Transforming growth factor-beta induces apoptosis in activated murine T cells through the activation of caspase 1-like protease

Role and action mechanisms of miR-149 and miR-31 in regulating function of pig cumulus cells and oocytes

Understanding the mechanisms for oocyte maturation and optimizing the protocols for in vitro maturation (IVM) are greatly important for improving developmental potential of IVM oocytes. The miRNAs expressed in cumulus cells (CCs) play important roles in oocyte maturation and may be used as markers for selection of competent oocytes/embryos. Although a recent study from our group identified several new CCs-expressed miRNAs that regulate cumulus expansion (CE) and CC apoptosis (CCA) in mouse oocytes, validation of these findings and further investigation of mechanisms of action in other model species was essential before wider applications. By using both in vitro and in vivo pig oocyte models with significant differences in CE, CCA and developmental potential, the present study validated that miR-149 and miR-31 improved CE and developmental potential while suppressing CCA of pig oocytes. We demonstrated that miR-149 and miR-31 targeted SMAD family member 6 (SMAD6) and transforming growth factor β2 (TGFB2), respectively, in the transforming growth factor-β (TGF-β) signaling. Furthermore, both miR-149 and miR-31 increased CE and decreased CCA via activating SMAD family member 2 (SMAD2) and increasing the expression of SMAD2 and SMAD family member 4. In conclusion, the present results show that miR-149 and miR-31 improved CE and developmental potential while suppressing CCA of pig oocytes by activating the TGF-β signaling, suggesting that they might be used as markers for pig oocyte quality.

Expression of immune regulatory genes in early, mid and late stages of pig (Sus scrofa domesticus) gestation

Semi-allogeneic foetus and placenta exploit various mechanisms to avoid immune-mediated maternal rejection. Several factors and cytokines are attributed for production of immune tolerance during gestation and very little information on expression of these immune-regulatory genes is available in pig. Chorioallantoic membrane (CAM) from early, mid and late gestational stages (n=4) were analysed for expression of immune regulatory genes, viz. Fas ligand (FasL), transporter for antigen processing-1 (TAP-1), transforming growth factor β1 (TGF-β1) and macrophage migration inhibitory factor (MIF) whereas Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was employed as housekeeping gene. FasL gene expression was significantly higher in mid (13.46 fold) and late (28.77 fold) gestation than the early (1 fold) stage.TAP-1 mRNA expression was enhanced by 4.95 fold and 2.69 fold during mid and late gestation respectively in comparison to the early (1 fold) stage. TGF-β1 gene expression was up regulated in mid (2.43 fold) and late (2.29 fold) gestation than the early (1 fold) stage. MIF mRNA expression was enhanced in mid (3.04 fold) and late (1.59 fold) gestation in relation to the early (1 fold) stage. Placenta of pig remains entirely epitheliochorial which may minimise immune recognition and is supposed to diminish potent immune-regulatory mechanisms. However, our present study revealed consistent expression for immune regulatory factors which suggests immune modulation does exist in pig and may impart a role in pregnancy success.

Placental trophoblasts shifted Th1/Th2 balance toward Th2 and inhibited Th17 immunity at fetomaternal interface

The aims were to clarify the effect of placental trophoblasts on T lymphocytes by assessing production of cytokines and expression of transcription factors regulating Th1, Th2, and Th17 immunity in T lymphocytes. Placental trophoblasts were isolated and conditioned medium was made after trophoblast cultivation for 72 h. T lymphocytes were cultured in presence or absence of conditioned medium. ELISA was used to detect concentration of IL-2, TNF-α, IFN-γ, IL-4, IL-10, and IL-17 in supernatants of T cell and real-time PCR was used to detect the status of Th1 (T-bet, STAT-4), Th2 (GATA-3, STAT-6), and Th17 (RORC) immunity in T lymphocyte. We found that the level of IL-2, IFN-γ, TNF-α, and IL-17 was significantly decreased when T lymphocytes were cultured in conditioned medium compared with control, while IL-10 and IL-4 level were not significantly changed. The presence of conditioned medium significantly decreased the ratio of Th1/Th2. The expression of GATA-3 and STAT-6 were significantly increased and STAT-4 was reduced when T lymphocyte was cultured in conditioned medium, while the expression of T-bet and RORC was not significantly different. We concluded that placental trophoblast-induced shift of Th1/Th2 balance toward Th2 and inhibition of Th17 might be among the mechanisms involved in maternal tolerance to fetus.

