Antioxidative behavior of a2-macroglobulin in intervertebral disc degeneration

Abstract

Background: To clarify if a2-macroglobulin (a2M) has an antioxidative effect during the progression of the intervertebral disc degeneration (IVDD). Methods: The content of a2M and reactive oxygen species (ROS) were measured to compare mildly and severely degenerated human nucleus pulposus (NP) tissue by immunohistochemistry, mass spectrometry, and enzyme-linked immunosorbent assay (ELISA). Additionally, exogenic a2M was used to culture severely degenerated NP tissue in vitro. The effects of a2M on hypochlorite (HOCl)-treated NP cells were evaluated, containing antioxidative enzymes, ROS level, collagen II, and aggrecan expression, MMP3/13, and ADAMTS4/5. Results: ROS level increased in severely degenerated NP, accompanying with a decreased a2M content. Supplement of a2M could decrease the ROS level of cultured NP in vitro, meanwhile, the MMP13 and ADAMTS4 expression were also reduced. It was found that treatment of HOCl resulted in oxidative damage to NP cells and decreased a2M expression in a dose and time-dependent manner. Furthermore, exogenic a2M stimulation reversed the HOCl-triggered ROS accumulation. The promotion of SOD1/2, CAT, GPX1, collagen II, and aggrecan, and suppression of MMP3/13, ADAMTS4/5 expression caused by a2M were also observed. Conclusions: Our study indicates that a2M has an antioxidative ability in degenerated NP cells by promoting the antioxidative enzyme production.