Reelin/PI3K-AKT-mTOR信号通路在妊娠期母体低T4血症所致后代孤独症的作用机制研究

Thyoid hormones play important roles in fetus brain development. In the first 20 weeks of gestation, neuropsychologic development of the fetus is mostly dependent on thyroxine from the mother. The data from epidemiological studies showed that thyoid hormones insufficiency in the first half duration of pregnancy can not only impair neuropsychological development of the offspring irreversibly，lower the MDI and PDI level,but also increase the risk of autism in the offspring. The data from the recent study performed by our group confirmed an successful maternal hypothyroxinemia rat model induced by PTU(normal serum TSH, only low level of serum FT4). Meanwhile, the offsprings suffered from social behavioral deficits and repetitive and perseverative behavior conformed by behavior tests. In this study, we will detect the indexes of neuron migration related reelin signal pathway and dendritic growth related PI3K/AKT/mTOR signal pathway, in order to evaluate the roles of reelin and PI3K/AKT/mTOR signal pathways in the autism of the pups from dams with hypothyroxinemia. We will confirm the roles of these pathways in vitro. Levothyroxine will be given to the dams with hypothyroxinemia at different time points. Then we will get an appropriate time point to start levothyroxine treatment according to the changes of signal pathways and behavior tests. This will be helpful for doctors to select the most appropriate time point to treat maternal hypothyroxinemia during pregnancy.

甲状腺激素对于胎儿脑发育至关重要，妊娠20周前，胎儿甲状腺激素仅来源或主要来源于母体甲状腺。流行病学研究证实，妊娠前半期母体甲状腺激素缺乏不仅可以导致胎儿不可逆的脑损伤，降低儿童的智力、运动水平，同样可增加后代孤独症患病风险。本课题组已成功应用PTU建立低T4血症Wistar母鼠、孕鼠模型（血清TSH正常，仅FT4降低），并且通过行为学实验证实其后代存在社会交往障碍、重复刻板行为，成功建立妊娠期母体低T4血症所致后代孤独症动物模型。本课题拟检测可调控神经元迁移及树突生长的reelin和PI3K-AKT－mTOR信号通路的相关指标，探讨妊娠期母体低T4血症与后代孤独症发生的可能机制，并通过体外实验进行验证；同时应用左甲状腺素 (L-T4)在不同时点干预治疗低T4血症孕鼠，通过信号通路相关指标、行为学实验的变化，确定干预最佳时间，从而为临床医生选择妊娠期低T4血症的最佳干预时间提供理论依据。

甲状腺激素对于胎儿脑发育至关重要，妊娠20周前，胎儿甲状腺激素仅来源或主要来源于母体甲状腺。流行病学研究证实，妊娠前半期母体甲状腺激素缺乏不仅可以导致胎儿不可逆的脑损伤，降低儿童的智力水平、运动水平，同样可增加后代孤独症患病风险。本课题组已成功应用PTU建立低T4血症Wistar母鼠模型（血清TSH正常，仅FT4降低），并且通过行为学实验证实其后代存在社会交往障碍、重复刻板行为，成功建立妊娠期母体低T4血症所致后代孤独症动物模型。本课题检测可调控神经元迁移及树突生长的reelin和PI3K-AKT－mTOR信号通路的相关指标。低T4血症组后代出生后0天（P0）仔鼠皮层树突发育相关蛋白MAP2表达水平降低，同时可见结构异常。免疫荧光标记的mTOR、MAP2在低T4血症P0天后代仔鼠的皮层、海马表达降低，低T4血症后代仔鼠皮层细胞骨架结构异常。低T4血症P0天后代仔鼠前额叶皮层甲状腺反应基因Reelin mRNA、RC3 mRNA以及树突发育相关因子mTOR mRNA的表达水平明显降低，P0天后代仔鼠前额叶皮层Reelin、mTOR信号通路相关蛋白p-MTOR、p-S6K1、S6K1表达水平下调。上述结果提示孕早期低T4血症致后代孤独症发生可能与甲状腺激素缺乏后抑制了reelin信号通路，进一步抑制mTOR信号通路，从而影响神经元突出发育、细胞骨架形成有关。通过体外实验进行验证；同时应用左甲状腺素 (L-T4)在不同时点干预治疗低T4血症母鼠，通过信号通路相关指标、行为学实验的变化，确定干预最佳时间，从而为临床医生选择妊娠期低T4血症的最佳干预时间提供理论依据。成功建立的低T4血症母鼠、孕鼠动物模型，以及其所致的后代孤独症动物模型，目前正在申请专利，未来能够为该领域的研究做出一定贡献。