A putatively functional haplotype in the gene encoding transforming growth factor beta-1 as a potential biomarker for radiosensitivity

PURPOSE

To determine whether genetic variability in TGFB1 is related to circulating transforming growth factor-β1 (TGF-β1) plasma concentrations after radiotherapy and to radiosensitivity of lymphoid cells.

PATIENTS AND METHODS

Transforming growth factor-β1 plasma concentrations (n=79) were measured in patients 1 year after radiotherapy and chromosomal aberrations (n=71) ex vivo before therapy start. Furthermore, TGF-β1 secretion and apoptosis were measured in isolated peripheral blood mononuclear cells of 55 healthy volunteers. These phenotypes were analyzed in relation to five germline polymorphisms in the 5' region of the TGFB1 gene. Because of high linkage disequilibrium, these five polymorphisms reflect frequent genetic variation in this region. A presumed impact of TGF-β1 on DNA damage or repair was measured as micronucleus formation in 30 lymphoblastoid cell lines.

RESULTS

We identified a hypofunctional genetic haplotype termed H3 tagging the 5' region of the TGFB1 gene encoding TGF-β1. H3 was associated with lower TGF-β1 plasma concentrations in patients (p=0.01) and reduced TGF-β1 secretion in irradiated peripheral blood mononuclear cells (p=0.003). Furthermore, cells with H3 were less prone to induction of chromosomal aberrations (p=0.001) and apoptosis (p=0.003) by irradiation. The hypothesis that high TGF-β1 could sensitize cells to DNA damage was further supported by increased micronuclei formation in 30 lymphoblastoid cell lines when preincubated with TGF-β1 before irradiation (p=0.04).

CONCLUSIONS

On the basis of TGF-β1 plasma levels and radiation sensitivity of lymphoid cells, this study revealed a putatively hypofunctional TGFB1 haplotype. The significance of this haplotype and the suggested link between TGF-β1 function and DNA integrity should be further explored in other cell types, as well as other experimental and clinical conditions.

Bioinformatic and functional analysis of TGFBR1 polymorphisms

OBJECTIVES

The transforming growth factor-beta (TGFB) pathway has substantial impact on cellular functions, cell proliferation, and apoptosis. We used bioinformatics, gene expression, and cell biological assays to evaluate the functionality of frequent inherited germline polymorphisms in the TGFB receptor 1 (TGFBR1).

METHODS

In an exploratory (n=55) and confirmatory (n=106) study, we analyzed the TGFB1 pathway after incubation with TGFbeta1 ligand and after exposure to X-rays in peripheral blood human mononuclear cells. Expression of TGFB pathway genes was assessed by real-time PCR, and cellular viability was analyzed by flow cytometry. A total of six polymorphisms including the deletion variant (*6A) were identified to tag currently known common genetic variations in TGFBR1 and were analyzed in relation to the phenotypes.

RESULTS

In accordance with a negative feedback mechanism, incubations with the ligand TGFbeta1 was followed by up-regulation of the intracellular SMAD7 and down-regulation of the SMAD3 mRNA molecules. The TGFBR1*6A deletion variant attenuated the suppression of SMAD3 in response to TGFbeta1 (P=0.02, in both studies). Moreover, cells harboring *6A were more sensitive toward cytotoxic effects of irradiation (P=0.001 after adjustment for age and sex). Cells were particularly prone toward radiation toxicity when carrying, in addition to *6A, the variant allele of rs11568785, which exhibits a strong genetic selection signature.

