Background: Intervertebral disc (IVD) is a highly rhythmic tissue, which experiences a diurnal cycle of high/low mechanical loading via the changes of activity/rest phase. There are signs that disruption of the peripheral IVD clock is related to the process of intervertebral disc degeneration (IDD). However, it is still unclear whether inflammation could disturb the IVD clock and thus induce the process of IDD.
Methods and results: In this study, we used IL-1β, a commonly used inflammatory factor, to induce IDD and found that the IVD clock was dampened in degenerated human nucleus pulposus specimens, rat nucleus pulposus (NP) tissues, and cells. In this study, we found that the circadian clock of NP cells was totally disrupted by knockdown of the core clock gene brain and muscle arnt-like protein-1 (Bmal1), which thus induced the dysfunction of NP cells. Next, we explored the mechanism of dampened clock-induced IDD and found that knockdown of Bmal1 decreased the expression of nuclear factor erythroid2-related factor 2 (NRF2), a downstream target gene of Bmal1, and increased inflammatory response, oxidative stress reaction, and apoptosis of NP cells. In addition, NRF2 activation attenuated the dysfunction of NP cells induced by the dampened IVD clock and the degenerative process of NP tissues in an organotypic tissue-explant model.
Conclusions: Taken together, our study extends the relationship between peripheral clock and IVD homeostasis and provides a potential therapeutic method for the prevention and recovery of IDD by targeting the clock-controlled gene Nrf2.
Keywords: Bmal1; Circadian rhythms; Inflammation; Intervertebral disc degeneration; NRF2.
© 2022. The Author(s).