Pharmacological Disruption of Phosphorylated Eukaryotic Initiation Factor-2α/Activating Transcription Factor 4/Indian Hedgehog Protects Intervertebral Disc Degeneration via Reducing the Reactive Oxygen Species and Apoptosis of Nucleus Pulposus Cells

Excessive reactive oxygen species (ROS) and apoptosis in nucleus pulposus (NP) cells accelerate the process of intervertebral disc degeneration (IDD). Here, we integrated pathological samples and in vitro and in vivo framework to investigate the impact of phosphorylation of eukaryotic initiation factor-2 alpha (eIF2 alpha)/activating transcription factor 4 (ATF4)/Indian hedgehog (Ihh) signaling in the IDD. From the specimen analysis of the IDD patients, we found phosphorylated eIF2 alpha (p-eIF2 alpha), ATF4 and Ihh protein levels were positively related while the NP tissue went degenerative. In vitro, tumor necrosis factor (TNF)-alpha caused the NP cell degeneration and induced a cascade of upregulation of p-eIF2 alpha, ATF4, and Ihh. Interestingly, ATF4 could enhance Ihh expression through binding its promoter region, and silencing of ATF4 decreased Ihh and protected the NP cells from degeneration. Moreover, ISRIB inhibited the p-eIF2 alpha, which resulted in a suppression of ATF4/Ihh, and alleviated the TNF-alpha-induced ROS production and apoptosis of NP cells. On the contrary, further activating p-eIF2 alpha aggravated the NP cell degeneration, with amplification of ATF4/Ihh and a higher level of ROS and apoptosis. Additionally, applying cyclopamine (CPE) to suppress Ihh was efficient to prevent NP cell apoptosis but did not decrease the ROS level. In an instability-induced IDD model in mice, ISRIB suppressed p-eIF2 alpha/ATF4/Ihh and prevented IDD via protecting the anti-oxidative enzymes and decreased the NP cell apoptosis. CPE prevented NP cell apoptosis but did not affect anti-oxidative enzyme expression. Taken together, p-eIF2 alpha/ATF4/Ihh signaling involves the ROS level and apoptosis in NP cells, the pharmacological disruption of which may provide promising methods in preventing IDD.

Automated summary

The study reveals that the eIF2 alpha/ATF4/Ihh signaling pathway is involved in regulating ROS levels and apoptosis in NP cells, and disrupting this pathway may provide promising methods in preventing IDD.