CONCLUSION

The *6A deletion and the linked rs11568785 polymorphisms seem to attenuate TGFB signaling. This should be considered not only for clinical-epidemiological studies on cancer susceptibility but may also be relevant for side effects from drugs or radiotherapy.

TGF-beta and regulatory T cell in immunity and autoimmunity

INTRODUCTION

The immune response is controlled by several inhibitory mechanisms. These mechanisms include regulatory T cells, which exist in multiple classes. Notable among these are Foxp3-expressing regulatory T cells (Treg), NKT cells, and Tr1 cells. Common to these mechanisms are inhibitory cytokines such as interleukin-10 and transforming growth factor-beta (TGF-beta). TGF-beta and Foxp3-expressing Treg cells are critical in maintaining self-tolerance and immune homeostasis.

DISCUSSIONS

The immune suppressive functions of TGF-beta and Treg cells are widely acknowledged and extensively studied. Nonetheless, recent studies revealed the positive roles for TGF-beta and Treg cells in shaping the immune system and the inflammatory responses. In this paper, we will discuss the role of these mechanisms in the control of immunity and autoimmunity and the mechanisms that underlie how these molecules control these responses.

'Yin-Yang' functions of transforming growth factor-beta and T regulatory cells in immune regulation

Transforming growth factor-beta (TGF-beta) and forkhead box p3-expressing T-regulatory (Treg) cells are critical in maintaining self-tolerance and immune homeostasis. The immune suppressive functions of TGF-beta and Treg cells are widely acknowledged and extensively studied. Nonetheless, recent studies revealed the positive roles of TGF-beta and Treg cells in shaping the immune system and the inflammatory responses. This review discusses our and other's efforts in understanding the negative (Yin) as well as the positive (Yang) roles for TGF-beta and Treg cells in immune regulation.

Murine CTLL-2 cells respond to mIL12: prospects for developing an alternative bioassay for measurement of murine cytokines IL12 and IL18

Cell line-based bioassays are becoming increasingly popular for assessment of biological activities of cytokines primarily because these are easy to perform and are not subject to donor variation. A well characterised cell line with world wide availability would further minimise the inter-assay variations. C57BL/6 mice derived T cell line; CTLL-2 fits this criterion. We explored the potential of CTLL-2 cells to develop a bioassay to detection of murine (m) IL12 and mIL18. Both cytokines have shown significant activity against a number of cancers and importantly, act synergistically via mutual upregulation of each other's receptors. The preliminary flow cytometric analyses of immunostained CTLL-2 cells showed that approximately 65% expressed mIL12 and approximately 5% expressed mIL18 receptors suggesting that these may respond to mIL12. As predicted, cells incubated with different doses of mIL12 or mIL18 for 72 h were responsive to mIL12 and not to mIL18. However, when pre-treated with mIL12 for 24 h prior to incubation with mIL18, there was a significant enhancement in response. The sensitivity of the response was comparable to that obtained using the conventional splenocyte-based IFNgamma release assay. The cytokine specificity of the response was proven unequivocally when significant reduction in CTLL-2 response was observed in the presence of the relevant neutralising antibodies. Finally, we could successfully detect lowest doses of approximately 0.1 pg/microL mIL12 or 40 pg/mL of mIL18 in cell supernatants in a cytokine specific manner, which is lower than the resting levels of these cytokines in mouse sera. Again the sensitivity was comparable to that observed in the conventional IFNgamma release assay. Hence, we have demonstrated the potential of CTLL-2-based bioassay to detect biologically active mIL12 and mIL18 in biological samples accurately and reproducibly.

