Formation of human prostate tissue from embryonic stem cells

Prostatic lineage differentiation from human embryonic stem cells through inducible expression of NKX3-1

BACKGROUND

Understanding the lineage differentiation of human prostate not only is crucial for basic research on human developmental biology but also significantly contributes to the management of prostate-related disorders. Current knowledge mainly relies on studies on rodent models, lacking human-derived alternatives despite clinical samples may provide a snapshot at certain stage. Human embryonic stem cells can generate all the embryonic lineages including the prostate, and indeed a few studies demonstrate such possibility based on co-culture or co-transplantation with urogenital mesenchyme into mouse renal capsule.

METHODS

To establish a stepwise protocol to obtain prostatic organoids in vitro from human embryonic stem cells, we apply chemicals and growth factors by mimicking the regulation network of transcription factors and signal transduction pathways, and construct cell lines carrying an inducible NKX3-1 expressing cassette, together with three-dimensional culture system. Unpaired t test was applied for statistical analyses.

RESULTS

We first successfully generate the definitive endoderm, hindgut, and urogenital sinus cells. The embryonic stem cell-derived urogenital sinus cells express prostatic key transcription factors AR and FOXA1, but fail to express NKX3-1. Therefore, we construct NKX3-1-inducible cell line by homologous recombination, which is eventually able to yield AR, FOXA1, and NKX3-1 triple-positive urogenital prostatic lineage cells through stepwise differentiation. Finally, combined with 3D culture we successfully derive prostate-like organoids with certain structures and prostatic cell populations.

CONCLUSIONS

This study reveals the crucial role of NKX3-1 in prostatic differentiation and offers the inducible NKX3-1 cell line, as well as provides a stepwise differentiation protocol to generate human prostate-like organoids, which should facilitate the studies on prostate development and disease pathogenesis.

Engineering prostate cancer in vitro: what does it take?

A key challenge in the clinical management and cause of treatment failure of prostate cancer (PCa) is its molecular, cellular and clinical heterogeneity. Modelling systems that fully recapitulate clinical diversity and resistant phenotypes are urgently required for the development of successful personalised PCa therapies. The advent of the three-dimensional (3D) organoid model has revolutionised preclinical cancer research through reflecting heterogeneity and offering genomic and environmental manipulation that has opened up unparalleled opportunities for applications in disease modelling, high-throughput drug screening and precision medicine. Despite these remarkable achievements of organoid technology, several shortcomings in emulating the complex tumor microenvironment and dynamic process of metastasis as well as the epigenome profile limit organoids achieving true in vivo functionality. Technological advances in tissue engineering have enabled the development of innovative tools to facilitate the design of improved 3D cancer models. In this review, we highlight the current in vitro 3D PCa models with a special focus on organoids and discuss engineering approaches to create more physiologically relevant PCa organoid models and maximise their translational relevance that ultimately will help to realise the transformational power of precision medicine.

Human prostate organoid generation and the identification of prostate development drivers using inductive rodent tissues

The reactivation of developmental genes and pathways during adulthood may contribute to pathogenesis of diseases such as prostate cancer. Analysis of the mechanistic links between development and disease could be exploited to identify signalling pathways leading to disease in the prostate. However, the mechanisms underpinning prostate development require further characterisation to interrogate fully the link between development and disease. Previously, our group developed methods to produce prostate organoids using induced pluripotent stem cells (iPSCs). Here, we show that human iPSCs can be differentiated into prostate organoids using neonatal rat seminal vesicle mesenchyme in vitro. The organoids can be used to study prostate development or modified to study prostate cancer. We also elucidated molecular drivers of prostate induction through RNA-sequencing analyses of the rat urogenital sinus and neonatal seminal vesicles. We identified candidate drivers of prostate development evident in the inductive mesenchyme and epithelium involved with prostate specification. Our top candidates included Spx, Trib3, Snai1, Snai2, Nrg2 and Lrp4. This work lays the foundations for further interrogation of the reactivation of developmental genes in adulthood, leading to prostate disease.

Prostate organogenesis

Prostate organogenesis begins during embryonic development and continues through puberty when the prostate becomes an important exocrine gland of the male reproductive system. The specification and growth of the prostate is regulated by androgens and is largely a result of cell-cell communication between the epithelium and mesenchyme. The fields of developmental and cancer biology have long been interested in prostate organogenesis because of its relevance for understanding prostate diseases, and research has expanded in recent years with the advent of novel technologies, including genetic-lineage tracing, single-cell RNA sequencing and organoid culture methods, that have provided important insights into androgen regulation, epithelial cell origins and cellular heterogeneity. We discuss these findings, putting them into context with what is currently known about prostate organogenesis.

A Review of Prostate Organogenesis and a Role for iPSC-Derived Prostate Organoids to Study Prostate Development and Disease

The prostate is vulnerable to two major age-associated diseases, cancer and benign enlargement, which account for significant morbidity and mortality for men across the globe. Prostate cancer is the most common cancer reported in men, with over 1.2 million new cases diagnosed and 350,000 deaths recorded annually worldwide. Benign prostatic hyperplasia (BPH), characterised by the continuous enlargement of the adult prostate, symptomatically afflicts around 50% of men worldwide. A better understanding of the biological processes underpinning these diseases is needed to generate new treatment approaches. Developmental studies of the prostate have shed some light on the processes essential for prostate organogenesis, with many of these up- or downregulated genes expressions also observed in prostate cancer and/or BPH progression. These insights into human disease have been inferred through comparative biological studies relying primarily on rodent models. However, directly observing mechanisms of human prostate development has been more challenging due to limitations in accessing human foetal material. Induced pluripotent stem cells (iPSCs) could provide a suitable alternative as they can mimic embryonic cells, and iPSC-derived prostate organoids present a significant opportunity to study early human prostate developmental processes. In this review, we discuss the current understanding of prostate development and its relevance to prostate-associated diseases. Additionally, we detail the potential of iPSC-derived prostate organoids for studying human prostate development and disease.

Single-cell transcriptomics identifies a distinct luminal progenitor cell type in distal prostate invagination tips

The identification of prostate stem/progenitor cells and characterization of the prostate epithelial cell lineage hierarchy are critical for understanding prostate cancer initiation. Here, we characterized 35,129 cells from mouse prostates, and identified a unique luminal cell type (termed type C luminal cell (Luminal-C)) marked by Tacstd2, Ck4 and Psca expression. Luminal-C cells located at the distal prostate invagination tips (termed Dist-Luminal-C) exhibited greater capacity for organoid formation in vitro and prostate epithelial duct regeneration in vivo. Lineage tracing of Luminal-C cells indicated that Dist-Luminal-C cells reconstituted distal prostate luminal lineages through self-renewal and differentiation. Deletion of Pten in Dist-Luminal-C cells resulted in prostatic intraepithelial neoplasia. We further characterized 11,374 human prostate cells and confirmed the existence of h-Luminal-C cells. Our study provides insights into the prostate lineage hierarchy, identifies Dist-Luminal-C cells as the luminal progenitor cell population in invagination tips and suggests one of the potential cellular origins of prostate cancer.

