From Environmental Exposure to Intervertebral Disc Degeneration: First Evidence of Pro-Degenerative Effects of Polyamide 6 Microplastics

Background: Polyamide 6 microplastics (PA6-MPs), as emerging environmental pollutants, have attracted increasing attention due to their potential health risks. Their accumulation in human intervertebral disc tissue (86.4 particles/g) suggests a possible role in intervertebral disc degeneration (IVDD). However, direct evidence and mechanistic understanding remain limited. This study aimed to investigate the association between PA6-MPs exposure and IVDD, based on the hypothesis that PA6-MPs promote IVDD progression by targeting key regulatory molecules and disrupting cellular homeostasis. Methods: Potential PA6-related targets were predicted using multiple public databases, and IVDD-related differentially expressed genes were obtained from the GEO database. Overlapping targets were identified and analyzed through protein–protein interaction (PPI) network construction, Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses to screen core targets and pathways. Molecular docking was performed to evaluate PA6–protein binding. In vitro validation was conducted using primary human nucleus pulposus cells exposed to PA6-MPs, with cell viability, proliferation, and phenotypic changes assessed by CCK-8, EdU, live/dead staining, and immunofluorescence (IF). Results: A total of 222 PA6-related targets and 1035 IVDD-associated genes were identified, yielding 10 overlapping targets. Four core targets, including NR3C1 and HDAC1, were selected. Molecular docking and experiments demonstrated stable binding and concentration-dependent inhibition of cell viability and proliferation. Conclusion: PA6-MPs may accelerate IVDD progression in a concentration-dependent manner by targeting key molecules and perturbing inflammatory homeostasis. These findings link environmental exposure to IVDD and provide a basis for future risk assessment and targeted intervention strategies.