Mouse model of weak depression exhibiting suppressed cAMP signaling in amygdala, lower lipid catabolism in liver and correlated gut microbiota

To establish a mouse model of weak depression, we raised six-week-old C57BL/6N mice in single (SH) or group housing (GH) conditions for two weeks. The SH group showed less social interaction with stranger mice, learning disability in behavioral tests, and lower plasma corticosterone level. The cecal microbiota of the SH group showed significant segregation from the GH group in principal coordinate analysis. Transcriptome analysis of the amygdala, and liver detected multiple differentially expressed genes (DEGs). In the amygdala of SH mice, suppression of the cyclic adenine monophosphate (cAMP) signal was predicted and confirmed by the reduced immunoreactivity of phosphorylated cAMP-responsive element binding protein. In the liver of SH mice, down-regulation of beta-oxidation was predicted. Interestingly, the expression levels of over 100 DEGs showed significant correlation with the occupancy of two bacterial genera, Lactobacillus (Lactobacillaceae) and Anaerostipes (Lachnospiraceae). These bacteria-correlated DEGs included JunB, the downstream component of cAMP signaling in the amygdala, and carnitine palmitoyltransferase 1A, a key enzyme of beta-oxidation in the liver. This trans-omical analysis also suggested that NAD synthesis in the liver may be linked to the occupancy of Lactobacillus through the regulation of nicotinamide phosphoribosyltransferase and kynureninase genes. Our results suggested that SH condition along with the presence of correlated bacteria species causes weak depression phenotype in young mice and provide suitable model to study food ingredient that is able to cure weak depression. Transcriptome analysis of amygdala, hypothalamus, and liver. MIcrobiome analysis of cecal content. Correlational analysis between transcriptome and micorbiome.为构建轻度抑郁小鼠模型，我们将6周龄的C57BL/6N小鼠分别置于单笼饲养（single housing, SH）与群养（group housing, GH）环境中饲养两周。单笼饲养组小鼠表现出对陌生小鼠的社交互动减少、行为学测试中出现学习障碍，且血浆皮质酮水平更低。通过主坐标分析可见，单笼饲养组小鼠的盲肠微生物群与群养组存在显著分离。对杏仁核与肝脏进行转录组分析，共检测到多个差异表达基因（differentially expressed genes, DEGs）。在单笼饲养小鼠的杏仁核中，环磷酸腺苷（cyclic adenine monophosphate, cAMP）信号通路被抑制的预测结果，已通过磷酸化cAMP反应元件结合蛋白的免疫反应性降低得到验证。在单笼饲养小鼠的肝脏中，β-氧化过程下调的现象得到了预测。值得注意的是，超过100个差异表达基因的表达水平，与两个菌属——乳杆菌属（*Lactobacillus*，乳杆菌科Lactobacillaceae）、厌氧杆菌属（*Anaerostipes*，毛螺菌科Lachnospiraceae）——的定植丰度存在显著相关性。这些与菌群相关的差异表达基因包括杏仁核cAMP信号通路下游组分JunB，以及肝脏β-氧化过程的关键酶肉碱棕榈酰转移酶1A（carnitine palmitoyltransferase 1A）。本次跨组学分析还显示，肝脏中烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide, NAD）的合成，可能通过调控烟酰胺磷酸核糖转移酶与犬尿氨酸酶基因，与乳杆菌属的定植丰度产生关联。本研究结果表明，单笼饲养环境与相关菌群的共同作用，可诱导幼年小鼠产生轻度抑郁表型，同时为筛选可改善轻度抑郁的食品成分提供了合适的动物模型。本研究的分析内容包括：杏仁核、下丘脑与肝脏的转录组分析；盲肠内容物的微生物组分析；以及转录组与微生物组的关联分析。