先天性甲状腺功能减退症伴双等位基因甲状腺球蛋白(Tg蛋白,由TG基因编码)突变是一种内质网(ER)贮积病。许多患者(和动物模型)生长出甲状腺肿大(甲状腺肿),但有些人没有。成年后,甲状腺功能减退的TGcog/cog小鼠(携带Tg-L2263P突变)表现出较大的甲状腺肿,而带有TGrdw/rdw突变(Tg-G2298R)的成年WIC大鼠表现出甲状腺发育不良。纯合TG突变与甲状腺细胞死亡有关,以前认为Tg-G2298R蛋白的细胞毒性解释了WIC-TGrdw/rdw大鼠甲状腺肿的缺乏。然而,最近的研究表明,TGcog/cog小鼠也表现出广泛的ER应激介导的甲状腺细胞死亡,然而在持续的反馈刺激下,甲状腺细胞增殖超过其死亡。这里,为了检查Tg-G2298R蛋白的相对蛋白毒性,我们已经使用CRISPR-CRISPR相关蛋白9技术产生了纯合的TGrdw/rdw敲入小鼠,其品系背景与TGcog/cog小鼠相同。TGrdw/rdw小鼠表现出相似的Tg蛋白折叠缺陷表型,甲状腺组织学异常,甲状腺功能减退,和生长迟缓。TGrdw/rdw小鼠没有显示出比TGcog/cog小鼠更大的ER应激反应或应激介导的细胞死亡的证据,两种小鼠模型都表现出持续的甲状腺细胞增殖,具有可比的甲状腺肿生长。相比之下,在WIC-TGrdw/rdw大鼠中,作为衰老的函数,甲状腺细胞增殖率急剧下降。我们得出的结论是,突变体Tg-G2298R蛋白本质上并不比Tg-L2263P更具蛋白毒性;相反,细胞增殖维持的衰老依赖性差异是限制因素,这说明成年WIC-TGrdw/rdw大鼠没有甲状腺肿。
Congenital hypothyroidism with biallelic thyroglobulin (Tg protein, encoded by the TG gene) mutation is an endoplasmic reticulum (ER) storage disease. Many patients (and animal models) grow an enlarged thyroid (goiter), yet some do not. In adulthood, hypothyroid TGcog/cog mice (bearing a Tg-L2263P mutation) exhibit a large goiter, whereas adult WIC rats bearing the TGrdw/rdw mutation (Tg-G2298R) exhibit a hypoplastic thyroid. Homozygous TG mutation has been linked to thyroid cell death, and cytotoxicity of the Tg-G2298R protein was previously thought to explain the lack of goiter in WIC-TGrdw/rdw rats. However, recent studies revealed that TGcog/cog mice also exhibit widespread ER stress-mediated thyrocyte death, yet under continuous feedback stimulation, thyroid cells proliferate in excess of their demise. Here, to examine the relative proteotoxicity of the Tg-G2298R protein, we have used CRISPR-CRISPR-associated protein 9 technology to generate homozygous TGrdw/rdw knock-in mice in a strain background identical to that of TGcog/cog mice. TGrdw/rdw mice exhibit similar phenotypes of defective Tg protein folding, thyroid histological abnormalities, hypothyroidism, and growth retardation. TGrdw/rdw mice do not show evidence of greater ER stress response or stress-mediated cell death than TGcog/cog mice, and both mouse models exhibit sustained thyrocyte proliferation, with comparable goiter growth. In contrast, in WIC-TGrdw/rdw rats, as a function of aging, the thyrocyte proliferation rate declines precipitously. We conclude that the mutant Tg-G2298R protein is not intrinsically more proteotoxic than Tg-L2263P; rather, aging-dependent difference in maintenance of cell proliferation is the limiting factor, which accounts for the absence of goiter in adult WIC-TGrdw/rdw rats.