Pluripotent stem cell differentiation as an emerging model to study human prostate development

Prostate development is a complex process, and knowledge about this process is increasingly required for both basic developmental biology studies and clinical prostate cancer research, as prostate tumorigenesis can be regarded as the restoration of development in the adult prostate. Using rodent animal models, scientists have revealed that the development of the prostate is mainly mediated by androgen receptor (AR) signaling and that some other signaling pathways also play indispensable roles. However, there are still many unknowns in human prostate biology, mainly due to the limited availability of proper fetal materials. Here, we first briefly review prostate development with a focus on the AR, WNT, and BMP signaling pathways is necessary for prostate budding/BMP signaling pathways. Based on the current progress in in vitro prostatic differentiation and organoid techniques, we propose human pluripotent stem cells as an emerging model to study human prostate development.

Propagation of human prostate tissue from induced pluripotent stem cells

Primary culture of human prostate organoids and patient‐derived xenografts is inefficient and has limited access to clinical tissues. This hampers their use for translational study to identify new treatments. To overcome this, we established a complementary approach where rapidly proliferating and easily handled induced pluripotent stem cells enabled the generation of human prostate tissue in vivo and in vitro. By using a coculture technique with inductive urogenital sinus mesenchyme, we comprehensively recapitulated in situ 3D prostate histology, and overcame limitations in the primary culture of human prostate stem, luminal and neuroendocrine cells, as well as the stromal microenvironment. This model now unlocks new opportunities to undertake translational studies of benign and malignant prostate disease.

Novel therapeutic approaches of tissue engineering in male infertility

Male reproductive organ plays an important role in sperm production, maintenance and entry to the female reproductive tract, as well as generation and secretion of male sex hormones responsible for the health of male reproductive system. The purpose of this paper is to discuss the experimental and clinical evidence on the utilization of tissue engineering techniques in treating male infertility. Tissue engineering (TE) and regenerative medicine have developed new approaches to treat patients with reproductive disorders such as iatrogenic injuries, congenital abnormalities, and trauma. In some cases, including congenital defects and undescended testis or hypogonadism, the sperm samples are not retrieved. This makes TE a possible future strategy for restoration of male fertility. Here, we have summarized the recent advances in experimental and clinical application of cell-, tissue-, and organ-based regenerative medicine in male reproductive disorders.

Engineering Prostate Cancer from Induced Pluripotent Stem Cells-New Opportunities to Develop Preclinical Tools in Prostate and Prostate Cancer Studies

One of the key issues hampering the development of effective treatments for prostate cancer is the lack of suitable, tractable, and patient-specific in vitro models that accurately recapitulate this disease. In this review, we address the challenges of using primary cultures and patient-derived xenografts to study prostate cancer. We describe emerging approaches using primary prostate epithelial cells and prostate organoids and their genetic manipulation for disease modelling. Furthermore, the use of human prostate-derived induced pluripotent stem cells (iPSCs) is highlighted as a promising complimentary approach. Finally, we discuss the manipulation of iPSCs to generate 'avatars' for drug disease testing. Specifically, we describe how a conceptual advance through the creation of living biobanks of "genetically engineered cancers" that contain patient-specific driver mutations hold promise for personalised medicine.

Cellular and Molecular Mechanisms Underlying Prostate Cancer Development: Therapeutic Implications

Prostate cancer is the most frequent nonskin cancer and second most common cause of cancer-related deaths in man. Prostate cancer is a clinically heterogeneous disease with many patients exhibiting an aggressive disease with progression, metastasis, and other patients showing an indolent disease with low tendency to progression. Three stages of development of human prostate tumors have been identified: intraepithelial neoplasia, adenocarcinoma androgen-dependent, and adenocarcinoma androgen-independent or castration-resistant. Advances in molecular technologies have provided a very rapid progress in our understanding of the genomic events responsible for the initial development and progression of prostate cancer. These studies have shown that prostate cancer genome displays a relatively low mutation rate compared with other cancers and few chromosomal loss or gains. The ensemble of these molecular studies has led to suggest the existence of two main molecular groups of prostate cancers: one characterized by the presence of ERG rearrangements (~50% of prostate cancers harbor recurrent gene fusions involving ETS transcription factors, fusing the 5' untranslated region of the androgen-regulated gene TMPRSS2 to nearly the coding sequence of the ETS family transcription factor ERG) and features of chemoplexy (complex gene rearrangements developing from a coordinated and simultaneous molecular event), and a second one characterized by the absence of ERG rearrangements and by the frequent mutations in the E3 ubiquitin ligase adapter SPOP and/or deletion of CDH1, a chromatin remodeling factor, and interchromosomal rearrangements and SPOP mutations are early events during prostate cancer development. During disease progression, genomic and epigenomic abnormalities accrued and converged on prostate cancer pathways, leading to a highly heterogeneous transcriptomic landscape, characterized by a hyperactive androgen receptor signaling axis.

Identification of genes expressed in a mesenchymal subset regulating prostate organogenesis using tissue and single cell transcriptomics

Prostate organogenesis involves epithelial growth controlled by inductive signalling from specialised mesenchymal subsets. To identify pathways active in mesenchyme we used tissue and single cell transcriptomics to define mesenchymal subsets and subset-specific transcript expression. We documented transcript expression using Tag-seq and RNA-seq in female rat Ventral Mesenchymal Pad (VMP) as well as adjacent urethra comprised of smooth muscle and peri-urethral mesenchyme. Transcripts enriched in female VMP were identified with Tag-seq of microdissected tissue, RNA-seq of cell populations, and single cells. We identified 400 transcripts as enriched in the VMP using bio-informatic comparisons of Tag-seq and RNA-seq data, and 44 were confirmed by single cell RNA-seq. Cell subset analysis showed that VMP and adjacent mesenchyme were composed of distinct cell types and that each tissue contained two subgroups. Markers for these subgroups were highly subset specific. Thirteen transcripts were validated by qPCR to confirm cell specific expression in microdissected tissues, as well as expression in neonatal prostate. Immunohistochemical staining demonstrated that Ebf3 and Meis2 showed a restricted expression pattern in female VMP and prostate mesenchyme. We conclude that prostate inductive mesenchyme shows limited cellular heterogeneity and that transcriptomic analysis identified new mesenchymal subset transcripts associated with prostate organogenesis.

