Quercetin Reverses Tendon Stem Cell Aging and Accelerates Repair in Elderly Rats

Tendon injuries in elderly individuals are notoriously difficult to treat because aging tendons harbor an accumulation of senescent tendon stem/progenitor cells (TSPCs) that secrete pro-inflammatory senescence-associated secretory phenotype (SASP) factors. This creates a chronic inflammatory microenvironment that impairs endogenous repair, accelerates further stem cell dysfunction, and drives reactive oxygen species (ROS)-mediated mitochondrial damage in a self-reinforcing vicious cycle. Current treatments — corticosteroid injections, shock wave therapy, and surgery — show limited efficacy in this population, making new mechanistic targets urgently needed.

This study investigated whether quercetin, a naturally occurring flavonoid with established antioxidant and senolytic properties, could attenuate TSPC senescence and restore regenerative function. TSPCs were isolated from the Achilles tendons of 18-month-old rats and treated with quercetin in vitro. The researchers used SA-β-galactosidase staining, scratch migration assays, osteogenic differentiation assays, qRT-PCR, and Western blotting to profile senescence markers, SASP factor expression, and tenogenic differentiation capacity. Mitochondrial health was assessed via MitoTracker staining, JC-1 membrane potential assays, ROS fluorescent probes, and LC3B immunofluorescence to evaluate mitophagy flux.

Quercetin significantly reduced SA-β-gal positivity and SASP factor secretion in senescent TSPCs, while improving migration, proliferation, and tenogenic differentiation. Mechanistically, quercetin inhibited AKT phosphorylation, which in turn suppressed NF-κB nuclear translocation and downregulated NLRP3 inflammasome activation. This signaling cascade stabilized mitochondrial membrane potential, reduced intracellular ROS, and promoted mitophagy — the selective autophagic clearance of damaged mitochondria — thereby breaking the oxidative stress-inflammation feedback loop driving senescence. Pharmacological inhibition and pathway-specific knockdown experiments confirmed the AKT/NF-κB/NLRP3 axis as the primary mechanistic route.

To address quercetin's poor oral bioavailability and rapid systemic degradation, the team encapsulated it in a previously validated dual dipeptide hydrogel (DPH) composed of self-assembling peptides P11-4 and P11-8. The DPH@QUE system demonstrated sustained quercetin release, favorable swelling/degradation kinetics, and excellent cytocompatibility by SEM, FTIR, and in vitro cell viability assays. When injected locally into Achilles tendon injuries of aged rats, DPH@QUE produced markedly superior outcomes at 8 weeks versus controls: improved histopathological tendon architecture (collagen alignment, reduced fibrosis), attenuated local inflammatory infiltration, restored expression of tendon-specific markers, and functional recovery consistent with enhanced endogenous regeneration.

These findings identify the AKT/NF-κB/NLRP3-mitophagy axis as a druggable target in tendon aging and establish quercetin-loaded dipeptide hydrogel as a translationally promising local therapy. Limitations include the exclusive use of rodent models and absence of human TSPC validation, as well as the need for longer-term biomechanical testing. Nonetheless, the study provides a strong mechanistic framework and a proof-of-concept delivery platform for future clinical development.