The roles for cytokines in the generation and maintenance of regulatory T cells

As an essential mechanism for self-tolerance, immune suppression has attracted much attention since the discovery of suppressor T cells, now called regulatory T cells (Tregs), in the 1990s. Different types of Tregs have been described based on distinct expression patterns of surface markers and cytokines. Cytokines are not only essential for function but also important for the generation of Tregs. Interleukin-2 (IL-2), transforming growth factor-beta, IL-10, and other immunoregulatory molecules have been shown to control the generation of Tregs. The presence of other types of cells, in particular antigen-presenting cells (APCs), is critical for the generation of Tregs. Cytokines can serve as either initiators or intermediates for the interactions between APCs and Tregs. This review discusses our current knowledge of how cytokines regulate the generation and maintenance of Tregs.

Clonal restriction of the expansion of antigen-specific CD8+ memory T cells by transforming growth factor-{beta}

Recent evidence showed that transforming growth factor-beta (TGF-beta) regulates the global expansion of CD8+ T cells, which are CD44hi, a marker for memory cells. However, it is not clear whether this regulatory mechanism also applies to the antigen-specific CD8+ memory cells. By using a murine mixed lymphocyte culture (MLC) model, we examined the effect of TGF-beta on antigen-specific CD8+ memory cells [cytotoxic T lymphocyte (CTL)]. We found that the secondary CTL response in CD8+ memory cells from untreated MLC was not affected by TGF-beta but augmented by interleukin (IL)-2, whereas the CD8+ memory cells from TGF-beta-pretreated MLC (MLC-TGF-beta) failed to mount a significant, secondary CTL response, even when IL-2 was added. In exploring this dichotomy, in combination with flow cytometry analysis, we found that prolonged exposure to TGF-beta reduces the CTL activity in CD8+ memory cells. The increase by IL-2 and the reduction by TGF-beta of the CTL responses were clonal-specific. TGF-beta did not affect the CTL response to a third-party antigen or polyclonal T cell activation. Experiments performed with transgenic 2C cells gave similar results. Cell-cycle study performed with adoptive transfer of the cell tracker-labeled MLC cells revealed that the in vivo expansion of CD8+ memory cells from MLC-TGF-beta was restricted severely, and the restriction was clonal-specific, thus offering direct evidence to show that TGF-beta induces clonal restriction of CD8+ memory cell expansion.

Caspase-dependent apoptosis and -independent poly(ADP-ribose) polymerase cleavage induced by transforming growth factor beta1

Apoptosis is an important cell suicide program which involves the caspases activation and is implicated in physiological and pathological processes. Poly(ADP-ribose) polymerase (PARP) cleavage is often associated with apoptosis and has been served as one hallmark of apoptosis and caspase activation. In this study, we aimed to determine TGF-beta1-induced apoptosis and to examine the involvement of caspases and its relationship with PARP cleavage. TGF-beta1 induces strong apoptosis of AML-12 cells which can be detected by DNA fragmentation, FACS, and morphological assays. Z-VAD-fmk, a selective caspase inhibitor, partially inhibits the TGF-beta1-induced apoptosis; but has no effect on TGF-beta1-induced DNA fragmentation and PARP cleavage. However, BD-fmk, a broad-spectrum caspase inhibitor, completely suppresses TGF-beta1-induced apoptosis, but unexpectedly does not inhibit TGF-beta1-induced PARP cleavage. Furthermore, Z-VAD-fmk treatment is able to completely inhibit the daunorubicin-induced apoptosis in A-431 cells, but only slightly blocks the daunorubicin-induced PARP cleavage, whereas BD-fmk can inhibit both daunorubicin-induced apoptosis and PARP cleavage completely. In addition, we observed that both TGF-beta1-induced apoptosis and PARP degradation in AML-12 cells can be completely blocked by inhibiting the protein synthesis with cycloheximide. These results demonstrate for the first time that TGF-beta1-induced caspase-dependent apoptosis is associated with caspase-independent PARP cleavage that requires the TGF-beta1-induced synthesis of new proteins. The results indicate that caspase-3 is not a major caspase involved in TGF-beta1-induced apoptosis in AML-12 cells, and is not required for apoptosis-associated DNA fragmentation. The results also suggest that PARP cleavage may occur as an independent event that can be disassociated with cell apoptosis.

