Conformational adaptation of nuclear receptor ligand binding domains to agonists: potential for novel approaches to ligand design

Ligands occupy the core of nuclear receptor (NR) ligand binding domains (LBDs) and modulate NR function. X-ray structures of NR LBDs reveal most NR agonists fill the enclosed pocket and promote packing of C-terminal helix 12 (H12), whereas the pockets of unliganded NR LBDs differ. Here, we review evidence that NR pockets rearrange to accommodate different agonists. Some thyroid hormone receptor (TR) ligands with 5′ extensions designed to perturb H12 act as antagonists, but many are agonists. One mode of adaptation is seen in a TR/thyroxine complex; the pocket expands to accommodate a 5′ iodine extension. Crystals of other NR LBDs reveal that the pocket can expand or contract and some agonists do not fill the pocket. A TRβ structure in complex with an isoform selective drug (GC-24) reveals another mode of adaptation; the LBD hydrophobic interior opens to accommodate a bulky 3′ benzyl extension. We suggest that placement of extensions on NR agonists will highlight unexpected areas of flexibility within LBDs that could accommodate extensions; thereby enhancing the selectivity of agonist binding to particular NRs. Finally, agonists that induce similar LBD structures differ in their activities and we discuss strategies to reveal subtle structural differences responsible for these effects.     

Design of thyroid hormone receptor antagonists from first principles

It is desirable to obtain TR antagonists for treatment of hyperthyroidism and other conditions. We have designed TR antagonists from first principles based on TR crystal structures. Since agonist ligands are buried in the fold of the TR ligand binding domain (LBD), we reasoned that ligands that resemble agonists with large extensions should bind the LBD, but would prevent its folding into an active conformation. In particular, we predicted that extensions at the 5′ aryl position of ligand should reposition helix (H) 12, which forms part of the co-activator binding surface, and thereby inhibit TR activity. We have found that some synthetic ligands with 5′ aryl ring extensions behave as antagonists (DIBRT, NH-3), or partial antagonists (GC-14, NH-4). Moreover, one compound (NH-3) represents the first potent TR antagonist with nanomolar affinity that also inhibits TR action in an animal model. However, the properties of the ligands also reveal unexpected aspects of TR behavior. While nuclear receptor antagonists generally promote binding of co-repressors, NH-3 blocks co-activator binding and also prevents co-repressor binding. More surprisingly, many compounds with extensions behave as full or partial agonists. We present hypotheses to explain both behaviors in terms of dynamic equilibrium of H12 position.     

Selective modulation of thyroid hormone receptor action

Thyroid hormones have some actions that might be useful therapeutically, but others that are deleterious. Potential therapeutically useful actions include those to induce weight loss and lower plasma cholesterol levels. Potential deleterious actions are those on the heart to induce tachycardia and arrhythmia, on bone to decrease mineral density, and on muscle to induce wasting. There have been successes in selectively modulating the actions of other classes of hormones through various means, including the use of pharmaceuticals that have enhanced affinities for certain receptor isoforms. Thus, there is reason to pursue selective modulation of thyroid hormone receptor (TR) function, and several agents have been shown to have some β-selective, hepatic selective and/or cardiac sparring activities, although development of these was largely not based on detailed understanding of mechanisms for the specificity. The possibility of selectively targeting the TRβ was suggested by the findings that there are - and β-TR forms and that the TR-forms may preferentially regulate the heart rate, whereas many other actions of these hormones are mediated by the TRβ. We determined X-ray crystal structures of the TR and TRβ ligand-binding domains (LBDs) complexed with the thyroid hormone analog 3,5,3′-triiodithyroacetic acid (Triac). The data suggested that a single amino acid difference in the ligand-binding cavities of the two receptors could affect hydrogen bonding in the receptor region, where the ligand's 1-position substituent fits and might be exploited to generate β-selective ligands. The compound GC-1, with oxoacetate in the 1-position instead of acetate as in Triac, exhibited TRβ-selective binding and actions in cultured cells. An X-ray crystal structure of the GC-1-TRβ LBD complex suggests that the oxoacetate does participate in a network of hydrogen bonding in the TR LBD polar pocket. GC-1 displayed actions in tadpoles that were TRβ-selective. When administered to mice, GC-1 was as effective in lowering plasma cholesterol levels as T₃, and was more effective than T₃ in lowering plasma triglyceride levels. At these doses, GC-1 did not increase the heart rate. GC-1 was also less active than T₃ in modulating activities of several other cardiac parameters, and especially a cardiac pacemaker channel such as HCN-2, which may participate in regulation of the heart rate. GC-1 showed intermediate activity in suppressing plasma thyroid stimulating hormone (TSH) levels. The tissue/plasma ratio for GC-1 in heart was also less than for the liver. These data suggest that compounds can be generated that are TR-selective and that compounds with this property and/or that exhibit selective uptake, might have clinical utility as selective TR modulators.     

