Mini-review: Cell surface receptor for thyroid hormone and nongenomic regulation of ion fluxes in excitable cells

Thyroid hormone has been shown experimentally to affect cellular ion fluxes. For example, thyroid hormone-induced modulation has been described of cellular sodium current (I_Na), inward rectifying potassium current (IKir) and sodium pump (Na, K-ATPase) and of calcium pump (Ca²⁺-ATPase) activities. Certain of these actions appear to reflect nongenomic mechanisms of hormone action that are initiated at the plasma membrane receptor for iodothyronines described on integrin αvβ3. One such action is the recent demonstration of enhancement by the hormone of I_Na in neurons. Nongenomic actions of thyroid hormone initiated at the plasma membrane may be specifically inhibited by tetraiodothyroacetic acid (tetrac), a deaminated thyroid hormone analogue.Important behavioral changes are associated with clinical states of excessive or deficient thyroid function. The molecular basis for these changes has not been established. It is proposed that nongenomic actions of thyroid hormone in neurons—such as that on sodium current—underlie certain of these behaviors. The contribution of such nongenomic actions of the hormone to animal behavioral paradigms possibly relevant to thyroid hormone actions in human subjects may be tested in vivo with tetrac.     

Elevated repetitive behaviors are associated with lower diurnal salivary cortisol levels in autism spectrum disorder

Previously, we reported a subgroup of children with autism spectrum disorders (ASD) had consistently high rates of repetitive behaviors (RBs) with abnormal sensory sensitivity. Given evidence of lower cortisol levels in response to stress and associated sensory sensitivity in the ASD population, this pilot study evaluates whether the presence of RBs reflects an underlying pathophysiology related to cortisol regulation. Diurnal salivary cortisol from 21 children with ASD and high versus low occurrence RBs were collected at four time points over three consecutive days. Although a typical decline in salivary cortisol was observed, participants in the high RB group showed 36% lower diurnal salivary cortisol than the low RB group. Age, IQ, RB type, and sleep quality were unrelated to observed differences. These findings suggest that RBs may serve to mitigate distress or that the glucocorticoid system has been down regulated in association with prolonged distress in this sample population.     

Integrin alpha(v)beta(3) expression in colon carcinoma correlates with survival.

Integrin alpha(v)beta(3) is expressed by newly formed blood vessels in diseased and neoplastic tissue and can therefore be used as a marker for angiogenesis. We investigated its expression on the vasculature of 40 colon carcinomas using the anti-alpha(v)beta(3)-specific monoclonal antibody LM609. The average relapse-free interval and overall survival in patients suffering from colon carcinomas with high vascular expression of alpha(v)beta(3) integrin was significantly reduced compared with that in patients with low alpha(v)beta(3) integrin expressing tumor vasculature. Moreover, the expression level of alpha(v)beta(3) integrin correlated with the presence of liver metastases. In conclusion, we propose vascular expression of alpha(v)beta(3) integrin as a prognostic indicator for colon carcinoma.     

Inflammation alters sodium currents and excitability of temporomandibular joint afferents

Inflammation-induced changes in voltage-gated sodium currents (I(Na)) in primary afferent neurons may contribute to hyperexcitability and pain. The present study was designed to test the hypothesis that persistent inflammation of the temporomandibular joint (TMJ) increases I(Na) in TMJ afferents. Acutely dissociated retrogradely labeled TMJ afferents were studied using whole-cell patch clamp techniques three days following Complete Freund's Adjuvant-induced inflammation of the TMJ. Inflammation was associated with a decrease in tetrodotoxin (TTX)-sensitive Na+ conductance and no significant change in slowly inactivating TTX-resistant Na+ conductance. However, inflammation increased the excitability of TMJ afferents. These results suggest that changes in ion channels other than those underlying TTX-sensitive and the slowly inactivating TTX-resistant Na+ conductance are likely to account for the inflammation-induced increase in the excitability of TMJ afferents.     

