The matrikine N-acetylated proline-glycine-proline induces premature senescence of nucleus pulposus cells via CXCR1-dependent ROS accumulation and DNA damage and reinforces the destructive effect of these cells on homeostasis of intervertebral discs

Intervertebral disc (IVD) cell senescence is a recognized mechanism of intervertebral disc degeneration (IDD). Elucidating the molecular mechanisms underlying disc cell senescence will contribute to understanding the pathogenesis of IDD. We previously reported that N-acetylated proline-glycine-proline (N-Ac-PGP), a matrikine, is involved in the process of IDD. However, its roles in IDD are not well understood. Here, using rat nucleus pulposus (NP) cells, we found that N-Ac-PGP induced premature senescence of NP cells by binding to CXCR1. N-Ac-PGP induced DNA damage and reactive oxygen species accumulation in NP cells, which resulted in activation of the p53-p21-Rb and p16-Rb pathways. Moreover, the RT2 profiler PCR array showed that N-Ac-PGP down-regulates the expression of antioxidant genes in NP cells, suggesting a decline in the antioxidants of NP cells. On the other hand, N-Ac-PGP up-regulated the expression of matrix catabolic genes and inflammatory genes in NP cells. Concomitantly, N-Ac-PGP reinforced the destructive effects of senescent NP cells on the homeostasis of the IVDs in vivo. Our study suggests that N-Ac-PGP plays critical roles in the pathogenesis of IDD through the induction of premature senescence of disc cells and via the activation of catabolic and inflammatory cascades in disc cells. N-Ac-PGP also deteriorates the redox environment of disc cells. Hence, N-Ac-PGP is a new potential therapeutic target for IDD.