甲状腺激素在两栖动物变态过程中的作用

两栖动物的幼体变态是研究甲状腺激素调节组织和器官重构的理想模式。本文主要综述了近年来两栖动物甲状腺激素合成过程中3种脱碘酶D1、D2和D3的特点及其生物学功能;甲状腺激素受体的蛋白结构、类型和机能;以及甲状腺激素对两栖动物幼体变态过程中各个类型组织和器官重构的调节;甲状腺激素、甲状腺激素受体和脱碘酶的互作,并展望了今后的研究方向。     

养殖条件下3种锦蛇甲状腺相关激素和生长的比较研究

为深入了解人工饲养条件下棕黑锦蛇(Elaphe schrenckii)、赤峰锦蛇(E.anomala)和王锦蛇(E.carinata)生长情况及与甲状腺相关激素的关系,本研究在蛇类非冬眠时期的5月、7月和9月,以尾静脉采血获得3种锦蛇的血清,检测其血清中促甲状腺激素释放激素(TRH)、促甲状腺激素(TSH)和甲状腺素(T4)含量,并记录观察期间3种蛇的体重和体长的增长以及进食量。检测结果,王锦蛇的促甲状腺激素释放激素(TRH)、促甲状腺激素(TSH)和甲状腺素(T4)含量均低于其他2种锦蛇,3种锦蛇促甲状腺激素释放激素(TRH)、促甲状腺激素(TSH)含量最高值均出现在7月份;除了赤峰锦蛇外,棕黑锦蛇和王锦蛇的甲状腺素(T4)含量最高值也出现在7月份,与蛇类快速生长的时间相一致。另外,棕黑锦蛇甲状腺素(T4)含量与进食量的相关系数高于赤峰锦蛇和王锦蛇,而其饲料的转化率也高于后两者,其间存在的关系还需要深入研究。由上述结果可以看出,3种锦蛇促甲状腺激素释放激素(TRH)、促甲状腺激素(TSH)和甲状腺素(T4)含量和变化趋势有着明显的差别,且血清甲状腺素(T4)含量与蛇的进食量、生长和饲料转化率之间有密切的关系。     

Surface plasmon resonance assay of inhibition by pharmaceuticals for thyroxine hormone binging to transport proteins

We developed a surface plasmon resonance (SPR) assay to estimate the competitive inhibition by pharmaceuticals for thyroxine (T4) binding to thyroid hormone transport proteins, transthyretin (TTR) and thyroxine binding globulin (TBG). In this SPR assay, the competitive inhibition of pharmaceuticals for introducing T4 into immobilized TTR or TBG on the sensor chip can be estimated using a running buffer containing pharmaceuticals. The SPR assay showed reproducible immobilization of TTR and TBG, and the kinetic binding parameters of T4 to TTR or TBG were estimated. The equilibrium dissociation constants of TTR or TBG measured by SPR did not clearly differ from data reported for other binding assays. To estimate the competitive inhibition of tetraiodothyroacetic acid, diclofenac, genistein, ibuprofen, carbamazepine, and furosemide, reported to be competitive or noncompetitive pharmaceuticals for T4 binding to TTR or TBG, their 50% inhibition concentrations (IC₅₀) (or 80% inhibition concentration, IC₈₀) were calculated from the change of T4 responses in sensorgrams obtained with various concentrations of the pharmaceuticals. Our SPR method should be a useful tool for predicting the potential of thyroid toxicity of pharmaceuticals by evaluating the competitive inhibition of T4 binding to thyroid hormone binding proteins, TTR and TBG.     

超声引导下微波消融在甲状腺良性结节中的价值分析

目的:分析超声引导下微波消融治疗甲状腺良性结节中的价值。方法:选取我院接受治疗的140例甲状腺良性结节患者,根据治疗方法分成两组,微波消融组接受超声引导下微波消融治疗,药物治疗组接受甲状腺激素药物治疗。对比分析两组患者甲状腺结节体积和数量、甲状腺功能变化,并比较两组副反应发生率。结果:微波消融组治疗后结节体积低于药物治疗组,而体积缩小率高于药物治疗组,组间差异存在统计学意义(P0.05)。治疗后,患者血清学T3、T4、TSH改善明显,其中微波消融组改善最显著,组间差异存在显著性(P0.05)。结论:超声引导下微波消融能够减小甲状腺良性结节数目和体积,促进甲状腺功能逐步恢复,建议临床推广。     