The influence of blood chemistry on T4 and FT4I in major depression

The pathophysiology underlying thyroid dysfunction in some depressed patients has not yet been determined. In order to clarify possible biochemical influences on thyroid regulation in these patients, we retrospectively examined several thyroid indices in charts from 81 depressed inpatients and 82 psychiatric controls. The depressed group had significantly higher T4 levels and free T4 index (FT4I), as well as lower chloride (CL) levels than controls. Albumin (ALB) also tended to be higher in the depressives. After adjustment for previously reported effects of ALB and CL on thyroid hormone binding in plasma, the initial differences in thyroid indices became non-significant. We suggest from these findings that plasma biochemical factors contribute significantly to the transient changes in thyroid function observed in some acutely depressed patients. Potential explanations for these biochemical alterations are discussed.     

Evolutionary adaptation of a mammalian species to an environment severely depleted of iodide

Lack of dietary iodine is associated with thyroid insufficiency and its dire consequences including cretinism, yet territories severely deficient in iodine are home to many species of wild animals. The premise of our work is that an adaptation must be in place in order to allow these animals to thrive. We collected phyllotine rodents of the genus Auliscomys from the Altiplanic region of North Chile, an area historically associated with goitre and other manifestations of iodine deficiency disorders. The iodide concentration in the stream water in this locality, at <1 micro g l(-1) would undoubtedly result in widespread thyroidal insufficiency in humans and domestic livestock. The animals we collected, identified as Auliscomys boliviensis, showed no evidence of thyroidal insufficiency. There was no enlargement of the thyroid glands; the serum concentrations of thyroid hormone (measured as T4) and thyroid-stimulating hormone were comparable to laboratory rats. Serum iodide concentration was about 40% of that measured in laboratory rats. We conclude that these animals have established a specialised adaptive mechanism, most probably at the level of the Na(+)/I(-) symporter, that acts to enhance the uptake of dietary iodide into the gut and again from the serum into the follicular cells of the thyroid gland.     

Effect of vitamin A on the hypothalamo-pituitary-thyroid axis

This study reports the effects of the administration of pharmacologic doses of vitamin A on multiple parameters of thyroid function. Vitamin A decreased total T4 and T3 levels. With vitamin A treatment, there was a marked increase in the percentage dialyzable T3 and T4 both in vivo and in vitro. The serum-free T3 and T4 levels as measured by dialysis were on the whole normal in vitamin A-treated rats. Following thyroidectomy, the total T4 levels were still decreased, suggesting that vitamin A produced its effects by increasing peripheral clearance of thyroxine. Vitamin A did not alter basal thyroid stimulating hormone (TSH) or its response to thyroid releasing hormone, suggesting a relatively normal hypothalamic-pituitary-thyroid axis in vitamin A-treated animals. Vitamin A may decrease tissue responsiveness to thyroid hormones as evidenced by the tendency to decreased Na-K-ATPase activity in the livers from vitamin A-treated rats and the decreased growth hormone response to T3 in GH3 pituitary cultures as shown in this study and by the decreased basal metabolic rate found after vitamin A in previous studies. Vitamin A decreased thyroid gland size and increases 125I thyroid uptake. In vitro, vitamin A enhanced T4 to T3 conversion in hepatic homogenates.     

Thyroid hormone regulates excitability in central neurons from postnatal rats

A lack of thyroid hormone in the postnatal period causes an irreversible mental retardation, characterized by a slowing of thoughts and movements accompanied by prolonged latencies of several evoked potentials and slowed electroencephalographic rhythms. Here we show that in cultured hippocampal and cortical neurons from postnatal rats treatment with thyroid hormone not only up-regulates Na(+)-current densities but also increases rates of rise, amplitudes and firing frequencies of action potentials. Furthermore, we show that the regulation of the Na(+)-current density by thyroid hormones also occurs in vivo: recordings from acutely isolated cortical neurons obtained from hypothyroid, euthyroid and hyperthyroid postnatal rats showed that hypothyroidism decreases the ratio of Na(+) inward- to K(+) outward-currents while hyperthyroidism upregulates Na(+)-currents with respect to K(+)-currents. Our observation of a regulation of neuronal excitability by thyroid hormone offers a direct explanation for the origin of various neurological symptoms related to thyroid dysfunction.     

