Melatonin mitigates matrix stiffness-induced disc degenetation by inhibiting reactive oxygen species and melatonin receptor mediated-PI3K/AKT/NF-κB pathway.

ABSTRACT

Intervertebral disc degeneration (IVDD) may lead to an increase in extracellular matrix (ECM) stiffness, contributing to the progression of the disease. Melatonin reportedly mitigates IVDD; while its potential to attenuate elevated matrix stiffness-induced IVDD remains unexplored. Therefore, we aimed to investigate whether melatonin can alleviate the progression of IVDD triggered by increased matrix stiffness and elucidate its mechanisms. Nucleus pulposus (NP) tissues were collected from patients, and ECM stiffness, reactive oxygen species (ROS) levels, apoptosis rates, and p65 expression in these tissues with varying Pfirrmann scores were determined. In vitro experiments were conducted to investigate the effects of melatonin on the NP cells cultured on soft substrate with differing stiffness levels. Our findings revealed a positive correlation between ECM stiffness in human NP tissue and degree of IVDD. Additionally, phosphorylation of P65 exhibited a strong association with matrix stiffness. Enhanced levels of ROS and cellular apoptosis were observed within degenerated intervertebral discs. In vitro experiments demonstrated that melatonin significantly inhibited catabolism and apoptosis induced by stiff matrices, along with elevated ROS levels. Furthermore, we observed that melatonin inhibited NP cell catabolism and apoptosis by reducing the melatonin receptors mediated activation of the PI3K/AKT and NF-κB pathways. Also, we found that the reduction of ROS by melatonin can assist in inhibiting the activation of the NF-κB pathway. The outcomes of the in vivo experiments corroborated the results of the in vitro experiments. Collectively, melatonin can potentially alleviate high matrix stiffness-induced IVDD by reducing intracellular ROS levels and inhibiting the PI3K/AKT/NF-κB pathway.