Transferrin gene expression and secretion in rat sertoli cells

Do porcine Sertoli cells represent an opportunity for Duchenne muscular dystrophy?

Sertoli cells (SeC) are responsible for the immunoprivileged status of the testis thanks to which allogeneic or xenogeneic engraftments can survive without pharmacological immune suppression if co‐injected with SeC. This peculiar ability of SeC is dependent on secretion of a plethora of factors including maturation factors, hormones, growth factors, cytokines and immunomodulatory factors. The anti‐inflammatory and trophic properties of SeC have been largely exploited in several experimental models of diseases, diabetes being the most studied. Duchenne muscular dystrophy (DMD) is a lethal X‐linked recessive pathology in which lack of functional dystrophin leads to progressive muscle degeneration culminating in loss of locomotion and premature death. Despite a huge effort to find a cure, DMD patients are currently treated with anti‐inflammatory steroids. Recently, encapsulated porcine SeC (MC‐SeC) have been injected ip in the absence of immunosuppression in an animal model of DMD resulting in reduction of muscle inflammation and amelioration of muscle morphology and functionality, thus opening an additional avenue in the treatment of DMD. The novel protocol is endowed with the advantage of being potentially applicable to all the cohort of DMD patients regardless of the mutation. This mini‐review addresses several issues linked to the possible use of MC‐SeC injected ip in dystrophic people.

FSH-stimulated PTEN activity accounts for the lack of FSH mitogenic effect in prepubertal rat Sertoli cells

Follicle-stimulating hormone (FSH) controls the proliferation and differentiation of Sertoli cells of the testis. FSH binds a G protein-coupled receptor (GPCR) to stimulate downstream effectors of the phosphoinositide-3 kinase (PI3K)-dependent pathway, without enhancing PI3K activity. To clarify this paradox, we explored the activity of phosphatase and tensin homolog deleted in chromosome 10 (PTEN), the PI3K major regulator, in primary cultures of rat Sertoli cells. We show that, within minutes, FSH increases PTEN neo-synthesis, requiring the proteasomal degradation of an unidentified intermediate, as well as PTEN enzymatic activity. Importantly, introducing an antisense cDNA of PTEN into differentiating Sertoli cells restores FSH-dependent cell proliferation. In conclusion, these results provide a new mechanism of PTEN regulation, which could serve to block entry into S phase of Sertoli cells, while they are proceeding through differentiation in prepubertal animals.

Une nouvelle fonction pour la transferrine exprimée par le testicule

Chez l’homme, les oligospermies sévères sont associées à un faible taux de transferrine dans le liquide séminal. La transferrine apparaît comme un bon indicateur pour définir les dysfonctionnements testiculaires. Son niveau d’expression dans le testicule doit être parfaitement contrôlé. Elle y joue un rôl dans le transport du fer. Mais de récents résultats montrent l’existence d’une forme dimérique de la transferrine sertolienne comme puissant régulateur de la phagocytose des corps résiduels par les cellules de Sertoli.

Transferrin: structure, function and potential therapeutic actions

There are many proteins that can multi-task. Transferrin, widely known as an iron-binding protein, is one such example of a multi-tasking protein. In this review, the multiple biological actions of transferrin, including its growth and cytoprotective activities, are discussed with the view of highlighting the potential therapeutic applications of this protein.

The testicular-derived Sertoli cell: cellular immunoscience to enable transplantation

There is a renewed enthusiasm for the potential of cellular transplantation as a therapy for numerous clinical disorders. The revived interest is largely due to the unprecedented success of the "Edmonton protocol," which produced a 100% cure rate for type I diabetics following the transplantation of human islet allografts together with a modified immunosuppressive regimen. While these data provide a clear and unequivocal demonstration that transplantation is a viable treatment strategy, the shortage of suitable donor tissue together with the debilitating consequences of lifelong immunosuppression necessitate a concerted effort to develop novel means to enable transplantation on a widespread basis. This review outlines the use of Sertoli cells to provide local immunoprotection to cografted discordant cells, including those from xenogeneic sources. Sertoli cells are normally found in the testes where one of their functions is to provide local immunologic protection to developing germ cells. Isolated Sertoli cells 1) engraft and self-protect when transplanted into allogeneic and xenogeneic environments, 2) protect cografted allogeneic and xenogeneic cells from immune destruction, 3) protect islet grafts to reverse diabetes in animal models, 4) enable survival and function of cografted foreign dopaminergic neurons in rodent models of Parkinson's disease (PD), and 5) promote regeneration of damaged striatal dopaminergic circuitry in those same PD models. These benefits are discussed in the context of several potential underlying biological mechanisms. While the majority of work to date has focused on Sertoli cells to facilitate transplantation for diabetes and PD, the generalized ability of these unique cells to potently suppress the local immune environment opens additional clinical possibilities.