A computational systems approach identifies synergistic specification genes that facilitate lineage conversion to prostate tissue

To date, reprogramming strategies for generating cell types of interest have been facilitated by detailed understanding of relevant developmental regulatory factors. However, identification of such regulatory drivers often represents a major challenge, as specific gene combinations may be required for reprogramming. Here we show that a computational systems approach can identify cell type specification genes (master regulators) that act synergistically, and demonstrate its application for reprogramming of fibroblasts to prostate tissue. We use three such master regulators (FOXA1, NKX3.1 and androgen receptor, AR) in a primed conversion strategy starting from mouse fibroblasts, resulting in prostate tissue grafts with appropriate histological and molecular properties that respond to androgen-deprivation. Moreover, generation of reprogrammed prostate does not require traversal of a pluripotent state. Thus, we describe a general strategy by which cell types and tissues can be generated even with limited knowledge of the developmental pathways required for their specification in vivo.

Contribution of Caudal Müllerian Duct Mesenchyme to Prostate Development

A fundamental understanding of prostate development and tissue homeostasis has the high potential to reveal mechanisms for prostate disease initiation and identify novel therapeutic approaches for disease prevention and treatment. Our current understanding of prostate lineage specification stems from the use of developmental model systems that rely upon the embryonic preprostatic urogenital sinus mesenchyme to induce the formation of mature prostate epithelial cells. It is unclear, however, how the urogenital sinus epithelium can derive both adult urethral glands and prostate epithelia. Furthermore, the vast disparity in disease initiation between these two glands highlights key developmental factors that predispose prostate epithelia to hyperplasia and cancer. In this study we demonstrate that the caudal Müllerian duct mesenchyme (CMDM) drives prostate epithelial differentiation and is a key determinant in cell lineage specification between urethral glands and prostate epithelia. Utilizing both human embryonic stem cells and mouse embryonic tissues, we document that the CMDM is capable of inducing the specification of androgen receptor, prostate-specific antigen, NKX3.1, and Hoxb13-positive prostate epithelial cells. These results help to explain key developmental differences between prostate and urethral gland differentiation, and implicate factors secreted by the caudal Müllerian duct as novel targets for prostate disease prevention and treatment.

Stem Cells as Hormone Targets That Lead to Increased Cancer Susceptibility

Major advances during the past decade have permitted a clearer understanding of processes that regulate stem cell self-renewal and lineage commitment toward differentiated progeny that populate all tissues. Considerable evidence has also accumulated to indicate that aberrations in the stem and progenitor cell populations can lead to increased cancer risk in specific organs systems. It is long recognized that environmental factors play a major role in cancer etiology, and emerging data suggest that endocrine-disrupting chemicals (EDCs) may contribute to an increased cancer risk. Using the prostate gland as a model system, the present review highlights recent data that find that estrogens and EDCs can reprogram prostate stem and progenitor cell populations, leading to increased cancer susceptibility. We propose that stem cell programming during early development in hormone-regulated tissues may lead to heightened sensitivity to early-life EDC exposures and that aberrant stem cell reprogramming by EDCs may contribute to the developmental basis of adult cancer risk.

Directed Differentiation of Human Embryonic Stem Cells into Prostate Organoids In Vitro and its Perturbation by Low-Dose Bisphenol A Exposure

Studies using rodent and adult human prostate stem-progenitor cell models suggest that developmental exposure to the endocrine disruptor Bisphenol-A (BPA) can predispose to prostate carcinogenesis with aging. Unknown at present is whether the embryonic human prostate is equally susceptible to BPA during its natural developmental window. To address this unmet need, we herein report the construction of a pioneer in vitro human prostate developmental model to study the effects of BPA. The directed differentiation of human embryonic stem cells (hESC) into prostatic organoids in a spatial system was accomplished with precise temporal control of growth factors and steroids. Activin-induced definitive endoderm was driven to prostate specification by combined exposure to WNT10B and FGF10. Matrigel culture for 20–30 days in medium containing R-Spondin-1, Noggin, EGF, retinoic acid and testosterone was sufficient for mature prostate organoid development. Immunofluorescence and gene expression analysis confirmed that organoids exhibited cytodifferentiation and functional properties of the human prostate. Exposure to 1 nM or 10 nM BPA throughout differentiation culture disturbed early morphogenesis in a dose-dependent manner with 1 nM BPA increasing and 10 nM BPA reducing the number of branched structures formed. While differentiation of branched structures to mature organoids seemed largely unaffected by BPA exposure, the stem-like cell population increased, appearing as focal stem cell nests that have not properly entered lineage commitment rather than the rare isolated stem cells found in normally differentiated structures. These findings provide the first direct evidence that low-dose BPA exposure targets hESC and perturbs morphogenesis as the embryonic cells differentiate towards human prostate organoids, suggesting that the developing human prostate may be susceptible to disruption by in utero BPA exposures.

Novel In Vivo model for combinatorial fluorescence labeling in mouse prostate

BACKGROUND

The epithelial layer of prostate glands contains several types of cells, including luminal and basal cells. Yet there is paucity of animal models to study the cellular origin of normal or neoplastic development in the prostate to facilitate the treatment of heterogenous prostate diseases by targeting individual cell lineages.

METHODS

We developed a mouse model that expresses different types of fluorescent proteins (XFPs) specifically in prostatic cells. Using an in vivo stochastic fluorescent protein combinatorial strategy, XFP signals were expressed specifically in prostate of Protein Kinase D1 (PKD1) knock-out, K-Ras(G) (12) (D) knock-in, and Phosphatase and tensin homolog (PTEN) and PKD1 double knock-out mice under the control of PB-Cre promoter.

RESULTS

In vivo XFP signals were observed in prostate of PKD1 knock-out, K-Ras(G) (12) (D) knock-in, and PTEN PKD1 double knock-out mice, which developed normal, hyperplastic, and neoplastic prostate, respectively. The patchy expression pattern of XFPs in neoplasia tissue indicated the clonal origin of cancer cells in the prostate.

CONCLUSIONS

The transgenic mouse models demonstrate combinatorial fluorescent protein expression in normal and cancerous prostatic tissues. This novel prostate-specific fluorescent labeled mouse model, which we named Prorainbow, could be useful in studying benign and malignant pathology of prostate.

Sex specific retinoic acid signaling is required for the initiation of urogenital sinus bud development

The mammalian urogenital sinus (UGS) develops in a sex specific manner, giving rise to the prostate in the male and the sinus vagina in the embryonic female. Androgens, produced by the embryonic testis, have been shown to be crucial to this process. In this study we show that retinoic acid signaling is required for the initial stages of bud development from the male UGS. Enzymes involved in retinoic acid synthesis are expressed in the UGS mesenchyme in a sex specific manner and addition of ligand to female tissue is able to induce prostate-like bud formation in the absence of androgens, albeit at reduced potency. Functional studies in mouse organ cultures that faithfully reproduce the initiation of prostate development indicate that one of the roles of retinoic acid signaling in the male is to inhibit the expression of Inhba, which encodes the βA subunit of Activin, in the UGS mesenchyme. Through in vivo genetic analysis and culture studies we show that inhibition of Activin signaling in the female UGS leads to a similar phenotype to that of retinoic acid treatment, namely bud formation in the absence of androgens. Our data also reveals that both androgens and retinoic acid have extra independent roles to that of repressing Activin signaling in the development of the prostate during fetal stages. This study identifies a novel role for retinoic acid as a mesenchymal factor that acts together with androgens to determine the position and initiation of bud development in the male UGS epithelia.

