髓核细胞外泌体miR-221调控椎间盘干细胞迁移参与压力环境下椎间盘内源性修复的机制研究

Intervertebral disc (IVD) stem cells play an important role in endogenous repair of IVD degeneration. Under pressure, IVD tissue could initiate endogenous repair. One of the important mechanisms of endogenous repair is recruitment of IVD stem cells by IVD cells into IVD through chemokines, exosomes, and other types of intercellular communication. Our preliminary experiments showed that under overpressure, the regulatory effect of nucleus pulposus (NP) cells on IVD stem cell migration was inhibited, accompanied by significant decrease of expression level of miR-221 in NP cells, NP cell exosomes, and IVD stem cells. However, the mechanism of the inhibitory effects on NP cells regulated IVD stem cell migration remains to be clarified. The role and mechanism of NP cell exosome and its miR-221 in the regulation of IVD stem cell migration are still unclear. This study intends to investigate the regulatory effect of NP cell exosome miR-221 on the migration of IVD stem cells under pressure, and further to explore its molecular mechanism. We applied "controlled axial loading induced rabbit lumbar disc degeneration model" to evaluate the potential promotion effects on migration of IVD stem cells and repairing effects for IVD degeneration by NP cell exosomes with overexpressed miR-221. The study would provide new ideas for mechanism and treatment researches of IVD degeneration.

椎间盘干细胞在椎间盘内源性修复中扮演重要角色。压力环境下椎间盘组织会启动内源性修复，而其中一种重要机制是盘内细胞通过趋化因子、外泌体等细胞间通讯途径，募集椎间盘干细胞进入盘内。本课题组预实验显示，在过度压力环境下，髓核细胞调控椎间盘干细胞迁移的作用受到抑制，同时，髓核细胞、髓核细胞外泌体及椎间盘干细胞内miR-221含量均明显下降。但髓核细胞对椎间盘干细胞迁移的调控如何受到抑制有待阐明，髓核细胞外泌体及其miR-221在椎间盘干细胞迁移调控中的作用及机制仍不清楚。本课题拟研究压力环境下髓核细胞外泌体miR-221对椎间盘干细胞迁移的调控作用，并进一步研究其分子机制。采用“可控轴向压力致兔腰椎间盘退变模型”评价过表达miR-221的髓核细胞外泌体对椎间盘干细胞迁移的促进作用和对椎间盘退变的修复作用，为椎间盘退变的机制及治疗研究提供新思路。

压力诱导的髓核细胞损伤是椎间盘退变发生发展的重要环节，椎间盘干细胞向椎间盘内迁移并修复受损的髓核细胞是椎间盘内源性修复的重要方式。压力环境下髓核细胞对椎间盘干细胞迁移的调控如何受到抑制是内源性修复失效机制研究的重要方向。在本研究中，我们成功提取了髓核细胞外泌体和髓核干细胞，并发现髓核细胞可分泌外泌体来促进髓核干细胞迁移。压力可下调髓核细胞外泌体中的miR-221水平，进而使得髓核干细胞迁移能力下降。进一步研究发现，髓核细胞外泌体miR-221可通过抑制髓核干细胞PTEN/PI3K/Akt通路来促进其迁移。体内实验也表明，过表达miR-221的髓核细胞外泌体通过促进干细胞迁移来缓解椎间盘退变。此外，我们发现，压力环境下受损髓核细胞不仅可以被骨髓间充质干细胞（BMSC）来源外泌体修复，还可以与BMSCs建立TNT进行线粒体转运来得到修复。本研究加深了对椎间盘干细胞迁移及其修复机制的认识，具有治疗椎间盘退变相关疾病的应用价值，并且为探索椎间盘内源性修复机制以及椎间盘退变的治疗新策略提供新理论依据。