Background Intervertebral disc degeneration (IVDD) is closely associated with senescence. Annulus fibrosus (AF) cell senescence is a crucial driver of AF tissue tearing and fissures, thereby exacerbating IVDD. Increased advanced oxidative protein products (AOPPs) were found in human degenerative discs and aged rat discs and may be involved in IVDD. This study aimed to explore the mechanism of AOPPs-induced senescence in AF cells. Methods The pathological effects of AOPPs in vivo were investigated using a rat lumbar disc persistent degeneration model and a rat caudal disc puncture model. Rat primary AF cells were selected as in vitro models, and AOPPs were used as direct stimulation to observe their pathological effects. Setanaxb (NOX1/4 inhibitor), apocynin (NADPH oxidase inhibitor) and adenovirus (ADV) packed NADPH oxidase 4 (NOX4) specific shRNAs were used for pathway inhibition, respectively. Finally, adeno-associated viruses (AAVs) packed with NOX4-specific blocking sequences were used to inhibit the in vivo pathway. Results AOPPs accumulated in the rat lumbar and caudal degenerative discs. Intra-discal loading of AOPPs up-regulated the expression of NOX4, p53, p21, p16, IL-1β, and TNF-α, ultimately accelerating IVDD. Exposure of AOPPs to AF primary cells up-regulated NOX4 expression, induced phosphorylation of mitogen-activated protein kinases (MAPK), triggered senescence and increased IL-1β and TNF-α. Apocynin, setanaxib, and ADV pre-cultured AF cells abrogated AOPPs-induced senescence. AAV-mediated inhibition of NOX4 expression in vivo reduced the expression of p53, p21, p16, IL-1β and TNF-α in vivo and delayed IVDD. Conclusions AOPPs induced AF cell senescence through a NOX4-dependent and MAPK-mediated pathway.

Lipid metabolism is a critical process that occurs in the lipid-rich spinal cord during damage and repair. Here, we integrated ultrastructural characteristics with multi-omics analysis as well as transcriptomic, untargeted, targeted proteomic, lipidomic, and N6-methyladenosine (m6A) epitranscriptomic profiling in a clinically relevant spinal cord injury (SCI) model. We observed lipid accumulation, lysosome-based autophagy of lipid droplets, and remyelination in the lesion of the chronic phase. The analysis also revealed molecular alterations associated with the enhancement of glycolysis, tricarboxylic acid cycle, and fatty acid metabolism, marked increases in triglyceride species with C16:0 fatty acyl chains, and adaptive changes in cholesterol metabolism. These changes included decreased uptake of cholesterol through Mylip upregulation, decreased synthesis through downregulation of Fdps and Hmgcs1, and increased efflux through Apoe upregulation. Among these, Mylip and Hmgcs1 are regulated by m6A methylation. Altogether, our findings revealed endogenous mechanisms in response to microenvironment changes, highlighting the potential of exploring lipid regulators for SCI treatment.