An altered response in the induction of cell membrane (Na + K)ATPase by thyroid hormone is characteristic of senescence in cultured human fibroblasts

There have been numerous investigations of thyroid function during senescence in humans. However, very little information is available on thyroid hormone action at the cell level during senescence. Therefore, we have investigated thyroid hormone induction of cell membrane (Na + K)ATPase during human senescence using three experimental fibroblast cell culture systems: (1) cells from premature aging syndrome, progeria; (2) aging in vitro; and (3) early passage cells from aged patients. In all cases senescence is associated with a dramatic alteration from the normal dose-dependent thyroid hormone induction of (Na + K)ATPase. Senescent cells depleted of thyroid hormones demonstrated an elevated activity of (Na + K)ATPase, while non-senescing cells exhibit the characteristic basal enzyme activities in the hypothyroid state. These results indicate that human senescence is associated with extreme alterations in thyroid hormone regulation of (Na + K)ATPase; and may suggest a more general change in thyroid hormone action at senescence. These changes may be associated with important alterations in cell metabolism and intracellular ionic environment during senescence.     

Russell bodies consist of heterogenous glycoproteins in B-cell lymphoma cells.

The phenotypic expression of Russell bodies (RB) in the tumor cells of two patients with different types of B-cell lymphoma and of one patient with plasma cell myeloma were examined. In both B-cell lymphomas, the RBs reacted consistently with anti-Leu 8 and anti-immunoglobulin M. The RBs in one case also reacted with other monoclonal antibodies, including anti-CD5, CD19, CD22, and CD25. The membranes of most of the tumor cells containing RBs did not stain. In the myeloma, the RBs reacted only with anti-immunoglobulin, and the myeloma cells expressed no surface antigens associated with B lymphocytes. This finding suggests that RBs do not form in cells that can transport glycoproteins to the cell membrane, but rather occur as a result of defective transport or process of certain glycoproteins by plasmacytoid cells.     

Pathogenesis of Rushton bodies: A novel hypothesis

Rushton bodies (RBs) are one of the characteristic features seen in the epithelial lining of odontogenic cysts mainly radicular, dentigerous and odontogenic keratocyst. It has two different histo-morphological appearances; granular and homogeneous. Although widely investigated, the exact pathogenesis and histogenesis of RBs is still an enigma. Many hypotheses were made in the literature but none has explained conceivably the two histo-morphological appearances of RBs and their association with inflammation. In the present paper the various pathogenesis for the formation of RBs proposed till date are discussed along with proposal for a novel hypothesis. The given hypothesis is mainly related to inflammation and its effect on pore size of basement membrane of odontogenic cystic epithelium. It explains RBs association with inflammation as well as existence of two histo-morphological appearances. The proposed hypothesis also justifies the RB’s presence inside the lining epithelium of odontogenic cyst despite its hematogenous origin. Future studies are advocated for isolating RBs using laser capture microdissection and subsequent biochemical, histochemical and electron microscopic analysis to substantiate the proposed hypothesis.     

Characterization of the slowly inactivating sodium current INa2 in canine cardiac single Purkinje cells.

The aim of our experiments was to investigate by means of a whole cell patch-clamp technique the characteristics of the slowly inactivating sodium current (I(Na2)) found in the plateau range in canine cardiac Purkinje single cells. The I(Na2) was separated from the fast-activating and -inactivating I(Na) (labelled here I(Na1)) by applying a two-step protocol. The first step, from a holding potential (V(h)) of -90 or -80 mV to -50 mV, led to the quick activation and inactivation of I(Na1). The second step consisted of depolarizations of increasing amplitude from -50 mV to less negative values, which led to the quick activation and slow inactivation of I(Na2). The I(Na2) was fitted with a double exponential function with time constants of tens and hundreds milliseconds, respectively. After the activation and inactivation of I(Na1) at -50 mV, the slope conductance was very small and did not change with time. Instead, during I(Na2), the slope conductance was larger and decreased as a function of time. Progressively longer conditioning steps at -50 mV resulted in a progressive decrease in amplitude of I(Na2) during the subsequent test steps. Gradually longer hyperpolarizing steps (increments of 100 ms up to 600 ms) from V(h) -30 mV to -100 mV were followed on return to -30 mV by a progressively larger I(Na2), as were gradually more negative 500 ms steps from V(h) -30 mV to -90 mV. At the end of a ramp to -20 mV, a sudden repolarization to approximately -35 mV fully deactivated I(Na2). The I(Na2) was markedly reduced by lignocaine (lidocaine) and by low extracellular [Na(+)], but it was little affected by low and high extracellular [Ca(2+)]. At negative potentials, the results indicate that there was little overlap between I(Na2) and the transient outward current, I(to), as well as the calcium current, I(Ca). In the absence of I(to) and I(Ca) (blocked by means of 4-aminopyridine and nickel, respectively), I(Na2) reversed at 60 mV. In conclusion, I(Na2) is a sodium current that can be initiated after the inactivation of I(Na1) and has characteristics that are quite distinct from those of I(Na1). The results have a bearing on the mechanisms underlying the long plateau of Purkinje cell action potential and its modifications in different physiological and pathological conditions.     