Establishment and characterization of immortalized ovine Sertoli cell lines

The objective of this study was to generate immortalized Sertoli cell lines from prepubertal lamb testes to facilitate investigations during the course of testicular differentiation. The Sertoli cells were enzymatically isolated and immortalized by transfection, with the sequences coding for the SV40 large T-antigen fused downstream of regulatory elements from the human vimentin gene. The different cell lines were positively stained with antibodies to vimentin and transferrin, in agreement with their Sertoli origin. Reverse transcriptase polymerase chain reaction was used to analyze the specific expression of molecular markers (clusterin/sulfated glycoprotein ISGP-2], follicle-stimulating hormone [rFSH], alpha-inhibin, anti-Müllerian hormone, Wilms' tumor gene [WT-1], steroidogenic factor 1 [SF-1], SRY-related HMG box gene g [SOX9], and sex-determining region of Y chromosome) normally expressed in this cellular type. All were shown to express messenger ribonucleic acids for SGP-2, alpha-inhibin, WT-1, SOX9, and SF-1 (except SF-1 for clone no. 1). Moreover, we performed alkaline phosphatase and receptor tyrosine kinase p145 (c-kit) detection to ensure the absence of contamination by peritubular, germ cells, and Leydig cells. Both tests were negative for all the seven cell lines. These ovine Sertoli cell lines are the first ones obtained from livestock that exhibit specific Sertoli cell characteristics resembling different stages of phenotypic development. They provide useful in vitro model systems for toxicological investigations, coculture, and transfection experiments, making it possible to study signal transduction pathways, cell-cell interactions, and gene expression in species other than rodents.

The ERK-dependent signalling is stage-specifically modulated by FSH, during primary Sertoli cell maturation

Primary cultures of Sertoli cells provide an interesting model to study how signalling pathways induced by a single hormone in a single cell type evolve, depending on the developmental stage. In vivo, follicle-stimulating hormone (FSH) induces proliferation of Sertoli cells in neonate and controls the subsequent differentiation of the entire population. Molecular mechanisms underlying Sertoli cell pleiotropic responses to FSH have long been investigated. But to date, only cAMP-dependent kinase (PKA) activation has been reported to account for most FSH biological activities in male. Here, we demonstrate that FSH activates the ERK MAP kinase pathway following dual coupling of the FSH-R both to Gs and to Gi heterotrimeric proteins, in a PKA- and also Src-dependent manner. This activation is required for FSH-induced proliferation of Sertoli cells isolated 5 days after birth. Consistently, we show that the ERK-mediated FSH mitogenic effect triggers upregulation of cyclin D1. In sharp contrast, at 19 days after birth, as cells proceed through their differentiation program, the ERK pathway is dramatically inhibited by FSH treatment. Taken together, these results show that FSH can exert opposite effects on the ERK signalling cascade during the maturation process of Sertoli cells. Thus, signalling modules triggered by the FSH-R evolve dynamically throughout development of FSH natural target cells.

