Abstract: Osteoarthritis (OA) is a degenerative joint disease characterised by progressive cartilage degradation, inflammation, and pain that diminishes quality of life. Although mesenchymal stem cell (MSC) therapies have shown promise, patient outcomes are heterogeneous; some patients report marked improvement, while others experience minimal relief. Emerging evidence indicates that this variability may be linked to senescence within the joint environment. Specifically, the senescence-associated secretory phenotype (SASP) may create a hostile joint milieu, affecting MSC efficacy.
Despite the recognised impact of senescence in OA, there is no established strategy to address it; thus, we investigated two novel interventions using nicotinamide mononucleotide (NMN) and doxorubicin (DOX) in an in vitro OA model. Specifically, NMN was used to treat pelleted MSCs in chondrogenic medium supplemented with TNFα (mimicking in-situ treatment of cells within a hostile environment). In contrast, DOX was used as a pre-conditioning regimen for MSCs prior to chondrogenic induction (mimicking a pre-treatment strategy).
In our in vitro models, we first confirmed that exposure to OA-associated SASP factors (TNFα) impairs MSC chondrogenic potential and upregulates senescence- and SASP-associated factors. We then assessed a DOX pre-treatment of MSCs, finding that this pre-conditioning enhanced chondrogenesis- (Agg, COMP) and suppressed senescence- (p16, p53) and SASP-associated (IL-1α) markers. Finally, when continuously treated with NMN, MSCs exposed to a hostile senescent OA-like environment exhibited significant reductions in senescence- (p16, p21, p53) and SASP-related (TNFα, IL6) genes. These findings demonstrate the potential of targeted interventions to recapitulate the regenerative efficacy of MSCs in senescence-driven OA, providing the framework for optimising MSC-based therapies by addressing senescence.
These results demonstrate that targeting senescence in OA can restore MSCs' regenerative potential in hostile environments, and stratifying patients based on the senescent OA endotype – rather than grouping all cases – can improve therapeutic consistency. This approach offers a model for refining regenerative therapies in OA and addressing other pathologies driven by cellular senescence.
