Apoptosis in thyroid tissue from patients with Hashimoto's thyroiditis

Experimental rat models for Hashimoto's thyroiditis

PURPOSE

Hashimoto's thyroiditis (HT) is an autoimmune thyroid disease characterized by T lymphocyte-mediated destruction of thyroid follicles. To study the pathogenesis of HT and the efficacy of new substances for its treatment, an easily obtained and adequate to the human disease experimental model is needed. The aim of our study was to find out whether it is possible to induce experimental autoimmune thyroiditis (EAT) similar to Hashimoto's thyroiditis by injecting with thyroglobulin (Tg) without using agents that enhance its thyroiditogenicity and without taking into account the genetic sensitivity of animals.

METHODS

Wistar rats were immunized with freshly isolated rat Tg or porcine Tg. In 8 weeks, histological studies of the thyroid and parathyroid glands were performed. Thyroid function and total serum calcium level were also evaluated.

RESULTS

Immunization with both rat and porcine freshly isolated Tg caused T lymphocytic infiltration of the thyroid gland, thyroid follicle atrophy and degradation in Wistar rats. EAT caused by porcine Tg was characterized by greater severity than EAT induced with rat Tg. In 55% of rats with porcine Tg-induced EAT, oxyphilic metaplasia was detected in the parathyroid glands. In addition, low total serum calcium was observed in these rats.

CONCLUSION

Two rat models of autoimmune thyroiditis were obtained. EAT caused in Wistar rats by immunization with rat Tg is similar to Hashimoto's thyroiditis. EAT induced with porcine Tg was accompanied by oxyphil cell metaplasia in the parathyroids and hypocalcemia.

A Predictive Role of Autoantibodies Against the Epitope aa168–183 of ENO1 in the Occurrence of Miscarriage Related to Thyroid Autoimmunity

Objective

The aim of the research is to study the association between the serum levels of autoantibodies against one important epitope (¹⁶⁸FMILPVGAANFREAMR¹⁸³, designated as P6) of α-enolase (ENO1-P6Abs) and miscarriage among euthyroid females with thyroid autoimmunity (TAI).

Methods

Anti-ENO1-P6 total IgG was investigated in 432 euthyroid women, and its four subclasses were analyzed in 184 euthyroid women. The serum FT4, TSH, TgAb, and TPOAb levels were determined using an electrochemiluminescence immunoassay. The serum ENO1-P6Ab and anti-protein disulfide isomerase A3 autoantibody (PDIA3Ab) levels were determined using an enzyme-linked immunosorbent assay.

Results

The serum levels of anti-ENO1-P6 total IgG, IgG2, IgG3, and IgG4 were significantly higher in euthyroid TAI females than in non-TAI controls. Additionally, anti-ENO1-P6 total IgG and its 4 subtypes were all markedly higher in euthyroid TAI females with pregnancy loss than those without miscarriage. Moreover, logistic regression analysis showed that highly expressed anti-ENO1-P6 total IgG, IgG1, IgG2, and IgG3 subtypes in the serum were all independent risk factors for euthyroid TAI-related miscarriage, and its IgG1 was also for non-TAI-related abortion. According to the trend test, the prevalence of miscarriage was increased in a titer-dependent manner with the raised levels of serum anti-ENO1-P6 total IgG and IgG1, IgG2, and IgG3 subtypes among euthyroid TAI females. The receiver operating characteristic curve analysis of anti-ENO1-P6 total IgG and IgG1, IgG2, and IgG3 subclass expressions in the serum for miscarriage prediction in euthyroid TAI females exhibited that the total areas under the curves were 0.773 ± 0.041, 0.761 ± 0.053, 0.827 ± 0.043, and 0.760 ± 0.050, respectively (all P <0.0001). Their corresponding optimal cut-off OD450 values were 0.68 (total IgG), 0.26 (IgG1), 0.97 (IgG2), and 0.48 (IgG3), with sensitivities of 70.8, 87.5, 83.3, and 85.4%, and specificities of 70.8, 59.1, 77.3, and 56.8%, respectively. There was an additive interaction between serum anti-ENO1-P6 and anti-PDIA3 total IgGs on the development of miscarriage (RERI = 23.6, AP = 0.79, SI = 5.37).

Conclusion

The highly expressed ENO1-P6Abs may be important risk factors for euthyroid TAI-related miscarriage. The serum levels of ENO1-P6Abs may become good predictive markers for pregnancy loss in euthyroid TAI females, especially its IgG2 subclass expression.

Simulation Model for Hashimoto Autoimmune Thyroiditis Disease

Hashimoto thyroiditis (HT) is a pathology that often causes a gradual thyroid insufficiency in affected patients due to the autoimmune destruction of this gland. The cellular immune response mediated by T helper lymphocytes TH1 and TH17 can induce the HT disease. In this pathologic condition, there is an imbalance between the TH17 and Treg lymphocytes as well as a gut microbiota dysfunction. The objective of this work was to describe the interactions of the cell subpopulations that participate in HT. To achieve this goal, we generated a mathematical model that allowed the simulation of different scenarios for the dynamic interaction between thyroid cells, the immune system, and the gut microbiota. We used a hypothetical-deductive design of mathematical modeling based on a system of ordinary differential equations, where the state variables are the TH1, TH17, and Treg lymphocytes, the thyrocytes, and the bacteria from gut microbiota. This work generated a compartmental model of the cellular immune response occurring in the thyroid gland. It was observed that TH1 and TH17 lymphocytes could increase the immune cells' activity, as well as activate effector cells directly and trigger the apoptosis and inflammation processes of healthy thyrocytes indirectly. Likewise, the model showed that a reduction in Treg lymphocytes could increase the activity of TH17 lymphocytes when an imbalance of the gut microbiota composition occurred. The numerical results highlight the TH1, TH17, and bacterial balance of the gut microbiota activities as important factors for the development of HT disease.

Genotype association of IP6K3 gene with Hashimoto’s thyroiditis in Algerian population (Aures region)

Background

Hashimoto’s thyroiditis (HT) is a chronic autoimmune disease of the thyroid gland and is also the main cause of hypothyroidism. A recent genome-wide association study (GWAS) suggested an association of three novel genetic variants with HT in a population of Caucasian origin (Croatian). A case-control study was performed to investigate the association of these three newly suggested genetic variants with HT in a non-Caucasian ethnic group, an Arab-Berber from Algeria.