Plasma thyroid hormones, thyroid stimulating hormone, and insulin during acute hypometabolic states in man

Acute behavioral rest states in man are associated with marked hormonal and metabolic changes. In order to complete a hormonal profile of these states and to identify possible metabolic regulators, we measured thyroid hormones (T3 and T4), thyroid stimulating hormone (TSH), and insulin during the stylized mental practice of "transcendental mediation" (TM) and during ordinary unstylized eyes closed rest. Except for TSH, which declined acutely, hormone levels were normal and stable throughout the experiment. The stability of T3 and T4, and insulin make it unlikely that these hormones regulate the acute metabolic changes associated with these behavioral states. Decreased TSH, along with stable thyroid hormone levels, may suggest change of the set point for feedback control of TSH secretion during TM and is consistent with primarily neural modulation of TSH secretion by this behavior.     

A new combined thyroid hormone index based on thyroxine, triiodothyronine and resin uptake.

A new thyroid hormone index, based on measurements of thyroxine (T4), triiodothyronine (T3) and resin uptake (RT3U), is proposed. In contrast to previous thyroid hormone indices, it incorporates both T3 and T4 measurements. This combined thyroid hormone index appears to have superior predictive value in terms of clinical correlation with thyroid disease.     

A multi-analyte immunoassay for thyroid related analytes

We describe the development and validation of multianalyte immunoassays (MAIA) for three analytes, viz., thyroxine (T4), thyroid stimulating hormone (TSH), and thyroglobulin (Tg) essential for assessment of thyroid function but having widely varying molecular weights. Using polycarbonate (PC) track-etched membranes (TEM) as an immobilization support and ¹²⁵I as the tracer, both competitive assay for T4 and non-competitive assay for TSH and Tg were performed on the same TEM. MAIA was found to be highly sensitive and precise with clinically useful working range and correlated very well with individual analyte immunoassays. While we have demonstrated this assay format with radiotracer, it can be used with non-isotopic tracers equally well.     

Thyroxine (T4) and tri-iodothyronine (T3) determinations: techniques and value in the assessment of thyroid function

Hormonal production of the thyroid gland is constituted of thyroxine or T4 (80%) and triiodothyronine or T3 (20%). In the circulation, whole T4 originates from thyroid secretion but most of T3 (80%) is produced extrathyroidally from T4 deiodination. Conversion of T4 to T3 may be influenced by various conditions and circulating T3 is a less reliable reflection of thyroid hormone production than T4. In serum most of T4 and T3 is bound to binding proteins and only 0.02% of T4 and 0.3% of T3 is free. Because of their higher diagnostic performance, free T4 (FT4) and free T3 (FT3) measurements have superseded total (free + bound) hormone determination. Total hormone measurements remain useful for research studies or in case of severe hyperthyroidism. Equilibrium dialysis/RIA is considered as the reference method for free hormone measurements. Routine clinical laboratories use automated direct two-step or one-step immunoassays with a high molecular weight ligand or labelled antibody. Free hormone measurement remains technically demanding, especially in sera from severe non-thyroid ill patients with low serum thyroxine binding capacity. Interference from anti-thyroid hormone antibodies and familial dysalbuminemic hyperthyroxinemia depends on the assay method, but is now less marked and less frequently detected. To be able to correctly interpret the results of an assay, it is necessary to assess its performance in biologically and clinically well-characterised serum samples. FT4, and FT3 measurements, if FT4 is normal and hyperthyroidism suspected, are used to confirm and assess the level of hypo and hyperthyroidism (overt or subclinical). When the thyroidal status is unstable (first months of a thyroid treatment, altered L-T4 dose, subacute thyroiditis) or when the hypothalamic-pituitary function is disturbed (central hypothyroidism), TSH determination is diagnostically misleading and only free hormone measurements are reliable for thyroid function assessment.     

