Thyroid-stimulating hormone, a novel, locally produced modulator of human epidermal functions, is regulated by thyrotropin-releasing hormone and thyroid hormones.

Several elements of the hypothalamic-pituitary-thyroid axis (HPT) reportedly are transcribed by human skin cell populations, and human hair follicles express functional receptors for TSH. Therefore, we asked whether the epidermis of normal human skin is yet another extrathyroidal target of TSH and whether epidermis even produces TSH. If so, we wanted to clarify whether intraepidermal TSH expression is regulated by TRH and/or thyroid hormones and whether TSH alters selected functions of normal human epidermis in situ. TSH and TSH receptor (TSH-R) expression were analyzed in the epidermis of normal human scalp skin by immunohistochemistry and PCR. In addition, full-thickness scalp skin was organ cultured and treated with TSH, TRH, or thyroid hormones, and the effect of TSH treatment on the expression of selected genes was measured by quantitative PCR and/or quantitative immunohistochemistry. Here we show that normal human epidermis expresses TSH at the mRNA and protein levels in situ and transcribes TSH-R. It also contains thyrostimulin transcripts. Intraepidermal TSH immunoreactivity is up-regulated by TRH and down-regulated by thyroid hormones. Although TSH-R immunoreactivity in situ could not be documented within the epidermis, but in the immediately adjacent dermis, TSH treatment of organ-cultured human skin strongly up-regulated epidermal expression of involucrin, loricrin, and keratins 5 and 14. Thus, normal human epidermis in situ is both an extrapituitary source and (possibly an indirect) target of TSH signaling, which regulates defined epidermal parameters. Intraepidermal TSH expression appears to be regulated by the classical endocrine controls that determine the systemic HPT axis.

Thyrotropin powers human mitochondria.

Here we demonstrate that the neuropeptide hormone thyrotropin (TSH), which controls thyroid hormone production, exerts a major nonclassical function in mitochondrial biology. Based on transcriptional, ultrastructural, immunohistochemical, and biochemical evidence, TSH up-regulates mitochondrial biogenesis and consequently activity in organ-cultured normal human epidermis in situ. Mitochondrial activity was assessed by measuring 2 key components of the respiratory chain. The abundance of mitochondria was assessed employing 2 independent morphological techniques: counting their numbers in human epidermis by high-magnification light microscopy of skin sections immunostained for mitochondria-selective cytochrome-c-oxidase subunit 1 (MTCO1) and transmission electron microscopy (TEM). Treatment with 10 mU/ml of TSH for 6 d strongly up-regulates the number of light-microscopically visualized, MTCO1-demarcated mitochondria. On the ultrastructural level, TEM confirms that TSH indeed stimulates mitochondrial proliferation and biogenesis in the perinuclear region of human skin epidermal keratinocytes. On the transcriptional level, TSH up-regulates MTCO1 mRNA (quantitative RT-PCR) and significantly enhances complex I and IV (cytochrome-c-oxidase) activity. This study pioneers the concept that mitochondrial energy metabolism and biogenesis in a normal, prototypic human epithelial tissue underlies potent neuroendocrine controls and introduces human skin organ culture as a clinically relevant tool for further exploring this novel research frontier in the control of mitochondrial biology.

Thyroid hormones directly alter human hair follicle functions: anagen prolongation and stimulation of both hair matrix keratinocyte proliferation and hair pigmentation.

CONTEXT: Both insufficient and excess levels of thyroid hormones (T3 and T4) can result in altered hair/skin structure and function (e.g. effluvium). However, it is still unclear whether T3 and T4 exert any direct effects on human hair follicles (HFs), and if so, how exactly human HFs respond to T3/T4 stimulation. OBJECTIVE: Our objective was to asses the impact of T3/T4 on human HF in vitro. METHODS: Human anagen HFs were isolated from skin obtained from females undergoing facelift surgery. HFs from euthyroid females between 40 and 69 yr (average, 56 yr) were cultured and treated with T3/T4. RESULTS: Studying microdissected, organ-cultured normal human scalp HFs, we show here that T4 up-regulates the proliferation of hair matrix keratinocytes, whereas their apoptosis is down-regulated by T3 and T4. T4 also prolongs the duration of the hair growth phase (anagen) in vitro, possibly due to the down-regulation of TGF-beta2, the key anagen-inhibitory growth factor. Because we show here that human HFs transcribe deiodinase genes (D2 and D3), they may be capable of converting T4 to T3. Intrafollicular immunoreactivity for the recognized thyroid hormone-responsive keratins cytokeratin (CK) 6 and CK14 is significantly modulated by T3 and T4 (CK6 is enhanced, CK14 down-regulated). Both T3 and T4 also significantly stimulate intrafollicular melanin synthesis. CONCLUSIONS: Thus, we present the first evidence that human HFs are direct targets of thyroid hormones and demonstrate that T3 and/or T4 modulate multiple hair biology parameters, ranging from HF cycling to pigmentation.