Three variants (rs12944194 located 206 kb from SDK2, rs791903 inside IP6K3, and rs75201096 inside GNA14) were genotyped using real-time PCR.

Results

There were no significant differences in allele frequencies of the three genetic variants between HT cases and controls. However, the present study showed nominal significance in the genotype distribution of rs791903 (IP6K3 gene) between HT patients and the control group (P = 0.024); we observed a decrease in the frequency of rs791903 recessive homozygotes (CC) in HT cases versus controls (OR = 0.476, P = 0.025).

Conclusion

This is the first study that showed the genotypic association of IP6K3 intronic variant with decreased risk for HT in non-Caucasian, Algerian, population, whereas we did not confirm the association of SDK2 and GNA14 genetic variants with HT. The IP6K3 gene (inositol hexaphosphate kinase 3), located near major histocompatibility complex (MHC), has previously been associated with other common autoimmune diseases beside HT, such as Graves’s disease and rheumatoid arthritis, which is providing more evidence of a good candidacy for the genetic contribution to the development of HT and autoimmunity.

Hashimoto's thyroiditis: An update on pathogenic mechanisms, diagnostic protocols, therapeutic strategies, and potential malignant transformation

Hashimoto's thyroiditis, characterized by thyroid-specific autoantibodies, is one of the commonest autoimmune disorders. Although the exact etiology has not been fully elucidated, Hashimoto's thyroiditis is related to an interaction among genetic elements, environmental factors and epigenetic influences. Cellular and humoral immunity play a key role in the development of the disease; thus, a T and B cells inflammatory infiltration is frequently found. Histopathologic features of the disease include lymphoplasmacytic infiltration, lymphoid follicle formation with germinal centers, and parenchymal atrophy. Moreover, the occurrence of large follicular cells and oxyphilic or Askanazy cells is frequently associated to Hashimoto's thyroiditis. Clinically, Hashimoto's thyroiditis is characterized mainly by systemic manifestations due to the damage of the thyroid gland, developing a primary hypothyroidism. Diagnosis of Hashimoto's thyroiditis is clinical and based on clinical characteristics, positivity to serum antibodies against thyroid antigens (thyroid peroxidase and thyroglobulin), and lymphocytic infiltration on cytological examination. The mainstream of treatment is based on the management of the hypothyroidism with a substitution therapy. A relationship between Hashimoto's thyroiditis and a possible malignant transformation has been proposed in several studies and involves immunological/hormonal pathogenic links although specific correlation is still debated and needs to be further investigated with prospective studies.

Uterus globulin associated protein 1 (UGRP1) is a potential marker of progression of Graves' disease into hypothyroidism

Approximately 20% of Graves' disease (GD) patients may result eventually in hypothyroidism in their natural course. Uterus globulin-associated protein 1 (UGRP1) was associated with GD in our previous study. Here we investigated the role of UGRP1 in the development of autoimmune thyroid disease (AITD). The results showed that UGRP1 was expressed in the thyrocytes of most Hashimoto's thyroiditis (HT) patients and a proportion of GD patients (293 HT and 198 GD). The pathologic features of UGRP1-positive thyrocytes resembled "Hürthle cells", and were surrounded by infiltrated leukocytes. The positivity rate of TPOAb in UGRP1-positive GD patients was much higher than that in -negative GD patients. Moreover, UGRP1 was co-expressed with Fas and HLA-DR in the thyrocytes of AITD patients. We also found IL-1β but not Th1 or Th2 cytokines was able to upregulate the expression of UGRP1. Our findings indicated that UGRP1 may be a novel marker in thyrocytes to predict GD patients who develop hypothyroidism.

Molecular Insights Into the Relationship Between Autoimmune Thyroid Diseases and Breast Cancer: A Critical Perspective on Autoimmunity and ER Stress

The etiopathologies behind autoimmune thyroid diseases (AITDs) unravel misbehavior of immune components leading to the corruption of immune homeostasis where thyroid autoantigens turn foe to the self. In AITDs lymphocytic infiltration in the thyroid shows up a deranged immune system charging the follicular cells of the thyroid gland (thyrocytes) leading to the condition of either hyperthyroidism or hypothyroidism. The inflammation in AITDs consistently associate with ER function due to which disturbances in the ER protein homeostasis leads to unfolded protein response (UPR) that promotes pathogenesis of autoimmunity. The roles of ER stress in the instantaneous downregulation of MHC class I molecules on thyrocytes and the relevance of IFN γ in the pathogenesis of AITD has been well-documented. Thyroglobulin being the major target of autoantibodies in most of the AITDs is because of its unusual processing in the ER. Autoimmune disorders display a conglomeration of ER stress-induced UPR activated molecules. Several epidemiological data highlight the preponderance of AITDs in women as well as its concurrence with breast cancer. Both being an active glandular system displaying endocrine activity, thyroid as well as breast tissue show various commonalities in the expression pattern of heterogenous molecules that not only participate in the normal functioning but at the same time share the blame during disease establishment. Studies on the development and progression of breast carcinoma display a deranged and uncontrolled immune response, which is meticulously exploited during tumor metastasis. The molecular crosstalks between AITDs and breast tumor microenvironment rely on active participation of immune cells. The induction of ER stress by Tunicamycin advocates to provide a model for cancer therapy by intervening glycosylation. Therefore, this review attempts to showcase the molecules that are involved in feeding up the relationship between breast carcinoma and AITDs.

The Pathogenesis of Hashimoto's Thyroiditis: Further Developments in our Understanding

Hashimoto's thyroiditis (HT) is part of a spectrum of thyroid autoimmune conditions and this review provides an update on the latest developments in the field. HT has a genetic predisposition with a number of immune-related and thyroid-specific genes conferring disease susceptibility. However, disentangling genes with protective and predisposing effect is a complex process that requires further work. The recent increase in the incidence of HT implicates environmental factors in disease pathogenesis including improved hygiene, increased dietary iodine intake, new treatment modalities and chemical agents. Additional unmodifiable predisposing factors include stress, climate, age and gender. Both cellular and humoral immunity play a role in HT pathogenesis. Defects in T regulatory cells and increased activation of follicular helper T cells may have a role in disease initiation/perpetuation. Infiltrating lymphocytes can be directly cytotoxic to thyroid follicular cells (TFC) or may affect cell viability/function indirectly through cytokine production, which alters TFC integrity and modulates their metabolic and immune function. Thyroid peroxidase and thyroglobulin antibodies are present in the majority of HT patients and help with management decisions. Antibodies against the sodium iodide symporter and pendrin are present in a minority with little known about their clinical relevance. In addition to immune cells, recent work has identified DNA fragments, generated following cell death, and micro RNA as potential factors in HT pathogenesis. Despite the large number of studies, the mechanistic pathways in HT are still not fully understood and further work is required to enhance our knowledge and identify novel preventative and therapeutic clinical targets.

