Wang Junwen, Duan Guangbing, Zhan Tingting, Dong Zhiyu, Zhang Yan, Chen Ying, Sun Huihui, Xu Shuchang
Department of Gastroenterology, Tongji Institute of Digestive Diseases, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China.
Front Mol Neurosci. 2022 Jul 28;15:908911. doi: 10.3389/fnmol.2022.908911. eCollection 2022.
Early adverse life events (EALs), such as maternal separation (MS), can cause visceral hypersensitivity, which is thought to be a key pathophysiological mechanism of irritable bowel syndrome (IBS). Previous studies mainly focused on EALs-induced visceral hypersensitivity in adulthood but did not consider that it may have occurred in the preadult period. We previously found that rats who experienced MS suffered from visceral hypersensitivity starting from the post-weaning period. Moreover, the hippocampus is considered to be critical in regulating the formation of visceral hypersensitivity induced by MS. But the underlying mechanisms throughout different life periods are unclear. In this study, behavioral tests, RNA-seq, lentiviral interference, and molecular biology techniques were applied to investigate the molecular mechanism in the hippocampus underlying MS-induced long-lasting visceral hypersensitivity. It was found that both visceral sensitivity and anxiety-like behaviors were significantly increased in MS rats in post-weaning, prepubertal, and adult periods, especially in the prepubertal period. Subsequently, RNA-seq targeting the hippocampus identified that the expression level of Netrin-1 was significantly increased in all periods, which was further confirmed by quantitative real-time PCR and Western blot. Knocking-down hippocampal Netrin-1 in the post-weaning period by lentivirus interference alleviated visceral hypersensitivity and anxiety-like behaviors of MS rats in the later phase of life. In addition, deleted in colorectal cancer (DCC), instead of neogenin-1(Neo-1) or uncoordinated (UNC5), was proved to be the specific functional receptor of Netrin-1 in regulating visceral hypersensitivity, whose upregulation may result in the most severe symptoms in the prepubertal period. Furthermore, the activation of the Netrin-1/DCC pathway could enhance long-term potentiation (LTP) in the hippocampus, probably recruitment of the AMPA receptor subunit GluA1, which finally resulted in the formation of visceral hypersensitivity. These novel findings suggest that long-lasting over-expression of Netrin-1 can mediate visceral hypersensitivity and anxiety disorder from the post-weaning period to adulthood by activating DCC/GluA1 pathway in the hippocampus. Moreover, early intervention of Netrin-1 in the post-weaning period could lead to significant symptom relief afterward, which provides evidence that the Netrin-1/DCC/GluA1 signaling pathway may be a potential therapeutic target for the treatment of visceral hypersensitivity in clinics.
早期不良生活事件（EALs），如母婴分离（MS），可导致内脏超敏反应，这被认为是肠易激综合征（IBS）的关键病理生理机制。以往的研究主要集中在成年期EALs诱导的内脏超敏反应，而未考虑其可能在成年前期就已发生。我们之前发现，经历过母婴分离的大鼠从断奶后就开始出现内脏超敏反应。此外，海马体被认为在调节母婴分离诱导的内脏超敏反应形成中起关键作用。但在不同生命阶段的潜在机制尚不清楚。在本研究中，应用行为测试、RNA测序、慢病毒干扰和分子生物学技术来研究海马体中母婴分离诱导的长期内脏超敏反应的分子机制。结果发现，断奶后、青春期前和成年期的母婴分离大鼠的内脏敏感性和焦虑样行为均显著增加，尤其是在青春期前阶段。随后，针对海马体的RNA测序确定，在所有时期Netrin-1的表达水平均显著升高，这通过定量实时PCR和蛋白质免疫印迹进一步得到证实。通过慢病毒干扰在断奶后时期敲低海马体中的Netrin-1可减轻母婴分离大鼠在生命后期的内脏超敏反应和焦虑样行为。此外，已证明在调节内脏超敏反应中，结直肠癌缺失基因（DCC）而非新生蛋白-1（Neo-1）或不协调蛋白（UNC5）是Netrin-1的特异性功能受体，其上调可能导致青春期前阶段出现最严重的症状。此外，Netrin-1/DCC通路的激活可增强海马体中的长时程增强（LTP），可能是招募了AMPA受体亚基GluA1，最终导致内脏超敏反应的形成。这些新发现表明，Netrin-1的长期过度表达可通过激活海马体中的DCC/GluA1通路，介导从断奶后到成年期的内脏超敏反应和焦虑症。此外，在断奶后时期对Netrin-1进行早期干预可导致随后症状显著缓解，这为Netrin-1/DCC/GluA1信号通路可能是临床上治疗内脏超敏反应的潜在治疗靶点提供了证据。