TGF-beta, T-cell tolerance and anti-CD3 therapy

Recent studies by Chatenoud and co-workers suggest that non-mitogenic F(ab′)2 fragments of anti-CD3 antibodies, which cannot bind the Fc receptor, induce a prolonged period of tolerance and prevent diabetes in nonobese diabetic (NOD) mice. Tolerance is established by regulatory T cells through the production of transforming growth factor-β1 (TGF-β1), but the mechanism by which TGF-β1 confers this activity is unclear. Analysis of mice deficient in TGF-β1 suggests that TGF-β1 raises the threshold at which intracellular calcium activates T cells to a level that prevents an autoimmune response.

The role of the combination of IL-2 and TGF-beta or IL-10 in the generation and function of CD4+ CD25+ and CD8+ regulatory T cell subsets

Recently, considerable attention has been focused on thymus‐derived CD4⁺ regulatory T cells that constitutively express CD25 and have a contact‐dependent, cytokine‐independent mechanism in vitro. However, peripheral CD4⁺ and CD8⁺ T cells can also be induced to become regulatory T cells. Here we review our studies using the combination of IL‐2 and transforming growth factor β (TGF‐β) to generate regulatory T cell subsets ex vivo, and the work of others using IL‐10 to induce suppressive activity. Under certain conditions, the autocrine effects of TGF‐β and IL‐10 induce peripheral T cells to produce immunosuppressive levels of each of these cytokines. This effect of TGF‐β is IL‐2 dependent. Under other conditions IL‐2 and TGF‐β can induce CD4⁺ cells to develop potent contact‐dependent, cytokine‐independent regulatory activity. At present, there is considerable confusion concerning the mechanism of action of CD4⁺ CD25⁺ cells because cytokine‐producing regulatory T cells generated in the periphery can express CD25 and other markers displayed by naturally occurring, thymus‐derived regulatory T cells. We, therefore, propose a nomenclature that identifies thymus‐derived and peripheral regulatory cells, and that also differentiates T regulatory cells from T helper cells. Because T regulatory cells broadly control T helper cell reactivity, the mechanisms that control regulatory cell function are also reviewed. Finally, the potential use of regulatory T cells generated ex vivo as an adoptive immunotherapy for certain autoimmune diseases, to prevent organ graft rejection, or to prevent pathologic host responses to infectious agents is discussed.

TGF-beta 1 regulates lymphocyte homeostasis by preventing activation and subsequent apoptosis of peripheral lymphocytes

TGF-beta1 plays an important role in the maintenance of immune homeostasis and self-tolerance. To determine the mechanism by which TGF-beta1 prevents autoimmunity we have analyzed T cell activation in splenic lymphocytes from TGF-beta1-deficient mice. Here we demonstrate that unlike wild-type splenic lymphocytes, those from Tgfb1(-/-) mice are hyporesponsive to receptor-mediated mitogenic stimulation, as evidenced by diminished proliferation and reduced IL-2 production. However, they have elevated levels of IFN-gamma and eventually undergo apoptosis. Receptor-independent stimulation of Tgfb1(-/-) T cells by PMA plus ionomycin induces IL-2 production and mitogenic response, and it rescues them from anergy. Tgfb1(-/-) T cells display decreased CD3 expression; increased expression of the activation markers LFA-1, CD69, and CD122; and increased cell size, all of which indicate prior activation. Consistently, mutant CD4(+) T cells have elevated intracellular Ca(2+) levels. However, upon subsequent stimulation in vitro, increases in Ca(2+) levels are less than those in wild-type cells. This is also consistent with the anergic phenotype. Together, these results demonstrate that the ex vivo proliferative hyporesponsiveness of Tgfb1(-/-) splenic lymphocytes is due to prior in vivo activation of T cells resulting from deregulated intracellular Ca(2+) levels.