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We show that sex specific retinoic acid is required for male UGS bud initiation.

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An increase in retinoic acid can lead to prostate-like formation in females.

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We find that activin repression is a downstream target of RA signalling.

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RA is a novel mesenchymal signal regulating bud initiation along the UGS.

A preclinical xenograft model identifies castration-tolerant cancer-repopulating cells in localized prostate tumors

A lack of clinically relevant experimental models of human prostate cancer hampers evaluation of potential therapeutic agents. Currently, androgen deprivation therapy is the gold standard treatment for advanced prostate cancer, but inevitably, a subpopulation of cancer cells survives and repopulates the tumor. Tumor cells that survive androgen withdrawal are critical therapeutic targets for more effective treatments, but current model systems cannot determine when they arise in disease progression and are unable to recapitulate variable patient response to treatment. A model system was developed in which stromal-supported xenografts from multiple patients with early-stage localized disease can be tested for response to castration. The histopathology of these xenografts mimicked the original tumors, and short-term host castration resulted in reduced proliferation and increased apoptosis in tumor cells. After 4 weeks of castration, residual populations of quiescent, stem-like tumor cells remained. Without subsequent treatment, these residual cells displayed regenerative potential, because testosterone readministration resulted in emergence of rapidly proliferating tumors. Therefore, this model may be useful for revealing potential cellular targets in prostate cancer, which exist before the onset of aggressive incurable disease. Specific eradication of these regenerative tumor cells that survive castration could then confer survival benefits for patients.

Prostatic inflammation enhances basal-to-luminal differentiation and accelerates initiation of prostate cancer with a basal cell origin

Chronic inflammation has been shown to promote the initiation and progression of diverse malignancies by inducing genetic and epigenetic alterations. In this study, we investigate an alternative mechanism through which inflammation promotes the initiation of prostate cancer. Adult murine prostate epithelia are composed predominantly of basal and luminal cells. Previous studies revealed that the two lineages are largely self-sustained when residing in their native microenvironment. To interrogate whether tissue inflammation alters the differentiation program of basal cells, we conducted lineage tracing of basal cells using a K14-CreER;mTmG model in concert with a murine model of prostatitis induced by infection from the uropathogenic bacteria CP9. We show that acute prostatitis causes tissue damage and creates a tissue microenvironment that induces the differentiation of basal cells into luminal cells, an alteration that rarely occurs under normal physiological conditions. Previously we showed that a mouse model with prostate basal cell-specific deletion of Phosphatase and tensin homolog (K14-CreER;Pten(fl/fl)) develops prostate cancer with a long latency, because disease initiation in this model requires and is limited by the differentiation of transformation-resistant basal cells into transformation-competent luminal cells. Here, we show that CP9-induced prostatitis significantly accelerates the initiation of prostatic intraepithelial neoplasia in this model. Our results demonstrate that inflammation results in a tissue microenvironment that alters the normal prostate epithelial cell differentiation program and that through this cellular process inflammation accelerates the initiation of prostate cancer with a basal cell origin.

Hedgehog signaling is active in human prostate cancer stroma and regulates proliferation and differentiation of adjacent epithelium

BACKGROUND

Contribution of stromal Hedgehog (Hh) signaling is evident in the prostate gland in mice, but needs translation to human tissues if Hh therapeutics are to be used effectively. Our goal was to determine if primary human prostate fibroblasts contain cilia, and respond to prostate Hh signaling.

METHODS

Primary human prostate cancer-associated (CAFs), and adjacent non-malignant (NPFs) fibroblasts isolated from human tissue specimens were analyzed using immunofluorescence, real-time PCR, and available array data. Cell culture and tissue recombination were used to determine responsiveness of human fibroblasts to Hh pathway manipulation and the paracrine effects of stromal Hh signaling, respectively.

RESULTS

Prostatic fibroblasts were capable of forming primary cilia, with the capacity for active Hh signaling as seen by Smo co-localization to the tip of the primary cilium. Expression of genes known to represent a signature of active Hh signaling in the prostate (especially Fgf5 and Igfbp6) were increased in CAFs compared to NPFs. The level of canonical Hh genes and prostate Hh signature genes were rarely synchronous; with lower doses of Purmorphamine/BMS-833923 regulating canonical transcription factors, and higher doses effecting prostate Hh signature genes. Grafts consisting of NPFs with constitutively active Hh signaling induced increased proliferation and dedifferentiation of adjacent non-malignant BPH-1 epithelial cells.

CONCLUSIONS

These data show that human prostatic fibroblasts have the capacity for Hh signaling and manipulation. Increased expression of a signature of prostatic Hh genes in the prostate tumor microenvironment suggests a role in the epithelial transformations driving prostate cancer (PCa).

A novel model of urinary tract differentiation, tissue regeneration, and disease: reprogramming human prostate and bladder cells into induced pluripotent stem cells

BACKGROUND

Primary culture and animal and cell-line models of prostate and bladder development have limitations in describing human biology, and novel strategies that describe the full spectrum of differentiation from foetal through to ageing tissue are required. Recent advances in biology demonstrate that direct reprogramming of somatic cells into pluripotent embryonic stem cell (ESC)-like cells is possible. These cells, termed induced pluripotent stem cells (iPSCs), could theoretically generate adult prostate and bladder tissue, providing an alternative strategy to study differentiation.

OBJECTIVE

To generate human iPSCs derived from normal, ageing, human prostate (Pro-iPSC), and urinary tract (UT-iPSC) tissue and to assess their capacity for lineage-directed differentiation.

DESIGN, SETTING, AND PARTICIPANTS

Prostate and urinary tract stroma were transduced with POU class 5 homeobox 1 (POU5F1; formerly OCT4), SRY (sex determining region Y)-box 2 (SOX2), Kruppel-like factor 4 (gut) (KLF4), and v-myc myelocytomatosis viral oncogene homolog (avian) (MYC, formerly C-MYC) genes to generate iPSCs.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The potential for differentiation into prostate and bladder lineages was compared with classical skin-derived iPSCs. The student t test was used.

RESULTS AND LIMITATIONS

Successful reprogramming of prostate tissue into Pro-iPSCs and bladder and ureter into UT-iPSCs was demonstrated by characteristic ESC morphology, marker expression, and functional pluripotency in generating all three germ-layer lineages. In contrast to conventional skin-derived iPSCs, Pro-iPSCs showed a vastly increased ability to generate prostate epithelial-specific differentiation, as characterised by androgen receptor and prostate-specific antigen induction. Similarly, UT-iPSCs were shown to be more efficient than skin-derived iPSCs in undergoing bladder differentiation as demonstrated by expression of urothelial-specific markers: uroplakins, claudins, and cytokeratin; and stromal smooth muscle markers: α-smooth-muscle actin, calponin, and desmin. These disparities are likely to represent epigenetic differences between individual iPSC lines and highlight the importance of organ-specific iPSCs for tissue-specific studies.

