Role of microglial IRF8 in the developmental consequences of early adversity

项目摘要 在生命早期暴露于不可预测和复杂的压力会增加患焦虑症的风险 以及杏仁核、前额叶皮质（PFC）和海马体（HPC）之间的异常连接。 早期生活压力（ELS）如何改变额边缘连接以及这些变化如何有助于 增加的焦虑是很难在人类身上研究的问题。具体来说， ELS与性相互作用以改变额叶边缘系统连接，目前人类无法解决焦虑问题 问题研究为了澄清这些问题，我们开发了一种ELS小鼠模型，我们命名为Unpredictable 出生后应激（UPS），其中小鼠在生命早期暴露于不可预测和复杂的压力。我们发现 UPS引起了小鼠焦虑的强烈增加，而在暴露于简单和可预测的形式的小鼠中没有观察到这种情况。 ELS，称为有限寝具（LB）。此外，我们发现UPS和LB优先增加焦虑 在雄性小鼠中。使用静息态fMRI（rsfMRI）、高分辨率弥散MRI（dMRI）和逆行追踪 我们发现雄性UPS小鼠在幼年期和成年期的连接性增加， 与焦虑高度相关。dMRI的初步数据表明，额叶边缘系统的连通性不是 在女性中改变，这些性别特异性效应与异常突触修剪有关， 转录因子IRF8在雄性小胶质细胞中的水平降低，但在雌性小胶质细胞中没有。我们假设 杏仁核与前额叶皮层和前额叶皮层的连接在大脑皮层的活动过程中经历了小胶质细胞介导的修剪。 产后时期这一过程需要出生后小胶质细胞中高水平的转录因子IRF8， 对青少年时期和成年期的焦虑水平至关重要。UPS减少了 IRF8在雄性小鼠中，但不是雌性小鼠。这反过来又导致UPS中额边缘连接和焦虑的增加 男性，但不是UPS女性。目标1中的工作将使用rsfMRI、dMRI和双逆行追踪来表征 UPS，性别和年龄对额边缘连接的影响。目标2中的研究将测试是否减少IRF8 在出生后的小胶质细胞中足以复制UPS对焦虑，额边缘连接， 小胶质细胞基因表达和吞噬活性。在目的3中，我们询问是否在出生后的小鼠中过表达IRF8， 小胶质细胞可以使UPS小鼠的焦虑和额边缘连接正常化。成功完成本 应用程序将定义小胶质细胞IRF8在改善额边缘连接和编程中的新作用 这是一个重要的发现，因为IRF8在引导免疫反应中起着保守的作用。 人类和小鼠的反应。此外，这项工作将提供一个新的范式来解释如何ELS 差异影响小鼠的小胶质细胞功能、杏仁核连接和焦虑。

Project Abstract Exposure to unpredictable and complex stress early in life increases the risk for developing anxiety disorder and abnormal connectivity between the amygdala, the prefrontal cortex (PFC), and the hippocampus (HPC). Exactly how early life stress (ELS) modifies fronto-limbic connectivity and how these changes contribute to increased anxiety are questions that are difficult to investigate in humans. Specifically, the question of how ELS interacts with sex to alter fronto-limbic connections and anxiety are not addressable with current human studies. To clarify these issues we developed a mouse model of ELS that we have named Unpredictable Postnatal Stress (UPS), in which mice are exposed to unpredictable and complex stress early in life. We found that UPS caused robust increase in anxiety that was not seen in mice exposed to simple and predictable form of ELS, known as limited bedding (LB). Moreover, we found that UPS and LB preferentially increased anxiety in male mice. Using resting state fMRI (rsfMRI), high resolution diffusion MRI (dMRI), and retrograde tracing we found increased connectivity in male UPS mice that was present during the juvenile period and adulthood and was highly correlated with anxiety. Preliminary data with dMRI indicate that fronto-limbic connectivity is not altered in females and that these sex specific effects are associated with abnormal synaptic pruning and reduced levels of the transcription factor IRF8 in male microglial, but not female microglia. We hypothesize that amygdala connectivity with the PFC and the HPC undergoes microglial-mediated pruning during the postnatal period. This process requires high levels of the transcription factor IRF8 in postnatal microglia and is critical for programming levels of anxiety during the juvenile period and adulthood. UPS reduces expression of IRF8 in males, but not female mice. This in turn leads to increase fronto-limbic connectivity and anxiety in UPS males, but not UPS females. Work in aim 1 will use rsfMRI, dMRI, and dual retrograde tracing to characterize the effects of UPS, sex and age on fronto-limbic connectivity. Studies in aim 2 will test whether reducing IRF8 in postnatal microglia is sufficient to phenocopy the effects of UPS on anxiety, fronto-limbic connectivity, microglial gene expression, and phagocytic activity. In aim 3 we ask whether overexpressing IRF8 in postnatal microglia can normalize anxiety and fronto-limbic connectivity in UPS mice. Successful completion of this application will define a novel role for microglial IRF8 in refining fronto-limbic connections and programming anxiety in the mouse; an important finding given the conserved role that IRF8 plays in guiding immune responses in humans and mice. In addition, this work will provide a new paradigm to explain how ELS differentially affects microglial function, amygdala connectivity, and anxiety in mice.