Data_Sheet_2_RNA-Binding Protein HuR Suppresses Inflammation and Promotes Extracellular Matrix Homeostasis via NKRF in Intervertebral Disc Degeneration.docx

Intervertebral disc degeneration (IVDD) has been reported to be a major cause of low back pain. Studies have demonstrated that IVDD may be dysregulated at the transcriptional level; however, whether post-transcriptional regulation is involved is still unknown. The current study aimed to illustrate the role of Human antigen R (HuR), an RNA binding protein involved in post-transcriptional regulation, in IVDD. The results showed that the expression of HuR was decreased in degenerative nucleus pulposus (NP) tissues as well as in TNF-α-treated NP cells. Downregulation of HuR may lead to increased inflammation and extracellular matrix (ECM) degradation in TNF-α-treated NP cells; however, these effects were not reversed in HuR overexpressed NP cells. Inhibition of the NF-κB signaling pathway attenuates inflammation and ECM degradation in HuR-deficient NP cells. A mechanism study showed that HuR prompted NKRF mRNA stability via binding to its AU-rich elements, and upregulation of NKRF suppressed inflammation and ECM degradation in HuR-deficient NP cells. Furthermore, we found that NKRF, but not HuR, overexpression ameliorated the process of IVDD in rats in vivo. In conclusion, HuR suppressed inflammation and ECM degradation in NP cells via stabilizing NKRF and inhibiting the NF-κB signaling pathway; NKRF, but not HuR, may serve as a potential therapeutic target for IVDD.

椎间盘退变（Intervertebral disc degeneration, IVDD）已被证实是引发下腰痛的主要病因。研究表明，IVDD的发生可能存在转录水平的调控异常，但转录后调控是否参与其中仍尚不明确。本研究旨在阐明参与转录后调控的RNA结合蛋白人类抗原R（Human antigen R, HuR）在IVDD中的作用。结果显示，HuR在退变髓核（nucleus pulposus, NP）组织以及经肿瘤坏死因子-α（TNF-α）处理的髓核细胞中表达均下调。敲低HuR可加剧经TNF-α处理的髓核细胞的炎症反应与细胞外基质（extracellular matrix, ECM）降解，但过表达HuR并未逆转上述效应。抑制核因子κB（NF-κB）信号通路可减轻HuR缺陷型髓核细胞的炎症反应与ECM降解。机制研究表明，HuR通过结合NKRF的富含AU元件，增强了NKRF信使RNA（mRNA）的稳定性；而上调NKRF的表达可抑制HuR缺陷型髓核细胞的炎症反应与ECM降解。进一步的体内实验发现，过表达NKRF（而非HuR）可改善大鼠IVDD的病变进程。综上，HuR通过稳定NKRF并抑制NF-κB信号通路，从而抑制髓核细胞的炎症反应与ECM降解；NKRF（而非HuR）或可作为IVDD潜在的治疗靶点。