Prediction of progression to overt hypothyroidism or hyperthyroidism in female relatives of patients with autoimmune thyroid disease using the Thyroid Events Amsterdam (THEA) score.

BACKGROUND: Genetic and environmental factors are involved in the pathogenesis of autoimmune thyroid disease (AITD). Family members of patients with AITD are at increased risk for AITD, but not all will develop overt hypothyroidism or hyperthyroidism. Our goal was to develop a simple predictive score that has broad applicability and is easily calculated at presentation for progression to overt hypothyroidism or hyperthyroidism within 5 years in female relatives of patients with AITD. METHODS: We conducted a prospective observational cohort study of 790 healthy first- or second-degree female relatives of patients with documented Graves or Hashimoto disease in The Netherlands. Baseline assessment included measurement of serum thyrotropin (TSH), free thyroxine (FT(4)), and thyroid peroxidase (TPO) antibody levels as well as evaluation for the presence and levels of Yersinia enterocolitica antibodies. We also gathered data on family background, smoking habits, use of estrogen medication, pregnancy, and exposure to high levels of iodine. In follow-up, thyroid function was investigated annually for 5 years. As main outcome measures, termed events, we looked for overt hypothyroidism (TSH levels >5.7 mIU/L and FT(4) levels <0.72 ng/dL) or overt hyperthyroidism (TSH levels <0.4 mIU/L and FT(4) levels >1.56 ng/dL). RESULTS: The cumulative event rate was 7.5% over 5 years. The mean annual event rate was 1.5%. There were 38 hypothyroid and 13 hyperthyroid events. Independent risk factors for events were baseline findings for TSH and TPO antibodies in a level-dependent relationship (for TSH the risk already starts to increase at values >2.0 mIU/L) and family background (with the greatest risk attached to subjects having 2 relatives with Hashimoto disease). A numerical score, the Thyroid Events Amsterdam (THEA) score, was designed to predict events by weighting these 3 risk factors proportionately to their relative risks (maximum score, 21): low (0-7), medium (8-10), high (11-15), and very high (16-21). These THEA scores were associated with observed event rates of 2.7%, 14.6%, 27.1%, and 76.9%, respectively. CONCLUSIONS: An accurate simple predictive score was developed to estimate the 5-year risk of overt hypothyroidism or hyperthyroidism in female relatives of patients with AITD. However, in view of the small number of observed events, independent validation of the THEA score is called for.

Too early to dismiss Yersinia enterocolitica infection in the aetiology of Graves' disease: evidence from a twin case-control study.

BACKGROUND: Yersinia enterocolitica (YE) infection has long been implicated in the pathogenesis of Graves' disease (GD). The association between YE and GD could, however, also be due to common genetic or environmental factors affecting the development of both YE infection and GD. This potential confounding can be minimized by investigation of twin pairs discordant for GD. AIM: To examine whether YE infection is associated with GD. DESIGN: We first conducted a classical case-control study of individuals with (61) and without (122) GD, and then a case-control study of twin pairs (36) discordant for GD. METHODS: Immunoglobulin (Ig)A and IgG antibodies to virulence-associated Yersinia outer membrane proteins (YOPs) were measured. MAIN OUTCOME MEASURES: The prevalence of YOP IgA and IgG antibodies. RESULTS: Subjects with GD had a higher prevalence of YOP IgA (49%vs. 34%, P = 0.054) and YPO IgG (51%vs. 35%, P = 0.043) than the external controls. The frequency of chronic YE infection, reflected by the presence of both IgA and IgG YOP antibodies, was also higher among cases than controls (49%vs. 33%, P = 0.042). Similar results were found in twin pairs discordant for GD. In the case-control analysis, individuals with GD had an increased odds ratio (OR) of YE infection: IgA 1.84 (95% CI 0.99-3.45) and IgG 1.90 (95% CI 1.02-3.55). In the co-twin analysis, the twin with GD also had an increased OR of YE infection: IgA 5.5 (95% CI 1.21-24.81) and IgG 5.0 (95% CI 1.10-22.81). CONCLUSION: The finding of an association between GD and YE in the case-control study and within twin pairs discordant for GD supports the notion that YE infection plays an aetiological role in the occurrence of GD, or vice versa. Future studies should examine the temporal relationship of this association in more depth.