Iodine increases and predicts incidence of thyroiditis in NOD mice: Histopathological and ultrastructural study

Prolonged intake of large amounts of iodine has been reported to increase the incidence of hypothyroidism in humans, as well as in animals which are prone to spontaneously developing autoimmune thyroiditis. We sought to investigate the histopathological consequences of large amounts of dietary iodine on the thyroid gland and observe the occurrence of lymphocytic infiltration associated with the time of exposure to iodine. An experimental model using non-obese diabetic (NOD) mice was analyzed. A potassium iodide intake of 0.2 mg/animal/day was administered via drinking water, in experimental groups of 60 and 90 days (EG60 and EG90). Distended rough endoplasmic reticulum, degenerated mitochondria, debris and amorphous spaces or ‘ill-defined’ spaces were observed with electron microscopy (EM). Lymphocyte infiltration was observed in the two groups and the time of exposure to iodine did not increase the appearance of lymphocyte infiltration but significantly associated with the development of necrosis. The results of the present study demonstrated that the NOD mouse is a feasible experimental model for thyroiditis induced by iodine administration and may represent an opportunity to analyze the steps and factors associated with genetic autoimmune thyroiditis. High doses of ingested iodine were observed to precdict and increase the incidence of the thyroiditis process.

A comparative study of DNA damage in patients suffering from diabetes and thyroid dysfunction and complications

Objective

The apoptotic DNA levels in blood leukocytes of patients with type 2 diabetes (T2D) and thyroid dysfunctionism were evaluated.

Materials and methods

Single-cell gel electrophoresis (comet assay) detects migration of DNA from individual cell nuclei following alkaline treatment. Comet assay pattern was studied in individuals with T2D, hypothyroid (HT), hyperthyroid (HeT), and patients suffering from both diabetes mellitus and HT (HT + DM). Results were compared with the normal subjects (n = 9 in each group). The percentage apoptotic cell populations were calculated from the tail length.

Results

T2D patients showed 92.24% of cell damage compared to HT or HeT patients (51.04% or 54.64%, respectively). Further, increase in cell damage was also observed in HT + DM subjects (P < 0.05). Pharmacologic therapy significantly influenced cell damage. However, age and duration of disease did not show any definite influence on apoptosis.

Conclusion

Dependence of disease seems to be the major contributor of the cell damage. However, thyroid dysfunction did not show any deleterious effects on individual cells under the study.

Effect of type I interferon(s) on cell viability and apoptosis in primary human thyrocyte cultures

BACKGROUND

Interferon (IFN) therapy may induce a generalized activation of the immune system, hence triggering or exacerbating autoimmune disease. Apoptosis contributes to the development of hypothyroidism in autoimmune thyroiditis. IFN can affect all phases of the cell cycle and may induce apoptosis in several cell lines from varied histologies. To date, no data exist on the possible effect of type I IFN(s) on FAS/FASL system and cell apoptosis of human thyroid follicles. Therefore, we evaluated the effect of both IFN-alpha and -beta on apoptosis in primary human thyrocyte cultures and the potential role of the FAS/FASL pathway.

METHODS

Thyrocytes were cultured in monolayers and FAS, FASL, and Bcl-2 mRNA expression was determined by reverse transcriptase polymerase chain reaction after exposure to 10 mIU/mL bovine thyroid-stimulating hormone alone or in combination with increasing doses of IFN-alpha or -beta for 24, 48, and 72 hours. The percentage of apoptotic hypodiploid cells was evaluated by flow cytometry.

RESULTS

Thyroid-stimulating hormone significantly decreased FAS and increased Bcl-2 mRNA expression while reducing the percentage of hypodiploid cells. The concomitant addition of either IFN-alpha or -beta reduced cell viability and increased the number of hypodiloid cells, but only IFN-beta modulated the expression of FAS and Bcl-2 mRNA expression in a proapoptotic sense.

CONCLUSIONS

Both type I IFN(s) increase apoptosis in primary thyrocyte cultures, but only IFN-beta modulates FAS and Bcl-2 gene expression toward a proapoptotic pathway. Because apoptosis plays an important role in thyroid homeostasis and disease, this mechanism may contribute to the development and progression of type I IFN(s) therapy-associated thyroid disease.

p53 codon 72 proline/arginine polymorphism and autoimmune thyroid diseases

p53 protein participates in the processes of apoptosis, which is involved in a number of immunological reactions. In order to test whether the p53 gene could be used as a genetic marker for the prediction of the development of autoimmune thyroid diseases (AITD), we screened, by using polymerase chain reaction (PCR) analysis, for the C (CCC)/G (CGC) polymorphism at the p53 codon 72 (Pro 72/Arg 72) to determine the genotypes of 107 Hashimoto's thyroiditis (HT) and 90 Graves' disease (GD) patients, and 105 normal controls. The data demonstrated that, for the genotype analysis, HT patients featured an enhanced numerical ratio for the Arg/Arg homozygous genotype (33.7%) and a diminished ratio for the Arg/Pro heterozygous genotype (41.1%) at the p53 codon 72 than was the case for normal controls (Arg/Arg: 17.1% and Arg/Pro: 61.9%; P=0.005). The odds ratio for the risk of the Arg/Arg genotype's appearance, compared with that of the Arg/Pro and Pro/Pro genotypes combined, for the HT patient group was 2.450 (95% confidence interval: 1.274-4.716). With respect to allelic analysis, we did not observe significant difference in the frequency of appearance of the Arg allelic variant and the Pro allelic variant for the p53 codon 72 when comparing the HT patient group with the control group (P=0.208). On the other hand, GD patients presented no significant difference in distribution for both genotype and allelic frequencies (P=0.344 and 0.245, respectively) when compared with normal controls. In conclusion, HT patients feature a greater ratio of arginine homozygosity at p53 codon 72 than in the case for normal subjects. The p53 codon 72 proline/arginine polymorphism may be a genetic marker to predict the increased susceptibility of development of HT.