CONCLUSIONS

IPSCs provide an exciting new model to characterise mechanisms regulating prostate and bladder differentiation and to develop novel approaches to disease modelling. Regeneration of bladder cells also provides an exceptional opportunity for translational tissue engineering.

Formation of human prostate epithelium using tissue recombination of rodent urogenital sinus mesenchyme and human stem cells

Progress in prostate cancer research is severely limited by the availability of human-derived and hormone-naïve model systems, which limit our ability to understand genetic and molecular events underlying prostate disease initiation. Toward developing better model systems for studying human prostate carcinogenesis, we and others have taken advantage of the unique pro-prostatic inductive potential of embryonic rodent prostate stroma, termed urogenital sinus mesenchyme (UGSM). When recombined with certain pluripotent cell populations such as embryonic stem cells, UGSM induces the formation of normal human prostate epithelia in a testosterone-dependent manner. Such a human model system can be used to investigate and experimentally test the ability of candidate prostate cancer susceptibility genes at an accelerated pace compared to typical rodent transgenic studies. Since Human embryonic stem cells (hESCs) can be genetically modified in culture using inducible gene expression or siRNA knock-down vectors prior to tissue recombination, such a model facilitates testing the functional consequences of genes, or combinations of genes, which are thought to promote or prevent carcinogenesis. The technique of isolating pure populations of UGSM cells, however, is challenging and learning often requires someone with previous expertise to personally teach. Moreover, inoculation of cell mixtures under the renal capsule of an immunocompromised host can be technically challenging. Here we outline and illustrate proper isolation of UGSM from rodent embryos and renal capsule implantation of tissue mixtures to form human prostate epithelium. Such an approach, at its current stage, requires in vivo xenografting of embryonic stem cells; future applications could potentially include in vitro gland formation or the use of induced pluripotent stem cell populations (iPSCs).

Induced pluripotency of human prostatic epithelial cells

Induced pluripotent stem (iPS) cells are a valuable resource for discovery of epigenetic changes critical to cell type-specific differentiation. Although iPS cells have been generated from other terminally differentiated cells, the reprogramming of normal adult human basal prostatic epithelial (E-PZ) cells to a pluripotent state has not been reported. Here, we attempted to reprogram E-PZ cells by forced expression of Oct4, Sox2, c-Myc, and Klf4 using lentiviral vectors and obtained embryonic stem cell (ESC)-like colonies at a frequency of 0.01%. These E-PZ-iPS-like cells with normal karyotype gained expression of pluripotent genes typical of iPS cells (Tra-1-81, SSEA-3, Nanog, Sox2, and Oct4) and lost gene expression characteristic of basal prostatic epithelial cells (CK5, CK14, and p63). E-PZ-iPS-like cells demonstrated pluripotency by differentiating into ectodermal, mesodermal, and endodermal cells in vitro, although lack of teratoma formation in vivo and incomplete demethylation of pluripotency genes suggested only partial reprogramming. Importantly, E-PZ-iPS-like cells re-expressed basal epithelial cell markers (CD44, p63, MAO-A) in response to prostate-specific medium in spheroid culture. Androgen induced expression of androgen receptor (AR), and co-culture with rat urogenital sinus further induced expression of prostate-specific antigen (PSA), a hallmark of secretory cells, suggesting that E-PZ-iPS-like cells have the capacity to differentiate into prostatic basal and secretory epithelial cells. Finally, when injected into mice, E-PZ-iPS-like cells expressed basal epithelial cell markers including CD44 and p63. When co-injected with rat urogenital mesenchyme, E-PZ-iPS-like cells expressed AR and expression of p63 and CD44 was repressed. DNA methylation profiling identified epigenetic changes in key pathways and genes involved in prostatic differentiation as E-PZ-iPS-like cells converted to differentiated AR- and PSA-expressing cells. Our results suggest that iPS-like cells derived from prostatic epithelial cells are pluripotent and capable of prostatic differentiation; therefore, provide a novel model for investigating epigenetic changes involved in prostate cell lineage specification.

A preclinical xenograft model of prostate cancer using human tumors

Most cases of prostate cancer are now diagnosed as moderate-grade localized disease. These tumor specimens are important tools in the discovery and translation of prostate cancer research; however, unlike more advanced tumors, they are notoriously difficult to grow in the laboratory. We developed a system for efficiently xenografting localized human prostate cancer tissue, and we adapted this protocol to study the interactions between the specific subsets of epithelial and stromal cells. Fresh prostate tissues or isolated epithelial cells are recombined with mouse seminal vesicle mesenchyme (SVM) and grafted under the renal capsule of immunodeficient mice for optimum growth and survival. Alternatively, mouse mesenchyme can be replaced with human prostate fibroblasts in order to determine their contribution to tumor progression. Grafts can be grown for several months to determine the effectiveness of novel therapeutic compounds when administered to host mice, thereby paving the way for personalizing the treatment of individual prostate cancers.

Human epithelial basal cells are cells of origin of prostate cancer, independent of CD133 status

Normal prostatic epithelium is composed of basal and luminal cells. Prostate cancer can be initiated in both benign basal and luminal stem cells, but because basal cell markers are not expressed in patient tumors, the former result was unexpected. Since the cells of origin of prostate cancer are important therapeutic targets, we sought to provide further proof that basal stem cells have tumorigenic potential. Prostatic basal cells were enriched based on α2β1integrin(hi) expression and further enriched for stem cells using CD133 in nontumorigenic BPH-1 cells. Human embryonic stem cells (hESCs) were also used as a source of normal stem cells. To test their tumorigenicity, we used two alternate stromal-based approaches; (a) recombination with human cancer-associated fibroblasts (CAFs) or (b) recombination with embryonic stroma (urogenital mesenchyme) and treated host mice with testosterone and 17β-estradiol. Enriched α2β1integrin(hi) basal cells from BPH-1 cells resulted in malignant tumor formation using both assays of tumorigenicity. Surprisingly, the tumorigenic potential did not reside in the CD133(+) stem cells but was consistently observed in the CD133(-) population. CAFs also failed to induce prostatic tumors from hESCs. These data confirmed that benign human basal cells include cells of origin of prostate cancer and reinforced their importance as therapeutic targets. In addition, our data suggested that the more proliferative CD133(-) basal cells are more susceptible to tumorigenesis compared to the CD133(+)-enriched stem cells. These findings challenge the current dogma that normal stem cells and cells of origin of cancer are the same cell type(s).

