The role of Fas-mediated apoptosis in thyroid autoimmune disease

NaCS-PDMDAAC immobilized cultivation of recombinant Dictyostelium discoideum for soluble human Fas ligand production

Dictyostelium discoideum is a promising eukaryotic host for the expression of heterologous proteins requiring post-translational modifications. However, the dilute nature of D. discoideum cell culture limits applications for high value proteins production. D. discoideum cells, entrapped in sodium cellulose sulfate/poly-dimethyl-diallyl-ammonium chloride (NaCS-PDMDAAC) capsules were used for biosynthesis of the heterologous protein, soluble human Fas ligand (hFasL). Semi-continuous cultivations with capsules recycling were carried out in shake flasks. Also, a scaled-up cultivation of immobilized D. discoideum for hFasL production in a customized vitreous airlift bioreactor was conducted. The results show that NaCS-PDMDAAC capsules have desirable biophysical properties including biocompatibility with the D. discoideum cells and good mechanical stability throughout the duration of cultivation. A maximum cell density of 2.02 × 10(7) cells mL(-1) (equivalent to a maximum cell density of 2.22 × 10(8) cells mL(-1) in capsules) and a hFasL concentration of 130.40 μg L(-1) (equivalent to a hFasL concentration of 1434.40 μg L(-1) in capsules) were obtained in shake flask cultivation with capsules recycling. Also, a maximum cell density of 1.72 × 10(7) cells mL(-1) (equivalent to a maximum cell density of 1.89 × 10(8) cells mL(-1) in capsules) and a hFasL concentration of 106.10 μg L(-1) (equivalent to a hFasL concentration of 1167.10 μg L(-1) in capsules) were obtained after ∼170 h cultivation in the airlift bioreactor (with a working volume of 200 mL in a 315 mL bioreactor). As the article presents a premier work in the application of NaCS-PDMDAAC immobilized D. discoideum cells for the production of hFasL, more work is required to further optimize the system to generate higher cell densities and hFasL titers for large-scale applications.

TRAIL and DR5 promote thyroid follicular cell apoptosis in iodine excess-induced experimental autoimmune thyroiditis in NOD mice

Death receptor-mediated apoptosis has been implicated in target organ destruction in patients with chronic autoimmune thyroiditis. Several apoptosis signaling pathways, such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), have been shown to be active in thyroid cells and may be involved in destructive thyroiditis. Thyroid toxicity of iodide excess has been demonstrated in animals fed with an iodide-rich diet, but its pathogenic role remains unclear. The effects of excessive iodine on TRAIL and its death receptor expression in thyroid were investigated. Experimental autoimmune thyroiditis (EAT) was induced by excessive iodine and thyroglobulin (Tg) in non-obese diabetic mice. The expression of TRAIL and its death receptor DR5 was detected by immunofluorescence staining. Following administration of excessive iodine alone, Tg, and excessive iodine combined with Tg, TRAIL-positive cells appear not only in follicular cells but also in lymphocytes infiltrated in the thyroid, whereas DR5-positive cells appear only in follicular cells. Large numbers of CD3-positive cells and a few CD22-positive cells were detected in thyroid. A great amount of follicular cells were labeled specifically by terminal deoxynucleotide transferase-mediated deoxynucleotide triphosphate nick-end labeling assay. Taken together, our results suggest that excessive iodine could induce TRAIL and DR5 abnormal expression in thyroid. TRAIL band with DR5 to promote follicular cells apoptosis thus mediate thyroid destruction in EAT.

Effects of elevated thyroid hormone on adult rabbit extraocular muscles

PURPOSE

Human extraocular muscles (EOM) are preferentially susceptible to thyroid eye disease. Although the specific cause of this autoimmune disorder is unknown, it is often associated with elevated thyroid hormone levels. Thus, the effect of elevated thyroid hormone levels on cross-sectional area, myofiber size, satellite cells, and myosin heavy chain (MyHC) isoform expression was examined in adult rabbit EOMs, to determine how elevated thyroid hormone alters EOM biology.

