Abstract: BACKGROUND: Nucleus pulposus cell apoptosis is the main pathological basis for intervertebral disc degeneration, and inflammation and peroxidation are important factors leading to apoptosis in the nucleus pulposus. Studies have shown that matrine has antioxidant, senescent, inflammatory and apoptotic effects, and may be a potential drug for the treatment of disc degeneration.
OBJECTIVE: To investigate the effect of matrine on apoptosis of nucleus pulposus cells in rats with intervertebral disc degeneration by regulating the cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) signaling pathway. 
METHODS: (1) Nucleus pulposus cells of rats at a logarithmic phase were randomly separated into a control group, a model group, a low-dose matrine group, a high-dose matrine group, an empty group, and a high-dose matrine+cGAS overexpression group. Except for the control group, cell models of intervertebral disc degeneration were established in the other groups through oxygen-glucose deprivation. At the same time of modeling, the low-dose and high-dose groups were treated with 0.4 and 0.8 mmol/L matrine, respectively, and the empty group was transfected with the empty plasmid, while the high-dose+cGAS overexpression group was treated with 0.8 mmol/L matrine with the transfection of the cGAS overexpression plasmid. After 24 hours of treatment, cell activity and apoptosis, intracellular levels of reactive oxygen species, superoxide dismutase, tumor necrosis factor α and interleukin 1β, and intracellular expression of apoptotic proteins and cGAS-STING pathway proteins were detected. (2) Sixty Sprague-Dawley rats were randomized into six groups (n=10 per group): control group, model group, low-dose matrine group, high-dose matrine group, empty group, and high-dose+cGAS overexpression group. After 12 weeks of modeling, 60 and 120 mg/kg matrine were given by gavage in the low-dose and high-dose matrine groups, respectively (once a day), and the empty plasmid was injected into the tail vein in the empty group (2 times/week), while the high-dose+cGAS overexpression group was given 120 mg/kg matrine by gavage and injected with cGAS overexpression plasmid to the tail vein. Treatment in each group was given consecutively for 3 weeks. Samples were taken after drug administration and assayed for apoptosis, levels of reactive oxygen species, superoxide dismutase, tumor necrosis factor α and interleukin 1β, as well as apoptotic protein and cGAS-STING pathway protein expression.
RESULTS AND CONCLUSION: Compared with the control group, in the model group, cell activity and superoxide dismutase levels were decreased (P < 0.05), and apoptosis rate, levels of reactive oxygen species, tumor necrosis factor α and interleukin 1β, and the expression of cGAS, STING, cleaved caspase-3 and Bax proteins were elevated (P < 0.05). Matrine dose-dependently ameliorated the above changes in each index due to cellular modeling (P < 0.05), whereas cGAS overexpression partially antagonized the ameliorative effect of high-dose matrine. Similar results to the in vitro cellular experiments were obtained in animal experiments. These results indicate that matrine could inhibit inflammation and oxidative stress by blocking the cGAS-STING signaling, which in turn attenuates apoptosis and elevates the activity of nucleus pulposus cells in rats with intervertebral disc degeneration.

Key words: matrine, cGAS-STING pathway, intervertebral disc degeneration, nucleus pulposus cell, apoptosis