Cells of origin for cancer: an updated view from prostate cancer

The cells of origin for cancer are the cells within tissues that serve as the target for transformation. Understanding the nature of these cells will benefit disease prevention, diagnosis and prognosis. During the past decade, much progress has been made in understanding the cellular origin for prostate cancer. This review aims to summarize the previous findings, describe the most recent results and discuss some controversies and unresolved issues in this field.

In vivo directed differentiation of pluripotent stem cells for skeletal regeneration

Pluripotent cells represent a powerful tool for tissue regeneration, but their clinical utility is limited by their propensity to form teratomas. Little is known about their interaction with the surrounding niche following implantation and how this may be applied to promote survival and functional engraftment. In this study, we evaluated the ability of an osteogenic microniche consisting of a hydroxyapatite-coated, bone morphogenetic protein-2-releasing poly-L-lactic acid scaffold placed within the context of a macroenvironmental skeletal defect to guide in vivo differentiation of both embryonic and induced pluripotent stem cells. In this setting, we found de novo bone formation and participation by implanted cells in skeletal regeneration without the formation of a teratoma. This finding suggests that local cues from both the implanted scaffold/cell micro- and surrounding macroniche may act in concert to promote cellular survival and the in vivo acquisition of a terminal cell fate, thereby allowing for functional engraftment of pluripotent cells into regenerating tissue.

Bladder expression of CD cell surface antigens and cell-type-specific transcriptomes

Many cell types have no known functional attributes. In the bladder and prostate, basal epithelial and stromal cells appear similar in cytomorphology and share several cell surface markers. Their total gene expression (transcriptome) should provide a clear measure of the extent to which they are alike functionally. Since urologic stromal cells are known to mediate organ-specific tissue formation, these cells in cancers might exhibit aberrant gene expression affecting their function. For transcriptomes, cluster designation (CD) antigens have been identified for cell sorting. The sorted cell populations can be analyzed by DNA microarrays. Various bladder cell types have unique complements of CD molecules. CD9(+) urothelial, CD104(+) basal and CD13(+) stromal cells of the lamina propria were therefore analyzed, as were CD9(+) cancer and CD13(+) cancer-associated stromal cells. The transcriptome datasets were compared by principal components analysis for relatedness between cell types; those with similarity in gene expression indicated similar function. Although bladder and prostate basal cells shared CD markers such as CD104, CD44 and CD49f, they differed in overall gene expression. Basal cells also lacked stem cell gene expression. The bladder luminal and stromal transcriptomes were distinct from their prostate counterparts. In bladder cancer, not only the urothelial but also the stromal cells showed gene expression alteration. The cancer process in both might thus involve defective stromal signaling. These cell-type transcriptomes provide a means to monitor in vitro models in which various CD-isolated cell types can be combined to study bladder differentiation and bladder tumor development based on cell-cell interaction.

Adult murine prostate basal and luminal cells are self-sustained lineages that can both serve as targets for prostate cancer initiation

The prostate epithelial lineage hierarchy and the cellular origin for prostate cancer remain inadequately defined. Using a lineage-tracing approach, we show that adult rodent prostate basal and luminal cells are independently self-sustained in vivo. Disrupting the tumor suppressor Pten in either lineage led to prostate cancer initiation. However, the cellular composition and onset dynamics of the resulting tumors are distinctive. Prostate luminal cells are more responsive to Pten null-induced mitogenic signaling. In contrast, basal cells are resistant to direct transformation. Instead, loss of Pten activity induces the capability of basal cells to differentiate into transformation-competent luminal cells. Our study suggests that deregulation of epithelial differentiation is a critical step for the initiation of prostate cancers of basal cell origin.

Brief report: a bioassay to identify primary human prostate cancer repopulating cells

Cancer cells are heterogeneous in both their phenotypes and ability to promote tumor growth and spread. Xenografting is used to identify the most highly capable cells of regenerating tumors, referred to as cancer repopulating cells. Because prostate cancers (PCa's) rarely grow as xenografts, indentifying PCa repopulating cells has not been possible. Here, we report improved methods to xenograft localized primary PCa tissues using chimeric grafts with neonatal mouse mesenchyme. Xenograft survival of tumor tissue was significantly increased by neonatal mesenchyme (six of six patients, 66% of grafts, versus four of six patients, 41% of grafts) and doubled the proliferation index of xenografted cancer cells. When applied to isolated PCa cells, neonatal mesenchyme effectively reconstituted PCa's and increased xenograft survival (four of nine patients; 32% of grafts with mesenchyme and 0% without), and supported active cancer cell proliferation. Using this assay, we showed that unfractionated α2β1integrin(hi) and α2β1integrin(lo) cells from primary localized PCa's demonstrated tumor formation at comparable rates, similar to previous reports using metastatic specimens. Thus, this new protocol efficiently established tumors and enabled proliferative expansion of both intact tumor tissue and fractionated cancer cells, providing a bioassay to identify and therapeutically target PCa repopulating cells.

Reactivation of embryonic nodal signaling is associated with tumor progression and promotes the growth of prostate cancer cells

BACKGROUND

Nodal is a member of the transforming growth factor β (TGFβ) superfamily that directs embryonic patterning and promotes the plasticity and tumorigenicity of tumor cells, but its role in the prostate is unknown. The goal of this study was to characterize the expression and function of Nodal in prostate cancer and determine whether, like other TGFβ ligands, it modulates androgen receptor (AR) activity.

METHODS

Nodal expression was investigated using immunohistochemistry of tissue microarrays and Western blots of prostate cell lines. The functional role of Nodal was examined using Matrigel and soft agar growth assays. Cross-talk between Nodal and AR signaling was assessed with luciferase reporter assays and expression of endogenous androgen regulated genes.

RESULTS

Significantly increased Nodal expression was observed in cancer compared with benign prostate specimens. Nodal was only expressed by DU145 and PC3 cells. All cell lines expressed Nodal's co-receptor, Cripto-1, but lacked Lefty, a critical negative regulator of Nodal signaling. Recombinant human Nodal triggered downstream Smad2 phosphorylation in DU145 and LNCaP cells, and stable transfection of pre-pro-Nodal enhanced the growth of LNCaP cells in Matrigel and soft agar. Finally, Nodal attenuated AR signaling, reducing the activity of a PSA promoter construct in luciferase assays and down-regulating the endogenous expression of androgen regulated genes.

CONCLUSIONS

An aberrant Nodal signaling pathway is re-expressed and functionally active in prostate cancer cells.

Generation of human female reproductive tract epithelium from human embryonic stem cells

Background

Recent studies have identified stem/progenitor cells in human and mouse uterine epithelium, which are postulated to be responsible for tissue regeneration and proliferative disorders of human endometrium. These progenitor cells are thought to be derived from Müllerian duct (MD), the primordial female reproductive tract (FRT).

