Reduced expression of glutamate decarboxylase 67 (GAD67), encoded by the Gad1 gene, is a consistent finding in postmortem brains of patients with several psychiatric disorders, including schizophrenia, bipolar disorder and major depressive disorder. The dysfunction of GAD67 in the brain is implicated in the pathophysiology of these psychiatric disorders; however, the neurobiological consequences of GAD67 dysfunction in mature brains are not fully understood because the homozygous Gad1 knockout is lethal in newborn mice. We hypothesized that the tetracycline-controlled gene expression/suppression system could be applied to develop global GAD67 knockdown mice that would survive into adulthood. In addition, GAD67 knockdown mice would provide new insights into the neurobiological impact of GAD67 dysfunction. Here, we developed Gad1tTA/STOP−tetO biallelic knock-in mice using Gad1STOP−tetO and Gad1tTA knock-in mice, and compared them with Gad1+/+ mice. The expression level of GAD67 protein in brains of Gad1tTA/STOP−tetO mice treated with doxycycline (Dox) was decreased by approximately 90%. The GABA content was also decreased in the brains of Dox-treated Gad1tTA/STOP−tetO mice. In the open-field test, Dox-treated Gad1tTA/STOP−tetO mice exhibited hyper-locomotor activity and decreased duration spent in the center region. In addition, acoustic startle responses were impaired in Dox-treated Gad1tTA/STOP−tetO mice. These results suggest that global reduction in GAD67 elicits emotional abnormalities in mice. These GAD67 knockdown mice will be useful for elucidating the neurobiological mechanisms of emotional abnormalities, such as anxiety symptoms associated with psychiatric disorders.

中文翻译：

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谷氨酸脱羧酶 67 的整体敲低引起小鼠情绪异常

由 Gad1 基因编码的谷氨酸脱羧酶 67 (GAD67) 表达降低，这是在患有多种精神疾病（包括精神分裂症、双相情感障碍和重度抑郁症）的患者死后大脑中的一致发现。大脑中 GAD67 的功能障碍与这些精神疾病的病理生理学有关；然而，成熟大脑中 GAD67 功能障碍的神经生物学后果尚不完全清楚，因为纯合子 Gad1 敲除在新生小鼠中是致命的。我们假设四环素控制的基因表达/抑制系统可用于开发可存活到成年的全球 GAD67 敲低小鼠。此外，GAD67 敲低小鼠将为 GAD67 功能障碍的神经生物学影响提供新的见解。这里，我们使用 Gad1STOP-tetO 和 Gad1tTA 敲入小鼠开发了 Gad1tTA/STOP-tetO 双等位基因敲入小鼠，并将它们与 Gad1+/+ 小鼠进行了比较。用强力霉素 (Dox) 治疗的 Gad1tTA/STOP-tetO 小鼠脑中 GAD67 蛋白的表达水平降低了约 90%。Dox 处理的 Gad1tTA/STOP-tetO 小鼠大脑中的 GABA 含量也降低。在旷场测试中，Dox 处理的 Gad1tTA/STOP-tetO 小鼠表现出超运动活动并减少在中心区域的持续时间。此外，在 Dox 处理的 Gad1tTA/STOP-tetO 小鼠中，听觉惊吓反应受损。这些结果表明 GAD67 的整体减少会引起小鼠的情绪异常。这些 GAD67 敲低小鼠将有助于阐明情绪异常的神经生物学机制，