METHODS

After 1 month of elevated thyroid hormone levels, the EOMs were removed and prepared for histologic examination. Total muscle mass, myofiber size, patterns of MyHC isoform expression, and the number of satellite cells were determined.

RESULTS

Elevated thyroid hormone levels significantly decreased muscle mass, total number of myofibers, and mean cross-sectional area of the myofibers. Alterations in MyHC isoform expression were extremely complex, but several basic patterns emerged. The percentages of neonatal- and developmental-positive myofibers decreased in almost all EOM regions examined, and the percentages of slow-positive myofibers significantly increased. In contrast to normal EOMs, which retain a population of activated satellite cells throughout life, elevated thyroid hormone levels resulted in the virtual disappearance of MyoD-positive cells and a decrease in Pax7-positive cells.

CONCLUSIONS

The reductions in EOM size, number of fibers expressing developmental and neonatal MyHC, and number of MyoD- and Pax7-positive satellite cells suggest that elevated thyroid hormone levels decrease the ongoing myofiber remodeling normally seen in the EOM. These catabolic changes have important implications for maintenance of function in the EOMs.

Apoptotic study in Graves disease treated with thyroid arterial embolization

OBJECTIVE

To investigate apoptosis in the thyroid of Graves disease (GD) induced by thyroid arterial embolization.

MATERIALS AND METHODS

Forty one patients with clinically and laboratorily ascertained GD were treated with thyroid arterial embolization and followed up for 3-54 months following embolization. Prior to embolization and at 1, 3, 6, 12 and 36 months following embolization, thyroid autoimmunue antibodies were tested respectively, including thyroid stimulating antibody (TSAb), thyroglobulin antibody (TGAb) and thyroid microsomal antibody (TMAb). Thyroid biopsy was performed under the guidance of computed tomography for immunohistochemistry examination using semi-quantity analysis.

RESULTS

The positive staining of Fas and FasL was mostly in the cytoplasma and cell membrane, the positive expression of Bax was mainly in the cytoplasma, and no positive expression of P53 was detected in the thyroid cells before embolization. After arterial embolziation, the positive cell number and staining degree of these genes were both greater than before embolization.

CONCLUSION

The treatment method of thyroid arterial embolization can effectively enhance the positive expression of pro-apoptotic genes of Fas, FasL, Bax, Bcl-2 and P53 in GD thyroid, thus promoting apoptosis of GD thyroid and helping restore the thyroid size and function to normal conditions.

Differential expression of Fas system apoptotic molecules in peripheral lymphocytes from patients with Graves' disease and Hashimoto's thyroiditis

OBJECTIVE

To examine whether the Fas system apoptotic molecules are differentially expressed in Graves' disease (GD) and Hashimoto's thyroiditis (HT), the two opposite phenotypes of autoimmune thyroid disease (AITD).

DESIGN

The expression of Fas and Fas ligand (FasL) on peripheral CD4 and CD8 lymphocytes, and non-lymphoid immune cells as well as their soluble forms in serum from untreated patients with GD and HT were evaluated.

METHODS

Flow cytometry was performed for the study of peripheral immune cells from 70 newly diagnosed patients with AITD (55 with HT and 15 with GD) and 20 controls. ELISA was used for the measurement of soluble Fas (sFas) in serum samples from a subgroup of 35 AITD patients.

RESULTS

An increase in the proportion of CD4 and CD8 cells expressing Fas was found in both GD and HT, albeit with some differences, when compared with controls. Importantly, in GD patients, the intensity of Fas expression on CD4 and CD8 lymphocytes was reduced and sFas levels in serum were simultaneously increased when compared with HT patients and controls.

CONCLUSIONS

The Fas system apoptotic molecules appear to be differentially expressed on peripheral lymphocytes in the two opposite phenotypes of AITD.

