DEVELOPMENT OF THE CONDITIONALLY IMMORTALIZED TESTICULAR SERTOLI CELL LINE TTE3 EXPRESSING SERTOLI CELL SPECIFIC GENES FROM MICE TRANSGENIC FOR TEMPERATURE SENSITIVE SIMIAN VIRUS 40 LARGE T ANTIGEN GENE

In Vitro and In Vivo Models for Drug Transport Across the Blood-Testis Barrier

The blood-testis barrier (BTB) is a selectively permeable membrane barrier formed by adjacent Sertoli cells (SCs) in the seminiferous tubules of the testes that develops intercellular junctional complexes to protect developing germ cells from external pressures. However, due to this inherent defense mechanism, the seminiferous tubule lumen can act as a pharmacological sanctuary site for latent viruses (e.g., Ebola, Zika) and cancers (e.g., leukemia). Therefore, it is critical to identify and evaluate BTB carrier-mediated drug delivery pathways to successfully treat these viruses and cancers. Many drugs are unable to effectively cross cell membranes without assistance from carrier proteins like transporters because they are large, polar, and often carry a charge at physiologic pH. SCs express transporters that selectively permit endogenous compounds, such as carnitine or nucleosides, across the BTB to support normal physiologic activity, although reproductive toxicants can also use these pathways, thereby circumventing the BTB. Certain xenobiotics, including select cancer therapeutics, antivirals, contraceptives, and environmental toxicants, are known to accumulate within the male genital tract and cause testicular toxicity; however, the transport pathways by which these compounds circumvent the BTB are largely unknown. Consequently, there is a need to identify the clinically relevant BTB transport pathways in in vitro and in vivo BTB models that recapitulate human pharmacokinetics and pharmacodynamics for these xenobiotics. This review summarizes the various in vitro and in vivo models of the BTB reported in the literature and highlights the strengths and weaknesses of certain models for drug disposition studies. SIGNIFICANCE STATEMENT: Drug disposition to the testes is influenced by the physical, physiological, and immunological components of the blood-testis barrier (BTB). But many compounds are known to cross the BTB by transporters, resulting in pharmacological and/or toxicological effects in the testes. Therefore, models that assess drug transport across the human BTB must adequately account for these confounding factors. This review identifies and discusses the benefits and limitations of various in vitro and in vivo BTB models for preclinical drug disposition studies.

Establishment and applications of male germ cell and Sertoli cell lines

Within the seminiferous tubules there are two major cell types, namely male germ cells and Sertoli cells. Recent studies have demonstrated that male germ cells and Sertoli cells can have significant applications in treating male infertility and other diseases. However, primary male germ cells are hard to proliferate in vitro and the number of spermatogonial stem cells is scarce. Therefore, methods that promote the expansion of these cell populations are essential for their use from the bench to the bed side. Notably, a number of cell lines for rodent spermatogonia, spermatocytes and Sertoli cells have been developed, and significantly we have successfully established a human spermatogonial stem cell line with an unlimited proliferation potential and no tumor formation. This newly developed cell line could provide an abundant source of cells for uncovering molecular mechanisms underlying human spermatogenesis and for their utilization in the field of reproductive and regenerative medicine. In this review, we discuss the methods for establishing spermatogonial, spermatocyte and Sertoli cell lines using various kinds of approaches, including spontaneity, transgenic animals with oncogenes, simian virus 40 (SV40) large T antigen, the gene coding for a temperature-sensitive mutant of p53, telomerase reverse gene (Tert), and the specific promoter-based selection strategy. We further highlight the essential applications of these cell lines in basic research and translation medicine.

Establishment of adult mouse Sertoli cell lines by using the starvation method

Sertoli cells were isolated from the testes of 6-week-old mice and stable Sertoli cell lines with higher proliferation rates were subcloned after starvation of primary cultured cells. After two rounds of this subcloning, 33 subcloned lines were selected on the basis of their proliferation rates. In addition, these subclones were screened according to their phagocytic activity and the characteristics of mature Sertoli cells, such as the expression of androgen receptors (ARs) and progesterone receptors, by using western blotting and immunocytochemical analysis, in addition to their morphology and proliferation rates. After the third round of subcloning, 12 subclones were selected for the final selection using RT-PCR for identification of genes specifically expressed by various testicular cells. Three clones were selected that expressed Sertoli-cell-specific genes, i.e. stem cell factor, clusterin, AR, α-inhibin, transferrin, Wilms' tumour-1, Müllerian inhibitory substance, sex-determining region Y-box 9, FSH receptor (Fshr) and occludin; however, these clones did not express globulin transcription factor 1, steroidogenic factor or androgen-binding protein. These clones also expressed growth and differentiation factors that act on germ cells, such as leukaemia inhibitory factor, transforming growth factor β1 and basic fibroblast growth factor 2, but did not express c-kit (specific for germ cells), LH receptor and 3β-hydroxyl-dehydrogenase (specific for Leydig cells). Immunocytochemical data confirmed the expression of clusterin in these clones. Furthermore, the Bromodeoxyuridine incorporation assay confirmed the proliferation activity of these clones throughFshrafter treatment with FSH. These clones are considered to be valuable tools for the study of Sertoli cell-specific gene expression and function.