Lack of association between interleukin-4 gene polymorphisms and autoimmune thyroid diseases amongst Taiwanese Chinese

Graves' disease (GD) and Hashimoto's thyroiditis (HT) are both common autoimmune diseases of the thyroid gland (AITD). The IL-4 is involved in both humoral and cellular immunity. The aim of this study was to test whether the IL-4 gene could be used as a genetic marker to predict the development of AITD amongst the Chinese population of Taiwan. For this study, a normal control group of 105 healthy subjects and two experimental groups featuring individuals afflicted with either GD (104 patients) or HT (109 patients) were examined. Polymerase chain reaction (PCR) was used to analyze the variable number of tandem repeats (VNTRs) polymorphism for the IL-4 gene intron 3 and PCR-based restriction analysis using endonuclease BsmFI was undertaken for the same gene at the promoter -590 position. We found no significant difference in the frequencies of presence of genotype and allelic variants for the IL-4 gene at both the intron 3 and the promoter regions between the normal control group and each of the two patient groups. These findings suggest that the IL-4 gene polymorphisms that arise at either intron 3 or promoter -590 positions are not suitable genetic markers for AITD among Taiwanese Chinese.

The role of stress in the clinical expression of thyroid autoimmunity

During stress, activation of the hypothalamic-pituitary-adrenal axis and the sympathoadrenal system leads to increased secretion of glucocorticoids and catecholamines, respectively, in order to maintain homeostasis. Recent evidence suggests that stress hormones, acting on antigen-presenting immune cells, may influence the differentiation of bipotential T helper (Th) cells away from Th1 and toward a Th2 phenotype. This results in suppression of cellular immunity and potentiation of humoral immunity. Thyroid autoimmunity is clinically expressed as Hashimoto's thyroiditis (HT) and its variants (sporadic or postpartum thyroiditis) or as Grave's disease (GD). The different phenotypic expression of thyroid autoimmunity is largely dependent on the balance of Th1 versus Th2 immune response. A predominantly Th1-mediated immune activity may promote apoptotic pathways on thyroid follicular cells leading to thyroid cell destruction and HT. Conversely, predominance of Th2-mediated immune response may induce antigen-specific B lymphocytes to produce anti-TSH receptor (TSHr) antibodies causing GD. The weight of evidence from epidemiological and case-control studies supports an association between stress and GD. On the other hand, there is little information available on the effect of stress on HT, but there is evidence for an increase in postpartum thyroiditis, following the cellular immune suppressive effect of pregnancy. Whether stress has a causative effect on GD remains elusive. Circumstantial evidence supports the hypothesis that stress may influence the clinical expression of thyroid autoimmunity in susceptible individuals favoring the development of GD by shifting the Th1-Th2 balance away for Th1 and toward Th2. Conversely, recovery from stress or the immune suppressive effect of pregnancy may induce a Th2 to Th1 "return shift" leading to autoimmune (sporadic) or postpartum thyroiditis, respectively.

Role of fine needle aspiration cytology in thyroiditis

Fine needle aspiration (FNA) of thyroid is a cost-effective, simple, diagnostic tool in the initial screening of patients with thyroid lesions. Its role in a minimally enlarged thyroid in a symptomatic patient suspected of thyroid dysfunction is now well known. It plays an important role in the medical management of all nonpalpable/minimally enlarged thyroid (goiter) in patients suspect for thyroid pathology and/or in combination with thyroid-stimulating hormone, T3 and T4 levels by diagnosing early cases of thyroiditis. FNA may be of assistance in the early detection of subclinical hypothyroidism, which is of utmost importance in pregnant women, and further makes possible the availability of baseline values for future reference. With the implementation of this protocol of FNA thyroid with/without imaging, we affirm that the practice of cytology has differed in different geographic areas and from country to country, depending on economy and availability of infrastructure.

Evaluation of the Cell Death Pathway and Apoptosis-Stunning Effect Relationship After Low- and High-Dose I-131 Administrations in Rat Thyroid Tissue

OBJECTIVES

This study had two aims; (1) to describe the cell death pathway (apoptosis or necrosis) induced by a low and high dose of radioiodine (I-131) in rat thyroid tissue in in vivo conditions and (2) to determine the role of apoptosis in the development of "stunning effect" in the thyroid tissue with low and high doses of I-131 application.

DESIGN

The experimental group consisted of 18 rats; low and high I- 131 doses with a 1-week interval were administered to this group. At first, low doses were injected intraperitoneally (i.p.) (net injected dose was 51.54 +/- 8.6 microCi). After 1 week of the low-dose injection, high doses were also injected (net injected dose was 934.9 +/- 211.8 microCi). Thyroidal I-131 uptakes for both low- and high-dose applications were calculated by using a gamma camera after 24 hours of injections. Immediately after the uptake calculation, thyroid tissues were resected. A control group of 10 rats was also included in the study; in this group, I-131 was not administered. Thyroid tissues of this group rats were also resected. DNA was extracted from thyroid tissues, and damage was examined with the "DNA ladder by agaroz gel electrophoresis."

RESULTS

Thyroidal I-131 uptakes were calculated as 11.3% +/- 3.6% and 9.8% +/- 5.3% at the 24th hour after low- and high-dose I-131 applications, respectively. When the low- and high-dose uptake values were compared for each rat; a significant relationship was not found between thyroidal uptakes and injected low and high doses of I-131. When the chromosome images were examined, there was healthy DNA appearance in 1 rat; in 4 rats, only necrotic hyperfragmentations were observed; in 9 rats, both apoptotic specific fragmentations and necrotic hyperfragmentations were observed; and in 4 rats, apoptosis, necrosis, and healthy DNA appearances were seen together. In none of the rats, specific fragmentations concordant only with apoptosis was found. When the thyroidal uptake alterations were taken into consideration, significant difference was not found between first and second uptake calculations (p = 0.28). No significant relationship was also observed between thyroidal uptake alterations and apoptosis-necrosis-healthy DNA findings. Additionally, when we take into consideration the DNA results of only 13 of the rats that had reduced thyroidal uptake, a significant relationship could also not be observed between reduced uptake and apoptotic, necrotic, or healthy tissue findings. Interestingly, apoptotic and necrotic tissue or only necrotic, tissue findings were observed in the other 5 rats which had increased thyroidal uptake.

