Resistance to thyroid hormone (RTH) and PPARa activation

In this study we used the d337T TRb transgenic mouse that has been created to reproduce the human genetic disease known as resistance to thyroid hormone (RTH) as a model to determine if the d337T TRb mutation would have an effect on PPARa activation. A single amino acid deletion (d337T) abrogates thyroid hormone (T3) binding and transforms the thyroid hormone receptor (TRb) into a constitutive repressor. The principle goal was to determine if T3 regulates myocardial energy metabolism through its nuclear receptors. We introduced a known PPARa activator (WY14, 643) into control and d337T TRb transgenic mice then examined cardiac gene expression using Affymetrix 430_2 expression arrays and RT-PCR. We compared the gene expression of PPARa, RXRb and TRa,b and three PPARa target genes among four studies groups [control, control with WY14, 643, d337T TRb, and d337T TRb with WY14, 643] consisting of seven mice per group. Microarray analysis revealed that these genes responded to the WY14, 643 treatments of control and d337T TRb mice. Analysis of the array and RT-PCR data indicates that mRNA expression levels of PPARa and mRXRb decrease after a six hour drug treatment in both control and d337T TRb mice (P<0.01) as did the array mRNA expression levels for TRa & b (P<0.025). Three target genes (AMPD3, PDK4 and UCP3) of PPARa were up regulated in control and down regulated in the d337T TRb transgenic mouse, indicating a direct action on these metabolic genes when the TRb becomes a repressor. In conclusion, PPARa activation by WY14, 643 has a positive effect on control mice and a negative effect on the TRb transgenic mice which supports our hypothesis that T3 regulates myocardial energy metabolism through its nuclear receptors. Keywords: treatment and deletion effects 7 control, 7 deletion strain individuals, 7 controls with a PPARalpha activator, 7 deletion strain individuals with a PPARalpha activator

本研究采用构建用于模拟人类遗传性疾病甲状腺激素抵抗（resistance to thyroid hormone, RTH）的d337T TRb转基因小鼠作为模型，旨在探究d337T TRb突变是否会对过氧化物酶体增殖物激活受体α（PPARα）的活化产生影响。单氨基酸缺失（d337T）可消除甲状腺激素（T3）结合能力，并将甲状腺激素受体β（TRb）转变为组成型阻遏蛋白。本研究的核心目标在于明确T3是否通过其核受体调控心肌能量代谢。我们向野生型对照组与d337T TRb转基因小鼠体内注入已知的PPARα激动剂WY14,643，随后通过Affymetrix 430_2表达芯片与逆转录聚合酶链反应（RT-PCR）检测心肌基因表达水平。我们在四组实验小鼠（每组7只：野生型对照组、给予WY14,643的野生型对照组、d337T TRb转基因模型组、给予WY14,643的d337T TRb转基因模型组）中比较了PPARα、维甲酸X受体β（RXRβ）、甲状腺激素受体α、β以及三种PPARα靶基因的表达情况。芯片分析结果显示，上述基因在野生型对照组与d337T TRb转基因模型小鼠中均对WY14,643给药产生了应答。对芯片与RT-PCR数据的分析表明，给药6小时后，野生型对照组与d337T TRb转基因模型小鼠体内PPARα与RXRβ的mRNA表达水平均显著下调（P<0.01），甲状腺激素受体α、β的mRNA表达水平亦出现下调（P<0.025）。三种PPARα靶基因——AMP脱氨酶3（AMPD3）、丙酮酸脱氢酶激酶4（PDK4）和解偶联蛋白3（UCP3）——在野生型对照组中表达上调，而在d337T TRb转基因模型小鼠中表达下调，这表明当TRb转变为阻遏蛋白时，其对这些代谢基因存在直接调控作用。综上，WY14,643介导的PPARα活化对野生型小鼠具有正向调控作用，而对d337T TRb转基因小鼠则产生负向调控效果，这一结果验证了我们的假说：T3通过其核受体调控心肌能量代谢。关键词：给药与缺失效应、7只对照组小鼠、7只基因缺失型个体、7只给予PPARα激动剂的对照组小鼠、7只给予PPARα激动剂的基因缺失型个体