Efficient expression and primary purification of 6-his tagged human Fas ligand in Dictyostelium discoideum

Human Fas ligand (hFasL) is a member of the tumor necrosis factor (TNF) family with many medical interests. To produce this protein efficiently, an improved vector which could express the recombinant hFasL protein with a 6-his tag at its C-terminal was constructed. The new vector was transformed into Dictyostelium discoideum AX3 which then produced 157 microg hFasL l(-1). Using one-step Ni-affinity chromatography, it was purified with a recovery of 92% and purity of 91%.

Novel Negative Regulator of Expression in Fas Ligand (CD178) Cytoplasmic Tail: Evidence for Translational Regulation and against Fas Ligand Retention in Secretory Lysosomes

Fas ligand ((FasL) CD178), a type II transmembrane protein, induces apoptosis of cells expressing the Fas receptor. It possesses a unique cytoplasmic tail (FasLCyt) of 80 aa. As a type II transmembrane protein, the early synthesis of FasLCyt could affect FasL translation by impacting FasL endoplasmic reticulum translocation and/or endoplasmic reticulum retention. Previous studies suggest that the proline-rich domain (aa 43-70) in FasLCyt (FasLPRD) inhibits FasL membrane expression by retaining FasL in the secretory lysosomes. This report shows that deletion of aa 2-33 of FasLCyt dramatically increased total FasL levels and FasL cell surface expression. This negative regulator of FasL expression is dominant despite the presence of FasLPRD. In addition, retention of proline-rich domain-containing FasL in the cytoplasm was not observed. Moreover, we demonstrated that FasLCyt regulates FasL expression by controlling the rate of de novo synthesis of FasL. Our study demonstrated a novel negative regulator of FasL expression in the FasLCyt region and its mechanism of action.

Production of the soluble human Fas ligand by Dictyostelium discoideum cultivated on a synthetic medium

Human Fas ligand (hFasL) is of considerable interest since it is a type II transmembrane glycoprotein that induces programmed cell death, or apoptosis. In this study Dictyostelium discoideum was used to produce a soluble form of the human Fas ligand. The recombinant cells were adapted to a modified synthetic FM medium, called SIH medium. Cells adapted to the SIH medium reached about 2 times higher cell densities and hFasL concentrations on this medium compared with cells growing on the standard complex medium HL-5C. Even higher values were achieved by a dissolved oxygen-controlled fed-batch cultivation in a conventional stirred bioreactor on SIH medium. Cell densities of up to 5.5 x 10(7) ml(-1) and a maximum hFasL concentration of 148 microgl(-1) were obtained. These results were further improved by means of continuous cultivation of D. discoideum in a bioreactor equipped with cell retention by microfiltration. At low space velocity very high cell densities of up to 2.4 x 10(8) ml(-1) and hFasL concentrations of up to 205 microgl(-1) were achieved.

Defective function of Fas in T cells from paediatric patients with autoimmune thyroid diseases

Triggering of the Fas receptor induces T cell apoptosis and is involved in shutting-off the immune response. Inherited defects impairing Fas function cause the autoimmune lymphoproliferative syndrome, and may play a role in other autoimmune diseases. The aim of this work was to analyse the Fas function in paediatric patients with thyroid autoimmunities. We found that T cells from 24/28 patients with Graves' disease (GD) and 12/35 patients with Hashimoto's thyroiditis (HT) displayed defective Fas function. In HT, the defect was more frequent in patients requiring replacement therapy (11/20) than in those not requiring (1/15); moreover, in untreated HT the highest defect was displayed by patients with the highest levels of autoantibodies. Fas was always expressed at normal levels and no Fas mutations were detected. Analysis of the healthy parents of seven Fas-resistant patients showed that several of them were Fas-resistant, which suggests a genetic component. Fusion of Fas-resistant T cells with the Fas-sensitive HUT78 T cell line generated Fas-resistant hybrid cells, which suggests the presence of molecules exerting a dominant negative effect on Fas function. Analysis of Fas-induced activation of caspase-8 and -9 showed decreased activity of both caspases in HT, whereas activity of caspase-9 was increased and that of caspase-8 was decreased in GD. These data suggest that heterogeneous inherited defects impairing Fas function favour the development of thyroid autoimmunities.