Decreased radioiodine uptake of FRTL-5 cells after (131)I incubation in vitro: molecular biological investigations indicate a cell cycle-dependent pathway.

PURPOSE: In radioiodine therapy the "stunning phenomenon" is defined as a reduction of radioiodine uptake after diagnostic application of (131)I. In the current study, we established an in vitro model based on the "Fisher rat thyrocyte cell line no. 5" (FRTL-5) to investigate the stunning. METHODS: TSH-stimulated FRTL-5 cells were incubated with (131)I. Time-dependent (131)I uptake and the viability of FRTL-5 cells were evaluated at 4-144 h after radioiodine application. All data was corrected for number of viable cells, half life and (131)I concentration. Sodium iodide symporter (NIS) and the housekeeping gene (beta-actin, GAPDH) levels were quantified by quantitative polymerase chain reaction (qPCR). Additionally, immunohistochemical staining (IHC) of NIS on the cell membrane was carried out. RESULTS: FRTL-5 monolayer cell cultures showed a specific maximum uptake of (131)I 24-48 h after application. Significantly decreased (131)I uptake values were observed after 72-144 h. The decrease in radioiodine uptake was correlated with decreasing mRNA levels of NIS and housekeeping genes. In parallel, unlike in controls, IHC staining of NIS on FRTL-5 cells declined significantly after (131)I long-term incubation. CONCLUSIONS: It could be demonstrated that during (131)I incubation of FRTL-5 cells, radioiodine uptake decreased significantly. Simultaneously decreasing levels of NIS mRNA and protein expression suggest a NIS-associated mechanism. Since mRNA levels of housekeeping genes decreased, too, the reduced NIS expression might be provoked by a cell cycle arrest. Our investigations recommend the FRTL-5 model as a valuable tool for further molecular biological investigations of the stunning phenomenon.

Increased radioiodine uptake of thyroid cell cultures after external irradiation.

BACKGROUND: Radioiodine uptake (RIU) is one of the main prognostic factors for curative results of radioiodine therapy in patients with differentiated thyroid cancer. Some days after application of (131)I, the uptake of a subsequent administration of radioiodine was found to be reduced. In contrast, early after irradiation with high-energy photons glucose and amino acid uptake were observed to be increased. Effects of external irradiation on RIU of thyrocytes using high-energy photons have not been investigated so far. MATERIAL AND METHODS: Two different cell lines (FRTL-5 and ML-1 cells) derived from thyroid tissue were studied in vitro. Cell lines were either incubated with (131)I only (controls) or additionally irradiated with single doses of 6 or 10 Gy of high-energy photons using a linear accelerator. Cell number and RIU were determined 24-96 h after (131)I application. RIU measurements were repeated after application of sodium perchlorate in excess to investigate specificity of the uptake. Statistical analyses were performed using non-parametric tests. RESULTS: Incubation with radioiodine as well as irradiation with high-energy photons slowed down proliferation in investigated cell lines significantly. Irradiation with solely (131)I resulted in stable or slightly decreased iodide uptake. Compared to those cells, the RIU increased significantly in externally irradiated cells, i. e., additional irradiation with 10 Gy resulted in an almost threefold increase of RIU in FRTL-5 after 72 h. The increase of RIU after irradiation was dose-dependent in both cell lines and could be blocked by perchlorate excess. CONCLUSION: It could be demonstrated that external irradiation increases RIU in thyroid cell cultures early after irradiation. The increase was dose-dependent and specific, as it could be blocked by perchlorate. This effect appears to be similar to the increase of other actively transported substances after irradiation with high-energy photons. Therefore, the results of this study may contribute to the knowledge of a generalized irradiation-induced mechanism which causes the activation of different cellular transporters. The clinical impact of these findings on combined therapy concepts has to be investigated in further experiments.