Nanozyme-EV System Continuously Repairs DNA to Halt Disc Degeneration

Low back pain caused by intervertebral disc degeneration (IVDD) affects hundreds of millions of people globally. The nucleus pulposus cells (NPCs) that maintain disc integrity are progressively destroyed by oxidative stress, which generates reactive oxygen species (ROS) that damage DNA, trigger cellular senescence, and cause senescent cells to release inflammatory mediators — a state called the senescence-associated secretory phenotype (SASP). This inflammatory cascade recruits macrophages, degrades the extracellular matrix, and accelerates disc collapse. Despite the prevalence of antioxidant biomaterial strategies, the upstream role of DNA damage in perpetuating this cycle has been largely overlooked.

The research team first validated the disease mechanism using single-cell RNA sequencing of clinical human disc samples (GSE244889). They identified eight cell clusters in nucleus pulposus tissue, with macrophages prominent in degenerated discs. Sub-clustering of NPCs revealed that stress-responsive cells (marked by CP, a glutathione peroxidase mimic) persisted across all degeneration stages, while progenitor and regenerative NPC populations declined with severity. Gene ontology and GSEA analyses confirmed enrichment of oxidative stress, DNA damage, inflammatory, and myeloid differentiation pathways in severely degenerated samples. Pseudotime analysis showed early expression of DNA repair genes (NEIL3, BRCA2, ERCC1) that progressively declined as senescence and inflammation markers rose. These findings were corroborated by elevated γ-H2AX (DNA damage marker) staining in human tissue and by LPS-induced senescence models in isolated human NPCs.

To address this cascade, the team engineered AuCu-Cur-EVs: a gold-copper bimetallic nanozyme co-loaded with curcumin and anchored to extracellular vesicles derived from human umbilical cord mesenchymal stem cells (hUCMSC-EVs), then encapsulated in alginate hydrogel for sustained intradiscal release. The AuCu nanozyme mimics superoxide dismutase and catalase activity, efficiently neutralizing superoxide and hydrogen peroxide. Curcumin provides a second layer of protection by upregulating NEIL3, a DNA glycosylase that excises oxidized guanine and other damaged bases through base excision repair, directly addressing genomic instability rather than merely reducing ROS. The hUCMSC-EVs serve dual roles: they dramatically improve curcumin bioavailability and deliver endogenous regenerative cargo (RNAs, growth factors, proteins) that activates the p-JNK pathway to stimulate collagen and aggrecan synthesis, promoting disc matrix regeneration.

In vitro, the system reduced ROS levels, decreased γ-H2AX foci, suppressed SASP cytokines, and shifted macrophage polarization from pro-inflammatory M1 to anti-inflammatory M2. In the rat tail needle-puncture model, intradiscal injection of AuCu-Cur-EVs in hydrogel significantly preserved disc height, restored matrix composition, and reduced inflammatory infiltration compared to controls.

This study presents a conceptually novel sequential DNA repair strategy — ROS scavenging → DNA base excision repair → matrix regeneration — that addresses IVDD at multiple mechanistic levels simultaneously. The platform also hints at broader applicability to other aging-associated diseases driven by DNA damage and cellular senescence.