Role of inherited defects decreasing Fas function in autoimmunity

Fas is a death receptor belonging to the TNFR superfamily and induces cell apoptosis by both activating a caspase cascade and altering mitochondria. In the immune system, Fas is involved in the switching-off of the immune responses and cell mediated cytotoxicity. In humans, genetic defects decreasing Fas function cause the Autoimmune Lymphoproliferative Syndrome (ALPS) where autoimmunities are associated with accumulation of polyclonal lymphocytes in the secondary lymphoid tissues and expansion of T cells lacking both CD4 and CD8 (DN cells). Expansion of DN cells is absent in an ALPS variant, named Dianzani's Autoimmune Lymphoproliferative Disease (DALD). The observation that DALD patients' families display increased frequency of autoimmune diseases different from ALPS suggests that defects of Fas function may also play a role in development of "common" autoimmune diseases. This possibility is supported by detection of defective Fas function in substantial proportions of patients with the multiple autoimmune syndrome or aggressive forms of type 1 diabetes or multiple sclerosis. This article reviews data suggesting that development of autoimmune/lymphoproliferative patterns may involve several alterations hitting the Fas system, but might also involve alterations in other systems contributing to the switching-off or proliferation of lymphocytes.

Autoimmune thyroid diseases: etiology, pathogenesis, and dermatologic manifestations

Autoimmune thyroid disease (AITD) including Graves' disease, Hashimoto's thyroiditis, and idiopathic hypothyroidism (atrophic Hashimoto's thyroiditis) is of vital concern to the dermatologist. This article reviews the cutaneous manifestations of Graves' disease and Hashimoto's thyroiditis. Recognition of dermatologic manifestations of AITD may alert practitioners to investigate for these disorders. The immune response involved in the pathogenesis of AITD is detailed. Current understanding of the role of genetic and environmental factors, antigens, and apoptosis are elaborated. The future holds exciting insight into the etiology, pathogenesis, and treatment of AITD.

High levels of exogenous C2-ceramide promote morphological and biochemical evidences of necrotic features in thyroid follicular cells

CD95 and ceramide are known to be involved in the apoptotic mechanism. The triggering of CD95 induces a cascade of metabolic events that progressively and dramatically modifies the cell shape by intense membrane blebbing, leading to apoptotic bodies production. Although the CD95 pathway has been abundantly described in normal thyrocytes, the effects of cell permeable synthetic ceramide at morphological and biochemical levels are not fully known. In the present study, we show that thyroid follicular cells (TFC) exposed to 20 microM of C(2)-ceramide for 4 h are characterized by morphological features of necrosis, such as electron-lucent cytoplasm, mitochondrial swelling, and loss of plasma membrane integrity without drastic morphological changes in the nuclei. By contrast, TFC treated with 2 microM of C(2)-ceramide for 4 h are able to accumulate GD3, activate caspases cascade, and induce apoptosis. Furthermore, we provide evidence that 20 microM of C(2)-ceramide determine the destruction of mitochondria and are not able to induce PARP cleavage and internucleosomal DNA fragmentation, suggesting that the apoptotic program is not activated during the death process and nuclear DNA is randomly cleaved as the consequence of cellular degeneration. Pretreatment with 30 microM of zVAD-fmk rescued TFC from 2 microM of C(2)-ceramide-induced apoptosis, whereas, 20 microM of C(2)-ceramide exposure induced necrotic features. Deltapsi(m) was obviously altered in cells treated with 20 microM of C(2)-ceramide for 4 h (75% +/- 3.5%) compared with the low percentage (12.5% +/- 0.4%) of cells with altered Deltapsi(m) exposed to 2 microM of C(2)-ceramide. Whereas, only 20% +/- 1.1% of cells treated with anti-CD95 for 1 h showed altered Deltapsi(m). Additionally, Bax and Bak, two pro-apoptotic members, seem to be not oligomerized in the mitochondrial membrane following ceramide exposure. These results imply that high levels of exogenous ceramide contribute to the necrotic process in TFC, and may provide key molecular basis to the understanding of thyroid signaling pathways that might promote the apoptotic mechanism in thyroid tumoral cells.

