Moeller Lars C, Alonso Manuela, Liao Xiaohui, Broach Vance, Dumitrescu Alexandra, Van Sande Jacqueline, Montanelli Lucia, Skjei Stephen, Goodwin Charles, Grasberger Helmut, Refetoff Samuel, Weiss Roy E
Department of Medicine, The University of Chicago, Chicago, IL 60637, USA.
Endocrinology. 2007 Oct;148(10):4727-33. doi: 10.1210/en.2007-0236. Epub 2007 Jul 19.
The genetic basis for differences in TSH sensitivity between two rat strains was examined using consomic rats generated from original strains salt-sensitive Dahl (SS) (TSH 1.8 +/- 0.1 ng/ml; free T(4) index 4.9 +/- 0.4) and Brown Norwegian (BN) (TSH 5.5 +/- 0.6 ng/ml, P < 0.05; free T(4) index 4.3 +/- 0.1, P not significant). Consomic rats SSBN6 [BN chromosome (CH) 6 placed in SS rat] and SSBN2 (BN CH 2 placed in SS rat) have TSH concentrations intermediate between pure SS and BN strains (2.9 +/- 0.3 and 3.1 +/- 0.3 ng/ml, respectively; P < 0.05). Candidate genes on rat CH 2 included TSH beta-subunit and on CH 6 the TSH receptor (TSHR). TSH from sera of BN, SS, SSBN6, and SSBN2 strains had similar in vitro bioactivity suggesting that the cause for the variable TSH concentrations was not due to an altered TSH. Physiological response to TSH was measured by changes in serum T(4) concentrations upon administration of bovine TSH (bTSH). Rat strain SS had a greater T(4) response to bTSH than BN (change in T(4), 1.3 +/- 0.1 vs. 0.4 +/- 0.1 microg/dl, P < 0.005), suggesting reduced thyrocyte sensitivity to TSH in BN. Sequencing of the TSHR coding region revealed an amino acid difference in BN (Q46R). This substitution is unlikely to contribute to the strain difference in serum TSH because both TSHR variants were equally expressed at the cell surface of transfected cells and responsive to bTSH. Given similar TSH activity and similar TSHR structure, TSHR mRNA expression in thyroid tissue was quantitated by real-time PCR. BN had 54 +/- 5% the total TSHR expression compared to SS (100 +/- 7%, P < 0.0001), when corrected for GAPDH expression, a difference confirmed at the protein level. Therefore, the higher TSH level in the BN strain appears to reflect an adjustment of the feedback loop to reduced thyrocyte sensitivity to TSH secondary to reduced TSHR expression. These strains of rat provide a model to study the cis- and trans-acting factors underlying the difference in TSHR expression.
利用从原始品系盐敏感型 Dahl（SS）（促甲状腺激素（TSH）1.8±0.1 ng/ml；游离 T4 指数 4.9±0.4）和挪威棕鼠（BN）（TSH 5.5±0.6 ng/ml，P<0.05；游离 T4 指数 4.3±0.1，P 无显著性差异）培育出的染色体代换系大鼠，研究了两种大鼠品系之间 TSH 敏感性差异的遗传基础。染色体代换系大鼠 SSBN6[将 BN 染色体（CH）6 置于 SS 大鼠中]和 SSBN2（将 BN CH2 置于 SS 大鼠中）的 TSH 浓度介于纯 SS 和 BN 品系之间（分别为 2.9±0.3 和 3.1±0.3 ng/ml；P<0.05）。大鼠 CH2 上的候选基因包括 TSHβ亚基，CH6 上的候选基因是 TSH 受体（TSHR）。BN、SS、SSBN6 和 SSBN2 品系血清中的 TSH 在体外具有相似的生物活性，这表明 TSH 浓度变化的原因并非 TSH 改变所致。通过给予牛 TSH（bTSH）后血清 T4 浓度的变化来测量对 TSH 的生理反应。大鼠品系 SS 对 bTSH 的 T4 反应比 BN 更大（T4 变化，1.3±0.1 对 0.4±0.1 μg/dl，P<0.005），这表明 BN 中甲状腺细胞对 TSH 的敏感性降低。TSHR 编码区测序显示 BN 存在一个氨基酸差异（Q46R）。这种替代不太可能导致血清 TSH 的品系差异，因为两种 TSHR 变体在转染细胞的细胞表面均等量表达且对 bTSH 有反应。鉴于 TSH 活性相似且 TSHR 结构相似，通过实时 PCR 对甲状腺组织中 TSHR mRNA 表达进行定量。与 SS（100±7%，P<0.0001）相比，校正 GAPDH 表达后，BN 的 TSHR 总表达量为 54±5%，这一差异在蛋白质水平得到证实。因此，BN 品系中较高的 TSH 水平似乎反映了反馈环对甲状腺细胞对 TSH 敏感性降低的一种调整，这种降低继发于 TSHR 表达减少。这些大鼠品系为研究 TSHR 表达差异背后的顺式和反式作用因子提供了一个模型。