Isolation, culture, and characterization of canine Sertoli cells

Primary Sertoli cell cultures have been established from several animals including the sheep and rhesus monkey; however, not for the domestic dog, Canis familiaris. Sertoli cells are the only readily accessible cell type in the body which expresses all six type IV collagens. These collagens play key roles in tissue structure, basement membrane formation, and filtration. The study of these genes is necessary to determine their exact roles and regulation in the aforementioned functions and to investigate diseases associated with mutations in these genes. For such studies, a cell culture system is a requisite tool. Therefore, Sertoli cells were targeted, and a culture was established from cells isolated from canine testes. Cultures maintained consistent morphology and steady growth for up to seven passages. Cultured cells were identified as Sertoli cells through positive Western blot results for SOX9 and Clusterin B proteins and transcript sequence verification of SOX9 as well as the presence of type IV collagen transcripts. Primary cultures of canine Sertoli cells will provide a useful tool for study of the function and regulation of collagen genes and will permit new research pertaining to canine health while also serving as a model for the study of human diseases.

The immortalized cell lines with differentiation potentials: their establishment and possible application

Approximately 200 types of the cells are qualified as differentiated cells in the human body. If these different types of cells can be separated from each other (or cloned) and obtained in sufficient quantity, it will be beneficial for studying development, morphogenesis, tissue maintenance, cancer and aging, and for reconstructing functional tissues in vitro for regenerative medicine. We produced the transgenic mouse and rat harboring SV40 T-antigen gene to make the immortalized cell lines in the primary tissue culture and succeeded in establishing many functionally active cell lines from various tissues. Many immortalized cell lines from various tissues are shown to exhibit the unique characteristics of tissue functions and they should be useful as an in vitro model of various tissues for physiological and pharmacological investigations. Future application of these cells to drug screening is discussed.

Identification of genetic networks involved in the cell injury accompanying endoplasmic reticulum stress induced by bisphenol A in testicular Sertoli cells

To identify detailed mechanisms by which bisphenol A (BPA), an endocrine-disrupting chemical, induces cell injury in mouse testicular Sertoli TTE3 cells, we performed genome-wide microarray and computational gene network analyses. BPA (200muM) significantly decreased cell viability and simultaneously induced an increase in mRNA levels of HSPA5 and DDIT3, endoplasmic reticulum (ER) stress marker genes. Of the 22,690 probe sets analyzed, BPA down-regulated 661 probe sets and up-regulated 604 probe sets by >2.0-fold. Hierarchical cluster analysis demonstrated nine gene clusters. In decreased gene clusters, two significant genetic networks were associated with cell growth and proliferation and the cell cycle. In increased gene clusters, two significant genetic networks including many basic-region leucine zipper transcription factors were associated with cell death and DNA replication, recombination, and repair. The present results will provide additional novel insights into the detailed molecular mechanisms of cell injury accompanying ER stress induced by BPA in Sertoli cells.

PSPC1, NONO, and SFPQ are expressed in mouse Sertoli cells and may function as coregulators of androgen receptor-mediated transcription

In Sertoli cells of testis, androgen receptor-regulated gene transcription plays an indispensable role in maintaining spermatogenesis. Androgen receptor activity is modulated by a number of coregulators which are associated with the androgen receptor. Non-POU-domain-containing, octamer binding protein (NONO), a member of the DBHS-containing proteins, complexes with androgen receptor and functions as a coactivator for the receptor. Paraspeckle protein 1 alpha isoform (PSPC1, previously known as PSP1) and Splicing factor, proline- and glutamine-rich (SFPQ, previously known as PSF), other members of the DBHS-containing proteins, are also found in androgen receptor complexes, suggesting that these DBHS-containing proteins may cooperatively regulate androgen receptor-mediated gene transcription. We demonstrated that PSPC1, NONO, and SFPQ are coexpressed in Sertoli cell line TTE3 and interact reciprocally. The effect of the DBHS-containing proteins on the transcriptional activity was assessed using the construct containing androgen-responsive elements followed by a luciferase gene. The results showed that all the DBHS-containing proteins activate androgen receptor-mediated transcription, and PSPC1 is the most effective coactivator among them. Furthermore, we confirmed the presence of PSPC1, NONO, and SFPQ proteins in Sertoli cells of adult mouse testis sections. These observations suggest that PSPC1, NONO, and SFPQ form complexes with each other in Sertoli cells and may regulate androgen receptor-mediated transcriptional activity.