CONCLUSIONS

Following I-131 administration, two types of cell death--both apoptosis and necrosis findings--have been observed in most of the rats. We think that the decreased uptake values are because of the probable stunning effect in thyroid tissue. We also investigated whether the stunning effect is related to apoptosis. According to our results, it can be concluded that the stunning effect is not related to tissue damage, cell decrease, or cell death. Alternatively, we think that this can be related to a radiation-induced reduction of iodine uptake/metabolism or a modified iodine transport mechanism. For further in vivo studies, this experimental model using normal rat thyroid tissue may be useful in investigating the cell death pathways induced by I-131 and its probable roles in the development of the stunning phenomenon.

Death ligand tumor necrosis factor-related apoptosis-inducing ligand inhibits experimental autoimmune thyroiditis

The role of TNF-related apoptosis-inducing ligand (TRAIL) in autoimmune thyroiditis is unclear. We used experimental autoimmune thyroiditis to clarify the contribution of TRAIL to the development of autoimmune thyroiditis. CBA/J mice were immunized with murine thyroglobulin, and spleen cells from these mice were subsequently injected into irradiated recipient CBA/J mice. One week later, the recipient mice were treated with recombinant TRAIL or a control protein. Compared with control animals, TRAIL-treated mice developed a milder form of the disease with a significant decrease in mononuclear cell infiltration in the thyroid and less thyroid follicular destruction. Furthermore, the number of apoptotic thyrocytes and also thyroglobulin-specific T helper-1 cell responses in TRAIL-treated mice was lower than that in the control animals. This study suggests that exogenous TRAIL suppresses the development of autoimmune thyroiditis via altering the function of cells involved in the immune response. These findings may contribute toward a novel treatment autoimmune thyroiditis.

Immunohistochemical analysis of bcl-2, Bax and Bak expression in thyroid glands from patients with Graves' disease

In order to clarify the role of apoptosis and the expression of Bcl-2 family proteins in the pathology of Graves' disease (GD), we evaluated the apoptosis by in situ end-labeling of fragmented DNA and the expression of Bcl-2, Bax and Bak by immunohistochemistry in thyroid tissues from 20 patients with GD and in normal thyroid tissues from 6 patients with follicular adenoma (N). Apoptotic nuclei were found in thyrocytes and in germinal center of lymphoid follicles. Bcl-2 was strongly expressed in both GD and N thyrocytes. Bax was not expressed in either GD or N thyrocytes. Bak was expressed in thyrocytes from 5 of 20 patients with GD, while it was detected in all N thyrocytes. In lymphoid follicles Bcl-2 was expressed in the mantle zone, while Bax and Bak were both expressed in the germinal center. The percentage of apoptotic nuclei in GD thyrocytes was low (0~3.6%), and negatively correlated with the weight of the thyroid glands resected (rs = -0.43, P<0.05). It was greater in Bak-positive GD thyrocytes than in Bak-negative ones (mean +/- SD; 1.7 +/- 0.7% vs. 0.7 +/- 0.9%, P<0.05). These findings suggest that the differential expression of Bcl-2 family proteins in both thyrocytes and lymphoid follicles may be involved in the pathology of GD.

Thyrocytes isolated from autoimmune-diseased thyroids secrete soluble tumor necrosis factor-R1 that is related to their elevated protein kinase C activity

Soluble tumor necrosis factor (TNF)-alpha receptors have the potential to modulate TNF-alpha activity during autoimmune thyroiditis. In this study we examined cell-surface TNF-alpha receptors and soluble TNF-alpha receptor production by thyrocytes from normal and MRL-lpr(-/-) (diseased) mice, which spontaneously develop autoimmune thyroiditis. We found that murine thyrocytes possess the 55-kd receptor (TNF-R1). Examination of soluble TNF-R1 production revealed that diseased thyrocytes produced sevenfold more soluble TNF-R1 than normal thyrocytes. Furthermore, basal protein kinase C (pKC) activity in diseased thyrocytes was 67% higher than that found in normal murine thyrocytes. The elevated basal pKC activity in diseased thyrocytes was related to their enhanced production of soluble TNF-R1 because inhibition of pKC activity with calphostin C caused soluble TNF-R1 production to decrease significantly. Additionally, soluble TNF-R1 production by murine thyrocytes was not a result of cell-surface receptor shedding but through secretion of a truncated version of TNF-R1. This was evident when cell-surface TNF-R1 levels were unchanged after treatment of diseased thyrocytes with calphostin C. Also, the 28-kd form of TNF-R1, which corresponds to the soluble receptor, was present in the intracellular membranes of the diseased thyrocytes.

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.

Fas and Fas ligand gene mutations in Hashimoto's thyroiditis

To clarify whether Fas and Fas ligand (FasL) mutations are involved in the pathogenesis of Hashimoto's thyroiditis (HT), we examined the open reading frame of Fas and FasL in 21 cases. Mutations of Fas and FasL genes were detected in 8 (38.1%) and 1 (4.8%) of 21 cases, respectively. All but one of the Fas mutations were frameshift mutations, which affect the cytoplasmic region (death domain) known to be involved in apoptotic signal transduction and thus could be loss-of-function mutations. FasL mutation in one case was a 46-bp deletion from nucleotide 349 to 394, which corresponded to exon 2. Lack of exon 2 results in a frameshift, which generates a stop codon at residue 128. This mutant encodes the protein that contains only a part of the intracellular domain, thus the abnormal protein might not be expressed on the cell surface. The cells with Fas mutations were confined to the mantle zone and the germinal center, as determined by microdissection methods. These findings suggest that the cells with Fas mutations might accumulate in those areas and might be involved in the pathogenesis of Hashimoto's thyroiditis.

Apoptosis and apoptosis-related proteins in thyroid myopathies

DNA fragmentation and apoptosis-related proteins have been investigated in thyroid cells and there is evidence that Fas-mediated apoptosis is inhibited by thyroid stimulating hormone (TSH). We investigated DNA fragmentation by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and Bcl-2 and Fas antigen expression by immunocytochemistry in skeletal muscles from 12 patients with hypothyroid myopathy and 5 patients with hyperthyroid myopathy. The finding of very few TUNEL-positive muscle fibers in both conditions suggests that apoptosis does not play a role in the pathogenesis of thyroid myopathies. Bcl-2 expression increased significantly in hypothyroid myopathy, correlating with high serum TSH levels, and not with either triiodothyronine (T3) or thyroxine (T4) serum levels. By contrast, Fas antigen was overexpressed in hyperthyroid myopathy, correlating with low TSH levels. These findings suggest an anti-apoptotic role for TSH itself in skeletal muscle.

