina Propria Network of the Urinary Bladder of Rat Pups

The lamina propria contains a dense network of cells, including interstitial cells (ICs), that may play a role in bladder function by modulating communication between urothelium, nerve fibers and smooth muscle or acting as pacemakers. Transient receptor potential vanilloid 4 (TRPV4) channels allow cation influx and may be involved in sensing stretch or chemical irritation in urinary bladder. Urothelium was removed from rats (P0-Adult), cut into strips, and loaded with a Ca²⁺ fluorescent dye (Fluo-2 AM leak resistant or Cal 520) for 90 min (35-37°C) to measure Ca²⁺ events. Ca²⁺ events were recorded for a period of 60 seconds (s) in control and after drug treatment. A heterogeneous network of cells was identified at the interface of the urothelium and lamina propria of postnatal rat pups, aged ≤ postnatal (P) day 21, with diverse morphology (round, fusiform, stellate with numerous projections) and expressing platelet-derived growth factor receptor alpha (PDGFRα)- and TRPV4-immunoreactivity (IR). Ca²⁺ transients occurred at a slow frequency with an average interval of 30 ± 8.6 s. Waveform analyses of Ca²⁺ transients in cells in the lamina propria network revealed long duration Ca²⁺ events with slow upstrokes. We observed slow propagating waves of activity in the lamina propria network that displayed varying degrees of coupling. Application of the TRPV4 agonist, GSK1016790 (100 nM), increased the duration of Ca²⁺ events, the number of cells with Ca²⁺ events and the integrated Ca²⁺ activity corresponding to propagation of activity among cells in the lamina propria network. However, GSK2193874 (1 μM), a potent antagonist of TRPV4 channels, was without effect. ATP (1 μM) perfusion increased the number of cells in the lamina propria exhibiting Ca²⁺ events and produced tightly coupled network activity. These findings indicate that ATP and TRPV4 can activate cells in the laminar propria network, leading to the appearance of organized propagating wavefronts.

Platelet-derived growth factor receptor alpha-positive cells: a new cell type in the human ureteropelvic junction

BACKGROUND

Ureteropelvic junction (UPJ) obstruction is the most common cause of congenital hydronephrosis. Normal ureteral motility requires coordinated interaction between neurons, smooth muscle cells (SMCs), and interstitial Cajal-like cells (IC-LCs). Recently, a new type of interstitial cell, platelet-derived growth factor receptor α-positive (PDGFRα⁺) cells, was discovered in the gastrointestinal tract and bladder.MethodsWe used immunohistochemistry to study PDGFRα protein distribution in normal human UPJ and congenital UPJ obstruction. Western blot and real-time PCR (RT-PCR) were used to study PDGFRα protein and gene expression levels. In addition, closely associated cells and small conductance Ca²⁺-activated K⁺ (SK) channels were investigated.ResultsPDGFRα⁺ cells were distinct from IC-LCs and SMCs and were in close proximity to nerve fibers. PDGFRα⁺ cells expressed SK3 channels, which are thought to mediate purinergic inhibitory neurotransmission in SMCs. The distribution of PDGFRα⁺ cells was similar in UPJ obstruction vs.

CONTROLS

However, the expression of SK3 channels in PDGFRα⁺ cells was decreased in UPJ obstruction vs.

CONTROLS

ConclusionThis study shows, for the first time, the PDGFRα⁺ cell expression in the human UPJ. Altered SK3 channel expression observed in PDGFRα⁺ cells in UPJ obstruction suggests that the impairment of SK3 activity across the UPJ may perturb upper urinary tract peristalsis in this urological condition.

A new cellular type in invertebrates: first evidence of telocytes in leech Hirudo medicinalis

Telocytes, a peculiar cell type, were recently found in vertebrates. Hence this cell system has been reported as ubiquitous in the bodies of mammals and interpreted as an important player in innate immunity and tissue regeneration, it is reasonable to look for it also in invertebrates, that rely their integrity solely by innate immunity. Here we describe, at morphological and functional level, invertebrate telocytes from the body of leech Hirudo medicinalis (Annelida), suggesting how these cells, forming a resident stromal 3D network, can influence or participate in different events. These findings support the concepts that leech telocytes: i) are organized in a cellular dynamic and versatile 3D network likewise the vertebrate counterpart; ii) are an evolutionarily conserved immune-neuroendocrine system; iii) form an immuno-surveillance system of resident cells responding faster than migrating immunocytes recruited in stimulated area; iv) communicate with neighbouring cells directly and indirectly, via cell-cell contacts and soluble molecules secreted by multivesicular bodies; v) present within neo-vessels, share with immunocytes the mesodermal lineage; vi) are involved in regenerative processes. In conclusion, we propose that HmTCs, integrating so different functions, might explain the innate immune memory and can be associated with several aged related diseases.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

Premature contractions of the bladder are suppressed by interactions between TRPV4 and SK3 channels in murine detrusor PDGFRα+ cells

