SP1/CTR1 mediated oxidative stress-induced cuproptosis in intervertebral disk degeneration

Abstract Intervertebral disk degeneration (IDD) is the primary pathology responsible for lower back pain. Oxidative stress-induced cell death plays a fundamental role in IDD pathogenesis. Cuproptosis is a recently discovered form of programmed cell death dependent on copper availability. Whether cuproptosis is involved in IDD progression remains unknown. Herein, we established in vitro and in vivo models to investigate the presence of cuproptosis in IDD and the mechanisms by which oxidative stress interacts with copper sensitivity in nucleus pulposus cells (NPCs). We found that expression of the key cuproptosis regulator ferrodoxin-1 (FDX1) increased with disk degeneration in both rat and human disks. Sublethal oxidative stress on NPCs led to increased FDX1 expression and cell death in the presence of Cu 2+ at physiological concentrations, whereas knockdown of FDX1 inhibited cell death. Since copper homeostasis is involved in copper-induced cytotoxicity, we investigated the role of copper transport-related proteins, including importers (transporter copper transporter 1 [CTR1] ) and efflux pumps (ATPase transporter, ATP7A, and ATP7B). We found that expression of CTR1 and ATP7A increased under oxidative stress, and blocking CTR1 significantly reduced oxidative stress/copper-induced cell death. Moreover, we found that oxidative stress promoted the expression of specific protein 1 (SP1) and SP1-mediated CTR1 transcription. SP1 inhibition improved cell viability and decreased cell death rates, which was reversed by the administration of elesclomol, a copper ionophore. Importantly, SP1 inhibition both significantly preserved disk hydration and alleviated tissue degeneration. This suggest that oxidative stress mediates cuproptosis by increasing copper flux through the promotion of SP1-mediated CTR1 transcription. This study highlights the importance of cuproptosis in IDD progression and provides a promising therapeutic target for IDD treatment.