Methods for detecting apoptosis in thyroid diseases

Over the last few years, the importance of apoptosis in determining the fate of thyrocytes in autoimmune thyroid disease has been the topic of intense investigation. It is now clear that thyrocytes from patients with Hashimoto's thyroiditis are destroyed as a result of an apoptotic process. However, there is no general consensus on whether the intrathyroidal lymphocytes or the thyrocytes themselves are responsible for their death. The use of a wide range of techniques has contributed to the assessment of this process both in situ on thyroid sections and in vitro on thyroid cell preparations. The apoptosis field of research is rapidly evolving and as the pathways to cell death become unravelled, novel methods will emerge. As each technique offers some advantage, it is critical to know the most suitable method for a specific study. Equally, each method also has intrinsic limitations. Thus, to achieve reliable results, it is necessary to use more than one technique per study. In addition, techniques related to the measurement of the expression of pro-apoptotic and anti-apoptotic genes have been contributing to the study of the susceptibility of the cells to apoptosis and/or to their ability to kill themselves or neighbouring cells. In this review we will focus on the most relevant techniques.

Circulating nuclear matrix protein in Graves' disease

The Fas/Fas ligand system induces apoptosis, while soluble Fas (sFas) blocks the system and soluble Fas ligand (sFasL) functions to induce apoptosis. The assay of nuclear matrix protein (NMP) released from dead or dying cells can be used to quantitate cell death. Therefore, we evaluated the relationship among serum levels of NMP, sFas, and sFasL in patients with Graves' disease. We measured serum levels of sFas, sFasL, NMP, thyroid hormones and TSH receptor antibody in 20 normal control subjects (5 men, 15 women; mean age, 44.3 years), 32 patients with untreated Graves' disease (4 men, 28 women; mean age, 44.1 years), and 10 patients with Graves' disease treated by methimazole (3 men, 7 women; mean age 39.2 years). Serum NMP was significantly lower (10.4 +/- 4.3 IU/ml, p < 0.02) in patients with untreated Graves' disease than in patients with treated Graves' disease (16.4 +/- 7.3 IU/ml) and control subjects (15.3 +/- 8.9 IU/ml). Serum sFas and sFasL were significantly higher in patients with untreated Graves' disease than in patients with treated Graves' disease and in control subjects. In the patient groups with Graves' disease, serum NMP was negatively correlated with sFas (r = -0.612, p < 0.001) and serum sFas was positively correlated with FT4 (r = 0.360, p < 0.05) and TRAb (r = 0.384, p < 0.05). Serum NMP was correlated with sFas. These results suggest that serum NMP is decreased in patients with untreated Graves' disease, and that cell death or apoptosis in patients with Graves' disease is affected by soluble Fas under the influence of thyroid function.

Accelerated production of nucleosome in cultured human mononuclear cells in untreated Graves' disease

The apoptosis of lymphocytes, which occurs in autoimmune diseases, is usually induced by the Fas/Fas ligand system. As the assay of nucleosomes produced by apoptotic cells can be used to quantitate apoptosis, we evaluated nucleosome and soluble Fas ligand (sFasL) levels of cultured mononuclear cells to clarify the apoptosis of mononuclear cells in patients with autoimmune thyroid diseases by enzyme-linked immunosorbent assay. Nucleosome levels of cultured mononuclear cells in patients with untreated Graves' disease were significantly higher (3.27+/-2.90 U/ml) than those of control subjects (1.39+/-0.24 U/ml) and euthyroid patients with treated Graves' disease (1.53+/-0.33 U/ml). Nucleosome levels of cultured mononuclear cells were positively correlated with sFasL levels (r=0.544, p<0.01). It is therefore likely that increased sFasL levels elicit apoptosis of these cells in untreated Graves' disease.

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.

A unique combination of inflammatory cytokines enhances apoptosis of thyroid follicular cells and transforms nondestructive to destructive thyroiditis in experimental autoimmune thyroiditis

Treatment of cultured primary human thyroid cells with IFN-gamma and TNF-alpha uniquely allows the induction of Fas-mediated apoptosis. To investigate the role of this cytokine combination in vivo, CBA/J mice were immunized with thyroglobulin and then injected with IFN-gamma and TNF-alpha. Compared with control animals, mice treated with IFN-gamma and TNF-alpha showed significantly sustained lymphocytic infiltration in the thyroid, which was associated with the destruction of portions of the follicular architecture at wk 6 after initial immunization. Furthermore, the number of apoptotic thyroid follicular cells was increased only in the thyroids from mice treated with the IFN-gamma and TNF-alpha. We also analyzed the function of the Fas pathway in vivo in cytokine-treated mice by using an agonist anti-Fas Ab injected directly into the thyroid. Minimal apoptosis of thyroid epithelial cells was observed unless the mice were pretreated with IFN-gamma and TNF-alpha. These data demonstrate that this unique combination of inflammatory cytokines facilitates the apoptotic destruction of thyroid follicular cells in experimental autoimmune thyroiditis, in a manner similar to what is observed in Hashimoto's thyroiditis in humans.