妊娠期甲状腺疾病诊断及治疗的研究进展

妊娠期妇女体内激素水平会发生变化,使妊娠妇女甲状腺激素水平的测定和判断存在一定的困难,应选择适用于妊娠妇女的甲状腺激素水平特异值,进而正确评估甲状腺功能状态及对母体和胎儿的影响。孕前及妊娠期测定促甲状腺素和游离甲状腺激素有很大的必要性,因为甲状腺疾病以及单纯性甲状腺抗体阳性会导致多种妊娠不良结局,尤其是甲状腺功能减退对胎儿智力发育和认知功能具有非常大的影响。孕期甲状腺激素的监测对评估甲状腺功能状态及疾病预后具有非常大的作用,可以提示临床医师是否给予药物干预及如何调整药量。对于孕期甲状腺激素补充治疗后应达到的目标值以及甲状腺抗体阴性的亚临床甲状腺功能降低的妊娠患者是否给予干预,目前仍有异议。     

甲状腺癌患者血清促甲状腺激素和甲状腺激素表达水平及临床意义

目的:探讨甲状腺癌患者血清促甲状腺激素和甲状腺激素表达水平及临床意义。方法:应用电化学发光方法检测甲状腺癌组、甲状腺良性病变组和正常对照组血清促甲状腺激素(TSH)和甲状腺激素(TT3、FT3、TT4、FT4)水平。结果:①血清TSH在三组中比较有统计学意义(P〈0.001),甲状腺癌组血清TSH水平(3.56±0.93ulU/ml)明显高于甲状腺良性病变组(2.82±0.70ulU/ml)和正常对照组(2.04±0.56ulU/ml);TSH与肿瘤病理分期和肿瘤大小呈正相关(P<0.05)。②血清FT3、FT4水平在三组中有统计学意义(均P〈0.001),甲状腺癌组FT3、FT4水平处于较低水平,二者均明显低于甲状腺良性病变组和正常对照组(P<0.001);FT3与肿瘤病理分期和淋巴结转移呈负相关(P<0.05)。③TT3和TT4水平在三组之间比较均无统计学意义(P>0.05)。结论:高水平TSH可增加甲癌复发的危险性。低甲状腺激素水平在甲状腺癌形成中可能起到一定的作用,因此可以将其作为预测甲癌复发的重要指标之一。     

Severe impairment of cerebellum development in mice expressing a dominant-negative mutation inactivating thyroid hormone receptor alpha1 isoform

Thyroid hormone deficiency is known to deeply affect cerebellum post-natal development. We present here a detailed analysis of the phenotype of a recently generated mouse model, expressing a dominant-negative TRα1 mutation. Although hormonal level is not affected, the cerebellum of these mice displays profound alterations in neuronal and glial differentiation, which are reminiscent of congenital hypothyroidism, indicating a predominant function of this receptor isoform in normal cerebellum development. Some of the observed effects might result from the cell autonomous action of the mutation, while others are more likely to result from a reduction in neurotrophic factor production.     

Understanding the role of thyroid hormone in Sertoli cell development: a mechanistic hypothesis

More than a decade of research has shown that Sertoli cell proliferation is regulated by thyroid hormone. Neonatal hypothyroidism lengthens the period of Sertoli cell proliferation, leading to increases in Sertoli cell number, testis weight, and daily sperm production (DSP) when euthyroidism is re-established. In contrast, the neonatal Sertoli cell proliferative period is shortened under hyperthyroid conditions, but the mechanism by which thyroid hormone is able to negatively regulate Sertoli cell proliferation has been unclear. Recent progress in the understanding of the cell cycle has provided the opportunity to dissect the molecular targets responsible for thyroid-hormone-mediated effects on Sertoli cell proliferation. In this review, we discuss recent results indicating a critical role for the cyclin-dependent kinase inhibitors (CDKI) p27^Kip1 and p21^Cip1 in establishing Sertoli cell number, testis weight, and DSP, and the ability of thyroid hormone to modulate these CDKIs. Based on these recent results, we propose a working hypothesis for the way in which thyroid hormone regulates the withdrawal of the cell cycle by controlling CDKI degradation. Finally, although Sertoli cells have been shown to have two biologically active thyroid hormone receptor (TR) isoforms, TRα1 and TRβ1, experiments with transgenic mice lacking TRα or TRβ illustrate that only one TR mediates thyroid hormone effects in neonatal Sertoli cells. Although significant gaps in our knowledge still remain, advances have been made toward appreciation of the molecular sequence of events that occur when thyroid hormone stimulates Sertoli cell maturation. We gratefully acknowledge the support of this work by the NIH, USDA, the University of Illinois, the Lalor Foundation, and the Thanis A. Field Endowment at the University of Illinois. D.R. Holsberger was supported by postdoctoral fellowships from the Lalor Foundation and Reproductive Biology Research Training Program (NIH grant T32 HD07028), University of Illinois at Urbana–Champaign.     