Goiter formation following prostaglandin administration in rats.

Prostaglandins (PGE1 and PGE2) induced a hyperplastic microfollicular goiter with a high radioiodine (131I) thyroid uptake, increased endocytosis, a heavy autoradiographic (125I) reaction, and a moderate increase of thyroid hormones (T4, T3), thyroxine-binding globulin (TGB), and thyrotropin (TSH) concentrations in adult rats. Ultrastructurally, both prostaglandins (E1 and E2) markedly stimulated the thyroid cell activity and increased the number of pseudopodia, the size of colloid and dense granule populations, and the number of polysomes. Conversely, a hypofunction of thyroid glands with low radioiodine (131I) thyroid uptake, a decreased autoradiographic (125I) reaction, and a moderate decrease in T4, T3, TGB, and TSH concentrations were observed following prostaglandin F 2alpha. Ultrastructurally, a decrease in size of the colloid and dense granule population and the number of degenerative mitochondria occurred infollicular cells. An intense hyperplasia of parafollicular (C) cells, with abundant population of characteristic dense granules, could be seen in PGF 2alpha-treated rats. A marked decrease of radioiodine (131I) uptake, endocytosis, and autoradiographic (125I) reaction and a sharp decline in T4, T3, and TBG were observed in hypophysectomized and chronically prostaglandin-treated rats. Light and electron microscopy revealed signs of an advanced thyroid hypofunction with flat cuboidal cells, reduced microvilli, scarce endoplasmic reticulum, and few dense droplets. The present findings demonstrate that the chronic administration of prostaglandins exerts significant effects of thyroid gland and goiter formation (goitrogenesis), radioiodine metabolism, and hormone synthesis, and that these effects are mediated by TSH secretion.     

载脂蛋白（a）对血管平滑肌细胞增殖及其信号通路的影响

目的： 探讨载脂蛋白（a）［apo（a）］对血管平滑肌细胞增殖的影响及其机制。方法：原代培养血管平滑肌细胞并给予传代以进行实验，并采用α-actin抗体进行免疫组化细胞鉴定；分别给予apo（a）、apo（a）+整合素αⅤβ3单克隆抗体LM609及单独LM609干预细胞，采用细胞计数和MTT实验观察细胞增殖情况，采用Western blotting分析相关信号蛋白的变化。结果：所用实验细胞经鉴定均为血管平滑肌细胞；apo（a）能促进血管平滑肌细胞增殖，但这一作用能被整合素αⅤβ3单克隆抗体LM609所对抗，单独的LM609干预对细胞生长并无影响；Western blotting显示apo（a）能促进黏附斑激酶（FAK）磷酸化，并使总的转化生长因子β1（TGF-β1）及其磷酸化形式均表达减少，而LM609能对抗apo（a）的这些作用。结论：Apo（a）促进血管平滑肌细胞增殖的作用是通过整合素αⅤβ3介导的， 以致FAK活化，进而TGF-β1表达及磷酸化均减少。     

Diurnal profiles of thyroid hormones are altered in depression.

Free thyroxine index (FT4I), serum thyroxine (T4) and thyrotrophin concentrations were measured in 45 depressed subjects and 23 controls. The FT4I am/pm ratio was significantly higher in depressed subjects than in controls. This elevated diurnal ratio of thyroid hormones in depression adds to the literature on the chronobiology of affective disorders, and may help to explain differences in thyroid hormone levels in depressed patients in other studies, where time of sampling has seldom been reported.