摘要
Ⅱ型脱碘酶(D2)是一种重要的含硒蛋白酶,负责将甲状腺素(T4)的外环去碘化,形成生物活性更高的三碘甲状腺素(T3),从而调节体内的新陈代谢、生长发育和能量平衡。D2的活性受到多种因素的调控,包括自身甲状腺激素水平、cAMP途径、泛素化、内质网应激以及环境等。D2不仅与甲状腺疾病的发生、发展密切相关,而且在调节细胞增殖方面具有重要作用,因此被认为可能是有用的癌症标志物。此外,Ⅱ型脱碘酶基因(DIO2)Thr92Ala多态性已被证实是甲状腺疾病的相关因素,了解这种多态性与甲状腺疾病的关系,不仅可以帮助预测个体患病的风险,还有望为个性化治疗提供依据。本综述重点介绍D2的调控机制及其在甲状腺疾病中的重要作用,以及DIO2 Thr92Ala多态性在疾病发展中的影响,为今后的研究与临床实践提供指导。
甲状腺分泌的甲状腺素(T4)转化为三碘甲状腺素(T3),以发挥其生物活性,这种转化受Ⅰ型脱碘酶(type Ⅰ deiodinase,D1)和Ⅱ型脱碘酶(type Ⅱ deiodinase,D2)调节,其中还包括一种灭活酶,即Ⅲ型脱碘酶(type Ⅲ deiodinase,D3),可以同时灭活T4和T3。甲状腺的生物活性主要是由D2调控,由Ⅱ型脱碘酶基因(type Ⅱ iodothyronine deiodinase gene,DIO2)编码,主要调节体内的新陈代谢、生长发育和能量平
D2是一种经典的Ⅰ型膜蛋白,驻留在内质网膜上,由于泛素化和蛋白酶体的摄取,它的半衰期相对较短(约45 min)。在健康人体内,大约30%的血清T3来自甲状腺分泌,70%来自D1和D2催化的T4向T3的甲状腺外转
D2的调控受到转录和转录后的精密控制,其启动由各种发育、代谢或环境线索触发,包括肾上腺素能和外源物激活的cAMP途径。DIO2作为cAMP的响应基因,主要受肾上腺素/cAMP信号通路的调控,之前的研究指出,TSH和TSH受体(TSHR)的相互作用通过产生cAMP影响了位于DIO2启动子区域上游的cAMP响应基因。由于DIO2启动子区域含有一个cAMP反应元件,这导致在共转染蛋白激酶A的催化亚基上,DIO2启动子活性增加了10
D2的泛素化是一种修饰D2半衰期的分子机制,它通过将泛素与D2结合,使酶失活并在蛋白酶体中被靶向降解,泛素化被认为是通过破坏D2∶D2二聚体的构象而使D2失活,这对酶活性至关重
内质网应激通过抑制D2从头合成来降低D2活性。在内质网应激期间,D2活性和蛋白质水平迅速降低,从而有效地降低了D2表达细胞中的细胞内T3产生和甲状腺激素信号传导。而D2活性和局部T3产生的损失是由真核引发因子2(eIF2a)途径有效抑制D2 mRNA翻译的结
Sun
DIO2多态性,特别是其中的Thr92Ala多态性,是当前甲状腺激素代谢领域备受关注的研究课题。这种多态性指的是DIO2中的一种常见基因变异,其中第92位密码子由苏氨酸(Thr)变为丙氨酸(Ala)。这一变异导致了D2结构上的微小改变,但其对甲状腺激素代谢和相关疾病的影响却是显著的。分子生物学研究表明,D2-Thr和D2-Ala具有类似的亚细胞定位,已被确定与D2速率降低有
DIO2中的Thr92Ala多态性在甲状腺激素代谢和治疗反应方面至关重要。口服左旋甲状腺素(L-T4)抑制TSH水平是分化型甲状腺癌(differentiated thyroid cancer,DTC)患者术后临床管理和治疗中最常用的方法,实际上,约70%的循环T3是由D2介导的T4向T3的外周转化产生的,然而,并非所有接受L-T4治疗的甲状腺切除患者在外周组织中具有相同的将T4转化为T3的能力,最近关于DIO2多态性的研究试图解决接受L-T4治疗的受试者转换T4为T3的异质性能力,发现这种差异与DIO2 Thr92Ala多态性密切相关;另有研
