Role of microglial IRF8 in the developmental consequences of early adversity

项目摘要 在生命早期暴露在不可预测的复杂压力下会增加患焦虑症的风险 杏仁核、前额叶皮质(PFC)和海马体(HPC)之间的异常连接。 早期生活应激(ELS)究竟如何改变额叶-边缘连接，以及这些变化如何促进 焦虑的增加是很难在人类身上研究的问题。具体地说，如何 ELS与性相互作用改变额叶-边缘连接和焦虑不是现代人所能解决的 学习。为了阐明这些问题，我们开发了一个ELS的老鼠模型，我们将其命名为不可预测 出生后应激(UPS)，即小鼠在生命早期暴露于不可预测的复杂应激。我们发现 UPS导致焦虑情绪显著增加，这在暴露于简单且可预测的形式的小鼠中是看不到的 ELS，称为有限卧具(LB)。此外，我们发现UPS和LB优先增加焦虑 在雄性小鼠身上。使用静息状态功能磁共振成像(RsfMRI)、高分辨率扩散磁共振成像(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 并与焦虑高度相关。Dmri的初步数据表明，额叶-边缘连接不是 这些性别特有的影响与异常的突触修剪和 转录因子IRF8在男性小胶质细胞中的水平降低，但在女性小胶质细胞中没有。我们假设 杏仁核与PFC和HPC的连接在小胶质细胞介导的修剪过程中进行 产后期。这一过程需要出生后小胶质细胞中高水平的转录因子IRF8，并且是 对青少年时期和成年期间的焦虑程度至关重要。UPS减少了对 IRF8在雄性小鼠中存在，但在雌性小鼠中不存在。这进而导致UPS额叶至边缘的连通性增加和焦虑 男性，但不是UPS女性。AIM 1的工作将使用rsfMRI、dMRI和双重逆行追踪来表征 UPS、性别和年龄对额-边缘连接性的影响。AIM 2上的研究将测试是否减少IRF8 在出生后的小胶质细胞中，足以显示UPS对焦虑、额叶至边缘连接、 小胶质细胞基因表达和吞噬活性。在目标3中，我们询问在出生后是否过度表达IRF8 小胶质细胞可以使UPS小鼠的焦虑和额缘连接正常化。成功完成这项工作 应用程序将定义小胶质细胞IRF8在精炼额叶至边缘连接和编程中的新角色 小鼠的焦虑；一个重要的发现，因为IRF8在引导免疫方面扮演着保守的角色 在人类和小鼠身上的反应。此外，这项工作将提供一种新的范式来解释ELS是如何 不同地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.