Medical Prospect of Melatonin in the Intervertebral Disc Degeneration through Inhibiting M1-Type Macrophage Polarization via SIRT1/Notch Signaling Pathway

Abstract

The study aims to explore the medical prospect of melatonin (MLT) and the underlying therapeutic mechanism of MLT-mediated macrophage (Mφ) polarization on the function of nucleus pulposus (NP) in intervertebral disc degeneration (IDD). RAW 264.7 Mφs were induced by lipopolysaccharide (LPS) to simulate Mφ polarization and the inflammatory reaction of Mφs with or without MLT were detected. Conditioned medium (CM) collected from these activated Mφs with or without MLT treatment were further used to incubate NP cells. The oxidative stress, inflammation and extracellular matrix (ECM) metabolism in NP cells were determined. Then, the changes in SIRT1/Notch signaling were detected. The agonist (SRT1720) and inhibitor (EX527) of SIRT1 were used to further explore the association among MLT. The interaction between SIRT1 and NICD was detected by immunoprecipitation (IP). Finally, puncture-induced rat IDD models were established and IDD degrees were clarified by X-ray, MRI, H&E staining and immunofluorescence (IF). The results of flow cytometry and inflammation detection indicated that LPS could induce M1-type Mφ polarization with pro-inflammatory properties. MLT significantly inhibited the aforementioned process and inhibited M1-type Mφ polarization, accompanied by the alleviation of inflammation. Compared with those without MLT, the levels of oxidative stress, pro-inflammatory cytokines and ECM catabolism in NP cells exposed to CM with MLT were markedly downregulated in a dose-dependent manner. The inhibition of SIRT1 and the enhancement of Notch were observed in activated Mφs and they can be reversed after MLT treatment. This prediction was further confirmed by using the SRT1720 and EX527 to activate or inhibit the signaling. The interaction between SIRT1 and NICD was verified by IP. In vivo study, the results of MRI, Pfirrmann grade scores and H&E staining demonstrated the degree of disc degeneration was significantly lower in the MLT-treated groups when compared with the IDD control group. The IF data showed M1-type Mφ polarization decreased after MLT treatment. MLT could inhibit M1-type Mφ polarization and ameliorate the NP cell injury caused by inflammation in vitro and vivo, which is of great significance for the remission of IDD. The SIRT1/Notch signaling pathway is a promising target for MLT to mediate Mφ polarization.

Sirtuins in intervertebral disc degeneration: current understanding

“…These findings suggest that the beneficial effects of melatonin are mediated through the SIRT1/autophagy pathway (Zhang et al 2019b). Melatonin inhibits M1-type macrophage polarization and ameliorates inflammation-induced NP cell injury through the SIRT1/gap signaling pathway, which is important for the remission of IVDD (Dou et al 2023).…”

Musculoskeletal Diseases: From Molecular Basis to Therapy

“…IDD is characterized by an increase in inflammatory cytokines in the intervertebral disc, and it has been demonstrated that macrophages (Mφs) are able to infiltrate the nucleus pulposus (NP) after the rupture of the annulus fibrosus in the early stage of IDD [34]. Dou et al investigated the effects of melatonin, a hormone produced mainly by the pineal gland and involved in regulating circadian rhythms, on macrophage polarization in IDD [8]. Melatonin ameliorated NP cell injury caused by inflammation in vitro and vivo, partially inhibiting M1-type polarization of Mφ by regulating the SIRT1/Notch signaling pathway.…”