LncRNA TUG1 Promotes the Intervertebral Disc Degeneration and Nucleus Pulposus Cell Apoptosis Though Modulating miR-26a/HMGB1 Axis and Regulating NF-κB Activation

Abstract

Background: The core feature of intervertebral disc degeneration (IDD) is the reduction in the number of nucleus pulposus cells (NPCs) and the loss of extracellular matrix (ECM). Emerging studies have shown that long-chain non-coding RNAs (lncRNAs) taurine upregulated gene 1 (TUG1) plays a key role in the development of IDD. However, the relevant mechanisms of TUG1 in the development of IDD are not yet clear. Objective: This study investigated the effect of TUG1 on apoptosis and ECM degradation of human degenerative intervertebral disc NPCs and its mechanism. Methods: The expression of TUG1 in the human IDD NP tissues and NPCs was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The effects of overexpression or knockdown of TUG1 on cell proliferation and apoptosis were examined by EdU assay and flow cytometry, respectively. Utilizing bioinformatics methods, luciferase activity assay, the possible interacted miRNA and Mrna were explored. Western blot analysis determined the expression levels of collagen II, aggrecan, MMP-3 and MMP-13. Additionally, the effect of TUG1 on NF-κB pathway was analyzed by western blot assay and immunofluorescence staining. Results: The expression of TUG1 and HMGB1 protein in human degenerative disc NP tissues and NPCs was significantly increased, while the level of miR-26a was significantly decreased. Overexpression of TUG1 inhibited the proliferation while promoted apoptosis and ECM degradation of human degenerative intervertebral disc NPCs. Simultaneously, the effect of TUG1 knockdown on NPCs was opposite. Interestingly, TUG1 acts as an endogenous sponge to down-regulate the expression of miR-26a in NPCs by direct binding to miR-26a.Overexpression of miR-26a reversed the effect of TUG1 overexpression on apoptosis and ECM degradation. Additionally, HMGB1 is a target gene of miR-26a.The increased expression of HMGB1 induced by TUG1 overexpression can be reversed by the introduction of miR-26a mimic. Overexpression of TUG1 significantly upregulated the expression of p65 in the nucleus, and overexpression of TUG1 partially abolished the inhibition of NF-κB by NF-κB specific inhibitor QNZ pretreatment. Conclusion: TUG1 can promote the apoptosis and ECM degradation of degenerated intervertebral disc NPCs by regulating the miR-26a/HMGB1, which may be involved in the activation of NF-κB pathway. Funding Statement: The authors stated that no funding was received. Declaration of Interests: The authors report no conflicts of interest in this work. Ethics Approval Statement: This study was approved by the Ethics Committee of Chinese Academy of Medical Sciences Peking Union Medical College Hospital.