During filling, urinary bladder volume increases dramatically with little change in pressure. This is accomplished by suppressing contractions of the detrusor muscle that lines the bladder wall. Mechanisms responsible for regulating detrusor contraction during filling are poorly understood. Here we describe a novel pathway to stabilize detrusor excitability involving platelet-derived growth factor receptor-α positive (PDGFRα⁺) interstitial cells. PDGFRα⁺ cells express small conductance Ca²⁺-activated K⁺ (SK) and TRPV4 channels. We found that Ca²⁺ entry through mechanosensitive TRPV4 channels during bladder filling stabilizes detrusor excitability. GSK1016790A (GSK), a TRPV4 channel agonist, activated a non-selective cation conductance that coupled to activation of SK channels. GSK induced hyperpolarization of PDGFRα⁺ cells and decreased detrusor contractions. Contractions were also inhibited by activation of SK channels. Blockers of TRPV4 or SK channels inhibited currents activated by GSK and increased detrusor contractions. TRPV4 and SK channel blockers also increased contractions of intact bladders during filling. Similar enhancement of contractions occurred in bladders of Trpv4 ^-/- mice during filling. An SK channel activator (SKA-31) decreased contractions during filling, and rescued the overactivity of Trpv4 ^-/- bladders. Our findings demonstrate how Ca²⁺ influx through TRPV4 channels can activate SK channels in PDGFRα⁺ cells and prevent bladder overactivity during filling.

Adaptive changes of telocytes in the urinary bladder of patients affected by neurogenic detrusor overactivity

Urinary bladder activity involves central and autonomic nervous systems and bladder wall. Studies on the pathogenesis of voiding disorders such as the neurogenic detrusor overactivity (NDO) due to suprasacral spinal cord lesions have emphasized the importance of an abnormal handling of the afferent signals from urothelium and lamina propria (LP). In the LP (and detrusor), three types of telocytes (TC) are present and form a 3D-network. TC are stromal cells able to form the scaffold that contains and organizes the connective components, to serve as guide for tissue (re)-modelling, to produce trophic and/or regulatory molecules, to share privileged contacts with the immune cells. Specimens of full thickness bladder wall from NDO patients were collected with the aim to investigate possible changes of the three TC types using histology, immunohistochemistry and transmission electron microscopy. The results show that NDO causes several morphological TC changes without cell loss or network interruption. With the exception of those underlying the urothelium, all the TC display signs of activation (increase in Caveolin1 and caveolae, αSMA and thin filaments, Calreticulin and amount of cisternae of the rough endoplasmic reticulum, CD34, euchromatic nuclei and large nucleoli). In all the specimens, a cell infiltrate, mainly consisting in plasma cells located in the vicinity or taking contacts with the TC, is present. In conclusion, our findings show that NDO causes significant changes of all the TC. Notably, these changes can be interpreted as TC adaptability to the pathological condition likely preserving each of their peculiar functions.

The Telocyte Subtypes

Several cells are endowed in the interstitial space of the connective tissue; among them, a peculiar type has been recently described and named telocyte (TC). The increasing interest on this cell type has allowed identifying it in almost all the organs. All TCs have a proper ultrastructural feature that makes them undoubtedly recognizable under the transmission electron microscope (TEM). On the contrary, a complex often confusing picture comes out from the immunohistochemical investigations either due to the technical procedures used or, intriguingly, to the possibility that diverse subtypes of TC might exist.Among the several markers used to label the TC, the most common are the CD34 and the PDGFRalpha, and, in many organs, the TC expresses both these markers. An exception is represented by the human urinary bladder where none of the TC, as recognized under the TEM, was double labelled. All the data indicate that TCs show immunohistochemical differences depending on the organ where they are located and/or the animal species.On the basis of their ubiquitous distribution, TCs are unanimously considered organizers of the connective tissue because of their ability to form 3-D networks. Close to this common role, numerous other roles have been attributed to the TC. Indeed, each of the TC subtype likely plays an own organ-/tissue-specific role contributing to different aspects of physiological regulation in the various anatomical niches they occupy.

Proliferation of Interstitial Cells in the Cyclophosphamide-Induced Cystitis and the Preventive Effect of Imatinib

Cyclophosphamide- (CYP-) induced cystitis in the rat is a well-known model of bladder inflammation that leads to an overactive bladder, a process that appears to involve enhanced nitric oxide (NO) production. We investigated the changes in the number and distribution of interstitial cells (ICs) and in the expression of endothelial NO synthase (eNOS) in the bladder and urethra of rats subjected to either intermediate or chronic CYP treatment. Pronounced hyperplasia and hypertrophy of ICs were evident within the lamina propria and in the muscle layer. IC immunolabeling with CD34, PDGFRα, and vimentin was enhanced, as reflected by higher colocalization indexes of the distinct pairs of markers. Moreover, de novo expression of eNOS was evident in vimentin and CD34 positive ICs. Pretreatment with the receptor tyrosine kinase inhibitor Imatinib prevented eNOS expression and ICs proliferation, as well as the increased voiding frequency and urinary tract weight provoked by CYP. As similar results were obtained in the urethra, urethritis may contribute to the uropathology of CYP-induced cystitis.