Methodology/Principal Findings

We have developed a model of human reproductive tract development in which inductive neonatal mouse uterine mesenchyme (nMUM) is recombined with green fluorescent protein (GFP)-tagged human embryonic stem cells (hESCs); GFP-hESC (ENVY). We demonstrate for the first time that hESCs can be differentiated into cells with a human FRT epithelial cell phenotype. hESC derived FRT epithelial cells emerged from cultures containing MIXL1⁺ mesendodermal precursors, paralleling events occurring during normal organogenesis. Following transplantation, nMUM treated embryoid bodies (EBs) generated epithelial structures with a typical MD phenotype that expressed the MD markers PAX2, HOXA10. Functionally, the hESCs derived FRT epithelium responded to exogenous estrogen by proliferating and secreting uterine-specific glycodelin A (GdA).

Conclusions/Significance

These data show nMUM can induce differentiation of hESC to form the FRT epithelium. This may provide a model to study early developmental events of the human FRT.

Estrogen-initiated transformation of prostate epithelium derived from normal human prostate stem-progenitor cells

The present study sought to determine whether estrogens with testosterone support are sufficient to transform the normal human prostate epithelium and promote progression to invasive adenocarcinoma using a novel chimeric prostate model. Adult prostate stem/early progenitor cells were isolated from normal human prostates through prostasphere formation in three-dimensional culture. The stem/early progenitor cell status and clonality of prostasphere cells was confirmed by immunocytochemistry and Hoechst staining. Normal prostate progenitor cells were found to express estrogen receptor α, estrogen receptor β, and G protein-coupled receptor 30 mRNA and protein and were responsive to 1 nm estradiol-17β with increased numbers and prostasphere size, implicating them as direct estrogen targets. Recombinants of human prostate progenitor cells with rat urogenital sinus mesenchyme formed chimeric prostate tissue in vivo under the renal capsule of nude mice. Cytodifferentiation of human prostate progenitor cells in chimeric tissues was confirmed by immunohistochemistry using epithelial cell markers (p63, cytokeratin 8/18, and androgen receptor), whereas human origin and functional differentiation were confirmed by expression of human nuclear antigen and prostate-specific antigen, respectively. Once mature tissues formed, the hosts were exposed to elevated testosterone and estradiol-17β for 1-4 months, and prostate pathology was longitudinally monitored. Induction of prostate cancer in the human stem/progenitor cell-generated prostatic tissue was observed over time, progressing from normal histology to epithelial hyperplasia, prostate intraepithelial neoplasia, and prostate cancer with local renal invasion. These findings provide the first direct evidence that human prostate progenitor cells are estrogen targets and that estradiol in an androgen-supported milieu is a carcinogen for human prostate epithelium.

Estrogen action and prostate cancer

Early work on the hormonal basis of prostate cancer focused on the role of androgens, but more recently estrogens have been implicated as potential agents in the development and progression of prostate cancer. In this article, we review the epidemiological, laboratory and clinical evidence that estrogen may play a causative role in human prostate cancer, as well as rodent and grafted in vivo models. We then review recent literature highlighting potential mechanisms by which estrogen may contribute to prostate cancer, including estrogenic imprinting and epigenetic modifications, direct genotoxicity, hyperprolactinemia, inflammation and immunologic changes, and receptor-mediated actions. We discuss the work performed so far separating the actions of the different known estrogen receptors (ERs), ERα and ERβ, as well as G-protein-coupled receptor 30 and their specific roles in prostate disease. Finally, we predict that future work in this field will involve more investigations into epigenetic changes, experiments using new models of hormonal dysregulation in developing human prostate tissue, and continued delineation of the roles of the different ER subtypes, as well as their downstream signaling pathways that may serve as therapeutic targets.

Novel human prostate epithelial cell culture models for the study of carcinogenesis and of normal stem cells and cancer stem cells

Research into the mechanisms of prostate cancer progression has been limited by the lack of suitable in vitro systems. A hurdle in understanding the molecular genetic changes in prostate cancer has been the difficulty in establishing premalignant lesions and primary prostate tumors as in vitro cell cultures. Primary prostate epithelial cells grow for a finite life span and then senesce. Immortalization is defined by continuous growth of otherwise senescing cells and is believed to represent an early stage in tumor progression. To examine these early stages, we and others have developed in vitro models of prostate epithelial cell immortalization. Generation of primary human prostate epithelial (HPE) cells has been achieved using the serum-free condition. Retrovirus containing human telomerase reverse transcriptase (hTERT) was successfully used for the immortalization of primary HPE cells. Putative stem cell markers CD133 and CXCR4 were further identified in hTERT-immortalized primary nonmalignant and malignant tumor-derived HPE lines. In addition, an hTERT-immortalized nonmalignant HPE cell were found to retain the properties of multipotent stem cells. These in vitro prostate cell culture models should be useful for the study of carcinogenesis and of normal and cancer stem cells. Prostate cancer is the most common male cancer in the Western World and second leading cause of male cancer death in the United States [1]. The therapy most widely used against advanced disease is androgen ablation and, initially, it almost always produces objective clinical responses. However, most patients eventually relapse with ablation-resistant prostate cancer and develop metastatic disease; currently, there is no treatment that will cure progressive hormone-refractory metastatic prostate cancer. The mechanisms of progression of prostate cancer have been extensively studied, yet are poorly understood. One of the concepts that has been evolved is that cancer arises from the neoplastic transformation of normal prostate epithelial stem cells or transit amplifying cells. Understanding normal stem cells and cancer stem cells (CSCs) may provide insight into the origin of and new therapeutics for prostate cancer. However, research in this field is limited by the lack of suitable in vitro systems.

Early life inorganic lead exposure induces testicular teratoma and renal and urinary bladder preneoplasia in adult metallothionein-knockout mice but not in wild type mice

Inorganic lead compounds are carcinogenic in animals and have carcinogenic potential in humans. In mice, lead (Pb) is a transplacental carcinogen in the kidney. Metallothionein (MT) is a metal-binding protein that can reduce the toxicity of various metals, including Pb, either by direct sequestration or as an antioxidant for metals that generate reactive oxygen species. Although MT appears to reduce Pb carcinogenicity in adult mice it is unknown how MT deficiency may affect Pb carcinogenicity from early life exposure. Thus, groups (n=10) of pregnant MT-I/II double knockout (MT-null) or 129/SVJ MT wild type (WT) mice were exposed to Pb acetate in the drinking water (0, 2000, 4000ppm Pb) from gestation day 8 through birth and during lactation. Maternal drinking water Pb exposure continued to wean at 4 weeks of age and the male offspring were then directly exposed to Pb until 8 weeks of age and observed until 2 years old. High dose (4000ppm) but not low dose (2000ppm) Pb reduced survival in the latter part of the study in both MT-null and WT mice. In MT-null mice, but not WT, early life Pb exposure caused a dose-related increase in testicular teratomas, to a maximum incidence of 28% compared to control (4%). Pb-induced renal cystic hyperplasia, considered preneoplastic, was a prominent occurrence in MT-null mice but nearly absent in WT mice. Pb dose-related increases in renal cystic hyperplasia occurred in adult MT-null with early life exposure with maximal incidence of 52%. Pb-treated MT-null mice also showed dose-related increases in urinary bladder hyperplasia with occasional papilloma that were absent in WT mice. Thus, MT deficiency made mice more sensitive to early life Pb exposure with regard to testes tumors, and renal and urinary bladder preneoplastic lesions.