左甲状腺素钠片联合甲状腺片用于甲状腺癌术后TSH抑制治疗的临床效果评价

摘要 目的：探究左甲状腺素钠片联合甲状腺片用于甲状腺癌术后促甲状腺激素（TSH）抑制治疗的临床效果。方法：选择2021年1月-2022年6月本院收治的甲状腺癌手术并进行碘131清甲治疗后行TSH抑制治疗的80例患者为本次研究对象,开展动态分组法,对照组及观察组,n=40。单纯左甲状腺素钠片治疗为对照组,左甲状腺素钠片联合甲状腺片治疗为观察组。比较甲状腺功能、肝肾功能、治疗效果及不良反应。结果：治疗后,游离三碘甲状腺原氨酸（FT3）、游离四碘甲状腺原氨酸（FT4）水平,观察组及对照组均较治疗前提高,但观察组低于对照组;TSH水平,两组均较治疗前降低,且观察组较对照组低（P＜0.05）;治疗前,肌酐（Scr）、谷丙转氨酶（ALT）、谷草转氨酶（AST）水平,观察组及对照组比较无差异（P＞0.05）,治疗后,各指标水平,两组均较治疗前降低,且观察组较对照组低（P＜0.05）;观察组治疗有效率高于对照组（P＜0.05）;观察组及对照组不良反应率比较无差异（P＞0.05）。结论：左甲状腺素钠片联合甲状腺片用于甲状腺癌术后TSH抑制治疗可明显改善患者甲状腺功能,提高免疫功能及治疗效果,效果优于左甲状腺素钠片单独治疗,且安全性较高。     

术前血清促甲状腺激素水平与甲状腺结节相关性的研究

目的：探讨术前血清促甲状腺激素（TSH）水平与甲状腺结节良恶性的关系。方法：回顾性分析了1499例甲状腺结节手术切除患者术前血清TSH、甲状腺B超,手术记录、术后病理诊断报告。根据术后病理报告判定甲状腺结节良恶性,分析术前血清TSH水平在甲状腺良恶性结节中的不同分布。结果：分化型甲状腺癌（DTC）患者术前血清TSH水平明显高于甲状腺良性结节组（2．179±2．017vsl．259±0．884μIU／mL）,P〈0．001;在DTC患者中,有淋巴结转移较无淋巴结转移、TNM分期Ⅲ、Ⅳ期较Ⅰ、Ⅱ期以及肿瘤直径≥1cm较〈1cm的患者术前血清TSH明显升高（均P〈0．001）。结论：术前血清TSH水平是预测甲状腺结节良恶性的重要指标。     

Mechanisms of action of thyroid hormones in the skeleton

Background

Thyroid hormones regulate skeletal development, acquisition of peak bone mass and adult bone maintenance. Abnormal thyroid status during childhood disrupts bone maturation and linear growth, while in adulthood it results in altered bone remodeling and an increased risk of fracture

Scope of Review

This review considers the cellular effects and molecular mechanisms of thyroid hormone action in the skeleton. Human clinical and population data are discussed in relation to the skeletal phenotypes of a series of genetically modified mouse models of disrupted thyroid hormone signaling.

Major Conclusions

Euthyroid status is essential for normal bone development and maintenance. Major thyroid hormone actions in skeletal cells are mediated by thyroid hormone receptor α (TRα) and result in anabolic responses during growth and development but catabolic effects in adulthood. These homeostatic responses to thyroid hormone are locally regulated in individual skeletal cell types by the relative activities of the type 2 and 3 iodothyronine deiodinases, which control the supply of the active thyroid hormone 3,5,3’-L-triiodothyronine (T3) to its receptor.

General Significance

Population studies indicate that both thyroid hormone deficiency and excess are associated with an increased risk of fracture. Understanding the cellular and molecular basis of T3 action in skeletal cells will lead to the identification of new targets to regulate bone turnover and mineralization in the prevention and treatment of osteoporosis. This article is part of a Special Issue entitled Thyroid hormone signaling.     

术前血清促甲状腺激素水平与甲状腺结节相关性的研究

目的:探讨术前血清促甲状腺激素(TSH)水平与甲状腺结节良恶性的关系。方法:回顾性分析了1499例甲状腺结节手术切除患者术前血清TSH、甲状腺B超,手术记录、术后病理诊断报告。根据术后病理报告判定甲状腺结节良恶性,分析术前血清TSH水平在甲状腺良恶性结节中的不同分布。结果:分化型甲状腺癌(DTC)患者术前血清TSH水平明显高于甲状腺良性结节组(2.179±2.017vs1.259±0.884μIU/mL),P<0.001;在DTC患者中,有淋巴结转移较无淋巴结转移、TNM分期III、IV期较I、II期以及肿瘤直径≥1cm较<1cm的患者术前血清TSH明显升高(均P<0.001)。结论:术前血清TSH水平是预测甲状腺结节良恶性的重要指标。