Disc1異型合子基因小鼠睡眠剝奪72 小時後之反應

Abstract

思覺失調症是一種嚴重的精神疾病，好發於青少年晚期到成年早期。人口盛行率大約是百分之一。Disc1基因缺損被認為是其中一個相關因子，我們已經建立了Disc1基因缺損的小鼠模型，包含同型及異型合子基因突變鼠。兩者並沒有表現出嚴重的行為異常，我們認為或許還需要加上其他因子的共同作用。 據報導精神障礙患者常有睡眠問題，造成的睡眠不足可能加劇精神疾病之症狀，表明睡眠不足和精神疾病之間存在相互作用。相較正常小鼠，Disc1異型合子突變鼠表現不同的睡眠活動，指出Disc1參與睡眠之恆定調節。 在先前的研究中，我們使用C57BL/6成年公小鼠觀察海馬迴的神經新生情形以及微膠細胞的反應狀態。在72小時水平台睡眠剝奪操弄後，神經新生的數量都顯著性下降，微膠細胞的密度與形態都有趨向激活的改變。本研究中，我們用同樣的操弄觀察Disc1異型合子突變鼠，其海馬迴的神經新生情形以及微膠細胞的反應狀態，藉以探討Disc1基因缺損與睡眠剝奪的交互作用。 我們發現野生型的小鼠以及Disc1異型合子突變鼠，在經過睡眠剝奪之後，與控制組及大平台控制組相比，其神經新生的數量皆有顯著性下降。值得被注意的是，Disc1基因缺損與睡眠剝奪的交互作用下，Disc1異型合子突變鼠神經新生數量更有顯著下降。而微膠細胞為中樞神經系統中之巨噬細胞，參與細胞新生之過程。Disc1異型合子突變鼠中經睡眠剝奪後，微膠細胞的密度與形態都有趨向激活的改變，特別是在神經新生的齒迴內側區。在野生型小鼠中，微膠細胞的密度與形態不受睡眠剝奪的影響。我們又測量了發炎相關的細胞激素(含TNF-α、IL-1β與IL-6)，結果發現Disc1異型合子突變鼠海馬迴中，IL-1β在睡眠剝奪後表現提高，而IL-6只有在Disc1異型合子突變鼠提升，顯示Disc1異型合子突變鼠比起野生型小鼠有更嚴重的發炎反應。但另一方面，在海馬迴中，腦衍生神經滋長因子的上升不如野生型小鼠明顯。 在我們的結果顯示，睡眠剝奪與Disc1基因缺損確實有交互作用，兩者加成之下，海馬迴的微膠細胞呈現神經發炎的徵象，對於精神疾病之發病扮演重要角色。

Schizophrenia is a severe mental disorder that occurs in the early stage of life and affects approximately 1% of the population. One susceptibility gene related to neurodevelopmental mental diseases is Disrupted-in-Schizophrenia 1 (DISC1). We have generated a Disc1 mutant mouse line. Both homozygous (Homo) and heterozygous (Het) knockout mice exhibit subtle behavioral difference compared with wildtype controls. We therefore considered these mutant mice are in a prodromal stage. The full-blown psychiatric symptoms might be expressed subsequent to certain challenges. Sleep problems are commonly reported by patients with psychiatric disorders while insufficient sleep may deteriorate the symptoms of mental diseases, suggesting a mutual contribution between insufficient sleep and mental illness. Animals with Disc1 mutation exhibit altered sleep-activity pattern, indicating a role of Disc1 in sleep homeostasis. We therefore adopted the multiple platform-over-water paradigm of sleep deprivation (SD) as an environmental challenge and examined the interplay between Disc1 mutation and sleep insufficiency. In particular, the degree of adult neurogenesis in the dentate gyrus (DG) and the responses of microglia proximal to this neurogenic niche after 72 hour SD were examined. On previous study, the significant decreased of adult neurogenesis in the DG and the responses of microglia proximal to this neurogenic niche were presented in C57BL/6 adult male mice after 72 hour SD. In the present work, the density of Ki67-positive cells were significantly decreased in SD groups of WT and Disc1 Het mice compared with home cage (HC) or big-platform control groups (BP), indicating the impact of 72-hour SD on the neurogenic activity. Notably, the density of Ki67-positive cells were significantly decreased in SD groups of Disc1 Het mice, which indicated the interplay between Disc1 mutation and sleep insufficiency impacted on the neurogenic activity more severely. The density and morphology of microglia, resident phagocytes in the CNS involved in the homeostasis of neurogenesis, were then examined. In Disc1 Het mice, microglial density was increased in the subgranular zone (SGZ) after SD, but not in other subregions. Besides, significant changes of microglial morphology were noticed in Het mice. Reduced numbers of bifurcation nodes, terminal ends, segments, and complexity were found in SD group of Het mice, especially in microglia collected from the hilus and SGZ. These changes would lead to reduced total process length. Together, these results indicated signs of microglial activation in after SD in Het mice particularly in the hippocampal neurogenic niche. The mRNA levels of three pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6, were measured. The level of IL-1β was increased in SD groups of both genotypes, whereas the level of IL-6 was augmented only in the SD group of Disc1 Het mice, suggesting a greater inflammatory reaction in Het mice after SD relative to that in WT mice. The mRNA and protein levels of BDNF were increased in the SD group of WT mice but not in Het mice, suggesting a fault of neuroprotective BDNF expression in Het mice after 72h SD. Our results suggested an interaction between sleep deprivation and genetic disruption of Disc1 in the reaction of microglia and neuroinflammatory status in the hippocampus which might contribute to the pathogenesis of mental disorders.