How early life experience alters microglia function in shaping hypothalamic circuits.

亲子关系对大脑发育至关重要，并具有持续到成年的长期发育影响。啮齿动物研究表明，在生命的头几周，母婴互动的增加会导致神经元形态的持久变化，影响神经网络活动以及情绪和认知行为。此外，母婴护理如何影响出生后关键时期的神经回路尚不完全清楚。在这一关键时期，小胶质细胞已成为塑造神经网络的关键角色。小胶质细胞是专门驻留在大脑中的免疫细胞，负责保护大脑的健康。根据环境刺激，小胶质细胞可以产生炎性细胞因子来对抗感染或产生抗炎细胞因子，并积极地移除受损组织以促进修复。来自几个实验室的新数据表明，小胶质细胞不仅调节神经元的健康，而且在维持突触--神经元之间的动态连接--方面也很重要。有证据表明，神经活动时分泌的神经元细胞因子可能会在小胶质细胞中启动一系列信号级联反应，从而调节小胶质细胞的分化和功能：剥离或维持突触。小胶质细胞与神经元相互作用的分子机制仍然不清楚。早期的生活经历对小胶质细胞重塑神经元突触的功能有什么影响也尚不清楚。我们正在进行的由NSERC支持的发现基金已经证明，加强产后护理(EPC)可以减少焦虑，并提高成年后对社会失败的适应能力。EPC诱导抗炎基因表达，降低下丘脑炎症细胞因子的产生。有趣的是，突变的小胶质细胞不能分化为抗炎程序的小鼠，对EPC的抗焦虑作用没有反应。这表明，EPC通过小胶质细胞来塑造与焦虑有关的神经回路。因此，这种遗传的小鼠模型为揭示EPC塑造焦虑神经回路的分子机制提供了一个独特的工具。我们发现，EPC影响小胶质细胞的功能，特别是在下丘脑。通过无偏RNAseq分析，我们发现4个细胞外/分泌的神经元蛋白(PTGDS、Prg4、Itih2、Bpifa1)与EPC的降低焦虑作用有关。蛋白多糖4(Prg4)和细胞外基质蛋白酶抑制剂Itih2是细胞外基质的一部分，而PTGDS和Bpifa1是分泌因子。在这份更新提案中详细描述的未来5年的目标是阐明这4个新的细胞和分子候选如何影响下丘脑功能，以调节EPC的小胶质细胞依赖的抗焦虑效应。影响与意义：了解早期生命经历如何塑造哺乳动物的神经回路并影响对应激源的反应，可能会为改善人类新生儿育儿和畜牧业提供有价值的见解。

Parent-child relationships are critical for brain development and have long-term developmental effects that persist into adulthood. Rodent studies showed that increased maternal-infant interactions during the first few weeks of life produce enduring changes in neuronal morphology that affect neural network activity and emotional and cognitive behaviors. How maternal care influences neural circuits during the critical postnatal period is not fully understood. Microglia have emerged as key players shaping neural networks during this critical period. Microglia are specialized brain-resident immune cells that guard the health of the brain. Depending on environmental stimuli, microglia can produce inflammatory cytokines to fight infection or produce anti-inflammatory cytokines and are active in removing injured damaged tissue to promote repair. New data from several laboratories show that microglia not only regulate the health of neurons but also are important in maintaining the synapses, the dynamic connections between neurons. Evidence suggests that neuronal cytokines secreted upon neural activity may initiate a cascade of signaling in microglia and thereby modulate microglial differentiation and function: to strip away or to maintain the synapses. The molecular mechanisms whereby microglia cross-talk with neurons remain elusive. It is also not known what impact early life experience has on the function of microglia to remodel neuronal synapses. Our ongoing NSERC-supported Discovery grant has demonstrated that enhanced postnatal care (EPC) reduces anxiety and increases resilience to social defeat in adulthood. EPC induces anti-inflammatory gene expression and lowers inflammatory cytokine production at the hypothalamus. Intriguingly, mice with mutant microglia unable to differentiate to an anti-inflammatory program fail to respond to the anxiolytic effect of EPC. This indicates that EPC works through microglia to shape neural circuits involved in anxiety. Hence, this genetic mouse model offered a unique tool to unveil the molecular mechanisms whereby EPC shapes the neural circuits of anxiety. We found that EPC affects microglia function specifically in the hypothalamus. By unbiased RNAseq profiling, we found 4 extracellular/secreted neuronal proteins (Ptgds, Prg4, Itih2, Bpifa1) implicated in the anxiety-reducing effect of EPC. Proteoglycan 4 (Prg4) and the extracellular matrix protease inhibitor Itih2 are part of the extracellular matrix, whereas Ptgds and Bpifa1 are secreted factors. The goal for the next 5 years, detailed in this renewal proposal, is to elucidate how these 4 novel cellular and molecular candidates affect hypothalamic function to modulate the microglia-dependent anxiolytic effect of EPC. Impact & Significance: Understanding how early life experience molds mammalian neural circuits and influences the response to stressors may provide valuable insight to improve human neonatal childcare and animal husbandry.