Retinoic acid inhibits the pyroptosis of degenerated nucleus pulposus cells by activating Sirt1-SOD2 signaling.

Aim: Intervertebral disc (IVD) degeneration is a common disease initiated by the degeneration of the nucleus pulposus (NP). The pyroptosis of degenerated NP cells (dNPCs) plays an important role in NP degeneration. The purpose of this study is to identify a feasible solution that can inhibit NP cell pyroptosis to therapy the degeneration of the intervertebral disc.

Methods: Cell viability and proliferation were quantified by Cell Counting Kit-8 assay. The measurement of cellular reactive oxygen species (ROS) was detected by 2,7-Dichlorodi-hydrofluorescein diacetate. The death of cells was analyzed by the Terminal Deoxynucleotidyl Transferase-mediated dUTP Nick-End Labeling (TUNEL) method of fluorescence analysis. The pyroptosis of cells was assessed by flow cytometry analyses. The contents of sulfate glycosaminoglycans were detected by a blyscan assay kit.

Result: In this study, we determined the effects of retinoic acid (RA) on dNPCs and investigated the underlying mechanism of RA-mediated pyroptosis in dNPCs. We also verified the effects of RA on IVD degeneration in vivo. Our results demonstrated that RA significantly increased the proliferation and the protein expression of sox9, aggrecan, and collagen II of dNPCs. Pyroptosis-related proteins and the pyroptosis rate of dNPCs were significantly decreased by RA. We found that Sirt1-SOD2 signaling was activated, while ROS generation and TXNIP/NLRP3 signaling in dNPCs were inhibited after the addition of RA. Furthermore, RA also recovered the structure of NP and increased the contents of sulfated glycosaminoglycans and collagen in vivo.

Conclusion: Our study demonstrated that RA could inhibit the pyroptosis and increase the extracellular matrix synthesis function of dNPCs and verified that RA has a protective effect on IVD degeneration.