而为了研究DIO2上的三个单核苷酸多态性(SNPs)位点rs225014(Thr92Ala)、rs225015、rs12885300(ORFa-Gly3Asp)和单羧酸转运蛋白10(MCT10)基因上的SNP位点(rs17606253)的关联,Carlé
因此,在甲状腺乳头状癌(papillary thyroid carcinoma,PTC)患者的DIO2多态性可能在术后TSH水平抑制不佳的精确定义和个体化治疗方法中发挥关键作用,提示这些患者应接受DIO2多态性的筛查。然而,关于DIO2 Thr92Ala的作用及其临床影响仍存在争议。尽管普遍认为DIO2 Thr92Ala可能降低D2的速度,但由于该单核苷酸多态性在普通人群中较为常见,且所有具有该多态性的大部分受试者在甲状腺功能检测中未表现出典型特征,这一结论仍有待更多研究的证
甲状腺功能亢进的主要原因之一是Graves病,又称毒性弥漫性甲状腺肿,是一种自身免疫性甲状腺疾病。这种疾病是多种因素的综合结果,是由于机体免疫系统紊乱引起
桥本甲状腺炎以甲状腺特异性自身抗体为特征,是最常见的自身免疫性疾病之
脱碘酶在不同类型的癌症中的表达呈现多样性,这暗示脱碘酶可能是一种有用的癌症标志物,或者在调节细胞增殖方面发挥作用。在癌细胞中,脱碘酶的复杂和动态表达受到生长因子、致癌蛋白和miRNA网络的调控。这种精细的调节使得癌细胞处于动态变化的甲状腺激素浓度环境中,从而刺激或抑制细胞功
脱碘酶及其与其他经典途径的相互作用可能成为对抗肿瘤发生过程的潜在重要靶点。脱碘酶的表达紊乱不仅仅限于调节肿瘤细胞内T4和T3水平,更是反映了参与致癌关键信号通路的过度激活或抑制。由于不同肿瘤具有独特的组织特征,研究脱碘酶在特定肿瘤环境中的作用有助于更好地理解其是肿瘤细胞失衡的原因还是结果。这种研究不仅有助于揭示肿瘤发生机制,也为开发针对性的抗癌治疗提供了重要线
甲状腺乳头状癌(papillary thyroid carcinoma,PTC)是甲状腺最常见的恶性肿瘤类型,而D2在该癌症的发展和进展过程中可能发挥一定的作
D2的过表达导致人类疾病的潜力已被明确证明,同样,在甲状腺滤泡状癌(follicular thyroid cancer,FTC)中发现D2活性高于正常甲状腺组织,并且D2的异常表达可引起FTC转移患者的甲状腺毒
甲状腺髓样癌(medullary thyroid carcinoma,MTC)是一种罕见的起源于滤泡旁C细胞的神经内分泌恶性肿
甲状腺未分化癌(undifferentiated carcinoma)又称间变性癌(anaplastic carcinoma,ATC)是一种罕见的侵袭性肿瘤,仅占所有甲状腺癌的1%,但其导致的死亡约占所有甲状腺癌死亡的1/
综上所述,D2不仅在甲状腺激素代谢中具有关键作用,还在甲状腺疾病的发展和癌症调节中发挥重要功能。通过深入研究D2及其相关基因多态性的研究为理解甲状腺疾病的发生机制提供了重要参考,不仅可以加深对甲状腺激素代谢的理解,还有望为个体化治疗和疾病预防提供新的研究方向,对促进临床医学的发展和提高患者生活质量具有积极影响。D2在甲状腺激素代谢调节及其甲状腺疾病中的作用机制仍缺乏深入了解,对脱碘酶多态性在临床实践中的重要性仍不确定,有待进一步研究探讨。
作者贡献声明
彭友、许丹晴负责论文选题,整体框架设计;许丹晴、张淼负责论文资料收集;许丹晴负责论文撰写;周力、丁金旺、许丹晴负责论文修订。
利益冲突
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