Oxygen-Sensing Nox4 Generates Genotoxic ROS to Induce Premature Senescence of Nucleus Pulposus Cells through MAPK and NF-κB Pathways.

Chencheng Feng,Minghui Yang,Huan Liu,Yang Zhang,Bo Huang,Yue Zhou,Minghong Lan

doi:10.1155/2017/7426458

Chencheng Feng, Minghui Yang + Show 5 more

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https://doi.org/10.1155/2017/7426458

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Abstract

Senescence is a crucial driver of intervertebral disc degeneration (IDD). Disc cells are exposed to high oxygen tension due to neovascularization in degenerative discs. However, the effect of oxygen tension on disc cell senescence was unknown. Herein, rat nucleus pulposus (NP) cells were cultured under 20% O2 or 1% O2. Consequently, ROS induced by 20% O2 caused DNA damage and then activated p53-p21-Rb and p16-Rb pathways via ERK signaling to induce NP cell senescence. It also induced catabolic and proinflammatory phenotype of NP cells via MAPK and NF-κB pathways. Furthermore, 20% O2 was found to upregulate Nox4 in NP cells. Small interfering RNA against Nox4 reduced ROS production induced by 20% O2 and consequently suppressed premature senescence of NP cells. On the contrary, NP cells overexpressing Nox4 produced more ROS and rapidly developed senescent signs. In consistent with the in vitro studies, the expression of Nox4, p21, and Rb was upregulated in rat degenerative discs. This study, for the first time, demonstrates that Nox4 is an oxygen-sensing enzyme and a main ROS source in NP cells. Nox4-dependent ROS are genotoxic and a potent trigger of NP cell senescence. Nox4 is a potential therapeutic target for disc cell senescence and IDD.

Highlights

The accumulation of senescent intervertebral disc (IVD) cells is a hallmark of IVD degeneration (IDD) [1, 2]
The expression of methionine sulfoxide reductase A (MsrA), MsrB1, and MsrB2 in nucleus pulposus (NP) cells was upregulated by 20% O2 (Figure 1(b))
High oxygen tension increased the percentage of γ-H2A.X-positive cells, indicating an enhanced DNA damage induced by high oxygen tension (Figures 1(c) and 1(d))

Summary

Introduction

The accumulation of senescent intervertebral disc (IVD) cells is a hallmark of IVD degeneration (IDD) [1, 2]. An aberrant secretion of extracellular matrix (ECM) catabolic proteases and proinflammatory mediators is strongly associated with the senescence-associated secretory phenotype (SASP) of disc cells [3, 4]. The SASP causes ECM turnover and inflammation in the microenvironment of IVDs and exerts negative effects on neighboring normal disc cells [5, 6]. Disc cell senescence is crucial to the establishment and progression of IDD [7, 8]. Investigating the molecular mechanism underlying disc cell senescence contributes to understanding the pathogenesis of IDD further in depth

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