自閉症（Autism spectrum disorders; ASD）是一種早期腦神經發育障礙。其特徵是社交障礙，重複性和缺乏興趣的行為樣態。目前已知自閉症的發生並非由單一種因子異常所導致的，許多因素都被報導與自閉症的發生具有相關性，例如：遺傳易感性，環境因素（例如病毒或細菌感染、藥物使用等）。然而這樣的多因子促成自閉症的假說仍未被清楚說明。根據臨床流行病學得研究指出，ASD患者的人類T細胞淋巴瘤侵襲和轉移2 (T-cell lymphoma invasion and metastasis 2；TIAM2) 基因組及其轉錄表現量相較於正常人都有顯著的變異。我們先前的發表指出，只有TIAM2S (short form)蛋白表現於人類腦部組織，參與大腦可塑性之調節，並且TIAM2S基因減弱(TIAM2S-knockdown)下，所影響之基因與神經行為發育障礙疾病(例如：自閉症)具有相關性。因此，我們假設TIAM2S參與了ASD的發病機理。在這個研究中，我們使用人類TIAM2S的基因轉殖公鼠(male TIAM2S-TG mice)與野生型母鼠(female WT mice)進行交配，預估其子代會有各半基因轉殖鼠與野生型鼠的機率。並通過使此懷孕母體內暴露於丙戊酸(Valproic acid; VPA)的處理（maternal VPA treatment），來觀察其產下之不同基因型之幼鼠是否具有社交行為異常，作為探討TIAM2S是否參與ASD形成的動物模型。結果顯示maternal VPA treatment不僅降低同窩仔的數量，還增加了其同窩仔的斷奶前致死率和先天性白內障。有趣的是存活下來的幼鼠中有著較少的母鼠與TIAM2S的基因轉殖鼠，顯示性別和TIAM2S基因型在VPA的致畸作用扮演角色。在進一步的行為實驗中亦證實，在maternal VPA treatment處理下，雌性的TIAM2S基因轉殖鼠表現出運動協調能力障礙與社交障礙。此外，分子機制研究顯示在maternal VPA treatment處理下，雌性的TIAM2S基因轉殖鼠腦中前扣帶迴(anterior cingulate area; ACA)和主要體感覺皮質區 (primary somatosensory area; SSp)的氧化壓力增加並伴隨著成熟神經元的下降。因此，我們認為氧化壓力是導致自閉症相關行為發生的重要因素之一，而使用過氧化氫酶來抑制氧化壓力則有效的反轉雌性TIAM2S基因轉殖鼠的運動協調能力障礙與社交行為異常以及腦中增加的氧化壓力且伴隨減少的成熟神經元。綜合上述，我們的研究首次證實當帶有人類TIAM2S基因的雌性且在丙戊酸處理之下，腦中氧化壓力會增加並進一步導致自閉症的發生。

Short form of human T-cell lymphoma invasion and metastasis 2 (TIAM2S) protein is abundant in both the fetal and adult brain as a novel regulator for neuroplasticity. Consistent with clinical epidemiology reports, our whole-transcriptome and enrichment analysis with total RNA sequencing reveals that TIAM2S is strongly associated with the cellular processes of the structural development of the brain and the disease markers representing neurodevelopmental disorders such as autism spectrum disorder (ASD). Characteristics of ASD include qualitative impairment in communication, aberrant social interaction, and restrictive patterns of behaviors. Thus, we hypothesized that TIAM2S participates in the ASD pathogenesis. By exposing pregnant mice (E9.5) to maternal valproic acid (VPA) that carried the fetus with 50% WT (wild type) and 50% TIAM2S-TG genotypes as an ASD animal model, we determined that the functional roles of TIAM2S for ASD development and its mechanism. Our data showed that maternal VPA exposure significantly not only reduced the number of the newborn pups, but also increased pre-weaning lethality. In comparison with a saline-treated group, maternal VPA exposure decreased the number of female and TIAM2S-TG genotype littermates and there was a higher incidence of congenital cataracts at a young age. Our data implied that female gender and human TIAM2S gene both are critical factors to force teratogenic action of VPA. Furthermore, animal behavioral tests (locomotor, social‐interaction, or anxiety‐related behaviors) were conducted to evaluate if the maternal VPA-treated TIAM2S-TG littermates would develop ASD-like behaviors. Interestingly, our results revealed that only the female mice with the TIAM2S-TG genotype under maternal VPA exposure displayed motor coordination difficulties and impairment of social interaction. A mechanism study revealed a decrease in mature neuron marker NeuN with higher oxidative stress in the anterior cingulate area (ACA) and primary somatosensory area (SSp) of the maternal VPA-treated female TIAM2S-TG mice. In addition, pre-treatment with PEG-catalase, a chemical inhibitor of oxidative stress, a day before maternal VPA exposure was performed to determine if increased oxidative stress would play a role in development of the ASD-like behaviors. Our data reveled that inhibition of oxidative stress using PEG catalase reverse the maternal VPA-induced social interaction deficit in the female TIAM2S-TG mice. Together, our results illustrate a novel multiple-hit theory related to maternal VPA exposure suggesting that the human TIAM2S gene and female gender are related to impairment of normal brain development due to increased oxidative stress and maybe involved in ASD pathogenesis.

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