Expression of androgen and estrogen receptors in sertoli cells: studies using the mouse SK11 cell line

Sertoli cells (Sc) play a major role in the establishment and maintenance of spermatogenesis. In the adult testis, Sc contain androgen receptor (AR) and estrogen receptor (ER)-beta but exhibit a loss of steroid responsiveness when maintained in primary culture. In the present study, we demonstrated that a transformed murine cell line (SK11) has retained a Sc phenotype and remains steroid responsive. SK11 cells expressed mRNAs found in Sc (aromatase, sulfated glycoprotein-1, sulfated glycoprotein-2, GATA-1, Sry-type high-mobility-group box transcription factor-9, testatin, dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1) including those for AR and ERbeta but not ERalpha. AR and ERbeta were immunolocalized to cell nuclei, and their ability to activate gene expression was investigated using transient transfections with reporter constructs containing either 3xERE or pem-androgen-responsive element promoters. Expression of the 3xERE reporter was induced after incubation with 17beta-estradiol (E2), 5alpha-androstane-3-beta, 17beta-diol (3betaAdiol), or testosterone (T); up-regulation of the pem-androgen-responsive element reporter was detected only in the presence of T or dihydrotestosterone. Activation of the ERE reporter did not occur after targeted knockdown of ERbeta mRNA. Expression of AR and ERbeta mRNAs was increased after incubation of cells with T or E2, respectively. In conclusion, we have demonstrated that the SK11 Sc cell line contains functional AR and ERbeta and that treatment of the cells with their respective steroids results in an increase in the amount of their mRNAs. Our results suggest that E2 or 3betaAdiol acting via ERbeta might modulate Sc function in vivo and that SK11 cells provide a useful model that can be used to complement studies using Sc selective gene ablation.

Genes involved in nonpermissive temperature-induced cell differentiation in Sertoli TTE3 cells bearing temperature-sensitive simian virus 40 large T-antigen

Sertoli TTE3 cells, derived from transgenic mice bearing temperature-sensitive simian virus 40 large T (tsSV40LT)-antigen, proliferated continuously at a permissive temperature (33 degrees C) whereas inactivation of the large T-antigen by a nonpermissive temperature (39 degrees C) led to differentiation as judged by elevation of transferrin. To clarify the detailed mechanisms of differentiation, we investigated the time course of changes in gene expression using cDNA microarrays. Of the 865 genes analyzed, 14 genes showed increased levels of expression. Real-time quantitative PCR revealed that the mRNA levels of p21(waf1), milk fat globule membrane protein E8, heat-responsive protein 12, and selenoprotein P were markedly elevated. Moreover, the differentiated condition induced by the nonpermissive temperature significantly increased mRNA levels of these four genes in several cell lines from the transgenic mice bearing the oncogene. The present results regarding changes in gene expression will provide a basis for a further understanding of molecular mechanisms of differentiation in both Sertoli cells and cell lines transformed by tsSV40LT-antigen.

Functional characterization of a conditionally immortalized mouse epididymis caput epithelial cell line MEPC5 using temperature-sensitive simian virus 40 large T-antigen

A conditionally immortalized epididymis caput cell line, MEPC5, was established by infecting primary cultured mouse epididymis caput cells with a temperature-sensitive simian virus 40 large T-antigen. At a permissive temperature of 33 degrees C, the large T-antigen was expressed and the cells grew continuously. However, the downregulation of T-antigen at a nonpermissive temperature of 39 degrees C and the upregulation of cell density at 33 degrees C were associated with growth arrest and the increased protein expression of p21(waf1), a cell cycle inhibitor. The cells expressed epididymal caput-expressed genes such as phosphatidylethanolamine binding protein, polyoma enhancer activator 3, ME1, sulfated glycoprotein-2 (SGP-2), androgen receptor, and retinoic acid receptor alpha. Interestingly, the expression levels of ME1 and SGP-2 were significantly elevated under the cell growth-restricted conditions. The established mouse epididymis caput epithelial cell line MEPC5 retains some characteristics of differentiated epididymis epithelial cells, and should prove an excellent model for studies of gene expression and the physiological functions of epididymis caput epithelial cells.