TGF beta 1 inhibits Ca2+-calcineurin-mediated activation in thymocytes

TGFbeta1 is a polypeptide growth modulatory and differentiation factor involved in many biological processes including immune homeostasis and self-tolerance. Tgfb1 knockout mice die around weaning age due to severe inflammation in most major organ systems, but the mechanism underlying this disease is not understood. In this study we demonstrate that Tgfb1(-/-) CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes are hyperresponsive to receptor-mediated and receptor-independent mitogenic stimulation. A suboptimal concentration of ionomycin in the presence of PMA fully activates Tgfb1(-/-) thymocytes, whereas the inhibitors of Ca(2+) influx and calcineurin, EGTA and FK506, eliminate the hyperresponsiveness. Hence, the hypersensitivity of Tgfb1(-/-) thymocytes is due to a lowered threshold for Ca(2+)-dependent activation. Further, we demonstrate that the hypersensitivity of thymocytes results from the absence of TGFbeta1 and not from the inflammatory environment because the thymocytes are hyperresponsive in preinflammatory-stage Tgfb1(-/-) mice. Our results suggest for the first time that TGFbeta1 functions to inhibit aberrant T cell expansion by maintaining intracellular calcium concentration levels low enough to prevent a mitogenic response by Ca(2+)-independent stimulatory pathways alone. Consequently, TGFbeta1 prevents autoimmune disease through a Ca(2+) regulatory pathway that maintains the activation threshold above that inducible by self-MHC-TCR interactions.

Influence of gangliosides on the IL-2- and IL-4-dependent cell proliferation

Ganglioside-induced apoptosis in the cells of IL-2-dependent cytotoxic murine cell line CTLL-2 was shown to be caspase dependent: GM1-, GM2-, and GD3-induced suppression of cell proliferation was cancelled by a general caspase inhibitor Z-VAD-FMK. Ganglioside-induced apoptosis pathways are different for different individual glycolipids; the differences exist both at the initiation and effector stages of the caspase cascade. Only for GM1-induced process, molecular mechanisms of signal transduction coincide with the ones for CD95 and TNFalpha: the participation of both the main initiation caspases 8, 1, and 4, and caspases 3 and 9 as well, has been shown. Caspase 3 participates in the pathway induced by GM3, GD1a, GD1b, and GT1b, but not by GM2. As morphological features show, tumor-associated ganglioside GM2 is also a stimulus of programmed cell death (PCD) for CTLL-2 cell line: addition of GM2 into cell culture has resulted in appearance of annexin V-positive cells and in accumulation of DNA breaks (shown by the TUNEL direct dyeing of the open ends). But a caspase 3 inhibitor Z-DEVD-FMK did not restore the cell proliferation suppressed by GM2, and addition of a fluorescent substrate of caspase 3 Ac-DEVD-AFC did not result in the fluorescence development. So caspase 3 does not participate in downstream pathways of GM2-induced cell apoptosis, and a PCD-effector system other than the apoptosome-mediated one is involved here.

The potential of human regulatory T cells generated ex vivo as a treatment for lupus and other chronic inflammatory diseases

Regulatory T cells prevent autoimmunity by suppressing the reactivity of potentially aggressive self-reactive T cells. Contact-dependent CD4+ CD25+ 'professional' suppressor cells and other cytokine-producing CD4+ and CD8+ T-cell subsets mediate this protective function. Evidence will be reviewed that T cells primed with transforming growth factor (TGF)-beta expand rapidly following restimulation. Certain CD4+ T cells become contact-dependent suppressor cells and other CD4+ and CD8+ cells become cytokine-producing regulatory cells. This effect is dependent upon a sufficient amount of IL-2 in the microenvironment to overcome the suppressive effects of TGF-beta. The adoptive transfer of these suppressor cells generated ex vivo can protect mice from developing chronic graft-versus-host disease with a lupus-like syndrome and alter the course of established disease. These data suggest that autologous T cells primed and expanded with TGF-beta have the potential to be used as a therapy for patients with systemic lupus erythematosus and other chronic inflammatory diseases. This novel adoptive immunotherapy also has the potential to prevent the rejection of allogeneic transplants.