Autoimmune thyroid disease: new models of cell death in autoimmunity

Autoimmunity to thyroid antigens leads to two distinct pathogenic processes with opposing clinical outcomes: hypothyroidism in Hashimoto's thyroiditis and hyperthyroidism in Graves' disease. The high frequency of these diseases and easy accessibility of the thyroid gland has allowed the identification of key pathogenic mechanisms in organ-specific autoimmune diseases. In early investigations, antibody- and T-cell-mediated death mechanisms were proposed as being responsible for autoimmune thyrocyte depletion. Later, studies on apoptosis have provided new insights into autoimmune target destruction, indicating the involvement of death receptors and cytokine-regulated apoptotic pathways in the pathogenesis of thyroid autoimmunity.

Inflammatory cytokine regulation of TRAIL-mediated apoptosis in thyroid epithelial cells

Death receptor-mediated apoptosis has been implicated in target organ destruction in chronic autoimmune thyroiditis. Depending on the circumstances, inflammatory cytokines such as IL-1, TNF and IFNgamma have been shown to contribute to either the induction, progression or inhibition of this disease. Here we demonstrate that the death ligand TRAIL can induce apoptosis in primary, normal, thyroid epithelial cells under physiologically relevant conditions, specifically, treatment with the combination of inflammatory cytokines IL-1beta and TNFalpha. In contrast, IFNgamma is capable of blocking TRAIL-induced apoptosis in these cells. This regulation of TRAIL-mediated apoptosis by inflammatory cytokines appears to be due to alterations of cell surface expression of TRAIL receptor DR5 and not DR4. We also show the in vivo presence of TRAIL and TRAIL receptors DR5 and DcR1 in both normal and inflamed thyroids. Our data suggests TRAIL-mediated apoptosis may contribute to target organ destruction in chronic autoimmune thyroiditis.

Thyrocyte targets and effectors of autoimmunity: a role for death receptors?

In Hashimoto's thyroiditis, thyrocytes die by apoptosis. Whether this is the result of impaired antiapoptotic gene expression or hyperexpression of proapoptotic signals or other mechanisms is not fully established. Following the suggestion that thyrocytes from Hashimoto's glands die by a fratricidal killing mediated by Fas/Fas ligand, we have investigated whether thyroid cells from different clinical conditions are able to kill Fas-expressing target cells. We have studied whether this effector ability was mediated by Fas/Fas ligand, perforin or other death receptors/ligands, i.e., tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/tumor necrosis factor-related apoptosis-inducing ligand receptor (TRAIL-R). We have confirmed that thyroid preparations can kill Fas-expressing HUT78 targets through apoptosis. Cell death was only partially dependent on Fas/Fas ligand but it was trypsin-sensitive. Blocking perforin did not affect Fas-expressing target killing while caspase inhibitors had a consistent although limited effect. Thyroid cells were not sensitive to TRAIL/TRAIL-R. We have also found that both thyrocytes and lymphocytes from Graves' disease thyroids were effective at killing autologous and heterologous Fas-expressing targets. Conversely, killing of these targets could be shown only with lymphocytes (but not with thyrocytes) from Hashimoto's glands. In Hashimoto's thyroiditis, thyrocytes were poorly functional while lymphocytes were able to operate as effectors. It is envisaged that thyrocyte death in Hashimoto's would result from autologous thyrocyte killing perpetrated by lymphocytes. Death receptors/ligands would appear to play a role. However, a caspase-independent mechanism may also coexist and contribute to cell death in Hashimoto's thyroiditis.