Fas/FasL mediated apoptosis of thyrocytes in Graves' disease

We examined in the present study the possible involvement of Fas and its ligand (FasL) in the process of Graves' disease. Immunohistochemical analysis showed that few normal thyrocytes expressed Fas but many thyrocytes in Graves' disease expressed this molecule. The percentage of FasL-positive thyrocytes in Graves' thyroids was, however, less than in normal thyroids. Several apoptotic thyrocytes and infiltrating mononuclear cells (MNCs) were detected scattered throughout Graves' thyroid tissues and abundant proliferating cell nuclear antigen (PCNA)-positive thyrocytes were present. Apoptotic cells, as well as PCNA-positive cells, were scarcely detectable in normal thyroid glands, however. In vitro treatment of thyrocytes by IL-1beta a cytokine found to be expressed in Graves' thyroid glands, increased Fas but reduced FasL expression. IL-1beta-stimulated thyrocytes became sensitive to apoptosis by anti-Fas IgM monoclonal antibody (mAb). Activated T cells, which strongly expressed FasL, showed cytotoxic activity toward IL-1beta-stimulated thyrocytes but not toward unstimulated thyrocytes. This cytotoxic activity involved the Fas/FasL pathway. Importantly, unstimulated thyrocytes could kill activated, but not resting, T cells. IL-1beta-stimulated thyrocytes, with down-regulated FasL expression, could not efficiently kill activated T cells. The cytotoxic activity of unstimulated thyrocytes toward activated T cells was inhibited by anti-FasL mAb. Interestingly, unstimulated thyrocytes induced apoptosis in IL-1beta-stimulated thyrocytes but not in unstimulated thyrocytes. These interactions were also blocked by anti-FasL mAb. Our results suggest that the apoptotic cell death of both thyrocytes and infiltrating MNCs found in Graves' thyroid glands is regulated by IL-1beta through Fas/FasL interactions.

The role of Fas-mediated apoptosis in thyroid autoimmune disease

Apoptosis is a carefully regulated mechanism of cell death that differs from necrosis and plays an important role in normal tissue development and homeostasis, as well as disease processes. Apoptosis also plays an important role in autoimmunity. Defective apoptosis can cause systemic autoimmunity by allowing the survival of autoreactive lymphocytes. It may also be involved in the pathogenesis of organ-specific autoimmune diseases, such as Hashimoto's thyroiditis, through altered target organ susceptibility. Apoptosis signaling pathways can be initiated through activation of death receptors. One of these pathways employs the death receptor Fas and its ligand (FasL). Fas expression and death pathway signaling have been demonstrated in the thyroid, but there is controversy surrounding the expression of FasL and its role in thyroid autoimmunity. A number of proteins, including FAP-1, Bcl-2 and I-FLICE may regulate the Fas pathway in the thyroid and provide potential mechanisms for modifying the pathogenesis of autoimmune thyroid disease.

Newer insights into the pathogenesis of experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT), produced in the mouse by immunization with murine thyroglobulin plus complete Freund's adjuvant, represents a valuable model for studying the pathogenesis of human chronic (Hashimoto's) thyroiditis. A major issue requiring clarification is the difference between benign autoimmunity, characterized solely by production of autoantibodies to thyroglobulin, and pathogenic autoimmunity where injury occurs to the thyroid cells. In this article, we describe the role of two key cytokines, IL12 and IFNgamma, in modifying the pathogenic immune response. EAT, defined by cellular infiltration of the thyroid and the development of thyroglobulin-specific autoantibodies, is a dynamic process. Consequently, a cytokine may exert a different effect at different times during the disease process. For purposes of discussion, we propose that there are three stages in the development of EAT: priming; initiation; and progression. Administration of anti-IL12 during the priming stage and initiation dramatically decreases disease and lowers autoantibody levels. In contrast, injection of recombinant IL12 after disease was established significantly decreases the severity of disease and reduces autoantibody levels. Unlike IL-12, IFNgamma was not essential for the priming of EAT. However, the severity of disease in the anti-IFNgamma-treated initiation- and progression-treated animals was higher than in controls, implying a regulatory role for IFNgamma. These findings emphasize that EAT involves a complex array of pathogenic mechanisms. The balance of cytokines produced during the early phase of the autoimmune reaction probably determines the progression from a harmless autoimmune response to autoimmune disease.

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.

Apoptosis in human disease: a new skin for the old ceremony?

Naturally occurring cell death or apoptosis is essential for the maintenance of tissue homeostasis and serves to remove extraneous or dangerous cells in a swift and unobtrusive manner. Recent studies have indicated a role for apoptosis in a plethora of human diseases. Hence, dysregulation of apoptosis has been implicated in autoimmune disease, acquired immune deficiency syndrome, and other viral (and bacterial) infections, as well as in neurodegenerative disorders and cancer. Furthermore, dysregulated apoptosis signaling may impinge on other age-related disorders such as osteoporosis and atherosclerosis and perhaps on the process of aging itself. The present review provides an overview of human diseases, which are associated with defective or inadvertent apoptosis, with examples of pathological conditions in which putative apoptosis defects have been elucidated at the molecular level. Novel apoptosis-modulating therapeutic strategies are also discussed.

Inflammatory cytokine regulation of Fas-mediated apoptosis in thyroid follicular cells

The occurrence of apoptosis in thyroid follicular cells induced by Fas activation has been a subject of much debate. This is due, in part, to the fact that no physiologically relevant treatment conditions have been reported to cause rapid and extensive Fas-mediated apoptosis in thyroid cells, whereas treatment with the protein synthesis inhibitor cycloheximide prior to Fas activation allows for massive cell death. This indicates that the Fas signaling pathway is present but that its function is blocked in the overwhelming majority of cultured thyroid cells. To reconcile the conflicting reports, we set out to identify physiologically relevant conditions in which rapid, massive thyroid cell apoptosis in response to Fas activation could be demonstrated. We determined that susceptibility to Fas-activated apoptosis could be influenced by certain combinations of inflammatory cytokines. Although no single cytokine was effective, pretreatment of thyroid cells with the combination of gamma-interferon and either tumor necrosis factor-alpha or interleukin 1beta allowed for massive Fas-mediated apoptosis. Susceptibility to Fas-induced death correlated with an increase in expression of a tunicamycin-inhibitable high molecular weight form of Fas but not with aggregate expression of Fas.

TRAIL death pathway expression and induction in thyroid follicular cells

To determine whether programmed cell death in thyroid follicular cells can be related to activation of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway, we examined the expression and function of this pathway in primary thyroid follicular cells and a papillary thyroid carcinoma cell line in vitro. Despite the expression of TRAIL receptors death receptor 4 and death receptor 5, purified TRAIL could not induce programmed cell death (PCD) in any of the thyroid follicular cells examined. However, pre-incubation with cycloheximide before TRAIL facilitated the induction of rapid and massive PCD. This suggested that despite the presence of a labile inhibitor of the TRAIL pathway, TRAIL could mediate PCD under appropriate conditions. To determine whether there were sources of TRAIL in the thyroid that could interact with thyroid follicular cell TRAIL receptors, RNase protection assays were used to determine TRAIL mRNA expression. TRAIL message was expressed in intrathyroidal lymphocytes isolated from a patient with thyroiditis, and unexpectedly, thyroid follicular cells themselves could be induced to express abundant TRAIL message in the presence of the inflammatory cytokines interferon gamma, tumor necrosis factor alpha, and interleukin 1beta. Furthermore, the papillary thyroid carcinoma cell line could be induced to kill the TRAIL-sensitive lymphoma cell line BJAB through a TRAIL-dependent mechanism.