Spermatogonial stem cells, in vivo transdifferentiation and human regenerative medicine

IMPORTANCE OF THE FIELD

Embryonic stem (ES) cells have potential for use in regenerative medicine, but use of these cells is hindered by moral, legal and ethical issues. Induced pluripotent cells have promise in regenerative medicine. However, since generation of these cells involves genetic manipulation, it also faces significant hurdles before clinical use. This review discusses spermatogonial stem cells (SSCs) as a potential alternative source of pluripotent cells for use in human regenerative medicine.

AREAS COVERED IN THE REVIEW

The potential of SSCs to give rise to a wide range of other cell types either directly, when recombined with instructive inducers, or indirectly, after being converted to ES-like cells. Current understanding of the differentiation potential of murine SSCs and recent progress in isolating and culturing human SSCs and demonstrating their properties is also discussed.

WHAT THE READER WILL GAIN

Insight into the plasticity of SSCs and the unique properties of these cells for regenerative applications, the limitations of SSCs for stem-cell-based therapy and the potential alternatives available.

TAKE HOME MESSAGE

If methodologies for isolation and conversion of adult human SSCs directly into other cell types can be effectively developed, SSCs could represent an important alternate source of pluripotent cells that can be used in human tissue repair and/or regeneration.

Lineage enforcement by inductive mesenchyme on adult epithelial stem cells across developmental germ layers

During development, cell differentiation is accompanied by the progressive loss of pluripotent gene expression and developmental potential, although de-differentiation in specialized cells can be induced by reprogramming strategies, indicating that transdifferentiation potential is retained in adult cells. The stromal niche provides differentiating cues to epithelial stem cells (SCs), but current evidence is restricted to tissue types within the same developmental germ layer lineage. Anticipating the use of adult SCs for tissue regeneration, we examined if stroma can enforce lineage commitment across germ layer boundaries and promote transdifferentiation of adult epithelial SCs. Here, we report tissue-specific mesenchyme instructing epithelial cells from a different germ layer origin to express dual phenotypes. Prostatic stroma induced mammary epithelia (or enriched Lin(-)CD29(HI)CD24(+/MOD) mammary SCs) to generate glandular epithelia expressing both prostatic and mammary markers such as steroid hormone receptors and transcription factors including Foxa1, Nkx3.1, and GATA-3. Array data implicated Hh and Wnt pathways in mediating stromal-epithelial interactions (validated by increased Cyclin D1 expression). Other recombinants of prostatic mesenchyme and skin epithelia, or preputial gland mesenchyme and bladder or esophageal epithelia, showed foci expressing new markers adjacent to the original epithelial differentiation (e.g., sebaceous cells within bladder urothelium), confirming altered lineage specification induced by stroma and evidence of cross-germ layer transdifferentiation. Thus, stromal cell niche is critical in maintaining (or redirecting) differentiation in adult epithelia. In order to use adult epithelial SCs in regenerative medicine, we must additionally regulate their intrinsic properties to prevent (or enable) transdifferentiation in specified SC niches.

Use of tissue engineering in treatment of the male genitourinary tract abnormalities

INTRODUCTION

A variety of congenital and acquired male genitourinary tract abnormalities can lead to organ damage or tissue loss that requires surgical reconstruction. Traditional reconstructive methods do not produce consistent satisfactory structural or functional replacement and may damage the genitourinary tract. Tissue engineering provides a promising alternative for the treatment of these disorders.

AIM

The aim of this article is to provide an update on clinical and experimental evidence concerning the application of tissue engineering to treatment of abnormalities in the male genitourinary tract system.

METHODS

A PubMed search was performed to retrieve relevant clinical and basic literature.

MAIN OUTCOME MEASURES

The topics discussed in this review include the experimental and clinical application of tissue engineering for reconstruction of the urethra, penis, testis, and prostate.

RESULTS

Tissue engineering techniques can provide a plentiful source of healthy tissue for reconstructive purposes. Acellular matrix scaffold and seed cells are two key elements in tissue engineering. Proper employment of seed cells and scaffold material may result in synergistic effects. Moreover, new tissue engineering technologies are being transferred from the laboratory to clinical practice.

CONCLUSIONS

Tissue engineering provides biological substitutes that can restore and maintain normal function in diseased and injured tissues, thus providing an effective technique for regeneration of the male genitourinary tract.

Directed differentiation of human embryonic stem cells into functional retinal pigment epithelium cells

Dysfunction and loss of retinal pigment epithelium (RPE) leads to degeneration of photoreceptors in age-related macular degeneration and subtypes of retinitis pigmentosa. Human embryonic stem cells (hESCs) may serve as an unlimited source of RPE cells for transplantation in these blinding conditions. Here we show the directed differentiation of hESCs toward an RPE fate under defined culture conditions. We demonstrate that nicotinamide promotes the differentiation of hESCs to neural and subsequently to RPE fate. In the presence of nicotinamide, factors from the TGF-beta superfamily, which presumably pattern RPE development during embryogenesis, further direct RPE differentiation. The hESC-derived pigmented cells exhibit the morphology, marker expression, and function of authentic RPE and rescue retinal structure and function after transplantation to an animal model of retinal degeneration caused by RPE dysfunction. These results are an important step toward the future use of hESCs to replenish RPE in blinding diseases.

Dual-label centromere and telomere FISH identifies human, rat, and mouse cell contribution to Multispecies recombinant urogenital sinus xenografts

BACKGROUND

Recombinant xenografts of human cells growing in immunocompromised rodents are widely used for studying stem cell biology, tumor biology, and epithelial to mesenchyme transitions. Of critical importance is the correct interpretation of the cellular composition of such xenografts.

METHODS

Here we present a rapid and robust method employing protein nucleic acid (PNA) FISH probes to dual-label centromeres and telomeres (Cen/Tel FISH). Such labeling allows unambiguous discrimination between human, mouse, and rat cells in paraffin-embedded tissue sections, providing significant advantages over current methods used to discern human versus rodent cell types.

RESULTS

Using an in vivo prostatic developmental system where rat embryonic urogenital sinus mesenchyme is recombined with human prostate epithelial organoids and grown in an immunocompromised mouse, Cen/Tel FISH documents that all three species contribute to the development of glandular structures.

CONCLUSIONS

The method is an indispensable tool to analyze xenograft/host interactions and prevent misinterpretation of data using tissue recombination approaches.