Fas-FasL in Hashimoto's thyroiditis

Hashimoto's thyroiditis is a common chronic autoimmune disease characterized by the loss of thyroid follicular cells (thyrocytes) that are gradually replaced by lymphocytic infiltration and diffuse fibrosis. These morphological findings suggested that autoreactive T-cell clones were responsible for thyrocyte destruction and hypothyroidism through effector-target cytotoxic recognition. Later, autonomous interaction between thyrocyte Fas and FasL has been proposed as a major mechanism of thyrocyte depletion in Hashimoto's thyroiditis. Here, we analyze the possible role of Fas and FasL in the pathogenesis of Hashimoto's thyroiditis. We suggest that the Fas-FasL system dictates the outcome of the autoimmune response by acting on both immune and target cells.

Death of the autoimmune thyrocyte: is it pushed or does it jump?

Programmed cell death or apoptosis is central both in physiology during development and in disease. The mechanism of apoptosis is under the control of antiapoptotic survival genes of the Bcl-2 family and proapoptotic death receptors of the TNF superfamily (Fas, TNFR, TRAILR). Following death signal, the death receptor binds to its own receptor and initiates, through binding of adaptors, a cascade of events mediated by the autoproteolytic activation of specific enzymes called caspases. This enzyme activation is ultimately responsible for the dissembly of basic nuclear and cytoplasmic cell structures leading to cell death. In certain cell systems, antiapoptotic genes of the Bcl-2 family prevent the proapoptotic pathway. One of their roles is to maintain mitochondrial function integrity. In autoimmune destructive thyroiditis high levels of apoptosis have been demonstrated particularly within the destructed follicles near the infiltrated areas in comparison to Graves' disease and non autoimmune glands. In Hashimoto's thyroiditis Fas expression has been found increased on thyrocytes and in vitro can be modulated by proinflammatory cytokines. FasL expression on thyrocytes remains controversial. Thyroid cells from Graves' disease and multinodular glands are known to kill Fas expressing target cells although Hashimoto's thyrocytes are not efficient effector cells. Intrathyroidal lymphocytes from Hashimoto's thyroids maintain functional killer activity. These findings would suggest that intrathyroidal lymphocytes could be responsible for thyrocyte death in vivo. Whether this mechanism is Fas/FasL, TRAIL/TRAILR dependent can not be confirmed as specific blocking reagents were not able to inhibit cell induced death. In Hashimoto's thyroiditis an impairment of Bcl-2 and Bcl-X anitapoptotic genes on thyrocytes has also been detected. Bcl-X expression can be down-regulated in vitro by incubation with cytokines. These findings suggest that thyrocyte death may not exclusively be the result of specific interactions between death receptor and their ligands but it may involve simultaneous impairment of protective genes of the Bcl-2 family. Whether the impairment of the Bcl-2 family is a direct consequence of environmental stimuli or is the result of an intrinsic thyrocyte (mitochondrial?) alteration is as yet not known.

Thyroid cell apoptosis. A new understanding of thyroid autoimmunity

Apoptosis is a highly regulated mechanism of cell death involved in normal development, immune regulation, and homeostasis. Abnormal apoptotic activity has been implicated in a variety of diseases including cancer, autoimmunity, and degenerative disorders. In the thyroid, altered cell death may play a role in the pathogenesis of autoimmune disorders such as Hashimoto's thyroiditis and Graves' disease. Apoptosis-signaling pathways can be initiated through activation of death receptors or in response to cellular damage, such as in gamma irradiation. It has been demonstrated that Fas, tumor necrosis factor, and tumor necrosis factor-related apoptosis-inducing ligand pathways are present and functional in the thyroid, although the expression of these molecules and their roles in thyroid autoimmunity have been debated. Thyroid apoptosis is regulated at multiple levels, including receptor and ligand expression, and the expression of antiapoptotic proteins, such as FAP-1 and Bcl-2. These factors may provide potential mechanisms for modifying the pathogenesis of autoimmune thyroid disease.