Spatiotemporal analysis of spontaneous myogenic contractions in the urinary bladder of the rabbit: timing and patterns reflect reported electrophysiology

The dynamics of propagating myogenic contractions in the wall of the resting ex vivo urinary bladder of the rabbit were characterized by spatiotemporal maps and related to cyclic variation in intravesical pressure (P_ves). Patches of propagating contractions (PPCs) enlarged and involuted in near synchrony with peaks in P_ves [mean 3.85  ± 0.3 cycles per minute (cpm)] and were preceded by regions of stretch. The maximum area of the bladder undergoing contraction (55.28 ± 2.65%) and the sizes of individual PPCs (42.61 ± 1.65 mm²) coincided with the peak in P_ves PPCs originated and propagated within temporary patch domains (TPDs) and comprised groups of nearly synchronous cyclic propagating individual contractions (PICs). The TPDs were located principally along the vertical axis of the anterior surface of the bladder. The sites of origin of PICs within PPCs were inconsistent, consecutive contractions often propagating in opposite directions along linear maps of strain rate. Similar patterns of movement occurred in areas of the anterior bladder wall that had been stripped of mucosa. P_ves varied cyclically with area of contraction and with the indices of aggregation of PPCs, indicating that they grew by peripheral enlargement and collision without annihilation. The synchronization of PICs within PPCs was sometimes lost, uncoordinated PICs then occurring irregularly (between 4 and 20 cpm) having little effect on P_ves We postulate that the formation and involution of PPCs within a TPD resulted from cyclic variation in excitation that increased the incidence and distance over which component PICs propagated.

[Role of telocytes in the heart in health and diseases]

This review summarizes the data available in the literature on the development, structure, and function of telocytes (TCs) and their role in the heart in health and diseases. At the present time, TCs have been found in many organs of mammals and humans. TC is a small oval cell that contains a nucleus surrounded by small amounts of cytoplasm, with extremely long and thin processes named telopodias. TCs have unique ultrastructural and immunohistochemical features; double positive labeling for CD34/PDGFR-β and CD34/vimentin is suitable for their identification. The role of TCs in the heart at different study stages is the subject of debate. There are currently available data on a decline in the number of cardiac TCs in patients with various heart diseases. Relying on a number of investigations showing that TCs are present in the subepicardial stem cell niches, the authors consider a hypothesis for the key role of cardiac TCs in the regeneration and reparation of the heart.

Teaching a changing paradigm in physiology: a historical perspective on gut interstitial cells

The study and teaching of gastrointestinal (GI) physiology necessitates an understanding of the cellular basis of contractile and electrical coupling behaviors in the muscle layers that comprise the gut wall. Our knowledge of the cellular origin of GI motility has drastically changed over the last 100 yr. While the pacing and coordination of GI contraction was once thought to be solely attributable to smooth muscle cells, it is now widely accepted that the motility patterns observed in the GI tract exist as a result of a multicellular system, consisting of not only smooth muscle cells but also enteric neurons and distinct populations of specialized interstitial cells that all work in concert to ensure proper GI functions. In this historical perspective, we focus on the emerging role of interstitial cells in GI motility and examine the key discoveries and experiments that led to a major shift in a paradigm of GI physiology regarding the role of interstitial cells in modulating GI contractile patterns. A review of these now classic experiments and papers will enable students and educators to fully appreciate the complex, multicellular nature of GI muscles as well as impart lessons on how shifting paradigms in physiology are fueled by new technologies that lead to new emerging discoveries.

The stem cell growth factor receptor KIT is not expressed on interstitial cells in bladder

The mast/stem cell growth factor receptor KIT has long been assumed to be a specific marker for interstitial cells of Cajal (ICC) in the bladder, with possible druggable perspectives. However, several authors have challenged the presence of KIT⁺ICC in recent years. The aim of this study was therefore to attempt to clarify the conflicting reports on KIT expression in the bladder of human beings, rat, mouse and guinea pig and to elucidate the possible role of antibody‐related issues and interspecies differences in this matter. Fresh samples were obtained from human, rat, mouse and guinea pig cystectomies and processed for single/double immunohistochemistry/immunofluorescence. Specific antibodies against KIT, mast cell tryptase (MCT), anoctamin‐1 (ANO1) and vimentin were used to characterize the cell types expressing KIT. Gut (jejunum) tissue was used as an external antibody control. Our results revealed KIT expression on mast cells but not on ICC in human, rat, mouse and guinea pig bladder. Parallel immunohistochemistry showed KIT expression on ICC in human, rat, mouse and guinea pig gut, which confirmed the selectivity of the KIT antibody clones. In conclusion, we have shown that KIT⁺ cells in human, rat, mouse and guinea pig bladder are mast cells and not ICC. The present report is important as it opposes the idea that KIT⁺ICC are present in bladder. In this perspective, functional concepts of KIT⁺ICC being involved in sensory and/or motor aspects of bladder physiology should be revised.