Alternative splicing prevents transferrin secretion during differentiation of a human oligodendrocyte cell line

Transferrin, the iron-transport protein of vertebrate serum, is synthesized mainly in the liver, from which it is secreted into the blood. Transferrin is also synthesized in oligodendrocytes and is an early marker of their differentiation. We have analyzed the regulation of transferrin expression in HOG cells, a human oligodendrocyte cell line. Transferrin expression was correlated with the appearance of oligodendrocyte differentiation markers when cells were exposed to differentiation medium. In contrast to the protein expressed in hepatocytes or in Sertoli cells, transferrin was secreted by neither HOG cells nor immature rat primary oligodendrocytes in vitro. Moreover, transferrin appears to be localized in the cytosol and not in the secretory compartment, as is expected for secreted proteins. This transferrin localization was correlated with the synthesis of a specific transcript, resulting from an alternative splicing, which leads to the elimination of the signal peptide sequence. These results suggest the existence of a functional difference between transferrin synthesized in the brain and in other organs such as liver and testis. They are in accordance with the hypothesis that transferrin plays a specific role, other than iron transport, in oligodendrocyte maturation and in the myelination process.

Heregulins or neu differentiation factors and the interactions between peritubular myoid cells and Sertoli cells

Interactions between (mesenchymal) peritubular myoid cells and (epithelial) Sertoli cells play an important role in the control of Sertoli cell function and spermatogenesis. The factors involved, however, have only partially been identified. Heregulins or neu differentiation factors (NDFs) mediate mesenchymal-epithelial interactions in a variety of tissues, but their role in the testis has not been investigated. Here we demonstrate that recombinant human heregulin-alpha (Her-alpha) and Her-beta stimulate transferrin and androgen-binding protein production by cultured rat Sertoli cells up to 2.5-fold. These effects are more pronounced than those of previously identified growth factors active in this assay, such as insulin-like growth factor I and basic fibroblast growth factor. Combination with these factors results in additive effects and in marked morphological changes in the Sertoli cell cultures, including formation of tubule-like structures. Stimulation of androgen-binding protein secretion is paralleled by increased levels of the corresponding messenger RNA. This parallelism was less consistent for transferrin. Semiquantitative RT-PCR indicates that the expression of NDF-alpha and NDF-beta is more pronounced in peritubular cells than in Leydig or Sertoli cells. Conversely, the main receptors for heregulins/NDFs, HER-3 and HER-4, are predominantly expressed in Sertoli cells. A displacement assay confirms the presence of high-affinity binding sites for [125I]Her-beta on intact Sertoli cells and reveals parallel displacement curves for Her-beta, Her-alpha, and concentrated peritubular cell-conditioned medium (PTCM; estimated ED50 values: 1 ng/ml, 50 ng/ml, and 130 microg protein/ml, respectively), indicating that peritubular cells secrete one or more factors able to compete for heregulin receptors. It is concluded that heregulins/NDFs may play a role in mesenchymal-epithelial interactions in the testis. Estimates of the concentrations of heregulins in PTCM, however, make it unlikely that they contribute significantly to the effects observed with low concentrations of PTCM and ascribed to the putative mediator PModS (peritubular factor that modulates Sertoli cell function). Further investigations will be required to define the exact role of heregulins in the testis.

In vitro regulation of rat Sertoli cell transferrin expression by tumor necrosis factor alpha and retinoic acid

In the present study, we examined the in vitro regulation of 20-day-old rat Sertoli cell transferrin expression by tumor necrosis factor alpha (TNFalpha), a paracrine factor produced by germ cells. Addition of TNFalpha to highly purified cultured Sertoli cells resulted in a dose and time-dependent enhancement in the levels of transferrin mRNA (Northern-blot) and protein (RadioImmunoAssay) with an ED50 of 120 pM. Co-treatment of Sertoli cells with the optimal dose of retinoic acid (RA, a potent inducer of transferrin) and TNFalpha induced a stimulation of transferrin that was significantly higher than the FIRT combination, a well known mixture of transferrin activators. Actinomycin D inhibited the effects of TNFalpha and of RA, suggesting that ongoing RNA synthesis was required to enhance transferrin. We next demonstrated that RA and TNFalpha exerted additive effects on transferrin expression as assessed by dose-response and kinetics studies. Moreover pre-treatment with RA, while greatly increasing the amount of transferrin produced, did not modify Sertoli cell responsiveness to TNFalpha. Together these results show that TNFalpha and RA are likely to act independently, additively and at least at the transcriptional level to increase transferrin expression.