Testicular cell lines

The range of in vivo or in vitro immortalized cell lines currently available provides a variety of model systems for studies of normal and pathological cell functions. The cell lines have been derived from spontaneous or experimentally induced tumors, or through in vitro immortalization. The transgenic (TG) techniques provide a powerful approach, allowing the production of in vivo animal models for a variety of diseases, including malignant tumors, through tissue-specific expression of oncogenes or other tumor-promoting genes. The TG techniques also enable the production of cell lines with specific characteristics, through insertion of desired genes into specific cell types, which can then be immortalized upon cell culture. The use of temperature-sensitive immortalizing genes offers an additional advantage of controlling gene expression, including the proliferation and differentiation of the cells to be immortalized. As regards the male reproductive system, a number of cell lines of testicular somatic cells are currently available. This review covers mainly the immortalized cell lines of testicular Leydig and Sertoli cells, with special reference to murine cell lines for the study of testicular endocrine function and tumorigenesis. These cell lines also provide useful tools to investigate the molecular basis of hormone actions and testicular cell interactions.

Rat Sertoli cells express epithelial but also mesenchymal genes after immortalization with SV40

A new immortal Sertoli cell line from pubertal rat testis was established and characterized. We have generated the clonal line SCIT-C8 expressing established markers for Sertoli cells (SC) like transferrin, clusterin and steel factor/stem cell factor (SCF). Additionally, the immortalized cells express afadin, a protein which is a member of tight and adherens junctions, therefore the cells may be useful for studies of the blood-testis barrier (BTB) in vitro. In contrast to primary SC, the immortalized cells lost expression of androgen receptor and responsiveness to androgens and follicle-stimulating hormone. Surprisingly, we found mRNA expression and protein secretion of the mesenchymal markers, fibronectin and entactin-1, which we also observed for the immortalized SC lines, ASC-17D and 93RS2. In comparison to primary SC, the immortalized cells demonstrated enhanced adhesion in vitro. This correlated with the expression of entactin-1 because adhesion was strongly reduced by antibody perturbation experiments. Additionally, we found the alternatively spliced and primarily muscle cell-specific long variant of TGF-beta2 not only in peritubular cells (PC), but also in the primary and immortalized SC. Furthermore, all immortalized cell lines secreted higher amounts of TGF-beta2 than primary SC. In conclusion, the immortalized SC lines from different developmental stages showed a similar pattern of epithelial and mesenchymal markers.

Development of cell model with specific functions and its application to the study of global gene expression

The use of in vitro cell culture models has been of central importance in the development of our understanding of the cellular and molecular biology of organs and tissues. Transgenic mice and rats harboring temperature-sensitive simian virus 40 large T-antigen genes are useful for establishing cell lines from organs and tissues that have proved difficult to culture in vitro. Many conditionally immortalized cell lines with normal specific functions were generated from transgenic animals. DNA microarray technology has broad applications and is directed toward the study of global gene expression. Using established cell lines and DNA microarrays, we identified many genes that were up- and down-regulated in the process of the cell differentiation or cell death. In this review, the characteristics of established cell lines and possible applications of the study of global gene expression are discussed.

Oligo-astheno-teratozoospermia in mice lacking Cnot7, a regulator of retinoid X receptor beta

Spermatogenesis is a complex process that involves cooperation of germ cells and testicular somatic cells. Various genetic disorders lead to impaired spermatogenesis, defective sperm function and male infertility. Here we show that Cnot7(-/-) males are sterile owing to oligo-astheno-teratozoospermia, suggesting that Cnot7, a CCR4-associated transcriptional cofactor, is essential for spermatogenesis. Maturation of spermatids is unsynchronized and impaired in seminiferous tubules of Cnot7(-/-) mice. Transplantation of spermatogonial stem cells from male Cnot7(-/-) mice to seminiferous tubules of Kit mutant mice (Kit(W/W-v)) restores spermatogenesis, suggesting that the function of testicular somatic cells is damaged in the Cnot7(-/-) condition. The testicular phenotypes of Cnot7(-/-) mice are similar to those of mice deficient in retinoid X receptor beta (Rxrb). We further show that Cnot7 binds the AF-1 domain of Rxrb and that Rxrb malfunctions in the absence of Cnot7. Therefore, Cnot7 seems to function as a coregulator of Rxrb in testicular somatic cells and is thus involved in spermatogenesis.

cDNA microarray analysis reveals chop-10 plays a key role in Sertoli cell injury induced by bisphenol A

We examined the time course of changes in gene expression in detail using cDNA microarray analysis of mouse Sertoli TTE3 cells treated with bisphenol A (BPA). A subtoxic dose of BPA (200 microM) transiently increased intracellular Ca(2+) concentration and time-dependently induced an increase in mRNA level of 78-kDa glucose-regulated protein, indicating that BPA induces endoplasmic reticulum stress. Of the 865 genes analyzed, 31 genes showed increased levels of expression. TaqMan analysis confirmed that the mRNA levels of chop-10, fra-2, c-myc, and ornithine decarboxylase were increased, and showed that chop-10 is the most sensitive gene. The expression level of chop-10 protein and cell injury induced by BPA were significantly reduced in stable TTE3 cells overexpressing full-length chop-10 antisense RNA. We conclude that chop-10 plays a key role in Sertoli cell injury induced by BPA.

