Gain of bipolar disorder-related lncRNA AP1AR-DT in mice induces depressive and anxiety-like behaviors by reducing Negr1-mediated excitatory synaptic transmission [SK-N-SH RNA-seq]

Bipolar disorder is a complex polygenetic disorder that is characterized by recurrent episodes of depression and mania, the heterogeneity of which is likely complicated by epigenetic modifications that remain to be elucidated. Here, we performed transcriptomic analysis of peripheral blood RNA from monozygotic twins discordant for bipolar disorder and identified a bipolar disorder-associated upregulated long non-coding RNA (lncRNA), AP1AR-DT. We observed that overexpression of AP1AR-DT in the mouse medial prefrontal cortex (mPFC) resulted in a reduction of both the total spine density and the spontaneous excitatory postsynaptic current (sEPSC) frequency of mPFC neurons, as well as depressive and anxiety-like behaviors. A combination of the results of brain transcriptome analysis of AP1AR-DT overexpressing mice brains with the known genes associated with bipolar disorder revealed that NEGR1, which encodes neuronal growth regulator 1, is one of the AP1AR-DT targets and is reduced in vivo upon gain of AP1AR-DT in mice. The results of the present study demonstrated that overexpression of recombinant Negr1 in the mPFC neurons of AP1AR-DTOE mice ameliorates depressive and anxiety-like behaviors and normalizes the reduced excitatory synaptic transmission induced by the gain of AP1AR-DT. Furthermore, the study provides evidence that AP1AR-DT reduces NEGR1 expression by competing for the transcriptional activator NRF1 in the overlapping binding site of the NEGR1 promoter region. The epigenetic and pathophysiological mechanism linking AP1AR-DT to the modulation of excitatory synaptic function provides etiological implications for bipolar disorder. Overall design: To investigate the function of the DE-lncRNA AP1AR-DT in bipolar disorder, AC109347.1 was overexpressed in the SK-N-SH cells.

双相情感障碍（Bipolar disorder）是一类复杂的多基因遗传病，以反复发作的抑郁与躁狂发作为核心特征，其异质性可能因尚未阐明的表观遗传修饰（epigenetic modifications）进一步复杂化。本研究针对表型不一致的同卵双生子，对其外周血RNA开展转录组分析，鉴定出一种与双相情感障碍相关的上调长链非编码RNA（long non-coding RNA，lncRNA）AP1AR-DT。
我们发现，在小鼠内侧前额叶皮层（medial prefrontal cortex，mPFC）中过表达AP1AR-DT，可导致mPFC神经元的总树突棘密度降低、自发性兴奋性突触后电流（spontaneous excitatory postsynaptic current，sEPSC）频率下降，并引发抑郁样与焦虑样行为。将AP1AR-DT过表达小鼠的脑组织转录组分析结果与已知的双相情感障碍关联基因相结合后发现，编码神经元生长调节因子1（neuronal growth regulator 1）的NEGR1是AP1AR-DT的靶基因之一，且在小鼠体内过表达AP1AR-DT后，NEGR1的表达水平会降低。
本研究结果证实，在AP1AR-DT过表达（AP1AR-DTOE）小鼠的mPFC神经元中过表达重组型NEGR1，可改善其抑郁样与焦虑样行为，并使AP1AR-DT过表达所诱导的兴奋性突触传递受损状态恢复正常。此外，本研究提供的证据表明，AP1AR-DT可通过在NEGR1启动子区域的重叠结合位点上竞争转录激活因子NRF1（transcriptional activator NRF1），从而降低NEGR1的表达。这种将AP1AR-DT与兴奋性突触功能调控相联系的表观遗传与病理生理机制，为双相情感障碍提供了病因学层面的研究启示。
实验整体设计：为探究差异表达长链非编码RNA（differentially expressed lncRNA，DE-lncRNA）AP1AR-DT在双相情感障碍中的功能，本研究在SK-N-SH细胞中过表达了AC109347.1。