1Alpha,25-dihydroxyvitamin D3 up-regulates Bcl-2 expression and protects normal human thyrocytes from programmed cell death

Apoptosis is thought to play an important role in the pathogenesis of autoimmune thyroid disease. 1alpha,25-dihydroxyvitamin D3 (VD3) has been shown to suppress several autoimmune diseases. However, the mechanism by which VD3 has these effects is not known. We evaluated the alterations in apoptosis, induced by VD3. Thyrocytes were treated with VD3, and the expression of the Bcl-2 family molecules was studied at both the messenger RNA and protein levels. It was found that VD3 significantly induced the expression of Bcl-2 messenger RNA and protein in thyrocytes but had no effect on the expression of Bcl-xl and Bax. The increase in Bcl-2 expression, mediated by VD3, correlated with protection of thyrocytes against the induction of apoptosis by either staurosporine or UV irradiation. VD3-induced increases in the expression of Bcl-2 could be mimicked by VD3 analogs with high nuclear receptor affinity, but not by analogs only with nongenomic actions. These data indicate a role for Bcl-2 in the regulation of apoptosis in thyrocytes and raise the possibility that VD3 or its agonists may have therapeutic benefit in thyroid disorders.

Fas/Fas Ligand-Driven T Cell Apoptosis as a Consequence of Ineffective Thyroid Immunoprivilege in Hashimoto’s Thyroiditis

Hashimoto’s thyroiditis (HT) is a chronic autoimmune disease resulting from Fas-mediated thyrocyte destruction. Although autocrine/paracrine Fas-Fas ligand (FasL) interaction is responsible for thyrocyte cell death during the active phases of HT, the role of infiltrating T lymphocytes (ITL) in this process is still unknown. Therefore, we investigated the expression and function of Fas and FasL in ITL. All ITL expressed high levels of Fas and CD69, an early marker of T cell activation associated with functional Fas expression in T cells in vivo. In contrast to thyrocytes that were found to produce high levels of FasL, ITL did not express significant amounts of FasL, suggesting that ITL are not directly involved in thyrocyte destruction. The analysis of ITL purified from HT thyroids showed that ITL were massively killed by Fas crosslinking and that a considerable number (24–36%) underwent spontaneous apoptosis within 36 h of culture. Accordingly, in situ TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) staining revealed that a significant number (10–15%) of ITL in proximity to FasL-producing thyroid follicles were apoptotic. Moreover, virtually all ITL in proximity to thyroid follicles were preapoptotic, as they expressed high levels of GD3 ganglioside, a killer glycolipid responsible for the generation of irreversible apoptotic signals that accumulate in hematopoietic cells shortly after Fas crosslinking. These data demonstrate that ITL are not directly involved in thyrocyte cell death during HT, suggesting that autocrine/paracrine Fas-FasL interaction is a major mechanism in autoimmune thyrocyte destruction.

Apoptosis and thyroiditis

The origin of the various forms of autoimmune thyroiditis remains unclear. Most investigations into the pathogenesis of these disorders have focused on immune abnormalities that might lead to an autoimmune response. However, no unique immune response to thyroid autoantigens has been identified that either is limited to patients with thyroiditis or is absolutely correlated with clinical disease expression. CD8 T-cell-mediated cytotoxicity is thought to be a major cause of thyroid follicular cell damage in thyroiditis. This damage is produced in part through the induction of apoptosis in thyroid cells. Recent studies have demonstrated that programmed cell death is regulated in thyroid cells and that a major pathway for immune-mediated apoptosis, the Fas pathway, is blocked by labile inhibitors in a manner that could prevent cytotoxicity. This review also examines several other types of regulation of apoptotic pathways in thyrocytes. We hypothesize that the regulation of programmed cell death pathways in the thyroid may alter the expression of autoimmune thyroid diseases by modifying the susceptibility of thyroid cells to immune-mediated apoptosis.

Serum concentration of soluble Fas in patients with autoimmune thyroid diseases

Fas is an apoptosis-signaling receptor molecule found on the surface of a number of cell types. Malfunction of the Fas system accelerates autoimmune diseases, whereas its exacerbation may cause tissue destruction. Soluble Fas (sFas) molecule lacks the transmembrane domain due to alternative splicing and blocks Fas-mediated apoptosis. This study investigated serum levels of sFas in autoimmune thyroid diseases. Serum levels of sFas were determined by enzyme-linked immunosorbent assay in 46 patients with Graves' disease, 32 patients with Hashimoto's thyroiditis, 14 patients with silent thyroiditis, and 24 normal controls. Compared with normal subjects (1.43+/-0.37 ng/mL), sFas was increased in thyrotoxic patients with Graves' disease (1.89+/-0.47 ng/mL, p < 0.001), and was decreased in patients with Graves' disease in remission (1.02+/-0.41 ng/mL, p < 0.001) and in euthyroid patients with Hashimoto's thyroiditis (0.97+/-0.25 ng/mL, p < 0.0001), but was normal in hypothyroid patients with Hashimoto's thyroiditis and in thyrotoxic patients with silent thyroiditis. Thus, changes in serum levels of sFas could not be explained by changes in serum thyroid hormones, although sFas concentration correlated with free thyroxine (r = 0.692, p < 0.0001). Also, the levels of sFas significantly correlated with the activities of TSH receptor antibody in Graves' disease (r = 0.671, p < 0.0001). Increased sFas in Graves' disease suggests increased expression of alternatively spliced Fas mRNA variant that produces sFas protein and decreased of cell surface expression of Fas, and may induce thyroid cell growth and production of TSH receptor antibody by protecting against apoptosis of thyroid cells and autoreactive B cells. Decreased sFas in Hashimoto's thyroiditis suggests decreased Fas mRNA variant and increased full-length Fas mRNA and membrane Fas, and may induce destruction of thyroid cells by promoting apoptosis of thyroid cells.