Development of a conditionally immortalized testicular Sertoli cell line RTS3-3 from adult transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene

Transgenic mice and rats harboring temperature-sensitive simian virus 40 (tsSV40) large T-antigen gene are useful for establishing cell lines from tissues. We succeeded in establishing a conditionally immortalized testicular Sertoli cell line, RT3-3, from adult transgenic rats harboring the oncogene. The cells grew at permissive (33 degrees C) and intermediate (37 degrees C) temperatures but not at nonpermissive temperature (39 degrees C). Large T-antigen was expressed at 33 and 37 degrees C, whereas the expression level was gradually decreased at 39 degrees C, suggesting that the temperature-sensitive growth characteristics arise as a result of the function of tsSV40 large T-antigen. The cells showed biochemical features associate with normal Sertoli cells including expressions of mRNAs of sulfated glycoprotein-2 (SGP-2), transferrin (TF) and steel factor. Quantitative polymerase chain reaction revealed that nonpermissive temperature induced increase in the level of SGP-2. Moreover, levels of SGP-2 and/or TF were significantly elevated in the cells treatment with sodium butyrate and retinoic acid, inducers of cellular differentiation. To our knowledge, this is the first report of the establishment of a testicular Sertoli cell line from the transgenic rats. Thus, the conditionally immortalized cell line RTS3-3 with unique characteristics may serve as good experimental in vitro models for basic and applied biology of testicular Sertoli cells.

DNA microarray analysis of differentially expressed genes responsive to bisphenol A, an alkylphenol derivative, in an in vitro mouse Sertoli cell model

To identify genes elicited by bisphenol A (BPA) in Sertoli cells, we carried out a microarray analysis of TTE3 cells (a mouse Sertoli cell line) treated with BPA. BPA (100, 200 and 400 microM) induced cell death concentration-dependently, with levels being 25%, 33% and 96%, respectively. Of the 1,081 genes analyzed, 3 genes showed decreased levels of expression while the remaining 10 genes showed increased levels in the cells treated with a subtoxic dose of BPA (200 microM). The expressions of six genes were confirmed by the TaqMan assay. These findings suggest that DNA microarray analysis is a useful tool for investigating the molecular mechanisms of the toxic effects of BPA in testicular cells.

Development and characterization of conditionally immortalized gastric epithelial cell lines from transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene

Conditionally immortalized gastric epithelial cell lines were established from transgenic rats harboring temperature-sensitive simian virus 40 (tsSV40) large T-antigen gene. Gastric mucosal cells and epithelial tissues isolated from the stomach of the transgenic rats were cultured at permissive temperature (33 degrees C), and proliferative cells were cloned by colony formation. Six cell lines (designated as RGE1-01, RGE1-02, RGE1-03, RGE1-21, RGE1-22 and RGE2-01) showing epithelial-like morphology have been established. All cells grew at 33 degrees C, but did not at nonpermissive temperature (39 degrees C). High expression level of large T-antigen in the nuclei was observed at 33 degrees C, whereas the expression level was gradually decreased in a time-dependent manner at 39 degrees C. These results suggest that the temperature-sensitive growth characteristics arise as a result of a function of the tsSV40 large T-antigen. None of the cell lines were transformed as judged by anchorage-independent growth assay. Immunocytochemical findings indicated that all cells expressed epithelial cell markers including cytoskeletal (cytokeratin and actin), basement membrane (laminin and collagen type IV) and junctional complex (ZO-1 and desmoplakin I+II) proteins at 33 degrees C. All cells expressed mRNA of cathepsin E, a pit cell marker. Moreover, transepithelial resistance was observed between apical and basolateral sides in the cells. RGE1-22 cells produced prostaglandin E(2). Levels of mRNA for cathepsin E, transepithelial resistance and prostaglandin E(2) were influenced by the nonpermissive temperature. Thus, these conditionally immortalized gastric cell lines which preserve some epithelial cell characteristics will provide a useful in vitro model of gastric epithelium.